Patent ID: 7526230
Filing Date: 2009-04-28
Classification: G03G

Abstract:
1. A mark sensing device for sensing a plurality of marks formed on a turnable body in a preselected periodic light pattern, said mark sensing device comprising: a light source emitting a light; a slit mask positioned on an optical path between the turnable body and the light source and formed with a plurality of slits configured to split the light emitted from said light source; a light receiving portion configured to receive a received light and output an electric signal based on the received light, wherein the received light is the light split by said slit mask, reflected by a mark on the turnable body; and a signal generating unit configured to produce a control signal that controls an amount of turn of the turnable body from said electric signal, wherein the slit mask is positioned on an optical path between the light source and the mark on the turnable body, said plurality of slits of said slit mask each belong to either one of two slit regions one of which is shifted from the other by (2n+1)/2 (n being a natural number including zero) of the period of the preselected periodic light pattern of the plurality of marks, said light receiving portion is further configured to receive the received light in two light receiving portions each corresponding to one of said two slit regions and output two electric signals based on the received light, and said signal generating unit produces said control signal from said two electric signals output from said light receiving portion by using a crossing point of the two electric signals as a threshold value.