Note: Descriptions are shown in the official language in which they were submitted.
T~e invention ~ener~lly
pertains to control techniques and apparatus for operating
a transfer machine with improved efficiency. More particu-
larly, the invention peItains to transfer machine control
apparatus which is capable of activating respective work
units of a txansfer machine to perform their respective
work tasks only when parts are present at their individual
work stations. Even more particulaLly, the invention per-
tains to control apparatus of the above type wherein the
movement of parts through a transfer machine is monitored
by shifting digital data bits through a shift register in
synchronous relationship with the movement of parts through
the machine.
l~
.....
,. . ~
As is well known in various mar.ufacturing activities, a
transfer machine is a machine or machining system which is
structured to receive a succession of work pieces or parts,
and which performs a sequence of discrete work tasks upon
each part. During each part transfer cycle in a succession
of part transfer cycles~ a transfer mechanism operates to
move a part from a load station to the first work station in
a work station sequence, to move a part from the final work
station in the sequence to an unload station, and to advance
each of the other parts in the machine by one work station in
the work station sequence. After each transfer cycle, the
transfer machine commen_es a work unit cycle during which a
work unit at each of the work stations performs one of the
discrete work tasks upon a part which has been advanced by
the transfer mechanism.
Transfer machines of the above type have found wide
application in the machining of metallic parts, particularly
where large part volume is required. By locating a spindle-
driven cutting tool at each work station, and by providing an
2~ electronic controller device to direct operation of the cut~ing
tools and the transfer mechanism, a transfer machine can
automatically perform a number of machining processes on each
part in a continuous stream of parts, in a comparatively
short period of time. However~ the efficiency of transfer
machine operation may be significantly reduced if, for some
reason, there is a failure to load a part into the machine
between part transfer cycles. When such ~ailure occurs,
automatic, continuous operation of the transfer machine ceases.
The machine can then be operated only in a manual mode, or
by operator intervention. Such operation, however, may create
gaps in the stream of parts moving along the sequence of work
stations. The creation of gaps, in turn, causes needless wear
of the work unitsl since a unit will sometimes be cycled, or
activated, when there is no part present at its particular
work station.
--3--
In addi~ion, if a work unit is cycled when a part is not
present at its ~ork station, the time requixed to machine a
succession of parts will be unnecessarily increased. Generally,
the work units require different amounts of time, or cycling
times, to perEorm their respective work tasks, and it will be
readily apparent that the period of time between two successive
part transfer cycles can be no less than the longest of such
cycling times. If the unit having the longest cycling time is
operated when a part is absent from its work station, there
will be a needless increase in the amount of time required be-
fore the next transfer cycle can take place.
Through his invention, the Applicant enables the operation
of a transfer machine to be continued in spite of periodic
failures to load parts into the machine. In addition, the ir-
vention enables a work unit to be cycled ollowing a part trans-
fer cycle only if a part is present at the unit, the time be-
tween part transfer cycles being limited to the longest cycl-
ing time of the units at which parts are actually presen~. The
Applicant's invention may be practiced by a comparatively simple
adaptation of a conventional transfer machine controller device.
However, it is by no means intended to limit the scope of the
invention thereto.
SUMMARY OF THE INVENTION
In the present invention, transfer machine apparatus is
provided which includes a load station for receiving parts
during at least some of the part reception periods in a suc-
cession of part reception periods, and which further includes
a number of selectively located work units for performing pre-
specified work tasks upon received parts. ~ transfer means is
provided for moving a given one of the received parts from the
load station to each of the work units in a prespecified se-
quence, the given received part being moved from one of the
4_
work units to another one of the work units during a part trans-
fer cycle in a succession of part transfer cycles. A digital
code storage means receives a digital code duriny each of the
part reception periods, the storage means receiving a first
digital code if a part is received by the load station during
the part reception period and the storage means receiving a
second digital code if a part is not received by the load sta-
tion during the part reception period. The storage means is
provided with a~number of discrete digital code storage posi-
tions, each of the work units uni~uely corresponding to one ofthe storage positions. A shift means shifts the received disi-
tal code within the storage means in synchronous relationship
with the movement of received parts so that at the conclusion
of a selected number of part tranC cyclesl the digital code
contained in a given one of the storage positions comprises a
first or second digital code, according to whether a received
part is or is not present, respectively, at the work unit cor-
responding to the given storage position. A selective enabling
means, responsive to the contents of each of the storage posi-
tions, enables the work unit corresponding to the given stor-
age position to perform its prespecified work task at the con-
clusion of the selected number of part transfer cycles if a
first digital code is contained in the given storage position,
and otherwise prevents the work unit from performing its pre-
specified work task.
