US1749389A - Controller for electric motors - Google Patents

Description

March 4, 1930. w. R. MILBURN 1,749,339

CONTROLLER FOR ELECTRIC MOTORS Filed Nov. 26, 1926 2 SheetsSheet 1 M TORS1& Z

MOTOR-1 NVENTOR. Wm fimm/w W A TTORN-EY March 4, 1930. w. R. MILBURN 1,749,389

CONTROLLER FOR ELECTRIC MOTORS Filed Nov. 26, 1926 2 Sheets-Sheet 2 I I'NVENTOR. WWW fimm %MWMM ATTORNEY Patented Mar. 4, 1930 UNITED: STATES PATENTQFFICE WILLIAM R. MILBURN, OF SHOREWOOID, WISCONSIN, ASSIGNOE, BY MESNE ASSIEGN- MENTS, TO ourtnaimnrrsn me, or or DELAWARE cenrnotnnr.

Application filed November This invention relates to controllers for electric motors, and the invention more particularly relates to combined push button and drum controllers.

lVhile not limited thereto the invention is particularly applicable to the control of a plurality of motors employed for positioning a boom conveyor carried by a ship. Such conveyors may comprise an endless belt which is adapted for transferring bull: material from or to the ship. It is necessary to swing the boom conveyor to one side or the other with respect to the ship for loading or unloading the latter, and this is accomplished by rotation of a drum attached to the vertical axle of the boom. On account of the possibility of rough seas or listing of the ship when turning the boom it is necessary to have two ropes attached to and wound around the drum in opposite directions, with means for always maintaining said ropes taut whereby the same will pull against each other,-the pull of one of said ropes preponderating to provide for movement of the boom in the 5 desired direction.

The herein described means .for effecting operation of said ropes comprises a pair of motors to be controlled by a common drum controller in combination with a plurality of push button stations. The arrangement is such that said motors may be operated jointly to effect swinging movement of the boom conveyor to the desired position. Moreover, when the boom conveyor is brought to its inoperative position in the center line of the ship it is usually lashed down to a support and the ropes are disconnected from the drum. It is then necessary to operate the motors individually to provide for stowing the aforementioned ropes or cables, and to permit reverse operation of the motors to release the ropes for attachment thereof to the boom.

An object of my invention is to provide a controller capable of performing the desirable functions aforementioned.

Another object isto provide such a controller which may comprise a combination of more or less standard control instrumentalities.

MILW'AUKEE, VJTmCGNSIIrT, A CORPORATION ELECTRIC liIDTQR-S 28, 1926. Serial No. 150,939.

Another and more specific object is to provide controller of the above character which is capable of manipulation by a single operative.

Other objects and advantages will hereinafter appear.

The accompanying drawing illustrates one mbodiment which the invention may assume in practice,-it being understood that various changes in the details of construction and operation of the controller may be effected with out departing from the spirit and scope of my invention as defined in the appended claims.

In the drawing,

Figure 1 is a schematic and diagrammatic view of a controller constructed in accordance with my invention, and

Fig. 2 is an across-the-line diagram of the circuits and connections illustrated in Fig. 1.

Referring first to Fig. 1, M and M designate the armatures of a pair of direct current motors adapted to be operated either jointly or individually in .the 'manner hereinafter set forth; said motors being respectively pro vided with series fields SF SF shunt fields SHF SHF and shunt connected brake coils BB Motor M is adapted to be controlled selectively by pairs of single-pole electromagnetically operable switches F F and B B", said pairs of switches being adapted when energized to provide for operation of said motor in reverse directions, respectively. Motor M is similarly adapted to be controlled selectively by pairs of single-pole electromagnetically operable switches F, F and 13 13 said pairs of switches being adapted when energized to provide for operation of said motor in reverse directions, respectively.

An electroresponsive relay MB is adapted when energized to provide for 'energization of switches F and F F jointly; said relay being in turn subjected to control by push button stations P or P, in conjunction with certain contacts and segments on the drum controller indicated generally at D.

Switches F F and F, F when simultaneously closed are adapted to provide a common energizing circuit for motors M and M for operation of the latter in a given direction, respectively, whereas one or the other of said motors will predominate, depending upon the direction in which the drum controller D is thereafter moved, as hereinafter more fully set forth.

