US1812818A - Motor control system - Google Patents

Description

MOTOR CONTROL SYSTEM Filed May 16, 1928 Inventor:

Ha' ry AL \A/inne b zZw/amw His Attorney Patented June 30,1931

UNITED STATES PATENT OFFICE HARRY A. Wm, 01 SOHEN'EOTADY, NEW YORK, ASSIGNOR '20 GENERAL ELECTRIC COMPANY, A. CORPORATION OF YOIQK MOTOR common sirsrmr Application filed Kay 16,

My invention relates to electric motor control systems, more particularly to control systems" for electric motors employed to drive reels for winding up strip materials,

5 such as cold rolled strip steel, and has for its object the provision of a control system for the driving motor which is of simple construction and which is convenient and efiicient in operation. 7

In the manufacture of various sheet materials such as cold rolled strip steel, the finished product is wound on reels. In winding the material on the reel it is desirable not only to main a constant tension in the material while it is being wound, but also to maintain a tension in the material when the mill is stopped so that the material will remain tightly wound upon the reel. My invention, therefore, contemplates the promsion of control'means for the reel driving motor whereby regardless of the speed of mill operation, a predetermined constant pull will be exterted upon the material being wound, and whereby when the mill is stopped the material will be held under a desired tension.

In carrying my invention into effect in one form thereof, I rovide the reel driving motor with a contro system which includes a current re lator jointly dependent upon a function of the feed of the material to the reel and the armature current of the motor so that the motor will operate to maintain a constant tension in the material as it is be ing wound. The control system further includes means responsive to the speed of the strip for causing a certain amount of resistance to be inserted in the motor power circuit when the speed of the strip has been reduced to a .predetermined value so that the motor will maintain the strip under tension even though the mill is brought to rest.

For a more complete understanding of my invention reference should be had to the accompanying drawing in which the single figure is a diagrammatic representation of a system of control embodying my invention.

Referring to the drawing, I have shown my invention in one form as applied to a 1928. Serial No. 278,248.

direct current motor em loyed to drive the collecting reel of a col rolled strip steel r'nill. As shown, a direct current motor 10, provided with an armature 11 and a field winding 12, is directly connected to drive a reel 13 which serves to collect and wind the strip material 14 passing from the last stand of the main finishing rolls 15. A suitable source of direct current supply '16, preferably of substantially constant voltage, is provided for the motor 10, both the armature 11 and the field winding 12 being supplied by the source 16. A switch 17 is inserted in the connections "between the armature 11 and the source 16. Any suitable means may.

be provided for'driving the finishing rolls 15. As shown, an electric motor 18 is provided for this purpose, the motor 18 preferably being of the adjustable speed direct current type and supplied with power from the source 16. A switch 18a is inserted in the connections between the motor 18 and the source 16.

It will be understood that in the manufacture of cold rolled strip steel and similar materials it is desirable to maintain a certain constant tension in the material between the last stand finishing rolls and the winding reel. It will be further understood that as long as the lineal speed of the strip the reel motor must be constant in order to maintain a constant tension in the strip. Therefore, in order to maintain a constant tension inthe strip under all conditions, the horse power input to the reel motor must increase or decrease proportionately as the speed of the last stand rolls increases or degiven constant speed of the motor 18, the

eld of the motor 10 must be gradually in- 30 remains, constant, the horse power input to creased with the gradual increase in the effective diameter of the reel 13 in order to maintain a constant current input to the motor.

In order that the current input to the motor 10 may be so regulated that a predetermined constant tension will be maintained in the strip 14, suitable control means are provided for the motor. The control means comprises a regulator 19, which is provided not only for regulating the current input to the motor, so as to maintain the current substantially constant, by varying the speed of the motor 10 according to variations in the effective diameter of the reel 13, but also for adjusting the current input to compensate for variations in the lineal speed of the strip.

As shown, the regulator 19 comprises a bar 20 pivoted at a point adjacent its center, a coil 21 having its core connected to the bar 20 at one end thereof, and a coil 22 having its core connected to the bar 20 at a point adjacent its other end. The coil 21 is connected across a shunt in the circuit of the armature 11 of the reel motor so that the current in the coil and consequently its pull on its core are proportional to the current drawn by the motor 10 from the source 16. The pull exerted by the coil 22 should be proportional to the speed of the last stand rolls, and in order to effect this proportionality a suitable pilot generator 25, provided with an armature 26, and a field winding 27 excited from the source 16, is mounted to be driven by the main driving motor 18. The coil 22 is connected across the armature 26 of the generator so that its pull upon its core will be proportional to the voltage of the generator and consequently to the speed of the last stand rolls.

