A 6-DOF Double-layer Programmable Remote Center of Motion Robot for Vitreoretinal Surgery

During vitreoretinal surgery, surgeons are required to precisely manipulate surgical tools within a confined workspace of an eye, which is roughly 2.5 cm spherical in shape. Because the surgical view can only be obtained by a microscope placed above the eyeball through the pupil, the eyeball needs to be moved or rotated during the operation to see a larger portion of the retina. At this point, general Remote Center of Motion (RCM) mechanisms require additional actuators or manual modification. On the other hand, a programmable RCM mechanism can reduce surgery time without a physical alignment procedure. This study introduces a novel six-degree-of-freedom (DoF) programmable RCM mechanism capable of generating the RCM at random positions in 3D space. Our approach combines two planar 5-bar linkage mechanisms placed in parallel, creating a double-layered configuration to establish the programmable RCM mechanism. We optimized the workspace of each planar mechanism to a customized workspace for a general eyeball model using genetic algorithms, focusing on maximizing the manipulability of the target workspace. The Phantom Omni device was utilized as a remote controller to remotely control the proposed mechanism in a transparent eyeball model with a diameter of 4 cm. Evaluation of the functionality of the programmable RCM mechanism at various RCM points showed that the overall error was less than 1 millimeter. The repeatability of the mechanism was tested and showed an accuracy of about 127 micrometers.