A DMD-based method for fabricating small pitch grating scales of optical linear encoders

Abstract

The width of the pitch period on grating scales is fundamental and critical to the accuracy of optical linear encoders. This paper presents a novel digital lithography-based method for fabricating small-pitch grating scales. A digital micro-mirror device (DMD) from Texas Instruments serves as the primary component for generating dynamic grating line patterns. A 405nm wavelength fibre laser is employed as the light source. The fabrication process of the grating scale involves dynamic pattern modulation using DMD and coordinated platform motion. In our exposure experiment, the S1813 photoresist is utilized as the sensitive material, applied to the substrate via a novel meniscus-coating method to achieve a 1.2µm thickness with any shape on a flat surface. The experimental results demonstrated that the fabricated grating scales have a pitch period of 10µm with adjustable duty cycles. These small pitch grating scales are crucial for the development and research of ultra-high accuracy optical linear encoders in future works.