Design of the optical sensor head for the evaluation of pitch deviation of a diffraction grating based on the laser autocollimation

Abstract

An optical setup for measurement of the pitch deviation of a diffraction grating has been designed and developed. Multiple autocollimation units are employed in the setup so that the angles of diffraction of diffracted beams can be detected simultaneously. This enables the optical sensor head to evaluate the scale pitch deviation while separating the contributions from the scale local slope and the scale angular error motion that cannot be achieved by the conventional laser diffraction methods. In this paper, firstly, the resolution needed for the angle sensor is estimated using a theoretical analysis. After that, the design of an optical head for the angle sensor is carried out. A built prototype optical head is also used to conduct some feasibility tests, and the measurement of the pitch deviation of a scale grating brought from a commercial optical linear encoder is demonstrated.