Hydraulic automatic gauge control (AGC) system is the core control system to ensure the thickness accuracy of cold-rolled plate, and the reliability of its load roll system is the key to guarantee the rolling process with high precision, high speed, continuity and stability. However, the working mechanism of hydraulic AGC system is complex. And it possesses some features such as high nonlinearity, time variability and strong coupling. The vertical vibration easily happens in its working process. Moreover, the stability of system is seriously affected. Nevertheless, the incentive is difficult to determine. In this paper, the theory and method of nonlinear dynamics were introduced to establish the load vertical vibration (LVV) model of HAGC system under nonlinear action. The model was solved with multi-scale method, and the amplitude-frequency characteristic equation of system was obtained. Moreover, the research object of this article also focused on the nonlinear elastic force, nonlinear damping force and nonlinear excitation force, and deeply explored the effect of nonlinear parameters change on the amplitude-frequency characteristics of LVV system. The mechanism and incentive for LVV of hydraulic AGC system were further revealed. The research results lay a theoretical foundation for the vibration inducement and suppression of hydraulic AGC system.

Amplitude-frequency characteristics analysis for vertical vibration of hydraulic AGC system under nonlinear action

Optimization of a pressure control valve for high power automatic transmission considering stability

As the core control system of a rolling mill, the hydraulic automatic gauge control (HAGC) system is key to ensuring a rolling process with high speed, high precision and high reliability. However, a HAGC system is typically a mechanical-electric-hydraulic coupling system with nonlinear characteristics. The vertical vibration of the load easily occurs during the working process, which seriously affects the stability of the system and the causes are difficult to determine. In this work, the theory and method of nonlinear dynamics were employed. The load vertical vibration model of the HAGC system was established. Then, the multi-scale method was utilized to solve the obtained model, and the singularity theory was further applied to derive the transition set. Moreover, the research object of this article focused on some nonlinear factors such as excitation force, elastic force and damping force. The effects of the above feature parameters on bifurcation behavior were emphatically explored. The bifurcation characteristic of the load vertical vibration of the HAGC system was revealed. The research results indicate that the bifurcation curves in each sub-region, divided by the transition set, possess their own topological structure. The changes of the feature parameters, such as the nonlinear stiffness coefficient, liquid column height, nonlinear damping coefficient, and external excitation have an influence on the vibration amplitude of the HAGC system. By reasonably adjusting the nonlinear stiffness coefficient to effectively avoid the resonance region, the stability of the system will be facilitated. Furthermore, this is conducive to the system’s stability as it properly controls the size of the liquid column height of the hydraulic cylinder. The appropriate nonlinear damping coefficient can decrease the unstable area, which is beneficial to the stability of the system. However, large external excitation is not conducive to the stability of the system.

https://www.mdpi.com/2227-9717/7/10/718/pdf

Bifurcation Characteristic Research on the Load Vertical Vibration of a Hydraulic Automatic Gauge Control System

Dynamic surface disturbance rejection control for electro-hydraulic load simulator

Digital fluid power (DFP) technology may lead to a paradigm shift in large-scale transmission systems in, e.g., wind and wave energy. Therefore, the development of applicable control algorithms is of major importance, but is complicated by the non-smooth behavior of the DFP displacement machines. The power throughput of a full stroke operated digital displacement machine is quantized by the number of pressure chambers. The dynamics of each pressure chamber may be described by highly nonlinear continuous differential equations, whereas the input is discretely updated and binary (active or inactive). This paper contributes with a feedback control strategy for a digital displacement machine, where the binary inputs are handled by a pulse density modulator. The paper presents a linearization method of handling the many nonlinearities and thereby enabling the use of Discrete Linear Time Invariant (DLTI) control theory. The control strategy is validated for control of a digital fluid power wind turbine transmission, where both a deterministic and a stochastic optimal controllers are synthesized. The study is based on the NREL 5-MW reference wind turbine, where its model is combined with a nonlinear model of the DFP transmission and full-field flow wind profiles are used for a realistic performance evaluation scenario. By simulation, it is found that the performance of the optimal controllers using the DFP transmission is similar to that of the NREL controller using a conventional transmission.

Optimal control of a wind turbine with digital fluid power transmission

The electrohydraulic servo system (EHSS) has been widely utilized in industry and national defense. However, it is a complex dynamics system composed of many parts. The anomalies are easy to happen in operation, such as nonlinear vibration, noise, impact and so on. These anomalies significantly influence the stability of EHSS. Hence, in order to reveal the incentives, a nonlinear dynamic model was established. Then, the bifurcation characteristics and typical nonlinear dynamics behaviors implied within system were revealed. Moreover, the dynamic signals were measured from an experimental system and deeply analyzed by the effective methods of nonlinear dynamics. Results indicate that the variation of excitation force, spring force nonlinear term and damping can result in complicated nonlinear dynamic behaviors. The measured vibration signals of EHSS possess chaotic characteristic. Therefore, EHSS is a nonlinear dynamic system. This research provides a potent base for the study on nonlinear dynamics behavior of EHSS and makes the comprehensive analysis on nonlinear dynamics characteristics of EHSS become closer to reality.

Zhi Zheng

Papers

Study on nonlinear dynamics characteristics of electrohydraulic servo system