SUMMARYThis paper deals with the analytical modeling and the analysis of the orientation error of the RAF translator due to the clearances in the joints. This model presents the orientation error as a function of the nominal pose, the external load applied to the platform, the manipulator structural parameters, and the joints clearances. Based on this model, an algorithm is developed in order to map the pose error within a desired workspace of the manipulator. It is shown that the orientation error variation depends essentially on the parallelogram configuration of the passive legs out of its plane. The orientation error magnitude is mainly caused by the parallelogram revolute joints radial clearances. Moreover, the orientation error around the z-axis presents some discontinuities due to the contact mode change of the parallelogram revolute joints.

This work deals with the estimation and the sensitivity analysis of the 3-UPU parallel robot error. Based on the Newton–Euler formalism, the robot dynamic model is given in a closed form. This model is validated by the software ADAMS. Using the interval analysis method, a new algorithm is proposed, which estimates the errors in the motion of the end-effector and the errors in the actuator forces as a function of the design parameters uncertainties. The obtained results show that the kinematic errors are minimal at the workspace center. Moreover, these errors increase as the platform moves along the vertical axis. It is also shown that kinematic errors in the actuator joints are the most influential parameters on the manipulator accuracy. Therefore, using actuators with a higher accuracy can highly reduce the errors in motion of the platform.

This paper deals with the sensitivity analysis and the prediction of the orientation error limits of a three-DoF translational parallel manipulator (3-TPM). An analytical model relating the robot accuracy to the design parameters uncertainties, the joints clearances, the nominal pose, and the external load is developed. Based on this model, an analytical sensitivity analysis is performed to show the influence of each parameter on the orientation error. An algorithm based on the interval analysis is used to predict the bounds of the translator orientation error. Using the RAF robot as an example, it is shown that the pin length of the revolute joint, the width of the parallelogram structure and the radial clearance in the revolute joints are the most influential parameters on the orientation error of the manipulator. Moreover, one of the main results of this analysis is that an increase of the tolerances on certain parameters does not necessarily lead to an increase of the orientation error of the robot, for this specific example.

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