GB2084759A - Method of and apparatus for closed-loop control of a positioning drive by means of a setpoint transmitter - Google Patents

Abstract

An auxiliary signal (H) preset at least to the maximum travelling speed and deceleration is reduced substantially proportionally to the travel distance (5), and is compared with the fed-back output signal (A) of a setpoint transmitter and the output signal (A) is thereby reduced as a function of the characteristic of the auxiliary signal (H). The setpoint transmitter comprises a device (1) for producing an auxiliary signal (H) substantially proportionally to the travel distance (5), a comparator device (2) for comparing the auxiliary signal (H) with the setpoint transmitter output signal (A) and for producing an output (x) for H > A effecting at the most the maximum preset acceleration and an output signal (y) for H < A effecting at the most the maximum preset deceleration, an integrator device (3) for deriving the output signal (A) from the signals (x) and/or (y), and a feedback device (4). <IMAGE>

Description

SPECIFICATION Method of and apparatus for closed-loop control of a positioning drive by means of a setpoint transmitter This invention relates to a method of and apparatus for closed-loop control of a positioning drive, typical lyfortransport cabins, by means of a setpoint transmitter.

In the case of such transport systems with closedloop control, the objective is to cover the distance between start and destination jerk-free and in as short a time as possible, a feature being that acceleration, terminal speed and deceleration cannot and/or must not exceed values resulting from the drive of from the operating conditions. At the same time, optimization of travel time should be achieved with economically justifyable means. It must not, for instance, lead to oversizing of the drive. In addition, adjustment of the drive during commissioning and maintenance should make the lowest possible demands on the personnel. The setpoint transmitter controlling the speed variations is of special importance in this respect.

Operating methods and setpointtransmitters according to prior art (e.g. German Patent Specification 26 54 327) permit the adjustment of acceleration, terminal speed and deceleration. This system is operated in a manner that the deceleration phase is followed by a period during which operation is at a low speed, the so-called positioning (spotting) speed until the stopping point is reached. The transition from movement and terminal speed to deceleration is initiated when the conveyors (e.g. a cabin for passenger transport) passes a mark alongside the travel path located at a predetermined distance from the stopping point. The shortest possible travel time is then attained when deceleration is completed just when positioning speed is attained, i.e. when practically no path has to be covered at positioning speed.

Such prior-art systems suffer from an important drawback in as much as such an adjustment of deceleration does not allow any margin for any disturbing factors. This means that the drive has to be sized so that it will be capable of following the setpoint precisely even under most adverse load conditions, the result being oversizing of the drive.

Therefore, what is done in practice is, although this is not beneficial, that a certain travel distance is covered at positioning speed in order to obtain a safety margin to compensate for any possible effect of temperature and ageing of components.

Another disadvantage exists where travel distances are short and the starting point is not far enough from the intended mark for maximum speed to be reached as the mark is passed because, in that case, deceleration will be completed far ahead of the stopping point, i.e. a long distance will have to be covered at positioning speed. In order to avoid this latter disadvantage, various methods have become known in order to shift the deceleration point relative to the mark along the travel distance. The German Patent Specification 26 54327 and the German Patent Specification 2641 983 already disclosed how a time can be calculated by which the start of deceleration has to be displaced in the case of short travel distances.Despite these improvements, however, the first-cited disadvantages of prior-art equipment persist undiminished, the remedy provided by the apparatus proposed in the German Patent Specification 26 14386 being only insufficient. There, it is proposed that, between the mark and the stopping point alongside the travel distance, another mark be provided which is required to be passed at a predetermined desired speed for optimum deceleration, the deviation of the actual speed found from the desired speed being processed as a correcting quantity by the setpoint transmitter. As a result, however, disturbing factors arising after passing the second mark can no longer be allowed for and, in addition, the correction can only be correct for a given speed characteristic between the first and second mark.True, this can be remedied according the German Patent Specification 21 02 583 by providing additional marks along the deceleration distance with the aid of which effective adaptation of deceleration is possible irrespective of what the speed was during passing of the first mark, although this involves considerable complexity for the installation and scanning of the mark which, in particular where several stopping points are provided along the travel distance, make the system uneconomical.

