Displacement sensor and method for producing target feature thereof

Abstract

A device for measuring the displacement of a movable object includes a stationary light source that produces an incident light beam. A target feature, attached to, or integral with, the object, reflects the incident light beam and forms a first image of the light source in close proximity of the target feature. An imaging lens receives the reflected light beam and reforms the first image of the light source as a second image on the photodetector. The photodetector, spaced from the object, receives the reflected light beam and, in response thereto, produces an electric signal having a characteristic (such as amplitude) which is proportional to a received location on the photodetector of the second image and which represents a position of the object. The target feature includes a curved surface that reflects the light beam such that a small, point-like or line-like first image of the light source is formed and reformed as a second image on the photodetector. The displacement sensor device is particularly useful in a disk drive servo system application. The target feature is formed by ruling a groove within a surface of the object.