Reduction of end effector oscillations of a parallel mechanism with modified motion profiles

This paper addresses the efficient and user-friendly application of input shaping to a nonlinear parallel mechanism, i.e. the delta robot. The objective is the reduction of residual end effector oscillations at the end of a point-to-point (PTP) movement, without a need for profound user experience. Hence, a detailed identification of system characteristics and computationally intensive model equations are avoided. Instead, configuration dependent oscillation characteristics are followed by an adaptive look-up table. The data acquisition is based on existing standard sensors, in order to avoid additional hardware investments. Uncertain natural frequencies and nonlinear oscillations are handled by the selection of a robust input shaper design with adjustable insensitivity. The performance of the method is proven by experimental validation on a delta robot, that is operated by a standard industrial PLC motion control system. The experiments show an extensive decrease of residual oscillations and, hence, reduced decay times at the end of a commanded motion. Due to the system specific motion profiles, basic motion constraints as acceleration and jerk can be significantly increased for a further reduction of motion time.