Trajectory Planning of the Exit Point for a Cable-Driven Parallel Mechanism by Considering the Homogeneity of Tension Variation

Considering the uniformity of cable tension variation, in this paper, the trajectory planning problem of the exit point for a continuously reconfigurable four-cable-driven two-degrees-of-freedom (DOF) parallel mechanism was studied. Furthermore, an improved quadratic programming model-based trajectory planning method is proposed, which greatly reduces the change in cable tension and can be used to solve the problem of excessive cable tension change when the existing mechanism moves on the moving platform. First, the structural characteristics of the parallel mechanism with a fixed exit point were analyzed, and the static model was established. Considering the cable length and tension constraints, the feasible workspace of the mechanism force was solved. Then, based on the dynamic modeling, an improved quadratic programming model was used to solve the cable tension values under the typical trajectory in the force-feasible workspace. Finally, considering the influence of structural parameters on the change in cable tension, the improved quadratic programming model was transformed, and an exit point trajectory planning model was proposed. The uniform change in cable tension was realized by continuously changing the exit point position. The results show that the cable tension can change uniformly in a very small range by planning the trajectory of the exit point, and the stability of the moving platform movement is guaranteed to the greatest extent.