US3777855A

US3777855A - Pattern generator for the control of motion of a body movable over a predetermined path

Info

Publication number: US3777855A
Application number: US00271083A
Authority: US
Inventors: G Boyldew; J Shumack
Original assignee: Elevators Pty Ltd
Current assignee: Elevators Pty Ltd
Priority date: 1971-07-19
Filing date: 1972-07-12
Publication date: 1973-12-11
Anticipated expiration: 1990-12-11
Also published as: DE2354503A1

Abstract

A system of deriving a speed pattern for an elevator car power circuit which comprises utilizing electrical impulses whose number is a measure of distance along the shaft. Firstly determining how far the car has to travel to a destination which may be either its next stop or where it will first reach maximum speed. Secondly, producing a high frequency train of impulses indicative of the necessary travel, and producing a second train of impulses indicative of progressive movement of the car towards the destination. Thirdly, totalling in a counter the first series of impulses and subtracting therefrom the second series of impulses, and fourthly, deriving a control signal from a digital to analogue converter responding to the total in the counter and applying it to the power circuit for the car to determine the speed of the car.

Description

United States Patent 1191 Boyldew et al.

Dec. 11,1973

PATTERN GENERATOR FOR THE CONTROL OF MOTION OF A BODY Primary Examiner-Bernard A. Gilheany MOV BL V A PREDETERMINED Assistant Examiner-W. E. Duncanson, Jr. PATH Attorney-S. Devalle Goldsmith et al.

[75] Inventors: Graham Edward Boyldew,

Randwick, New South Wales; John Lindsay Shumack, Grays Point, New [57] ABSTRACT South Wales. both of Australia A system of deriving a speed pattern for an elevator [73] Assigneez Elevators my Limited Waterloo car power circuit which comprises utilizing electrical New South Wales Augtralia impulses whose number is a measure of distance along the shaft. Firstly determining how far the car has to Flledl J y 1972 travel to a destination which may be either its next 21 A L N I 271 083 stop or where it will first reach maximum speed. Se- 1 pp 0 condly, producing a high frequency train of impulses indicative of the necessary travel, and producing a Forelgrl pp at Prrorlty second train of impulses indicative of progressive July 19, 1971 Australia PA 5590 movement of th car t wa ds t d na y, totalling in a counter the first series of impulses and [52] U.S. CI 187/29 R ubtracting therefrom the second series of impulses, [51] Int. Cl B66b 1/16 and fourthly, deriving a control signal from a digital to [58] Field of Search 187/29 analogue converter responding to the total in the counter and applying it to the power circuit for the car [56] References Cited to determine the speed of the car.

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a: hum u -v PATENIEDuEc 1 1 m5 SHEET 50F 5 mdE an uucuumucmou PATTERN GENERATOR FOR THE CONTROL OF MOTION OF A BODY MOVABLE OVER A PREDETERMINED PATH This invention relates to pattern generators suitable for the control of motion of a body movable over a fixed path. The invention is of especial value when applied to the control of elevator cars but it also has useful application in other spheres. Other applications include the control of other bodies movable over a fixed vertical, inclined or horizontal paths.

The device of the invention will be frequently referred to in the following description in its application to an elevator system and in this form it specifically incorporatesan incremental shaft encoder, binary logic elements, digital-analogue converter and operational amplifier for the generation of a velocity pattern signal for precise control of the motion of an elevator car. From an understanding of the ensuing description it will be apparent in what respects modification, if any, will be required to suit the device to another application.

Previous devices which have been utilised for this purpose have been either of an analogue nature involving time based pattern signal generation, or have required position sensing devices mounted on-the car, along the path of travel of the car or on a scale model of the system. Such devices have imposed severe limitations on the precision with which the control pattern was generated. Other limitations, particularly concerning the use of sensing devices, include the increasing number of such devices required with increase of the speed of the system and the difficulty in mounting them. Furthermore, most of these arrangements require a plurality of configurations of the basic device to suit a range of applications.

