US2575717A

US2575717A - Motor control system

Info

Publication number: US2575717A
Application number: US62212A
Authority: US
Inventors: George E King
Original assignee: Westinghouse Electric Corp
Current assignee: CBS Corp
Priority date: 1948-11-26
Filing date: 1948-11-26
Publication date: 1951-11-20
Anticipated expiration: 1968-11-20

Description

Nov. 20, 1951 I KlNG 2,575,717

MOTOR CONTROL SYSTEM Filed Nov. 26, 1948 Fig.|.

Return Fig.2.

WITNESSES: 1 M 5 INVENTOR 2- 5%? BY ecfrge E. Kmg. %w-

W 42 5| WLW ATTO RN EY Patented Nov. 20, 1951 UNITED STATES PATENT OFFICE MOTOR CONTROL SYSTEM Application November 26, 1948, Serial No. 62,212

3 Claims. 1

This invention relates generally to control systems for an electric motor and, more particularly, to a control system embodying automatic operation of a driving motor to eliect reciprocation of a machine tool element, such as a planer platen. It should be understood, however, that the present control system is likewise useful for other reciprocating devices such as machine tools for effecting relative movement between :a work piece and tool while the tool performs its cutting of other deforming operation, for example, draw-cut and push-cut shapers, roll grinders, transfer tables and the like, and. generally wherein an adjustable or variable is supplied to the motor.

'Heretoiore, in the operation of reciprocating machine tools, such as, for example, planers, great diiiiculty has been experienced in attempts to obtain quick short stroke operation, such as cut strokes 'of seventy or more per minute, due

to the appreciable transfer time required for operation of the reversing relays.

It has been proposed to electrically interlock the coils of the reversing relays, that is, the socalled out and return relays, which relays strikes the cut limit switch and deenergizes the cut relay, causing it to drop out. A normally closed interlock on the cut relay will effect energization of the return relay coil through the return limit switch and the return relay will. close. :turn relay can pick up, the cut relay must drop out. Likewise, in the operation of the planer platen in going from the return to the out direction, the return relay must drop out before the cut relay can pick up. This considerably retards the speed of reversal of the motor and limits the number of out strokes obtainable per minute since it is necessary to wait for complete dropping out of one reversing relay before the other one can begin to pick up.

An object of the present invention is to provide a control system for controlling the relative reciprocating movement between a tool and work piece in a planer :or other reciprocating :device, which control system will allow rapid However, before the rereversal of the driving motor from full selected speed in one direction to full selected speed in the opposite direction so that a very small portion of the total time required to complete one operating cycle will be used in the reversing oporation.

A further object of this invention is to provide a quick yet smooth reversal of a driving motor of a reciprocating machine tool, such as a planer, so as to eliminate any undue strain on the gears of the machine so that cut strokes upwards of seventy per minute are readily obtainable.

A more specific object of this invention is to provide a motor control system for driving a planer platen or other reciprocating machine tool part, which control system includes a pair of reversing relays which are sequentially operated to effect reversal'of the drive of the platen, each of which relays includes normally closed contacts and normally open contacts so that when a dog hits a limit switch, either near the end of the cut, or near the end of the return stroke, the normally closed contacts will open to deenergize the particular relay, causing drive in a given direction, and the normally open contacts will close to complete an energizing cir cuit for the other relay to effect reversal of the direction of drive, so that as one relay .is dropping out, the other will be picking up, therefore considerably shortening the transfer time required for operation of the relays to cause reversal of the drive.

Other objects and advantages not specifically hereinbcfore recited will become more apparent from a study of the following specification when considered in conjunction with the accompanying drawing in which:

Fig. 1 is a diagrammatic representation, in the form of a wiring diagram, of a complete control system, in accordance with myinvention. for a reversing motor for operating a planer platen or other reciprocating mechanism, and

Fig. 2 is an 'elevational view, somewhat clingrammatic, of a planer having a platen which is reciprocated by the control system shown in Fig. 1.

