Radiant energy – Photocells; circuits and apparatus – Optical or pre-photocell system
Patent
1984-06-18
1986-08-05
Laroche, Eugene R.
Radiant energy
Photocells; circuits and apparatus
Optical or pre-photocell system
340347P, G01D 534
Patent
active
046045210
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to an optical absolute encoder, more particularly to an optical absolute encoder wherein fluctuations in the voltage level of reference signals due to leakage of light are prevented.
BACKGROUND ART
In general, optical absolute encoders are provided with a light emitting element, a rotary code plate and fixed plate, for example, affixed to a motor shaft, and light receiving elements. That part of the light from the light emitting element passing through light passage portions provided in the rotary code plate and slits provided in the fixed plate is converted into electric signals by the light receiving elements, thereby allowing detection of the angle of rotation and the position of rotation of the motor, etc. The light passage portions of the rotary code plate are comprised of a plurality of concentric code patterns and a reference pattern. The slits of the fixed plate are provided corresponding to the code patterns and reference pattern.
Conventionally, the slits provided in the fixed plate have been arranged in a line in the radial direction of the rotary code plate. Therefore, light passing through the code patterns also leaks to the slits corresponding to the reference pattern. As a result of this, there have been the problems that the voltage level of the reference signals fluctuates and errors are caused in the output signals.
DISCLOSURE OF THE INVENTION
The object of the present invention is, in consideration of the above problems in the prior art, to prevent fluctuations in the voltage level of reference signals due to leakage of light in an optical absolute encoder, and thus to prevent errors in output signals, based on the idea of arranging those slits provided on the fixed plate which correspond to the reference pattern in the direction of rotation of the rotary code plate.
The gist of the present invention, for achieving the above object, lies in an optical absolute encoder provided with a rotary code plate having a plurality of concentric code patterns with light passage portions, for passing light from the light emitting element, and light blocking portions alternately arranged on the same circle and having a reference pattern comprised of just a light passage portion arranged concentrically with said code patterns; a fixed plate provided with light passage slits provided corresponding to the code patterns and reference pattern of the rotary code plate; and light receiving elements for receiving light from the light emitting element passing through the light passage portions of the rotary code plate and the light passage portions of the fixed plates, the optical absolute encoder being characterized in that the reference pattern included on the rotary code plate is arranged sandwiched between two adjoining code patterns and in that the fixed plate is provided with two code pattern slit groups arranged at first predetermined intervals in correspondence with said code patterns in the radial direction of said rotary code plate and reference pattern light passage portions arranged at positions corresponding to the reference pattern at positions separated by exactly second predetermined intervals from the center line of the code pattern light groups.
BRIEF DESCRIPTION OF THE DRAWINGS
The above objects and features of the present invention and other features of the same will become clearer from the following description of an embodiment in reference to the attached figures.
FIG. 1 is a schematic side view of a conventional optical absolute encoder;
FIG. 2 is a plan view of the rotary code plate shown in FIG. 1;
FIG. 3 is a plan view of the fixed plate shown in FIG. 1;
FIG. 4 is a circuit diagram of an example of a comparison circuit for comparing output signals of light receiving elements in the optical absolute encoder of FIG. 1;
FIG. 5 is a waveform diagram of input and output signals of the comparison circuit of FIG. 4;
FIG. 6 is a plan view of a rotary code plate included in an optical absolute encoder according to an embodiment of the pre
REFERENCES:
patent: 4266125 (1981-05-01), Epstein et al.
patent: 4410798 (1983-10-01), Breslow
patent: 4423958 (1984-01-01), Schmitt
patent: 4445110 (1984-04-01), Breslow
Takekoshi Yoshitaka
Ushiyama Shigeyuki
Fanuc Limited
LaRoche Eugene R.
Mottola Steven J.
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