Note: Descriptions are shown in the official language in which they were submitted.
7~
, _a~ ound o~ the Invention
',' This invention relates in general to hydraulie drive
and contrel sy~tems for process line equipment. More sp~cifi-
c~lly, it relates ~o an electrohydraulic drive and control system
particularly useful for a spo~ler (also kno~ln as a traverse
winder or level winder) that both winds ~nd pays out an
indefinite length of metallic ~randO
!
In the production of many materials, whether metal,
paper, plastic films or otherwise, the product is in the form of
lo a moving strand or web~ In the case of a strand, i~ can be a
solid wire, tubing, s~rip, or a variety of other ~orms~
Processing of the material occurs ~on the fly~ as it moves
' through the produetion equipmentO Typically when the processing
: is complete, the material is wound on~o a zpool, core, reel or
! mandrelO In some ~pplica~ions, ~he material i~ wound and then
. later unwound for urther proc~3~ingO Regardle~3 of ~he nature
I o the material, its foYm, or the type ~f proc~ssing, it is
i always ~mportant to contr~l the speed ~nd Ssnsion of the material
during the proces~ing.
,. Speed control is important bec~use different mate~ials
or opera~ion may require diferen~ ~peed~0 A drive system must
jbe able to pr~duce, ~nd/or match~ a wid~ rang~ ~f lin~ ~peeds, ~o ¦
' adjust the line speed, to jog at ~low speeds ~with and ~ithout
l tension in ~he ~trandl~ ~o ~ccelera~ ~nd dec~l~rate, and in
¦~winding o- unwindlng ~o vary the ~trand speed ~s a function o
llthe coil diameterO ~orque control 1~ also very important in
jl~stablishing ~ correct degree of tension in the strand~ The
,Idrive ~y~tem c~n be a mas~r or sl~Ye in s~tting or f~llowing th~ !
,i . ..
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line speed and all following sl~ve d~ives nor~311y need to
operate in a tension control mode on a taut ~trand.
Tension control is important for ~any re~sons~ If it
is too high, the stxand may break or be damaged~ If i~ o
slack, various operations may not be performed effectively or the ¦
strand may jul~p out of guides, catch on projection3, etc~ In
winding or unwinding, the strand tension should usually be
substantially constant in the processing line, but it i5 often
necessary to vary th0 tension at the spool~r ~ a func~ion of the il
, coil di~meter in order to form ~ good coil. ~ven for constant
tension~ torque must changs with coil di~met~r. It i5 also
impor~ant to be able to vary ~he tension ko accommodate different
;products or for other reasons.
Ano~her important requirement is ~h~ th~ drive system
exhibit ~s smoo~h ~ tran3ition as po~sible a~ i~ acceler~tes or
decelerates betwe~n different ~peed3 ~r restO ~ dl continuou.~, ¦
~ jerky transition can break the strand or in~roduce variat~on~ in
',the ~en~ion ~hich adversely aff~ct the ~ual~ty of the product. A
l controlled eMsrg~ncy stop c~pabillty 1~ also important. These
20 1l operation~l characteristics are p~rticularly d~Xficul~ to achieve !
'in winding and unwinding oper~t$ons for me~allic strands where a
! ~ull coil can weigh up to many tons~ line ~peedfi c~n be quite
hi~h ~up to 3,000 eet per minuee) and rotation of ~he coil at
,~even ~ moderate speed produces ~ high degree of iner~ia.
i¦ ~n the pa t, a wide variety of drives ~nd controls have
¦I been used for winders; unwinders, and other line drive elemen~s
l! ~uch as pinch rolls and hrldl~s. Rnown 3ystems have used AC
¦I motors, DC motorsr ~nd hydr~ulic motors ~s the final drive
l' l
7(:~
ele~ent. Drive control m~chanisms have included adjust~ble
brakes, va-iable clutches, variable displacement hydraulic
mot~s, as well as mech~nical and hyd-aulic transmissions, and
va-iab~e voltage, current, ~nd/or frequency to electric motors.
.
U.S. Patent No~ 3,053,46h to Zernov et al, for exampl~,
descri~es a hydraulic drive system where a mechanical cam ~yQt~m
senses the diame~er of the roll being wound to control the rata
of rotation of the drive. U.S. Patent No. 2,677,080 deseribe~
, the control of ~ hydraulic motor or pump through a balancing of
the hydraulic fluid pressure against a set pres~ure. UOSO P~tent I
; Nos. 2,960,277 and 2,573,938 disclose a solenoid operated direc-
~ional valve~ cc~nnected in a hydraulic syst~m for control of ~che
~ystem in respon~e to an electr~cal ~ignal., U.S. Paten~ No. ~,
' 2,988,297 describes ~ pneumatic ~ystem for con~rolling a slip
;clutch in th~ driv~ tra~n o a spooler. U.5. Patent No,
3j784,123 d~crib-s ~ hydr~ulic ~ystem where ~ mechhnic~l ~y~tem
~conver~s a w~b ~nsion lnto a c~rre~pondin~ hydraulic prcs~ure.
A hydr~ulic circuit Gompares ~his pressure ~ a reference value.
