Agent-based FMS control

To simulate and debug or diagnose manufacturing systems is always challenging. This paper presents a hybrid PLC-controlled and PC Visual Basic (VB)-based Human-Machine Interface (HMI) platform based on Petri net (PN) theory for Manufacturing Systems. An augmented PN model was adopted to design and simulate the operational sequence of the Flexible Manufacturing System (FMS) at the National Kaohsiung First University of Science and Technology (NKFUST). With the simulated PN model, the control sequences were quickly translated into PLC programs. A PC-based HMI monitoring system based on the PN model was developed to provide an intuitive offline simulation and online diagnostic tools for the FMS. This hybrid system shows many of advantages by using the economical discrete control unit with PLC, and PC-based HMI using PN model as a base. The discrete event control sequence of an FMS can be easily modeled and evaluated before its build-up. More importantly, it can be diagnosed online when the system is malfunctioning. That is, the presented system provides an adequate means for offline system design, simulation, performance evaluation, and quick online system diagnostic.

Deadlock/livelock problems can cause catastrophic results in flexible manufacturing systems (FMS) by forcing them to stop production processes at an unpredictable stage of production. Therefore, they must be handled properly in order to obtain flawless production in FMS. Petri net (PN) based deadlock/livelock studies for FMS have been widely carried out to obtain live PN models. When a PN model is live, this ensures that the modelled FMS is deadlock-free. Firstly, an uncontrolled (plant) PN model is constructed for the FMS suffering from deadlocks/livelocks. Then reachability graph (RG) analysis of this PN model is carried out to provide all possible reachable states of the modelled system. An RG of a PN model of an FMS suffering from deadlock/livelock problems can be split into the live zone (LZ) and the deadlock zone (DZ). The former is the set of system states considered to be legal (good), while the latter is the set of system states regarded to be illegal (bad). The LZ represents the optimal (maximally permissive) system behavior that must be provided by an optimal control policy. Generally, in PN based liveness studies, a liveness enforcing supervisor (LES) consisting of a set of control places (CP) is computed. Then the controlled (closed-loop) PN model is obtained by merging the plant PN model and the LES. If the number of reachable live states of the controlled PN model is the same as the ones that exist in the LZ, then the controlled model is optimal. Otherwise, it is suboptimal. The greater the number of live reachable states of the RG, the more products to be produced within the FMS. Therefore, the number of reachable live states of the controlled PN model is considered as a quality measure. It defines the behavioral permissiveness of the controlled model. In the literature, to verify the behavioral permissiveness of the PN models, the PN tool called INA (Integrated Net Analyzer) has been widely used. Recently, by means of INA, a method was proposed to compute the number of states within the LZ and the DZ of a given PN model suffering from deadlocks/livelocks. Unfortunately, INA cannot compute RGs of large PNs having a few millions of states. Therefore, in this paper by means of TINA (TIme petri Net Analyzer), an alternative faster and much more efficient method is proposed for the computation of the number of states within the LZ and the DZ for PN models with large RGs. In addition, in order to enable the development of new PN based deadlock prevention methods, further computations are also proposed. These include the computation of the set of states in the DZ, LZ and first met bad markings (FBMs) for a given PN model suffering from deadlocks/livelocks. The applicability and the effectiveness of the proposed methods are demonstrated by considering several well-known examples of FMS from the relevant literature.INDEX TERMS Flexible manufacturing systems (FMS), deadlock, deadlock prevention, Petri Nets (PN), liveness enforcing supervisor (LES), PN computation tools.

This paper presents a new approach for modeling discrete manufacturing systems using Petri nets. Starting with the literature review of the classical approaches, this paper describes the new approach known as Activity-Oriented Petri Nets (AOPN). The AOPN approach provides expressive Petri net models that are powerful enough for modeling complex and large-scale manufacturing systems. The AOPN approach provides compact Petri net model too when a large number of resources are used in the manufacturing system. GPenSIM is a software implementation of AOPN on MATLAB platform. Using a flexible manufacturing system as a running example, this paper also shows how a real-life manufacturing system can be modeled and simulated with the GPenSIM software using AOPN approach.

A flexible manufacturing system (FMS) is an integrated system of numerically-controlled machine tools and an automated material handling system under the supervision and control of an on-line host computer (Draper, 1984). An FMS can simultaneously process a number of different part-types of medium batch sizes in a random manner. FMS is fast becoming an appropriate production method for mid-volume batch manufacturing. This is due to the fact that FMS has dual advantages over conventional production methods, especially the job shop production system. The advantages are, namely, higher production efficiency and greater flexibility with regard to part-type variety and production.

In this paper we present an approach for modelling and analyzing flexible manufacturing systems (FMSs) using Petri nets. In this approach, we first build a Petri net model (PNM) of the given FMS in a bottom-up fashion and then analyze important qualitative aspects of FMS behaviour such as existence/absence of deadlocks and buffer overflows. The basis for our approach is a theorem we state and prove for computing the invariants of the union of a finite number of Petri nets when the invariants of the individual nets are known. We illustrate our approach using two typical manufacturing systems: an automated transfer line and a simple FMS.

In this paper, we use Petri nets to analyse flexible manufacturing systems (FMS) to achieve the following objectives. The first objective is to derive a theorem for checking the buffer overflows in an FMS. The second objective is to schedule the earliest starting times for a sequence of operations in an FMS by the timed Petri net. The FMS may involve many part types, machines, pallets and so on. The third objective is to detect the deadlock phenomenon by a corrected algorithm of the P-invariant theory for Petri nets. This method will enable us to know whether there exists any deadlock in an FMS. The algorithm is implemented in the Turbo Pascal language. The fourth objective is to search for the optimal scheduling rule in an FMS. The search procedure is also implemented in the Turbo Pascal language¨ The optimal machine scheduling rule can result in a better throughput.

