US2689934A - Induced-current brake traction drive control - Google Patents

Description

p 21, 1954 F, w. WENDELBURG 2,689,934

INDUCED-CURRENT BRAKE TRACTION DRIVE CONTROL Filed May 27, 1949 2 Sheets-Sheet l 3 INVENTOR.

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dlt'arny P 21, 1954 F. w. WENDELBURG 2,689,934

INDUCED-CURRENT BRAKE TRACTION DRIVE CONTROL Filed May 27, 1949 2 Sheets-Sheet 2 INVENTOR. fflowaua BY M q 5 m dkorney Patented Sept. 21, 1954 INDUCED-CURRENT BRAKE TRACTION DRIVE CONTROL Frank W. Wendelburg, to Harnischfeger Cor Milwaukee, Wis., assignor poration, Milwaukee, Wis.,

a corporation of Wisconsin Application May 27, 1949, Serial No. 95,807

9 Claims. 1

This invention relates to electrically actuated propelling and controlling means for self propelled traction apparatus such as travelling overhead cranes and it resides in an improved form of such apparatus in which novel driving andbraking means operate in such manner as to cause the travelling movement to be arrested without hazardous or undesirable mechanical shock, said result being accomplished through the use of induced current or eddy-current torque resisting means, mounted in driven relationship to the propelling mechanism, the same being energized so as to become active to restrain motion, only when an operator actuates a controller from a higher speed driving position to a position calling for deceleration.

One object of this invention is to provide a propelling and controlling apparatus which will permit motion to be smoothly terminated without dependence upon manually operated brakes.

Another object of this invention is to provide propelling and controlling means for the bridge of an electrically driven travelling overhead crane wherein motion is arrested smoothly by means which may be controlled from a point located in a travelling operators cab attached to the crane trolley.

Another object of this invention is to provide a propelling and controlling apparatus for the bridge of an electrically driven overhead crane which will safely and smoothly arrest motion of the crane in the event of power failure.

Another object of this invention is to provide a propelling and controlling apparatus for the bridge of an electrically driven overhead crane which will make practical increased rates of travel of the bridge of the crane in spite of the use of a trolley mounted operators cab, without hazard to the operator due to excessive mechanical shock during stopping.

The foregoing and other objects and advantages of this invention are explained in the description which follows, which description is set forth with reference to the accompanying drawings forming a part hereof, in which there is shown, for purposes of illustration and not of limitation, one form in which the apparatus of this invention may be embodied.

In the drawing, Fig. 1 is an electrical circuit diagram of one form of the apparatus of this invention,

Fig. 2 is an end view in elevation diagrammatically depicting one form of crane with which the circuit set forth in Fig. 1 may be employed, and

Fig. 3 is a diagrammatic side view in elevation of the crane shown in Fig. 2.

For the driving of overhead cranes and other traction devices it is desirable at times to employ alternating current driven electrical equipment. The usual wound rotor induction motor, having control means for reversing the same and regulating the speed thereof, used for this purpose is subject to certain limitations, one being the fact that such a motor is ill adapted to perform a braking function. Consequently such arrangements have usually depended upon friction service brakes, which are manually applied to produce the desired gradual deceleration prior to the sudden stoppage produced by the usual electro-magnetically released, normally applied, friction holding brakes which become applied whenever power supplied to the motor is interrupted. This arrangement, however, has been suitable only in cranes or other devices having the operators cab so mounted as to make feasible the necessary mechanical or hydraulic connections between the operators cab and the service brakes.

