F.J.A.M. van Houten

Maintenance : Changing Role in Life Cycle Management

As attention to environmental problems grows, product life cycle management is becoming a crucial issue in realizing a sustainable society. Our objective is to provide the functions necessary for such a society while minimizing material and energy consumption. From this viewpoint, we should redefine the role of maintenance as a prime method for life cycle management. In this paper, we first discuss the changing role of maintenance from the perspective of life cycle management. Then, we present a maintenance framework that shows management cycles of maintenance activities during the product life cycle. According to this framework, we identify technical issues of maintenance and discuss the advances of technologies supporting the change in the role of maintenance.

Review of research in Feature-based design

Research in feature-based design is reviewed. Feature-based design is regarded as a key factor towards CAD/CAPP integration from a process planning point of view. From a design point of view, feature-based design offers possibilities for supporting the design process better than current CAD systems do. The evolution of feature definitions is briefly discussed. Features and their role in the design process and as representatives of design-objects and design-object knowledge are discussed. The main research issues related to feature-based design are outlined. These are: feature representation, features and tolerances, feature validation, multiple viewpoints towards features, features and standardization, and features and languages. An overview of some academic feature-based design systems is provided. Future research issues in feature-based design are outlined. The conclusion is that feature-based design is still in its infancy, and that more research is needed for a better support of the design process and better integration with manufacturing, although major advances have already been made.

The Virtual Maintenance System: A Computer-Based Support Tool for Robust Design, Product Monitoring, Fault Diagnosis and Maintenance Planning

Digital (geometric) product models can be used for maintainability analysis and maintenance planning. It is not feasible to build digital product models for maintenance purposes only, but if a digital product model is available, it may be used to support many maintenance-related engineering tasks. Examples are: Product life cycle simulation (the influence of product use on product performance), deterioration analysis (the influence of wear on product function), Failure Mode Effect Analysis (FMEA), product model-based monitoring (to relate sensor signals to failure modes), failure diagnosis, disassemblability analysis (for repair and replacement), maintenance ergonomic analysis (to ease the work of maintenance personnel), etc. At the University of Tokyo, a Virtual Maintenance System has been developed to support the activities mentioned above. The system makes it possible to relate predicted product behaviour and specific signals, which can be detected by sensors and can be used to avoid catastrophic failure. This creates better possibilities for condition-based maintenance and Design for Maintainability. Future CAD systems should support product life cycle issues right from the start of the design process.

A computer aided tolerancing tool I: tolerance specification

current tolerancing practice, designers have to manually specify tolerances: either on a drawing or in a CAD system. Different designers will possibly arrive at different tolerance specifications for the same nominal geometry. The paper demonstrates that this situation can be avoided in the case of functional tolerancing with a focus on the geometry relevant for functioning. Under this restriction, the specification of too tight or too many tolerances can also be avoided. The paper describes a tool for functional tolerance specification which supports the user in automatically proposing geometric tolerance types where the user only has to give in the tolerance values. Apart from this semi-automatic tolerance type specification, manual specification is still possible.

A computer aided tolerancing tool II: tolerance analysis

A computer aided tolerance analysis tool is presented that assists the designer in evaluating worst case quality of assembly after tolerances have been specified. In tolerance analysis calculations, sets of equations are generated. The number of equations can be restricted by using a minimum number of points in which quality of assembly is calculated. The number of points needed depends on the type of surface association. The number of parameters in the set of equations can be reduced by considering the most critical direction for the assembly condition. The latter direction, called virtual plan fragment direction, is determined using a virtual plan fragment table, based on an analogy to the plan fragment table used in degrees of freedom (DOF) analysis. This reduced set of equations is then solved and optimized in order to find the maximum/minimum values for the assembly condition using simulated annealing. This method for tolerance analysis has been implemented in a feature based (re-)design support system called FROOM, as part of the functional tolerancing module.