, The outpu~ of thi~ ~ircuit con~rols ~he di~placement of a
20 i,l hydr~ulic mo~or operating a~ a constant pressure to vary the out-
pu~ ~orqueO This pa~en~ ~15O di~cu~ses many of the deficienci~s
. of other prior ~rt ~ension control ~ys~ems, whether mechanical,
hydraulic or electr$calO
Oft~n known driv~ ~ys~ems for wlnders and o~her process
line equipment in the manufacture o~ metall~c ~trand ~nd ~hee~
product~ use a regener3tiYe, four quadrant DC motor ~nd control
~drave~)~ How~v~r, thi~ drive i5 l~rge, compl~x, ~nd
compar~tively costly. In op~ration, it cannot maint~in a larg~
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stall ~ension indefinitely (even with ~n exp~nsive cooling
system), i~ cannot make ~ smootht stepless t ansition from
motoring to braking, and it does not possess extra braking torque
for controlled rapid stops ~rom high speeds.
In general, known hydraulic driv~ systems suffer frotn
" limited operating ranges with respect ~o both spe~d ~nd ten~ion,
a stepped, jolting transition between mo~oring and braking and
bet~/een diffe~ent speed and tension settings on the fly, an
;;inability to brake ~uddenly without jolts, and a limi~ation as to ,
the contrDls th~t can int~r~ce wi~h the sys~em. Also, known
hydraulic ~ystems do not provide a ~tepless transition between
speed control and ten~ion control mudes. Also, most hydraulic
~ systems are comparatively co~tly ~nd complex.
! It i5 ~horeforo the prin~ipal object oÇ this invention
to provide 4 driVB ~nd control 8ystem for winder~ unwinders ~nd
o~her process lin~ ~quipm~nt that Dperate~ over a wide r~nge of
sp~eds and tension~ ~nd in a variety o modes while a~ ~he ~me
time provid~ng a ~moo~h a~eler~ion, deceleration and tr~n~ition
betwe~n motoring 2nd braking, and between speed ~nd t~nsion
i! controlO
¦ !
il Another object of the invention is to provide a 8y5tem
! with the foregoing &dvant~es ~h~t al50 brakes smoothly and
¦ rapidly under emeryen~y condi~ion~ rom a high l$ne 5peed to ~ ¦
~op evsn when ~he ~ystem i3 driving a high lnertia load.
¦l Another object of the invention is to provide ~ drive
I¦ and ccntrol sy~tem that operat~ well in winding or unwindlng
¦; coil~ of mate-ial having a large mass ~nd a high rot~tion~l
Il inerti~.
t7~9
1,
Another object of the invention is to ~srovide ~ drive
and control system that interfaces with ~ variety of manual and
automatic c~ntrols including computer controls, switches, relays
; and a variety of transd~cers.~
¦ Another object of the invention is to provide a drive
system which can maintsin a moder~te to large stall tension for
an indefinite period of time.
ll
And still another object csf ~he invention is to provide
. a drive system and control that automatically tapers the tension
during winding and acco.~.odates for theS sy~2tem inertia on ~cce-
lera~ion or deceleration to maintaln a desired tension level in
; the material.
,., I
Yet ano~her object of theS invsntion is to provide a
..drive and control ~ystem th~t is formed through a comparatively
!' ~mall nu~ber asf componenS~, has a r,~31atively uncomplicat2d
design, and has a comparatively moderat~s cost as compared to
known drive and control ~ystems.
A still urther obj~c~ of the inven~ion is to provide
'jan elcctrohydraulic driv~ and ~ontrol ~Ry~tem for traversing a
~ ~pooler that main~a~ns the ~rand being wound or p~yed out in a
, precisely predetermined la~eral posltion.
i
! ~,~
.,
The pre~-ent inven~ion provides an electrohydraulic
drive and control ~ystem for pr~ce~ line equipment such a~ win-
llders, unwind~rs (collectively ~spooler~~, pinch rolls ~nd
! bridl,~s. The sys~em includ,ss a bi-directional, vari~ble
" displacement hydraulic mc,tor thAt rotates a spool or other member
;i 'I
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(3 4
that engages the product, whether a web or strand. Hydraulic fluid is
directed by a feed line from a constant pressure, variable flow rate supply
to a directional valve connected to the motor. Fluid exiting the motor
through the directional valve is directed back to the power suppl7 by a return
line.
A pressure reducing valve controlled by a proportional electrlcal
actuator is connected in the feed line. A sequence valve located in return
line maintains the pressure upstream of the valve at a predetermined and
adjustable value. When the drive system is "~otoring", typically in a winding
or jogging mode, the entire output flow from the motor is directed via the
sequence valve to the supply. When the motor is operating in a pay-out or
braking mode, the motor acts as a pump. In this mode, the fluid exiting the
motor flows through a regeneration circuit connected between the return line
and the feed line. The regeneration circuit includes a flow divider that
directs a significant portion of the flow from the return line back to the feed
line to conserve the fluid, Cavitation is prevented under braking conditions
by continuing to supply additional fluid from the feed line to maintain a
positive pressure at the motor inlet at all times. A s~aller portion is
directed back to the power supply, The regeneration circuit includes a second
adjustable sequence valve set a~ a pressure less than that of the first
sequence valve and a check valve which prevents a flow of the fluid directly
from the feed line to the return line. The directional valve is preferably
a four-way, double solenoid directional valve with forward, reverse and
neutral positions.
