GB2131256A

GB2131256A - Method of supervising an instruction-transmitting system and circuit arrangement for carrying out the method

Info

Publication number: GB2131256A
Application number: GB08330327A
Authority: GB
Inventors: Gustav Rohr
Original assignee: Jungheinrich Unternehmensverwaltung KG
Current assignee: Jungheinrich AG
Priority date: 1982-11-18
Filing date: 1983-11-14
Publication date: 1984-06-13
Also published as: GB8330327D0; SE8305672D0; FR2536560A1; SE8305672L; DE3242514A1

Abstract

For the supervision of an instruction-transmitting system for electric signals, comprising a signal input device 1 and a receiver 2 which is connected to the signal input device by a line 4, 5, the signal input device is supplied with electric signals, which are different in kind, particularly in frequency, from the control signals which represent the instruction. The receiver is preceded by a comparator, which is supplied with signals of said different kind, particularly at said different frequency, and the transmission state of which is controlled at the frequency of the electric signals of said different kind in such a manner that, in dependence on the comparison of the signals of said different kind, a control signal will be transmitted or an error signal for disabling the receiver will be generated. The electric signals of the different kind are generated by an oscillator 7 which is connected to the signal input device and to a synchronous detector 12 disposed close to the receiver. <IMAGE>

Description

SPECiFICATION Method of supervising an instruction-transmitting system and circuit arrangement for carrying out the method This invention relates to a method of supervising an instruction -transmitting system for transmitting electric signals, comprising a signal input device and a receiver, which is connected to the signal input device by a line. The invention relates also to a circuit arrangementforan instruction-transmitting system for transmitting electric signals, comprising a signal input device and a receiver, which is connected to the signal input device buy a line. Such receiver may consist of a pulse generator or a computer. The method and circuit arrangement are preferably used in an industrial truck.

The use of a pulse generator is particularly contemplated in conjuction with the control of a vehicle, particularly an industrial truck. In that case the signal input device may consist, e.g., of a travel controller.

Such travel control systems are known in various forms. For instance, Laid-open German Applications 2739 538 and 21 07 304 and German Utility Model 1,791,648 disclose opto-electric travel control switches having movable diaphragms. Said travel control switches are not provided with safety devices although they comprise a considerable amount of electronic components. Whereas the design disclosed in the above-mentioned German utility model comprises a rugged control cylinder for an actuation of relays or contactors, that arrangement also permits errors to occur in the case of a short circuit oran interruption of connecting lines. Moreover, optical components may exhibit a change in dependence on temperature or operating time.Similar remarks are applicable to a non-contacting control element which is operable by hand orfootand has been disclosed in Laid-open German Application 22 17 502 and is used in an inductive arrangement in which a shielding disc is movable in a high-frequency magnetic field between primary and secondary coils.

Laid-open German Application 23 33 209 discloses a vehicle which comprises means for detecting any leakage current. The circuit for detecting any leakage current is provided with a device for delivering an a.c.

signal via the chassis to a sensor, which is responsive to a shortto ground.

German Patent Specification 688,825 discloses the use of an oscillator in an arrangement for supervising the insulation of vehicles powered from an overhead line. The supervision is effected with the aid of a superimposed alternating current and for this reason is independentofthe polarityofthe overhead line.

This invention uses a circuit arrangementcomprising electronic components. The reliability of such circuit arrangements decreases with an increase ofthe number of electronic components. Particularly for a reliable transmission of instructions, the signal input device should be simple and inexpensive but should have a high service life. That device may consist, e.g.

of a so-called plastic potentiometer. In that case, the instruction or control signal consists of a modulated d.c. signal. This is includedwithin the scope of the invention.

The receiverforconverting the instruction signals received from the signal input device is connected to the signal input device by a relatively long line.

Interferences which are due to distortions ofthe electromagneticfield orto pulses generated by other vehicle control systems as well as short circuits may affectthat line as well as the signal input device.

