Type Synthesis of 1R1T Remote Center of Motion Mechanisms Based on Pantograph Mechanisms

The remote center of motion (RCM) mechanism is an important component of a minimally invasive surgery (MIS) robot. The feature of the RCM mechanism is that the output link can rotate around a fixed point and translate along an axis which passes the point; however, there is no revolute joint at the fixed point. The 3R1T RCM mechanism, which meets all the degrees-of-freedom (DOF) requirements of arbitrary MIS tools, can be assembled through many methods. An effective method is combining a planar closed-loop 1R1T RCM mechanism and two revolute joints. In this paper, we present an approach to construct 1R1T RCM mechanisms from pantograph mechanisms. First, pantograph mechanisms are divided into seven classifications according to the geometric transformations they represent. The concept of rigid motion tracking mechanism (RMTM) is proposed by combining two equivalent pantograph mechanisms. Then, a novel type synthesis method for 1R1T RCM mechanisms is discussed in detail, and it shows that a 1R1T RCM mechanism can be constructed by assembling an RMTM and a 1R1T mechanism. By this method, several examples are constructed.