Proximity detector

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). Different transmitter/receiver pairs may transmit on different frequencies, and means for suppressing unwanted reflected signals is provided. Means for transmitting data signals on a two conductor power supply cable for the system is also disclosed.

Description: The invention relates to a proximity detector for the detection of the presence and position of objects and people or parts thereof in the path of moving mechanical devices, such as automatic sliding doors, automatic swing doors or moving vehicles of robots, to, for example, enable corrective safety action to be taken. It is common practice in the construction of automatic doorways to include means of ensuring that the doors cannot close on a person causing discomfort or injury. A number of contactless systems are known for detecting the presence of a person in a doorway, particularly the presence of a person in the space which the door is approaching. British Patent Specifications 711515, 856985, and 1108884, are but a few which describe systems of this nature. All of them involve positioning a proximity detector on the door establishing conditions whereby a person can be identified in the space or volume which the door is approaching but being able to ignore walls and other fixed objects by balance bridge techniques or by reducing the sensitivity when the door is 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 firing 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 conditions, then 'nulls' often occur where detection is not possible. US Patent Specification No. 3 719 938 discloses an intruder detection device in which a transmitter transmits energy into an area to be monitored and a receiver receives reflections of the transmitter energy reflected by an intruder in the monitored area. The received signal is processed to eliminate both slow and fast transients so as to limit its detection essentially to the presence of intruders and so avoid detecting stationary objects and rapid interference such as lightening. US Patent specification No. 3,992,102 describes a smoke detector in which a light transmitter is shielded from a light detector by a shield. Only the presence of smoke will deflect light from the transmitter towards the detector. European Patent application No. 0 097 139 A2 describes a detection system for detecting obstructions in doorways. The system comprises an elongate box like unit having a longitudinal slit therein. A transmitter is located at one end of the box and a receiver is located at the other end. Light from the transmitter after multiple internal reflections is emitted from the slit. If an obstruction is present it is reflected by the obstruction back through the slit, undergoes multiple reflections and eventually is received by the receiver. European Patent application No. 0 144 882 A2 describes a swing door carrying a bank of transmitters and receivers in side by side locations. The control system is responsive to the position of the door to selectively switch the transmitter and receivers in and out of circuit as the door opens and closes. The sequence of switching is such that each transmitter/receiver is switched out of circuit whenever a door frame or other structure is likely to be detected by the transmitter/receiver. It will thus be seen that in the latter patent, a detector is mounted on the door surface to monitor the gap between the door and the surface on which it closes to detect obstructions. Because some radiation is directed to impinge at right angles on the surface on which the door closes the detectors will detect that surface. The specification goes to considerable lengths to avoid detecting the surface, in particular by providing a complex circuitary which monitors the spacial position of the door and in response thereto cuts out certain transmitters/receivers thereby inhibiting the detection of such reflections. The present invention recognizes this problem and overcomes it in a very simple but effective manner. The transmitter is directed at the surface on which the door closes at an angle other than right angles ie at an acute angle. This ensures that any reflected signal from the surface does not return to the transmitter (or the receiver located at its side) and so no provisions have to be made for inhibiting such signals. 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 as 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 edge or side of the door, this detection range must be adequate to prevent a person (hand, foot, etc.) being touched by the door, i.e. to be greater than the stopping distance of the door. 2) For a person approaching a door, detection is necessary to establish the presence of the person to delay the door closure. 3) With building sliding doors it is necessary to establish detection of a person approaching a door to 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 stop 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 of the door opening to allow timely response. The invention uses as its basis an apparatus for controlling the range and angular vision of a detection unit which is mounted on or near a moving object (e.g. door) for the purpose of providing information as to the position of 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 present invention there is provided a movable door having a leading edge mounted for movement towards an object having a reflective planar surface towards which the door closes, the planar surface extending generally parallel to the leading edge, the movable door incorporating a proximity detection system arranged to sense obstructions in the gap between the leading edge and the planar surface, the system comprising a transmitter and a receiver mounted