Note: Descriptions are shown in the official language in which they were submitted.
~7~35
sLocK POSITION AND SPEED TRANSDUCER FOR COMPUTER-CONTROLLED OIL
DRILLING RIG
This application is a division of Canadian patent
application Serial No. 296,905 filed February 15, 1978.
BACKGROUND OF THE INVENTION
Field of the Invention
This invention relates to a computer-controlled oil
drilling rig, or derrick and in particular to a block position ~:
and speed transducer therefor.
435
Description of the Prior Art
The physical structures utili~ed in the generation
of a hydrocarbon producing well are known in the art. For
e~ample, drawworks have been long utilized in oil drilling
rigs, or derricks, to raise or lower pipe stands and drill
string into and out of the bore. Tongs are well known for
making and breaking joints between pipe stands and the drill
string. United States Patent 3,881,375, issued to Robert R.
~elly and assigned to the assiqnee of the present invention,
generally relates to a tongs. Racker arrangements for
moving pipe stands from a storage location on a "set back"
to an operating location within the derrick are also well-
known. United States Patent 3,501,017, issued to Noal E.
Johnson et al. and United States Patent 3,561,811, issued to
John W. Turner, Jr., both relate generally to well pipe
rackers and are both assigned to the assignee of the present
invention.
Usually, each of the broad functions performed by
the mentioned structural systems requires the superintendence
of many skilled derrick operators. Further, the work is
often inefficiently performed, adding to the overall cost of
the well. Yet further, even if the work is periodically
efficient, it is difficult to maintain peak operating levels
whereby each operation of the associated structures mesh so
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as to maintaill the task o~ ma~ing-up or breakinc3-out a drill
string at a minimum from a time standpoint consistent with
safety of the personnel and the bore.
It is therefore advantageous to provide each of
those structural systems with an appropriate èlectronic
control system and to utilize a pro~ra~ed general purpose,
digital colnputer to superintend and sequence thc proper
operation of the physical structures to most efficiently
control derrick operations. It is appreciated that the
lQ elimination of manual control increases the effi,ciency al~d
lowers the cost of well drilling operations.
By way of particular examples, in the prior art,
the lifting or hois-ting of the travelling block and elevator
is done by the manual control of the electric motor drive on
the derrick. The lowering motion of the travelling block is
normally manually controlled by a drum brake. The lowering
motion of a loaded travelling block (having a drill string
thereon) is done by the manual control of the drum brake and
using an auxiliary brake which absorbs the potential ener~y
'~ of the string during lowering. The manual control oE these
functions may be inefficient during foul weather or other-
wise detrimental environments. It would be advantageous to
provide an electronlc control system in cooyerative
association with a programmed digital computer to control
the lifting and lowering cycles, and specifically the
velocity and position of the travelling block and elevatGr.
The loading on the travelling block and elevator,
and specifically the increase in block loading when in the
brea~-out cycle occasioned by friction in the bore as well as
3(i the decrease in block loading in the make-up cycle occasioned
by an obstruction in the bore, present problems in the manual
control of the derrick. It is therefore advantageous to
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~L~47435
provide an electronic load sensing arrangcment to provide
inputs to an electronic drawworks control to adjust the
velocity and position of the travelling block in response
thereto and to recogni~e potential dangerous loading con-
ditions on the block.
The tongs are, as is known in the art, a hydrauli-
cally powered arrangement capable of making and breakinc3
joints in a drill string. It is advantageous to provide
an electronic network controlling the operations of the
1~ tongs, and to interconnect that control network with a
programmed general purpose digital computer so as to
repeatedly and efficiently operate the tongsto perfoLm its
function. Of course, since various of the physical
structures discussed are actuated by hydraulic or pneumatic
operators, sui-table electro hydraulic or electro-pneumatic
interfaces must be provided. It is also advantageous to
provide a sensor arrangement to locate the backup and power
driven tong in vertical symmetry with respect to a horizontal
plane passing through the tool joint.
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7L~35
SU~IMARY OF THE INVENTION
The invention to which th:is divisional application is
directed pe~tains to an apparatus for indicating the position
and velocity of a travelling block with respect to a vertical
guide track within a computer-controlled oil drilling rig. The
apparatus includes a friction wheel mounted on the travelling
block and biased into contact with the guide track, displacement
of the travelling block upwardly or downwardly with respect to
the guide track rotating the friction wheel in a first or a
second angular direction, respectively, at an angular velocity
related to the velocity of the travelling block. A toothed
wheel is mechanically coupled to the frictlon wheel for rotation~
therewith. A magnetically responsive element is operatively
associated with the toothed wheel and is adapted to generate an
electrical signal representative of the direction of motion of
the toothed wheel and to generate a pulse each time a tooth on
the toothed wheel passes in proximity thereto. A converter
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7435
arrangement response to the frequency of the pulses output from
the magnetically responsive element is provided for generating a
current signal representative of the velocity of the travelling
block and a counter arrangement counts upwardly or downwardly
the pulses output from the magnetically responsive element in
accordance with the electrical signal representative of the
direction of motion of the travelling block. A further
converter is responsive to the count output from the counter
arrangement for generating a current signal representative of
the position of the travelling block with respect to the guide
track.
More particularly the invention herein relates to a
block position and speed transducer for indicating the position
of a travelling block along a vertical axis of a computer-
controlled oil drilling rig. The transducer includes
magnetically responsive means for generating an output pulse
when a metallic member, as a tooth in a gear wheel, passes in
proximity thereto. Counting means for counting the pulses from
the magnetically responsive means are provided. Means
associated with the counting means output a current signal, the
magnitude and polarity of which are functionally related to the
position and direction of movement of the travelling block.
Further, means for outputting a signal functionally related to -
the number of pulses for a predetermined unit of time to
indicate the velocity of the travelling block is included.
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7~35
BRIEF DESC~IPTION OF Tll~ DR~WINGS
The invention will be more fully understood from
the following detailed description of a preferred en~bodiment
thereof, taken in connection with the accompanying drawings,
which form a part of -this application, and in which:
Fig~re 1 is a generalizeA block diagram illus-
trati}lg the interactions between derrick structure and
control systems therefor and a digital computer in accor-
dance with the teachings of this invention;
Figure 2 is an illustration of the structural
elements included on an oil derrick, drilling rig, or and
the various structural systems disposed thereon;
Figure 3 is a more detailed block diagram of the
dra~orks control system embodying the teachings of this ~:
invention;
Figure 4 is a simplified signal diagram illustrating :
the principles of operation of the motor and brake control
subsystems of a drawworks control system embodying the
teachings of this invention, appearing with Figure l;
Figures 5 and 6 are more detailed signal~diagrams
~: based upon the signal diagram of Figure 4 and specifically
relating to a brake control subsystem and to a motor control~
; subsystem, respectively, each embodying the teachings of
this invention; ~ :~
Figure 7 is a schematic diaqram of the electronic-
to-pneumatic interface associated with the drawworks brake
actuator; :~
: Figures 8A and 8B are detailed schematic diagrams
of the brake control subsystem shown in the block diagram
Figure 3;
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7~35
Figures 9A and 9s are detailed schematic diagrams of
~he motor control subsystem shown in the block diagram Figure 3;
Figure 10 is a detailed schematic diagram of the
velocity comparator shown in the block diagram Figure 3;
Figure 11 is a detailed schematic diagram of the
travelling block position and speed transducer shown in the
block diagram Figure 3;
Figures 12A and 12B are detailed schematic diagrams of
the elevator load control subsystem shown in the block diagram
Figure 3; and
Figure 13 is a detailed schematic diagram of
associated safety networks and override arrangements embodied,~by
the invention.
~7435
DESCRIPTION OE PREFERRED EMBODIMENT
Throughout the following description, similar
reference characters and reference numerals refer to similar
elements in all Ei~ures of the drawings.
Referring first to Figure 1, a generali~ed block
diagram of a computer controlled oil drilling rig, or
derrick embodying the teachings of this invention is il-
lustrated. Generally speaking, the derrick includes three
broad structural systems each performing a particular set of
functions relating to the drilling of an oil well, and a
control system related to each structural system to control
the physical actions performed thereby.
The derrick 20 (Figure 2) includes a drawworks
structural system 22 having a drawworks control system 21
associated therewith. The drawworks systems generally pro-
vide the hoisting (or lifting) and lowering functions
associated with the generation of a well bore. Command
signals output from the drawworks control system 21 are
input to the structural system 22, as diagrammatically
illustrated by a line 23, and initiate or cease the physical
actions of elements within the structural s~/stem 22. Feed-
back signals representative of various physical parameters
associated with each of the structural elements within the
drawworks structural system 22 are input to the control
system 21, as illustrated by a line 24.
The derrick also includes a power tongs structural
system 28 and a tong control system 29 associated there-
with. The tong systems generally provide the make-up or
break-out o~ individual pipe stands into or out of a drill
string. Command signals initiatin~ or ceasing the physical
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~7~35
actions oE structural elements of the ton~s structural
system 28 are input thereto from the tongs control system as
29, as illustrated by a line 30. Feedback signals represen-
tative of various physical parameters associated with each
of the structural elements wi-thin the tongs structural
system 28 are input to the tongs control sys-tem 29 as
illustrated by a line 31.
Also provided is a racker structura] system 34
which, in general, provides the structure necessary for
carrying individual pipe stands from a storage location to a
location along the vertical axis of the derrick for make-up
or from the location along the vertical axis of the derrick
to the storage location during break-out. The storage
location is known in the art as the "set back". A racker
control system 35 is provided, with control signals being
output therefrom to the structural system 34, as illus-
trated by a line 36. Feedback signals from the structural
system 34 are input to the racker control system 35, as
illustrated by a line 37. The racker structural system 34
and control system 35 have been disclosed and claimed in the
copending application of Loren B. Sheldon, James R. Tomashek,
Robert R. Kelly, and James S. Thale, Cdn. Ser. No. 243,613,
filed January 15, 1976, now Canadian Patent No. 1,069,4~3, ~;
granted January 8, 1980, and assigned to the assignee of the
present invention.
A general purpose programmable digital computer 40
is interfaced with each of the above-mentioned control
systems, as illustrated diagrammatically by a line 41 (to
the drawworks control system 21), a line 42 (to the power
tong control system 29) and a line 43 ~to the racker control ;
system 35). Each of the control systems feed back various ; ;
signals to the computer 40, as illustrated by the lines 44,
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~7435
45, and 46, from the drawworks control system 21, tongs
control system 29, and racker control system 35, respectively.
Further, the computer 40 receives direct data input of
physical parameters, as illustrated as by a line 47.
The computer, in accordance with the programmed
instructions, sequentially initiates the operations oE
various of the structural systems to perform various physical
functions within the derrick. To economize operating time
and maximize efficiency, control of the systems may be on a
time shared basis, as with control of the drawworks and
racker systems. Any interactions between the systems, as
between drawworks and tongs, are through the computer 40. A
respective listing of the program for the digital computer
40 is appended to applicant's U.S. patent No. 4,128,888
granted December 5, 1978.
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1~47435
STRUCTURE
Referring to Figure 2, shown is an illustration oE
the oil drilling rig, or derrick 20 incorporating the basic
rig features and having thereon the structural elements which
are included in the structural systems outlined in connec-
tion with Figure 1. These structural systems are in co-
operativelassociation with their associated control systems
to initiate and cease the operation of the physical functions
performed by the structural systems. The derrick 20 is
illustrated in simplified form, with various structural
supports, sway bars, and other similar members being omitted
for clarity.
The basic derrick structure 20 includes corner posts
51 and 52 e~tending su`bstantially upwardly from suitable base
members. The base members are supported on a drilling floor
53, the drilling floor 53 being mounted on the surface of
the earth, on an off-shore drilling platform or on a drill
ship. A rotary table is provided in the floor 53 of the
derric~ and provides the rotational energy whereby a drill
string, comprised of end-to-end connected drill pipe stands,
ma~- be advanced toward a hydrocarbon producing formation.
Slips 55 are shown on the floor 53. When engaged, the slips
55 support the full weight of the drill string depending
therebeneath. In Figure 2, the upper end of the drill
string, or more precisely, the upper end of the uppermost
pipe stand con~ected within the drill string, is shown as
protruding above the slips 55. Each upper end of the pipe ~;
stand has a distended joint 56 used in connection with the ~ ~
tong operation. The programmable general purpose digital ; ~ ;
computer 40 may be convenientIy housed in a structure 57 on ~ ;
the floor 53.
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The axis of the bore being ~enerated beneath the
floor 53 of the derrick extends centrally ancl axi~llly thro~(Jh
the derrick. A racker structural system, generally indicated
bv the reference numeral 34, carries individual pipe s~ands
between a storage location, or "set back", disposed at the
side of the derrick and a location along the vertical axis
thereof. It is along the vertical axis of the derrick 20
that the drill string is retracted from or lowered into the
bore being generated. The racker structure 34 includes a
lifting head 58, an upper arm 59 with a latch thereon,
carriages 60 and 61 for the head 58 and for the arm 59,
respectively, and a racker board 62 for receiving and sup-
porting individual pipe stands. The racker structure and
control systems has been disclosed and claimed in the above- ~-~
referenced copending Canadian Serial No. 243,613.
The corner posts 51 and 52 are interconnected with
and supported by transverse supports at various elevations
along the derrick 20. The derrick 20 is capped by a water `
table 65 which supports the usual crown block 66. Suspended
from the crown block 66 b~ a cable arrangement 67, or
reaving, are elements of the drawworks structural system,
including a travelling block 68. The travelling block 68
supports a hook structure 70 by interengaged bales 71.
~ Elevator links 72 are suspended from ears 73 on the hook
; structure 70. The links 72 have an elevator 75 swingably
attached at the lower ends thereof. The elevator 75 is
~; ~ offset below the travelling block 68 by a predetermined ;
distance h. The elevator 75 includes a gripping arrange~
ment to grasp or release the distended~joints 56 of a pipe
stand.
A block retractor arrangement~78 lS connected to the ~;
travelling block 68 and serves to retract the travelling
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1L~47435
block (~ith depending elcvator 75) away from the vertical.
axis of the derrick along which it usually depcnds. The
retractor 78 includes a carriage 79 which is rectillnearly
moveable through a wheeled arrangement along a substan-
-tially ~Jertically extending retractor guide track 80.
block position and speed transducer (B.P.S.T.) 83 is mounted
on the retractor carriage 79 and produces output feedback
signals representative of the actual physical position of
the travelling block 68 along the track 80. These feedback
signals, as will be seen, are provided both to the draw-
works control system 21 (Figure 1) and to the computer 40.
The block position transducer 83 also provides a feedback
signal representative of the velocity at which the traYel-
ling block 68 is moving along the track 80. Of course, i.t
~ay be readily appreciated that since the elevator 75 is
vertically offset by the distance h from the travelling block !~
68, the position of the travelling block 68 along the track
80 also indica-tes the position of the elevator 75 with
respect thereto, and vice versa. And, since the travellin~
~o block 68 and the elevator 75 are generally extended to move
along the vertical axis of the derrick, the position
(elevation), and velocity of the travelling block 68 with ;
respect to the vertical axis of the derrick ~0 may be
: accurately monltored by the block position and speed trans-
ducer 83. The structure and internal circuitry of the block
position and speed transducer 83 is set forth in full herein.
For a purpose more fully disclosed herein, upper and lower
limit switches 84 and 85 (Fig. 11) are provided on the :
carriage 81. An upper target 86 and a lower target 87 a~re
provided at predetermined locations on:the retractor guide
track 80.
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1~47~35
As is the usual practice in the art, the cabLe
arran~ement 67 which supports the travelling bloc~ 68 and
structures (including the elevator 75) depending therefrom
are reaved about the block 66. One end 88 of the cable
arrangement 67, known as the "dead line" in the art, is
anchored to the derrick 20 as illustrated at 89. The second
end 90 of the cable arrangement 67, known as the "fast line"
is connected to other elements included in the drawworks
structural system. More particularly, the fast line 90 is
attached to a spool or drum 91 of the drawworks. The drum
91 is driven by an electric motor 92 of any suitable type as
diagrammatically illustrated in Figure 2. For example, a
motor manufactured by the Electromotive Division of General
Motors, sold under Model No. D79GB and rated at 800 horse-
power for drilling is a typical motor for a drawworks
structural system. Determination of a motor lies well
within the skill of the art. The motor 92 is provided with
a motor drive 93, such as a THYRIG manufactured by Baylor
Company, although any other motor drive arrangement may be
used. The motor 92 may be wound in any predetermined con- ;~
figuration to meet the needs of a particular rig. It is
noted, however, that the motor 92 imparts the ener(3y whereby
the travelling block 68 and the structures depending there-
from may be moved with respect to the vertical axis of the
derrick 20 from a first predetermined to a second pre-
determined elevation. Therefore, control of the motor drive
93, and in turn, of the motor 92, effectively controls the
velocity and acceleration of the travelling block f8 as it
is lifted from a first to a second elevation. The drawworks
includes a suitable clutch and gear arrangement therein.