Switches F F are also ada ted when closed to provide for operation 0 motor M individually in a given direction; whereas switches B B are adapted when closed to provide for operation of said motor in the reverse direction ;completion of the motor circuit in either case being dependent upon movement of drum D in a given direction from its intermediate or neutral position. Energization and closure of switches F, F and B, B is subject to control by push button stations P and P respectively, in conjunction with certain contacts and segments on drum D.

Similarly, switch F, F are adapted when closed to provide for operation of motor M individually in a given direction; whereas switches 13, B are adapted when closed to provide for operation of said motor in the reverse direction; completion of the I110- tor circuit being likewise dependent upon movement of drum D in a given direction from its intermediate or neutral position. Energization and closure of switches F, F and B, B is likewise subject to control by push button stations P and P, respectively.

As aforeindicated the push button switches P to P respectively, are ineffective for initiating the operation of motors M M either individually or ointly, except when the drum D is in its intermediate or neutral position, thus providing against improper operation of the control system.

As shown in Figs. 1 and 2 the switches BS and BS are provided with main contacts 51 and 56 adapted to control energization of brake coils BR and BB", respectively; Whereas relay MB is provided with main contacts 52 and 53, normally open a n2;- iliary contacts 54 and normally closed auxiliary contacts 55. Switch F is rovided with main contacts 57 and normal y closed auxiliary contacts 58; whereas switch F is provided with main contacts 59 and normally open auxiliary contacts 60, 61 and 62. Switch B is provided with main contacts 63 and normally open auxiliary contacts 64. 65 and 66; whereas switch B is provided with main contacts 67 and normally closed auxiliary contacts 68. Switch F is provided with main contacts 69 and normally closed auxiliary contacts 70; whereas switch F is provided with main contacts 71. and normally open auxiliary contacts 72, 7 3 and 74. Switch B is provided with main contacts and normally open auxiliary contacts 76, 77 and 78; whereas switch B is provided with main contacts 79 and normally closed auxiliary contacts 80.

Drum controller D as shown comprises contacts 11 to 29, inclusive, and segements 1 to 1, inclusive, and 2 to 2, inclusive, on opposite sides of the drum to cooperate with certain of said contacts selectively. Segment 1 is adapted to engage its cooperating contact 25 in the intermediate position of the drum and in all positions of the latter during movement thereof in one direction; whereas seg ment 2 is similarly adapted to engage its cooperating contact 24 in the intermediate position of the drum and in all positions of the latter during movement thereof in the opposite direction. Said drum is also provided with segments a: and g which are adapted to engage their cooperating contacts 22 and 23, respectively, only during intermediate or neutral positioning of the drum. As will be apparent the drum consists of but three electricall independent groups of segments one 0 said groups comprising segments 1 to 1 and 2 to 2 inclusive; another group comprising segments w, 3 1 1 and 2", 2; and the third group comprising segments 1*", 2 1 and 2.

Interposed between respective contacts 12 to 20, inclusive, are resistance sections R to R inclusive, adapted to be initially included in the common circuit of motors M and M during joint operation of the latter said drum being arranged to provide for gradually excluding said resistance sections from the circuit of one of said motors through a shunt around the other of said motors, whereby predominance of the ull of either motor with respect to the ot er may be effected. The shunt around the armature of motor M includes a resistance R, whereas the shunt around the armature of motor M includesa resistance R.

