Type Synthesis of Novel Remote-Center-of-Motion Parallel Mechanisms

Abstract

Abstract. Parallel mechanisms (PMs) with remote center of motion (RCM) are indispensable for minimally invasive surgery (MIS), as they minimize patient trauma, yet their design is fundamentally limited by strict geometric condition. To overcome this limitation, this article proposes a unified topology design and type synthesis framework for RCM and V-RCM PMs based on degree-of-freedom (DOF) mutation inspired by arthropod metamorphosis. By introducing extra mutated closed loop (EMC) and coupling them with a basic closed loop, DOF mutation is realized by replacing original output component with another component of EMC. Two topological types of DOF mutation are formulated according to the coupling relationship, and the constraint and motion characteristics are systematically analyzed based on screw theory. Rhombic and parallelogram EMCs are employed to realize various RCM. It is shown that constraint forces are no longer required to intersect and that the RCM point becomes independent of joint axes. Furthermore, leveraging the motion-mapping property of the parallelogram EMC, the proposed method is extended to derive the characteristics of different V-RCM with variable RCM points. The type synthesis framework for RCM and V-RCM PMs is established according to constraint screw principles. Multiple novel RCM and nine types of V-RCM PMs are synthesized. A representative 2R1T-RCM PM is analyzed to demonstrate the joint-independent RCM point and favorable motion/force transmission performance. The proposed approach provides a systematic and effective solution for the design and synthesis of RCM and V-RCM PMs.