The application of expert systems to manufacturing process control

In recent years the control of the manufacturing process has received prime focus of manufacturers throughout the world. Expert systems technology allows for the implementation of sophisticated and efficient process control systems. This paper provides a framework for the application of expert systems to manufacturing process control. It details the unique features of such a system and explains the constitution of the knowledge base.     

新型的应用于过程控制的半实物仿真系统

为了满足连续型流程工业生产仿真、培训和测试的需要,在全数字仿真系统的基础上,提出了一种新型的半实物仿真系统.该系统采用OPC技术,实现了全数字仿真模型与系统硬件的通信,进而实现了计算机仿真信号到实际工业现场信号的转换,因此该仿真系统提供给过程控制系统的信号与实际现场设备完全一样.这种仿真系统能够模拟工业现场设备的运行与信号,从而为过程控制系统提供了更为真实的控制对象,同样也使得该系统的应用更加便捷且适用范围更加广泛.     

A simulation model for eliciting scheduling knowledge: an application to the precast manufacturing process

This paper discusses the process of eliciting scheduling knowledge from a simulation model and the development of a dynamic modelling approach to the scheduling process in the precast concrete industry. Due to the problems associated with eliciting scheduling knowledge from an ‘expert’ in the precast industry or perhaps in most of the manufacturing industries, simulation is used to complement human knowledge in this paper. Such knowledge will be used for online support to advise production schedulers and for further development of the simulation model by incorporating the knowledge in the model and making it more dynamic. The paper suggests that dynamic selection of scheduling rules during real-time operation has been recognised as a promising approach to the scheduling process in the precast industry. For this strategy to work effectively, sufficient knowledge is required to enable the model to predict the most effective scheduling rule to meet current factory status. The paper concludes that if the knowledge rules are used effectively, they could be a considerable managerial tool for exploring and improving managerial practices. Recommendations have been made regarding the development of a more realistic and practical scheduling system.     

Production system with process quality control: modelling and application

Over the past decade, there has been a great deal of research dedicated to the study of quality and the economics of production. In this article, we develop a dynamic model which is based on the hypothesis of a traditional economic production quantity model. Taguchi's cost of poor quality is used to evaluate the cost of poor quality in the dynamic production system. A practical case from the automotive industry, which uses the Six-sigma DMAIC methodology, is discussed to verify the proposed model. This study shows that there is an optimal value of quality investment to make the production system reach a reasonable quality level and minimise the production cost. Based on our model, the management can adjust its investment in quality improvement to generate considerable financial return.     

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。     

Development of an internet and fuzzy based control system of manufacturing process

The aim of this work is to develop an Internet and fuzzy based control and data acquisition system for an industrial process plant which can ensure remote running and fuzzy control of a cement factory. Cases studies of the proposed system application in three cement factories in Algeria, SCAEK (Setif), SCIMAT (Batna), and SCT (Tebessa), are discussed. The remote process control consists of alarms generated during running of the processes while maintaining and synchronizing different regulation loops thus ensuring automatic running of processes smoothly. In addition, fuzzy control of the kiln and the other two mills ensures that the system is operational at all times with minimal downtime. The process control system contains different operator station (OP), alarms table and a provision to monitor trends analysis. The operator can execute any operation according to his authorised access assigned by the system administrator using user administration tool. The Internet technology is used for human security by avoiding all times presence of operators at site for maintenance. Further, in case of a breakdown, the problem would be remotely diagnosed and resolved avoiding requirement of an expert on site thus eliminating traveling cost, security risks, visa formalities, etc. These trips are difficult to organize (costs, visas, risks). So the enterprise can reduce downtimes and travel costs. In order to realize a process control system guided by operators in the main control room or through Internet, the process control is based on programming in PCS 7 utilizing Cemat library and Fuzzy Control++ Siemens tools.     

Evaluation of techniques for manufacturing process analysis

In the last 20 years, several methodologies, models and tools have been developed for the analysis and optimisation of manufacturing systems in order to propose general improvements. Many of these techniques make extensive use of data modelling, simulation, decision-making support, expert systems and reference models. This paper presents the first outcome of a piece of research work to integrate manufacturing process analysis into an integrated modelling framework covering all aspects related to the shop-floor as it really is. The main methodologies and software tools have been identified and evaluated and the results tested on industrial examples. As a result of this evaluation it has been possible to identify the inefficiencies of the techniques. These problems are connected with integrating the different types of data to be analysed—such as quality, time, costs, resource capacity, productivity, flexibility or improvements—into a single analysis environment. The inefficiencies detected enable us to present a general framework for making better use of modelling techniques for manufacturing process analysis. Received July 2005 / Accepted January 2006     

