The present invention relates to detector systems.

Sliding lift or elevator doors are generally provided with detector systems to detect the presence of an obstruction in the doorway to inhibit the closure of the doors or, if the doors are in the process of closing, to reverse their movement so that they return to a fully open condition. Previously proposed detection systems have involved at least one transmitter and one receiver mounted on opposite sides of the opening. The transmitter produces a beam of light which is received by the receiver. When the beam is interrupted (eg by the passage of a person) the output of the receiver changes and the signal is used to inhibit or reverse the door closing action.

Such an arrangement will only detect an obstruction at one level across the opening. To monitor the opening more comprehensively it is necessary to provide an array of transmitters (each at a different height) along one side of the opening and an array of receivers (each at a different height) along the other side of the opening. Each receiver is positioned in line of sight with a corresponding transmitter. In order to prevent cross-overs between receivers and transmitters (ie a receiver responding to a transmitter other than its corresponding transmitter because of beam divergence), a multiplexing system is used to energise each transmitter in turn and at the same time to enable each receiver in synchronism with the energisation of its corresponding transmitter.

Such an arrangement is complex and requires a multicable link between the transmitter and

receivers on opposite sides of the opening.

It is an object of the invention to provide an improved detector system.

According to the present invention there is provided a detection system for monitoring an opening, the system comprising a plurality of detection groups, each comprising first and second transmitters and first and second receivers, said first transmitter and said second receiver being mounted on one side of the opening and said first receiver and second transmitter being mounted on the other side of the opening, the first transmitter and„ first receiver being in line of sight with each other, and said second transmitter and second receiver being in line of sight with each other, means connecting the output of the first receiver with the input of the second transmitter, and including delay means for delaying the transmission of a signal from the first receiver to the second transmitter, wherein the output of the delay means between the first receiver and second transmitter of each group is used to enable the first receiver of the next group, means for energising the first transmitter and means for sensing the output of the second receiver to determine whether the transmission between the transmitters and receivers is obstructed.

A detector system embodying the invention will now be described by way of example, with reference to the accompanying diagrammatic drawings in which:

Figure 1 is a front elevation of a detector system mounted on the double sliding doors of a lift or elevator: Figure 2 is a block diagram of the detector

system of Figure 1 :

Figure 3 is a front elevation of another detector system mounted on the double sliding doors of a lift or elevator; Figure 4 is a block diagram of the detector system of Figure 3;

Figure 5 is a fragmentary block diagram of a redundancy system for the detector system of Figure 4; and Figure 6 shows an interlaced system of detectors.

As shown in Figure 1 an opening 2 is opened and closed by a pair of sliding doors 4 and 6. The opening may be the opening in a lift or elevator car and the doors mounted slidably on the lift or elevator car. Alternately the opening may be the opening on a particular landing served by the elevator car and the doors slidably mounted on the landing. The door 4 is provided with a transmitter 8 and a receiver 10 mounted on the leading edge at different levels. The door 6 is provided with a receiver 12 and transmitter 14 mounted on the leading edge at levels corresponding to that of the transmitter 8 and receiver 10 respectively.

The receiver 12 is positioned in line of sight of the transmitter 8 and the receiver 10 is positioned in line of sight of the transmitter 14- The output of the receiver 12 is coupled directly to the input of the transmitter 14. The input of the transmitter 8 is connected to an input terminal 16 and the output of the receiver 10 is connected to an output terminal 18.

In operation when a signal is applied to the input terminal 16, the transmitter 8 is energised

to transmit a light beam to the receiver 12 which in turn energises the transmitter 14 to transmit a light beam to the receiver 10. Any interruption of one of the beams (which are at different levels) will be reflected in a change in output at the terminal 18 and this can be used by the control circuitry (not shown) controlling the doors.

The block diagram of the control circuit is shown in Figure 2. As shown an oscillator 20 feeds the transmitter 8 which transmits an infra red beam to the receiver 12. The receiver 12 in turn enables the transmitter 14 which transmits an infra red beam to the receiver 10. An output unit 22 responds to the output of the receiver 10. With this arrangement it will be appreciated that all the control circuitry for the system is located on the door 4- Such circuitry as there is on the door 6 merely needs a power supply connection. The need for control cables linking the two doors 4 and 6 is obviated. Figures 3 and 4 show a more comprehensive detector system which provides an array of beams across the opening at all levels.

