US2521568A - Elevator control - Google Patents

Description

p 1950 H. c. CRANE 2,521,568

ELEVATOR CONTROL Filed Nov. 7, 1946 4 Sheets-Sheet 1 INVENTOR HAROLD C. CRANE I rr! Sept. 5, 1950 I H. c. CRANE 2,521,568

ELEVATOR CONTROLI Filed Nov. 7, 1946 4 Sheets-Sheet 2 INVENTOR fin/mm C. CnA/ws m Sept. 5, 1950 H. c. CRANE 2,521,568

ELEVATOR CONTROL Filed Nov. 7, 1946 4 Sheets-Sheet 3 Hm om' C. C/imva P 950 H. c. CRANE 2,521,568

ELEVATOR CONTROL fl/m u) 6. (Rn E Patented Sept. 5, 1950 UNITED STATES PATENT OFFICE ELEVATOR CONTROL Harold C. Crane, Toronto, Ontario, Canada Application November 7, 1946, Serial No. 708,332 In Canada June 29, 1946 This invention relates to automatic relevelling devices for elevators and thelike, and the object of the invention is to devise a simple relevelling device which will. not require a separate motor and reduction worm, and the operation of which isautomatically adjusted to the amount of overrun or under-run so as to reduce or eliminate hunting in arriving at the proper floor level.

Relevelling serves two functions, (a) it will correct the errors in stopping which are due to the efiect of load-an elevator tends to stop lower as the load is increased, and this is true irrespective of in what direction the elevator travels, (b) it can correct for errors in stopping due to wear of the brake lining and to other factors.

The operation .of the relevelling system disclosed and claimed herein is briefly as follows:

A conventional stopping switch is adjusted to cut off the power supply .to the motor and apply the brake at such a point that the car will stop level with the floor at balanced load. With this adjustment, the car will stop low with any load greater than balanced load; to correct this low stop, the car must be relevelled upward. To move the car upward With more than balanced load on it, requires positive motor torque. In the system disclosed herein, to obtain this torque the motor is controlled by several accelerating switches which successively increase the motor torque as they .close in timed succession. As soonas the motor starts to move, the accelerating sequence is stopped by a reed governor, and this stopping of the accelerating sequence prevents a further increase in torque. Since it takes less torque to keep the elevator moving once it has been started than it does to start it, as soon as the accelerating sequence is arrested there is reintroduced in the .motor circuit some starting resistance by means of a fstep-back switch.

An elementary form of relevelling switch would consist of two contacts, one placed, say, one-half inch below the floor and the other placed onehalf inch above the floor. The contacts would be so constructed and located that they would be open if the car stops within one-half inch of the floor, but if the car stops lower than this limit, the upper contact would close and connect the power supply to the motor, thereby moving the car upward toward the floor. Obviously the other contact would perform a similar function if the car stops more than one-half inch above the floor.

With the above simple relevelling scheme, it

is found that the point where the car will come I 10 Claims. (Cl. 187-29) to rest after a relevelling operation, depends .on how far the oil-level elevator travels before it reaches the point where it is assumed to be level. For example, if the car has travelled only a'short distance during the relevelling operation, say, inch, the speed will not have increased to any considerable extent and the car will therefore stop close to the floor. If, on the other hand, the car has travelled three inches, it will during the relevelling operation reach a considerable speed and may slide to a position one inch above the .floor. A second relevelling operation will. then be required because the car is more than one-half inch above the floor.

It is obvious that the aforedescribed simple switch will'not be satisfactory. What is required is a switch which will take into account the distance which the car has to travel during the relevelling operation to reach the floor, and as the distance increases, the switch will shift the cutoff pointfarther away from the floor, thus anticipating the increased slide. The apparatus as-described and claimed herein provides such areature in a simple, inexpensive, and efiicient'manner.

The invention is hereinafter described in detail and illustrated by way of example in the accompanying drawings, in which Fig. 1 is a plan .view of the relevelling device in inoperative position.

Fig. 2 is a front elevation of the device in inoperative position.

Fig. 3 is a section on the. line .33 in Fig. .2,

Fig. 3A is an enlarged perspective view of the levelling switch mechanism and associated operating mechanism. Fig. 3B is an enlarged perspective view of the lever mechanism for actuating the levelling switch opening and closing member.

