United States Patent: 3584706

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United States Patent	3,584,706
Hall , et al.	June 15, 1971

SAFTIES FOR ELEVATOR HOIST MOTOR CONTROL HAVING HIGH GAIN NEGATIVE FEEDBACK LOOP

Abstract

A variable voltage hoist motor control wherein a pattern signal is compared with a feedback signal in a high gain closed loop and the signals at critical points in the control are monitored to ascertain unsafe operating conditions. Indicated unsafe conditions alter the control to either a safe operating mode or shut down the system. Monitored signals include the error signal at the summing point for the pattern and feedback signals, rate of change of the feedback signal, signal level at the high power levels for the motor control during the period the elevator car is to be stationary and to be driven at leveling speeds.

Inventors:	Hall; Donivan L. (Toledo, OH), Loshbough; Richard C. (Toledo, OH)
Assignee:	Reliance Electric Company (Euclid, OH)
Appl. No.:	04/758,776
Filed:	October 10, 1968

Related U.S. Patent Documents


Application Number	Filing Date	Patent Number	Issue Date
373136	Jun., 1964	3435916	Apr., 1969

Current U.S. Class: 187/289

Current International Class: B66B 1/28 (20060101); B66B 1/30 (20060101); B66b 005/02 ()

Field of Search: 187/29 317/13 318/20.070,20.085,141--143,309--311,329--331,436,445,449,450

References Cited [Referenced By]

U.S. Patent Documents


2620898	December 1952	Lund
2695376	November 1954	Emms et al.
3023351	February 1962	McLane et al.
3365637	January 1968	Safar

Primary Examiner: Rader; Oris L.
Assistant Examiner: Duncanson, Jr.; W. E.

Parent Case Text

CROSS-REFERENCE TO RELATED APPLICATIONS

This is a divisional continuation-in-part of application, Ser. No. 373,136 filed June 4, 1964 in the names of Robert E. Bell, Donivan L. Hall and Richard C. Loshbough now U.S. Pat. No. 3,435,916 entitles "Elevator Motor Speed Control Including a High Gain Forward Loop and Lag-Lead Compensation" which issued Apr. 1, 1969.

Claims

We claim:

1. A hoist motor control for an elevator having a guided path of travel comprising a hoist motor; means for generating a signal proportional over said performance parameter signal for disabling a performance parameter of said hoist motor as it drives the elevator along its path of travel; means for generating a performance parameter command signal to command said hoist motor to accelerate the elevator, to decelerate the elevator and to move the elevator at constant velocity along its path of travel; means for comparing said performance parameter signal and said command signal to develop an error signal; means for controlling the operation of said hoist motor in accordance with said error signal; and means responsive to an error signal representing a predetermined excess of said performance parameter signal over said command signal and responsive to an error signal representing a predetermined excess of command signal over said performance parameter signal for disabling the response of said motor to said error signal whereby said performance parameter signal is confined within predetermined magnitudes of said command signal during acceleration, deceleration and constant velocity operation of the elevator along its path of travel.

2. A hoist motor control for an elevator having a guided path of travel comprising a hoist motor; means for generating a signal proportional to a performance parameter of said hoist motor as it drives the elevator along its path of travel; means for generating a performance parameter command signal to command said hoist motor to accelerate the elevator, to decelerate the elevator, and to move the elevator at a constant velocity along its path of travel; means for comparing said performance parameter signal and said command signal to develop an error signal; means to amplify said error signal to control the operation of said hoist motor; and means responsive to an amplified signal representing a predetermined excess of said command signal over said performance parameter signal for disabling the response of said motor to said amplified signal, whereby said performance parameter signal is confined within predetermined magnitudes of said command signal during acceleration, deceleration and constant velocity operation of the elevator along its path of travel.

3. A hoist motor control for an elevator having a guided path of travel comprising a hoist motor; means for generating a signal proportional to a performance parameter of said hoist motor as it drives the elevator along its path of travel; means for generating a performance parameter command signal to command said hoist motor to accelerate the elevator, to decelerate the elevator, and to move the elevator at a constant velocity along its path of travel; means for comparing said performance parameter signal and said command signal to develop an error signal; means for controlling the operation of said hoist motor in accordance with said error signal; and means responsive to an error signal representing a predetermined excess of said performance parameter signal over said command signal and responsive to an amplified signal representing a predetermined excess of said command signal over said performance parameter signal for actuating an indicator.

4. A hoist motor control for an elevator having a guided path of travel comprising a hoist motor; means for generating a signal proportional to a performance parameter of said hoist motor as it drives the elevator along its path of travel; means for generating a performance parameter command signal to command said hoist motor to accelerate the elevator, to decelerate the elevator, and to move the elevator at a constant velocity along its path of travel; means for comparing said performance parameter signal and said command signal to develop an error signal; means to amplify said error signal to control the operation of said hoist motor; and means responsive to an amplified signal representing a predetermined excess of said performance parameter signal over said command signal and responsive to an amplified signal representing a predetermined excess of said command signal over said performance parameter signal for actuating an indicator.

5. A combination in accordance with claim 1 including means responsive while said elevator is stopped to enable said disabling means and responsive while said elevator is moving to render said disabling means ineffective.

6. A hoist motor control for an elevator including a car serving a plurality of landings comprising a hoist motor; means for stopping said car at one of said landings; means for sensing a misalignment of said car with said landing at which it is stopped; means for generating an elevator performance parameter signal proportional to a performance parameter of the elevator; means for generating a performance parameter command signal; means for comparing said performance parameter signal and said command signal to develop a performance parameter error signal for controlling said hoist motor, means for actuating said command signal generator in response to a misalignment of said car with said landing at which it is stopped to generate a signal tending to correct said misalignment; and means responsive to an error signal exceeding a predetermined level during the operation of said misalignment responsive control of said hoist motor for disabling the response of said motor to said error signal. &. A combination in accordance with claim 1 wherein said performance parameter is hoist motor speed; and including means amplifying said error signal;

and means applying said amplified signal to control said hoist motor. 8. A combination in accordance with claim 2 wherein said performance parameter

is hoist motor speed. 9. A hoist motor control for an elevator including a car serving a plurality of landings, said control comprising a hoist motor; means to stop said car at said landings; means to sense misalignment of said car with a landing at which it is stopped; means for generating a signal proportional to an operating parameter of said elevator; means for generating an operating parameter command signal; means for comparing said operating parameter signal with said command signal for producing an error signal; means to amplify said error signal; means to apply said amplified signal to said hoist motor to control said motor, first check means responsive to an error signal exceeding a first level; second check means responsive when said elevator is stopped at a landing to an amplified signal in excess of a second level; means to actuate said command signal means to issue a signal tending to align said car with a landing at which it is stopped in response to said sensing means, third check means effective while said actuating means is responsive, said third check means being responsive to an amplified signal in excess of a third level; and means responsive to the response to an excessive level of any of said check means for disabling the response of

said motor to said amplified signal. 10. A combination in accordance with claim 1 including an alternate motor control effective upon the disabling of the response of said motor to said error signal to continue operation

of said motor in response to said alternate motor control. 11. A combination in accordance with claim 1 including an alternate motor control responsive to said command signal upon the disabling of the response of said motor to said error signal to continue operation of said

motor in response to said alternate motor control. 12. A combination in accordance with claim 2 including an alternate motor control effective upon the disabling of the response of said motor to said amplified signal to continue operation of said motor in response to said alternate motor

control. 13. A combination in accordance with claim 2 including an alternate motor control responsive to said command signal upon the

disabling of the response of said motor to said amplified signal. 14. A combination according to claim 1 wherein said hoist motor is a direct current motor, said combination including a direct current generator supplying a variable voltage to the armature of said hoist motor; said generator having a shunt field divided into at least two portions; a first portion of said shunt field of said generator being connected to receive said command signal; a second portion of the shunt field of said generator being connected to receive said error signal and said disabling means interrupting the application of said error signal to said second portion

of said shunt field. 15. A combination according to claim 2 wherein said hoist motor is a direct current motor, said combination including a direct current generator supplying a variable voltage to the armature of said hoist motor; a shunt field for said generator divided into at least two portions; a first portion of said shunt field of said generator being connected to receive said command signal; a second portion of said shunt field of said generator being connected to receive said amplified signal; said disabling means interrupting the application of said amplified signal

to said second portion of said shunt field. 16. A combination according to claim 2 including means responsive while said elevator is stopped to

enable said disabling means. 17. A combination according to claim 2 including an elevator car driven by said hoist motor, closure means for said car, means sensing the opening of said closure means, and means responsive while said closure means is open to enable said disabling

means. 18. A combination according to claim 1 including means amplifying said error signal; means applying said amplified signal to control said hoist motor; and means responsive to an amplified signal in excess of a predetermined level for disabling the response of said motor to said error

signal. 19. A combination according to claim 1 including a generator supplying power to said motor; a shunt field for said generator; said means for controlling said hoist motor supplying power to said generator shunt field; and said disabling means disconnecting said controlling means

from said generator shunt field. 20. A hoist motor control for an elevator comprising a hoist motor; means for generating a signal proportional to an actual performance parameter of said elevator; means for generating a performance parameter command signal; means for comparing said performance parameter signal and said command signal to develop an error signal; means for controlling the operation of said hoist motor in accordance with said error signal; and means responsive to a rate of change of one of said signals at a rate in excess of a predetermined level for disabling the

response of said motor to said error signal. 21. A combination according to claim 20 wherein said one signal is that proportional to said actual

performance parameter. 22. A combination according to claim 21 wherein said performance parameter is velocity and said rate of change of said

performance parameter is acceleration. 54 23. A combination according to claim 22 including manually operable emergency stop means for said hoist motor, whereby excessive rates of change of motor velocity are imposed and means responsive to the reset of said emergency stop means for resetting said disabling means whereby said motor is rendered responsive to said error signal.