An electronic control circuit for the proportional actuator
includes an integrating servo-amplifier, an analog multiplier, a diode, and
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a linear power amplifier. The integrating servo-amplifier receives the
output signal from a tachometer which measures the actual speed of rotatlon of
the motor and an electrical speed command signal from a controller. U~less
these signals are the same7 the integrating amplifler will change its output
signal upwards or downwards, depending upon the sign of the error. The output
signal of the integrating amplifier is applied to the analog multiplier which
also receives a pressure limit command signal that is proportional to a
preselected desired maximum pressure for the hydraulic feed line. The output
of the multiplier, which will correspond to from 0 to 1.0 times the maximum
pressure setting~ is applied through a diode to a linear power amplifier which
produces an output signal of suitable magnitude to operate the proportional
actuator on the pressure reducing valve. The control system also includes a
second proportional actuator that controls the displacement of the motor in
response to a remote electrical control signal.
In a preferred form, the speed limit, pressure limit, and displace-
ment command signals, typically DC voltages, are generated by a digital
computer acting through a multi-channel digital-to-analog converter. The
rotational speed from the tachomeeer and an output signal from a transducer
that measures the tension in the strand being processed are applied to the
computer through a multi-channel analog-to-digital converter. The computer
also receives command signals from conventional manually operated switches
and a keybosrd terminal. The computer can execute automatic controls such
as a tapering of the tension in the strand as the diameter of a coil being
wound on the spool increases and compensating for the inertia of the spooler
during acceleration or decelerationO
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The system also includes an electrohydraulic drive and control for
a spooler that traverses the spooler with the strand that ls belng wound or
pald out maintaining a generally constant passline. ~ hydraulic cylinder
drives the spooler. The velocity and direction of movement of the actuating
member of the cylinder ls controlled by a hlgh speed servo valve ~7hich in
turn is controlled by an electrlcal control slgnal from a servo-amplifier.
The servo-ampllfler receives information from a spooler position transducer,
a spooler velocity transducer and the tachometer. Ad~ustable electrical
controls set the limits o~ travel and the pitch of the spooler in winding
mode. In payoff mode operation, a strip position sensor sends a signal to a
different servo-amplifier, which also receives a traverse velocity signal,
and which controls the traverse to keep the strip centered on the position
sensor.
These and other features and objects of the invention will be
described in greater detail in the following detailed description of the
preferred embodlments which should be read in conjunctlon with the accompanying
drawlngs.
Brief Descrlption of the Drawlngs
Fig. 1 is a circuit schematic for an electrohydraullc drive and
control system accordlng to the present inventlon that allows a s oth, highly
controlled bi-directional rotation of a spooler or other process line
equipment;
Flg. 2 ls a schematlc drawlng showing the electrohydraulic drive and
control system of Fig. 1 winding a metallic strand on a spooler and also
showing the electronic components whlch generate the input control slgnals for
the electronic circuit component shown in Fig. l; and
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Fig. 3 is a schem~tic drawi~g o' an elec~-ohyd ~ulic
dri~e and control sys~em according to this invention for t-avers-
in~ a 5p~01er in a highly controlled manner ~ith the later~l
position of the strand b~ing wound or ~nwound ~eing substantiall~ I
const~nt. _ ¦
Detailed Description of the Preferred Embodiment~
Figs. 1 and 2 show an electrohydraulic drive and
control system 12 tha~ includes a bi-directional hydraulic motor
, 14 that has a variable displacement. ~he motor 14 can be of the
lo ' axial piston type wi~h an adjustabla swashplatQ~ Depending up~n
the r~lative fluid pressures applied ~o its inle~ 14a and outlet
14b, the motor can func~ion as eith~r a motor or ~ pump. The
motor 14 is connected ~o drive a spool 16 ~hrough a winding arbor
l? ei~her dir~ctly or through a conven~ional speed reducer ~uch
' as a gearbelt (not ~hown~. Th~ drive, tr~nsmission and spool
I will be r2f~rr~d to herein collec~lvely as the ~pooler~, whether ¦
, it is used for winding or unwind$ng. As ~hown in Pig. 2, the
spool 16 is rotating ~n a clockwi~e direction to wind ~ narrow
strand 18 of met~l such as copper or bronze as it leav2s a
processing line at ~he line ~peed. While the m~terial can be
,I non metallic and in the form oP ~ wide web, for ~implicity ~he
following discu~sion i8 limited ~o ~he proces~ing of a metallic
~rand. The r~io of ~he diameter of the emp~y spool ~o that of
a ull ~oil 19 wound on the 3pool 16 can Y~ry from unity to more
than 12 to lo A fully coiled ~pool can typically c~rry up to 6
ton~ oP metallic strand, ~o ~ccommodat~ ~ ~low jog ~s well ~ ~
~; high ~peed runnin~ mode, the ~pooler 6hould operate rom 0 to 125
rpmr or fas~er? depending upon requirements~
l!
