Radiant energy – Photocells; circuits and apparatus – Optical or pre-photocell system
Patent
1991-12-23
1993-07-20
Nelms, David C.
Radiant energy
Photocells; circuits and apparatus
Optical or pre-photocell system
340602, H01J 4014
Patent
active
052296024
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
The invention is based on a circuit arrangement for an optoelectronic contamination sensor for detecting foreign bodies on a transparent element
More particularly, it relates to a circuit arrangement for an optoelectronic contamination sensor for detecting foreign bodies on a transparent element, which has a dynamically driven reflection light barrier whose receiver is fed by a supply voltage via a working resistor. It is known that dust, dirt, rain or snow adversely affect the light transmission on windscreens or headlamp lenses of a motor vehicle. In order to eliminate the contamination, the window or lens is to be automatically cleaned. The cleaning of the window or lens is triggered by an optoelectronic contamination sensor which is insensitive to extraneous light which originates from light in the surroundings or the oncoming light of other headlamps or the vehicle's own headlamps.
German Offenlegungsschrift 36 19 208 discloses a device which detects a wet or dry contamination on the surface of a headlamp lens and, in the event of contamination, activates a cleaning system. In this device, an optical transmitter and receiver are arranged on the inside of the lens. The radiation emitted by the optical transmitter is reflected by contamination particles on the lens. The reflected radiation is largely picked up by the receiver and fed to an evaluation circuit.
It was shown in practice that the sensor signal was temporarily disturbed in particular by the reflection of the vehicle's own headlamp light such that, despite increasing contamination of the lens, the sensor signal no longer reached the trigger threshold for the switching on of the cleaning system. The circuit arrangement of the contamination sensor was then incapable of functioning.
The same problem occurred when there was a very large light incidence from oncoming vehicles, which is very troublesome in particular during night driving.
SUMMARY OF THE INVENTION
According to the invention, the circuit arrangement for detecting foreign bodies on a transparent element comprises a dynamically driven reflection light barrier having a receiver for light reflected from foreign bodies on a transparent element, advantageously a phototransistor; a resistor connected electrically with the receiver through which a voltage is supplied to the receiver; and a working point controller means connected electrically to the receiver for controlling a voltage difference across the receiver as a function of an incident extraneous light intensity to compensate for the extraneous light intensity and to obtain a dynamic output voltage portion substantially dependent only on the light reflected from the foreign bodies.
The dynamically driven reflection light barrier also has a light emitting diode (LED) and pulse generator driving the light emitting diode so that it produces light which varies periodically in its intensity. The dynamic output voltage portion from the receiver varies according to the periodic variations of the light produced by the LED and depends only on the light produced by the LED which is reflected.
Advantageously a voltage raising circuit operative is also provided for raising an operating voltage to a supply voltage for the receiver.
The circuit arrangement according to the invention has the advantage in comparison with the above that the operational reliability of the circuit particularly when there is a high level of extraneous light interference on the sensor is ensured.
A further advantage is to be found in the control of the working point of the receiver, since the DC portion, generated by the extraneous light, of the output voltage is compensated independently of the amplitude of the incident extraneous light. In the case of a high level of extraneous light, a phototransistor connected as receiver would switch, for example, through to saturation without control, as a result of which the useful signal capable of being evaluated would be greatly reduced. By the working point controller means, the useful signal can
REFERENCES:
patent: 4128760 (1978-12-01), Del Signore, II
patent: 4538064 (1985-08-01), Kovacs
patent: 4816667 (1989-03-01), Meinert
patent: 4851689 (1989-07-01), Hasegawa
patent: 4987296 (1991-01-01), Kajioka et al.
Le Que T.
Nelms David C.
Robert & Bosch GmbH
Striker Michael J.
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