The operation of my controller will now be described with more particular reference to the diagram of Fig. 2. Thus with drum D in its intermediate position, as shown. joint operation of motors M and M for purposes heretofore set forth may be effected by temporary closure of push button switch P, which completes an energizing circuit for the winding of relay MR. Said circuit may be traced from line L through normally closed auxiliary contacts 55 of said relay, thence to contact 23 and segment y of drum D, thence to segment a: and contact 22 through said push button switch P, and through the winding of relay MR to line L Relay MR in closing provides a maintaining circuit for itself through closure of its normally open auxiliary contacts 54, said contacts 54 and 55 being suitably elongated or otherwise arranged to provide for closure of the former prior to opening of the latter. Said maintaining circuit may be traced from line L through normally closed push button switch P, thence through a suitable protective resistance r to and through said auxiliary contacts 54, and through the winding of relay MB to line L Upon closure of main contacts 52 and 53 of relay MR the device is preset for completion of energizing circuits for the windings of switches F F and F, F upon movement of drum D in either direction from its neutral position. Thus, assuming movement of said drum in a counter-clockwise direction to position 1 1), segments 1 and 1 will be brought into engagement with contacts 28 and 29. The energizing circuit thus provided for windings F and F may be traced from line L through push button switch P then to and through contact 28, segments 1 and 1 and contact 29, through main contacts 53 of relay MR and by conductor 90 through normally closed auxiliary contacts 68 of switch B, and thence through the windings of switches F and F in parallel to line L An energiz ing circuit is simultaneously provided for the windings of switches F and F said circuit extending from line L to contact 29,

- as just traced thence through main contacts 52 of relay MR, by conductors 91 and 92 through normally closed auxiliary contacts of switch B and thence through the windings of switches F and F in parallel to line L Also upon such movement of the drum, segments 1 1 and 1 will be brought into engagement with contacts 11, 12 and 18, respectively, thereby including re sistance section B in a shunt around the armature of motor M while simultaneously excluding resistance section B from the common circuit of said motors.

lVith switches F F and F F thus closed and with the drum in a position to short-circuit resistance section B the common circuit of the motors extends from line L through series field SF and contact 57, thence through the armature of motor M and through the main contacts 59 of switch F thence through resistance sections R to R inclusive, and through the main contacts 69 of switch F through the armature of motor M and the main contacts 71 of switch F and thence through series field SF to line L Moreover, by the arrangement aforedescribed a shunt is provided around the armature of motor M thereby reducing the torque of the latter with respect to that of motor M The pull of motor M will therefore predominate to a certain degree over the pull of motor M with consequent overhauling of the latter to effect swinging or turning of the boom conveyor in the desired direction. The torque of motor 11 with respect to that of motor M may be further varied in an inverse relation by continued movement of drum D in a counterclockwise direction to gradually exclude resistance sections R to R inclusive, from the circuit of motor M and from the shunt circuit around the armature of motor M It will benoted that switch F in closing effects opening of its normally closed auxiliary contacts 58, thereby preventing possible energization of the windings of reversing switches B B of motor M through closure of push button switch P inadvertently or otherwise. Similarly, switch F in closing effects opening of its auxiliary contacts 70 to prevent possible energization of the windings of reversing switches B, B of motor M through closure of push button switch P Upon closure of switch F the uorn'ially open auxiliary contacts 60 and 61 thereof act to complete an energizing circuit for the winding of bralte switch BS which circuit may be traced from line L through switch P by conductor 93 through said contacts (30 and 61, and by conductors 9i and 95 through said winding to line L. Upon closure of contacts 51 of switch BS an energizing circuit is provided for the brake coil BB for releasing the brake on motor M said circuit being obvious.

Similarly, upon closure of switch F the normally open contacts 72 and 73 thereof act to complete an energizing circuit for the winding of brake switch BS which circuit may be traced from line L through switch P, by conductor 98 through said contacts 72 and 73, and by conductors 96 and 97 through said winding to line L Upon closure of contacts 56 of switch BS an energizing circuit is provided for the brake coil BB for releasing the brake on motor M said circuit being obvious.

When the boom conveyor has been brought to the desired position operation of motors M and M may be stopped by depressing push button P, which interrupts the onergizing circuits of switches F F and F, F and the maintaining circuit of relay It, thereby resetting said devices for subsequent operation. To effect swinging movement of the boom conveyor in a reverse direction the drum controller is brought back to its intermediate or neutral position and the push button P is temporarily depressed to pro vide an energizing and maintaining circuit for the winding of relay MR, with consequent closure of contacts 52 and 53 of the latter as aforedescribed. Thereupon drum D is moved in a clockwise direction to position 1 (Fig. 1), wherein segments 2 and 2 are brought into engagement with contacts 28 and 29, respectively. lVi-th contacts 28 and 29 bridged in this manner "the energizing circuits for switches F F and F, F will be otherwise the same as atoredescribed. Moreover, in this position of the -d-rum a shunt will be provided around the armature of motor M (through engagement of segment 2 with contact 21, Fig. 1) thus providing for initial and continued predominance of the pull of motor M during movement of the drum in a clockwise direction.