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'I 10
Turning to Fig. 1, the hydraulic system includes a hydraulic fluid
supply 20 that provides a variable volume of the hydraullc fluld ("oll") at
a substantially constant supply pressure. The supply 20 can be a reservolr
that supplies a pressure-compensated variable-displacement piston pump wit~ an
accumulator on the discharge side. A feed line 22 conducts the oil from the
supply 20 to the motor 14. A central feature of this -invention is a pressure
reducing valve 24 connected in the feed line and controlled by a remote
electrical signal through a proportional actuator 30 such as a torque motor
or a proportional solenoid. The valve 24 maintains a constant pressure in the
downstream feed line 22 regardless of the flow rate of the hydraulic fluid
through the valve. The pressure varies generally linearly from a low value
such as 100 psi to approximately the supply pressure of the source 20 as a
function of the amplitude of the control signal applied cver a line 28 to the
proportional actuator 30.
The motor 14 is reversible and ac~s as a motor or a brake depending
on the pressure difference applied across its inlet and outlet ports 14a and
14b, and a directional valve 26 that controls the oil flow direction through
the motor. The valve 26 is preferably a four-way, three-position valve
operated by double solenoids. In one position the valve 26 provides a forward
operation, in another position it reverses the flow direction and hence the
direction of rotation. In a neutral position shown in Fig. 1, the hydraulic
lines to and from the motor 14 are interconnected at the valve 26. This puts
a ~ero pressure differential across the motor 14 which is useful for manual
rotation of the spooler. Hydraulic fluid exiting the motor 14 through the
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9'~
outlet 14b and the valve 26 i5 carried by a return line 32 back to the
reservoir or tank feeding the supply 20.
A sequence valve 34 connected ln the return l-lne 32 limits the
pressure in the return line 32 upstream of the valve to a fixed value that is
independent of the flow rate of the oil. The set value oE the sequence valve
is adjustable by a manual screw 38. Oil discharged from the valve 34 is at
substantially zero pressure and flows to the supply 20.
A "regeneration" circuit 40 connected between the return line 32
and the feed line 22 is another significant feature of this invention. It
provides a flow path for the hydraulic fluid from the line 32 to the line 22
during braking. The c~rcuit 40 includes a sequence valve 42 which is
adjustable via a manual screw 44, a flow divider 48 and a check valve 52.
The sequence valve 42 limits the upstream pressure in line 46 to a value
lower than the set pressure of the sequence valve 34. Oil flowing through the
regeneration circuit pass~s through the positive-displacement fluid divider 48
which directs a substantial portion of the flow through line SO and the check
valve 52 to the feed line 22. A smaller portion of the flow9 typically
one-quarter, is directed via line 54 to the reservoir or tank of the supply 20.
The magnitude of the flow through the line 50 conserves oil flow from the
supply 20. The remaining fluid requirement during braking is supplied through
valve 24, which will never allow the pressure in line 22 to fall below about
lOO psi~ thus preventing any possibility of motor-damaging cavitation. The
hydraulic fluid dumped into the line 54 is sufficient to cool the motor 14
during braking.
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The motor 14 has a displacement per revolution which may be
continually varied during operation. Variation of the displacement and/or
the pressure difference across the motor 14 determines the torque developed
by the motor. The displacement of the motor 14 i8 controlled ~y a proportional
actuator 56 which like the actuator 30 is controlled by a remote electrical
signal carried on a line 58. The actuator 56 may also be a torque motor or
a proportional solenoid. Preferably the motor 14 is one whose displacement
can be varied continuously over a significant range, for example 3 1/2 to 19
while the motor is in operation.
With reference to Fig. 1, an electronic servo-amplifier circuit
indicated generally by reference numeral 60 is another significant aspect of
the present invention. It receives inputs, typically in the form of DC
voltages, from three sourcest and produces as an analog output the control
signal on line 28 for the actuator 30. One input is an analog signal
produced by a tachometer 61 that measures the actual speed of rotation of the
tor 14. Another input on line 62 is a speed limit control signal which
is generated by a controller (in the preferred form, a computer 92 and a
multichannel digital-to-analog conuerter 98 as shown in Fig. 2). A pressure
limit command signal is applied over line 64 to the circuitry 60. The
pressure limit command provides an electrical signal that is proportional to
the desired maximum pressure in the feed line 22 downstream of the pressure
reducing valve 24.
An integrating servo-amplifier 66 receives the output signal of
the tachometer 61 carried on line 68 and the spe~d limit command carried on
line 62. An RC loop 70 provides the feedback which allows the amplifier 66
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~99~
to operate as an integrator. In operation, the servo-amplifier 66 will
integrate towards a saturation voltage (e.g. ~10 volts or -10 volts dependinz
on the direction of rotation of the'motor 14) whenever there i8 a difference
in the signals on the lines'68 and 62. If there is a large difference in
these signals, the amplifier 66 will rapidly integrate towards its saturation
output voltage, whereas if the signals differ by a small amount the amplifier
66 will integrate less rapidly. 'When the signals are equal, the output on
line 72 will remain constant. The signal 72 is proportional to a fraction
(ranging in absolute value from 0 to 1.0) of the pressure limit to be used.
The output signal of the amplifier 66 is applied over line 72
to an analog multiplier 74 which also receives the pressure limit command
signal carried on the llne 64. The multiplier is appropriately weighted to
produce an output signal that rapidly (limited in speed by the reaction time
of valve 24) brings the pressure in the feed line 22 to the appropriate value
corresponding to the pressure limit command signal multiplied by the 0 to 1.0
multiplier on line 72. The output signal of the analog multiplier 74 is
supplied through a diode 76 that eliminates negative products (since oil
pressure is always positive). The rectified output signal of the diode is
applied to a linear power amplifier 78 including an associated resistive
feedback loop 80. ~e power amplifier 78 produces an electrical control
signal on the line 28 of sufficient voltage and current magnitudes to operate
the proportional actuator 30.