adjacent said leading edge, the transmitter being orientated to direct energy across the gap to impinge upon said planar surface at an acute angle, characterised by a barrier mounted between the transmitter and the receiver to prevent energy transmitted by the transmitter from being directly received by the receiver, in that the transmitter and receiver are mounted side by side and in that the receiver is orientated to receive energy transmitted from the transmitter when reflected by obstructions in the gap but not energy reflected by the planar surface. The invention will now be described, by way of example, with reference to the accompanying diagrammatic drawings, in which: Figure 1 shows a sensor or detector unit and an object with a smooth planar surface; Figure 2 shows a sensor 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 of the door; Figure 5 shows a sliding door with a detection unit on the bottom of the door; Figure 6 shows a sliding door with six detection units; Figure 7 shows a plan of a swing door with two detection units; Figure 8 shows a plan of a swing door with twelve detection units; Figure 9 is a diagram of a multisensor unit; Figure 10A shows a section through a detection unit along line W-W in Figure 10B; Figure 10B 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 10C shows a plan to Figure 10B; Figure 11 is a circuit diagram of a blanking circuit; and Figure 12 is a pulse diagram for the circuit of Figure 11. Referring to Figure 1, a transmitter 1 is sending out energy in the direction 4. Receiver 2 is sensitive to this energy in the direction 7 and will give 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 energy between 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 object 5 has a reflective surface. It is assumed that the energy signal in direction 4 obeys laws similar to the laws governing the reflection of light and so bounces in direction 6 away from the receiver 2. Similarly in Figure 2 there will be a return energy signal from the object 9 in the direction 7 towards the receiver 2 if the point of reflection lies on a tangent 8 with equal angles of incidence and reflection. Using these principles, a system may be constructed to differentiate between smooth and textured surfaces. In the case of a textured surface which is made up of a multitude of curved surfaces some will be in such an orientation as to cause reflection of energy in the direction 7 towards the receiver 2. Referring to Figure 3 the said transmitters or receivers may be transducers of acoustic or electromagnetic energy (for example in the infrared region of the spectrum). These transducers can be manufactured in such a way that they exhibit maximum radiant intensity (transmitters) or maximum sensitivity (receivers) in the direction of the X axis. The intensity or sensitivity of the transducers will fall off in proportion to the angle of their deviation from the X axis. It follows therefore that these transducers may be considered to radiate (transmitters) or receive (receivers) energy in the form of a conical profile 10. A textured object 11 will cause reflection of many signals in the direction 4 from the transmitter 1 into the receiver 2 (signals in the direction 7). The size of the receiver signals will be proportional to: (1) Surface area of the object 11 within the conical detection area 10. (2) Reflective constant of the surface of the object 11 (texture, colour, reflectivity, etc.). (3) The total distance travelled 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 preset threshold level is exceeded. The threshold may be such that the object 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 the objects to be detected and objects to be ignored, it is possible to control the space or volume in which detection occurs. Referring to Figure 4, a sensor unit 1-3 is mounted at the top of an automatic sliding door 12. The door 12 slides in the direction S. The barrier 3 is between the transmitter 1 and the receiver 2 and restricts the direct signal path. The axis X is tilted away from the vertical so as to produce a detection profile 10 which extends from the door edge 12A into the opening. It is preferable that no signal may be emitted from the transmitter 1 in such a direction as to cause reflection from the edge 5 back towards the receiver 2. The edge 5 is assumed to be a relatively smooth surface and as such will not return any significant signal to the receiver 2 from the transmitter 1. The object 9, situated within the detection profile 10, possesses textured surfaces and offer points some of which reflect signals from the transmitter 1 to the receiver 2 (Figure 2). As the door 12 moves in the direction S and gets very close to the edge 5, the signals transmitted from the transmitter 1 are reflected back and forth between the leading edge 12A of the door 12 and the edge 5 thereby increasing the density of the transmitted and returned signals. This has the advantage of increasing sensitivity to small objects (e.g. fingers) 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 detected and yet allow for detection of objects on the floor (e.g. feet). This application is therefore most suitable for acoustic transmitters/receivers using the relatively slow speed of 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 objects, 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 otherwise the same 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 5B is higher than the detection height of the object 9. However, the detection range in the direction S rapidly diminishes towards the floor 5A. For more critical applications an arrangement of sensors may be used. Figure 6 shows a possible arrangement of four sensor units 21-24 mounted along the door edge 12A of which units 21 and 22 face downwards