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~7435
~ drum tachometer 94 is physica~ly locatccl in adj.l-
cency to the spool 9l. The output of the drum tachometer
94 is a feedback signal to the drawwor}:s control svstem 21
representative of the velocity of the drum 91 which si~Jnal
is directly proportional to the velocity of the travelling
block 68 and depending structures. Within the dead line 88
is provided a transducer 95 known as the dead line force
sensor (D.L.F.S.). The transducer 95 provides a feedback
signal to the drawworks control system 21 related to the
physical loading of the structures supported by the cable
arrangement 67. Of course, the eable arrangement 67 at all
times supports the travelling block 68 and its clepending
structures. The unloaded, statie weight of these structures
defines a "tare" weight of the structure supported by the
cable arrangement 67. When the elevator 75 acquires a lo~d,
the D.L.F.S. 95 appropriately reacts. Similarly when the
elevator load is properly relinquished, the sensor 95
responds accordingly. Yet further, during movement of a
loaded travelling block 68, frietional or other forces may
alter the load carried by the elevator 75. The D.L.F.S. 95
therefore provides an accurate feedback signal as to the
; instantaneous loading on the elevator 75 of the drawworks
structure. As lS generally the ease with the other trans-
dueers, other eonvenient physieal loeations therefor may be ;
used to measure the desired parameters. In addition, any ~ ~ ;
appropriate means for measuring the desired parameters may
also be utilized, as is appreeiated by those skilled in the ~ ~
art. ~ ;
~lso included within the drawwork~s structural systcm
~30 is a brake. The drawworks brake includes a primary hrake
the functiOn of which is to control the velocity and de-
celeration of the drawworks travellincJ hlock (when unloaded)
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1~7435
and to stop the motion thereof. An auxiliary brake is also
provided within the drawworks structural system to sub-
stantially absorb the potential energy associatecl with the
lowering of a loaded travellinq b:Lock. In the particular
embodiment of the invention shown in Figure 2, the primary
brake is a drum brake 96, manually operable by a pivotable
lever 97. A spring 9~ biases the drum brake 96 into its
fully asserted position. The lever 97 may be connected to a
brake actuator assembly generally indicated by the numeral
99. As seen also in Figure 7, the brake actuator assembly
99 includes a cylinder 100 having a piston 101 therein. The
piston 101 is coupled to the lever 97. The brake actuator
99 also includes an electronic-to-pneumatic interface 102
(Figure 7) such that the cylinder 100 may be coupled to a
suitable supply of pressurized air or any other fluid such
that introduction of the fluid into the cylinder 100 moves
the piston 101 therein which moves the lever 97 so as to
modulate the force on the brake.
As mentioned above, it isknown to those skilled in
the art that the secondary brake is provided to absorb the
energy when the loaded travelling block is moved downwardly
from an upper to a lower elevation. ~ manually controlled
hydromatic brake may be used as an auxiliary brake. How-
ever, an electric brake, such as an ELMAGCOTM brake sold by
Baylor Company could typically be used. The brake control
subsystem of the drawworks control system ~1 can be readily
interfaced with an auxiliary brake by those havin~ skill in
the art so as to provide the desired velocity and decelera-
tion control. Final positions are ultimately controlled by
the drum brake 96.
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~7~35
It is important to note that whate~er auxiliary
brake configuration and act~lator therefor is utilized, the
drawworks structure includes ~ brake which is controlled by
the dra~orks control system 21 so that the desired velocity
acceleration of the travelling block 68 is maintained as it
moves from an upper to a lower final positlon. ~lso, the
brake is operable to set and hold a liftecl or hoistecl loa-l
in the upper position. If the operator deems it necessary
to halt the movement of the physieal structures associated .,
lo with the dra~orks, the operator may at any time override
the electrical signal output from the drawworks control
system by actuating a switch 103 mounted on the lever 97.
The operator may also, at any time, override the electrical
signal output from the dra~orks control system 21 by de-
pressing a push-button switch loeated in the control panel
103a. The spring 98 may be manually overridden to release
the brake.
The raeker strueture 34 is operable to carry a pipe
stand from the vertieal centerline of the derrick to the set
'0 baek. In a make-up cycle, the pipe stand to be added is
stabbed into the already emplaeed and eonneeted stands which
comprise the drill string. When joined to the drill string,
the raeker strueture 34 relinquishes the load to the draw-
works, whieh lowers the string into position. In a breakout
eyele, the drawworks strueture 22 withdraws the drill string,
and, as eaeh pipe stand therein is disconneeted from the
string, the raeker strueture 34 aeeepts the load from the
drawworks and moves the pipe stand to a storage loeation.
The aetual eonneetion and diseonnection of pipe stancls
~0 Erorn t:he drill string is aeeomplishecd by the power tongs
strueture 28 uncler the eontrol of the tongs eontrol system
29. Very briefly, the tongs ineludes a baekup, which holds
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~7435
the lower pipe element defining the joint, while a second
element of the tongs - the power driven tong - connects or
disconnects a pipe stand to the upper pipe element thereto.
The tongs also includes a lift to move the associated
backup-jaws structure at a predetermined speed to a pre-
determined operating elevation with respect to the vertical
axis of the derrick. The backup and the jaws usually
circumferentially surround the dr:ill string as it advances
in the bore. Put another way, the vertical axis of the
derrick usually extends through the openings in the backup
and jaws of the tongs to facilitate gripping and dis-
connection or connection operations. Until needed, the
tongs are stored in a lowermost storage position. When it
is convenien~ to do so, the tongs are lifted to a standby
position which is proximate to the elevation at which the
distended joint 56 of the drill string is raised by the
dra~works. To sense the distended joint 56, a joint sensor
1025 is provided to contact the exterior of the drill string ;
as the tongs are moved from the standby to the operating
position. The movement from the standby to the operating
position is at a slower speed, of course, than the speed at
hich the tongs are moved from the storage position to
standby position. The particular joint sensor 1025 embodied
by the teachings of this invention is made clearer herein.
The details of the structure of the tongs, the joint
sensor and the tongs control system (including an electro-
hydraulic interface) is discussed in detail herein.
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7~35
OP~RATION
~ aving defined the elements of the various structural
systems, the operating sequency thereof during a typical
make-up or break-out cycle is presented, to graphically
illustrate the physical interactions between the defined
structures. Once this is done, a detailed description of
each of the control systems initiating and ceasing the
physical operations performed ~y the structuxal systems is
set forth.
In the break-out cycle, the objective is to dis-
assemble the drill string into its constituent pipe stands
as the drill string is lifted from the bore. With the upper
end of the still-attached pipe stand to be next-removed held
by the slips at a predetermined elevation along the vertical
axis of the derrick, the travelling block with the elevator
suspended therefrom is lowered under the control of the
drat~works portion of the computer program and under the
influence of the drawworks brake control subsystem which
stops and sets the brake at an elevation so as to permit
the elevator to accept the pipe stand. During this period
the racker is placing the last-removed pipe stand in a
storage location on the set back, and will eventually be
moved under control of racker portion of the computer
program to a position to accept the next-removed pipe
stand. The drawworks program and racker program operate on
a time-shared basis. The tongs are in a storage position.
The computer sends an actuating signal to the
elevator load control subsystem which derives its input
signals from the dead line force sensor. A momentary signal
output ~rom the computer samples the weight of the unloaded
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435
travelling block and elevator. This tare weight is used, as
discussed herein, to ascertain the instantaneous loading on
the travelling block and elevator. The elevator then acc~pts
the loading of the drill string, and an output feedback signal
to that effect from the elevator load control subsystem is
used to coordinate opening of the slips. The computer
outpu-ts a momentary load sample signal before the velocity
of the loaded elevator is increased. This static or initial
load signal is used, as discussed herein, when modified by a
predetermined fractional multiplier, as a basis for deter-
mining whether the instantaneous loading on the elevator has
exceeded a permissible range of values as selected by an
experienced drilling operator.
In response to an actuating signal from the computer,
the drat~works motor control subsystem provides a throttle
signal to the drawworks motor drive to hoist the drill
string to a predetermined elevation. It may be necessary to
move the block slightly, or creep to engage the drawworks
clutch. The drill string is hoisted under the control of
the drawworks motor control subsystem. A logic network
operates to release the brake whenever the hoisting velocity
exceeds a preset threshold value and tends to apply the
brake at hoisting speeds below this threshold velocity (the
drum brake being a self-energizing brake).
The motor control subsystem provides output signals
to the drawworks motor drive to lift the drill string in a
manner wh ch takes into account the position error (the
difference between the actual position and command position
of the drill string being lifted), a predetermined command
3~ velocity output by the computer, and -the dynamic loading.
During the major portion of the travel the load is hoisted
at an uniform velocity equal to the command velocity. As
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~7~35
the precletermined command position is approclche(l, the
hoisting velocity is reduced in a manner proportional to the
position error. Put another way, the drawworks motor control
sybsystem responds to position and velocity feedback si~nals
input to it from the block position and speed transducer
and the drum tachometer, respectively, to move the travelling
block and elevator to a predetermined command elevation at
a predetermined command velocity output by the computer.
During the hoisting operation, signals from the
elevator load control subsystem are taken into consideration
in determining the magnitude of the output signal to the
draw~Jorks motor. For if the actual loading on the elevator
exceeds the predetermined value by which actual load may
deviate from the static loading, the motor is slowed to
bring the loading into the acceptable limits. ~f course, if
the deviation goes beyond a threshold above even the scaled
initial value range, indicating that the string is caught in
the bore, the automated control shuts the system down and
the system reverts to manual control.
~0 As the block is hoisted and approaches the final
position, the motor is stopped and the brake is set. The
brake is applied when the lifting velocity drops below the
predetermined threshold mentioned. The motor is stopped
when the position reaches within some predetermined close
distance to the command elevation. During lifting, if the
block is indicated as moving in the wrong direction of -
travel or at a greater than commanded velocity, the automated `~
sequence is halted and the system reverts to manu~l con~rol.
The block final elevation is selected such that the
height at which the upper end of the pipe stand to be
removed finally stops will also place the joint between thc
pipe stand and t:he next lower pipe stand at an elevation for
- 22 -
. - ~ , . , ,
~474L~S
operation by the power tongs. When the ~loc~ velocity is
sufficiently close to zero, a zero v~locity signal is
returned to the computer. This sigllal, along with a block
position feedback signal sufficiently close to the command
position signal are necessary conditions before the actuating
command to set the slips to retain the load-is out~ut from
the comp-lter. Only with the slips set and supporting the
full load of the dr.ill string will the elevator relin~luish
the pipe stand to the racker structure. ~s mentioned, after
~o rackillg the previous stand, the racker is moved back toward
the vertiGal centerline of derrick, so as to be in a
position to accept the nex-t pipe stand. The elevator and
block are retracted away from the vertical centerlin~ of the
derrick and drop under the control of the drawworks brake to
be in position to repeat the lifting sequence.
When the lifting movement started, the power tongs
~Yere in the storage position above the floor of the derrick.
After the ele~ator had been hoisted above a potentially
obstructing position the tongs were actuated and moved to a
standby position. After the pipe stand has been finally
positioned and the slips set, a jOillt sensor associated with
the tongs controls a slower lifting move~ent to bring the
tongs into operating position. When the tongs are positioned
properly with respect to the joint, the motion thereof is -
halted, and the joint sensor retracted. The tong backup
then engages the drill string, the tong jaws engage the
pipe stand to be removed, and the pipe stand is separated
therefrom. The racXer then begins to store the now-
separated pipe stand, while the tongs are moved to the
storage position. The elevator then is brought into the
clevation alon~ the central a~is of the derrick where it may
engage the upper end of the still-attached pipe stand to be
'
- 23 -
7435
next-removed and the breakout process repeated.
* * *
In the make-up cycle, the objective is to assemble
the drill string from its constituent pipe stands and to
lower the string into the bore. With the upper end of the
last-connected pipe stand supported at a predetermined
elevation by the slips, the drawworks motor control subsystem
lifts the block and elevator along the vertical axis of the
derrick to a position at which it will receive a pipe stand
from the racker.
The tongs are moved upwardly from the storage to the
standby position at a first, normal, speed. The tongs
continue to move upwardly at a second t slower, speed beyond
the standby position wi-th the joint sensor extended. When
the joint is sensed, upward motion is halted with the tongs ~
at the operating elevation and the backup is closed. A pipe ~ ;
stabber is extended to guide the lower end of the pipe stand
being made up into the threaded connection at the distended
upper end of the drill string. When the pipe is stabbed, ;~
the tongs proceed to make up tlle joint. Thereafter, the
tongs are lowered to the storage position. The elevator, at
the upper elevation, is raised at a creep speed to acquire
the drill string load. After the elevator load control
subsystem dete~cts that the drill string load is acquired by
the elevator, the slips are raiQed and the drill string is
hoisted further to disengage~the slips from the drill
string. At this time, the rackers, under control of the
computer racker program, proceed to acquire the next pipe ;~ ;
stand and carry it toward the vertical centerline of the
:: ~
~ 24 ~
- . . - . , - . ~ ~ ,,:
~ ~ ~7435
derrick to the racker standby position. From there t}le
rac~ers proceed to the vertical centerline of the derric~.
In response to con~and velocity and col~land position
sigllals output from the computer, and utilizing a position
feedbac~ signal from the block positi~n and speed trans-
ducer, and a v~locity feedback signal ~rom the dra~orks
drum tachometer, the drawworks brake control subsystem
supervises the lowering of the drill string to a predeter-
mined ]ower elevation. The brake control subsystem outputs
control signals to the drawworks brake actuator so as to
maintain the block velocity near the comnland velocity for
the major portion of the travel, and to position the bloc~
as close as possible to the command position during the
final position of the travel.
The elevator load control is activated by the
computer and is responsive to a momentary signal to sample
the loading of the block and elevator in the unloaded
condition. This signal is used to discern whether or not
the elevator is supporting any of the drill string load.
Also in response to a signal output from the computer, the
loading on the elevator is sampled and held after the lo(~d
is acquired but before the downward velocity ~hereof is
appreciable. This initial static loading signal is used,
; when appropriately modified by a predetermined factional
multiplier, as the basis for determination as to whether or
not the instantaneous loading on the elevator has exceecled
. .
a permissible range of loading normally anticipated during a
~ lowering operation.
; During the lowering operation, the outputs to the
bra~e actuator from the brake control subsystem take into
account the signals relative to loading;from the elevatox
~- 25 ~
~7~3S
load control subsystem. If the actual loading is deviating
from the initial s-tatic condition by more than the specified
amount, the drat~works brake control slows the velocity ~o
brin~ the loading back to acceptable limits. If the actual
loadinq is deviating by more than a predetermined threshold
below the scaled static value (indicating that the bore is
obstructed and the drill string unable to penetrate), then
the automated control sequence is terminated, reverted to
manual control, and the system is shut down. Other inter-
rupt conditions may occur if, during the lowering operation,an indication tha-t excessive speed has been reached, or that
the block is moving in a wrong direction of travel.
As the block reaches the command position, the dif-
ferences in the actual position and velocity from the com-
mand position and velocity are such that the brake is set.
That is, when the block and elevator come within a pre-
determined distance of the command position, the brake is
set. Zero position error and zero velocity are necessary
conditions which must be met before the computer sets the
slips. ~ith the slips set, and the weight of the drill
string supported thereby, the elevator surrenders the load,
and the block and elevator lifted to the upper most position
to accept the next-to-be lowered pipe stand. The process is
then repeated.
,
- 26 -
3~
DR}~WWORI;S ~ONTROL SYSTr.M
The dra~works structural system 22 is the collection
of the structural elements on the ~errick which perform all
of the physical ac-ts associated with the lifting or lowerirl-7
of the drill string. These structural elements have been
detailc?d in connection with Figure 2.
The physical actions performed by the drawworks
structural system 22 are controlled by an arrangement k}Iown
as the dra~orks control system, indicated by reference
numeral 21 on the general block diagram Figure 1 and on the
more detailed drawworks control system block diagram Figure
3. The computer is interfaced with the drawworks control
system 21 through a plurality of input and output lines,
each of which will be cliscussed herein. FurtiIer, the draw-
works control system 21 i5 input with various feedback
si~nals representative of physical quantities associated
with the structural system, such as velocity, position,
direction, etc. Through the use of the computer commands
and the feedback signals, the drawworks control system 21
outputs signals initiating or ceasing the functions performed
by certain structural elements. All inputs and outputs of
the drawworks control 21 to and from the physical structures
with which it is associated will be detailed herein.
he drawworks control system 21 includes several
interconnected subsystems, as follows: the drawworks brake
control subsystem lO5; the drawworks motor control subsystem
]06; the drawworks elevator ]oad control subsystem 107; ~n(l
the dra~orks velocity comparator subsystem 108. Further,
;: ~
logic 109 is connected within the drawworks control 21 in
~Q cooperative association wlth the brake control subsystem 105
and the motor control subsystem 106. -~
27
7435
Feedback signals to the drawworks control system 21
are provided from the block position and speed transducer
(s.P.S.T.) 83, which speci~ically provides position feedback
signals to -the brake and motor control subsystems, 105 and
106 respectively. The block position and speed transducer
~3 also ~urnishes a velocity feedback signal to the velocity
~omparator 108. However, the primary velocity feedback
signal to the drawworks control 21 is the signal from the
drawworks drum tachometer 94 provided to the velocity com-
parator 108. The deadline force sensor (D.L.F.S.~ 95 pro-
vides feedback current signal of 4-20mA to the`drawworks
control system 21, particularly to the elevator load control
subsystem 107 on a line 110. Any of these feedback signals
may be conditioned, recorded or otherwise operated upon
prior to their input to the control system 21.
