In manufacturing processes like injection molding or die casting, a 2-piece mold is required to be separable, that is, having both pieces of the molds removed in opposite directions while interfering neither with the mold nor with each other. The fundamental problem is to find a viewing (i.e. separating) direction, from which a valid partition line (i.e. the contact curves of the two mold pieces) exists. While previous research work on this problem exists for polyhedral models, verifying and finding such a partition line for general freeform shapes, represented by NURBS surfaces, is still an open question. This paper shows that such a valid partition exists for a compact surface of genus g, if and only if there is a viewing direction from which the silhouette consists of exactly g + 1 nonsingular disjoint loops. Hence, the 2-piece mold separability problem is essentially reduced to the topological analysis of silhouettes. It follows that the aspect graph, which gives all topologically distinct silhouettes, allows one to determine the existence of a valid partition as well as to find such a partition when it exists. We present an aspect graph computation technique for compact free-form objects represented as NURBS surfaces. All the vision event curves (parabolic curves, flecnodal curves, and bitangency curves) relevant to mold separability are computed by symbolic techniques based on the NURBS representation, combined with numerical processing. An image dilation technique is then used for robust aspect graph cell decomposition on the sphere of viewing directions. Thus, an exact solution to the 2-piece mold separability problem is given for such models.
The tolerancing process links the virtual and the real worlds. From the former, tolerances define a variational geometrical language (geometric parameters). From the latter, there are values limiting those parameters. The beginning of a tolerancing process is in this duality. As high precision assemblies cannot be analyzed with the assumption that form errors are negligible, we propose to apply this process to assemblies with form errors through a new way of allowing to parameterize forms and solve their assemblies. The assembly process is calculated through a method of allowing to solve the 3D assemblies of pairs of surfaces having form errors using a static equilibrium. We have built a geometrical model based on the modal shapes of the ideal surface. We compute for the completely deterministic contact points between this pair of shapes according to a given assembly process. The solution gives an accurate evaluation of the assembly performance. Then we compare the results with or without taking into account the form errors. When we analyze a batch of assemblies, the problem is to compute for the nonconformity rate of a pilot production according to the functional requirements. We input probable errors of surfaces (position, orientation, and form) in our calculus and we evaluate the quality of the results compared with the functional requirements. The pilot production then can or cannot be validated.
When designing a product that needs to fit the human shape, designers often
use a small set of 3D models, called design models, either in physical or
digital form, as representative shapes to cover the shape variabilities of the
population for which the products are designed. Until recently, the process of
creating these models has been an art involving manual interaction and
empirical guesswork. The availability of the 3D anthropometric databases
provides an opportunity to create design models optimally. In this paper, we
propose a novel way to use 3D anthropometric databases to generate design
models that represent a given population for design applications such as the
sizing of garments and gear. We generate the representative shapes by solving a
covering problem in a parameter space. Well-known techniques in computational
geometry are used to solve this problem. We demonstrate the method using
examples in designing glasses and helmets.
The influence of viscous damping and delay on the stability of haptic systems is studied in this paper. The stability boundaries have been found by means of different approaches. Although the shape of these stability boundaries is quite complex, a new linear condition which summarizes the relation between virtual stiffness, viscous damping and delay is proposed. This condition is independent of the mass of the haptic device. The theoretical results are supported by simulations and experimental data using the DLR light-weight robot.
this paper, a unique way of detecting and diagnosing these types of failures by using Virtual Factories is discussed. A Virtual Factory was developed by building and linking several software modules to predict and diagnose propagated errors. A multi-station assembly system was modeled and a previously discussed "off-line prediction and recovery" method was applied. The obtained results showed that this method is capable of predicting propagated errors, which are too complex to solve for a human expert
Surface reconstruction from unorganized sample points is an important problem in computer graphics, computer aided design, medical imaging and solid modeling. Recently a few algorithms have been developed that have theoretical guarantee of computing a topologically correct and geometrically close surface under certain condition on sampling density. Unfortunately, this sampling condition is not always met in practice due to noise, non-smoothness or simply due to inadequate sampling. This leads to undesired holes and other artifacts in the output surface. Certain CAD applications such as creating a prototype from a model boundary require a water-tight surface, i.e., no hole should be allowed in the surface. In this paper we describe a simple algorithm called Tight Cocone that works on an initial mesh generated by a popular surface reconstruction algorithm and fills up all holes to output a water-tight surface. In doing so, it does not introduce any extra points and produces a triangulated surface interpolating the input sample points. In support of our method we present experimental results with a number of difficult data sets.
