In a minimally invasive surgical (MIS) robot, the remote center of motion (RCM) mechanism is usually used to realize the constrained motion of the surgical instrument. In this paper, a novel synthesis method for planar 2-DOF RCM mechanisms is proposed based on closed-loop cable transmissions. The concept is to utilize several coupled cable transmissions to constrain an optimized serial kinematic chain. Through the analysis and determination of the transmission ratios for these cable transmissions, a class of planar 2-DOF RCM mechanisms without any active or passive translational joints is obtained, which provides large workspace and low collision risk for the MIS robots. One of the resulting mechanism is designed in detail and kinematically analyzed. To evaluate the influence of the elastic cables, a new error model for the proposed RCM mechanism is established through static analysis and cable deformation analysis. Utilizing this model, the cable-induced error distributions of the tip and the RCM point are obtained, which show that these errors are within a relatively small range. Furthermore, the prototype of the proposed mechanism is built, and the accuracy experiments are conducted.

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A multi-objective optimization method for uncertain structures is developed based on nonlinear interval number programming (NINP) method. The NINP method is employed to transform each uncertain objective function into a deterministic single-objective optimization problem. Using the constraint penalty function method, a deterministic multi-objective and non-constraint optimization problem is formulated in terms of penalty functions. Then the micro multi-objective genetic algorithm and the intergeneration projection genetic algorithm are adopted as outer layer and inner optimization operator to solve the nesting optimization problem, respectively. Finally, four numerical examples are provided to demonstrate the e ectiveness of the present method. ARTICLE HISTORY

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