Description

Related motor controls particularly applicable to elevator hoist motors are disclosed in U.S. Pat. application, Ser. No. 380,385 filed July 6, 1964 in the names of Donivan L. Hall, Richard C. Loshbough and Gerald D. Robasziewicz entitled "Elevator Control," and U.S. Pat. application, Ser. No. 757,929 filed Sept. 6, 1968 in the name of Richard C. Loshbough entitled "Motor Control Having a Feedback Stabilized Generator."

SUMMARY OF THE INVENTION

This invention relates to motor controls and more particularly to controls for the hoist motor of an elevator.

Elevator hoist motors, particularly those employed for relatively high-speed operation of the elevator car, e.g., 800 feet per minute and above, are subject to rather critical control requirements due to the large inertial masses which are to be driven under a wide range of loadings, the precision with which the elevator car must be positioned when brought to a landing, and the smooth and comfortable accelerations and rates of change of acceleration which must be satisfied. It is common practice to counterbalance the elevator car and a portion of its load capacity, usually 40 percent of rated load. Thus, five conditions of loading are encountered on an elevator counterbalanced at 40 percent of rated load. When the car is loaded at 40 percent of capacity, only the inertia of the load must be overcome. For any other loading a variable, uncontrolled, unbalanced load is superimposed upon this inertia. When it is loaded less than 40 percent of rated load, the car when descending must be driven downward or retarded when ascending. When the load is greater, the car when ascending must be driven and when descending must be retarded.

Since floor to floor time is a major criteria of high caliber elevator service maximum comfortable smooth acceleration is sought under all of these conditions. Slowdown and stopping of the car should follow similar maximum decelerations for all loadings. Precise control of the elevator speed throughout its travel is therefore highly desirable in order that accurate initiation of slowdown and stopping of the car level with the landing is obtained at all loadings.

Heretofore the preferred elevator motor control has been a DC motor having a variable voltage source for its armature and a shunt field winding that can be energized at a constant level or with some limited range of variation to provide speed control. This type of control has been subjected to much refinement and to the superposition of auxiliary equipment in an effort to achieve the characteristics noted above. These have included numerous compensation means for variations in load, speed signal developing means which are fed back to the motor control, variable braking means dependent upon load or speed, supplemental motors to absorb some of the load torque particularly as the car is brought to a landing, and regulating generators responding to the factors noted including speed, loading and direction of travel.

Frequently, such variable voltage controls have been adjusted to incipient instability in an effort to achieve the maximum characteristics wherein adjustment has been critical, requiring the efforts of highly skilled personnel to adjust and frequently readjust the system. Further apparently identical lifting motors and lifting motor controls often required different adjustments and provide different operating characteristics under identical conditions. These systems have been sensitive to temperature variations, brush and commutator condition, brush position and to aging.

As set forth in the aforenoted related applications, these variations in operating parameters and their effects on the ride afforded by a hoist motor can be swamped out by closing a feedback loop on the control and introducing gain into the loop sufficient to force the error in control to acceptable levels. In elevator applications this usually involves a closed negative feedback loop having a loop gain in the order of 10 and the inclusion of suitable compensation to attenuate the closed loop gain as a function of increasing frequency sufficiently to reduce the closed loop gain to a value less than unity at and above the natural resonant frequency of the resonant circuit comprising the total inductance and resistance in the hoist motor armature circuit and capacitive effect of the total driven mass, including the elevator car, the driving means for the car and the counterweight, coupled into said armature circuit through the hoist motor. Elevators are suitably compensated by a lag-lead network having a lead break frequency in the range of 2.5 to 5 radians per second.

With a loop gain of 10, controls of the nature under consideration can respond to excursions of the signals which may be experienced in a manner resulting in unsafe operation of the elevator car. For example, where a controlled source feeds the shunt field of a generator supplying the motor armature, gains of 15 or more can be present in the source and the generator may have a gain of 4. Where a direct controlled drive for the motor is employed it may have a gain of 60. Excessive error signals to such controlled source or excessive outputs therefrom can be dangerous to both passengers and equipment.

It is an object of the present invention to obviate the above difficulties in a motor control system having the operating characteristics sought for high-speed elevators.

Another object is to apply a high level of gain to a signal representative of a performance parameter of an elevator hoist motor while avoiding instability of the system.

A further object is to avoid unsafe operating conditions in an elevator and its hoist motor, particularly with regard to high gain elements which upon certain malfunctions might operate the hoist motor at excessive speeds.

A fourth object is to monitor the feedback signal of a motor control system for transients indicative of a malfunction.

A fifth object is to monitor the error signal from the summing point of a closed negative feedback loop for excessive error signal levels.

A sixth object is to detect excessive signals in the feedback loop of a motor control occurring at times when only limited signal levels should be present.

In accordance with the above objects one feature of this invention resides in the provision of safety interlocks which are utilized to limit the energization of the motor in a high gain negative feedback closed loop elevator hoist motor control in the event of an excessive error signal, an excessive releveling signal or an appreciable speed signal prior to the start of the motor. More particularly, the interlocks may either reduce the response of which the motor is capable to acceptable levels or they may shut down the motor to avoid further operation under the potentially unsafe conditions.

Another feature involves an auxiliary control available to operate the motor to advance the elevator to the next landing at a reduced speed when an unsafe operating condition or an excessive signal is sensed. In one embodiment utilizing a Ward Leonard type system, the amplifier and its associated error signal circuitry is supplanted by a direct pattern control of the current in the generator shunt field.

DESCRIPTION OF THE DRAWINGS

The above and additional objects and features of this invention will be appreciated more fully from the following detailed description when read with reference to the accompanying drawings in which:

FIG. 1 is a functional block diagram of the system illustrating many of the salient features of the invention;

FIG. 2 is a schematic diagram of the system of FIG. 1 showing a velocity signal control of an elevator hoist motor;

FIG. 2a is a spindle diagram arranged to be aligned with FIG. 2 to locate the relay contacts shown in FIG. 2;

FIGS. 3 through 11 are waveforms of the signals appearing at various points in the firing circuit and output of the phase controlled, controlled rectifier source supplying the shunt field of the generator supplying the hoist motor in FIG. 2, the signals representing those present when a zero input signal is applied to the circuit;

FIGS. 3a through 11a are waveforms of the signals appearing at the same points as for FIGS. 3 through 11 respectively when a positive signal is applied to the input of the circuit;

FIG. 12 is a schematic diagram of a monitoring circuit suitable for providing the velocity error signal check, the zero signal check and the leveling signal check for the system of FIG. 2 as functionally represented in FIG. 1;

FIGS. 13 and 14 are across the line diagrams of certain of the elevator system controls which enter into the control of the hoist motor operation, particularly with respect to stopping the elevator, leveling it at landings and enabling it to apply its unbalanced load to the hoist motor, together with certain safety and bandwidth control functions;

FIG. 15 is a composite diagram partially in block form and partially in schematic form showing another embodiment of this invention wherein the entire generator shunt field is controlled through a closed negative feedback loop having high gain and showing particularly certain details of the safety monitors; and

FIG. 16 is an across the line diagram of fragments of the controls for the system of FIG. 15 showing the relay logic of the safeties for the system.

Before proceeding with a detailed description of one embodiment of the invention, certain aspects of the drawings will be discussed. A number of relay contacts are shown in FIGS. 2 and 13 through 16. These contacts are all depicted in the condition they assume with their actuating coils deenergized and their armatures released. Two forms of diagram have been employed. In the schematics of FIGS. 2 and 15 the contacts of relays, the actuating coils and energizing circuits for which are shown in FIGS. 13, 14 and 16, are disclosed. The spindle diagram of FIG. 2a is provided to facilitate the location of these contacts. When FIGS. 2a and 2 are placed side by side in alignment the contacts on FIG. 2 are horizontally aligned with their vertical position along the spindles of FIG. 2a.

The across the line diagrams of FIGS. 13, 14 and 16 are arranged with the contacts physically separated from their operating coils. In order to provide a correlating means these diagrams are provided with a marginal index on the right side. Line or zone numbers are assigned to horizontal bands extending across the diagrams and are set forth in the index in the first column to the right of the diagrams. Each zone containing an operating coil has that coil listed in the index next to the zone number and all contact depicted in the diagrams are listed by their zone number next to the reference character for the coil. Those contacts which are normally closed and are opened when the coil is energized or the armature pulled in, back contacts, have their zone numbers underlined to distinguish them from front contacts which are also listed by their zone numbers. Certain of the contacts on FIGS. 14 and 16 are mechanically operated as by the position of a cam shaft employed in generating the pattern command for the hoist motor or by the position of the doors. The cam shaft contacts are provided with the prefix V, the door contacts are numbers.

In order to further facilitate an understanding of the circuits a list of the relay symbols set forth in alphabetical order with their functional designations and, where shown, the zone location of their actuating coils follows: ##SPC1## ##SPC2##

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

A block diagram of the system of this invention is shown in FIG. 1. In the illustrative embodiment a speed pattern or speed command generator which comprised a group of resistors selectively connected and disconnected in a combination of series and parallel circuits is supplied from a direct current power source. The resistor interconnections can be controlled by a group of inductor switches mounted on the elevator car so as to be actuated as the car moves along the hatchway and they are carried into proximity with ferromagnetic vanes secured in the hatchway at critical positions spaced from the landings. Other resistor connections are made by means of cam actuated switches which are driven through suitable motion reduction devices in accordance with the car position with respect to its starting or stopping position. Such a system is set forth in detail in U.S. Pat. application, Ser. No. 343,301 filed Feb. 7, 1964 for Elevator Control in the names of Robert O. Bradley and Paul F. DeLamater.

During the running of the elevator from a landing and until it enters the final portion of its stopping region, the speed pattern is fed to a first section of the shunt field of the generator supplying the variable voltage to the armature of the hoist motor. In addition to supplying a portion of the generator field flux the first section tends to smooth the steplike pattern developed from the closure of switches in the pattern generator.