One output from the drawworks control system 21,
spe_ifically from the brake control subsystem 105, is con-
nected to the brake actuator 99 which is connected to the
brake. The brake actuator 99 includes the electronic-to-
pneumatic interface 102 (discussed in detail herein) which
converts electrical output signals from the brake control ~
subsystem 105 into pneumatic signals compatible with draw- ~ -
works brake cylinder 100. Another output from the draw-
works control system 21 is connected to the motor drive 93
of the drawworks. For convenience of operation, various
voltage-to-current (as the converter 274, for example) and
current-to-voltage conversions are effected, with the
electronic arrangements for effecting these conversions
being detailed herein.
Input to the drawworks control system 21 are signals
from various safety overrides present on the physical
structure of the drawworks. For example, the STOP control
- 28 -
~74~5
button located on the driller's console is an element of an
interlocking circuit. When the STOP button is depressed,
it functions to d~nergize the A~TO/MANUAL bus. This bus
is input to the motor control subsystem 106 by a line 111.
The line 111 connects to a relay coil 112 and a solenoid
cGil 113 of a valve 114. Actuation of the STOP button
causes the system to revert from automated to manual control.
g~,de-energizing the relay 112 the throttle signal from the
motor control subsystem 106 is disconnected from the motor
drive 93, stopping the motor 92. By d~-energizing the coil
113 of the valve 114, the actuator pneumatic signal to the
cylinder 100 is disconnected and the cylinder 100 is vented
to the atmosphere, thus applying a full braking signal.
The electronic arrangement of each of the recited
drawworks control subsystems, the operation of each, and the
interactions between them are now discussed.
- 2g - :~
~7435
DRA~ORKS BRAKE AND MOTOR CONTROL SUBSYSTEMS
The dra~orks brake and motor control subsystems 105
and 106 are now discussed. Both the brake control sub-
system 105 and the motor control subsystem 106 receive a
4-20n~ analog signal COMMAND POSITION output from channel A
of the computer 40. The COMMAND POSITION signal is carried
by lines 115B and 115M as inputs to the brake control sub-
system 105 and motor control subsystem 106, respectively.
The magnitude of the COM~AND POSITION signal is related to
the elevation to which it is desired the travelling block 68
to be raised or lowered by the motor 92 or brake under the ;
control of the motor or brake control subsystems. ACTUAL
POSITION voltage signals are received from the block
position transducer 83 by the brake control subsystem 105
and the motor control subsystem 106, respectively, on lines
116B and 116M. The derivation of the position signal is ~ ~-
discussed in connection with the block position transducer ~ ;
83.
Both the brake control subsystem 105 and the motor
control subsystem 106 receive a 0-10v COMMAND VELOCITY
signal from the velocity comparator 108 on lines 132B and
132M, respectively. The magnitude of the COMMAND VELOCITY
signal is related to the velocity to which it is desired to
lift the travelling block 68 to the desired elevation.
ACTUAL VELOCITY voltage signals, also from the velocity
comparator 108, are input to the brake control subsystem 105
and the motor control subsystem 106 on the lines 134B and
134M, respectively. The magnitude of the ACTUAL VELOCITY ~ ~:
signal is functionally related to the speed at which the ~ - ;
travelling block 68 is moving under the control of the motor
:.
- 30 - ~
743S
or brake. The origin of these signals will be discussed in
connection with the description of the velocity comparator
108.
The brake control subsystem 105 and the motor control
subsystem 106 each receive an ACTUAL LOAD vol-tage signal
related to the actual load on the elevator 75 from the
elevator load control subsystem 107 on lines 136B and 136M,
respectively. Moreover, from the elevator load control
subsystem 107, the brake control subsystem 105 receives an
appropriately scaled INITIAL LOAD voltage signal on a line
138B while an appropriately scaled INITIAL LOAD voltage
signal is input to the motor control subsystem 106 on a line
138M. The derivation of thesè load si~nals is discussed in
connection with the elevator load control 107.
Although the interaction of the logic 109, the brake
control subsystem 105 and the motor control subsystem 106
is set forth in detail herein, for present purposes it should
~be noted that the logic 109 outputs MOTOR RUN voltage signals
to the brake control subsystem 105 and to the motor control
subsystem 106 on lines 140B and 140M, respectively. A BRAKE
RUN signal on a line 142 is output from the logic 109 to the
brake control subsys-tem 105. The logic ].09 receives MOTOR
MODE SELECT command on a line 144 from the computer channel
B. The logic 109 receives a BRAKE SELECT command from the
: channel C on a line 145. As mentioned earlier, the motor
control subsystem 106 receives a signal from the override
switch 103 on the line 104. As is more clearly shown herein, :
information concerning a manual override is transmitted from
the motor control subsystem 106 to the brake control sub-
system 105 on a line 147.
Computer channels H and I respectively output CREEP
and CREEP TO ` ENGAGE CLUTCH to the motor control subsystem 106
~7~35
on lines 150 and lSl. Upon receipt of a CRE~P signal on the
line 150, the motor control subsystem 106 outputs a signal
CREEP FLIP-FLOP to the brake control subsystem 105 on a
line 152.
The output signal from the brake control subsystcm
105 is carried by a line 158 to the brake actuator 99. ~he
output signal from the motor control subsystem 106 is
carried by a line 159 to the motor drive 93 (throuqh a
converter 274). In the preferred embodiment of the inven-
tion, both of these output signals are ~-20mA current signals.
In general, it may be stated that current signals are pre-
ferred for carrying information over the longer of the con-
duction paths used in the preferred embodiment. Current
signals provide high noise immunity over long cable runs ~-
through electrically noisy environments.
As alluded to earlier, the AUTO/MANUAL bus is con-
nected to the dra~orks control system 21, and in parti-
cular, to the motor control subsystem 106 by the line 104.
The effect of this signal, as discussed in detail herein,
is to isolate the motor and brake control output signals
from their associated controlled apparatus. The loss of
AUTO/~NUAL bus voltage de-energizes the coils 112 and 113.
The effect of de-energizing the coil 112 is to interrupt
the motor control output line 159. In the case of the coil
113, de-energization thereof opens a brake solenoid valve
114 to disconnect the brake pneumatic system (Figure 7)
from the cylinder 100.
The brake control subsystem 105 and the motor control
subsystem 106 are basically similar to each other, at least
insofar as to the basic operating principles. They can,
there~ore, be discussed together to illustrate how each of
the above-enumerated inputs interact to generate brake or
- 32 -
.
~7~35
motor control output signals. They differ, of course, in
the implementation thereof due to differences in technical
requirements and functions to be performed. Preferred
embodiments of each subsystem are discussed herein.
Referring to the simplified block diagram shown in
Figure 4, the six enumerated inputs utilized in generating
an output control signal from either the brake or motor
control subsystems are: the COMMAND VELOCITY; the COMM~ND
POSITION; the ACTUAL VELOCITY; the ACTUAL POSITION; the
ACTUAL LOAD; and, the initial load signal multiplied by a
predetermined constant. (This last-mentioned signal is
symbolized hereinafter by INITIAL LOAD-(KN), where N = 1 or
2). In both the motor and the brake control subsystems, the
first two listed signals are provided by the computer using
certain input rig data, operating conditions, etc. The
next-three listed signals are instantaneously provided by
outputs from the transducers. The last mentioned input
signal is an appropriately scaled representation of the
initial load on the elevator taken while the elevator is in
~0 a relatively static cvndition. The scaling factor is ;;
selected by an experienced driller to define an acceptable
range within which the instantaneous actual load may deviate
from the static load during displacement of the travelling
block. It is noted that the scaling factor K is different
for each subsystem.
In operation, as seen in Figure 4, the analog signal
representative of the actual position of the travelLing ~ `
block (ACTUAL POSITION~ is substracted at a differential
:
ampliiier 200 from the analog signal representative of the
~redetermined final position selected by the computer
(COMM~ND POSITION). The resulting difference, or position
error signal Ep, taken from the output of the differen-tial
- 33 ~
- .. , . . . , :
~7~5
amplifier at the node 201 is summed at a summing junction
202 with -the ACTUAL VELOCITY signal to define a position
error plus velocity signal, Ep+ V. The COMMAND VELOCITY
signal is input to an amplifier 204 and a series diode, the
combination of which acts as a limiter to limit the magni-
tude of the position error signal Ep present at the node
201 ~ This effectively results in the magnitude of the
COMMAND VELOCITY signal establishing a maximum velocity at
which the travelling block is displaced from a first to a
second predetermined position. The position error plus
velocity signal, Ep+ V, together with a signal related to a
load factor VLF, are input to a difference amplifier 208.
At the output 210 of the difference amplifier 208 is a
total error signal ET, from which the output signal of the
motor or bra~e control subsystem is derived.
The load factor signal VLF is derived from the ACTUAL
I.OAD and the INITIAL LOAD-(KN) signals. These signals are
summed algebraically to input to an amplifier 212. If the
ACTUAL LOAD signal deviates from the initial static
20 elevator load by a fraction greater than the appropriately
selected scaling constant KN, an output is emitted from the
amplifier 212 related to the difference. This output is the
load error, or load factor VLF. An adjustable portion of
the load factor signal (adjustable through the potentiometer
KL) is input to an implifier 214, the output of which is
applied as the scaled load factor signal tKL)-(VLF) to the
difference amplifier 208. The effect of the load factor
signal VLF is to change the total error signal ET in a
direction such as to reduce the drawworks velocity otherwise ;;~
prevailing. Of course, if the load factor signal VLF is
zero (indicating that the actual load on the elevator during
the movement has not exceeded the allowed range of devia-
. .
7~35
tions from the initial static load) -the total error signal
ET is then derived exclusivcly from thc position error plus
velocity signal, Ep-~ V.
The total error signal ET, comprised of the above-
mentioned input factors, is, in effect, used as an input to
a closed-loop servo control system operative to drive the
controlled elements, either the drawworks motor or drawworks
brake, in a manner so as to change the total error signal in
a direction such as to reduce the drawworks velocity other-
wise prevailing. In accordance with this invention' the totalerror signal ET is applied as the input to an integrator-
amplifier network 218. When the total error signal ET,
reaches zero, the output 220 of the integrator-amplifier net-
work 218 is constant and uniform drawworks velocity is main-
tained. The output 220 of the integrator-amplifier network
218 operates to maintain the drawworks motor or brake at the
veloci;-~y producing the zero total error signal ET.
As may be appreciated, the magnitudè of the total
error signal ET determines the rate of change of velocity.
The greater the absolute magnitude of ET, the greater is the
rate of change of block velocity - effected either by
increased driving signals to the drawworks motor or de-
creased application of the drawworks brake. ~he smaller the
absolute magnit~de of ET, the smaller is the rate of change
of block velocity - either through decreased driving signals
to the drawworks motor or increased application of the
drawworks brake. To reiterate, however, the nature of the
motor and brake control subsystems is such that the magnitude
of the total error signal ET tends toward zero. As the
magnitude of the output of the integrator-amplifier network
218 increases, the motor speeds up (if in motor mode) or the
brake goes on (if in brake mode), ais explained in connection
with Figures 5 and 6.
35 -
7~3~
The load factor VLF tends to change the total error
ET so as to reduce the hoisting or lowering velocity. The
effect of the load factor VLp is to limit the actual
velocity of the travelling block to a value less than the
programmed command velocity and a value necessary to
maintain the instantaneous elevator load within the range
of limits set by the factor ~N~
Having described the general operating principles
behind the drawworks brake and motor control subsystems,
~o reference is invited to Figures 5 and 6, which are sirn-
plified signal diagrams patterned upon the signal diagram
of Fi~ure 4 and which are directed toward the brake
control subsystem 105 and the motor control subsystem 106,
respectively. Figures 5 and 6 elaborate more fully upon
an operative embodiment of both the brake and motor control
subsystems. In the Figures, the prevailing polarity at
the designated circuit points are indicated by reference
symbols comprising circled positive or circled negative
signs.
In both Figure 5 (brake) and Figure 6 (motor), those
inputs recited in connection with Figure ~ are, of course,
utilized, and need not be summarized again. In Figure 5,
i
the position signals are input to the termlnals of the
differential amplifier 200B, as shown. The position error
signal (Ep)B is adjustable through a potentiometer (Kp)B
and amplified by an amplifier 230B havin~ a resistor 231B `~
at its output. At the node 201B, the readjusted portion
of the position error signal (Kp)B (Ep)B from th~ output ~ ~of the amplifier 230B is connected to the summin~ junction ~ -202B through a resistor 232B. The ACTUAL VELOCITY signal
is connected through a resistor 233B to the junction 202B.
- 36 ~
.. , . . ... .- ~ . . . .. . . .. . .
LgL7~35
The magnitude of the adjusted position error signa1
(Ep)B-(Kp)B at the node 201B is limited by the macJnitude
of the CO~ND VELOCITY signal taken through the amplifier
204B and the diode 234B. In effect, the magnitude of the
voltage at the node 201B is equal to the output of the
amplifier 200B (adjusted by (Kp)B) as long as the adjusted
position error is less than the magnitude of the COMMAND
VELOCITY. If the magnitude of the position error exceeds
the magnitude of the COMMAND VELOCITY signal, it is
limited thereby and the COMMAND VELOCITY signal is summed
at the junction 202B. In this manner a maximum velocity
for the lowering motion of the block is programmed by the
computer. The composite position error plus velocity
signal (Ep+ V)B (appropriately limited by the COMMAND
VELOCITY if necessary) is applied to the inverting input
of the difference amplifier 208B.
The non-inverting input to the difference amplifier
208B is presented with a signal related to the load factor
signal (VLF)B derived from the load signals input to the
brake control subsystem 105. Note that the INITIAL LOAD
signal input is scaled by a factor (-Kl), chosen by a
skilled well operator for reasons discussed in connection
with the elevator load control subsystem 107. The load
signals are connected through resistors 235B and 236B and
algebraically summed at the amplifier 212B. The output of
the amplifier 212B is the basic load factor signal (VLF)B
indicative of the magnitude ~y which the actual load
differs from a predetermined fraction Kl of the initial
static load. 'rhis load factor signal is connected through
a diode 237B to the potentiometer (KL)B~ The ampli~ier
214B is connected to the potentiometer (KL)B, with the ~ ~
amplifier output being connected to the difference ~ -
- 37 - ~
~:
:
- - - . : . .
3~
amplifier 208B. The voltage value input to the difference
amplifier 208B is, of course, equal to zero or to the value
(~L)B-(VLF)B. A zero output signal is present at the
amplifier 214 output as long as the ACTUAL LOAD signal is
greater than or equal to the absolute value of the pro-
duct of INITIAL LOAD- (-Kl). However, if the ACTUAL LOAD
signal is less than the absolute value of the quantity
defined, an output signal equal to the magnitude by which
the ACTUAL LOAD is exceeded is applied to the potentio-
meter (KL) B. This is the basic load factor signal (VLF)B
applied for scaling by the potentiometer (KL)B.
The total error signal (ET)B at the output 210B ofthe difference amplifier 208B iS applied to the integrator-
amplifier network 218B. The magnitude of the ou-tput of the
integrator-amplifier 218B on the line 220 determines the
velocity at which the block is moved downwardly. In
general, the larger the signal on the line 220, the smaller
is the block velocity. The net braking effort is pro-
portional to the output signal from the integrator-amplifier ~-
218B. That is, the smaller the signal on the line 220,
the less the brake is applied, and the faster the block
moves downwardly. The effect of a load ractor signal, if
one is present, is to reduce the velocity of the block.
Thus, the block is limited in its velocity to the lower of
the maximum COMMAND VELOCITY programmed into the computer
(which limits the signal at the node 202B) or the velocity
level required to maintain the elevator load at the pre-
determined factor Kl of the initial value.
In the drawworks brake control subsystem the inte-
grator-amplifier network 218B comprises two parallel con-
duction paths. The total error signal (ET)B is split at anode 238B, with an adjustable portion thereof taken by a
- 38 -
,. ~
7~35
potentiometer (KFF)B and input to an amplifier 239B con-
nected to a resistor 240B. This path improves the overall
dynamic response of the network 218B to step-changes in the
total error siynal. The other parallel branch includes a
potentiometer (KINT)B which pres~ents an adjustable portion
of the error signal (ET)B to an integrating amplifier 241B.
The output oE the integrating amplifier 241B is connected
to a resistor 242B and summed at a junction 243B. The
signal at the junction 243B is input to an amplifier 244B.
The brake control subsystem output signal at 220B is
carried by a resistor 245B to a voltage-to-current con-
verter 246B. This network converts the signal output to a
current for reasons discussed. A negative reference
voltage is applied to the current-to-voltage converter 246B
through a resistor 247B. The reference voltage is summed
with the brake signal on the line 220B. The difference
signal (since the polarities are opposite) is converted to
a 20-4mA current signal and is presented on the line 158 to
the brake actuator 99, which includes an electronic-to-
pneumatic interface 102 described in full detail hereafter.