Preferrably, the digital code storage means in the aboveapparatus comprises a shift register which is provided with
a number of positions for storing discrete digital bits, each
of the bit storage positions comprising one of the digital
code storage positions. Each of the first digital codes com-
prises a digital bit of a first logic level, such as a logic
1 bit, and each of the second digital codes comprises a digi-
tal bit of a second logic level, such as a logic 0 bit. Pre-
ferrably also, the shift means comprises means for shifting a
;~ 3
--5~
given one of the digital bits from a first one of the bit stor-
age positions during one of the part transfer cycles. The work
unit which corresponds to the first storage position precedes
the work unit which corresponds to the second storage position
in the afcrementioned work unit sequence.
In a preferred embodiment of the invention, each of ~he
work units comprises a spindle-driven tool Eor performing a
prespecified cutting operation on a metallic part~ The trans-
fer means for such embodiment comprises a transfer bar struc-
ture which is capable of operating during each of the parttranser cycles to move a received part ~rom the load station
to the first work unit in the work unit sequence, to move a
received part from the final work unit in the sequence to an
unload station, and to advance each of the other received parts
by one work unit in the work unit sequence. Also in the pre-
ferred embodiment, the selective enabling means comprises means
for either activating or deactivating a work unit after a part
transfer cycle, according to whether a digital bit of a first
or second logic level is contained in the bit storage position
corresponding to the work station after the transfer cycle.
Alternatively, the present invention may be viewed as a
method for controlling the operation of a transfer machine,
such method comprising the steps ofo entering a first digital
bit into a shift register during a given part reception period,
in a succession of part reception periods, if a part is re-
ceived at a load station of the transfer machine during the
given part reception period; entering a second digital bit into
the shift register during the given part reception period if
a part is not received at the load station during the given
part reception period; moving one of the received parts to
each of a number of work stations included in the transfer ma-
chine in a prespecified sequence; establishing a unique corres-
pondence between each of the work stations and each of a number
of bit storage positions which are included in the shift regis-
ter; shifting the first and second digital bits within the
shift register in synchronous relationship with the movement
of received parts to respective work stations of the transfer
machine; activating a given one of the work stations at a
given time to perform a prespecified work ~ask upon one of
the received parts if a first digital bit is contained in the
storage position which corresponds to the given work station
at the given time; and preventing activation of the given
work station at the given time if a second digital bit is
contained in the bit storage position corresponding to the
given work station at the given time.
OBJECTS OF THE INVENTION
An object of the present invention is to provide a trans-
fer machine wherein a transfer operation or cycle will occur
even if a part or workpiece is no~ present at the load station
of the transfer machine.
Another object is to provide a transfer machine of the
above type wherein a work unit of the transfer machine is ac
tivated to perform an assigned work ~ask during a work unit
cycle only if a part is located at the w~ k unit during the
work cycle.
Another object is to provide a transfer machine of the
above type wherein the length of a work unit cycle is limited
to the time which is required for all of the work units at
which parts are present to complete their respective work
tasks.
Another ob~ect is to provide an electronic controller
device for controlling the operation of a transEer machine of
the above type.
Another object is to provide electronic control apparatus
for a transfer machine which activates or prevents activation
of respective work units of the machine during a work cycle,
in accordance with digital data which is stored in a shift
register at the beginning of the work cycle.
-7--
These and other objects of the invention will become more
readily apparent from the ensuing specification, when taken to-
gether with the drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
Figure 1 is an elevational view showing a generalized form
of a transfer machine.
FigO 2 is a block diagram showing a controller device for
directing the operation o the transfer machine of Fig. 1.
Figs. 3-10 in which Fig. 10 appears on the same sheet as
Fig. " 7 show ladder diagrams which may be employed to structure
the controller device of Fig. 2 for operation in accordance
with the invention.
