An integrated methodology for fixture design

In this paper, a methodology to perform fixture design as an integrated aspect of process planning is proposed. A three-phase methodology for the fixture design activity has been developed. The three phases include predesign analysis (phase I), functional analysis (phase II), and productivity improvement (phase III). In phase I, the product design information is studied, and initial fixture design aspects are developed. In phase II, the clamping and location aspects of fixture design are addressed for the given initial process sequence and product design information. Phase III involves studying ways to increase the productivity including using simultaneous machining approaches, multiclustering, use of specialized jigs, etc.     

A genetic algorithm based approach to optimal fixture configuration

In this paper the application of genetic algorithms (GAs) to the fixture configuration optimisation problem is presented. A general purpose fixturing verification system has been developed to check the validity of individual fixture configurations by analysing various contact types in the workpiece-fixture system. Based on the information provided by the verification system, a genetic algorithm based approach carries out the evaluation process to determine the most statically stable fixture configuration among a large number of candidates. The preliminary implementation is introduced to demonstrate the ability of GAs and two different coding schemes are tested to explain their influence on the performance of GAs.     

A multi-agent approach to fixture design

The design of fixtures is a highly complex process that requires the human designer to draw from his rich experience. In addition, for a given workpiece, multiple solutions may exist. By exploiting the recent advances in CAD/CAM and Artificial Intelligence techniques, one may constrain the multiple solutions such that only good designs (measured through performance measures) are considered.In this paper, a multi-agent fixture design system is proposed that harnesses the advantages of genetic algorithms and neural networks. This system attempts to capture the relevant domain knowledge and uses it to produce acceptable solutions efficiently. The system is applied to a case problem and the suggested fixturing solution is compared to one offered by a human designer. The agreement between the two solutions is very close.     

Development of an Internet-enabled interactive fixture design system

Fixture design is a complex and an intuitive process. An efficient fixture design system is essential to cut costs and reduce the product lead-time. In today's manufacturing landscape, various computer-aided systems exist to aid the various stages of manufacturing. A fixture design system should be able to transfer information with the various other systems to bring about a seamless product design and manufacturing environment. A fixture design system should also be portable on different operating platforms. This paper addresses the development of an Internet-enabled interactive fixture design system. The Internet and the use of XML as a file format provide a means for the transfer of information and knowledge between the various computer-aided manufacturing systems. The system has been implemented using Java and is based on a three-tier Thin Client-Fat Server architecture. This ensures the platform independent performance of the system. A locating scheme independent interactive fixture design method has also been developed in this work for detailed fixture design.     

Efficient simplex computation for fixture layout design

Fixture, to hold an object by making multiple contacts, is a fundamental tool in manufacturing. A fixture layout is an arrangement of contacts on an object’s surface. Designing a fixture layout of an object can be reduced to computing the largest simplex and the resulting simplex is classified using the radius of the largest inscribed ball centered at the origin. We present three different algorithms to compute such a simplex: a simple randomized algorithm, an interchange algorithm, and a branch-and-bound algorithm. We also present methods to combine different algorithms to improve the performance and highlight their performance on complex 3D models consisting of thousands of triangles. Our randomized algorithm computes a feasible fixture layout in linear time and is well-suited for real-time applications. The interchange algorithm computes an optimal simplex in linear time such that no single vertex can be changed to enlarge the simplex, and it provides a practical method for complex 3D objects. The branch-and-bound algorithm computes the largest simplex by using lower and upper bounds on the radius of the inscribed ball, by which the computation time is reduced by a factor of five in comparison with the brute-force search.     

Tolerances in computer-aided geometric design

In the design of discrete part shapes, the specification of tolerance constraints can have major consequences for product quality and cost. Traditional methods for tolerance analysis and synthesis are timeconsuming, and have limited applicability. This paper presents the results of research into the use of solid modeling technology for the automated solution of tolerancing problems. A linear programming method is presented for the solution of tolerance analysis problems on a worst-case basis. A Monte Carlo method is presented for both worst-case and statistical tolerance analysis. Both methods automatically derive all necessary geometric relationships from a solid model of the assembly. Example problems are solved using the experimental GEOTOL geometric design system.     

Ten challenges in computer-aided design

This short paper presents 10 challenging research areas in the general field of computer-aided design. The research problems come from the author's personal experience, and as such are highly subjective. All findings and opinions are those of the author and do not represent any of the institutions the author is affiliated with.     

