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

Laser encoders are 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 article, we present a laser encoder employing a grating-pyramid configuration. This configuration realizes double diffraction via a single retroreflector (RR), which offers the following two advantages: 1) providing high-resolution output signals due to optical quadruple frequency and 2) improving alignment tolerance due to retroreflection of the single pyramid. Its operating principle is described in detail, and the performance is evaluated. The simulation result presents that the stand-off error and the pitch error are the critical head-to-scale tolerance for the developed laser encoder. The 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.