CA1303177C - Proximity detection system for doors and the like - Google Patents

Abstract

ABSTRACT
A movable door incorporates a proximity detection system for sensing obstructions in the path of the door. The system comprises an array of transmitter/receiver pairs (21, 22 and 23), each pair comprising a transmitter (1) for transmitting an energy pulse, a receiver (2) located adjacent the transmitter and directed to receive any reflected transmitter pulses, and a shielding (3) for shielding the receiver (2) from receiving energy pulses directly from the transmitter (1). At least two transmitter/receiver pairs (21, 23) are mounted on a leading edge or face of the door (12) to transmit energy pulses in a direction which is not at right angles to the leading surface or edge of the door, to monitor for obstructions in the path of the door (12). Another two transmitter/receiver pairs (26 and 28) are mounted on the leading edge or surface of the door (12) to transmit energy pulses at right angles to the surface or edge of the door (12). One of the latter two receiver pairs (26) has a different response to the other pair (27) so that when the door (12) approaches a stationary object the one pair (26) detects the object ahead of the other pair (27).
Means are provided to respond to the output of the one pair (26) indicating the detection of an object to inhibit the output of the other pair (27).

Description

~BQ~IMITY ~ TQ~
The invention relates to a proximity detector for the detection of the presence and position of objects and people or parts ther~of in the path of moving mechanical devic~s, su~h as automatic sliding doors, automatic swing doors or moving vehicles of robots, to, for example, enable corrective safety action to be taken.
Tha present application has been divided from Canadian patent application No. 522,201.
It is common practice in the construction of automatic doorways to include means of ensuring that the doors cannot close on a peræon causing discomfort or injury. A numb~r of aontactless sy6tem are known for detecting the pre3ence of a person in a doorway, particularly the presence o~ a person in the space which the door is approaching. British Patent Specifications 711515, 856985, 1108884, and European Patent 0097139 are but a few which de cribe sy tems of this nature.
All of them involve positioning a proximity detector on the door establishing conditions whereby a person can be identified in th~ space or volume which the door is approaching but being able to ignore walls and other fixed ob~ects by balance bridge t~chniques or by reducing the sensitivity when the door i~ close to the fixed object.
While this approach works satisfactorily in many instances, it is not always reliable in practice and tends to be prone to false ~iring under changing site conditions. For example, when very close to fixed objects the slightest variation in door position may cause a balance bridge circuit to give a false detection, If the sensitivity is reduced under these condition~, then 'nulls' often occur where detection is not possible.
This invention provides a means of increasing the sensitivity and range of detection and maintaining and often increasing the sensitivity when the sensor is very close to objects not to be detected, without false firing.
It is preferable with sliding or swing doors to provide types of protection aB follows:
1) For a person very close to the leading edge or side of a closing door detection is necessary over the full length of the leading ~dge or side o~ the door, this detection range must be adequate to prevent a person ~hand, ~oot, etc.) belng touched by the door, l.e. to be greater than the ~topplng distance og the door.
2) For a person approaching a door, detection is necessary to establish the presence of the person to delay -~ 10 the door closure.
3) With building sliding doors it is necessary to e~tablish detection o~ a person approaching a door ~o open the door.
4) With a swing door it is necessary to establish separate detection of persons approaching a door from either side to operate a ætop circuit to prevent the door from hitting one of the persons.
5) With a swing door it is necessary to establish detection also outside the path o~ the door opening to allow timely response.
The lnvention uses as its ~asis a method of, and apparatus for, controlling th~ range and annular vision of a detection unit which i8 mounted on or near a moving object (e.g. door) for the purpose of providing information as to th2 posi~ion o~ other objects, stationary or movable, within a specified space or volume.
Two types of detection units are discussed, namely reflective acoustic (e.g. sonic or ultrasonic) and electromagnetic.