This article presents an overview of the state-of-the art in modeling and simulation, and studies to which extent current simulation technologies can effectively support the design process. For simulation-based design, modeling languages and simulation environments must take into account the special characteristics of the design process. For instance, languages should allow models to be easily updated and extended to accommodate the various analyses performed throughout the design process. Furthermore, the simulation software should be well integrated with the design tools so that designers and analysts with expertise in different domains can effectively collaborate on the design of complex artifacts. This review focuses in particular on modeling for design of multi-disciplinary engineering systems that combine continuous time and discrete time phenomena. INTRODUCTION Modeling and simulation enables designers to test whether design specifications are met by using virtual rather than ...
One of the fundamental unsolved problems in geometric design of mechanical solids has been the lack of a proper notion of family or class. Numerous heuristic and often incompatible definitions are used throughout the CAD industry, and it is usually not clear how to generate members of a family or, to decide if a given object belongs to an assumed family. Until these difficulties are resolved, no guarantees or standards for parametric modeling are possible, and all efforts to allow exchange of parametric representations between different CAD systems are likely to remain futile. Standardizing on a particular definition may be difficult, because parametric families depend intrinsically not only on shape but also on its representation. We classify families into parameter-space and representation-space, and show that both types are representation-induced families. We propose a formal framework for families based on the notion of topological categories. Every parametric family is defined by the representation-induced topological space of solids that are closed under the continuous maps in the assumed topology. We illustrate several well defined families and formally define a special but important case of CSG-induced family that generalizes to the more general case of feature-induced families.
Significant cycle time saving can be achieved in 2.5-D milling by intelligently selecting tool sequences. The problem of finding the optimal tool sequence was reduced to finding the shortest path in a single-source single-sink directed acyclic graph. The nodes in the graph represented the state of the stock after the tool named in the node was done machining and the edges represented the cost of machining. In this paper a novel method for handling tool holder collision in the graph-based algorithm for optimal tool sequence selection has been developed. The method consists of iteratively solving the graph for the shortest path, validating the solution by checking for tool holder collisions and eliminating problematic edges in the graph. Also described is a method to intelligently build the graph such that in presence of tool holder collisions, the complexity of building the graph is greatly reduced.
Many applications of geometric nature can be modeled by geometric problems defined by constraints in which the constraint parameters have interval uncertainty. In a previous work, we developed a method for solving geometric constraint problems where parameters are narrow intervals in the domain of the geometric problem. Based on this work, we present a new approach to solve more general problems with non-trivial-width interval parameters that may not necessarily be in the domain of the problem. We show how our approach is successfully applied to a number of problems like solving geometric problems with tolerances, checking constraint feasibility and analyzing link motion of planar mechanisms.
This paper presents a framework for shape matching and classification through scale- space decomposition of 3D models. The algorithm is based on recent developments in efficient hierarchical decomposition of a point distribution in metric space ~ p,d! using its spectral properties. Through spectral decomposition, we reduce the problem of matching to that of computing a mapping and distance measure between vertex-labeled rooted trees. We use a dynamic programming scheme to compute distances between trees corre- sponding to solid models. Empirical evaluation of the algorithm on an extensive set of 3D matching trials demonstrates both robustness and efficiency of the overall approach. Lastly, a technique for comparing shape matchers and classifiers is introduced and the scale-space method is compared with six other known shape matching algorithms. @DOI: 10.1115/1.1633576#
The following paper aims to apply the concept of the small displacements torsor (SDT) in order to predict the defects of a part resulting in successive machining set-up. The proposition is to enlarge the 1D dispersion method to a 3D analysis of the feasibility of a machined part. This paper follows our previous works on the development of a method using this concept to simulate a manufacturing process. These developments are adapted to the turning process and its particularities. The relevant parameters allowing to describe the manufacturing and positioning defects are determined. These defects are analyzed with regards to the functional specifications of a part.
