Models Of Flexible Manufacturing Systems Research Articles

Modeling and logic controller specification of flexible manufacturing systems using behavioral traces and Petri net building blocks

This paper deals with the definition of a general approach to the modeling and control specification of flexible manufacturing systems (FMS). The development and the analysis of complex FMS models can greatly benefit from the automatic synthesis of the complete models and the availability of a graphic tool to describe them in a concise way. The automatic synthesis helps the designer to succeed in the error-prone task of building complex Petri net models or sequential functional charts, while the graphic representation makes it easier to understand them. The paper puts together a trace-based formal specification method and a compositional Petri nets approach with predefined building blocks, leading to a unified framework whose goal is to cope with the complexity of the FMSs behaviors and constraints. The problem of logic controller specification is also considered introducing in the behavior description the interaction with the environment via input and output signals.

A comprehensive survey and future trend of simulation study on FMS scheduling

Since the late 1970s when the first collection of papers on scheduling of flexible manufacturing systems (FMSs) has been published, it has been one of the most popular topics for researchers. A number of approaches have been delivered to schedule FMSs including simulation techniques and analytical methods, whereas the former is the most widely used tool for modeling FMSs. The objective of this paper is to review scheduling study on FMSs and analyse future trend that employed simulation techniques as the analyzing tool. Scheduling methodologies are categorized into, namely traditional simulation techniques with single criterion scheduling approaches, traditional simulation techniques with multi-criteria scheduling approaches, and artificial intelligence (AI) approaches in FMSs. It is concluded that AI approaches will be dominating in future study.

Autonomy-subnet based structural synthesis and liveness guarantying policy of Petri net model of flexible manufacturing system

In this paper, an autonomous subnet based structural methodology for bottom-up synthesis of Petri Nets for Flexible Manufacturing Systems is proposed. Furthermore, the theoretical analysis of the model constructed by the method is carried by intensively using model’s structural information, such as invariants, siphons, etc.. As a result, the analysis leads us to draw the general conclusion that the model obtained is conservativeness and thus bound, and characterize its liveness in terms of zero-marking minimal siphons. It is based on model’s structural information that distinguishes our method from others. In line of this thought, a liveness guarantying policy for the obtained model is proposed. Some control subnets are merged into the original model according to the proposed synthesis rules in this paper to ensure that no minimal siphons are emptied in any state, therefore the liveness is guaranteed. As a result, a live, conservative and revertible Petri Nets is obtained. A practical example is also presented to demonstrate the effectiveness of this method.

Component and agent-based FMS modeling and controller synthesis

In order to reduce manufacturing control software design cycle and costs, it is imperative to reuse off-the-shelf software components, ensure system properties at design time, and automate software design process. To this end, a component and an agent-based plant modeling of three structures and systematic controller synthesis approaches are proposed under a hierarchical flexible manufacturing system (FMS) architecture. That is, the static structure is modeled using class diagrams of Unified Modeling Language (UML); the dynamic structure is modeled using Petri net (PN); the functional logic is modeled using rule sets. A plant PN controller can be derived systematically with the approach proposed in this article while the desirable system behaviors (e.g., liveness and cyclicness) will be obtained.

Iterative methods for flexible manufacturing systems

This paper presents an Markovian model for flexible manufacturing systems (FMSs). The model captures two important features of a FMS: the reliability of machines and the capacity of the maintenance facility. A fast numerical algorithm based on preconditioned conjugate gradient (PCG) method is developed to solve the steady state probability distribution of the system. We prove the fast convergence rate of the PCG method. The performance analysis of the FMS can be evaluated by making use of the steady state probability distribution.

Limit Cycles in a Class of Hybrid Dynamical Systems

This paper deals with qualitative analysis of the so-called switched fluid networks. Such networks are used to model communication, computer, and flexible manufacturing systems. We prove that for any deterministic network from a specific class, there exists a finite number of limit cycles attracting all the trajectories of the system. Furthermore, we determine this number.

A knowledge Petri net model for flexible manufacturing systems and its application for design and verification of FMS controllers

The development of a Flexible Manufacturing System (FMS) controller is a very complicated task, both in the aspects of hardware and software. The design and verification of the controller is crucial for the development of FMS prior to putting it into test and use. This paper presents a knowledge-based Petri net model for FMS and its application for design and verification of an FMS controller. The modelling of FMS is implemented through incorporating Petri net techniques with general problem-solving strategies in AI and knowledge-based system techniques. The places and transitions and their relations of the knowledge Petri nets are annotated, based on an object oriented representation and programming techniques, from which the knowledge Petri nets can be formulated. A template can be first defined for a knowledge Petri net model, and then the model for FMS individuals is established in the form of instances of the template. The design and verification of an FMS controller is based on the checking for the control parts of FMS with the help of temporal relationships between the specification and physical operations of the FMS controller. The approach makes it simple to express FMS controls, and procedural language can be used for knowledge and information processing. It is thus possible to make a computer programme generate a Petri net for a given FMS, which is envisaged as necessary for the design and verification of an FMS controller. The developed knowledge Petri net system for FMS is internetenabled and implemented through Java. It can be used for modelling and simulation of FMS, the design and verification of an FMS controller both as a standalone application and a www browser applet on the internet. Case studies are provided for the modelling and analysis of a FMS, and the design and verification of the FMS controller, to show the effectiveness over development with conventional methods and systems.

