Abstract
To overcome the problems of structural parametric uncertainty and cable transmission model complexity, a nonlinear controller based on time-delay estimation and fuzzy self-tuning is proposed. The unknown dynamics and disturbances are estimated by time delaying the state of motion immediately before. The control gains are self-tuned by a fuzzy controller, which can reduce the errors caused by system’s uncertainties and external disturbances. Compared with the conventional Proportional-derivative (PD) and time-delay control, the result shows that the proposed control scheme based on time-delay estimation can improve the joint trajectory tracking accuracy of cable-driven robot by significantly reducing the control gains. With the PD gains self-tuned by fuzzy strategy, the mean square errors of trajectory tracking are decreased approximately by 5–20% more than the conventional time-delay control with constant gains. In addition, the experimental result shows that the proposed method has an effective inhibitory effect on dead zone in cable-driven joints. Experiment performed on position tracking control of a 2-degree-of-freedom cable-driven robot is presented to illustrate that the controller has the advantages of simple and reliable structure, model-free, strong robustness, and high tracking accuracy.
Highlights
Cable-driven robot usually mounts motor, reducer, and other transmission mechanisms on the base or away from joints, and the motion and force are transmitted by cables between actuator and joint.[1]
A nonlinear control technique based on time-delay estimation (TDE) with fuzzy self-tuning is proposed, which can estimate the unknown dynamics parameters by the last motion state, and reduce the errors caused by system uncertainties and external disturbances
The calculation of the complex dynamics for cable-driven robot can be avoided. It has the advantages of high trajectory tracking accuracy and strong robustness
Summary
Cable-driven robot usually mounts motor, reducer, and other transmission mechanisms on the base or away from joints, and the motion and force are transmitted by cables between actuator and joint.[1]. To solve the complexity of dynamic modeling and external disturbances, time-delay estimation (TDE) technique provides a good control method.[12,13] The core of TDE is that the system dynamics at the current moment can be estimated by the last motion state of the closed-loop system, so as to compensate for the various uncertainties and disturbances.[14,15] It is a model-free control algorithm with simple structure and fast calculation to achieve good effects, and it has been widely applied in various fields.[16,17,18] Many TDE-based sliding mode controllers have been proposed to perform high-precision and high-speed control with fast-tracking convergence and smooth motor inputs.[19,20,21,22] To overcome slow data acquisition rate of an autonomous underwater vehicle, an integral sliding mode controller with conventional TDC was used to improve the performance. A model-free method based on TDE combined with fuzzy strategy should be developed to realize high-precision tracking control of cable-driven robot
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