Petri net based process scheduling: A model of the control system of flexible manufacturing systems

In this paper, we propose a class of algorithms for the sub-optimal solution of a particular class of problems of process scheduling, particularly focusing on a case study in the area of flexible manufacturing systems (FMSs). The general class of problems we face in our approach is characterized as follows: there is a set of concurrent processes, each formed by a number of temporally related tasks (segments). Tasks are executable by alternate resource sets, different both in performance and costs. Processes and tasks are characterized by release times, due dates, and deadlines. Time constraints are also present in the availability of each resource in resource sets. It has been proven that such a problem does not admit an algorithm for an optimal solution in polynomial time. Our proposed algorithm finds a sub-optimal schedule according to a set of optimization criteria, based on task and process times (earliness, tardiness), and/or time independent costs of resources. Our approach to process scheduling is based on Timed Coloured Petri Nets. We describe the structure of the coordination and scheduling algorithms, concentrating on (i) the general-purpose component, and (ii) the application-dependent component. In particular, the paper focuses on the following issues: (i) theautomatic synthesis of Petri net models of the coordination subsystem, starting from the problem knowledge base; (ii) the dynamic behavior of the coordination subsystem, whose kernel is a High Level Petri net executor, a coordination process based on an original, general purpose algorithm; (iii) the structure of the real-time scheduling subsystem, based on particular heuristic sub-optimal multi-criteria algorithms. Furthermore, the paper defines the interaction mechanisms between the coordination and scheduling subsystems. Our approach clearly distinguishes the mechanism of the net execution from the decision support system. Two conceptually distinct levels, which correspond to two different, interacting implementation modules in the prototype CASE tool, have been defined: theexecutor and thescheduler levels. One of the outstanding differences between these levels is that the executor is conceived as a fast, efficient coordination process, without special-purpose problem-solving capabilities in case of conflicts. The scheduler, on the other hand, is the adaptive, distributed component, whose behavior may heavily depend on the problem class. If the scheduler fails, the executor is, in any case, able to proceed with a general-purpose conflict resolution strategy. Experimental results on the real-time performance of the kernel of the implemented system are finally shown in the paper. The approach described in this paper is at the basis of a joint project with industrial partners for the development of a CASE tool for the simulation of blast furnaces.     

Evaluation and optimisation of integrated manufacturing system operations using Taguch's experiment design in computer simulation

The application of computer simulation have been proposed and implemented to solve the problems of variation in integrated manufacturing systems. However, a simulation model only acts as a tool in examining performance. It is essentially a trial and error methodology, and does not directly provide explanations for observed system behaviours. Therefore, in this paper the use of Taguchi's Experiment Design in simulation is studied to solve decision-making problems in integrated manufacturing systems. In particular, we use the case of a steel soaking-pit/rolling-mill plant to demonstrate how the approach works. The results reveal that this approach can take into account the evaluation and optimisation of operating conditions in complex systems simultaneously.     

A manufacturing system with general stationary failure process:stability and IPA of hedging control policies

This paper concerns a new methodology for the adaptive optimization of piecewise deterministic non-Markovian systems via a simple example of interest in manufacturing. This methodology takes into account the fact that piecewise deterministic systems are rarely Markovian and that classical control theory based on dynamic programming of Markovian systems cannot provide quantitative answers in most realistic situations. The example considered is that of a single-machine/single-part production system, from the point of view of the control theory by Kimemia and Gershwin (1983). We obtain stochastic gradient estimates via the perturbation analysis of Ho and Cao (1991) by the “regenerative” method of Konstantopoulos and Zazanis (1992), in view of stochastic optimization. Its mathematical justification requires a careful study of the “regenerative” structure of the process. In particular, we give the necessary and sufficient conditions of stability of this system via the method of Loynes (1962)     

An object-oriented manufacturing control system

This paper presents the development of an event-driven control architecture and its implementation in a physical simulator of a computerized manufacturing system using object-oriented techniques. The architecture was developed to improve the efficiency of handling concurrent control events in the DOS environment. In the implementation, the control system of the physical simulator consists of four distinct layers of control devices: a PC/386 computer, a microcontroller, I/O modules and the system's control devices such as motors, solenoids and sensors. A control program residing in the PC/386 coordinates system-level tasks such as event scheduling, while a BASIC program running on the microcontroller handles all low-level control tasks such as sensor monitoring and motion control. The concepts and developments presented in this paper should help in implementing an efficient control system for both CIM systems and their physical simulators.     