It will be understood that the maximum difference in the torque of motors M and M will be attained at the respective limits of movement of drum D in opposite directions. That is to say, the maximum torque of motor M coincident with minimum torque of motor M will result from movement of drum D in a counterclockwise direction to position 9, whereas the maximum torque of motor M coincident with minimum torque of motor M will result from movement of drum D in a clockwise direction to position 9 (Fig. 1).

As aforeindicated it is necessary or desirable to provide for operation of motors H and M individually in opposite directions after detachment of the respective ropes from the boom or prior to attachment thereof to the boom. The means for controlling individual operation of motor M comprises a normally open push button switch P adapted when closed under given conditions to effect operation of motor M in one direction, and a normally open push button switch P adapted when closed under given conditions to effect operation of said motor in the reverse direction. Thus, assuming intermediate positioning of drum D, closure of switch P will complete an energizing circuit for the windings of switches F and F which circuit may be traced from line L through auxiliary contacts of relay MR to contact 23, segments 1 and 1', and contact 25 of the drum, thence by conductor 98 through said switch P and by conductors 99 and 90 through the windings of switches F, F 2 in parallel, as previously traced. Upon closure of main contacts 57 and 59 of switches F and F respec tively, motor M is preset for operation in a given direction upon movement of drum D in a counterclockwise direction (Fig. 1). However, such movement of drum D from its intermediate or neutral position would tend to interrupt the energizing circuit of switches F, F through disengagement of contact 23 and segment y. I therefore arrange the segment 1 in such manner as to provide for engagement thereof with contact 26 of the drum prior to disengagement of contact 23 and segment y under the aforementioned conditions. The alternative energizing circuit thus provided for the windings of switches F, F may be traced from line L through switch P, thence by conductor 93 through auxiliary contacts 60 and 62 (which a e closed due to closure of switch F to contact 26 and connected segments 1 and 1", thence to contact 25, and by conductor 98 to line L as just traced. It will be noted that segments 1 and 1 are adapted to engage their corresponding contacts 25 and 26 in all operative positions of drum D during movement thereof in said counterclockwise direction.

Thus upon movement of drum D in a counterclockwise direction to its first operative position the energizing circuit of motor M may be traced from line L through series field SF contacts 57 through the armature of said motor and through contacts 59 through resistance sections R to R inclusive, thence through the drum segments and resistance B through series field SF to line L The speed of operation of motor M may be varied by continued movement of drum D in a counterclockwise direction to effect exclusion of resistance sections R to R sequentially; it being understood that energization of switches F, F 2 is dependent upon continued closure of push button switch P, which is preferably required to be manually held in closed position. Thus stopping of motor M may be effected by release of push button switch P or by return of drum D to its intermediate osition. Energization of brake switch B 1 and the associated brake coil BR is controlled through closure or opening of auxiliary contacts 60, 61 of switch F as aforedescribed.

Operation of motor M in a reverse direction is controlled in a substantially similar manner through closure of push button switch P ,the initial connection of conductor 98 with line L during intermediate positioning of drum D, being exactly as aforedescribed, whereas the alternative connection therefor upon movement of said drum in a counterclockwise direction is effected through closure of auxiliary contacts 66, 65 of switch B, as will be obvious.