Connected within the brake actuator 99 is the brake solenoid
valve 114 (Figure 3).
The electronic-to-pneumatic interface 102 associated
;~ with the brake actuator 99 is illustrated schematically in
Figure 7. As discussed previously, movement of the actuator
lever 97 against the bias of the spring 98 moves the brake
(Figure 2) toward the release position. The lever 97 is
physically connected to the piston cylinder arrangement such
that the introduction of a pressurized fluid into the
~0 cylinder 100 moves the piston 101 and the lever 97 attached~
thereto so as to disengage the brake. It is apparent that
the force applied to the brake lever 97 by the piston 101 is
~7435
proportional to press~lre of the fluid in the cylind~r 100.
~s discussed immediately above, the output of the voltac~e-
to-current converter 246B is a current signal the m.lgnitude
of which determines the degree to which the brake is
applied. The output line 158, (together with a common line)
is connected to a current-to-pressure transducer 265. Of
course, the output signal on the line 158 may be operated
upon by any suitable signal conditioners, ramp or d~lay
circuits or the like, in a manner known to those skilled in
the art.
Dependent upon the magnitude of the input current
signal, the transducer 265 outputs a three-to-fifteen p.s.i.
air signal on a line 266 connected- to a hiqh-volume three-
to-one booster relay 267. The output of the booster relay
267 is applied through a line 268 to the brake air cylinder
100. The output of the relay 267 is limited by a regulator
269 disposed in a line 270 from the supply to the relay
67. Similarly, the output of the transducer 265 is held
within predetermined limits by a regulator 271 disp3sed
within a line 272 connecting the downstream side of the
regulator 2~9 to the transducer 265.
Disposed downstream of the booster relay 267 in the
- : :
line 268 is the brake solenoid valve 114. In the event of
~ an interrupt, or any other condition resulting in the de-
;~ ~ energization of the AUTO/MANUAL bus, the valve 114 discon-
nects the booster 267 from the cylinder 100 and vents the
cylinder 100 to atmosphere, thus applying full braking
effort. In connection with the Figure 7, it is noted that
the operator may manually override the brake control sub~
:30 system by applying a physically superior force on the lever
97 in opposition to the force of the fluid within the
cylinder 100. An electrical override signal applied to the
:~
~~40
3S
line 104 by actuating of the switch 103 would be a preferred
mean~.of overriding the brake (Fiqure 3). The effec~ of
such an override signal on the motor and brake subsystems is
discussed herein. Similarly, the brake may be released by
manually applying a force to overcome the force of the
spring 98.
Shown in Figure 6 is a simplified signal diagram for
the motor control subsystem 106. The operation of the motor
control subsystem 106 is very similar to that discussed in
connection with the brake control subsystem 105. The
position error signal (Ep)M at the output of the differen-
tial amplifier 200M (derived from the difference between the
COMMAND POSTION and ACTUAL POSITION signals) is adjustable
through a potentiometer (Kp)M and amplified by the amplifier
~30MI having a resistor 231M tied to the output thereof. The
adjusted portion of the position error signal (Kp)M- (Ep)M ~-
at the output of the amplifier 230M is connected to the
surnming junction 202M through a resistor 232M. The ACTUAL
VELOCITY signal is connected to the surnming junction 202M
20 through a resistor 233M.
The magnitude of the adjusted position error signal
: :
(Ep)M at the node 201M is~limited by the magnitude of the
COMMAND VELOCITY signal taken through the a~nplifier 204M
:
and the diode 234M. The magnitude of the voltage at the
node 201M is equal to the output of the differential amp-
lifier 200M (adjusted by (Kp)M) as long as the adjusted
position error is less than the magnitude of the COMMAND ~; ;
~ -,
VELOCITY signal. If the magnitude of the position error
exceeds the magnitude of the COMMAND VELOCITY signal, it is ~ -
limited thereby and the COMM~ND VELOCITY signal is sumrned
at the summing junction 202M. The effect of the above~
described arrangement is to~effectively limit the maximum
- 41 -
'
- . . .
~7435
velocity of the block while it is beill~ hoisted. This
maximum velocity is programmable into the computer and ~ro-
tects the bore from the detrimental effects of swabbing.
The appropriately limited (if necessary) composite position
error plus velocity signal (Ep+ V~M is presented to the
inverting input of the difference amplifier 208M.
To the non-inverting input of the difference amplifier
208M is applied a signal related to the load factor signal
(VLF)M, derived from the load signals input to the motor
control subsystem 106, including the ACTUAL LOAD and the
INITIAL LOAD scaled by the appropriate factor ~-K2). The
load signals are algebraically summed at the input of the
amplifier 212M. The output of the amplifier 212M is the
basic load factor signal tVLF)M. It represents the dif-
ference between the ACTUAL LOAD and the INITIAL LOAD
multiplied by a factor (K2). The load factor signal is
connected through a diode 237M to the potentiometer (KL) M.
The output of the potentiometer (KL) M is applied through
the amplifier 214M to the difference amplifier 208M. The
20 voltage applied to the diffPrence amplifier 208M is equal
either to zero or the adjusted load factor (KL)M- (VLF)M.
A zero signal is present at the output of the amplifier
214M as long as the ACTUAL LOAD signal is less than or equal
to the absolute value of the INITIAL LOAD signal scaled by a
factor K2. Thus, the actual load may range as high as
(INITIAL LOAD)- (K~) without causing a load factor output.
However, if the ACTUAL LOAD increases beyond the INITIAL
LOAD multiplied by a factor K2, an outpùt signal equal to
the difference betwePn the ACTUAL LOAD and the scaled INITIAL
LOAD is applied to the potentiometer (KL)M. This load factor
output is suitably scaled by the potentiometer (KL)M.
- 42 -
7435
The total error signal ~ET)M is applied to the
in~egrator-amplifier network 218M. The magnitude of the
output of the integrator-amplifier network 218M on the line
220 determines the velocity at which the block is moved up-
wardly. In general, the larger the signal on the line 220,
the greater is the block velocity and the larger the total
error signal (ET)M, the greater is the rate of chan~e of
veloci-ty. That is, the greater the total error signal
(ET)M, the lar~er the driving current input to the motor,
and the faster the block moves upwardly. The load factor
signal, if present, changes the total error signal so as to ~ ;
reduce the velocity of the block. The maximum lifting
velocity attainable is that predetermined by the computer
program. The dynamic loading on the block is limited by
controlling the velocity at which the block is lifted. This
prevents excessive damage to the bore during hoisting by
excessive hydrostatic forces caused by excessive hoisting -~
velocity.
As in the brake control subsystem, the integrator-
amplifier network 218M in the motor control subsystem 106
includes first and second parallel paths. The total error
signal (ET)M is split at the node 238M, with an adjustable
portion thereof taken by a potentiometer (K~F)M and to the
inverting input of the amplifier 244M. This path improves
.
the overall dynamic response of the integrator-ampli~ier
218M to step-chcmges in the total error signal. The other
parallel branch includes a potentiometer (KINT)M which
takes an adjustable portion of the total error signal and
inputs that signal to the integrating amplifier 241. The
output o~ the integrating amplifier 241M is presented to
the non-inverting input of the ampllfier 244M.
, , ~
_ 43 _
7~35
The output 220M of the integrator-amplifier network
218M is applied to a voltage-to-current converter 246M
through a resistor 245M. A 4-20MA current siynal propor-
tional to the voltage output of the integrator-amplifier
network 21~M is connected by the line 159 to the motor
drive 93, which drive 93 includes a suitable current-to-
voltage converter 274 discussed herein. Within the motor
control subsystem 106 is the solenoid relay 112, operable
to interrupt the current flow from the converter 246M to
the current-to-voltage converter 274. The output of the
converter 274 is connected to thP motor drive 93.
Within current-to-voltage converter 274, the current
signal output on the output line 159 of the motor control
subsystem 106 is applied to a resistor 275 connected at its
opposite end to a negative potential. The negative poten-
tial may be supplied by a reference amplifier network,
including a feedback path around a transistor, in a manner
known to those skilled in the art. The voltage present
across the resistor 275 is applied to the non-inverting
input of an amplifier 276 driving a transistor 277 to define
a unity ~ain voltage follower. The output voltage signal
taken at the emitter of the transistor 277 is connected to
the motor drive 93 to drive the drawworks mo.tor 92 at a
speed related to the output of the integrator-amplifier
network 218M.
Detailed descriptions of the brake control subsystem
105, the motor control subsystem 106 and the logic 109 are
now set forth.
.;~
- 4 4
, .,,
. ~ : :
74~35
13R~KE CONTROL SUBSYSTEM SCII~MATIC
Referring -to Figure 8, the detailed description of
the brake control subsystem 105 :is shown. The COMM~ND
POSITION signal is input on the :Line 115B (Figure 3) and
connected through a resistor 284 to the inverting input of
the differential amplifier 200B. The ACTUAL POSITION signal
is input on the line 116B and is presented to the non-
inverting input of the differential amplifier 200B through
the resistor 285. The non-inverting input is connected
through a resistor 286 to ground potential. Both the ACTU~L -~
and COM~ND POSITION signals are current signals. They are
each converted to an appropriate voltage for application to
the differential amplifier 200B by the resistor arrangement
of 287, 288, 289 and 290 connected, as shown, in pairs
between the position input signals and a negative potential.
The output of the differential amplifier 200B is fed back
to the inverting input through a resistor 291. This
resistor, in combination with the resistor 284, determines
the amplifier gain. A capacitor 292 reduces the amplifier'~ `high-frequency respPnse. The output is also taken by a line
293 to the non-inverting input of a final position com-
parator 294, discussed in more detail herein. The output of
the differential amplifier 200B is connected to the
potentiometer (Kp)B. An adjustable portion of the position
error signal is presented through a resistor 295 to the
non-inverting input of the amplifier 230B. The inverting
input of the amplifier 230 is connected through a resistor
; 296 to the wiper of~a potentiometer 297, the high end of
which is tied to a negative potential through a resistor
3n 298. The purpose of the potentiometer 297 is to set a
- 45 ~
,
7~35
minimum velocity. The output of the ampl:ifier 230B is fed
back through a resistor 299 to the inverting input thereof.
This, in combination with the resistor 296, determines the
amplifier gain. The output of the amplifier 230B is tied
through the resistor 231B to the node 201B which is also
connected to the output of the amplifier 204B through the
diode 239B. The COMMAND VELOCITY signal is input from the
line 132B to the non-inverting in~put of the amplifier 204B
through the resistor 300. The inverting input is con-
nected to the output through the resistor 301 and ~he diode234B. This effectively fixes the amplifier gain at unity.
Since the output is taken at the junction of the resistor
and the diode, the effects of diode voltage drop are
eliminated. The limiting effect of the diode 234B ir.
combination with the amplifier 204B on the potential at the
node 201B has been previously discussed.
The signal at node 201B is connected to the summing
junction 202B through the resistor 232B. At the summing
junction the composite position error plus velocity signal
is formed, as discussed, by the summation of the adjusted
position error signal with a signal representative of the
ACTUAL VELOCITY taken from the input line 134B through the
`
resistor 233B. The velocity signal may be derived from the
drum tachometer 94, or, alternatively, from the block
position transducer 83. The ACTUAL VELOCITY signal is
applied to the inverting input of a comparator 302 by a
line 356, as discussed herein. The signal at the summing
junction 202B is presented to the inverting input of the
difference amplifier 208B. The non-inverting input is con-
nected to ground through a resistor 303. As discussed,
however, the non-inverting input of the difference amp- ~
lifier 208B is also presented with an adjusted portion of a ~`
load factor signal.
- 46 -
~ 7435
ACTU~L LOAD si~nals are input on the line 136B and
the appropriately scaled (INITIAL LOAD) (Kl) signal is input
on the line 138B. These are summed at the inverting input
of the amplifier 212B through the resistors 235B and 236~,
respectively. The non-inverting input of the amplifier 212B
is connected to ground potential through a resistor 304.
The output of the amplifier 212B is fed back to the in-
verting input through a loop including the diode 305 and t~e
resistor 306. The output of amplifier 212B is connected
through the diode 237B to the potentiometer (KL) B. The
cathode of the diode 237B is connected with the inverting
input of the amplifier 212B through a resistor 307. The
wiper of the potentiometer is connected through a resistor
308 to the non-inverting input of the amplifier 214B. The
inverting input is connected to ground potential thro~gh a
resistor 309. The output of the amplifier 214B is fed back ;~
to the inverting input thereof through the resistor 310 and
is also connected to the non-inverting input of the differ- :
ence amplifier 208B through a resistor 31OA.
The output of the difference amplifier 208B is con- ?
nected to the integrator-amplifier network 218B. The out-
put is also fed back to the inverting input through the
resistor 311. The integrator-amplifier network 218B takes
:: the output of the difference amplifier 208B from the node ~.
- 238B (Figure 8B) along parallel conduction paths. Once such
path includes the potentiometer (KFF) B ~ the wiper of which
is connected to the in~erting input of the amplifier 239B
through a resistor 312. The non-inverting input is tied to ;~
ground potential through a resistor 313. The output of the
amplifier 239B is fed back through a resistor 314 to the
inverting input thereof and is also connected to the node
243B through the resistor 242B. The second parallel path
- ~7 -
~;,'' :
~7~3~
includes the potentiometer (KINT)B, the wiper of which is
connected through a resistor 315 to the inverting input of
the inte~rating amplifier 241B. The non-inverting input of
the amplifier 241B is tied to ground potential through a
resistor 316. The offset of the integrating amplifier 241B
is set to zero by a potentiometer 317. The output of the
integrating amplifier 241B is fed back through a capacitive
network 318 to the inverting input thereof. The output is
also connected to the node 243B through the resistor 240B.
The signals at the node 243B are applied to the inverting
input of the amplifier 244B. The non-inverting input is
tied to ground potential through a resistor 319. The out-
put of the amplifier 244B is fed back to the inverting
input through a resistor 320.
The output 220B of the integrator-amplifier network
218B is connected through a potentiometer 321 and the re-
sistor 245B to the inverting input of an amplifier 322.
This input signal is summed with a reference signal de-
veloped across the zener diode 331 and is applied through
the combination of resistors 329 and 333 and a potentiometer
330. The network including amplifiers 322 and 324 forms a
voltage-to-current converter. The output of the amplifier
322 drives the NPN-type transistor 324 connected as an
emitter follower. The collector of the transistor 324 is
tied to a positive potential. The signal at the emitter of
the transistor 324 is fed back to the inverting input of the
amplifier 322 through a resistor network 325. These re-
sistors, in combination with the resistor 245B and the
potentiometer 321 establish the conversion gain of the
network 246B. The output of th~ brake control subsystem 105
is taken from the emitter bf the transistor 324 at the
junction of the resistors 326 and 327 and is carried by the
:
- 48 -
.~ - . . . .
7435
output line 158. The emitter of the transistor 324 is
connected to the ungrounded side of the resistor 323
through tile s~ries connection of the resistors 326 and 327
and a pc~tentiometer 328. This cornbination of resistors
makes the output on the line 158 a constan-t current source.
The potentiome-ter is adjusted to make the output current
independent of load resistance.
The inverting input of the amplifier 322 is connected
through the resistor 329 and the potentiometer 330 to the
lQ anode of the zener diode 331. The anode of the diode 331 is
also tied to a negative potential through the resistor 427s.
The resistor 333 shunts the resistor 329. This network acts
to set an initial signal output in the line 158.
A brake control override 334 is operative in xesponse
to a BRAKE RUN signal from the logic 109 on the line 142 or
in response to an override signal from the motor control
subsystem 106 on the line 1~7 to impose a suitable voltage
on the inverting inputs of the amplifiers 239B and 241B so
tha-t the brake is asserted regardless of the total error
signal present at the output of the difference amplifier
208B. The line 142 BRAKE RUN from the loclic 109 is con-
nected through a diode 335 and a node 336 to switches 337
and 338. The override line 147 from the motor control
subsystem 106 is connected to the node 336 through a diode
339. Both of the switches are connec-ted at one side to a
positive potential and at the other sides, through resistors
340 and 341, respectively, to the inverting inputs of the
amplifiers 239B and 241B. When energi~ed, the positive
pot:entials are presented to the amplifiers such that the
brake is imposed - i.e. the brake is applied - regardless
of -the magnitude of the total error output signal from the
difference amplifier 208B.
' ~`:
-- d~ 9 -- : ~
"
~7~35
Another override circuit of a sort is provided at
342. This network response to a MOTOR RUN signal from the
logic 109 on the line 140B to release the brake despite the
signal inpu-t to the amplifier 244B. The logic 109, in
general, outputs a MOTOR RUN signal when in receip-t of a
MOTOR MODE SELECT signals, as is discussed fully herein.
