POSITION MEASURING APPARATUS

摘要

PROBLEM TO BE SOLVED: To provide a position measuring apparatus which includes a reflection type measuring scale allowed to be optically scanned and detected and surrounded like a ring and is configured so that a fringe pattern period on a detection surface is not related to a scanning detection distance.SOLUTION: A cylindrical object 20 having a reflection type measuring scale 21 surrounded like a ring is arranged so as to freely rotate around an object longitudinal axis. A scan detection unit 10 which is stationary oppositely to the rotatably arranged object 20 to optically scan and detect the reflection type measuring scale 21 includes a light source 11, a light-emitting side grating 13 and a detector 12. Light flux emitted from the light source 11 is abutted on the reflection type measuring scale 21 through the light-emitting side grating 13, and thereby, the light flux is reversely reflected to a detector direction, so that a position signal corresponding to rotation is generated through the detector 12. An optically effective normal distance V' between the detector and the reflection type measuring scale is selected as a larger or smaller distance correspondingly to a radium R of the cylindrical object as compared with an optically effective normal distance U' between the light-emitting side grating and the reflection type measuring scale.