Individual operation of motor M in a given direction may likewise be effected by closure of push button switch P (drum 1) being in its intern'iediate position) thus providing an energizing circuit for the winding; of switches 1 ,1 which may be traced from line L through auxiliary contacts 55 of relay MR, thence to contact 23, segments ;1 and 2*. and contact 24 of drum D, by conductors 10 i and 101 through switch P, by conductor 92 through auxiliary contacts of switch B and thence through the windings of switches F, F in parallel to line L Contacts 69 and 71 of said switches are thereby closed to preset the energizing circuit of motor M for completion upon movement of drum D in a clockwise direction (Fig. 1) said circuit in the first operative position of the drum including resistance sections R to R and resistance R, as will be obvious. Segment 2 is arranged to engage contact 27 of the drum prior to disengagement of segment y and confact 23, whereby an alternative energizing circuit may be provided for the windings of switches F, F during movement of the drum to its several operative positions. Said alternative circuit may be traced from line add L through switch I by conductor 93 through auxiliary contacts 72 and 7d of switch F thence by conductor 102, contact 27 and segment 2 to segment 2 connected with the latter, and thence by contact 2% and conductor 100 to and through said windings to line L as previously traced. Closure of. auxiliary contacts 72 and 73 of switch F likewise completes an energizing circuit for the winding of brake switch BS as will be obvious, whereas the contacts 56 of the latter act to complete an energizing circuit for brake coil BB Similarly with drum I) in its intermediate position an energizing circuit may be provided for the windings of switches B, B through closure of push button switch P the initial energizing circuit therefor extending from line L to conductor 100 exactly as heretofore traced with reference to the windings of switches F, F; whereas the alternative energizing circuit for the windings of switches B B becomes effective (due to closure of auxiliary contacts 77, 78

. of switch 13) upon movement of drum D in a clockwise direction out of neutral position. Auxiliary contacts 77, 76 of switch B act to complete the energizing circuit of brake switch BS under these conditions, for the purpose aforedescribed. As aforeindicated with reference to individual control of motor M motor M may be stopped when operating in either direction by moving drum D to neutral position, or by releasing the push button switch P or P as the case may be.

From the foregoing description it will be apparent to those skilled in the art that I have provided an extremely flexible and eiiicient control system for effecting either joint or individual control of aplurality of electric motors.

lVhile I have disclosed the use of singlepole reversing switches, it is to be understood that double-pole switches may be used for this purpose if desired.

What I claim as new and desire to secure by Letters Patent is:

1. In combination, a plurality of electric motors, common resistance to be included in circuit with one or more of said motors, a

master controller for commutatin said resistance, and means including a plurality of manually operable push button switches cooperating with said master controller, said switches being operable selectively to provide for joint or individual control of said motors upon a given operation of said master con troller.

2. In combination, a plurality of reversible electric motors, resistance to be included in circuit with one or all of said motors, a master controller for commutating said resistance, and means including a plurality of manually operable push button switches cooperatingwith said master controller, said push button switches being operable independently of each other to selectively provide for joint or individual control of said motors, and certain of said push button switches when so operated being adapted to selectively provide for forward or reverse operation of said motors indii 'idually.

3. In combination, a plurality of reversible electric motors, resistance to be included in circuit with one or all of said motors, a master controller for commutating said resistance, and means including a plurality of manually operable push button switches cooperating with. said master controller, said push button switches being operable independently of each other to selectively provide for joint or individual control of said motors, and other of said push button switches when so operated being adapted to provide for predominance of the torque of one or the other of said motors in accordance with the direction of operation of said master controller from a given intermediate position.

a. In combination, a pair of reversible motors, resistance to be included in circuit with either or both of said motors, a master controller movable in opposite directions respectively from a given intermediate position for commutating said resistance, a plurality of push button switches cooperable selectively with said controller for preselecting either joint or individual control of said motors, and means for rendering said push button switches ineffective pending intermediate positioning of said controller.

5. The combination with a plurality of electric motors, of control means for effecting operation of said motors ointly or alternatively for effecting operation thereof individually in reverse directions respectively, said means comprising a master controller movable in opposite directions from a neutral position, a push button switch adapted upon closure thereof to effect completion of an energizing circuit for said motors jointly upon neutral positioning of said controller. and means adapted upon movement of said controller in a given direction to provide a shunt around the armature of one of said motors to thereby decrease the torque of the latter.

6. The combination with a pair of reversible motors to be operated jointly in a given direction or alternatively to be operated individually in reverse directions selectively, of control means for effecting such operation of said motors, said means comprising a common control drum movable in opposite directions from neutral position, a plurality of push button switches cooperable with said drum for initiating operation of said motors either jointly or individually, and means rendering said push button switches ineffective pending neutral positioning of said drum.

