GB1567532A

GB1567532A - Synchronizing control device

Info

Publication number: GB1567532A
Application number: GB33184/77A
Authority: GB
Original assignee: Individual
Current assignee: Individual
Priority date: 1976-08-06
Filing date: 1977-08-08
Publication date: 1980-05-14

Description

(54) SYNCHRONIZING CONTROL DEVICE (71) I, WALTER VOGLER, of Schwyzerstrasse 1. CH-5304 Wettingen/AG, Switzerland, of Swiss nationality, do hereby declare the invention, for which I pray that a patent may be granted to me, and the method by which it is to be performed. to be particularly described in and by the following statement: The present invention relates to a synchronizing arrangement for an electric drive system comprising a plurality of drive units, each having a motor and a tracing element, and a central control circuit which is connected to all drive units.

Hitherto, different synchronizing arrangements have been used for hoisting devices, more particularly those for heavy vehicles and rail vehicles. to ensure uniform hoisting and lowering of the individual hoisting spindles or hoisting jacks over the entire hoisting range.

For example, in multi-column hoisting platforms the drive is applied through only one spindle or one hoisting jack. while the other spindles are co-driven through mechanical transmission means by the driving unit of the first spindle.

It has been found a disadvantage in these known svstems that the mechanical transmission means confine and restrict the working space between the hoisting device and between the individual columns. Furthermore. such inter-connection between the individual hoisting spindles presents an accident hazard. particularly if mechanical or hydraulic defects or failures occur while the hoisting platform is raised.

The prior art also discloses hoisting devices in which a separate drive is provided for each hoisting column. Expensive and technically complicated devices have however so far been necessary to achieve synchronism for controlling the individual hoisting columns relative to each other and such devices also included welter eilirr the provision of separate tracing means for each hoisting column to supply a hoisting height signal which is supplied to a comparator device so adapted that an electric three-phase switch supplies a reduced current to the three-phase motor which, for example, leads the motor which drives the first hoisting column.

The known synchronizing control device calls for analog hoisting position transducers involving substantial costs and technical complexity. Furthermore. such a system is not suitable for any desired number of drive units since in such a case it would be necessary for the largest and smallest hoisting height signal to be defined in an extremely awkward manner.

The present invention seeks to provide a synchronizing arrangement which can be used in hoisting systems with any desired number of hoisting columns and does not call for a continuousllv operating position transducer and is also substantially independent of mechanical transmission means.

According to one aspect of the present invention. there is provided a synchronizing arrangement for an electric drive system comprising a plurality of drive units, each having a motor, a control circuit and a tracing element for sensing the actual position of the drive unit. and a central control circuit connected to all drive units. in which the tracing element of each drive unit is an angle function switch and is operative to deliver an angle function signal when a rotating part of the drive unit reaches a specified trip angle, and the control circuit of each respective drive unit is provided with a circuit breaker operative to disconnect the motor current supply under the control of the respective angle function switch and to store the corresponding angle function signal, the arrangement further comprising a reclosing trip operative to enable reclosing of all the circuit breakers only wnen an angle function signal has been stored in all the respective control circuits.

According to another aspect of the present invention there is provided a method of synchronizing a plurality of drive units which involves providing each drive unit with an angle function switch for detecting an increment of movement of the driven member, actuating each drive unit in response to the transmission of a command signal from a central control circuit to all drive units, each drive unit being actuated until the driven member has moved by only one increment. and preventing the central control circuit from transmitting a further command signal until all driven members have been moved bv one increment.

The advantage of the subject of the invention can be seen more particularly in that each drive unit calls for only a simple switch which is actuated bv the tracing element of the relevant drive unit and that substantially only binary switching signals and not analog signals are used. Known relay technology or electronic signalling technology can therefore be employed extensively and at low cost.

One further advantageous embodiment of the subject of the invention is arranged so that the circuit breaker of each drive unit can be switched off in dependence on the angle function signal of the associated angle function switch, This achieves a particularly simple construction for the entire switching system.

It is also advantageous that the trip angle in each angle function switch is provided for the angle function signal of more than one whole rotation, preferably of two whole rotations.

This construction is particularly suitable for hoisting synchronizing control in which a difference of one to two rotations of the hoisting spindle is permissible during operation of the drive unit and closer final position tolerances. which occur only through overshooting after switching off. are demanded for the final condition. This also results in a reduced switching frequency.

It is also advantageous to arrange that the angle function switch has an associated output signal for at least one intermediate angle within the trip angle.

By utilizing the binary signal structure, this makes it possible to provide for additional monitoring steps for the individual drive units.

