US2403125A - Control system - Google Patents

Description

CONTROL SYSTEM Filed Oct. 4, 1944 2 Sheets-.Sheet 1 4X2 Di..

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w Y UVU W U 511525 la s The hoisting motor HM is illustrated as a three-phase single speed alternating current motor comprising a stator having windings il, i2 and i3 and a rotor Il. The stator windings may be connected to a suitable alternating current supply represented by the conductors Ll, L2 and L3 (Fig. 2) by means oi an up direction switch U and a down direction switch D and a car running relay M. Although a motor of this character is called a constant speed motor, it is well known that its speed will vary somewhat in accordance with the loading and direction of operation of the car.

A car switch CS is mounted in the car for starting it and for causing it to be stopped at the various floors. Rotation of the switch in a clockwise direction will energize the down direction switch D to connect the motor windings to move the car downwardly, and rotation of the switch in counterclockwise direction will energize the up direction switch to connect the motor windings to move the car upwardly. Centering the car switch will cause its stopping system to stop the car at the next floor.

The energy for operating the direction switches, the stopping system, etc., may he supplied through. a pair of conductors L-i-l and L-l which are connected for energization through a full-wave rectifier il to the supply conductors Li and L3.

The means for stopping the car at the next oor after the car switch CS is centered 'for a stop comprises an inductor relay S provided with normally closed contacts in the holding circuit or the direction switches U and D. The inductor relay S is mounted on the top of the car (Fig. l) and usually at one side thereoi' in position to closely adjacent to an up inductor plate UP and a down inductor plate DP at each ilocr when the car moves up and down in the hatch way. energizing coil and a normally closed pair ol stopping contacts Si. The inductor plates are constructed ci magnetic material and are mounted in the hatchway in a position to co operate with the relay and open its contacts when its coil is in an' energized condition as the car approaches the inductor plates. We have shown inductor plates for only one floor, hut it is to be understood that similar inductor plates will be mounted in the hatchway at each floor.

When the car switch CS is closed, one of the direction switches is energized i'lrst by a circuit through the car switch and next by a self-holding circuit through its own self-holding contacts and the normally closed contacts of the inductor relay. The center point of the car switch is con nected to energize the inductor relay when the car switch is in its central position, so that the car will stop at the next floor after the switch CS is centered. Hence, when the car switch is centered for a stop, the inductor relay is energized, and, when it cornes opposite the inductor plates at the next fioor, it is operated to open its contacts in the holding circuit and deenergizes the direction switch. The deenergized direction switch opens the circuit for the hoisting motor and the brake.

When the motor circuit and the brake circuit are opened at the same time; the motor is deenergized'immediately and the brake is applied immediately to stop the car. However, the car will driftl or coast a short distance after the brake is applied and this amount of drift will depend upon the loading and direction of operation of the car. Under normal conditions the The inductor relay is provided with an dll car will stop approximately level with the iioor,

,ibut at other times, it may overrun or underrun the iioor. In general, with the normal speed of the car designed for, say, feet perminute, the normal drift of the car will be approximately seven inches for a normal stop, and the automatic stopping means for the car, such as the inductor plates, will be set at such a point in the hatchway as to cut off the motor and the brake when the car is seven inches from the floor level.

However, when the car is moving upwardly with a full load and is brought to a stop, it may drift only three inches and thus stop four inches short of being level with the floor. On the other hand, with the same load down. the car may drift `as much as eleven inches thus overrunning the floor as much as four inches.

ln our invention, we cause the car to stop approximately level with the floor under all conditions by providing a means for delaying the starting movement of the brake plunger after the motor circuit and the brake circuit have been opened, for a length of time proportioned to the load on the motor (produced by the load on the car and its direction of operation) so that the brake will be applied to the motor at a point distant from the door which will cause the car to drift into and stop level with the :door regardless o its load and direction of operation.

The means for delaying the starting movement oi the hralre plunger after the power is cut off the hralre coil comprises means for soaking the brake coil above the saturation point of its core or magnetic circuit, by attaching a low discharge resistance circuit to the brake coil, by attaching a high discharge .resistance circuit l" to the hralre coil and by providing means lor controlling the resistance value ci the low discharge resistance circuit accordance with the load on. the hoisting motor.

