Technical investment planning of flexible manufacturing systems—The application of practice-oriented methods

Flexible manufacturing systems (FMS) exhibit a high degree of automation of the machining system and of the workpiece, and for the information flow systems. Therefore, these systems are amongst the most complex production installations and their technical investment planning must be undertaken with great care.This paper introduces a strategic planning procedure and describes auxiliary aids for the selection of the components and for structuring of the overall system. Computer programs for the selection of machine tools and for the simulation of the manufacturing process sequence are part of this procedure. The application of the methods is illustrated by means of several problem situations arising from industrial production companies; the examples show the practical usefulness of the developed auxiliary techniques. The planning accuracy possible by these methods reduces the investment risk associated with the use of these complex manufacturing systems.Also described is an integrated system for the technical investment planning of flexible manufacturing systems which comprises both existing methods and new auxiliary means for planning the machining systems and the technical/organizational overall concept.     

Optimum loading for GT/MRP manufacturing systems

A hierarchical planning procedure to utilize the potential advantages of coexistence of Group Technology (GT) and Material Requirement Planning (MRP) systems is presented. In addition, a multi-period linear programming model is proposed to determine the minimum cost loading schedule of manufacturing cells used in batch production environment. The proposed model provides the optimum work force for each cell over the planning horizon.     

Improving performance in flexible manufacturing systems

The need for flexible manufacturing systems (FMSs) has become of utmost importance over the last years due to the fierce competition present in the manufacturing industry as well as the ever decreasing product life spans and the markets attempts to respond to customers’ changing needs. These systems allow us to react quickly to changes, however this flexibility costs both time and money. Given this fact, it would be desirable to reduce costs by testing potential implementations before using them.We will use a timed process algebra called BTC (for bounded true concurrency) to face up to this challenge. We have developed this algebra by extending CSP in order to consider the duration of actions and the context (resources) in which processes are executed. This new algebra is able to take into account that the resources in a system must be shared by all the processes. So, we can find two kinds of delays in the execution of a process: delays related to the synchronization of processes, and delays related to the allocation of resources.Once FMSs are specified by means of BTC, we will focus our attention on the performance of the system which will be variable depending on the number of available resources. For this, we have developed a performance algorithm and a tool which implements it.Three examples are used to show how an FMS can be specified and how the algorithm and the tool work, allowing us to obtain the best performance with the lowest cost.     

Path-clearing policies for flexible manufacturing systems

In practical manufacturing settings it is often possible to obtain, in real-time, information about the operation of several machines in a flexible manufacturing system (FMS) that can be quite useful in scheduling part flows. The authors introduce some scheduling policies that can effectively utilize such information and they provide sufficient conditions for the stability of two such policies     

A STEP-based manufacturing information system to share flexible manufacturing resources data

The paper describes the design and implementation of a Manufacturing Information System as a solution to share and exchange manufacturing data. The Manufacturing Information System possesses relevant features for data sharing and exchanging, that are compliant to the standard ISO 10303, known as STEP¹. It is known that manufacturing planning and execution activities require data from machine-tools, robots, ASRSs², AGVs³ and, on the other hand, computer-based applications (CAM⁴, CAPP⁵ or PAC⁶) use proprietary formats to store flexible manufacturing resources data. The way the proprietary formats are built has lead to incompatibilities and interoperability problems among the applications. It is argued that by solving these problems a qualitative functional synergy will result during manufacturing planning and execution activities. The suggested solution is using a STEP-based information system, a server and a prototype client application. These three programs are implemented in Java classes to facilitate data sharing and exchanging of flexible manufacturing resources.This revised version was published in June 2005 with corrected page numbers.     

Using scheduling in flexible manufacturing systems

In this paper the concept of recursive Allen temporal algebra is fully described, along with its relationship to the smart scheduler program and the concept of smart scheduling in general. Flexible manufacturing systems (FMS) are described, and their relationship with smart scheduling is explored. A case study that shows the utility of SSP in an FMS environment is presented in detail. Conclusions about the concept of smart scheduling are presented in closing.     

A survey of flexible manufacturing systems

In this report, the different flexible manufacturing systems used for machining and assembling in the following countries are reviewed: the United States, Japan, the Federal Republic of Germany, the German Democratic Republic, Italy, Great Britain, Sweden, Norway, France, Czechoslovakia and Hungary.Three categories of systems discussed are (1) flexible modules and units, (2) flexible transfer lines, and (3) “unaligned” flexible systems. Within each category are several sub-groups, divided up mainly according to the conveyor system and operating mode. This classification shows the effective French position in this field.     

Strategies for planning and implementation of flexible fixturing systems in a computer integrated manufacturing environment

In general, for any manufacturing operation to be successful, parts must be located and held to remain in position and orientation when subjected to external forces during the manufacturing operations. The traditional approach to fixturing involves designing and manufacturing special-purpose fixtures. These fixtures are generally dedicated devices designed and manufactured for specific parts and manufacturing operations. Flexible fixturing technology involves employing a single fixturing system to hold workpieces of various shapes and sizes. Such systems have reached the embryonic stage of implementation into manufacturing environment. Therefore the integration of current and future flexible fixturing systems into the manufacturing processes becomes an important issue for future work in computer-integrated manufacturing (CIM) environment.

