bluuebunny/crossref_metadata_2025 huggingface dataset:
Improved Molecular Model of a Peptide Unit for Proteins
Authors: Subramanian Raghavendran , Kazerounian Kazem
Published: June 2008

Pauling, Corey and Branson in their seminal paper in 1951 reported numerical values for the bond lengths and bond angles for a peptide unit in proteins. These values became the standard model for several decades after that. This classic peptide model was either confirmed or improved upon by other researchers over the years, by using more advanced X-Ray diffraction equipments. In this paper, we have made an attempt to calibrate the values of these bond lengths and bond angles based on a systematic and deterministic approach applied to a collection of proteins defined structurally in the Protein Data Bank (PDB). Our method is based on the assumption that a peptide chain is a serial chain of identical rigid bodies connected by revolute joints (i.e. dihedral angles). The proposed procedure first computes the best estimate for the dihedral angles in the presence of inaccuracies in the atoms’ coordinates data. Then these values are used to find the conformation of the peptide chain using the calibrated model of the peptide unit. Through an optimization process, the structural error (RMSD of all atoms) between the resultant conformation and the PDB data is minimized to yield the best values for the bond length and bond angles in the calibrated peptide unit. Our numerical experiments indicate that by making small changes in the Pauling-Corey peptide model parameters (0.15% to 8.7%) the structural error is reduced significantly (3.0% to 57.4%). The optimum values for the bond angles and bond lengths are as follow: Bond Lengths: N-C(A): 1.4721Å, C(A)-C: 1.6167Å, C-N: 1.2047Å, C=O: 1.1913Å and N-H: 0.9621Å. Bond Bending Angles: N-C(A)-C: 109.6823°, C(A)-C=0: 119.518°, C(A)-C-N: 114.5553°, O=C-N: 125.9233°, C-N-H: 123.5155°, C-N-C(A): 121.5756°, C(A)-N-H: 114.901°. Peptide bond torsion angle: ω: 179.4432°.
A Kriging Metamodel Assisted Multi-Objective Genetic Algorithm for Design Optimization
Authors: Li Mian , Li Genzi , Azarm Shapour
Published: June 2008

The high computational cost of population based optimization methods, such as multi-objective genetic algorithms, has been preventing applications of these methods to realistic engineering design problems. The main challenge is to devise methods that can significantly reduce the number of computationally intensive simulation (objective/constraint functions) calls. We present a new multi-objective design optimization approach in that kriging-based metamodeling is embedded within a multi-objective genetic algorithm. The approach is called Kriging assisted Multi-Objective Genetic Algorithm, or K-MOGA. The key difference between K-MOGA and a conventional MOGA is that in K-MOGA some of the design points or individuals are evaluated by kriging metamodels, which are computationally inexpensive, instead of the simulation. The decision as to whether the simulation or their kriging metamodels to be used for evaluating an individual is based on checking a simple condition. That is, it is determined whether by using the kriging metamodels for an individual the non-dominated set in the current generation is changed. If this set is changed, then the simulation is used for evaluating the individual; otherwise, the corresponding kriging metamodels are used. Seven numerical and engineering examples with different degrees of difficulty are used to illustrate applicability of the proposed K-MOGA. The results show that on the average, K-MOGA converges to the Pareto frontier with about 50% fewer number of simulation calls compared to a conventional MOGA.
Design Semantics Capturing With Product Models to Support Information Sharing in Collaborative Design
Authors: Yang Q. Z. , Zhang Y.
Published: June 2008

A challenge in effective sharing of product information in collaborative design is the lack of explicit and compatible semantics in the product digital content. Substantial difficulties arise in understanding and interpreting the intended meaning of product data across collaborating design teams and applications. This paper presents a method to capture design semantics with product models for more consistent representation, understanding and interpretation of data semantics to support heterogeneous information sharing. The method incorporates the STEP based interoperability standard, ontology engineering, and object-oriented product modeling to capture and share the semantically interoperable product information. It focuses on: modeling of product data with additional semantics in object-based representations; extension of STEP with supplementary design information; domain ontology development; and semantics-driven schema mapping. A software prototype has been implemented to validate the method and tested with case studies.
Type Synthesis of 3-DOF Translational Parallel Manipulators Based on Atlas of DOF Characteristic Matrix
Authors: Yu Jingjun , Dai Jian S. , Liu Xin-Jun , Bi Shusheng , Zong Guanghua
Published: June 2008