Referring more particularly to the drawing, a direct current motor M is mechanically coupled to drive a machine tool element, such as a planer platen l, :as shown in Fig. 2, mounted on a support or base '2 and which platen is mounted on suitable guideways to reciprocate in a horizontal direction thereon. A generator G is provided having its armature 3 connected 26 and conductor 25 to the lead L2.

in series with a generator series field winding 4, and with armature 5, of the motor M. The generator G is provided with separately excited field windings 6 and I wound in opposite directions so that energization of one winding will cause current fiow through the generator-motor armature circuit in one direction to effect operationof the motor in one direction, and energization of the other win-ding will reverse the current fiow in this circuit and effect operation of the motor in reverse direction. A separately excited motor field Winding 8 is provided for motor M, which field winding is connected across line terminals LI and L2. The line terminals LI and L2 are energized by means of an exciter E including an exciter armature 9, a shunt field winding Ill, a variable shunt resistor H and a series field winding I2. The exciter is operated at constant speed from a suitable prime mover, and in a well known manner, supplies 'a constant potential to the line terminals LI and L2. may be mechanically coupled to, and driven by a .-;motor (not shown), such as, for example, an

Both the generator G and exciter E alternating current motor or other prime mover. Referring to Fig. 2 of the drawing, as motor in the return direction. Likewise, when the dog |5, which is secured to the platen I, strikes the -,return limit switch l6 near the end of the re- -'turn stroke, it will cause deenergization of the -.return relay and initiate reversal of the motor so as to cause drive in the out direction as will be described in detail hereinafter.

Automatic cut operation More specifically, and referring to Fig. 1 of the drawing, assume that it is desired to initiate operation of the motor in the out direction.

Automatic out pushbutton switch ll is temporarilv depressed, thereby closing its contacts 18, which will complete a temporary energizing circuit through coil C of the cut relay l9. This circuit may be traced from terminal Li, through conductor 20, contacts Hi, the normally closed contacts 2| of the automatic return pushbutton switch 22. normally closed upper contacts 23 of the out limit s itch I4, relay coil C, conductor 25 to terminal L2.

As the relay l9 picks up the

contacts

23 and 33 are closed and the contacts 62 are opened.

'The closing of contacts 26 establishes an energizing circuit for the field winding 5. This circuit may be traced from lead Ll through the resistor 21, contacts 69, field winding 6, contacts The lefthand half of resistor 3| provides a shunt for field 6. The resistance value of resistor 3| is so chosen as not to afiect normal o eration but yet pro- Vides a suitable discharge path for the field.

Since the contacts 69 shunt the rheostat 28, the field 5 is heavily ener ized to provide for a rapid building up of the voltage of the generator G to a higher t an normal value to thus provide a heavy starting torque for the motor M.

v The o ening of contacts 62 revents energization of the generator field suicide oontactor 1|.

Picking up of relay 9 will also e fect energization of coil AR of the relay 39 having a small inherent time delay to assure the above 1611- tioned heavy starting torque. The circuit for coil AR may be traced from terminal Ll, through conductor 23, contacts 58, conductor 32, contacts 33 of the out relay |9, conductors 3d and 35, stop pushbutton contacts 36, coil AR, conductor 3'! to terminal L2. Energization of coil AR will effect closing of its contacts 33 which will complete a sealing circuit to maintain the relay 39 in the energized position, which circuit may be traced from terminal Ll, through conductor 49, contacts 38, conductors 4| and 35, stop pushbutton contacts 35, coil AR, conductor 31 to terminal L2. Coil AR will therefore seal itself in so long as the stop pushbutton is not depressed, and as will appear hereinafter, its contacts 33 complete a circuit through either of the reversing relay coils C or R, depending on the direction of drive of the motor. As relay 39 picks up, its contacts 69 and Til open to remove the shunt circuits for the rheostats 28 and 45- also, its contacts 5|, open. A sealing circuit for coil C will thus be com leted which may be traced from line terminal Ll to conductor contacts 38, conductors 4|, 35 and 34, contacts 33, conductor 32, contacts 2| and 23, coil C, conductor 25 to terminal L2. Hence, even after release of the automatic cut pushbutton switch 2?, coil C will remain energized.

After contacts 25 are closed and contacts 59 are opened by the operation of relay 39, a new energizin circuit is established for the generator field winding 6. This circuit may be traced from line terminal Ll through resistor 2i, rheostat 28, conductor 29, generator field winding 3, conductor 30, contacts 26, conductor 25 to terminal L2. A shunt path is also provided through the left hand portion of resistor 3|. Energization of the generator field winding 6 through rheostat 28 will cause the normal automatic cut operation voltage on the generator and in conseouence the motor M will operate at its normal automatic cut speed.

