External environment of an autonomous manufacturing agent: dynamics and representation

A formal representation of an agent's external environment is proposed, that can be used in information flow analysis. An autoregressive process of second order is applied as the mathematical tool. The dependency X(t) = f[X[0), X(1)] is derived and the characteristic features of the dynamics of the external environment are discussed. The proposed formal representation increases the set of tools for modelling and simulation of autonomous functioning manufacturing agents. It allows for the agent rigorous information input definition and assists systems analysts in the evaluation of an information structure using different attributes of the external environment.     

Shelf life considerations in a family production context

In this paper we consider a piece of manufacturing equipment dedicated to the production of a family of items. With known level demand rates for the individual items the policy used is to cycle through production of all of the items every T units of time. The paper addresses the choice among two adjustment options when the cost-minimizing T value leads to potential spoilage of an item because of shelf life considerations. The less obvious option of slowing the production rate of the concerned item is shown to be more cost effective than simply reducing the T value.     

IDENTIFYING SYSTEM FUNCTIONS

This article provides certain fairly rigorous, although still heuristic, methods for identifying the functional components of systems in such a way as to facilitate making relationships between the components and the overall system. Based on the definitions of function commonly used, making such a relationship is not always as easy as it could be made. Specific matters discussed herein include the following: functions and objectives-oriented thinking; logical versus physical thinking; functional outputs versus functional objectives; functional objectives versus system mission; directness of relationship to an objective; relationships between multiple functional objectives; distinguishing specific objectives within more general ones; the need to develop a consistent set of terms; etc.     

Analysis of material and capacity requirements with Q-GERT

The purpose of this paper is to report on research conducted to develop a simulation model which incorporates the basic MRP logic into the modelled production process. The objective of the modelling effort is to provide information necessary for planning and controlling of the material and capacity requirements of a production process that includes stochastic processes. The modelling and analysis procedure exploits the fact that the structure of the production process can be logically modelled as a network flow process. The technique employed to facilitate the network modelling is Q-GERT (Graphical Evaluation and Review Technique) modelling and simulation language. A case application is presented to demonstrate a prototype model, followed by a report of the simulation results. The model is designed to provide answers and insights to the following questions: (1) how long must each production centre operate to yield the specified quantities of finished products, (2) what is the expected lead time required to complete the production of finished products, (3) what are the utilization rates for various processing stations, and/or percentage idle times due to lack of preprocess inventories, and (4) where do bottlenecks occur in the production process, as evidenced by large queues of materials or subassemblies prior to the machine centres.     

CONCURRENT ENGINEERING DESIGN FOR ENVIRONMENT

This paper attempts to give a brief overview of the concept of design for environment (DfE) as part of the concurrent engineering philosophy. DfE includes designing for recyclability, reuseability, durability, and maintainability. DfE also promotes the reduction of energy consumption and product emissions as a means of environmental consciousness. As part of this research into DfE, five Hunter Valley–based Australian businesses were used as case studies in an attempt to discover what role DfE plays in local Australian industry.     

A comparison between two photographic methods for the determination of relative bidirectional reflectance

Two simple photographic methods have recently been proposed for the measurement of relative bidirectional reflectance (Lillesand and Kiefer 1979, Curran 1980). These two methods were used to calculate the relative bidirectional reflectance of ten contrasting surfaces. The photographic relative bidirectional reflectance so recorded, was then compared with the radiometric bidirectional reflectance for each surface. Two conclusions were drawn: first, that relative bidirectional reflectance can be measured using these simple photographic techniques, and second, that there was no significant difference between the Lillesand and Kiefer and Curran methods for photographically deriving relative bidirectional reflectance.     

A synthesis of Lyapunov functions for non-linear time-varying control systems

The formulation of a class of Lyapunov functions for time-varying nonlinear control systems which occur in the stability analysis of control systems is considered. A new approach is presented, which is an extension of a generation technique for time-invariant non-linear systems. This approach, which uses by analogy the classical theory of Hamilton, permits stability and transient information to be obtained from system equations with time-varying damping as well as time-varying gain. A second and third-order example is used to illustrate the application of this new result.     

A control system for coordinated inventory replenishment*

There are frequent occasions where the coordination of replenishment orders for selected groups of items can lead to significant savings in the costs of replenishment. This paper is concerned with a practical procedure for selecting the order-up-to-levels, can-order points and must-order points of a particular coordinated control system. Demand is Foisson and a fixed non-zero replenishment lead time is assumed. Cost comparisons with the best independent control strategy indicate that substantial savings (averaging 18-8% over some 104 examples) are possible through coordination.