Referring to Fig. 1, there is shown a transfer machine 10
which is disposed to receive a stream of metallic parts 12 and
to perform N work tasks on each received part, in a prespeci-
fied sequence. Transfer machine 10 is provided with a trans-
fer bar or other part advance structure 14, and is further
provided with a transfer bar driving mechanism 16, for mani-
pulating the transfer bar through successive part transfer
cycles. In addition, transfer machine 10 is provided with a
load station 18, an unload station 20, and N work units 22.
Each work unit 22 performs one of the above work tasks during
a work unit cycle, and is located at one of the N work sta-
tions. The work units are respectively arranged at the work
statiGns so that if a part 12 is moved consecutively from work
station -1 to work station N, N work tasks will be performed
thereupon, in the above prespecified sequence.
Each of the work units 22 usefully comprises a machine
tool which is provided with a fixture 24, a spindle 26, and a
spindlehead 2B. A fixture 24 is provided to selectively retain
a part 12, and a spindle 26 is provided to drive a cutting tool
30, such as a tool for performing milling, boring or other con-
..l~
ventional metal cutting operations. The spindlehead 28 of a
work unit 22 is movable in relation to a part 12 retained in
the fixture of the work unit, to enable a tool 30 to be con-
trollably fed into a retained part~ It is to be understood
that the specific forms of work units 22, as well as the other
components of transfer machine 10, will be dependent upon the
application which is to be made of the transfer machine. Con-
sequently, Fig. 1 shows respective components of transfer ma
chine 10 in very simplified or generalized forms.
Referring further to Fig. 1, there is shown a controller
device 32j such as a programmable electronic controller,
coupled to each oE the components of transfer machine 10.
Controller 32 is structured to operate respective components
of transfer machine 10 in synchronous relationship with one
another, so that the transfer machine will execute a succes-
sion of alternating part transfer and work unit cycles. In
addition, controller 32 is structured, as hereinafter described
to operate respective components of the transfer machine in
accordance with the invention.
At the beginning of a part transfer cycle, controller 32
directs transfer bar driving mechanism 16 to raise transfer
bar 14 upwardly. Bar 14 is thereby caused to engage every
part 12 which is residing at a work unit 22 or at load station
18. Then, bar 14 is advanced, whereby a part at load station
18 is moved to the work unit at work station 1, a part at the
work unit of station N is moved to unload station 20, and a
part at the unit of work station m is moved to the unit at
work station m~l, where m CN. Thereafter, bar 14 is lowered
and then returned to its initial position, concluding the
part transfer cycle.
After a part transfer cycle is concluded, controller 32
executes a worlc unit cycle. During a work cycle, every work
unit 22 at which a part 12 is present is activated to feed
its tool 30 into the part, at a controlled feedrate. The
- 9 -
tool 30 of a work unit is fed to a depth which is predetermined
in accordance with the work task which i5 to be performed by
the unit. When all of the activated work units have reached
their respective depths, the spindles and tools thereof are
returned to their respective initial positions, whereupon con-
troller 32 executes another part transfer cycle. Controller
32 is structured to limit the duration of a work cycle to the
time which is required for the activated work units to com-
plete their respective tasks.
After each part txansfer cycle, load station 18 becomes
disposed, during a part reception period, to receive a part
for the next-following part transfer cycle. During a part
reception period, controller 32 is responsive to both the re-
ception and the non reception of a part at load station 18. If
a part is present at unload station 20 after a transfer cycle,
it is removed therefrom.
Referring to Fig. 2, there is shown a programmable con-
troller device 32 of a type which is presen~ly used to control
transfer machines or other work systems, and which may be
adapted to operate transfer machine 10 in accordance with the
present invention. Such controller 32 includes a processor
34, which i5 coupled to a power supply 36, a programming key-
board 38, and an I/O (input/output~ section 40. ~eyboard 38
is employed to enter a set of instructions into processor 34,
whereby controller 32 becomes structured to perform specified
sequences of logic operations as transfer machine 10 receives
and processes a succession of parts 12. Results of respective
logic operations cause control signals to be coupled to trans-
fer machine 10, through I/O section 40, and also provide con-
ditions for further logic operations. Other conditions forthe logic operations are established by signals which are
coupled into processor 34 from the transfer machine through
I/O section 40. Such input signals indicate the state or con-
dition of respective components of the transfer machine at
various times during successive transfer and work cycles.
