US1963484A - Elevator control system - Google Patents

Description

Jane 19, 1934. B DE 1,963,484

ELEVATOR CONTROL SYSTEM Filed March 2, 1933 4 Sheets-Sheet l IN VEN TOR By W74 iZATTORNEY.

June 19, 1934. H, BORDEN 1,963,484 ELEVATOR CONTROL SYSTEM Filed March 2, 1935 4 Sheets-Sheet 2 v L? asv T T ,Sc

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IN VEN TOR.

* T ATTORNEY.

I June 19, 1934. H, BQRDEN I 1,963,484

ELEVATOR CONTROL SYSTEM Filed March 2, 1933 4 Sheets-Sheet 3 I I J I J52 I V 13 Z2 INVENTOR- 7 wxew ATTORNEY.

June 19, 1934. J BORDEN 1,963,484

ELEVATOR CONTROL SYSTEM Filed March 2, 1933 4 Sheets-$heet 4 I 23 I? .29 +Laz [I :3 52 I 18 0 I 1 I I i A} q Q q n1 I l] 45 I I I I I 55a l 22 21 1 LIE ATTORNEY.

Patented June 19, 1934 I ELEVATOR CONTROL SYSTEM Joseph H. Borden, Elkins Park, Pa.

Application March 2, 1933, Serial No. 659,324

A 20 Claims.

My invention relates to methods of and apparatus for controlling elevators and the like, and.

particularly, for high speed elevator systems.

In accordance with one aspect of my invention, as an elevator car, or equivalent, approaches a 'pre-selected landing or floor, the energy to the car motor is progressively reduced at points whose distances from the desired landing vary in accordance with speed of approach of the car to the landing to ensure rapid and smooth deceleration of the car and to bring the car to a stop level with the floor, without need for re-leveling.

Further in accordance with my invention, the aforesaid reductions are controlled by spaced elements, whose positions correspond to the position of the car, and which successively cooperate with a controlled member whose position is determined by the speed of the car, or more specifically, the speed of the car and the concurrent load of the car motor.

In accordance with another aspect of'my invention, vanes, or equivalent, preferably carried by a rotatable drum in spaced relation are moved by the car to intercept light to a photo-cell, or

. the like, the resulting and successive change of current in the photo-cell circuit effecting successivereductions of the energy supplied to the car motor; more specifically, the photo-cell is carried by the above controlled member in order 3 that the speed, or load and speed, of the car shall vary the relative positions of the vanes and the photo-cell for any given position of the car.

My invention further resides in the system and arrangement hereinafter described and claimed.

Fig. 1 diagrammatically illustrates an elevator system embodying the invention.

Fig. 1a is a modified form of motor connection.

Fig. 2 is a simplified wiring diagram of the system of Fig. 1.

Fig. 3 is a detail view on enlarged scale of a control device included in the system of Fig. 1.

Fig. 4 is an end view of Fig. 3.

Fig. 5 is a detail view on enlarged scale of the optical system of the control device of Fig. 3.

Fig. 6 illustrates a control arrangement appli cable to the system of Fig. 1.

Referring to Fig. 1 which is exemplary of a typical elevator system embodying the invention, the motor 1 for raising and lowering the car 2 50 is energized from the generator 3 which is driven by motor 4 connected across the line L1, L2 supplied by a suitable source of currentPP (Fig. 2). The direction and speed of motor 1 is controlled by the car switch 5, or equivalent, which through relays A to G, as more specifically hereinafter described, controls the direction and amplitude of current through the shunt field 6 of the generator for variation of voltage applied to the motor 1.

Assuming that the car is stationary and it is so desired to go to a higher floor, the car switch 5 is swung in clockwise direction ,first to engage contact U1 which energizes the up" contactor A, the closure of whose contacts A1, A2 completes a circuit through the field 6 of generator 3, and provides for flow of current through the field in proper direction for hoisting by motor 1. The circuit completed by the contacts A1, A2 includes all of r sistance R in series with the shunt field 6 so tha the voltage generated is low for correspondingly low speed of motor 1. The closing of contact U1 of the car switch also effects release of the usual solenoid brake (not shown). The car switch next engages contact U2 to complete a circuit through the coil of relay D 7 5 whose co'ntact,Dl, thereupon moves to shunt the section d of resistance R so that the output voltage of generator 3 is increased to increase the speed of motor 1. Similarly, continued movement of the car switch'efiects engagement of contact U3 which effects energization of relay E whose contact E1 is thereupon actuated to shunt the section e of the generator field resistance R further to increase the speed of hoisting of the car. I