Fig. 4 is a front elevation of the outer or front part of the mechanism shown in Fig. 2, on an enlarged scale with the relevelling switches removed in order to show in inoperative position the mechanism for putting the said relevelling switches in operative position.

Fig. 5 is a front elevation of the device in operative position on the same scale as Fig. 5, showing the up relevelling switch closed and thedown" relevelling switch open.

Fig. 6 is a circuit diagram, in what is known'as the straight line style, of an elevator control sys tem embodying the invention.

In the drawings corresponding numerals in the different figures refer to corresponding parts,

The device is mounted on the elevator car in 3 a suitable position adjacent to the shaft. It may be mounted in a suitable box or frame I which is shown in the drawings as being open on one side, but which may, of course, be provided with suitable covers. Extending between the ends of the frame I is a main supporting member 2 on which the mechanism is mounted. The device comprises two main parts or assembles, which, are, in effect, superimposed one on the other, one of which is the relevelling switch mechanism and the other of which is the means for setting the relevelling switch mechanism in operative position after the elevator has been stopped by the operating circuit; the relevelling switch mechanism is in inoperative position during floor to floor runs. In addition, the invention includes an operating circuit shown diagrammatically and which will be described after the mechanical features of the invention have been fully explained. The means for retaining the relevelling device inmormal inoperative position and placing it in operative position when required will first be described. This means is shown in Figs. 2 and 3 inassociation with the relevelling switch mechanism and particularly in Fig. 4 with the relevelling.- switch mechanism removed for the sake of clarity.

For convenience the device will so far as is feasible be described only with respect to the mechanism for levelling up which is shown in the upper half of Figs. 2 and 3, inasmuch as the mechanism for levelling down is a duplicate thereof. It will be understood that the device is mounted on the car with the upper part of the apparatus as shown in the drawing up and the lower part of the. apparatus as shown in the drawing down so that Figs. 2, 4, and 5 show the apparatus as viewed from the car looking toward the side of the shaft.

The apparatus is actuated by means of upper andloweroperating wheels 3 each of which is swingably mounted on an arm 4 and is adapted when in. operating position, to engage a cam member 5; (shown in dot-dash lines in Fig. 5) which is mounted on the side of the elevator shaft. .For the sake of simplicity, neither the elevator shaft nor the car is shown in the draw ings. The cam 5 slopes upwardly from each end and has a fiat or straight portion between the ends. When the car is properly levelled the upper and lower operating wheel will be out of contact with the cam or else engaging the cam at each end thereof at a predetermined low position with the high part of the cam between the two operating wheels.

Inasmuch as there will be a cam located at each floor level, it is desirable that the operating wheelsbe moved so that they will not contact the cams except when the elevator stops at a floor, when it is desired to put the relevelling mechanism intooperation. This is achieved by the means hereinafter described.

l; If the car stops off-level auto-level magnets A are-energized by means of the electrical circuit hereinafter described. Armatures I, I are drawn torthe magnets when they are energized. Attached to lugs 0n the armatures are links 8, 8 both of which are pivotally connected to a floating lever 9. The movement of the armature draws the floating lever 9, through the links 8, to, contact with adjustable stops I0.

Referring for convenience only to the rear port ignoiFig. 2 shown in the background, which is better shown particularly in Fig. 4, the floating lever 9 is provided at its lower end with spaced depending lugs 45 (only one of which can be seen in the drawings) which are pivotally connected by a pin H to lever l2. At its other end floating lever 9 is connected by links 45-45 (only one of which can be seen in the drawings) to another lever also numbered l2. Since the upper and lower parts of the mechanism are substantially identical, the same numeral is given to corresponding parts. Lever I2 is pivotedby means of pivot pin [3 to arm 2| which is journalled on a shaft 22 which extends through a bearing 23 in the main supporting member '2, and to the outer end of which is secured arm 4 On which operating wheel 3 is rotatably mounted. An adjustable stop 24 engages the end of arm 2| to limit the movement of said arm when it shifts to the inoperative position. To lever I2 is slidably secured a pin 14 which passes through a hole in the said lever adjacent to the pin II. The said pin l4 reciprocates through a. hole in a bracket l5 which extends from the support 2. A spring [6 is coiled around pin I, said spring being provided with suitable washers ll, H at its end. Cotter pins 3 and 19 at each end of pin [4 tend to retain the spring under compression so that pin [4 normally draws lever l2 to the left hand side, as shown in the drawings, against the action of floating lever 9, thus returning the operating wheels 3 to inoperative position as soon as auto-level magnets A are de-energized and the floating lever is thereby released. The lower end of lever I2 bears against adjustable stop 20, thus regulating the movement of the other end of the lever.

