Instability Condition Derivation for Hydraulic AGC System under Pressure Closed‐Loop Control

Sensors fault diagnosis of hydraulic automatic gauge control system based on neural network optimized by genetic algorithm

Abstract-Because the request to the quality of cold rolling sheet strips is higher and higher, the hydraulic AGC (Automatic Gauge Control) has been a requisite means for improving the quality of cold rolling strips' finished products. But the PID control strategy, being comprehensively used in the locale, is difficult to satisfy the request of improving the control precision of cold rolling mill, because robustness is not very strong. The dynamic matrix control, brought forward by Cutler, is one of predictive control theories. It adopts the non-parameter model based the step response of the controlled object, and adopts strategies of multi-step prediction, receding-horizon optimization and feedback correction, which has the good tracking characteristic. The dynamic matrix control has succeeded to be applied in the industry field, so it is indispensable and feasible to explore its application in the hydraulic AGC system of the cold rolling mill. But the step response of the whole hydraulic AGC can't be gained easily in the practical project, so it restricts the application of the dynamic matrix control in the hydraulic AGC. In this article, using for reference the thought of the cascade control, the predictive control is combined in the cascade structure. In the thickness loop of the hydraulic AGC, it adopts PID control. And in the inner loop of the screw-down servo system, it adopts the dynamic matrix control. The cascade predictive control in this article solves the problem of gaining the step response of the whole hydraulic AGC difficultly. When adopting the dynamic matrix control, the state observer is constructed, which makes the control system have the state feedback form with the observer, strengthens robustness of the system by correcting the predictive model, and makes the system have the intelligence. It synthesizes merits of PID control, which possesses of the easy algorithm and adjusting the parameter conveniently, the characteristic of the dynamic matrix control including of good tracking characteristic and strong robustness. The result of the experiment shows that the adopted control strategy makes the dynamic quality of the system improved largely. The response time and the control precision of the screw-down servo system are improved. And the thickness precision of the strip is improved too.

The thickness of the steel strip is an important indicator of the overall strip quality. Deviations in thickness are primarily controlled using the automatic gauge control (AGC) system of each rolling stand. At the last stand, the monitoring AGC system is usually used, where the deviations in thickness can be directly measured by the X-ray thickness gauge device and used as the input to the AGC system. However, due to the physical distance between the thickness detection device and the rolling stand, time delay is unavoidably present in the thickness control loop, which can affect control performance and lead to system oscillations. Furthermore, the parameters of the system can change due to perturbations from external disturbances. Therefore, this paper proposes an identification and control scheme for monitoring AGC system that can handle time delay and parameter uncertainty. The cross-correlation function is used to estimate the time delay of the system, while the system parameters are identified using a recursive least squares method. The time delay and parameter estimates are then further refined using the Levenberg-Marquardt algorithm, so as to provide the most accurate parameter estimates for the complete system. Simulation results show that, compared with the standard Proportion Integration Differentiation (PID) controller approach, the proposed approach is not affected by changes in the time delay and parameter uncertainties.

To reduce longitudinal gauge deviations of the head sections at the hot strip mill rolling it is reasonable to profile band of variable thickness due to the length provided by the linear motion of the screw-down arrangements under load. The paper considers the structure of the automatic gauge control system (ACGS) of the indirect type. It estimates the accuracy of screw-down arrangement position control in the single-loop automatic position control system. It also justifies the use of automatic position combined control system. The introduction of the additional channel of control due to the first derivative of the reference input signal was proved to provide the required accuracy values of the strip gauge control. The paper presents data of the pilot study of the developed system at OJSC Magnitogorsk Iron and Steel Works' mill 2,000; they confirm its efficiency.

The dead-zone input and hydraulic cylinder friction of the pump-controlled automatic gauge control (AGC) system introduce significant challenges to the high-precision rolling of lithium battery pole pieces. To address these nonlinearities, this paper establishes the friction and dead-zone model of the pump-controlled AGC system, and a slide-mode observer is designed to estimate the friction state z in the LuGre model. Furthermore, an adaptive compensation method is adopted to identify the unknown parameters of the input dead-zone and friction models. Meanwhile, combined with the framework of backstepping control design, both matched and mismatched disturbances are effectively compensated. Stability analysis guarantees the convergence of the estimation errors and closed-loop signal boundedness. Finally, experimental results validate the effectiveness and robustness of the proposed control strategy.

The hydraulic load-sensing system is a more efficient system solution than constant pressure system in mobile machine. However, the overall system efficiency for multiple actuators is still low since this centralized hydraulic control system only adapts to the highest load pressure. Therefore, in this article, a distributed hydraulic control system where each function is powered by a hydraulic free piston engine is proposed. Compared with centralized solution, it is more efficient since the power of hydraulic free piston engine is tailored to each function. By integrating small inertia linear engine and pump piston in one unit, the hydraulic free piston engine is an efficient and fast response hydraulic power source. Since the hydraulic free piston engine is essentially a digital hydraulic power source, a digital load-sensing control is proposed in this study. The system architecture, modeling, controller design and performance of the digital hydraulic load-sensing control system are presented. A test bench is developed to verify the system feasibility and performance.

