Patent ID: 7132647

Claim:
An optical displacement measuring apparatus comprising: a light emitting portion, a main scale on which light transmitting portions or light reflecting portions for transmitting or reflecting a light flux emitted from said light emitting portion are provided at substantially regular intervals, the main scale being movable relative to said light emitting portion, and a light receiving portion for receiving a light flux from the light transmitting portions or light reflecting portions of said main scale to convert it into an electrical signal, wherein at least one portion of the light transmitting portions or the light reflecting portions disposed at regular intervals is absent; a signal processing portion which processes said electric signal obtained from said light receiving portion, and detects a relative moving amount between said main scale and said light receiving portion and an absolute position of said main scale; a received light quantity stabilizing circuit which adjusts a current value flowing into said light emitting portion so as to make quantity of light received by said light receiving portion at a predetermined value, and wherein said absent portion on said main scale is detected on the basis of a variation of said current value.