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Usefully, controller 32 comprises a controller device,
such as a Modicon 584, which receives instructions in the
form of a series of ladder diagrams. As is well known in
the art, a ladder diagram is a graphic representation of
5 some of the logic operations which are performed by a controller,
in order to generate control signals which will cause a
transfer machine 10 to operate in a specified manner. A
ladder diagram is comprised of a number of hori~ontal lines,
known as rungs, each rung including one or more logic elements
or relay contacts. ~ach contact represents a condition of a
transfer machine component, a contact being shown in a ladder
diagram as being open or closed to indicate the normal state
of the condition during transer machine operation. In
addition to relay contacts, a rung of a ladder diagram may
include a function box, such as a timer or a register.
In a ladder diagram, power can flow along a rung only
from left to right. A coil, located at the right end of a
rung, is therefore activated when all of the contacts of the
rung are simultaneously in a closed state. Alternatively, a
coil may become activated if vertical paths are provided be-
tween the rung of the coil and adjacent rungs, to establish
a power flow path which includes segments of different rungs.
Power may flow either upwardly or downwardly through such
vertical paths.
It will be apparent that various conditions which are
represented by the relay contacts of the ladder diagrams will
be continually changing as transfer machine 10 is operated
through successive part transfer and work unit cycles. Con-
troller 32 therefore repetitively scans the contacts of each
of the ladder diagramsr at intervals which are very brief. If
one or more of the conditions which specify the activation or
deactivation of a coil changes, the state of the coil will be
appropriately changedd, during the very next scan. Consequently,
when a set oE conditions occurs in the transfer machine which
specifies a particular contro~ signal, the control signal
will be immediately generated hy the controller and coupled
to the transfer machine.
A normal convention in a ladder diagram is to represent
an open contact by means of two vertical, spaced-apart parallel
lines, and to represent a closed contact b~ means o vertical
spaced-apart lines which are join,ed by a diagonal line. A
contact which is closed for only one scan, following the
activation of a coil with which the contact is associated,
may be represented by placing an upwardl~ pointing arrow
between two spaced-apart vertical lines. As a further convention,
if the activation of a coil causes a control signal to be
coupled out of controller 32, the coil may be represented by
a circle placed at the right end of a rungO On the other
hand, if activation of a coil only provides a condition for
further logic operations within the controller, the coil is
represented by a rectangle.
In order to operate respective components of transfer
machine 10, as the transfer machine executes successive part
2~ transfer and work unit cycles, a number of well-known or
conventional instructions, in ladder diagram format, are
entered into controller 32 through keyboard 38. One of such
conventional ladder diagrams is an interlock circuit, which
generates signals which are simultaneously coupled to each
work unit 22 to insure uniform operation thereof. Such
interlock circuit, as well as a number of other conventional
ladder diagrams entered into controller 32, are not modified
by the present inventiGn from their respective standard forms,
and are thereore not described in detail herein. However,
several other ladder diagrams entered into controller 3~ are
not conventional, as far as is known, and are therefore
described herein in conjunction with Fiys. 3-5. A number of
other ladder diagrams, while basically conventional in the
art, have required modification in light of the invention,
and are therefore described in conjunction with Figs. 6-10.
'#~ 3
-12-
Referring to Fig. 3, there is shown a ladder diagram
wherein a shift register 42 is coupled to rungs 44, 46, 48,
50, 52 and 54. Reference numerals 42a-d of Fig. 3 are employed
to indicate how respective rungs interact with register 42,
to shift data ~herein, and to load data thereinto. Shift
register 42 usefully comprises one of the aforementioned
function boxes of controller 32, and is provided with N
consecutive positions for storing digital data bits. If a
particulax digital data bit is loaded into shift register 42
during a particular part reception period, and if data in
shift regis~er 42 is shifted or rotated once in response to
each part transfer period, the particular data bit will be
in the nth bit storage position after n transfer cycles,
following the particular part reception period~ Also, if a
part 12 is received at load station 18 during the particular
part r~ception period, such part will be present at the nth
work station after n transfer cycles.
