Wire and cable process control apparatus

Cable processing control apparatus employs driven cable source and cable take up reels, or sheaves, and two variably spaced idling cable sheaves bearing multiple loops of cable as a fluctuating cable reservoir to accommodate pay off/take up reel discontinuities. A microprocessor, cable discontinuity and reservoir sheave spacing transducers and output driver circuitry are utilized to efficiently and flexibly control the spacing between the idler sheaves as required, for example, to permit continuous cable processing when cable pay off/take up reels are replaced.

DISCLOSURE OF THE INVENTION 
This invention relates to wire and cable processing and, more specifically, 
to improved process control apparatus and methodology for controlling reel 
or sheave dynamics--as during an active sheave substitution operation. 
In wire and cable fabrication, it is common in a continuous process to pay 
out cable from a reel or sheave thereof to and through a processing 
station (e.g., a plastic or rubber jacket insulation extruder) onto a take 
up or output sheave. Some provision must be made to accommodate sheave 
replacement when the cable on the pay out sheave is exhausted (or, 
similarly, when the take up reel full). One method is simply to stop the 
production processes until cable on the next, replacement sheave can be 
spliced to the end of the previous cable (or until the emerging cable is 
cut and transferred to the next take up reel). This is usually 
undesirable--both from a speed of production standpoint and also by reason 
of many process constraints or desiderata--e.g., the requirement for 
continuous plastic or rubber insulation extrusion operation to assure 
insulation jacket thickness uniformity without core eccentricity. 
One prior art approach has been to develop a reservoir of input cable 
stored in multiple loops of cable about two idler sheaves having a 
variable inter-sheave spacing. The idler sheaves move closer together to 
pay out cable for continuous processing when cable is unavailable from a 
source reel--as during reel changeover. After changeover to a new source 
or pay off sheave, the idler sheaves move apart toward their original 
spacing to replenish cable storage. Similar but inverse operation may be 
employed at the take up station if desired. 
Such prior art apparatus has been characterized by substantial 
difficulties. Thus, for example, the movable idler sheave is typically 
very heavy on the order of hundreds of pounds. Sensing a desired 
quiescent, extended position for a movable sheave, as via a limit switch 
or other transducer, and then rapidly stopping the sheave, has been 
difficult--and often very wearing and destructive of the equipment 
involved. 
It is an object of the present invention to provide improved cable 
processing apparatus. 
More specifically, it is an object of the present invention to provide 
cable sheave control apparatus which flexibly, reliably and automatically 
accommodates substitutions in pay off/take up reels during a cable or 
other strand fabrication operation. 
The above and other objects of the present invention are realized in a 
specific, illustrative cable processing control apparatus employing driven 
cable source and cable take up sheaves, and two variably spaced idler 
cable sheaves bearing multiple loops of cables as a fluctuating cable 
storage reservoir to accommodate pay off/take up reel discontinuities. 
A microprocessor, cable discontinuity and reservoir sheave spacing 
transducers and output driver circuitry are utilized to efficiently and 
flexibly control the spacing between the idler sheaves--as required, for 
example, to permit continuous cable processing when cable pay off/take up 
reels are replaced.

Referring now to FIG. 1, there is shown specific, illustrative apparatus 
for controlling the pay out of cable for a process operation of any kind, 
e.g., to extrude rubber or plastic insulation about a cable center 
conductor or a group of center conductors 8 assumed to be initially stored 
on a pay off reel or sheave 23. Comparable equipment may also be employed 
to control the take up apparatus not shown. 
As above discussed with respect to prior art apparatus, the pre-processed 
cable 8 contained on pay off sheave 23 passes to and about a first idler 
sheave 12 of a cable storage reservoir sheave couplet 12-15. In 
particular, cable 8 passes in multiple loops around the periphery of the 
sheaves 12 and 15 such that a substantial length of cable is stored 
thereabout. The final turn of the cable 8 about the sheaves 14 and 15 
passes to the processing station, e.g., to an extruder for an assumed 
cable jacketing operation. As will be readily apparent to those skilled in 
the art, after passage through the processing station, the processed 
cable, e.g., the jacketed core or conductor passes to and is gathered up 
by a take up sheave (not shown). 