The soaking of the bralrc coil is obtained hy applying large enough niunher ol ampere turns to the "oralre coil, to run the flip: up to a raamt mum value considerably alcove the saturation point ci its core or magnetic circuit.

li desired, soule other point in saturation may be used instead oi that indicated by scali-ing, just so there is always a constant pointJ :from which the delay may he started.

The low discharge resistance circuit K is connected in a circulatory circuit with the brake coil BC by the contacts M5 of the car running relay lvl, so that it will he connected with the bralre coil only during stopping operations and will` be disconnected at ani7 time the hoisting motor is energized to run the carn The resistance circuit K is divided into a plurality of resistors Rl, im, Rt and R5.

The high resistance discharge circuit P is permanently connected in circulatory relation with the brake coil BC and is never disconnected at any time. IlThis circuit includes the resistor R6. The high discharge resistor' circuit P is provided to give a slight time delay in the discharge of the brake coil after its power is out olf until the contacts M5 close to connect the low discharge resistance circuit K to the brake coil IBC.

The purpose of the low discharge resistance circuit K is to delay the deenergization of the brake coil after the power to the brake coil circuit is broken and thus cause a delay in the starting of the brake plunger to apply the brake after the power is cut off the hoisting motor and the brake coil. The circuit K does not give an and as the voltage produced by the tachometer builds up in accordance with the load in the car. the load measuring relay IH is operated by the circuit L+2, IH, QI, L-2. The energized relay IH closes its contacts IHI, thus energizing the resistor relay IX by the circuit L+I, FI, iX, IHI, L-I. The energized relay IX closes its self-holding contacts IX! so that it will be locked in until the end of the next braking operation and also opens its contacts I X I, thereby inserting the resistor section R2 in the low discharge resistance circuit K. Of course this resistor RI has no effect on this circuit at present because the contacts M5 are open,

When the relay IH was energized it also closed I its contacts IH2, thereby preparing relay 2H for energization. It will be assumed now that the load in the car is suicient to increase the voltage output of thetachometer G to the point where it also energizes the load responsive relay 2H by the circuit L+2, IHZ, 2H, Q2, lil-3i. The enen1 gized relay 2H closes its contacts 2H I and 2K2. The closed contacts 2H2 prepare the relai` ilH for operation if and when the voltage produced by the tachometer is sufllcient to operate it. The closed contacts IHI energize the resistor relay 2X by the circuit L-ti, Fi, Elli, l-i. The energized relay 2X closes self-holding coml tacts 2X2 and opens its contacts thus serting the resistor R3 in the low discharge sistance circuit K.

By the foregoing operation it ecco holt' movement from one stop to how the resistor sections i brake coil circuit are cet up next stop is made in accor" of the hoisting motor on the car and its directlol'i. of or ic start of the car movement. 'Llf'his op place rather rapidly and, w the load timing' relay T lio 'L that now, at the end ci to times out and opens its co to the tachomete-r armato the tachometer armature il l in further measuring voltage ior op responsive relays, also the heating current is discontinued, tia-r s] stantially independent of heating".

When the tachometer G is deeuerggizcrl lily i opening of the contacts T2, that reduces 'the tro i age in the load responsive relays Trl to they return to their normal positions ready iol" oor. This operation energizes the stop inductor relay S by the circuit L+I, S. CS2, L-i. The energized inductor relay S is now ready for opera tion to stop the car at the next floor. As the car moves in to the next floor, it moves the inductor relay S into close relationwitli the down stopping plate DP and the influence of that plate causes the inductor relai7 to open its contacts Pi, thereby deenergizing the car running relay M and the down direction switch D to stop the car. The deenergized relay M opens its contacts MT, thereby deenergizing the brake timing relay F n' the low resistance ops level ivi and this relay will time out, after the expiration of one-half second` for the purpose of limiting the delay in the start of the braking action to that period and for then returning the resistor relays to their normal condition.

