Experimental Analysis of Type II Singularities and Assembly Change Points in a 3UPS+RPU Parallel Robot

Moreover, PRs have other advantages over their serial counterparts, such as lower weight, higher working speed with high precision, and lower power consumption [1,2]. These advantages, mainly due to the closed kinematic chain architecture, are key aspects that have increased the interest in studying their use in the academic, industrial, and robotics service fields over the last three decades. However, the PR architecture reduces not only the size of the robot workspace but also its kinematic performance, owing to the possible presence of singularities within the workspace. Initially, Gosselin and Angeles [3] studied the singularities of a PR using Jacobian matrices obtained from constraint equations, and classified them into i) inverse kinematic or Type I singularity, where the robot loses at least one degree of freedom (DOF), and ii) Forward Kinematic or Type II singularity, where the PR gains at least one DOF. In particular, Type II singularities could be critical because the mobile platform at the singularity is unable to bear the external forces despite having all the actuators locked (losing control of the PR motion).