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.

Qualitative Analysis of a Discretely Controlled Continuous Switched Fluid Network

The paper deals with qualitative analysis of the so-called switched fluid networks. Such networks are used to model communication, computer, and flexible manufacturing systems. We prove that for any deterministic network from a certain specific class, there exists a finite number of limit cycles attracting all trajectories. Furthermore, we determine this number.

The applications of flexible manufacturing technologies in business process reengineering

Through radical redesign of business processes and systems, policies, and organizational structures, the business process reengineering (BPR) effort was initiated in the manufacturing industry to seek performance breakthroughs. This paper describes a novel approach to the BPR, which applies flexible manufacturing systems (FMSs) design and analysis technologies, such as simulation, multicriteria decision support, and artificial intelligence (AI). These technologies are integrated to design and analyze specific FMS models related to the proposed technical and managerial changes in an industrial case. First, the literature is reviewed to obtain an understanding of the BPR concept and the role of FMS design and analysis in BPR. Second, a decision-making support system is developed to illustrate how the FMS design and analysis would affect BPR. Finally, a summary of the integrated approach practice in industry and conclusions are presented. The paper shows that the key to a successful BPR approach is the identification and analysis of specific proposed models. It also demonstrates that the integrated approach enables engineers to improve the efficiency of BPR.

Comments on "Deadlock avoidance policy for Petri net modeling of flexible manufacturing systems with shared resources

In the domain of flexible manufacturing systems, given a structural (static) model of the system, the existence of cycles of resources in such a model is a necessary condition for a deadlock to be reached. This condition is not sufficient in the general case because we cannot ensure that a state which establishes a circular-wait situation is reachable (cycles of resources are only potential circular-waits). In the above mentioned paper (Xing et al., 1996) and Ezpeleta et al. (1998), two results which directly imply that the existence of cycles of resources is also a sufficient condition are presented. These results are established for a subclass of FMS, where choices are not allowed in the process plans, and where each part uses one and only one system resource in each state during its processing. Both approaches use Petri nets to model the systems, namely production Petri nets (PPN), and linear systems of simple sequential processes with resources. In fact, both models are very similar. Here we show that the proof of the result in the Xing et al. is not correct, we also show that the result itself is correct (it is implied by the result in Ezpeleta et al.). Moreover, we think that the approach in Ezpeleta et al. is clearer, and that it provides more insight into the problem.

A Methodology to the Specification and Analysis of a Generic Model for Flexible Manufacturing Systems

The purpose of this article is to elaborate a global methodology of specification design and analysis of the flexible manufacturing systems control covering the coordination level which deal with interaction manage between different workshop resources and principally with synchronization problems. This methodology is backed by a functional approach using object Petri net for specification and analysis which is performed by using the theory of invariants.

A PN Reachability Analysis Branching Scheme for the Scheduling of FMS

A branching scheme for the solution of scheduling problem based on reachability analysis of timed Petri net (PN) models of Flexible Manufacturing Systems (FMS) is described in this paper. The method reduces search by avoiding the generation of paths that do not represent an advantage with respect to already generated candidates. Experimental analysis shows that interesting results are obtained when applied to Branch and Bound, Best first A*, and incomplete search methodologies such as Beam Search.

A generic Petri net model for flexible manufacturing systems and its use for FMS control software testing

Developing a flexible manufacturing system (FMS) controller is a complicated task both in the hardware development and software development. To test the control software prior to putting it into use is crucial for the development of a FMS controller. An intelligent testing environment for FMS controllers is under development, the aim of which is to reduce manual work in the testing. To reach this objective the automatic building of a behavioural model of the FMS is demanded. This paper proposes a generic Petri net (GPN) model and approach for the development of control software for FMSs. The principle of this approach is based on checking the control parts of FMSs with the help of temporal relationships between physical operations, and the specification of the FMS controller with GPN. The strategy of GPN modelling is then incorporated with more general problem solving strategies in artificial intelligence. A template is first defined for a GPN model, and then the model for FMS individuals is established in the form of instances of the template. The transitions of the GPN are represented with the proposed general expressions with two syntaxes, 'verb+ noun' and 'verb+ noun+ where', from which the GPN can be formulated. GPN makes it simple to express FMS controls, and procedural language can also be used for information processing. A case study for the testing of FMS controller software is provided to show effectiveness and cost saving over development with conventional methods in which only ordinary Petri net and procedural language are used.