The deenergized relay D opens its contacts DI to D6. The opening of the contacts DI and D2 deenergizes the hoisting motor HM, and the opening of the contacts DI deenergizes the circuit to the brake coil BC. Inasmuch as the brake coil is soaked or oval-saturated, the opening of the contacts DI does not cause the brake plunger I to start movement immediately. The reason for this is that the opening of the circuit to the brake 4coil brings the circulatory circuit P into operation. The resistor circuit P insures the giving of a slight time delay in the discharge of the brake coil until the contacts M5 close and conneet the low discharge resistor K to the broke coil lEiC.

It `will he recalled that the resistors R2 and R3 have been inserted in the low discharge resistance circuit K in accordance with the loading and direction of operation ci? the cor at the start ci' this movement. Therefore, the braise coil now discharges through the IioW rests to stai-'t its brake applying fr the expiration oi o length o:

the stort licor when the discharge or the or l ly, the "pl t apply th enc` the sorir ion two seconds of its me Assuming now that the period or the or-nire timi.,- f "ce crimine' resistor relays i. mi d there to normal condition for the neA z breitling operation.

Also, the closed contacts l? 'ii energize the load, timing" relay T to propere it for operation. during the next storting action of 'the car.

If a heavier load, say full load, had entere@r the car at the second ooi, then the speed. would have heen .higher and the tachonicter generator voltage would have been higher and all four relays iH to 4H would have been energized. Under these conditions resistor relays i to Illi'. would have picked up and locked in thus insert ing a` high resistance in the low discharge ein cuit connected to the brake coil. The brake would set quickly under these conditions and the car, due to its load, would slide the correct distance through the brake to stop the cer with its platform at floor level.

If the car had been empty, the motor would Ihave had to lift part of the weight of the coun terweight, the speed would have been low, and none or possibly only IH of relays IH to BH would have closed thereby connecting a small amount of resistance in the low discharge resistance ciri 9 l cuit. The small amount of resistance would cause the brake coil to become deenergized more slowly, so the car would be closer to the iloor when the brake nnally does engage, and there would be less distance available to stop the car in before :door level. However, when empty, the car stops quicker and a level stop would again occur.

The other relays,` H and X, will give interino` diate brake application time corresponding to intermediate loads.

From the aoove it will be seen thatwe have provided a simple and effective meansfor measuring the load on a hoisting motor caused by the load in the car and its direction of operation and have used this loading or resultant speed for measuring the time or the distance at which a brake plunger should he released to effect the stopping oi a car level with the fioor.

'it will also loe apparent that the apparatus is simple and eiicient in operation and that the tachometer and parts responsive thereto provide a generous range oi voltage for operating the measuring relays so that adjustment oi the relay piclnup will not loe critical nor seriously atfected by ambient temperature variations. though We have illustrated and described only one speciiic embodiment of our invention. it is to be understood that changes therein and modi" @cations thereof may be made without departing 'from the spirit and scope ofthe invention.

We claim as our invention:

l. n an elevator system for operating a car past a floor, a motor for operating the car, a brake for the motor, said brake having a spring applying means and a brake coil releasing means, circuits for the motor and the brake coil, con= trol means for energizing the circuits for the motor and the brake coil to start the car and l0 control means to stop the car for connecting the low discharge circuit to the brake coil and keeping it connected thereto during the stopping operation, whereby the deenergization of ythe brake coil will be delayed to cause application of the brake at a point in the car travel which willoause the car to stop approximately level with the iloor.

