Singularity analysis and workspace optimization of a novel symmetrical 4-limb 5-DOF hybrid robot

Considering the complex structure and large size of multiple axes rotary spindle heads and the small workspace of parallel modules, a 5-degree of freedom (DOF) hybrid robot is proposed, which is a symmetrical 4-limb parallel module in series with a single axis rotary spindle head. Screw theory was used to analyze the mobility and kinematics of the hybrid mechanism. The singularity of the symmetrical 4-limb parallel module was studied, and the analysis results were verified by the Grassmann linear geometry principle. According to the singularity analysis results, the kinematic pairs’ positions of the robot were determined, so the hybrid robot model was constructed. Considering the workspace volume, and optimizing the Latin hypercube sample algorithm, a combinatorial numerical optimization algorithm is proposed to optimize dimension parameters of this hybrid robot, which combines non-linear programming by quadratic Lagrangian (NLPQL) algorithm with the optimized Latin hypercube sampling (Opt LHS) algorithm. Through this optimization algorithm, the workspace volume of the robot is increased by 1.93 times. The research method in this paper is also suitable for the analysis and optimization of other hybrid robots.