GB2203239A

GB2203239A - Object detection apparatus

Info

Publication number: GB2203239A
Application number: GB08807764A
Authority: GB
Inventors: Douglas Henry Clayfield; Terence John Thomas Murphy
Original assignee: R V Ltd
Current assignee: R V Ltd
Priority date: 1987-04-06
Filing date: 1988-03-31
Publication date: 1988-10-12
Anticipated expiration: 2008-03-31
Also published as: GB2203239B; GB8807764D0; GB8708167D0

Abstract

Objects such as intruders, are detected by the interruptions of beams of radiation 15 using a pair of transmitters 12, 14 which transmit spaced beams towards a pair of receivers 20, 21. The transmitters are energised such that they alternately produce pulses of radiation. Control circuitry 23-29 processes the receiver outputs to produce an alarm when both beams are interrupted and also to give an indication of which beam is interrupted when only one beam is interrupted or absent, so that faults in the operation of the apparatus may be detected. The radiation may be infrared or ultrasonic. <IMAGE>

Description

IMPROVEMENTS IN OR RELATING TO DETECTION APPARATUS DESCRIPTION This invention relates to detection apparatus of the type in which objects are detected by the interruption of one or more beams of radiation transmitted from a transmitter to a receiver. Such apparatus is used, for example, as an intruder detector and typically employs infra red or ultra sonic radiation.

Known devices comprise a pair of vertically spaced transmitters located in a housing and a pair of receivers disposed at an appropriate distance (typically up to lOOm) from the transmitters. When used in a security system an alarm output is generated only when the beams from both transmitters are broken. Two vertically spaced beams are used to avoid the alarm being triggered by objects such as leaves which usually only break one beam.

There is also a requirement to provide a separate or fault output if a single beam is interrupted or obscured e.g. when setting up it is necessary to know that the apparatus is operating correctly. This has not been possible with conventional equipment.

At the transmitter-receiver spacings involved it is inevitable that each receiver receives transmitted energy from both transmitters. Thus if, for example, one transmitter ceases to transmit both receivers will still receive a signal.

The present invention is designed to overcome this problem.

According to the present invention there is provided detecting apparatus of the type in which objects are detected by the interruption of beams of radiation transmitted from a transmitter to a receiver said apparatus comprising a pair of transmitters for generating a pair of spaced beams of radiation, a pair of receivers for receiving said beams of radiation, means for energising said transmitters so that they produce alternately pulses of radiation and control circuitry arranged to receive the outputs of said receivers and to cause generation of an alarm or similar indication when both beams are interrupted and to provide a further indication when a single beam is interrupted or inoperable.

The radiation may be infra red radiation or ultra sonic radiation.

By pulsing the transmitters alternately it is possible using appropriate timing circuits in the control circuitry to identify when a single beam is interrupted.

The beams are preferably spaced in a generally vertical plane.

The control circuitry may comprise an OR gate arranged to receive the output of each receiver, an AND gate arranged to receive the output of each receiver, a first circuit for sensing missing pulses coupled to the output of the OR gate and a second circuit for sensing missing pulses coupled to the output of the AND gate.

The radiation pulses themselves may be modulated.

The receivers may be connected to the AND gate by delay timer circuits.

The output of each circuit for sensing missing pulses may be coupled to a respective delay timer.

The circuitry may be arranged so that an output from one delay timer is indicative of a single beam interruption and an output from the other is indicative of a double beam interruption.

The invention will be described now by way of example only with particular reference to the accompanying drawings. In the drawings: Figure 1 is a block schematic diagram of a first embodiment of detection apparatus in accordance with the present invention; Figure 2 shows a series of pulse waveforms which illustrate the operation of the apparatus of Figure 1; Figure 3 is a block schematic diagram of a second embodiment of detection apparatus in accordance with the present invention; Figure 4 shows the same basic arrangement as Figure 3, but with a different beam arrangement; and Figures 5 to 7 show pulse waveforms which illustrate the operation of the apparatus of Figures 3 and 4.