The line 140B is connected to a switch 343. The switch
343 is connected at one side to a positive potential and
at the other side through a resistor 344 to the inverting
input of the ~mplifier 244B. When the switch 343 is
energized, the positive potential is applied to the
inverting input of the amplifier 244B. This has the effect
of maintaining the output of the amplifier 244B at zero
volts. A 20mA output signal from the converter 246B to
the ou'put line 158 due to the reference signal input is
effective to fully release the brake. The zener diode 345
prevents the output of the amplifier from going negative
and limits the positive output of the amplifier 244B to
the zener voltage. The application of the MOTOR RUN output
on the line 140B from the logic 109 is discussed her~in.
Various other components illustrated in Figure 8A,
but not as yet discussed, are now set forth for future
reference. The position error signal from the differential
amplifier 200B on the line 293 is applied to the lnverting
input of the position comparator 294. A signal derived
from a final position potentiometer 351 ~onnected to a
positive potential through a resistor 352 is applied
through a resistor 350 to the non-inverting input of the
comparator 294. The po-tenti~meter 351 sets a predetermined
voltage signal so that when the position of the block is
within a predetermined close distance of the command
position, the comparator 294 output signal connected
, ' ' .
through a resistor 353 and a diode 354 switches from a
logic 0 to a logic 1.
- 50 -
7435
This signal is carrie~ by a line 355 into the logic 109.
Similarly, a brake release comparator 302 derives
its inverting input from the ACTUAL POSITION signal on the
line 356. The non-inverting input is connected through a
resistor 357 to a point between resistors 358 and 359 con-
nected in serles between a positive potential and ground.
The comparator 302 is connected through a resistor 360 an(l
a diode 361 and carried by a line 362 to the logic 10~.
This establishes a switching threshold voltage for the
comparator 302, and thus a threshold velocity. During the
motor mode, the ACTUAL VELOCITY is positive. Durinq the
motor mode, when the velocity exceeds the threshold
velocity, the comparator switches so that the line 362
switches from a logic 1 to a logic 0. The function of this
network is to "release" the brake above some threshold
velocity. Note that the line 355 and the line 362 have
been omitted from Figure 3 for clarity.
The CREEP FLIP-FLOP line 152 output from the motor
control subsystem 106 (Figure 3) is input to the brake
control subsystem 105 and to a switch 365 thereof. The
switch 365 is connected between the inverting inputs of the
integrating amplifier ~41B (Figure 8B) and the difference
amplifier 208B output, and in series with a resistor 366
(Figure 8A). A junction diode 368 is connected between the `~junction of the switch 365 and the resistor 366 and ground.
This network is provided so that when a signal is present
on the line 152 the integrator gain is effectively in-
creased so that the integ~ator-amplifier 218B responds more `~
rapidly to the small creep velocity signal.
- 51
~;
7~35
I.OGIC OPERATION
The logic 109 includes input lines 194 (MOTOR MOD~
SELECT) and 145 (BRAKE MOD~ S~LECT) from the computer
channels 3 and C respectively (Figure 3). Output lines
140B (MOTOR RUN) and 142 (~RAKE RUN) from the logic 109 are
connected within the brake control subsystem 105 as dis-
cussed above. The output line 140M (MOTOR RUN) (Fic3ure 3)
from tlle logic 109 i9 input to the motor control subsystem
106. The logic 109 includes cross-coupled NAND gates 370C
and 370D with inverter gates 370A and 370B. These are
connected to form an EXCLUSIVE OR function. The purpose of
that portion of the logic 109 is to ascertain that only one
signal-either MOTOR MODE SELECT from channel B of the
computer of BRAKE MODE SELECT from channel C - is effective
at one time. If both are asserted, for any reason, neither
is effective due to the EXCLUSIVE OR gating described. The
logic also includes NOR gates 382, 384 and 386. The NOR
~ate 382 is input with one output of the NAND gate 370C and
at the other with the line 355 from the final position
comparator 294. The NOR gate 384 is input at one terminal
with the output of the NAND gate 370D and at the other with
the line 362 from the velocity comparator 302. The output
of the NOR gate 384 is carried from the logic 109 on the
line 140B (MOTOR RUN) to the switch 343 to assert the MOTOR
RUN function thereof. The output of the NOR gate 384 is
also input to the NOR gate 386. The other input to the NOR
~ate 386 is derived from the output of the NOR gate 382.
The output of the gate 386 is carried by the line 142 (BRAKE -~
RUN) to the brake control override 334 to assert the BRAKE
RUN function thereof.
- 52 -
'" '
,
.
~L~47435
The logic 109 is respectively input on the lines 144
and 145 with MOTOR MODE SELECT or BRA~E MODE SELECI' signals
from channels B and C of the computer 40 (Figure 3).
Output lines 140B and 142 from the logic 109 carry MOTOR
RUN (line 140B) and BRAKE RUN (line 142) to the overrides
342 and 334 connected within the brake control subsystem
105, as discussed above. The output line 140M (MOTOR RUN)
(Figures 3 and 8A) from the logic 109 is input to -the motor
control subsystem 106.
The tied inputs of the inverter gate 370A are con-
nected to the line 145, BRAKE MODE SELECT, through a diode
371 and a capacitor 372. The inputs are normally high, due
to their connection to a positive potential connected
through a resistor 373. The tied inputs of the inverter
gate 370B are connected to the line 144, MOTOR MODE SELECT,
through a diode 374 and a capacitor 375. These inputs are
normally high due to the positive potential connected
through the resistor 376. This portion of the logic 109
functions to accept only one signal-either MOTOR MODE SELECT
from channel B or BRAKE MODE SELECT from channel C - from
the computer at one time. If, for any reason, the lines 194
and 145 are both asserted (logic 0), the EXCLUSIVE OR
functions to make neither signal effective. Note the output
of the NAND gate 370D is connected to the motor control sub-
system 106 on the line 140M.
As noted, the logic 109 also includes NOR gates 382,
384 and 386. The NOR gate 382 derives its inputs from the
output of the NAND gate 370C and from the final position
comparator 294 on the line 355. The output of the NOR gate
372 is one input to the NOR gate 386.
The NOR GATE 384 derives one input from the output of
the inverter gate 370B. The second inputs to the NOR gate
384 is derived from the velocity comparator 302 on the line
'
-- 5 1 -- :
,.~.,. -.. - - - ' :
43~
362. 1'he output of the NOR ga-te 384 is the second input to
the NOR GATE 386, and also is connected to the line 140B
(MOTOR RUN) leading from the logic 109 to the switch 343
in the override 342. The output of the NOR gate 386 is
connected by the line 142 (BRAKE RUN) from the logic 109 to
the override 334 to assert the BE~KE RUN function.
If the computer asserts the BRAKB MODE S~I.ECT line
145 (i.e., the block is travelling downward) and if this is
the only asserted signal (as checked by the EXCLUSIVE OR)
the motor control subsystem 106 is disena~led on the line
140M and the NOR gates 382, 384 and 386 operate to switch
the line 142 to logic 0, thus not asserting the BRAKE RUN
function (on the line 142). During the greater part of the
downward journey of the block, the brake control subsystem
105 operates on the basis of the total error to modulate
the brake and control the block velocity within the command
limits. As the block approaches the final position, an
output from the final position comparator interacts with
the logic 109 to assert the BRAKE RUN function (on the line
142) and sets the brake to stop the block.
Therefore, with a BRAKE MODE SELECT input on the line
145, and MOTOR MODE SEI,ECT on the line 144 not asserted,
for the greater part of the downward movement of the block
the following conditions would prevail: The A and B
terminals of the inverter gate 370B and the B terminal of
the NAND gate 370C are at logic 1 condition~ Both terminals
of the inverter gate 370A and the A terminal of the NAND
gate 37 OD are in the logic 0 condition.
The output of the inverter gate 370A is therefore a
logic 1, placing this condition (logic 1) at the A input of
the NAND gate 370C. The output of the inverter gate 370B
is a logic 0, placing this condition at the B input of the
-
- 54 ~
3~
NAND gate 370D. Thus, the output of the NAND clate 370C is
at logic 0 and the output of the NAND gate 370D is at
logic 1. These are the conditions at the A input of the
NOR gate 372 ~logic 0 from the output of the NAND gate
370C) and at the A input of the NOR gate 374 (logic 1 from
the output of the N~ND gate 370D). Note tllat the logic 1
at the output of the NAND gate 370D is carried by the line
140M to the motor control subsystlem 106 enabling the motor
override ne-twork therein.
With regard to the NOR gate 384, the presence of a
logic 1 at the A input thereof insures that the output
thereof is a logic 0, despite the signal presented at the
B input leading from the velocity comparator 302 on the ~,
line 362. Thus, in the brake mode, the velocity comparator
302 is not effective in releasing the brake. Thus, the
output from the NOR gate 384 and the B input of the NOR
gate 386 are both at logic 0 as long as a BRAKE MODE SELECT
condition is present on the line 145. Accordingly, the
output line 140B from the logic 384 to the override 342 is
a logic 0. That is, the MOTOR RUN function is not asserted.
Note that the output of the velocity comparator-is not
effective in a BRAKE MODE SELECT condition.
With regard to NOR gate 832, the A input thereof is
at a logic 0 at all times that a BRAKE MODE SELECT is
asserted on the line 145. The B input to the NOR gate 382
is derived from the output of the final position comparator
294 on the line 355. Therefore, during the greater portion
of the downward travel of the block, the output on the 355
to the B input of the NOR gate 382 is at a logic 0. Thus,
the output of the NOR gate 382 is a logic 1. The logic 1
input condition to the A input of the NOR gate 386 results
in the situation that as long as the block is greater than
- 55 -
~7~3S
the threshold distance (set by the potentiometer 351) from
the final, command position, the line 142 (BRAKE RUN) is at
logic 0, allowing the normal control subsystem functions
derived from the magnitude of the total error signal (ET)B
to be controlling the velocity of the block.
However, as the block approaches the final position,
the output of the comparator 294 switches and provides a
logic 1 output on the line 355 connected to the B terminal
of the NOR gate 382. This results in the output thereof,
and the A input to the NOR gate 386, switching to a logic 0.
As a result, the output of the NOR gate 386 goes to a logic
1, and BRAKE RUN output line 142 is energized. With a logic
1 at the output of the NOR gate 386 and on the line 142, the
switches 337 and 338 are turned on. With such an occurrence
full braking is applied since the positive inputs to the
amplifiers 239B and 241B overriding the normal brake control
subsystem, and setting the brake when the position error has
reached an acceptably low value.
If the computer asserts the MOTOR MODE SELECT line
(i.e., the block is hoisted upwardly) and if this is the
only asserted signal (as checked by the EXCLUSIVE OR) the
motor control subsystem is enabled on the line 140M (MOTOR
RUN). However, the brake is kept asserted b~ the logic 109
even though the computer has asserted the motor mode, until
~;~ the block reaches a predetermined threshold velocity. This
is implemented as set forth herein.
With the MOTOR MODE SELECT signal on the line 144,
`~
the A and B ter~inals to the inverter gate 170A are at a
logic 1 condition. Likewise, the A input of the NAND gate
370D. The A and B inputs to the inverter gate 370B, and
the B input to the NAND gate 370C, are at a logic 0
condition. Thus, the output of the inverter gate 370A,
- 56 -
~L47~35
and the A input to the MAND gate 370C, are at a logic 0
condition. Accordingly, the output of the NAND gate 370C
and the A input to the NOR gate 382 are in a logic l
condition. The output of the inverter gate 370B, and the
B input of the NAND gate 37OD are in a logic l condition.
Accordingly, the output of the NAND gate 370D and the A
output to the NOR gate 383 are in a logic 0 condition. The
output of the NAND gate 37OD is conducted to the motor
control subsystem 106 on the line 140M. The motor is, in
effect, enabled because the MOTOR RUN line 140B is at logic
O.
With respect to the NOR gate 382, as long as a MOTOR
MODE SELECT condition is asserted on the line 144, the A
input is a logic l. The output of the NOR gate 382, there-
fore, is at all times a logic 0, regardless of the signal
present on the line 355 from the final position comparator -
294. Thus, the position comparator in the brake control
subsystem 105 is not effective during a MOTOR MODE SELECT
condition. The A input to the NOR gate 386 is at all times
~0 a logic 0.
With respect to the A input of the NOR gate 384, it
is at all times a logic 0. However, as long as the velocity
at which the motor lifts the block is less than the velocity
represented at -the inverting input of the comparator 302,
the output thereof on the line 362 connected to B input of
the NOR gate 3E34 is a logic l. Therefore, the output of
the NOR gate 384 is a logic 0 as long as the velocity of
the block is below the threshold. The B input of the NOR
gate 386 is also a logic 0, resulting in a logic l output
therefrom. Accordingly, the line 140B (MOTOR RUN) is not
asserted (due to logic 0 at the output of the NOR gate 384)
while the BRAKE RUN function at the output of the NOR gate
- 57 - ~
-
.
74~3S
386 on the line 142 is asserted. The result is when the
motor mode is selected (the override being disenabled), the
bra~e is asserted as long as the velocity is below the
defined threshold.
When the block is li~ted at a velocity exceeding the
threshold, the output of the velocity comparator 302
switches, placing a logic 0 at the B input of the NOR gate
384. The output thereof shifts to logic 1 r asserting the
MOTOR RUN function on the line 140B. The switch 343 is
turned on, overriding the signals presented to the in-
verting inputs of the amplifier 244B. Thus, when the
velocity exceeds the predetermined threshold velocity, the
override 342 is enabled in the manner described to prevent
unnecessary wear on the brake as the block is raised.
Fur-ther, the B input to the NOR gate 386 is also switched
to the logic 1 state, thereby placing a logic 0 at the out-
put thereon, disenabling the BRAKE RUN function on the line
142~
Of course, during this period of the block travel,
the velocity is controlled by the time integral of the
total error (ET)M, as discussed. As the block nears its
final position, the total error (ET)M tends to go positive
thus decreasing the velocity of the block. As the velocity
of the block falls below the threshold set by the velocity
comparator 302, the output thereof switches back to a logic
1, changing the B input to the NOR gate 384, and switching
the output of the NOR gate 384 to a logic 0. This dis-
enables the MOTOR RUN line~ and switches the output of the
NOR gate 386 to a logic, enabling the line 142 (BRAKE RUN)
to set the brake. As will be seen herein, within the motor
control subsystem 106, a position comparator, similar to
that discussed above, is operable when the block approaches
- 58 -
7~35
within a predeterminecl distance oE the command position,
to assert a motor override and top the hoisting motion.
MOTOR CONTROL SUBSYSTEM SC~IEMATIC
Referring now to Figure 9, a detailed description of
the motor control subsystem 106 :is set forth. The basic
features of the motor control subsystem 106 are similar to
those of the brake control subsystem 105, as seen in
earlier discussions.
The COM~ND POSITION signal is input on the line
115M (Figure 3) and connected through a resistor 402 to the
inverting input of the differential amplifier 200. The
ACTUAL POSImION signal is input on the line 116M and is ~;
presented to the non-inverting input of the differential
amplifier ~OOM through the resistor 403. The non-inverting
input is connected through a resistor 404 to ground poten-
tial~ Both the ACTUAL POSITION and the COMMAND P~SITION
signals are current signals and are converted to an appro-
priate voltage for application to the differential amplifier
200~1 by the resistor arrangement 405, 406, 407 and 408,
connected in pairs between the input signals lines 115M and~
116M and a negative potential. The output of the differ-
;~ ` ential amplifier 200M is fed back through a resistor 409 to ;
the inverting input. This xesistor, in combination with the
resistor 402, establishes the amplifier gain. The position
,
error signal output is taken by a line 410 to the non~inver-ting input of a position comparator 412. The in-
vertin~ input of the position comparator 412 is furnished
with a signal derived from a potentlometer 414 connected to
a negative pot~ntial through a resistor 415. The wiper o~
the potentiometer is connected through a~resistor 416 to
- 59 -
743S
the inverting input. The position comparator 4l2 outputs a
signal through a diode 417 to a line 418 when the position
error signal at the output of the dif~erential amplifier
200~1 is less than the voltage level as set by the poten-
tiometer 419. As seen herein, this condition overrides the
motor control to shut off the motor.
The output of the differential amplifier 200M is
connected through a resistor 420 to the potentiometer (Kp)M.
An adjustable portion as set by (Kp)M of the position
error signal is applied through a resistor 421 to the non-
inverting input of the amplifier 230M. The inverting
input of the amplifier 230M is connected through a re-
sistor 422 to the wiper of a potentiometer 423 tied to a
positive potential through a resistor 424. The purpose of
the potentiometer is to set a minimum velocity signal. The
output of the amplifier 230M is fed back through a resistor
425 to the inverting input thereof. The output of the
amplifier 230M is tied through the resistor 231M to the
node 201M to which is also connected the output of the
amplifier 204M through the diode 234M. The limiting effect
at the node 201M of the combination of the amplifi~r 204M
and the diode 234M has been discussed earlier in con-
nection with the simplified signal diagrams of the draw `
~orks motor control.
