Feedforward control of blast furnace stoves

This paper is concerned with the control of a system of blast furnace stoves when subject to changes in load and operated according to the ‘by-pass main’ principle. A limiting condition for stable cyclic equilibrium at maximum thermal efficiency is first developed for any given combination of the two load variables, blast temperature and flowrate, assuming, in the first part of the paper, zero changeover time. The condition may be used to predict whether a given load change will lead, for constant hot gas flow rate, to the establishment of a new cyclic equilibrium state or to an instability condition called ‘collapse’ by Zuidema. The gain of a feedforward compensator which manipulates hot gas flow rate may also be evaluated so that a wider range of load changes may be satisfied without collapse. Non-zero changeover time markedly reduces the maximum thermal efficiency attainable from a given stove installation and is predicted to lead to the existence of two possible states of cyclic equilibrium for a given hot gas flow rate. The most efficient operating state may be selected by combined feedforward/feedback control over average hot gas flow rate. A new method of digital simulation for regenerator systems is described which uses standard engineering simulation packages and which has a number of advantages when simulating transient stove operation.     

泡沫玻璃窑炉温度控制系统的设计与应用

针对泡沫玻璃生产线窑炉温度控制的工艺要求,设计并应用了P L C温度控制系统、P I D控制算法。现场应用表明,该系统运行稳定可靠,设计先进,界面友好,控制精度高,具有较高的实用价值,从而保证了产品的质量,降低了能耗,提高了企业竞争力。     

Dynamical modelling and control of plastics extrusion processes

Alternative methods for determining plastics extrusion process models, suitable for high level control, are examined and the importance of time-series techniques for feedforward control is demonstrated. The results of extrusion process dynamic model identification experiments, carried out on a single screw extruder used for processing polyethylene, are described. Some results of exploratory control strategy simulations are included. Control of plastics melt pressure and temperature at the die is suggested as an effective indirect means of controlling die flow rate in most industrial situations.     

模糊前馈-反馈控制在药品酯化过程控制的应用

针对制药生产过程控制中间歇式反应釜温度控制非线性和大滞后的特点，提出了模糊前馈—反馈控制的方法，并对模糊控制器的一般设计方法进行了研究，简化了模糊控制器的设计过程，实际控制结果表明本设计方案的可用性和有效性。     

基于DSP前馈模糊PI的舵机控制算法

针对负载转矩对舵机转速的影响,建立负载力矩的数学模型,提出带前馈模糊自整定比例积分参数的速度环控制算法,利用前馈控制器补偿负载变化对电机转速的影响。当直流无刷电机特性和力矩变化时,通过动态调整控制参数使系统具有良好的鲁棒性和控制精度。设计以数字信号处理器为核心的模糊控制器,采用高精度的绝对编码器作为位置环反馈。实验结果表明,该控制器具有较强鲁棒性,且响应速度快、超调小、控制精度高。     

Production scheduling of parallel machines with model predictive control

This paper considers the problem of optimizing on-line the production scheduling of a multiple-line production plant composed of parallel equivalent machines which can operate at different speeds corresponding to different energy demands. The transportation lines may differ in length and the energy required to move the part to be processed along them is suitably considered in the computation of the overall energy consumption. The optimal control actions are recursively computed with Model Predictive Control aiming to limit the total energy consumption and maximize the overall production. Simulation results are reported to witness the potentialities of the approach in different scenarios.     

A distributed expert control system for a hydrometallurgical zinc process

A distributed expert control system (DECSHZ) has been built for a hydrometallurgical zinc process, whose basic steps are leaching, purification and electrolysis. It consists of a central computer management system and three local expert control systems, one for each of the basic steps. This paper deals with the design and application of DECSHZ, especially its distributed architecture and main functions; expert control strategies based on rule models and a combination of rule models and steady-state mathematical models; system implementation; and the results of actual runs. DECSHZ has been found to provide not only a very pure product, but also significant economic benefits.     

基于模糊控制的模温机控制器的设计与实现

在借鉴解析式模糊控制方法的基础上,剖析了系统存在较大超调的原因,进而引入跟踪受控对象瞬时状态的升温速率因子.并提出根据该因子在控温过程中从宏观上合理安排控制策略的分层控制方法.用以实现模温机的温度控制.实验数据表明该方法能有效抑制超调现象,从总体上优化系统的控制性能.     

