Hierarchical control model for automated manufacturing systems

A mathematical model is presented to determine the hierarchical computer control requirements for a completely automated flexible manufacturing systems. This model can estimate the number and capacity of hierarchical computers needed to control a specified automated manufacturing system. The hierarchical control system is described by the major operating components common to all controlling computers and computer numerical controlled (CNC) machines: central processing unit, memory, input/output and communications. Each of these components is evaluated with respect to its operating speed and capacity. Costs are then determined as a function of the component's processing speed and capacity.A three-tier control system is examined. Starting with the CNC machines' speeds and capacities, each level of the computer hierarchical control system is modeled and related to the next tier by communication and data requirements. The physical machine layout required for a hierarchical control system is discussed. Part scheduling and process information requirements are also addressed. The model's utility is illustrated by an example using a typical manufacturing system.Optimization of this model is readily obtained using standard dynamic programming techniques. Being totally independent of any specific computer hardware technology, the model can be applied to present and future automated manufacturing systems.     

Computer vision for quality control in automated manufacturing systems

On-line automated inspection for quality and process control is becoming an important element of automated manufacturing systems. Enabling non-contact, thus non-destructive inspection, optical techniques are especially well suited to industrial inspection needs. In this paper, an image processing system for inspecting round parts is proposed and described. Several measures of out-of-roundness are discussed. Different sampling plants are investigated and the proper sampling plan is suggested.     

Logic control law design for automated manufacturing systems

To respond rapidly to the highly volatile market, the reconfigurable manufacturing systems (RMS) have brought forward challenging issues. First of all there is a need to build a formal model of a manufacturing configuration. Second it has to be rather easy to derive the models associated to the manufacturing configuration changes (reconfiguration) from such an initial model. An off-line method of rapid design of an optimal logic control law (configuration) based on Petri net (PN) is presented in this paper. From a controlled system modeling point of view, the main characteristics of the level 1 of the CIM architecture are depicted. Subsequently, the formal tool used in the automated planning field is extended to provide a controlled system model. The concept of operation is structured in order to introduce the behavioral properties of the operations. A four-step method is then proposed to design a logic control law that satisfies several goals: reduction of the lead time, satisfaction of the work orders objectives, minimization of the time cycle. Finally, the proposed design method is illustrated on a manufacturing cell.     

Human software requirements engineering for computer-controlled manufacturing systems

Computers as integral systems components determine the quality of work of operators in industrial production. This paper contributes to improving the design of man-machine systems by proposing a formal aid to human software requirements definition and design. First, the need for considering human requirements is stressed. Since technology is to be considered as ‘non-deterministic’, the designer is faced with a degree of freedom in his design decisions which can be and should be utilized for raising the quality of work of people operating computer-controlled man-machine systems. Then, a hierarchy of human quality criteria applicable for ergonomic judgement of work design measures is derived. Following the principle of prospective work design, these criteria must be considered as design goals just like technical and economic requirements. As a formal aid for making design decisions meeting these comprehensive requirements, the Requirements/Quality Criteria Matrix is proposed. Finally, this method of considering human requirements is illustrated by designing some man-machine interface features for operators of a hypothetical flexible manufacturing system.     

Deadlock control methods in automated manufacturing systems

As more and more producers move to use flexible and agile manufacturing as a way to keep them with a competitive edge, the investigations on deadlock resolution in automated manufacturing have received significant attention for a decade. Deadlock and related blocking phenomena often lead to catastrophic results in automated manufacturing systems. Their efficient handling becomes a necessary condition for a system to gain high productivity. This paper intends to present a tutorial survey of state-of-the art modeling and deadlock control methods for discrete manufacturing systems. It presents the updated results in the areas of deadlock prevention, detection and recovery, and avoidance. It focuses on three modeling methods: digraphs, automata, and Petri nets. Moreover, for each approach, the main and relevant contributions are selected enlightening pros and cons. The paper concludes with the future research needs in this important area in order to bridge the gap between the academic research and industrial needs.     

Object-oriented specification of automated manufacturing systems

The design of automated manufacturing systems (AMSs) requires an effective system specification that helps designers to deal with the changes in system requirements. This paper presents an object-oriented rule-based methodology for the specification of AMSs, which extends the capability of the existing object-oriented specification methods to support system integration and the explicit representation of control policies. The methodology is characterised by the use of rule-based modelling techniques to specify object behaviours in terms of processes. The application of the methodology is illustrated by the specification of a flexible manufacturing system.     