Optimal design for flexible manufacturing systems: generalized analytical methods

Advanced manufacturing systems such as Flexible Manufacturing Systems (FMSs) are capital-intensive. Designing functional yet cost-effective FMSs is a challenging task because it involves the solution of a complex series of interrelated problems. In this paper, we study a design problem for FMSs that consist of multiple types of machines. Using closed queueing network models for FMSs, this problem seeks the minimum cost design subject to meeting throughput requirements. The design decisions include the number of machine groups, the number of machines for each group, the workload allocation among machine groups, the number of pallets, the number of transporters, and the batch size. Since these design decisions are highly interdependent, we present the optimum and heuristic methods that simultaneously determine them. To our knowledge, these methods are the most general analytical methods for FMS design. Development of the heuristic methods is crucial because of the time-consuming nature of the optimum method as the number of machine types increases. Computational results show that the heuristic methods are both effective and efficient.

Incremental modeling and verification of flexible manufacturing systems

An FMS is a typical real-time concurrent system composed of a number of computer-controlled machine tools, automated material handling and storage systems that operate as an integrated system under the control of host computer(s). The growing demand for higher performance and flexibility in these systems and the interlocking factors of concurrency, deadline-driven activities, and real-time decision making pose a significant challenge to FMS design, especially in terms of control and scheduling. A formal engineering approach that helps handle the complexity and dynamics of FMS modeling, design and analysis is needed. A real-time architectural specification (RAS) model and its application in the modeling of flexible manufacturing system (FMS) are presented. RAS combines mature operational and descriptive formal methods, in particular time Petri nets (TPN) and real-time computational tree logic (RTCTL), to form an integrated system model for architectural specification and analysis of real-time concurrent systems such as FMS. The contribution of RAS is twofold: First, it provides a formal system to systematically maintain a strong correlation between (real-time) requirements and design and to verify the conformance of the design to the requirements, which helps enhance traceability and thus to help us to achieve high assurance in design. Second, it offers better scalability in modeling and analysis, which provides an effective way to deal with complexity in the application of formal methods. These two features together make RAS a suitable model for the design of FMS.

Optimal design for flexible manufacturing systems: generalized analytical methods

Advanced manufacturing systems such as Flexible Manufacturing Systems (FMSs) are capital-intensive. Designing functional yet cost-effective FMSs is a challenging task because it involves the solution of a complex series of interrelated problems. In this paper, we study a design problem for FMSs that consist of multiple types of machines. Using closed queueing network models for FMSs, this problem seeks the minimum cost design subject to meeting throughput requirements. The design decisions include the number of machine groups, the number of machines for each group, the workload allocation among machine groups, the number of pallets, the number of transporters, and the batch size. Since these design decisions are highly interdependent, we present the optimum and heuristic methods that simultaneously determine them. To our knowledge, these methods are the most general analytical methods for FMS design. Development of the heuristic methods is crucial because of the time-consuming nature of the optimum method as the number of machine types increases. Computational results show that the heuristic methods are both effective and efficient.

An architecture for flexible manufacturing cells with alternate machining and alternate sequencing

One of the characteristics of flexible manufacturing systems (FMSs) is that they can consider multiple part routing due to alternate machining and alternate sequencing in the processing of parts. This paper presents a new architecture based on colored Petri nets (CPNs) that allows the supervisory controller of a flexible manufacturing cell to consider alternate machining and alternate sequencing in real time control of the cell. This capability for real time alternate routing is an extension of prior research on the application of CPN to modeling FMSs.

Hybrid Aspects of Modelling Manufacturing Systems Using Modified Petri Nets

This paper presents a new special view on hybrid modelling of flexible manufacturing systems using a new description method basing on Petri nets (Hybrid Dynamic Nets, HDN). It shows, why hybrid modelling is useful for the design process instead of the currently preferred view based on discrete events. In order to solve handling problems, arising from the system complexity of larger systems, we combine this method with the object oriented paradigm. In the result we get Hybrid Object Nets (HON)

Automated construction of GSPN models for flexible manufacturing systems

Generalized stochastic Petri nets (GSPNs) are often used to specify flexible manufacturing systems (FMSs) and their control systems. While GSPNs are a powerful tool for system modeling, their complexity can become unmanageable for all but the simplest `toy' systems. Thus, manual construction of GSPNs can quickly become unacceptably slow and error-prone. In this paper, a formal method is developed to automatically construct a GSPN model for a given FMS. An FMS description language (FMSDL) is presented as the language for the input file of a GSPN construction program named FMSPet. FMSPet translates FMSDL input files into a GSPN system model, maps the specified process plans onto the given physical system, and attaches control stubs to resolve conflicts. The output GSPN is formatted as an input file for the stochastic Petri net package (SPNP) to support the analysis and evaluation of the structural and temporal properties of the net.