According to the pr2s~nt invention there is provided a two conductor transmi~sion ~ystem for transmitting power and data betw~en two ~tations, the system comprising a first station linked to a second station by only first and gecond conductors, the first station including a DC
source for supplying the first and second conductors with DC power, a synchronisation pulse generator, a first modulator for modulating the DC power fed to the i30~177 conductors with the synchronisation pulses, a data torminal connected to said first conductor for receiving data trans~itted from th~ sQcond tation, and first inhibiting means respons$vs to the synchronisation pulses to inhibit the passagQ o~ data to th~ data terminal during the transmission of 6ynchronisation pulses, the second station comprising data signal generating means connected to the first and sacond conductors to receive DC power and synchronisation signals therefrom, the data signal generating means being arranged to generate data signals indicative of a monitored condition, a second modulator for modulating the DC power flowing along the first conductor in respons~ to the generated data signals, and second inhibiting mean~ responsive to the data signals generated to render thQ data signal generating means insensitive to the data signals appearing on the first conductor.
~he invention will now be described, by way of exampl~, with ref~rsnce to the accompanying d$agrammatic drawings, in which:
Figure 1 shows a ~ensor or detector unit and an object with a smooth planar ~.urface;
Figur~ 2 ~hows a sen80r unit with a curved object;
Figure 3 shows a sensor unit and its detection profile;
Figure 4 shows a sliding door with a detection unit on the top Or the door;
Figure 5 shows a sliding door with a detection unit on the bottom Or the door;
Figure 6 shows a sliding door with six detection units;
Figure 7 shows a plan o~ a swing door with two detection units;
Figure 8 shows a plan of a swing door with twelve detection units:
Figure 9 shows a plan of a swing door and various arrangements of detection units;

Figure lOA shows a section through a detection unit along line W-W in F~gure lOB:
Figure lOB shows a front elevation of a detection unit in a position in which it is mounted on the leading edge of a sliding door:
Figure lOC shows a plan to Figure lOB;
Figure 11 shows a circuit diagram;
Figure 12 is a circuit diagram of one of the comparators shown in the diagram of Figure 11:
Figure 13 is a block diagram of the synchronisation circuit for the sensor or det~ctor unit;
F$gura 14 i~ a diagram o~ a multisensor unit;
Figura 15 is a circuit diagram of a blanking circuit; and Figur~ 16 is a pulse diagram for the circuit of Figure 15.
Referring to Figure 1, a transmitter 1 is sending out energy in the dir~ction 4. Rec~iver 2 is sensitive to this energy in the direction 7 and will givs an electric response thereto. Barrier 3 between the transmitter 1 and the receiver 2 is impermeable to this energy and restricts the direct coupling of the en~rgy betwe~n transmitter 1 and receiver 2. In the embodiment shown in Figures 1 to 8, the elements 1, 2 and 3 form a single sensor unit. The illustrated ob~ect 5 has a reflective surface. It is assumed that the energy s~gnal in direction 4 obeys laws similar to the laws governing the reflection of light and so bounces in direction 6 away form the receiver 2.
Similarly in Figure 2 there will be a return energy signal from the ob~ect 9 in the directlon 7 towards the rece~ver 2 if the-point of re~lection lies on a tangent 8 with equal angles of incidencQ and reflection. Using these principles, a system may be constructed to d~fferentiate between ~mooth and textured surfaces. In the case o~ a textured sur~ace which is made up o~ a multltude o~ curved surfaces ~ome will be in such an orientation as to cause re~lection of energy in the direction 7 towards thQ receiv~r 2.
