GB2442521A

GB2442521A - Doorway obstacle detector using light pipe

Info

Publication number: GB2442521A
Application number: GB0619419A
Authority: GB
Inventors: Terence Christopher Platt
Original assignee: Memco Ltd
Current assignee: Memco Ltd
Priority date: 2006-10-02
Filing date: 2006-10-02
Publication date: 2008-04-09
Also published as: GB0619419D0

Abstract

A light pipe 24 is configured as part of an obstruction detector for a doorway. The pipe is positioned along one edge of the doorway, and is in the path of radiation emitted from one or more transmitters 20. The pipe is a transparent solid plastic rod, and may, be formed of polymethyl methylacrylate. The pipe has a convex cross-section, with the front surface forming a lens adapted to focus incident radiation towards the back surface. Extending at spaced locations on the back surface of the light pipe is a series of rectangular radiation-reflecting members 26, 28, 30 that block the exit of the radiation and cause it to be reflected within the light pipe. One end of the light pipe is a radiation reflector 34, and the other end is tapered and culminates in a receiver photodiode 38.

Description

DOORWAY OBSTRUCTION DETECTOR USING LIGHT PIPE

The subject invention relates to an apparatus for detecting an obstruction at a doorway, more particularly, to an obstruction detector that includes a light pipe for receiving radiation from transmitters on an opposite side of the doorway.

Various types of obstruction detectors for doorways, particularly elevator doorways, are known. One common type uses an array of transmitters spaced along one side of a door opening, or a door in the opening, to transmit respective radiation beams to an array of receivers spaced along the other side of the door opening. Each receiver is electri-cally connected to equipment that measures the strength of received signals, and an obstacle in the door opening is detected when the signal strength measured by one of more of the receivers drops below a prescribed value. Each trans-mitter normally includes a diode emitting infrared radiation, and each receiver normally includes an infrared photodiode.

A typical pattern of radiation beams that extend across a door opening from seven transmitters to seven receivers is illustrated in Figure 1.

The cost of such systems is dependent upon the number of transmitters and receivers utilized. Reducing the number of transmitters is normally a limited option, since effective coverage of a door opening requires that the spacing between adjacent transmitters, which are normally infrared emitter diodes acting as point sources of light, be kept below a defined value. The difficulty with reducing the number of receivers is similar in that delineation of an obstacle improves with the number of receivers. An increase in the number of transmitters and/or receivers not only involves the cost of the infrared emitter diodes and/or photodiodes, but also the sophisticati9n of connected equipment. There is the further difficulty that a transmission system that has a large spacing between adjacent transmitters and/or adjacent receivers, such as the system shown in Figure 1, does not work effectively when the spacing between the transmitters and receivers is less than 400mm, which occurs for instance when the doors of an elevator are closing or the door of a single-door elevator is moving toward the slam post. Below 400imii, such receivers do not see a sufficient amount of radi-ation from the transmitters. Such cases may require that the transmitters and/or receivers be set back from the door edge.

The subject invention utilizes a light pipe to detect radiation. In one aspect, the subject invention provides an obstruction detector for a doorway, the detector including at least one elongate light pipe configured to receive radiation incident on the detector from one or more transmitters dis-posed to direct radiation across the doorway, the light pipe being configured to conduct the incident radiation longi-tudinally thereof to a sensor at an end of the light pipe.

Preferably, the light pipe is configured to receive the incident radiation into a side surface thereof. More pre-ferably, the light pipe comprises means for reflecting or otherwise re-directing the incident light lonitudirially of the light pipe.

Preferably, the light pipe is configured to receive the incident radiation at a plurality of spaced-apart locations along its length.

Preferably, the re-directing means is such as to reflect the incident radiation in many directions, i.e. to diffuse it.

Preferably, the re-directing means is arranged to re-direct an increasing fraction of the incident radiation, the fraction increasing with the distance between the sensor arid the respective location at which the radiation is incident on the side surface of the light pipe.

Preferably, the re-directing means includes a plurality of discrete radiation reflectors spaced apart along the length of the light pipe. More preferably, a reflector further from the sensor has a larger effective reflecting area than one closer to the sensor. Even more preferably, each of the reflectors is a reflective coating disposed on the surface of the light pipe opposite to where the radiation is incident thereon, or each of the reflectors includes one or more grooves in the surface of the light pipe.

Preferably, an end of the light pipe is arranged to reflect back, within the light pipe, incident radiation.