The regulator 19 is provided with contacts 30 connected across an adjustable resistance 31 which is in turn connected in the circuit of the reel motor field winding 12 so that when the contacts are open the resistance will be inserted in the field circuit and when the contacts are closed the resistance will be short circuited. It will be understood that normally the control switch 33 will be thrown toward the left, as viewed in the figure, so that the short circuit may be completed for the resistance 31. It will be observed therefore, that the strength of the field 12 and consequently the current intake of the motor 10 will depend upon the relative values of the currents that energize the coils 21 and 22. The regulator is so adjusted that when the current in the reel motor armature is less than a predetermined value to be maintained to give the desired tension in the strip, the pull of the coil 21 will be overbalanced by that of the coil 22 and the contacts 30 will be held in their open position, thus inserting the resistance 31 in the circuit of the field 12. The field will then be weakened which will cause more current to flow through the armature 11. It will be understood that since the reel motor speed is fixed by the speed at which the strip is fed to the reel, the speed of the reel motor will remain constant notwithstanding its field variations as long as the strip speed remains constant. When the current in the armature 11 increases to a value above the predetermined current to be maintained, the pull exerted by the coil 21 will increase to such a degree that the coil 22 will be overpowered and the contacts 30 will be closed to short circuit the resistance 31 whereby the strength of the field 12 will be increased. As a result, the motor 10 will draw less current from the line until when the armature current is less than the predetermined value the coil 21 will be overpowered by the coil 22 and the contacts 30 will be opened to re-insert the resistance in the field circuit. The motor current will now increase and the cycle of operation will be repeated as pre viously described. The regulator 19 will thus have a vibratory motion, alternately short circuiting and inserting the resistance 31 in the field circuit of the motor 10. As the contacts rapidly vibrate, the effective resistance in the field circuit will depend upon the proportion of time that the contacts are in their open position, and assuming that the motor 18 runs at a constant speed, the Vibrator 19 will maintain a constant current input to the motor 10 whereby the motor will apply a constant tension to the strip 14. An anti-hunting coil 32 is provided for assisting the coils 21 and 22 to efiect the vibratory motion. This coil 32 has its core connected to the bar 20 so that the coil will act in opposition to the coil 21, and as :iIUV, 11 its core is connected to the same end of the bar as the core of the coil 21. As shown. the coil 32 is connected in series in the cir cuit of the field 12 so that as soon as the contacts 30 are closed the momentary increase in the field current will cause the pull exerted by the coil 32 upon its core to increase, whereby the coil 22 with the assistance of the coil 32 will immediately open the contacts 30.

' Even though the motor 18 runs at a constant speed, the speed of the reel motor 10 must gradually decrease since the effective diameter of the reel 13 gradually increases, due to the winding of the strip 14. As the reel diameter increases the reel speed obviously decreases and as a result the motor will tend to apply a torque of such increased value that unless suitably compensated for there would result an increase in the tension in the strip. This action of the motor however causes its armature current to increase whereby the regulator operates to close the contacts 30 and strengthen the mtor field until the armature current has been that the contacts 30 rema n closed will gradually increase. As a result of this action in maintaining the armature current constant, the effective field resistance will be gradually reduced and the motor field current thereby increased with the result that the motor torque is increased so as to maintain a constant tension in the strip 14.

It is often desired to adjust the tension in the strip 14 to different values. To eifect this adjustment, an adjustable rheostat 34 is connected in series with the coil 22 of the regulator 19. Assuming that the generator 25 is running at a constant speed and it is desired to decrease-the tension in the strip, the resistance 34 will be increased so that the current in the coil 22 will be decreased. Consequently, the pull exerted by the coil 22 upon the bar 20 will decrease and the resistance 31 will be short circuited for a greater portion of time, whereby the field 12 will be strengthened and the armature current of the motor will be decreased to a value sufiicient to correspond to the reduced pull of the coil 22, and will be held at its decreased value by the vibratory action of the regulator 19. It will be understood that the tension upon the strip will be decreased proportionately with the decrease in the armature current. Similiarly by decreasing the resistance 34 the tension upon the strip will be increased.

Any variation in speed of the rolls re sults in a change in the voltage applied to the coil 22 by the generator and consequently in a change in the current setting of the regulator whereby a different current will be maintained in the armature of the motor 10 so as to maintain the predetermined tension in the strip. Assuming that the speed of the last stand rolls increases, the voltage of the pilot generator 25 will increase and consequently the pull of coil 22 will increase proportionately to the increase in speed. To balance the increased pull of the coil 22, the pull of the coil 21 must increase which means that the current and consequently the horse power input to the-motor 10 must increase correspondingly. This will be accomplished by the regulator 19 which will hold the contacts open for a greater proportion of the time, thereby increasing the effective resistance in the field circuit of the reel motor so that its speed will increase proportionately with the increase in the speed of the main motor 18. Should the speed of the last stand rolls be decreased, the pull exerted by the coil 22 will be decreased and the current and consequently the horse power input to the motor 10 will be proportionatelydecreased so that its speed will be reduced in accordance with the reduction in speed of the main motor.