Low-degree-of-freedom (Low-DOF) parallel manipulators (PMs) have drawn extensive interest, particularly in type synthesis in which two main approaches were established in the reciprocal screw system theory and Lie group theory. This paper aims at proposing a new type synthesis method to complementing the above methods. For this purpose, the concept of the DOF characteristic matrix, originated from displacement subgroup and displacement submanifold, is proposed. A new but general approach based on the atlas of DOF Characteristic Matrix is addressed for both exhaustive classification and type synthesis of low-DOF PMs. Compared to the method based on Lie group, the proposed approach is prone to construct an orthogonal structure and easy to realize the complete classification and exhaustive enumeration of a class of low-DOF PM. In order to verify the effectiveness of the proposed method, type synthesis of Translational PMs (TPMs) particularly in ones with an orthogonal structure is performed, resulting in some novel orthogonal TPMs.
Selection-Integrated Optimization (SIO) Methodology for Optimal Design of Adaptive Systems
Authors: Khire Ritesh A. , Messac Achille
Published: June 2008

Many engineering systems are required to operate under changing operating conditions. A special class of systems called adaptive systems have been proposed in the literature to achieve high performance under changing environments. Adaptive systems acquire this powerful feature by allowing their design configuration to change with operating conditions. In the optimization of the adaptive systems, designers are often required to select (i) adaptive and (ii) non-adaptive (or fixed) design variables of the design configuration. Generally, the selection of these variables, and the optimization of adaptive systems are performed sequentially, thus leaving a likelihood of a sub-optimal design. In this paper, we propose the Selection-Integrated Optimization (SIO) methodology that integrates the two key processes: (1) the selection of the adaptive and fixed design variables, and (2) the optimization of the adaptive system, thereby leading to an optimum design. A major challenge to integrating these two key processes is the selection of the number of fixed and adaptive design variables, which is discrete in nature. We propose the Variable-Segregating Mapping-Function (VSMF) that overcomes this roadblock by progressively approximating the discreteness in the design variable selection process. This simple yet effective approach allows the SIO methodology to integrate the selection and optimization processes, and help avoid one significant source of sub-optimality from typical optimization formulations. The SIO methodology finds its applications in a variety of other engineering fields as well, such as product family optimization. However, in this paper, we limit the scope of our discussion to adaptive system optimization. The effectiveness of the SIO methodology is demonstrated by optimally designing a new air-conditioning system called Active Building Envelope (ABE) System.
Design for Customer Satisfaction in One-of-a-Kind Production Environment
Authors: Hong G. , Hu L. , Xue D. , Tu Y. L. , Xiong Y. L.
Published: June 2008

This research addresses the issues to identify the optimal product configuration and its parameters based on the requirements of customers on performance and costs of products in one-of-a-kind production (OKP) environment. In this work, variations of product configurations and parameters in an OKP product family are modeled by an AND-OR tree and parameters of the nodes in this tree. Different product configurations with different parameters are evaluated by performance and cost measures. These evaluation measures are converted into comparable customer satisfaction indices using the non-linear relations between the evaluation measures and the customer satisfaction indices. The optimal product configuration and its parameters with the maximum overall customer satisfaction index are identified by genetic programming and constrained optimization.
2-D Deposition Pattern and Strategy Study on Rapid Manufacturing
Authors: Ruan Jianzhong , Ren Lan , Sparks Todd E. , Liou Frank
Published: June 2008

Different from the traditional machining processes, the quality of parts produced by the metal deposition process is much more dependent upon the choice of deposition paths. Due to the nature of the metal deposition processes, various tool path patterns will result in different shapes in the metal deposition process with about the same input geometry. This paper presents the research conducted on the effect of various scanning patterns and strategies for the deposition results. Triangle and rectangle patterns are selected as basic 2-D “cells” to plan the scanning path. Several criteria, like minimum angle, minimum length of edge, etc. are defined to categorize the different “cell” shapes. Based on deposition results, the suitable patterns are determined for each type. The previously defined patterns are applied for each cell in order to achieve the optimal quality. The experiment has demonstrated that the pattern and strategy selection has improved the deposition quality significantly.
Material Property Identification and Sensitivity Analysis Using Indentation and FEM
Authors: Ge Long , Kim Nam Ho , Bourne Gerald R. , Sawyer W. Gregory
Published: June 2008

Mechanical properties of materials in small-scale applications, such as thin coatings, are often different from those of bulk materials due to the difference in the manufacturing process. Indentation has been a convenient tool to study the mechanical properties in such applications. In this paper, a numerical technique is proposed that can identify the mechanical properties by minimizing the difference between the results from indentation experiments and those from finite element analysis. First, two response surfaces are constructed for loading and unloading curves from the indentation experiment of a gold film on the silicon substrate. Unessential coefficients of the response surface are then removed based on the test statistics. Different from the traditional methods of identification, the tip geometry of the indenter is included because its uncertainty significantly affects the results. In order to validate the accuracy and stability of the method, the sensitivity of the identified material properties with respect to each coefficient is analyzed.
Development of Evaluation System for Style Design Using Mixed Reality Technology
Authors: Kimishima Yu , Aoyama Hideki
Published: June 2008