The reservoir sheaves 14 and 15 have a variable spacing therebetween. This 
may be accomplished, for example, by having the sheave 14 freely rotate 
about a fixed axle 14, while the sheave 15 rotates about an axle 16 which 
is free to linearly translate in a mounting frame slot 18 in a direction 
towards or away from the sheave 12. The sheave 15 is biased in a direction 
away from the fixed sheave 12, as by a torque motor 20 applying tension 
via any mechanical coupling 21, e.g., via a belt or chain attached to a 
bearing on the axle 16. 
A transducer, e.g., a potentiometer 28, is utilized to provide an 
electrical output signal identifying the instantaneous spacing between the 
sheaves 12 and 15. This may be accomplished, for example, by a belt 30 
which translates around laterally fixed bearings 28 and 33, with a bearing 
29 on movable axle 16 being connected to the belt 30 at one point. As the 
belt 30 moves responsive to translation of axle 16 and sheave 15, the belt 
30 rotates a shaft 28 of the potentiometer, changing its electrical 
output. For the particular orientation and connection shown in the 
drawing, movement of the sheave 15 to the left will cause a clockwise 
rotation of potentiometer shaft 28, changing its resistance value in a 
first direction. Correspondingly, translation of the sheave 15 to the 
right will cause counter-clockwise rotation of the potentiometer shaft 28 
and a corresponding opposite change in the potentiometer output. In 
various forms well known to those skilled in the art the resistance 
exhibited by the potentiometer 28 may be employed in a bridge to directly 
supply an electrical output signal to an analog-to-digital converter 60. 
Alternatively, the resistance value itself may be a sufficient electrical 
signal--as by inclusion directly in a lattice network; in a voltage 
divider; in a bridge containing in the analog-to-digital converter; or the 
like. 
The cable 8 paid off the source sheave 23 passes through a normally 
disengaged vise 11 to the first reservoir idler roller 12, vise 11 having 
normally open contacts 13 which close to signal when the vise is in an 
engaged position. When cable on a particular pay off sheave 23 is 
exhausted, the vise 11 is engaged to retain access to the end of the cable 
previously contained on that specific sheave 23. The beginning end of the 
next or successor pay off sheave 23 (not shown) is then spliced to the 
prior cable length end secured in vise 11. When the splicing operation is 
complete, vise 11 is disengaged and cable pay off proceeds in its normal 
manner from the substituted pay off sheave. Multiple sheaves can be 
coaxially mounted on a common shaft 24. Alternatively, separate sheave 
mountings and drives may be utilized. 
During normal operation, the pay off sheave 23 is driven by a motor 58 
which is controlled by a microprocessor 40 in a manner below discussed. 
The cable played out from sheave 23 freely passes through quiescently 
unengaged vise 11; proceeds in multiple turns about the storage idler 
rollers 12 and 15; passes to the work station, e.g., the extruder; and is 
finally collected about a take up reel and take up apparatus. At the end 
of a pay off reel, the cable end is fixed in a vise 11 as above noted--but 
without impeding or stopping the cable processing operation, i.e., without 
stopping the extrusion. The cable pulled through the extruder under 
tension from the take up apparatus removes cable from the reservoir as 
required. That is, the cable take up progressively forces the movable 
idler sheave 15 to the left in the drawing such that monotonically less 
cable is looped about the two idler sheaves 12 and 15 as the cable 8 is 
consumed for processing. 
When the cable splicing operation is complete such that the next pay off 
sheave 23 is ready for operation, the vise 11 is disengaged and the pay 
off sheave is rotated by the controlled driven motor 58 at a rate which 
exceeds that required for processing. This excess capacity is taken up by 
the movable sheave 15 which extends to the right, consuming the more rapid 
cable pay out under the urging of the force provided by the torque motor 
20 through the mechanical linkage 21. After the desired storage capacity 
is restored to the sheaves 12-15, motor 58 again drives the pay off sheave 
23 at the same rate as the take up equipment. 
In accordance with one aspect of the present invention, attention is 
focused on the particular way in which the sheave 15 moves to the right, 
or increasing cable storage position. This operation is effected without 
any undue deceleration or other mechanical shock-producing movements to 
assure regular and efficient operation of the composite pay out structure 
shown in the drawing as well as the longevity of service of such 
equipment, and also good quality of cable fabrication unimpaired by 
shock-induced faults in the finished cable. 
To this end, after the vise 11 is released when a new or replaced pay off 
sheave 23 has been spliced into operative connection, the cable 15 is 
moved at a constant velocity from its initial or closest proximity to 
sheave 12 until a predetermined transition point is reached. From the 
transition point until the sheave 15 reaches the actual or desired spacing 
location, sheave 15 moves towards its right or apart position in the 
drawing using position rather than velocity control. 