This paper describes algorithms for computing global accessibility cones for each face (i.e., the set of directions from which faces are accessible) on a polyhedral object. We describe exact mathematical conditions and the associated algorithm for determining the set of directions from which a planar face with triangular boundary is inaccessible due to another face on the object. By utilizing the algorithm to compute the exact inaccessibility region for a face, we present algorithms for computing global accessibility cones for each face on the object. These global accessibility cones are represented as a matrix structure and can be used to support a wide variety of accessibility queries for the object.
Parametric modeling is becoming the representation of choice for most modern solid modelers. However, when generating the finite-element mesh of the model for simulation and analysis, most meshing tools ignore the parametric information and use only the boundary representation of the model for meshing. This results in re-meshing the model basically from scratch each time a parametric change is instantiated, which happens numerous times throughout the design process. In this paper we look at ways to use the parametric information during the meshing procedure to prevent unnecessary re-meshing. The paper examines existing meshing techniques developed for other purposes, which can be applied to this problem. It also suggests several new mesh modification techniques specifically designed for efficient mesh adjustment after parametric model changes.
This paper describes a previously unreported application of virtual environments - the prediction of product aesthetic quality. Successful prediction of aesthetic quality without the production of a physical prototype requires the integration of a number of 'software' models: an assembly model representing the manner in which the product is put together; an environment model providing a real world graphical context for the product; a behavior model representing how the product moves and deforms under use conditions; and a tolerance model representing the allowable variation in the product due to manufacturing variation. This paper presents the results of applying these models within an automotive design and manufacturing process during the development of a new automobile.
The goal of this paper is to discuss the key issues in the computer-aided surface modeling tools used in the industrial aesthetic design workflow and to highlight the problems that still make styling activities difficult. Based on the experience gained while working on two different European projects, with the collaboration of industrial designers of different fields, a general industrial design workflow is illustrated, pointing out the main differences between the automotive and non-automotive sectors. Among the emerged critical issues, particular emphasis is given to the high request of tools more suitable for the mentality of creative users; short research surveys aimed to meet this request are included , and finally authors indicate a branch of research in which they are investigating and they consider particularly worth exploring further.
Interoperability characterizes the ability of CAD models to accurately represent objects in concurrent engineering environments. The diagnostic set of available software for interoperability testing is described. This set is utilized to develop a visual catalog of possible interoperability errors. The value of utilizing interoperability testing software is appraised by way of a real-world case study. Numerous significant errors are identified in a suite of 140 parts "Geometry errors" are shown to be more common than "topology errors". The case study suggests that sensitizing the designer to the nature of typical errors leads to improvement in initial model quality. Example errors are described to illustrate their nature and how to eliminate them. Informal guidelines to improve quality upon initial design are deduced. The development of errors due to inconsistent system accuracy settings during data exchange is explored.
Computer-aided fixture design (CAFD) techniques have advanced to the point that fixture configurations can be generated automatically, for both modular fixtures and dedicated fixtures. Computer-aided fixture design verification (CAFDV) is a technique for verifying and improving existing fixture designs. This paper introduces a first comprehensive CAFDV framework which uses both geometric and kinetic models to verify locating completeness, locating accuracy, and fixturing stability. The models can be also used for locating tolerance assignment and the determination of minimum clamping force required in machining operations. The system is integrated with commercial CAD package and applied in industrial real-cases.
The quality of the interfaces between parts ensures the assembly requirements of a mechanism and the right positioning of functional surfaces. When defining a mechanism, a designer analyzes the failures generated by the geometrical defects of the junction surfaces between the parts. To formalize the design intents clearly, the method proposed, named TLIC, uses positioning tables of the parts to clearly indicate the set up surfaces associated as features and the preponderance order of the features. The requirements of assembly between parts and the tolerancing of the interfaces can then be generated automatically by defining the reference systems.
