US2571023A - Mechanism for controlling the speed of motors - Google Patents

Description

Oct. 9, 1951 E. w. ERTNER 2,571,023

MECHANISM FOR CONTROLLING THE SPEED OF MOTORS Filed May 27, 1948 Patented Oct. 9, 1951 ,MECHANISM FOR CONTROLLING THE SPEED OF MOTORS Edward W. Ertner, Berwyn, Ill., assignor to Western Electric Company, Incorporated, New York N. Y., a corporation of New York Application May 27, 1948, Serial No. 29,513

This invention relates to mechanism for controlling the speed of motors. and more particularly to a takeup motor control mechanism for maintaining a substantially constant spooling speed and tension on a wire during the takeup operation on a wire drawing machine.

In high speed wire drawing machines used in the manufacture of fine wire, where the wire is advanced from the machine at a constant speed and taken up on a motor driven spool, it is essential that the R. P. M. of the take-up spool diminish as the spool is being filled in order to maintain a substantially constant tension on the wire. This has been accomplished for many years while drawing coarse wire with a torque motor of the three phase squirrel cage construction. The air gap, resistance of rotor, and stator construction in a motor of that type are designed so that the characteristic thereof is such that the motor develops a constant horsepower at the speeds at which it operates from an empty to a full spool. This motor characteristic will provide for a uniform and constant tension in the material being spooled throughout the spooling operation. Theoretically, this type of takeup drive is ideal because of its simplicity and cost. In drawing fine copper wire, for example, wire of 40 gage or smaller, at high speeds on large spools, bearing friction, windage and slight voltage changes, which vary considerably, introduce variations which become important and must be compensated for.

It is an object of the present invention to provide a simple and eilicient takeup motor control mechanism for maintaining a substantially constant spooling speed and tension on fine material being wound on a takeup spool.

In accordance with one embodiment of the invention as applied to the spooling of very line drawn wire being advanced at a constant rate of speed from a capstan of a wire drawing machine, there is provided a mechanism comprising a takeup spool driven by a variable speed squirrel cage induction type electric motor, the driving torque of which is varied between selected limits by means of variable auto-transformers driven by a reversible type motor whereby the voltage to the takeup motor is varied up and down in accordance with variations in the tension on the wire from a predetermined normal value as it advances from the capstan and is taken up on the spool. The circuit to the driving motor of the transformer whereby the driving torque of the takeup motor is varied up and down is controlled by means operable 5 Claims. (Cl. 24245) directly by the tension on the wire. This control means includes three pulleys between which the wire is looped, two of the pulleys being mounted on a fixed axis and the other being carried on the outer end of a pivotal arm, spring urged in one direction to produce the desired normal tension on the looped wire. A variable length supply of wire is thus constantly maintained between the capstan and the takeup spool due to variations in the tension on the wire effected as the diameter of the mass of wire wound on the spool increases or due to irregularities in spooling. As the adjustable loop of wire contracts or expands beyond predetermined normal limits eilected by variations in the tension on the wire from the normal value, the arm oscillates and a cam carried thereby actuates a pair of microswitches included in the circuit to the transformer motor to vary the voltage to the takeup motor and consequently the driving torque thereof up or down between selected limits in accordance with variations in the ten: sion on the wire from a predetermined normal value.

Other objects and advantages of this invention will more fully appear from the following detailed description, taken in conjunction with the accompanying drawing in which a single figure shows diagrammatically a motor control mechanism embodying the features of this invention for obtaining a uniform tension on wire being wound on a takeup spool.

In the drawing, a takeup spool I0 is shown mounted directly on a rotor shaft ll of a variable speed electric motor l2, preferably of the three-phase squirrel cage induction type. A wire I3 is shown being taken up on the spool N, the wire being fed in the direction of the arrow at a constant rate of speed, for instance, 3,000 feet per minute, from the last step of a multiple diameter drawing capstan H of a wire drawing machine. From the last step of the capstan H, the wire i3 is directed over an upper guide roller ll, rotatable about a fixed axis, thence to a lower guide roller I8, also mounted to rotate about a fixed axis. The wire l3, after being passed under and around the lower guide roller I8, is directed to a guide roller I! carried on the free end of a pivotal tension arm 20, having. its opposite end fixed to a shaft 2| rotatable about a fixed axis. After being directed under and around the guide roller IS, the wire is directed over and again under a companion guideguide rollers I8, l9 and 22. From the companion guide roller 22, the wire 13 is associated with a reciprocable distributor device 24, which distributes the wire longitudinally upon the rotating takeup spool l in uniform layers of hellcal formation, the diameter of the mass of wire wound on the spool increasing with each successive layer wound onto the spool.

