Design of entry strip thickness controls for tandem cold mills

The ideal characteristics of a strip thickness control system operating on the upstream stands of a tandem mill are defined. The historical development of tandem mill control system design is described and several recently published control systems are compared on the basis of how well they achieve the ideal characteristics.An entry end control system is then described which combines a stand 1 thickness gauge feedback system with a feedforward controller employing non-interactive concepts. A modified gaugemeter system is recommended for the first stand of hydraulic mills which incorporates an additional force control loop for minimising the effects of roll eccentricity. Typical computer simulation results are presented. The final system has excellent error attenuation properties with a minimum of complexity and is suited to implementation on tandem mills rolling sheet or tinplate and with electric or hydraulic rollgap positioning.Preliminary performance results from a recently upgraded 5-stand cold mill are included which confirm the merits of the control system described. Brief details are given of other significant features in this system.     

End mill design and machining via cutting simulation

This paper describes a design process for an end mill. A solid model of the designed cutter is constructed together with the computation of the cutter’s geometry, wheel geometry, and wheel positioning data for fabricating end mills with the required cutter geometry. The main idea of the process is to use the cutting simulation method to obtain the machined shape of an end mill by using Boolean operations between a given grinding wheel and a cylindrical workpiece (raw stock). The major design parameters of a cutter, such as rake angle and inner radius, can be verified by interrogating the section profile of its solid model. This study investigates the relationship between various dimensional parameters and proposes an iterative approach to obtain the required geometry of a grinding wheel and cutter location (CL) data for machining an end mill that satisfies the design parameters. This research was implemented using a commercial computer aided design (CAD) system with API function programming and is currently used by a commercial tool maker in Korea. It can eliminate the need to produce a physical prototype during the design stage and can be used in virtual cutting tests and analyses.     

Neural network modeling and control of cement mills using a variable structure systems theory based on-line learning mechanism

It is well known that the major cause of instability in industrial cement ball mills is the so-called plugging phenomenon. A novel neural network adaptive control scheme for cement milling circuits that is able to fully prevent the mill from plugging is presented. Estimates of the one-step-ahead errors in control signals are calculated through a neural predictive model and used for controller tuning. A robust on-line learning algorithm, based on sliding mode control (SMC) theory is applied to both: to the controller and to the model as well. The proposed approach allows handling of mismatches, uncertainties and parameter changes in the model of the mill. The simulation results from indicate that both the neural model and the controller inherit the major advantages of SMC, i.e. robustness. Furthermore, learning is achieved in a rapid manner.     

Nonlinear coal mill modeling and its application to model predictive control

Coal mills play an important role in the overall dynamic response of coal fired power plants and there is significant potential to improve the load ramp rates of coal fired power plants through improvements of coal mill control strategies. This potential can be employed to compensate for the power fluctuations generated by renewable but intermittent energy sources such as wind and solar in a more efficient way. In this paper a three state coal mill model based on heat and mass balances as well as a single step coarse to fine particle grinding relationship is presented with the purpose of predicting the dynamic behavior of coal mills during both start-up and in normal operation. The parameters of the model were identified and later validated with measurements obtained from a hard coal fired power plant. During these studies several parameters were found to be time varying. In order to estimate the values of these time varying parameters and the internal states of the coal mill an extended Kalman filter was designed. The proposed solution is observed to achieve very good agreement with measurements and can be used for various applications such as model-based control, performance monitoring, fault detection, and maintenance scheduling. In order to demonstrate one of these use cases a nonlinear model predictive control (NMPC) application was developed based on the coal mill model and the performance of the NMPC was compared to a conventional coal mill control strategy for tracking load change references and for rejecting disturbances caused by variations in coal moisture. The results demonstrate that the coal mill control system performance can be significantly improved through the use of the model presented in this paper.     

An EKF observer to estimate semi-autogenous grinding mill hold-ups

A non-linear observer model of a semi-autogenous grinding mill is developed. The observer model distinguishes between the volumetric hold-up of water, solids, and the grinding media in the mill. Solids refer to all ore small enough to discharge through the end-discharge grate, and grinding media refers to the rocks and steel balls. The rocks are all ore too large to discharge from the mill. The observer model uses the accumulation rate of solids and the mill's discharge rate as parameters. It is shown that with mill discharge flow-rate, discharge density, and volumetric hold-up measurements, the model states and parameters are linearly observable. Although instrumentation at the mill discharge is not yet included in industrial circuits because of space restrictions, this study motivates the benefits to be gained from including such instrumentation. An extended Kalman filter is applied in simulation to estimate the model states and parameters from data generated by a semi-autogenous mill simulation model from literature. Results indicate that if sufficiently accurate measurements are available, especially at the discharge of the mill, it is possible to reliably estimate grinding media, solids and water hold-ups within the mill. Such an observer can be used as part of an advanced process control strategy.     