3. In an elevator system for operating a car past a floor, a motor for operating the car, a brake device for decelerating the car to a stop, said device having a spring-applied brake and a brake coil for moving the brake to its oil Vposition and for releasing it to its on position, circuits for the motor and the brake coil, control means ior energizing the circuits for the motor and the brake coil to start the car, a discharge resistance circuit associated with the brake coil for delaying the deencrgization ci the brake coil after the brake coil circuit is decnergized, means responsive to the speed of'the hoisting motor for a predetermined 'time after the car starts for adjusting the value oi the resistance in the discharge resistance circuit to thereby prepare the discharge circuit to delay the deenergization oi the braise coil after the brake coil circuit is de- @neigized for the next stop for a length of time commensurate with the load on the car and its direction of operation, and a stopping means for deenerglzing the motor and brake coil circuits and for connecting the discharge circuit to the brake coil when the car arrives at a predeter- V mined distance from the oor to cause the car for deenergizing said circuits when the car is a predetermined distance from the floor to stop the car thereat, a low discharge resistance cir cuit for the brake coil, means responsive to the speed of the motor for adjusting the value of the resistance in the low discharge resistance circuit in accordance with the load on the car and its direction of operation, and means re-n sponsive to operation of the control means to stop the car for connecting the low discharge circuit to the brake coil and keeping it connected thereto during the stopping operation, whereby the deenergization of the brake coil Vwill he delayed to cause application of the brake at a point in the car travel which will cause the car to stop approximately level with the floor.

2. In an elevator systemfor operating a. car past a licor, a. motor for operating the car, a. brake for the motor, said brake having a. spring applying means and a brake coil releasing means, circuits for the motor and the brake coil, control means for energizing the circuits for the motor and the brake coil to start the car and i'or deenergizlng said circuits when the car is at a predetermined distance from the floor to stop kthe car thereat, a. discharge resistance circuit for the brake coil, a tachometer connected for operation Hny the motor, said tachometer having a series field winding, a sell-excited shunt neld winding and a separately excited shunt field winding to cause it to give a. greater than oneto-one measure of the load on the hoisting motor,

meansresponsive to the operation of the tachometer for adjusting the value of the resistance in the discharge resistance circuit in accordancev with the load on the car and its direction of operation, and means responsive to operation ofthe `of the car, means the car,

cuits for the motor and the brake coil, control means for energizing the circuits for the motor and the brake coil to start the car, a discharge resistance circuit associated with the brake coil for delaying the deenergization of the brake coil after the brake coil circuit is deenergized, e, speed responsive device connected for operation by the motor for measuring the speed of the motor as it is ailected by the load on the car and its direction of operation during the starting action responsive to operation of the speed device for adjusting the value of the resistance in the discharge resistance circuit and thereby 'prepare the discharge circuit to delay the deenergization of the brake coil after the brake coil circuit is deenergized for the next stop for a length of time commensurate with the load on the car and its direction of operation, and a. stopping means for deenergizing the motor and brake coil' circuits and for connecting the low discharge circuit to the brake coil when the car arrives at a predetermined distance from the floor to cause the car to stop the'reat.

5; In an 'elevator system for operating a car past a. floor, a motor for operating they car, a brake device for decelerating the car to a stop, said device having a spring-applied brake and a plunger with a. brake coil for moving the brake to its off position, circuits for the motor and the brake coil, control means for energizing the circuits for the motor and the brake coil to start a discharge resistance circuit for the brake coil, a tachometer connected for opera.- tion by the motor for measuring the speedvof the motor as it is a ected by the load on the a motor for operating the car, a-

car and its direction of operation. means responsive to operation of the tachometer for ad- ,iusting the value of the resistance in the discharge resistance circuit to accord with the load on the car and its direction of operation for preparing the coil to delay its release of the plunger and thereby the application of the brake for a length of time sufficient to cause the car to stop approximately level with the floor when the next stop is made, and a stopping means for deenergizing the motor and brake coil circuit and for connecting the low discharge resistance circuit prepared by the adjusting means to the brake coil when the car arrives at a predetermined distance from the iioor to` cause the car to stop thereat.

6. In an elevator system for operating a car past a floor, a, motor for operating the car, a brake device for decelerating the car to a stop, said device having a spring-appliedv brake and a plunger with a brake coll for moving the brake to lts 01T position, circuits for the motor and the brake coil, control means for energizing the cir cuits for the motor and the brake coil to start the car, a discharge resistance circuit for the brake coil, a tachometer connected for operation by the motor for measuring the speed of the motor as it is affected by the load on the car and its direction of operation, a load timing device for rendering the tachometer effective for a predetermined length oi' time when the car is started, means responsive to operation of the tachometer for adjusting the value of the resistance in the discharge resistance circuit to accord with the load on the car and its direction of operation for preparing the coil to delay its release of the plunger and thereby the application o1' the brake for a length of time sufficient to cause the car to stop approximately level with the :door when the next stop is made, and a stopping means for deenergizing the motor and brake coil circuits and for connecting the low discharge circuit to the brake coil when the car arrives at a predetermined distance from the floor to cause the car to stop thereat.

