High-Accuracy and High-Tolerance Laser Encoder With a Grating-Pyramid Configuration

Abstract

Laser encoders is promising positioning sensors for nanometer measurement. It is a key challenge for laser encoders to offer high accuracy while ensuring high tolerance in service. In this paper, we present a laser encoder employing a grating-pyramid configuration. This configuration realizes double diffraction via a single retro-reflector, which offers the following two advantages: (i) providing high-resolution output signals due to optical quadruple frequency; (ii) improving alignment tolerance due to retro-reflection of the single pyramid. Its operating principle is described in detail, and the performance are evaluated. Simulation result presents that stand-off error and pitch error are the critical head-to-scale tolerance for the developed laser encoder. Experiment result shows that the laser encoder offers a stand-off tolerance of ±0.68 mm and a pitch tolerance of ±1.67°. Furthermore, an interpolation accuracy of 3 nm is achieved, which indicates that the laser encoder would achieve nanometer-level resolution. Both simulation and experimental results demonstrate its high-accuracy and high-tolerance.