自动制造系统的稳健控制方法的综述

随着科学技术的快速发展,制造自动化在制造工厂已经成为一个主流方向.在过去的几十年中,研究人员已经对自动制造系统的死锁问题做了大量的研究.但是大多数解决方案总是假设分配的资源不会故障.然而,任何一个制造研究者都知道,资源故障来自各种各样的原因,包括工件破损、传感器故障、零件缺失和电器失灵等.显然,一旦资源发生故障,后续加工路径中需要使用这个故障资源的进程将停滞,不能完成其加工生产,直到故障资源被修复.那些不使用故障资源的支路也会被发生停滞的进程所阻塞.最坏的情况就是一个简单的资源故障可能会导致整个系统的崩溃.因此,制造系统中的资源故障问题急需解决.通过分析大量的文献资料,本文对解决死锁和阻塞问题的控制方法做了系统的总结研究.同时,对本文提出的稳健无死锁控制策略以及亟待开展的研究工作做了详细的介绍.     

"Optimal" operating rules for automated manufacturing systems

In modeling automated manufacturing systems such as transfer lines and flexible manufacturing systems it is necessary to make assumptions about how such systems will be operated. Hence, it is desirable to determine the "optimal" operating rules. In this paper a number of examples are given of how the "optimal" rules are determined so that consideration is given to the control options that can be used, the information available to the operator and the typical multilevel nature of the system's control.     

Architectural requirements for rapid development of agile manufacturing systems

As product life cycle becomes shortened, high product quality becomes necessary for survival, and continuous and unexpected change becomes key obstacles in success, the need for a method of rapidly and cost-effectively developing products, production facilities and supporting software including design, process planning, shop floor control systems becomes urgent. The essence of this concept of manufacturing would be characterized by adopting a new term “agility”. Agile manufacturing can be successfully accomplished using various well-defined system architecture. This paper provides a primary sketch of architectural requirements for rapid development of agile manufacturing systems.There are several aspects of system architecture : control, function, process, information, communication, distribution, development, and implementation.In the past, the confusion of those architectures prohibited the successful construction of the automated CIM systems.     

Interoperability in the cyber-physical manufacturing enterprise

New technologies supporting cyber-physical enterprise systems with respect to online decision-making based on up-to-date data, require networked sensor and actor systems in place. Interoperability is a key factor when supporting systems in a system-of-systems. In this paper, we survey approaches on Enterprise Interoperability with special attention to the Cyber-Physical Manufacturing Enterprise. The paper identifies the need for interoperability in system-of-systems in contrast to integration in a single system. Also identified are issues due to insufficient support for physical aspects of systems. An application scenario from the manufacturing domain will serve to underpin the developed approach.     

Optimal deadlock avoidance Petri net supervisors for automated manufacturing systems

Deadlock avoidance problems are investigated for automated manufacturing systems with flexible routings. Based on the Petri net models of the systems, this paper proposes, for the first time, the concept of perfect maximal resource-transition circuits and their saturated states. The concept facilitates the development of system liveness characterization and deadlock avoidance Petri net supervisors. Deadlock is characterized as some perfect maximal resource-transition circuits reaching their saturated states. For a large class of manufacturing systems, which do not contain center resources, the optimal deadlock avoidance Petri net supervisors are presented. For a general manufacturing system, a method is proposed for reducing the system Petri net model so that the reduced model does not contain center resources and, hence, has optimal deadlock avoidance Petri net supervisor. The controlled reduced Petri net model can then be used as the liveness supervisor of the system.     

Optimal deadlock avoidance Petri net supervisors for automated manufacturing systems

Deadlock avoidance problems are investigated for automated manufacturing systems with flexible routings. Based on the Petri net models of the systems, this paper proposes, for the first time, the concept of perfect maximal resourcetransition circuits and their saturated states. The concept facilities the development of system liveness characterization and deadlock avoidance Petri net supervisors. Deadlock is characterized as some perfect maximal resource-transition circuits reach their saturated states. For a large class of manufacturing systems, which do not contain center resources, the optimal deadlock avoidance Petri net supervisors are presented. For an general manufacturing system, a method is proposed for reducing the system Petri net model so that the reduced model does not contain center resources and, hence, has optimal deadlock avoidance Petri net supervisor. The controlled reduced Petri net model can then be used as the liveness supervisor of the system.     

