Models Of Flexible Manufacturing Systems Research Articles

From Nash Q-learning to nash-MADDPG: Advancements in multiagent control for multiproduct flexible manufacturing systems

The emergence of flexible manufacturing systems (FMS) capable of processing multiple product types is a result of the growing demand for product customization and personalization. Such multiproduct systems are characterized by a higher level of uncertainty and variability when compared to traditional manufacturing systems. This paper proposes a Nash integrated multiagent deep deterministic policy gradient method (Nash-MADDPG) to control the mobile robots’ assignment in a multiproduct FMS to enable intelligent decision-making, interaction, and dynamic learning capabilities. A mathematical model of a multiproduct FMS from a previous study is described, and system dynamic property is characterized by permanent production loss (PPL). Then, by observing PPL of the system and market demand for each product type, the multi-agent control scheme is developed to assign mobile robots to load/unload various product types at various machines. First, a Nash game is developed among the mobile robots and to improve the cooperation, a collaboration cost is defined. This collaboration cost is then used in the reward function of the multiagent deep deterministic policy gradient (MADDPG) algorithm. Second, the actions are jointly defined based on the action values of MADDPG, and the mobile robots’ strategies in the Nash game, which update the environment to a new state. The performance of the proposed method is verified by comparing it with conventional Nash Q-learning, vanilla MADDPG, Q-learning based single agent reinforcement learning (SARL) and a first-come-first-serve (FCFS) based control. The results demonstrate that the multi-agent control scheme under the proposed Nash-MADDPG is effective in dealing with cooperative FMS environment that involves complicated dynamics and uncertainties.

An energy-aware optimisation model to minimise energy consumption and carbon footprint in a flexible manufacturing system

This paper proposes an energy-aware production schedule model for flexible manufacturing systems (FMSs) that aims to minimise energy costs and carbon tax while considering rising energy costs and environmental policies motivated by climate change concerns. The model is based on a sequence-dependent five-machine FMS scheduling problem, which is flexible in levels of parts, tools, machines, and routings. The proposed model is solved as a multi-objective problem, with tardiness and energy consumption as primary goals and carbon footprint reduction policies incorporated into the framework as control strategies. The machine ON/OFF strategy is also introduced to reduce idle energy. The study analyses the trade-off between minimising tardiness and carbon emissions to achieve both service level and environmental sustainability of the FMS. The proposed model reduced total energy consumption and carbon emissions by 20% and 21%, respectively, without compromising manufacturing deadlines. Future research may explore the integration of renewable energy sources and storage systems, considering more complex manufacturing scenarios, such as stochastic demands, machine failures, and workforce constraints.

An Analytic Hierarchy Process (AHP) Framework for Selecting Flexible Manufacturing System

The main objective of this paper is to propose a structured model for evaluating different Flexible Manufacturing System (FMS) using the Analytic Hierarchy Process (AHP). The paper aims to demonstrate how the model can help in taking correct decisions regarding the type of manufacturing flexibility needed for best FMS. This is because huge amount of money is invested to implement FMS in the industry. Hence, managers need to take judicious decision regarding the type and level of manufacturing flexibility. There are a number of manufacturing flexibility being reported in the literature. In this paper the most fundamental types i.e., machine, routing and product flexibility are examined. The AHP is aimed at integrating different measures into a single overall score for ranking decision alternatives. Its main characteristic is that it is base on pairwise comparison judgment. A usability evaluation of the AHP based model of FMS along with structure of the hierarchy is developed. The framework that is used in this example could serve as one of the tools for making a strategic decision. The effectiveness of our model is demonstrated through numerical examples.

Perancangan Model Stacker Crane Flexible Manufacturing System untuk Pembelajaran di Institusi Pendidikan

Flexible Manufacturing System (FMS) is one of the modern production systems that support the implementation of Industry 4.0. An educational institution plans to build an FMS model for learning the modern production systems. The FMS is a manufacturing system consisting of a set of automatic workstations connected to a material handling system where all activities are controlled by a computer system. The material handling system consists of a material storage system and a transportation system, one example of a transportation system is the stacker crane. In this research, the stacker crane model has been built which consists of three main components, which are the bottom frame, the mast, and the carriage. This component is equipped with stepper motors, leadscrews that are controlled by the micro controller and an application on Android. The stacker crane model is tested to retrieve and deliver the stereofoam material model to the destination which is controlled by the user using an application on Android. The characteristics of the stacker crane model can move the workpiece with a maximum error of 2 mm in the positive x-axis direction, 2 mm in the negative x-axis movement, up to 2 mm positive y-axis, downward at negative y-axis direction 2 mm.

