Richard Bowden

A background to shop floor control systems

Within batch production systems the lead time or throughput time for a batch through the shop floor is typically much greater than the processing time. It is not unusual for the actual processing (including set-up time) to represent less than five per cent of the total throughput time in conventional batch production systems. The throughput time or lead time is made up of four major components, the set-up time, the process time including inspection time, the transport time and the queuing time, as illustrated in Fig 1.1. In real life this latter component is frequently the largest, often representing in excess of 80% of total throughput time.

A design tool for shop floor control systems

This chapter describes a design tool which can be used to support the design, development and implementation of shop floor control systems within a particular manufacturing environment. This chapter illustrates the use of the design tool to support the development of PAC systems at the cell level of manufacturing. It is important to emphazise that the tool may also be used to support the development of suitable control structures for FC, although it is not suitable to experiment with production environment design techniques. This design tool, the Application Generator (AG), is collection of software modules which interact together in a distributed computing environment. The interesting aspects of the AG are twofold: firstly it uses an artificial intelligence approach to aid in the selection of suitable control strategies (scheduling and dispatching); secondly, its distributed simulation approach identifies a clear migration path from the experimental world of simulation modelling to the reality of real-time manufacturing. Within this chapter the overall objectives of the AG will be discussed, and each of the software modules which constitute the AG will be described in detail.

A review of production environment design strategies

The factory coordination task which we described in Chapter 2 earlier, involves a production environment design element. The production environment design element reorganizes a product based layout to accommodate new products and to operate more efficiently. We argued that the production environment task should be regarded as a selection of techniques which support manufacturing personnel in maintaining a product based layout within their manufacturing system. We identified three procedures within this element as being significant in the organization of a product based manufacturing system; product based manufacturing, process planning, and manufacturing systems analysis.

A review of scheduling strategies

Scheduling is an important activity within FC and PAC. Research in scheduling has absorbed the creative talents of many academics over the past thirty years or so. Despite the numerous developments in scheduling, a common complaint from shop floor personnel is that scheduling techniques and solutions developed by academic researchers are ‘out of touch’ with the reality of the shop floor. In a sense this perception of a wide gap between research and practice is accurate, and we will suggest that many scheduling techniques developed over the years are restricted in their application. Yet recent developments in computer based scheduling solutions suggest that the gap between the research world and the shop floor is being slowly bridged.

An information technology architecture for shop floor control

In this chapter, we examine our proposed architecture for shop floor control from an information technology (IT) viewpoint. The aim of this IT reference architecture is to compliment the overall understanding of our architecture for shop floor control, and also to provide the basis for future software developments in this domain.

An architecture for shop floor control systems

In this chapter we present an architecture for the activities which occur at the operational level of the PMS hierarchy, namely, the day-to-day tasks involved in planning and controlling production on a shop floor. Production Activity Control (PAC) and Factory Coordination (FC) provide a framework which integrates the requirements planning functions of MRP type systems and the planning and control activities on a shop floor, and in doing so close the loop between the tactical and operational layers of the PMS hierarchy.

Implementation technologies for shop floor control systems

In the previous chapter we presented an information technology reference architecture for FC and PAC. We now describe some Information Technology tools and standards, currently available and under development, which we believe may be important in realizing successful implementations of FC and PAC. Our primary objective in this chapter is to examine our information technology reference architecture for shop floor control systems, and associate with it specific hardware and software tools. We briefly review the most important information technology tools and standards, and give examples of how these tools can be applied in real-life shop floor control systems. Furthermore, we stress the importance of portability, flexibility and inter-operability for shop floor control systems, attributes which we believe are vitally important in a multi-vendor computing environment. The structure of this chapter is as follows: 1 We present an initial overview of information technology, highlighting the importance of flexibility, inter-operability and portability of IT systems. A general computing model is then introduced, and this contains four essential elements required to realize an information technology implementation of shop floor control. These elements are communication systems, data management systems, processing systems and user-interface systems. 2 The main body of the chapter describes the relevant state-of-the-art technologies of the four elements included in the general computing model. At the conclusion of each section, a synthesis of what we believe are the most suitable technologies is presented, in the form a shop floor control model for each particular computing element. Thus, we also present a communication systems model, a data management model, a processing model and an user-interface model for the implementation of FC and PAC systems. 3 Finally, we focus our attention on the emerging object-oriented technology, which holds the promise of highly portable, flexible and interoperable solutions within the domain of shop floor control.

An approach to the implementation of factory coordination and production activity control systems

In the preceding chapters, we described the necessary functional and software requirements of a shop floor control system, which consists of a Factory Coordination (FC) system controlling a number of Production Activity Control (PAC) systems. In this chapter, we are concerned with the design and implementation of such a shop floor control system. The structure of the chapter is as follows: 1 We shall discuss some principles which are relevant in terms of ensuring a successful implementation of the functional and software requirements of FC and PAC systems. In particular, we stress the importance of preparing a suitable environment both socially and technically for FC and PAC systems to function. We will argue that this best fit of the social and technical subsystems, achieved through the sociotechnical design approach, helps to create a suitable manufacturing environment. 2 We shall discuss the contribution that sociotechnical design can make towards the implementation of production management systems, by using the experiences from the implementation of Materials Requirement Planning (MRP) systems and Flexible Manufacturing Systems (FMS) to outline the argument in favour of sociotechnical design. 3 Finally, we shall examine the characteristics of the most suitable social and technical sub-systems within an organization for the operation of FC and PAC.

A structured functional model for shop floor control

In the last chapter, we described an architecture for a new approach to shop floor control. The architecture consisted of two levels; a Factory Coordination (FC) task operating at factory level and a number of production activity control (PAC) systems each operating at cell level. In this description we adopted a bottom up approach to describing the architecture. This approach started with a description of the PAC task within each cell of the factory. Each of the five basic building blocks of PAC, and their relationship with each other was outlined. Then we went on to describe the next level in the architecture, that of FC. In our description of FC, we recognized the link between the production environment design element and the control element. Then taking each of the two elements in turn we described the individual tasks of each one.

Implementation of a PAC system

In Chapter 10, we presented the host environment for the case study. We now proceed to the application of the architecture, design tools and implementation models in a real manufacturing environment. The PAC development life cycle (outlined in Chapter 9), provides an excellent opportunity to experiment with possible PAC solutions. But, it may not adequately emphasize the difficulties of the transition from PAC simulation to full implementation in a manufacturing site. This migration path is paved with an array of site-specific technical and social parameters within the target environment, including the integration with existing applications (such as MRP and data collection systems), and the promotion of PAC, as a viable operational production control method, among those currently responsible for production operations.