It is an object of the invention to provide a method and a circuit arrangement which are of the kinds described first hereinbefore and in which the susceptibilityto interference is reduced with simple means and safety is ensured even in case of an interference, such as a short circuit.

This object is accomplished in the method in that the signal input device is supplied with electric signals which are different in kind, preferably in frequency, from the control signals which represent the instruction, the receiver is preceded by a comparator, which is supplied with electric signals of said different kind, preferably at said differentfrequency, and in dependence on the comparison of said electric signals of said different kind the control signal is transmitted or an errorsignal is generated by which the receiver is disabled.The signals of said different kind, particular ly at said different frequency, can be used for making at different points of the signal line a comparison for supervising the proper condition ofthe signal line.

The electric signals of the different kind consist preferably of a.c. voltage signals, which are used as the supply voltage forthe signal input device. The term "a.c. voltage" includes a sine voltage although a.c. voltages having other waveforms may also be used, particularly square-wave voltages, which afford special advantagesforthe supervision.

The circuit arrangement comprises an oscillator which has at least one output, which is connected to the signal input device for determining a signal transmission frequency and to a synchronous detetor which is provided in the connecting line and the transmission state of which is controlled by the oscillator in dependence on the signal transmission frequency. This arrangement including a large number of electronic components if the detector and the signal input device are provided at different ends of the line which is to be supervised. In that manner, an interference by signals which differfrom the frequency ofthe oscillator will be prevented. That arrangement is desirable for numerous applications, particularlyfor industrial trucks.

In a preferred arrangement, the synchronous detector is disposed close to the receiver, which particularly consists of a pulse generator or a computer. Pulse generators are particularly used to control industrial trucks. The use of a computer opens up different applications but will afford advantages also in circuit arrangements of an industrial truck.

The synchronous detectorpreferablysucceedsa high-pass filter, to which an auxiliary voltage is applied, which has such a magnitude that in case of a failure ofthe line or interference affecting the line an error signal will be generated which has such a potential thatthe recieverwill assume a safe state. The high-pass filter provides for a suitable supervision for that purpose and will be dimensioned in dependence on the signal transmission frequency.

The application of the auxiliary voltage ensures that in the absence of an instruction signal the receiverwill be held in a non-responsive state, in that case, a signalling device may also be actuated.

It will be desirable to provide between the synchro- nous detector and the receiver a low-pass filterfor generating an average-value for controlling a pulse generator or for activating an analog-to-digital converter, e.g., in a microcomputer.

In a particularly preferred embodiment, the signal input device having a long service life comprises a potentiometer. That potentiometer may consist of any ofthetypes used in the above-mentioned kinds of instruction signal generators, particularly of a wire potentiometer, but also of a plastic-based sheet potentiometer. The term "potentiometer" is used in this connection in its broadest sense and includes also a digital switching elementwhich has virtually only two states, i.e., an ON state and an OFF state.

In accordance with a special feature the oscillator constitutes a voltage source for the signal input device so that the circuit arrangement is greatly simplified and a signal having an exactly defined phase displacement is generated. This permits an exact frequency selection. The control frequency determined by the oscillator is preferably the signal transmission fre quency,which isten to twenty times the frequency corresponding to the rate ofthe change imparted to the instruction signal by the signal input device so that a transmission of the signal is ensured in conjunction with a maintenance ofthe supervision frequency. The rate of the change imparted to the instruction signal by the signal input device will depend on the type ofthat device and on the intended control ofthe implement forwhich the circuit arrangement is used.

In a particularly preferred em bodiment the oscillator is adapted to be set to a predetermined control frequency, by means of a computer which is used as a receiver. That setting can be initiated buy a manual operation. In pulse control systems controlled by a microprocessor, the signal transmission frequency determined by the oscillator may be so determined that a signal will be delivered which depends on instantaneous conditions, which may include settings ofthe signal input device. It is preferred to use a signal transmission frequency or control signal frequency which underthe instantaneous conditions must not be an integral multiple of an interference frequency which may be expected.In connection with control systemsfor vehicles, different signal transmission frequencies may be set, e.g., in dependence on different speeds ofthe vehicle or of its drive means.

