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Robust Control for Uncertain Hybrid Robot with Fluid Resistance Using Unmeasured Auxiliary Variables-based Time-varying Gain Extended State Observer

Qiuyue Qin, Guoqin Gao*, Junwen Zhong, and Mengyang Ye
International Journal of Control, Automation, and Systems, vol. 20, no. 11, pp.3678-3688, 2022

Abstract : For the trajectory tracking control of uncertain hybrid robot with fluid resistance, the matched and mismatched uncertain problem is a challenge. The matched uncertainties include joint friction, modeling error and so on. And the fluid resistance may cause the time-varying discontinuous mismatched uncertainty. Thus, the unmeasured auxiliary variables-based second-order sliding mode control with time-varying gain extended state observer for the hybrid robot is proposed. By defining unmeasured auxiliary state variables, the dynamic equation of hybrid robot with mismatched uncertainty of fluid resistance is reconstructed into a state equation with only matched uncertainty structure. To observe and compensate the lumped uncertainty including matched uncertainties, fluid resistance uncertainty and unmeasured auxiliary state variables of hybrid robot, an extended state observer is designed, which only needs the condition of bounded uncertainty change rate. Moreover, by devising the continuous adjustment rule for observer gain’s transient process, the observed error converges quickly and the initial peaking value of system state observation is reduced. To suppress the residual error of uncertainty compensation, the unmeasured auxiliary variables-based super-twisting sliding mode control algorithm is combined with the time-varying gain extended state observer, which could enhance system robustness and weaken chattering of the sliding mode control. The stability of the closed-loop system is proved by Lyapunov stability theorem. Finally, taking the hybrid robot for automobile electro-coating conveying as an example, simulations and experiments are conducted on the prototype system to demonstrate the effectiveness of the proposed control method.

Keyword : Dynamic control, extended state observer, hybrid robot, mismatched uncertainty, sliding mode control.

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