bluuebunny/crossref_metadata_2025 huggingface dataset:
Development and Validation of an S-N Based Two Phase Bending Fatigue Life Prediction Model
Authors: Singh Avinash
Published: September 2003

The stress-life S-N method along with the Palmgren-Miner cumulative damage theory is the simplest and the most commonly used fatigue life prediction technique. Its main advantage is that the material properties needed are easy to collect and life calculation is simple. However under many variable amplitude loading conditions, life predictions have been found to be unreliable. Various modifications have been proposed to the Palmgren-Miner theory, but they have not lead to more reliable life predictions. In this paper, a two-stage cumulative damage model will be developed and validated. This model divides fatigue life into two phases—a crack initiation phase and a crack propagation phase. It will be shown that the proposed method results in greatly improved life prediction capabilities. Also, the proposed method retains the simplicity of the S-N based approach in that the material data is still relatively simple to generate and the calculations are straightforward.
A New Method for Detection of Graph Isomorphism Based on the Quadratic Form
Authors: He and P. R. , Zhang W. J. , Li and Q. , Wu F. X.
Published: September 2003

This paper proposes a new method for detection of graph isomorphism using the concept of quadratic form. Graphs/kinematic chains are represented first by quadratic form, and the comparison of two graphs is thus reduced to the comparison of two quadratic form expressions. If both the lengths and the directions of the semiaxes of quadric surfaces, which are characterized by the eigenvalues and eigenvectors, are the same, the associated graphs/kinematic chains are isomorphic. An algorithm is developed based on this idea, and tested for the counter-examples known to other methods.
Optimization of the Closure-Weld Region of Cylindrical Containers for Long-Term Corrosion Resistance Using the Successive Heuristic Quadratic Approximation Technique*
Authors: Ceylan Zekai , Trabia Mohamed B.
Published: September 2003

Welded cylindrical containers are susceptible to stress corrosion cracking (SCC) in the closure-weld area. An induction coil heating technique may be used to relieve the residual stresses in the closure-weld. This technique involves localized heating of the material by the surrounding coils. The material is then cooled to room temperature by quenching. A two-dimensional axisymmetric finite element model is developed to study the effects of induction coil heating and subsequent quenching. The finite element results are validated through an experimental test. The container design is tuned to maximize the compressive stress from the outer surface to a depth that is equal to the long-term general corrosion rate of the container material multiplied by the desired container lifetime. The problem is subject to several geometrical and stress constraints. Two different solution methods are implemented for this purpose. First, an off-the-shelf optimization software is used. The results however were unsatisfactory because of the highly nonlinear nature of the problem. The paper proposes a novel alternative: the Successive Heuristic Quadratic Approximation (SHQA) technique. This algorithm combines successive quadratic approximation with an adaptive random search within varying search space. SHQA promises to be a suitable search method for computationally intensive, highly nonlinear problems.
Investigation into the Effect of the Nut Thread Run-Out on the Stress Distribution in a Bolt Using the Finite Element Method
Authors: Hobbs J. W. , Burguete R. L. , Patterson E. A.
Published: September 2003

By means of comparing results from finite element analysis and photoelasticity, the salient characteristics of a finite element model of a nut and bolt have been established. A number of two-dimensional and three-dimensional models were created with varying levels of complexity, and the results were compared with photoelastic results. It was found that both two-dimensional and three-dimensional models could produce accurate results provided the nut thread run-out and friction were modeled accurately. When using two-dimensional models, a number of models representing different positions around the helix of the thread were created to obtain more data for the stress distribution. This approach was found to work well and to be economical.
Design of Fused-Deposition ABS Components for Stiffness and Strength
Authors: Rodrı´guez Jose´ F. , Thomas James P. , Renaud John E.
Published: September 2003