It will be apparent that while the wire it is being fed from the last step of the capstan It at a constant rate of speed, as hereinbefore mentioned, such as 3,000 feet per minute, the diameter of the mass of wire on the spool is constantly increasing by very small increments, thus tending to increase the linear speed of the wire which will finally result in an increased deleterious tension on the wire from a desired predetermined normal value unless compensated for. As a direct result of this increased tension on the wire from a predetermined normal value, a contraction of the loop of wire 23 between the guide rollers i0, i9 and 22 occurs and the tension arm 20, with its shaft 28, is caused to rotate in a clockwise direction and thus the contracting loop of wire causes the automatic control to slow down the takeup spool to the desired speed. In the case of a decrease in the tension on the wire I3 from a predetermined normal value, an expansion of the loop of wire 23 occurs and the tension arm 20, with its shaft 2!, will rotate in a counter-clockwise direction, the extent of this latter movement of the arm being limited by the engagement of a bumper 25 on the tension arm 20 adjacent the guide roller i9 with a stop member 26 arranged in its path. The expansion of theloop of wire 23 causes the automatic control to speed up the takeup spool to the desired speed. A coiled tension spring 21, having its opposite ends connected to an adjustably positioned pin 30 and an arm 3!, respectively, the arm extending at an angle from the lower end of the tension arm 2i! and beyond the axis of rotation of the shaft 2i. functions to produce the desired normal tension on the wire it and thus maintain the loop 23 of wire taut. Any increase or decrease in the tension on the wire is from a desired predetermined normal value is compensated for by varying the driving torque of the motor 52 between selected limits. in accordance with variations in the tension on the wire from that desired.

The driving torque of the takeup motor i2 is controlled by varying the voltage thereto up and down directly from the tension on the wire 88 acting through the oscillatory movement of the tension arm '20 in the following manner:

The tension arm shaft 2i carries a segmental shaped cam 32, which is adapted to engage a pair of actuators 33 and 34 of microswitches 37 and 38, respectively. These microswitches 31 and 30 are arranged in the path of the periphery of the cam 32, the switch 3'! being normally closed, whereas switch 38 is normally open. The switches control the direction of drive of a single phase reversible type motor 39, which drives variable tandem type auto transformers 40 connected in open delta having a pair of contact brushes or arms 4! attached to, but insulated from, a driving shaft 44. The shaft 44 is driven from the motor 39 by suitable speed reduction mechanism comprising a pinion 45 attached to a rotor shaft 48 of the motor, the pinion meshing with a spur gear 41 fixed to a shaft 48 normally clutched to an aligned shaft 49. A clutch, indicated at 52, comprising cooperating clutch members attached to adjacent ends of the two shafts dB and 49,

- serves normally to connect the shafts together till so that'they will rotate in unison. A compression spring 59 surrounding the shaft 49, and with its opposite ends abutting the clutch member carried by such shaft and a fixed stop member 54, serves normally to maintain the clutch members in operative engagement, as shown in the drawing. In order to manually disengage the clutch members, a control knob 55 is provided on the shaft 39, whereby an operator may longitudinally move such shaft a slight distance to disengage the clutch members. Upon the shaft 49 is secured a sprocket 58, which drives a sprocket 59 fixed to the driving shaft 44 of the auto transformer 40 by means of an interconnecting sprocket chain 60.

It will be understood that by means of the described speed reduction mechanism interconnecting the rotor shaft 46 of the transformer motor 39 with the driving shaft 44 of the variable auto transformer 40, the contact arms 4! may be automatically shifted at the desired rate of speed along the windings of the transformer in either direction to vary the voltage supplied to the takeup motor i2, depending upon the direction of rotation of the rotor shaft 46 of the reversible motor 39. The setting of the auto-transformer contact arms 0! along the transformer windings is readily effected by the operator grasping the hand knob 55 and pulling the shaft 49 in a longitudinal direction to disengage the clutch 52 and, thereafter, rotating the shaft 49 in one direction or the other, thereby shifting the contact arms to provide a desired voltage to the takeup motor $2 in starting operations or other periods when found necessary. Upon the desired setting of the contact arms 4i being accomplished, a release of the control knob 55 effects a. reengagement of the clutch 52, thus again completing the drive from the auto-transformer motor 39 to the transformer contact arms 4!.

