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To achieve an effective integration framework for manufacturing systems, a formal model of a system is highly desired. In spite of significant work on automated manufacturing systems, human operators still play a critical role in virtually every system, especially for material-handling processes. To build a model for control and analysis of a system where a human operator is integrated, a formal functional specification of a human material handler (MH) is presented in a hierarchical framework. Two types of human operational errors associated with material-handling tasks are also classified and discussed. A shop floor control example is provided to illustrate the proposed modeling framework. Index Terms--Functional specification, human errors, human material handler, integration framework.

A method for rapid computer numerically controlled (CNC) machining is being developed in an effort to automatically create functional prototypes and parts in a wide array of materials. The method uses a plurality of simple two-and-a-half-dimensional (2 1/2-D) toolpaths from various orientations about an axis of rotation in order to machine the entire surface of a part without refixturing. It is our goal to automatically create these toolpaths for machining and eliminate the complex planning traditionally associated with CNC machining. In this paper, we consider a problem that arises in automating this process--visibility to the surface of a model that is rotated about a fourth axis. Our approach involves slicing the computer-aided design (CAD) model orthogonal to the axis of rotation. The slice geometry is used to calculate two-dimensional visibility maps for the set of polygons on each slice plane. The visibility data provides critical information for determining the minimum number and orientation of 2 1/2-D toolpaths required to machine the entire surface of a part. [DOI: 10.1115/1.2039100] Keywords: visibility, rapid prototyping, machining, slice geometry

This paper presents a formal approach to resolve an important question concerning changes in the control of computerized manufacturing systems when a human operator is involved as a task-performing agent. It requires building a model of human functional specifications used in executing tasks and integrating it into a control scheme for the model. More importantly, analysis of control complexity needs to be conducted to build an effective control mechanism. In this paper, a human material handler is considered, and an assessment of part flow complexity affected by human tasks in a highly automated manufacturing system is presented. For this purpose, a formal model of human task-performing processes is proposed in terms of a part and location(s) of a task. A classification for human material handling tasks is presented based on the proposed model. Furthermore, human errors and the impact of human errors on part flow are considered. Part flow complexity of a manufacturing system from the control perspective is then investigated in terms of the human tasks and errors. A shop floor control example where a human operator performs material handling tasks is provided to illustrate the proposed model. Index Terms--Computerized manufacturing systems, human functional specification, material handling tasks, part flow complexity.

The past two decades have seen significant improvements in optimization modeling and software solvers for large-scale optimization problems, especially discrete problems. We feel that a critical feature of many of these systems is being overlooked. That is, the process control engineer adjusts process parameters while only considering the local efficiency or not considering process efficiency at all. Production control engineers, while optimizing the global system performance, consider process parameters as given and fixed, i.e., unchangeable. Combining the optimization of the process parameters with a global system view can significantly improve the overall system performance. in practice, "hot jobs" are treated in this ad hoc manner, making sure that all resources are available and operate at peak efficiency (minimum production time) for these critical products. This phenomenon occurs not only in manufacturing but also in many other industries. This modeling part of the optimization problem can be even more important than "optimal versus heuristic"-based solution decisions made. In this paper, we present an aggregative high-fidelity modeling approach and illustrate the formulation of parameter variability in three different domains: manufacturing, air travel, and food processing. Our early investigation into this problem has yielded remarkable improvements in performance. Index Terms--High-fidelity modeling, parameter variation.

Currently, most control implementations of flexible manufacturing cells have been developed specific to a particular facility, and no generic format or tools exist for the systematic planning and creation of control. This paper presents the first phase of research in automatic generation of control software. It focuses on the development of theoretical foundations and generic issues necessary to understand and implement control. Specific formal models are developed for the physical activities, system actions, and individual machines comprising the manufacturing cell. In a subsequent paper, the formal models presented here are used to provide the basis for creating context free control grammars which are used to automatically generate software for controlling flexible manufacturing cells.

Flexible manufacturing systems are capable of producing a broad variety of products and changing their characteristics quickly and frequently. This flexibility provides for more efficient use of resources, but makes control of these systems more difficult. Control problems previously unstudied now require practical resolution, like system deadlock. A system deadlock is a situation that arises due to resource sharing in manufacturing systems, when the flow of parts is permanently inhibited and/or operations on parts cannot be performed. This problem has been ignored by most scheduling and control studies, which usually assume infinite machine queue capacity and unlimited tooling resources. FMS's, however, have little or no queue capacity and limited tooling resources. In this paper, graph-theoretic deadlock detection and resolution procedures are presented which are suitable for real-time control of manufacturing systems. These procedures determine whether part movement in the system causes system deadlock or not. To this end, a system status graph representing part routings is virtually updated for every part movement before parts move physically to the next destination. Two types of system deadlocks, part flow deadlock and impending part flow deadlock, are detected using the updated system status graph. If a deadlock detection and recovery method is used to recover from a deadlock using a storage buffer, only part flow deadlocks need to be detected. On the other hand, if no buffer is available, both types of existing as well as impending system deadlocks need to be detected to avoid a deadlock situation.

This paper discusses a Group Technology (GT) and Computer Aided Process Planning (CAPP) installation at JLG Industries, Inc., an international manufacturer and marketer of specialized hydraulic machinery. An efficient architecture for the design, development and implementation of the system is presented along with system design requirements and characteristics. A GT software shell is described, and for the architecture that is defined, a formal model of the process planning system is developed. The model is used as the basis for the creation of a generic semi-generative CAPP system. Implementation of the model along with experience with the system is included. Run time examples of the system are provided to illustrate the features of the system.

The bottleneck in creation of Flexible Manufacturing Systems (FMS) is the development of control software. This paper presents a systematic approach to automate the development of control software for flexible manufacturing cells both at the workstation and cell controller level. Context-free grammars are proposed as the formal basis, and the FMS system is controlled as a by-product of recognizing the context free grammars. The underlying system architecture, along with the physical, system and functional models are presented for the various components of the FMS. Implementation of the proposed approach is also discussed.

This paper presents a collection of models of humans involved in complex systems with a focus on control of the system while allowing human participation in decisions for system operation. The existence of a formal model that captures human behaviour in a complex system allows for the efficient development of modelling and control software of man-machine systems. This paper provides a foundation for modelling and software development for complex systems that includes human activities. A modelling formalism, based on the automata theory for human-machine cooperative systems is demonstrated in this paper in consideration with the ecological concept of affordance. [ABSTRACT FROM AUTHOR]