Positioning error improvement based on ultrasonic oscillation for a linear motion rolling bearing during sinusoidal motion

Friction can be a major disturbance to precision positioning. This study presents a method for improving positioning error in a linear motion rolling bearing based on ultrasonic oscillations. Experiments were conducted in which a single-axis linear motion rolling bearing was driven in a sinusoidal motion to simulate circular motion. Two ultrasonic actuators excited both the rail and the carriage of the guide to create relative displacements between raceways and rolling elements. The carriage of the linear motion rolling bearing was driven by a frictionless voice coil motor (VCM). The displacement of the carriage and the friction force were measured by a springless linear encoder and the VCM's current, respectively. The early stages of the experiments focused on several oscillating patterns, and their consequent impacts on positioning error during sinusoidal motion were investigated. Finally, the oscillating pattern that maximally improved the positioning error was proposed and tested. By applying the proposed pattern, the maximum displacement error, exhibited just after velocity reversal, was reduced by approximately 40%, while the average error was reduced by 26%.