The research presented in this paper is the design and implementation of a force feedback hand master called AirGlove. The device uses six ports arranged in a Cartesian coordinate frame setting to apply a point force to the user's hand. Compressed air is exhausted through the ports, creating thrust forces. The magnitude and direction of the resultant force are controlled by changing the flow rate of the air jets and by activating different ports. The AirGlove can apply an arbitrary point force to the user's hand. However, the main goal of this research is to reflect gravitational forces to the user so that sensation of weight of a virtual object can be created. After introduction of the main concept of the AirGlove, the paper presents design and implementation details of the device. Integration of the AirGlove with a virtual assembly system called VADE is explained next. Finally, details of experiments with the device are presented and discussed. Results indicate that users wearing the AirGlove can feel a minimum mass of about 100 grams (∼1N weight) and the device can create a fairly realistic weight sensation.
As part of a strategy for obtaining preliminary design specifications from the House of Quality, genetic algorithms are used to generate and optimize preliminary design speci- fications for an automotive case study. This paper describes the House of Quality for an automotive case study. In addition, the genetic algorithm chosen, the genetic coding, the methods used for mutation and reproduction, and the fitness and penalty functions are described. Methods for determining convergence are examined. Finally, test results show that the genetic algorithm produces reasonable preliminary design specifications.
Direct Surface Manipulation (DSM) allows a designer to add a raised or indented feature to an existing surface. The user bounds the feature with a closed curve, and defines an influence center that indicates the point or curve of maximum displacement from the original surface. As we move radially outward from the influence center to the boundary curve, the magnitude of displacement is scaled gradually by a one-dimensional polynomial basis function whose values range from 0 to 1. In this paper we present a new technique for assigning parameter values in the radial direction, i.e., u, to points within a DSM feature. The new technique poses parameter distribution as a steady state heat conduction problem and uses a finite element method to solve for u(x, y). The new method overcomes some stringent geometric conditions inherited from a fundamentally geometric-based reparameterization scheme and allows us to work with non-star-shaped and multiply connected DSM features. Thus it allows us to apply this surface feature technique to a wider variety of surface applications.
The conceptual design review process is a critical cost determining step for complex products such as ground vehicles. The use of virtual environments (VEs) in this process has become increasingly popular with the advancement of 3D visualization technologies. Important to feelings experienced by participants in a VE are two parameters: presence and immersion. Presence is defined as the subjective experience of being in one place while physically being situated in another. Immersion is a state characterized by perceiving oneself to be enveloped by, included in, and interacting in an environment that provides a continuous stream of stimuli. While different virtual reality (VR) devices provide different degrees of presence and immersion, the amount of each is also dependent on the individual. In this paper, a relationship among presence, immersive tendencies of individuals, and design comprehension are explored. Further, a methodology to find the best design review process subject to certain criteria is presented. The results of two experiments involving the CAVE Automatic Virtual Environment CAVE™2 are discussed and evaluated. In one case, the U.S. Army investigates the use of the CAVE as a conceptual design review environment for advanced military vehicles in a comparison test with its present method of concept presentation and review. In a second experiment, CAVE users responded to a survey to determine the potential of VEs to improve design comprehension and immersive tendencies. In both cases, positive presence and immersion results support the idea that VEs offer advantages for conceptual design reviews over more traditional methods.
This paper describes a new approach to computer-aided spatial linkage design which uses the dynamic binding feature of Java to provide a extensible software system. The spatial linkages that we focus on are constructed from one or more spatial open chains that are connected to a single workpiece. Each open chain has less than six degrees of freedom and is termed a serial chain primitive. The goal of the design system is to determine the dimensions of a set of primitives each of which has a workspace that includes the set of specified workpiece positions. These chains are then assembled together to form candidate parallel linkage designs. There are many serial chain primitives each of which has a specialized constraint solver. These primitives can be assembled into many different parallel linkages, each of which needs an analysis routine. Our approach to the challenge of generating all of these routines is to abstract the design process and structure our computer-aided linkage design system to allow integration of specialize synthesis and analysis routines developed over time by user-collaborators.