To increase the safety of trouble-free operation of the entire slewing or hoisting operation, it is advantageous that the reclosing trip has a reclosing signal which persists up to an intermediate angle output signal of the angle function switch, since reclosing will then be ensured bv a switching instruction of sufficient length.

It is particularly advantageous that a monitoring circuit be provided which is controllingly connected to the reclosing trip and to the angle function switches of all drive units and triggers a safety switching function in dependence on the existence of a reclosing signal and/or one of the drive units simultaneously reaching a trip angle.

In this way it is possible to immediately and in a simple manner detect jamming of one of the drive units. for example due to overloading. and the entire system is switched off before damage occurs. Another advantage of the inventive embodiment of the synchronizing control device can be seen in the simplicity of the monitoring logic circuit because the binary signal flow can be directly used to this end.

The abovementioned features of a synchronizing arrangement enable a relatively high synchronizing accuracy to be achieved in a simple manner, but the frequent switching operations of the circuit breakers and the corresponding frequent interruption of the motor drives mav have an adverse effect.

In accordance with a feature of the invention, a delay element is connected in the circuit between the angle function switch of each drive unit and the associated circuit breaker to delay switching off of the associated motor for a predetermined time interval after an angle function signal is produced.

The invention will now be described further. by way of example, with reference to the accompanying drawings. in which: Figure 1 shows diagramatically the complete circuit of a synchronizing arrangement according to the invention, Figure 2 shows the circuit diagram of a control stage of the general circuit according to Figure 1, Figure 3 is a waveform diagram which explains the operation of a control stage of the circuit according to Figure 1.

Figure 4 shows the circuit diagram of a module for additional monitoring purposes, Figure 5 shows the circuit diagram of another module of the general circuit of Figure 1.

Figure 6 is a circuit diagram of a modified synchronizing device, Figure 7 shows the circuit diagram of one detail of Figure 6, and Figure 8 is a waveform to explain the method of operation of the circuit of Figure 6.

According to Figure 1. E' designates one of several drive units in which the raised index refers consistently hereinbelow to the serial number of the drive unit or the associated circuit parts. Each circuit unit comprises an electric motor M' which is coupled to a driven object Fi, not shown, for example a hoisting spindle or the like, and an angle function switch G' which is coupled to a rotating part of the driven object F' and is driven at a controlled speed which is suitably stepped down with respect to the motor speed and in the present embodiment is constructed as a cam switch. The cam switch has one control contact g' to generate, for example, one control pulse for each rotation.

A central control circuit H is connected to all drive units Ei through an associated feed and control cable Ki and comprises switching stages L', appropriately associated with each drive unit, and a common switching stage N. The drive motors are fed from three-phase mains, with phases R, S, T and a dc power supply, whose negative terminal is connected to ground, has its positive terminal connected through switching stages Li associated with the drive units but not shown in detail.

Each switching stage Li comprises a circuit breaker LS in the three-phase feed of the motor of the associated drive unit and a bistable relay LD' which is driven by a control stage LZ' or by the common switching stage N and has a pull-in winding D1 and a throw-off winding D1 in which a NO-contact (normally open) d,'is connected into the control circuit of the energizing coil LSp' of the circuit breaker LS'.The throw-off winding D of the control circuit LDl is connected to one control output LZa' of the control stage LZ' which in turn is supplied from the positive terminal of the dc supply with control pulses on a control input LZe via a control line of the cable K1 and the contact g' of the angle function switch G.The energizing winding D1 of the control relay LD' is controlled via a NC (normally closed) contact xl of a reclosing trip which is incorporated in the common switching stage N and takes the form of a bistable reclosing relay NX.

The common switching stage N contains the control circuits for the energizing winding X and the throw-off winding X of the bistable reclosing relay NX, comprising a series connection of NC contacts d,i of the control relays LD' of all switching stages L' within the control circuit of the energizing winding, as well as a manual switch NH and contains in the control circuit of the throw-off winding a minimum interval switch NP for metering the time of transferring the reclosing signal from the reclosing trip to the working units. The common switching stage N is also provided with an additional monitoring circuit NQ which detects impermissible non-synchronism of the working units and is able to act on the three-phase feed in dependence thereon.

