Patent ID: 7486409

Claim:
A displacement sensor comprising: a projector; a photoreceiver including an aperture; and a lens unit including a lens reciprocatable along an optical axis of a coaxial optical system adjusted so that a light emission position of the projector and the aperture have a conjugate relation, the displacement sensor for measuring a displacement of an object to be measured on the basis of the position of the lens when a light reception amount signal of the photoreceiver displays a maximum value, wherein a light port is formed, in a position opposite to a lens face of a lens at the final stage in the lens unit, in a casing enclosing the coaxial optical system, a lens holder in which an objective lens is supported is detachably disposed in the light port, and the lens unit converts light from the projector into parallel rays and leads the parallel rays to the objective lens through the light port at a predetermined time point during the reciprocatable lens reciprocates once.