Radiant energy – Photocells; circuits and apparatus – Photocell controlled circuit
Patent
1985-06-19
1987-09-15
Westin, Edward P.
Radiant energy
Photocells; circuits and apparatus
Photocell controlled circuit
307310, 307311, H01J 4014
Patent
active
046941576
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention is directed to an opto-electric position detector circuit, and more particularly to an opto-electric position detector circuit adapted for use in an encoder or the like which detects the position and speed for the purpose of measuring and controlling the motion of robots, processing machines, recorders or the like.
BACKGROUND ART
Generally, position detectors and angle detectors are classified into different systems according to the detecting means employed, opto-electric system utilizing light, magnetic system utilizing magnetism, and contact system utilizing resistance value. Taking an encoder as an example in order to provide an explanation, with the opto-electric system infra-red light emitted from a light emitter such as a light emitting diode (infra-red LED) is alternately permitted and interrupted to pass by the combination of a fixed plate (phase plate) with peripheral slits permitting the transmission of the light and a plate (code wheel) formed with like peripheral slits and rotating together on a shaft whose motion is to be measured. The resulting intermittent light passing through the plates is received by a photodetector such as a photo-diode which produces a varying electric current, such current variations are then utilized for detection of the position (angle) and the rotational speed of the shaft.
Also included in the above opto-electric system is a detector of linear type operating on the same principle as the above rotary type for detecting the position of a linear motion. Each of the above two types is further divided into transmissive and reflective types depending upon the relative position of the light emitter with the photodetector with respect to the code wheel and phase plate. In the reflective type, the code wheel or the phase plate has its portion mirror-finished and both the light emitter and photodetector are positioned on the same side of the code wheel or the phase plate.
Further, there are incremental and absolute types depending upon the kind of output signal obtained. For example, with the absolute type the output is in the form of a four-bit signal in order to determine the absolute positions (in such a case 16-divided).
The light received by the photodetector causes changes in the electric current, which is in turn converted into changes in the voltage by a resistance inserted in series with the light emitter. The voltage change is such that the voltage level is gradually decreased as the slits in the phase plate become closed by the rotating code wheel and gradually increased as the slits in the phase plate become aligned with the slits in the code wheel to thereby produce a quasi-sine wave with an average value of direct current level above zero. The quasi-sine wave is fed into the Schmitt trigger circuit with a threshold level in the vicinity of the above average value in order to provide a rectangular waveform output with a 50% duty cycle.
The prior opto-electric encoders, however, will suffer from variations in the output from the photodetector when subjected to variations in the power supply voltage or to raised operating temperatures so that the duty cycle of the output wave will fluctuate with said threshold level remaining unchanged, resulting in the malfunction or counting error in a controller or a counter utilizing the output of the encoder.
Following is the explanation of the above in conjunction with the attached figures.
FIG. 1 shows a light receiving section employed in a prior opto-electric rotary encoder of transmissive type. The light receiving section includes a series combination of a light emitting diode LED and a resistor R inserted between the power source V.sub.cc and ground, a series combination of photodiode PD and load resistance R.sub.PD likewise inserted between the power source V.sub.CC and ground, and a set of code wheel 1 and phase plate 2 positioned between the light emitting diode LED and the photodiode PD.
The connection point between the photodiode PD and the load resistance R.sub.PD is conne
REFERENCES:
patent: 3670325 (1972-06-01), Mathevosian
patent: 3705316 (1972-12-01), Burrous et al.
patent: 4327362 (1982-04-01), Hoss
patent: 4438348 (1984-03-01), Casper et al.
Matsushita Electric & Works Ltd.
Westin Edward P.
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