Case based reasoning method for computer aided welding fixture design

This paper presents a case-based reasoning (CBR) method for welding fixture design, a critical issue in the manufacturing of large and complicated equipment. However, previous fixture design research has mainly focused on machining fixtures rather than welding fixtures. In this paper, an approach of data abstraction for fixture design information representation is proposed, first to systemize and manage myriads of fixture related resources, e.g., past fixture design solutions, fixture units depository. Based on this approach, a multi-level CBR method for welding fixture design is then presented. This method could help designers, by referencing previous design cases, to make a conceptual fixturing solution quickly and, finally, finish the detailed solution of fixture design.     

A feature-based fixture design methodology for the manufacturing of aircraft structural parts

In fixture design for the manufacturing of aircraft structural parts, there are various challenges and serious problems in industry, such as difficulty in design knowledge capture and reuse, and the arbitrary or non-standard nature of design, which influence the efficiency and quality of fixture design. This paper proposes a feature-based fixture design methodology in which previous fixture design cases and design rules are described in association with features and thus the design knowledge is integrated with geometric information of aircraft structural parts, which are the main concern of this project. In this methodology, machining features of the structural parts and their associated attributes are identified by feature recognition technique from the 3 dimensional (3D) part models defined based on model-based definition (MBD) technique. The feature-based part information models are then established and are used to retrieve previous fixture design cases and design rules stored in the knowledge base. Fixture designers will choose the appropriate retrieved design cases as the starting point for new fixture design or use previous designs to assess his/her current design. In this way the process of new fixture design can be improved. In the current stage of the research, a prototype feature-based fixture design system based on CATIA for the manufacturing of aircraft structural parts has been developed and used by a large airplane manufacturer.     

A desktop virtual reality-based interactive modular fixture configuration design system

Modular fixture configuration design is a complicated task requiring strong professional background and practical experience. However, automated or semi-automated computer aided modular fixture systems based on CAD packages still are not well accepted by the manufacturing industry due to the lack of intuitive interaction and immediate feedback compared with traditional models such as paper and physical models. In this paper, a novel Virtual Reality-based system for interactive modular fixture configuration design is presented. We use a multi-view based modular fixture assembly model to assist information representation and management. In addition, the suggested strategy is compatible with the principles of virtual environment and it is easy to reutilize the element model. Based on geometric constraints, we propose a precise 3D manipulation approach to improve intuitive interaction and accurate 3D positioning of fixture components in virtual space. Thus, the modular fixture configuration design task can precisely be performed in virtual space.     

A geometric approach to automated fixture layout design

Fixtures are used in many manufacturing processes to hold objects. Fixture layout design is to arrange fixturing elements (fixels) on the object surface such that the object can be held in form-closure and totally immobilized. It is well known that 4/7 fixels are sufficient for immobilizing a 2D/3D object without rotational symmetry and their locations satisfy form-closure if and only if the convex hull of their primitive wrenches forms a 3D/6D simplex in the wrench space containing the origin as an interior point. This paper presents a method for finding form-closure locations of 4/7 fixels with enhanced immobilization capability. First, the Gilbert-Johnson-Keerthi distance algorithm and the Gram-Schmidt process are used to yield the fixel locations such that the simplex with vertices at their primitive wrenches is 3D/6D and contains the origin. Then, an interchange algorithm is developed for altering the fixel locations to meet form-closure and increase an immobilization capability index of fixture layouts. The meanings of this index in fixture localization accuracy and force balance capability are elucidated as well. Its value is proved to be equal to the minimum distance from the wrench origin to the facets of the wrench simplex in terms of a unit-invariant norm for wrench vectors. Without using any general optimization techniques, this method determines an optimal fixture layout very efficiently, so that it can be tried with various initial conditions to attain a result approaching the global optimum or with other good performance qualities.     

Towards computer-aided configuration design for the life cycle

In modern design, life-cycle concerns such as recycling and service are receiving increased attention. The configuration design phase, where the product and component structure is established, is of particular importance when designing for the life cycle. In this paper, the foundation for a CAD system supporting configuration design for the life cycle is presented. A prototypical CAD system, called CODA (Configuration Design of Assemblies), is under development based on this foundation. A discussion on the supported product and component representation is given, followed by a portrayal of some of the capabilities to support life-cycle design. Specifically, requirements are identified for the information needed to support design for assembly, disassembly, service, recycling, and reuse. A case study involving the (re)design of a hand-held tape recorder with respect to improved disassemblability and recyclability is utilized to highlight some of the capabilities of the current system. With the new product and component representation embodied in CODA, improved support over current CAD systems is provided for configuration design and life-cycle design assessments.     