Currently industrial design is mainly done by CAD and mock-up is created to evaluate the design. This process is repeated from the rough sketches to the final detailed mock-up until the designer is satisfied. In this process, creating the mock-up, especially detailed mock-up, is quite costly. Hence, there is a need to improve the efficiency of mock-up fabrication. One of the strategies for realizing this is to use virtual models (VM) instead of mock-up. VM is a model which is created on computer by 3D computer graphics, and it allows realistic graphical modeling which can be modified easily, reduces time considerably, and enables dynamic viewing of models from any angle and orientation. Despite this, mock-ups are still required because the process of design evaluation by touching physical models (PM) is still important to designers. To resolve this disadvantage of VM, this paper proposes a new evaluation system for industrial design. With this system, VM and the rapid prototyping mock-up are overlapped in virtual space to produce a tangible VM. This new type of VM functions just like a detailed mock-up but can be created much faster and cheaper. This system employs the concept of Augmented Virtuality (AV), which is mainly based on virtual space and real objects are added to reinforce the virtual space. In this case, haptic information from the rapid prototyping mock-up is added to optical information from the VM. When estimating the 3D position of a real object, optical information is used considerably more than haptic information. Therefore, if there are only a few positional or geometrical differences between the rapid prototyping mock-up and the VM, the differences can be offset by the (incorporated into the) optical information. For this reason, if the designer needs to modify the product shape, only the VM needs to be modified, allowing old mock-ups to be used repeatedly. This means that designers can evaluate a variety of product designs with only one mock-up, thus reducing both time and the costs for creating a mock-up. The operator wears a data glove on his/her hand to construct a virtual hand in the virtual space. With this virtual hand, the operator can also evaluate the user interface (UI) of the product by means of pushing buttons or watching display on the VM. This paper also provides a new method for overlapping the virtual space and real space.
SMARP: A Tool for Parallel Manipulators Design and Simulation
Authors: Lahouar Samir , Zeghloul Said , Romdhane Lotfi
Published: June 2008

We present a new tool used to design and simulate parallel robots in their environments. Explicit kinematic equations, for a given architecture, are generated automatically. The user has the choice of specifying, among all the variables, the input and the output of the mechanism. We also present a method to generate a path of the end effector and to detect singularities along the generated path.
Formulating and Searching Assembly Sequence Design Spaces to Increase the Utilization of Current Assembly Plant Resources
Authors: Reddy Shilpitha Bomi , Siddique Zahed
Published: June 2008

Efficient procedures for generation of feasible assembly sequences and effective utilization of available assembly plant resources can greatly reduce the development time and cost for platforms for the new product family members. This paper presents a method application to generate feasible assembly sequences and an approach to select an assembly process that reduces the existing plant modification cost. Assembly sequence design space is combinatorial in nature. Mathematical models to solve the effects of constraints on these spaces and algorithms to efficiently enumerate feasible spaces are presented. An algorithm that selects assembly process that can reduce the modification cost of the existing assembly plant is developed. A software application that implements the method and algorithms is also presented. The program uses the concept of recursive partitioning of set of components to generate assembly sequence space. The assembly processes are then evaluated to determine the process that maximized resource utilization. The application of the proposed approach and software is demonstrated using automotive underbody front structure product family.
Mobility and Workspace of a 3-5R Translational Parallel Mechanism
Authors: Huda Syamsul , Takeda Yukio
Published: June 2008

A study about mobility and workspace of a 3-5R translational parallel spatial mechanism that has three symmetric limbs is presented. Mobility analysis based on the screw theory and numerical calculations were carried out to show if the proposed mechanism enabled the pure translational motion of a platform. The size and shape of workspace of the mechanism were also evaluated.
Topology Optimization of Micromachined Structures With Surface Micromachining Manufacturing Constraints
Authors: Alwan Aravind , Ananthasuresh G. K.
Published: June 2008

Topology optimization methods have been shown to have extensive application in the design of microsystems. However, their utility in practical situations is restricted to predominantly planar configurations due to the limitations of most microfabrication techniques in realizing structures with arbitrary topologies in the direction perpendicular to the substrate. This study addresses the problem of synthesizing optimal topologies in the out-of-plane direction while obeying the constraints imposed by surface micromachining. A new formulation that achieves this by defining a design space that implicitly obeys the manufacturing constraints with a continuous design parameterization is presented in this paper. This is in contrast to including manufacturing cost in the objective function or constraints. The resulting solutions of the new formulation obtained with gradient-based optimization directly provide the photolithographic mask layouts. Two examples that illustrate the approach for the case of stiff structures are included.
An Effective Trajectory Segmentation and Processing Method for Hand Motion Based Shape Conceptualization
Authors: Varga Edit , Horva´th Imre , Rusa´k Zolta´n
Published: June 2008

