US3688874A

US3688874A - Elevator motor control system employing power amplifier with output current limiting arrangement

Info

Publication number: US3688874A
Application number: US170072A
Authority: US
Inventors: John Lusti; William Paul Reid
Original assignee: Otis Elevator Co
Current assignee: Otis Elevator Co
Priority date: 1971-08-09
Filing date: 1971-08-09
Publication date: 1972-09-05
Anticipated expiration: 1989-09-05
Also published as: JPS4825458U; AU462309B2; AU4539172A; JPS5412835Y2; GB1385093A; CA960386A; ZA725374B

Abstract

An arrangement for an elevator control system employing a power amplifier for supplying excitation current to a dynamo winding for controlling the speed of the elevator car wherein the magnitude of the current of both polarities which the amplifier is capable of supplying is limited in response to the approach of the car to a predetermined distance of a landing at which it is stopping and wherein only the limitation for one polarity is removed in response to the generation of a signal to start in a direction corresponding to that one polarity.

Description

United States Patent Lusti et al.

[54] ELEVATOR MOTOR CONTROL SYSTEM EMPLOYING POWER AMPLIFIER WITH OUTPUT CURRENT LIMITING ARRANGEMENT [72] Inventors: John Lusti, River Vale; William Paul Reid, Westwood, both of NJ.

[73] Assignee: Otis Elevator Company, New

York, NY.

22 Filed: Aug. 9, 1971 21 Appl.No.: 170,072

[52] US. Cl. ..187/29 R, 318/158 [51] Int. Cl. .1B66b 1/28 [58] Field of Search ..l87/29; 318/142, 158

[56] References Cited UNITED STATES PATENTS 3,410,367 11/1968 Bradley et al "187/29 1 l 1 24 I RAF Lin CAF [451 Sept. 5, 1972 3,536,969 10/1970 Laas .,318/158 Primary ExaminerBemard A. Gilheany Assistant Examiner-W. E. Duncanson, Jr.

Att0rney.loseph L. Sharon et al.

57 ABSTRACT An arrangement for an elevator control system employing a power amplifier for supplying excitation current to a dynamo winding for controlling the speed of the elevator car wherein the magnitude of the current of both polarities which the amplifier is capable of supplying is limited in response to the approach of the car to a predetermined distance of a landing at which it is stopping and wherein only the limitation for one polarity is removed in response to the generation of a signal to start in a direction corresponding to that one polarity.

5 Claims, 1 Drawing Figure s2 ux /HXI 1 I9 81 we (SF! o 665 c- G\F2 G\F4 GT6 2 eat 0x I HX 2 RDF ELEVATOR MOTOR CONTROL SYSTEM EMPLOYING POWER AMPLIFIER WITII OUTPUT CURRENT LIMITING ARRANGEMENT This invention relates to elevators and more particularly to an arrangement for improving the safe operation of elevators employing power amplifiers for supplying energy to the elevator hoist motor control equipment.

In high speed elevator systems it is becoming more prevalent to employ a hoist motor control system having a power amplifier. This is true whether the motor control system is of the closed loop type control which employs a relatively high gain negative feedback loop or of the open cycle type control not employing such a feedback loop. In either case the power amplifier is often used to provide excitation current to the field coil of a generator in a Ward Leonard type motor control system.

In such an arrangement the armature of a direct current hoist motor is connected in a closed circuit with the armature of a direct current generator which is driven by a suitable a.c. or d.c. motor. The power amplifier supplies variable excitation current to the field of the dc. generator to control its output and thus ultimat'ely the speed of the elevator car. The excitation current capable of being supplied must be of both polarities to enable the car to operate in both the upward and the downward directions. In addition, the magnitude of the excitation current capable of being supplied must be sufficient to enable the car to operate at a predetermined rated speed.

It is evident that if the power amplifier fails in its fully on condition when the elevator car is stopped or stopping at a landing and its doors are open or in the process of opening, a less than completely safe condition occurs because with such a failure the generator field starts to build up to its maximum excitation. Thus the generator armature and the motorarmature start to develop substantial electromotive forces. All of this occurs before any of the known safety arrangements sense the misoperation and prevent the system from further operation. Accordingly, by the time such safety equipment operates, considerable energy has been stored in the system, all of which must be dissipated before the safety equipment can bring the car to a complete stop and prevent it from further operation.