Generalized nets and intuitionistic fuzzy pairs as tools for modelling of flexible manufacturing systems

Generalized nets and intuitionistic fuzzy pairs as tools for modelling of flexible manufacturing systems

A Study on Modelling of Flexible Manufacturing System

A Study on Modelling of Flexible Manufacturing System

Performance evaluation of a carousel configured multiple products flexible manufacturing system using Petri net

This study presents a schematic approach to model, simulate and analyze the overall performance of an FMS, comprising a carousel layout surrounded by manufacturing and assembly cells capable to deliver a variety of multiple products. All manufacturing and assembly cells are consisting of multiple multifunctional production and assembly machines, served by material loading and unloading robots, connected through a material transporting conveyor. Inter-cellular and intra-cellular routing flexibility are employed in the system through production resources operational and breakdown modes. Colored Petri net tools are used to develop a compact, editable and deadlock-free flexible manufacturing system model reveals important information about dynamic behavior and system performance measures e.g.; throughput, mean cycle time, and work-in-process (WIP) with reference to material handling and supply system, production resources reliability and process execution input variables. Variation in input factors namely mean machining and assembly time, material loading and unloading time, number of operations between failure, repair time, parts inter-arrival time, conveyor speed and buffer capacity have shown a substantial effect on the system performance. The results indicate successful applicability of colored Petri net tools for modelling, simulation, and evaluation of carousel configured multiple products flexible manufacturing system. Further, the optimal solution represents a deep relationship between the different production modes and responses to maximize the performance of a carousel configured multiple products FMS.

Optimal enforcement of liveness for decentralized systems of flexible manufacturing systems using Petri nets

The decentralized supervisory structure has drawn much attention in recent years. Many studies are reported in the paradigm of automata while few can be found in the Petri net model. This paper proposes a new method for decentralized supervisory control using the Petri net paradigm. Two efficient Algorithms are developed in the proposed method. Algorithm 1 is used to compute decentralized working zones from the given LS3PR Petri net model for flexible manufacturing systems. Algorithm 2 is used to compute the decentralized controllers that enforced liveness to the decentralized working zones. The sequential assembling is used to reconnect and controlled the working zones via decentralized controllers. The decentralized controller is added to the decentralized working zones that have common elements, that is, common transitions. The proposed method has the following advantages: (i) it can be applied to a complex Petri net model for flexible manufacturing systems, (ii) the proposed methods has less computational complexity when compared with the previous methods, (iii) the proposed method can obtain a minimal number of decentralized controllers that enforce liveness of the uncontrolled Petri net model. Experimental examples are presented to explore the applicability of the proposed methods.

Modelling of flexible manufacturing systems

This paper describes an original approach to one of the key problems in modern mechanical engineering – modelling of modern manufacturing systems with regard to the choice of relevant model type. It is shown that in terms of systemology, all the existing models are divided into the imitating (replicating) and optimising ones, while manufacturing system design belongs to semi-structured issues. Therefore, at the macro-designing stage one should use optimising models, rather than the imitating ones. The study provides a broad definition of the technological process as a set of actions aimed at product manufacturing, designing the sequence of relevant steps. It defines production flexibility and adaptation of the manufacturing system to changing conditions. These solutions can be used in automation in manufacturing, computer aided design (CAD) and modelling (CAM), computer aided engineering analysis, flexible manufacturing systems, flexible automation and production engineering.

Modelling of flexible manufacturing systems

This paper describes an original approach to one of the key problems in modern mechanical engineering – modelling of modern manufacturing systems with regard to the choice of relevant model type. It is shown that in terms of systemology, all the existing models are divided into the imitating (replicating) and optimising ones, while manufacturing system design belongs to semi-structured issues. Therefore, at the macro-designing stage one should use optimising models, rather than the imitating ones. The study provides a broad definition of the technological process as a set of actions aimed at product manufacturing, designing the sequence of relevant steps. It defines production flexibility and adaptation of the manufacturing system to changing conditions. These solutions can be used in automation in manufacturing, computer aided design (CAD) and modelling (CAM), computer aided engineering analysis, flexible manufacturing systems, flexible automation and production engineering.

Global Supervisory Structure for Decentralized Systems of Flexible Manufacturing Systems Using Petri Nets

Decentralized supervisory structure has drawn much attention in recent years to address the computational complexity in designing supervisory structures for large Petri net model. Many studies are reported in the paradigm of automata while few can be found in the Petri net paradigm. The decentralized supervisory structure can address the computational complexity, but it adds the structural complexity of supervisory structure. This paper proposed a new method of designing a global controller for decentralized systems of a large Petri net model for flexible manufacturing systems. The proposed method can both reduce the computational complexity by decomposition of large Petri net models into several subnets and structural complexity by designing a global supervisory structure that can greatly reduce the cost at the implementation stage. Two efficient algorithms are developed in the proposed method. Algorithm 1 is used to compute decentralized working zones from the given Petri net model for flexible manufacturing systems. Algorithm 2 is used to compute the global controller that enforces the liveness to the decentralized working zones. The ring assembling method is used to reconnect and controlled the working zones via a global controller. The proposed method can be applied to large Petri nets size and, in general, it has less computational and structural complexity. Experimental examples are presented to explore the applicability of the proposed method.

