Radiant energy – Photocells; circuits and apparatus – Photocell controls its own optical systems
Patent
1987-08-24
1991-08-27
Westin, Edward P.
Radiant energy
Photocells; circuits and apparatus
Photocell controls its own optical systems
315151, G05D 2502, G01J 132
Patent
active
050435655
DESCRIPTION:
BRIEF SUMMARY
The invention concerns a method of compensating for changes in the parameters of an optical emitter and an optical receiver in an optical scanner that detects different luminosities, whereby the optical receiver receives light from the optical emitter.
Optical scanners are employed for example in light barriers and reflex couplers.
Reflex couplers are described in AEG-Telefunken, Reflexkoppler CNY 70, Halbleiterinformationsdienst 7.81.
The optical emitter in a reflex coupler beams light onto an object, which reflects it onto an optical receiver. A reflex coupler can be employed for example to determine whether the object is moving, rotating, or changing its position or reflectivity. Table 1 on page 1 of the aforesaid reference lists fields of application for reflex couplers. To recognize colors or read marks the reflex coupler must be able to distinguish various luminosities because the object varies its reflectivity. The same problem occurs in a light barrier, wherein the optical emitter and the optical receiver are directly opposite each other, when translucent objects that can attenuate the light to different extents are inserted between the emitter and the receiver. In order for example to evaluate the different shades of gray of a filter inserted between the emitter and the receiver the receiver must emit a different signal for every shade, so that the different shades can be differentiated by means of the different output signals. The same output signal must always be released in relation to the same shade of gray, so that the evaluation can be reversed.
The requirement of reversibility cannot be satisfied in a simple system consisting of an optical emitter and an optical receiver because the parameters of the emitter and of the receiver vary with temperature and age. In the aforesaid example for instance the same shade of gray does not always result in the same output signal at the receiver as would be desired. Precise evaluation of various luminosities or shades of gray is impossible with optical emitters and optical receivers alone due to variations in temperature and aging on the part of the components.
The object of the invention is a method that can be employed with an optical scanner and that will compensate for changes in the parameters of the optical emitter and optical receiver due to temperature variations and aging.
This object is attained in accordance with the invention in that the output voltage U.sub.A of the optical receiver E is compared with a reference voltage U.sub.K and in that the output voltage U.sub.A is clamped to the reference voltage when the energy of the light received by the optical receiver assumes an extreme value.
IN THE DRAWING
FIG. 1 illustrates circuitry for carrying out the method recited in claim 2,
FIG. 2 illustrates output voltage U.sub.A as a function of the shades of gray of a filter F,
FIG. 3 illustrates circuitry for carrying out the method recited in claim 3, and
FIG. 4 illustrates output voltage U.sub.A as a function of the shades of gray of a filter F.
The output terminal of the operational amplifier OP illustrated in FIG. 1 is connected to the anode of an optical emitter in the form of a photodiode S, the cathode of which is at reference potential. The inverting input terminal of operational amplifier OP is also connected to reference potential through a first resistor R1 and to a voltage +U through another resistor R2. The non-inverting input terminal of operational amplifier OP is connected to voltage +U through a third resistor, R3 and to reference potential through a capacitor C. The non-inverting input terminal of operational amplifier OP is also connected to the anode of a diode D, the cathode of which is connected to voltage +U through a fourth resistor R4 and to the collector of an optical receiver in the form of a phototransistor E. The emitter of phototransistor E is at reference potential. Output voltage U.sub.A is picked up at the collector of phototransistor E.
The circuitry illustrated in FIG. 1 will now be specified with reference to
REFERENCES:
patent: 3436553 (1969-04-01), Bevis
patent: 4203032 (1980-05-01), Haunstetter et al.
Deutsche Thomson-Brandt GmbH
Fogiel Max
Westin Edward P.
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