A singularity improvement method for 4-DOF proper-constraint parallel mechanism

To address the singularity issues in 4-degree-of-freedom (4-DOF) proper-constraint parallel mechanism, a novel method for singularity improvement was designed. The singularity of the traditional 4-DOF proper-constraint parallel mechanism was analyzed using Grassmann's linear geometry, and four improved structural schemes were proposed. The complete Jacobian matrix of the improved structures was established based on screw theory, and the motion performance of the improved structures was analyzed using the condition number metric. A comprehensive optimization objective function, reduced in dimensionality through principal component analysis, was employed, and the dimensions of the improved structures were optimized using a single-objective genetic algorithm. The results show that the condition number metric improved by 90.71%, the workspace volume increased by 29.63%, and the manipulability metric improved by 85.01% compared to the pre-optimization values. Additionally, the distributions of the condition number and manipulability metrics were stable, with no abrupt changes. The final optimized values were c i =[0.0296,0.0309,0.0586,0.0571] T . This method provides theoretical support for the singularity optimization of 4-DOF proper-constraint parallel mechanism.