Finally, the German Patent Specification 25 16448 disclosed how the start of deceleration can be calculated as a point on the path between start and destination, the precondition being that the distances required for acceleration and deceleration being at a fixed ratio. Here again, it is not possible to make sufficient allowance for the occurrence of possible disturbance factors.

The starting consideraton of the invention is that a maximum value is given for the acceleration which may result, for instance, from the adhesion between the wheel and the rail or the adhesion between the rope and rope sheave or, in the case of passenger transport, from physiological aspects, it being not certain that the drive will be capable of actually performing this acceleration at full load in every case. Furthermore, allowance has to be made for the fact that the set maximum speed will not be attained at every load. Consequently, it cannot be taken for granted in respect of the deceleration that reproducable operating conditions will prevail as the one mark is passed which, for cost considerations, is desired to be sufficient.Thus, it is not possible either to calculate the starting point of deceleration from the operating conditions prior to reaching the mark, especially as disturbance quantities are liable to occur during the deceleration phase. The only precondition which the conveying system is required to satisfy according to the invention is that the mark along the travel distance should be placed at such a distance from the stopping point that the drive is capable of slowing down on the travel path even under most adverse conditions from a speed which is at least equal to or greater than the maximum possible travelling speed. The system is desired to cope also where the mark is not available along the travel distance in every case or where the starting point may be situated between the mark and the stopping point.

Accordingly, it is the object of the invention to obviate the disadvantages of known positioning drive control systems and to provide a method and apparatus affording a high degree of operating safety coupled with an optimum transport capacity within economically acceptable costs.

This is achieved in the case of a system of the type initially referred to in that an auxiliary signal preset at least according to the maximum travelling speed and deceleration is reduced substantially proportionately to the travel distance, compared with the fed-back output signal of the setpoint transmitter, and the output signal is thereby reduced as a function of the characteristic of the auxiliary signal.

To implement the method, a setpointtransmitter is used which is distinguished by a feature to produce an auxiliary signal H which is substantially proportional to the travel distance, by a comparator device to compare the auxiliary signal H with the setpointtransmitter output signal A and to produce an output signal x for H > A producing at the most the maximum predetermined acceleration and an output signal y for H < A producing at the most the maximum predetermined deceleration, by an integ rator device to derive the output signal Afrom the signals x and y respectively and by a feedback device.

The auxiliary signal H can be reduced in a manner that it will have dropped to zero at the end of the travel distance or attained a value shortly before the end of the travel distance which corresponds to the positioning speed. In the case where a mark is provided along the travel distance and the starting point is in front of the mark, the reduction of the auxiliary signal H is effected only on and after passing the mark. The auxiliary signal H represents a lower level below which the setpoint must not decrease in the deceleration range in order to prevent the drive from coming to a standstill before the stopping point is reached or a relatively great part of the distance having to be covered at positioning speed. In other words, rapid and, at the same time, reliable positioning is achieved in this manner.

At the start of the travelling motion, the auxiliary signal H is set at a value which is equal to or greater than the setpoint for maximum speed and which corresponds to the speed from which the drive can decelerate under most adverse conditions on the distance between the starting point and the stopping point and/or between the mark and the stopping point.

A special advantage is gained, if the auxiliary signal H is produced by discharging a capacitor. The charging potential at the start of the discharge, which can be readily varied, corresponds to the starting value of the auxiliary signal H to be adjusted.

For the discharge of the condenser to be proportional to the travel distance and, consequently, for the auxiliary signal H to decrease at a corresponding proportion, it is possible either to couple a tachogenerator with the drive motor, the tachogenerator having an integration element connected in series whose output voltage ensures a continuous discharge of the capacitor or, alternatively, a pulse generator can be coupled to the drive motor whose pulses are employed for the capacitor discharge. Generation of the auxiliary signal H will then be in the fashion of a stepped function but, in the mean, it will be proportional to the travel distance.