7. In an elevator system for operating a car past a iloor, a motor for operating the car, a brake device for decelerating the car to a stop, said device having a spring-applied brake and a plunger with a brake coil for moving the brake to its of! position, circuits for the motor and the brake coil, control means for energizing the circuits for the motor and the brake coil to start the car, a stopping means for deenergizing the motor and brake coil circuits and when the car arrives at a predetermined distance from the floor in making a stop, a discharge resistance circuit for the brake coil, a tachometer connected for operation by the hoisting motor, having a series iield winding, a self-excited shunt field winding and a separately excited shunt iield winding to cause it to give a greater than one-to-one measure of the load on the hoisting motor, means responsive to operation of the tachometer for varying the value of the resistance in accordance with the load on the car and its direction of operation, whereby the action of the coil will delay the release of the plung er for a length of time suiilcient to cause the car to stop approximately level with the floor, connecting the low discharge circuit to the brake coil, a load timing device responsive to starting and stopping of the ear for limiting the operation of the tachometer tc a predetermined length of time.

8. In an elevator system for operating a car past a licor, a motor for operating the car, a brake device for decelerating the car to a stop, said device having a spring-applied brake and a plunger with a brake coil for moving the brake to its oil position, circuits for the motor and the brake coil, control means for energizing the motor and brake coil circuits to start the car and for deenergizing the said coil circuits to cause the car to stop at the floor, a discharge resistance circuit for the brake coil, a tachometer connected for operation by the hoisting motor, means responsive to operation of the tachometer for adjusting the value of the resistance in the discharge circuit to accord with the load on the car and its direction of operation for delaying the release of the plunger by the coil for a length of time sufiicient to cause the car to stop approximately level with the floor, means responsive to operation of the control means in stopping lthe car for connecting the low discharge circuit to the brake coil, and a load timing device responsive to starting and stopping of the car for limiting the operation of the tachometer to a predetermined length of time.

' 9, In an elevator system for operating a car past a oor, a motor for operating the car, a brake device for decelerating the car to a stop, said device having a spring-applied brake and a plunger with a brake coil for moving the brake to its oil position, circuits for the motor and the brake coil, control means for energizing the circuits for the motor and the brake coil to start the car, a stopping means for deenergizing the motor and brake coil circuits when the car arrives at a predetermined distance from the door in making a stop, a discharge resistance circuit for the brake coil, a tachometer connected for operation by the hoisting motor, having a series iield winding, a self-excited shunt eld winding and a separately excited shunt eld winding to cause it to give a greater than one-to-one measure of the load on the hoisting motor, means responsive to operation of the tachometer for varying the value of the resistance in the discharge resistance circuit to accord with the load on the car and its direction of operation, whereby the action of the coil will delay the release of the plunger for a length oi.' time suiiicient to cause the car to stop approximately level with the floor, means responsive to operation of the stopping means for connecting the low discharge circuit to the brake coll, and a load timing device responsive to starting. and stopping of the car for limiting the eifective operation of the tachometer to a predetermined length of time.

10. In an elevator system for operating a car past a floor, a motor for operating the car, a brake device for decelerating the car to a stop, said device having a spring-applied brake and a plunger with a llorake coil for moving the brake to its off position, circuits for the motor and the brake coil, control means for energizing the circuits for the motor and the brake coil to start the car, a stopping means for deenergizing the motor and lbrake coil circuits when the car arriY es at a predeter mined distance from the floor in making a stop, a low discharge resistance circuit for the brake coil, a tachometer connected for operation by the hoisting motor, a plurality of resistors associated with the low discharge circuit, means responsive to operation of the tachometer for inserting a nulmber of resistors corresponding to the output of the tachometer in the low discharge circuit for delaying the release of the plunger after the brake circuit is deenergized for a length of time commensurate with the load on the car and its direction of operation, means responsive to operation of the stopping means for connecting the low discharge circuit asconditioned by the resistors to the brake coil, and a load timing device responsive to starting and stopping of the car for limiting the operation of the tachometer to a predetermined length of time when the car starts operating.