Efficient support of conceptual design requires dedicated computer-based systems that feature new kinds of interaction and visualization techniques. As input means for this kind of systems, various modalities have been considered. Hand motions have been found to be especially efficient at describing shapes and expressing shape related operations directly in the 3D space. Therefore a formal hand motion language (HML) has earlier been developed by the authors. Computer interpretation of HML is however challenging not only because of the technological complexity of the problem, but also because of the need for real-time computation. Our hypothesis has been that the HML interpretation problem can be reduced to motion detection, trajectory segmentation, hand posture recognition, and command mapping sub-problems. The objective of trajectory segmentation is to find the non-transient parts of the hand motion that can be mapped to the words of HML. In this paper we propose a method which combines trajectory segmentation and hand posture recognition. Based on the postural information that is conveyed by the individual frames of the recorded motion, the beginning and the end of the meaningful segments are identified. In addition, the spatial and geometric information related to the formal HML words is also gathered. These pieces of information are combined in order to reconstruct and visualize the control commands in the shape conceptualization system. The current results shows that the necessary computer algorithms are fast enough and do not impose restrictions on the process of hand motion interpretation. Future research will concentrate on the integration of hand motion detection and reconstruction with visualization and manipulation of shape concepts in a fully volumetric imaging environment.
Dynamic and Input Tuning Analysis of a Piezodriven 3-DOF Micro-Positioning Stage Utilizing Flexure Hinges
Authors: Zhang Xianmin
Published: June 2008

The elastic dynamic performances are studied for a piezodriven 3-DOF compliant precision micro-positioning stage with flexure hinges. Firstly, the dynamic equations of motion of the system are developed. The flexure hinges are modeled by using the varying section frame element, and the element stiffness and mass matrices are presented. Secondly, the lower order modal frequencies and damping factors are experimentally identified and the analysis model is proved to be feasible. Finally, an input-tuning concept aimed to improve dynamic actuation performances is proposed. The quintic tuning function is employed in the dynamic analysis for the system. Simulation results show that the residual vibration and the input couplings induced by the inputs are improved significantly after the tuning function is applied during actuation.
An Objective Evaluation of Displacement-Amplifying Compliant Mechanisms for Sensor Applications
Authors: Krishnan Girish , Ananthasuresh G. K.
Published: June 2008

Displacement-amplifying compliant mechanisms (DaCMs) reported in literature are mostly used for actuator applications. This paper considers them for sensor applications that rely on displacement measurement, and evaluates them objectively. The main goal is to increase the sensitivity under constraints imposed by several secondary requirements and practical constraints. A spring-mass-lever model that effectively captures the addition of a DaCM to a sensor is used in comparing eight DaCMs. We observe that they significantly differ in performance criteria such as geometric advantage, stiffness, natural frequency, mode amplification, factor of safety against failure, cross-axis stiffness, etc., but none excel in all. Thus, a combined figure of merit is proposed using which the most suitable DaCM could be selected for a sensor application. A case-study of a micro machined capacitive accelerometer and another case-study of a vision-based force sensor are included to illustrate the general evaluation and selection procedure of DaCMs with specific applications. Some other insights gained with the analysis presented here were the optimum size-scale for a DaCM, the effect on its natural frequency, limits on its stiffness, and working range of the sensor.
Simultaneous Geometry Optimization and Material Selection for Truss Structures
Authors: Rakshit Sourav , Ananthasuresh G. K.
Published: June 2008

In this work, we explore simultaneous design and material selection by posing it as an optimization problem. The underlying principles for our approach are Ashby’s material selection procedure and structural optimization. For the simplicity and ease of initial implementation of the general procedure, truss structures under static load are considered in this work in view of maximum stiffness, minimum weight/cost and safety against failure. Along the lines of Ashby’s material indices, a new design index is derived for trusses. This helps in choosing the most suitable material for any design of a truss. Using this, both the design space and material database are searched simultaneously using optimization algorithms. The important feature of our approach is that the formulated optimization problem is continuous even though the material selection is an inherently discrete problem.
A Kinematic Theory for Planar Hoberman and Other Novel Foldable Mechanisms
Authors: Patel Jiten , Ananthasuresh G. K.
Published: June 2008

In this paper, we present a kinematic theory for Hoberman and other similar foldable linkages. By recognizing that the building blocks of such linkages can be modeled as planar linkages, different classes of possible solutions are systematically obtained including some novel arrangements. Criteria for foldability are arrived by analyzing the algebraic locus of the coupler curve of a PRRP linkage. They help explain generalized Hoberman and other mechanisms reported in the literature. New properties of such mechanisms including the extent of foldability, shape-preservation of the inner and outer profiles, multi-segmented assemblies and heterogeneous circumferential arrangements are derived. The design equations derived here make the conception of even complex planar radially foldable mechanisms systematic and easy. Representative examples are presented to illustrate the usage of the design equations and the kinematic theory.
A Two-Stage Design Method for Compliant Mechanisms Having Specified Non-Linear Output Paths
Authors: Kobayashi Masakazu , Yamakawa Hiroshi , Nishiwaki Shinji , Izui Kazuhiro , Yoshimura Masataka
Published: June 2008