In the circuit of the control stage LZ' as illustrated in Figure 2 the index i relating to the association with a drive unit has been omitted in the interests of simplicity. The circuit states of relay contacts in this illustration are designated by an overlined lower case letter on the affected contact side for the drop-out position and by a corresponding simple lower case letter on the other contact side for the energizing position. The control stage comprises a relay LZA which has an associated changeover contact LZa and is periodically switched on and off once for each rotation via an input a0 of the angle function switch G' of the associated drive unit. The said relay therefore produces a periodic control pulse sequence with switching states or binary signal values a and a.This pulse sequence drives two bistable relays LZB and LZC with energizing winding B, or C and throw-off windings B or C, namely via first changeover contacts LZc, and LZb, which are alternately associated with said windings. The coordination of the switching states of the two last-mentioned contacts to be energizing or throw-off state of the two bistable relays LZB and LZC is designated by the lower case letters cl/c, and b,/b, marked on the contacts. Two second contacts LZb2 and LZc, of these relays are connected in series with the positive terminal of the dc supply and the throw-off winding D' of the previously-mentioned control relay LDl. The coordination of the switching states is correspondingly designated as already described.

The operation of the control stage with the contact switching states as indicated in Figure 3 is obtained from this circuit lay-out as follows: The first waveform of Figure 3 indicates the control pulse sequence of the switching stages a/a which synchronizes the control stage from the drive unit. Due to the alternating control of the relays LZB and LZC by means of their first contacts, the said relays operate with a time offset equal to the drop-out interval of the relay LZA as indicated in the second and third waveforms of Figure 2 and with a sequence frequency which is halved in terms of the control pulse sequence.This provides simple means for unequivocally marking a switching state. for example a. in each second period of the control pulse sequence by the coincidence of two switching states of LZB and LZC to be utilized for the periodic switching off of the affected drive unit when two full rotations have been completed. In the exemplified embodiment, these two full rotations represent the trip angle but this can also be made greater or smaller. The combination of switching states, in the exemplified embodiment b . c (i.e. the conjunction of b and c), or the corresponding throw-off signal d is therefore stored in the relay LD' of the control circuit and represents the controlling angle function signal. This is achieved in the circuit according to Figure 2 by the series connection of the contacts LZb2 and LZc2 with the coordination as marked of the switching states of these contacts. At the time to the fourth waveform of Figure 3 indicates the corresponding energization of the throw-off winding Di with the changeover from d to d. As indicated in Figure 1, the circuit breaker of the affected drive unit is switched off via the contact d,i. The relays LZB and LZC continue to be switched if the drive unit overshoots due to mass inertia so that the corresponding intermediate angles of the control cycle which extends over two rotations are recorded and are processed as having already been covered with respect to the next reclosing operation.By dimensioning the control cycle to cover two rotations such overshooting of up to two rotations is thus permissible without the need for summating synchronizing errors over the entire operating period.

The individual drive units are therefore switched off in this manner in the sequence in which one control cycle is completed. The lagging drive units thus make up their deficiency with each control cycle. Since the associated NC contact dz of the control relay LD' completes closing of the contact series connection in the energizing circuit of the pull-up winding in the reclosing relay NX, the drive unit switched off last triggers the energization of all pull-up windings D' via the contacts x' and thus again switches on all drive units for the next control cycle. Such reclosing of the switches also depends on the operation of the manual switch NH in the sense of manual control of the plant.

The minimum interval transmitter NP indicated in Figure 1 ensures that the reclosing signal is of adequate duration by applying correspondingly delayed energization of the throw-off winding X in the reclosing relay NX. Such delay can be obtained by conventional means, not shown, through a delay element. Figure 4, however, shows an embodiment in which the throw-off winding X is energized in dependence on a specific condition regarding the total circuit state of the relays LZB and LZC.This contact network contains third contacts LZbA and LZcss of the relays LZA and LZB of all control stages in the illustrated mode of inteconnection and with the coordination as marked of the switching states b', / b3 and C3 / c,'. It embodies the logic function P = ( b1 . cl + b . c + ) = = Fb1 + cl) . Ub + c) ...... (1) This function P corresponds to the Yes" output signal of the minimum interval transmitter NP as shown in Figure 1 and results in the reclosing relay NX being reset only if all of the drive units have reached the first intermediate angle after the time to, i.e. when the starting state has been reliably overcome.

The monitoring circuit NQ illustrated in Figure 5 is also a contact network and contains the fourth contacts LZb; and LZc, as shown. It embodies the logic function Q = bl, cl + b2 . c- + b" . cn + +d' . d2 . d3 '' dn (2) where n = the total number of drive units, and renders the supply of dc to all drive units dependent on the non-occurrence of a condition in which one of the drive units is still to reach the next but one intermediate angle after tc, (see Figure 3) and another drive unit has already reached the end of a control cycle.