P、I参数在控制系统中的应用

0　引　言Ｐ、Ｉ参数控制在实际控制系统中应用较多 ,然而对不同实际系统中的Ｐ、Ｉ参数如何设定 ,使得被控对象既不产生振荡 ,又能快速地达到状态 ,就显得极为重要了。现将在ＤＣＳ系统中不同的系数的Ｐ、Ｉ参数的设定分别介绍如下。1　对于液位、料位控制Ｐ、Ｉ参数的确立设一被控对象如图 1所示 ,为木片仓料位与卸料螺旋速度之间的关系。　　 (1)　将被控对象首先设定到手动状态 ,然后调节螺旋的输出位。使木片仓的料位稳定下来 ,不再增高 ,也不再下降 ;(2 )　给卸料螺旋在原基础上加一个阶跃信号Ａ ,如Ｄ % ,如图 2所示 ;　　 (3)　从给…     

Semiconductor manufacturing process control and monitoring: A fab-wide framework

The semiconductor industry has started the technology transition from 200 mm to 300 mm wafers to improve manufacturing efficiency and reduce manufacturing cost. These technological changes present a unique opportunity to optimally design the process control systems for the next generation fabs. In this paper we first propose a hierarchical fab-wide control framework with the integration of 300 mm equipment and metrology tools and highly automated material handling system. Relevant existing run-to-run technology is reviewed and analyzed in the fab-wide control context. Process and metrology data monitoring are discussed with an example. Missing components are pointed out as opportunities for future research and development. Concluding remarks are given at the end of the paper.     

Design for manufacturing meets advanced process control: A survey

Nanometer IC designs are increasingly challenged to achieve manufacturing closure, i.e., being fabricated with high product yield due to feature miniaturizations and process variations. Realizing the critical importance of addressing manufacturability/yield during design (which is loosely termed as DFM, design for manufacturing), there has been a surge of research activities recently from both academia and industry under the “DFM” umbrella. While the primary goal of DFM is to enlarge the manufacturing process yield window, DFM needs to work together with advanced process control (APC) to meet such window, which may be shrinking and changing from design to design. The paper will survey the key DFM activities and discuss related advanced process control issues (i.e., the counterpart of manufacturing for design) to provide a holistic perspective on the design and process integration.     

Feedback control logic for forbidden-state problems of marked graphs: application to a real manufacturing system

This paper addresses the forbidden-state problem of general marked graphs with uncontrollable transitions. The models need not to be safe nor cyclic. Control requirements are expressed as the conjunction of general mutual exclusion constraints (GMEC) of markings of so-called critical places. Structural properties such as influence paths and influence zones are proposed to perform the worst-case analysis for each GMEC specification with any given initial marking when only uncontrollable transitions are allowed. Efficient solutions are proposed for the determination of the maximal uncontrollably reachable marking of any critical place, and this for many possible, more or less general, configurations of the net structure, even for the case of overlapping paths of critical places. Besides, we demonstrate that these results can be easily extended to unbounded nets and when critical places have negative weights. For the most general case, when analytical solution is not available, a linear programming approach is proposed. The great advantage of the proposed approach over existing methods is emphasized by using it to solve the supervisory control problem of the automated manufacturing system of Atelier Inter-etablissements de Productique Rhone Alpes Ouest (AIP-RAO), Lyon, France.     

Time-optimal production control in a manufacturing system

This study demonstrates the use of control engineering techniques to regulate the product inventory levels of a workshop in a manufacturing system by manipulating the number of machines and the labour time employed during production. The production policy that minimizes the production time is obtained by time-optimal control techniques.     

电厂锅炉燃烧系统先进过程控制实验仿真平台

锅炉燃烧控制系统是一个多变量、强耦合、非线性、大时滞的不确定性系统,因此APC控制策略已成为解决其控制问题的主要手段。本文设计了一套涵盖优化层、监控层及过程层的,半实物的锅炉燃烧系统APC控制实验仿真平台。基于以太网及OPC通信,该平台实现了控制器、虚拟对象、组态系统及优化模型之间数据的互联互传。本文以模糊神经网络控制算法作为APC控制策略示例进行系统功能验证,仿真结果表明该平台有助于工程设计人员在现场调试前对锅炉燃烧系统的顺序逻辑控制和先进控制策略进行验证。     

Message-oriented decomposition for supervisory control in manufacturing system

Supervisory control in manufacturing systems is achieved through messages between the supervisory controller and processing devices. This paper presents a message-oriented model for supervisory control. The model supports realistic states for processing stations and some material handling devices. The major characteristics of the model are the decomposition of the system into small state models for components that cooperate via messaging as well as the algebraic manipulation for state progression. This paper also presents a definition of controllability meaningful in the design and analysis of supervisory control systems. The modeling and analysis are illustrated with a flow line example and a robotic cell example.