Semi-heterarchical Allocation and Routing Processes in FMS Control: A Stigmergic Approach

This paper deals with the production process control in flexible manufacturing systems (FMS), in which heterarchical relations exist between some decisional entities. After presenting a brief state-of-the art of the literature on the heterarchical concept we propose a semi-heterarchical control structure (composed of DAP: dynamic allocation process and of DRP: dynamic routing process), and explain the objective of our study. After presenting the concept of stigmergy, we focus in this paper on our innovative approach to routing in DRP including the active product concept. We then describe our two levels model and its main components (a virtual level VL in which virtual active products evolve stochastically in accelerated time, and a physical level PL in which physical active products evolve deterministically in real time). Our innovative approach exploits the capacity of a stigmergic routing control model to automatically find efficient routing paths for active products in FMS undergoing perturbations. After a brief presentation of the Netlogo simulation context, the qualitative and quantitative results are presented. The results illustrate the advantages of our routing approach and its capacity to surmount perturbations. The integration and implementation of our approach at the AIP-PRIMECA center in Valenciennes France is then detailed. Finally, we provide a brief overview of our future research concerning: firstly, a way to link our DRP model with the DAP distributed control system, secondly, the re-formulation of our model within the HMS (holonic manufacturing system) concept, and thirdly, the development of a new challenging and innovative concept of “hypervision”.     

A review of pseudospectral optimal control: From theory to flight

The home space for optimal control is a Sobolev space. The home space for pseudospectral theory is also a Sobolev space. It thus seems natural to combine pseudospectral theory with optimal control theory and construct “pseudospectral optimal control theory”, a term coined by Ross. In this paper, we review key theoretical results in pseudospectral optimal control that have proven to be critical for a successful flight. Implementation details of flight demonstrations onboard NASA spacecraft are discussed along with emerging trends and techniques in both theory and practice. The 2011 launch of pseudospectral optimal control in embedded platforms is changing the way in which we see solutions to challenging control problems in aerospace and autonomous systems.     

Agent-based FMS control

Future manufacturing systems will be integrated into the networks of distributed resources, and at the same time, such systems will be capable of processing both knowledge and material. It will probably be required that manufacturing systems be agile, flexible, and fault-tolerant. Petri nets (PN) and object-oriented design (OOD) are used together in order to develop the integrated agent-based FMS control system. The flexible manufacturing system (FMS) consists of machines, workstations, and automated material handling system, distributed buffer storage sites and computer-based supervisory control, all which can be modeled as an agent in OOD with PN. This paper introduces the design of an agent-based FMS control system through PNs and evaluates the performance using timed placed Petri nets (TPPN). In order to do so, the agent control design, FMS structure has been evaluated in detail and the agent definitions have been submitted. The system includes the sharing and distribution of tasks among agents and the mentioned structure has been simulated by TPPN. The simulation procedure has been realized through Petri Net 2.0—MATLAB Demo Program [Mahulea CF, Motcovschi MH, Pastravanu O. Department of Automatic Control Industrial Informatics, Technical University “Gh. Asachi” of Iasi, Blvd., Mangeron 53A, 6600 Iasi, Romania, 〈http://www.ac.tuiasi.ro/pntool,pntool@ac.tuiasi.ro〉, 2004.]. Each case is modeled, and then the agent's machine processing time is considered in this program. As for the evaluation of the study, the system performance is assessed through the waiting time of the parts in queue and the task distributions.     

Attractor dynamics approach to formation control: theory and application

In this paper we show how non-linear attractor dynamics can be used as a framework to control teams of autonomous mobile robots that should navigate according to a predefined geometric formation. The environment does not need to be known a priori and may change over time. Implicit to the control architecture are some important features such as establishing and moving the formation, split and join of formations (when necessary to avoid obstacles). Formations are defined by a formation matrix. By manipulating this formation matrix it is also possible to switch formations at run time. Examples of simulation results and implementations with real robots (teams of Khepera robots and medium size mobile robots), demonstrate formation switch, static and dynamic obstacle avoidance and split and join formations without the need for any explicit coordination scheme. Robustness against environmental perturbations is intrinsically achieved because the behaviour of each robot is generated as a time series of asymptotically stable states, which contribute to the asymptotic stability of the overall control system.     