The above-described control is effected by the microprocessor 40 connected 
via data and address buses 42 and 43 to a number of elements below 
discussed, including a stored program containing read only memory 47 and a 
read/write or RAM memory 49. The buses 42 and 43 are connected to a latch 
53 to provide a digital output word corresponding to the drive speed 
desired for the motor 58 and the shaft 24 for the pay off sheave 23. The 
desired motor 58 drive speed stored in digital form in latch 53 is 
converted to analog by a digital-to-analog converter 54, amplified by a 
power amplifier 56 and applied to a control port of the drive motor 58. 
Accordingly, the pay off sheave 23 is directly controlled by the 
microprocessor 40 and rotates at the requisite speed determined by the 
stored contents of latch 53. 
A number of input variables are communicated to the microprocessor 40 via a 
multiplexer 51 and the data bus 42. As above noted, an analog-to-digital 
converter 60 communicates to the microprocessor via multiplexer 51 and the 
data bus 42 the output of potentiometer 28, thereby communicating to the 
microprocessor the instantaneous separation between the sheaves 12 and 15. 
The state of the vise 11 contacts 13 is a second input to the multiplexer 
51. 
Finally, four registers 62, 63, 66 and 68 communicate to the microprocessor 
40 via the multiplexer 51 various constants which define the motion 
desired for the sheave 15. The registers may comprise any standard data 
storing registers well known per se to those skilled in the art. One 
particularly useful form of such registers is a multidecade variable 
switch having an output binary coded decimal or other Boolean coding which 
identify the instantaneous setting or value for each switch decade. The 
switch or register 62 is loaded with the desired velocity value for 
movement of sheave 15 to its extended (right in the drawing) position 
before it reaches the transition point (computational variable DVAL 
discussed below). Register 63 is loaded with the computational processing 
value of the velocity gain desired; i.e., the rate at which error in 
velocity movement of the sheave is corrected (processing variable VGAIN). 
Register 66 is loaded with and communicates to the microprocessor 40 the 
spacing transition point from the velocity to the position mode above 
described (variable TRP.0.S) and, finally register 68 has a position mode 
error correction gain factor (PGAIN). 
By reason of its importance and possible injury caused by misuse if 
external access were provided, a further processing variable corresponding 
to the desired spacing between sheaves 12 and 15, i.e., the position of 
movable sheave 15 within slot 18 (computational variable DP.0.S) is 
included as an integral part of the stored program. Alternatively, if a 
variable position is desired, a further register/switch may be employed to 
communicate the variable DP.0.S to microprocessor 40. 
Functioning for the microprocessor 40 to effect the above-described mode of 
operation is depicted in flow chart form in FIG. 2. It is assumed that the 
microprocessor 40 has previously read into RAM memory 49 the variables 
DVAL, VGAIN, TRP.0.S, PGAIN and DP.0.S above described. This may be done 
on a one time basis at system initialization. Alternatively, the 
microprocessor 40 may periodically poll the registers 62, 63, 66 and 68 
via the data and address buses 42 and 43. 
Microprocessor control of the position of sheave 15 is depicted in FIG. 2 
and begins with a starting point 72. As a first matter, processing reads 
in the instantaneous position of the sheave 15 (computational value 
IP.0.S) by issuing a command to the multiplexer on address bus 43 to 
correct the output of analog-to-digital converter 60 to the microprocessor 
40 via the data bus 42. This, of course, communicates to the 
microprocessor the instantaneous output value for potentiometer 28, and 
thereby also the instantaneous distance or separation between the sheaves 
12 and 15. A following test 76 determines whether or not the instantaneous 
sheave 15 position (IP.0.S) is greater or equal to the transition position 
(TRP.0.S). If it is ("YES" test result), meaning that the sheave 15 is to 
the right of the transition point in the orientation of FIG. 1, the 
processing operates in a position mode and follows the left branch of the 
test 76. If it is not, as in the period just following splicing of a new 
pay off sheave 23 when the sheave 12 and 15 most closely approach, a N.0. 