Figure 1 shows detection apparatus which is designed to be used as an intruder detector in a security system. The apparatus generates two generally vertically spaced beams and produces an alarm signal when both beams are interrupted. The apparatus comprises a transmitting unit 10 and a receiving unit 11. These units will be appropriately spaced (typically by up to 100m) in a region to be protected. The transmitter unit, typically an infra red unit, includes a pair of transmitters 12, 14 which are generally vertically spaced in an appropriate housing. The housing can have a suitable window to allow the beams 15 to be transmitted from each transmitter. The actual beam shape is determined by the optics within the housing.The energising circuit for the transmitters includes a clock 16, a divide by 2 divider 17 coupling the clock to the transmitter 12 and a divide by (2+1) divider 18 coupling the clock to the transmitter 14. The clock produces a regular train of pulses shown by waveform (a) in Figure 2. The output of the divider 17 is shown as waveform (b) and the output of the divider 18 is shown as waveform (c). As can be seen from waveforms (b) and (c) the transmitters 12 and 14 are energised so that they produce alternate pulses of radiation i.e. when transmitter 12 is producing a pulse transmitter 14 is not and vice versa.

The receiver unit 11 comprises a pair of receivers 20 and 21 which respond to radiation pulses received from the transmitter unit and generate corresponding electrical pulse outputs. The receivers can be photoelectric cells with appropriate amplifiers. The output from each receiver is connected to an OR gate 23 and to an AND gate 24. The output of the OR gate 23 is connected to a circuit 25 which senses missing pulses and the output of the AND gate 24 is connected to a similar circuit 26. The circuit 25 is arranged to generate an output signal when it senses the absence of a pulse at its input for a period of t2 and the circuit 26 is arranged to generate an output signal when it senses the absence of a pulse at its input for a period tl.

The output of the circuit 25 is connected to a delay timer 28 and the output of the circuit 26 to a delay timer 29.

The operation of the apparatus will now be described with reference to Figure 2. In this Figure waveform (d) represents the output of receiver 20, waveform (e) the output of receiver 21, waveform (f) the output of the OR gate 23, waveform (g) the output of the AND gate 24, waveform (h) the output of the circuit 25 and waveform (i) the output of the circuit 26. The waveforms are divided into vertical sections illustrating the different modes of operation.

As has been explained the transmitter clock produces a regular chain of pulses (a) which are fed alternately to the transmitters 12, 14. The infra red pulses produced alternately frpm the transmitters are transmitted over an optical path to the receivers 20, 21.

In normal operation the received amplified signals from the receivers 20, 21 are shown in the first section of waveforms (d) and (e) under the heading (1). The corresponding OR and AND gate outputs are shown at (f) and (g). It can be seen that there are no missing pulses so in normal operation the circuits 25 and 26 do not produce an output (see (h) and (i)). The timing periods tl and t2 of circuits 26 and 25 are illustrated in Figure 2 under the heading (6). Thus in normal operation there is no alarm or fault signal.

Suppose now there is a beam blockage at A in Figure 1. The signals are then shown by the waveform sections under the heading (2) in Figure 2. The receivers 20,21 no longer receive a signal from the transmitter 12 but both receive from transmitter 14. The resulting OR and AND gate signals can be seen in (f) and (g). The circuit 25 does not generate an output since, although it receives less pulses than in normal operation, these still appear more frequently than the period t2. The circuit 26 produces an output (waveform (i)) since the pulses at its input appear less frequently than the period tl. Thus this combination of outputs can be used to indicate the existence of the blockage A.

The delay timers 28 and 29 are used so that an output, in this case output SB from the timer 29, is produced only after the interruption has been sensed as present for a pre-selected time. The signal SB is used to provide the indication that a single beam has been interrupted.

It will be appreciated that a beam blockage at B will result in a similar operation.

Consider now a beam blockage at D in Figure 1.

Receiver 21 is completely interrupted and does not receive from either transmitter but receiver 20 receives from both. The waveforms are as shown in the section headed (3). The OR output is normal but there is no output from the AND gate 24. Circuits 25 does not produce an output but after time period tl the circuit 26 produces an output (i) indicating interruption of a single beam. Similar considerations apply to an interruption at C.

For a blockage at E in Figure 1 the waveform section is that shown under heading (4) in Figure 2. The path between transmitter 12 and receiver 20 is broken but receiver 20 still receives from transmitter 14 and receiver 21 receives from both transmitters. The OR output is normal so circuit 25 does not produce an output. The pulses at the output of the AND gate 24 occur less frequently than time period tl so circuit 26 produces an output indicating a single beam interruption.

Similar considerations apply to an interruption at F.

