US1861994A - Control system - Google Patents

Description

June7, 1932. I w. R WICKERHAM 1,861,994

CONTROL SYSTEM Filed June 19, '1930 2 Sheets-Sheet 1 INVE NTOR 7161111211: R. Wafer/1am 7 ATTORNEY J1me 1932- w. R. WICKERHAM 1,361,994

CONTROL SYSTEM Filed June 19, 1930 2 Sheets-Sheet 2 INVENTOR Mllz'amRWiaKez/mm A'TTQRNEY Patented June 7, 1932 UNITED STATES PATENT QFFICE;

WILLIAM R. WICKERHAM, OF \VILKINSBURG, PENNSYLVANIA, ASSIGNOR TO WESTING- HOUSE ELECTRIC & MANUFACTURING VANIA Application filed June 19,

My invention relates to hoisting machinery, and more particularly to an electrical control system for operating the motor of a hoist grab-bucket.

One of the objects of my invention is to provide for electrically controlling the closing and opening operations of the jaws of a grab-bucketby means of a simple electrical control system.

A further object of my inventionv is the provision of electrical means mounted on the grab-bucket to close the jaws of the bucket, and by reason of my novel control system operate the jaws to closed position by said means a force not exceeding a predetermined value.

It is also an object of my invention to electrically limit the opening speed of the jaws of the bucket when subject to a heavy overhauling load, whereby damaging slack in the operating cables for the jaws and excessive clashing of the jaws is prevented.

Other objects and advantages will be apparent from a study of the following specification when taken in conjunction with the accompanying drawings, in which:

Figure 1 is a view in side elevation of a grab-bucket hoist.

Figs. 2 and 3 are perspective views of the grab-bucket showing the electrical equipment mounted on the bucket; and,

Fig. 4 is a diagram of the electrical control system for controlling the operation of the motor operating the jaws of the bucket.

Referring more particularly to Fig. 1 of the drawings, R designates a rail along which the frame of the grab-bucket hoist is caused tooperate in a conventional manner. A pair of trolley wires 1 and 2 are disposed in parallel relation to the rail and constitute the source of direct current power for operating the electrical equipment mounted on the hoist frame and the grab-bucket.

Mounted on the frame is a motor 11 for operating the hoisting drum 12 upon which a cable or chain 13 is arranged for lowering and raising the grab-bucket 60 shown in Figs. 2 and 3. The power for operating the motor 11 and the other equipment on the hoist frame is collected from the trolley wires 1 and 2 by COMPANY, A- CORIOEATION OF PENNSYL- CONTROL SYSTEM 1930. Serial No. 462,222.

means of the trolley wheel-assemblage 3 and 4. A conduit 4' carries the electric energy from the trolley wheel-assemblage to controller l4 and controller 9 located with controller 14 shown in the operatorsca'ge (see Fig. 1). The controller 9 is disposed to controlthe operation ofthe motor 11,.and the motor provided for actuating the hoist crane. The controller 9 and the electrical equipment thereby controlled constitute no part of my invention and therefore need in full detail.

The controller 14 provided with a controller lever 14, controls the operation of the elecnot be described trical equipment mounted intermediate the directional contactors 24, 26, 48 and 49 and a rugged copper ozide rectifier for selectively controlling the operation of the magnetically operated directional contactors, are all mounted on the grab-bucket. A limit switch 52 is also mounted on the grab-bucket and is operably associated with the cable 72 (see Fig.

4) for operating the levers 59 to close the jaws 61 of the grab-bucket.

The function of the limit switch 52 is to interrupt the circuit for the motor 56 and'to cause the locking of the brake mounted on the grab-bucket. The limit switch is actuated either when the jaws have completely opened and a slack occurs in the cable 72 or when a slack occurs. in the cable 72 because of the:

fact that the jaws have engaged an obstruction-and thus cannot open.