When the car switch engages contact U4, the relay F is energized to shunt the section 1 of the generator field resistance R by its contact F1 so that the motor runs at fourth speed. The contact F2 of relay F closes the circuit of relay H through contact C1 of relay C which was energized concurrently with energization of relay A, whereupon contact H1 closes to complete a lock-in circuit for fourth-speed relay H which includes ,contact '01 of relay C. Contact 1-12 of relay H irfseries with contact C2 of relay C and contact A3 of relay A completes a lock-in circuit for relays A and C. Contact H3 of relay H in series with contact D2 of relay D completes a lock-in circuit for second-speed relay D. Contact H4 of relay H in series with contact E2 of relay E completes a lock-in circuit for thirdspeed relay E. Similarly contact H5 of relay H in series with contact F3 of relay F completes a seal-in circuit for the fourth-speed relay F.

Movement of the car switch to its final or fifth-speed position closes contactlU5 to effect energization of relay G whose contact G1 shunts section g of the generator field resistance R. C ntact C2 of the relay G completes its seal-in circuit. The car is now being hoisted at maximum speed for example, at the rate of about 600 feet per minute.

In accordance with the present invention, the operator wishing to make an automatic stop at one of the upper floors, returns the car switch to center position suitably in advance of that floor. This operation leaves all of the foregoing relays locked in circuit and closes the contact CS.

For clarity of further explanation, it is assumed that the approximate distances at which the different speeds are cut-out are as follows: high speed, 12 feet; fourth speed, 6 feet; third speed, 3 feet; second speed, 1 feet; and first speed, four inches. As will hereinafter more clearly appear the actual point of cut-off of first and second speeds are made to vary in accordance with the load and speed of the car.

As the car reaches a position 12 feet below the desired floor, the car switch having been previously closed contacts SSU are closed by meehanism correlated to position of the car hereinafter more specifically described, to complete, through the closed contacts CS of the car switch and closed contact A4 of relay A, a circuit in shunt to relay coil G effectively to de-energize it.

Contact G1 thereupon opens to insert resistance section (7 in the generator field circuit to effect deceleration of the car; contact G2 opens to break the seal-in circuit of relay G; and baclccontact GS of the relay closes.

When the car arrives at a position 6 feet below the desired floor, contact 4SU is closed, by the aforesaid mechanism to be hereinafter described, to complete, through ear switch CS, contact A4 of relay A, and back-contact GB of relay G, a circuit in shunt to relay coil E which is thereby effectively de-energized. The contacts F1 of the relay open to introduce resistance section f into the generator field circuit for further deceleration of motorl. Contacts F3 open to brealr the hold-in circuit of the relay F. The back contacts F; of the relay close to complete through closed contacts C1 of relay C and closed contact 1-11 of relay H circuit including the lamp or bulb 8, whose purpose will hereinafter be explained.

The closing of contact F4 also completes a circuit through the coil of notching relay I which moves contact arm 9 to its first position. In a short time, the filament of lamp 8 heats to sufficient brilliancy to cause the photo-electric cell 12 to effect energization of relay K whose contact K1 opens to de-energize coil I of the notching relay, arm 9 remaining held in its deflected position by pawl 11.

When the car arrives at a position approximately three feet below the desired landing, the vane 13U, as hereinafter described, momentarily intercepts the beam of light from bulb 8 to photocell to effect de-energization of relay K, whose I contact K1 in closing again energizes the notching relay I to advance arm 9 to engagement with contact 9E. In this second position, the arm 9 shunts the relay E whose contact E1 thereupon opens to effect further reduction of the motor speed by reinserting section e of generator-field resistance R. Contact E2 of the relay opens to break its seal-in circuit.

When the car running at reduced speed arrives at approximately eighteen inches from the floor, vane MU momentarily interrupts the light beam to effect movemert of arm 9 to its'tbird position in engagement with contact 9D to shunt relay coil D. The contact D1 of the relay opens to reinsert section (1 of the generator-field resistance in circuit. Contact E2 opens to break the hold-in circuit of the relay.