Consider now a beam blockage at A and B or at C and D in Figure 1. The waveform sections which apply are those under the heading (5). Receiver 20 does not receive from either transmitter nor does receiver 21. The output from the OR gate 23 becomes zero and after a period t2 circuit 25 produces an output (see(h)), and this generates via delay timer 28 an output DB indicating both beams interrupted.

Also for the period to after beam interruption circuit 26 produces an output to signal a single beam interruption via delay timer 29. In a practical unit the outputs DB and SB can be interlocked as required according to application and can then drive a relay or solid state outputs for control purposes.

It should be noted that for normal applications if the beams are interrupted at E and F the intervening region between E and F is also obscured so that neither receiver receives from either transmitter. The operation is therefore as described for an interruption at A and B or at C and D.

In the above embodiment both receivers can receive from both transmitters and this is a requirement for correct operation of the apparatus.

Figure 3 and 4 show arrangements in which this need not be the case. The transmitter sections of Figures 3 and 4 are the same as Figure 1 and are shown by like reference numerals. The receiver sections include corresponding elements shown by like reference numerals. In Figures 3 and 4 however the receiver outputs are connected to the AND gate 24 by delay timers 30 and 31. These timers extend the received pulse period by a time tl. This is illustrated, for example, by waveforms g and h in Figure 6 which shows the outputs of the timers 30 and 31 respectively.

The transmitter waveforms are shown in Figure 5 and are the same as those of Figure 2. Figure 6 shows the receiver waveforms for Figure 3 and Figure 7 shows the receiver waveforms for Figure 4.

As can be seen in Figure 3 receiver 20 cannot receive from transmitter 14 and receiver 21 cannot receive from transmitter 12. In normal operation (1) receivers 20, 21 receive alternate pulses (waveforms (d) and (e)). The OR output (f) is a train of pulses which repeat more frequently than t2 so that circuit 25 does not produce an output (j) The pulses from the receivers 20, 21 are processed by the timers 30 and 31 to produce the wider pulses of waveforms (g) and (h). The resulting signal at the output of AND gate 24 has a period shorter than tl (waveform (i)). Thus there is no output from circuit 26 (see waveform (k)).

Consider now a blockage at Al in Figure 3. The waveform section (2) of Figure 6 applies. Receiver 20 does not receive from either transmitter and receiver 21 receives from transmitter 14 only. the OR output (f) has a repetition period shorter than t2 so there is no output from circuit 25 (j). The output from timer 30 falls to zero after time tl (g) and thus the AND output also becomes zero (i). The circuit 26 thus produces an output after time tl (k) to indicate via delay timer 29 a single beam interruption. The response time of the timers 28 and 29 are set to suit the particular application.

A blockage at B1 results in a similar operation.

For a blockage-at D1 the waveform section (3) applies. The receiver 20 receives from transmitter 12 only and 21 does not receive any signal. The conditions are similar to an Al blockage. The OR output (f) has a repetition rate greater than t2 so there is no output from circuit 25 (j). The output from the timer 31 (h) falls to zero after tl and thus the output of AND gate 24 (i) also falls to zero. Thus circuit 26 produces an output (k) after time tl to indicate a single beam interruption via delay timer 29 (signal SB).

A beam interruption at C1 produces a similar result.

For a blockage at El the conditions are identical to that described for Al. The waveform section is (4) and the result is as for an Al blockage. The same applies for F1.

For a blockage at Al and Bl, El and F1, or C1 and D1 the waveform section (5) applies. The receivers 20, 21 do not receive any signals. The OR output (f) is thus zero and there is an output from circuit 25 after a time t2. Thus delay timer 28 produces a signal DB indicative of both beams interrupted.

Also after a period tl + tl there is an output from circuit 26 indicating a single beam interruption.

In a practical arrangement the signals Sb and DB will probably be interlocked as described for Figure 1.

In Figure 4 the circuit elements are the same as for Figure 3 but in this case receivers 20 and 21 can each receive from both transmitter. The waveforms of Figure 7 apply for the receiver unit.

In normal operation the OR output (f) has a repetition rate greater than t2 and there is therefore no output from the circuit 25 (waveform (j)). The time delay circuits 30 and 31 operate to maintain the output (i) of the AND gate 24 high and thus there is no output from circuit 26. Thus there is no alarm or fault signal.