From the above relationshipst it will be seen that if a
logic l data bit is loaded into shift register 42 when a
part 12 is received by transfer machine lO durin~ a part
reception period, if a logic 0 is loaded into the register
when a part 12 is not received during a part reception period,
and if the register is shifted once in response to each
transfer cycle, the data contained in shift register 42 will
indicate, at any given time, the presence of absence of a
part 12 at each of the work units 22 of transfer machine lO.
By judicious selection of the contacts included in rungs 44,
46 and 48, shift register 42 may be operated in accordance
with the above requirements.
Referring further to Fig. 3, there is shown the load
terminal of shift register 42 coupled to the right end of rung
48, rung 48 being provided with a contact 48a. Contact 48a
is closed by a signal received Erom load station 18 which in-
dicates that a part is present thereat, whereupon a logic l is
-13-
coupled to the load terminal of register 42. If a part is not
present at the load station, contact 48a remains open, and a
logic 0 is coupled to the load terminal of register 42. Opera-
tion of contact 4~a is synchroniæed in time with the reception
or non-reception o~ parts at load station 18. during successive
part reception periods, and with the periodic shifting of regis-
ter 42.
To shift or rotate data in shift register 42 in response
to each part transfer cycle, the shift or clock terminal of
the register is coupled to rung 46, which is interconnected
with rung 44 through vertical paths. Rung 44 includes an
"advance transfer" contact 44a, which is closed when transfer
bar 14 is advancing during a transfer cycle, and further in-
cludes a "transfer returned" contact 44b, which is closed
when transfer bar 14 is returned prior to the beginning of a
transfer cycle. Therefore, coil 44d is activated when a trans-
fer cycle has been initiated and each part 12 in transfer ma-
chine 10 is being shifted by one work station. Coil 44d is
used for the contacts 46a and ~6b in rung 46, so that register
42 will be shifted by the very next scan following transfer
cycle initiation.
Referring once more to Fig. 3, ~here is shown shift regis-
ter 42 coupled to rungs 52 and S4. Rung 52 is provided with
a "force all parts present" push button contact 52a, and rung
54 is provided with "power onto controller" contact 5~a. ~y
providing rung 52, a part may be removed from a work station
of transfer machine 10, for some reason, and then be replaced
in the work station, a number oE transfer cycles later, when
a part is not present at the work station. When an "all parts
present" push button is depressed, contact 52a will be closed,
causiny logic 1 data bits to be entered into all W bit storage
positions of register 42. The movement of the replaced part
to subseq~ent work stations, to complete the processing there-
o by transfer machine 10, will thereby be accompanied by a
-14-
logic 1 data bit in the shift register. Rung 52 may also be
employed to enter a part directly into one of the work stations
of transfer machine 10, without first placing the part in load
station 18.
Referring to Fig. 4, there is shown a ladder diagram
which is employed to provide notice if an error occurs in the
operation of shift register 42. The ladder diagram of Fig. 4
romprises rungs 56, 58 and 60, interconnected as shown, rung
56 including contacts S6a-e and rung 58 including a contact
58a. Contact 56a is generally closed during the operation of
transfer machine 10, but is opened at the conclusion of a part
transfer cycle if a logic 1 is present in the Nth bit storage
position of shift register 42. Contact 56b is normally open
during transfer machine operation. However, if a limit switch
located at work station N senses that a part is present at
work station N at the conclusion of a transfer cycle, a siy-
nal is coupled to controller 32, through I/O section 40, to
close contact 56b. Contacts 56c and 56d become closed when
transfer bar 14 is respectively advanced and lowered, whereby
the closing of contacts 56c and 56d indicate the occurrence
of a transfer cycle. Contact 56e, a "start/reset" control,
is normally in a closed condition.
From the above logic conditions specified by rung 56, it
will be apparent that coil 56f, coupled to the right end of
rung 56, becomes activated only when a part 12 is present at
work station N at the same time that a logic 0 data bit is
contained in the Nth storage position of shift register 42.
The occ~rrence of such conditions together indicates a fault
in the operation of register 42r in monitoring the flow of
parts through transEer machine 10. Consequently, the activa-
tion of coil 56f causes a signal to be coupled to transfer
machine 10, to activate a shift register fault indicator
light. Notice is thereby provided to a transfer machine opera-
tor that a part at work station N may not have been properly
machined. If movement of the part through the transfer ma-
chine was accompanied by a logic 0 moving through shift regis-
ter 42, various work units would not have been activated to
perform their respective work tasks when such part was at their
work stations.
