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The nonlinear factors, the external interference, and the coupling between the two hydraulic cylinders in the electro-hydraulic position servo system seriously affect the synchronous control accuracy. In this paper, based on the establishment of the state space equation of double hydraulic cylinders, the cross-coupling control structure was adopted, and the synchronous controller based on dynamic soft variable structure control was designed. The synchronous controller based on sliding mode control was used as a comparison for co-simulation and experimental analysis. The results showed that under the control of two synchronization controllers, the controlled dual cylinders could track the given positioning signal in a short time, and the synchronization error was always within the specified range. The synchronization controller based on dynamic soft variable structure control could shift smoothly without significant impact when the given positioning signal suddenly changes, avoiding the chattering problem in the sliding mode control.

An adaptive sliding mode variable structure control method is proposed for the shipboard cranes in the presence of unknown parameters. The proposed method can solve the problem of frequent controller tuning and effectively reduce the payload pendulation. First, the length change of the rope and unmodeled disturbance are considered in the model, then the model is divided into the actuated and unactuated parts. The error function is induced into the sliding mode surface to design the equivalent control law, and unmodeled disturbance is estimated by the nonlinear extended state observer. Then, the mass of the payload is equal to the estimated parameter, and an adaptive law is designed to eliminate errors of them. Moreover, the asymptotic stability of the closed-loop system is assured by carefully designed Lyapunov techniques. Finally, a comparative study of numerical simulation under different conditions is investigated. The results show that the proposed method can effectively reduce payload swing, which further illustrates the satisfactory performance of the proposed method.

Due to the multiple nonlinear composite disturbance problems such as gap, friction, hydraulic spring force and external load disturbance force in the double closed-loop digital hydraulic cylinder position control system, traditional or single structure controllers have no obvious effect on improving the performance of this complex nonlinear system. In this paper, the high-order state equation is obtained for the existing mathematical model of the double closed-loop digital hydraulic cylinder. Then, using ADRC, the high-order double closed-loop digital hydraulic cylinder control system is equivalent to a second-order integral series control system. Applying sliding mode variable structure control to ADRC, in order to improve the control accuracy of the sliding mode controller and reduce the influence of chattering, utilizing the external disturbance in the ESO observation system in ADRC, a control term f ( x ) in the system, which is an uncertain nonlinear variable due to the time-varying and unknown internal parameters of the system. RBF neural network is used to approximate f ( x ). Based on this, the RBF neural network sliding mode active disturbance rejection control strategy (RBFSMADRC) is proposed. The control law and adaptive law of the system are derived based on the Lyapunov method, and the stability of the whole closed -loop system is ensured by adjusting the size of the adaptive weight. Specifically, the effectiveness of the proposed control method is validated through simulation and experimentation.

This study proposes a method for operating wheeled cross-coupled systems. Wheeled cross-coupled systems are more sensitive to disturbances than other cross-coupled systems. When the slip phenomenon occurs in wheels, it causes synchronous errors between axles, resulting in differences in the controller outputs of the two axles. In the worst case, the two axles can end up competing. To solve this problem, this study introduces base controllers to each axle using a discrete-time variable structure control system with a decoupled disturbance compensator and an auxiliary controller, called a synchronous error compensator (SEC), to minimize synchronous errors arising from differences in the states of the two axles. Experiments are conducted on a verification system with a similar form of overhead hoist transfer (OHT) to demonstrate the effectiveness of the proposed method. Results reveal that the SEC generates control commands to make the control inputs (current command) and state variables (velocity feedback) of the two axles similar.

To address the low efficiency of compressors driven by rotating motors in refrigeration equipment, an electromagnetic linear actuator directly driven compressor is designed. A multi-field coupling mathematical model of machinery, electricity, and magnetism is established through theoretical analysis of the working mechanism and structure of the electromagnetic linear actuator directly driven compressor. Based on MATLAB/Simulink, a dual-loop Proportional—Integral—Derivative (PID) control algorithm and a sliding mode variable structure control algorithm with a nonlinear extended state observer are designed and simulated, enabling the function of the linear compressor to change its stroke and frequency according to different working conditions. Subsequently, a real-time simulation test platform based on dSPACE is built for the semi-physical real-time simulation tests. The test results demonstrate that the control algorithm can meet the variable working conditions of the compressor, and the test results are consistent with the simulation results. Moreover, the accuracy of the sliding mode variable structure control algorithm with a state observer is 2.5%, which is higher than the 5% accuracy of PID, meeting the performance requirements of the compressor.

