Performance Evaluation of the 3UPS-PRU Robot in the Workspace and Increasing Its Degrees of Freedom by Structural Modification

Parallel robots consist of a moving platform connected to a fixed base through multiple links arranged in parallel. The closed-chain kinematics of parallel robots result in greater structural rigidity and stiffness, leading to higher accuracy compared to open-chain (serial) robots. In this study, the structure of the 3UPS-PRU robot is first analyzed, followed by the derivation of its inverse kinematics. After establishing the kinematic equations, the eigenvalues of the Jacobian matrix are computed, and the robot's condition number is evaluated at different points within the workspace. The distribution of the condition number throughout the workspace is then analyzed. Furthermore, investigations reveal that variations in height lead to changes in the global condition number, affecting the overall performance of the mechanism. Finally, by adding a universal joint at the connection between the central link and the fixed base of the 3UPS-PRU robot, a new structure, termed 3UPS-UPRU, is introduced, which increases the robot’s degrees of freedom. To control the additional degrees of freedom, a geared universal joint (planetary gear) is designed and implemented.