The objective of this paper is to demonstrate an innovative and practical technique in which multidisciplinary optimization can be carried out while there exist points in the design space for which a response cannot be evaluated. It will also be demonstrated how design of experiment and response surface approximations are used to eliminate other complications associated with optimization of large-scaled designs. A multidisciplinary highly coupled air-to-air sparrow like missile design problem will be introduced to demonstrate the practical side of design optimization. The intention here is to provide practical engineering recommendations to others attempting to optimize industrial type design problems.
A genetic algorithm-based optimization method is proposed for solving the problem of nesting arbitrary shapes. Depending on the number of objects and the size of the search space, realizing an optimal solution within a reasonable time may not be possible. In this paper, a mating concept is introduced to reduce the solution time. Mating between two objects is defined as the positioning of one object relative to the other by merging common features that are assigned by the mating condition between them. A constrained move set is derived from a mating condition that allows the transformation of the object in each mating pair to be fully constrained with respect to the other. Properly mated objects can be placed together, thus reducing the overall computation time. Several examples are presented to demonstrate the efficiency of utilizing the mating concept to solve a nesting optimization problem.
The first Technical Note in this series  introduced the international standard ISO 10303, informally known as STEP (STandard for the Exchange of Product model data). Subsequent Technical Notes discussed various issues faced by users of STEP and how the ISO TC184/SC4 committee is addressing these issues. This paper presents the current move to modularize the STEP application protocol architecture. This paper describes the initial STEP architecture, requirements for improvements to the architecture, features of the new modular architecture, status and issues.
The most fundamental, and perhaps most important, task in the tolerance analysis of assemblies is to test whether or not the components with tolerances are actually able to fit together (called assembleability). Another important task of tolerance analysis is to check how the tolerances affect the quality or functionality of a product when they are assembled together. This paper presents the way the tolerance analyses are implemented by an assembly model, called the GapSpace model. The model can not only capture the necessary and sufficient conditions for assembleability analysis, but also transfers the functionality into the modeling variables (gaps). The assembleability analyses based on the GapSpace model for nominal components and those with worst case or statistical tolerances are introduced through an example. The problems of testing the quality of assemblies and calculating sensitivities are solved quickly and precisely using the model. The GapSpace model is more suitable for certain GD&T tolerancing methods than for parametric plus/minus tolerancing.
This paper reports on part of a project related to the development of a computer model for GD&T (Geometric Dimensioning and Tolerancing) to support tolerance specification, validation and tolerance analysis. The paper examines the basic elements involved in geometric variation and their interrelations. Logical tolerance classes are defined in terms of a target, a datum reference frame, and metric relations. ASME Y14.5 tolerance classes are mapped to these logical classes. The development of a data model for GD&T and its application in supporting design specification, validation, and tolerance analysis are discussed.
Slop (or backlash) in mechanical assemblies is often present and is usually undesirable from both craftsmanship and performance points of view. It is our belief that this phenomenon is not that well understood and that current methods of assessment are based largely on only qualitative, common-sense approaches. The focus of this paper is on developing an analytical theory for accurately characterizing slop, and on presenting an illustrative example. As one might expect, in principle, with a better understanding of slop, CAD (computer-aided-design) software package designers can create more refined software tools, mechanical engineers can design better products, and manufacturing engineers can be prepared to measure and improve craftsmanship levels. The underlying theory is based on combining concepts from differential geometry, including envelopes, constrained piecewise-smooth sweeps, and sweep vector fields (SVFs), along with basic configuration space (C-space) methods. In essence, the volumetric (or areal) error, which is generated as the movable part in an assembly is swept throughout its complete constrained volume (or area), may be viewed as a quantitative manifestation of craftsmanship errors. A 2-dimensional (2D) idealization of a common assembly that often suffers from poor craftsmanship due to slop, i.e., a doorknob assembly with exaggerated slop, is analyzed. The swept area is calculated using both traditional and SVF methods with the aid of Mathematica. High quality Mathematica visualization of interesting sweeps along the bounding edges of the nonlinear slop constraint region, including generation of all of the envelope curves, is done. Finally, this work attempts to serve as a paradigm for characterizing slop based on engineering criteria.