Compliant mechanisms generated by traditional topology optimization methods have linear output response, and it is difficult for traditional methods to implement mechanisms having non-linear output responses, such as nonlinear deformation or path. To design a compliant mechanism having a specified nonlinear output path, a two-stage design method based on topology and shape optimization is constructed here. In the first stage, topology optimization generates an initial and conceptual compliant mechanism based on ordinary design conditions, with “additional” constraints that are used to control the output path at the second stage. In the second stage, an initial model for the shape optimization is created, based on the result of the topology optimization, and the additional constraints are replaced by spring elements. The shape optimization is then executed, to generate a detailed shape of the compliant mechanism having the desired output path. In this stage, parameters that represent the outer shape of the compliant mechanism and the properties of spring elements are used as design variables in the shape optimization. In addition to configuration of the specified output path, executing the shape optimization after the topology optimization also makes it possible to consider the stress concentration and large displacement effects. This is an advantage offered by the proposed method, since it is difficult for traditional methods to consider these aspects, due to inherent limitations of topology optimization.
Designing Synchronous Belt Transmissions With Variable Velocity Ratio
Authors: Innocenti Carlo , Paganelli Davide
Published: June 2008

The paper presents a new procedure to design a two-pulley synchronous belt transmission connecting, with no belt tensioner, two parallel-axis shafts with a variable velocity ratio. The procedure takes into account the limited number of choices for pitch and length of off-the-shelf synchronous belts, which translates into the need of fine-adjusting either the center distance or the law of motion. Differently from other approaches reported in the technical literature, the suggested method is based on the numerical solution of a set of functional equations. A numerical example shows application of the proposed method to a case study.
A Multicriteria System-Based Method for Simulation-Driven Design Synthesis
Authors: Bolognini Francesca , Shea Kristina , Vale Christopher W. , Seshia Ashwin A.
Published: June 2008

This paper presents an algorithmic, physics-based, design synthesis method aimed at facilitating synthesis through automated generation of a range of feasible and optimally directed design alternatives. The method assists designers in the exploration of performance limits and trade-offs for synthesis tasks as well as reducing design time through rapid, computational generation. The method introduced combines a multicriteria generate-and-test search algorithm, called Burst, with a Connected Node System (CNS) design representation and provides automatic links to multiphysics simulation for quantitative evaluation of design performance throughout the synthesis process. The CNS-Burst method is applied to two benchmark synthesis tasks in the domain of MEMS to validate the method. The solutions generated meet the modeled design requirements and the variety of designs generated offers designers the possibility of selecting devices according to their preferences among performance trade-offs. The potential for extension to larger, more complex MEMS design synthesis and optimization tasks is discussed.
Design Analysis and Precision Control for a Piezo-Driven Planar Platform
Authors: Ting Yung , Li Chun-Chung , Jar Ho-Chin , Huang Jeng-Lin
Published: June 2008

An XY planar platform for nanoscale positioning objective is developed in this study. The platform is constructed with flexure hinge mechanism, and each axis of the platform is driven by piezoelectric stack actuator. Note that the entire structure of the platform for the two axes is on the same plane not like the usual XY platform piled up with independent axial structure. It is found mutual disturbance exists in such a planar platform by both ANSYS analysis and practical experiment. As the mutual disturbance is defined by an approximate linear function, and the nonlinear hysteresis effect is solved by means of the Preisach model, appropriate command signal is computed. The feedforward controller on the basis of the established hysteresis model, the PID-based feedback controller with the optimal gains searched by the Ziegler-Nichols method and the genetic algorithm, and the composite (feedforward+feedback) controller are designed and examined by experiment respectively. From the experimental results, it indicates each type of controller can achieve a certain level of accuracy. The composite controller, of course, performs best, and is able to reach the target of about 10nm for large stroke and 1nm for fine stroke. It concluded that the designed planar platform has the advantage of small space and low cost can still be controlled well to satisfy the nanoscale precision requirement.
A Generic, Geometric Approach to Accurate Machining-Error Predictions for 3-Axis CNC Milling of Sculptured Surface Parts: Part I — Modeling and Formulation
Authors: Chen Zezhong C. , Cai Wei
Published: June 2008

