Patent ID: 7326919

Claim:
An optical displacement measuring apparatus comprising: a light emitting portion; and a main scale with a plurality of light transmitting portions or a plurality of light reflecting portions for transmitting or reflecting a light flux emitted from the light emitting portion to a light receiving device having a plurality of light receiving parts which are disposed in equal intervals relating to the intervals of the plurality of light transmitting portionsor the plurality of light reflecting portions, and the light receiving device converts the light flux into electrical signals, the main scale being movable relative to said light emitting portion, wherein the main scale has a first area and a second area each having a plurality of light transmitting portions or a plurality of light reflecting portions disposed in first intervals in the first area and in second intervals in the second area, the first intervals and second intervals being different from each other, and wherein the electric signals from light receiving parts selected in respective predetermined intervals are added to obtain two phased signals and the first intervals of the scale and the second intervals of the scale are determined so that the mutual replacement between the scale and the light emitting portion obtained by processing the two phased signals are equal in the first area and second area and so that the first area or the second area is determined based on the difference of light quantity obtained by processing the electrical signals.