© 2001 by CRC Press LLC analogous to the one used for the composition of the input branch. The selection of working principles and models of shape is done using the AHP method. 7.6 Assessment of a CAD System for the Conceptual Design of Mechanical Drive Units Assessment of the Conceptual Design Model A conceptual design model consists of the basic model and control procedures derived from the basic function structure. The basic conceptual design model is simple and identical for all types of technical systems, and our experience to date suggests no problems. The difficult phases of preparation of a computer-aided system are setting up the basic function structure, derivation of control procedures separately for each type of technical system, and the recording of the content of attribute vectors. In fact, all phases are crucial for the proper functioning of the model and its computer implementation, and they need to be produced manually by experts. A good approach to the production of basic function structures of complex technical systems is to create the basic function structures of individual functional subassemblies (in an automobile, these are the engine, gear box, suspension, etc.), which makes mastering the entire technical system easier. The derived control proce- dures then call the basic conceptual design model. The difficulty of describing models of shape is shown above all in finding neutral basic and binding functions, which, in fact, provide for a variety of uses of the available models of shape. With the design engineer’s cooperation, a computer-aided system for conceptual design of mechanical drive units is capable of designing flexible function structures (and, naturally, model ones) of single-stage and multiple- stage mechanical drive units with one input and output of mechanical energy, and of finding the relevant working principles and models of shape for each function. In multiple-stage mechanical drive units, it is possible to use different working principles for individual stages. The design engineer’s cooperation means assigning the required function and design requirements and selecting the most suitable working principles and models of shape from among the appropriate ones using the AHP method. The result of conceptual design is a flexible function structure and the most appropriate models of shape assigned to functions and described together with their characteristics. Assessment of the AHP Method The AHP method is suitable for the selection of the most functionally appropriate working principles and models of shape in the conceptual design phase, because it is characterized by the qualitative character of available information; no standard criteria or absolute measures are available for the assessment of functional appropriateness. Using the AHP method, the above problem is solved by pairwise comparisons of both design requirements and appropriate working principles and models of shape (alternatives in general). By mutual comparison of design requirements, the design engineer indirectly determines their importance, which is naturally reflected in determining the final ranking of alternatives. The design engineer can assess the functional appropriateness of alternatives through pairwise comparisons, since, as said, he does not have any absolute criteria available, but he knows that a certain alternative is more or less suitable than the other for individual design requirements. The application section presents a comprehensive assessment method, which could, in fact, deter users from using it. For everyday use, a more suitable method for the preparation of such a computer-aided system may perhaps be a method in which the user performs only mutual comparisons of criteria, while the remaining pairwise comparisons and relevant design requirements have already been determined by an expert and are ready to use. Naturally, the system needs to be constantly upgraded with new models of shape, and all mutual comparisons need to be updated. © 2001 by CRC Press LLC 8 Computer Assembly Planners in Manufacturing Systems and Their Applications in Aircraft Frame Assemblies 8.1 Introduction 8.2 Techniques of Computer Assembly Planners Algorithmic Approach • Integrated Interactive/Algorithmic Approach • Knowledge-Based Approach • Case-Based Approach 8.3 Methods for Input/Output Representation Representation of Assembly Model • Representation of Assembly Sequence(s) 8.4 Applications in Aircraft Frame Assemblies Assembly Model Representation • Sequence Generation • Plan Representation 8.5 Conclusions 8.1 Introduction Most products around us are assemblages of components. Some are relatively simple, consisting of a few different parts joined by a selected means. For example, some kitchen knives have wooden handles that are attached to the knife blade with metal fasteners. Others, such as automobiles and airplanes, are more complex. Complicated products normally use a greater number of parts of different sizes, shapes, and materials. All of these parts must be assembled using one or several joining methods such as welding, brazing, soldering, adhesive bonding, or mechanical fastening. One or more of these joining methods is consistently found in a manufacturing system built to produce a specific product. For example, welding is the major joining method used for shipbuilding, oil platform, and pipeline fabrications. Soldering is critical to electronic manufacturing. On the other hand, a high percentage of aircraft assembly operations require riveting. T. Warren Liao Louisiana State University . LLC analogous to the one used for the composition of the input branch. The selection of working principles and models of shape is done using the AHP method. 7.6 Assessment of a CAD System for the Conceptual. for a variety of uses of the available models of shape. With the design engineer’s cooperation, a computer-aided system for conceptual design of mechanical drive units is capable of designing flexible. the Conceptual Design of Mechanical Drive Units Assessment of the Conceptual Design Model A conceptual design model consists of the basic model and control procedures derived from the basic function