Multi-input/single-output computer-aided control design using the quantitative feedback theory

The quantitative feedback theory is an engineering design technique of uncertain feedback systems having robust stability and robust performance specifications. The crux of the quantitative feedback theory is a transformation of robust stability and robust performance specifications into domains in the complex plane, referred to as bounds, where a nominal loop transmission should lie within. To date, a quantitative feedback theory design is being carried out using manual (i.e. graphical) procedures or search algorithms. This paper shows that there exists a formal map from the uncertain plant and each closed-loop specification to these bounds. In particular, it is shown that each map has a closed form consisting of a quadratic inequality. These maps greatly simplify the computational aspects of the quantitative feedback theory in design of single-loop feedback systems. Based on this new development, a simple-to-implement, efficient computer algorithm is outlined.     

Web-based learning in the computer-aided design curriculum

Abstract This study attempts to apply the principle of constructivism and virtual reality (VR) technologies to computer-aided design (CAD) curriculum by integrating network, CAD and VR into a web-based learning environment. Through VR technologies, it is expected that the traditional two-dimensional (2D) computer graphics course can be expanded into a three-dimensional (3D) real-time simulation one. VR technologies provide a novel method to enhance user visualisation of complex three-dimensional graphics and environments. Experience and environmental interaction allow users more readily to perceive the dimensional interrelations of graphics which are typically portrayed through static multiview or pictorial representations. A web-based learning system ( WebDeGrator ) has been developed to simulate a computer graphics learning system for learning. Future developments of the proposed web-based learning framework are also discussed.     

A PDES/STEP-based information model for computer-aided process planning

Computer Aided Process Planning (CAPP) constitutes one of the most essential elements in Computer Integrated Manufacturing (CIM). Although many CAPP systems have been reported in literature during the last two decades, few of them are compatible enough to integrate easily with other systems in the CIM environment. One major reason is the lack of an effective method to represent the information required by CAPP, and to unify such information with the information of other systems in the CIM environment. Indeed, this problem has received relatively inadequate attention in the recent research of CAPP systems. In this paper, an information model for CAPP is developed by using the object-oriented modeling and the Product Data Exchange Step/STandard of Exchange Product data (PDES/STEP) techniques. The model consists of the part information model, the process plan information model, and the production resource information model. The EXPRESS language or the EXPRESS-G diagram is used to represent these models. Indeed, the proposed information model will greatly improve the CAPP system's capability of effective integration with other systems in the CIM environment, and, ultimately, to facilitate the implementation of the whole CIM strategy in manufacturing enterprises.     

Computer-aided design via optimization: A review

Many design problems, including control design problems, involve infinite dimensional constraints of the form φ(z, α) ≤ 0 for all α ? $\text{A}$, where α denotes time or frequency or a parameter vector. In other design problems, tuning or trimming of certain parameters, after manufacture of the system, is permitted; the corresponding constraint is that for each α in $\text{A}$ there exists a value τ (of the tuning parameter) in a permissible set T such that φ(z, α, t) < 0. Recent algorithms for solving design problems having such constraints are summarized.     

An object-oriented database management system for computer-aided design of tall buildings

An effective database and database management system is the key to the success of an integrated approach to software engineering applications in general, and Computer-Aided Design (CAD) for structural applications in particular. Due to the inherent nature of CAD data such as dynamic modeling, a wide range of data types, large data volume, etc., the traditional database models, such as hierarchical, network and relational models, are unable to handle the aforementioned applications satisfactorily. An object-oriented data modeling is known to be the most effective approach. However, many of the commercial object-oriented databases are designed for information management, and they are inadequate for CAD application due to the different features of the object-hierarchy and varying data management objectives during the design cycles. This paper presents a hierarchical index-based object-oriented database management model for CAD applications. To deal with the object hierarchy encountered in CAD for the design of tall buildings, the proposed database consists of several salient features: a hierarchical object model, its related storage structure, a data dictionary, a class factory and an index system. The proposed database management model has been implemented into an integrated CAD system for design application of tall buildings.     

A symbolic system for computer-aided development of surface interpolants

The design and implementation of a symbolic input end computation package and its application to the development of several new surface interpolation schemes are described. Capabilities such as the composition of operators and symbolic differentiation have been incorporated into the system. This allows, in particular, the specification of Boolean sum projectors. The new schemes which have been implemented include an interpolant to randomly spaced data and a 'shape operator1 which has quadratic precision.     

Algorithms for a class of computer-aided design problems: A review

This paper reviews some recent results on algorithms for a class of computer aided design problems arising in control, circuit theory and steel structure design.