In CNC machining, machining errors are usually caused by some of the sources such as cutting tool deflection, cutting tool wear, machine tool vibration, improper coolant/lubrication, and negative thermal effect. To increase product accuracy, much research has been carried out on the prediction of machining errors. However, in milling of sculptured surface parts, due to their curved shapes, the geometries of cutting tools do not match the parts’ surfaces well if the tools cut along the tool paths on the surfaces in a point-to-point way. As a consequence, machining error is inevitable, even if there is no other source of error in ideal machining conditions. To predict machining errors caused by this tool-surface mismatch, several methods have been proposed. Some of them are simple, and some represent the geometry of machined surfaces using cutter-swept surfaces. But none of these methods is accurate and practical. In this research work, a generic, geometric approach to predicting machining errors caused by the tool-surface mismatch is proposed for 3-axis sculptured surface milling. First, a new geometric model of the furrow formed by an APT tool moving between two neighboring cutter contact (CC) points is built. Second, the mathematical formula of cutting circle envelopes is derived. Then an algorithm for calculating machining errors in each tool motion is provided. Finally, this new approach is applied to two practical parts for the accurate machining-error predictions, and these predictions are then compared to the inaccurate predictions made by two established methods to demonstrate the advantages of this approach. This approach can be used in tool path planning for high precision machining of sculptured surface parts.
A Generic, Geometric Approach to Accurate Machining-Error Predictions for 3-Axis CNC Milling of Sculptured Surface Parts: Part II — Applications and Analysis
Authors: Chen Zezhong C. , Cai Wei
Published: June 2008

As sculptured surfaces are widely used in mechanical design, machining sculptured surface parts accurately is highly demanded in industry; however, it is quite challenging to meet their demand. Due to the geometric complexity of these surfaces, the tool-surface geometric mismatch always causes machining errors when the tool cuts along the tool paths. To prevent surface gouging, where the machining error is greater than the part tolerance, state-of-the-art CAM software usually determines cutter contact (CC) points on the tool paths first, and then simulates the machining to check the errors caused by this tool-surface mismatch. If surface gouging occurs, the CC points are adjusted using the CAM software. But this established method is quite time consuming and sometimes ineffective. To overcome these problems, a new system, based on the accurate predictions of machining errors, is proposed in this research paper for the optimization of CC points on the tool paths. First, two established CC point generation methods, the chordal deviation method and the circular arc approximation method, are introduced; and their limitations are addressed. Second, a sensitivity study of the machining errors with respect to the cutting tools is conducted. Then a system implementing the generic, geometric approach to accurate machining-error predictions is proposed to optimize CC points on the tool paths. Finally, this CC point optimization system is applied to two practical parts to demonstrate its advantages over the two established methods. This proposed work provides a profound understanding of the machining errors caused by the tool-surface mismatch and contributes to tool path planning for 3-axis CNC milling of sculptured surface parts.
Applications of Genetic Algorithms in Process-Planning: Tool Sequence Selection for 2.5D Pocket Machining
Authors: D’Souza Roshan M. , Ahmad Zaryab
Published: June 2008

Rapid tool change mechanisms in modern CNC machines have enabled the use of multiple tools (sequence of tools) to machine a given pocket. Larger diameter tools that have higher material removal rates are used to clear large open spaces, smaller tools are used for clean up. The challenge lies in selecting that particular combination of tools that minimizes total cost. Previously, we developed algorithms based on network optimization to find the best tool sequence given a list of cutters, cutting parameters and pocket geometry. The formulation was based on certain assumptions that did not account for tool holder geometry. It also required the evaluation of all possible tool-pair combinations for a given tool set. This can get time consuming if the tool set is large. In this paper, we present a genetic algorithm based method to select optimal tool sequences. The algorithm was implemented and bench marked against the graph algorithm. We have found that the GA based method is able to find a near optimal tool sequence without evaluating up to 30% of all possible tool-pairs.
Multifunctional Topology Design of Cellular Material Structures
Authors: Seepersad Carolyn Conner , Allen Janet K. , McDowell David L. , Mistree Farrokh
Published: June 2008

Prismatic cellular or honeycomb materials exhibit favorable properties for multifunctional applications such as ultra-light load bearing combined with active cooling. Since these properties are strongly dependent on the underlying cellular structure, design methods are needed for tailoring cellular topologies with customized multifunctional properties that may be unattainable with standard cell designs. Topology optimization methods are available for synthesizing the form of a cellular structure—including the size, shape, and connectivity of cell walls and the number, shape, and arrangement of cell openings—rather than specifying these features a priori. To date, the application of these methods for cellular materials design has been limited primarily to elastic and thermo-elastic properties, however, and limitations of standard topology optimization methods prevent direct application to many other phenomena such as conjugate heat transfer with internal convection. In this paper, we introduce a practical, two-stage, flexibility-based, multifunctional topology design approach for applications that require customized multifunctional properties. As part of the approach, robust topology design methods are used to design flexible cellular topology with customized structural properties. Dimensional and topological flexibility is embodied in the form of robust ranges of cell wall dimensions and robust permutations of a nominal cellular topology. The flexibility is used to improve the heat transfer characteristics of the design via addition/removal of cell walls and adjustment of cellular dimensions, respectively, without degrading structural performance. We apply the method to design stiff, actively cooled prismatic cellular materials for the combustor liners of next-generation gas turbine engines.
The Risk in Early Design (RED) Method: Likelihood and Consequence Formulations
Authors: Grantham Lough Katie , Stone Robert B. , Tumer Irem
Published: June 2008