In certain instances,- it is necessary that the operators cab be movable in relation to the traction device per so, as is thecase where the cab is attached to the trolley of an overhead crane, so as to move lengthwise of the bridge of the crane to permit the operator to maintain a position approximately above the load being lifted. Such cranes are particularly useful where special grapples are employed enabling the operator to engage and release a load without assistance of a ground crew, as for example in the case of lumber cranes. Trolley mounted cabs are also of use in foundry cranes where pouring from a moving ladle is desired and also to a smaller extent in cranes employing clam shells, magnets or other devices which load without the attention of a ground crew. Heretofore in cranes having trolley mounted operators cabs, because of the difiiculty of connecting up manually actuated service brakes, stopping of bridge travel has usually been made to depend upon the so-called holding brake which becomes applied upon discontinuance of power supplied to the propelling motor. The sudden stopping produced by the holding brake, particularly when applied while the bridge is drifting at a rapid rate, causes serious mechanical shocks. As a result it has been customary to limit the rate of travel of the bridge of such cranes to speeds which are but a minor fraction of bridge-travel speeds otherwise considered suitable. Unless this precaution is observed the mechanical shocks are sufficiently severe to subject the entire structure to conditions endangering its structural soundness and to throw the operator about in his control cab with such violence as to make injury likely.

Through the use of the improved apparatus of this invention it is possible to provide alternating current driven traction devices such as overhead cranes in which the rate of travel can be greatly increased without hazardous or undesirable shocks during stopping and without dependence upon manually actuated service brakes.

The apparatus of this invention is suitable for use in connection with a wide range of electrically driven self-propelled apparatus and particularly in connection with cranes of the general type diagrammatically depicted in Figs. 2 and 3. The crane there shown includes a traction device in the form of a horizontal bridge I mounted upon end trucks 2 and 3 which in turn are carried for horizontal rolling movement upon runways 4 and 5. Mounted for horizontal transverse movement across the top of bridge I is a trolley 6 from which hoisting lines 1 and 8 extend downwardly as shown. Secured to the trolley 6, through extensions 9 of the trolley frame, is an operator's cab l8.

The propelling apparatus causing motion of the bridge I upon the runways 4 and comprises, as shown more clearly in Fig. 3, a propelling motor II to which a normally applied holding brake I2 is secured and from which an output shaft l3 extends. Also forming a part of the propelling apparatus is a reduction gearing |4 connected in driven relationship to the shaft l3. From the reduction gearing [4, cross shafts l5 and I6 extend to and drivingly join with the trucks 2 and 3 at the ends of the bridge.

In accordance with this invention there is associated in torque resisting relationship to the drivin train of the bridge I, an eddy-current or induced-current brake H which is mounted in the instance shown on an extension of shaft l3. The induced-current brake I1 is of well known form, comprising stationary and rotating magnetic members with windings which may be energized to establish a magnetic field mutual to the two members which field gives rise to torque-resisting, induced currents when relative rotation between the two members takes place. Since the details of induced-current or eddycurrent brakes (with and without conductor bars) are well known and form no part of this invention the same are not shown herein otherwise than diagrammatically and the term induced-current brake is used herein as descriptive of the general class of such devices.

As shown more clearly in Fig. 1, the primary supply leads l8, I9 and28 of motor II are joined with trolley conductors 2|, 22 and 23 mounted upon the bridge I, but not there shown. Extending from the operators cab ID in sliding electri-v cal contact with conductors 2|, 22 and 23 are primary supply connections 24, 25 and 26 which join as shown with main reversing contactors 21 and 28. The reversing contactors 21 and 28 are connected in turn through appropriate leads with power supply mains 29,38 and 3|. Mains 29, 38 and 3| in turn receive power, from trolley conductors 32, 33 and 34 attached to bridge I.

The admission and regulation of power supplied to motor is arranged to be controlled by a drum or other suitable type of controller designated generally by, the numeral 35'... Controller 4 35, in the particular instance shown, is provided with an off position and five forward and five reverse positions.

First forward position of controller Upon movement of controller 35, shown in off position in Fig. 1, to the first forward position, segments 36 and 31 engage their respective stationary contacts which are joined by leads 38, 39 and 48 with power main 3|, thus establishing a control-current supply connection for all of the segments of controller 35. At the same time segment 4| of controller 35 makes contact with its. respective stationary contact and thus through lead 42 provides a circuit which joins with winding 43 of contactor 28. The opposite terminal of winding 43 is joined in turn through lead 44, inter-locking contacts 45, and leads 46, 41 and 48 with supply main 29. Contactor 28 is thus caused to close, establishing current supply to the primary of motor H for forward driving of the same. The secondary of motor II is joined throughleads 49, 58 and 5| with trolley conductors 52, 53 and 54, and thence by sliding contact leads 55, 56 and 51, with a resistance grid, generally designated by the numeral 58. Under this condition the full resistance of the grid, 58 is included in the secondary circuit of the motor I and forward driving at the lowest speed of motor takes place.