It will be observed from the above description that when the device has been set in operating position by means of auto-level coil A, floating lever 9 and pin H on which lever 12 is fulcrumed, are held in fixed position throughout the relevelling operation; these parts can therefore be considered as stationary parts during the relevelling operation. Their only function is to prevent contact of the operating wheels with the cam in the hatch-way as the elevator travels at high speed.

Referring to Fig. 5, the operation of the relevelling mechanism will now be described with particular reference to the upper portion of the device, namely that portion which levels up when there is an under-run. This mechanism comprises primarily an up level switch which is actuated when the operating Wheel strikes the cam. The switch consists of a switch bar 25 having bearings 25a. thereon through which the shaft 22 passes, said bar 25 being pivoted on said shaft 22.

The upper end of the switch bar 25 carries movable bridge conductor 26 in a manner hereafter more fully described, and it is adapted to engage fixed contacts 2'1, 21. (See Fig. 3.) The other end of the switch bar 25 is hingedly secured to a pin 28, which is secured to and extends outwardly from the lower end of lever I2.

- As shown in Fig. 3B the movable bridge conductor is a U-shaped member which embraces an insulated member 30 which is flexibly connected to the switch bar 25 by means of a pin 3| which extends through said bar to the insulating member 30 and is provided with a coil spring 32 which extends between the bar and the washer 33. Cotter pins are provided at each end of the pin 3| to retain the parts in assembly. The insulated member 30 is backed at one end by a metal clip 34 which bears on the bottom of a pronged bracket 35 which is secured to the bar 25. Insulated member 30 is connected to the bridge lconductor 26 by means of :a pin 36 which extends through holes in the insulated member, and the pin is encircled by a coil spring 31 adapted to normally hold the insulated member and the bridge member in contact, but also adapted to contract when the bridge conductor 25 engagesfixed contacts 21, -21 topermit further movement of the insulated member toward the contacts 2'], 21 against compression'of the spring.

If the elevator on its down travel passes the floor level after the operating circuit has been cut, the operating wheel 3 will run up on the cam 5, and arm 4 will turn shaft 22 which will swing arm "2| causing lever l2 to pivot on the pin 4 I so thatthe lower endof lever l2 which carries the pin 28 will swing outwardlyyfrom the stop 20. Pin 28 will swing the lower end of switch bar 25 outwardly, thus causing said switch bar to pivot on shaft 22 and causing the other end of said bar to swing inwardly until bridge conductor 26 engages contactsZ'l, 21, thus closing a circuit hereinafter described which will cause the elevator operating motor to translate the car up to a level at which the operating wheel 3 is out of engagement with the cam-5 or runs sufficiently far down the slope of the cam to reverse the operation above described and break the contact, at which time the elevator operating motor will be cut out and the elevator will slide to rest.

When the elevator stopped originally, previously to the levelling operation, the operating wheel 3 ran a lesser or greater distance up the incline of the cam depending on the amount of under-run. When the wheel runs up the cam past the point at which the bridge conductor 26 engages contacts 21, 21, thefurther rocking movement imparted to switch bar 25 is taken up by spring 31 which permits insulated member 30 to move relative to bridge conductor 26. When the relevelling apparatus functions to reverse the movement of the car, causing the wheel 3 to run down the incline of the cam, lever I2 will swing in the opposite direction and there will be a timed delay until insulated member 30 again bears against bridge conductor 26 before the contact is broken. In other words, the contact will be made and broken at the same pointin every case regardless of the amount of under-run, and if the under-run has been great, the speed of the elevator during the relevelling operation will be correspondingly great, tending tocause the'elevator to slide above the floor level.

Should the elevatorrise too much above floor level during the relevelling operation, the lower operating wheel will run on the cam and put into operation the necessary circuit for causing the elevator to be moved down, and this process will be repeated, if necessary, until the elevator comes to rest within a predetermined distance from the floor level at which point both operating wheels will be out of contact with the cam or at such predetermined position with respect to the cam as will not cause the levelling circuit to be closed.