Suppose there is a blockage at A2. The waveform section (2) applies. Receiver 20 does not receive from either transmitter and receiver 21 receives from transmitter 14 only. The OR gate output (f) has a zero period less than t2 so the circuit 25 does not produce an output.

The outputs from timers 30 and 31 ((g) and (h)) fall to zero after time tl and thus the output (i) of AND gate 24 also falls.

The circuit 26 generates an output (k) after time tl indicating a single beam interruption.

A blockage at B2 has a similar effect.

For a blockage at D2 the waveform section (3) of Figure 7 applies. Receiver 20 receives from the both transmitters and a receiver 21 does not receive at all. The OR output (f) is normal so circuit 25 does not produce an output.

As there is not output from receiver 21 after a time tl the timer output (h) falls to zero and hence the AND output (i). The circuit 26 produces an output (k) after time tl to indicate a single beam interruption.

An interruption at C2 has a similar effect.

For a blockage at E2 the waveform section (4) of Figure 7 applies. Because of signal overlap this blockage does not generate an alarm condition or indication from either of circuits 25 or 26.

Similarly for a blockage at F2. It is however considered that for standard applications a single beam interruption indication is unnecessary as the system is still maintained by a minimum of two beam paths, transmitter 12 to receiver 21 and transmitter 14 to receiver 20.

For a blockage at A2 and B2 or at C2 and D2 the waveform section (5) of Figure 7 applies. Receivers 20 and 21 do not receive from either transmitter.

The output (f) from the OR gate 23 falls to zero and hence there is an output (j) from circuit 25 after time t2 thereby indicating via delay timer 28 a double beam interruption.

The outputs (g) and (h) of timers 30 and 31 fall to zero after time tl and thus the AND gate output (i) also falls. Circuit 26 thus produces an output indicative of a single beam interruption.

It should be noted that in practice for normal applications if the beams are interrupted at E2 and F2 the intervening region will also be obscured so that receiver 20 will not receive from transmitter 14 and receiver 21 will not receive from transmitter 12. Thus the conditions are the same as for an interruption at A2 and B2 or C2 and D2.

It will thus be seen that the above embodiments provide detectors which can provide an indication of whether there is a single beam interruption or a double beam interruption. The apparatus does not require any electrical connection between the transmitter and receiver units and there is no requirement for multiplexing receive the circuits.

This arises in the main from the use of transmitters which are pulsed alternately. It will be appreciated that the pulses themselves can be modulated. Modulating the pulses reduces the average power whilst maintaining the pulse power.

The above embodiments have been described with reference to two transmitted beams. It will be appreciated that the technique can be applicable to arrangements which use more than two beams with appropriate modifications to the logic circuitry.

Claims

CLAIMS:

1. Detecting apparatus of the type in which objects are detected by the interruption of beams of radiation transmitted from a transmitter to a receiver said apparatus comprising a pair of transmitters for generating a pair of spaced beams of radiation, a pair of receivers for receiving said beams of radiation, means for energising said transmitters so that they produce alternately pulses of radiation and control circuitry arranged to receive the outputs of said receivers and to cause generation of an alarm or similar indication when both beams are interrupted and to provide a further indication when a single beam is interrupted or inoperable.

2. Apparatus according to claim 1, wherein the radiation is infra red radiation of ultra sonic radiation.

3. Apparatus according to claim 1 or claim 2, wherein the beams are spaced in a generally vertical plane.

4. Apparatus according to any preceding claim, wherein the control circuitry comprises an OR gate arranged to receive the output of each receiver, an AND gate arranged to receive the output of each receiver, a first circuit for sensing missing pulses coupled to the output of the OR gate and a second circuit for sensing missing pulses coupled to the output of the AND gate.

5. Apparatus according to any preceding claim wherein the radiation pulses themselves are modulated.

6. Apparatus according to claim 4, wherein the receivers are connected to the AND gate by delay timer circuits.

7. Apparatus according to claim 4, wherein the output of each circuit for sensing missing pulses is coupled to a respective delay timer.

8. Apparatus according to claim 6, wherein the circuitry is arranged so that an output from one delay timer is indicative of a single beam interruption and an output from the other is indicative of a double beam interruption.

9. Detecting apparatus substantially as hereinbefore described with reference to and as shown in Figures 1 and 2, or Figures 3, 5 and 6 or Figures 4, 5 and 7 of the accompanying drawings.