Kinematic optimization of a spherical mechanism for a minimally invasive surgical robot

Advances in surgical technology allow physicians to more effectively provide care to their patients. Minimally invasive surgery (MIS) has revolutionized the way a significant number of procedures are performed. Recent advances in technology have led to the fusion of MIS techniques and robotic devices; however, such systems are currently large and cumbersome. By optimizing a spherical mechanism based on in-vivo data collected during MIS procedures, this paper focuses on a bottom-up approach in developing a new class of surgical robot arms. The spherical mechanism is a rotational manipulator with U axes intersecting at the center of the sphere. Locating the rotational center of the mechanism at the NUS port makes this class of mechanism a suitable candidate for the first two links of a surgical robot for both minimally invasive and open surgery. For optimizing the mechanism structure, the forward and inverse kinematics, as well as the Jacobian matrix, were derived. Using the Jacobian, mechanism isotropy was considered as the performance metric. The dexterous workspace (DWS) is defined as a high dexterity region defined by a right circular cone with a vertex angel of 60degrees in which 95% of the tool motions are contained based on in-vivo measurements. The extended dexterous workspace (EDWS) is defined as the workspace required to reach the entire abdominal cavity with MIS instruments and defined by a cone with an eltiptical cross section created by two orthogonal vertex angels of 60degrees and 90degrees Optimization across both the DWS and a superset of the EDWS led to a mechanism configuration with link length angles of 74degrees and 60degrees that maximizes kinematic performance and compactness. The workspace of this design covers the entire EDWS and is the optimal design for the next generation of surgical manipulator. By directly applying in-vivo experimental data from MIS in order to optimize the spherical manipulator a design that maximizes performance and minimizes size has been developed. A pair of prototype manipulators will be developed based on these results.