7. The combination with a pair of reversible motors to be operated jointly in a given direction respectively or alternatively to be operated individually in reverse directions selectively, of control means for effecting such operation of said motors, said means c0mpris ing a common control drum movable in opposite directions from neutral position, a plurality of push button switches cooperable individually with said drum for initiating operation of said motors either jointly or individually, means rendering said push button switches ineffective pending neutral position- .ing of said drum, and means adapted upon initiation of operation of said motors jointly to maintain the circuit connections for said motors independently of the respective push button switch.

8. The combination with a pair of reversible motors to be operated jointly in a given direction respectively or alternatively to be operated individually in reverse directions selectively, of control means for effecting such operation of said motors, said means comprising a common control drum movable in opposite directions from neutral posit-ion, a plurality of push button switches cooperable individually with said drum for initiating operation of said motors either jointly or individually, means rendering said push button switches ineffective pending neutral positioning of said drum, and means adapted upon movement of said drum in one direction from neutral position to decrease the torque of one of said motors while increasing the torque of the other motor.

9. The combination with a pair of reversible motors to be operated jointly in a given direction respectively or alternatively to be operated individually in reverse directions selectively, of control means for effecting such operation of said motors, said means comprising a common control drum movable -in opposite directions from neutral position,

a plurality of push button switches cooperable individually with said drum for initiating operation of said motors either jointly or individually, means rendering said push button switches ineffective pending neutral positioning of said drum, and means adapted upon movement of said drum in one direction or the other from neutral position to decrease the torque of one motor and increase the torque of the other, or vice versa, whereby the pull of either of said motors may be made to predominate.

10. The combination with a plurality of electric motors, of means for effecting joint operation thereof, said means comprising resistance to be included in a common circuit of said motors and a drum controller for commutating said resistance in steps, said drum including means for providing a shunt of predetermined resistance value around the armature of one of said motors to thereby insure predominance of the torque of another of said motors with respect thereto.

11.. The combination with a pair of reversible motors, of control means for effecting operation of said motors jointly or alternatively for effecting operation of either of said motors individua ly, said means comprising a common control drum for said motors, and a plurality of push button switches cooperable selectively with said drum for preselecting said joint or individual control, said drum being adapted upon movement thereof in a given direction from neutral position during joint operation of said motors to provide for decreasing the torque of one of said motors while simultaneously effecting an increase in the torque of the other of said motors.

12. The combination with a pair of reversible motors, of control means for effecting operation of said motors individually at will, said means comprising a common control drum for said motors, a plurality of push button switches cooperable selectively with said drum for preselecting the motor to be operated and the direction of operation thereof, a plurality of resistance sections to be included in circuit with either of said motors, and means on said drum for commutating said resistance sections with respect to the circuit of one of said motors upon movement of said drum in a given direction.

13. The combination with a pair of reversible motors, of control means for effecting forward or reverse operation of said motors individually at will, said means comprising a common control drum for said motors, a plurality of push button switches cooperable selectively with said drum for preselecting the motor to be operated and the direction of operation thereof, speed controlling means comprising a plurality of resistance sections to be included in circuit with either of said motors, and means on said drum for commutating said resistance sections with respect to the circuit of one of said motors upon movement of said drum in a given direction from neutral position, said means being also adapted to commutate said resistance sections with respect to the circuit of the other motor upon movement of said drum in the opposite direction from neutral position.

14. The combination with a pair of reversible motors, of control means for effecting forward or reverse operation of said motors individually at will, said means comprising a common control drum for said motors, a plurality of push button switches cooperable selectively with said drum for preselecting the motor to be 0 erated and the direction of operation thereo speed controlling meaus comprising a plurality of resistance sections to be included in circuit with either of said motors, and another push button switch cooperable with said drum during neutral positioning of the latter to effect joint operation of said motors.

