cable-driven parallel robot

Trajectory planning in cable-driven robots is more challenging than rigid-link ones. To maintain the robot control, the cable tensions must be positive during motion. This paper presents a direct collocation approach to solve the optimal trajectory planning based on the minimization of a robot's tension and tension-rate objective functions. Besides, during robot motion, the cables must be tensile. The configuration of a cable parallel robot composed of a 3-cable and a prismatic actuator neutralizes the moving platform’s weight while improving tensionability. To generate smooth trajectories, the proposed method is compared with two standard approaches: GPOPS-II software package which uses Legendre-Gauss-Radu quadrature orthogonal collocation polynomials and direct collocation by using B-spline interpolation curves. Despite the efficiency of using B-spline functions in trajectory planning, numerical simulations demonstrate that the Hermite-Simpson direct collocation approach has a substantial benefit in the computation cost and accuracy for trajectory planning of a cable-driven parallel robot. Also, by choosing appropriate constraints and cost functions, the cable forces in the parallel robot can be well managed.

Known for their lower costs and numerous applications, cable robots are an attractive research field in robotic community. However, considering the fact that they require an accurate installation procedure and calibration routine, they have not yet found their true place in real-world applications. This paper aims to propose a new controller strategy that requires no meticulous calibration and installation procedures and can handle the uncertainties induced as a result of that. It is well known that kinematic uncertainties can lead to loose cables when one deals with a redundantly actuated robot. The control methodology presented in this paper is a simple yet powerful controller based on wave-based theory that can handle the aforementioned loosened cables. Thus, through applying this novel controller, the applications of cable robots to real-world problems has become more feasible. This paper also investigates the performance of the proposed controller and its effectiveness through some practical experiments. We observed that the‎ proposed controller outperforms conventional cascade topologies in‎ ‎terms of tracking smoothness‎.