I'he signal at the node 201M is connected to the
summing junction 202M through the resistor 232M. At the
summing junction 202M the composite position error plus
velocity signal, ~Ep+V)M, is formed, as discussed, by the
summation of the adjusted position error signal with the
signal representative of the ACTUAL VELOCITY ta~en from the
input line 134~1 through the resistor 233M. The velocity
signal may be derived from the drum tachometer 94 or,
.~
- 60 -
~74~5
alternativel~, from the 1~lock position transducer 83. '1'he
~CT~1AL vrLocITY signal is applied to the invertin~ terminal
of a comparator 430, as is discussed herein. The siqnal at
the summing junction 202M is applied to the invertinq in~)ut
of the difference amplifier 208M. The non-invertinc3 input
is connected to grollnd potential through a resistor 431.
As discussed, however, an adjusted portion of a load factor
signal is also applied to the non-invertin~ input.
An ACTU~L LOAD si~nal is applied on the line 136M
and the appropriately scaled INITIAL LOAD-(-K2) si~nal is
input on the line 138M. These load signals are summed at
the inverting input of the comparator 212M through the :: :
resistor 235M and 236M, respectively. The non-inverting
input of the amplifier 212M is connected to ground through
a resistor 433. The output of the amplifier 2]2M is fed ::
back to the inverting input through a loop including the :~
aiode 434 and the resistor 435 as well as the loop in- .
cluding a resistor 436 and a diode 437. These components
in combination with the input resistors 235M and 236M
establish the amplifier gain. The output of the amplifi.er ;~
212M is connected to the potentiometer (KL)M. The output
is taken from the junction of the resistor 436 and diode
437 to remove the effects of diode 437 voltage drop. The
wiper of -the ~otentiometer (KL)M is connected through the
resistor 437 to the non-inverting input of the amplifier
~1'lM. The lnverting input of the amplifier 214M is con-
nected to ground potential through a resistor 438. The
output of the amplifier 214M is fed back to the invcrting
input through a resistor 439 and is also tied to the non~
3n inverti.nc; terminal of the difference ampllfier 208M.
The output of the difference ampl.ifier 208M is con-
nected to the integrator-amplifier network 218M (Figure 9B).
,,
- 61 ~
~74;~5
This output is also fed back to the inverting input
through the resistor 440. The integrator-ampli~ier network
21~ takes the OUtpllt of the difference ampli~ier 208M from
the node 238M along two parallel paths. One path includes
the potentiometer (KFF)M, the wiper of which is connectecl
to the inverting input of the diff~rential amplifier 244M
through a resistor 441. The second parallel ~ath includes
the potentiometer (KINI~)M, the wiper of which is connccted
through a resistor 442 to the inverting input of the
integrating amplifier 241M. The non-inverting input is
tied to ground potential through the resistor 444. A
potentiometer 445 sets the zero point of the integrating
amplifier 241M. The output of the integrating amplifier
241M is fed back through a capacitive network 44fi to the
inverting input thereof. The output of the integrating
amplifier 241M is connected through a resistor 447 to the
non-inverting terminal of the amplifier 244M. The non-
inverting terminal is also tied to ground potential
through a resistor 448. The circuit details of the motor
control subsystem differs from that of the brake control
subsystem in that the parallel paths within the integrator-
amplifier network 218M are not summed at a node 243B.
Instead, the output of the integrating amplifier is com-
bined differentially with the potentiometer output in the
amplifier 244M. The output of the amplifier 244M is fed
back through a parallel path including the resistors 449
and the diode 450.
The output 220M of the integrator-amplifier network
218M is connected through the resistor 245M to the voltaye-
to-current converter 246M. The converter 246M is sub-
stantially identical to the inverter described earlier in
connection with the brake control subsystem 105 except for
'' ~ "
- 62 - ~ ~
~' ~
.47~35
the ma~nitude of the reference voltage applied to the
amplifier 453. T}le resistor 245M is connected to ~ poten-
tiometer 451 and a resistor 452 throu~h which it is also
connected to the inverting input of an amplifier 453. The
non-invertiny input of the amplifier 453 is ticd to groun-~
through a resistor 454. The output of the amplifier dri~Je~
a transistor 455 of the NPN type, the collector of which i5
connected to a positive potential. The emitter of the
transistor 455 is fed back through a feedback resistive
network 456 to the inver-ting input. The emitter is con-
nected to the high side of the resistor 454 through a
series connection of resistors 457 and 458 and a potentio-
meter 459. The output of the motor control subsystem is
taken at the junction of the resistors 457 and 458. The
output line 159 has a relay contact operated by the coil
112 therein.
An initial voltage condition is applied -to the in-
~rerting input of the comparator 453 and includes a resistor
461 and potentiometer 462 in series with a negative poten-
tial. A resistor 463 shunts the resistor 461. The purpose
of this networ~ is to supply a reference voltaye so a~s to
obtain a 4m~ current output under a æero signal input
condition.
The motor control subsystem 106 is connected (Figure
9B~ to the computer output channel I through the line 151.
rrhis line is connected through a diode 470 to the inputs o~
a NAND gate 471 having both the inputs tied to a positive
po-tential through a resistor 472. ~ switch 473 is tied to
a positive potential on one side, and on the other throu~h
a resistor 474 to the non-inverting input of the comparator
453 within the voltage-to-current converter 246M. Upon
receipt of a CREEP TO ENGAGE CLUTCH command signal from the
- 63 - ;
.~:
-
computer on the line 151 (line 151 goes to logic 0), a
predetermined current signal is output to the motor dri~e
93 on the line 159 to move the motor 92 very slowly to
permit the clutch to engage for further hoisting operations.
The motor control subsystem 106 has a CREEP control
network 480 tFigure 9A) connected therein. The network
includes the inverting amplifier 430. The ACTUAL VELOCITY
signal on the line 134M is applied to the non-inverting
input through the resistor 481. The inverting input of the
comparator 430 is tied to the ground potential through a
resistor 4~2. The output of the comparator is fed back to
the inverting and non-inverting inputs through the paths
including the diode 483 and resistor 484, and the diode 485
and the resistor 486, respectively. The output of the
amplifier 430 is connected through a resistor 487 to the
inverting input of a creep comparator 490. The non-
inverting input of the comparator 490 is connected through
a resistor 491 to a voltage divider network including re-
sistors 492 and 493 connected between a positive and ground
potential.
The output of the creep comparator 490 is connected
through a resistor 495 to the reset input of a creep flip-
flop network 500. A diode 496 with a capacitor shunt 497
is connected between the reset input and ground. The set
input of the flip-flop network 500 is connected through a
diode 502 to the CREEP signal (channel H) from the computer
on the line 150. The output of the flip-flop network 500
conne~ted to the input of a switch 503. The output of the
amplifier 208M is connected to a resistor 504A and a diode
504B in series. The switch 503 is connected between the junc~
tio~ ~ the resistor 504A and the diode 504~ and the non-
inverting input of the integrating amplifier 241M. The
- 64 -
;
7~3~
output of the flip-flop network 500 is also connectcd
through the line 152 to the switch 365 in the brake control
subsystem 105 (Figure 8~).
The purpose of a CREEP command is to slowly raise the
travelling block so as to acquire the drill string load with
the elevator as discussed in connection with the operation
section earlier.
Upon receipt of the CREEP COMMAND a signal at the set
input from the line 150 causes an output from the flip-flop
network 500 to switch to logic 1. This closes the switch
503. This effectively increases the gain of the integrating
amplifier 241M. At the same time, the output on the line
152 from the flip-flop ne-twork 500 closes the switch 365 in
the brake control subsystem 105 to increase the gain of the
integrating amplifier 241s ~Figure 8). Thus, the CR~E~
command signal, in conjunc-tion with other signals, is used
to slowly raise or lower the elevator to acquire or to
release a load, as the case may be. Higher velocities are
programmed after acquirinq or releasing the load. When the
velocity e~ceeds a creep threshold velocity determined by
the combination of resistors 492 and 493, the comparator 490 ~;~
switches to logic 0 to reset the flip-flop network 500 to
the normal condition.
A motor control override network 510 (Figure 9B) in- ~
cludes a primary and secondary override path connected to ~-
the MOTOR RUN line 140M. The line 140M is output from the
logic 109 and when the motor control subsystem 106 is dis-
enabled the logic 109, the line 140M has a loqic high slgnal
thereon. The line 140M is connected to a diode 511, the
output line from the diode 511 being indicated as MOTOR OFF
line 512. The primary override path includes a zener diod
513 connected through a resistor 514 to ~he base of an NPN
.
:, , ~
- 65 -
.
~: : ' -~
:
131 ~7435
transistor 515. The emitter of the transistor 515 is con-
nected to a negative potential. The emitter of the tran-
sistor 515 is tied to the anode of the zener diode 513 by a
resistor 516. The collector of the transistor 515 is con-
nected through a resistor 517 to a diode 518. The primary
override is connected to the inverting input of the inte-
grating anplifier 241M. The second path of the override 510
includes a switch 524 connected between the junction of
resistors 525 and 526 and ground. The resistor 525 is tied
to a positive potential. The non-inverting input of the
amplifier 527 is tied to ground through resistor 528. The
output of the amplifier 527 is applied through a diode 529
to the inverting input of the voltage-to-current converter
2~6M. The output is also fed back through the inverting
input to a resistor 530.
When an appropriate signal (a logic 1) is received ;
from the logic 109 on the line 140M, the motor control over-
Lide 510 is actuated to effectively turn off the motor,
regardless of the output of the amplifier 244M. When the
signal on the line 140M is applied to the diode 511 the out-
put is a signal on the MOTOR OFF line 512 which renders the
transistor 515 conductive, effectively setting the output o~ ;
the integrating amplifier 241 to zero. The secondary path,
when in receipt of the MOTOR OFF signal on the line 512,
: :
renders the switch 524 conductive, groundiDg~the junction of the
resistors 525 and 526. This holds the input to the voltage-
, :
to-current at zero. This precaution is taken since there
may still be a signal at the output of the amplifier~244
; even though the integrating amplifier 241M is overridden. ;
The MOTOR OFF line 512 can be energized in ways other than
by receipt of a computer command via the logic 109.
- 66 -
: .;
~: .
435
In order to shut the motor off when the ~)osltion o~
the block comes within a predetermined close tolerance to the
command position, an output signal from the position com-
~arator 412 on the line 418 operates the override 510 in a
manner exactly as discussed.
Further, when the operator asserts the override on the
line 104, a signal is applied to an optical coupler 536
(Figure 9A) acting as a switch. When energized the switch
536 connects a positive potential to the line 512 through a
diode 537. A resistor 538 ties the line 512 to ground.
Upon receipt of a manual override signal, the switch 536 is
concluctive, placing a high signal on the line 512 to turn
the motor off by the override 510 in a manner discussed
above. At the same time, the line 147 (OVERRIDE) is at logic
1 due to its connnection to the switch 536, thereby asserting
the override network 334 (Figure 8).
Having completely discussed the brake control sub-
system 105, the motor control subsystem 106, and the logic
109, attention is directed to Figure 10, which is a detailed
schematic diagram of the velocity comparator 108.
- 67 -
" ,.
7435
VELOCITY COMPARATO~
Shown in Figure 10 is a detailed schematic dia~3ram
of the velocity comparator 108 utilized in the drawworks
control system 21. As seen from the block diagram Figure 3,
the velocity comparator 108 is input from the computer
channel G on the line 165 with a 4~20mA signal representative
of the CO~ND VELOCITY, the velocity at which it is desired
to move the travelling block 68 from a first to a second
elevation within the rig or derrick 20(Figure 2). With
reference to Figure 10, the current input signal is taken on
a line 570 and conver-ted to a voltage by the action of the
resistor 571 connected between the line 570 and a negative
potential. The resulting voltage signal is filtered by a
filter 572 comprising a resistor 573 and a capacitar 574
and is applied to the non-inverting input of an amplifier
575. ~he output of the amplifier 575 is fed back to the
inverting input throu~h a resistor 576, and is also con-
nected to the output line 132 which carries the 0-10 volt
COMMAND VELOCITY signal to the brake control subsystem 105
and the motor control subsystem 106, on the lines 132B and
132M respectively.
The velocity comparator 108 is also input, on the
line 166 with a bi-polar voltage signal derived from the drum -
; tachometer 94. The magnitude of the signal from the drum
tachometer 94 is representative of the ACTUAL VELOCITY at
which the travelling block 68 (Figure 2) is moving. The
; polarity of the voltage signal on the line 166 is repre-
.
sentative of the direction of travel of the travelling block
68. ConsequentLy, a positive polarity indicates an upward
direction of travel with respect to th~e vertical axis of the
- 68 ~
: ~:':
derrick 20. An upward direction of travel, of course,
implies that the motor mode is being asserted. A negative
polarity of the signal on the line 166 indicates downward
motion of the travelling block 68 with respect to the derrick
axis, and implies the brake mode is being asserted by the
computer.
The ACTUAL VELOCITY signal is filtered to remove com-
mutatinq spikes by a single-pole, low-pass filter network
580 which is comprised of a resistor 581 and a capacitor
582. Diodes 583 and 584, respectively connected to positive
and negative potentials, limit the signal to an amplifier
586. The filtered ACTUAL VELOCITY signal is presented
through a resistor 585 to the inverting input of the ad-
justable gain amplifier 586. t The non-inverting input of the
amplifier 586 is connected to ground potential through a
resistor 587. Connected in a feedback loop from the output
of the amplifier 586 to the input thereof is an adjustable
resistor 588. The gain of the amplifier 586 depends upon
the setting of the resistor 588. The output may be adjusted ~
to represent some nominal velocity, for example, 1 volt per -;
foot per second.
The output of the amplifier 586 is applied to the
inverting input of a unity gain inverter amplifier 590
through a resistor 591. The non-inverting input of the
amplifier 590 is connected to ground potential through a
resistor 592. The output of the amplifier 590 is fed back
to the inverting input thereof through a resistor 593. The
output is also connected by a line 594 to -the output line
134, which is the ACTUAL VELOCITY signal lnput to the brake
control subsystem 105 and the motor control subsystem 106 on
the lines 134B and 134M, respec~ively. With the circuit ~ ~
configuration described, the magnitude of the voltage signal ~ -
'
74~;
on the line 134 repres~nts the actual velocity o~ the bloc~,
with a positive polarity indicating upward movement at a
negative polarity indicating downward motion.
The output of the amplifier 586 is taken by a line
597 to a wrong direction indicating network 598. The network
598 includes comparators 599 and 600, and transistors 601
and 602 connected in a lo~ic OR configuration. The in-
verting input of the comparator 5~9 and the non-inverting
input of the comparator 600 are connected with the output of
the amplifier 586 through resistors 603 and 604, respec-
- tively. The switching points of the comparators are fixed
at a nominal, predetermined threshold level, for example, a
level corresponding to the velocity of about .5 foot/second.
The non-inverting input of the comparator 599 is connected
to a positive voltage from a positive potential source
through the resistors 605 and 606. The inverting input of
the comparator 600 is connected to a potential source
through the resistors 607 and 608.
The output from the comparator 599 is connected
through a diode 609 and a resistor 610 to the base of the
NPN transistor 602. The junction of the transistor 602 and
the resistor 610 is connected to ground potential through a
resistor 611. The output of the comparator 600 is connected
through a diode 612 and a resistor 613 to the base of the
NPN transistor 601. The junction of the base of the tran-
sistor 601 and the resistor 613 is tied to ground potential
through a resistor 614. ~,
One or the other of the comparators 599 or 600 is
disenabled, dependent upon whether a signal is present on the
line 615 or 616,, The line 615 is connected to a line 167
tied -to the MOTOR MODE SELECT line 144 from the computer.
The line 616 i5 connected to a line 168 tied to the BRAK
- 70 -
- - : . . ~
7435
MODE SELECT line 145 from the computer. A diode 617 is
connected in the line 615 to the junction between the diode
609 and the resistor 610. A diode 618 is connected in the
line 616 to the junction between the diode 612 and the
resistor 613. The diodes 617 and 618 are normally forward
biased, due to the connection of the anode of each diode 617
and 618 to a positive potential throu~h the resistors 619
and 620, respectively.
The output of the wrong direction network 598 is
taken from -the collector of the transistor 602 by a line 621.
The line 621 is connected to a line 169 connec-ted to the com-
puter input channel E. The network 598 operates to give a
WRONG DIRECTION OF MOTION signal on the line 169 if the
motion of the block exceeds the nominal setting 0.5 feet/
second in the wrong direction. If this occurs, either
transistor 602 or 601 ceases to conduct. A WRONG DIRECTION
OF MOTION signal is an interrupt condition, which disables
all systems and halts the program. As with all other
interrupt conditions, the entire system reverts to manual
control and all automatic operation is halted.
The enabling signals on the lines 167 and 168 from
the computer to the motor and brake control are applied,
through the lines 615 and 616, respectively, to the com~
parator outputs through the diodes 617 and 618. These
signals enable the appropriate comparator so that only the
"correct" wrong direction is sensed. If, for example, the ~ -~
motor control subsystem is controlling a hoisting motion,
the MOTOR MODE SELECT line 144 is low and the BRAKE MODE
SELECT line 145 is high so that the output of the comparator
599 is enabled and the outp~t of the comparator 600 is not
enabled. During hoisting the ACTUAL VELOCITY signal
polarity at the non-inverting input of the comparator 600
- 71 -
~ ~7~35
is negative so that the transistor 601 would tend to be
turned off, but the comparator output 600 is disconnected
since the diode 612 is back-biased. In this condition, the
transistor 601 is maintained in conduction by the signal
applied through the diode 618. However, if the ACTUAL
VELOCITY signal at the inverting input of the comparator 699
should become positive with a magnitude greater than ap-
proximately 0.5 volt, indicating a "wrong" direction of
travel, neither the diode 609 nor the diode 617 conducts, so
that the transistor 602 becomes non-conductive, signaling an
interrupt condition on the line 169 to the computer. The
"wrong" direction during a braking motion operates in a
similar manner.