When the car running at low speed reaches a point about four inches below the landing, vane 15U momentarily intercepts the light beam to the photo-cell whereupon arm 9 moves to its final position in engagement with contact to shunt out the relay coil C. Contact C2 of the relay opens to break the circuit of relay A whose contacts Al, A2 thereupon open to breal: the circuit of the generator field 5 so that current is no longer supplied to the car motor 1 and simultaneously with de-energization of the motor, the brake is applied to bring the car to a stop. The back.- contacts A5, B5 may be utilized to complete a ch. cuit across the generator output circuit including the differential field which prevent generator 3 from functioning as a series generator. Contact C1 of the relay opens to brealr the circuit lay H and of lamp 8. Contact C3 the closes to energize coil J to lift pawl ll. wher spring 16 or equivalent returns a. n 9 to its original or first position at which opens switch 10 to tie-energize coil J. All of the elements are now in the same position as at the beginning of the run.

The slowing down of the motor in several steps avoids jarring or jclting of the car, and particularly with the compensating system hereinafter described ensures that the car will stop level with the landing without need for releveling either automatically, or manually.

If less than a twofloor run is to be made, the operator should move the car switch to the fourth speed contact H4 in which event relay G is not energized and the automatic stopping will be initiated by contact 4SU. The operation is otherwise as above described.

The operation for down direction of the car is similar; the car switch is swung counter-clockwise successively to engage the down contact DNl to BN4, or DNl to BN5, which effects acceleration of the car motor substantially as above described; the only difference is that the down relay B is energized instead of the up relay 4 to effect flow of current through the generator field 6 in proper direction.

For illustration of the mechanism for operating contacts 5SU, 4SU, 58D, 48D, reference is made to Figs. 3 and 4. The control cable 17 which is wound around the control drum i8 and passes over the lower pulley 19 is connected to the car so that the drum 18 is rotated as the car changes its position. Preferably the cable 1'7 is divided into two sections, one of which starts from the top of the car, winds around the drum and is anchored to one end of drum, and the other of which starts from the bottom of car, passes around sheave 19, leads up to drum and is anchored on the opposite end of drum from the first section. In addition to its rotation, the drum changes its position along its axis of rotation with change in position of the car due to threaded engagement with the threaded shaft 20 whose opposite ends are secured to the standards 21, 21 extending upwardly from the base member 22.

The groove 23 of the drum receives the end of the member 24 which extends upwardly from the carriage 25 which is movable along the rails 26. Each of the switch operating members 2'7U supported by the carriage are adapted to operate the switches 5SU, 4SU in succession as the car in its upward movement passes the 12 foot and 6 foot points below each floor; similarly. the members 27D are adapted to operate the switches 58D, 45D K50 in succession as the car in its downward movement passes the slowdown points above each fioor. The operation of these switches is of course without effect upon the speed of the car unless car switch 5 has been centered to close contacts CS which are in series with 5SU, 4SU etc., as most clearly shown in Fig. 2.

While additional switches of this type could be used automatically to cut-in sections of resistance R at definite fixed distances from the desired floor, I prefer to have the distances at which final sections are out in, variable in accordance with actual running conditions as the car approaches the desired landing. The speed at which the car may approach any landing is determined by many variable factors as temperature eflect upon the equipment, condition of the commutator and brushes of the motor and generator, the load of the car, length of run, condition of the rails, etc.

The arrangement now described ensures that the car Will be brought smoothly to a stop, level with the desired landing, and regardless of all of these variable factors, without need for releveling and notwithstanding the high speed at which the to the position shown in Fig. 4 by springs 32 or equivalent.

The vanes 13U, 13D, etc., above mentioned, a set of each for each fioor are arranged helically along the periphery of the control drum. 18 so that each in turn passes through the slot 33 of housing 29 to intercept the beam of light from lamp 8 to the photo-cell. Preferably as shown in Fig. 5, the mirror 34 reflects light from the lamp 8 to mirror 35 which in turn reflects it to a light-responsive device, as the photo-cell 12, and the vanes pass through the focal point of the lens 36 between the mirrors. The photo-cell is preferably of the type generating current upon exposure to light, though a photo-cell of any of the resistance-variation types may be utilized. In the car case the jumper x is removed and a suitable source of current inserted in circuit.

It is understood that for each intermediate floor there is a set of up vanes and a set of down vanes which control the notching relay I through the photo-cell and relay K of course, only one set of vanes is needed for the top and bottom fioors, as they are approached by the car from only one direction. As thus far described, the vanes efiecting cut-out of sections of resistance R at definite or fixed differences from the chosen landing in generally the same manner'as contacts 5SU, 4SU or 58D, 48D.