The smoothed pattern signal is combined with a hoist motor speed error signal as that representing the difference between the pattern speed commanded and the current elevator or hoist motor speed. This error signal is then fed through a compensating network which adjusts both the phase and magnitude of the signal to permit an increase in both the gain and the bandwidth of the system within which it will operate without instability.

A high gain buffer amplifier, one having a gain of from 50 to 100, applies the amplified and compensated speed error signal to a second portion of the generator shunt field to determine the voltage level applied by the generator to the armature of the hoist motor. It should be noted that with this arrangement, a car can be driven by the first portion of the generator shunt field once it has attained full speed and the speed signal will supply a correcting flux to overcome only such losses as those due to unbalanced load, generator saturation, and windage. Further, excessive speed error signals indicative of a malfunction can be readily sensed and made to actuate controls which control the speed of the hoist motor and car only through the first portion of the generator shunt field and the speed pattern generator, effectively eliminating the amplified error signal from control until corrective action or inspection and reset of the system has been completed.

Returning to the first portion of the generator shunt field, during the final approach of the elevator to the landing at which it is to stop, this portion of the field is rendered ineffective and the pattern and speed signals are compared to effect control of the car entirely through the second portion of the field. Under these conditions the system exhibits broad bandwidth characteristics which are advantageous for picking up the load, stopping accurately, and releveling, if required.

In the illustrative example the amplified and compensated velocity error signal controls the phase of a firing circuit for a pair of controlled rectifiers connected with like polarity electrodes each connected to one of the two terminals of a single phase alternating current source. These rectifiers are triggered, for zero signal input to their firing circuit, by an alternating current shifted 1350.degree. from the line phase so that they are each conductive a like period and the net DC derived therefrom is zero. Changes in this supply to the load are achieved by raising or lowering the base of the firing signal to increase the conduction interval in one rectifier over that in the other for a first polarity of pulsating unidirectional current and to reverse that relationship for the opposite polarity when the base of the signal is shifted to the other side of the zero signal level.

The rectifiers are illustrated as supplying a portion of the shunt field of a direct current generator having an armature connected to the armature of the hoist motor. The high gain amplifier and compensator can effectively be applied to control the hoist motor by other techniques in accordance with this invention. For example controlled rectifiers can be employed to supply the hoist motor armature directly, advantageously in a polyphase arrangement. Accordingly, this invention contemplates an amplifier which can be considered a composite of a buffer amplifier, a controlled rectifier or magnetic amplifier power stage and control circuits for the power stage applied directly to the hoist motor or the amplifier can be considered to include the controlled rectifier and the direct current generator in the present example.

Since the primary concepts of elevator hoist motor control involved in the present system include the utilization of a high gain amplifier with suitable compensation to avoid instability and responsive to a principal operating parameter to swamp out the effect of the numerous variables inherent in hoist motor controls, it is to be appreciated that these concepts can be applied to other than a velocity based system. While the exemplary embodiment utilizes a hoist motor speed signal as derived from the counter e.m.f. of the motor corrected for armature current and brush drop effects or from a tachometer, it is to be appreciated that other operating parameters of the system might be employed as the basis of control. Monitoring the motor armature current to measure the required torque can be related to acceleration in a manner to provide effective control. Where signal proportional to an operating parameter other than speed is employed, a suitable modification of the command signal to produce the desired operating parameter is made so that the command signal and the operating parameter signal can be compared to produce a suitable error signal. However, the compensation and amplification of this error signal will involve the same considerations presented here.

In any such system where amplification of the signal to the hoist motor can result in excessive speeds, acceleration, or rate of change of acceleration, the check and interlock functions of the present example are advantageously incorporated. Thus the velocity error check is made at the summing point of the command signal and hoist motor speed signal. This check occurs prior to amplification of the signal but effectively checks the amplifier since any tendency of the amplifier to run away will result in an excessive error signal at the summing point. The check of the zero signal when the elevator is stopped and the leveling signal check when it is leveling is made on the amplified signal. Thus in the example this check is made at the input to the generator shunt field. If any of these checks indicate an excessive signal the alternating supply is disconnected from the controlled rectifiers thereby disabling the supply to the shunt field or, in the case of a zero check, starting is prevented.

The schematic diagram of FIG. 2 shows the principal elements of the system as represented in the block diagram of FIG. 1. A three-phase supply 11 feeds a suitable rectifying circuit including filters to provide a smooth output from the block 12. This output is fed to a speed pattern generator of the type discussed above or an equivalent thereof, represented by a rheostat 13 having sequentially operated contacts 14, and through brake relay and main switch contact BK-3 and M to a reversing circuit.

The reversing circuit applies the pattern signal to a portion of the generator shunt field PF hereinafter termed the pattern field. This circuit is controlled by conventional generator field relays of the elevator circuit as by up generator field relay UF or by down generator field relay DF to reverse the polarity. The inductance of the pattern field tends to smooth the current through resistance 16 and parallel potentiometer 17 in which the difference between the smoothed pattern voltage and a speed voltage derived from the hoist motor 18 is developed as a speed error signal. This summing point thus constitutes means for comparing the speed or other performance parameter signal with the pattern or command signal to produce an error signal. Since the speed pattern lags the command from rheostat 13, when the elevator car approaches the landing at which it is to stop, this lag becomes detrimental and precise positional control is sought. Accordingly, it is advantageous to eliminate the pattern field at this time. This is done by opening the back contact R14 in series with the pattern field and by closing contact R14 around the field whereby the pattern is fed directly to the resistances 16 and 17. At this time the circulating current in the field is dissipated through resistance 19 which can be of the order of 500 ohms whereby the pattern field will decay in about 0.2 seconds. In the event the rapid decay produces an undesired response in the generator 21 supplying hoist motor 18, the pattern can be adjusted to overcome this effect at the time it occurs.

Hoist motor 18 is provided with a shunt field 24 energized from a suitable source of direct current, as shown at 231 of FIG. 14, which may include some control of the current therein as a speed control supplementing the primary control afforded by the voltage impressed across the motor armature. Generator 21 provides a controlled motor armature voltage. Its armature is driven at a constant speed by a suitable prime mover (not shown) and its output voltage is controlled by control of the current in its shunt field made up of pattern field PF and error field EF. Error field EF is supplied with current from rectifiers controlled by the amplifier 25 and in turn the error signal from potentiometer tap 22.

The speed signal is fed to potentiometer 17 on lead 26. It is derived from a bridge arrangement as disclosed in Robert O. Bradley U.S. Pat. application, Ser. No. 368,623 which was filed May 19, 1964 and is entitled Motor Speed Control, now U.S. Pat. No. 3,358,204 which issued Dec. 12, 1967. This arrangement provides a voltage proportional to the e.m.f. generated in the motor, and thus the motor speed, while eliminating the effects of brush drop and armature current on that voltage. It involves providing pilot brushes 27 and 28 on motor armature 18. A potentiometer 29 is connected across the generator interpole winding GIP, one main brush 30 of the motor and the motor armature 18 to pilor brush 28. A second potentiometer 31 is connected from pilot brush 27 across main brush 30. With the taps 32 and 33 of potentiometers 29 and 31 set so that the resistance of their upper portions is related to the resistance of their lower portions in the same proportion as the external resistance provided by the generator interpole windings GIP is related to the motor armature resistance, the voltage developed between taps 32 and 33 is proportional to the speed voltage of the motor. In the example tap 33 is grounded and tap 32 is connected through lead 34 to the voltage divider provided by series resistance 35 and resistance 36 connected to ground so that a signal also proportional to the speed voltage of the motor is fed on lead 26 to potentiometer 17.

The error signal taken as a voltage at tap 22 of potentiometer 17 is applied through loop gain adjustment potentiometer 37 to the compensating filter 38. This filter adjusts the magnitude of the signal applied to the input of amplifier 25 as it results from an error signal in accordance with the rate of change of that error signal whereby the effective signal is attenuated when its effective frequency is in the range where the system is unstable. This filter passes constant signals effectively without attenuation through the serially connected resistances 39 and 41 since its insertion loss is made up in the amplification around the loop. It also passes very high frequencies without significant attenuation through the bridging capacitance 42. At intermediate frequencies, attenuation is caused by the passing of a portion of the signal to ground as through resistance 43 and capacitance 44 and in the following section through resistance 45 and capacitance 46. The effect of this compensating network will be discussed in more detail below. However, it can be characterized as attentuating the closed loop gain as a function of increasing frequency sufficient to reduce that closed loop gain to a value less than unity at and above the natural resonant frequency of the resonant circuit comprising the total inductance and resistance in the hoist motor armature circuit and the capacitive effect of the total driven mass coupled into the armature circuit through the hoist motor.

From compensating network 38 the error signal is passed over lead 47 to notch filter 48 which is tuned to reject 60 cycle per second signals which might be picked up through spurious coupling to the line supplying the system. This filter is made up of a parallel-T network including resistances 49 and 51 with capacitance 52 to ground and capacitances 53 and 54 with resistance 55 to ground. Capacitance 56 connects the output of the network to ground.

The output of the filter 48 is connected by lead 57 to the input of direct current amplifier 25 at the base of transistor Q1. This amplifier is stabilized by negative feedback to provide the desired amplifier gain. It comprises a plurality of transistor amplifier sections biased from a bus 58 held at positive 12 volts and a bus 59 held at negative 12 volts. Terminal 60 is also connected to a positive 12 volt supply to produce a voltage divider for zero adjustment potentiometer 61. This potentiometer is accurately regulated by forward biased diodes 62 to ground so that it can be adjusted for zero voltage at the emitter of transistor Q9 with zero input on lead 57.