Referring to Figure 3 the said transmitters or receivers may be transducers of acoustic or ele~tromagnetic ~nergy (~or example in the infrared region of the spectrum). These transducers can be manufactured in suah a w~y that they exhibit maximum radiant intensity (transmitters) or maximum sensitivity (receivers) in the direction of the X axis. The intensity or sensitivity of the transdua~r3 w~ all of~ in proportion to the angle of their deviation ~rom the X axis. It follows therefore that these transducers ~ay be considered to radiate (transmitters) or receive (recaivers) energy in the form of a conical pro~ile lo. A textured ob~ect 11 will cause re~lection o~ many signals in the direction 4 ~rom the transmitter 1 into the receiver 2 (signals in the direction 7). The size o~ the receiver signals will be proportional to:
(1) Sur~ace area Or the ob~ect 11 wlthin the conical detection area 10.
(2) Reflective constant o~ the surface of the ob~ect 11 ttexture, colour, reflectivity, etc.).
(3) The total distance ~ravelled by the signals.
(4) The distance of the object 11 from the X axis in the direction of Y and/or Z axes.
The receiver 2 could be connected to a measuring device (not shown) which gives a response (detection) only when a present threshold level i8 exceeded. The threshold may be such that the ob~ect 11 only gives a response with the conical profile 10. Within this conical profile, detection will occur. By arrangement of the attitude of the transmitter 1, barrier 3 and receiver 2 with respect to each other and to thQ ob~ects to be detected and objects to be ignored, it i~ possible to control the space or volume in which dstection occurs.
Referring to Figure 4, a sensor unit 1-3 is mounted at the top o~ an automatic sliding door 12. The door 12 slides in the direction S. ~he barrier 3 is between the Y
\

~03177 transmitter 1 and the rQcoiver 2 and re6tricts the direct signal path. The axis X i8 tilted away from the vsrtical so as to produce a det~ction pro~ile 10 which extends from the door edge 12A into the opening. It is preferable that no signal may bQ ~mitted from the transmitter 1 in such a direction as to cause reflection from the edge 5 back towards the rece~ver 2.
The ~dge 5 is assumed to be a relatively smooth surface and as ~uch will not return any significant signal to the receiver 2 ~rom the transmitter 1. The object 9, situated within the d~tection profile 10, possesses textured surfaces and offer points some o~ which reflect signals from the transmittar 1 to the receiver 2 (~igure 2).
As the door 12 moves in the direction S and gets very close to the edge 5, the ~ignals transmitted ~rom the transmitter 1 are re~l~cted back and ~orth between the leading edge 12A of the door 12 an~ the edge 5 thereby increasing the density Or the transmitted and returned signals. This has the advantage o~ increasing sensitivity to small ob~ects (e.g~ f~ngers~ when the door is nearly closed.
The range along the axis X of the sensor unit has to be accurately controlled to prevent the floor 5A from being detectedl and yet allow ~or detection of objects on the floor (e.g. feet). This application $s therefore most suitable for acoustic transmitters/receivers using the relatively slow speed o~ sound. When using acoustic transducers range can be controlled on a "time till received" basis. In addition, time slot 'blanks' can be incorporated in the circuit to ignore signals from protruding ob~ects, e.g. door knobs and frames. This will be disclosed in more detail in connection with Figures 15 and 16 described hereinafter~
Figure 5 shows an alternative arrangement with the sensor unit 1-3 mounted at the bottom of the leading edge 12A of the door 12. The arrangement is othPrwise the same 1303~77 as that in Figure 4 and the same principles of detection apply. Here the range along the X axis is no longer critical provided that the ceiling 5~ is higher than the detection height o~ the ob~ect 9. Howevar, the detection range in the dir~ction S rapidly diminishes towards the floor 5A.
For more critical applications an arrangement of sensors may be used. Figure 6 show~ a possible arrangement o~ four sensor units 21-24 mounted along the door edge 12A o~ whic~ units 21 and 22 ~ace downwards and units 23 and 24 face upwards. Each sensor unit comprises a transmitter, a barrier and a receiver as in the prsvious ex~mples. The angle o~ detection in the Y and Z axes (Figure 3) has to be increased to give the same range ~rom the door edge 12A in th~ direction S as in Figure 5.
~owever, the detection range in the X axis is no longer critical due to the overlapping of the detection profiles.