There exist a large body of work in the field of assembly, sometimes involving the use of a virtual environment to assist the user in assembly analysis. Typically, these environments limit the user’s interaction with the environment to one sense, sight, and two dimensions, the table upon which the mouse rests. The introduction of a haptic interface into the computer-aided design environment allows users to incorporate both a third dimension and a second sense, that of touch, into their work. In this paper, the development of an application called HIDRA (Haptic Integrated Dis/Re-assembly Analysis) is discussed, which integrates haptic feedback into an assembly/disassembly simulation environment. In particular, the focus is on the computer architecture developed to support such haptic simulations and the methods that have been created to meet some of the application time constraints unique to haptic simulation. Although focused on assembly and disassembly simulations, these issues and developments are relevant for the broader development of haptically enabled simulations in general.
This paper describes a system for the automatic recognition of assembly features and the generation of disassembly sequences. The paper starts by reviewing the nature and use of assembly features. One of the conclusions drawn from this survey is that the majority of assembly features involve sets of spatially adjacent faces. Two principle types of adjacency relationships are identified and an algorithm is presented for identifying assembly features which arise from “spatial” and “contact” face adjacency relationships (known as s-adjacency and c-adjacency respectively). The algorithm uses an octree representation of a B-rep model to support the geometric reasoning required to locate assembly features on disjoint bodies. A pointerless octree representation is generated by recursively subdividing the assembly model’s bounding box into octants which are used to locate: 1. Those portions of faces which are c-adjacent (i.e. they effectively touch within the tolerance of the octree). 2. Those portions of faces which are s-adjacent to a nominated face. The resulting system can locate and partition spatially adjacent faces in a wide range of situations and at different resolutions. The assembly features located are recorded as attributes in the B-rep model and are then used to generate a disassembly sequence plan for the assembly. This sequence plan is represented by a transition state tree which incorporates knowledge of the availability of feasible gripping features. By way of illustration, the algorithm is applied to several trial components.
Despite the apparent advantages and recent advances in the use of visualization in engineering design and optimization, we have found little evidence in the engineering literature that assesses the impact of fast, graphical design interfaces on the efficiency and effectiveness of engineering design decisions or the design optimization process. In this paper we discuss two examples—the design of an I-beam and the design of a desk lamp—for which we have developed graphical and text-based design interfaces to test the impact of having fast graphical feedback on design efficiency and effectiveness. Design efficiency is measured by recording the completion time for each design task, and design effectiveness is measured by calculating the error between each submitted design and the known optimum design. The impact of graphical feedback is examined by comparing user performance on the graphical and text-based design interfaces while the importance of rapid feedback is investigated by comparing user performance when response delays are introduced within each design interface. Experimental results indicate that users of graphical design interfaces perform better (i.e., have lower error and faster completion time) on average than those using text-based design interfaces, but these differences are not statistically significant. Likewise, we found that a response delay of 0.5 seconds increases error and task completion time, on average, but these increases are not always statistically significant. Trials using longer delays of 1.5 seconds did yield significant increases in task completion time. We also found that the perceived difficulty of the design task and using the graphical interface controls were inversely correlated with design effectiveness—designers who rated the task more difficult to solve or the graphical interface more difficult to use actually performed better than those who rated them easy. Finally, a significant "playing" effect was observed in our experiments: those who played video games more frequently or rated the slider bars and zoom controls easy to use took more time to complete the design tasks.