It is also possible to arrange the comparator device so that, with little difference between the signals A and H, output signals between x andy are produced, the integrator beng arranged so that the rate of variation of its output A assumes values between the maximum acceleration and the maximum deceleration.

The invention will now be more particularly described with reference to the accompanying drawing, wherein Figure lisa graphical representation of the auxiliary signal H as a function of the travel distance S when using a pulse generator to produce the auxiliary signal H.

Figure 2 is the same representation as in Figure 1, where a mark M is provided along the travel distance; Figure 3 is a graphical representation of the dependance of the signals H, A, x andy as a function of the travel distances; Figures 4 and 5 are representations according to Figure 3 using a mark M along the travel distance; Figure 6 shows the dependence of the signals A, H, v according to Figure 5 as a function of the travel times; Figure 7 shows the dependance of the signals H, A and the output signal of the comparator device as a function of the travelling time, the arrangement being such that output signals between x (max) and y (max) are produced, basing on the operating conditions represented in Figure 6;; Figure 8 is a graphical representation of the signals H and K as a function of the travel distance S under the operating conditions shown in Figure 7; Figure 9 is a graphical representation according to Figure 8 plotted against the travelling time t; Figure 70 is a graphical representation of the dependance of the output signal A on the travel time tduring starting.

Figure 11 is a schematic circuit diagram of one embodiment of a setpoint transmitter according to the invention, and Figure 12 is a schematic circuit diagram of another embodiment of a setpoint transmitter according to the invention.

The setpoint transmitter illustrated in Figure 11 comprises as essential components the device 1 to produce the auxiliary signal H, the comparator device 2 and the integrator device 3. The device 1 for producing the auxiliary signal H in this typical embodiment is formed with a pulse generator 4 which is coupled with the motor shaft 5 which is only shown schematically. The auxiliary signal H is preset by means of a potentiometer 6 whereby the capacitor C1 is charged. As soon as the switch 7 is opened, the potential of the capacitor C1 is reduced according to the path increments.

The comparator device 2 is formed with a differential amplifier P1 to compare the auxiliary signal H and the output signal A of the integrator device 3. If the auxiliary signal H is greater than the output signal A (acceleration), the differential amplifier P1 provides its negative saturation voltage. The output current x of the comparator device 2 can be adjusted by means of the resistor R1 (maximum acceleration).

If the auxiliary signal H is smaller than the output signal A (deceleration), the maximum deceleration i.e. the output current y, can be adjusted by means of the resistor R2. The integrator device, which is connected in series with the comparator device 2 and which generates the output signal A whih corresponds to the setpoint signal, consists of the amplifier P2 and the capacitor C2.

Another typical embodiment of the setpoint transmitter according to the invention is illustrated in Figure 12. Again in this case, the essential components are the device 1' to produce the auxiliary signal H, the comparator device 2' and the integrator device 3'. In addition, there is an operational amplifier P5 in the comparator device 2' which is formed with a feedback circuit R3 whereby, when small deviations exist between the output signal K and the output signal A, lower output values are produced than the maximum values x (max) andy (max) for the initial acceleration or deceleration. When K and A are equal, the output of the comparator device 2' is zero. The feedback circuit R4 of the integrator device 3' permits the rate of increase of the output signal A to increase as the values of K increase.The influence of this feedback circuit, as a result of the diodes N1 and N2, will be effective only as long as the output of P5 is smaller than zero, i.e. only during the acceleration, while K is greater than A.

The auxiliary signal H is here produced by means of a tachogenerator 9 which is coupled with the drive 5 in a manner which is not shown in detail.