It will be observed that utilizing the construction above described, if the initial stop of the car is a considerable distance below the floor, and the relevelling device comes into operation to bring the car up to the floor level, the car will attain a considerable speed before the relevelling apparatus cuts off the motor whichdrives the car and apply the brakes causing it to stop, so that in that case there would be a tendency for the car to over-run and have to be brought down again by the relevelling device, with the result that therewould be an objectionable "hunting operation before the final level was reached. Likewise if the .car stopped a shorter distance below the proper level, the relevelling device might shut off the motor and apply. the brakes too early so that itwould not reach the desired floor level.

It .is clearv that to overcome this .difficulty the switch must be devised so that it willtake into accountthe distance the car has to travel to reach the floor and as the said distance increases it will shift the cut-off point farther and farther away from the floor, thereby anticipating the increasedrslide. This result has been achieved in accordance with the present invention by the means hereinafter described. This means comprises a lever 38v pivoted by means of a U-shaped bracket 39 to the shaft 22. The upper end of this lever extends in the space between switch bar-25 and the metal backingmembert l of the insulated member 30 and has an inturned end which normally engages the switch bar 25. A slot through the lever 38 adjacent the bend receiveslalprojectingtongueon the end ,ofathemetal backing member 34 providing a hinged connection. (See Fig. 3A).

The other end of lever 38 has secured thereto on bracket 40 a flat leaf spring 4!. At the free end of the flat spring 4| is a metal armature 42 which is adjacent to core 43 of zone compensating magnet Z which is connected to one side of the frame I.

After the elevator has stopped and is about to be relevelled, the relevelling circuit is closed by the contact of bridge conductor 25 with contacts 21, 21 and a circuit through zone compensating magnet. Z is closed-through 'thereed governor, as hereinafter explained. Therefore, armature 42 will be attracted by core 43 of magnet Z and it will be retained and locked in the most advanced positionto which it has been carried by the switch bar 25 which engages the other end of the lever 38 rotating it on shaft 22 thus carrying the armature 42 forward. The further the switch bar 25 swings anti-clockwise as shown in the drawings the greater will be the movement of the armature. When the switch bar 25, under the influence of the operating wheel swings clockwise the magnet will hold the armaturein its most advanced position so that the upper end of the lever 38 will not move with the switch bar 25 but will remain stationary and will trip the end of the insulated member 30 causing it to fulcrum on pronged bracket 35 and accelerate the retraction of the bridge conductor 26 away from the contacts 21, 21 so that the control circuit which regulates the elevator motor and brakes will be broken sooner than would have been the case had the insulated member 30 been rigidly connected to the lever bar 25. i

As soon as the contact is broken, zone compensating magnet Z is de-energized, releasing the leaf spring 4| and permitting the lever 38 and the insulated member 30 to resume their original positions relative to the switch bar 25 under the influence of spring 32. It will be observed that the acceleration of the breaking of the contacts will vary depending upon the movement of the switch bar 25. The greater the movement of the lever 25, the greater the relative acceleration of the breaking of the contacts. Since the movement of the lever depends upon how far up the slope of the cam the operating wheel travels, and that depends on how far the elevator stops away from the floor, it will be seen that the further the elevator stops from the floor the greater is the acceleration of the breaking of the contact which cuts out the operating motor. The further the elevator stops from the floor level, the greater the speed it will develop returning to the floor level and therefore the greater the distance requiredto stop the elevator at the floor level. By the means just described the point at which the operating motor is cut out is varied to compensate for the varying time required to slide to a full stop at floor level.

The circuit diagram (Fig. 6) is in the straight line style, and it is referenced in a manner which is conventional in the elevator industry. Thus, the coils or solenoidsof the various switches and relays are represented by a main symbol, (e. g. SB) whereas the contacts of said relays or switches are represented by the same symbol with a superscript (e. g. SE). The superscript represents the number of the contact of the particular switch or relay.

In this description it is assumed for the sake of simplicity that the elevator disclosed herein travels between three floor levels, namely the first, second and third floors and at each floor are push buttons B B and B Obviously in the actual elevator, there would be similar buttons insid the elevator car and the necessary additional switches and relays operated by these extra buttons would be required in order to provide satisfactoryoperation.