The output of the amplifier 590 is also connected to
a zero velocity detector network 624. The network 624 in-
cludes comparators 625 and 626 connected as zero velocity
detectors. Since the output of the drum tachometer 94 is a
bipolar signal, two comparators 625 and 626 are required,
one effective for each direction. The inverting input of
the comparator 625 is connected to the output of the ampli-
fier 590 through a resistor 627. The non-inverting input is
connected to a switching point voltage set by the "down"
potentiometer 628, connected to ground on one side and to a
negative potential through a resistor 629 Oll the other. The
output of the comparator 625 is fed back to the non-
inverting terminal thereof through a loop including
resistors 630 and 631, and a capacitor 632. This positive
feedback loop provides hysteresis so that the comparator 625 ~`
will provide pc~sitive signal action with signals close to
the switching polnt.- The non-inverting lnput of the com-
parator 626 is also connected to the output of the ampli-
fier 59~ throucJh a resistor 63~. The inverting input lS ~ '
i2 ~
79~5
connected through a resistor 635 to a switching point
voltage set by the "up" potentiometer 636 which is connectod
to ground on one side and to a positive potential through
a resistor 637. The output of the comparator 626 is fed
bac~ to the non-inverting terminal thereof through a loop
including a resistor 638 and a capacitor 639. This positive
feedbac~ loop insures that the comparator 626 will provide a
positive switching action at input signals near threshold.
The outputs of the comparators 625 and 626 are con-
nected, through diodes 640 and 641, respectively, and a
through network including the resistor 642 and capacitor 649
to the base of an NPN-type transistor 645. The emitter of
the transistor 645 is connected to ground. The cathodes of
the diodes 640 and 641 are connected to ground through a
resistor 646. The collector of the transistor 645 is tied
to a positive potential through a resistor 647. The col-
lector of the transistor 645 is connected to the base of an ;~
NPN transistor 648. The emitter of the transistor 648 is
tied to ground, with the collector thereof being tied to an
output line 649. A diode 650 is connected between the line
649 and a positive potential. The output line 649 is con~
nected to a line 170, ZERO VELOCITY, (Figure 3) to the
computer channel D. The switching points of the comparators
625 and 626 are set by the potentiometers 628 and 636,
respectively, such that a predetermined small velocity in ~ ;
either the downward or upward direction is recognized AS a
zero velocity condition and a signal to that effect is
applied on the :Line 170 to the computer. Zero velocity on
the line 170, indicated by the transistor 648 being switched
on, is only one of the two necessary conditions for the
computer to recognize that the block is at its programmed
destination.
~ - 73 -
:: :
. , . ~ . . ~ :
As will be set forth in detail herein, the block
position and speed transducer 83 outputs a 0-10mA velocity
signal on a line 171 to the velocity comparator 108. This
unipolar current signal on the line 171 is applied to a
maximum velocity network 653. The current signal is con-
verted to a voltage signal by the action of a resistor 654
tied to ground potential. The voltage signal is applied to
the non-inverting input of a voltage follower amplifier 655
through a resistor 656, with a capacitor 657 tied to ground
potential. An adjustable maximum velocity signal derived
from a potentiometer 659 connected to a negative potential
through a resistor 660 is applied to the non-inverting input
of a voltage follower 662. The opposed polarity outputs of
the voltage followers 655 and 662 are applied through re-
sistors 664 and 665, respectively, and are summed at the
inverting input of an amplifier 667 effectively operating as
a comparator. The non-inverting input is tied to ground
through a resistor 668. The output of the comparator is fed
back to the non-inverting input thereof through parallel
~0 feedback paths including a resistor 669 and a capacitor 670.
The output of the comparator 667 is tied through a diode 671
and resistor 672 to the base of an NPN transistor 674. The
emitter of the transistor 674 is tied to ground, while the
output thereof is tied to a line 675. The line 675 is
connected to an output line 172. This M~XIMUM VELOCITY
signal on the line 172 is connected to the computer input
channel F.
The maximum velocity threshold set by the potentio-
meter 659 is normally greater than the actual velocity signal
3n to the follower 6S5, so that the output of the comparator 667
is at positive saturatlon, holding the transistor 674 in
conduction. How~ver, if the BLOC~ VELOCITY from the B.P.S.T.
:: ~
7~ _ ~
~7~35
83 exceeds the threshold however, the transistor 674 is
cutoff. The indication that the maximum velocity is ex-
ceeded is thus output to the computer on the llnes 675 and
172. Note that on both the lines 621 and 675, a normal
condition is indicated by current flow. When an abnormal
condition is sensed, that current signal drops to zero.
Diodes 677 and 678 are, respectively, tied between the lines
621 and 675 and a positive potential.
t
:
- 75 -
.
435
BLOCK POSITION ~ND SP~ED TR~NSDUCE~
Referring to Figure 11, a detailed schematlc ~iagram
of the block position and speed transducer (B.P.S.T.) 83 is
shown. As mentioned, the B.P.S.T. 83 outputs a position
feedback signal to the computer input channel J on the line
116. Further, a position signal is input to the brake
control subsystem 105 and the motor control subsystem 106 on
the lines 116B and 116M, respectively. Also, as discussed
in connection with Figure 10, the B.P.S.T. 83 puts a 0-lOmA
BLOCK VELOCITY signal on the line 171 to the velocity com-
parator 108.
The B.P.S.T. 83 associated with the block 68 and is
mounted on the carriage of the block retractor 78 for travel
therewith along the guide track 80. The travelling block 68,
of course, moves with the carriage 78. The mounting details
are illustrated diagrammatically ~ith any suitable means of
mounting being within the contemplation of this invention.
A friction wheel 690, manufactured of any suitable material,
as urethane, is contacted against the retractor guide track
80. A spring 691 biases the wheel 690 into contact with the
track 80. Displacement of the carriage 78 causes rotation
of the wheel 690 and a shaft 692 suitably coupled thereto.
At the opposite end of the shaft 692 is coupled a toothed
wheel 693 which is driven by movement of the wheel 690.
The B.P.S.T. 83 includes a zero velocity magnetic
pickup 635, such as that manufactured by Airpax and sold
under Model No. 4-000~. The pickup 695 outputs a square
wave pulse each time a tooth of the wheel 693 passes in
proximity to the pickup 695. This signal is hereafter
referred to as the "A" signal. The pickup also outputs a
signal, either a logic 1 or a logic 0, indicative of the
- 76 -
- . .
~7435
direction in which the teeth of the wheel 69~ are ~)assing.
This sigllal is hereafter referred to as the "B" sigllal. It
is quickly appreciated that a predetermined yiven number of
output pulses from the pickup calibrated and used to repre-
sent displacement of the block a predetermined rectilinear
distance along the track 80. Similarly, the frequency of
the pulses is proportional to the speed at which the carriage
?8 moves. The "A" and "B" signals of the pickup 695 are
connected to a signal le~el translator 697. A suitable
translator 697 is that manufactured by Motorola and sold
under Model No. MC 666. The function of the translator 697
is to translate the magnitudes ofthe "A" and "B" signals to
a level compatible with the electronic components which
follow. The "A" signal is also transmitted by a line 698 to
the input of a frequency-to-voltage converter 699. Any
suitable converter 699 may be utilized, such as that manu-
factured by Teledyne Filbrick and sold under Model No. 4702.
The frequency-to-voltage converter 699 serves to pro-
vide an average output voltage proportional to the frequency
of the square wave input signal. Potentiometers may, of
course, be provided to adjust the zero and full scale out-
pu~t. For example, a nominal sensitivity of 1.0 volt/foot/
second with a full scale of 10 volts, or any other pre-
determined setting may be utilized. The output from the
converter 699 is applied to a unity gain inverting amplifier
700 (shown schematically). The output of the inverting
amplifier 700 is applied to a voltage-to-current converter ;
701. The converter 701 is similar in circuit details to
the voltage-to-current converter 246B shown in Figure $B.
The converter functions to provide a O-lOmA output propor-
tional to the O to -10 volt input signal. A suitable
trimming resistor may be provided to adjust the output
~7435
current to a predetermined value, for example, IOmA when
the input voltage is 10 volts. Resistors or potentiometers
may also be provided to make the current output independent
of load resistance. A O-lOmA output current signal on the
line 171 is functionally related to the frequency of the
square wave input on the line 698 and, accordingly, to the
speed of the carriage 78 and the travelling block 68
associated therewith. As before, the current signal is
preferred due to the high noise .;mmunity offered thereby.
Further, the constant current source characteristic ma~es
the cable resistance and/or cable length uncritical. Thus,
long cable runs through electrically noisy environments
using economical unshielded cable are possible. The output
from the voltage-to-current converter 701 is connected by
the line 171, discussed above, to the velocity comparator
108. Although the velocity feedback signals are received
at the velocity comparator 108 from the drum tachometer 94,
it is noted that redundancy is provided by the velocity
signal output from the B.P.S.T. 83. The velocity signal
from the B.P.S.T. 83 provides excess velocity information
should the drum tachometer 94 develop a malfunction.
As noted, the "A" and "B" output signals ~rom th`e
pickup 695 are output from the level translator 697. A
line 703 carrying the "A" signal (also input to the con-
verter 699), and a line 704, carrying the "B" signal
representative of the direction of motion of the wheel 693
are both input to a cascaded array of counters, 706A, 706B,
and 706C, such as those manufactured by Motorola and sold
under model number MC14516CP. The counters register the
number of pulses received on the line 703 during the
motion of the block. Thus, the total count is the measure
of the vertical distance traversed. The directional signal
~ 78 -
~7~35
input on the line 70~ ~letermines whether th~ count is to ~c
ad~ed or subtracted (i.e., countup or countdown) from the
initial value. In the Figure, the array of counters 706
provides a total count of 4096.
The parallel outputs Q(N) of t}~e counters 706 are
applied to a digital-to-analog converter 710, such as that
manufactured by Hybrid Systems Corporation and sold under
the model number DAC 380-12. The output of the converter
710 is a current proportional to the magnitude of the count
received. Potentiometers 711 and 712 are, respectively,
provided to adjust the zero and full scaIe current levels.
These potentiometers may be set, for example, so that a 4mA
signal corresponds to a zero count and a 20mA current
corresponds to a register count of 4095. The output
current, is, therefore, proportional to the elevation of
the travelling biock. The output current signal, sharing
the same attributes as discussed above, is applied to the
output line 116 to the computer (on input channel J) and to
the brake and motor control subsystems 105 and 106,
respectively on the lines 116B and 116M.
Since the B.P.S.T. ls an incremental position sensing
system, a reset is employed to establish a definite and
repeatable correlation between the count registered and the
physical position of the block 68. As noted earlier in
connection with Figure 2, two proximity switch sensors 8~
and 85 are located on the carriage 78 which are actuated by
metal targets 86 and 87. This arrangement provides un- ~;
ambiguous reset points near the upper and lower ends of the
retractor guide 80. Each reset switch output is applied to
an anti-bounce network 715 and 716, each utilizing two
cross-coupled NOR gates 718 and 719. The output of each of
the networks 715 and 716 is applied to a bistable network
'
- 79 - ~
~7~35
720. The output of the network 720 ~unctions to ~aintain
one or the other or reset buses 721 or 722 high (i.e., at
logic 1), depending upon which reset switch 715 or 716 is
actuated.
The upper reset bus 721 and the lower reset bus 722
each have a diode-resistor network wire thereto which forms
a pattern to the preset inputs ;r (N) of the counters 706
representing a predetermined count for the physical
elevation of each target. The output of the anti-bounce
networks are fed through a NAND gate 723 to the preset
inputs of the counters 706. Thus, the counters 706 are
preset to a predetermined count each time a sensor passes
its respective target.
NAND gates 724A, 724B and 724C are connected as a
Schmitt trigger network. The output of the trigger network
pro~ides a reset pulse to the reset inputs of each counter
706 through a capacitor 725 and a diode 726. The output
of the trigger network resets the counters 706 at a fixed
time delay after the system power is applied. This time
delay is set by the resistor 728 and the capacitor 725.
Any predetermined time delay may be used. As a result, the
counters 706 are automatically set to zero count each time
the system is powered-up.
However, there remains the possibility that after the
counters 706 are ~eset to zero following power-up, one
spurious count combined with a down signal from the magnetic
pickup could cause the counters 706 to register a full
count of 4095. To prevent this situation, the reset pulse
described above is also applied to a NAND gate 727
functioning as an inverter. It5 output functions to switch
the lower reset: bus 722 to logic 1 through the diode 728.
During a predetermined additional time interval, set by
:'
- 80 -
~.... . - ~ .
435
the capacitor 730 and resistor 731, the preset pin of the
middle counter 706B is enabled through an inverter 732 and
a diode 733. The result is that a preset count is entered
following each power-up. In this example, a count of 48
is entered, although any value can be preset by appropriate
rearrangement of the logic.
~' ' , '
~ ~.
- 81 -
743~i
ELEVATOR I.OAD CO~TROL
As alluded to above, during both the make-up and
break-out cycles it is necessary and desirable to ~onitor
the load being carried by the elevator 75 (Figure 2).
~cc~rdingly, as discussed in connection with the brak~ control
subsystem 105 and the motor control subsystem ]06, feedback
signals from the elevator 102d control subsystem 107 are
utilized in the determination by the motor or brake controls
of the speed at ~Ihich the drill string is lifted (by the
motor) during break-out cycle or the speed at which the
string is permitted to ~all (by the brake) during make-up
cycle. The necessity and advantage of considering the
elevator loading is apparent. If the drill string is
encumbered as it is lifted out of or lowered into the bore,
the loading on the elevator departs from a predetermined
preset minimum (during lowering) or a predetermined preset
maximum (during hoisting). In either case damage to bore
may occur if the velocity of the block is not limited.
As seen in Figure 3, the basic drawworks control
block diagram, it is noted that the elevator load control
subsystem receives output signals from computer channels N,
0, and P on lines 175, 176 and 177, respectively. Feedback
signals to the computer channels K, L, and M are carried
from the elevator load control subsystem are carried on
lines 178, 179 and 180, respectively. It is also noted that
a feedback signal representative of the actual elevator load
is output to bol:h the brake control subsystem 105 and the
motor control subsystems 106 through the lines 136B and
136M, respectively, while appropriately scaled initial load
feedback signals are respectively output to the brake and
motor control subsystems through the lines 138B and 138M,
~'
- 82 ~
,
~7~3S
respectively. The derivation of these signals is discussed
herein.
The elevator load control subsystem 107 derives its
operating input from the deaclline force sensor (D.L.F.S.) 95
on the line 110 (Figure 3). The signal from the D.L.F.S. 95
may be conditioned, if desired. As is the case with all
signals derived from relatively distance transducers, the
signal from the D.L.F.S. is a 4-20m~ current signal, chosen
for the reasons outlined above.
Rererring now to Figure 12 r which is a detailed
schematic diagram of the elevator load control subsystem
107, the 4-20mA signal is taken from the input line 110 and
converted to a voltage signal by the action of resistor 735
connected to a negative potential. This is a configuration
similar to that used throughout the invention to convert a
current to a voltage signal. The voltage signal is filtered
by a filtering network 737 including a resistor 738 and a
capacitor 739. The filtered voltage signal is taken through
a buffer amplifier 740 and carried by a line 741 to the non-
inverting input of a comparator 742 through a resistor 743.
The non-inverting input of the comparator 742 is tied to
ground potential through a resistor 744. A potentiometer
745 connected to a positive potential adjusts the zero point
of the comparator 742.
The output of the amplifier 740 representative of
the loading on the elevator 75 (Figure 2) at any given
instant is conne~ted by a line 747 to a sample-and-hold
network 748. The network 748 includes a buffer amplifier
749 connected to its non-inverting input to the line 747.
The output of the amplifier 749 is taken through a diode
750 and a resistor 751 to a bilateral switch 752.
The junction of the diode 750 and the resistor 751 is tied
- 83 -
.. . :
to ground potential through a resistor 753 while a Zener
diode 754 is interposed between the junction of the re-
sistor 751 and the switch 752. The output of the switch 752
is connected to the gate of a field effect transistor 755
with the gate also being connected to ground po-tential
through a capacitor 756. The drain of the transistor 755
is connected to a positive potential. The source is con-
nected to a negative potential through a resistor 757. The
output of the sample-and-hold network 748 is taken by a line
759 at the source of the transistor 755 and applied through
a resistor 760 to the inverting input of the differential
amplifier 742. The output of the differential amplifier
742 is fed back to its inverting input through a resistor
761. The switch 752 is connected through a NAND 763, both
inputs thereof being tied through a diode 764 to the line
SA~IPLE ZERO LOAD line 175 leading from computer channel N.