This study focuses specifically on the relationship between function and risk in early design by presenting a mathematical mapping from product function to likelihood and consequence risk assessments that can be used in the conceptual design phase. An investigation of a spacecraft orientation subsystem is used to demonstrate the proposed mappings. The risk assessment presented in this paper is a tool that will aid designers by identifying risks as well as reducing the subjectivity of the likelihood and consequence value from a risk element, provide four key risk element properties (design parameter, failure mode, likelihood, and consequence) for numerous risk elements with a simple calculation, and provide a means for inexperienced designers to effectively address risk in the conceptual design phase. The investigation demonstrates that the method presented in this paper is a useful tool for preliminary identification and assessment of product risks.
A Feature-Based Approach for Cutter/Workpiece Engagement Calculation in 2-1/2D End Milling
Authors: Wang Jue , Yip-Hoi Derek
Published: June 2008

Machining process modeling requires cutter/workpiece engagement geometry in order to predict cutting forces. The calculation of these engagements is challenging due to the complicated and changing intersection geometry that occurs between the cutter and the in-process workpiece. Solid modelers can be used to perform these calculations by executing intersection operations between cutter and workpiece surfaces at successive cutter locations. These operations utilize parametric surface/surface intersection (SSI) algorithms. For the large number of engagements that can occur in machining a complicated workpiece this can be a time-consuming and sometimes unreliable process. In this paper, in-process machining features are introduced into machining process modeling for 2 1/2 D end milling, and a feature based approach is presented for addressing the computational complexity and robustness issues in the cutter/workpiece engagement calculations. Geometric Invariant (giF) and Form Invariant Machining Features (fiF) are modeled to help represent engagement conditions analytically. Volume decomposition and composition algorithms are described that extract these two types of machining features from the removal volumes generated at each tool pass. Cutter/workpiece engagements can be analytically extracted from giFs and fiFs without applying repetitive SSI operations. This paper presents one part of ongoing collaborative research into developing Virtual Machining Systems. The engagement conditions that are found are inputs to machining process models that identify cutting forces, predict stability and that optimize the process.
A Multi-Agent System for Distributed, Internet Enabled Cutter/Workpiece Engagement Extractions
Authors: Wang Jue , Peng Xiaobo , Yip-Hoi Derek
Published: June 2008

Cutter/workpiece engagement (CWE) extraction is an important problem in process modeling. One approach is to use a B-rep solid modeler to perform the calculations. However, this can have a high computational overhead especially for complicated workpieces. This paper presents a multi-agent system for B-rep based CWE extraction that allows distributed processing of the modeling steps over the Internet. The CWE calculation utilizes distributed agents for performing swept volume and removal volume construction in addition to the extraction of the CWE geometry itself. These distributed agents provide the capability to perform many of the calculations in parallel. The proposed methodology thus makes the best use of available, distributed computing resources leading to greatly improved efficiency in the CWE calculations. If agents are available to perform these calculations using other non-B-rep approaches the proposed framework facilitates their integration. This paper presents the architecture of the framework. This requires a specification of each agent in the framework. The mechanisms adopted for the three primary agent actions, task scheduling, master agent selection and results passing are presented. Interaction protocols are provided to explain how agents cooperate with each other to achieve parallel computation. Finally a prototype implementation and an example are given to show the effectiveness and efficiency of the system.
Determine Mesh Orientation by Voxel-Based Principal Component Analysis
Authors: Tonshal Basavaraj , Chen Yifan , Buttolo Pietro
Published: June 2008

In this paper we propose a new method to determine the part orientation of a 3D mesh based on Principal Component Analysis (PCA). Although the idea and practice of using PCA to determine part orientation is not new, it is not without practical issues. A major drawback of PCA, when it comes to dealing with meshes comprised of nodes and elements, is that the results are tessellation-dependent because of its sensitivity to variability. Two CAE meshes derived from the same CAD model but with different mesh node distribution characteristics, for instance, can yield different principal components. This is an undesirable outcome because the primary concern in model reorientation is shape, not the representational details of the shape. In order to reduce the influence of node characteristics, weight factors were proposed in the past, but the improvement is limited. To overcome this limitation, we must eliminate the influence of mesh node distribution. We achieve this by introducing an intermediate workspace, which is subsequently voxelized. We then find the intersection of the mesh model with the voxelized workspace. We collect the intersecting voxels to form an intermediate, tessellation-independent representation of the mesh. Applying PCA to this “neutralized” representation allows us to achieve mesh-property-independent results. The voxel representation also provides an opportunity of computational efficiency. We implemented an octree data structure to store the voxels and implemented a fast intersection (between a mesh element and a voxel) check procedure utilizing the interval overlap check derived from the separating axis theorem. Practical issues concerning determination of the voxel space resolution is addressed. A two-step trial and correction approach is proposed to enhance the consistency of results. Our voxel-based PCA is robust, fast, and straightforward to implement. Application examples are shown demonstrating the effectiveness and efficiency of this approach.
A New Design Paradigm Based on Sketch and Retrieval
Authors: Pu Jiantao , Ramani Karthik
Published: June 2008

