Sliding Mode Control of Under-Constrained Cable Driven Parallel Robots

Abstract

Under-constrained cable driven parallel robots (CDPRs) have many advantages in comparison with conventional parallel robots and link-based manipulators in terms of simple structure, large workspace and low inertia. Its end-effector hangs with less than six cables; therefore, under-constrained CDPRs have uncontrollable degrees of freedom. Due to this property, unwanted swaying motion and oscillations occur and tracking performance is diminished. In this paper, a controller to improve tracking performance of under-constrained CDPRs with n cables is proposed based on sliding mode control and adaptive control. In order to track well given trajectory at the under-constrained CDPRs, a hierarchical sliding surface is used. In addition, it is proposed that the algorithm which guarantee pulling force since cables cannot deliver only pushing force. And stability is guaranteed by adding adaptive control scheme. The effectiveness of the proposed controller was verified in computer simulations.