Motor 58 is a torque motor which operates the winding drum 57 for paying out the elec trical cable 21 and is so designed that it;

holds the cable 21 taut atall times, thereby preventing unnecessary wear on the cable and also possible rupture of the cable due to unusual operating conditions. It is of course understood that winding drum 57 may be operated by a spring mounted within the in fully closed or usually contained from four to five :conductors, and it is one of the novelcharacteristics of my control system, that the cable for conducting the electrical energy to the electrical 1 equipment on the grab-bucket contains but two conductors. In consequence the" drum 57 and the operating mechanisms associated with it may be relatively light and inexpensive.

. A more detailed understanding of my in vention may be had from a discussion ofFig.

4. InFig. 4 the controllers .9 and '14 and the supporting structure 70 are shown sche- ,zmatically in dotted lines. The elements 11, II'12,.57-,158,.56, 71, .etc.. refer to the elements ....heretofore.discussedin connection to Figs. 1, i .2 and 3.

The operation of my control system to actuate the grab-bucket 60'is as follows: Assum- .ingthat trolley wires 1 and 2-are supplied Lwith direct current volta e of a redetermined value,..then upon the closing of the safetyswitch 8-the controller. 9 is energized anclwhen thecontrol lever 9 is'actuated. the

hoisttrame may be caused to move along the 1 =rail R and themotor llmay be caused to operate Motor 58, since it operates on the prin- ,ciple of atorque motor is supplied with energy under constant conditions and is thus not sub- I hen-the safety switch 5 is closed and the j ect to any special control.

. -segments of the controller 14 are actuated to the right, toxany-position .otherzthan position 6, a. circuit isestablishedwhichumay be traced from the positive trolley wire 1 through trolley wheel 3, safety switch 5, over- ..:load circuit breaker F, actuating coil 16 of Ethe torque limiting. relay. 17, contact fingers 18 bridged by the-controller segment 18,

= conductor. 19, slip ring 20, cable. 21, conductors 22 and 23, the actuating coils of the directional contactors 24; and 26, the copper oxideu'ectifier' 27, conductor 28, cable 21, slip :1 ring- 29, conductor 30,-:contact fingers 31 bridged by the; controller-segment 31, contductor 32-,starting resistor 33, -conductor 34,

:overload' circuit breaker l3:-,sa-fety switch 5 and trolley wheel 4 to thenegatively energized trolley wire 2.

The copper'oxide rectifier 27 operates as an electric valve, permitting current to flow only in the direction indicated by the arrow. Furthermore this rectifier is 'well known in the trade and is of very rugged design, capa 'ble of withstanding severe shocks andother abuses in service over-long periods of time without undergoing any material changes in operating characteristics.

Immediately upon operation of directional contactors 24 and 26 a circuit is established which extends from the positively energized conductor22 through thecoil of the magnetic brake 35, the seriesfield windings 36 of the motor 56, jamming resistor 37, conductor 38, the contact members of the directional conta'ctor 24,--conductor 39', the armature 40 ol -the motor 56, conductor 41, the contact members of the directional contactor' 26 to the negatively energized conductor 28. It will be noted that during the closing operation of the jaws 61 of the grabbucket 60, the armature shunt resistor 54, is not connected in shunt relation to the armature 40, but is connected shunt relation to the circuit extending from the junction 69 through the contacts of. the directional contactor 24 to the junction 68. 'Since this last traced circuit is of low resistance value, .the effect of resistor 54 isunimportant.

Movement of the controller segment 42' to bridge the ..contact fingers .42, that is movement of the controller drum 14 tov position 6 establishes a cir cuit which extends from'the right hand. terminal of the energized coil 16. through the contact fingers 42 bridged by the. controller. segment 42, the actuating coil of the accelerating ..re lay..43, conductor 44, backcontacts of torque-limit relay 17 to the negatively energized conductor 34. Operation ofthe accelerating relay 43 establishes a. shunt .circuit for. the starting resistor 33. i

If during the closing of the jaws an obstruction is encountered by. the jaws, it is very desirable-that the jaws benot urged to closed position by an excessive force, first, because of-the danger'to the electricalequipment resulting from theheavy current-thus taken from the line and second, because it is usually desirablenot to' crush-:the object intermediate the jaws. In the devices of the prior art, a friction clutch was genera lly provided which, during. the'condltions just specified, wouldslip and thuspermit continued rotation of the motor; It is thus obvious that mal-adjustment of thefriction clutch may nevertheless cause damage'to the motor and at the-same time crush the object intermediate the jaws. -Further,ifthe friction'clutch be adjusted. tooloosely theob- 'ject intermediate-the aws may drop' after having been hoisted toa considerable height with consequent. danger to attendantsv and workmen in the vicinity of the hoist.