From theory to national application—A Finnish experiment

In 1968 the Finnish National Fund for Research and Development started a 3 year project to ‘introduce ergonomics into Finnish production’. A multidisciplinary group, comprising five persons sponsored by the Institute of Occupational Health, was formed.

The concept of ergonomics, at the time the project was founded, was relatively unknown in Finland, although as early as 1962 international course activity on the subject was begun at the Institute of Occupational Health. Little competent ergonomic knowledge existed in the realm of industry, which at that time claimed 500000 workers, and what did was poorly used.

The adopted strategy of the 3 year project was as follows: (a) an attempt was made to convince potential users of ergonomic knowledge of its utility by working out a number of examples on the application of ergonomics; and (b) the availability of ergonomic information was to be improved. By the time the project was completed in 1971, ergonomic activities had reached such a degree of acceptance that it was deemed necessary to maintain the multidisciplinary group and provide it with additional resources. These extended activities are outlined in this paper.     

Application of grey system theory to phosphorite sinter process: From modeling to control

The sintering process of phosphorite ore occurs with a large amount of return caused by untimely process control. The control task of phosphorite ore sintering is to regulate the parameters of the process to obtain a high quality sinter. The parameter clearly responsible for sinter quality is the temperature in the wind box. Therefore, in order to solve the control task, it is necessary to predict the highest temperature of the charge (also known as the burn through point (BTP)). In this paper, the theory of grey systems is used as a predictive model, which makes it possible to obtain an adequate model that uses a small number of initial samples of real temperature data. Based on the grey model GMC(1,n) a new optimal model is presented, which is constructed by using optimization algorithm. Optimal model predicts the BTP, and to establish an optimal regulation, a control synthesis is carried out through an optimization of the prediction according to the “particle swarm” algorithm.     

On implicit modelling theory: Basic concepts and application to adaptive control

The paper aims at presenting a unifying theory regarding the so-called “implicit models”. In adaptive control theory, this term commonly indicates system models which do not correspond to the true one, although they convey all the necessary information for the synthesis of the optimal controller, and are simpler to be identified. In the paper, ARX implicit models are considered and their possible use in adaptive control algorithms based on LQ or pole assignment control criteria is discussed.     

FMS control design: an information value approach

The work presented in this paper demonstrates a new approach to design of an information-efficient automatic supervisor of manufacturing systems. Such a supervisor ignores some available information without a significant decrease in the expected performance of the system. In addition to efficient supervisor (space and time), this leads to a design that requires less sensory equipment. The design process itself is made simpler and cheaper. The model of an automated system combines the basic concepts of the theory of controlled discrete event systems with some ideas of the information economics. A constructive algorithm of control design uses heuristic techniques of stochastic optimization. The method is applied to design of a flexible manufacturing cell.     

An application of fuzzy set theory to inventory control models

A method for solving an inventory control problem, of which input data are described by triangular fuzzy numbers will be presented here. The continuous review model of the inventory control problem with fuzzy input data will be focused in, and a new solution method will be presented. For the reason that the result should be a fuzzy number because of fuzzy input data, and the certain number about order quantity is prefered in the real-world, it is necessary to transform the fuzzy result to crisp one. The interval mean value concept is used here to help to solve this problem. Under the condition of total cost minimum, the interval order quantity maximum can be obtained.     

Iterative learning control — 2D control systems from theory to application

It has long been recognized that iterative learning control is a 2D system, i.e. information propagation occurs in two independent directions. In this paper, the application of so-called norm optimal iterative learning control, which has its origins in the theory of the class of 2D systems known as linear repetitive processes to an experimental testbed in the form of a chain conveyor system is reported. This includes the motivation for applying iterative learning control to such systems, the design and construction of the testbed, and its use to demonstrate that norm optimal iterative learning control gives superior performance over alternatives. As such, it provides an application for 2D systems theory where distinct advantages arise from using such a setting for modelling and control.     

Temporal databases: From theory to applications

Problems concerning the date and time representation in databases are well studied in scientific literature. Temporal databases are required in many applications including the conventional applications of DBMSs such as financial systems. However, commercial systems and standards for the query language do not support temporal data features. A simple and efficient approach for implementing temporal capabilities over conventional commercial DBMSs is proposed and various aspects of its practical applications are described.     

