Hoda A. ElMaraghy

Evolution and Future Perspectives of CAPP

Abstract Modern manufacturing is characterized by low volume, high variety production and close tolerance high quality products. Computer Integrated Manufacturing (CIM) is recognized as an effective platform for increasing manufacturing competitiveness. Computer Aided Process Planning is an essential key for achieving CIM. The integration of design, computer aided process planning (CAPP) and production planning and control (PPC) is becoming essential especially in a concurrent engineering environment where many product life cycle factors are of concern. An overview of the major development thrust in CAPP is presented along with some of the evolving trends and challenges such as rapid, generic, dynamic and/or distributed process planning. Related issued of quality and evolving standards are also discussed.

Changeable and Reconfigurable Manufacturing Systems

Part I: Definitions and Strategies Changeability: An Introduction H. ElMaraghy and H.-P. Wiendahl Changing and Evolving Products and Systems: Models and Enablers H.A. ElMaraghy Focused Flexibility in Production Systems W. Terkaj, T. Tolio and A. Valente Part II: Physical Enablers Part IIa: Manufacturing Machinery and Hardware Control of Reconfigurable Machine Tools G. Pritschow, K-H. Wurst, C. Kircher and M. Seyfarth Reconfigurable Machine Tools for a Flexible Manufacturing System M. Mori and M. Fujishima Reconfigurable Machine Tools and Equipment E. Abele and A. Worn Changeable and Reconfigurable Assembly Systems B. Lotter and H.-P. Wiendahl Part III: Logical Enablers Part IIIa: Reconfigurable Control Systems for Robots Unified Dynamic and Control Models for Reconfigurable Robots A.M. Djuric and W.H. ElMaraghy Reconfigurable Control of Constrained Flexible Joint Robots Interacting with Dynamic and Changeable Environment Y. Cao, H. ElMaraghy and W. ElMaraghy Part IIIb: Process Planning Reconfiguring Process Plans: A New Approach to Minimize Change A. Azab, H. ElMaraghy and S.N. Samy Part IIIc: Production and Capacity Planning and Control Adaptive Production Planning and Control - Elements and Enablers of Changeability H-H. Wiendahl Component Oriented Design of Change-Ready MPC Systems M. Ismail and H.A. ElMaraghy Dynamic Capacity Planning and Modeling Its Complexity A. Deif and H. ElMaraghy Part IV: Managing and Justifying Change in Manufacturing Part IVa: Products and Systems Design, Planning and Management Design for Changeability G. Schuh, M. Lenders, C. Nussbaum and D. Kupke Changeability Effect on Manufacturing Systems Design T. AlGeddawy and H. ElMaraghy Managing Change and Reconfigurations of CNC Machine Tools R. Hedrick and J. Urbanic Part IVb: Cost and Quality Management Economic and Strategic Justification of Changeable, Reconfigurable and Flexible Manufacturing O. Kuzgunkaya and H.A. ElMaraghy Quality and Maintainability Frameworks for Changeable and Reconfigurable Manufacturing W.H. ElMaraghy and K.T. Meselhy Maintenance Strategies for Changeable Manufacturing A.W. Labib, M.N. Yuniarto Part V: Future Directions The Cognitive Factory M.F. Zaeh, M. Beetz, K. Shea, G. Reinhart, K. Bender, C. Lau, M. Ostgathe, W. Vogl, M. Wiesbeck, M. Engelhard, C. Ertelt, T. Ruehr, M. Friedrich and S. Herle Migration Manufacturing - A New Concept for Automotive Body Production T.P. Meichsner Changeable Factory Buildings: An Architectural View J. Reichardt and H-P. Wiendahl

Deadlock prevention and avoidance in FMS: A Petri net based approach

The use of structure theory of Petri nets to develop efficient deadlock prevention and deadlock avoidance methods for flexible manufacturing systems (FMSs) modelled by S4R nets is demonstrated. Major synchronisation patterns, such as generalised parallel and sequential mutual exclusion, frequently observed in FMS contexts can be represented by this class. The liveness property of a given S4R net (deadlock-freeness in the context of FMSs) is characterised in terms of structural Petri net elements called siphons. An efficient method for controlling minimal siphons of a given S4R net is developed where local control places are added to the net. A sufficient condition for liveness of the augmented net is provided. This constitutes a deadlock prevention approach. When the net liveness condition is not satisfied, an on-line controller, using a dynamic resource allocation policy, is developed for the augmented net. The performance of the proposed approaches is illustrated using several examples.

Expert System for Inspection Planning

Abstract An expert inspection task planning system for Coordinate Measuring Machines(CMM) is developed in PROLOG. It is generative in nature and is bused on a feature-oriented computer-aided modelling system which has been developed in association with the planning system. The planning system takes into consideration the CMM characteristics, inspected part function and geometric properties, geometric tolerancing theory as well as the data extracted from the modelling system. New ideas regarding feature accessibility, feature representation in terms of the geometric elements used by CMM, inspection priority of datum features, measurement grouping according to the nature of geometric elements, checking all possible accessible features before changing a probe and/or part orientation, grouping tolerance checking tasks together based on corresponding datums, etc. and associated algorithms are proposed and implemented in this reseach. These concepts were verified and found to be feasible. Syntactic Pattern Recognition technique is used to identify a part directly from a feature-based CAD database from inspection planning point of view. The developed Feature-Oriented Modelling and Planning System, using artificial intelligence techniques, is discussed. Inspection knowledge representation and planning logic are described and illustrated with examples. Sample planning rules and inspection plan are also included. It is believed that this research can provide some useful contributions towards the development of automated inspection task planning, systems especially for coordinate measuring machines.