Therefore instead of the acoustic units used in the previous examples other, e.g. infrared or microwave, units may be used. Other arrangements of units may be used to provide the required detection profile.
The detection profile still diminishes towards the floor 5A, so that it i8 still difficult to detect an object near the floor. This can be easily overcome by using two additional units 26 and 27. Both these units are looking forward i.e. with their X axes in the direction S. The sensor unit 26 positioned at the floor le~el will detect ob~ect~ at th~ floor level. The sensor unit 27 may have a pro~ila along its X axis greater than the sensor unit 26 but within the prorile of the sensor unit 24, and i8 used solQly to disabl~ the ~ensor unit 26 when the door i8 close to the edge 5 to prevent detection of the edge.
Figure 7 ~hows the plan view of a sensor unit 1-3 mounted on the ~ide A o~ a swing door 12 near its pivot point 16. The detection profile in the X axis (Figure 3) is horizontally across the door opening and tilted away ~rom the door 12 so as to produce a detection profile lOA
which extends from the door on the side A into the opening area. It is assumed that a wall 35 (or other barrier extending perpendicular to the door when in its normally closed position) has a r~latively smooth surface and will not reflect a ~ignal from the transmitter 1 to the receiver 2 when the door i~ open. As the door 12 comes to close proximity with th~ wall 35, th~ signals transmitted from the transmitter l are re~lected back and forth between the door 12 and the wall 35 giving an increased density of transmission and incre~sed detection ~ensitivity to ~mall ob~ct~. A~ with single sensor unit arrangements on ~liding doors (Figure 4) the range along the axis X of the unit has to be accurately controlled.
This application i~ therefor~ most suitable for acoustic implementation (SeQ for exampl~ Figures 12 and 13).
Signals reflected from thQ door jam 13 may be used to calibrate the overall time ~lot rangs 17 to allow for automatic site setting to different door widths and to provide immunity to atmospheric and environmental changes.
Further, the signal reflected ~rom the door jam 13 may be used to provide its own tim~ 810t blank 14 thus avoiding detection of the face of the door jam 13. Further time 810t blanks may be insert~d as requested. A similar sensor pair 15 may exi t on the other side B of the door 12. This arrangement giva~ detection on both sides of the door in detection area~ lOA and lOB to allow the door to be controlled appropriately.
Figure 8 show~ the plan view o~ a sensor unit arrangement 21-27 mounted along the face of a swing door 12. The X axes o~ the units 21 and 22 face at an angle to the door away rrO~ ths pivo~ point 16, and the X axes of the unit8 23 and 24 face at an angle to the door towards the pivot point 16. The det~ction profile in the Y and Z
axes has to be increased to give ~he same range in the area A as before ~Pigure 7). More care is needed with the detection profiles o~ units 23 and 24 to prevent 1~0317~

reflection from the wall 35 as the door ~wings about the point 16 towards the wall 35. Th~ X axis of the detector 26 faces away from the door 12 along a tangent to the arc of the door. Th~ unit 27 may face in the same direction as the unit 26 with its detection profile greater than that of the unit 26 but within that of the unit 24. The signal from the uni~ 26 serve~ to compensate for the diminished range of d~tection o* the unit 24 near the leading edge 12A of the door 12. The uni~ 27 disables the lo unit ~6 when the door 12 1~ close to the wall 35 to prevent detection thereof. ~ore or less units may be needed in the arrangement to provide the required detection profile. A similar sensor unit arrangement may exist on the other side B o~ the door 12 to give detection on both sides of the door.
The principle related are extendable to transmitters and receivers which are situated not next to each other but on dir~erent moving or statlonary surfaces.
As long as the transmitter 8ignals have no direct line of sight to the receiver and the trans~itter signals cannot bounce off fixed or moving ob~ects which are not to be detected, e.g. doors, wall or roof, into the receiver to produce sufficient ~ignal to swamp signals bounced off ob~ects to be detected, then the transmitters and receivers and barriers can bQ positioned anywhere.