The motor will continue to drive in the out direction until near the end of the cut stroke, the dog l3 will hit the cut limit switch 25, thereby o ening its normally closed contacts 23 and closing its normally open contacts 42. Opening of contacts 23 will efiect deenergization of coil C, thereby opening contacts 28 and deen ergizing generator field winding 6. Closing of contacts 42 will com lete an energizing circuit through coil R to eiTect o eration of the ret rn relay 43, The circuit through coil R may be traced from terminal Ll, through conductor 40, contacts 38, conductors 4| and 35, contacts 42, conductor 39,

contacts

50 and 5|, conductor 52, relay coil R, conductor 25 to terminal L2. Upon energization of coil R, contacts 44 close to complete a circuit through shunt field winding 1 which may be traced from terminal Ll through resistors 21 and rheostat 45, conductor 45, field winding 1, conductor 3?, con tacts 44, conductor 25 to terminal L2. A shunt path is also provided through the right half of resistor 3|. Since field winding 7 is wound oppositely to field winding 6, there will circulate current through the armatures of the generator and motor in an opposite direction so as to effect reverse operation of the motor M and movement of the planer platen in the return direction. In other words, while the cut relay 5% is dropping out, field winding 6 is deenergized and field winding 1 is energized.

As coil R is energized, relay 43 picks up and its ocontacts #53 :close to -.complete as sealing izcircuit through coil 3R which :may be :traced :irom :line terminal Ll through conductor lll, .contacts :38, conductors 4 I 2'35 and :34, contacts '53, conductors 160, contacts SQ 'and 5 I ,TCOIIdIICtOI 'SL12813310011 1R, conductor 25 to terminal L2. 'Thus :thezmotor will operate .in the return direction.

.Near theend'of the.return .strol e,-'dog .l.5wlll hit the"return limit-switch l6 so as to open its lower contacts -5| to-cause ideenergization of i5 "and 1 were simultaneously connected to the leads Li and L2.

It is one of the :outstanding advantages :of this invention that these'cond field winding, as-field winding 1, of the main generator for-efiecting the :reverse operation of the :motor connected to the generator is energized at substantially the very instant the generator .field, caused by the first field winding, as fieldwinding .6, is-decaying. The tfield reversalisthuszexpeditediin the extreme. It

isthus apparent thatthereissno delay'atthe ends 1' of the planer platen strokes, with the resultthat many more strokes per unit of 'timeare obtained than with'prior art controls.

Automatic return operation When it is desired to initiate drive o'fthe'motor in the return direction to obtain automatic return operatiomthe automatic return pushbutton switch '22 is temporarily depressed, thereby opening contacts 2| which effect de'energization of coil C and of field "winding '5 and closing of contacts '58 which completes an energizing circuit through coil -Rwhich maybe "traced "from terminal Ll through conductor 59,'eontacts 58, conductor-49,-

contacts

50 and 5|, conductor '52, relay coil R,'conductor 25 to'terminal'L'2.

As-the relay 53 picks up the contacts 44 'and'53 are closed and 'contacts 63 areop'ene'd. 'Thecl'os- 'ing of contacts 4'4 establishes an-energizing circuit for thefield'winding I. This circuitmay be traced from terminal Ll through the resistor 45, contacts 10, 'field'winding I, contacts 44 and conductor 25 to the lead L2. The right-hand half of resistor 3| provides a shunt for the field 7. The resistance valve of resistor 31 is so chosen to provide for normal operation but yet to'provide a suitable discharge'path *forthe field 1. Since the contacts "'58 shunt the rhe'ostat 45, the field is heavily energized to provide fora rapid building up of the voltage of the generator G 'to .a

higher than normal value to thus provide a heavy r turn starting torque for the motor M.

The opening of contacts 6-3 prevents energize.-

tion of the generator field suicide 'conta'ctor 'H.