The high degree of automation of Solid Freeform Fabrication (SFF) processing and its ability to create geometrically complex parts to precise dimensions provide it with a unique potential for low volume production of rapid tooling and functional components. A factor of significant importance in the above applications is the capability of producing components with adequate mechanical performance (e.g., stiffness and strength). This paper introduces a strategy for optimizing the design of Fused-Deposition Acrylonitrile-Butadiene-Styrene (FD-ABS; P400) components for stiffness and strength under a given set of loading conditions. In this strategy, a mathematical model of the structural system is linked to an approximate minimization algorithm to find the settings of select manufacturing parameters, which optimize the mechanical performance of the component. The methodology is demonstrated by maximizing the load carrying capacity of a two-section cantilevered FD-ABS beam.
Dynamics of Rotary Vane Engine
Authors: Librovich B. V.
Published: September 2003

This paper broadly discusses aspects of the novel Rotary Vane Engine (RVE). It also considers, in detail, the geometrical structure of work unit and the entire engine. The rigorous mathematical description of work unit and torque transmission mechanism are presented for a first time in literature. Although the RVE is a simple structure possessing a small number of moving parts, it is this property that provides the RVE with an important advantage when compared to a usual reciprocating engine. The main idea is to use noncircular gears in torque transmission mechanism together with Kauertz-Virmel work unit. It is found that the rotary engine can produce almost constant angular velocity of the flywheel, which would result in an efficient and smooth performance.
Target Cascading in Optimal System Design
Authors: Kim Hyung Min , Michelena Nestor F. , Papalambros Panos Y. , Jiang Tao
Published: September 2003

Target cascading is a key challenge in the early product development stages of large complex artifacts: how to propagate the desirable top level design specifications (or targets) to appropriate specifications for the various subsystems and components in a consistent and efficient manner. Consistency means that all parts of the designed system should work well together, while efficiency means that the process itself should avoid iterations at later stages, which are costly in time and resources. In the present article target cascading is formalized by a process modeled as a multilevel optimal design problem. Design targets are cascaded down to lower levels using partitioning of the original problem into a hierarchical set of subproblems. For each design problem at a given level, an optimization problem is formulated to minimize deviations from the propagated targets and thus achieve intersystem compatibility. A coordination strategy links all subproblem decisions so that the overall system performance targets are met. The process is illustrated with an explicit analytical problem and a simple automotive chassis design model that demonstrates how the process can be applied in practice.
Synthesis of Inertially Compensated Variable-Speed Cams
Authors: Demeulenaere B. , De Schutter J.
Published: September 2003

Traditionally, cam-follower systems are designed by assuming a constant camshaft speed. Nevertheless, all cam-follower systems, especially high-speed systems, exhibit some camshaft speed fluctuation (despite the presence of a flywheel) which causes the follower motions to be inaccurate. This paper therefore proposes a novel design procedure that explicitly takes into account the camshaft speed variation. The design procedure assumes that (i) the cam-follower system is conservative and (ii) all forces are inertial. The design procedure is based on a single design choice, i.e., the amount of camshaft speed variation, and yields (i) cams that compensate for the inertial dynamics for any period of motion and (ii) a camshaft flywheel whose (small) inertia is independent of the period of motion. A design example shows that the cams designed in this way offer the following advantages, even for non-conservative, non-purely inertial cam-follower systems: (i) more accurate camshaft motion despite a smaller flywheel, (ii) lower motor torques, (iii) more accurate follower motions, with fewer undesired harmonics, and (iv) a camshaft motion spectrum that is easily and robustly predictable.
Investigation of Parallel Manipulators Using Linear Complex Approximation
Authors: Wolf A. , Shoham M.
Published: September 2003

This investigation deals with singularity analysis of parallel manipulators and their instantaneous behavior while in or close to a singular configuration. The method presented utilizes line geometry tools and screw theory to describe a manipulator in a given position. Then, this description is used to obtain the closest linear complex, presented by its screw coordinates, to the set of governing lines of the manipulator. The linear complex axis and pitch provide additional information and a better physical understanding of the type of singularity and the motion the manipulator tends to perform in a singular point and in its neighborhood. Examples of Hunt’s, Fichter’s and 3-UPU singularities, along with a few selected examples taken from Merlet’s work [1], are presented and analyzed using this method.
Physics-Based Modeling for Heterogeneous Objects
Authors: Qian Xiaoping , Dutta Debasish
Published: September 2003