Figure g shows but a few possible arrangements. In one of them the tran~mitter 1 i5 mounted remotely from the receiver 2. The barriers 3A and 3B at the receiver 2 define a conical detection profile while the barriers 3C
and 3D at the transmitter 1 define a conical transmission profile. The inter~ection of these two conical profiles defines a d~tection spac~ 10 within which detection of reflective ob;ects will occur. As is apparent from Fig.
9, there i8 no dirsct line of sight between the transmitter 1 and receiver 2. ~t will be understood that by suitable screening or focusing the transmitt~d and detected energy can acquire any desired profile and 1303~77 thereby the shape of the detection space or volume produced by their intersQc~lon can be defined at will. It will ~e further und~rstood that the stlle or walls 35A and 35B can be used for said screening. Ob;ect 9, anywhere within the detection space 10 w~ll cause reflection of the signals from the transmitter 1 into the receiver 2. As the door 12 opens in the direction S into the detection space 10 it will it~elf cause a moving shutter effect by virtue of its impermeability to the energy used, leaving a desirable (albei~ r~ducad) detection spacs or volume extending at all times from the region of the leading edge 12A of the door 12. In prior art designs this has been the most desirable yet most difficult area in which to provide detection.
Any other transmittcr-receiver-~arrier combinations may be arrang~d u~ing thi~ deslgn to cover any space, e.g.
transmitter 4 in combination with r~ceiver 6 to cover a space nearer the closed door, and/or transmitter 1 with receiver 7 covering th~ whol~ region between the door 12 and wall or stile 35A, and/or transmitter 8 with receiver 11 to cover the region of the leading edge 12A on the other side o~ the door wh~n the door is open.
Figures 10A, 10B and 10C show a method of shuttering an in~rared sensor unit (transmitter 1 and receiver 2) on the leading edge of the 81~ ding door 12 o~ an elevator car to give the desired detection profile (space) in the Y and Z axes. The shuttering i8 achieved by the barriers 3, 4 and 6. The barrier 6 is a channel which restricts the 2 axis profile, the barrier 4 restricts the Y axis profile to prevent forward vision in the direction S, and the barrier 3 restricts the direct coupling of signals between the transmitter 1 and the receiver 2. The shuttering unirormly modifie~ the det~ction profile of the units so that tolerances (the variation between optical and mechanical axis Or the units which gives the inherent profile of individual transmitters and the receivers within the units) are no longer critical.

The sensor unit is tilted away ~rom the leading edge o~ the door 12 by an angle P to give the direction deslred for the X axis (see Fig. 4). The sensor unit may al~o be tilted at an angle Q to give the desired direction o~ the X axis away from the lift car towards the landing.
If the wall being approached has a diffused or textured surface, it may be desirable to colour it with a matt-black finish to prevent nuisance detection. The inside o~ the channel 6 i 8 preferably matt-black to prevent internal reflectlons corrupting the desired profile. This is alse de~irable for a pair o~ centre-opening doors in which the detector~, mounted on the leading edges of both doors, co~e face to face.
The outside lip 7 of the channel 6 i~ angled and made reflective. Thus, when the door is very close to the surface being approached, reflections will bounce back and forth between the lip8 7 and that surface, thereby increasing the density of transmis~ion and therefore the sen~itivlty to æ~all ob~ects (~.q. finger6) i8 further increased.
Figure 11 shows a circuit which may be used with infrared detectors shown in Figure 6. Known circuit techniques can be used to implement it. Each of the sensor units 21 to ~7 i8 conne¢t~d to its own non-linear amplifier 8 to 13 through a respective rectifier and smoothing filter 48 to 53. outputs of amplifiers 8 to ll are connected to a ~umming amplifier 14, the output of which ig connected to ons input of each of four comparators 16 to 19. ~h~ other input of each comparator 16-19 is conneated to one output of the respective one of the amplifiers 8 to 11. ~ha outputs of the amplifiers 12 and 13 are conne¢ted to two separate inputs of the comparator 20. The output of all the comparator~ 16 to 20 are connected to th~ input~ of ~h~ logical ''ORIl gate 41.