1l. In an elevator system for operating a car past a floor, a motor for operating the car, a

brake device for decelerating the car to a stop,

said device having a spring-applied brake and a plunger with a brake coil for moving the brake to its off position, circuits for the motor and the brake coil, a switch for energizing the circuits for the motor and the brake coil to start the car, a stopping means for deenergizing the motor and brake coil circuits to stop the car, a discharge resistance circuit for the brake coil, a tachometer connected for operation by the hoisting motor, a plurality of measuring relays connected for ac.s

cumulative operation in accordance with the output ci 'the tachometer, a plurality of resistors associated with the low discharge circuit, one for each measuring relay, 4:leans responsive to operation of the measuring relays for inserting their resistors in the low discharge circuit for delaying the release of the plunger after the brake circuit is deenergized for a length of time commensurate with the load on the car and its direction of opere ation, means responsive to operation of the stopping means for connecting the low discharge circuit as conditioned by the resistors to the plunger with a brake coil for moving the brake to its oi position, circuits for the motor and the brake coil, control means for energizing the circuits for the motor and the brake coil to start the car, a stopping means for. deenergizing the motor and .brake coil circuits when the car arrives at a predetermined distance from the iloor in making a stop, a discharge resistance circuit forthe brake coil, a tachometer connected for operation by the hoisting motor, a plurality of measuring relays connected for accumulative operation in accordance with the output of the tachometer, a plurality of resistors associated with the low discharge circuit, one for each measuring relay, means responsive to operation of the measuring relays for inserting their corresponding resistors in the low discharge circuitfor delaying the release of theplungcr after the brake circuit is deenergized for a length of time commensurate with the load on the car and its direction of operation, means responsive to operation of the stopping means for connecting the 10W discharge circuit as conditioned by the resistors to the brake coil, and a load timing device responsive to starting and stopping of the car for limiting the operation of the tachorneter to a predetermined time. l

13. In an elevator system for operating a, car past a floor, a motor for operating the car, a brake device for decelerating the car to a stop, said device having a spring-applied brake and a plunger with a brake coil capable of energizing its magnetic circuit to approximately its saturation point for moving the brake to its oi position. circuits for the motor and the brake' coil, a switch for energizing the circuits for the motor and the brake coil to start the car, a stopping means for deenergizing the motor and brake coil circuits when the car arrives at a predetermined distance from the oor in making a, stop, a low discharge resistance circuit for the brake coil, a high discharge resistance circuit permanently connected tol the brake coil, a tachometer connected for 0D- eration by the hoisting motor, said tachometer having a series eld winding, a self-excited shunt field Winding and a separately excited shunt eld winding to cause it to give a greater than one-to- Y' one measure of the load on the hoisting motor, a plurality of measuring relays connected for accumulative operation in accordance with the outu put of the tachometcr, a plurality of resistors associated with the low discharge circuit, one for each measuring relay, means responsive to operation of the measuring relays for inserting their resistors in the low discharge circuit for delaying the release of the plunger after the brake circuit is deenergized for a length of time commensurate with the load on the car and its direction of operation, means responsive to operation of the stopping means for connecting the low discharge circuit as conditioned by the resistors to the brake coil, and a load timing device responsive to starting and stopping of the car for limiting the oper ation of the tachometer to, a predetermined period when the car starts operating.