To improve the efficiency and naturalness of computer-aided design (CAD), this paper introduces a new design paradigm in which a highly interactive sketch-based user interface and a design-knowledge reuse based on retrieval are combined seamlessly. Freehand sketching serves as a cognitive tool to support users’ intuitive abilities by exploring the visual components of a design. Design knowledge reuse is achieved by searching for similar designs in an existing library. To demonstrate the validity of this design paradigm, we have implemented two prototype systems aimed at 2D and 3D design, respectively. They both use the same key components: sketch beautification module, a constraint solver, a 2D&3D search engine, and a sketch-based user interface. The preliminary usability evaluation shows that our proposed design paradigm is more natural for usage and has higher efficiency than the traditional CAD systems.
Three Novel Discontinuously Movable Spatial 7-Link Mechanisms
Authors: Lee Chung-Ching , Herve´ Jacques M.
Published: June 2008

Three kinds of new discontinuously movable (DM) spatial 7-link mechanisms named hybrid planar-spherical 7R, hybrid spherical-spherical 7R, and hybrid planar-planar 6R1P DM mechanisms are synthesized by combining planar and spherical 4R trivial chains. Their discontinuous mobility is explained using the Lie group algebraic properties of the displacement set. In addition, the same given spatial arrangement of joints can be linked in two ways thus constituting two distinct chains with a quite different mobility. One chain has two global degrees of freedom (dofs), which disobey the general Grubler-Kutzbach mobility criterion. The other chain exhibits a singular pose, which is a bifurcation towards two distinct working modes of one-dof mobility. As a result, the set of relative motions between any two specific links is not a manifold but consists of the union of displacement 1-dimensional manifolds.
Application of a Genetic Algorithm to Concept Variant Selection
Authors: Hutcheson Ryan S. , Jordan Robert L. , Stone Robert B. , Terpenny Janis P. , Chang Xiaomeng
Published: June 2008

This paper outlines a framework for applying a genetic algorithm to the selection of component variants between the conceptual and detailed design stages of product development. A genetic algorithm (GA) is defined for the problem and an example is presented that demonstrates its application and usefulness. Functional modeling techniques are used to formulate the design problem and generate the chromosomes that are evaluated with the algorithm. In the presented example, suitable GA parameters and the break-even point where the GA surpassed an enumerated search of the same solution space were found. Recommend uses of the GA along with limitations of the method and future work are presented as well.
A Hybrid Method for Parametric Conceptual Vehicle Design Using Legacy Components and Parametric Surfaces
Authors: Wan Jian , Wang Nanxin , Gomez-Levi Gianna
Published: June 2008

Early conceptual design is one of the most important stages in vehicle product development. At this stage, vehicle design information is limited. In many cases, historical or benchmark vehicle data are used as surrogates in decision making. Some of the legacy components may be reused in the new vehicle design in order to reduce development and manufacturing costs. Nowadays, parametric modeling methods have been developed and employed for conceptual vehicle design. However, how to quickly reuse the previous design and legacy vehicle data in parametric design is still a challenge. A hybrid method for parametric conceptual vehicle design is presented in this paper, which uses both legacy components and parametric surfaces. This method allows easy reuse of historical data together with new parametric surfaces for early vehicle design. It enables mix and match of legacy components with newly designed parametric surfaces in representing a new design. This method provides a systematic way to enforce the commonality and reusability in a vehicle design.
Design and Verification of a New Computer Controlled Seating Buck
Authors: Wang Nanxin , Kiridena Vijitha , Gomez-Levi Gianna , Wan Jian , Sieczka Steven , Pulliam David
Published: June 2008

Appraising vehicle package design concepts using seating bucks — physical prototypes representing vehicle package, is an integral part of the vehicle package design process. Building such bucks is costly and may impose substantial burden on the vehicle design cycle time. Further, static seating bucks lack the flexibility to accommodate design iterations during the gradual progression of a vehicle program. A “Computer controlled seating buck”, as described in this paper, is a quick and inexpensive alternative to the traditional seating bucks with the desired degree of fidelity. It is particularly useful to perform package and ergonomic studies in the early stages of a vehicle program, long before the data is available to build a traditional seating buck. Such a seating buck has been developed to accommodate Ford vehicle package design needs. This paper presents the functional requirements, the high level conceptual design of how these requirements are realized, and the methods to verify, improve and sustain the dimensional accuracy and capability of the new computer controlled seating buck.