Upon closure of main contactor 28, closureof auxiliary contacts 59 provides a connection from supply main 3| through lead 48, lead 68 and lead 6| with lead 62 which joins in turn with the winding of lock-in relay 64. The other end of the winding of relay 64 is joined in turn through lead 65 with lead 41 and thus throughlead 48 with supply main 29. The lock-in relay 64 is thus caused to close for a purpose hereafter described.

Movement of the controller 35 from "off" to the first forward position also bring segments 66,61 and 68 into engagement with their respective stationary contacts but theseengagemenrs are temporarily without effect for reasons which will be more fully explained.

In order that motor ll be permitted to freely rotate with the controller in the first forward position it is necessary that holding brake "be released and provision for such release is made through holding brake windings 69 and 18. The windings 69 and 18 are joined by a commonlead 1| with one output terminal of rectifier 12 and by leads 13 and 14, which extend through the contacts of normally open holding brake relay 15 and lead 16 to the opposite output terminal, of rectifier 12. The rectifier 12- is supplied with alternating current whenever, the primary of motor H is energized through leads 11 and 18 which extend to primary leads l9 and 28 of motor Leads 11 and 18 also serve to energize the winding of holding brake relay 15. Thus whenever the primary of motor is energized holding,

brake relay 15 is caused to close and the output of rectifier 12 is applied to the windings 69 and 18 to release the brake l2.

Second forward position of controller Upon movement of controller 35 from its first into its second forward, position segment 19 comes into engagement with its respective stationary contact thus extending a control current circuit through lead 88, the previously closed contacts of lock-in relay 64 and lead 8| to the. winding of a second step contactor 82, the opposite terminal of which winding is joined by lead 48 with supply main 23 This causes contactor 82 to close reducing the amount of resistance of grid 58 which is included in the secondary circuit of motor II. Motor II is thus caused to rotate with increased speed. H

Closure of contactor 82 also brings about closure of auxiliary lock-in contacts 83 which prepares a circuit to be subsequently utilized.

Third forward position of controller Upon movement of controller 35 from its second into its third forward position segment 84 is brought into engagement with its respective stationary contact establishing a current control circuit'extending from lead 40 through lead 85, auxiliary lock-in contact 03 and lead 85 to one terminal of the winding of a third step contactor 81. The opposite terminal of the winding of the third step contactor 81 is joined by lead 88 with lead 48 thus completing a circuit which causes third step contactor 81 to close, thus further reducing the amount of resistance of grid 58 which is included in the secondary circuit of motor II. At the same time auxiliary lock-in contacts 89 are caused to close thus preparing a circuit to be subsequently utilized.

Movement of the controller 35 into the third position also brings segment 90 into engagement with its respective stationary contact thus extending a control circuit through lead 9| to one terminal of the winding of a decelerating relay 52 the opposite terminal of which winding is joined by lead 93 with the lead 48. The relay 92 is thus caused to close for the purpose of preparing certain circuits to be subsequently utilized. In closing, relay 02 establishes for itself a maintaining circuit extending from lead 40 through segment 56, its respective stationary contact, lead 94, and maintaining contacts 95 to lead 96. This maintaining circuit causes the relay 92 to remain closed until such time as segment 56 departs from its respective stationary contact. This action of the relay 92 is preparatory, establishing conditions to be subsequently utilized in a manner later described.

