Singularity analysis of a new spatial rotation 3-DOFs parallel manipulator based on actuating performance index

In this paper, singular configurations of a new spatial rotation 4-SPS-1-S parallel manipulator are examined. The 4-SPS-S parallel manipulator has 3 purely rotational degrees of freedom in the space, and can perform spatial roll, pitch and yaw rotation motions. It possesses high load capacity, stiffness and stability. Inverse position analysis and velocity mapping equations of the mechanism are presented, and then Jacobian matrices are built. Transformation from output velocity to input velocity is explored and computed. The square root of determinant of J^TJ matrix is adopted as an actuating performance index, serving as a criteria to judge singularities of the mechanism. A numerical example is presented to illustrate the distribution of actuating performance indexes across the workspace followed by singularity analysis. The paper provides crucial information for the design of this type of parallel manipulator.