With reference to Fig~ 2, the electrohydraulic drive and control
system 12 described above with reference to Fig. 1 is delineated by dashed
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~ 14 -
lines. The remaining components show a preferred arrangement for generating
the command signals for speed, pressure and ~otor displacement on lines 62,
64 and 58~ respectively. As noted above, the rotational speed of the motor 14
is measured by the tachometer 61. The output signal of the tachometer ls
applied both to the circuitry 60 over line 68 and to a multi-channel analog-to-
digital converter 82 over line 69. This converter also receives an input
from a tensiometer 84 which operates in conjunction with two fixed passline
rolls 86, 86' that are near the tensiometer and oppose a roller 84a associated
w~th the tensiometer. The rollers 84a, 86 and 86' all engage the strand 18.
The force on the roller 84a is proportional to the tension in ~he strand
and is converted by the tensiometer B4 into an analog output signal, typically
a DC voltage, applied over line 88-to the converter 82. Digital representations
of the strand tenslon and the rotational speed are applied over line 90 to
the computer 92. The computer also receives inputs from an operator switch
station 94 and a video keyboard terminal 96. The switch station 94 includes
manual operating switches to control on-off, forward9 reverse, acceleration
or deceleration of the line, and to vary the tension in the strand. The
terminal 96 allows an operator to set the operating parameters for the
system such ~s the line speed or tension to be maintained in the strand 18,
or allows an input of information concerning the nature of the strand 18
being processed such as its cross-sectional shape, dimensional material in
the form of packagin~ desired, i~e. the amount of strand to be wound onto the
spool 16. During the spooling operation, the computer 92 can include an
internal program for tapering the strand tension (i.e. reducing tension as
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1~97~
the di~mete inc-eases) to procluce a coil on th2 spool 16 tna~ i~
neatly wound wi thout damage.
Output co~trol signals gen~rated ~y the comput~r 92 ar~
direc~ed to a mul~i-channel digital-to-an~log converter 98 that
has (at least) thre~ oùtput channel~. As noted above, th~ output
~peed limit command signal i5 applied over line 62, ~he output
pressure limit command signal is applied over line 64 and a motor
displacement control signal i~ applied oYer line 58. A linear
amplificr 100 connected in line 58 produces a con~rol signal
having the appropri~te voltagc and current magnitudes ~o operat~
the proportional actuator 56. The computer 92 also generates an
output to a video display 102 which provides thc opcrator with a
readout of the current operating conditions of the ~ystem such ~5 !
the line speed, strand tension and the quan~ty of s~rand wound
onto the spool 16.
;' Fig~ 3 hows in a schema~ic form anotAer el~ctro- ¦
hydraulic drive and control syst~m 104 ~hich oontrol6 ~he linear
traverse of ~he ~pool 16 alo~g its ~xi~ o ro~ation. ~h~ tr~- j
verse mechani~m produc~s a compact, even and le~el wound coil of
~ the strand 1~ on the spool 16 with a ~ubstantia~ly const~nt
¦ passline (when vi~w~d from above) ~or the ~trand en~erin~ or
leaving the ~poolq The traYerse drive i~ po~er~d by a hydraulic
I cylinder 106 which i~ connected throu~h a linkage 106a to main
i b~a~ings 108 th~ 3uppor~ th~ pool 16~ The cylinder 106 ha~ a
~mall orifice (n~t shown) through i~ pi~ton to provid~ damy1ng
~nd ~cilitate air ~limination.
¦ Input information to control the oper~tion of the
cylinder is proYid~d by ~our ~ransducers; ~ tacho~eter 110 (which
Il
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~ 16- 1
is usually the tachometer 61 of Figs. 1 and 2) coupled to the mandrel or
shaft of the spool 16 through a linkage 112; a linear position transducer 114
that indicates the lateral position of the spool 16; a llnear velocity
transducer 116 that indicates the instantaneous llnear veloclty of the spool
16; and an optical sensor 118 that determines the lateral posltlon of the
strand 18 and generates an output voltage proportional to the sensed posltlon.
The cyllnder 106 ls supplled oll by a hlgh quallty servo valve 136,
whlch in turn obtains lts control slgnal from one of two servo-ampllflers 126
or 138 according to the state of a veloclty relay 142. The output slgnal of
the ampllfler 126 ls applied to the relay 142 over line 150 and the output
signal of ~he amplifier 138 is applied to the relay 142 over line 152.
The amplifier 138 is the position control servo-amplifier, which
is used (a) to hold the spool in a fixed traverse position for indefinite
periods, (b) for manual traversing of the spool, and (c) for payoff operation
under the control of the strip position sensor 118. Relay 144 is the payoff
relay, which is energized to connect sensor 118 and de-energized to connect
the spooler position sensor 114 ~position signal on line 127). The output
signal of the velocity sensor 116 is connected via line 124 to provide
velocity compensation at high payoffs speeds. A pos1tlon cornmand signal
over llne 154 from an external source such as the computer is used for manual
traverse of the spooler. Durlng position control operation, the arnplifier 138
will adjust valve 136 to minimize the position error of the s~rip or spool.