Operation of the amplifier 25 to control the firing point of the controlled rectifiers supplying field EF will best be appreciated from a consideration of its operation. Application of a positive input on lead 57 will raise the emitter voltage of Q1 through the increase in the current flowing in resistance 63. The resultant increase in base voltage of transistor Q2 causes an increase in current in resistance 64 to raise the emitter of Q2 and Q3.

The base of Q3 is held at a constant voltage so that the increase of Q3 emitter voltage reduces the collector current and causes a rise in the potential at junction 65. Transistor Q4 is a constant current source in the collector circuit of transistor Q3 and causes this stage to have extremely high gain.

In order to ensure stability transistors Q1 and Q5 are mounted to maintain uniform temperatures. Q5 offsets any base-to-emitter voltage of Q1 by establishing the base voltage of Q3.

When the voltage at junction 65 and the base of transistor Q1 rises, the emitter of Q6 increases its voltage be decreased current flow in resistance 66. This increases the base voltage on transistor Q7 causing the emitter of Q7 to increase its voltage with the reduced drop in resistance 67. The emitter voltage of transistor Q8 is increased thereby causing an increase of Q8 collector current since the base of Q8 is held at a constant level by Zener diode 68. The increased collector current through collector resistor 69 raises the voltage on lead 71 to the base of transistor Q9 forcing the emitter of Q9 to raise the voltage at junction 72.

Amplifier stability is ensured by feeding a portion of the Q9 emitter voltage back to the base of Q5 through resistor 73. Resistor 73 is shunted by a condenser 74 which imparts stability to the feedback loop by introducing some lead into that loop. The magnitude of resistor 73 determines the amount of negative feedback in accordance with well-known principles and if desired can be adjustable. The amount of signal fed back is also determined by ground resistor 75. This arrangement is such that the increase in Q9 emitter voltage in response to an increase in input or Q1 base voltage (e.g., by a factor of 500) causes the Q.sub.5 base voltage to be increased by the same amount as the input. Such an increase at Q5 base voltage results in a current change in resistor 77 increasing Q.sub.5 emitter by the same voltage and thus Q.sub.3 base by that voltage. It will be recalled that Q.sub.3 emitter voltage increased by the amount of input voltage change. Therefore the base-to-emitter voltage of Q3 is the same at this new signal level as when zero input was present. The system is thus stabilized since a tendency of Q.sub.9 emitter voltage to drop causes a corresponding rise in Q.sub.3 collector voltage which forces the Q.sub.9 emitter voltage to rise.

Condenser 78 passes high frequency components of the signal at Q4 collector to ground to stabilize the amplifier and condenser 79 from the base of Q.sub.9 is also included for stabilization.

The firing circuit of the controlled rectifiers is based upon a displacement of the firing wave from the applied line wave so that a pair of back-to-back rectifiers are fired symmetrically to produce no net current at zero signal and are fired assymmetrically to apply either a positive or negative net current on the generator shunt field EF depending upon the direction of the shift in firing angle.

Transformers T.sub.1 and T.sub.2 are each driven from the same line voltage so that their inputs are in phase. The output of transformer T.sub.1 is phase shifted 135.degree. by the three, cascaded, phase shifting networks each comprising a condenser 81 and a resistor 82. Exact adjustment of this shift is obtained by means of potentiometer 83. This voltage is summed with the output of the amplifier 25 in the summing network of resistors 84 and 85. Resistor 86 connected from a highly regulated positive source of direct current (not shown) to lead 87 and the base of transistor Q10 offsets any threshold voltage of Q.sub.10.

In considering the firing circuit two sets of waveforms will be considered. The first set represents the signals at various points in the circuit when zero input is applied at lead 57. The second represents the signals at corresponding points when a positive input or error signal exists. The second set will be distinguished by a lower case a.

The waveform across the resistor 85, which is applied on lead 87 in a form modified by the clamping action of diode 88 and the base-emitter diode of transistor Q10 to the base of Q10 with no output from amplifier 25, is shown in a sine wave A shifted 135.degree. from line sine wave B and having its origin shifted as shown in FIG. 3. The waveform at the collector of Q10 is shown in FIG. 4. Excessive reverse bias on Q10 from the AC signal on 87 is avoided by the diode 88 which passes negative signals above its threshold to ground. When applied voltage reaches the threshold voltage of Q10, the transistor begins conducting current and the drop in resistor 89 causes the collector voltage to drop at junction 91. The collector waveform corresponds to the input until the transistor becomes saturated and the curve flats.

Transistor Q11 is an emitter-follower whose emitter voltage would correspond to the signal at junction 91 but for the clamping action of the base-emitter diode of transistor Q12. The dashed line in FIG. 4 is the emitter waveform of Q11.

The collector wave of Q12 is shown in FIG. 6, and the waveform of Q13 is shown in FIG. 5. Transistors Q12 and Q13 and their associated circuitry constitute a Schmitt trigger wherein the triggering signal is developed at junction 91. When zero signal is present at 91, transistor Q13 is conductive and transistor Q12 is held off.

As the base of Q12 goes positive with the emitter of Q11, collector Q12 draws current through resistors 92 and 93 reducing the voltage on base Q13 below its sustaining level and terminating conduction in Q13 whereby its collector voltage rises at junction 94. The increased voltage on the control electrode of silicon-controlled rectifier SCRA causes that rectifier to conduct when its applied anode-cathode voltage from transformer T2 is in the forward direction. At this time the voltage at junction 95 is the forward drop of diode 96 above ground and, in view of the forward drop of diodes 97, the voltage on the control electrode of SCRB is brought to ground through resistor 98 to enable its conduction to be terminated.

When the base of Q12 returns to ground, it is cut off and the voltage at the collector of Q12 rises. This voltage is applied through the voltage divider of resistors 99 and 101, and diode 102 to the base of Q13 so that it initiates conduction. The voltage at junction 94 falls below the threshold of diodes 103 so that the control electrode of SCRA is grounded through resistor 104. At this time the potential at junction 95 has risen so that when it exceeds the threshold of diodes 97 the control electrode of SCRB is driven positive beyond its threshold of conduction to enable SCRB to fire.

The collector signals of Q13 and Q12 as shown in FIGS. 5 and 6 are at levels V2 and V1 determined by the conduction drop of the gates of SCRA and SCRB and the threshold voltages of the diodes 103 and 97 in the collector circuits. The voltage in series with the SCR's and load is in phase with the line supplying the primary of T2. If the load were resistive, the voltage across SCRB is shown in FIG. 7 while that across SCRA would be similar for the other half cycle. The resulting waveform across a resistive load would appear as in FIG. 8.

The circuit for SCRA would extend from grounded junction 105 through rectifier 106, junction 107, brake relay contact BK-5, resistor 108, contact BK-4, junction 109, closed "power" switch 111, contact SCR-2, the secondary of transformer T2, fuses 112, switch 111, contact SCR-1, SCRA and junction 105. The corresponding circuit for SCRB is traced through rectifier 113. It should be noted that pilot lamp 114 is connected across the secondary of transformer T2 to indicate power is applied to the firing circuit at terminals 115 and 116 connected to T1 and to the SCR circuit. When the generator field power is on, pilot lamp 117 is illuminated.

The true load on the SCR's is the highly inductive generator field EF and the resistor 108 is significant only when the generator suicide connections are made to permit the decay of the field. This inductive load imposes limits upon pulsating current so that virtually no DC flux could be developed in the field winding alone. However, circulating currents are permitted without any direct current loss by shunting field winding EF with a large capacitance 118, e.g., 1,500 mf. This arrangement is further enhanced in its operating characteristics, particularly with respect to the surge currents through SCRA and SCRB, by including a relatively low inductance 119 in series with the capacitance as a limiting means, e.g., 0.01 henry and 0.16 ohm. This LC series circuit has substantial advantage over a shunting resistor of low value in that no DC power loss is incurred and the efficiency of the circuit is enhanced. Resistor 120 is of a relatively high value, e.g., 1,000 ohms, and therefore passes negligible current to the applied signal. Its function is to provide a discharge path for the LC circuit when the power is disconnected.

As a result of the high inductive load presented by field EF to the SCR's the current reaches its peak when the input voltage is zero. The SCR's do not turn off until the current goes to zero even if the impressed voltage has reversed sign. Therefore, the voltage across the inductive load of field EF is shown in FIG. 9. The voltage across SCRB for this load is shown in FIG. 10. A corresponding voltage is developed across SCRA for the other half cycle under this load.

The filter composed of capacitance 118 and inductance 119 employed to overcome the high impedance presented to pulsating voltages by field EF and to smooth the SCR outputs has a current form as shown in FIG. 11.

Since the areas under the curves of FIG. 11 representing flow in each direction for SCRA and SCRB and in the filters are equal the net of DC value is zero and the generator shunt error field EF receives zero input where the signal from amplifier 25 is zero.

A positive or negative signal from amplifier 25, indicating a velocity error signal, as it appears at junction 72 will alter the firing circuit and produce a net DC input to the shunt error field by shifting the phase of the firing signal. A positive signal indicative of a hoist motor speed less than the speed commanded when the commanded speed is plus, increases the conduction interval of SCRB while decreasing the conduction interval of SCRA. This change tends to change the generator voltage in a manner to increase the motor speed and decrease the error. Conversely, a negative signal at junction 72 for the same command signal will decrease the conduction interval of SCRB while increasing that of SCRA. This will tend to retard the motor speed by reducing the current in the field EF to reduce or reverse the impressed voltage on the armature thereby decreasing the motor speed to tend to decrease the error.

If a positive voltage is present at junction 72 the waveforms are as shown in FIGS. 3a through 11a. The firing circuit voltage waveform Aa is shifted positively as shown in FIG. 3a with the result that it achieves the threshold of Q10 earlier and sustains that threshold later to lengthen the interval of conduction for SCRB as shown in FIG. 6a and shorten the interval for SCRA as shown in FIG. 5a. The resulting change in the voltage applied to the field EF is shown in FIG. 9a. It will be noted that the flow in SCRB is substantially greater than in SCRA and a net current results causing a generator armature voltage which drives the motor 18. When the motor approaches the desired speed, so that the speed voltage on lead 26 balances the pattern voltage on potentiometer 17, the error signal approaches zero, the voltage at output junction 72 of the amplifier 25 is zero and the net DC into the fields is zero. Any change in motor speed results in a speed error signal which forces the motor back to its proper speed.