The transformer contact arms M are connected by conductors 6! and 62 directly to the operating winding of the takeup motor i2. One end of each of the transformer windings may be connected to a three-phase source of power 65 through a three-pole switch 66 and conductors 61 and 68, the opposite ends of the windings being connected to the switch 66 by a common conductor 69. The conductor 69 is connected to the operating winding of the takeup motor l2 by a conductor 10. It will be apparent that the position of the contact arms 4| along the transformer windings will determine the voltage output of the auto-trans-- nected, by conductors 8| and 82, to other terminals 83 and 84 of the microswitches 31 and 38, respectively. For the purposeof protectin the auto-transformer 40 and gear train in case the contact arms 4| come to the end of their travel in either direc-- tion, an actuator 81 of the normally closed microswitch TI is arranged in the path of a cam member 88 fixed to the transformer driving shaft 44.

The arrangement is such that whenever the contact arms 4| reach the limit of travel at either end of the transformer windings, the cam member 88 will engage and move the microswitch actuator 91 to disengage it from a contact 89 of the microswitch 11, thus opening the circuit to the transformer motor 39.

The operation of this control mechanism is as follows: It will be assumed that the wire I3 to be taken up on the reel I is being fed from the last step of the wire drawing capstan I4 at a constant rate of speed, for instance, 3,000 feet per minute, when normal speed is attained, and that the spooling operation has just begun upon an empty reel, the switches 66 and 14 having previously been closed to supply current to the motors I2 and 39, respectively. Also, at the start ofthe spoolin operation, in order to quickly accelerate to running speed, the operator had, in the manner previously described. disengaged the clutch 52 and set the auto-transformer contact arms II manually along the transformer windings to the position shown in the drawing, thus providing the initial required voltage to the takeup motor I2 to obtain the necessary spool starting and running speed torque which, in cooperation with the action of the spring 21 upon the tension arm 20, will bring the spool up to normal speed and, with the proper number of wraps of wire on the last capstan, will provide the desired tension in the wire I3 between the capstan I4 and the spool Ill. In operation, the wire I3 is advanced from the machin at a practically constant speed and passes around the sheaves IB, I9 and 22 in the order given, and then between the distributor fingers 24 and onto the spool Ill. The spring 21 has been adjusted so that the arm 20 will remain in its extreme left hand position against the bumper stop member 26, when the wire is not being taken up as fast as it could be delivered. The arm 20 will remain in this position when, upon starting with an empty spool, the operator does not raise the voltage high enough with the manual control knob 55 or when the line volta e drops or when the automatic control arm 20 overshoots the desired position. During this period, the normally closed microswitch 31 is maintaining the circuit closed to the transformer motor 39 and the motor rotates in a counter-clockwise direction to effect an increase in the voltageto the take-up motor I2 and consequently increases its speed. As the effective speed of the spool I0 will tend to increase steadily because of the increased supply of voltage thereto, the eifective speed of the spool I0 will reach the speed at which wire is supplied to it by the capstan I4. As the spool I0 continues to take up wire, its effective diameter will'be increased and consequently it will tend to take up wire at a speed faster than the wire is delivered by the capstan I4. This will cause a contraction of the wire loop 23 and consequently the arm 20 will swing in a clockwise direction. As the arm 20 will continue to move in a clockwise direction asthe effective diameter of the spool I II increases, the arm 20 will ultimately cause the cam 32 to engage the actuator 33 of the switch 31 and thus open the circuit to the transformer motor 39. Continued filling up of the spool I0 will result in an increase in its effective diameter and further movement will be imparted to the arm 20 in a clockwise direction until the cam 32 engages the actuator 34 of the switch 39 to close the circuit to the transformer control motor 39 in a reverse direction. The motor 39 will then drive in a clockwise direction to decrease the voltage supplied to the takeup motor I2 and consequently decrease its speed. I

The single loop of wire 23 between sheaves I8, I9 and 22 may be increased to a double or triple loop if additional mechanical advantage is required to swing the arm 20 when ultra fine wire is being drawn. Increasing the number of loops also provides more wire and, thereby allows more time for the take-up motor I2 to slow down. Microswitches 31 and 38 may be mounted in an adjustable bracket (not shown) so that they may be brought into play when desircd. In general, the microswitch 31 should be adjusted to increase the voltage only when the arm 20 is at rest against the bumper stop member 26 or very close to it. The microswitch 38 should be adjusted to decrease the voltage when the arm 20 swings in a clockwise direction and a substantial distance away from the bumper stop member 26. The voltage decrease will continue as the arm continues to swing in a clockwise direction to its extreme clockwise position. With the proper pinion 45 and spur gear 41 ratio, the arm will remain most of the time approximately in a neutral position, where the voltage control motor 39 is inactive. The proper pinion and gcar ratio to use will depend upon the rate of build-up of the wire I3 on the take-up spool I9, and the response of the motor I2 to voltage changes, design of variable vcltage transformer, et cetera.

