Research On Dynamic Control Strategies In The Cable Length Space For Cable-driven Parallel Robots

Cable-driven parallel robots(CDPRs)are a kind of special parallel robot that connects the moving platform(or End-effector)with the static platform through cables instead of rods.They have unique advantages such as large work space,small movement inertia,high load/mass ratio,low production cost and easy modularity et al.However,cable can only provide tension,and the characteristics of the cable have bring great challenges to the research of motion control of the CDPRs.This dissertation studies the dynamic control,synchronous control between cables and adaptive control for CDPRs.Under the guidance of theoretical research,experiments were performed on the CDPRs platform constructed in our laboratory.The main work of the paper is summarized as follows:(1)Considering the unidirectional force characteristic of the cable,the dynamic model of winch unit is established in the cable length space(or joint space)for a 3-DOF CDPR.Two controllers with tension compensation are proposed on the basis of the dynamic model.The asymptotic stability of the closed-loop system under the two control laws is proved by the mean-value theorem for vectorial functions and the Lyapunov method respectively.The trajectory tracking control experiments are implemented on an actual 3-DOF CDPR platform,and the experimental results indicate that the proposed two control methods can achieve high control accuracy.(2)The main challenges of CDPRs stem from the fact that cables should be in tension during motion control.Cable tension is closely related to the synchronization motion relation between cables which is often omitted in the existing controllers for CDPRs.To solve it,this dissertation proposes a synchronization controller in the cable space to realize the synchronization motion between cables,and finally increase the tracking accuracy of the moving platform.The synchronization controller is proven to guarantee asymptotic convergence to zero of both tracking error and synchronization error by using Lyapunov method.The trajectory tracking experiments are implemented on a self-built CDPR,the experimental results indicate that,the tracking error of the moving platform and the synchronization error between cables decrease greatly by using the synchronization controllers.(3)Aiming at the uncertainty of the winches dynamic model parameters,a adaptive controller is proposed,and the convergence of tracking error is proved by the Lyapunov method.Finally,the adaptive controller is used for trajectory tracking control of the CDPR.An adaptive synchronization control scheme is proposed by combining the adaptive control and synchronization control in the cable length space.The adaptive control of dynamic model parameters can improve the trajectory tracking accuracy,and the synchronous movement between the cables is improved through the synchronization control.The asymptotic stability of the closed-loop system is strictly proved by using Lyapunov method and Barbalat Lemma,the convergence of the trajectory tracking error and synchronization error is analyzed.The experimental results of the trajectory tracking are compared with the experimental results of the adaptive controller.