High-precision miniaturized low-cost reflective grating laser encoder with nanometric accuracy

This paper presents a novel optical encoder, M-encoder, which can be used within high-precision metrology systems based on the technology of customized prism and homodyne detection. The M-encoder is an exposed encoder measuring reflective glass and metal scale, which is targeting the biggest area of the encoder market, 20 µm pitch, and has a resolution under 100 nm. The error of 23 nm for 100 mm traveling distance has been measured. The applied technology has successfully improved alignment tolerances, in which the tolerance of installation achieved to ±0.5∘, ±0.5∘, and ±1∘ for pitch, yaw, and roll angle, respectively. The accuracy of results has been verified by comparing them with one of the commercial encoders and also by using an HP interferometer. The results show the resolution and accuracy can be compatible with the market products. In addition, a new method of grating calibration has been described based on the Littrow configuration, and the pitch of the fabricated scale by a femtosecond laser has been measured with the accuracy of 2 nm.