Generalized Bayesian inference in a fuzzy context: From theory to a virtual reality application

A generalized Bayesian inference framework in order to embed fuzzy sets and partial probabilistic information is provided. The general framework of reference is that of coherent conditional probabilities, which allows giving a rigorous interpretation of membership function as a conditional probability, regarded as a function of the conditioning event. The inferential problem needs to be studied in situations where the prior can be partial; moreover, membership and prior can be given on different classes of events. This inferential model is applied for the virtual representation of a female avatar.     

LF炉电极控制原理及应用

LF炉是目前最广泛应用的炉外精炼设备之一,LF炉的主要任务包括脱氧、脱硫、去气、去夹杂物、升温并调整出钢温度,合金化并调整钢水化学成分。电极调节是LF炉冶炼的关键技术,本文介绍攀钢方坯连铸LF炉电极控制系统的结构及原理,详细描述了系统的调节模式。     

An effective potential field approach to FMS holonic heterarchical control

This paper points out the capabilities of a heterarchical control approach, based on potential fields, to simultaneously solve the problems of dynamic allocation and routing in a real flexible manufacturing system. This paper proposes a “Potential fields” approach, as the key reactive mechanism to handle the transient state of ADACOR designed by Leitão & Restivo (2006) and its real implementation. First, a “Potential fields” model, which takes certain constraints into account, such as dynamic transportation times and limited resource storage capacities is presented. Then, the flexibility and robustness of the approach are highlighted, with a set of scenarios performed in simulation and on a real physical system: the AIP-PRIMECA cell. These results are compared to the results provided by a mixed-integer linear model that was used to compute lower bounds.     

An application of control theory to a problem in educational planning

The paper treats an example arising from a problem in educational planning. The provision of places in a sector of education to satisfy an unknown social demand is treated as a "dual-control" process. Dynamic programming is used to determine the sequence of decisions which extremizes a performance criterion. Results are obtained for different forms of a priori distributions of the unknown demand. Because answers can be obtained analytically without approximation, the optimum policy can be compared with the nonoptimum policy of optimizing stage by stage. The paper also discusses the effect of the decision maker's a priori knowledge upon the infinite stage process.     

A CONWIP model for FMS control

Production inventory control is one of the most important aspects of a flexible manufacturing system (FMS) design. CONstant Work In Process (CONWIP), which is a hybrid of push-and-pull type systems, offers an alternative to effective utilization of the expensive FMS equipment while still meeting customer requirements. In the selection of an FMS control method, material handling often becomes one of the capacity constraints which forms the basis of various research interests. In this paper, a structure-based model for a CONWIP-controlled FMS is proposed, and within it, the node type characteristics concept is used to describe the constraints in FMS. Furthermore, simulation is used to determine the card number based on the structure-based model. The simulation results demonstrate that the model is suitable for the design and operation of FMS. The model can be used as a manufacturing execution system of enterprise resources planning. An architecture for this integrated design based on Internet/Intranet systems is also proposed.     

From irreversible thermodynamics to a robust control theory for distributed process systems

In this paper we combine recent results that link passivity, as it is understood in system's theory, with concepts from irreversible thermodynamics to develop a robust control design methodology for distributed process systems. In this context, we show that passivity and stabilization of systems where non-dissipative phenomena are taking place is possible under very simple, finite dimensional control configurations. These include, boundary and high gain controllers, which combined with robust identification schemes should be able to provide efficient plant operation.     

An object-oriented model for FMS control

The flexible manufacturing system (FMS) is a distributed network of heterogeneous programmable manufacturing machinery, such as assembly lines and numerically controlled machines. Despite these interconnected, programmable hardware elements, the success of building a truly flexible manufacturing system has been limited so far, owing to the lack of flexibility in its control software layer. In integrating heterogeneous machinery, many existing FMS control software systems depend structurally on specific machinery and job-scheduling strategies, and thus it is difficult to incorporate new developments in FMS organization and operational requirements. In searching for an open architecture for the FMS control software system, this paper presents an object-oriented FMS data model. Among others, it represents each physical cluster of related machinery (called a flexible manufacturing cell) as an object. To facilitate the integration of heterogeneous physical cells, such cell objects share a common protocol of interacting with the main control process through inheritance from the abstract cell class. Other related physical and abstract entities in FMS are also modelled as objects, with their similarity and difference captured in inheritance hierarchies. To verify the proposed approach experimentally, a prototype FMS control software system named FREE (FMS Runtime Executive Environment) has been implemented on top of a commercial object-oriented database system.