Feedforward control of the transverse strip profile in hot-dip galvanizing lines

Hot-dip galvanizing is a standard technology to produce coated steel strips. The primary objective of the galvanizing process is to establish a homogeneous zinc layer with a defined thickness. One condition to achieve this objective is a uniform transverse distance between the strip and the gas wiping dies, which blow off excessive liquid zinc. Therefore, a flat strip profile at the gas wiping dies is required. However, strips processed in such plants often exhibit residual curvatures which entail unknown flatness defects of the strip. Such flatness defects cause non-uniform air gaps and hence an inhomogeneous zinc coating thickness. Modern hot-dip galvanizing lines often use electromagnets to control the transverse strip profile near the gas wiping dies. Typically, the control algorithms ensure a flat strip profile at the electromagnets because the sensors for the transverse strip displacement are also located at this position and it is unfeasible to mount displacement sensors directly at the gas wiping dies. This brings along that in general a flatness defect remains at the gas wiping dies, which in turn entails a suboptimal coating.In this paper, a model-based method for a feedforward control of the strip profile at the position of the gas wiping dies is developed. This method is based on a plate model of the axially moving strip that takes into account the flatness defects in the strip. First, an estimator of the flatness defects is developed and validated for various test strips and settings of the plant. Using the validated mathematical model, a simulation study is performed to compare the state-of-the-art control approach (flat strip profile at the electromagnets) with the optimization-based feedforward controller (flat strip profile at the gas wiping dies) proposed in this paper. Moreover, the influence of the distance between the gas wiping dies and the electromagnets is investigated in detail.     

浮法玻璃熔窑温度和窑压的自动控制

浮法玻璃熔窑是一个复杂的热工设备，过程比较复杂，具有变量多、参数时变、部分非线性、强耦合和大滞后的特点，因此其控制相当复杂。针对熔窑温度和窑压这两个参数提出了对应的控制方法，采用GPC-PID串级控制方案控制温度和采用带前馈的PID来控制窑压，事实证明极大地提高了控制精度。     

Identification and adaptive control of a glass furnace

The paper presents the modelling and control of a glass furnace. A portable process computer laboratory was applied. The computer was provided by a process control program and control tasks.Based on normal operating records experiments were designed and a model with three inputs and outputs of the furnace was elaborated. By means of identified models the glass level was successfully controlled by a self-tuning regulator.     

最优控制在过程工业中的应用与展望

最优控制理论在过程工业中应用的越来越广泛,过程工业包括石油化工、电力、冶金化工等诸多行业,他们在我国国民经济中起着举足轻重的作用。随着最优控制理论重要性不断增强,本文综合性的阐述了关于最优控制的基本原理,最优控制的实现过程是通过建立受控系统的动态方程,在容许控制以及选定目标集范围内达到性能指标的最大或最小。本文还阐述了它所用于研究的主要过程控制问题、最优控制问题的主要解决方法,以及近几年最优控制在过程控制方面的最新进展和发展前景。     

A model for integrating process planning and production planning and control in machining processes

The goal of process planning is to propose the routing of a previously designed part and results in a sequence of operations and their parameters. It concerns and requires detailed information about the process. The goal of production planning, on the other hand, is to schedule, sequence and launch the orders introduced on the routing sheet into the job-shop according to the enterprise's strategic goal and the actual conditions of the production plant. The goals, information and decisions taken in process planning and production planning and control are often very different and, because of that, it is very difficult to integrate them.

The objective of this work is to develop a model that can be applied in the future to the development of an integrated process planning and scheduling tool using an integrated definition (IDEF) methodology to design an activity model, which integrates process and production planning in metal removal processes. An activity model will be used to develop a system that allows the user to plan the process and the production at the same time in collaborative engineering work. To design the activity model, a wide range of parts were evaluated and processed in an actual job-shop factory. Several activities were developed in detail to be tested in real cases, and an example of one of them is introduced in this article.     

Nonlinear predictive control of smooth nonlinear systems based on Volterra models. Application to a pilot plant

There is a large demand to apply nonlinear algorithms to control nonlinear systems. With algorithms considering the process nonlinearities, better control performance is expected in the whole operating range than with linear control algorithms. Three predictive control algorithms based on a Volterra model are considered. The iterative predictive control algorithm to solve the complete nonlinear problem uses the non‐autoregressive Volterra model calculated from the identified autoregressive Volterra model. Two algorithms for a reduced nonlinear optimization problem are considered for the unconstrained case, where an analytic control expression can be given. The performance of the three algorithms is analyzed and compared for reference signal tracking and disturbance rejection. The algorithms are applied and compared in simulation to control a Wiener model, and are used for real‐time control of a chemical pilot plant. Copyright © 2009 John Wiley & Sons, Ltd.     

