US1807418A - System of motor control - Google Patents

Description

May 26, 1931. c. F. LEE 1,807,418

SYSTEM OF MOTOR CONTROL Filed Jan. 24, 1929 FOR WARD REVZRSE HAND 52' 7 AUTOMATIC Inventor: Charles F. Lee,

by HLS Attomey.

Patented May 26, 1931 UNITED STATES PATENT OFFICE CHARLES F. LEE, OF CINCINNATI, OHIO, ASSIGNOR T GENERAL ELECTRIC COMPANY, A CORPORATION OF NEW YORK SYSTEM OF MOTOR CONTROL Application filed January 24, 1929. Serial No. 334,824.

This invention relates to systems for controlling the operation of electric motors, more particularly to control systems for motors employed in various reversing operations, for example in driving paper plating machines, and the like, wherein a stack or book of material is driven forward and backward between pressure rolls and has for an object the provision of an arrangement for' automatically reversing the direction of rotation of the motor and for predetermining the .number of reversing cycles of the motor after which the material is forced from the rolls.

In the operation of paper plating machines, a plurality of sheets of the material to be plated are stacked with alternate sheets of another material to form a book. If the material to be plated, for example paper, is

to have a smooth glossy finish, the alternate sheets will preferably be smooth sheets of metal, whereas if a rough finish resembling a linen fabric is desired, alternate sheets of linen are employed. The book is then placed upon the table of the plating machine and driven rapidly forward and backward between the pressure rolls. Those skilled in the art will understand that equipment is required that will reverse the rolls of the plater after a few turns in either direction and that reversals may be as frequent as twenty times per minute.

In carrying out my invention in one form I have shown it as adapted for controlling the motor for driving the rolls of a paper plating machine or similar machine and in accordance with my invention, I provide reversing switch mechanism for controlling the direction of rotation of the driving motor and limit switches which are operated by the material being operated upon, for example the above mentioned book to control the reversing switches to reverse the motor at each limit of the travel of the material,

' together with means operable in response to the operation of the reversing switches for predetermining the number of reversing cycles of the motor.

For a better and more complete understanding of my invention reference should be made to the following specification and to the accompanying drawing the single figure of which is a diagrammatical representation of an embodiment of the invention.

Although this invention is generally applicable for driving machines in which material is operated upon by being passed back and forth a given number of times in the machine, it will be described in connection with a paper plating machine for the purpose of clearly illustrating its operation.

eferring now to the drawing, an alternating current motor 10, preferably of the wound rotor type, is connected to drive a suitable load such for example as the rolls of a plating machine. For the purpose of simplifying the drawing, the plating machine and the rolls have been omitted since the invention may readily be understood from a description of the control circuits. Electric power is supplied to the motor 10 from a suitable source represented in the drawing by the three supply lines 11, through the contacts of either the forward contactor 12, or the reverse contactor 13, and a suitable overload temperature relay 14. Undervoltage protection of the apparatus is provided by the undervoltage relay 15 which controls the energizing circuits of the reversing contactors 12 and 13, and prevents their operation unless and until the undervoltage relay is operated to the closed position.

A run switch 16 having normally open contacts in the energizing circuit of the undervoltage relay is provided for initial starting of the apparatus, whilst a stop switch 17 having normally closed contacts in the circuit of the undervoltage relay is provided for stopping the motor and returning all the apparatus to its normal or pre-startlng position.

Limit switches 18 and 19 located at the rear and front ends of the table respectively are arranged to be actuated by the book at each limit of its travel, and control the forward and reverse contactors to reverse the direction of rotation of the motor.

Reversal of the motor in both direct-ions is accomplished by plugging. In order to avoid damage to the motor and apparatus during the reversal period a resistor 21 is included in the secondary circuit of the motor 10 in addition to the torque limiting resister 20. The motor is always plugged with the resistor 21 in the secondary circuit. A secondary contactor 22 is provided for short-circuiting the plugging resistor after the motor has been stopped and started in the opposite direction, and this secondary contacto r is in turn controlled by a friction relay 23 connected to the motor shaft.

The number of reversal operations or passes that. can be made with any one book in the rolls may be limited as desired by the adjustable indexing device 24 which for the purposes of illustration is shown as a notching relay the contact actuating arm 25 of which may be initially adjusted to any one of a plurality of positions with respect to the contact 26 controlled thereby, by means of the stop pin 27, and a sector 28 provided with a plurality of holes the number of which corresponds to the maximum number of passes that is likely to be required for any material. An energizing coil 29 is arranged to hav'e'its circuit completed by auxiliary contacts on the reversing contactor 13 each time the latter is operated to the closed position. 'The advance movement of relay 2 1 is controlled by upward movement of pawl 30 in response to energization of coil 29, and the return of relay 24 to its initial position is accomplished by a reset switch 31.

