Abstract：The position and orientation precision is an important index of the mechanism, and it is a difficult issue in parallel mechanism analysis. Aiming at the problem of accuracy decreasing resulting from neglecting the higher-order terms in error analysis of the 3-RSS/S parallel mechanism, the numerical method is proposed to analyze the position and orientation error. Firstly, the input parameters of the mechanism are computed by using the error-free dimension parameters through inverse kinematic calculation based on the inverse kinematics model, and the actual position and orientation values of the moving platform are calculated based on the nonlinear forward kinematics model with the iterative initial given pose value, then the pose errors can be computed.Secondly, the parameter errors are randomly generated by using the Monte Carlo method based on the specific law of the error source, and then the distribution law of the position and orientation error is gotten. Lastly, the distribution law of the position and orientation error in the whole working space is computed by going through the whole working space. The numerical method is verified by the three-dimensional modeling method, and the effectiveness and feasibility of the proposed method is verified through the numerical computation examples.The study lays a foundation for accuracy research of the 3-RSS/S parallel mechanism.

Keyword：3-RSS/S parallel mechanism;position and orientation error;forward kinematics solution;numerical method;