Wrench Feasibility and Workspace Expansion of Planar Cable-Driven Parallel Robots by a Novel Passive Counterbalancing Mechanism

Abstract

This article focuses on the essential limitations of planar point-mass cable-driven parallel robots (CDPRs) in covering all poses of their footprint, which results in concave-shape static workspaces (SW) and also providing a zero force level on the borders of such a SW. Accordingly, a novel passive counterbalancing mechanism is proposed which not only expands SW to fully cover the footprint but also enables CDPR's platform to balance a desired minimum force magnitude in any arbitrary direction all over the SW. Maximizing such force magnitude is defined as an optimization problem which is used to find the optimal values of the proposed mechanism's design parameters. By comparing the SW of different CDPRs with and without the proposed mechanism, effectiveness of the proposed approach is demonstrated. In some examples, it is shown that the effects of the proposed method on the SW size increment is more than doubling the size and number of actuators. Finally, two experimental setups are presented and tested, where effectiveness of the proposed approach in covering the CDPRs’ footprint and also providing the desired minimum force level over the SW are demonstrated.