In Figure 3 parts similar to those in Figure 1 are similarly referenced. In Figure 3 instead of just one group of two pairs of transmitters and receivers there are four groups. The transmitters and receivers of the second to the fourth groups are similarly referenced to the transmitters and receivers of the first group except with a respective suffix A to C. The output of the first group is linked to the input of the second group and so on an until the fourth group where the output is connected to the output terminal 18.

Also in order to prevent the problem of crossover, the linked receiver and transmitter of

each group is coupled by a delay circuit 24 and the link between groups includes a delay circuit 26.

The block diagram of the control circuit is shown is Figure 4. The trasmitter 8 is supplied with pulses from a pulse generator 20 and a pulsed infra red beam is transmitted to the receiver 12. Upon receipt of the first pulse the receiver 12 feeds a signal to a memory 30 (for example, a bistable multivibrator) which it then set and the output from the memory 30 is fed to a delay circuit 24. After a predetermined delay, the output of the delay circuit 24 energises the transmitter 14 and simultaneously enables the receiver 12A. The transmitter 14 transmits a light beam to the receiver 10 . Upon receipt of this light beam the receiver 10 feeds a signal to a memory 32 (for example a bistable multivibrator) which is then set. The output from the memory 32 is fed to a delay circuit 26. After a predetermined delay the output of the delay circuit 26 energises the transmitter 8A of the next group of detectors. The receiver 12A on being enabled responds to the light beam received from the transmitter 8A and feeds a memory 30A similar to the memory 30 and a delay circuit 24A with a signal. The circuitry of the second group of detectors responds in the same way as described in connection with the first group of detectors as does the circuitry of the third and subsequent groups.

When eventually a signal is received by the receiver 12N (not shown) of the Nth group of detectors, the memory 30N will be enabled and after a predetermined delay, by the delay circuit 24N, the transmitter 14N will be energised to transmit a light signal to the receiver 10N. At this point with all the memories 30 and

32 set there will have been a series of 2Η beams traversing the opening 2.

The output of the delay unit 24 ^" is also fed to a delay unit 34 which after a predetermined delay resets each of the memory's 30, and 30A to 30ΪT. Also when the output unit receives a signal from the receiver 10N, a reset signal is sent to all the memory's 32 to 32 ( -1 ) to reset them.

With all the memory's reset the system is ready to receive the next pulse from the pulse generator 20.

It will be appreciated that the sum of the delays effected by the delay units 30 to 30ΪT and 32 to 32 (F-1 ) and 34 should be less that the time internal between successive pulses generated by the pulse generator.

Control circuitry (not shown) monitors the output signal from the output unit. In operation when the output unit generates an output within a predetermined period following each pulse from the pulse generator 20, this indicates that the beams traversing the opening are not obstructed and so the sliding doors can safely be closed. If no output is generated within the predetermined period this indicates that an obstruction exists in the door way and so the closure of the sliding doors can be inhibited or reversed.

If for example the beam from transmitter 8A to receiver 12A is obstructed, the receiver 12A will not respond until the obstruction is cleared.

Following the clearance of the obstruction, the receiver 12A will generate an output, which will finally reach the transmitter 14N and receiver 10N ^" . At this point the memory's will be reset and the detection system will be ready to react to the next

pulse from the pulse generator.

With this arrangement it will be appreciated that the components mounted on door 6 need only a power supply connection to operate and do not need to be connected by signal conductors to the components mounted on the door 4. This enables considerable savings in the cost of assembly and manufacture.

Also because the receivers are inhibited from operating until just before a signal is transmitted from a corresponding transmitter, the receivers are substantially immune from receiving signals which may, because of divergence of a transmitted beam from another transmitter, impinge upon the wrong receiver.

Figure 5 shows part of a redundancy system which acts to selectively effect by-passes in response to a predetermined criterion. In Figure 5 parts similar to those in Figure 4 are similarly referenced.

