Method and apparatus for self-biasing a light beam obstacle detector with a bias light
First Claim
1. A light beam obstacle detector for signalling the presence of an object in a defined area, the detector being subject to varying ambient light, comprising:
- a light beam device including a transmitter disposed adjacent to the defined area for emitting a modulated light signal and a light receiver disposed adjacent to the defined area opposite the transmitter for generating a modulated electrical signal corresponding to the modulated light signal, the receiver being responsive to light above a light threshold level and below a saturation level so that the light signal alone is insufficient for detection by the receiver and the maximum expected ambient light combined with the received light signal is not great enough to saturate the receiver;
an auxiliary light source for illuminating the receiver to bias the receiver to respond to the light signal when the ambient light is below the light threshold level;
a closed loop circuit responsive to the modulated electrical signal for controlling the auxiliary light source to compensate for variations in ambient light and enable the receiver to respond to the light signal in any expected ambient light conditions.
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Accused Products
Abstract
A modulated light beam obstacle detector for use as a safety mechanism in an automatic closure operator which must operate in varying ambient light conditions. If the obstacle detector senses the interruption of the light beam, the motion of the door is arrested or reversed. The obstacle detector uses an auxiliary light source connected in a feedback circuit to maintain a constant background illumination on the light detector and thereby hold the light detector in conduction at all times. In this manner, the presence of the light beam can be sensed regardless of the ambient light conditions.
56 Citations
9 Claims
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1. A light beam obstacle detector for signalling the presence of an object in a defined area, the detector being subject to varying ambient light, comprising:
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a light beam device including a transmitter disposed adjacent to the defined area for emitting a modulated light signal and a light receiver disposed adjacent to the defined area opposite the transmitter for generating a modulated electrical signal corresponding to the modulated light signal, the receiver being responsive to light above a light threshold level and below a saturation level so that the light signal alone is insufficient for detection by the receiver and the maximum expected ambient light combined with the received light signal is not great enough to saturate the receiver; an auxiliary light source for illuminating the receiver to bias the receiver to respond to the light signal when the ambient light is below the light threshold level; a closed loop circuit responsive to the modulated electrical signal for controlling the auxiliary light source to compensate for variations in ambient light and enable the receiver to respond to the light signal in any expected ambient light conditions. - View Dependent Claims (2, 3, 4, 5)
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6. A method for automatically biasing a light beam obstacle detector for detecting the presence of an object in a defined area when the ambient light condition is variable comprising the steps of:
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supplying current to an auxiliary light source to illuminate a light sensitive receiver; transmitting a modulated light signal across a defined area; receiving the auxiliary illumination, the modulated light signal, and the ambient light by the light sensitive receiver; generating an electrical signal which corresponds to the light incident upon the receiver; passing a frequency band of the electrical signal containing the information contained in the modulated light signal to an output; passing low frequency components of the electrical signal generated by the receiver to a feedback circuit containing the auxiliary light source; controlling the current available to the auxiliary light source, and indirectly the intensity of the auxiliary light source, in a manner inversely proportional to the amplitude of the low frequency components of the electrical signal generated by the receiver.
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7. A method for automatically biasing a light beam obstacle detector responsive to interruption of the light beam wherein the detector is subject to variable ambient light conditions, comprising the steps of:
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transmitting a modulated light beam to a receiver; supplying bias light to the receiver; generating an electrical signal corresponding to the sum of the modulated light beam, the bias light, and ambient light incident on the receiver; passing a frequency band of the electrical signal containing the information in the modulated light beam to an output; deriving a control signal from low frequency components of the electrical signal; and controlling the intensity of the bias light by the control signal to offset the effects of the ambient light. - View Dependent Claims (8, 9)
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Specification