The activation of coil 56f is also employed as contact
58a in rung 58, which shunts contacts 56a-d of rung 56. The
activation of coil ~6f is thereby maintained until "start/reset"
control 56e is operated, regardless of whether any of the con-
tacts 56a-d become opened. Rung 60 of the ladder diagram of
Fig. 4, which does not contain any contacts, shows the flow
of power to controller 32.
Referring to Fig. 5, there is shown a ladder diagram
which is provided with an upper rung 62 coupled to a coil 62a,
a lower rung 64, and a number of intermediate rungs, each of
the intermediate rungs including a number of contacts. Each
of the contacts of the intermediate rungs, as well as contact
64a of lower rung 64, is connected by vertical paths between
upper rung 62 and lower rung 64 so that if at least one of the
contacts becomes closed, a power flow path will be established
to activate coil 62a. Contact 66a is closed when a signal is
coupled to control 32 to indicate that a part is present at
load station 18, and the contact of the nth work station is
closed by the presence of a logic 1 in the nth bit storage po-
sition of register 42. The activation of coil 62 thereforerepresents the presence of at least one part 12 in transfer
machine 10.
Referring to Fig. 6, there are shown rungs 68 and 70,
which are interconnected to activate a coil 68i when all of
the components of transfer machine 10 are operating in an
automatic mode, and in the absence of a fault or error in the
operation of shift register 42. Contact 68a of rung 68 is
closed when all of the components of transfer machine 10 are
operating in an automatic mode, and a contact 68b is closed
3~;~
-16
in the absence of an emergency condition in the transfer ma-
chine. Contact 68c remains closed unless transfer bar 14 mal-
functions, and contact 6Sd remairls closed in the absence of a
shift register fault. Contact 68e is a reset push button con-
tact, and contact 68f is operated by a push button for select-
ing an automatic mode of transfer machine operation. After
such mode has been selec~ed, coi:L ~8i i5 activated,whereupon
a signal is coupled to an automatic mode indicator light. The
activation of coil 68i is also employed as contact 70a of rung
70, which shuts push button contact 6~f after operation of the
machine commences. Contact 68g is closed to indicate that the
spindles of respective work units 22 are on, and contact 68h
is closed when the transfer machine is not being operated in
a manual mode.
Referring further to FigO 6, there are shown rungs 72-7B,
the activation of coil 72e of rung 72 being specified by con-
tacts 72a, 72d, 76a and 76b, the activation of coil 7~ indicat-
ing the coT~mencement of a part transfer cycle. Contact 72a
is closed when a selector switch is operated to place transfer
machine 10 in a mode of continuous operation, and contact 72d
is closed when the transfer machine is prepared, or set up,
for a transfer cycle. Contact 76a is closed to indicate that
structure at load station 18, which is employed to deposit a
part in the load station in preparation for a part transfer
cycle, has been withdrawn and will not interfere with move-
ment of transfer bar 14. Contact 76b is closed ~y the activa-
tion of coil 62a of Fig. 5, to indicate that at least one part
12 is present at either load station 18 or at one of the work
stations of transfer machine 10. By providing contact 76b, a
part transfer cycle will occur if even a single part is avail-
able to the machine for processing. However, if there are noparts available at all, the machine will not perform a part
transfer cycle.
-17~
~hen coil 72e is activated~ contacts 72c and 78a become
closed, whereby a shunt is placed across rung 76. As a part
transfer cycle proceeds, contact 72b is opened when transfer
bar 14 has been advanced, and contact 74a is opened when the
transfer bar has been lowered, whereby the part transfer cycle
is concluded.
Figs. 7-9 are ladder diagrams which are entered into con
troller 32 to direct the operation of the nth work unit 22,
located at the nth work station, during successive work unit
~ cyc]es. Referring to the ladder diagram of Fig~ 7, there are
shown rungs 80 and 82, interconnected to define the conditions
of activation of coil 80d, whereby the control of the nth work
unit is placed in an "on" state. To activate coil 80d, con-
tact 80a must be closed by operating a start/reset control,
and contact 80b must remain in a closed condition, indicating
the absence of a unit overload condition. In addition, con~
tact 80c must be closed by the operation of a master control
relay, which is conventionally included in controller 32.