If for any reason manual control of the apparatus becomes necessary or desirable, a transfer s'witch32 serves to transfer the control of the reversing contactors from the limit switches to the manually operated buttons 3S and 34.

' lVith the above understanding of the functions and relationships of the various elements, the operation which will be now described in detail will be readily understood. In the drawing the apparatus is shown in its normal or pre-starting position, that is to say, the elements are all in the positions in which they would be if the plating machine had been shut down after completing an operating cycle. From a knowledge of the nature of the material to be operated upon, the number of passes (each pass being considered asa complete forward and reverse movement of the book through the rolls) is determined, and the stop pin 27 placed in the hole in the sector 28 the number of which corresponds with the desired number of passes. In the drawing the pin is shown in the sixth hole which indicates that each book will receive six complete passesbefore being forced out of the rolls.

With the transfer switch 32 thrown to the position for full automatic control as shown in the drawing, the motor 10 may be started, by momentary depression of the run button 16 t0 b idge its normally open contacts and for the coil independent of the run button 16 which may now be released. A book is no placed on the front end of the table in which position it causes contact member 4.1 of front limit switch 19 to engage the stationary contacts with which it is associated, and contact member 42 todisengage the stationary contacts which it bridges. An energizing circuit for the operatingcoil of forward contactor 12 may now be traced from L over conductor v35, switch conductor- 13, upper contact of undervoltage r-elaylr), conductors A and l5, contact 4-1 of front limit switch, conductor 16 normally closed contact 26 on indexingswitch 24, conductor 47, lower auxiliary contacts on reverse contact-or 13 in the lower poiition, coil of forward contactor 12 to L In the closed position of the contactor a maintaining circuit independent of contacts 41 and 26 is established for its coil through contact member l8 of back limit sw tch 18, and middle auxiliary contacts of the forward centactor 12. The notor 10 is now connected to the supply lines 11, through 11 ,11 L and the contactor 12, and its 'di-. rection of rotation and that of the rolls drive on thereby is such that the book will be dr ven through the rolls toward the back end of the table. The book is now pushed into the rolls and no further attention will-.be required from the operative until the book is forced out of the rolls at the end of the operating cycle. As it leaves'the front end of the table, contact member ll of limit switch 19 will be retracted by its spring from its stationary contacts and contact member 12 will be permitted to reengage its stationary contacts.

After a fewturns of the motor, the book will have reached the back of the table in which position it will actuate contact'menie ber 48 of the back limit switch to the open position to interrupt the holding circuit for forward contactor 12, and actuate the contact member 19 into engagement with its stationary contacts to establish an energizing circuit for he coil of reverse co-ntactor 13 from conductor 14, through centact 19, lower auxiliary contact of contactor 12, conductor 50, coil of contactor 13 to L Centactor 13 closes to establishreverse power connections for motor 10., and in its closed position it establishes a maintaining circuit for its own coil independent of contact 4:9 of back limit Lil switch 18, through conductor 45, contact member 42 of limit switch 19, and middle auxiliary contact of contactor 13.

The rapid reversal of a. motor caused by disconnection from the line followed by immediate reconnection for the reverse direction of rotation is known as plugging the motor. As previously pointed out in this specification, the motor is plugged with an added resistance in the secondary circuit to limit the currents that will be caused to flow by the rapid dissipation of stored energy, thereby limiting the braking torque and bringing the motor quickly and evenly to rest. Assuming that when the forward contactor 12 is closed the direction of rotation of the motor is counterclockwise as indicated by the arrow on the pulley 51 of friction switch 23, the movable contact member will be held up against the upper stationary contacts by the force of friction between the cord 52 and the pulley 51, to complete an energizing circuit for secondary contact 22 from L to L that includes the upper auxiliary contact of forward contactor 12, the upper contacts of friction switch 23 and the coil of secondary contactor 22. Secondary contactor 22 is accordingly maintained closed and the resistance section 21 short-cirouited during the forward rotation of the motor, that is to say, during the time that the book is being driven from the front end to the back end of the table. When the forward contactor 12 opens in response to operation of the limit switches, the energizing circuit of contactor 22 is interrupted at the upper auxiliary contacts and the contactor 22 opens to insert the resistance 21 in the secondary circuit of the motor. The closing of the reverse contactor13 partially reestablishes an energizing circuit for the secondary contactor 22 from L through the upper auxiliary contacts of the reverse contactor to the lower contacts of the friction switch, and as the motor starts up in the reverse direction, the friction between the pulley 51 and the cord 52 is sufiicient to retract the movable contact of the friction switch from the upper contacts and pull it into engagement with the lower contacts to complete the energizing circuit for contactor 22 and again short-circuit the plugging resistor and increase the torque of the motor. The motor now drives the rolls in the reverse direction and the book is driven back toward the front of the table at which position it will operate the front cient value to start the book through the rolls in the reverse direction as the motor starts up in the reverse direction, and that a very rapid reciprocating movement of the book through the pressure rolls is thereby provided.