To eliminate the. undesirable characteristics just outl-ined, I have provided the torque limiting relay 17. If, during a closing operation of the jaws, an obstruction is encountered and an excessive current is taken by the motor then the actuating coil 16 operates to open the backcontact members of the object intermediate the edges of the jawswithout crushing the object and without drawing an excessive current from the line. Closing of the upper contact members of the torque-limit relay 17 merely establishes a holding circuit for the relay 17 through the coil 46, thereby preventing chattering of the relay.

During the stalling of the motor, as just explained, the voltage impressed on the coils Y or the closing directional contactors decreases, but since these coils are connected in parallel circuit relation with the coil of the magnetic brake 35, the series field windings 36 and the amming resistor 37 connected in series, the voltage impressed on the coils of the closing directional contactors is sufficient to maintain the motor circuit.

During the opening operation of the grabbucket 60 the controller 14 is moved to the left thereby. causing the bridging of contact fingers 53 and 47 by controller segments 53' and 47. A. circuit is thus established which may be traced from the positively energized right hand terminal of the actuating coil'16 through contact fingers 47 ridged by the controller segment 47 conductor 30, slip ring 29, cable 21, conductor 28, rectifier 27, the actuating coils of the opening directional contactor 4S and 49, conductor 50, contact members 51 of the limit switch 52, conductor 22, cable 21, slip ring 20, contact fingers 53 bridged by the controller segment 53, conductor 32, starting resistor 33 to the negatively energized conductor 34.

Immediately upon 0 eration of the directional contactors 48 an 49 a circuit is established which extends from the positively energized conductor 28 through the contact members of directional contactor 49, con ductor 39, armature 40, conductor 41, the contact members of directional contactor 48, the jamming resistor 37, series field winding 36 and the releasing coil of the magnetic brake to the negatively energized conductor 22. It will be noted that the resistor 54 is connected in parallel circuit relation with the armature and in consequence the speed of the motor during the opening operation, especially if the load is overhauling, is limited to a safe value.

lVhen the jaws 61 of the bucket have opened completely and also when the opening of the jaws is prevented by an obstruction, a slack occurs in cable 72 whereby the limit switch 52 is permitted to operate to open the circuit for the directional contactors 48 and 49, which in turn "causes an interruption of the energy supplied to the motor 56 and locking of the magnetic brake 35.

The motor 56 is accelerated in the opening direction in the same manner as it is accelerated in the closing direction, since movement of the controller segment 42" to bridge contact fingers 42 energizes the accelerating relay 43 which in turn establishes a shunt circuit for the starting resistor 33.

While the foregoing disclosure sets forth with particularity the circuit connection inherent in my invention and discloses the combination of these connections with the grabbucket and the means for operating the grab-bucket, I do not wish to be limited to the specific details disclosed but wish-to be limited only by the appended claims. I

I claim as my invention .1. A motor control system for an electrically operated grasping device, a grasping device, electrical devices mounted on the grasping device and including a motor for operating the grasping device, a contactor for connecting the motor to cause opening of the grasping device, a limit switch for causing the interruption of the connections established by the contactor when thegrasping device fails to open in response to the normal torque of the motor and a magnetic brake for holding the operated parts of the grasping device in the position to which they were moved by the motor at the instant of the operation of the limit switch.

' 2. In a control system for a motor mounted on a grab-bucket having jaws, means responsive to a predetermined overload on the motor during the closing of the jaws, caused either by the fact that the jaws have completely closed or by the fact that the jaws have encountered an obstruction during closing, for reducing the armature current of the motor to cause operation of the motor on the principle of a torque motor to hold the jaws against the obstruction or in closed position.