Preferably the light pipe tapers locally towards the sensor.

Preferably the light pipe has a convex cross-section so as to form a lens adapted to focus the incident radiation towards a surface thereof opposite that on which the radi-ation is incident. More preferably, the light pipe is of circular cross-section. And even more preferably, the re-directing means is localised in a region where the incident light is focussed.

Preferably the light pipe is of polymethyl methacrylate.

Preferably, the detector is configured to be disposed along or parallel to an edge of a doorway of a powered door, or to be disposed along or parallel to an edge of the powered door. More preferably, the powered door or doorway of the powered door forms part of an elevator system.

Preferably, the detector has a plurality of the light pipes, and more preferably, the light pipes are positioned in-line. Even more preferably, the light pipes are posi-tioned in pairs, each pair having their sensors positioned proximate each other.

In a further aspect, the subject invention provides an obstruction detection system for a doorway, the system including one of the detectors described above, and also including a plurality of radiation transmitters configured to be disposed along or parallel to an opposite edge of the doorway or a further door disposed therein.

Preferably, the system includes: means for energising said transmitters; means for receiving an output from the sensor(s) in response to reflected radiation received there-by; and, means for generating an alarm or control signal when an obstruction between the transmitters and the sensor(s) occludes the transmitted radiation. The transmitter energi-sing means may provide a scaled current to the transmitters, the transmitters transmitting to respective reflectors at increasing distance from the sensor(s) receiving respective higher energising current.

Preferably, each transmitter is adapted to emit a diverging beam of radiation that diverges for reception by more than one of the plurality of reflectors.

In a still further aspect, the subject invention pro-vides a method of detecting an obstruction in a doorway, the method including steps of directing radiation across the doorway to be incident on detecting locations distributed along, or parallel to, an edge of either the doorway or a door in the doorway, and conducting the incident radiation along at least one light pipe to a sensor.

Preferably, the sensor is at or adjacent a top or bottom edge of the doorway.

Preferably, said light pipe extends along or parallel to said door or doorway edge.

Preferably, the transmitted radiation is incident on a side surface of the at least one light pipe.

Preferably, the doorway and door of the obstruction detector, the obstruction detection system, and the method of obstruction detection are a doorway and a door of an elevator system.

Preferred features of the present invention will now be described, by way of example only, with reference to the accompanying drawings, in which:-Figure 1 illustrates a typical pattern of radiation beams that extend across a doorway having an array of trans-mitters on one side and an array of receivers on the other side; Figure 2 a schematic view of a doorway detection system having an array of transmitting emitter diodes on the right and a light pipe on the left; Figure 3 is a back view of the light-pipe receiver, the view looking toward the left side of the light pipe of Figure 2; Figure 4 is a side cross-sectional view of an embodiment of a light pipe in which a radiation-reflecting member is formed by three adjacent equiangular-shaped notches cut into the side of the light pipe; Figure 5 is a light pipe device formed by placing two light pipes end-to-end such that their sensors are adjacent; Figure 6 is a schematic plan view of the light pipe of Figure 2, the view illustrating the refraction of incident radiation by the light pipe, the radiation being refracted toward a focal line proximate the back surface of the pipe; and, Figure 7 is a schematic plan view of the light pipe, the view being similar to Figure 6 but additionally illustrating one of the radiation-reflecting members at the back of the light pipe and its effect in producing total internal ref lec-tion of the radiation refracted at the light pipe surface.

The array of emitter-diode transmitters 20 in Figure 2 are positioned on an edge portion 30 of an elevator door or one side of an elevator doorway from which the door extends.

The transmitters 20 transmit radiation beams 22 toward the light pipe, generally designated as 24 and extending on an edge portion (not shown) of a second elevator door or an opposite side of the elevator doorway. The light pipe 24 extends the whole height, or almost the whole height, of the elevator doorway.