Fourth forward position of the controller Upon movement of controller 35 from its third into its fourth forward position, segment 91 is brought into engagement with its respective stationary contact thus extending a control current circuit from lead 40 through lead 58, auxiliary contacts 80 and lead 09 to one terminal of the winding of a fourth step contactor I00. The opposite terminal of the winding of contactor I is joined by a lead IDI with the lead 48 thus completing a control circuit which causes contactor I00 to close further reducing the amount of resistance of the grid 58 which is included in the secondary circuit of motor II. Closure of contactor I00 causes closure of auxiliary lock-in contacts I02 for the purpose of preparing a circuit to be subsequently utilized.

Fifth forward position of the controller Upon movement of controller 35 from its fourth into its fifth forward position, segment I03 is brought into engagement with its respective stationary contact, establishing a control circuit extending from lead 40 through lead I04, lock-in contacts I02 and lead I05 to one terminal of the winding of a fifth step contactor I06. The opposite terminal of the winding of contactor I06 is joined by a lead I 07 with lead 48 thus completing a control circuit which causes contactor I06 to close thus further reducing the amount of recaused to operate at its maximum speed.

Deceleration from the forward driving positions of the controller As the controller 35 is moved from the fifth to the fourth forward position the control circuit of the fifth step contactor I06 is interrupted causing the latter to open thus increasing the resistance in the secondary circuit of motor II. Similarly when controller 35 is moved from the fourth to the third position the control current circuit of fourth step contactor I00 is interrupted causing the latter to open, further increasing the secondary resistance of the motor II. Thus a drifting deceleration of the bridge of the crane takes place upon shifting of the controller from its higher position.

In contrast movement of the controller 35 from the third to the second forward position causes segment 68, previously mentioned to come into engagement with its respective stationary contact thus establishing a control circuit extending from lead 50 through lead I08 to contacts I00 of decelerating relay 92 which contacts are found in closed position by reason of an action previously described. The control circuit in question then extends through lead IIO to the winding of an excitation relay II I and thence through lead I I2 to a connection with lead 48 thus completing a control circuit which causes excitation relay III to close.

The excitation current regulated by the relay I II is supplied by a transformer II3 the primary of which is connected through leads H4 and H5 with leads 40 and 4'! respectively. The secondary of transformer H3 is connected by leads H6 and II! to the input terminals of a rectifier Hi9. Rectified excitation current is drawn from the rectifier I59 through the lead II8 which extends to the contacts of excitation relay I II from whence it passes through lead I I9 resistance element I20 resistance element IZI and sliding contact I22 into trolley conductor I23. Trolley conductor I23 is electrically joined in turn by lead I24 with contacts I25 of power failure relay iZt. For reasons hereafter explained the contacts I25 are in closed position if power supply is being maintained and for this reason the circuit in question continues through lead I2? to the windings I 28 of the induced-current brake H. The excitation current circuit then extends from the windings I28 through lead I29 to trolley conductor I30 and thence through sliding contact I3i and lead I32 to the other output terminal of rectifier I49. Excitation current is thus supplied to the windings of eddy-current brake I'i in an amount determined by the resistance value of resistance elements I28 and I2I.

Movement of the controller 35 from the third to the second position also causes segment 84 to become disengaged from its respective stationary contact thus causing third step contactor 31 to open increasing further the amount of resistance of grid 58 contained in the secondary circuit of motor II. With power supplied to motor I I thus further reduced in amount and with a resisting torque now being exerted by eddy-current brake I'I, excited as above explained, a smooth but positive deceleration of the motor II and the crane driven thereby is brought about. As the rate of rotation of motor II decreases the resisting torque of induced-current brake I! also decreases in well known manner while at the same time,

since the use of brushes may be thus avoided and dependable operation secured after long years of operation without attention. This characteristic is important since normal operation of the apparatus will not reveal a derangement of this particular part, which may be called upon to act only infrequently and under conditions which are not expected. Hereafter for convenience the term generator is therefore used as meaning any suitable excitation source independent of the main power supply.