Deadlock analysis and control using Petri net decomposition techniques

Petri nets are an effective tool for modeling and analyzing deadlock problems of flexible manufacturing systems (FMSs). Based on Petri nets, this paper proposes a decomposition method for deadlock control of a class of Petri net modeling FMSs. It first decomposes a Petri net into two (or more) subnets via shared transitions and designs a liveness-enforcing Petri net supervisor for each subnet. Then the root of causing deadlocks is analyzed when merging the controlled subnets. Finally, control places are adjoined to the merged net to obtain a liveness-enforcing Petri net supervisor. The proposed method only needs to calculate the reachability graphs of the subnets, which are in general much smaller than that of the whole original net system. This method in general reduces significantly the computational overhead of designing a liveness-enforcing Petri net supervisor. A subnet can be further decomposed in a hierarchical way, which can further mitigate the computational burden. Typical examples are used to demonstrate the proposed methods.

An estimation of distribution algorithm for scheduling problem of flexible manufacturing systems using Petri nets

• This is the first report on applying estimation of distribution algorithm (EDA) to the studied problem. • A kind of PN-based deadlock controllers for FMSs is imbedded to exclude infeasible individuals. • An effective voting procedure is adopted to construct the probabilistic model of EDA. • The longest common subsequence is also embedded in the model for mining excellent genes. • A new modified variable neighborhood search is developed as an efficiency enhancement of EDA. Based on the place-timed Petri net models of flexible manufacturing systems (FMSs), this paper proposes a novel effective estimation of distribution algorithm (EDA) for solving the scheduling problem of FMSs. A candidate solution is represented as an individual with two sections: the first contains the route information while the second is a permutation with repetition for parts. The feasibility of individuals is checked and guaranteed by a highly permissiveness deadlock controller. A feasible individual is interpreted into a deadlock-free schedule while the infeasible ones are amended. The probabilistic model in EDA is constructed via a voting procedure. An offspring individual is then produced based on the model from a seed individual, and the set of seed individuals is extracted by a roulette method from the current population. The longest common subsequence is also embedded into the probabilistic model for mining good genes. A modified variable neighborhood search is applied on offspring individuals to obtain better solutions in their neighbors and hence to improve EDA’s performance. Computational results show that our proposed algorithm outperforms all the existing ones on benchmark examples for the studied problem. It is of important practice significance for the manufacturing of time-critical and multi-type products.

A collaborative CPN−Fuzzy modelling strategy for conflict solution in flexible manufacturing systems

The increasing usage of Flexible Manufacturing Systems (FMS) poses new challenges, such as conflict situations in manufacturing processes. Therefore, there is a need to implement modelling and control of FMS in order to prevent or deal with such occurrences. However, modelling and controlling an FMS is itself a complex task due to the many subsystems and elements that comprise an FMS. Moreover, the existing high coupling between these subsystems also makes modelling and control tasks difficult to implement. This paper proposes a modelling strategy of FMS, which the decomposes the system into smaller and cohesive subsystems. In such a strategy, a part of the system should be designed to address interlocking issue, based on Petri Nets (PN) model and, collaboratively, the other part of the system should be designed to address sequencing of operations, based on Fuzzy Logic. It enables to perform more complex calculus to decide issues regarding FMSs, considering, optimisation criteria like makespan and idleness system resources. This strategy was used for modelling a simulated factory with 6 machines, composed by input/output buffers, 3 AGVs (Automated Guided Vehicles), a load/unload station and AGVs park.

Deadlock and liveness characterization for a class of generalized Petri nets

Petri nets (PNs) are widely adopted for modeling flexible manufacturing systems (FMSs) since they are an effective tool for analyzing the latter’s dynamic behavior and synthesizing a supervisory controller to make a system deadlock-free. As an important subclass of PNs, the weighted system of simple sequential processes with resources (WS3PR) can be used to model many FMSs well. Based on the initial marking and structural properties of a WS3PR without using marking enumeration and state equations, this paper presents a method to check its liveness. We first define two classes of transitions for a resource subnet of WS3PR, based on which, the relationship between markings and strongly connected resource subnets (SCRSs) is analyzed. Next, functions used to check the liveness of a given WS3PR are developed, which take the full advantage of SCRS trees and WS3PR structure. It is shown that, by the proposed method, the computational complexity for a subclass of WS3PR named k-sharing bounded WS3PR is polynomial. Sufficient conditions to check liveness of a WS3PR are finally established. Two examples are used to illustrate the results.

