Vibration modelling analysis of defective parallel robots as machine tools for aerospace parts machining

The strict machining accuracy and surface finish requirements of manufactured products for aerospace parts make it particularly crucial to analyse the vibration performance of parallel robots as machining tools, which directly affects both of these factors. In this paper, a vibration modelling analysis for parallel robots with fewer-DOFs called defective parallel robots is presented, and the effects of four vibration models are also studied. The traditional spring-damping or elastic vibration models of two systems are presented, and the corresponding uncertain vibration systems are developed by considering the effects of gravity and the uncertain joint clearances. Taking a drilling defective parallel robot as an application example, four vibration models are derived, and the differences in natural frequency and vibration response are explored in numerical and experiment comparisons. The results shows that an uncertain system with six DOFs is closer to the experimental result (approximately 75.49%) than an elastic system (approximately 62.39%), which means that the accuracy has increased by 13.1%. The results of this paper reveal some of the reasons for the performance errors of the different vibration models for defective parallel robots, and the findings of this paper can provide a reference for the simplification and optimization of theoretical vibration models that ignore secondary factors.