The light pipe 24 is formed from a length of solid cylindrical plastic rod formed, for instance, from polymethyl methacrylate (known under the trade mark Perspex) or from polystyrene. The rod is configured in cross-section such that, as shown in Figure 4, the front surface through which radiation enters the light pipe focuses the radiation at a point proximate the back surface. Although ideally a light pipe could be specially constructed to have a cross-sectional profile such that the radiation-entry front surface is shaped to focus radiation on the back surface, it has been found that a light pipe with circular cross-section focuses mci-dent radiation sufficiently proximate the back surface to be usable. The described preferred embodiment therefore uti-lizes a cylindrical light pipe that is approximately 6mm in diameter. As shown in Figs. 2 and 3, along one longitudinal line on the surface of the plastic rod that forms the light pipe 24 is a series of rectangular radiation-reflecting members. In Figures 2 and 3, only three such members 26, 28 and 30 are shown; however, there exist approximately forty such members along the length of the two-metre-long light pipe 24 (extending the height of an elevator door). The centre of each member is spaced from the centre of each adjacent member by approximately 46mm (an industry standard spacing), and is opposite a respective one of forty trans-mitters. At one end of the light pipe 24 is a radiation-reflecting surface 34 and, at the other end, the light pipe 24 has an optical tapered end 36 to concentrate radiation toward a radiation detector 38, which in this embodiment is a photodjode. The angle of the optical tapered end 36 is suf-ficiently shallow that virtually all incident radiation on the internal surface is internally reflected.

The rectangular radiation-reflecting members exemplified by the three illustrated members 26, 28 and 30 vary in length with longitudinal position on the light pipe 24. As shown in Figures 2 and 3, the member with the shortest length (about 1mm) is the one closest to the optical tapered end 36, and the member with the longest length (about 5mm) is the one closest to the radiation-reflecting surface 34. As shown in Figure 3, all the members have a similar width (about 2mm) in the circumferential direction; this width has been shown to be sufficient to produce the desired effect, and making the members wider has no benefit. The amount of radiation that is diffused into the light pipe 24 increases in proportion to the length of the radiation-reflecting member. The increase in length compensates for the greater distance and internal reflection required for radiation entering the light pipe 24 further from the radiation detector 38 to reach the detector with an intensity equivalent to light entering the light pipe 24 closer to the radiation detector 38. In other words, it allows for all radiation to be treated the same by the detec-tor regardless of the longitudinal position of the entry of the radiation into the light pipe 24.

The radiation-reflecting members exemplified by the members 26, 28 and 30 are each formed by blocking exit of the radiation from the surface of light pipe 24 in some manner.

In this preferred embodiment, each of the members is formed by applying a paint spot to the light pipe 24. The paint spots act to reflect the radiation in many directions, e.g. acts to diffuse the radiation, and this has been found to be the most cost-effective way to produce radiation-reflecting members. However, it is also possible to produce members by forming each as a groove, or one or more parallel grooves, (typically, 0.5mm deep) in the surface of the light pipe in the circumferei-itia]. direction. Figure 4 is a side cross-sectional view of a light pipe having a radiation-reflecting member formed by three adjacent triangular grooves extending in the longitudinal direction of the light pipe, each groove having a width (into the page) of approximately 2mm. With such triangular-groove arrangement, the grooves can be shaped such that virtually all incident radiation is directed longi- tudinally in the light pipe. For reflecting incident radia-tion arriving normal to the light pipe surface, ideally each groove is configured such that its innermost angle is set at 90 , with the two angles formed at the light pipe surface being at 450* The number of adjacent triangles will depend upon the length of the radiation-reflecting member required.

However, as mentioned, this groove scheme is not as cost-effective as one that uses paint spots.

It is possible to improve the output signal by scaling currents to the transmitters such that the transmitter that is directed at the radiation-reflecting member closest to the radiation detector 38 receives a maximum current, the trans-mitter that is directed at the radiation-reflecting member closest to the radiation-reflecting surface 34 receives a minimum current, and each of the radiation-reflecting members intermediately positioned receives a current proportional to its position. This arrangement has been found to compensate for sensed signal strength reducing with reflection distance from the sensor.

It is possible to further improve the output signal by replacing the light pipe 24 of Figure 3 by two light pipes 40 each half as long as light pipe 24 and positioned with their radiation detectors 38 mounted on opposite sides of a joining block 42. This is illustrated in Figure 5. Such arrangement provides improved signal uniformity, and may be combined with the scaled transmitter currents mentioned above to achieve similar outputs from all of the radiation-reflecting members.

As shown in Figure 6 and briefly discussed above, the physics of refraction of radiation incident on the surface of a cylinder is such that radiation is refracted toward a focal line that is slightly behind a longitudinal line along the far surface of the cylinder. Positioning some type of light-ref lecting mechanism proximate that focal line, for instance on the far surface of the cylinder (see Figure 7), prevents most of the radiation from passing out through the far surface and instead it is reflected internally. The trapped radiation undergoes total internal reflection (TIR) within the cylinder and, with one end of the light pipe 24 formed into a mirror, all of the trapped light is directed toward the radiation detector 38 (in this embodiment, a photodiode) at the other end of the light pipe 24.