It is to be understood that the above-described arrangements are simply illustrative of the application of the principles of the invention. Numerous other arran ements may be readily devised by those skilled in the art which will embody the principles of the invention and fall within the spirit and scope thereof.

What is claimed is:

1. In a takeup mechanism for a material handling machine having means for feeding material at a constant rate of speed comprising a takeup spool, an induction motor for driving said spool, a voltage supply for said motor, resilient means for supporting a loop of wire between the feeding means and the spool, a lever movable in response to changes in the length of wire in said loop, a cam surface movable with said lever, contacts actuated by said cam surface, a reversible motor connected to be driven in opposite directions in response to actuation of the contacts by the movements of said cam surface, a voltage supply for said reversible motor, and an auto-transformer driven by said reversible motor for controlling the voltage supply to the spool driving motor.

2. A takeup mechanism for a material processing machine having means for delivering material at a constant rate of speed comprising a takeup spool, an induction motor for driving said spool. a voltage supply for said induction motor, means for regulating said voltage supply to the induction motor comprising means for maintaining a variable length loop of material between the delivering means and the spool, said means including a pivotal lever movable in response to variations in the length of said loop, a cam surface movable with said lever, an auto-transformer for controlling the voltage supplied to said induction motor, a reversible type motor for driving said auto-transformer, means for connecting the auto-transformer between said voltage supply and the induction motor, and means actuated by movements of said cam surface for supplying voltage to drive the auto-transformer driving motor in opposite directions responsive to variations in tension on the material between the delivering means and the spool.

3. In a takeup mechanism for a wire drawing machine having a constant speed capstan for delivering wire at a constant rate, a takeup spool, an induction motor for driving the takeup spool, a voltage supply for said induction motor, relatively movable wire guiding elements between the capstan and spool for forming a loop of wire of a length dependent upon the tension on the wire caused by variations in the difference in the effective speeds of the spool and capstan, a lever movable in response to variations in tension on the wire during relative movement between said guiding elements, a cam surface movable with said lever, anauto-transformer for controlling the voltage supplied to said induction motor, a reversible type motor for driving said auto-trans- I former, a voltage supply for said reversible motor,

and switching means arranged in the path of said cam surface for supplying voltage to drive the auto-transformer motor in opposite directions dependent upon movements of said cam surface responding to variations in the length oi said loop.

4. In a takeup mechanism for a wire drawing machine having a constant speed capstan for delivering. wire at a constant rate, a takeup spool, an induction motor for driving the takeup spool, a voltage supply for said induction motor, relatively movable wire guiding elements between the capstan and spool for forming a loop of wire of a length dependent upon the tension on the wire caused by variations in the difierence in the effective speeds of the spool and capstan, a lever for supporting one of said wire guiding elements and movable therewith upon changes in the length of the loop of wire, a cam surface movable with said lever, an auto-transformer for controlling the voltage supplied to said induction motor, a reversible type motor for driving said auto-transformer, a voltage supply for said reversible motor, and switching means arranged in the path of said cam surface for supplying voltage to drive the auto-transformer motor in opposite directions dependent upon movements of said cam surface responding to variations in the length of said loop.

5. In a takeup mechanism for a material handling machine having means for feeding material at a constant rate of speed comprising a takeup spool, an induction motor for driving said spool, a voltage supply for said motor, resilient means for supporting a loop of wire between the feeding means and the spool, a lever movable in response to changes in the length of wire in said loop, a cam surface movable with said lever, a reversible motor, a voltage supply for said reversible motor, a switching device between said reversible motor and its voltage supply operable under control of said cam surface and having three controlling positions eilective selectively to operate the reversible motor in either direction or to disconnect the motor from its voltage supply, and an auto-transformer driven by said reversible motor for controlling the voltage supply to the spool driving motor.

EDWARD W. ERTNER.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,706,164 Hull Mar. 19. 1929 1,706,166 Hull Mar. 19, 1929 2,353,408 Larsen July 11, 1944

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