The output signal 42 from thQ gate 41 i~ the detection signal indicativQ of ths presQncQ of a detected object.
In the sensor uni~ 21, 22, 23, 24, 26 and 27 the six infrared transmitter~ may be time-division multiplexed or modulated at the di~erent ~requencies 80 that the six rQceivers havQ means to distinguish their respective transmitter signals. Each receiver signal may be amplified using its own non-linear amplifier 8 to 13 with roll off in gain with increasing signal. This technique increases the dynamic rangQ of the circuit and will prevent saturation of the amplifier when strong signals are being received but maintains the sensitivity to detected objects substantially constant.
The output signal of the summing amplifier 14 represents the average level of the four input signals from the amplifiers 8 to 11. ~hi~ average signal is used as the reference level for one input to each of the comparator~ 16 to 19. The other inputs to the comparators are derived from the output ~ignals from the amplifiers 8 to 11. The respective comparators givs an output if their received ~ignal goe~ above or below a threshold band established from and contred on the reference level from amplifier 14. The comparator outputs are processed in the OR gate 41 to give a detection output signal 42. Figure 12 ~hows the comparator 16 in more detail.
The comparator 16 comprises a pair of zener diodes 60 and 61 connected in serie~ with respective resistors 62 and 63 to de~ine the desired threshold band. A pair of comparator units 64 and 65 each have one input connected to receive a æignal from amplirier 8. The other input of the comparator unit 64 i8 connected to the junction between the resistor 62 and thQ zener diode 60 and the other input o~ the comparator unit 65 is connected to the ~unction between the zener diode 61 and the resistor 63.
The output of the summing ampli~ier 14 is connected to the ~unction between the two zener diodes 60 and 61. The outputs of the comparative units 65 and 64 are connected in common to a respective input of the OR gate 41.
If a small rerlecting ob~ect increases the signal received by the receiver Or the un~t 21 by a specified ~303177 amount above that received by the remaining receivers, it wlll be detected as a signal from ampli~ier 8 above the upper limit o~ the threshold band and the comparator 16 will give an output. Conversely, i~ a large reflecting ob~ect increases th~ signal by a speci~ied amount to receivers of the un~t~ 22, 23 and 24, the comparator 16 will still give an output 81 gnal as the signal ~rom the amplirier 8 is now below the lower limit of the threshold band established from the now the increased average signal from the amplifier 14. In other words, any contrasting surfaces are detected.
In practice the wall b~ing approached may not be a perfect re~lector and will cause small signals to be received on receivers o~ the units 21 to 24 when the door i8 very close. The circuit Or Figure 11 however will not give an output 42 as all signal~ from the ampli~iers 8 to 11 lncrease equally and therefore the signal output from amplifier 14 correspondingly increases.
The average signal rrO~ the ampllfier 14 may be used manually or automatically to reset the outputs of amplifiers 8 to 11 to eguality at will and during initial setting. This average signal from the amplifier 14 may also be used during operation to adjust the outputs from the amplifiers 8 to 11 i~ there i8 a large, or rapidly increasing error signal or a continuous comparator signal output from the comparators 16 to 19.
Detector units 26 and 27 form the floor circuit (Figure 6).
Unit 26 i8 at th~ floor and unit 27 in the main detection area. The galn from th~ amplifier 12 receiving signals fro~ th~ unit 26 is 1GS8 than the gain from the amplifier 13 rec~iving ignal~ from the unit 27. If the ~ignal from amplifier 12 ~xc0eds tha signal from the amplifier 13, then ths comparator 20 gives a detection signal. This ~ 8 fQd to the OR gate 41 to give an output signal 42.