The graphical representations in Figures 1 - 6 relate to the use of a setpoint transmitter of the type shown in Figure 11, whereas the graphical representations in Figures 7 to 10 explain the conditions that can be maintained with a setpoint transmitter as shown in Figure 12. Figure 1 shows the characteristic of the auxiliary signal H as a function of the travel distance when using a pulse generator 4 coupled with the drive 5. Although the fine structure is step-shaped, a substantially linear pattern, i.e. a pattern porportional to the travel distance S, is obtained.If the switch 7 is not already closed when the movement starts and, as a result, the voltage built up via the potentiometer 6, which determines the level of the auxiliary signal H, is immediately reduced, but closing of the switch 7 is initiated by a mark M located alongside the travel distance S, the pattern represented in Figure 2 will be obtained. If the path increments are small enough or if a continuously integrated tacho-voltage is used, the stepped curve in Figures 1 and 2 becomes a straight line. The further explanations are based on this, although what is said equally applies to the stepshaped pattern.

The speed setpoint is formed by the integrator device 3 whose output signal A varies according to the maximum permissible acceleration if the output signal x of the comparator device 2 is applied to the input of the integrator device 3 and returns according to the maximum permissible deceleration if the output signal y is applied to its input. The changeover of the input of the integrator device 3 between the signals x andy is effected by the comparator device 2 which compares the output signal A of the integrator device 3 with the auxiliary signal H. If H is greater than A, the comparator device 2 supplies the output signal x, if H is smaller than A, the comparator device 2 supplies the output signal y. The variation of the signals H, A, x and y together with the travelling speed v is shown in Figures 3 to 5 plotted against the travel distance S.Figure 3 represents the case where no mark is used on the travel distance, whereas the representations in Figures 4 and 5 provide for the auxiliary signal H to be reduced only after a mark M has been passed.

Regarding the pattern of the speed v in Figures 3 to 5, the unfavourable case has been assumed where the drive 5 fails to reproduce the maximum values for acceleration and deceleration issued by the setpoint transmitter.

The conditions represented in Figure 5 are again plotted for easier reference as a function of the travelling time tin Figure 6. One can see the linearly rising setpoint A and the speed v following at a lower rate. In the range of the deceleration, the curve part H1 represents the characteristic of the auxiliary signal Hwhichwould be obtained ifthespeedv could follow the setpoint A and if the setpoint A of the maximum deceleration were adjusted so that, in turn, it could follow the auxiliary signal H. Since, however, the deceleration of the setpoint A is lower than the initial slope of the auxiliary signal H, the actual characteristic of the auxiliary signal H, because of the initially greater speed, is steeper.The turning point for the transition of the setpoint A from the run-up phase (acceleration phase) to the runback phase (deceleration phase) occurs at the momenu where H becomes smaller than A. This occurs neither at a certain time nor at a certain point along the path, but represents the most favourable point under the specific operating conditions where deceleration starts at the earliest. The actual start of deceleration depends on how great the actual speed is at the moment of the reversal of the setpoint or, rather, when the actual value becomes greater than the setpoint.

As can be seen from Figure 6, it is unimportant for the deceleration characteristic whether the drive can follow the maximum. deceleration imposed by the runback of the integrator device 3. In the flatter part of the setpoint curve, i.e. in the range where the integrator output signal A follows the auxiliary signal H, but, at the latest, at the stopping point, the speed will have caught up with the setpoint and, consequently, the control deviation will be zero.This follows from the premises stipulated initially, that the auxiliary signal H at the start of the movement is set at a value which is equal to or greater than the setpoint for the maximum speed and corresponds to the speed from which the drive can decelerate under worst conditions at the maximum permissible rate on the travel distance or, respectively, on the remaining distance between the mark M and the stopping point Where sensitive loads are handled, especially for passenger transport, it is a requirement that move mentshould bejerkfree. In respectofthesetpoint transmitter, this means that the transitions between acceleration and terminal speed or between terminal speed and deceleration should be rounded off.Same as the further embodiments described in the following, this is made possible by a setpoint transmitter of the type illustrated in Figure 12. There, the comparator device 2' is formed so that, with a small difference between the quantities A and H, output levels between x (max) and y (max) can be produced. The integrator device 3' is arranged so that, with inputs lying between x (max) andy (max), the rate of change of the output signal A assumes values which lie between the maximum acceleration and the maximum deceleration. This feature is explained in Figure 7 basing on the operating conditions illustrated in Figure 6. The rounding off of the setpoint curve results in the first part of the deceleration path being covered at a greater speed which results in a linearization of the time characteristic of the auxiliary signal H in the deceleration range.