In order that the work upon the regulator 19 may be materially reduced, a suitable adjustable rheostat 35 is inserted in the circuit of the field 12. This rheostat may be adjusted to take care of changes in speed of the reel motor due to changes in speed of the motor 18. If desired, this resistance may be mechanically connected to the rheostat connected in the field of the motor 18, so that as the operator varies the resistance in the field of the motor 18, the resistance in the field of the motor 10 will be automatically and proportionately varied. Thus with this arrangement, the rheostat 35 will automatically tend to adjust the speed of the reel motor as the speed of the main roll is adjusted. It is to be understood, however, that the rheostat 35 is provided merely to reduce the work upon the regulator, and that the regulator may wholly perform the function of accurately varying the current input to the motor 10 according to variations .in the speed. of the strip 14, as well as maintaining constant tension with a fixed speed of the strip.

It will be understood that the motor 10 is provided with starting resistance connected in series with its armature. As shown, the starting resistance 40 is connected in series with the motor armature 11, accelerating contactors 41, 42 and 43 being provided to progressively short circuit this resistance when the motor is started up. These contactors are controlled by suitable accelerating relays 44 in any well known manner.

The starting resistance 40 is also advantageously employed to allow a certain pull to be applied to the strip even though the mill is shut down. The return circuits of the contactors 41 and 42 are controlled by a relay 45. The relay 45 is connected across the armature 26 of the pilot generator and is so adjusted that it will open its contacts whenever the voltage of the generator drops below a preedtermined value. Thus if the generator voltage drops below the predetermined value, the contacts of the relay 45 will open and the accelerating contactors 41 and 42 will open and a certain amount of the starting resistance 40 will be inserted in series with the motor armature 11. Consequently, if .the operator should shut the mill down, as the speed of the strip drops to a certain predetermined value, the relay 45 will open its contact and insert the resistance in series with the reel motor armature so that the current to the armature will be limited by this resistance. Consequently, as the mill comes to rest, the reel motor may be left connected to its supply circuit and a certain amount oftension will be maintained in the strip due to the current which will still be flowing through the armature of the reel motor. \Vhcn the main roll motor 18 is again started up and the volta e of the generator 25 builds up to a predetermined value, the relay 45 will pick up and close its contacts whereby the contactors 41 and 42 will be closed in succession and full voltage applied to the reel motor armature.

In operation, it will be understood that the main motor 18 drives the main rolls 15 at any desired speed and that the motor 10 operates to maintain a certain predetermined tension in the strip 14 as determined by the adjustment of the rheostat 34:. When the motor 18 operates at a constant speed, the regulator 19 will operate to maintain a constant current input to the motor 10 so that it will maintain this desired constant tension in the strip. The regulator 19 further controls the current input to the motor 10 by gradually decreasing its speed as the efiective diameter of the reel gradually increases lVhen the motor 18 is adjusted to run at higher or lower speeds, the regulator 19, assisted by appropriate adjustment of the rheostat 35, will automatically adjust the effective resistance in the field circuit of the motor 10 so that it will operate at lower or higher speeds accordingly, whereby regardless of the speed of the mill any desired predetermined tension will be constantly maintained in the strip 14.

lVhen threading a strip in the reel to start a new coil the motor 10 must be run at a slow speed to permit the threading operation. To effect this, a push button 50 is so connected in the field winding circuit of the motor 10 that when it is closed the resistances 31 and 35 will be short circuited where by full field strength will be applied to the reel motor, as a result of which it will run at a very slow speed as long as button 50 is held in its closed position. On the other hand it may be desired to operate the reel motor at full speed when the mill itself is not running at all. In order to so operate the motor 10 the switch 33 is moved to its right hand position, as viewed in the figure, whereby the regulator is cut out and the contacts of the relay 45, which have been opened as the mill slowed down, are shortcircuited so that the accelerating contactors 40 and -11 will be allowed to close and all resistance thus cut out of the motor armature circuit. The motor will then operate at its full speed.

\Vhile I have described a particular em bodiment of my invention operating in a particular manner in accordance with the provisions of the patent statutes, it should be understood that I do not limit my invention thereto since various modifications thereof will suggest themselves to those skilled in the art without departing from the spirit of my invention the scope of which is set forth in the annexed claims.

What I claim as new and desire to secure by Letters Patent of the United States is:

1. The combination with a winding reel for a strip of material to be wound thereon, of means for feeding said strip to said reel, an electric driving motor for said reel, a source of electrical supply for said reel driving motor having a substantially constant potential irrespective of the feed of said strip to said reel and means dependent upon a function of the feed of said strip to said reel and the driving motor current for regulating said driving motor so as to maintain a tension in said strip.

