| 摘要 |
<p>PURPOSE:To dispense with a process that a circular board is very precisely corrected in eccentricity by a method wherein two photodetective elements of a transmission type detection device are formed into a rectangular shape, and the longitudinal direction of the photodetective element is coincident with the direction of the normal of the circular board. CONSTITUTION:A photodetective section 2 is composed of rectangular photodetective elements 4 and 5 disposed in array, where the photodetective elements 4 and 5 are so disposed as to make their long sides parallel with the normal of a circular board 1. Therefore, photodetected signals S and C outputted from the photodetective elements 4 and 5 corresponding to the change of the peripheral edge of the rotating circular board 1 in position are nearly equal to each other in fluctuation, so that signals a and b are equal to each other in fluctuation. In result, as a differential signal c hardly fluctuates and no zero crossing takes place, so that a positioning detection signal h is never transmitted erroneously from a transmission type detection device. By this setup, as the positional fluctuation of the peripheral edge of the circular board 1 caused by the eccentricity between the center of the board 1 and the center of rotation does not affect the differential signal c, the eccentricity of the center of the circular board 1 to the center of rotation can be made large in tolerance.</p> |
