Radiant energy – Invisible radiant energy responsive electric signalling – Infrared responsive
Patent
1993-09-16
1995-05-30
Fields, Carolyn E.
Radiant energy
Invisible radiant energy responsive electric signalling
Infrared responsive
2503417, 250349, 250221, 49 25, 187317, B66B 1326
Patent
active
054204305
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
The present invention relates to detection systems.
Detection systems have been used for detecting the presence of an obstruction in a lift doorway. In the most fundamental form an infrared transmitter is mounted on one side of the doorway and infrared detector is mounted on the other side of the doorway on the leading edge of the door. The optical axis of the transmitter is aligned with the optical axis of the receiver and so a light beam extends across the doorway from the transmitter to the receiver. The receiver thus generates an output signal indicative that the doorway is clear. When an obstruction interrupts the beam, the output from the detector changes to indicate the presence of an obstruction and control means are activated to stop the movement of the door and/or reverse the direction of movement.
The problem with this arrangement is that as the distance between the detector and the emitter decreases, the intensity of the light received by the detector increases very significantly. If an obstruction entering the doorway during the last stages of closure is slightly translucent eg a human hand, then light passing through the hand will be detected by the detector and so the door will continue to close on the hand. The problem has, to some extent, been overcome by providing additional circuitry which acts to reduce either the beam intensity of the emitter or the sensitivity of the detector as the door approaches closure. This is still unsatisfactory firstly, because only a step wise reduction is achieved and, secondly, because costly additional circuitry is required.
It is an object of the invention to provide an improved detection system.
SUMMARY OF THE INVENTION
According to the present invention there is provided a detection system comprising an emitter for emitting a beam of radiation, a detector for detecting the radiation of the emitter, and means for varying the radiation path length between the emitter and detector in response to a moving object and simultaneously varying the angle that the radiation path makes with at least one of the optical axes of the emitter and the detector, the radiation intensity transmitted by the emitter towards the detector being arranged to vary as a function of said angle in a sense such, that as the length of the radiation path progressively reduces, the radiation intensity at least during the final stage of closure and path length reduction emitted along said path to the detector decreases.
According to the present invention there is further provided a detection system comprising an emitter for emitting a divergent beam of radiation, a detector having a divergent field of view, the emitter and detector being constrained for relative movement so that the optical axis of the divergent beam and the optical axis of the divergent field of view are maintained substantially parallel to one another with a substantially predetermined spacing between the two axes, the detector being arranged to generate an output signal which is a function of both distance between the emitter and detector along said axes, and the angle between a said axis and the line joining the emitter to the detector, so that as a reduction in the distance between the emitter and detector acts to increase the output signal of the detector, an increase in angle acts to reduce the output signal.
BRIEF DESCRIPTION OF THE DRAWINGS
Detection systems embodying the present invention will now be described, by way of example, with reference to the accompanying diagrammatic drawings, in which:
FIG. 1 is a side elevation of one system;
FIG. 2 is a graph of distance versus light intensity;
FIG. 3 is a polar and coordinate graph of light intensity versus angular displacement for an infrared emitter;
FIG. 4 is a side elevation of another system;
FIG. 5 is a side elevation of the system of FIG. 4 when the emitters and detectors are close together;
FIG. 6 is a side elevation of yet another system; and
FIG. 7 is a side elevation of a further system.
DETAILED DESCRIPTION
As shown
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patent: 4794248 (1988-12-01), Gray
patent: 5149921 (1992-09-01), Picado
E.D.S. Microscan "S" Entrance Detector Screen, Brochure and Manual, T. L. Jones Ltd., 1989.
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Lambda 950 Infra-red Door Protection Device, Brochure, Otis Elevator Company, undated.
Panaseer Model 145 Door Safety System, Brochure, Memco Ltd., undated.
Fields Carolyn E.
Formula Systems Ltd.
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