The approach to CIM is dependent on the functional model of the company. Therefore, the implementation of any sub-systems within it must be studied on an individual basis. However, in order to plan and implement new technologies, such as flexible fixturing systems, within CIM environment, certain requirements must be met and guidelines must be followed. The strategies for planning and implementation of flexible fixturing systems within the larger frame work of CIM environment are presented. Some guidelines for designing and developing the interconnection of the data bases are also discussed.     

Phase change fixturing for flexible manufacturing systems

Fixturing is fundamental to many manufacturing operations, hence, if computer integrated flexible manufacturing systems are to be truly flexible, then the fixturing must also be flexible. That is, it must be capable of accomodating parts of different geometries and sizes. This paper reports on an innovative class of flexible fixtures which utilizes materials that undergo a phase change between solid and liquid states. When in the liquid state, the fixturing medium can accommodate a wide variety of different part geometries, while in the solid state the part is held fixed. A mathematical model is developed which governs the holding ability of a particular class of these fixtures and some results of parametric computer studies are then presented.     

Flexible manufacturing system (FMS) scheduling using filtered beam search

This paper reports our effort to develop a knowledge based system for scheduling jobs in a flexible manufacturing system (FMS). We view FMS scheduling as a two-stage process: static scheduling, followed by real-time rescheduling if unanticipated events were to occur. This paper deals with the static scheduling stage. The system uses a frame-based knowledge representation scheme and a problem-solving strategy based on filtered beam search. Filtered beam search views a scheduling problem as a state space search and generates a good schedule quickly by controlling the amount of search required. Evaluation functions are used to decide which branches are the most promising. An important feature of this system, in our view, is the explicit manner in which environmental, procedural and structural knowledge, (stored in the knowledge base using a frame-based scheme) can be used to improve the quality of the generated schedule. The system has been implemented and tested using Common Lisp on a Macintosh system with a 3MB main memory and a 40MB hard disk. Computational experience with our system is reported.     

Stable scheduling policies for flexible manufacturing systems

In this brief note we provide a new analysis of the transient behavior of the clear-a-fraction policy of Perkins and Kumar (1989). In addition, we show that a new “clear-average-oldest-buffer” policy and a “random part selection” policy (of which “first-come-first-served” is a special case) are stable. Finally, we introduce a stable and efficient “stream modifier” that can be used to obtain network level stability results     

Reactive mode handling of flexible manufacturing systems

This paper deals with a new modeling approach for mode handling of flexible manufacturing systems (FMS). Based on a review of the modeling methods and the specification formalisms in the existing approaches, we show that the mutual benefit of functional modeling and synchronous languages is very convenient for mode handling problem. We start by introducing the context of our work and the basic concepts of the proposed modeling approach. Then we present the steps of functional modeling and we illustrate them through an example of a flexible manufacturing cell. Functional modeling is completed by generic behavioral specifications representing the states of a subsystem or the whole system. The specification method is modular, hierarchical and supports reuse concept. The established model is generic and well adapted to our control system context. Mode handling function role within the control system is then studied. This function enables a reactive update of the availability of the resources and functions and the transmission of high level control and reconfiguration orders.     

Modelling flexible manufacturing systems using mean-value analysis

Flexible manufacturing systems (FMS) represent an important new development in automated manufacturing of parts with mid-volume demand. In the design and operation of these complex systems, it is useful to have tools that predict their performance under various conditions. This paper describes one such tool called MVAQ, a computer program based on mean-value analysis of queues. Part production rates, machine utilization and average work-in-process sizes are all easily obtained using MVAQ. The reader is advised on when MVAQ should be used for modelling FMSs and how the program can be used. A simple design example is given to illustrate the use of MVAQ. A brief tutorial on the theory behind MVAQ is also included.     

Applicability of expert systems to flexible manufacturing

The following report will discuss the applicability and impact of knowledge-based systems in flexible manufacturing using the Integrated Manufacturing and Assembly System at the Machine Tool Laboratory (WZL), Technical University of Aachen, as a potential application case.     

Model-based low-level control in flexible manufacturing systems

Low-level (supervisory) control of flexible manufacturing systems (FMS) assures conflict-free operation and enforces production requirements such as priorities. It forms a crucial link between medium and higher-level decision making, on the one hand, and the various machine-controllers and servomechanisms on the other. In the absence of a suitable control methodology, ad hoc development is the current practice and compromised results at high cost are far too common. Here we described a model-based framework for a new, systematic approach to supervisory control.     

Real-time feedback scheduling of flexible manufacturing systems

A genetic manufacturing environment is considered. The emphasis is on small-lot, discrete, and asynchronous type of manufacturing systems rather than high volume and continuous type. Two classes of scheduling policies are proposed to render the machine stable. The policies are of feedback type. The decision is made in real-time and on-line.