Elastic error analysis for a hybrid polishing robot considering branch-chain layout and gravity field

In examining the elastic error of parallel/hybrid robots, especially those with a horizontal layout, both external loads on the endpoint and the gravity field of components are crucial. This paper focuses on a 5-DOF large optical mirror polishing robot and divides it into serial and parallel systems to analyze the mapping between joint force and external load under gravity. Based on small deformation superposition and virtual work principle, an elastic stiffness model is built. The overall static stiffness model of the hybrid polishing robot (HPR) is obtained by superimposing the errors of the serial and parallel systems. This study analyzes the impact of branch-chain layout on HPR end elasticity error and its distribution in the workspace with gravity. Results show the HPR has the greatest resistance to the gravity field and external loads with fully symmetrical active branch-chains, and the elastic error of the HPR changes continuously with the robot motion parameters and demonstrates either symmetrical or anti-symmetrical distribution characteristics. Furthermore, the analysis of elastic error can precisely clarify how the gravity field and branch-chain layout affect the service performance of the HPR, and lay a foundation for enhancing processing accuracy and optimizing structural parameters.