In an arrangement using acoustic sensors, in order J

to avoid the sensors detecting fixed ob~ects such as the floor or a door knob, th~ blanking circuit shown in Figure 15 can be used. As shown in tha puls2 diagram o~ Figure 16 and under steady stat~ conditions, the transmitter 1 transmits a pulse signal A wh~ch is then reflected by the door knob a~d the floor to provide pulses Bl and B3 in the received signal B. Ths6Q signals if sustained will be mamorised by a reference unit 98, which will then generate blanking pulses Cl and C3 in ~ynchronism therewith. The outputs of the referenc~ unit 98 and the receiver 2 are fed to respactive inputs o~ an AND gate 99. In operation tha pulses B1 and B3 rec~ived by ths receiver will coincidQ wlth th~ blanking pu1~03 Cl and C3 and 80 no output D will occur from th~ AND gate 99.
When an ob~ect to be dQtQcted i8 sensed by the receiver 2, a pulse B2 will b3 generated. Because this is a transient pul~e, it will n~t have b~sn stored in the memory of the reference circuit 98. As a consequence no corresponding blanking pul8e will have been generated and so an output D2 will appear at the output of the A~ID gate 99 .
In this way stat~onary ob~ects re~lecting energy to the receiver will generally be automatically ignored and only transient objects will b~ detected.
With unmodulated infrared units it is preferable to synchronise transmission to tha mains supply ~requency to eliminate potential problems with modulated lighting (e.g. fluorescent or incande~cent lights) and periodic mains switching (.e.g. rrOm triac controllers nearby).
The synchronisation ~hould ~e per~ormed outside ~he zero voltage crossing point, a~ triaca e~c., o~ten switch close to zero voltage. If this feature is required, the synchronisation ~ignal deriYed ~rom the mains supply naeds to be made available at the unit on the moving door.
Further a two wire power path and a single wire return detection signal path are required rOr the unit. Other Xnown types of sensor units (e.g. capacitive) may also require di~erent control slgnal~ at the sensor units.
Prior art systems send these signals 6eparately via a multicore cable which is susceptible to fatigue and breakage. It is preferable to use a minimum of conductors in the flexible cable leading to the moving door to all~viate this problem and to reduce the speci~ication and cost. A two-wire system may be used according to the invention to supply the unit.
The synchronisatlon oircuit ~or transmitting power and data is shown more clearly in Figure 13. As shown an AC supply unit 71 supplies AC power to an AC to DC
converter 72 to provide a DC source. A resistor 73 and the emitter/collector path of a transistor 74 are connected in series across the output o~ the converter 82.
First and second conductors in the form of flexible wires or cables 75A and 75B connec~ the emitter/collector path of transistor 74 in parallel ~ith the emitter/collector path for a tran istor 76 (mounted on the movable door) and also feed the sensor unit 79 with power through a rectifier and filter provided by a diode 77 and a capacitor 78.
A ~odulator formed by a pulse generator 69 connected to the AC supply 71 supplies pulse3 synchronous with the mains frequency to the base of ths transistor 74.
The output from the sensor unit 79 feeds the base of the transistor 76 and also one input of an exclusive OR
gate 80. The other input of the exclusive OR gate 80 is connected to the wir~ 75A.
The wire 75A i~ al80 connacted to one input of another exclusive OR gate 70 forming an inhibiting means.
The outer input of tho gate 70 i8 connected to the output of the pulse genera~or 69. ~he output of the exclusive OR
gate 70 ~B connected to a remote data terminal device 76, for example, for a door controller, and/or to provide further synchronisat$on s~gnals and control signals e.g.
$or further units.
In operation the pul~e~ generated by tho pulse ~303~77 genQratOr 69 modulate the power supply fed via line~ 75A
and 75B to the sensor 79 mounted on the movable door.