and units 23 and 24 face upwards. Each sensor unit comprises a transmitter, a barrier and a receiver as in the previous examples. The angle of detection in the Y and Z axes (Figure 3) has to be increased to give the same range from the door edge 12A in the direction S as in Figure 5. However, 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 is 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 level will detect objects at the floor level. The sensor unit 27 may have a profile along its X axis greater than the sensor unit 26 but within the profile of the sensor unit 24, and is used solely to disable the sensor unit 26 when the door is close to the edge 5 to prevent detection of the edge. Figure 7 shows the plan view of a sensor unit 1-3 mounted on the side A of 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 from the door 12 so as to produce a detection profile 10A 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 relatively smooth surface and will not reflect a signal from the transmitter 1 to the receiver 2 when the door is open. As the door 12 comes to close proximity with the wall 35, the signals transmitted from the transmitter 1 are reflected back and forth between the door 12 and the wall 35 giving an increased density of transmission and increased detection sensitivity to small objects. As with single sensor unit arrangements on sliding doors (Figure 4) the range along the axis X of the unit has to be accurately controlled. This application is therefore most suitable for acoustic implementation (see for example Figures 12 and 13). Signals reflected from the door jam 13 may be used to calibrate the overall time slot range 17 to allow for automatic site setting to different door widths and to provide immunity to atmospheric and environmental changes. Further, the signal reflected from the door jam 13 may be used to provide its own time slot blank 14 thus avoiding detection of the face of the door jam 13. Further time slot blanks may be inserted as requested. A similar sensor pair 15 may exist on the other side B of the door 12. This arrangement gives detection on both sides of the door in detection areas 10A and 10B to allow the door to be controlled appropriately. Figure 8 shows the plan view of a sensor unit arrangement 21-27 mounted along the face of a swing door 12. The X axes of the units 21 and 22 face at an angle to the door away from the pivot point 16, and the X axes of the units 23 and 24 face at an angle to the door towards the pivot point 16. The detection profile in the Y and Z axes has to be increased to give the same range in the area A as before (Figure 7). More care is needed with the detection profiles of units 23 and 24 to prevent reflection from the wall 35 as the door swings about the point 16 towards the wall 35. The X axis of the detector 26 faces away from the door 12 along a tangent to the arc of the door. The 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 unit 26 serves to compensate for the diminished range of detection of the unit 24 near the leading edge 12A of the door 12. The unit 27 disables the unit 26 when the door 12 is close to the wall 35 to prevent detection thereof. More 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 of the door 12 to give detection on both sides of the door. The principles related are extendable to transmitters and receivers which are situated not next to each other but on different moving or stationary surfaces. As long as the transmitter signals have no direct line of sight to the receiver and the transmitter signals cannot bounce off fixed or moving objects which are not to be detected, e.g. doors, wall or roof, into the receiver to produce sufficient signal to swamp signals bounced off objects to be detected, then the transmitters and receivers and barriers can be positioned anywhere. Figures 10A, 10B and 10C show a method of shuttering an infrared sensor unit (transmitter 1 and receiver 2) on the leading edge of the sliding door 12 of an elevator car to give the desired detection profile (space) in the Y and Z axes. The shuttering is achieved by the barriers 3, 4 and 6. The barrier 6 is a channel which restricts the Z 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 uniformly modifies the detection profile of the units so that tolerances (the variation between optical and mechanical axes of 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 from the leading edge of the door 12 by an angle P to give the direction desired for the X axis (see Fig. 4). The sensor unit may also be tilted at an angle Q to give the desired direction of 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 of the channel 6 is preferably matt-black to prevent internal reflections corrupting the desired profile. This is also desirable for a pair of centre-opening doors in which the detectors, mounted on the leading edges of both doors, come face to face. The outside lip 7 of the channel 6 is angled and made reflective. Thus, when the door is very close to the surface being approached, reflections will bounce back and forth between the lips 7 and that surface, thereby increasing the density of transmission and therefore the sensitivity to small objects (e.g. fingers) is further increased. In an arrangement using acoustic sensors, in order to avoid the sensors detecting fixed objects such as the floor or a door knob, the blanking circuit shown in Figure 11 can be used. As shown in the pulse diagram of Figure 12 and under steady state conditions, the transmitter 1 transmits a pulse signal A which is then reflected by the door knob and the floor to provide pulses B₁ and B₃ in the received signal B. These signals if sustained will be memorised by a reference unit 98, which will then generate blanking pulses C₁ and C₃ in synchronism therewith. The