A position sensing technique by using the light diffracted from a small circular grating is proposed. The circular grating is attached to the surface of the object as a reference for the measurement (reference point). The grating is irradiated by laser light and the elliptical pattern generated by diffraction is measured by a CCD image sensor. By processing the diffraction pattern, the distance from the detector to the reference point is obtained. In addition, it is possible to derive the three dimensional position of the reference point and the inclination of the work surface. The experiments were carried out by using a circular grating of 20, μm pitch and 0.6 mm diameter. The accuracies of the measurements are also discussed.