GAPP: A generative assembly process planner

Abstract This paper presents results of exhaustive research in automated assembly planning. A generative assembly process planner (GAPP) has been developed that takes as input a solid model of the product to be assembled and outputs its feasible assembly sequences. Once the product has been modeled as a solid using a commercial solid modeler, the resulting solid models boundary representation (B-Rep) file is interpreted by the GAPP to generate mating information among parts in the form of a relational graph. This graph becomes the input of a search graph process whose constrained expansion reveals all feasible assembly sequences from a geometric, stability, and accessibility point of view. The relative goodness of different feasible assembly sequences can be determined using pertinent criteria such as the number of reorientations involved or the clustering of similar assembly operations into successive ones. The expansion engine is very flexible and enables many different types of assembly problems to be handled uniformly, for example, finding disassembly repair sequences not requiring complete product disassembly or generating assembly sequences that force the building of predefined subassemblies. Examples with real industrial products are provided to illustrate the potential of using this tool.

Manufacturing Systems Configuration Complexity

A new Complexity Coding System is introduced to classify and code the machines, buffers and material handling equipment in manufacturing systems. A Code-based Structural Complexity Index is proposed to capture the amount and variety of information related to these components. The probability of a manufacturing systems success in delivering the desired production capacity, as function of the availability of its components, is used as an additional measure of the system complexity in meeting the targeted forecast production volume with its variation. The application of the Coding System and two Complexity Indices in comparing manufacturing system configurations is demonstrated using a cylinder block-machining example with consistent results.

Automatic sampling for CMM inspection planning of free-form surfaces

Coordinate measuring machines (CMMs) are used to examine the conformity of the produced parts with the designers intent. The inspection of free-form surfaces is a difficult process due to their complexity and irregularity. Many tasks are performed to ensure a reliable and efficient inspection using CMMs. Sampling is an essential and vital step in inspection planning. Efficient and reliable approaches to determine the locations of the points to be sampled from free-form surfaces using the CMM were developed. Four heuristic algorithms for sampling based on the NURBS features of free-form surfaces are presented. The sampling criteria are equiparametric, surface patch size and the surface patch mean curvature. An algorithm for automatic selection of sampling algorithms performs complexity checks on NURBS surfaces, including the surface curvature changes and surface patch size changes, and selects the suitable sampling algorithm. Extensive simulations were performed using the developed methodologies to evaluate their performance using free-form surfaces with different degrees of complexity and compared with the uniform sampling pattern. The CMM measurement errors and manufacturing form errors have been simulated in these studies. The developed algorithms provide a useful tool in selecting the effective sampling plans for the tactile CMM inspection planning of free-form surfaces.

Changeability – An Introduction

Manufacturing has been experiencing dynamically changing environment that presents industrialists and academics with formidable challenges to adapt to these changes effectively and economically while maintaining a high level of responsiveness, agility and competitiveness. Advances in manufacturing technologies, equipment, systems and organizational strategies are helping manufacturers meet these challenges. The ability to change and effectively manage this change is a fundamental pre-requisite for surviving and prospering in this turbulent environment. Changeability is presented as an umbrella concept that encompasses many change enablers at various levels of an industrial company throughout the life cycle of the manufacturing system. In this introduction, the scope of manufacturing changeability is outlined, the objects of change are defined, the change enablers are introduced and discussed and the change management strategy is highlighted.

Planning of Products Assembly and Disassembly

Summary Previous research in assembly process planning focused on the generation and evaluation of all possible assembly plans for the product under consideration. While this approach ensures completeness, it is inefficient, time consuming and costly. This paper presents the results of our research which aims at improving the efficiency of the assembly planning process and producing optimal assembly and disassembly plans. Geometric feasibility and accessibility constraints are induced to reduce the size of the directed assembly graph to be searched. Four criteria have been introduced and formalized to optimize the resulting assembly plans. These are: stability, number of reorientations, concurrency of operation, and grouping of similar operations. Graph search methods which guarantee optimality of plans are briefly described. Examples of real products are used to illustrate the generation of: assembly plans, disassembly plans for repair and maintenance, and plans to recover from assembly execution errors.

Scheduling of manufacturing systems under dual-resource constraints using genetic algorithms

Abstract Scheduling belongs to the special class of NP-hard problems for which no polynomial time algorithm has been found. Therefore, a schedule that is the best possible near-optimal solution is often acceptable. This paper presents a scheduling approach, based on Genetic Algorithms (GAs), developed to address the scheduling problem in manufacturing systems constrained by both machines and workers. This genetic algorithm utilizes a new chromosome representation, which takes into account machine and worker assignments to jobs. A set of experiments for determining the best staffing level and machine and worker assignment to jobs was performed. A study was conducted using dispatching rules with various performance measures for two types of shop characteristics: (i) dual-resource (machines and workers) constrained, and (ii) single-resource constrained (machines only). An example is used for illustration and comparison. The resulting scheduling methodology is capable of determining the best staffing level and dispatching rules for the chosen performance measure in both single and dual-resource constrained shops. Decisions to adopt the prescribed staffing strategy to improve the primary performance measures such as mean flow time, mean tardiness, and mean waiting time must be balanced by managers against the potential increase in direct cost. The developed scheduling approach and formulation proved to be very useful for optimizing production performance under the realistic conditions imposed by both machine and worker availability constraints. Such a tool should be used to define a priori the best dispatching rules and schedules for a given set of production requirements and objectives.