A new method for evaluation of the pitch deviation of a linear scale grating by an optical angle sensor

A new method for measurement of the pitch deviation of a scale grating by an optical angle sensor based on the laser autocollimation is proposed. In the proposed method, the scale pitch deviation is evaluated through detecting the change in the angles of diffraction of the first-order diffracted beams, which is associated with the change in the scale pitch deviation. The optical angle sensor unit is designed to measure the angles of diffraction of both the positive and negative first-order diffracted beams simultaneously so that the influences of the scale form error and the roll error motion of the linear slide for the scanning of a linear scale can be canceled through the differential operation. The optical angle sensor unit based on the laser autocollimation is newly designed and developed, and the pitch deviation of a linear scale from a commercial interferential scanning-type linear encoder is evaluated by the developed setup to verify the feasibility of the proposed method in experiments. The scale form error obtained through the differential operation is also compared with the one evaluated by a commercial Fizeau interferometer. Furthermore, the uncertainty analysis on the proposed pitch deviation measurement is carried out based on GUM to theoretically verify the feasibility of the proposed method.