As illustrated in Figure 1, a transmitted beam diverges with distance from the source, having its greatest intensity on the symmetrical axis. As previously mentioned, each of the radiation-reflecting members is positioned to be on or proximate the symmetrical axis of the beam from a respective one of the transmitters at a corresponding height. If a transmitter and a respective radiation-reflecting member are positioned sufficiently close (e.g. when the door or doors is/are almost closed), only that member will receive the radiation of that transmitter. However, as the distance separating the particular member and transmitter increases, the member above and the member below the particular member (the adjacent members) will receive some of the radiation.

If only the particular member is receiving the radiation, an interposing object will reduce the radiation received at the member by approximately 50%. If, however, the separation distance has increased such that the adjacent members are also receiving radiation from the particular transmitter, an interposing object will reduce the radiation at the member by only approximately 25%. Thus, with increasing distance each radiation-reflecting member is reflecting the radiation of more and more of the transmitters. Based on such factors, the criteria for a determination of an interposed object is set to be a 10% to 15% reduction in the radiation received at the radiation detector 38. The software used in the system for measuring the level of received radiation and judging whether an interposed object is present must take into con- sideratiori the pattern of radiation divergence with separ-ation distance. The software utilized makes a determination every 50 milliseconds as to whether either, or both, of a "static trigger" and "dynamic trigger" are present. A static trigger involves a determination made by the software that the amount of radiation is a defined amount below a reference amount to be expected when no obstacle is present. A dynamic trigger involves a determination that the amount of received radiation is a defined amount below the amount of radiation made in the preceding measurement (5Oms earlier). With the dynamic trigger, a 30% drop in measured radiation is con-sidered to be indicative of the presence of an obstacle.

Cylindrical plastic rods made from polymethyl methacry-late (sold under the trade mark "Perspex") were found to be effective. Polystyrene was found to be usable, but not found to be as effective as Perspex. Other clear plastics (as well as toughened glass) with high transparency and a refractive index of at least approximately 1.4 may also be usable.

The transmitters used with the light pipe receiver were infrared emitter diodes known as usurface emitters". These emitter diodes are mountable on a printed circuit board to produce infrared beams extending parallel to the board and of very small divergence (<5 ). When mounted on printed circuit boards as an array of transmitters, such emitter diodes are fired sequentially (e.g. with 40 transmitters, each has a duty cycle of only 2.5%). With the radiation detector, how-ever, it is not necessary for the reception photodiode 38 to have an ON/OFF cycle as in some prior art systems. Instead, the photodiode 38 stays on permanently.

While the present invention has been described in its preferred embodiments, it is to be understood that the words which have been used are words of description rather than limitation, and that changes may be made to the invention without departing from its scope as defined by the appended claims.

Each feature disclosed in this specification (which term includes the claims) and/or shown in the drawings may be in-corporated in the invention independently of other disclosed and/or illustrated features.

The text of the abstract filed herewith is repeated here

as part of the specification.

A light pipe is configured as part of a receiving unit for an obstruction detector for a doorway. The light pipe is positioned along one edge of the doorway or a door in the doorway, and is in the path of radiation emitted from one or more transmitters. The light pipe is in the form of a trans-parent solid plastic rod, and may, for instance, be formed of polymethyl methylacrylate. Radiation enters the light pipe through a front surface, and is refracted according to the angle of incidence with the surface. The light pipe has a convex cross-section, with the front surface forming a lens adapted to focus incident radiation towards the back surface.

Extending at spaced locations on the back surface of the light pipe is a series of rectangular radiation-reflecting members that block the exit of the radiation and cause it to be reflected within the light pipe. One end of the light pipe is a radiation reflector, and the other end is tapered and culminates in a receiver photodiode. Each radiation- ref lecting member is preferably positioned opposite a res-pective transmitter on the doorway and, dependent on its separation distance from that transmitter, may collect radi-ation from other transmitters in proportion to its position relative to those transmitters. To compensate for their differing distances from the photodiode, radiation-reflecting members increase in length with distance from the photodiode.

