Development of a Novel RPR-RP+3-RPS Precision Hybrid Polishing Robot

Background: With the development of smart manufacturing, virtual reality, and high-- precision technologies, there is a growing demand for ultra-precision freeform surfaces, especially in optics and aerospace. However, traditional machining methods have limitations in handling high-precision machining of complex freeform surfaces, so the need for new processing equipment is becoming increasingly urgent. Objective: A hybrid robot combining RPR-RP and 3-RPS parallel mechanisms was designed and analyzed, and it is mainly used for freeform surface ultra-precision machining. This robot aims to solve the problems of the limitations of the existing series mechanism and the parallel mechanism (such as the insufficient stiffness and accuracy of the series mechanism, and the limited working space of the parallel mechanism) and combines the advantages of the two to improve the machining accuracy and efficiency of the freeform surface. Methods: The closed-loop vector equation method was used to establish a global kinematic model of the RPR-RP+3-RPS hybrid robot. The velocity Jacobian matrix of the hybrid robot was derived using the velocity closed-loop vector equation, and the numerical analysis was carried out. Based on the velocity constraint equation and the virtual work principle, a comprehensive stiffness model is established, the stiffness changes in each degree of freedom direction in a given working space are analyzed, and the sensitive frequency range of the machine is clarified by harmonic response analysis, which effectively prevents the occurrence of resonance. Based on the principles of differential theory and differential vector method, an error model is established. Results: Through the speed performance analysis and kinematic analysis of the hybrid robot, the rationality of the structural design and the correctness of the kinematic model are verified. The error analysis results show that the rod length error is the main factor affecting the pose error of the hybrid robot. Conclusion: The newly designed RPR-RP+3-RPS hybrid polishing robot demonstrates excellent performance, effectively addressing the limitations of traditional parallel and serial mechanisms in ultra-precision machining of freeform surfaces. With its innovative design and broad application potential, a patent has been filed for this configuration.