Type Synthesis Of Parallel RCM Mechanisms And Analysis Of A Typical RCM Mechanism

Minimally invasive surgery(MIS) is one of three mainstream of medicine in 21 st century. The remote center of motion(RCM) mechanism is widely used in the MIS robot system. This paper focus on the type synthesis of different degree of freedom(DOF) RCM mechanisms and the analysis of the typical RCM mechanism 2-CRRR-CRR. The main contents are summarized as follows:To increase the diversity of RCM mechanisms. First, the legs which meet the condition that it always in motion planes are synthesized. Next, the legs are used to synthesis the different DOFs of RCM mechanisms. Some of the mechanisms have potential to be applied for robotic MIS.Since linear actuators are generally preferred in design of a parallel manipulator for higher rigidity and load capacity. So we choose the mechanism 2-CRRR-CRR to analyze it’s kinematics and performance. The screw theory is used to analyze the DOFs of the mechanism, it shows that the mechanism have two rotational and one translational DOFs. The kinematic model of the 2-CRRR-CRR mechanism is established. The inverse kinematics of the mechanism is carried out by using the closed-loop vector method. The closed-loop vector of three legs in three motion plans can be obtained, then the inverse kinematics also can be obtained.Differentiating the inverse kinematics formulation with respect to time t yields the velocity of the mechanism. By solving the corresponding matrix J and G, the inverse singularity forward singularity and combined singularity are obtained. Based on the numerical search method and excluding the singular configuration of the mechanism, the reachable workspace of the mechanism is calculated by MATLAB.The local transmission performance index(LTI) of the mechanism is analyzed. The parameters of the mechanism are optimized by using the force/motion transmission performance index LTI, which provide the foundation in the design of prototype. The control system is implemented in Lab VIEW 2011 running on a industrial personal computer.