Design and Kinematic Optimization of a Two Degrees-of-Freedom Planar Remote Center of Motion Mechanism for Minimally Invasive Surgery Manipulators

Abstract

Minimally invasive surgery (MIS) requires four degrees-of-freedom (DOFs) (pitch, translation, yaw, and roll) at the incision point, but the widely used planar remote center of motion (RCM) mechanisms only provide one degree-of-freedom. The remaining three DOFs are achieved through external means (such as cable-pulleys or actuators mounted directly on the distal-end) which adversely affect the performance and design complexity of a surgical manipulator. This paper presents a new RCM mechanism which provides the two most important DOFs (pitch and translation) by virtue of its mechanical design. Kinematics of the new mechanism is developed and its singularities are analyzed. To achieve maximum performance in the desired workspace region, an optimal configuration is also evaluated. The design is optimized to yield maximum manipulability and tool translation with smallest size of the mechanism. Unlike the traditional planar RCM mechanisms, the proposed design does not rely on external means to achieve translation DOF, and therefore, offers potential advantages. The mechanism can be a suitable choice for surgical applications demanding a compact distal-end or requiring multiple manipulators to operate in close proximity.