Design of double parallelogram remote-center-of-motion mechanisms

The double parallelogram type of remote center of motion (RCM) mechanisms is generally used as wrist module in minimally invasive surgery (MIS) assisted robots, which can provide a fixed entry point during operation process, enhance safety and quality of the surgery, and give facilities for surgeons. With type synthesis, 10 types of double parallelogram RCM mechanisms are enumerated. By making some links crooked, the virtual center can be arranged properly, which also makes the arrangements of end-effector and motor more convenient. In order to design a double parallelogram RCM mechanism, six independent parameters are needed. The forces and structure stiffness of linkage are analyzed to assist in determining sectional sizes of links. The driven moment is estimated to select a right motor. The analysis shows that a double parallelogram RCM mechanism can be balanced by one counterweight. At last, an example is given to illuminate the mechanism's feasibility and validity.