In addition to the foregoing, another less than completely safe condition can occur under those circumstances in which the elevator control system operates to enable the car to travel in one direction and -the power amplifier fails in the fully on condition producing current of the polarity associated with the other direction of travel. All of the normal operating equipment and the standard elevator safety equipment, except the final limit switches at the extreme ends of travel, are direction responsive. Thus, under the foregoing circumstances only the final limit switches can operate to stop the car, which means the car may strike either the buffer in the pit or the overhead beam at the upper end of travel.

It is, therefore, an object of this invention to improve the safety of elevator motor control systems employing power amplifiers.

In carrying out the invention in a preferred embodiment, a control system is provided for an elevator car which operates to transport loads between a plurality of landings in response to signals to start from and to stop at said landings. A hoisting motor is provided for imparting motion to the car and a generator applies voltage to the motor to control its speed. A field winding of the generator controls the magnitude of the voltage applied to the motor and a power amplifier supplies variable excitation current of either polarity to the field winding to enable the generator to apply sufficient voltage to said motor to operate the car at any speed from zero to a predetermined rated one in either the up or down direction of travel. A resistance circuit is connected in series with the power amplifier and the field winding to limit the magnitude of both polarities of current that the power amplifier is capable of supplying to the field winding and thus the speed of the car in both directions of travel is limited to a speed less than the predetermined rated speed. In response to a signal to start to travel in a particular direction, a conductance means provides a circuit in parallel with the resistance circuit to enable sufficient current of only the polarity associated with the particular direction to flow from the power amplifier to the field winding to enable the car to operate at the predetermined rated speed in the particular direction only. In response to the approach of the car to within a predetermined distance of a landing at which it is stopping, the parallel circuit established by the conductance means is interrupted.

One of the features of the invention is that the magnitude of the resistance connected in series with the power amplifier and the field winding is varied in accordance with the magnitude of the load in the elevator car so that the speed to which the car is limited while the resistance is effective is substantially the same throughout the range from a fully loaded up traveling car to an empty down traveling car.

Other objects, features and advantages of the invention will become evident from the following description when considered in conjunction with the appended claims and accompanying drawing, in which,

The sole FIGURE is a schematic wiring diagram of the circuitry of the presently preferred embodiment of the invention.

Referring now to the drawing, there is illustrated therein that portion of the motor control system disclosed in US. Pat. No. 3,442,352, granted to Otto Albert Krauer and Sidney Howard Benjamin on May 6, 1969, necessary to an understanding of the present invention as well as a presently preferred embodiment thereof. As explained in the foregoing Krauer et al patent, mounted on the shaft of armature 10 of a direct current elevator hoisting motor for rotation thereby is a traction sheave TS for the hoist ropes ll of an elevator car CA and its counterweight CW. An electromechanical brake BR is provided to be applied to a brake drum mounted on the shaft of armature 10 in any satisfactory well known manner. Main field 14 of the elevator hoisting motor is connected across a constant potential source schematically represented by battery 15. In accordance with the well known Ward Leonard principles of variable voltage control, motor armature 10 is connnected across the output of a direct current generator whose armature 16 is mounted on the same shaft as rotating element 18 of a suitable alternating or direct current drive motor, not otherwise shown. Main field 20 of the direct current generator is connected in series with resistor RDG and resistance circuit 19 between the center tap of the secondary of transformer 23 and the up and down polarity output circuits from the silicon controlled rectifier of reversible single phase full wave rectifying circuit, or power amplifier, 22.

The input connections to power amplifier 22 are across the secondary of transformer 23 by way of lines S1 and S2. The primary of transformer 23 is connected across a source of single phase, 60 cycle, alternating current indicated by lines 01 and 02. This same source is also connected to the input circuit of control device 24 which may suitably take the form of a magnetic amplifier. The output circuit of device 24 is connected to the gates of the silicon controlled rectifiers of circuit 22 to transmit firing pulses to these gates.

