Experimental Modal Analysis for a 3-DOF PKM Module

Abstract

To reveal the modal properties of a 3-dof PKM module, a wire-frame model is proposed and relative experimental modal test is conducted. The lower orders of natural frequencies, damping ratios are obtained and corresponding mode shapes are classified. The modal analysis reveals two categories of vibration modes for the PKM module. The first to the third orders of modes correspond to the overall vibration of the module while the fourth to the sixth orders of modes corresponding to pitch and yaw as well as their combination of the moving platform. The overall vibration modes of the module are expected to be eliminated through bolt-connection of the base and fixed frame. The moving platform vibration modes, however, rely on the weak stiffness of spherical joints. Thus, desirable dynamic performance of the PKM module demands delicate design for the spherical joint with high stiffness.