Picking up of :relay 43 also effects energizathrough conductor 59., contacts .58., conductors .49 and .fim-rontacts- 53, -.conductors 34 and, stop button36, coil.AR,-and-.conductor 31 .to lead-L2. Energization of coil AR will :efiect closing :o'f its own contacts 3.8 to establish itshold-in circuit. Asealing circuit forcoil R is thus established, which circuit'may betraced from lead Ll through conductor 40, contacts 38, conductors M 35 and 34, fcontact-s 53, conductors 60 and '49, contacts ii!) and "5.1, conductor 52, coil R, and conductor 25 ztoithe terminal, or lead, L2. Hence, relay '43 re- ;mains energized even though push button 22 is released.

:After contacts 44 are closed and contacts 10 iarezopened by the operation of relay 39 the field :1 is energized through rh'eostat disc that normal automatic :return operation voltage is provided :by'the generator G, and inconsequence them'otor M' will operate atits normal return speed.

Near the end of the return stroke, dog li hits the return limit switch i5, opening its contacts 51 soasxto deenergize relay coil R and closing its :contacts '53 to complete a circuit through coil C which may be traced from line L! through nonductor Adtcuntacts 38, conductors 4!, 35 and 51, :contacts "5'43, 21 and 23, coil C, conductor I25 to line terminal L2. Aholding circuit'will be com- :pleted for :coil C through its central contacts 33, which circuit may be traced from conductor 'Ll through conductor Ail, contacts 38, conductors, 35am 34, contacts 33, conductor 32, contacts 2| .and123, coil 0, conductor 25 to terminal L2. 'Contacts M of relay :3 will therefore complete an energizing circuit through coil 1. The motor M will therefore :drive in the'return direction until the cut limit switch is hit by dog l3, upon which the cycle will be repeated.

stoppage 0] motor drive T stop the'machine, the stop vpushbuttonis depressed, opening contacts 36 which will deenergize co'il AR, thereby opening contacts 38 which will effect deenergization of either coil C or coil R, depending upon the direction of movement of the planer-it being remembered that the holding circuit :for both coils C and R extend through contacts 38. As relay 39 drops out; contacts 61 close, and since relays i9 and 43 have both dropped out, contacts 62 and 63 also will close. Assoon as the voltage across the armature of the generator and motor falls below a predetermined value "(inasmuch as both generator field windings "6 and I are deenergized), coil DCR will become suific'iently 'd'e'energized as to cause its relay 8'4 to drop out, 'therebyclosing contacts 65 and completing an energizing circuit through coil 'DFR which may be traced from line Ll, through contacts Si, '62, 63 and B5, coil DFR to line terminal L2. Upon energization of coil DFR, contacts 61 close, which will efiect insertion of a generator shunt field winding 38 which is wound oppositely to the series field winding 4 so as to have aneutralizing or bucking effect on field winding .4 and "thereby bring the driving motor rapidly .to .a standstill. The dropping out of relay 33 also effects closure of contacts 59 and "it effecting 'br'idgingof the field 'rheostats .28 and 45 so as to prepare the circuit for a subsequent starting operation.

Thus it will be seen that have provided a highly efficient control circuit embodying quick acting reversing relays, whose operating or transfor time isreduced to a minimum, for effecting 'rapidreversal of thedirectionof drive of a driving motor, which in turn eiiects rapid reciprocating movements of a planer-platen or other reciprocating element. This allows a large number of cut strokes per minute, that is, in excess of seventy, which would be diificult or impossible if conventional relay circuits were used instead. 7 'While the control system embodying the prin ciples of my invention has been described in connection with the operation of a planer platen, it will be understood, of course, that it is likewise useful to effect relative reciprocating movement between a cutting or deforming element of any other machine tool and a work piece, irrespective of which is held stationary while the other is reciprocatedor, in fact, any reciprocating device.

While I have illustrated and described a certain specific embodiment of my invention, it will be understood that this is by way of illustration only,

and that variou changes and modifications may be made within the contemplation of my invention and within the scope of the following claims.

I claim as my invention:

1. A control system for a reciprocating planer platen provided with dogs for actuating certain limit switches constituting part of the control system, in combination, a reversible electric motor for driving said platen, said motor including an armature and a field winding, a generator including an armature and a pair of oppositely wound field windings, means, including electrical control apparatus, for energizing said motor and generator field windings, said control apparatus including a pair of reversing relay contactors, each of which upon energization is adapted to complete an energizing circuit through one of said generatactor and normally open contacts which when closed are adapted to complete an energizing circuit through the coil of the other contactor, so

that as one of said contactors drops out the other will immediately pick up, thereby considerably decreasing the transfer time required for operation of said contactors, one of said contactors including normally open contacts which when closedcompletes an energizing circuit through one of said generator field windings and the other of said contactors including normally open contacts which when closed completes an energizing circuit through the other of said generator field windings to that as said contactors operate in succession, the direction of drive of said motor is reversed so as to reverse the direction of movement of said planer platen.