Floor relays Fl, F2 and F3 are provided at each floor, the numeral after the letter indicating the number of the particular floor. As soon as a button B B or B is depressed, the button may I immediately be released without opening the circuit, since contacts Fl F2 or F3 thereof will be closed, thereby making the circuit self-maintaining.

A selector S is provided, usually at the top of the hatchway, but since this device is well known in the art, it need not be described herein. Essentially it consists of a series of switches driven by the car and which are synchronized with the car position and are so arranged so as to connect floor relays (Fl F2 or F3) above the car to relay UR and floor relays below the car to relay DR. The selector S which is illustrated shown therein comprises two metal plates S spaced and insulated from each other, said metal plates travelling up 4' or down in synchronism with the car as it moves upward or downward. The insulation or space between the two metal plates corresponds to the car position. Thus the car is shown as being at the second floor and if it is made to move upwardly, say, to the third floor, plates S will gradually travel upward and when the car reaches the third floor, the space between the two plates representing the car position will be at a level in the diagram corresponding to the line joining button B to coil F3.

The motor preferably used in the present invention is a three-phase slip ring electrical motor. It comprises a stator and a rotor, the stator being connected to the three-phase power supply Ll, L2, and L3. Contacts M and M of main switch M are respectively in series with power supply lines LI and L2. Contacts U and U of up motor switch U are respectively in series with power supply lines L2 and L3, whereas contacts D and D of down motor switch D are in series with power supply lines L2 and L3. It will be seen from the circuit diagram that when contacts D and D of the down motor switch are closed, the wiring to the stator is actually in reverse position to when contacts U and U of'the up motor switch are closed. The up motor switch is so arranged that it is impossible for both the up contacts U and U and the down contacts D and D to be closed together. This feature is provided by normally closed back contacts U and D of motor switches U and D which are respectively inserted in series with the coils of motor switches D and U. Thus if the coil of up motor switch U is energized, back contact U in series with the coil of down motor switch D will be open, thus preventing closure of said down motor switch D. Back contact D in-' serted in series with the coil of up motor switch U similarly .prevents the closure of up motor switch U when the coil of down motor switch is energized.

The three coils in the rotor are respectively connected through sli rings Tl, T2 and T3 to a plurality of resistors, the resistors in each of the groups being in series and the three groups meeting at a star point. It will be seen from the diagrams that the various resistors may respectively be by-passed by closing contacts numbered 6, I, and 8 of switches SB, RI, R2, R3 and R4. If all these switches are closed, the resistors will be completely by-passed, the rotor current will be at a maximum and thus maximum torque will be produced. On the other hand, if the aforementioned switches are left open, the current must pass through the various resistors and it will therefore be a minimum and the torque in the motor will be correspondingly small. Consequently the motor torque may be varied depending on the number ofresistors which are by-passed.

The coil K of the reed governor is tapped between any two of the rotor coils, and the reed governor is preferably tuned to lin frequency. Thus when the motor is not rotating, the rotor frequency willbe the'same as the stator frequency, the motor merely acting as a transformer. In this condition therefore, the frequency on the reed governor will be line frequency and since it is tuned to vibrate preferably at line frequency, it will thus Vibrate when the energized motor is not rotating, and on each vibration a contact will be made at point W. This will charge the electrolytic condenser Y, thereby energizing the coil of switch GR and closing the various contacts thereof as will be hereinafter described.

Any suitable source of direct current may be supplied to the control circuit. To describe the operation of the car on a floor to floor run, it will be assumed that the car is stopped at the second floor and that it is desired to travel from the second to the third floor. Obviously a down operation say, from the second to the first floor will be similar. Upon pressing button B the coil of floor relay F3 will be energized and current will flow through selector S to the coil of direction relay UR. Button B may be immediately released since as soon as floor relay F3 is energized, contact F3 will be closed thereby making the said circuit to the coil of relay F3 self-maintaining.

Since contacts F3 and UR are now closed by the respective actions of coils F3 and UR, a circuit through normall closed contact D to the coil of up motor switch U and to the coil of main switch M will be completed. It should be noted here that both main switch M and up motor switch U (or down motor switch D) must be closed in order to start the motor.

