Vibration-Generation Mechanism and Reduction Method in Linear Iron-Cored Permanent-Magnet Synchronous Motors at Stationary State

This article presents the theoretical studies and experimental validation of the vibration-generation mechanism and reduction method in linear iron-cored permanent-magnet (PM) motors at stationary state. While motor noise and vibration during moving operations have been extensively studied, such vibration issue at stationary state has been relatively less explored even though it can be critically problematic for high-precision applications where strict standstill of a motor is demanded. We identify a discrete position feedback in a servo control loop as a major culprit of the stationary-state motor vibration, and investigate the vibration-generation mechanism analytically and experimentally. Closed-loop dynamics related to such undesired vibration is analyzed by modeling a position-controlled linear iron-cored PM motor with a discrete encoder feedback. The analyzed model suggests that the dominant vibration frequency is determined by the control parameters regardless of the encoder quantization, while the corresponding vibration amplitude increases solely by the encoder quantization step size. Giving a standstill command to the linear motor stage testbed position controlled with different quantization step sizes, we have confirmed that the analyzed model consists of the experimental results as well as the simulated results. Understanding the vibration-generation mechanism of linear iron-cored PM motors, we also present a reduction method of such stationary-state motor vibration by a programmable-resolution incremental encoder. Using our method, we can reduce the motor vibration significantly while overcoming the speed limit of general quadrature encoders, providing a practicalsolution to various industrial applications that require both high-throughput and high-precision performance.