The output circuit of driving amplifier 26 is connected to another input circuit of device 24. Connected, in turn, to the input of driving amplifier 26 is summation network 28, which may suitably include a static element operational amplifier. Of the two input circuits to network 28, one is connected in a degenerative feedback arrangement through resistor RGF to generator field 20 and the other is coupled to summation network 30 through an RC stabilizing phase lag network 32 which symbolizes various passive networks those skilled in the art employ as suitable in different applications. Summation network 30, which also may suitably include a static element operational amplifier, is arranged with three input circuits. The first of these is connected to speed dictation apparatus described in detail in the foregoing Krauer et al. patent (not shown herein), the second to the output circuit of tachometer generator 34 mounted on the shaft of motor armature 10, and the third to feedback network 36 connected to the circuit of motor armature 10 through buffer amplifier 37 and condenser CAP and its parallel resistance RAF.

The manner in which the foregoing equipment (other than that which constitutes the disclosed embodiment of the present invention) operates to transport loads between landings Fl through F in response to signals to start from and to stop at those landings is fully explained in the foregoing Krauer et al patent and will not be repeated herein.

The subject matter which constitutes the disclosed embodiment of the present invention includes resistance circuit 19 comprising up direction resistor elements GFl, GF3 and GFS together with down direction resistor elements GF2, GF4 and GF6 in conjunction with their associated electro-magnetic switch contacts UXl, DXl, HXI, HX2, LlRl, L2R1 and L2R2. The coil circuits of the various electro-magnetic switches are not shown herein, but those skilled in the art will appreciate that that switch including contacts HXl and I-IX2 is operated to its actuated condition upon the generation of a signal to start to travel in either direction to enable the associated car CA to operate. Actuation of the switch engages its contacts I-IXl and I-IX2. The switch is operated to its unactuated condition to open its associated contacts HXl and l-IX2 upon the car approaching within a predetermined distance of a landing at which it is stopping. Similarly, the switches including contacts UK] and DXl are each operated in conjunction with the switch with which contacts HXl and HXZ are associated when the car travels in their respective up and down directions.

The switch including contacts HR] and LIR2 is operated to its actuated condition to close contacts LlRl and open contacts LlR2 upon a predetermined load being indicated as having entered car CA. This switch operates to its unactuated condition to reverse the condition of contacts LlRl and LlR2 upon less than this predetermined load being indicated as being in the car. The switch including contacts L2Rl and L2R2 similarly operates to its actuated and unactuated conditions upon the indication of a second predeter mined load being in the car and not being in the car, respectively. This second predetermined load is greater than the first mentioned predetermined load.

In order to understand the manner in which the present invention operates, assume that the elevator car CA is stopped at any of the landings. In these circumstances both contacts l-lXl and HXZ, as well as well as contacts UXl and DXl, are disengaged. As a result, depending upon the load indicated as being present in the elevator car, more or less of the up and down resistor elements GFl through GF6 are connected in the resistance circuits in series with generator field winding 20. Each of these series circuits limits the magnitude of its respective polarity of current which the power amplifier or full wave rectifying circuit 22 is capable of supplying to field winding 20. With the proper selection of resistor values, those skilled in the art will understand that the speed of the car in both directions of travel is limited to a magnitude substantially less than the installation s rated speed.

Upon the generation of a signal to start in a particular direction, one or the other of the circuits through contacts UXl and DXl is completed to provide a conductance path in parallel with the respective up or down direction resistor elements to enable the power amplifier to provide sufficient current to field winding 20 to enable car CA to operate at the installations rated speed in the particular direction indicated by the respectively engaged contacts UXl or DXl. Upon approaching within a predetermined distance of a landing at which the car is stopping, contacts l-lXl, l-IX2 and UXl or DXl again disengage to reinsert the appropriate resistor elements in series circuit with amplifier 22 and field winding 20 to again limit the speed of car CA.