Balancing path-following accuracy and error convergence with graceful motion in steering control is challenging due to the competing nature of these requirements, especially across a range of operating speeds and conditions. This paper demonstrates that an integrated, multi-tiered steering controller considering slip in kinematic control, dynamic control, and steering actuator rate commands achieves accurate and graceful path following. Kinematic and dynamic models are adapted to include slip. A path-following kinematic controller is then derived using a continuous, time-varying, and speed-based variable-structure controller (VSC) to balance safe and graceful motion with robust error convergence. Yaw rate commands from the kinematic controller are nested in a backstepping slip–yaw dynamic tracking controller to generate steering rate commands. A high-gain observer (HGO) estimates the sideslip and yaw rate, which are used in sensor-based output feedback control. Stability analysis of the output feedback controller is provided, and peaking is resolved. The work focuses on lateral control alone so that the steering controller can be combined with other speed controllers. Field results demonstrate gracefulness and accuracy along complex paths in variable terrain, in different weather conditions, and with perturbations.

In this paper, a novel robust adaptive fuzzy control is presented for a quite general class of multivariable nonlinear systems with actuators’ nonlinearities (saturation with dead zone) and uncertain dynamics. The backstepping concept in combination with the variable-structure control framework and Lyapunov approach is used to design this adaptive fuzzy control. The fuzzy systems are incorporated in the controller for approximating online the unknown system dynamics. In the controller design and stability analysis, the control gain matrices, which are not necessarily symmetric and definite, are decomposed via the so-called SDU matrix decomposition lemma into a product of three main useful matrices, namely a symmetric definite-positive matrix, a diagonal constant matrix with + 1 or − 1 in its main diagonal and a unity upper triangular matrix. It is shown that the proposed adaptive fuzzy control is able to ensure the uniform ultimate boundedness of all solutions of the closed-loop system, as well as the convergence of the underlying tracking errors. Finally, in a numerical simulation framework, the effectiveness of the presented controller is illustrated on two practical examples.

This paper investigates the fixed-time formation (FixF) control problem for second-order multi-agent systems (MASs), where each agent is subject to disturbance and the communication network is general directed. First, a FixF protocol is presented based on the backstepping technique, where the distributed cooperative variable structure control method is utilized to handle the bounded disturbances. Then, to remove the dependence of control gains on the global information, a practical adaptive FixF control is presented, where the MASs can achieve formation with a bounded error within fixed time. Finally, a numerical example is presented to validate the theoretical result.

During the operation of valve-controlled cylinder position systems, there are some problems, such as uncertainty and time-varying of the system parameters, imprecise modeling, and external interference. These problems will affect the position loading accuracy and safety reliability of the electro-hydraulic position servo system. This paper used the position servo system of a valve-controlled cylinder as the research object, and a mathematical model was established. Then, a sliding mode variable structure controller and dynamic soft variable structure controller were designed, and the Grey Wolf algorithm was used to adjust the controller parameters. The control effect of the two controllers in the valve-controlled cylinder system was verified with a simulation and experiment. The results showed that compared with the sliding mode variable structure controller, the dynamic soft variable structure controller had higher control precision and better stability and avoided the chattering phenomenon.

The adaptability of traditional PID, fuzzy PID and feedback linearization sliding mode variable structure control intelligent algorithm to automatic drilling is analyzed. The results show that the feedback linearization sliding mode variable structure control algorithm has more ideal response speed, control accuracy and robustness, which solves the nonlinear problem of the electro-hydraulic control system of the truck-mounted drilling rig and improves the tracking control accuracy of the system during automatic drilling.