When coil 80d is activated, contact 82a of rung 82 is closed,
shunting start/reset contact 80a. If contact 82b is closed
after the unit control comes on, by the operation of an auto-
matic/manual selector switch, automatic/manual control coil
82c becomes activa~ed.
Referring further to the ladder diagram of Fig. 7, there
are shown rungs 8-., 86 and 88 interconnected to specify the
conditions for activating coil 84e, that is, to activate the
spindle 26 of the nth work unit. Contact 84a of rung 84 is
closed by means of a "start spindle" push button, and contact
84b is closed by not selecting an automatic mode of operation,
by means of a selector switch. Contact 84c is closed by a
signal from the aforementioned interlock circuit, and contact
84d is closed by the activation of coil 82c.
Contacts 84a and 84b are shunted by rungs 86 and 88,
contact 86a of rung 86 being closed by a "start spindle" sig-
3~3
-18~
nal which is coupled thereto from the interlock circuit. Con-
tact 88a is closed by a "spindle on" signal received from a
spindle starting device, which is conventionally included in
each spindle 26, and contact 88b is closed when coil 84e be-
S comes activated. It will be seen that a power flow path isestablished through rung 88 only when (1) either the interlock
circuit of controller 32 indicates that the spindle should be
on, or else the spindle is not in an automatic mode and a manual
push button is operated, and ~2) coil 84e is activated, indi-
cating that the spindle actually is on.
Referring to rung 90 o Fig. 7, there are shown the con-
dition for activating a coil 90e, which indicates the partial
advance of the tool 30 of the nth work unit toward a part 12,
which is clamped in the fixture 24 of the nth unit. In order
to commence advancement, contact 90a must be closed, indicat-
ing that the fixture is in a clamped condition, and there must
be an absence of an emergency condition. In addition, coil
82c must be activated, to close contact 90b, and dwell contact
90c must be in a closed condition by the non-activation of
coil 98c, which is hereinafter referred to. Finally, in ac-
cordance with the invention, a logic 1 data bit must be con-
tained in the nth storage position of shift register 42, to
close contact 90d. If a logic 0 is contained in the nth bit
storage position, indicating the absence of a part at the nth
work station, contact 90d will remain open during the upcoming
work unit cycle, coil 90e will not be activated, and the tool
30 of the nth work unit will not be advanced.
Referring to Fig. 8, there is shown a ladder diagram
wherein rungs 92, 94 and 96 are interconnected to control the
~ rapid advance of the tool 30 of the nth work unit, and also
to control the feeding of the tool into a part which is
clamped in the fixt~re of the unit. The tool is rapidly ad-
vanced when it is moved through the air gap which lies between
the initial position of the tool and the clamped part. ~n
--19--
order to rapidly advance and then feed the tool, either con-
tacts 9~a-94e must be closed, or else contacts 92a and 92b
must be closedO Contact 92a is closed by operating an "advance
unit" push button, and contact 92b is closed by means of an
automatic selector switch contact. Also, contact 92c must be
closed by the activation of coil 90e. If the above conditions
are met, and if tool 30 of the nth work unit is initially in
a returned position, a power flo~w path is established to rapid
advance coil 92.
When coil 92f is activated, contact 92e is closed. If
contact 92d is also closed, by a signal received from a rapid
advance starting device, contact 94f will be shunted. The
activation of coil 92f will therefore be maintained as the
tool 30 of the nth work unit is moved from its returned posi-
tion.
To further maintain the activation of coil 92f, as well
as of coil 96c, contacts 94a-e of rung 9~ are provided to
shunt contacts 92a-b. Contact 94a is closed by a signal from
the controller interlock circuit which indicates that all of
the units should be in a work cycle, and contact 94b is closed
if a logic 1 da~a bit is presen~ in the nth bit storage posi-
tion of shift register 42. If a lo~ic 0 is present in the
nth bit position, indicating the absence of a part at the nth
work unit, advancement and feeding of the tool 30 of the nth
work unit cannot be maintained.
Referring further to rung 94, there is shown contact 9~c
representing the automatic selector switch. Contact 94d is
provided to prevent further advancement or feeding when the
tool of the nth unit has reached its specified depth, and
contact 9~e is provided to prevent feeding of the tool into
a part unless the spindle 26 of the nth work unit is on.
