Design of a spherical parallel mechanism with controllable center of rotation using a spherical reconfiguration linkage

It is well known that Remote Center of the motion (RCM) mechanisms are highly suitable for many medical applications. While it is sometimes preferable that the mechanism can control their Center of Rotation (CoR), most RCM mechanisms do not have this possibility without being mounted on large and heavy translational platforms. By using a new concept of Spherical Reconfigurable Linkage (SRL), the present study offers an alternative solution. These new linkages are designed to control their radius and they are connected to form an RCM mechanism with controllable CoR. The newly mounted mechanism now has two linear Degrees of Freedom (DoF) for the displacement of its CoR in addition to its two angular DoF. The linear kinematic model is derived along with the angular kinematic one while taking into account the reconfiguration of the SRL. The velocity model is calculated and all singular configurations are identified. The mechanism performances in terms of workspace and kinematic performances are is also assessed. Finally, motion capture experiments on a prototype validated the models.