The manner in which the indexing device functions to limit the number of passes will now be described. As shown in the drawing a spring serves to bias the ratchet disc 53 and the contact actuating arm 25 carried thereby to its initial position with the arm resting against the stop pin 27. It will be recalled at this point that the pin 27 was placed in the sixth hole to provide for six complete passes for the book. Each time the reverse contactor 13 closes to reverse the direction of, the motor to drive the book from the back end to the front end of the table the middle auxiliary contacts of the contactor are closed and establish a circuit for the coil 29 that may be traced from L over conductor 35, switch 7 32, conductors 43 and 54, lower auxiliary contact member in the upper position, coil 29 and conductor 39 to L In response to energization of the coil the horizontal member of the L-shaped pawl 30 notches the ratchet disk 53 one tooth in a counter-cloclnvise direction, in which position it will. be retained by the spring pressed pawl 55. This notching operation occurs only when the reverse contactor 13 closes, that is to say, but once for each com- 1' plete pass. After six complete passes, the contact actuating arm 25 will have been notched to its limit in which position it will press the movable contact 26 into engagement with the lower stationary contacts thus short circuiting the right hand contacts of front limit switch 19 that are normally bridged by contact member 42. As the book reaches the front of the table and operates the limit switch, the energizing circuit for the reverse contactor will be unaffected by the disengagement of movable contact 4-2 from its stationary contacts, and the motor will continue to drive the rolls in the same direction, thus causing the book to be passed out of the rolls.

To start the cycle of operations over again, it is only necessary to place a fresh book on the table so that an edge thereof is pressed in between the rolls and to depress the reset button 31 to open the energizing circuit for coil 29. The reset button must be kept depressed for a time sufficient to permit the movable member 56 of the dash pot to descend under the attract-ion of gravity to trip the spring pressed pawl and permit the ratchet disk 53 to be returned to its initial position. The timing of the dash pot is such that when the coil 29 is deenergized during the passing operations, the movable member will not have had time to descend the full distance before being returned to its uppermost position by the upward movement of pawl 30 due to reenergization of coil. 29 for the notching operation.

If it be desired to operate the machine by manual control the transfer switch 32 is operated to the hand position, the efiect of which is to deenergize the control circuits to the limit switches and the indexing. relay, and .-to give the control over to the manually opfil erated push buttons 33 and 34. The push button 33 controls the energizing circuit for the forward contactor 12', and the button 34 controls the circuit for the reverse contactor 13.

-- either, direction as long as desired by maintaining the appropriate button depressedfor thatperiod. l i

In accordance with the provisions of the patent statutes I'have described'my inventionas embodied in concrete form and as operating in a, specific manner. Butit should be understood that the invention is not limited to the specific embodiment illustrated since modifications and alterations will read ily suggest themselves to those skilled in the art without departing from the spirit or scope of the annexed claims.

That I claim as new and desire to secure 1 Letters Patent of the United States, is: 1. In a system of motor control, front and back limit switches located respectively at predetermined limits of motor operation and arranged to be operated respectively in response to operation of the motor in each direction, means including a forward contactor and a reverse contactor under the control of said limit switches for reversing themotor at both of said, limits of operation, energizing circuits for both of said contactors controlled by both of said limit switches through which one of said contac-tors is deenergized and the other energized at each of said limits, and an adjustable indexing device under the control of one of said contactors for establishing a short circuit about the limit switch ,con trolling said reverse contactor to prevent deenergization of said reverse contactor after a predetermined number of reversals thereof, to limit further operation of the motor to one direction of rotation.

2. In a system of motor control, a. forward and a reverse contactor for controlling the direction of rotation of the motor, means including limit switches located at predetermined limits of motor operation to deenergize one of said contactors and energize the other to reverse said motor at each of said limits, an adjustable notching relay having an energizing circuit controlled by one of said cont-actors for advancing'said'relay one Step for each operation of said contactor, connections through which said relay controls a short circuit about the contacts of one of said limit switches to prevent the deenergization of said reverse contactor and the energization of said forward contactor after a predetermined number of reversals to limit further operation of said motor to one direction of rotation, and'a reset switch and con .The motor 10 may be made to operate in nections controlled thereby forrestoring said indexing relay to its initial position.

3. A motor control system comprising in combination means including .a pair of switches responsive to limited operation. of the motor in opposite directions respectively, means including a pair of contactors respectively under the control of said switches for repeatedly reversing the direction of rotation of the motor, a notching relay, provided with a movable member, means including connections controlled by the operations of one of said contactors for actuating said relay toadvance said movable member a number of steps proportional to the number of operations of said contactor, and means responsive to a. predetermined number of steps of said movable member for rendering said reversing means ineffective after a predetermined number of reversals of the motor.

In witness whereof, I have hereunto set my hand this 22nd day of January, 1929. V

. CHARLES F LEE.

a .w. n.

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