Research On Dynamic Control Of Cable-Driven Parallel Robots With Model Uncertainties

By innovating the structure of traditional parallel robots,cable-driven parallel robots(CDPRs)are a new class of robots which utilize flexible cables instead of rigid links.Being beneficial from the specific structure,CDPRs own many significant advantages,including high speed,large workspace,high load capacity and easy to be modular.However,because of the structural characteristics of the cable-driven form,the control of CDPRs is always faced with the constraint that the cable tension must be kept positive and the challenge of model uncertainties.To address these problems,the synchronization motion between cables is combined with the advanced control schemes so that the novel control strategies are designed to achieve better control performance.Moreover,based on the theory,simulations and experiments are carried out.The main contents of the dissertation are as follows:1)By integrating the cable synchronization idea with the fast terminal sliding mode(FTSM),a novel FTSM control with synchronization error(FTSMC-SE)is proposed.Because of the advantage of the synchronization motion and the finite-time convergence property of the FTSM,the tracking accuracy of CDPRs can be improved from both synchronization and convergence speed in the FTSMC-SE strategy.The Lyapunov theory is utilized to prove the system stability with the error convergence,and the trajectory tracking simulations and experiments are implemented on a 6-DOF CDPR.System simulations are compared with the synchronization control(SC)strategy and the results indicate that the faster error convergence can be acquired by using the proposed FTSMC-SE strategy.Moreover,in comparison with the augmented proportional derivative(APD)strategy and the SC strategy in experiments,the results show higher-precision tracking accuracy of the FTSMC-SE strategy.2)Based on the topology of CDPRs,a new synchronization scheme regarding the cable global cooperation is proposed.Meanwhile,the adaptive law is designed to achieve faster convergence of the uncertain dynamic parameters.Afterwards,a highprecision adaptive control scheme with convergence guarantee(HAC-CG)is proposed while the stability of the system and the convergence of the parameters are analyzed in detail.In addition,numerical simulations and practical experiments are carried out to verify the performance of the HAC-CG strategy.The results indicate that the HAC-CG strategy can effectively ensure the synchronization motion of all cables,significantly adapt the dynamic parameters at a faster speed,and thus eventually achieve high-precision control performance of CDPRs.3)Considering the cable elasticity,the cables can be modeled as massless linear axial springs based on the dominant dynamics.Then the system modeling is completed and the cascade controller is designed.The inner loop is the PD controller to adjust the cable lengths,while the outer loop is the second-order sliding mode controller with synchronization error which combines the cable global cooperation idea with the second-order sliding mode to improve the control accuracy and alleviate the chattering effect.The stability of the closed-loop system is proved by the singular perturbation approach.Moreover,in order to verify the performance of the proposed controller,experiments are carried out on a 6-DOF CDPR using the camera and encoders to measure.