In view of the consequences of a malfunction in this system for an elevator hoist motor, particularly in the event the amplifier issues a large signal within the limits of the capacity of the element supplying power so that the power applied to the motor tends to cause excessive speed change, the present system has been provided with means for monitoring the signals and barring operation of the amplifier system when those signals exceed levels which are reasonable for the prevailing conditions. The monitoring is accomplished by completing enabling circuits for the amplifier system so that any failure of a monitoring element causes a "fail safe" operation and the amplifier system will not operate.

The armature of the generator is connected to the shunt field in the usual "suicide circuit" when the elevator car is stopped and the brake set as shown in FIG. 2. In this circuit a brake relay which is deenergized upon the setting of the brake closes its back contacts BK-1 and BK-2 to connect the generator armature to field EF, opens its contact BK-3 to field PF and opens both leads from SCRA and SCRB to EF at contacts BK-4 and BK-5. The suicide circuit causes armature current to flow in a manner to produce a flux opposing any buildup in the generator. The circuits of FIGS. 13 and 14 are shown across leads 158 and 159 which are supplied from a suitable source of direct current (not shown) connected across these leads.

While the elevator car is stopped, the elevator hoist motor shunt field 24, FIGS. 2 and 14 at line 231, has resistances 121 and 122 in series and is passing minimum current, the pattern signal source 13 is disconnected at main switch contact M and brake relay contact BK-3, the pattern field PF is isolated by open contacts of the up and down generator field relay UF-1, UF-2, DF-1 and DF-2, and the compensating network is discharged to ground through lead 26, potentiometer 17 and back contact BK-6 of the brake relay. A start signal is ineffective at this time unless the direct current output voltage is to be applied to the generator field EF is at the prescribed level. A zero check circuit as shown in FIG. 12 monitors this voltage and enables a start signal only if it is below a limiting level. The circuit of FIG. 12 is duplicated for monitoring the output from the amplifier when the elevator is releveling and for continuously monitoring the velocity error signal during a run. In the case of the zero check and leveling check the monitoring circuits corresponding to FIG. 12 are connected to FIG. 2 just ahead of the brake relay contacts between the source and generator field EF at terminals 107 and 109. The velocity error signal check is taken from a high input impedance amplifier 138 at terminals 130 and 130a. This amplifier derives its input as the difference between the speed signal feedback voltage and the input speed pattern voltage obtained from the high side of the gain potentiometer 37 of FIG. 2.

The voltage detector circuit employed for each of these monitoring functions, as shown in FIG. 12, comprises input leads 124 and 125 for connection respectively to the terminals 109 and 107 for zero and leveling monitors and terminals 130 and 130a for the velocity error monitor. A rectifier bridge 126 is provided to ensure that input signals of either polarity will result in a positive signal at resistor 127 and the upper end of potentiometer 128. Capacitance 129 avoids the effect of transients. The threshold signal places the 6-volt Zener diode 131 in conduction. Accordingly, the setting of potentiometer 128 establishes the desired threshold for each of the utilizations of this circuit.

An alternating voltage, e.g., 20 volts, is applied to leads 132 and 133. If the Zener diode 131 is subject to less than its threshold voltage, the base of transistor Q14 is at ground and the transistor is shut off. Under these conditions the half-wave current through the silicon-controlled rectifier SCRC energizes relay coil R since during the positive half cycle of the power supply Q14 collector voltage is high and turns on SCRC. The voltage across the relay coil R pulls in the relay while the diode 134 provides a conductive path for the current of the relay coil during the negative half cycles of the power supply.

When the voltage monitored across leads 124 and 125 is sufficient to raise the cathode voltage of the Zener diode 131 to its threshold for conduction, the voltage developed in resistors 135 and 136 raise the base voltage of transistor Q14 and turns it on. The collector current of Q14 causes sufficient drop at junction 137 to reduce the control electrode of SCRC below its trigger voltage. The absence of conduction in SCRC drops the relay having coil R.

Three relays ZCF, LCF and VCF respectively signifying safe signal levels when energized for the "zero check," the "leveling check" and the "velocity error signal check" have coils (none of which are shown) located in circuits as the coil R in FIG. 12. In the case of relay VCF the circuits of FIG. 12 is fed from a high impedance amplifier 138 as shown at the bottom of FIG. 2.

The error voltage amplifier 138 comprises an input 139 from gain potentiometer 37 to the base of transistor Q15 which is adjusted to a suitable potential by zero adjustment potentiometer 141 connected through resistors 142 and 143 to buses 144 and 145 respectively connected to suitable sources of direct current at negative 18 volts and positive 18 volts. When the brake relay is energized to open back contact BK-6, this circuit is effective. The emitter of Q15 is grounded. A positive error voltage applied to Q15 base reduces the collector voltage since the current in resistor 146 is reduced. This reduces the voltage applied through resistor 147 to the base of transistor Q16 thereby reducing the collector current of Q16 through resistor 148 to raise the voltage applied through resistor 149 to base of transistor Q17. Capacitance 151 between Q16 collector and ground prevents high frequency oscillation to stabilize the amplifier at high frequencies. The increase of voltage at base Q17 increases the collector current of Q17 thereby increasing the voltage drop across resistor 152 and reducing the voltage at terminal 130. A feedback path through lead 153 and resistor 154 stabilizes the amplifier by tending to decrease the effect of the increased error voltage. As in the preceding check circuits an increase in the absolute value of the signal between terminals 130 and 130a applied to the monitor of FIG. 12 causes velocity error check relay VCF having a coil as at R in FIG. 12 to drop.

As will be noted from FIG. 2, relay SCR must be energized to connect the alternating current to controlled rectifiers SCRA and SCRB through contacts SCR-1 and SCR-2. Relay SCR at 206 of FIG. 13 remains energized in normal operation. However, the check circuits are each effective to deenergize that relay or otherwise disable the amplifier feed to error field EF. Under these circumstances the pattern field PF, controlled by the command signal from rheostat 13 provides control for the elevator to bring it to a landing. Note that the deenergization of relay SCR also deenergizes the retard stop approach relay R14 at 238 by opening contact SCR at 238 whereby pattern field PF remains effective even when the elevator approaches a landing for a stop. An indicator "SCR OFF" is actuated by the drop of relay SCR to close its back contact at 210 and if the car was running or leveling during the drop of relay SCR, the relay is locked out by failure relay FE at 212 energized at back contact SCR at 212 and start relay contact ST and 212 to open back contact FE at 206 until FE is reset.

With the car stopped, the monitoring circuit for zero signal is effective, and if the threshold level is not exceeded relay ZCF is energized. With the doors open, as when stopped at a landing, and a start signal imposed, as during a normal starting sequence or during a releveling as might be required by a load change changing the stretch of the supporting cables, leveling signal monitoring is effective and if the signal is excessive relay LCF is deenergized to disconnect the amplifier. A car starting operation is initiated by energizing car starting relay CS (not shown) to close its contacts at 203 in the circuit of want to run relay WTR as shown in FIG. 13 at line 202. Pull in of WTR closes its contact at 214. If no velocity error has been sensed which is of a magnitude to drop relay VCF during the previous run of the elevator, relay SCR is energized through contacts FE and VCF at 206 and ST at 208 until the start signal is effective. With SCR energized contact SCR at 214 is closed. If the zero check relay is energized, indicating the zero signal below the threshold considered the lower limit of a malfunction, start relay ST is energized at line 214. Back contacts ST at 208 and 209 open while front contacts at 212, 215 and 220 close.

Contact ST at 208 enters in a leveling function and will be discussed below.

Contact ST at 209 opens the "off zero" indicator circuit so that the increased voltages applied to the generator field EF which result in the dropping of relay ZCF while the car runs, will have no effect. If during the stop ZCF had dropped at any time, the circuit at 209 would have been completed to actuate "off zero" indicator.

Failure relay FE at 212 locks out the system once it is energized by its seal contact FE at 213 and retains that state through its manually actuated reset switch at 213 until the switch is operated. Relay FE is energized by a coincidence of a start signal, which may be issued either as a conventional starting or by a releveling operation, to close contact ST at 212 and the drop of normally energized relay SCR to close back contact SCR at 212. As will be discussed relay SCR can be dropped by an excessive velocity error signal through the opening of contact VCF at 206 or during leveling, when contacts LG at 207 and ST at 208 are open by an excessive leveling signal which opens contact LCF. Thus, any leveling signal or velocity error signal exceeding the predetermined limits set for the two monitor circuits of relays LCF and VCF will drop SCR to pull in relay FE thereby locking out relay SCR by opening back contact FE at 206 and actuating the "reset" indicator by closing contact FE at 210. The drop of SCR will close back contact SCR at 210 to actuate the "SCR OFF" indicator, prevent energization of start relay ST by opening contact SCR at 214 and open the supply to SCRA and SCRB in FIG. 2.

Start relay ST can also be prevented from operation by an excessive zero check signal to deenergize relay ZCF and open contact ZCF at 214. In the event the zero check signal is within limits and the ST relay is pulled in, it seals itself at contact ST in line 215. This seal is required since, as the signal magnitudes are increased during the normal running of the car, contact ZCF at 214 will open.