In a corresponding manner it is possible for other pairs of switching states, characterized by an undesirable or impermissible lack of synchronism between the driving unit which leads by the greatest extent and the driving unit which lags by the greatest extent, to be characterized by corresponding logic functions and to be utilized for monitoring steps.

The embodiment of Figure 6 is similar to that of Figure 1 and like parts have been allocated the same reference numerals. In this embodiment, however, a delay element Z' is arranged between the control stage LZ' and the bistable relay LDi. Furthermore, a connection LZr' is provided from the D1 of the bistable relay LDi to the control stage LZi.

Additionally, capacitors CR', CS' and CT' are connected across the respective contacts of the circuit breaker LS'.

In Figure 6. the drop-out instruction for the circuit breaker LSi on reaching the pre-defined trip angle is applied by the output LZa' of the control stage LZ' to the throw-off winding D' of the control relay LD', however not directlv but via the delay element Zi with a pre-defined delay time interval Tv. Accordingly, the feed to the motor M' is not immediately interrupted when the trip angle is reached but a waiting period is interposed to determine whether the reclosing criterion is satisfied within the delay time interval Tv and therefore the energizing winding Dl of the delay LD' is energized via the contact x'.If the reclosing instruction occurs prior to the delayed drop-out instruction, the latter will not become effective and the motor will continue to operate without interruption. To this end, it is possible to ensure in a simple manner that the reclosing or continued operation instruction has priority over the drop-out instruction, for example by designing the energizing winding of the control relay LD' to have priority over the throw-off winding or as indicated in the example - by resetting the control stage LZi and terminating the drop-out instruction in dependence on the reclosing or continued operation instruction through the resetting input LZr' which is driven in the same sense as the energizing winding D' by the contact x.

In Figure 7, the delay element Z comprises an RC integrating element with an adjustable resistor RZ' and capacitor CZ' as well as a discharge resistor RZe' and a matching amplifier VZ which renders the charging operation of the capacitor independent of the throw-off winding D'. The optimum delay interval can therefore be adjusted at any time by means of RZ'.

To ameliorate switching surges on the motor M' and therefore to further improve the uniformity of the driving operation, the contacts of the circuit breaker LS' are linked in the manner shown in Figure 6 by means of capacitors CRI, CS and CT1. This achieves not only a comparatively slow decay of the motor current when switching off, i.e. on the arrival of the reclosing instruction after the end of the delay interval. but also reduced excess switching voltages on the contacts and therefore achieves a longer service life for the circuit breaker.

The use of semiconductor switches provides the advantage of calling for a lower voltage stability of the elements.

Figure 8 illustrates the characteristic with respect to time of the energizing state di of the control relay LDi and therefore the time characteristic of the switching state of the affected circuit breaker for four drive units or control relays LDl to LD4. According to the operating state indicated by the solid lines, the reclosing time t', defined by the slowest drive unit with the control relay LD2 still occurs within the delay interval Tv of all the other units, thus resulting in the indicated, uninterrupted energized state of all control relays and therefore the closed state of all circuit breakers.

The reclosing time t; in the operating state shown in broken lines no longer occurs within the delay interval Tv of the drive unit which is assumed to be the fastest. i.e. leading by the greatest extent, and having the control relay LD'. Only a brief switching-off signal Ta is therefore obtained for this drive unit so that the synchronizing condition is again restored.

As indicated, the delay interval is set shorter than the time interval Tmin required by the fastest drive unit for traversing through the trip angle (not shown). Falling out of step or lagging of one drive unit by more than a defined minimum is thus avoided while taking into account the run-out conditions in the particular case.

WHAT I CLAIM IS: 1. A synchronizing arrangement for an electric drive system comprising a plurality of drive units, each having a motor, a control circuit and a tracing element for sensing the actual position of the drive unit, and a central control circuit connected to all drive units, in which the tracing element of each drive unit is an angle function switch and is operative to deliver an angle function signal when a rotating part of the drive unit reaches a specified trip angle, and the control circuit of each respective drive unit is provided with a circuit breaker operative to disconnect the motor current supply under the control of the respective angle function switch and to store the corresponding angle function signal, the arrangement further comprising a reclosing trip operative to enable reclosing of all the circuit breakers only when an angle function signal has been stored in all the respective control circuits.

2. A synchronizing arrangement as claimed in claim 1. in which the circuit breaker of each drive unit is connected to be switched off in response to the angle function signal of the associated angle function switch.

3. A synchronizing arrangement as claimed in claim 1 or 2. in which the trip angle in each angle function switch is provided for the angle function signal of more than one whole rotation.