High quality and low-cost factors are among the main components of manufacturing. Nowadays, businesses need to keep up with technological innovations in order to meet these factors and survive in a competitive environment. These require the use of high-performance computer integrated manufacturing (CIM) technologies in order to manufacture products faster, inexpensively, flexibly and more efficiently. These technologies generally include computer-aided design (CAD) and computer-aided manufacturing (CAM), industrial robotics, automated material handling systems, group technology, flexible manufacturing systems (FMS), rapid prototyping (RP) operations and computer numerical controlled (CNC) machines. The main purpose of these advancements is to provide higher labour efficiency and flexibility, lower production time and a reduction of direct labour requirements. In this chapter, the effects of CIM technologies on manufacturing processes as well as product quality will be comparatively analysed. The effect of the internet of things (IoT), cyber-physical service (CPS) and cloud computing (CC) on smart manufacturing systems, which can be operated and integrated with CIM and contribute to increasing manufacturing efficiency by using information, will be revealed in detail.

The modeling of flexible manufacturing systems (FMS) under uncertainty and evaluation of a rule base for online scheduling is considered. To represent uncertain events in FMS, such as failure of machine tools, repair time and processing time, apply continuous-time and discrete-time stochastic Petri nets with hierarchical structure to constructing the FMS model. To obtain an efficient schedule of FMS with on-line real-time basis, the authors construct a rule base and evaluate the performance of the rule base using the FMS simulation system. >

Solving the deadlocks avoidance problem in Resource Allocation Systems (RAS) in Discrete-Event Systems (DES) is a rife problem, especially in Flexible Manufacturing Systems (FMS), alias Automated Manufacturing Systems (AMS). Petri Nets (PN) are an effectual tool often used at this procedure. In principle, there are two basic approaches how to deal with deadlocks in RAS based on PN. They are listed and illustrated here. First of the approaches is realized by means of the supervisor based on P-invariants of PN, while the second one is realized by means of the supervisor based on PN siphons. While the first approach needs to know the reachability graph/tree (RG/RT) expressing the causality of the development of the PN model of RAS, in order to find (after its thorough analysis) the deadlocks, the second approach needs the thorough analysis of the PN model structure by means of finding siphons and traps. Next, both approaches will be applied on the same PN model of RAS and the effectiveness of the achievement of their results will be compared and evaluated. Several simple illustrative examples will be introduced. For the in-depth analysis of the problem of deadlock avoiding, next Part 2 of this paper is prepared, where the newest research will be introduced and illustrated on more complicated examples. If necessary (because of the limited length of particular papers), also the third part – Part 3, will be prepared.

A flexible manufacturing system (FMS) due to its ability of being flexible in nature is concerned with automatic production of different parts in medium range. In short, it can be regarded as an automated manufacturing system. In this paper, an insight on previous work in the area of FMS modelling has been provided with an overview of research and development for better understanding of FMS. It serves as a medium for investigation of work that are accomplished by using different modelling techniques in FMS like mathematical, artificial intelligence, hierarchical, multi criteria decision-making method, Petri Nets and simulation. This paper will help researchers who are keen to do research in the area of FMS modelling, by highlighting contribution of available techniques in the field of FMS. It will also help them in deciding which modelling techniques can be used for a given problem. At last, comparison of different parameters considered in the recent papers of modelling FMS has been provided in the form of Table, along with a clear vision related to those works that still need to be investigated.

This paper presents a heuristic search approach for scheduling flexible manufacturing systems (FMS) with due dates based on the Petri net state equation. It is known that the state equation of a Petri net has a solution if the goal marking can be reached from the initial marking. In terms of scheduling, this denotes that the costs of jobs can be obtained from the solution. In this paper, the idea of jobwise Petri nets is introduced. A jobwise net is a part of the model of an FMS. It is only associated with one job and the resources that the job uses. A model of N jobs can be split into N jobwise net models. We combine jobwise Petri nets and the state equations to implement the search algorithm. The objective is to minimize weighted tardiness (lateness), which is the difference of the completion time of a job and its due date. In order to show that this scheduling method can get near-optimal solutions, we compare it with some commonly used dispatching rules by simulations.

Modelling Flexible Manufacturing Systems Based on Petri Nets

This paper describes the ways of using program tools for design and simulation of flexible manufacturing systems (FMS) for the purpose of teaching the undergraduate course Flexible Manufacturing Systems. The concept of the course is based on the synergism of theoretical knowledge and practical hands-on experience gained by studying numerous problem cases, using common tools for description of FMS (Petri nets, max-plus algebra and matrix modeling) and by working with more specialized program tools for FMS design and simulation. An emphasis is given to the description o the program tool FlexMan that enables elegant setting of an FMS configuration, supports automatic generation of a matrix-based FMS description and consequently, enables effective off-site design and simulation of the FMS by using virtual reality models and Internet-related technologies.

Ch. 1. Modeling and numerical methods in manufacturing system using control theory

Automated manufacturing systems, including flexible manufacturing systems (FMSs), belong to the class of discrete event dynamic systems. In such a system, potentially conflicting events may occur due to concurrency. The problem of collision and deadlock avoidance can be investigated using Petri nets which are powerful techniques suitable for modeling concurrent processes. A Petri net based approach is employed in this paper to model, detect and avoid collisions and deadlocks in FMSs. Unlike the existing Petri net based techniques, the proposed approach uses the concept of critical states to avoid the system from entering a state leading toward a deadlock state. A multirobot assembly example is used to illustrate the proposed scheme.