It is an object of this invention to provide a device for generating a velocity control pattern with respect to the distance of travel of a body movable along a fixed path, which is substantially free from the above defects.

Another object is to provide a device which will minimise the travelling time of the movable body between any initial starting point and a destination.

A further object is to obtain an increase in the accuracy of stopping the movable body at its destination.

In one general form the invention provides apparatus for generating an electrical control signal applicable to the control of a power unit for the movement of an object over a predetermined path, said apparatus comprising means for deriving electrical impulses whose number is indicative of a distance to he travelled by the body to reach a predetermined destination in said path, counter means for counting the electrical impulses so derived, and a digital to analogue converter responding to the total count in the counter means to provide at the converter output said control signal whose voltage is related to the distance to be travelled bythe body.

It should be understood that where reference is made above and elsewhere in this specification to the destination" of the body this may mean either the position in the path where the body is to stop or only an arbitrary position in the path whereat a particular speed, such as maximum limit speed, of the body occurs.

The invention will be described in detail by way of a preferred embodiment, serving for control of the motion of an elevator car within its shaft with reference to the accompanying drawing, in which FIG. 1 is ablock diagram of a hoist motor control loop shown under the control of equipment constructed according to the invention;

FIG. 2 shows typical velocity versus time patterns of the system;

FIG. 3 is a block diagram of the pattern generator of the invention;

FIG. 4 is a logic diagram of the Control Module of the invention;

FIG. 5 is a logic diagram of the divider of the invention; and,

FIG. 6 is a circuit diagram of the output stages of the pattern generator.

At the appropriate moment, such as at the instant of commencement of a run, the distance between a car in an elevator system and its destination is measured up to the distance required for the car to slow from its maximum velocity at a pre-selected rate of deceleration and rate of change of deceleration. An acceleration pattern with controlled rate of acceleration and rate of change of acceleration is generated, to which the hoist motor for the car responds. During motion of the car, the distance between the car and its destination is measured. When this distance is equal to, or less than, the distance required for the car to slow from maximum velocity, a deceleration pattern directly related to this distance is computed digitally. In responding to this pattern the lift car decelerates to a stop accurately at the floor level of its destination.

Referring to FIG. 1, which shows in block diagrammatic form the invention applied to a typical hoist motor control loop comprising a hoist motor HM to which the car is attached by ropes connected electrically to a motor generator MG set in a Ward-Leonard configuration. The motor generator field is energised via thyristors whose firing angles are controlled by the output of a summing amplifier 2. The pattern is fed to an input of the summing amplifier 2. A tachometer generator 5, driven by the hoist motor HM, provides a velocity related signal which is also fed to the summing amplifier 2. Also a proportion of the loop voltage is fed to this amplifier 2 as a damping signal to ensure stability of response of the control system. Such a system has been described in copending Application No. 16097/70.

By the invention, an incremental shaft encoder 6 also driven by the hoist motor HM provides a displacement signal to a pattern generator 1, which is utilised in computing the required pattern from the generator.

FIG. 2 shows typical velocity versus time patterns generated by the device. Curve (a) indicates the pattern generated for a run of a distance less than the distance required to slow from maximum velocity. As the car accelerates, the distance from the destination decreases. At velocity V 1 the pattern changes to a decelerate mode. Curve (b) indicates the pattern generated for a distance longer than the distance required to slow from maximum velocity. At time t l the car has reached this distance and when its velocity reaches V 2 the pattern changes to the decelerate mode. Curve (d) shows the pattern generated for a considerably longer run. The velocity rises to its maximum figure. At time 13 the distance between the car and its destination is reduced to that required for the car to slow from this speed and the pattern changes from a steady state to the decelerate mode.

FIG. 3 shows a block diagram of the pattern generator l. The position of the car within the shaft is represented by the count contained in a bi-directional binary register called a Search Register 9. If the car is positioned at its lowest point of travel in the shaft and the .count in the register is initialised, then as the car is moved up the shaft and pulses are added to the register by an incremental encoder 7 driven synchronously with the car, its position can be ascertained to an accuracy determined by the resolution of the encoder 7. When the car is moved down the shaft pulses are subtracted from the register 9. An incremental encoder 7 producing 100 pulses per foot of car travel will result in position determining accuracy of i 0.01 ft.. The size of the register 9 is related to the length of the shaft and the resolution of the encoder used. For a 1,000 ft. shaft and the above encoder 7 the register must be able to contain a count of l00,000. An 18bit binary register is adequate for this figure.