The start sequence involves other functions. As indicated above, the hoist motor is arranged to pick up the load rapidly by arranging the system to function with a broad bandwidth in its response to signals during the initiation of starting. The broad bandwidth is achieved by effectively eliminating the pattern field as the motor developes a load sustaining torque. Relay R14 at line 238 of FIG. 14 provides this function while energized. It opens back contact R14 and closes front contact R14 in FIG. 2 so that pattern field PF is bypassed by the pattern signal and the field decays by circulating current in resistor 19. R14 remains energized during the final portion of the door closing interval and incidental thereto the brake is lifted after the car is sufficiently closed to prevent further load exchanges whereby the system senses the unbalanced load prior to any significant motion of the car. When the hatchway and car doors are completely closed, the speed signal then initiates car motion.

The start signal issued by relay CS closes contacts to energize door control relay DT (not shown) and at 216 to energize door close relay CLA in conjunction with closed contacts of door open control relay OPS (not shown) open while the door is opening, minimum start time relay TR (not shown) open until the door open interval has expired, door open control relay DO (not shown), open upon a command for a door opening operation, and door control relay DT all at line 216. CLA seals itself around start signal relay contacts CS at 217, energizes the brake relay BK at contact CLA at 220 if the safety switches are all closed and the start relay ST is energized to close its contact at 220 and partially completes circuits for the up and down generator field relays UF and DF and the landing and gate relay LG.

Relay CS also opens the leveling controls for relays UF, DF and BK at back contact CS at 221. The motor field is increased by the start signal through closure of contact CS at 228 to energize motor field normal relay MFN and close its contact around resistance 121 in series with motor shunt field 24 at line 231. Relay MFN also closes at 221 to afford a partial path for relays UF, DF and BK which will be retained after relay CLA is dropped by the opening of contact DT.

The motor field thus builds up as the car and hatchway doors are driven toward their closed position. Pull in of relay BK causes the energization of main switch M at 218 by the closure of contact BK at 217. Contacts BK-3 and M connect command signal to the reversing circuit by the closure of contacts BK-4 and BK-5 and the opening of BK-1 and BK-2 connects error field EF of the generator to the amplifier. Main switch energizes motor full field relay MFL by closing contact M at 230 to short resistor 122 in the motor field circuit by closed contact MFL at 233.

With both M and BK energized to close their contacts in the brake solenoid circuit at 235 a partial energization of the brake is effected. This is insufficient to lift the brake in view of resistors 161 and 162 and hence the elevator is held by the brake. As the doors advance toward their closed condition and after they are sufficiently closed to prevent further load transfers, door limit switch 163a at 232 is closed. This pulls partial brake relay PBK at 234 to close contact PBK at 235 and complete the brake solenoid circuit to lift the brake.

Upon the energization of the car start relay the path for energizing the generator field relays UF and DF is opened by back contacts CS at 221. Landing and gate interlock contacts 164 and 165 which are open until the interlocks make up with the doors fully closed are also open at this time. Coincident with the lifting of the brake the generator field relays are enabled through the leveling circuit so that any movement of the car due to unbalanced load will actuate leveling switches and cause a correcting command signal from rheostat 13 to be applied to the error signal means, potentiometer 17 and lead 26. Contact 163b closes around open car starting contact CS at 222 to enable leveling relay contacts LU and LD to energize generator field relay UF or DF. This circuit can be traced from closed MFN contact at 221, through closed 22-inch leveling relay contact L22 (closed while the car is within 22 inches of level with the landing at which it is stopped), and door limit contact 163b at 222. If the car sags downward, contact LD at 222 is closed to complete a circuit for up generator field relay UF through LD AND LU at 221. If it sags upward, contact LU at 222 is closed to energize DF through LU and LD at 222. Thus, a command signal is generated by the leveling relays through the closure of contacts 14 to change the command from sheostat 13 and the generator field relays connect the command at DF-1 and DF-2 and UF-2 to the amplifier. With the pattern connected and the field EF of the generator connected a signal is developed to sustain the load while the system is in its rapid response, broad bandwidth mode of operation.

Once the doors are fully closed and the interlocks made up, landing gate relay LG at 227 is energized through closure of interlock contacts 164 and 165 at 224. These contacts remain closed so long as the doors are fully closed.

While the car is in the leveling zone back contact LDO at 225 of leveling door open relay is open. This contact closes when the car is outside the zone in which door operation is normally permitted, e.g., 8 inches from the landing. It closes to maintain the generator field and brake relays after the car has stopped accelerating. During acceleration contact ACR at 223 provides an energizing path for these relays. The makeup of the landing and gate interlocks causes the energization of acceleration relays ACR and ACC to initiate the generation of a speed pattern in rheostat string 13 tending to move the car away from the landing. If the rheostat is not subject to a correcting operation at this time, contact V1 at 224 is closed and the generator field relays are energized from interlocks 164 and 165 through contact V1 at 224, acceleration relay contact ACR at 223 either direction determining relay U or D the overtravel limits 167 or 168, interlocked back contacts DF or UF all at 223 or 226 and relays UF or DF. Also at the time acceleration away from the landing is initiated back contact ACC at 238 is opened to deenergize relay R14 and insert pattern field PF across the command signal, thereby reducing the bandwidth of the system. The car then proceeds to develop speed steps as by the operation of hatchway inductor switches while closely adjacent its starting landing followed by operation of rheostat cams controlling contacts 14 by car motion as described in the aforenoted Bradley-DeLamater patent application, or by the operation of time based acceleration steps followed by operation of said rheostat contacts 14.

The drop of relay R14 closes back contact R14 and opens front contact R14 in FIG. 2 to reconnect the pattern field PF of the generator to the pattern signal and to reduce the bandwidth of the system whereby the accelerating steps of the hatchway inductor switches and the rheostat switch contacts is smoothed as it is combined with the speed signal from the hoist motor to produce a smooth error signal at potentiometer 37.

Door time control relay drops a brief timed interval following the pull in of relay LG to drop relay CLA. At this time alternate circuits are available for those controlled by CLA earlier in the sequence. Brake relay BK is now controlled through the circuits controlling generator field relays UF and DF. The motor field relays and main switch are also controlled by either BK or UF or DF.

If at any time during the run of the elevator an excessive velocity error signal is issued, velocity error check relay VCF will drop out opening contact VCF at 206 of FIG. 13.

Failure relay FE responds to a drop of SCR either during a run or a releveling operation since start relay ST is energized at such times to close its contact S.sup.T at 212. When FE pulls in, it seals itself at contact FE in line 213 until the manual reset switch is opened at 213.

As the car continues to accelerate on a normal run and as it approaches full speed, a further speed step is achieved by weakening the shunt field of the hoist motor. This is accomplished by opening normally closed contact V12 at 230 to drop motor full field relay MFL and open its contact at 233. Resistor 122 is placed in series with motor shunt field 24 in this manner to reduce its current. Contact V12 can be controlled by the cam device which actuates rheostat switches 14 of FIG. 2 when that device has advanced to the final speed step. Similarly, when the command to the car is to reduce speed, the contact closes to strengthen the field by removing resistor 122 from the circuit.

Upon approaching a landing at which the elevator is to be stopped the rheostat 13 is increased in effective resistance by the opening of does switches 14 to produce a speed pattern calling for a lower speed. Since the actual speed signal indicated on lead 26 will exceed the lower speed a retarding error signal will be transmitted to compensator 38 from potentiometer 37. Start relay ST of FIG. 13 remains energized until the car is stopped level with the landing as does main switch M, brake relay BK, generator field relays UF and DF, the motor field relays MFN and MFL, partial brake relay PBK and the brake solenoid.

While the car is running and more than a certain distance, e.g., 14 inches, from level with the landing at which it is to stop, the narrower bandwidth system is effective in which the speed pattern steps are smoothed by the presence of pattern field PF in the circuit. The stopping of the elevator involves inserting the resistance of rheostat 13 in the pattern signal source by opening contacts 14. When the controller for contacts 14 has returned to a condition in which it has no speed pattern control, it permits contact V2 at 238 to close. At this time the speed pattern of the elevator is a function of its position as ascertained by inductor switches which are carried past vane secured in the hatchway to actuate those switches when they are in proximity.

Inductor switch control is provided for a number of contacts shown in FIGS. 13 and 14. Contacts L22 at 221 and L14 at 238 open as the car approaches the landing for a stop and close when the car is within a given distance of its level position, e.g., 22 inches and 14 inches respectively. Landing door zone relay LDO (not shown) is energized by inductor switches when the car is within a zone in which the doors can be opened, e.g., 8 inches from level. A dead zone comprising a range of positions centered around absolute level and ordinarily extending between a half inch and an inch is defined as its upper limit by a leveling up relay LU (not shown) and at its lower limit by a leveling down relay LD (not shown) each responsive to inductor switches so that LU is energized if the car is at or above the level limit and in the leveling zone and LD is energized when it is at or below that limit and in the leveling zone. Either of relays LD or LU deenergize a dead zone relay DZ (not shown) if they are energized.

Advance of the elevator to within the range of proximity of level defined by relay L14 closes back contact L14 at line 238. Since the car is not set to accelerate relay ACC is deenergized and back contact ACC is closed at 238. If the amplifier is controlling the error field EF, relay SCR is energized to close contact SCR at 238. Hence during the stopping sequence, 14-inch regulation relay R14 pulls in at 238 and transfers the system to its broad bandwidth operating condition by bypassing pattern field PF in FIG. 2. The controls thereafter respond more rapidly to pattern steps as generated by the operation of the inductor relays and smoothness of the elevator motion is achieved by employing relatively small signal steps. This operation of R14 can also be considered as occuring in response to a given command signal since the closure of contact L14 is also indicative of a command signal step from rheostat 13.

While the elevator is running outside of the leveling zone for the landing at which it is to stop and is not accelerating, the brake relay and the generator field relays are energized through safety switches at 218, start contact ST at 220, motor field normal contact MFN at 221, landing and gate interlocks 164 and 165 and pattern generator corrector contact V1 all at 224, contact LR1 and landing door zone contact LDO to junction 166. An ascending car having relay UF in maintains a circuit from 166 through contact UF at 224, upper overtravel limit switch 167 and back contact DF at 223 and relays UF and BK to lead 159. A descending car has a circuit for DF and BK from junction 166 through contact DF at 225, lower overtravel limit switch 168 and back contact UF at 226.

