Abstract
This paper is devoted to improving the synchronization and robustness performance of a parallel robot used for automobile electro-coating conveying via a novel synchronous robust sliding mode control (SMC). A sliding surface is designed based on a composite error, which is composed of the tracking error of each joint and the synchronization errors among the joints. By incorporating a nonlinear disturbance observer into the finite-time SMC based on the composite error, the synchronous robust SMC of the parallel robot is realized. The finite-time Lyapunov stability of the sliding variable and the asymptotic convergence of the tracking error and synchronization error have been proved theoretically. The lumped disturbance in the system is estimated by the proposed scheme, and restriction on the change rate of the lumped disturbance has been relaxed. Due to the feedforward compensation with the disturbance estimation value, the switching gain of SMC required is merely larger than the upper bound of the disturbance estimation error, rather than the upper bound of the disturbance, resulting in chattering attenuation. Finally, the numerical simulation and experiment on the prototype system of the parallel robot are implemented to validate the effectiveness of the synchronous robust SMC.
Highlights
As a pivotal element in the car body pretreatment process, an advanced electro-coating conveying robot can improve the quality of car body electrophoretic coating and the manufacturing efficiency
The main contributions are exhibited as following: 1) Due to the feedforward compensation with the disturbance estimation value, the switching gain of sliding mode control (SMC) required is merely larger than the upper bound of the disturbance estimation error, instead of the upper bound of the disturbance, the chattering of synchronous robust SMC (SRSMC) is suppressed for better implementation; 2) The change rate of the lumped disturbance term is only assumed to be bounded, rather than approximate to zero, relaxing the constraint on the lumped disturbance in system; 3) The asymptotic convergence of the tracking error and synchronization error has been theoretically proved, the synchronization performance among the joints is improved; 4) The finite time stability of the sliding variable is ensured via Lyapunov theory
Remark 6: An observation of Theorem 3 reveals that the switching gain K 1 in the SRSMC law (21) should be larger than the upper bound of disturbance estimation error
Summary
As a pivotal element in the car body pretreatment process, an advanced electro-coating conveying robot can improve the quality of car body electrophoretic coating and the manufacturing efficiency. In order to achieve the high performance control of the parallel robot, the problems of improving the robustness and synchronization performance of the system are considered in the paper. From the multi-branch closed-chain characteristic of the parallel robot and the actual operating environment, the mathematical model is complex and difficult to establish precisely, the modeling errors are inevitable and the external disturbance and the friction exist as well. These uncertainties may result in inaccuracy in the movement of the joints and end effector, and even instability of the overall system.
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