Heterogeneous objects are composed of different constituent materials. In these objects, material properties from different constituent materials are synthesized into one part. Therefore, heterogeneous objects can offer new material properties and functionalities. The task of modeling material heterogeneity (composition variation) is a critical issue in the design and fabrication of such heterogeneous objects. Existing methods cannot efficiently model the material heterogeneity due to the lack of an effective mechanism to control the large number of degrees of freedom for the specification of heterogeneous objects. In this research, we provide a new approach for designing heterogeneous objects. The idea is that designers indirectly control the material distribution through the boundary conditions of a virtual diffusion problem in the solid, rather than directly in the native CAD (B-spline) representation for the distribution. We show how the diffusion problem can be solved using the B-spline shape function, with the results mapping directly to a volumetric B-Spline representation of the material distribution. We also extend this method to material property manipulation and time dependent heterogeneous object modeling. Implementation and examples, such as a turbine blade design and prosthesis design, are also presented. They demonstrate that the physics based B-spline modeling method is a convenient, intuitive, and efficient way to model object heterogeneity.
Singularity Analysis of 3-DOF Planar Parallel Mechanisms via Screw Theory
Authors: Bonev Ilian A. , Zlatanov Dimiter , Gosselin Cle´ment M.
Published: September 2003

This paper presents the results of a detailed study of the singular configurations of 3-DOF planar parallel mechanisms with three identical legs. Only prismatic and revolute joints are considered. From the point of view of singularity analysis, there are ten different architectures. All of them are examined in a compact and systematic manner using planar screw theory. The nature of each possible singular configuration is discussed and the singularity loci for a constant orientation of the mobile platform are obtained. For some architectures, simplified designs with easy to determine singularities are identified.
Decomposition-Based Assembly Synthesis for Structural Stiffness
Authors: Lyu Naesung , Saitou Kazuhiro
Published: September 2003

This paper presents a method that systematically decomposes product geometry into a set of components considering the structural stiffness of the end product. A structure is represented as a graph of its topology, and the optimal decomposition is obtained by combining FEM analyses with a Genetic Algorithm. As the first case study, the side frame of a passenger car is decomposed for the minimum distortion of the front door panel geometry. As the second case study, the under body frame of a passenger car is decomposed for the minimum frame distortion. In both case studies, spot-weld joints are considered as joining methods, where each joint, which may contain multiple weld spots, is modeled as a torsional spring. First, the rates of the torsional springs are treated as constant values obtained in the literature. Second, they are treated as design variables within realistic bounds. By allowing the change in the joint rates, it is demonstrated that the optimal decomposition can achieve the smaller distortion with less amount of joint stiffness (hence less welding spots), than the optimal decomposition with the typical joint rates available in the literature.
A Finite-Element-Based Study of the Load Distribution of a Heavily Loaded Spur Gear System With Effects of Transmission Shafts and Gear Blanks
Authors: Yong-tao Tian , Cong-xin Li , Wei Tong , Chang-hua Wu
Published: September 2003

Spur gears were typically analyzed in the past using two-dimensional (2-D) Finite Element (FE) models. This is not adequate in many cases. A three-dimensional (3-D) FE model of a spur gear system, which accommodates all the gear teeth, the gear bodies, and the two transmission shafts, is developed in this paper using a sub-structuring method. The load between pinion and gear wheel is delivered by elastic frictional contact. The contact problem is solved according to the FE parametric quadratic programming method. The paper presents the shape of the contact region as well as the load distribution along the tooth width and profile. The results show that the transmission shafts have significant effects on the contact conditions including load distribution, contact region, and load deviation. The proposed method also applies to other types of gearing.
Analytical Target Cascading in Automotive Vehicle Design
Authors: Kim Hyung Min , Rideout D. Geoff , Papalambros Panos Y. , Stein Jeffrey L.
Published: September 2003

Target cascading in product development is a systematic effort to propagate the desired top-level system design targets to appropriate specifications for subsystems and components in a consistent and efficient manner. If analysis models are available to represent the consequences of the relevant design decisions, analytical target cascading can be formalized as a hierarchical multilevel optimization problem. The article demonstrates this complex modeling and solution process in the chassis design of a sport-utility vehicle. Ride quality and handling targets are cascaded down to systems and subsystems utilizing suspension, tire, and spring analysis models. Potential incompatibilities among targets and constraints throughout the entire system can be uncovered and the trade-offs involved in achieving system targets under different design scenarios can be quantified.
Solid Model Reconstruction of Wireframe CAD Models Based on Topological Embeddings of Planar Graphs
Authors: Inoue Keisuke , Shimada Kenji , Chilaka Karthick
Published: September 2003