When the coil of direction'relay UR is energized, contact UB closes. Since main switch M has been closed as previously described, contact M thereof closes and. therefore a circuit is completed through contact M and contact UR to the coil of step-back-switch SB. At the instant that up motor switch U and main motor switch M close, the stator of the motor is connected to the power supply through contacts M M, U and U As soon as step-back-switch SB is energized, three of the resistors in the rotor circuit are dropped out by means of contacts SE SB and SB respectively, thereby increasing the rotor current and thus causing more torque.

Since the reed governor is tuned substantially to line frequency, it will vibrate when the energized' motor is not rotating. so that the coil of governor relay GR will be energized'and thereby close contact GR The closure of contact GR) allows current to flow to the coil of switch'B-R, thereby releasing the magnetically operated brake. Also the closure of contact GR allows current to flow through. contact M and through contact SE to the coil of accelerating switch RI.

When the coil of switch RI is energized, this circuit becomes self-maintaining due to the closure of contact Rt in the said circuit; it should be noted that contact R3 in that circuit is normally closed. Switch RI will not close suddenly, but it will be retarded by means of a dash-pot used therewith. When it does close, however,

contacts R1 RI and RI" will cut off more of the resistance in the rotor circuit and therefore the motor torque will again be increased.

In a similar manner switch R2 which is retarded by a dash-pot will eventually close, the current being conducted through contacts SE and RI When it does close, the circuit be comes self-maintaining through contact R2 The closure of switch R2 cuts off moreof the effective rotor resistance through closure of contacts R2 R2 and R2 After switch R2 has closed, the closure of contact R2, thereof will complete a circuit through contact SB of relay SB to the coil of switch R3, which is also provided with a dash-pot, thereby closing' contacts R3 R3 and R3 and cutting out still more resistance in the rotor circuit, The closure of switch R3 will open back contact R3 and thereby render switch RI no longer selfmaintaining, for a purpose which will be hereinafter described.

The closure of contact R3 of switch R3 will complete a circuit'through contact SE of switch SB, thereby closing a circuit to the coil of switch R4, also provided with a dash-pot which. in turn by means of contacts R4 R4 and R4 cuts out more resistance in the rotor circuit and thereby short circuits the three slip rings. The motor now runs at full speed, causing the elevator to move up rapidly to the fioor above.

At a predetermined point in advance of the thirdfloor, the selector S opens the circuit between relay F3 and relay UR, thereby opening switches F3 and UR and breaking the circuit to motor switches U and main switch M and causing the elevator to stop.

However, if due to heavy loads or other causes, the elevator has stopped low, the circuit will be closed again through the instrumentality of zone compensating coil Z, auto-level coil A and the up level switch, as described in the first portion of this specification. These parts are shown diagrammatically in the dotted-line rectangle in Fig. 6. As soon as the elevator stops, back contacts UB and DR will close thereby allowing current to flow to auto-level coil A and energizing it. The up level switch is mechanically closed as previously described by means of autolevel coil A and therefore current will: now through back contact BN and energizes up; re levelling relay UN. It should be noted here that as soon as up relevelling relay UN is energized, the back contact thereof UN which'is normally closed, will open and thereby prevent current from flowing to downrelevelling relay DNj' this of course is a safety measure. When upralevelling relay UN is energized, contact "UN thereof is closed and a circuit will as hereinbefore described, be compl'etedthrough normally closed back contact D of the down motor switch D to up motor switch U and main motor switch M, thereby applying power to the motor. The starting sequence described above therefore once again begins.

It should be noted however, that when'relevelling the elevator the direction switches-UR and DR are not used, and therefore the circuit to the step-back-switch must pass through contact GR of thereed governor, it cannot flow through contacts UR or DR of the direction switch. Therefore. as soon as the reed governor stops operating, the step-back' swi'tch SB will open.