2. A control system for a reciprocating planer platen provided with dogs for actuating certain ,limit switches constituting part of the control system, motor for driving said platen, said motor including an armature and a field winding, a generator "including an armature and a pair of oppositely in combination, a reversible electric wound field windings, means, including electrical control apparatus, for energizing said motor and generator field windings, said control apparatus including a pair of reversing relay contactors, each of which upon energization is adapted to complete an energizing circuit through one of said generator field windings, a limit switch associated with each of said relay contactors and one adapted to be operated, by one dog on the i8 planer platen; near the end of its movement in'a given direction and the other adapted to be operated, by the other dog on the planer platen, near the end of its movement in the opposite direction, each of said limit switches including normally closed contacts in series with the coil of its associated contactor and normally open contacts which when closed'are adapted to complete an energizing circuit through the coil of the other contactor, so that as one of said contactors drops out the other will immediately pick up, thereby considerably decreasing the transfer time required for operation of said contactors, one of said contactors including normally open contacts which when closed complete an energizing circuit throughone of said generator field windings and the other of said contactors including normally open contacts which when closed complete an energizing circuit through the other generator field windings so that as said contactors operate in succession, the direction of drive of said motor is reversed so as to reverse the direction of movement of said planer platen, a manually operable pushbutton associated with each relay contactor in a manner so that temporary depression of the pushbutton will temporarily energize the associated contactor coil, a pair of hold-in circuits for maintaining each of said coils in an energized condition after release of the associated pushbutton, a contactor having contacts which are common to both said holding circuits and including an energizing coil; and a stop pushbutton switch in series with said last mentioned coil so that upon depression it will cause opening of said last mentioned contacts, deenergizing both of said holding circuits.

3. A control system for a reciprocating planer platen provided with dogs for actuating certain limit switches constituting part of the control system, in combination, a reversible electric motor for driving said platen, said motor including an armature and a field winding, a generator including an armature and a pair of oppositely wound field windings, means, including electrical control apparatus, for energizing said motor and generator field windings, said control apparatus including a pair of reversing relay contactors, each of which upon energization is adapted to complete an energizing circuit through one of said generator field windings, a limit switch associated with each of said relay contactors and one adapted to be operated, by one dog on the planer platen, near the end of its movement in a given direction and the other adapted to be operated, by the other dog on the planer platen, near the end of its movement in the opposite direction, each of said limlt switches including normally closed contacts in series with the coil of its associated contactor and normally open contacts which when closed are adapted to complete an energizing circuit through the coil of the other contactor, so that as one of said contactors drops out the other will immediately pick up, thereby considerably decreasing the transfer time required for operation of said contactors, one of said contactors including normally open contacts which when closed complete an energizing circuit through one of said generator field windings and the other of said contactors including normally open contacts which when closed complete an energizing circuit through the other generator field windings so that as said contactors operate in succession, the direction of drive of said motor is reversed so as to reverse the direction of movement of said planer platen, a manually operable pushbutton associated with each relay contactor in a manner so that temporary depression of the pushbutton Will temporarily energize the associated contactor coil, a pair of hold-in circuits for maintaining each of said coils in an energized condition after release of the associated pushbutton, a contactor having contacts which are common to both said holding circuits and including an energizing coil, and a stop puslibutton switch in series with said last mentioned coil so that upon depression it will cause opening of said last mentioned contacts, deenergizing both of said holding circuits, said reversing relay contactors including contacts which are in series with the associated holding circuit for the particular relay contactor coil and the circuit relationship with one of said first 10 mentioned pushbutton switches associated with said relay contactors.

GEORGE E. KING.

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

UNITED STATES PATENTS 10 Number Name Date 1,089,658 Mason Mar. 10, 1914 1,425,890 Merrill Aug. 15, 1922 2,069,493 Howe Feb. 2, 1937 2,205,566 Kollner June 25, 1940 15 2,299,152 King et a1 Oct. 20, 1942