2. The combination with a winding reel for a strip of material to be wound thereon, of means for feeding said strip to said reel, an electric driving motor for said reel, a source of electrical supply for said motor having a substantiall constant potential irrespective of the fee of said strip to said reel, and means jointly responsive to the rate of feed of said strip and to the driving motor current for regulating said drivi 0 motor so as to vary the current input thereto proportionately with the rate of feed of said strip.

3. The combination with a winding reel for a strip of material to be wound thereon, of an electric driving motor for said reel and a regulator jointly responsive to the rate of feed of said strip and to the driving motor current for regulating said driving motor so as to vary the current input thereto proportionately with the rate of feed of said strip.

4. The combination with a winding reel for a strip of material to be wound thereon, of a driving motor forsaid reel, a resistance adapted to be inserted in the circuit of the field winding of said motor, and vibratory controlling means for said resistance whereby said resistance is periodically inserted in the field circuit of said motor, said vibratory controlling means being responsive to the armature current of said motor and to the speed of said strip, whereby the current input to said motor is varied proportionately with the speed of said strip.

5. The combination with a winding reel for a strip of material to be wound thereon, of an operating motor for said winding reel, a substantially constant voltage source of electrical supply for said operating motor, an electric generator driven at a speed proportional to the speed of said strip, and a regulator electrically responsive to the voltage of said generator and to the armature current of said operating motor for governing the current input to said operating motor whereby a tension is maintained in said strip.

6. The combination with a winding reel for a strip of material to be wound thereon, of an operating motor for said winding reel, a resistance adapted to be inserted in the field circuit of said operating motor, an electric generator driven at a speed proportional to the lineal speed of said strip, and means electrically responsive to the voltage of said generator and to the armature current of said operating motor for regulating the insertion of said resistance whereby the current input to said operating motor is varied directly with the lineal speed of said strip.

7. The combination with a winding reel for a strip of material to be wound thereon, of an operating motor for said winding reel, a resistance adapted to be inserted in the field circuit of said operating motor, adjusting means for said resistance responsive to the speed of said strip and the armature current of said operating motor whereby the strength of said field winding is varied to cause the current input to said operating motor to vary directly with the speed of said strip, and circuit controlling means independent of said resistance adjusting means inserted in the field winding circuit whereby said resistance may be by-passed so as to permit said operating motor to run at its minimum speed.

8. The combination with a winding reel for a strip of material to be wound thereon, operating means for delivering said strip to said winding reel, a driving motor for said winding reel and a regulator for said driving motor jointly responsive to a function of the delivery speed and to the driving motor current for varying the horse power input to said driving motor so as to maintain a tension in said strip.

9. The combination with a winding ree for a strip of material to be wound thereon, operating means for delivering said strip to said winding reel, a driving motor for said winding reel, a resistance ada ted to be inserted in the circuit of the fie d winding of said driving motor, a generator driven at a speed proportionate to the delivery of said strip, and means for regulating the insertion of said resistance whereby the strength of the field of said driving motor is varied to vary the current input to the driving motor directly with the speed of said strip said regulating means comprising a pair of electrical contacts shunted across said resist ance, said contacts when opened inserting said resistance in the field circuit and when closed by-passing said resistance, an electromagnet responsive to the voltage of said generator for opening said contacts, and an electromagnet opposed to said first electromagnet and responsive to the armature cur rent of said driving motor for closing said contacts.

10. The combination with a winding reel for a strip of material to be wound thereon, operating means for delivering said strip to said reel, an electric motor for driving said winding reel, a source of electrical energy for said driving motor having a substantially constant potential irrespective of the rate of delivery of said strip to said reel, a

resistance adapted to be inserted in the circuit between said source and said driving motor, controlling means for said resistance responsive to the speed of said strip to said reel whereby when the speed of said strip has been reduced to a predetermined value said resistance will be inserted in the driving motor circuit so that said driving motor will. maintain a tension in said strip whenthe strip has beenstopped.

11. The combination with a winding reel for a strip of material to be wound thereon, operating means for delivering said strip to said winding reel, an electric motor for driving said reel, starting resistance for said driving motor, an electric generator driven at a speed proportional to the speed of said strip to said reel, regulating means for said driving motor jointly responsive to the armature current of said driving motor and to the voltage of said generator for varying the horse power input to said driving motor directly with the speed of said strip, and a relay for controlling said resistance responsive to the voltage of said generator, whereby when the speed of said strip has dropped to a predetermined value a portion of said starting resistance will be inserted in the motor circuit so as to cause said driving motor to thereafter maintain a tension of predetermined value in said strip.

In witness whereof I have hereunto set my hand this 15th day of May, 1928.

HARRY A. WINNE.

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