Claims

CLAIMS: i. An obstruction detector for a doorway, the detector

including at least one elongate light pipe configured to receive radiation incident on the detector from one or more transmitters disposed to direct radiation across the doorway, the light pipe being configured to conduct the incident radiation longitudinally thereof to a sensor.
2. A detector according to claim 1, wherein the light pipe is configured to receive the incident radiation into a side surface thereof.
3. A detector according to claim 2, wherein the light pipe comprises means for reflecting or otherwise re-directing the incident radiation longitudinally of the light pipe.
4. An obstruction detector according to claim 2 or 3, wherein the light pipe is configured to receive the incident radiation at a plurality of spaced-apart locations along its length.
5. A detector according to claim 4, wherein the re-directing means is arranged to re-direct an increasing fraction of the incident radiation, the fraction increasing with the distance between the sensor and the respective location at which the radiation is incident on the side surface of the light pipe.
6. A detector according to claim 4 or claim 5, wherein the re-directing means comprises a plurality of discrete radiation reflectors spaced apart along the length of the light pipe.
7. A detector according to claim 6, wherein a reflector further from the sensor has a larger effective reflecting area than one closer to the sensor.
8. A detector according to claim 6 or claim 7, wherein each of said reflectors is a reflective coating disposed on the surface of the light pipe opposite to where the radiation is incident thereon.
9. A detector according to claim 6 or claim 7, wherein each of said reflectors comprises one or more grooves in the surface of the light pipe.
10. A detector according to any preceding claim, wherein an end of the light pipe is arranged to reflect back, within the light pipe, incident radiation.
11. A detector according to any preceding claim, wherein the light pipe tapers locally towards the sensor.
12. A detector according to any preceding claim, wherein the light pipe has a convex cross-section so as to form a lens adapted to focus the incident radiation towards a surface thereof opposite that on which the radiation is incident.
13. A detector according to claim 12, wherein the light pipe is of circular cross-section.
14. A detector according to claim 12 or 13, wherein the reflecting means is localised in a region where the incident light is focussed.
15. A detector according to any preceding claim, wherein the light pipe is of polymethyl methacrylate.
16. A detector according to any preceding claim, wherein the detector is configured to be disposed along or parallel to an edge of a doorway of a powered door, or to be disposed along or parallel to an edge of the powered door.
17. A detector according to claim 16, wherein the powered door or doorway of the powered door forms part of an elevator system.
18. A detector according to any preceding claim, wherein the detector has a plurality of the light pipes.
19. A detector according to claim 18, wherein the light pipes are positioned in-line.
20. A detector according to claim 19, wherein the light pipes are arranged in pairs, each pair having their sensors positioned proximate each other.
21. An obstruction detection system for a doorway, the system comprising a detector according to any preceding claim, and further comprising a plurality of radiation transmitters configured to be disposed along or parallel to an opposite edge of said doorway or a further door disposed therein.
22. An obstruction detection system according to claim 21, wherein the system comprises: means for energising said transmitters; means for receiving an output from the sensor(s) in res-ponse to reflected radiation received thereby; and, means for generating an alarm or control signal when an obstruction between the transmitters and the sensor(s) occludes the transmitted radiation.
23. obstruction detection system according to claim 22, wherein the means for energising said transmitters provides a scaled current to the transmitters, the trans-mitters transmitting to respective reflectors at increasing distance from the sensor receiving respective higher energising current.
24. An obstruction detection system according to claim 22 when dependent on the detector of claim 6, wherein each transmitter is adapted to emit a beam of radiation that diverges for reception by more than one of said plurality of reflectors.
25. A method of detecting an obstruction in a doorway, comprising: directing radiation across the doorway to be incident on detecting locations distributed along, or parallel to, an edge of either the doorway or a door in the doorway; and, conducting the incident light along at least one light pipe to a sensor.
26. A method according to claim 25, wherein the sensor Is at or adjacent a top or bottom edge of the doorway.
27. A method according to claim 25 or claim 26, wherein said light pipe extends along or parallel to said door or doorway edge.
28. A method according to any one of claims 25, 26 or 27, wherein the transmitted radiation is incident on a side surface of the at least one light pipe.
29. A method according to any one of claims 25 to 28, wherein the detector is configured to be disposed along or parallel to an edge of a doorway of a powered door, or to be disposed along or parallel to an edge of the powered door.
30. A method according to any one of claims 29, wherein the door and doorway are part of an elevator system.
31. A detector, a detection system or a detection method, substantially as herein described with reference to the accompanying drawings.