When the elevator speed starts to increase and the frequency in the rotor to decrease, the said frequency is no longer that for which the reed governor is tuned, and therefore the governor stops vibrating. When the reed governorwas vibrating, the step-back switch SB and "one or more of the accelerating switches RE, R2; "R3 and R4 closed, the number of switches closing depending on the elapsed time before the reed governor stopped vibrating. When the reed governor stops vibrating, relay GR thereof drops out, which drops out the step-back switch S3 and prevents further operation of the accelerat ing switches RI, R2, R3 and R4. Dropping out step-back switch SB opens contacts SB, SB and SB and thereby increases the total amount of effective resistance in the motor circuit and de-' creases the torque. If the accelerating sequence has progressed to the point where relay R3 has closed, contact R3 thereof in the circuit to relay RI will open, and therefore the circuit to said relay will not be self-maintaining as may be seen from the diagram. Thus if the accelerat'- ing sequence has progressed to the point where R3 has closed, RI will necessarily drop out when SB drops out. This feature provides a greater reduction in torque than would have been'obtainedby the dropping out of SB alone. 'The reduction in torque is advisable although of 3 course not essential because running friction is less than starting friction.

It should be added that zone compensating coil Z in the relevelling switch is energized at the same time as the brake switch BR, that is the same instant as the governor relay GR picks up.

taken as a preferred example of the same and as various changes in the shape, size, and arrangement of parts may be resorted to, and that various modifications may be made in the elec.

What I claim' as my invention is:

1. In an automatic levelling device for elevators and the like, a levelling circuit, a switch in the levelling circuit, means for closing the switch to initiate starting of the elevator in the direction of floor level if the elevator stops more than a predetermined distance from floor level, a switch opening member advanceable a distance which varies with the distance that the elevator stops from said predetermined distance from the floor level, and means actuated by the levelling circuit when the switch is closed by said switch closing means to hold said switch opening member in its most advanced position, said switch opening member being adapted to open the switch and initiate stopping of the elevator at a place in the travel of the elevator toward floor level which varies with the distance that said switch opening member has advanced.

2. In an automatic levelling device for elevators and the like, a levelling circuit, a switch in the levelling circuit, means for closing the switch to initiate starting of the elevator in the direction of floor level if the elevator stops more than a predetermined distance from floor level, a switch opening member advanceable a distance which varies with the distance that the elevator stops from said predetermined distance from the floor level, and a magnet actuated by the levelling circuit when the switch is closed by said switch closing means to hold said switch opening member in its most advanced position, said switch opening member being adapted to open the switch and initiate stopping of the elevator at a place in the travel of the elevator toward floor level which varies with the distance that said switch opening member has advanced.

3. In an automatic levelling device for elevators and the like, a levelling circuit, a switch in the levelling circuit, including fixed contacts and a pivotally mounted bridging member, a pivotally mounted switch closing member swingable to close the switch by engaging the bridging member with the fixed contacts and thus initiate starting of the elevator in the direction of floor level if the elevator stops more than a, predetermined distance from floor level, a pivotally mounted switch opening member swingable a distance which varies with the distance that the elevator stops from said predetermined distance from the floor level, and means actuated by the levelling circuit when the switch is closed by the switch closing member to hold said switch opening member in its position of greatest swing, said switch opening member being adapted to engage the bridging member and pivot it out of engagement with the fixed contacts to break the levelling circuit at a place in the travel of the elevator toward floor level which depends upon the distance that the said switch opening member has swung, and hence depends on the distance the elevator has stopped from the said predetermined distance from thefloor level.

4. In an automatic levelling device for elevators and the like, a levelling circuit, a switch in the levelling circuit, a pivotally mounted switch member swingable to close the switch and initiate starting of the elevator in the direction of floor level if the elevator stops more than a predetermined distance from floor level, said switch including a bridging member pivotally mounted on the switch closing member and fixed contacts engageable by the bridging member when the switch closing member is swung at predetermined distance, a pivotally mounted switch opening member swingable a distance which varies with the distance that the elevator stops from said predetermined distance from the floor level, means actuated by the levelling circuit when the switch is closed by the switch closing member to hold said switch in its position of greatest swing, said switch opening member being adapted to engage the bridging member and pivot it out of engagement with the fixed contacts to break the levelling circuit at a place in the return travel of the elevator toward floor level which depends upon the distance that the said switch opening member has swung, and hence depends on the distance the elevator stops from the said predetermined distance from the floor level.