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~97~
For strip winding, ~he velocity servo-amplifie~ 126 is
used. The velocity command is obtained by first scaling the
sp~oler tachometer llO signal by a pitch poten~iometer 132,
corresponding to the desired trave~se per re~olution. This
signal ov~r line 146, which is always positive, is fed into an
; inverter circuit 140 controlled by a comparator circuit 128. The ¦
comparator circuit compares the actual traverse position ~ignal
127 with values ~et on traverse limits potg 130 (extend) and 134
(retract) and causes a control siynal on line 148 to change rom
a logical ~1~ (extend) to a logica~ uO~ (retract) ~t ~he end of
each cycle and back again. The inverter 140 will then either
invert the sign21 on line 146 ~o an equal negative value or not,
producing a veloci~y command signal on line 149. ~ Yelocity
feedback signal $s on line 124. ~or high speed operation, a
velocity derivative (no~ ~hown) may be added to improve
performance.
A typical cycle of oper~tion of the spool~r shown ln
Figs, 1 and 2 will include ~l) manually moving the machine to
~ecure the strand ~o the ~pool, ~2j jogging the spooler and the
&trand at a ~low forward speed wi~hou~ ~ension in the ~trand,
(3) establishing and holdin~ ~ s~all t~nsion, (4) acc~lerating to
a running speed, (S) maintaining ~ zunning mode, (63 decelerat-
ing, and t7) ~topping wi~h ~ ~all tension. The following
!; detailed discussion of these v~rious modes of operation
ustr~te ~he op~ration and flexibili~y of the presen~
invention. In this discus~ion the supply 20 i~ ~ssumed to be ~t
,, a ~ubstantially constant pressur2 of 3,000 p5i~ the sequenc~
.I valve 34 is ~et ~t 800 psi ~nd the sequence valve 42 in the
rege~ration circuit i5 set a~ 750 p~i. The 6ys'cem will operate
, with a wide variety of other pressure settings.
1 !
., ~
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Manual rotation is possible by placing the valve 26 in its center
position which cross-connects all of the lines and by applying a zero voltage
over the line 28 to produce a minimum pressure in the feed line 22. Under
these conditions, the motor 14 and spool 16 can be rotated Manually in either
direction.
To move from manual rotation to jogging without tension in the
strand material, the valve 26 is moved to a position associated with a forward
rotation of the motor 14. The torque range for the motor i8 selected by
ad~usting the displacement of the motor through a suitable control voltage
generated by the computer 92 acting through the amplifier 100 and the
proportional actuator 56. The computer also generates the desired jog speed
limit command to the line 62~ For example7 the ~C voltage speed limit signal
can correspond to 10 rpm. Finally9 the computer generates a pressure limit
command signal applied to the line 64. Given the pressure values noted
above, an appropriate pressure limit co~mand might be 1,400 psi.
Because the drive is initially at rest, the tachometer 61 produces
no voltage on the line 68. As a result, the amplifier 66 rapidly integrates
upwardly which causes the output signal on the line 28 to also increase
rapidly from zero. This causes a corresponding increase in the pressure in
the feed line 22 as set by the valve 24 ~ntil the pressure is sufficiently
in excess of the setting of the se~uence valve 34 (800 psi) to overcome
the breakway friction of the drive system. In practice the drive will begin
to rotate when the pressure in the feed line reaches typically 1,100 psi.
Once rotation be~ins, an output voltage generated by the tachometer appears
on the line 68. Assuming that the inertia of the drive system is large,
X
-- 19 --
which is usually true Eor spoolers, there will be a short delay before the
drive accelerates to the selected jog speed. Durlng this time, the output
of the amplifler 66 will continue to increase and may reach its saturatJon
value of 100%. This will cause the pressure in the feed line 2Z to reach
the pressure limit setting of 1,400 psi during the acceleration to the jogging
speed. However, once the selected jog speed is exceeded, the amplifier 66
wlll integrate rapidly downwardly and the pressure in the feed line will be
reduced to a value which will maintain the jog speed of approximately 10 rpm.
A typical feed line pressure value for this jog speed is 950 psi. In this
steady state condition9 the pressure difference across the motor is 150 psi
~950 - 800). The output torque of the motor 14 is therefore comparatlvely
small.
Frequently, the jogging mode of operation is used to ~ind slack
material. Once the slack is wound, however, the strand will suddenly become
taut. It is clearly i~portant that this sudden transition fro~ a slack state
to a taut state does not jerk the material with sufficient force to break or
damage it. It ls usually also desirable to be able to maintain the material
in a taut condition without movement. The electrohydraulic drive and control
system 12 oE the present invention achieves these objectives as follows.