4. A synchronizing arrangement as claimed in claim 1. in which the angle function switch has an associated output signal for at least one intermediate angle within the trip angle.

5. A synchronizing arrangement as claimed in claim 4, in which the reclosing trip has a reclosing signal which persists only up to an intermediate angle output signal of the angle function switch.

6. A synchronizing arrangement as claimed in claim 5, in which a monitoring circuit is provided which is connected to the reclosing trip and td the angle function switches of all drive units and is operative to trigger a safety switching function in dependence upon the existence of a reclosing signal and one of the drive units simultaneously reaching a trip angle.

7 A synchronizing arrangement as claimed in any preceding claim in which a delay element is connected in the circuit between the angle function switch of each drive unit and

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. instruction has priority over the drop-out instruction, for example by designing the energizing winding of the control relay LD' to have priority over the throw-off winding or as indicated in the example - by resetting the control stage LZi and terminating the drop-out instruction in dependence on the reclosing or continued operation instruction through the resetting input LZr' which is driven in the same sense as the energizing winding D' by the contact x. In Figure 7, the delay element Z comprises an RC integrating element with an adjustable resistor RZ' and capacitor CZ' as well as a discharge resistor RZe' and a matching amplifier VZ which renders the charging operation of the capacitor independent of the throw-off winding D'. The optimum delay interval can therefore be adjusted at any time by means of RZ'. To ameliorate switching surges on the motor M' and therefore to further improve the uniformity of the driving operation, the contacts of the circuit breaker LS' are linked in the manner shown in Figure 6 by means of capacitors CRI, CS and CT1. This achieves not only a comparatively slow decay of the motor current when switching off, i.e. on the arrival of the reclosing instruction after the end of the delay interval. but also reduced excess switching voltages on the contacts and therefore achieves a longer service life for the circuit breaker. The use of semiconductor switches provides the advantage of calling for a lower voltage stability of the elements. Figure 8 illustrates the characteristic with respect to time of the energizing state di of the control relay LDi and therefore the time characteristic of the switching state of the affected circuit breaker for four drive units or control relays LDl to LD4. According to the operating state indicated by the solid lines, the reclosing time t', defined by the slowest drive unit with the control relay LD2 still occurs within the delay interval Tv of all the other units, thus resulting in the indicated, uninterrupted energized state of all control relays and therefore the closed state of all circuit breakers. The reclosing time t; in the operating state shown in broken lines no longer occurs within the delay interval Tv of the drive unit which is assumed to be the fastest. i.e. leading by the greatest extent, and having the control relay LD'. Only a brief switching-off signal Ta is therefore obtained for this drive unit so that the synchronizing condition is again restored. As indicated, the delay interval is set shorter than the time interval Tmin required by the fastest drive unit for traversing through the trip angle (not shown). Falling out of step or lagging of one drive unit by more than a defined minimum is thus avoided while taking into account the run-out conditions in the particular case. WHAT I CLAIM IS:

1. A synchronizing arrangement for an electric drive system comprising a plurality of drive units, each having a motor, a control circuit and a tracing element for sensing the actual position of the drive unit, and a central control circuit connected to all drive units, in which the tracing element of each drive unit is an angle function switch and is operative to deliver an angle function signal when a rotating part of the drive unit reaches a specified trip angle, and the control circuit of each respective drive unit is provided with a circuit breaker operative to disconnect the motor current supply under the control of the respective angle function switch and to store the corresponding angle function signal, the arrangement further comprising a reclosing trip operative to enable reclosing of all the circuit breakers only when an angle function signal has been stored in all the respective control circuits.

the associated circuit breaker to delay switching off the associated motor for a predetermined time interval after an angle function signal is produced.

8. A synchronizing arrangement as claimed in claim 7. in which the delay element is adjustable.

9. A synchronizing arrangement as claimed in claim 7. in which the delay interval is dimensioned to a fraction of the delay interval which corresponds to the trip angle of the drive unit at the maximum driving speed.

10. A synchronizing arrangement as claimed in claim 7, in which the contacts of the circuit breaker are connected in parallel with respective capacitors.

11. A method of synchronizing a plurality of drive units which involves providing each drive unit with an angle function switch for detecting an increment of movement of the driven member, actuating each drive unit in response to the transmission of a command signal from a central control circuit to all drive units each drive unit being actuated until the driven member has moved by only one increment, and preventing the central control circuit from transmitting a further command signal until all driven members have been moved by one increment.

12. A synchronizing arrangement substantially as herein described with reference to and as illustrated in the accompanying drawings.