When the car is advancing in the leveling zone contacts L22 and CS at 221 are closed so that a leveling circuit for relays UF, DF and BK is available when the door zone is entered and back contact LDO at 225 is opened to interrupt the running circuit for those relays.

A car is stopped level when both of relays LU and LD are deenergized and the car is in the dead zone. This is accomplished since relays UF, DF and BK are all dropped to disconnect the generator and motor from the amplifier and set the brake. Front contacts LD at 221 and LU at 222 open to interrupt the circuit for relays UF, DF and BK and front contacts LD at 201 and LU at 202 open with generator field relay contacts UF at 204 and DF at 205 to drop want to run relay WTR and through the opening of contact WTR at 214 start relay ST.

A releveling operation as occasioned by changes in effective cable length due to changes in load, commonly termed "sag," functions through this system by operation of one of the leveling relays LU or LD. An upward sag energizes relay LU to cause releveling downward. A downward sag energizes relay LD to relevel upward.

If LD is energized a circuit is completed to pull in relay WTR at 202 through contacts LD and LU at 201. This completes a circuit for start relay ST at contact WTR at 214. If the zero check is within limits, contacts ZCF at 214 is closed and the closing of contact WTR energizes relay ST. If the leveling check indicates a signal from the amplifier within limits, contact LCF at 206 is closed and relay SCR remains energized, provided failure contact FE at 206 is not open and the velocity error check is within limits so that contact VCF at 206 is closed. The only circuit available to relay SCR at this stage in the releveling operation is through contact LCF at 206 since the car doors are open to deenergize landing gate relay LG and open contact LG at 207 and the energized start relay opened back contact ST at 208. Thus, if an excessive releveling signal is sensed during a releveling operation, relay SCR is dropped to disconnect the supply from the silicon-controlled rectifiers.

The sag of the elevator out of the dead zone also energizes the motor field 24 by closing dead zone relay back contact DZ at 229 to energize motor full field relay MFL. Contact MFL at 226 is closed to energize motor normal field relay MFN at 228 while full current is applied to field 24 through contact MFL at 233. Contact MFN at 221 is closed to complete a circuit for the generator field and brake relays, as in the case of a sag downward, through relay UF from lead 158, safety switches at 218, contact ST at 220, contact MFN at 221, leveling contact L22 at 221, back car start contact CS at 221, contact LD at 221, back contact LU at 221, back contact DF at 223, coils UF and BK and lead 159. The motor then drives the car upward with the brake relieved by the energization of leveling brake relay LBK (not shown) to parallel resistor 161 with lesser resistor 169 in the brake solenoid circuit through the closure of contact LBK at 237. Thus, upon energization of brake relay BK to close its contacts at 235 and in main switch M circuit at 217 to close contact M at 235 the brake is partially lifted to permit the hoist motor to move the elevator.

Another embodiment of the elevator safety circuits of this invention is disclosed in FIGS. 15 and 16. In this embodiment the generator shunt field is supplied from a single-controlled source and a more direct approach to the control of the hoist motor by the high gain negative feedback loop is employed. The safety considerations parallel those described above and illustrate that these considerations are in large part universally applicable to elevator hoist motor controls where a closed negative feedback loop having high gain is employed. Thus while the second embodiment employs a velocity based pattern, it is to be appreciated that a position based pattern or an acceleration based pattern could be employed. Both embodiments employ silicon-controlled rectifiers in the controlled power sources for which other controlled valves can be substituted and both employ as a motor armature feed a dynamoelectric generator which can be supplanted by other feed systems such as controlled rectifiers arranged to feed the motor armature directly, advantageously such controlled rectifier feeds are in a polyphase arrangement.

As shown in FIG. 15, a velocity pattern generator 171 is arranged to produce a voltage scale to velocity on a time base of the general form shown at 172 in which there is a gradual increase from zero velocity to a maximum acceleration, a period of constant maximum acceleration, a gradual transition from constant acceleration to maximum constant velocity, and then a slowdown including a gradual transition to maximum deceleration, an interval of constant maximum deceleration, and as the stop is approached a gradual transition from maximum deceleration to zero velocity. The hoist motor 173 is forced to closely follow the commanded velocity of this pattern by feeding a signal scaled to actual motor velocity, as derived from tachometer 174, over lead 175 and summing resistor 176 to summing point 177. Motor 173 drives hoist sheave 178 over which cables 179 supporting the car 181 and its counterweight 182 are trained. Tachometer 174 is coupled to be driven by the motor 173.

The pattern signal is differentially related to the actual speed signal at summing point 177 through summing resistor 183 by means of the directionally controlled switching matrix 184. The matrix is arranged to close a circuit across the pattern generator output terminals through back contacts UF and DF of the up and down generator field relays (not shown) when the elevator is not set to run. At this time the pattern input is also grounded through series back contacts of UF and DF. Tachometer 174 develops a negative signal at 177 for up travel of elevator 181 and a positive signal for down travel. The pattern signal is coupled to summing point 177 with a polarity opposing that of the tachometer signal by the connections through front contacts UF and DF in matrix 184.

The signal from 177 to lag-lead compensator 185 represents the velocity error between the commanded velocity and actual velocity. Compensator 185 enables the error signal to be amplified to a level forcing the error, the deviation of hoist motor speed from commanded speed, to a negligibly small value through the gain of the negative feedback loop without introducing instability in the system. A total loop gain is selected which is at least equal to the ratio of the unregulated open loop hoist motor speed error to the allowable closed loop hoist motor speed error. Gain may be set from about 5 to about 60. The compensator 185 attenuates the closed loop gain as a function of increasing frequency sufficiently to reduce the closed loop gain to a value less than unity at and above the natural resonant frequency of the resonant circuit comprising the total inductance and resistance, in the hoist motor armature circuit and the capacitive effect of the total driven mass, including the car, the driving means for the car and the counterweight, coupled into the armature circuit through the hoist motor. A lag-lead network of resistance and capacitance having a lead-break frequency of from 2.5 to 5 radians per second accommodates elevator hoisting systems as shown.

The compensated velocity error signal is amplified by an operational amplifier 186 and then fed to summing point 187. Generator linearization is achieved in accordance with the aforenoted Loshbough patent application by an inner closed negative feedback loop from the generator armature terminals. This generator loop can have a gain of the order of 10. It comprises generator armature 188, lead 189, resistance 191, main switch contact M and resistance 192 to summing point 187. The generator armature voltage error signal, resulting from the difference between the commanded generator armature voltage signal from amplifier 186 and the signal scaled to actual generator armature voltage, issues from summing point 187 to amplifier 193 where it is applied to gate control 194 which can be a phase control firing circuit, corresponding generally to that of FIG. 2, controlling the controlled rectifiers 195 and 196 through their gates.

Alternating current source 197 is coupled across the controlled rectifiers and their diodes 198 and 199 by the secondary S.sub.1 of transformer 201. Choke 202 and capacitance 203 are connected across the controlled rectifiers and the highly inductive load of the generator shunt field 204. Surge suppressing Thyrector 205 and resistance 206 are also connected across the output of the controlled rectifiers to accommodate circulating currents when main switch contacts M are open.

The main switch M is pulled in when the car is set to run and is dropped after the car is stopped. When dropped, a suicide circuit is established through resistance 207 and normally closed contacts M to the generator armature 188. Resistance 208 limits inductive surges during switching. The drop of switch M also inserts resistance 209 in the circuit between the armatures of the motor 173 and generator 188.

Two relays responsive to excess signal levels are arranged to shut down the hoist motor if the signals to which either responds exceed levels which are chosen to be within those acceptable for safe operation. As in the embodiment of FIGS. 1, 2, 12, 13 and 14 signals are sensed at the output of the controlled supply to the generator shunt field. This supply can be considered an amplifier and with appropriate modification could be employed to supply the hoist motor directly as when controlled rectifiers are connected to the motor armature. Accordingly, the monitoring circuit is termed the EXCESS AMPLIFIER OUTPUT safety and its relay is designated EAO.

The amplifier output is sensed through leads 211 and 212 across the capacitance 203 in order to take advantage of the smoothing action of inductance 202 and the capacitance 203. Surge protection is afforded the safety circuit by Thyrector 213 and resistance 214. The parallel-T network is a notch filter 215 for attenuating 60 cycle components in the amplifier output. Positive and negative signal levels are passed to leads 216 and 217 by rectifier bridge 218 and are further smoothed by capacitance 219. Negative excursions of signal at 217 are effective to drop relay EAO at a threshold level set by potentiometer 221. Sensitivity adjustment potentiometer has its wiper connected to the base of transistor Q21 such that a negative going signal at 217 reduces the base potential to cut off conduction in the collector of Q21 to reduce the drop in resistance 222 and raise the base potential of transistor Q22. This increases the drop in resistance 223 to provide feedback on lead 220 to the base of Q21 and further reduce its base potential while reducing the base potential on transistor Q23 to reduce its collector current and drop relay EAO.

Regulated bias is supplied the EAO safety circuit from secondary S.sub.2 of the transformer 201 through rectifier 224 and across smoothing capacitance 225 and regulating Zener diode 226. Rectifier 227 is across relay EAO to damp transients due to the inductance of its coil and resistor 228 limits current in the event the diode 227 is shorted. As will be discussed more fully, the drop of relay EAO under certain conditions, where greater than the preset threshold signal is present to indicate an unsafe condition, actuates emergency circuits which shut down the hoist motor.

This system is also shut down by the dropout of excess error signal relay EE. Relay EE is controlled through two channels, both of which must indicate signals within the threshold levels to maintain EE energized. One channel responds to an excessive error signal derived from summing point 228 and the other responds to an excessive rate of change of feedback signal as from tachometer 174 as derived from lead 175.

