Singularity analysis and avoidance for an SSRMS-type reconfigurable space manipulator with a non-spherical wrist and two lockable passive telescopic links

This study focuses on addressing kinematic singularity analysis and avoidance issues for a space station remote manipulator system (SSRMS)-type reconfigurable space manipulator. The manipulator is equipped with a non-spherical wrist and two lockable passive telescopic links (LPTLs), which enable it to have both active revolute and passive prismatic joints and operate in two distinct modes. To begin with the kinematic singularity analysis, the study derives the differential kinematic equations for the manipulator and identifies the dominant Jacobian matrix that causes singularities. Subsequently, an in-depth analysis of singularities from multiple perspectives is conducted. Firstly, a kinematic singularity map method is proposed to capture the distribution of singularities within the reachable workspace. Then, the influence of the two LPTLs on singularities is thoroughly examined. Finally, a new method based on the matrix rank equivalence principle is introduced to determine singularity conditions, enabling the identification of all the singular configurations for the SSRMS-type reconfigurable manipulator. Notably, this method significantly reduces computational complexity, and the singularity conditions obtained have more concise equations. For the singularity avoidance problem, a novel method is developed, which simultaneously addresses the requirements of real-time performance, high precision, and the avoidance of both kinematic singularities and joint limit constraints. Benefiting from these excellent properties, the proposed method can effectively resolve the singularity issues encountered separately by the SSRMS-type reconfigurable manipulator in its two operational modes. Several typical simulations validate the utility of all the proposed methods.