Singularity analysis and detection of 6-UCU parallel manipulator

• The singularities of the 6-UCU parallel manipulator caused by the active and passive joints are analyzed.
• Two singularities of the 6-UCU parallel manipulator caused by the passive joints are found.
• Singularity detection procedures of the 6-UCU parallel manipulator are proposed in this paper.
• The effectivenesses of the proposed singularity detection procedures are confirmed by studying cases.

6-UCU kind Gough–Stewart platform (GSP) has been used extensively in practice. The singularity of GSP has been studied by many scholars, but their works mainly focused on finding the methods to divide the cases of singularity or searching the solutions with Jacobian matrices. On the other hand, this paper studies the singularities of 6-UCU parallel manipulator caused by not only the active joints but also passive universal joints. Two types of singularity are derived based on a degree of freedom method by using screw theory. Singularity detection is essential to certify the absence of singularity within a prescribed workspace or a reachable workspace for a practical use of the 6-UCU parallel manipulator. Algorithms are proposed by using evolutionary strategy to detect the singularity in the desired or reachable workspace of the 6-UCU parallel manipulator. Case studies are presented to demonstrate the effectiveness of the proposed singularity detection methods.