Chell Roberts

An Overview of Object-Oriented Simulation:

With an immense increase in research, development, and application of object- oriented simulation (OOS) over the past decade, there is evidence that this technology is becoming the choice for modeling large, complex, and/or distributed systems. This paper discusses the features of OOS that dispose it to modeling these types of systems and compares the OOS approach with traditional simulation approaches. A review of OOS languages and environments is followed by a discussion of current issues pertaining to object- oriented simulation.

Generating resource based flexible form manufacturing features through objective driven clustering

The development of a new feature based technique for automated manufacturability evaluation (ME) of machined parts is reported in this article. Key to this approach is a new type of feature called a resource based flexible form manufacturing feature. This type of manufacturing feature incorporates available factory resources and permits unlimited variations in the geometric form as dictated by tool accessibility. A ME system based on this new feature definition is overviewed. Through a process of automatic feature recognition, a manufacturing feature based description of a part is generated which is then used as a form of high level operation plan on which accurate estimates of production cost and time can be made. This paper focuses on the feature recognition algorithm, which is termed Objective Driven Clustering. The recognition algorithm consists of generating feature primitives, which are operational subplans for subregions of a part. Subsequently, primitives are intelligently selected and grouped in a clustering process that uses heuristics, constraints and a user defined evaluation objective to form manufacturing features. The methodology accommodates parts with complex surfaces and interacting form features. It is also sensitive to a variety of part, factory and evaluation related parameters including the evaluation objective, accessibility, part material, D&T, available machines and tools, tool cost, tool change time and setup change time. A prototype system Arizona State University Manufacturability Evaluator (ASUME) used in validating the methodology is discussed.

Manufacturing communication: a review of the MMS approach

Abstract The introduction of computer-based machines on the shop floor has increased the productivity of the manufacturing industry. However, these machines work as stand-alone machines or work as small groups that optimize only a section of the shop floor. The full potential of automated machines will not be realized until all shop floor equipment is integrated so that the global enterprise goal is achieved in an optimum way. Because machines are manufactured by different vendors and use different proprietary protocols, they are typically integrated only with a custom-built interface. Hence, Manufacturing Message Specification (MMS) was designed as a communication standard for messaging between various manufacturing machines. This paper discusses some important features and principles of MMS. It also gives a survey of MMS objects and services with suitable examples. The last part of the paper discusses the merits and shortcomings of MMS.

Scheduling multi-purpose batch plants with junction constraints

SUMMARY There is an increasing trend in the chemical process industry to operate flexible batch plants because of their capability to manufacture multiple products simultaneously by sharing the same process resources. In this paper, the scheduling of multi-purpose batch chemical plants with junction (header) constraints is considered. A mixed-integer non-linear model for the scheduling of multi-purpose batch chemical plants is formulated that considers the connection between equipment sets, transfer times, variable batch sizes, alternative process plans, and batch merging. Because of the computational time complexity of the batch scheduling problem, a heuristic scheduling algorithm that minimizes the total tardiness is developed lo solve the model.

A review and classification of combined simulation

In this paper we have classified the major combined simulation languages into six approaches. The approaches are useful for understanding the historical development and current direction of combined simulation modeling. We have also characterized the functional capabilities of these languages. We have further traced the relationships of the languages over time. The relationships show which languages have evolved from other languages. Finally, from the context of the classification and relationships, many of the unresolved research issues are presented. While we have reviewed all of the languages, particular emphasis has been placed on the object-oriented languages since they have not been thoroughly reviewed to date.

An improved methodology for evaluating the producibility of partially specified part designs

Within the concurrent engineering (CE) paradigm, products must be designed in light of downstream lifecycle preferences and capabilities. One CE challenge is the need to estimate the downstream implications of partially specified part designs as earlyas possible in the design cycle.In this research, the hierarchical evaluation methodology for early design (HEMED) was developed to address this challenge for the fixed-principle design environment in the piece-part manufacturing industry. A prescriptive decision modelling approach was used to develop this methodology. HEMED models a companys preferences and priorities using a weighted hierarchy of business objectives, and it uses utility scoring logic to evaluate a part designs performance relative to these priorities. Utility scores are aggregated in a bottom-up manner to generate the part designs HEMED rating, which consists of both a score and its associated uncertaintyfactor for each objective in the hierarchy. Aprototype, proof-of-concept HEMED desig...

An object-oriented simulation architecture with real-time capabilities

Simulation that approximates real-time system response has previously been used to train operators in the use of system controllers. These simulations typically use architectures that are highly specific and tightly coupled to the system hardware. A formalized generic real-time simulation architecture is presented to decouple the simulation and provide a mechanism for implementation and rapid reconfiguration. This architecture distributes the state variables in the system by coupling them with manufacturing process equipment, specifically for the continuous process industries such as chemical, food and pharmaceutical. This design provides a mechanism for rapidly interchanging manufacturing equipment and simulation model components for discrete and continuous simulation, that facilitates operator training.

Representation of manufacturing systems in terms of entities and relationships

Abstract Implementation of computer integrated manufacturing (CIM) has become a major objective of many companies. Complex technologies with stringent control requirements are an integral part of todays manufacturing environment. With movement towards reduced life cycles and just-in-time operation to reduce costs, the inherent rigidity of cell control systems is a major roadblock in their implementation. To achieve configurability economically, a consistent software representation of manufacturing entities is required. It is necessary to insulate generic control functions from the wide variations found in low-level devices. System information must be organized in a standard format allowing other entities to understand and use the information effectively. Virtual manufacturing entities (VME) are intended to address problems faced in manufacturing integration. A VME is defined as an abstraction of a specific set of resources and functions possessed by a physical device. VMEs are a standardized representati...

An intelligent system for batch scheduling for the process industry

Abstract Traditional scheduling tools for continuous process industries have not been developed with batch processing in mind. Efficient batch processing requires intelligent scheduling tools. The principal contribution of this research is the development of an architecture which combines intelligent tools with a virtual plant for performing management tasks. One of the intelligent tools, a flexible scheduling algorithm based on object-oriented constructs to schedule batch processes, is presented. A virtual plant is used to map chemical processes with equipment in the plant. The scheduling algorithm then uses a database of current customer orders and a knowledge base that contains rules about customer priority, equipment cleaning, process preference, equipment history, batch sequencing rules, cost history, cost estimates, and other knowledge to aid the user in the selection of the appropriate schedule. The uniqueness of this approach is the integration of a virtual plant, which can be viewed as a static plant simulation model, with a rule-based scheduling approach.

A virtual plant modeller (VPMOD) for batch-chemical processes

This paper presents a virtual plant modeller (VPMOD), which formally characterizes and integrates chemical product designs, batch-chemical equipment (plants), the real-time scheduling of chemical batches, and the control of chemical transport through the plant. These models provide a framework for agile batch-chemical manufacturing that has the ability to reroute and control chemical product flow automatically in a flexible plant subject to unexpected events, such as changes in demand patterns and equipment failure. A formal logic model is generated to control the actual system events, which are non-deterministic. A simulation environment in VPMOD is used to validate schedules and control logic based on plant models supplied by industry. The formal models have been implemented in an object-oriented language.