The jog speed is selected so that the momentum of the spool and its drive
is moderate. Also, during jogging the torque (which is determined, for any
given displacement, by the pressure difference across the hydraulic motor 14
is comparatively small. Because of these conditions, when the material
becomes taut, the speed of the winter suddenly drops to zero. However,
the integrating
X
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7(~
amplifie- 66 will smoothly integr~te upwa-dly causing the
p-essure in t~e fe~d lin~ 22 ~o increasa f~om the jogging
pressure (9S0 psi) to the value set by the pressur~ limit
command, in this case 1,400 psi. The pressure in the return line
will remain at 800 psi as set by the sequence valve 34 80 that-
~600 psi pressure difference is created and m~int~ined acro~s the
motor without any ro~ation. This pressure dif~erence cr~ates the
desired stall tension. ~ small leakage flow of the hydraulic
fluid through the valves and the motor is (indica~ed by the
dashed lines in ~ig~ 1) provides the required cooling. A
significant advantage of this invention i5 that the stall t~n~ion
may be controlled accurately and held substantially indefinitely, I
and may be quit~ large when s~ desired~ i
To accelerate the strand material from rest to a
d~sired running ~peed, it i~ necessary to set ~he ~peed limit
com~and on ~he line 62 a~ ~ value larger ~han ~he line spe~d and
begin ~o move material along the line from its ~ource4 Because
the line ~peed ~s determined by ~he o~her equipment ln the pro-
cessing line and i5 held at ~ value less ~han the ~peed limit
' command value, the amplifi~r 66 remains saturated at~ for
'example, +10 Yol~s output, corresponding to lOO~o The ou~put
. torque of ~he elec~rohydraulic drive ~ystem 12 is ~h2n determined
by the pressur~ limit command on the line 64. The net efect $s
that th~ ~pooler rotates in a ~orward direction ~t ~n act~al
speed that matches the line speed, but at a tension determin~d by
~'the pressure diferential across the motor 14 (~ssuming that the
displacement of the moto~ is not changed during acceleration).
jAs ~n ~dded degree of precision in the control, the computer 92
.Ican be pr~grammed to increase ~he value of the pressure limit
" . I
,. I
,l -21-
co~nand on the line 64 during acc21eration to co~nsa~ fo~ ~he
inertia o~ the spooler and its drive system~ This syst~m
main~ains a generally constant tension in the strand ma~rial as
it i5 being accelera~e~ from rest ~o ~ ~teady state running
speed.
To plac~ the drive syst~m in a running mode for winding
the strand 18, the speed limit co~nand i5 set slightly above the
line speed and the pressure limit command is preferably ~a~ied in ¦
a pa~tern in accordance with the diameter.o the coil bean~
lo . formed on the -~pool 16. Again, with the speed limit co~nand
slightly above the llne speed, the ampllfier 66 will remain
satur~ted. However, if the material brakæs or otherwise loses
its back-t~nsion, the actual ~peed of the winder will quickly
, exceed the set speed limit comm~nd. In th~ situation the speed
,servo-ampl~fier quickly integrates downwardly which r2pidly
decr~a~ss the lin~ pre sure in the ecd line 22 to a low~r value
to main~ain ~peed ~t ~he ~peed limit value. Thi~ operation of
the ~ystem 12 therefore limit~ the ~runaway~ speed of the winder.
~'It should ~l~o be no~ed that t~ prccise value of the set speed
,Icommand i5 not critical; it i~ only nec~ssary that it be sligh~ly
gr~er th~n the line ~peed.
'I As noted ~bove, the pres~ure limit co~nand may be
varied at will during the running mode. Variations can be in
~¦ respon~e to a vari~ty of input~, either manual ones ~rom ~he
¦ operator switch ~ta~ion 94 or the video keyboard terminal 96~ sr
j ~utomatic ones in response to sensed strand tension from trAn~-
ducer~ ~uch ~s the tensiometer R2, 3 transducer that directly
! senses coil diameter, or through some othsr input ~uch as ~ read-
~..
-22- !
only ~.e~ory OC software prog~am in the computer 92 desl~ned to
vary the st~a~d ~e~sion as 3 function of the coil diameter. Coil
diameter is readily calcula~ed by the comp~te~ fro~ the
tachomet~r 61 and a line speed transducer ~not 6hown).
. The di~placement of the motor 14 ls generally main- ¦
tained at a constant value during the running mode. However
; prior to a cycle of operation, the displacement is usually pre-
set, primarily as a factor of the cross-sectional dimensions of
the strand material and the line speed. For example, small to
mode~ate torques a-e usually used for thin product~ being p~o-
duced at high speed. For ~hese applications the motor displace-
ment set by a control signal on the line 58 will usually be at a
minimum value to reduce the applied torque, increa~e horsepower
efficiency, minimize the amount of hydrnulic fluid consumed, and
to improve the ~ensi~ivi~y of the tensi~n control of ~he 3yst~m.
On the other hand~ other products require ~dium to large ten- ¦
sions and greatcr output torque~ from the motor. In these
situa~ions the ~otor displ2cement is increased to it~ maximum
, value.
20 ~I Decelerat~on typically involve~ ~nly adjusting the ¦~
j pr2ssure limit command to maintain th~ desired level of tension
in the strand. As with ~cceleration, an inertia compensation
insrement may be ubtracted from ~he pres~ure limit command
', signal in ~he ~ame manner described ~bove with respect to the
il acceleration increment. A ~pecial technique is employed~
1, however, for rapid deceleration p~rticularly for an cmergency
¦l ~top fro~ a high opera~ing spe~d with ~ high inertia load (many
Il tons of coil rot~ting ~o match ~he line ~peed).
!