Landing levels are located at various points within the shaft. The distances between these may be determined from the architectural plans of the shaft but to cope with variations from the planned distances, the encoder and search register can be utilised to measure these distances. The car is positioned at the lowest point in the shaft and the register initialised. The car is then driven up the shaft and stopped precisely at each landing level. The count contained in the Search Register 9 is noted for each level. This information is used to program a destination decoder by inserting pins in a matrix corresponding to the binary count for each level.

During normal operation, the count in the Search Register 9 representsthe position of the car within its shaft only when it is stationary. When the car is about to travel up, the control module 8 generates high frequency pulses which advance the count in the Search Register 9, or decrements the register 9 if the car is about to travel down. The destination decoder 10 generates output signals when the count equals that for the various landing levels and these are compared with registed destinations in a comparitor 11. When the advanced count encounters a destination demand a coincidence signal is generated which halts the stream of advance pulses. The number of pulses generated represents the distance between the car and its destination.

During the advance phase the pulses incrementing the Search Register 9 are passed via a divider 12 to another bidirectional binary register 13 called a Velocity Register. The count contained in this register 13 is thus directly related to the distance to be travelled and is used to produce an output voltage via a digitalanalogue converter 14. If during the advance phase the count in the Velocity Register 13 reaches a figure representing maximum velocity, a signal from the register 13 is used to halt the stream of advance pulses.

Thus the advance phase is terminated either by detection of Search Register count co-incident with a demand, or by the Velocity Register count reaching a predetermined maximum. This occurs before the lift commences to move.

As the car accelerates pulses are received from the incremental encoder 7. If the advance phase was terminated by a co-incidence signal the Search Register 9 remains locked and the encoder pulses are used to decrement the Velocity Register 13 after suitable scaling by the divider 12. The accelerate pattern increases as the Velocity Register count is decremented until the falling output of the digital-analogue converter 14 equals the rising accelerate pattern voltage. The pattern is then captured by the D-A converter 14 and is reduced to zero.

When the advance phase is terminated by a V max. signal from the Velocity Register 13, the pulses from the encoder 7 are used to increment the Search Register 9 if the car is travelling up; or decrement it if the car is travelling down. The Velocity Register 13 remains locked until co-incidence occurs. The Search Register 9 is then locked and the encoder pulses decrement the Velocity Register 13 as before.

A short distance from floor level the car encounters a levelling zone and control is transferred to a car mounted levelling transducer to decelerate the car accurately to floor level and hold it there, thus compensating for oscillations and sag due to momentum, load changes and elasticity of the ropes. The transducer output signal is shaped to constrain rate of change of deceleration. Levelling transducers are well known in the art.

The logic diagram of the control module is shown in FIG. 4. Pulse generator 15 produces a high frequency pulse train which is passed through gate G l on receipt of a RUN signal from the control system when the car is about to run and all safety conditions are satisfied. The R-S flip-flop is re-set whenever the RUN signal is lost. Thus the pulse train passes via gates G 2 and G 3 to the divider 12 (see FIG. 3), and via G 7 to the search register 9. Directional control of the Search Register 9 depends on whether the car is set to travel up, in which case a signal TUP is produced; or is set to travel down, when a signal TDN is produced by the control circuitry. Receipt of either a co-incidence or V max signal sets the flip-flop via Gate G 4 thus blocking the pulses from G 1 at G 2. If co-incidence had occurred encoder pulses pass gate G 5 to the divider 12. As the flip-flop has been set and the advance signal is lost, the divider and following Velocity Register 13 will be decremented. The inverted co-incidence signal blocks the encoder pulses from the Search Register 9 at G 6. If however the advance phase is limited by V max, encoder pulses are blocked from the divider 12 at G 5 but pass via G 6 and G 7 to the Search Register 9 until such time as a co-incidence occurs.