A multi-purpose tool for dynamic simulation of paper mills

A simulation environment for the dynamic simulation of paper or board mills has been developed. APMS (advanced paper mill simulator) provides tools for fast and easy modelling of the plant comprising e.g. stock preparation, approach system, wet end and dry end of the machine. The models are based on the first principles of physics and chemistry whenever it is possible. This mechanistic modelling principle with efficient equation solution techniques ensures fast and accurate simulation for the purposes of process and automation design, analysis and operator training.     

A G2-based hybrid modelling and simulation methodology and its application to a rolling mill

The paper describes the design of a hybrid modelling and simulation methodology, its implementation in the G2 real-time expert system, and its application to a rolling mill. The methodology is specifically designed for industrial control systems in which continuous-time subsystems interact with sequential control stations and the heuristic knowledge of a process operator. The pivotal concept in the methodology is a hybrid model base which is a repository of several paradigms. Hybrid simulation is based on the concurrent execution of the G2 continuous simulator, the G2 inference engine and a Grafcet simulator. The application of the methodology to a rolling mill demonstrates its potential for integrating a hybrid simulation model with the functionality of a real-time process.     

Robust stabilization of a nonlinear cement mill model

Plugging is well known to be a major cause of instability in industrial cement mills. A simple nonlinear model able to simulate the plugging phenomenon is presented. It is shown how a nonlinear robust controller can be designed in order to fully prevent the mill from plugging     

基于Expert-PID算法的矿山球磨机物联网控制系统的设计

针对矿山球磨机采用手动控制呈现出的工人劳动强度大、易受主观因素缺点,或者采用传统PID控制矿浆浓度中出现的稳定性差、波动大、精度低等落后状况,提出设计开发基于Expert-PID算法的矿山球磨机物联网控制系统;文中首先构建了一个五元组的球磨机的模型BallMill=,设计出包含感知层、汇聚层、操作层、应用层等四层物联网测控系统宏观结构,进而介绍了传统PID算法与Expert-PID算法详细内容,重点论述了矿山球磨机Expert-PID算法物联网控制系统的原理结构与专家调控规则;通过企业应用实践与对比实验表明,该系统采用Expert-PID算法比传统的PID算法具备更好的鲁棒性、稳定性与可靠性。     

Application of agent based modelling to aircraft maintenance manning and sortie generation

This research develops an agent based simulation model for application to the sortie generation process, focusing on a single fighter aircraft unit. The simulation includes representations of each individual maintainer within the unit, along with supervisory agents that provide direction in the form of dynamic task prioritization and resource assignment. Using a high-fidelity depiction of each entity, an exploration of the effects of different mixes of skill levels and United States Air Force Specialty Codes (AFSCs) on sortie production is performed. Analysis is conducted using an experimental design with results presented demonstrating the effects of maintenance manning decisions on the Combat Mission Readiness (CMR) of a fighter unit.     

模糊优化控制方法在中储式磨煤机制粉系统中的应用

磨煤机是火电厂大量采用的重要辅助设备之一。但是到目前为止,大多数电厂尚未能实现自动控制,主要是因为球磨机控制系统是一个多输入、多输出的强耦合、非线性、大延迟、大惯性的被控对象,动态特性复杂,数学模型难以准确建立,对于它的控制存在一定的难度。而对于常规的PID控制规律难以获得满意的控制效果。本文结合火电厂球磨机控制系统的实际情况,分析了球磨机的动态特性,探讨了模糊控制技术在球磨机自动控制中的应用,提出了模糊控制方案并进行仿真。结果表明,所设计的模糊控制系统有较强的抗干扰能力,使球磨机系统控制品质有所提高。     

The use of computer simulation in the pulp and paper industry

Pulp and paper mill processes have certain typical features in common with other simulation objects. However, computer simulation can serve as a useful tool in the design and construction of process units and the entire mill, as well as comparison of various production and control strategies of the pulp and paper mill processes. Simulation problems in this area are related to the adjustment of simulation models to mill material balances with many recycles. When the internal behaviour of the processes are considered the lack of sufficiently complete or applicable models sets a limitation on simulation studies.     

