Design and Testing of a Compact Optical Angle Sensor for Pitch Deviation Measurement of a Scale Grating with a Small Angle of Diffraction

The design and testing of different optical heads were performed to evaluate the pitch deviation of a diffraction scale grating with a small diffraction angle. Based on the proposed pitch deviation evaluation method employing optical angle sensors based on laser autocollimation, a modified optical head with position-sensitive detectors (PSDs) is first designed and constructed by following the conventional optical configuration. Owing to the small angle of diffraction of the first-order diffracted beams, the modified optical head has a large working distance, resulting in poor sensor stability. Therefore, a novel and compact optical head employing a pair of small prisms is designed and developed to shorten the working distance of the optical head. An additional modification was also made to the developed compact optical head in such a way that collimator objectives (COs) in the laser autocollimation units are removed to improve the sensor sensitivity. Experimental comparisons were conducted using the three types of optical heads to verify the feasibility of the developed optical angle sensor with PSDs.