Modal Control Design of Configuration-Dependent Linkage Vibration in a Parallel Robot Through Experimental Identification

Modal control algorithms have been widely used in suppressing structural vibration, where vibration characteristics are linear and constant. This paper presents experimental work demonstrating the application of modal control to closed-loop mechanisms, where flexible deformation is coupled with nonlinear rigid body motion. A PRR experimental planar parallel robot is used as the test platform. This lightweight planar parallel manipulator is designed to improve operational speed of "pick-and-place" processes and implement a "smart parallel manipulator" through the integration of a parallel mechanism architecture and active control of linkage vibration using lead zirconate titanate (PZT) transducers. Boundary conditions and mode shapes of intermediate linkage are not conventional due to the fact that the linkages undergo constrained rigid body motion. Experimental modal analysis (EMA) is used to determine the boundary conditions of flexible linkages. However, it is observed that linkage vibration exhibits configuration-dependency. Based on experimental observations, an assumption is taken to simplify the transfer function from the motor input to linkage vibration. Based on this simplification, a modal controller is designed and implemented. Experimental results demonstrate dramatic linkage vibration reduction