Hybrid heuristic search approach for deadlock-free scheduling of flexible manufacturing systems using Petri nets

Based on the Petri net models of flexible manufacturing systems (FMSs), this paper focuses on deadlock-free scheduling problem with the objective of minimizing the makespan. Two hybrid heuristic search algorithms for solving such scheduling problems of FMSs are proposed. To avoid deadlocks, the deadlock control policy is embedded into heuristic search strategies. The proposed algorithms combine the heuristic best-first strategy with the controlled backtracking strategy based on the execution of the Petri nets. The scheduling problem is transformed into a heuristic search problem in the reachability graph of the Petri net, and a schedule is a transition sequence from the initial marking to the final marking in the reachability graph. By using the one-step look-ahead method in the deadlock control policy, the safety of a state in the reachability graph is checked, and hence, deadlock is avoided. Experimental results are provided and indicate the effectiveness of the proposed hybrid heuristic search algorithms in solving deadlock-free scheduling problems of FMSs. Especially, the comparison against previous work shows that both new algorithms are promising in terms of solution quality and computing times.

A Minimal Supervisory Structure to Optimally Enforce Liveness on Petri Net Models for Flexible Manufacturing Systems

This paper presents a new method of computing a minimal supervisory structure that optimally enforces liveness on the Petri net models for flexible manufacturing systems (FMSs). The proposed method utilizes the structural properties of a Petri net model to avoid the computation of its reachability graph, which in general leads to the state explosion problem. This paper aims to design a single control place for each concurrent process of a Petri net model or a sub-net model, which thus provides a constant number of control places in a supervisor regardless of the number of resource places in a Petri net or sub-net model. It is shown that the structural size of a supervisor is minimal as the number of control places depends on the number of concurrent processes in the Petri net model. Precisely, two algorithms are developed in this paper. The first aims to compute active uncontrolled transitions and the second is concerned with a method to compute the generalized mutual exclusion constraints (GMECs) for each process of the Petri net model of an FMS. Furthermore, it provides an approach to design control places for each computed GMEC without solving integer linear programming problems, which greatly reduces the computational costs. When the computed control places are coupled with the uncontrolled Petri net model for an FMS, it optimally enforces liveness behavior of the Petri net model, and hence ensures the high utilization of resources in a considered system.

Performance Analysis of a Flexible Manufacturing System (FMS)

The performance of a flexible manufacturing system (FMS) has a great impact on a manufacturing firm success and the analysis of FMS justifies the high investment cost behind it. As the competition in the global market is growing, manufacturing companies compete not only on product cost and quality but also in time to market. FMS as a highly automated system typically comprised of a set of processing workstations allowing in an integrated manner to react rapidly and economically to production-oriented aspects of an enterprise in order to cope significant changes in its operating environment. This paper analysed the performance of a FMS through manufacturing process modelling and simulation. The modelling of a manufacturing system enables to grasp quickly how the current system is working and to evaluate the proposed process changes before actual decision making, on the other hand, the simulation of the system supports the idea of virtual manufacturing and gives prompt response to the decision maker. Moreover, integration of system dynamic analysis with reliability estimation methods enable engineers to find the most unreliable places in a production process and supports the decision making for reliability improvement of a production system. In this paper elaboration of the graphic simulation model of FMS operation has been described, FMS model parameters have been estimated, and criteria have been defined based on requirements regarding system reliability.

Прихована марківська модель надійності виробничної системи

The work discusses flexible manufacturing system modeling problem from its components’ reliability point of view, which heavily influences the overall system control process in case of operational management system based on synchronous model usage.Reliability model of flexible manufacturing system based on hidden markov models mathematical apparatus is proposed. Apart that, the work discusses certain problems of operational management, that can be solved using the proposed model. Such problems arise from the fact that different extraordinary situations happen during manufacturing process. Such situations are connected to manufacturing equipment itself and information subsystem of operational management system equipment either.

An Efficient Siphon-Based Deadlock Prevention Policy for a Class of Generalized Petri Nets

We propose a new deadlock prevention policy for an important class of resource allocation systems (RASs) that appear in the modeling of flexible manufacturing systems (FMSs). The model of this class in terms of generalized Petri nets is, namely, S4PR. On the basis of recent structural analysis results related to the elementary siphons in generalized Petri nets on one hand and an efficient deadlock avoidance policy proposed for the class of conjunctive/disjunctive (C/D) RASs on the other hand, we show how one can generate monitors to be added to a net system such that all its strict minimal siphons aremax′-controlled and no insufficiently marked siphon is generated. Thereby, a new, simple, and more permissive liveness-enforcing supervisor synthesis method for S4PR is established.