From the foregoing it should be understood that a resistance circuit is provided in series with the power amplifier and the generator field winding which limits the current magnitude for both polarities of current that the power amplifier is capable of supplying to the field winding. This limits the speed attainable by the car in both directions of travel to one less than the rated installation speed. In response to a signal to start in a particular direction, a conductance means provides a circuit in parallel with the forementioned resistance circuit to enable sufficient current of only the polarity associated with the particular direction of travel in which the car is to start to flow from the power amplifier to the field winding. This enables the car to operate at its rated speed only in the particular direction in which it is to start so that its speed in the other direction of travel is still limited to a magnitude less than the rated speed. In response to the approach of the car to within a predetermined distance of a landing at which it is stopping, the parallel circuit established by the conductance means is once again interrupted so that the speed attainable is again limited to a magnitude less than the rated speed for both directions of travel.

in addition, the resistance circuit contains two load responsive switches. Each of these switches operates in response to the indication of a separate magnitude of load in the elevator car and each has associated contacts in parallel with resistor elements in both the up and down direction polarity circuits. Thus, the magnitudesof the resistance of each of these circuits is variable in response to load in two steps. As a result, regardless of the load in the elevator car from empty car to full load, the speed at which the car is capable of operating within a predetermined distance of a landing at which it is stopping is limited to a predetermined magnitude less than its rated value.

, Various modifications are considered possible and for that reason the foregoing is intended to be illustrative and not to be considered limiting in any sense.

What is claimed is:

1. In a control system for an elevator car operable to transport loads between a plurality of landings in response to signals to startfrom and to stop at said landings, a hoisting motor for said car, a generator applying voltage to said motor to control the speed thereof, a field winding for said generator controlling the magnitude of the voltage applied to said motor, a power amplifier operable to supply variable excitation current of either polarity to said filed winding to enable said generator to apply sufficient voltage to said motor to operate said car at any speed from zero to a predetermined rated speed in either the up or the down direction of travel, a resistance circuit connected in series with said power amplifier and said field winding limiting the magnitude of both polarities of current said power amplifier is capable of supplying to said field winding thereby limiting the speed of said car in both directions of travel to a speed less than said predetermined rated speed and conductance means responsive to a signal to start to travel in a particular direction providing a circuit in parallel with said resistance circuit to enable sufficient current of only the polarity associated with said particular direction to flow from said power amplifier to said field winding to enable said car to operate at said predetermined rated speed in said particular direction only, said parallel circuit being interrupted in response to the approach of said car to within a predetermined distance of a landing at which it is stopping.

2. In a control system according to claim 1, wherein said resistance circuit includes separate up and down direction resistor elements, each limiting the current of its associated polarity.

3. In a control system according to claim 2, load responsive means operable to vary the magnitudes of the resistance of both the up and down direction resistor elements in response to the magnitude of the load in the elevator car.

4. In a control system according to claim 3, wherein said power amplifier includes an up polarity output circuit and a down polarity output circuit, said up and down direction resistance elements beingconnected to their respective output circuits.

5. In a control system according to claim 4, wherein said load responsive means includes a plurality of switches, each 0 erabl in res onse o ase rat nitude of load itvhereiiy the magnitudes f 531%- sistance of said up and down direction resistor elements are variable in a plurality of steps.

Claims

1. In a control system for an elevator car operable to transport loads between a plurality of landings in response to signals to start from and to stop at said landings, a hoisting motor for said car, a generator applying voltage to said motor to control the speed thereof, a field winding for said generator controlling the magnitude of the voltage applied to said motor, a power amplifier operable to supply variable excitation current of either polarity to said filed winding to enable said generator to apply sufficient voltage to said motor to operate said car at any speed from zero to a predetermined rated speed in either the up or the down direction of travel, a resistance circuit connected in series with said power amplifier and said field winding limiting the magnitude of both polarities of current said power amplifier is capable of supplying to said field winding thereby limiting the speed of said car in both directions of travel to a speed less than said predetermined rated speed and conductance means responsive to a signal to start to travel in a particular direction providing a circuit in parallel with said resistance circuit to enable sufficient current of only the polarity associated with said particular direction to flow from said power amplifier to said field winding to enable said car to operate at said predetermined rated speed in said particular direction only, said parallel circuit being interrupted in response to the approach of said car to within a predetermined distance of a landing at which it is stopping.

4. In a control system according to claim 3, wherein said power amplifier includes an up polarity output circuit and a down polarity output circuit, said up and down direction resistance elements being connected to their respective output circuits.

5. In a control system according to claim 4, wherein said load responsive means includes a plurality of switches, each operable in response to a separate magnitude of load whereby the magnitudes of the resistance of said up and down direction resistor elements are variable in a plurality of steps.