Use of a Reconfigurable Linkage for the Control of Center of Rotation: Application to a 3T3R Spherical Parallel Mechanism

Abstract Remote Center of Motion (RCM) architectures are known to rotate their end effector around a Center of Rotation (CoR). This characteristic makes them very suitable in the medical field due the increasing reliance on Minimally Invasive practices. In many applications, adjusting the position of the CoR is desirable, if not mandatory. A large number of RCM mechanisms have been designed in the recent years, but very few of them are capable of controlling the position of their CoR without using a large translational platform. The present study proposes a method to transform classical spherical mechanisms into reconfigurable ones to allow the direct control of their CoR position. A new Spherical Reconfigurable Linkage (SRL) is designed to change its radius and change the location of its center. By substituting them to classical spherical links with a specific assembly, new mechanisms are obtained with additional linear mobility for their CoR. This method is applied to the 3-RRR Spherical Parallel Mechanism, which classically generates an RCM with a 3R motion. The new 3-URRRP mechanism with SRL can now achieve a 3T3R motion and control its CoR through the reconfiguration of its linkages. Its inverse kinematic and velocity models are derived and its singular configurations are identified. A series of simulation are carried to evaluate its performance in terms of workspace and dexterity.