While the system thus far described has many advantages, I prefer to add compensation for variations in the load and speed of the car. Exact leveling by varying the cut-off points in accordance with existing conditions is accomplished by the torque motor T which positions the frame 31, 30 carrying the master-control housing 29 in the proper direction and to proper extent from the neutral position shown.

The circuit of the torque motor may be completed by the back contact E3 of relay E which is de-energized during automatic slow-down to second speed as above described, or more preferably,'closing of back contact E3shunts resistance TR fully to energize the motor. The torque motor is connected across the motor supply circuit in series with the armature 37 of the auxil- Eg=KI where Eg auxiliary generator voltage I=current to or from armature of motor 1.

For any given generator voltage, part is consumed in overcoming the armature resistance and the remainder in overcoming the counter-electromotive force of the armature; the lower the armature speed, the less the counter-emf and the greater the motor current and vice versa, i. e.,

EazRl+Eor where Ea voltage impressed on the armature of motor 1 Eor:counter-electromotive force of armature R armature resistance I=armature current The voltage applied to the torque motor is the algebraic sum of the voltage impressed on motor 1 and the voltage generated by the auxiliary generator: i. e.,

The effective output voltage of the auxiliary generator by design or by a suitable voltage dividing network, as potentiometer P, can be chosen to equal RI, or armature drop so that the torque motor voltage is proportional to the speed of the armature, i. e., the torque motorvoltage is proportional to the speed at which the car is approaching the landing.

Preferably by design, or adjustment of potentiometer P, the voltage introduced by the auxiliary generator in series with the torque motor is made to be greater than RI so that the voltage Eg is not only sufficient to cancel the RI component of the motor voltage but includes a further component varying with the load of the car. In other words, the voltage applied to the torque motor, at least during the stopping region; is a compositefunction of the speed and load of the car and since the voltage impressed on the torque motor determines the position of the control housing 29, the distances from the desired landing at which the relays are out out by the control vanes are each .determined by load and speed of the car.

Consequently, for example, if the car is approaching the desired upper landing at high speed and light load, the arm 31 is further to the left (Fig. 1) to meet plate 15U than for lower speed and/or lighter load. Moreover arm 31 follows the slow-down of the car so that the distances at which the plates 14U, and 13U intercept the light beam for further slow-down are each actually determined by the speed of the car as affected by the previous control. The system op- .erates properly under conditions of hoisting, lowering, regenerating or motoring, the polarity of the auxiliary generator reversing automatically since its field current changes direction with change of direction of current through the motor armature.

In many cases for very accurate compensation at all speeds, it is desirable to obtain a slightly rising torque-voltage characteristic of the torque motor. This is attainable by use of a compound wound torque motor in lieu of a simple shunt motor. In Fig. 1a are indicated the slight tit changes necessary. Briefly, the armature circuit of the torque motor is opened by removal of jumper y, and the conductors 3 1/ of Fig. 1a are connected to the terminals formerly bridged by the jumper to include the series field I'FS of the torque motor in circuit when either relay A or relay B is energized. 'I'he contacts A7, A8 of relay A and contacts B7, 138 of relay B constitute a reversing switch so that the excitation of the series field is always in the same sense as the excitation of the shunt field 'IF. The resistance FSR in shunt to the series field TFS is preferably variable to allow adjustment of the torque-voltage characteristic to meet the requirements of the installation.

The advantage of having the torque motor circuit closed in advance of closing of the back contacts of relay 3 lies in the fact that tendency of the arm 31 to overshoot or hunt its proper position is avoided. The value of resistance TR is chosen high enough to limit the current to the torque motor during high speed running of mo tor 1, to safe values, and low enough so that arm 31 is held against one or the other of stops 38 depending on whether the car is running up or down.

The control drum and its accessories may be located in the pent house, or other suitable location, where they are readily accessible for adjustment, replacement or repair.

By addition or the arrangement shown in Fig. 6, the car may be controlled by push-buttons, or the like, at or corresponding to the landings. Briefly, the contacts U1 to U4, for signal control,

- are connected respectively to the contacts ill to w: of the up relay M and correspondingly the contacts Bill to BN4 of the car switch are connected respectively to the contacts dnl to dn4 of the down relay N. I'he wire 35 is disconnected from the off-point of the car switch and the circuit from L1 to the off-point is completed through the back contacts CS1 and CS2 of relays S and 'I'. Contact U5 of the high-speed up relay S and 6125 of the high speed down relay T are connected to the point U5 and BN5 respectively of the car switch. In effect, the relays M and N replace or supplement the car switch.