The slowing distance for a body in motion is related to its velocity by well known mathematical formulae. For a constant rate of deceleration this distance is proportional to the square of the initial velocity. The number of pulses fed to the divider 12 during the advance phase is proportional to the distance to be travelled.

The divider output is the square root of the number of input pulses. This-is used to increment the Velocity Register 13 so that the count in this register is proportional to the square root of the distance from the destination or the distance required for the car to slow from its maximum velocity. After co-incidence occurs the divider 12 takes successive diminishing square roots and the output pulses decrements the Velocity Register 13 to maintain this count proportional to the distance remaining from the destination.

The logic of the divider 12 is shown in FIG. 5. The difference between any two successive squares varies from the difference between the previous successive squares by an increment of two. Input pulses are loaded into a bi-directional binary counter 16 called an Arithmetic Register. The count Contained within this register is compared with the count contained in a second bidirectional binary counter 17 called an Accumulator. When these counts are equal two high frequency strobe pulses increment the accumulator via G 6 and G 7. 1-K flip-flop toggles on receipts of the two pulses producing a single pulse which resets the Arithmetic Register 16 and provides an output pulse to the Velocity Register 13. After co-incidence occurs the two strobe pulses are used to decrement the Accumulator Register thus providing output pulses for decreasing successive squares.

Circuitry of the output stages is shown in FIG. 6. The outputs of the Velocity Register 13 drive the digitalanalogue converter 14 in the usual manner, the output being fed via an operational amplifier 18 with adjustable gain control to set the output voltage to the figure required for maximum velocity. The accelerate pattern is generated by the constant current circuit charging the capacitor C 1. An initial step function is achieved by R l C 2 to provide control of rate of change of acceleration in conjuction with feed back of the damping signal from the motor-generator MG (FIG. 1) and hoist motor loop. The ramp voltage across the capacitor C 1 rises until it is clamped by the operational amplifier 18 via diode D 1 at a constant level for steady maximum velocity, or by the falling output for deceleration. The operational amplifier l8 and constant current circuit are suitably compensated against drift with temperature fluctuations.

Whereas a single embodiment confined to the application of the device solely in an elevator system has been described, it is to be understood that other forms are possible within the scope of the invention. For example, an impulse count in the register 13 may be caused to influence the Digital-analogue converter 14 so that the output voltage therefrom falls with a progressive count. This output voltage may then be applied to a pattern generator which under the control of this voltage produces increasing power for the motor gener- 'ator MG proportional to increase in the said output voltage.

What we claim is:

1. Apparatus for generating an electrical control signal applicable to the control of a power unit for the movement of an object over a predetermined path, said apparatus comprising means for deriving two discrete series of electrical impulses, a first one of said series being produced by a high frequency source independent of movement of said body and having an impulse count indicative of a distance to be travelled by the body to reach a destination in said path, and a second one of said series being produced from a second source in response to travel by the body towards said destination and having an instantaneous impulse count indicative of the distance travelled by the body from its starting point, means for adding the impulses of said first series to obtain a total count and means for subtracting from said total count the impulses of said second series and, a digital to analogue converter responding to the instantaneous count in the counting means to provide at an output of the converter said control signal whose voltage is related to said distance to be travelled by the body.

2. Apparatus according to claim 1, wherein the means for deriving said series of electrical impulses is a control unit to which is connected said two sources of electrical impulses, said high frequency source being a static impulse generator, and said second source being an incremental encoder driven synchronously with movement of said body, said control unit controlling the relaying of impulses from said sources to the counting means.

3. Apparatus according to claim 2, including means for registering demands requiring travel of the body to a destination, and means for applying an input signal to the control unit when a demand is registered, said control unit responding to said input signal to send impulses from said first source to the counting means.

