| 摘要 |
PURPOSE: To obtain 4-phase signals having an equal duration from a mask without using any compensating circuit by disposing an encoder disk, a mask, and a detector in an encoder, and by making the dimensions of each section of the encoder and those of the mask have a certain relation to each other. CONSTITUTION: In an encoder disk 15, the outer circumferential length X of an optical gate section 151 of each control section 150 exists over an arc with a central angle of 4.5", and the outer circumferential length T of each control section 160 is 12". An opening A and an opening B respectively have the same outer circumferential length C with a central angle of 1.5", and are apart from each other by a distance obtained by adding a n integer multiple of the outer circumferential length T to 3". When the control section 150 of disk 15 is turned relative to the openings A and B, a signal is detected every time the openings A and B are superposed on section 151 of disk 15, or the superposition disappears. As a result, a combination of 4-phase output signals can be respectively obtained in a range of 3" without disposing a complex circuit. Speaking in short, the purpose of obtaining a combination of 4-phase output signals can be achieved by making the encoder have the relation ofθ=n±T/4, X+C=T/2 (θis the angle made by a pair of openings).
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