For simplicity of explanation, it is assumed that there are four 'iioors. With the car at the first floor. the member UD, carrying the contacts MC. ND, SC and TC connected respectively to the re lays M, N, S and T, is in the position shown; with the car at the second floor, contact ND is in engagement with the down contact lSD; contact MC in engagement with the up contacts 3SU and 4SU; and contact SC is in engagement with contact ll-IU. With the car at the third floor, contact ND is in engagement with contacts lSD and 2813; contact MC is in engagement with contact QSU; and contact TC is in engagement with contact lHD. With the car at the fourth floor, contact ND is in engagement with contacts 18D, 28D, and BSD; and contact TC is in engagement with contacts LED and 2HD.

Assuming the car to be at the first floor, and that button 4? at the fourth floor, or button 40, the fourth-floor button in a control panel in the car has been pushed; the relay 4L is energized to close contacts 4S which completes a hold-in circuit for the relay and effects energization of relay M through a circuit which includes contacts MC and SU; contact ll-I of the relay 4L completes a circuit through relay S as contacts SC and ZHU are closed. With the relays M and S energized, the result is the same as if the car switch had been moved to engage contacts U1 to U5, i. e., the car moves upward at high speed. Before the car reaches the position for which the fourth floor 5SU contact is engaged (Figs. 1, 2), the contacts SC pass beyond contact 4HU to de-energize relay S. The closure of the back contact CS1 of relay S effects the same result as centering of the car switch, and the car is brought automatically to a. stop as above described.

If the third floor button 3F, or 3C, is pushed with the car at the first floor the operation is similar. However, if the second floor button 2F, or 20, is pushed with the car at the first floor, the high-speed up" relay is not energized, and the car runs at slow speed as if in the system of Fig. l the operatorjdoes not move the car switch beyond the 4U contact. The car is brought automatically to a stop level with the selected floor.

In general with the push-button control system of Fig. 6, the car will run at high speed and automatically stop for a long run, as of two or more floors, and will run at lower speed and automatically stop for a one floor run.

While I have illustrated and described a preferred embodiment, it is to be understood that my invention is not limited thereto but is co-extensive in scope with the appended claims.

What I claim is:

1. In the art of controlling elevator cars or the like, the method of accurately stopping the car at a desired landing which comprises producing an effect of magnitude dependent upon the speed of approach of the car toward said landing, and discontinuing application of driving power to the car upon its arrival at a point whose distance from the desired landing is dependent upon the magnitude of said effect.

2. In the art of controlling elevator ears or the like, the method of accurately stopping the car at a desired landing which comprises producing an effect whose magnitude is a function of the speed of the car and of the power concurrently delivered to its driving motor, and discontinuing application of driving power to the car upon its arrival at a point whose distance from the desired landing is dependent upon the magnitude of said effect.

3. In the art of controlling elevator cars or the like, the method of accurately stopping the car at a desired landing which comprises producing an effect whose magnitude is determined by the speed of the car, and effecting successive reductions of the driving power applied to the car at points whose distances from the desired landing are dependent upon the magnitude of said effect.

4. In the art of controlling elevator cars or the like, the method of accurately stopping the car at a desired landing which comprises producing an effect whose magnitude is a function of the speed of the car and the concurrent load upon its driving motor effecting successive reductions of the driving power applied to the car at points whose distances from the desired landing are dependent upon the magnitude of said effect.

5. An elevator system comprising a car, a motor for hoisting and lowering, and means for effecting deceleration of said motor comprising a circuit and photo-cell therein, a source of light, structure for repeatedly interrupting light from said source to said cell as said car approaches a landing, relays, and means responsive to impulses of current in the photo-cell circuit for effecting successive actuation of said relays to reduce the power supplied to said motor.

6. An elevator system comprising a car, a

motor for hoisting and lowering, and means for effecting deceleration of said motor comprising a single circuit-controlling device, means for repeatedly actuating said device assaid car approaches a landing, relays, and a notching relay erator for supplying current to said motor, and

control means for said voltage-varying means comprising a circuit-controlling device, means for repeatedly actuating said device as the car approaches a landing, and means including a notching relay responsive to successive actuations of said device for progressively decreasing the voltage of. said generator.