Referring to rung 96, there is shown contact 96a, which
i5 closed by a feed signal from a feed start device, and there
is shown contact 96b, which is closed by the activation of
coil 96c.
-20-
Referring to rung 98 of Fig. 8, there is shown a contact
98a which is closed when the nth work unit has been fully ad-
vanced. Controller 32 receives notice of such condition from
a signal which is coupled to the controller rom a limit
switch at the nth unit, the limit switch being tripped by full
advancement of the unit. Rung 98 is further provided with a
timer function box 98b, which is structured to time a one-half
second period. Consequently, one-half second after the nth
work unit has been fully advanced, dwell coil 98c of rung 98
becomes activated.
Referring to rung 100 of the ladder diagram of Fig. 8,
there is shown a contact lOOa which is closed when the nth
work unit is returned to its initial position, at the conclu-
sion of a work unit cycle. Since contact lOOb is closed by
such time, coil lOOc is activated, to indicate that the work
unit has been returned. Contact lOOa is closed by a signal
which is provided by a second limit switch at the nth work
unitl the second limit switch being situated to generate a
signal when the work unit returns to its initial position.
Referring to the ladder diagram of Fig. 9, there are shown
rungs 102 and 104 which establish conditions for activating a
coil 102e, whereby the tool of the nth work unit is returned
to its initial position, at the conclusion of a work unit
cycle. Return of the tool may be initiated by means of a
"return unit" push button, to close contact 102a. However,
if the tool of the nth work unit has reached its specified
depth, return of the tool is initiated automatically, by means
of contact 104a of rung 104.
Referring to rung 110 of the ladder diagram of Fig. 9,
there is shown depth coil llOe being activated by the acti-
vation of dwell coil 98c and by the released state of the
aforementioned unit returned limit switch. However, if a part
is not present at the nth work unit during a work unit cycle,
the unit will not be activated, preventing the closure of
~21-
contact llOa. Consequently, contacts llOa and llOb of rung
110 are shunted by rung 108. Contact 108a is closed by a sig-
nal from the controller interlock circuit to cycle the work
units, and contact 108b is closecl by a logic 0 in the nth bit
storage position of shift register 42. By providing rung 108
as shown in Fig. 9, a power flow path will be established to
coil llOe even when the nth work unit 22 is not cycled during
a work cycle, because of the absence of a part at the unit.
When coil llOe is activated, contact 112a is closed, es-
tablishing a power flow path through rung 112.
Referring to Fig. 10, there is shown a ladder diagram hav-
ing a number of contacts connected in series, each contact be-
ing closed when the depth coil llOe of one of the work units 22
becomes activated. The activation of coil 114a indicates that
a work unit cycle has been completed, and that a part transfer
cycle may be commenced. Contacts of rung 114 which correspond
to work units at which parts are absent will remain closed
during a work cycle, due to the provision of rung 108 in the
ladder diagra~ of FigO 9, as aforementioned. Each of the
other contacts of rung 114 is closed when one of the work units
which is in operation during a work unit cycle completes its
work task Consequently, the duration of any given work unit
cycle is not longer than the longest cycling time of the work
units which are actually in operation during the work cycle.
From the foregoing description, it is seen that transfer
machine 10 is operated in accordance with the invention by
repetitively performing a number of logic operations, the re-
sults of a particular logic operation being determined by
states of various components of the transfer machine and by
the contents of a shift register. It will be readily apparent
that instead of performing the logic operations by means of a
controller which is structured by entering specified ladder
diagrmas thereinto, the logic operations could be performed
by a judicious interconnection of discrete standard electronic
-22~
components, such as AND gates and OR gates. The shift regis-
ter could also comprise a standard, hard-wired, component. The
interconnection of such components would be readily apparent
to one of skill in the art in light of the above ladder dia-
grams, which specify the various logic operations which mustbe performed.
It is anticipated that in a further modification of the
invention, a suitably programmed digital computer could be
employed to perform the required logic operations.
Obviously, many other modifications and variations of
the present invention are possible in light of the above
teachings, and it is therefore understood that within the
scope of the disclosed inventive concept, the invention may
be practiced otherwise than as specifically described.