As shown in Figure 5 each transmitter 8 to 8N has an output which feeds a respective gate 40 to 40N. Each gate 40 to 40R in turn feeds a respective time delay circuit 42 to 42N and the output of each time delay circuit 42 to 42N is connected to the output of a corresponding receiver 10 to 10N.

A delay circuit 46 supplies pulses to the gating inputs of GATES 40 to 40N via respective GATES 44 to 44N. The delay circuit 46 is supplied with pulses from the pulse generator 20 which pulses are suppressed when the delay circuit 46 receives a pulse from the output unit 22 within a predetermined period of time. Thus so long as none of the transmitters or receivers fail to generate an output, the redundancy

system is held inoperative.

The outputs of all the memories 32 to 32ΪT are fed to respective inputs of a logic circuit 48 composed of for example AND gates, and OR gates and which monitor the system failures to generate an alarm signal to terminal 50 when an unacceptable number combination of units have failed. In operation let it be assumed that the receiver 10 has failed. This will break the sequence of light beams across the doors and as a result there will be an absence of a confirmatory signal from the output unit 22. The next pulse which reaches the delay circuit 46 after a predetermined delay, feeds a signal to the input of gates 44 to 44A simultaneously. Normally at this point the receiver 10 would generate an output which would inhibit the GATE 44 but in the event that the receiver fails to transmit a signal, the GATE 44 will pass on a signal to enable GATE 40. Thus the output from the transmitter 8 is fed via the GATE 40 to a delay circuit 42 which after a predetermined delay feeds a signal to the output of the receiver 10 only just slightly later than the receiver 10 would have generated a pulse had it been operating normally. It will thus be seen that light paths between transmitter 14 and receiver 10 has been by-passed. The light path between transmitter and the receiver 12 must still exist in order to enable the receiver 12A (see Fig 4). This state will continue until the whole system is reset whereupon, if the receiver 10 remains inoperative, then by-pass will again be brought into operation.

The logic circuit 48 which monitors the memories 32 to 32N, determines when an unacceptable

number, or an unacceptable combination, of units has failed and provides an alarm signal at terminal 50 in response thereto. This alarm signal can be used to initiate emergency or other proceedures which ensures a fail safe operation of the system.

While the redundancy system has been described as providing a by-pass path between transmitters 8 and 8A, 8A and 8B and 8(N-l) to 8N it will be appreciated that the same arrangement can be used to provide a by-pass path from transmitters 14 to 14A, 14A to 1 B and 14(N-l) to 14N when appropriate.

The system may in some embodiments be modular or divided into discrete groups of transmitter/receiver pairs. In use, if say vertically spaced transmitter 8A and receiver 10A form a modular pair then if receiver 12A fails, the redundancy system would bypass both transmitter 8A and receiver 10A. The modular unit including transmitter 8A, receiver 1OA and their associated circuitry, delays, etc can be removed and replaced. This will, however, leave a relatively large unmonitored detection space. Therefore, software or hardware which serves to limit the amount of unprotected space may be provided, which, for example, limits the maximum number of bypasses or does not allow adjacent zones to be bypassed simultaneously.

Alternatively, or in addition to limiting the unmonitored spaces, the groups may be interlaced. One example of interlacing is shown schematically in Figure 6. Four interlaced Groups I to IV are shown. Group I is a typical group and comprises a first transmitter/receiver pair 8A,12A in line of sight and a second transmitter/receiver pair 14A,10A also in line of sight such that receiver 1OA is mounted on the same door as transmitter 8A but vertically

separated therefrom by respective transmitters 8B-8D. If an element in one of the groups fails, the remaining elements in the group are bypassed and a signal passes to the next group in turn. Due to the interlacing, the space which is unmonitored in the event of a failure may be less than that of a non¬ interlaced system.

While the described detection system has been described in connection with the operation of lift or elevator doors it will be appreciated that it can be used in other automatic door opening/closing systems (eg garage and shop doors) and that the system can also be used in other detection applications, for example, in the detection of intruders.