Error Analysis of a Spherical Capacitive Sensor for the Micro-Clearance Detection in Spherical Joints

Abstract

Spherical joints have attracted increasing interest in the engineering applications of machine tools, industrial robots, medical equipment, and so on. As one of the promising methods of detecting the micro-clearance in spherical joints, the measurement accuracy of a spherical capacitive sensor could be affected by imperfectness during the manufacturing and installation of the sensor. This work presents error analysis of a spherical capacitive sensor with a differential structure and explores the dependence of the differential capacitance on manufacturing and the installation imperfectness. Five error sources are examined: the shape of the ball and the capacitive plate, the axial and radial offset of the plate, and the inclined installation of the plate. The mathematical models for calculating the capacitance errors of the spherical capacitive sensor are deduced and validated through a simulation using Ansoft Maxwell. The results show that the measurement accuracy of the spherical capacitive sensor is significantly affected by the shape of plates and ball, the axial offset, and the inclined angle of the plate. In contrast, the effect of the radial offset of the plate is quite small.

Editorial for the Special Issue on Advances in Capacitive Sensors

“…The mathematical model for the rotational angles of a spherical joint and the capacitance are deduced, and the capacitance values of the capacitors at different rotations are simulated, suggesting the feasibility and effectiveness of the proposed capacitive detection method. The problem of detecting the micro-clearance in spherical joints, for which capacitive sensors are a very interesting solution, is also considered [4]. Five error sources of spherical capacitive sensors are examined, and their mathematical models are deduced and validated by simulation.…”