15. The combination with a pair of reversible motors, of control means for effecting forward or reverse operation or said motors individually at will, said means comprising a common control drum for said motors, a plurality of push button switches cooperable selectively with said drum for preselecting the motor to be operated and the direction of operation thereof, speed controlling means comprising a plurality of resistance sections to be included in circuit with either of said motors, another push button switch adapted to cooperate with said drum during intermediate positioning of the latter for etl'ecting operation of said motors jointly in a given direction, said drum being thereupon adapted when moved in a given direction from said intermediate position to effect a decrease in the torque of one of said motors while increasing the torque of the other motor to thereby provide for predominance of the pull of the latter.

16. The combination with a pair of reversi ble motors, of control means for effecting forward or reverse operation of said motors individually at will,saidmeans comprising a common control drum for said motors,a plurality otpush button switches cooperable selectively with said drum for preselecting the motor to be operated. and the direction of operation thereof, speed controlling means comprising a plurality of resistance sections to be in cluded in circuit with either of said motors, another push. button switch adapted to cooperate with said drum during intermediate positioning of the latter for etlectmg operation of said motors jointly in a given direction, said drum being thereupon adapted when moved in a given direction from said intermediate position to eitect a decrease in the torque of one of said motors while increasing the torque of the other motor to thereby provide for predominance of the pull of the latter, said drum being also adapted when moved in the opposite direction from said intermediate position to effect a decrease in the torque of the last mentioned motor while increasing the torque of the first mentioned motor.

1.7. in combination, a pair of reversible motors, electroresponsive forward and reverse switches for each of the same, an electroresponsive relay adapted when energized to effect closure of the forward switches of said motors jointly, a control drum movable in opposite directions from a given intermediate position, a normally open push button switch adapted when closed during such intermediate positioning of the drum to effect energization of said relay, a maintaining circuitfor said relay independent of said d rum and said push button switch, said drum being adapted when moved in one direction from said intermediate position to provide a shunt around the armature of one of said motors and being also adapted when moved in the opposite direction from said intermedi o position to provide a shunt around the arn'ieture or the other of said motors, said drum being also adapted during continued moven'ient t erect in a given direction to de crease the enective resistance in series with L 4/ id motors while increasing the value 2i .1. out in the shunt around the armature oi the other motor, whereby the pull of said motor may be varied inversely with respect to earn other, and a normally closed push button sw tch adapted when opened to interrupt ener ation of said relay for stopping of said motors jointly.

18. In combination, a pair of reversible motors, eloctroresponsive forward and reverse switches for each of the same, an electroresponsive relay adapted when energized to ettect closure of the forward switches of said motors jointly, a control drum movable in opposite directions from a given intermediate position, a normally open push button switch adapted when closed during such intermediate positioning of the drum to eitect enei ation of said relay, a maintaining circuit tor said relay, independent of said drum and said push button switch, said drum being adapted when moved in one direction "from said intermediate position to provide a shunt around the armature of one of said motors and being also adapted when moved in the opposite direction from said interme diate position to provide a shunt around the armature of the other of said motors, said drum bein also adapted during continued movemei'it thereof in a given direction to decrease the effective resistance in series with one of said motors while increasing the value oi current in the shunt around the armature of the other motor, whereby the pull of said motors may be varied inversely with to each other, and a plurality of nor nally open push button switches for direct control of the Forward or reverse switches of he respective motors individually at will,

to said. motors jointly, a control drum movable in opposite directions from a given intermediate position, a normally open push button witch adapted when closed during such iniate positioning of the drum to eilect mergization of said relay, a maintaining ciruit for said relay independent of said drum and said push button switch, said drum being adapted when moved in one direction from said intermediate position to provide a shunt around the armature of one of said motors and being also adapted when moved in the opposite direction from said intermediate position to provide a shunt around the armature of the other of said motors, said drum being also adapted during continued movement thereof in a given direction to decrease the effective resistance in series with one of said motors while increasing the value of current in the shunt around the armature of the other motor, whereby the pull of said motors may be varied inversely with respect to each other, and a plurality of normally open push button switches for direct control of the forward or reverse switches of the respective motors individually at will, said last mentioned push button switches being ineffective for initiating operation of the res ective motors individually controlled there y pending intermediate positioning of said drum and being also adapted upon release thereof to effect stopping of the motor respectively controlled thereby.

In witness whereof, I have hereunto subscribed my name.

WILLIAM R. MILBURN.

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