Spherical wrist dimensional synthesis adapted for tool-guidance medical robots

The objective of this paper is to present the dimensional synthesis of serial and parallel spherical wrists, an important step in the design process of medical robots. This step is carried out to obtain optimal dimensions of tool-guidance medical robots. In this goal, we have first studied the specifications of two robots with different medical applications: one for minimally invasive surgery and one for tele-echography examination. Then, we have established that the medical needs expressed by the expert were very different but the specifications in robotic terms have a lot of common points (kinematics, workspace, bulkiness). Both types of robots need a mobility of three rotations around a fixed point (trocar incision or probe contact point on the patient’s skin). So a spherical wrist structure is adapted to their needs. An important constraint related to medical applications is that the robot must be compact in order to not obstruct or collide with its environment (medical personnel or patient). We perform dimensional synthesis allowing determination of mechanism dimensions for a spherical wrist, serial and parallel for a tele-echography robot, and serial for the minimally invasive surgery robot. We use multi-criteria optimization methods minimizing a cost function to obtain both good kinematic performance and compactness for the structure. The differences between the presented studies are in the choice of design criteria describing the performance and the constraints of the robot. These parameters must faithfully represent the specifications of the robot so that its performance can respond to the medical requirements. We show, here, the different methods used for optimizing the chosen kinematic structure for the particular medical application. These studies lead to prototypes which are validated by medical experiments. This process of dimensional synthesis will be used to other medical applications with different sets of specified constraints.