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.

The objective of this paper is to pursue a wire rope control methodology for reducing the tension difference between two wire ropes of a hoisting system. As we know, complicated disturbances exist in the complex electro-hydraulic hoisting system, notably, some of these disturbances are coupled, such as high-speed airflow disturbances, structure vibrations and vibrations in flexible wire ropes. Furthermore, there are model errors in force modeling due to the Coulomb friction between two wire ropes and two moveable head sheaves in the real physical hoisting systems. To eliminate disturbances, two types of disturbance observers (DOs) are employed: a traditional disturbance observer (TDO) and a coupled disturbance observer (CDO), both of which are utilized to estimate and compensate for the Coulomb friction and coupled disturbances online. As a result, a nonlinear backstepping control scheme is presented with estimation values from the TDO and the CDO. The experiment’s results demonstrate the effectiveness of the proposed control methodology.

A double-rope winding hoisting system (DRWHS) is usually employed to transport weight or workers in mines usually from ultra-deep underground (>1000m). An electro-hydraulic servo system (EHSS), which consists of two hydraulic cylinders, two movable headgear sheaves and lots of indispensable sensors, is employed to actively coordinate two wire tensions. The nonlinear dynamic model of the DRWHS is introduced and it is divided into two subsystems, i.e., the hoisting system and the EHSS with state space representations. However, as a complex machine-electricity-hydraulic system, the accurate dynamic model of the DRWHS is usually hard to obtain. Therefore, a flatness-based controller (FBC), which is insensitive to unmodeled characteristics of the dynamic model and measurement noises of sensors, is proposed to improve the tension coordination of two wire tensions of the DRWHS. The explicit FBC design schemes for the DRWHS and the control law are presented, and the stability of the proposed controller are proved by defining a Lyapunov function. The controller proposed is characterized by no derivatives of state variables and lower controller design complication so that measurement noises of sensors and unmodeled characteristics are not amplified. An experimental bench of the DRWHS is established to verify the performance of the proposed controller. Experimental results show that the proposed controller exhibits a better performance on the tension coordination control of two wire ropes compared with a backstepping controller (BC) and a conventional proportional-integral (PI) controller.