Patent ID: 7875844

Claim:
An absolute-type optical encoder for judging an absolute position of a wheel body with respect to a light source, comprising: a primary grating unit having main gratings of first number and the main gratings arranged around a circumference of the wheel body; at least one secondary optical grating unit having sub gratings of second number, the sub gratings arranged around another circumference of the wheel body, wherein the second number is one less than the first number; a plurality of main light sensor units arranged corresponding to the primary grating unit and receiving light from the light source passing through the primary grating unit to obtain a first sensed result; at least one modulation light sensor unit corresponding to the at least one secondary optical grating unit and receiving light from the light source passing through the secondary grating unit to obtain a second sensed result; a controller electrically connected to the main light sensor units and the modulation light sensor unit, the controller configured with one revolution of the wheel body by means of continuously driving the wheel body to rotate a distance corresponding to a grating pitch of the sub gratings, finding a zero point in the second sensed result, and finding a sampled value of a first sensed result with reference to the zero point to obtain the absolute position of the wheel body based on the sampled values.