4. Apparatus according to claim 3, including a second counting means for impulses which also receives the impulses derived from the control unit, and comparitor means for comparing the distance represented by the count of impulses in the second counting means to a distance related to the registered demand, said comparitor means reacting to a predetermined relationship of said distances to each other to transmit an output signal to cause said control unit to cease relaying said impulses to both of said counting means, whereby the first mentioned counting means contains a count indicative of the distance the body is required to travel to said destination.

5. Apparatus according to claim 4, wherein while the body is in motion impulses from said second source are relayed by said control unit to the first mentioned counting means to subtract from the count therein of impulses from said second source to produce a change in the voltage of the control signal and a resulting change in the speed of the object.

6. Apparatus according to claim 5, wherein said change in speed of the object is an increased speed so that an acceleration pattern of the object is represented by the voltage of the control signal as the object departs from a rest position towards said destination.

7. Apparatus according to claim 1, wherein said destination is a position in said path where the object is intended to come to rest, and means are provided for producing in the control signal a deceleration pattern to slow the travel of the object after it has passed a predetermined part of the total distance to be travelled to reach said destination.

8. Apparatus according to claim 1, wherein said dstination is a position in the path where the body would first attain a maximum speed in responding to said de mand and including means responsive to a maximum count in the first mentioned counting means to cause the control unit to cease relaying the impulses from said second source to both said counting means and to cause impulses derived from said first source to be applied to add to the count in said first counting means, one of said output signals from the comparitor means causing the control unit to transfer impulses from said second source to said first mentioned counting means to subtract from the count therein.

9. An elevator system comprising at least one car movable along a shaft to service a plurality of landings, a hoist motor for effecting movement of said car, an electrical generator connected to supply power to the hoist motor, a power supply connected to energize at least part of the field of said generator, two sources of electrical impulses a first one of which is controlled by movement of the car to represent by the number of pulses produced a distance travelled by the car and a second one of which is of high frequency, two electrical impulse counters, a control unit for relaying the output of said sources to the counters, means for registering a demand for service by the car to instigate an input signal to the control unit to cause it to relay impulses from the second source to both said counters before the car commences to move, comparitor means for comparing the distance represented by the count in one of said counters with a distance related to the location of the destination of the car intended by the registered demand so as to transmit an output signal to said control unit when said distances bear a predetermined relationship to each other, said control unit responding to said output signal to cease relaying said impulses from the second source whereby the count in the other of said celeration pattern for the hoist motor.

I Y! t

Claims

8. Apparatus according to claim 1, wherein said dstination is a position in the path where the body would first attain a maximum speed in responding to said demand and including means responsive to a maximum count in the first mentioned counting means to cause the control unit to cease relaying the impulses from said second source to both said counting means and to cause impulses derived from said first source to be applied to add to the count in said first counting means, one of said output signals from the comparitor means causing the control unit to transfer impulses from said second source to said first mentioned counting means to subtract from the count therein.

9. An elevator system comprising at least one car movable along a shaft to service a plurality of landings, a hoist motor for effecting movement of said car, an electrical generator connected to supply power to the hoist motor, a power supply connected to energize at least part of the field of said generator, two sources of electrical impulses a first one of which is controlled by movement of the car to represent by the number of pulses produced a distance travelled by the car and a second one of which is of high frequency, two electrical impulse counters, a control unit for relaying the output of said sources to the counters, means for registering a demand for service by the car to instigate an input signal to the control unit to cause it to relay impulses from the second source to both said counters before the car commences to move, comparitor means for comparing the distance represented by the count in one of said counters with a distance related to the location of the destination of the car intended by the registered demand so as to transmit an output signal to said control unit when said distances bear a predetermined relationship to each other, said control unit responding to said output signal to cease relaying said impulses from the second source whereby the count in the other of said counters is then indicative of a distance to be travelled by the car, a digital to analogue converter responding to the count in said other counter to produce a control signal whose voltage is related to said distance, and means for modulating said power supply to the generator field under the control of the control signal, said control unit operating to apply to said other counter impulses originating from said first source to subtract from the count in said other counter and to change the voltage of the control signal thereby to produce an acceleration pattern for the hoist motor.