Thickness accuracy is the important quality index of the hot rolling strip. Therefore, the automatic gauge control (AGC) is always the important function that the control system of hot rolling trip completes firstly. Due to the complicated rolling process, nonlinearity and time-variation of the controlled system, the simple AGC system can't obtain desirable effect. In the paper, a new single neuron-Smith prediction control system of AGC is presented. Stability analysis and the simulated experiments on this system are carried out. The simulated results indicate that the new system has the advantages of quick response, low overshooting, small steady-state error and good anti-interference ability. New control system improves the control performance of system with time delay and the accuracy of strip thickness.

To enhance the competence of the product in construction machinery, a proper testing system should be established for the construction machinery hydraulic system. Considering multi-site test and massive control of data processing in most construction machinery hydraulic measurement and control system, a testing platform applicable to different construction hydraulic systems is designed and presented in this paper. Composed of the upper and lower computers, the system is simple and convenient by means of Virtual Instrument Technology. Then it runs very well and proves reliable after debugging operation. Finally, the test-control platform can set manifold experiments in different working conditions.

The non-weighing lysimeter system in the Minqin desert areas was firstly used in the 1970 s, and mainly performed the orientation research on the water consumption by the transpiration of several desert plants and the evaporation on the surface of sand, which aimed to provide the theoretical guide for the selection of afforestation density and the utilization of sand and water in Chinese sand areas. At present the system has been running for 30 years, most of the lysimeters showed the jam and leakage phenomenon, and the observation was by conventional artificial means. All the factors seriously affected the accuracy of the data monitoring. However, on the basis of the non-weighing lysimeter system structure and its testing principle, the evapotranspiration area could be extended, the capacity of testing soil column could be increased, more real natural environment conditions could be simulated and the limitations of weighing lysimeter could be overcome, in sum, the lysimeter's application field and adaptability were extended. Owing to the problems of low automation, and lack of scalability and reliability, the non-weighed lysimeter monitoring and control system in the Minqin desert areas has been retrofitted to improve its performance based on structure characteristics. The non-weighed lysimeter proving ground of 720 m2was designed in Minqin sand areas, where 30 individual lysimeters (120 cm×120 cm) of desert plant were upgraded and 12 small groups of desert plant lysimeters (400 cm×400 cm) were expanded and built, at the same time, the lysimeter groups in different types could be used to carry out the test of water supply for plant under the constant water level of 190, 290 and 390 cm. The lysimeter proving ground upgraded and expanding-built could realize synchronous observation for evapotranspiration test from the desert plant individual scale to small group scale, and the experiment platform was provided for studying water consumption of desert plants transpiration in different scale and its coupling relationship. The distributed monitoring scheme was adopted in the new automatic monitoring system, in which the superior industrial computer was set up as the center with multiple lower machine monitoring points, such as lysimeter constant water level control and water-supplying measurement system, drainage measurement system, atmospheric precipitation monitoring system, soil moisture monitoring system, environment temperature measurement and control system, SMS cat alarm system, data remote transmission and monitoring system, and UPS over-voltage protection system, and the RS485 bus, ISM wireless communication and TCP/IP network structure were used in the system. The automatic control of the lysimeter water level, water supply and drainage, the automatic monitoring of water metering, and the soil water content were designed, and the atmospheric rainfall and the temperature indoor were monitored in real time in the new system; the system also had the functions of real-time data collection and processing, information communication and data entering, historical data storage, data report printing and remote transmission download, and the power supply system was protected against over-voltage to enhance the reliability of system operation and the stability of data acquisition. Additionally, the internet-based remote monitoring and control system was used, and the users could process the abnormal situation. According to the monitoring data analysis by the regression method, we could know that the errors of data regression analysis were ± 2.2% for the pressure sensor, ± 2.0% for the drop counter and ± 12.5% for the moisture sensors. The research extended the scale for locating observation of the desert plant and implemented the automatic monitoring for evapotranspiration of the desert plant. © 2015, Chinese Society of Agricultural Engineering. All right reserved.

Hot strips are presently being rolled out with considerable thickness accuracy. This has been made possible due to superordinated control system comprising of adaptive setup model, monitor thickness control, automatic gauge control, tension and looper control, hydraulic gap control etc. The present work is, however, confined to modeling and simulation studies of hydraulic gap control system in the last stand of the finishig mill of a typical hot strip mill (HSM). The simulation results based on the model show that the system operates effectively to provide high thickness accuracy and good response behavior.

