A Michelson interferometer-based method for measuring the angle of rotation

Abstract

For measuring the angle of rotation of flat objects using projected fringes, the method of point-of-light triangulation and the method of line-of-light triangulation will breakdown when the grating lies on the axis of rotation. Therefore, a grating other than a point or linear lines is preferred. In this paper, a simple Michelson interferometer-based method for the generation and projection of circular gratings is described. The basic optical element in a Michelson interferometer is a beam-splitting cube. With this Michelson interferometer, a circular grating is observed when the screen is placed normal to the line containing the two point-light sources produced by the beam splitter. By placing an expander between the beam-splitter and the laser source, and by carefully adjusting the two mirrors beside the beam-splitting cube, the frequency of the circular grating can be adjusted. This paper also describes the use of the generated circular optical grating for measuring the amount of rotation of flat surfaced that are either diffuse or specularly reflective - the method is based on relating the distortion of the circular grating to the angular rotation of the surface.