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il -2~- l
7~
To p~oduce this ra2id decele-ation, the p essu e limit
coi~and is ra~idly reduced and the ~.oto displacemen~ is
inc~eased. Fo~ a maximum rate stop, the pressure limit co.~mand
is reduced to ze-o and the m~t~r displacement is increased to its
maximum value. These chAnges cause the pressure in the feed line
22 to drop to approximately 100 psi. The substantial lnertia of
the winde~ is now used to drive the hydraulic motor 14 as a purnp.
A fluid pressure drop in the feed generated by the pumping action
opens the chsck valve 52 and allows oil to flow through the
-egeneration circuit, set at 750 psi. (Note, the set pressure of
the sequence valve 42 in the regeneration circult is l~s ~Aan
that of the sequence valve 34.) The fluid flow from the motor 14 i
thsrefore passes through the flow divider ~8, preferably a rc~ary
type divider, which diverts approximately one-quarter of the
input flow to a supply tank for the power ~ource 2~ and
three-quarters of ~he low to the f~ed line 22A 'As ~ resul~, ¦
much of the oil flow needed for the mo~or 14 i~ supplied by the
regeneration circuit 40. ThiQ is important since a failure to
. .
supply all of ~he hydraulic fluid required by the motor would
, result in damaging the motor due to cavi~ation The additional
required flow to ~he mo~or 14 i8 supplied ~hrough ~he valve 24.
Ii This oil flow also compensa~s for ~ he leakage flows in the
system. The pressure in ~he feed line rsmain~ ~ approx}mately
~ 100 psi throughout ~he d~celeration ~braking~. The diversion of
., one-quar~er of th~ return lin~? fluid ~o the supply 20 provides
'~ the necessary heat dissip~tion or the Rys~em during ~he braking. ¦
The reigeneration circuit i8 ~lso important because the valve 24
i5 not ~ized to supply ~ the 1u~d flow requirements of the
mo~or 14 during this rapid deceleration when the speed i6 very
!
~ 4-
7Q~
hiyh and there is ~n accompanying inc-ease in th~ motor
dis2'acement ~o its ull vall~e.
Once the spooler h.~s decelerated ~o a ~top the p~ess~lre
limit comm~nd will maintain a stall tension on the strand 18 in
the same manne as described above with respect to a s~all wlth
tension prior to acceleration. To relax this ~ension the
pressure from the limit co~nand is set to zero and ~he valve 26
i5 placed in its center position to interconnect all of the
hydraulic lines. This sit~ation is analogous to the initial
lo situation described with respect to a manual rotation of the
spooler.
While the foregoing cycle of operation has been limited i
~o oper~ting the electrohydraulic drive and control system 12 and !
the spQoler 16 in a winding mode, the same equipment can slso be
used ~s an unwinder or ~payoffa drivcO In general, the hydraulic:
motor 14 durin~ unwinding or payoff oper~tes mo3~ of th~ time as
a pump and ~he xegenera~ion circui~ iR u~ed ~o provide the
necessary oil flow to ~he inle~ 14~ ~nd to cool he nys~e~. A
desired back-ten~ion on ~he s~rand 18 being paid off is s~t by
generating a pre~sure limit command which is b210w the value
which would cause the drive ~o motor ln the ~orwa~d direc~ion (in
. the ~oregoing example 950 p5i)~ Back-tension can al50 be
increased by increasing ~he displac~men~ of th~ mo~or. Therefore
adjustment of th~ prsssure limit command and the motor
; displ~cement signal provide a smooth and reliable control over
th~ back-tension of the material being paid off~ As will be
! e~ident, a forward jog ~nd r~ver~e motoring are also r~adily
provided when th~ system is oper~ting in the payoff mode~
!
_ ~ 5
r7(~ ~
The electrohydraulic drive and control system 12 described above
has a major advantage over known systems in that it provides a smooth,
stepless transition from motoring to braking by simply changing a control
voltage applied over the line 28 to a pressure controlling valve 24. In
partlcular, there are no on-off valves that are switched during rotation
which can produce shocks or discontinuitles in the tension control. Other
significant advantages, as noted above, are that the same equipment can
be used both for winding and unwinding, for clockwise and counterclockwise
rotation, the system is adaptable to meet a wide range of operating criteria,
it can maintain a stall condition with tension for an indefinite period, and
it has a rapid emergency braking capability, even with the very large
inèrtias involved in spooling metallic strand. The system is characterized
by a simplicity of design and cost advantages that are quite significant
compared to conventional electric drive systems widely used for winding
and unwinding metallic strands from a process line. This sytem is also highly
advantageous in that it is readily interfaced with a wide variety controls
such as potentiometers, relay circuits, external amplifiers7 transducers,
or~ as described9 a computer which receives inputs from manual controls
and a variety of transducers.
It is also significant to note that while the drive and control
system in the present invention has been described in its preferred setting
as a drive for a spooler, it can also be used in processing lines to drive
other equipment such as bridles~ pinch rolls, helper rolls, slitters, and
the like equipment where it is important to provide a differential in the
tension in the material located upstre2m and downstream of the equipment.
X
Whlle this invention has been described with respect to it~
preferred embodlments, it will be under~tood that variou~ modificatlon~
and variations will occur to those skilled in the art from the foregolng
description and theaccompanying drawings. Such modifications and variations
are intended to fall within the scope of the appended claims.
What is claimed is:
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