The invention will now be explained with reference to two illustrative embodiments which are diagrammaticallyshown on the drawing, in which Figure lisa circuit arrangement in which the components are symbolized and Figure 2 shows a modified circuit arrangement comprising a microcomputer as a receiver.

The circuit arrangement shown in Figure 1 includes a control secticn, which is provided at its input end with a signal input device 1 and at its output end with a receiver 2, particularaly a controller, which drives a servomotorora drive motor3; this will depend on the nature ofthe signals which are received or processed.

The signal input device 1 and the receiver 2 are connected by a relatively long line 4, which is unipolar in the embodiment shown but may be multipolar, if desired. It is stated in connection with Figure 1 that the line 4 is longerthan the other connections between components of the circuit arrangement; this means that the signal input device 1 is spaced a iarge distance from the remaining parts.

The control section generally designated 5 has associated with it in at least one part, in any case adjacent to the line 4, a loop 6, which includes an oscillator7, which generates an a.c. signal, which has a constant amplitude and a predetermined, constant frequency. That signal may be a square-wave signal or any other a.c. signal. A desirable sine signal will be described hereinafter.

The oscillator 7 has two outputs 8,9. The output 8 is connected by a two-wire line 1 to the signal input device 1. The output 9 is connected by a similar line 11 to a synchronous detector 12, which is included in the control section 5 close to the receiver 2. The synchronous detector 12 may be re-adjustable and is controlled by the oscillator 7 to assume a transmitting state at the frequency of that oscillator. The signal input device 1 is similarly connected and may consist, e.g., of a potentiometer 13 having an adjustable input lever 14. Thetwo wires of the line 10 are connected to respective ends of the potentiometer. In practice, a voltage source 31 is associated with or included in the oscillator7; this applies also to the oscillator 22 of Figure 2.

In this circuit, the parallel operation ofthe signal input device 1 and ofthe synchronous detector 12 results in a comparison because a transmission is permitted onlywhen thesignals are coincident. This permits a supervision with simple means. A more complete supervision is provided bythe provision of a high-pass filter 15, which precedes the synchronous detector 12 and is designed inaccordancewiththe frequency of the oscillator also as regards the width of the signal from the signal input device so that the high-passfilterprovidesfor a filter action. The high-passfilter has an additional input 16, to which an auxiliary voltage from a source 17 is supplied.That auxiliary voltage has such a magnitude that in response to a frequency shift detected bythe highpass filter a control signal will be delivered to the connecting line 18 and will serve to maintain the receiver in a safe state orto ajustthe recieverto a safe state and to initiate the operation of a signalling device atthe same time.

A low-pass filter 19 is connected between the synchronous detector 12 and the receiver 2 and is also supplied with an auxiliary voltage from the source 17.

The low-pass filter 19 generates an average-value signal, which is fed to the receiver 2.20 and 21 are the respective reference numerals designating the connecting lines between the synchronous detector 12 and the low-pass filter 12 and between the latter and the receiver.

The output of the low-pass filter 19 is the set-point signal forthe receiver 2, which consists of a pulse generator.

The improvement of the protection from interfer ence is determined by the following formulas: (11) U11=Osin(cot+(p) (1) (12) U10=k1 xusin(t+cp) (2) (18) U18=kl XO(XaSin(Wt+(P) (3) (20) Uo=k, xir2xcxsin2(wt+cp) (4) at the output of the synchronous detector 12 in the absence of interference. In that case, the mean value determined by the low-pass filter 19 will be (21) U21 = kg u2 x 1/2 x o: (5) In these formulae cp = electric phase displacement of the generator or oscillator k = transmission factor a = mechanical angle of the signal input device in case of a circular adjustment, as an amplitude factor.