The NA~D gate 763 inputs are connected to a positive
potential through a resistor 765.
When the switch 752 is closed momentarily by an
enabling signal on the line 175 from channel N of the com-
puter, the capacitor 756 is charged to a level corresponding
to the elevator load signal at the output of the amplifier
740. The signal level at the output of the transistor 755
on the line 759 remains at the level existing when the
switch 752 is gated off until the next gate signal is
applied. The computer is programmed such that channel N
the "SAMPLE ZERO LOAD" signal is activated when the elevator
and block are not in motion and at an appropriate point in
the cycle when the elevator has not acquired any load. The
signal presented at the inverting input of the comparator
742 may then be thought of as consisting of the tare weight
of the elevator and block plus any offsets and accumulated
- 84 -
long-term drifts existinc~ ln the load measuring networks.
At the diEferential amplifier 742, the zero signal is sub-
tracted from a signal representative of the instantaneous
elevator load input on the line 741 so that the instantaneous
signal representative of the actual loading on the elevator
at the output line 766 from the clifferential amplifier 742
is presented to the output line 136 ACTUAL LOAD.
The output from the field effect transistor 755 on
the line 759 is fed back through a line 767 to the inverting
ln input of the amplifier 749.
A substantially identical sample-and-hold network
770 is connected to the output of the comparator 7~2 through
the line 771. The non-inverting input of a buffer amplifier
772 is connected to the slgnal on the line 771. The output
of the amplifier 772 is connecte~ throu~h a diode 773 and a
resistor 774 to a bilateral switch 775. The junction be-
tween the diode 773 and the resistor 774 is connected to ~- -
ground potential through a resistor 776. The junction
between the resistor 774 and the switch 775 is connected to
ground potential through a zener diode 777~ The output of
the switch 775 is connected to a capacitor 779 and to the
gate of a field effect transistor 780. The drain of the
transistor 780 is connected to a positive potential while
the source thereof is connected to a negative potential
through a resistor 781. The output of the network 770 is
taken from the source of the transistor 780. This output is
also Eed back to the inverting input of the amplifier 772 by
a line 783. The output of the transistor 780 is also con-
nected through series resistors 784 and 785 to ground
potential. A llne 786 is connected at the junction of the
transistors 78~ and 785 for a purpose to be discussed
herein. The output of the sample-and hold network 770 is
.
connected by a line 787 to a switch 788.
- 85 -
~7~3~i
The switch 775 is connected to a NAND gate 790, the
tied inpu-ts of which are connected through a diode 791 to
the line SA*lPLE LOAD on the line 176 leading from the out-
put channel 0 of the computer. ~he inputs to the NAN~ ga-te
790 are connected to a positive E)otential through a
resistor 792. With the receipt of a signal from the com-
puter channel 0 on the line 176 the positive signal present
on the input of the NAND gate 790 connected as an inverter
switches to a logic 0. The output switches to a logic 1
which gates on the switch 775. With the switch 775 gated
on, the capacitor 779 charges to a signal level such that
the output of the transistor 780 on a line 787 is equal to
the signal level existing at the amplifier 742 output of
the line 771. This signal level at the line 787 remains
at the level existing when the switch 775 is gated off until
the next gating signal is applied. The signal from the
computer on the line 176 is activated at a point in the
cycle when the elevator has acquired a load but is not yet
in motion. Thus, the output of the transistor 780 on the
line 787 represents the "dead weight" of the drill string
load. This is the INITIAL LOAD and is the base value of
the drill string load used for comparison with the ACTUAL
LOAD by the brake control subsystem 105 and the motor control
subsystem 106, as discussed in connection with the de-
scription of those subsystems.
The switch 788 is connected at its input by a line
796 to the non-inverting input of a buffer amplifier 797.
The switch 788 is controlled by a transistor 798 of the NPN
type, the base of which is connected through a resistor 799
and the diode 800 to the line 177. The LO~D CONTROL ON
signal from the computer output channel P is applied on the
line 177. The signal end of th~ resistor 799 is connected
- 86 -
.:
.~ : . ~ .. . ..... .. .
`----
~474~5
to a positive potential through a resistor 802. The col-
lector of the transistor 798 is connected to a positive
potential through a resistor 803. The collector of the
transistor 798 is also connected to the control lead of the
bilateral switch 788. The signal end of the resistor 799
is also connected by a line 804 to the control lead of a
second switch 805. The switch 805 connects the output of
the amplifier 742 through a line 806 to the non-inverting
input of the buffer amplifier 797. Except during the CRE~P
mode, the LOAD CONTROL ON signal is asserted whenever the
drill string is being raised or lowered. When this signal
is asserted, the switch 788 is gated on and this switches
the signal representing the INITIAL LOAD on the line 787 ~
to the input of the amplifier 797. At the same time, the ~-
bilateral switch 805 is turned off. The INITIAI, LOA
signal at the output of the amplifier 797 is applied
through parallel paths including resistors 810 and 811 to
level control circuits 812 and 813, respectively.
Each of the level selectors comprises a bank of re-
sistors such that, depending upon the setting of the
selector switch, a predetermined fraction of the INITIAL
LOAD is applied through a resistor 815 to the inverting -
input of a buffer amplifier 816. The non-ihverting input
of the buffer amplifier is connected through a resistor
817 to ground potential. The output of the amplifier 816
is fed back through its inverting input through a resistor
818. The settin~ selected by a skilled driller and dialed ~;
into the level colltroller 812 is an adjustable fraction K
between 0 and 0.9 of the INITIAL LOAD. This level is in~
verted by the amplifier 816 and applied on the output line
819 to a connection with the line 138B input to the brake
control subsystem 105. ~ -
- 87 -
- -, . ,: . . , ~
~7435
The physical effect of choosin~ the factor Kl may be
seen by a consideration of the lowering operation. During
lowering, the actual load on the elevator will be less than
or equal to tlle initial INITIAL LOAD value due to frictional
forces on the moving pipe. Ther~efore, it is reasonable to
anticipate that some deviation of the actual load on the
elevator below that of the INITIAL LOAD may be encountered
during a normal lowering operation. The magnitude of the
allowable deviation is defined by the magnitude of the
constant Kl selectable by the level controller 812.
A portion of the signal at the inverting input of the
amplifier 816, the magnitude of that portion being defined
by the ratio of the resistors 821 to 822, is applied by a
line 823 to the inverting input of a comparator 824. The
non-inverting input of the comparator 824 is connected
through a resistor 825 to the actual load value carried
thereto by a line 826. The output of the comparator 824 is
connected through a diode 827 and a resistor 828 connected
to the base of an NPN transistor 829. A suitable base
resistor 830 is provided. The output of the transistor 829,
which is normally conducting, taken at the collector thereof,
is connected by a line 831 to the output line 178 leading
from the elevator load control subsystem 107 to the computer
input channel K. This is the LOAD UNDER LIMIT interrupt
signal. The junction of the diode 827 and the transistor
828 is connected through a diode 833 to the output taken at
the emitter of a transistor 834. The base of the transistor
834 is connected to the LO~D CONTROL ON line with the
collector thereof being tied to a positive potential. Thus, ~ ;
during those periods of time when the LOAD CONTROL ON is -
asserted by the computer, the transistor 834 is not con~
ducting and the output of the comparator 824 is enabled.
- 88 -
:'''
- \ -
~ ~7435
The resistors 8Zland 822 establish an under-limit switching
threshold for the comparator 824 for a given Kl selected.
When the value of the actual load falls below the preset
fraction of the scaled INITIAL L~AD at the inverting input
of the comparator 824, the comparator switches so that t~e
transistor 829 switches off. This constitutes an alarm
signal indicating that the elevator load is under pre-
determined limit and actuates an interrupt system, halting
the program and applying full braking effort as discussed
above. The interrupt causes the entire system to revert
from an automatic to manual mode.
The level selector 813 operates in a similar manner.
The signal at the output of the level controller 813 is
applied through a resistor 835 to the inverting input of a
comparator 836. The actual load signal carried by the line
826 through a resistor 837 is summed at the inverting input
of the a~plifier to produce a polarity inversion.
The non-inverting input is connected to ground potential
through a resistor 838 so that the comparator switching
threshold is zero potential. The output of the comparator
836 is connected through a diode 839 and a resistor 840 to
the base of an NPN transistor 841 having a base resistor ~ ~
842. The collector output of the transistor 841 is con- ;
nected to line 844 and the line 179 to the computer input
channel L. This is the LOAD UNDER LIMIT signal. A diode
845 is connected between the junction of the diode 83g and
the resistor 840. This maintains the transistor 841 in
conduction when the transistor 834 is in conduction (i.e.,
when the LOAD CONTROL ON signal is not asserted). Thus, the ;
function of the LOAD OVER LIMIT interrupt is inhibited.
During a hoisting operation, the actual load may be
increased over t:he INITIAL LOAD value through the effect of
89 ;~ ;
43~
friction between the pipe and th~ bore. Therefore, durin-~
a hois ing operation, the INITIAL LOAD is scaled by an
appropriate factor K2 selected from the level controller
813. The setting of the selector switch establishes the
gain of the amplifier 849. This appropriately scaled 1OA(1
is present~d by the line 834 to the output line 138M carried
to the motor control subsystem 105. As long as the ~CTUAL
LOAD signal stays within the range of values defined by
the constant K2, as described above, the motor control sub-
system 106 is permitted to control the hoisting velocity
without being affected by the load factor. However, as in
the case of the lowering motion, if the actual loading on
the elevator exceeds some preset fraction (set by the ratio
of the resistors 835 to 837), an interrupt sig~al is output
on the line 179 indicating that the elevator LOAD UNDER
LIMIT has been exceeded, interrupting the program and
causing the entire system to revert from automatic to
manual control. Note that when the LOAD CONTROL ON signal
is not asserted, the line 177 is at logic 1 and the tran-
2Q sistor 798 conducts and the switch 788 is gated off. At
the same time, the switch 805 is gated on. The ACTUAL LOAD ~`
value is continuously applied to the load level selector
rather than the INITIAL LOAD value. This effectively
inhibits the function of the load control subsystem.
The actual load value at the output of the amplifier ~;
742 is also applied by the line 771 to a load acquired
network 850. The signal is applied to a high-pass filter
network comprising a capacitor 852 and a resistor 853 con-
nected to ground potential. The filter is tied to the non-
inverting input of a buffer amplifier 854, the output of
which is connected by a line 855 to the inverting input of a
comparator 856 through a resistor 857. The non-inverting ~
- 9 0 - ~ . ,
: .
435
input of the comparator 856 is conducted by a line 858
through a resistor 8~9 from the output of a buffer amplifier
860. The non-inverting input of the amplifier 860 is taken
from the line 786. The output of the amplifier 860 is
applied through a diode 861 and is fed back to the inverting
input thereof through a resistor 862. The output of the
amplifier 860 taken through the diode 861 is applied
through resistor 863 to an amplifier 864. The non-inverting
input of the amplifier 864 is connected to ground potential
through a resistor 865 while the output thereof is fed back
to the inverting input through a resistor 866. The output
of the amplifier 864 is connected to the inverting input of
a comparator 868 through a resistor 869. The non-inverting
input of the comparator 868 is taken through a resistor
870 from the line 855.
The output of the comparator 856 is connected
through a diode 875 and a resistor 876 to the set pin of a
cross-coupled NAND 877A and 877B connected as a flip-flop
circuit. The output of the comparator 868 is taken through
a diode 878 and a resistor 879 to the reset input of the
flip-flop 877. The output of the flip-flop is taken
through a resistor 880 connected to the base of an NPN
transistor 881. The collector output of the transistor
881 connected by a line 882 to the output line 180 from the
elevator load control subsystem 107 to the computer on the
input channel N.
The output of the amplifier 854 and the line 85S is
the LOAD ACQUIRED signal. It is fed to the two comparators
856 and 868. The other signal being applied to the com- ;
parators is, as shown, a reference signal equal to approxi-~ ~ ;
mately 1/3 the value of the INITIAL LOAD signal as estab~
lished by the resistors 784 and 785. The reference sigl~al
to the comparator 868 is inverted by the amplirier 864 to
maintain the proper signal sense. The~reference signals are
-- 91 -- . ~
,:
:~4743S
necessary so that the comparators can accommodate a wide
range of hook loads. It adjusts the switching point of the
comparators 856 and 868 to a level consistent with the drlll
strin~ ]oad during the previous cycle. The change in
weight over a sequence cycle to cycle is equivalent to one
stand of pipe and so for a typical drill string make-up the
per cent change in weight is ne~ligible. The output of the
comparators 856 and 868 drive the flip-flop 877. Prior to
load acquisition, the normal steady state outputs of the
comparators 856 and 868 are at a logic 1 due to the
reference signals applied. The load acquired flip-flop is
at a logic 0. The capacitively coupled load acquired signal
momentarily switches the comparator 856, so its output
switches to logic 0. This sets the flip-flop 877 so its
output switches and remains at logic 1. Later, a negative
going load released signal momentarily swithces the com-
parator 868 so that its output pulse resets the flip-flop
and the flip-flop output switches to logic 0. The tran-
sistor 881 conducts during the interval that the elevator
75 is supporting the drill string load. Thus, during the
time that load is acquired by the elevator, a current
signal on the line 180 is applied to the computer channel
N. When the load has been released, the signal current
ievel drops to zero.
. .
- 92 -
~ ~ ~7435
ASSOCIATED S~FETY SYSTEMS
~ eferring to Figure 13, a schematic diagram of an
automatic sequence disenable and interrupt logic circuit 900
is shown. The purpose of this circuitry is to permit an
e~perienced driller on the derrick to manually correct some
physical problem on the ri~ which is causinc3 the automate~
sequence to "hang-up" (a temporary halt to the computer
pro~ram sequencing) and to perform that action without risk
of physical injury. Since it is possible that correction of
the structural disorder will enable the automated sequence
to continue, and perhaps imperil the operator, it is im-
perative from a personnel safety stand point that the
automatic disenable be provided. ~;
The driller's control console is provided with an
AUTO MODE switch 901 which in the NORMAL position applies a
positive voltage signal to a two-pole low-pass filter and
diode limiter 902 to apply a logic 1 signal to the A input
of NOR ~ate 903C. When a "hang-up" exists in the drawworks
program, indicating tha-t the elements controlled by the
drat~.~orks elements (Figure 2) are in a motionless condition,
the line 904 from the computer goes to logic 0. Similarly
the line 905 from the computer goes toa logic 0 condition
each time a "hang-up" exists in the racker control program.
Thus, all of the structural elements controlled by that
program (numeral 34, Figure 2) are also static or motion-
less. A "hanq-up" therefore occurs only when an appropriate
feedbac~ signal is absent due to a malfunction or at a point
where one program is awaiting a function which occurs in tlle ~ ~-
other program to be completed.
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7435
The NOR ~ates 903A, 903B, 903C and 903D are con-
nected as shown so that when the three signals (from the
switch 901, and on the lines 904 and 905) are logic 0, a
transistor 906 of the NPN type ceases conduction. This con-
stitutes an output siynal carried by the line 907 which
causes the AUTO/MANUAL bus to be de-energized. This in-
hibits all control function and the entire system reverts
to a manual mode, and all sequencing is halted. This con-
dition remains until the ~UTO MODE switch is returned to
the NORMAL position. Thus, after actuating the AUTO MODE
switch to the DISABLE position, the operator can safely
correct a malfunction without the danger of the system
immediately continuing on in the automatic sequence. Then
the repair has been effected, the switch 901 can be re-
turned to the NORMAL position and the automatic cycle is
resumed. Thus, a fault in the structural system (or any
other operator correctable malfunction) can therefore be
corrected without disrupting the computer program, and
thereby avoid the complicated start-up and reloading pro-
cedures.
A power-fail sensing system may also be provided.
The circuit includes the transistors 910, 911 respectively,
of the NPN and PNP types, and the optical coupler 912. This
;~ circuitry monitors the power supplies utilized in the in-
vention. The transistor 911 is normally biased off and is
non-conducting while the optical coupler 912 is conducting
and current in a line 914 is a normal condition. When any
of the monitored power sources fail, i.e., +15 VDC, -15 VDC,
-24 VDC (tong supply) and 26 V, 400 ~Iz. AC, the transistor
911 conducts whi.ch biases the optical coupler 912 to an off
or non-conducting state. Therefore, an output current
signal to the line 914 is interrupted. This constitutes an
~,
_ 9~
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.,
~147435
interrupt signal to the computer on the line 914. Of course,
loss of +24 VDC control power to the coupler 912 accomplishes
the same result.
The EXCLUSIVE OR gate 920 receives lnput signals on
the lines 921 and 922 from the high drum clutch and the low
drum clutch feedback switches. The drawwor~s control
utilizes two clutches in the particular embodiment shown.
One or the other of the clutehes may be damaged by simul-
taneous engagement of both. The EXCLUSIVE OR gate accepts
only one or the other of the eluteh signals, but not both.
This effectlvely prevents simultaneous engagement of the
elutchesO The output of the gate 920 drives a transistor
923 of the NPN type when, eondueting supplies a CLUTCH
EWGAGED feedbaek signal to the eomputer on the line 924.
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