5. In an automatic levelling device for elevators and the like, a levelling circuit, a switch in the levelling circuit, a pivotally mounted switch member swingable to close the switch and initiate starting of the elevator in the direction of floor level if the elevator stops more than a predetermined distance from floor level, said switch including a bridging member pivotally mounted on the switch closing member and fixed contacts engageable by the bridging member when the switch closing member is swung a predetermined distance, a lost motion device to permit movement of the switch closing member past the point at which the bridging member engages the fixed contacts a distance depending on the distance the elevator stops from the said predetermined distance from floor level, a pivotally mounted switch opening member engageable by Q the switch closing member in its switch closing movement and swingable by said switch closing member a distance which varies with the distance that the elevator stops from said predetermined distance from the floor level, means actuated by the levelling circuit when the switch is closed by the switch closing member to hold said switch in its position of greatest swing, said switch opening member being adapted to engage the bridging member and pivot it out of engagement with the fixed contacts to break the levelling circuit at a place in the return travel of the elevator toward floor level which depends upon the distance that the said switch opening member has swung, and hence depends on the distance the elevator stops from thesaid predetermined distance from the floor level.

6. In an automatic levelling-device for elevators and the like, an operating circuit, a levelling circuit in the operating circuit, a switch in the levelling circuit located on the elevator, a cam mounted on the elevator shaft and having a sloping cam face, a switch closing member, a member adapted to engage the cam face and operate the switch closing member to close the switch at a predetermined point in its travel over the cam face in one direction to initiate starting of the elevator in the opposite direction, and means for opening the switch at the point in the travel of the switch operatin member over the cam in said opposite direction depending on the distance the cam engaging member has travelled on the cam away from the predetermined switch closing point, said last mentioned means including a magnet in the operating circuit energized by closin the switch to hold the switch opening member at a point corresponding to the position of the cam engaging member over the cam face at substantially the instant when the starting of the elevator is initiated,

7. In an automatic levelling device for elevators and the like, an operatin circuit, a levelling circuit in the operating circuit, a cam mounted on the elevator shaft and having a sloping cam face, a member mounted on the elevator and adapted to engage the cam face, a pivoted switch closing member operated by the cam engaging member, fixed contacts in the levelling circuit, a contact bridging member carried by the switch closing member and adapted to engage and disengage the fixed contacts to close and open the leveling circuit, a lost motion device to permit movement of the switch closing member past the point at which the bridging member engages the fixed contacts a distance depending on the distance the cam engaging member travels over the cam surface, a switch opening member carried in switch closin direction by the switch closing member, and a magnet energized by the closing of the switch and adapted to hold the supplementary switch opening member at a point corresponding substantially to the position of maximum movement of the switch closing member in the switch closing direction, said switch opening member being adapted to engage the contact bridging member to disengage it from the fixed contacts when the switch closing member moves away from switch closing position.

8. In an automatic levelling device for elevators and the like, an operating circuit, a levelling circuit in the operating circuit, a cam mounted on the elevator shaft and having a s1oping cam face, a member mounted on the elevator and adapted to engage the cam face, a pivoted switch closing member operated by the cam engagin member, fixed contacts in the levelling circuit, a contact bridging member carried by the switch closing member, and adapted to engage and disengage the fixed contacts to close and open the levelling circuit, a lost motion device to permit movement of the switch closing member past the point at which the bridging member engages the fixed contacts a distance depending on the distance the cam engaging member travels over the cam surface, a switch opening member carried in switch closing direction by the switch closing member, and a magnet energized by the closing of the switch and adapted to hold the supplementary switch opening member at a point corresponding substantially to the position of maximum movement of the switch closing member in the switch closing direction, a member pivotally mounted on the switch opening and closing member for carrying the contact bridging member, said supplementary switch opening member being adapted to pivot the member which carries the contact bridging member to accelerate its movement away from the fixed contacts when the switch opening and closing member moves in a switch opening direction.

9. In an automatic levelling device for elevators and the like, as claimed in claim 5, means actuated by the operating circuit for moving the cam engaging member out of cam engaging position when the operating circuit is closed.

10. In an automatic levelling device for elevators and the like, as claimed in claim 6, means actuated by the operating circuit for moving the cam engaging member out of cam engaging position when the operating circuit is closed, said means including a magnet energized by the operating circuit, an armature, and link and lever system between the armature and the cam engaging member, whereby energization of the magnet moves the cam engaging member to noncam engaging position through the medium of said link and lever system.

HAROLD C. CRANE.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,781,792 Rodman Nov. 18, 1930 2,145,809 Taylor Jan. 31, 1939 2,414,562 Santini Jan. 21, 1947

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