A further advantage of bridge motion energized excitation of brake I1 is that the apparatus stands ready to func ion whenever the crane is left unattended with power supply interrupted. In such a case if there be a derangement of the brake l2, any force tending to put the bridge into motion will be resisted so that the maximum speed which may be attained will be low enough so that stops at the ends of the runway will halt movement of the bridge I without damage. Where cranes are installed in the open, windstorms of unexpected severity sometimes occur and instances of very extensive damage have arisen where cranes have been put into motion by action of the wind at a time when the holding brake, such as brake I2, was not inproper functioning order. This hazard, as above explained, is avoided in apparatuses constructed in accordance with this invention by the self restraining action of the eddy-current brake i1, excited by current derived from alternator I53.

I claim:

1. In an electrically propelled apparatus having traction means, a drive system therefor comprising an electric motor; mechanical power transmitting means drivingly connecting said motor to said traction means; an induced current brake having a driven member connected to said motor in driven relationship thereto, a stationary member secured in braking relationship to said driven member, and an excitation winding for magnetizing said driving and driven members; an electric power supply circuit connected to said motor including control means adapted to be moved to and from an off position and an adjacent lower speed on zone and a more remote higher speed on zone, a preparatory decelerating relay comprising a winding for closing the same and lock-in contacts and brake energizing contacts closeable when said winding is energized, preparatory contacts closeaole by said control means only on movement of the same into the higher speed on zone of the same in circuit with the winding of said preparatory decelerating relay for actuating the same to closed position, maintaining contacts closeable by said control means throughout the on zones thereof in circuit with the winding of said preparatory decelerating relay and the lockin contacts of the same for maintaining said relay upon closure in closed position until said control means is moved to oiT position, braking contacts closeable by said control means only in the lower speed on zone thereof in circuit with the brake energizing contacts of said preparatory decelerating relay, and relay means having a winding connected in series with said braking contacts and said brake energizing contacts and having contacts in circuit with the excitation winding of said induced-current brake for supplying excitation current thereto when said brakeing contacts and said brake energizing contacts both are closed.

2. In an electrically propelled apparatus having traction means, a drive system therefor comprising an electric motor; mechanical power transmitting means drivingly connecting said motor to said traction means; an induced-current brake having a driven member connected to said motor in driven relationship thereto, a stationary member secured in braking relationship to said driven member, and an excitation winding for magnetizing said driving and driven members; an electric power supply circuit connected to said motor including control means adapted to be moved to and from open and closed positions to apply and interrupt the supply of power to said motor; a normal excitation supply circuit connected to the winding of said induced-current brake including control means adapted to be shifted to excite and terminate excitation of said brake; interlockingmeans cooperatively associated with the power control means for said motor and with the excitation current control means for said brake operative to cause said brake to be excited only on movement of said power control means for said motor from closed toward open position; and an emergency excitation source for said induced-current'brake, an emergency excitation circuit joining said source and the winding of said brake, and means rendered operative upon failure of the electric power supply for said motor for causing said emergency excitation circuit to become closed.

3. The combination with an apparatus in accordance with claim 1 in which there is provided an electro-magnetically released normally set friction holding brake mounted in braking relation to said motor, a normal holding brake circuit joining said holding brake to the electric power supply for said motor operative to excite and release said brake when power is supplied to said motor, and in which the emergency excitation source includes an emergency excitation source for said holding brake and comprises a generator mechanically connected in driven relationship with said motor, a power failure relay means for said induced-current brake and said holding brake, an excitation circuit joining said holding brake and said induced-current brake to said generator through said power failure relay means, and an actuator circuit for said power failure relay means joining the same to the power supply for said motor operative upon failure of said motor power supply to cause said power failure relay means to close said emergency excitation circuit to continue excitation of said induced-current brake and to retain said holding brake in released position so long as the output of said generator is sufficient.