Virtual reality applications are making valuable contributions to the field of product realization. This paper presents an assessment of the hardware and software capabilities of VR technology needed to support a meaningful integration of VR applications in the product life cycle analysis. Several examples of VR applications for the various stages of the product life cycle engineering are presented as case studies. These case studies describe research results, fielded systems, technical issues, and implementation issues in the areas of virtual design, virtual manufacturing, virtual assembly, engineering analysis, visualization of analysis results, and collaborative virtual environments. Current issues and problems related to the creation, use, and implementation of virtual environments for engineering design, analysis, and manufacturing are also discussed. @DOI: 10.1115/1.1353846#
This paper describes with precision the steps adopted for the development of a digital functional assistance process for tolerancing, developed in collaboration with the RENAULT automobile group. This process is based on the formalization and digital integration of U.A.C.s. (Use Aptitude Conditions). Moreover, it uses the TTRS and the pseudo-TTRS model which then provides a tolerancing model that can be digitized and craft rules used, enabling capitalization on know-how in the tolerancing field. These steps are illustrated by a real case study.
Mold design can be a difficult, time-consuming process. Determining how to split a mold cavity into multiple mold pieces (e.g., core, cavity) manually can be a tedious process. This paper focuses on the mold construction step of the automated mold design process. By investigating glue operations and its relations with parting faces, an approach based on reverse glue operation is presented. The key of the reverse glue operation is to generate parting faces. A problem definition of parting face generation for a region is provided. Correspondingly, three face generating criteria are identified. Based on the parting lines of a region, our algorithms to generate the parting faces are presented. Our mold construction algorithms for two-piece molds and multi-piece molds are also presented with brief discussions. Some industrial examples are provided which illustrate the efficiency and effectiveness of our approach. We tested our mold designs by fabricating stereolithography mold inserts (a rapid tooling method) and molding parts.
Particularly for rapid tooling applications, delivering prototype parts with turnaround times of less than two weeks requires fast, proven mold design methods. We present a region-based approach to automated mold design that is suitable for simple two-piece molds (consisting of core and cavity), as well as molds with many additional moving sections. In our region-based approach, part faces are partitioned into regions, each of which can be formed by a single mold piece. The basic elements of our approach are concave regions (generalized pockets) and convex faces since these elements are central to the identification of regions. This paper focuses on the initial steps of automated mold design, including a problem formulation, methods for identifying the basic elements from part faces, and combining them into regions. By seeking to minimize the number of mold pieces, different partitions of faces into regions are explored until the smallest number of regions is found. During this process, a linear programming problem is adopted for finding a satisfactory parting direction of a region. Algorithms are presented for the region generating and combining process. Our approach is illustrated with several examples of industrial injection molded parts.
This paper describes a feature-based algorithm for automated design of multi-piece sacrificial molds. Our mold design algorithm consists of the following three steps. First, the desired gross mold shape is created based on the feature-based description of the part geometry. Second, if the desired gross mold shape is not machinable as a single component, then the gross mold shape is decomposed into simpler geometric components to make sure that each component is machinable using 3-axis CNC machining. The decomposition is performed to ensure that each component is accessible to end-milling tools, and decomposed components can be assembled together to form the gross mold shape. Finally, assembly features are added to mold components to eliminate unnecessary degrees of freedom from the final mold assembly to facilitate molding.
In the framework of Virtual CMM , virtual parts are proposed to be constructed as triangulated surface models. This paper presents a novel surface reconstruction method to the creation of virtual parts. It is based on the idea of identification and sculpting of concave regions of a Delaunay triangulation of the sample data. The proposed algorithm is capable of handling the reconstruction of surfaces with or without boundaries from unorganized points. Comparisons with other Delaunay-based algorithms show that it is more efficient in that it can optimally adapt to the geometric complexity of the sampled object. To validate the proposed algorithm, some detailed illustration are given.
Micro-electro-mechanical systems (MEMS) are very small devices that contain both mechanical and electrical elements with sizes in the order of microns. Design cycle time is an important consideration in the development and introduction of MEMS devices in the market. To develop extraction tools for MEMS designs, we need geometric algorithms to analyze the spatial layout of the mechanical portion of the MEMS device and extract a net-list of mechanical components. Such extracted net-list of mechanical components can be combined with the electronic component net-list to provide the complete device schematic. A key step in the extraction of mechanical elements is classification of various portions of the layout into structural elements. Because MEMS designs consist of a large number of elements, computational efficiency of the underlying extraction algorithm is very important for it to work on complex devices. This paper describes an efficient geometric algorithm for extracting structural elements from spatial layout of MEMS designs.