14. In an elevator system for operating a car past a floor, a motor for operating the car, a brake device for decelerating the car to a stop, said device having a spring applied brake and a plunger with a brake coil capable of energizing its mag-` netic circuit to approximately its saturation point for moving the brake to its off position, circuits for the motor and the brake coil, a switch for energizing the circuits for the motor and the brake coil to start the car, a. stopping means for deenergizing the motor and brake coil circuits when the car arrives at a predetermined distance from the floor in making a stop, a low discharge resistance circuit for the brake coil, a high discharge resistance circuit permanently connected to the brake coil for delaying the deenergization of that coil when a stop is being made until the low discharge resistance circuit is connected to the brake coil, a tachometer connected for operation by the hoisting motor, a. plurality of measuring relays connected for accumulativecperation in accordance with the output of the tachometer, a plurality of resistors associated with the low discharge circuit, one for each measuring relay, a. plurality of resistor relays provided with selfholding means, one of said relays for each measuring relay and responsive to operation of thatmeasuring relay for inserting the resistor corresponding to that measuring relay in the low discharge circuit, whereby the value of the resistance in the low discharge circuit will delay the release of the plunger after the brake circuit is deenergized for a length of time commensurate with the load on the car and its direction of operation, means responsive to operation of the stopping means for connecting the low discharge circuit as conditioned by the resistors to the brake coil, and a load timing device responsive to starting and stopping ofthe car Afor limiting the operation of the tachometer to a predetermined period when the car starts operating.

15. In an elevator system for operatinga, car past a floor, a motor for operating the car, a

brake device for decelerating the car to a stop, said device having a spring-applied brake and a plunger with a brake coil for moving the brake to its off position, circuits for the motor and the brake coil, a switch for energizing the circuits for the motor and the brake coil to start the car, a stopping means for deenergizing the motor and brake coil circuits when the car arrives at a predetermined distance from `the hoor in making a stop, a low discharge resistance circuit for the brake coil, a high discharge resistance circuit fermanently connected to the brake coil for deaying the deenergization of that coil when a stop is being made until the low discharge relsistance circuit is connected to the brake coil, a tachometer connected for operation by the hoisting motor, a plurality of measuring relays con nected for accumulative operation in accordance with the output of the tachometer, a plurality of resistors associated with the low discharge circuit, one for each measuring relay, a plurality of resistor relays provided with self-holding means, one of said relays for each measuring relay and responsive to operation of that measuring relay for inserting the resistor corresponding to that measuring relay in the low discharge circuit, whereby the value of the resistance in the low discharge circuit will delay' the release of the plunger after the brake circuit is deenergized for a length of time commensurate with the load on the car and its direction of operation, means responsive to operation of the stopping means for connecting the low discharge circuit as conditioned by the resistors to the brake coil, and a brake timing relay for returning the resistor relays to their normal condition at the end of a predetermined time after the brake circuit is deenergized.

16. In an elevator system for operating a car past a door, a motor for operating the car, a brake device for decelerating the car to a stop, said device having a spring-applied brake and a plunger with a brake coil capable of energizing its magnetic circuit to approximately its saturation point for moving the brake to its off position, circuits 16 for the motor and the brake coil, a switch for energizing the circuits for the motor and the brake coil to start the car, a stopping means for deenergizing the motor and brake coil circuits when the car arrives at a predetermined distance from the floor in making a stop, a low discharge resistance circuit for the brake coil, a high discharge resistance circuit permanently connected to the brake coil for delaying the deenergization of that coil when a stop is being made until the low discharge resistance circuit is connected to the brake coil, a tachometer connected for operation by the hoisting motor, said tachometer hav ing a series field winding, a self-excited shunt field winding and a separately excited shunt ileld winding to cause it to give a greater than oneto-one measure of the load on the hoisting motor, a plurality of measuring relays connected for accumulative operation in accordance with the cutput of the tachometer, a plurality of resistors associated with the low discharge circuit, one for each measuring relay, a plurality of resistor relays provided with self-holding means, one of said relays for each measuring relay and responsive to operation of that measuring relay for inserting the resistor corresponding to that measuring relay in the low discharge circuit, whereby the value of the resistance in the low discharge circuit will delay the release of the plunger after the brake circuit is deenergized for a length of time commensurate with the load on the car and its direction of operation, means responsive to operation of the stopping means for connecting the low discharge circuit as conditioned by the resistors to the brake coil, a load timing device responsive to starting and stopping of the car for limiting the operation of the tachometer to a predetermined period When the car starts operating, and a brake timing relay for returning the resistor relays to their normal condition at the end of a predetermined time after the brake circuit is deenergized. y

DANILO SANTINI. EDWARD H. HEATH.

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