To meet the high thickness accuracy requirements in cold-rolling processes, a roll eccentricity signal extraction method based on modified particle swarm optimization and wavelet threshold denoising (MPSO-WTD) with intrinsic time-scale decomposition (ITD) is proposed. The strong denoising ability of the wavelet is combined with the decomposition and recognition attributes of ITD for non-stationary signals. Periodic disturbances in strip thickness caused by roll eccentricity are actively compensated. First, the wavelet is used to denoise the signal and the MPSO algorithm is applied to determine a rational threshold and improve the calculation efficiency. Then, the denoised signal is decomposed into proper rotational components (PRCs) using the ITD method, and an appropriate PRC component representing the eccentricity signal is extracted. Finally, the eccentricity compensation signal is applied in the automatic gauge control (AGC) system of the cold rolling mill. During the rolling process, the rolling speed is not constant and will directly affect the frequency of the roll eccentricity signal. To solve this problem, an encoder is installed at the end of the roll and the compensation frequency of the roller eccentricity signal is determined in the roller eccentricity compensation system according to the pulse number output. The results of simulations and experiments show that roll eccentricity signals extracted using the proposed method can effectively remove the influence of interference signals. An average improvement of 62.3% in the roll eccentricity compensation effect was achieved under the stable rolling condition in the finishing rolling stage.

Continuous rolling of plate and strip is a typical complex, multi-variable and multi-objective system, which has shown the characteristics such as complication, large-scale and close coupling increasingly. Therefore, it has become more and more difficult to design complex industrial control systems. This paper describes a multi-agent control system for a strip rolling process. In order to realize the distributed and intelligent control of the system, after analyzing the characteristics and structure of this control system, the multi-agent theory was applied and then a control strategy was designed based on multi-agent interaction. Finally, the partition method, the coordination mechanism, and the model structure of the multi-Agent control system for the strip rolling process were analyzed. This paper concludes with a new control structure and system for strip rolling process, which helps to build up the generally integrated model, to eliminate the coupling among control systems, and to realize more intelligent control.

The advanced technology of the Internet and extensive agricultural transformation and upgrading have made the overall agricultural industry chain and modern agriculture better. In view of the high cost and suffering of traditional agricultural planting management, the Internet of Things (I O T) is applied to agriculture to realize real-time detection and intelligent management of crop growth conditions, remote control, and change the traditional agricultural equipment planting mode. The purpose of this article is to design and research the I O T automatic control (A C) system for smart agriculture. This article first introduces the core technology of the I O T through an overview of the basic theories of the I O T. Combined with the current status of agricultural automation in my country, the existing problems and deficiencies are analyzed. On this basis, use the core technology of the I O T to supplement and improve it. This article systematically expounds the overall scheme design, module function design and A C algorithm realization of the I O T brake control system. And use field investigation method, comparative analysis method and other research forms to carry out research on the theme of this article. Experimental research shows that the sampling data of the greenhouse is selected as the sample, the appropriate initial membership function is selected, and the fuzzy control rules obtained through the training of the fuzzy neural network algorithm are relatively correct. The output result of the automatic temperature control system is mostly consistent with the actual data on site. Overall, the temperature A C system designed in this subject can meet the A C requirements of agriculture.

In this paper, we introduce a three-dimensional triaxial apparatus with rigid walls. Its pressure chamber comprises four sliding rigid plates, a rigid specimen cap, and a rigid bottom plate. It has a three-dimensional servo hydraulic load control system, an intelligent control and data storage system, and a water-air suction control system. Considering a cuboid soil specimen as a true triaxial shear layer and a vertical principal stress transfer layer, the vertical principal stress is transferred from the transfer layer to the shear layer, and the orthogonal horizontal principal stress is applied by the horizontal slip rigid plates. That solves the technical problem of mutual interference observed in conventional three-dimensional rigid plate loading. The L-shaped loading plate is improved, which reduces the deflection and friction between them. Linear guides ensure that the horizontal stress is applied synchronously and the specimen is always centered during a test. True triaxial testing of Xi’an loess is reported, and the results confirm the applicability of the apparatus in soil testing.

This paper research on an electromechanical hydraulic mixture control system used in large scale die-forging press, based on the national major science and technology project (2009ZX04005-011). This mixture control system used in press machine accomplishes pressing, pressure-keeping, return. The control system uses hydraulic oil to control three-position five-path slide valve as hydraulic system main valve, for drive system of giant die forging press is characteristic of ultrahigh pressure and large flow, high power. This control system consists of two parts: firstly, establishing electromechanical hydraulic mixture control model by adding electronics and feedback section to servo slide system. Secondly, combining existing slide control hydraulic cylinder model and server slide system form main circuit closed-loop control system. The last but not least, Computer simulation was conducted by matlab got the ideal control curve.