Multiple-sensor integration of vision and touch probe sensors has been shown to be a feasible approach for rapid and high-precision coordinate acquisition [Shen, T. S., Huang, J., and Meng, C. H., 2000, “Multiple-sensor integration for rapid and high-precision coordinate metrology,” IEEE/ASME Trans. Mechatron. 5, pp. 110–121]. However, the automation of coordinate measurements is still hindered by unknown surface areas that cannot be digitized using the vision system due to occlusions. It is identified that the estimation and reasoning of unknown surface areas, and automatic sensor planning using multiple sensors are two key issues. In order to advance multiple-sensor integration technologies toward a fully automatic and agile coordinate metrology, information integration algorithms for estimating and reasoning unknown surface areas, and an automatic multiple-sensor planning environment are developed in this paper. Experimental and simulation results are also demonstrated.
In this paper, a systematic scheme is proposed and novel technologies are developed to automatically reconstruct a CAD model from a set of point clouds scanned from the boundary surface of an existing object. The proposed scheme is composed of three major steps. In the first step, multiple input point clouds are incrementally integrated into a watertight triangle mesh to recover the object shape. In the second step, mesh segmentation is applied to the triangle mesh to extract individual geometric feature surfaces. Finally, the manifold topology describing the connectivity information between different geometric surfaces is automatically extracted and the mathematical description of each geometric feature is computed. The computed topology and geometry information represented in ACIS modeling kernel form a CAD model that may be used for various downstream applications. Compared with prior work, the proposed approach has the unique advantage that the processes of recognizing geometric features and of reconstructing CAD models are fully automated. Integrated with state of the art scanning devices, the developed model reconstruction method can be used to support reverse engineering of high precision mechanical components. It has potential applications to many engineering problems with a major impact on rapid design and prototyping, shape analysis, and virtual reality.
Surrogate models play an important role in improving design productivity and discovering knowledge at early design stage. In this paper, a preliminary version of an EI volutionary MI odeling AI pproach (EMA) is presented to generate surrogate models for highly nonlinear system with a large design space and limited resources. Through an evolutionary process, less accurate surrogate models gradually evolve into more accurate ones as the quality of the sampling data set is improved. Its use is demonstrated through an application at the early stage of automotive bumper system design and analysis. The results are verified by both FEA and physical test data.
Applications of of the medial axis have been limited because of its instability and algebraic complexity. In this paper, we use a simplification of the medial axis, the θ-SMA, that is parameterized by a separation angle (θ) formed by the vectors connecting a point on the medial axis to the closest points on the boundary. We present a formal characterization of the degree of simplification of the θ-SMA as a function of θ, and we quantify the degree to which the simplified medial axis retains the features of the original polyhedron.We present a fast algorithm to compute an approximation of the θ-SMA. It is based on a spatial subdivision scheme, and uses fast computation of a distance field and its gradient using graphics hardware. The complexity of the algorithm varies based on the error threshold that is used, and is a linear function of the input size. We have applied this algorithm to approximate the SMA of models with tens or hundreds of thousands of triangles. Its running time varies from a few seconds, for a model consisting of hundreds of triangles, to minutes for highly complex models.
In this paper, a new shape optimization approach, feature-based optimization of beam structures, is proposed to provide an efficient optimization solution of beam components in complex mechanical structures represented by polygonal meshes. Our approach consists of two main steps: 1) feature recognition of beam components: 2) gradient-based shape optimization of these components by reducing a weighted compliance among all load cases. The main contribution is to propose a new scheme to automate time-consuming shape optimization processes on polygonal meshes with beam components. Numerical experiments have been conducted and the results indicate the effectiveness of the approach.