Decoupler and PID controller design of TITO systems

This paper treats controller design and tuning for systems with two input signals and two output signals in the process industry. Two design methods that can be combined to form a core in an algorithm for automatic design and tuning for the considered systems are presented. The proposed controller consists of a decoupler and a diagonal PID controller. The decoupler has the property that as little dynamics as possible is introduced in the decoupler. The PID design method is based on exhaustive search. The methods are combined and tested in an industrial environment in a paper mill.     

磨机负荷监测控制系统设计

文章介绍了磨机的运行特性,及其在选矿厂磨矿系统中的应用情况.针对磨机负荷难以测量的特点,分析了传统的基于磨机振动和磨机噪音的检测方法所存在的不足,并在此基础上对基于综合的磨机负荷测量方法进行了研究.     

Derivation and validation of a coal mill model for control

The paper presents development and validation of a coal mill model to be used for improved mill control, which may lead to a better load following capability of power plants fired by pulverized coal. The model is relatively simple, yet it captures all significant mill dynamics. The model is validated using data from four mills of a similar type from two different manufacturers. In the validation, model parameters are estimated using an efficient evolutionary algorithm called Differential Evolution. The model parameters are similar for all four mills, indicating that the model structure can be trusted.     

Reduced-order observer-based robust synchronisation control of cold rolling mills with measurement delay

To improve the quality of strip thickness, synchronisation control is investigated for cold rolling mills driven by dual-cylinder electro-hydraulic servo systems. Realising synchronised control in hydraulic automatic gauge control (HAGC) systems of cold rolling mills has challenges with not only the inherent nonlinearities of hydraulic servo systems and uncertainties of load variation but also measurement delay of strip thickness. Since all states are not measurable in practice, output feedback robust synchronisation control problem should be addressed for uncertain nonlinear systems with output delay. Thus, a reduced-order observer-based robust synchronous controller is presented by employing Lyapunov functional stability theory. The controller designed by incorporating the integral of the position synchronisation error of two pistons into state variables successfully guarantees asymptotic convergence to zero of both tracking errors and synchronisation error simultaneously regardless of the nonlinearities and uncertainties as well as the measurement delay. Simulation results in a model obtained from a real cold strip rolling mill demonstrate the effectiveness of the approach.     

Dual particle filters for state and parameter estimation with application to a run-of-mine ore mill

Measurements are not readily available for grinding mills owing to the nature of the milling operation. State and parameter estimation for a grinding mill which forms part of a run-of-mine ore milling circuit has been implemented. These estimates may then be used in an advanced control algorithm. The estimation was done with dual particle filters as well as with a simultaneous estimation scheme, on simulated data, to compare the performances. The sensitivity analyses for the different schemes show the class of systems in which dual estimation may produce superior results.     

面向DFA的板带轧机零部件特征建模的开发

针对传统串行设计方法的固有缺陷 ,提出面向DFA技术的板带轧机零部件特征建模的方法 ,文中给出了零部件的实体建模原理 ,求交运算和具体实现方法。实验结果表明 ,该方法思路正确 ,并有潜力解决轧机的并行设计问题。     

Optimization-based automatic flatness control in cold tandem rolling

For the problem of automatic flatness control (AFC) in cold tandem mills this paper proposes control techniques based on quadratic optimization and delay compensation. Three different strategies are presented and compared: a centralized solution based on a global quadratic programming (QP) problem that decides the commands to all the actuators, and two decentralized solutions where each actuator command is optimized locally. All schemes are based on a global exchange of information about the commands generated at the previous time step at each stand to compensate for the numerous delays present in the mill. Control algorithms are tested in simulation considering a tandem mill with five stands as a benchmark, and results are shown to demonstrate the performance of the proposed schemes.     

冷轧管机远程监控管理系统的设计

新型冷轧管机驱动电机的运行状态能够反映整机的性能和工作状态。针对实际应用需求,通过集成RS-485、蓝牙、GPRS、以太网等通信技术,设计了冷轧管机远程监控管理系统。该系统由现场监控器、手机、监控PC和远程管理PC组成,能够对冷轧管机驱动电机信号进行数据采集和传输,实现冷轧管机运行状态监控和运行数据管理。该系统为冷轧管机的现场调试和维护、生产运行监控、设备维护管理提供了有力的技术保障。