A novel impact-based dynamic motion planning of parallel kinematic forming robot under heavy load

Abstract

Dynamic accuracy is significant for industrial robot in application. To realize this, many methods such as increasing damping, changing materials, and optimizing structures are developed and applied to the robots with relative low load (thousands of Newtons). However, for the application of heavy load (millions of Newtons), the dynamic error generation mechanism is different, these methods are neither suitable nor economic. To address this issue, the dynamic error generation mechanism of industrial robots under heavy load is revealed and a novel impact-based motion planning method is proposed.

Take parallel kinematic forming robot (PKFR) with load of 6MN as an example, the rigid-flexible coupling dynamic model considering joint clearance is first established and experimentally validated by a 70 % prediction accuracy. The dynamic error reaches up to 3.26 mm in position and 5.5mrad in angle. The impact forces are up to 10–20 times of driving force and it occur 12 times in a working cycle when one of the driving force approaches to zero. Further, the dynamic error generation mechanism is revealed, namely dynamic error of platform is mainly generated by the vibration impact sourced from the high joint clearance and the high variation of drive velocity. Thus, a novel impact-based dynamic motion planning method is proposed through reduction of the slider velocity at moment of impact. Using this method, the dynamic error is greatly reduced (42.82 % of position error and 34.82 % of angular error) in theory. Finally, an aircraft window frame is formed, showing a 36.53 % reduction in outer thickness error and a 33.65 % reduction in inner thickness error by using the proposed method. This method provides a new approach to reduce the dynamic error of industrial robots under heavy load and has high application potential due to its economic benefits without change of mechanical system.