Tool paths and cutting technology in computer-aided process planning

This paper reports on the development of a module to calculate automatically tool paths and cutting conditions for metal cutting operations. Process planning must select correct cutting conditions to minimise disturbances on the shop floor owing to tooling problems. Tool path and cutting condition algorithms to generate reliable NC programs have been designed. The algorithms have been implemented in the framework of a generative computer-aided process planning system, called PART. Geometrical requirements to avoid chipping of cutting teeth are considered in tool-path calculation. The cutting conditions are calculated using metal cutting process models. A method has been developed to calculate cutting forces for milling operations based on experimental data of cutting forces in turning. In the process models, various constraints of the machine tool, cutting tool, and the workpiece are considered.

Product Modelling for Model-Based Maintenance

The paper describes the fundamental concepts of maintenance and the role that information technology can play in the support of maintenance activities. Function-Behaviour-State modelling is used to describe faults and deterioration of mechanisms in terms of user perception and measurable quantities. Fault diagnosis, repair and maintenance strategies are explained briefly. Model-based Maintenance is discussed in terms of inspection, monitoring, diagnosis and planning, based on functional, behavioural and state models. Some examples of mechanisms illustrate the advantage of using computer-based models as a reference for fault diagnosis. Underlying techniques like qualitative physics, tolerance analysis, and dynamic simulation are discussed. The proposed method is aiming at functionally robust designs, reduction of preventive maintenance cost and more effective fault diagnosis.

Workflow management based on Information Management

In manufacturing processes, the role of the underlying information is of the utmost importance. Based on three different types of integration (function, information and control), as well as the theory of information management and the accompanying information structures, the entire product creation process can be formulated in terms of the information requirements of distinct processes. So-called task chains can establish the correlation between processes. Using formal representations of the information content (ontologies), a flexible resolution of process-steps is achieved. Based on this, an improved method for workflow management comes within reach.

Strategy in Generative Planning of Turning Processes

This paper reports on the process and operations planning system ROUND and the strategies which underlie the decision making processes in the planning of turning operations. At first, an outline is given about the environment for which generative systems like ROUND are being developed. The differences between high volume production and job shop production, with respect to flexibility and productivity, are designated. The impact of automation on job shop production and its consequences for process and operations planning are discussed. In small batch manufacturing systems, relatively large amounts of process planning data have to be processed, which leads to an increasing interest for sophisticated computer aided process planning tools. Because available NC part programming systems usually do not support the generation of reliable and economic technological data, it is necessary to develop generative process and operation planning systems. Due to the relative complexity of the technological models, generative systems use a lot of computing power. Reduction of possible variants, combined with model refinement are techniques which are used in ROUND, in order to avoid excessive iteration. This is illustrated by the explanation of strategies which are implemented in two newly developed modules: The clamping module RNDFIX and the module for selection of tools for the roughing operation RNDRTL.

A Tolerancing Tool Based on Kinematic Analogies

A computer aided tolerancing tool is presented that assists the designer in functional tolerance specification. The theoretical concepts for subsequent tolerance analysis are also provided. The computer aided tolerancing tool is part of a feature based object oriented (re)-design support system, called FROOM. FROOMs assembly modelling capabilities provide basic information for functional tolerance specification. Assembly constraints are satisfied by means of degrees of freedom (DOF) analysis. This method is based on the use of kinematic analogies. The rotations and translations (macro--DOFs) that components are allowed to have, are inferred using this technique. The tolerance representation in FROOM is based on the TTRS method, by Clment et al., which is also based on kinematic analogies. In this method, the small displacements that are allowed in the tolerance zone can be described by a tolerance torsor or transformation matrix. Using the tolerance torsor or transformation matrix, tolerances are described as constraints. The small displacements that are still allowed by means of the torsor are referred to as micro-DOFs. For tolerance analysis, the torsor approach offers a mathematically correct description of tolerance zones, although a lot of equations are generated. These are reduced by applying a kind of degrees of freedom analysis considering both the macro-DOFs and the micro DOFs (tolerances).