Vibration Suppression of CDPRs Based on Differential Flatness

Cable-Driven Parallel Robots (CDPRs) are well adaptable to various environment and are energy effective system since they use cables as actuators unlike conventional robots. However, a cable can generate only tensile force; therefore, it is necessary for its controller to maintain a positive tension all the time. A cable has elasticity and may have nonlinear features such as nonlinear stiffness, hysteresis, creep, etc. The elasticity of cables particularly may cause undesirable vibrations of the end effector of a CDPR. In this paper, we propose a method to generate the desired trajectory of the motors of a CDPR to suppress vibration of the end-effector based on differential flatness and also proposes how the linear programming method is used to maintain at least a minimum positive tension at each cable. These methods assure that at least a minimum positive tension is generated at each cable and that vibration, particularly residual vibration, is suppressed even with a simple PD controller to track the designed trajectory. The effectiveness of the proposed methods was confirmed not only in computer simulations but also in experiments with a 2-D planar CDPR robot.