3. In a motor control system for an electrically operated grab-bucket, in combination, a grab-bucket, electrical devices mounted on the bucket and including a motor for opening and closing the bucket, closing contactors, opening contactors, a limit switch in series with the opening contactor and responsive to abnormal opening conditions of "for opening and closing the :bucket and-clos I wing. contactors for connectmg the motor to i came closing of the grab-bucket, a pair of conductors leading from the electrical devices, supply lines for supplying electric energy and a controller disposed-for operation to selectively connect the supply lines to 5. A motor control system for an electrically ooerated Tab-bucket havin aws com-- "I w b n u b prising, in combination, a motor mounted on the grab-bucket for opening and closing the grab-bucket, a palr of conductors-leading from the motor, supply lines for supplying electric energy, a controller remote from the motor for selectively connecting thesupply lines to the conductors thereby causing open- 1 ing or closing of the grab-bucket depending on the connection selected by the controller,

said controller including a starting resistor,

means responsive to a predetermined over load on the motor during the closing of the jaws caused by an obstruction encountered" by the jaws or by the fact that the jaws have completely closed, for connecting the starting resistor in series with the motor thereby pausing the aws to be held in closed position against the action of the motor operating on the principle of a torque motor.

6. In a control system for an electrically operated grab-bucket, electrical devices mounted on the grab-bucket and including a motor for operating the grab-bucket, a reversing contactor unit, aresistor'connected in series circuit relation withthe motor, said reversing contactor unit being connected in )arallel with the motor whereb the reversing contactor unit is maintained energized regardless of changes in counter-electromotive force of the motor, a magnetic brake and an electric valve for selectively controlling the re\'*ersingcont actor unit, a source of power, two conductors leading from the source of power and a double throw controller for selectively connectingthe two conductors to the source of power, said controller including a resistor, means for shunting the resistor and means responsive to a predetermined overload on the motor for deenergizing the resistor shunting means.

7. In a control system for an electrically operated grab-bucket having jaws, and having mounted thereon a motor for opening and closing the jaws, a magnetic brake, and

a resistor connected in series circuit relation with the motor, opening d1rect1onalcontactors and closing directional contactors in parallel with the motor, brake and 'IBSlStOI,

. the resistance drop across the resistor when sub ect to-normal operating voltage being sufficient to prevent the opening ofthe directional'contactor when in closed position, a speed control resistor arranged to be'connected in: parallel with. the motor armature when the motor is operating to open-thejaws of the'grab-bucket: thereby preventing excessive speeds in the opening direction.

8; Ina control system '-f0ri an electrically operated bucket having a movable aw, electrical devices mounted on the bucket and including, a motor for operating the-jaw, a contactor having contact members for c011- necting the motor to operate the jaw-and a -resistor connected in series-circuit relation with the motor, said cont'a'ctorpbeing"con; nectedito be responsive'to the resistance'drop across the resistor to prevent the actuation of the contact members to their OPGIIPQSltlOII, a controller, conductors connectmg electrical devices to the controller, means res onsive to. overload on the motor; for limiting thecurrent drawn by the motor whereupon thej aw is actuated by the motor operating on. the: principle of a torque motor.

9. In a control system for an electrically operated bucket, electrical devices mounted on the bucket and including a motor, a magnetic; brake,'current limiting means: for-:limitingthe motor current when the motor 1s operating 1n one direction, means for limitingthe speed of the motor when operating .in the opposite d1rect1on,.a reversing contactor unit and an electrlc valve for selectively controlxling the energization of the reversing. contactor unit, two conductors connected to'the'" .electrica-l devlces, a reel for the conductors'to maintain them taut, a source of power and a controller for connectmg the source ofpower to the conductors, current l1m1t1ng means mounted on the controller operating'jointly and additively with the current-limiting device on the bucket.

In testimony whereof, I have hereunto'subscribed my name this 17th day Jun'e; =1930.

WILLIAM R. I/VIGKERH AM.

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