Specification and design of logic controllers for automated manufacturing systems

The complexity of manufacturing systems makes it necessary to use adequate modelling tools based on a hierarchical and modular approach which highlights the dependency relationship between different system components. This paper presents a methodology which utilizes the hierarchical decomposition of structured analysis and design technique and the modularity of Petri nets to obtain the Grafcet, representing the implementation of the logic controller of an automated manufacturing system. This methodology aims at: (i) improving the communication between the manufacturing system designer and the control designer, (ii) generating the control logic starting from high-level specifications, and (iii) providing the basis for the validation of the control system.     

An integrated approach for the configuration of automated manufacturing systems

The paper proposes a new integrated approach for supporting firms in their decisions of dimensioning automated production systems. The problem is closely related to the performance evaluation of the system since discriminating indicators are necessary to rank different alternatives. Traditionally, analytical methods and simulation have been used to evaluate the production system performance, with minor emphasis on the relationships between the tools and their use. Given the complexity of the problem, it is not possible to use only analytical methods that cannot enter deeply in problem details; at the same time the space of potential system configurations is too large to be evaluated by means of detailed tools such as simulation. In the proposed methodology, the problem is decomposed hierarchically into different sub-problems; each one has a different level of detail and a specific performance evaluation tool is used. At each level of the analysis, each system configuration is compared, by means of statistical tests, with the other alternatives with the purpose of discarding unprofitable solutions.     

Petri net modelling of buffers in automated manufacturing systems

This paper presents Petri net models of buffers and a methodology by which buffers can be included in a system without introducing deadlocks or overflows. The context is automated manufacturing. The buffers and models are classified as random order or order preserved (first-in-first-out or last-in-first-out), single-input-single-output or multiple-input-multiple-output, part type and/or space distinguishable or indistinguishable, and bounded or safe. Theoretical results for the development of Petri net models which include buffer modules are developed. This theory provides the conditions under which the system properties of boundedness, liveness, and reversibility are preserved. The results are illustrated through two manufacturing system examples: a multiple machine and multiple buffer production line and an automatic storage and retrieval system in the context of flexible manufacturing.     

Tool requirements in manufacturing systems under dynamic tool sharing

This paper addresses a tooling problem in automated manufacturing systems under dynamic tool assignment policy. In this type of systems, while parts stay on a machine all through its operations, the tools required (but not available on the machine) are delivered in time for requirements. The system performance is restricted to a great extent by tooling constraints. This paper presents an analytical method to determine tool requirement levels under dynamic production environment. The appropriate tool duplication levels are determined by trading off tool duplication levels and tool waiting time. Simulation studies are used to verify the performance of the proposed analytical model.     

Petri-net-based robust supervisory control of automated manufacturing systems

Supervisory control that ensures deadlock-free and nonblocking operation has been an active research area of manufacturing engineering. So far, most of deadlock control policies in the existing literature assume that allocated resources are reliable. Additionally, a large number of methods are for systems of simple sequential processes with resources (S³PRs), where a part uses only one copy of one resource at each processing step. In contrast, we investigate the automated manufacturing systems (AMSs) that can be modeled by a class of Petri nets, namely S^*PUR. S^*PUR is a generalization of the S^*PR Petri net model, while S^*PR is a superclass of S³PR. This work addresses the robust supervision for deadlock avoidance in S^*PUR. Specifically, we take into account unreliable resources that may break down while working or being in idle, and the considered AMSs allow the use of multiple copies of different resources per operation stage. Our objective is to control the system so that: 1) when there are breakdowns, the system can continue producing parts of some types whose production does not need any failed resources; and 2) given the correction of all faults, it is possible to complete all the on-going part instances remaining in the system. We illustrate the characteristics of a desired supervisor through several examples, define the corresponding properties of robustness, and develop a control policy that satisfies such properties.     

A taboo search approach for deadlock-free scheduling of automated manufacturing systems

This paper addresses the scheduling problem of a class of automated manufacturing systems. A new manufacturing system model is proposed. In this model, a set of jobs is to be processed and each job requires a sequence of operations. Each operation may need more than one resource. Upon the completion of an operation, resources needed in the next operation of the same job cannot be released and the remaining resources cannot be released until the start of the next operation. The scheduling problem consists in sequencing the operations on the resources in order to avoid deadlocks and to minimize the makespan. The classical disjunctive graph representation is extended to model the scheduling problem. A taboo search algorithm is then proposed using an original neighborhood structure defined by two basic moves: the permutation of disjunctive arcs of critical paths and a deadlock recovery move if the former fails. Numerical results presented in the paper show the efficiency of the proposed algorithm.