'8. An elevator system comprising a car, a motor for hoisting and lowering, a variable voltage generator for supplying said motor, and control means comprising a circuit and photo-cell therein, a source of light, structure for repeatedly interrupting light by said source to said cell as said car approaches a landing, and means responsive to impulses of current in the photo-cell circuit for progressively. decreasing the generator voltage.

9. An elevator system comprising a car, a motor for hoisting and lowering, a generator for supplying said motor, a resistance, relays for inserting sections of said resistance in the field circuit of said generator, and control means comprising a circuit and photo-cell therein, a source of light, structure for repeatedly interrupting light from said source to said cell as said car approaches a landing, and means responsive to successive impulses of current in the photo-cell circuit for effecting actuation of said relays in succession to decelerate the car.

10. An elevator system comprising a car, a motor for hoisting and lowering, relays actuatable to reduce the power to said motor, a control -member movable concurrently with said car, a

circuit and photo-cell therein, a source of light, structure carried by said member repeatedly to preclude transmission of light from said source to said photo-cell as the car approaches a landing, and means responsive to successive current impulse in the photo-cell circuit for effecting actuation of said relays in succession.

11. An elevator system comprising a car, a

motor for hoisting and lowering, and means for or retard the position of said photo-cell in accord-,

anee with car speed, and means responsive to interruption of the light for effecting reduction of power to the motor.

12. An elevator system comprising a car, a motor for hoisting and lowering, and means for de-energizing the motor as the car approaches a desired landing at a distance from the landing determined .by the speed of approach of the car, comprising structure movable concurrently with said car and co-acting structure so mounted that it may be advanced or retarded, and means for varying the position of said coacting structure in accordance with the speed of the car and the load upon said motor.

13. An elevator system comprising a car, a motor for hoisting and lowering, and means for de-energizing the motor as the car approaches a desired landing at a distance from thelanding determined by the speed of approach of the car, comprising a photo-cell, a source of light, structure movable concurrently with said car for controlling transmission of light from saidsource to said cell, means for mounting said cell so that its cooperation with said structure may be advanced or retarded, and means responsive to the speed of approach of the car and the motor load for controlling said mounting means to determine the-position of said photo-cell relative to said structure.

14. An elevator system comprising a car, a motor for hoisting and lowering, a variable volt age generator for supplying the motor, a circuit and photo-cell therein, a source of light, structure movable concurrently with said car repeatedly to interrupt transmission of light from said source to said cell as the car approaches a landing,.an auxiliary generator, a torque motor for nected in series with said auxiliary generator in a. path in shunt to the car motor, and means responsive to current impulses in the photo-cell circuit for decreasing the voltage of said generator.

15, An elevator system comprising a car, a

-motor for hoisting and lowering, said car, and

means for effecting deceleration of said motor to stop the car accurately at a desired landing comprising spaced elements movable in accordance with movement of the car, relays for reducing the power supplied to said motor, and a circuit-controlling device coacting with said elements in succession repeatedly to close a single circuit to effect actuation of said relays in succession. I

16. An elevator system comprising a car, a motor for hoisting and lowering, and means for effecting deceleration of said motor comprising a single circuit-controlling device, means for repeatedly actuating said device as said car ap proaches a landing, relays for reducing the power supplied to said motor, and means responsive to successive actuations of said device to effect actuation of said power-reducing relays in succession.

17. An elevator system comprising a car, a motorfor hoisting and lowering, a variable voltage generator for supplying current to said motor, and control means for said voltage-varying means comprising a circuit-controlling device, means for repeatedly actuating said device as the car approaches a landing repeatedly to change the impedance of a circuit, and means included in said circuit to effect progressive decrease of the.voltage of said generator.

18, An elevator system comprising a car, a driving motor therefor, means for producing an effect varying in magnitude in accordance with the speed of the car, and means for de-energizing the motor as thecar approaches a desired landing, responsive to said effect to determine the distance from the landing at which the car is de-energized differently for each different speed of approach of the car to the landing.

19. An elevator system comprising a car, a driving motor therefor, means for de-energizing the motor as the car approaches a desired landcontrolling the position of said photo-cell coning, comprising structure whose position is a. continuous function or the position of the car, and co-acting structure whose position is a. continuous function 01' the speed of approach of the car to the landing.

20. An elevator system comprising a. car, a driving motor therefor, means for producing an eiiect whose magnitude is jointly determined by

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