Rotary encoder

A rotary encoder for producing output signal having a variable phase difference, comprising:

• a first plate which is rotatably supported and which is provided with a reference indicium of alternate non-light-transmitting and light-transmitting sections arranged at a predetermined pitch circularly around an axis of rotation of said plate;
• driving means for rotating said first plate in a plane defined by its surface;
• a light source for irradiating light radially from said light source to said first plate;
• a second plate which is provided with a pair of first and second indicia, each including at least one light transmitting section, said first and second indicia being arranged such that when either one of said first and second indicia is in phase with said reference indicium, the other is shifted in phase with said reference indicium with respect to the direction of movement of said reference indicium, and that said first and second indicia receive said light from said light source through said reference indicia at differing incidence angles;
• a pair of first and second light-receiving elements, said first light-receiving element being disposed to receive said light as passed through reference and said first indicia, and said second light-receiving element being disposed to receive said light as passed through said reference and said second indicia;
• and
• adjusting means for adjusting the position of at least one of said first and second plates variable with respect to the other and said light source such that a ratio between a distance from said light source to said first plate and a distance from said light source to said second plate is varied thereby correspondingly varying the relative phase of said output signals.