Each channel includes an operational amplifier and an absolute value circuit which responds to a signal of either polarity of greater than a preset value. They differ from each other only in the setting of the threshold level for dropping relay EE. Hence, but one channel will be described in detail.

The velocity error signal sensing channel is represented as a block 229 labeled EXCESS ERROR SENSOR. Block 229 includes an operational amplifier and an absolute value circuit set to respond to a deviation in velocity error of either polarity from a preset level. The input to block 229 is from summing resistors 231 and 232 respectively connected to pattern generator 171 and tachometer 174. The output from block 229 is a signal maintaining transistor Q24 conductive while acceptable error signals are produced whereby the coil of relay EE remains energized from the positive bus 230. That output places transistor Q24 in nonconductive condition to open the circuit to ground for the coil of relay EE and drop the relay when the error signal is excessive.

The rate of change of the feedback signal, a rate of change of velocity signal in the present system, is sensed through a differentiation circuit comprising a series resistance 233 and capacitance 234 in the lead from tachometer 174 to operational amplifier 235. Amplifier 235 passes excessive transient signal on lead 236 to absolute value circuit 237 which transfers transistor Q24 from a conductive to a cutoff condition by reducing the potential on the base of Q24. In the absence of a rate of change of the feedback signal exceeding the tolerable rate of change, base drive is maintained for transistor Q24.

When an excessive rate of change of feedback signal is imposed through amplifier 235 to the absolute value circuit, it tends to reduce the potential on the base of Q24 whereby the circuit supplying the coil of relay EE is effectively opened to drop the relay. When no excessive rate of change of feedback signal is present the signal on lead 236 is at a level to cause transistor Q26 to be cut off, transistors Q25 and Q27 to be conducting in saturation, and transistor Q28 to be cut off whereby the potential at the base of transistor Q24 is positive by virtue of the restricted current from positive bus 230 through resistor 238 of the voltage divider to negative bus 239. The conductive state of Q25 and the nonconductive state of Q26 is established by the base potentials derived from the voltage divider comprising resistances 241, 242, 243 and 244 between buses 230 and 239.

A positive going signal on lead 236 in excess of the threshold, e.g., +5 volts, causes transistor Q26 to become conductive thereby removing base drive from transistor Q27 by the voltage drop in resistance 245. The resultant opening of the path to ground for resistance 246 provides base drive for transistor Q28 effectively grounding resistance 238 to cut off transistor Q24 and open the coil circuit for relay EE.

A transient resulting in a negative going signal on lead 236 in excess of the threshold, e.g., -5 volts, causes transistor Q25 to become nonconductive by removing its base drive . This opens the path to ground for resistance 246 applying base drive from transistor Q28 to place it in conduction to ground resistance 238 and remove base drive from Q24. Thus for a positive excursion of the amplified signal indicative of an excessive rate of change of velocity, transistor Q27 is cut off to open the path from resistance 246 to ground through the collector-emitter circuits of Q25 and Q27, while a negative excursion indicative of an excessive rate of change of velocity in the opposite direction cuts off transistor Q25 to open that path. In each instance the application of base drive to Q28 causes relay EE to drop by terminating conduction through Q24 to ground.

Diode 247 is for surge protection in the circuit including the relay coil and resistance 248 to limit inducted current.

FIG. 16 shows the relay logic of the safety circuits of FIG. 15 in across the line form. When safe conditions exist to run the car, the conventional safety interlock contacts represented by cam actuated, normally closed switches 251 and 252 are closed and the manually actuated safety switches represented by normally closed pushbutton switch 253 are closed to complete a circuit energizing emergency relay EM at 278. The main switch coil M at 279 is also behind these safety switches and can be energized only when the safe conditions prevail. Main switch M also requires the system to be conditioned for operation with its electronic emergency relay EME at 275 energized to close its contact EME at 279, its field protective relay FP at 272 to be energized to close contact FP at 279 indicating there is current in the motor shunt field, its motor-generator set to run relay LR (not shown) energized to close contact LR at 279 indicating the motor driving the generator armature 188 is running, and a direction of running established by the energization of its up or down generator field relay UF or DF (not shown) to close contacts UF at 279 or DF at 280.

M switch is energized to start the elevator in motion. As noted above, it connects the generator armature to the motor armature, disconnects the suicide circuit, connects the controlled rectifiers to the generator shunt field, closes the generator linearizing negative feedback loop, and removes the ground connection to the velocity error signal summing point 177, all as shown in FIG. 15. In FIG. 16, the M switch when energized increases the current in the hoist motor shunt field by closing contact M at 271, and enables the brake solenoid circuit at contact M at 273 so the brake can be lifted when contacts of brake relay BK (not shown) are closed at 273.

Under normal conditions of stopping the drop of the M switch is delayed in operating sequence to permit a gradual stopping of the car. Delay is afforded by the resistance and capacitance in series with the leveling door open relay contact LDO all at 280. When the car is making a normal stop, relay LDO (not shown) is energized to connect the delay circuit across the coil of the M switch. On an emergency stop the LDO contact at 280 remains open and rapid drop of the M switch results.

The electronic emergency relay EME at 275 responds to the safety relays EE and EAO discussed above and to an interlock relay ITL such that the drop of any of these relays opens a contact at 276 to drop relay EME and thereby open the circuit for main switch M at contact EME at 279. This stops the elevator by setting its brake, disconnecting the feed to the generator shunt field and suiciding the generator. Interlock relay ITL (not shown) is energized when all connections to the units making up the system are completed. These connections include plug and socket connections and printed circuit board connections to the chassis. Each of the safety relays has a neon lamp indicator 254 at 275 which is illuminated when the respective safety relay contact is open.

In operation, the proper assembly of the system energized relay ITL to close contact ITL at 276. If at any drop of relay EE at any time is during the operation of the system an excess error signal is developed from the pattern signal and the feedback signal at summing point 228, this signal, which corresponds to the error signal at summing point 177 establishing the control signal, will cause relay EE to drop by placing the transistor corresponding to Q28 of circuit 237 in its absolute value circuit in conduction to remove over lead 249, base drive from transistor Q24. If the feedback signal is increased or decreased at an excessive rate any time during operation it will cause EE to drop. The drop of relay EE at any time is effective to drop relay EME by opening contact EE at 276. Thus, the threshold for the excess error signal should be set to permit error signals within the range encountered at summing point 177 when the system is operating in a satisfactory manner and the threshold for the excess rate of feedback signal (excess acceleration for a velocity feedback signal) should be beyond the range of suitable operation, that range normally being dictated by passenger comfort.

The excess amplifier output safety monitors the output at all times. However, it is effective only while the shunting circuit around contact EAO at 276 is open. This shunt is opened when the car doors are open beyond a point about two inches from closed to energize door close relay DCL (not shown) and open its back contact DCL at 277, or when the car brake is set and brake relay BK is dropped to open contact BK at 277. Thus, when the car is stationary, leveling in its final approach to a landing, or releveling when at a landing, the shunt at 277 is open and the opening of contact EAO at 276 is effective to light the excess amplifier output indicator lamp and drop relay EME. Under these conditions, the threshold for the drop of relay EAO is set for a signal level suitable for leveling the car. This threshold therefore may be below the peak levels encountered in running the car under normal circumstances and during normal runs contact EAO may be opened without effect in view of the shunt.

The safety circuits controlling relays EE and EAO restore themselves to the normal operating condition when their tripping condition is removed. Hence, contacts EE and EAO at 276 may be opened only briefly. Relay EME is arranged to respond to the brief interruptions of its energizing circuit by maintaining its deenergized state through open seal contact EME at 276.

Seal contact EME is paralleled by a back contact LR at 275 of the m-b run relay. When the system is conditioned for the car to run, relay LR is energized to open back contact LR at 275. Therefore, back contact LR is open when the EE and EAO safeties are effective. Contact LR enables the reset of relay EME by the stopping of the m-g set to close the contact. Thus reset is affected after an EE or EAO failure by stopping and restarting the m-g set.

Seal contact EME is also paralleled by a back contact EM at 277. When the elevator is subjected to an emergency stop as by the opening of the emergency stop switch 253 on the operating panel (not shown) in the car, the deceleration to which the car is subjected produces a rate of change of velocity exceeding the threshold of feedback rate responsive circuit 237 to drop excess error relay EE and drop EME at open contact EE. Under these circumstances the passenger can manually reset the emergency stop button from within the car. Such a reset is effective to run the car since the EME relay can be restored automatically while relay EM is deenergized and after the rate of change of velocity has been reduced below the threshold dropping relay EE, since a circuit will be available through contacts ITL, EE and EAO at 276 and back contact EM at 277. When relay EM is manually reset from within the car the system will continue to operate since EME will also be energized.

It is evident from the above embodiments that variations in the monitoring of the signals of a closed loop, high gain, negative feedback, elevator hoist motor control system, where a malfunction resulting in an excessive signal level can result in damaging forces being imposed by the motor, can be accomplished in a variety of ways, by monitoring various combinations of signals, by rendering certain of the signals effective at selected times in the operation of the system, and by enabling certain indicated failures to be corrected by passengers while others require a manual resetting under conditions dictating the presence of a skilled elevator technician. Further, the failed state of these controls can be employed to shut down the system by stopping the car as rapidly as is reasonable at any position or can be arranged to set the system for running at a reduced speed through auxiliary control means. These variations indicate that the system lends itself to many combinations of the safety mechanisms and functions. Accordingly, it is to be appreciated that the above embodiments are to be read as illustrative and not in a limiting sense.

* * * * *

Current U.S. Class:	187/289
Current International Class:	B66B 1/28 (20060101); B66B 1/30 (20060101); B66b 005/02 ()
Field of Search:	187/29 317/13 318/20.070,20.085,141--143,309--311,329--331,436,445,449,450