Abstract
This paper presents a robust nonlinear control scheme with time-varying output constraint for the electro-hydraulic force control system (EHFCS). Two typical double-rod symmetrical hydraulic cylinders are employed to simulate force environments in the EHFCS. Therefore, in order to improve the performance of the EHFCS, firstly, the model of the EHFCS is established with taking external disturbances, parameter uncertainties as well as structural vibrations into consideration. Secondly, in order to estimate external disturbances, parameter uncertainties and structural vibrations in the EHFCS and compensate them in the following robust controller design, two disturbance observers (DOs) are designed according to the nonlinear system model. Thirdly, with two estimation values from two DOs, a time-varying constraint-based robust controller (TVCRC) is presented in detail. Moreover, the stability of the proposed controller is analyzed by defining a proper Lyapunov functions. Finally, in order to validate the performance of the proposed controller, a series of simulation studies are conducted using the MATLAB/Simulink software. These simulation results give a fine proof of the efficiency of the proposed controller. What’s more, an experimental setup of the EHFCS is established to further validate the performance. Comparative experimental results show that the proposed controller exhibits better performance than the TVCRC without two DOs and a conventional proportional integral (PI) controller.
Highlights
Electro-hydraulic force control systems (EHFCSs) have been widely applied in industry, due to their great advantages such as small size-to-power ratios, being capable of handling large inertia and heavy loads, high accuracy and high dynamic response [1]
Some control strategies based on the model of the EHFCS, such as robust controllers [5,6,7,8], controllers based on feedback linearization technique [9,10,11,12], adaptive controllers [13,14,15,16], sliding mode controllers [17,18,19,20] etc., are developed to improve the force tracking performance
By employing disturbance observers (DOs) or extended state observers, these nonlinear factors can be compensated in the backstepping controller design, which will improve the performance of the controller
Summary
Electro-hydraulic force control systems (EHFCSs) have been widely applied in industry, due to their great advantages such as small size-to-power ratios, being capable of handling large inertia and heavy loads, high accuracy and high dynamic response [1]. Backstepping controllers can almost perfectly handle these nonlinear factors based on some disturbance observers, extended state observers, or some online parameter adaptive estimation approaches as long as proper Lyapunov functions are chosen [21]. By employing disturbance observers (DOs) or extended state observers, these nonlinear factors can be compensated in the backstepping controller design, which will improve the performance of the controller. Yao [21] proposed an extended state observer based backstepping controller for electro-hydraulic servo systems. Yang [32] proposed a dual extended state observer-based backstepping controller for the position tracking control of electro-hydraulic systems with time-varying output constraints and some simulation results verify the efficiency of the proposed controller. In this paper, we present a time-varying constraint-based robust controller (TVCRC) for the EHFCS with two disturbance observers (DOs).
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