A Novel Inductive Angular Displacement Sensor with Multi-Probe Symmetrical Structure

This paper develops a novel probe-type inductive angular displacement sensor based on time-grating, which is suitable for large-diameter hollow rotary table position detection of the heavy-duty machine tools. It abandons the traditional sensor precise marking lines in spatial domain, and integrates the tested mechanical component with the sensor, which realizes the angular displacement measurement directly. The sensor is divided into three parts: 1) a permalloy probe, which is adopted the simple structure to reduce the assembly errors; 2) a 45-steel rotor, which is a standard spur gear in a heavy-duty machine tool rotary table transmission system; 3) three groups of copper coils, which include sinusoidal coils, cosine coils and inductive coils. The theoretical model of angular displacement measurement is derived by means of mathematical equation in detail. Then the feasibility of the sensor structure is verified by finite element simulation. After that, a sensor prototype is built and tested in the laboratory, showing that the sensor has an original error of ±0.018° (approximately ±64") over a full 360° range. The error analysis found that the systematic error is the main component. As a result, the mechanical structure and angular displacement algorithm of the sensor are optimized, which can significantly reduce the original errors of the sensor. After optimization, the final accuracy of the sensor is within ±0.0012° (approximately ±4.4") in the range of 0°-360°.