Design of parallel multiple tuned mass dampers for the vibration suppression of a parallel machining robot

Abstract

Parallel machining robots have the potentials of high precision and high flexibility. However, their pose-dependent vibration characteristics may cause accuracy problems during machining, which poses a great challenge to the vibration suppression. Multiple tuned mass dampers (MTMDs) are widely used to suppress the vibration, owing to their significant vibration suppressing effect, great robustness, and compact structure. In this paper, a parallel MTMD system is designed to mitigate the forced vibration of a parallel machining robot. The elasto-dynamic model of the parallel robot is established to identify the modes and natural frequencies of the robot, and the results show that the frequency of the resonant mode varies from 91.0 Hz to 128.1 Hz. Based on the structure and natural frequency scope of the robot, the MTMD system is designed to be a parallel configuration in two directions and the impedance model of the MTMD system is built. Considering the pose-dependent dynamics and compact inner space of parallel robots, a multi-objective optimization method for varied vibration characteristics is proposed based on the impedance model. In this method, the suppression amplitude, robustness, and compactness are the main concerns. In the structural design, small-sized polymer material springs and viscous fluid damping inside the mass blocks are used to compose the MTMD system. Therefore, wide-band vibration suppression is realized in narrow spaces. Finally, verification experiments are performed. Modal tests show that the amplitudes of the resonant modes are decreased by 38.8% along the X axis and 40.7% along the Y axis. Machining tests show that a 20%-30% reduction of the vibration in the feed direction, a 40%-50% reduction in the radial direction, a 48%-55% harmonics reduction at the natural frequency are achieved. Precise surface measurements show a 32% reduction in waviness and a 17% reduction in roughness. This study provides a new structural design and optimization method of MTMDs adapted to vibration suppression for parallel machining robots.