It is apparentthatthe circuit arrangement will not be affected by interference voltages unless they are related by an integral multiple to the frequency ofthe control signal transmitted in line 11.

In the circuit arrangement according to Figure 2, identical or corresponding parts are designated with the same reference characters. The oscillator 7 of Figure 1 is replaced by a tunable oscillator 22, which has an input 23 and an output 24. A line 10 leads from the output 24to the signal input device 1 and is connected buy a branch line 25 to the synchronous detector 12 sothatthesetwo components are supplied with a supervision signal at the same frequency. In Figure 2 the low-pass filter 19 is connected to an analog-to-digital converter 26 of a microcomputer, which is generally designated 27.

That microcomputer is only symbolically shown and includes a signal memory 29 for storing different data words. The data memory is connected buy a control line 28to the input 23. For a selection from the several addresses of the data memory 29 in dependence on the signals generated by the signal input device 1, the analog-to digital converter 26 is connected to the data memory 29 by a functional link 30.

Claims

1. A method of supervising an instruction-transmitting system for transmitting electric signals, comprising a signal input device and a receiver, which is connected to the signal input device by a line, characterized in thatthe signal input device is supplied with electric signals which are different in kind, preferably in frequency, from the control signals which representthe instruction, the receiver is preceded by a comparator, which is supplied with electric signals of said different kind, preferably at said differentfrequency, and in dependence on the comparison of said electric signals of said different kind the control signal is transmitted or an error signal is generated by which the receiver is disabled.

2. Amethod according to claim 1, characterized in thatthe signals of said different kind consist of a.c.

voltage signals and are used as a supply voltage for the signal input device.

3. A circuit arrangement for an instruction-transmitting system fortransmitting electric signals, comprising a signal input device and a receiver, which is connected to the signal input device by a line, characterized by the provision of an oscillatorwhich has at least one output, which is connected to the signal input for determining a signal transmission frequency and to a synchronous detector which is provided in the connecting line andthe transmission state of which is controlled by the oscillator in dependence on the signal transmission frequency.

4. A circuit arrangement according to claim 3, characterised in that the oscillator is used as a voltage source for the signal input device.

5. A circuit arrangement according to claim 3 or 4, characterized in thatthe synchronous detector is disposed close to the receiver.

6. A circuit arrangement according to claim 5, characterized in that the receiver comprises a pulse generatorora computer.

7. A circuit arrangement according to any of claims 3to 6, characterized in thatthe synchronous detector succeeds a high-pass filter, to which an auxiliary voltage is applied, which has such a magni tune that in case of a failure ofthe line or interference affecting the line an error signal will be generated which has such a potential that the receiverwill assume a safe state.

8. A circuit arrangement according to any of claims 3 to 7, characterized by a low-pass filter connected between the synchronous detector and the receiver.

9. A circuit arrangement according to claims 7 and 8, characterized in that the auxiliary voltage is connected also to the low-pass filter.

10. A circuit arrangement according to any of claims 3 to 9, characterized in that the signal input device consists of a potentiometer.

11. Acircuit arrangementaccording to any one of claims 3 to 10, characterized in that the signal input device generates an output signal having an exactly predetermined phase displacement.

12. A circuit arrangement according to any of claims 3 to 11, characterized in that the receiver comprises a computerfortuning the oscillatorto a predetermined control signal frequency.

13. Acircuitarrangement according to claim 12, characterized in that the computer comprises a signal memory for storing a plurality of data words and said memory is adapted to be addressed via a functional link in dependence on output signals of the signal input device.

14. A circuit arrangement according to any of claims 3 to 13, characterized in thatthe oscillator is operated to generate control signals at a signal transmission frequency, which is aboutten to twenty times the frequency corresponding to the rate of the change imparted to the instruction signal by the signal input device.

15. A circuit arrangement substantially as hereinbefore described with reference to the accompanying drawing.

16. A method of supervising an instruction transmitting system fortransmitting electric signals, the method being substantially as hereinbefore described with reference to the accompanying drawing.