results from test 76 and processing follows the sequence beneath the test 
76 block in FIG. 2. Assuming a N.0. result such that the equipment is in 
the velocity mode as just following a splice, the potentiometer 28 is 
again read by passing the output of analog-to-digital converter 60 to the 
microprocessor 40 (operation 79). The instantaneous position of the sheave 
15 is stored in a variable location IP.0.S1. After a fixed and 
predetermined delay (a time DLY of fixed, constant extent, e.g., a 
constant one second), the potentiometer 28 setting is again examined and 
the contents stored in a variable location IP.0.S2. The instantaneous 
sheave 15 (IVEL) is then determined as a quotient of the movement divided 
by the period consumed (functional block 84), as by the programming 
statement: 
EQU IVEL=(IP.0.S2-IP.0.S1)/DLY. (1) 
It will be understood that statements such as (1) immediately above are 
written in schematic form and may be coded in any desired language a great 
many of which are known to and used by those skilled in the art. Finally, 
a proportional velocity correction process 85 generates an output signal 
(.0.UTPUT) which drives the motor 58. The .0.UTPUT signal is an error 
correcting signal and serves to drive the pay off sheave 23 in such an 
amount and to such an extent that any detected velocity error (VERR.0.R) 
or difference between the instantaneous velocity (IVEL) and the desired 
velocity (DVEL) is obviated. Many servo-mechanism like routines for 
correcting errors between measured and desired quantities are per se well 
known and may be employed, e.g., a Kalman filter. One simple but effective 
routine is simply to determine the error between the desired and actual 
velocities as by: 
EQU VERR.0.R=DVEL-IVEL; (2) 
and to update a correction variable (VC.0.RR) with the measured error, as 
by: 
EQU VC.0.RR=VC.0.RR+VERR.0.R. (3) 
Finally, the motor drive variable output .0.UTPUT is set equal to the 
product of the correction factor and the velocity gain, as by: 
EQU .0.UTPUT=VGAIN+VC.0.RR (4) 
Following such processing, digital processing returns to the start point 72 
to begin a next cycle of operation to assure continuous, accurate sheave 
15 movement. 
The above has considered the velocity mode of operation. If test 76 
indicates a position mode (IP.0.S.gtoreq.TRP.0.S), a proportional position 
correction routine 77 operates in a manner analogous to the velocity 
proportional correction routine 85 to act as a variable mechanism to move 
the instantaneous position of the sheave 15 to the desired position. This 
may simply involve setting a position error (PERR.0.R) equal to the 
difference between the sensed and the desired positions, as by: 
EQU PERR.0.R=DP.0.S-IP.0.S (5) 
A position correcting (PC.0.RR) and the output variables are then updated, 
as by: 
EQU PC.0.RR=PC.0.RR+PERR.0.R (6) 
and, 
EQU .0.UTPUT=PGAIN+PC.0.RR. (7) 
Again, following position updating, control loops back to the start 
position to begin a next cycle of operation. 
As will be apparent, the above digital processing will mantain the sheave 
15 at the desired spacing position DP.0.S throughout normal processing and 
cable pay out. Moreover, the processing will restore the movable sheave 15 
to its desired position to recapture lost cable following a pay off sheave 
replacement in the requisite velocity mode and following position mode 
operations in a regular, controlled, manner avoiding all mechanical 
shocks, system dislocations or the like. Thus, cable processing continues 
unabated notwithstanding pay off sheave 23 replacements, or the like. 
It is observed that the vise 11 signal via vise contacts 13 selectively 
signals the microprocessor 40 when the vise 11 is engaged. The 
microprocessor 40 may periodically poll the multiplexer to determine the 
state of the contacts 13 as shown in FIG. 1. Alternatively, the contacts 
may be connected to a microprocessor interrupt port for direct and 
constant communication. When the contacts 13 are closed, the 
microprocessor 40 removes drive actuation from the motor 58 until the 
contacts 13 again separate. Further, it is observed that the above 
discussion and FIG. 1 has focused specifically on the pay off sheave 23 
and a reservoir for controlling cable pay off. As described above, 
essentially identical structure may be employed as take up equipment 
either with or without the comparable equipment being used at the pay off 
end. That is, the apparatus functions in a manner directly comparable to 
that shown in the drawing, but in an inverse manner to absorb cable until 
a new take up reel can be connected, i.e., where the storage or reservoir 
sheaves extend during take up reel replacement and reduce the distance 
between them to resume normal spacing. 
The above-described arrangement is merely illustrative of the principles of 
the present invention. Numerous modifications and adaptations thereof will 
be readily apparent to those skilled in the art without departing from the 
spirit and scope of the present invention.