Frequency and time-domain analysis on performance of a production line operated by observer-based distributed control

This article deals with the problem of controlling a tandem line of manufacturing machines such that an unknown production demand is tracked with a desired accuracy. To study this problem, a manufacturing machine is approximated by an integrator which is subject to input saturation as a result of the finite capacity of the machine. To solve the problem in the case of unknown demand rate, a combination of feedforward–feedback controller with a reduced-order observer is proposed. The decentralised feedback control strategy for a line of machines is proposed and studied both in continuous time-domain and in frequency-domain representation. The presented illustrating example for a line of four machines underlines the efficiency of the proposed frequency-domain-based performance analysis tool.     

Verification in process algebra of the distributed control of track vehicles—A case study

A real-life example of parallel processes, namely, the distributed control of track vehicles, is modeled and analyzed on the design level using process algebra techniques.We report on the stepwise development, the verification is performed, and the errors found. We show how the complexity of verification handled and argue that the verification was only possible due to computer assistance, which was available as the tool PVE (Process Verification Environment). This nontrivial, industrially motivated example may also serve as a benchmark for other methods and tools.     

Atmospheric perturbation and control of a shuttle/tethered satellite

A simplified model of the strong atmospheric perturbation of a small satellite attached to the orbiter by a long, straight tether predicts undesirable uncontrolled libration motions similar to those from sophisticated models. The simplified model is used to compare performance limitations of two simple control systems that rely only on tether tension for three-dimensional control. Because the effects on libration of both the changing kinematic and atmospheric drag torques caused by changing length are largely predictable, the controller that models these changes has substantially better performance. In particular, the altitude variation of the tethered satellite above an oblate earth can be controlled substantially better with a controller that uses a length command adapted to these predictable changes than one that only reacts to tension changes. Also, small amplitude out-of-plane librations, that are coupled only to second-order with changing length, can be damped substantially faster by the controller that periodically commands properly phased length changes than by the controller that only reacts to the second-order changes in tension.     

玻璃助剂对厚膜NTC热敏电阻器的性能影响

系统研究了Mn-Co-Ni系厚膜NTC热敏电阻器的电阻性能与玻璃助剂质量分数的关系,结果表明:当玻璃助剂质量分数为(10～30)×10-2时,电阻性能参数(RT,ρT,B和αT)随玻璃助剂质量分数的增加而显著增长;当玻璃助剂质量分数继续增加,则电阻性能参数基本不变.但当玻璃助剂质量分数为5×10-2时,厚膜电阻因烧结性能变差而导致电阻性能不稳定,同时,电阻性能参数均异常增大.当玻璃助剂质量分数为30×10-2以上时,采用本工艺制备的厚膜NTC热敏电阻器具有良好的工艺性和热稳定性.     

烟叶复烤区温度与排潮率的解耦控制仿真研究

烟叶复烤是香烟生产中的一个重要的环节,复烤过程中温度、水分直接影响了复烤后的烟叶指标和后续烟叶的制丝、打包等工序,复烤干燥区是一个复杂多变量强耦合系统。为了获得较好的控制效果,针对云南某复烤厂仅控制温度而未考虑与湿度的耦合性,并且其控制效果不佳的问题,通过采集大量现场数据,在获得干燥区排潮率软测量模型和温湿度动态模型的基础上,采用前馈解耦控制方法进行了干燥区温度与排潮率的控制仿真研究。仿真研究结果表明,干燥区温度与排潮率的前馈解耦控制与未解耦PID控制相比,具有较好的控制效果。     

Adaptive control optimization of the EDM process using minicomputers

Electro-Discharge Machining (EDM) is an electro-physical machining process fulfilling a number of requirements making it suitable for the application of adaptive control. This paper describes the EDM machine with its adaptive control system, including a minicomputer, some sensors and control devices and their respective interfaces. Software, including some strategies implemented for searching optimal working conditions, are reported. Some preliminary results illustrate the overall performance of the adaptive control system.