outputs of the reference unit 98 and the receiver 2 are fed to respective inputs of an AND gate 99. In operation the pulses B₁ and B₃ received by the receiver will coincide with the blanking pulses C₁ and C₃ and so no output D will occur from the AND gate 99. When an object to be detected is sensed by the receiver 2, a pulse B₂ will be generated. Because this is a transient pulse, it will not have been stored in the memory of the reference circuit 98. As a consequence no corresponding blanking pulse will have been generated and so an output D₂ will appear at the output of the AND gate 99. In this way stationary objects reflecting energy to the receiver will generally be automatically ignored and only transient objects will be detected. In addition to the units shown in Figure 6 at least one further unit may be provided on the edge 5 such that there is a direct sight between this unit and one of the units on the door. In this way a 'curtain' detection beam extending across the door opening can be produced, which, when broken, can be arranged to give a detection signal. Further the 'curtain' signal may be used to desensitise units as necessary under adverse operating conditions by suitable modification of the arrangement of the units relative to each other. It will be understood tht several sensor units can be combined into an assembly which will then be used as described in connection with a single unit. Figure 9 shows a multi-element single sensor unit. As shown four sensors 90 to 93 are positioned on the leading edge 12A of a door so that the profiles overlap to such an extent that the combined profile 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 effect on the width of the combined profile. The transmitters of four sensors 90 to 93 are fed by common line 94 and the receivers are connected to respective inputs of a summing amplifier 95. It will be appreciated that this multi-element sensor unit can replace the single sensors of any of the embodiments hereinbefore described. With the embodiments described it will be readily apparent that the manner in which the sensors can be adjusted to cover any shape of detection space renders the system extremely flexible. Also while the beams produced 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 (e.g. parabolic) or by electromagnetic means. Experiments with a detector according to the invention were made in which objects were successfully detected up to a distance of 3 metres from the sensor units.

Claims: A movable door (12) having a leading edge (12A) mounted for movement towards an object (5) having a reflective planar surface (13) towards which the door closes, the planar surface extending generally parallel to the leading edge (12A), the movable door (12) incorporating a proximity detection system arranged to sense obstructions in the gap between the leading edge and the planar surface, the system comprising a transmitter (1) and a receiver (2) mounted adjacent said leading edge (12A), the transmitter being orientated to direct energy across the gap to impinge upon said planar surface at an acute angle, characterised by a barrier (3) mounted between the transmitter (1) and the receiver (2) to prevent energy transmitted by the transmitter (1) from being directly received by the receiver (2), in that the transmitter (1) and receiver (2) are mounted side by side and in that the receiver (2) is orientated to receive energy transmitted from the transmitter (1) when reflected by obstructions in the gap but not energy reflected by the planar surface (13). A movable door according to Claim 1 characterised in that said door is a sliding door for slidingly closing said gap, wherein said proximity detection system is located on the leading edge of the door (12) and further characterised in that said transmitter (1) and receiver (2) make such an acute angle with the leading edge (12A) of the door (12) that transmitted and received signals can be reflected backwards and forwards along the gap between the leading edge of the door (12A) and the planar surface (13). A movable door according to Claim 1 characterised in that said door is a hinged door mounted in an opening in the object (5) and is pivotable outwardly from opposite sides of the opening, wherein said proximity detection system is located adjacent least one side of the door at a position adjacent the pivotal axis of the door and is directed away from the pivotal axis of the door so that transmitted energy is directed into an area immediately adjacent the side of the door on which the detection system is mounted. A movable door according to Claim 2 wherein the power of the transmitter (1) is less than a predetermined magnitude so that any energy reflected by the surfaces of the object (5) adjacent said planar surface is not registered by the receiver (2). A movable door according to any one of Claims 2 to 4 characterised by inhibiting means (99) synchronised with the transmitter (1) for inhibiting the output of the receiver (2) during selected time slots related to the propagation speed of the energy and the distances at which stationary objects are located from the transmitter so as to exclude reflected signals from selected stationary objects. A movable door according to Claim 5 characterised in that inhibiting means (99) includes averaging means for averaging the output of the receiver over a plurality of periods and using the resulting average output to provide blanking pulses for inhibiting the output of the receiver over corresponding intervals during each said period.

Inventors: BRADBEER PETER FREDERICK, TRETT JOHN, BRADBEER, PETER FREDERICK, TRETT, JOHN
Applicants: FORMULA SYSTEMS LTD, FORMULA SYSTEMS LIMITED
Application year: 1986
Main classification: G01S15
IPC codes: B66B13, G01S17, G01S15, E05F15, H04B3