Coupling Motion Characteristics Analysis of a 2-DOF Cable-Driven Parallel Four-Linkage Mechanism

Owing to the motor indirectly driving the joint, the kinematic characteristics of the cable-driven mechanism are different from those of the motor directly driven mechanism. This study presents the coupling motion characteristics and the corresponding analysis of cable driving forces of a 2-DOF cable-driven parallel four-linkage mechanism (CD-PFLM) comprising two motors. The structure and three coupled motion phenomena are illustrated. The equivalent joint-driven and two quasi-static motion models are established in the case where one or two cable driving forces drive the 2-DOF CD-PFLM. Moreover, three quasi-static kinematic modes are obtained, namely, under-actuated motion mode, full-actuated motion mode, and redundant-actuated motion mode. On the basis of the three motion modes, the distributions of cable driving forces and coupled motion strategies are analyzed in two situations. Owing to the cable cannot withstand pressure, the theoretical whole workspace is divided into six regions, and the effective quasi-static motion space is not continuous and reachable in the whole workspace. The typical kinematic characteristic of the cable-driven mechanism is presented theoretically and graphically. Furthermore, three typical quasi-static coupled motion strategies and their corresponding cable driving forces are discussed. Five hypothetical quasi-static motion trajectories are designed to demonstrate the coupled motion strategies. Valid simulations are conducted to verify the accuracy of the quasi-static motion strategy. The analysis of this study can provide guidance and a theoretical reference for the motion analysis of the cable-driven mechanism and control of the cable-coupled-driven mechanism.