Discrete Manufacturing Processes Research Articles

Microprocessor Architecture for Discrete Manufacturing Control, Part II: Identification of System Requirements

This paper presents an analysis of the computer requirements for the lowest level computer in a hierarchical control structure. The objective of the paper is to identify those points of discrete manufacturing process control which require special consideration and to give the impact of these requirements on the computer architecture. The areas which are investigated are the instruction set, input/output system, interrupt structure, and computer-to-computer communications.

The Warehouse Location Formulation as a Special Type of Inspection Problem

This note presents a model for allocation of inspection resources to points within a discrete manufacturing process at minimum cost. An integer programming formulation is developed having identical structure to a warehouse (factory) location problem which has been the focus of a number of investigations.

Design Aspects of Computer Control in Discrete Manufacturing

This paper presents a survey of design problems associated with the implementation of computer control of discrete manufacturing processes. The two primary application requirements placed on the digital computers are identified and discussed; namely, the information system function and the equipment control system function. A tutorial survey is then given of three computer structures to implement control of manufacturing operations. The relative advantages and disadvantages of each of these systems are discussed, Finally a new structure is presented that uses a multilevel computer concept with satellite computers at the lowest level. A detailed view of the satellite computer, including hardware requirements, software requirements, and timing considerations, is given. Emphasis is placed on a modular design that meets the real-time needs at the most fundamental level of a manufacturing plant. Extensions are then given to computer requirements at upper levels, hardware and software configurations, and real-time versus interrupt capability.

The Role of Process Data in Controlling and Optimizing Manufacturing Processes

Historically, control functions for "make "and "test" operations in discrete manufacturing processes have been satisfied with special purpose hardware. In recent years, computers have replaced much of this special purpose hardware. The initial reasons for employing computers were to decrease capital and development costs while providing greater flexibility in responding to process changes. It now appears that the greatest benefits of applying computers in discrete manufacturing processes are the increased process yields and decreased rework through the use of Process

Multilevel Control Structures for Three Discrete Manufacturing Processes

Discrete manufacturing systems represent a large fraction of industrial processes and involve control problems whose dimension precludes straightforward solution. In general, such systems involve transformationfrom raw material to finished product and include a sequence of discrete operations (machining or parts, storage in and retrieval from inventory, etc.). Concornmitant with each of these operations are control problems including monitoring, reporting, scheduling, machine loading, start up, shut down, batch control, emergency actions, security enforcement, etc. The great differences among the disturbances and contingencies which can affect the operation of such processes suggests that the controls associated with each stage of the process and with each type or class of disturbance be handled as separate tasks. This decomposition of the control system, in turn, requires coordination between the subunits in order that the overall process objectives are achieved.Hierarchical control systems have proved to be effective models for the design of complex control systems for continuous processes. The objective of this paper is to demonstrate how a hierarchical structure can also lead to the effective control of discrete processes.Three examples are presented, each illustrating a different aspect of the discrete control problem formulation. It is shown, in each case, how the control tasks organize naturally into a multilayer hierarchical structure. The examples focus on problems of scheduling, control of discrete operations, and security control, the latter being control in the face of catastrophic disturbances. Generalizations are drawn from the experiences of these examples. Various features of the proposed structure are pointed up with specific reference made to problems of hardware and software implementation.

Transparent Interfaces

Man-machine interface devices and computer peripheral equipment have experienced a hardware proliferation with sufficient choices to meet virtually any control system interface requirement. By comparison, systems and application software packages needed to support these devices and to make the systems interfaces effective have been sparse. Efforts by users to develop such software result in substantial cost burdens. Industrial computer control systems at Ford Motor Company are used to illustrate the dynamic nature of discrete manufacturing processes and the functions performed by engineers, operators and managers which can be facilitated by desirable software features. Interface devices can be made more “transparent” through software that adapts control systems to user needs and changing management expectations.

A technique to control waiting time in a queue

The technique outlined gives a solution to the problem of optimizing the service rate(s) in a queuing system according to the given criteria. It should be noted that this solution is suboptimal in several respects. Whereas the stated objective of the procedure is to make W → W <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">d</inf> , the procedure actually makes E((w − W <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">d</inf> ) <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> )→O. The minimization of E((W − W <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">d</inf> ) <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> ) tends to weight deviations on either side of W <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">d</inf> equally. which implies that the cost of an item finishing ahead of schedule is the same as the cost of an item late by an equal time.