Where extremely short travelling times are important, it may be useful to linearize the characteristic of the H-curve over a greater range of the deceleration path. As a further development of the invention, this is made possible in that the auxiliary signal H is applied to the comparator device 2' via a non-linear element 8. The non-linear element comprises an amplifier P6 and a non-linear feed-back circuit 8'.

Preferably, the non-linear feed-back circuit 8' is arranged so that its output signal K is greater than A for small values of H and approaches the value of A for high values of H. This feature is illustrated in Figure 8 basing on the operating conditions of Figure 7. Figure 9 shows the time characteristic corresponding to Figure 8.

Another variant of the setpoint transmitter according to the invention relates to acceleration. In order to obviate a jerk during starting, it is useful to start at lower acceleration and then increase the rate of acceleration. According to the invention, this can be effected by keeping the rate of increase of the output signal A of the integrator device 2' produced by the signal x at a low level and, in addition, to feed back the output of the integrator device 3' to its input in a manner that the rate of increase of the output signal A increases as the level A rises, as shown in Figure 10. In order to prevent this feed-back feature disturbing the rounding-off of the setpoint curve during transition to terminal speed or deceleration, it can be deactivated when A is greater than H.

Claims (10)

1. A method of closed-loop control of a positioning drive, typically for transport cabins, by means of a setpoint transmitter, wherein an auxiliary signal (H) preset at least to the maximum travelling speed and deceleration is reduced substantially proportionally to the travel distance, is compared with the fed-back output signal (A) of the setpoint transmitter and the output signal (A) is thereby reduced as a function of the characteristic of the auxiliary signal (H).

2. A setpoint transmitter for performing the method according to claim 1, comprising a device for producing an auxiliary signal (H) substantially proportionately to the travel distance, a comparator device for comparing the auxiliary signal (H) with the setpointtransmitter output signal (A) and for producing an output (x) for (H) > (A) effecting at the most the maximum preset acceleration and an output signal (y) for H < A effecting at the most the maximum preset deceleration, an integrator device for deriving the output signal (A) from the signals (x) and/or (y), and a feedback device.

3. Asetpointtransmitter as claimed in claim 2, wherein the auxiliary signal producing device comprises a capacitor, a tachogenerator coupled with the drive, and an integrator element for integrating the output voltage of the tachogenerator.

4. A setpoint transmitter as claimed in claim 2, wherein the auxiliary signal producing device comprises a capacitor and a pulse generator coupled with the drive.

5. A setpoint transmitter as claimed in any one of claims 2 to 4, wherein the auxiliary signal (H) is supplied via a non-linear element of the comparator device.

6. Asetpointtransmitter as claimed in claim 5, wherein the output signal (K) of the non-linear element is greater than the setpoint transmitter output signal (A) for lower values of the auxiliary signal (H) and approaches the value of the signal (A) for high values of the auxiliary signal (H).

7. A setpoint transmitter as claimed in any one of claims 2 to 6, wherein the output signal (A) of the integrator device is fed back to the input thereof in a manner such that the rate of increase of the auxiliary signal (H) rises as the values of the output signal (A) increase.

8. A setpoint transmitter as claimed in claim 7, wherein the feed-back feature remains effective only as long as the auxiliary signal (H) is greater than the output signal (A).

9. A method for closed-loop control of a positioning drive by means of a setpoint transmitter as claimed in claim 1, and substantially as hereinbefore described.

10. A setpoint transmitter substantially as herinbefore described with reference to and as shown in Figure 11 or Figure 12 of the accompanying drawings.