Sensor 79 iB a data signal generatin~ means and generates data signals of the monitored condition. It al~o acts as a sQcond modulator to modulate the signal on the lines 75A
and 75B. The exclusiv~ OR gate 80 acts as a second inhibiting means to thG sen60r 79 in6ensitive to the modulation which th~ ssnsor 7g itself produces on the lines 75A and 75B. The Qxclusive OR gate 70 inhibits the passage of pulses generated by the pulse generator 69 to thQ remote device 76.
In this way only a two wir~ link i8 reguired between a first and second station ~the door and the door frame) thus reducing the problems of ~atigue.
In addition to the unit~ shown in Figure 6 at least one further unit may be provided on the edge 5 such that there is a direct sight between thi~ unit and one of the units o the door. In this way a 'curtain' deteotion beam extending acros~ th~ door opening oan be produced, which, when broken, can be arranged to give a detection signal.
Further the 'curtain' signal may be used to desensitise unit~ as necessary under adverse operat$ng conditions by suitable ~odi~ication o~ tha arrangement of the units relative to each other.
It will be understood that several sensor units can be combined into an assembly which will then be used as described in connection with a single unit.
Figure 14 shows a mul~i-element single sensor unit.
As shown four sensors 90 to 93 are positioned on the leading edge 12A o~ a door so that the proriles overlap ~o such an extent that the combined prorile 97 has an extremity which extends generally parallel to the edge 12A. In this way any variation in range of the individual profiles provided by the individual sensors will only have a reduced e~fect on the width of the combined profile.
The transmitters of ~our sensors 90 to 93 are fed by common line 94 and the receivers are connected to ~8 respectivQ inputs of a ~umming amplifier 95.
It will be appr~ciatQd that this multi-element sensor unit can replace th~ slngle sensors Or any Or the embodiments hereinbe~ore described.
With the embodiments described it will be readily apparent that the manner in which the sensors can be ad~usted to cover any shape Or detection space renders the system extremely flexible.
Also while the b~ams p~oduced by individual sensors are normally divergent to provide volumetric sensitivity they can instead be made convergent to provide point sensitivity.
The shape of the transmission and reception profiles of each sensor can be controlled in many different ways for example by collimated or divergent lenses, by reflectors (~.g. parabolic) or by electromagnetic means.
~urthermore instead of beams of energy each sensor may transmit or rece~ve beams o~ other media for example air ~ets.
In a modification the barrier 3 between the transmitter 1 and rece~Yer 2 can be omitted where a directional property i8 inherent in their construction or the control circuits are able to ignore a direct as opposed to a reflected signal.
Experiments with a detQctor according to the invention wera made in ~hich ob~ects w~re successfully detected up to a distance o~ 3 ~tres from the censor units.

Claims

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. A two conductor transmission system for transmitting power and data between two stations, the system comprising a first station linked to a second station by only first and second conductors, the first station including a DC
source for supplying the first and second conductor with DC power, a synchronization pulse generator, a first modulator for modulating the DC power fed to the conductors with the synchronisation pulses, a data terminal connected to said first conductor for receiving data transmitted from the second station, and first inhibiting means responsive to the synchronisation pulses to inhibit the passage of data to the data terminal during the transmission of synchronisation pulses, the second station comprising data signal generating means connected to the first and second conductors to receive DC power and synchronisation signals therefrom, the data signal generating means being arranged to generate data signals indicative of a monitored condition, a second modulator for modulating the DC power flowing along the first conductor in response to the generated data signals, and second inhibiting means responsive to the data signals generated to render the data signal generating means insensitive to the data signals appearing on the first conductor.

2. A system according to Claim 1 wherein each said inhibiting means comprises an EXCLUSIVE OR gate.

3. A system according to Claim 1 or to Claim 2 wherein each said modulating means comprises a transistor having its emitter collector path connected across said first and second conductors and its base connected to receive synchronisation or data signals.