4:. The combination with an apparatus in accordance with claim 2 in which there is provided an electro-1nagnetically released normally set friction holding brake mounted in braking relation to said motor, a normal holding brake cir cuit joining said holding brake to the electric power supply for said motor operative to excite and release said brake when power is supplied to motor, and in which the emergency excitation source for said induced-current brake in cludes an emergency excitation source for said holding brake and comprises a generator mechanically connected in driven relationship with motor, a power failure relay means for said induced-current brake and said holding brake, an excitation circuit joining said holding brake and said induced-current brake to said generator through said power failure relay means, and an actuator circuit for said power failure relay means joining the same to the power supply for said motor operative upon failure-of said motor power supply to cause said power failure relay means to close said emergency excitation circuit to continue excitation of said induced-current brake and to retain said holding brake in released p sition so long as the output of said generator is sufficient, said power failure relay means including contacts operative to open the normal excitation circuits of said induced-current brake and said holdin brake upon closure of said emergency excitation circuit.

5. The combination with an apparatus in accordance with claim 2 in which there is provided an electro-magnetically released normally set friction holding brake mounted in braking relation to said motor, a normal holding brake circuit Joining said holding brake to the electric power supply for said motor operative to excite and release said brake when power is supplied to said motor, and in which the emergency excitation source for said induced-current brake includes an emergency excitation source for said holding brake and comprises a generator mechanically connected in driven relationship with said motor, a power failure relay means for said inducedcurrent brake and said holdingbrake, an excitation circuit joining said holding brake and said induced-current brake to said generator through said power failure relay means, and an actuator circuit for said power failure relay means joining the same to the power supply for said motor operative upon failure of said motor power supply to cause said power failure relay means to close said emergency excitation circuit to continue excitation of said induced-current brake and to retain said holding brake in released position so long as the output of said generator is sufilcient, said power failure relay means including contacts operative to open the normal excitation circuits of said induced-current brake and said holding brake in advance of closure of said emergency excitation circuit and transfer contacts operative to shunt said holding brake to delay release of the same durin the interval between the opening of the normal excitation circuit for said holding brake and the closing of said emergency excitation circuit.

6. In a driving and braking circuit for electrically propelled apparatus the combination comprising an electric propelling motor; an induced current brake having a driven member connected to said motor in driven relation thereto, a stationary member secured in braking relation to said driven member and an excitation winding for establishinga field mutual to said driving and driven members; an electric power supply circuit including a controller for said motor, said controller having an off position and positions for lower and higher speed driving of said motor; and an excitation current source for said excitation winding including switching means rendered active to complete a circuit between said excitation current source and excitation winding when said controller is in a lower speed position and said motor has been supplied theretofore with power to drive the same at a speed higher than said lower speed.

7. In a driving and brakingcircuit for electrically propelled apparatus the combination comprising an electric propelling motor; an induced current brake having a driven member connected to said motor in driven relation thereto, a stationary member secured in braking relation to said driven member and an excitation winding for establishing a field mutual to said driving and driven members; an electric power supply circuit including a controller for said motor, said controller having an off position and a plurality of driving positions for driving said motor at different speeds; and an excitation current source for said excitation windingincluding switching means rendered active to complete a circuit between said excitation current source and said excitation windin when said controller is placed in one of its said driving positions having been first moved from its said off position to a predetermined activating position.

8. In a driving and braking circuit for electrically propelled apparatus the combination comprising an electric propelling motor; an induced current brake having a driven member connected to said motor in driven relation thereto, a stationary member secured in braking relation to said driven member and an excitation winding for establishing a field mutual to said driving and driven members; an electric power supply circuit including a controller for said motor, said controller having an off position and a plurality of driving positions for driving said motor at different speeds; and an excitation current source for said excitation winding including switching means rendered active to complete the circuit between said excitation current source and said excitation winding when said controller is placed in a predetermined driving position after first being moved through a driving position more remote from said off position,

9. In a driving and braking circuit for electrically propelled apparatus the combination comprising an electric propelling motor; an induced current brake having a driven member connected to said motor in driven relation thereto, a stationary member secured in braking relation to said driven member and an excitation winding for establishing a field mutual to said driving and driven members; an electric power supply circuit including a controller for said motor, said controller having an off position, a plurality of driving positions and a retarding position; and an excitation current source rendered active to complete a circuit between said excitation current source and said excitation winding when said controller has been moved first from its off position to one of its said driving positions and then to its said retarding position.

References Cited in the file of this patent UNITED STATES PATENTS

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