This paper describes a robust and versatile method based on graph embedding for reconstructing a solid model from a wireframe model. The robustness and versatility of the conventional methods are limited in that: (1) most of them are heuristic and thus less robust, and (2) the rest, deterministic ones, can handle only small class of wireframes. Unlike the conventional methods, our approach is deterministic and covers a larger class of wireframes that are topologically 2-connected planar multigraphs. The class includes wireframes that can be interpreted as a closed two-manifold in multiple ways. The proposed algorithm consists of three steps: (1) all topological solutions are exhaustively generated using triconnected component decomposition; (2) the surface geometries for all the topological solutions are generated; and (3) the solutions are pruned down to geometrically valid ones. We also show the algorithm is extendable to the class of general planar multigraphs. The approach is characterized by generating the complete set of topological solutions without referring to the geometry of the wireframe, which makes the process free from geometric errors and instabilities. The algorithm is also fast, because even when there are many topological solutions, the total number of different faces is very small. The proposed approach provides a method for easy and intuitive geometric modeling as well as a conversion tool for legacy wireframes.
A Study of Early Stage Self-Loosening of Bolted Joints
Authors: Jiang Yanyao , Zhang Ming , Lee Chu-Hwa
Published: September 2003

Both experimental investigation and finite element analysis were conducted to explore the mechanisms for the early stage self-loosening of bolted joints under transverse cyclic loading. The nuts were glued to the bolts using a strong thread locker in the self-loosening experiments to ensure that no backing-off of the nut occurred. Depending on the loading magnitude, the clamping force reduction ranged from 10% to more than 40% of the initial preload after 200 loading cycles. Three-dimensional elastic-plastic finite element analysis was conducted with the implementation of an advanced cyclic plasticity model. The finite element results revealed that the local cyclic plasticity occurring near the roots of the engaged threads resulted in cyclic strain ratcheting. The localized cyclic plastic deformation caused the stresses to redistribute in the bolt, and the result was the gradual loss of clamping force with loading cycles. The finite element results agreed with the experimental observations quantitatively. When the two clamped plates started to slip and the slip displacement was controlled, both experiments and finite element simulations suggested that the friction between the clamped plates has an insignificant influence on the early stage self-loosening.
An Approach to Decision-Based Design With Discrete Choice Analysis for Demand Modeling
Authors: Wassenaar Henk Jan , Chen Wei
Published: September 2003

In this paper, we present the importance of using a single criterion approach to Decision-Based Design (DBD) by examining the limitations of multicriteria approaches. We propose in this paper an approach to DBD as an enhancement to Hazelrigg’s DBD framework that utilizes the economic benefit to the producer as the single criterion in alternative selection. The technique of Discrete Choice Analysis (DCA) is introduced for constructing a product demand model, which is crucial for the evaluation of both profit and production cost. An academic universal motor design problem illustrates the proposed DBD approach. It appears that DBD, when applied correctly, is capable of unambiguously selecting the preferred alternative in a rigorous manner. Open research issues related to implementing the DBD approach are raised. The focus of our study is on demonstrating the approach rather than the design results per se.
A Review of Formulas for the Mechanical Efficiency Analysis of Two Degrees-of-Freedom Epicyclic Gear Trains
Authors: Pennestrı` Ettore , Valentini Pier Paolo
Published: September 2003

This paper, after a rigorous proof of the formulas originally proposed by Radzimovsky, demonstrates the numerical equivalence of the different approaches available for computing the mechanical efficiency of two degrees-of-freedom (d.o.f.) epicyclic gear trains. The paper includes also a discussion on the redundancy of data required by some formulas.
Discrete Event Simulation Implemented in a Virtual Environment
Authors: Kelsick Jason , Vance Judy M. , Buhr Lori , Moller Cheryl
Published: September 2003

Virtual reality (VR) technology provides a human-computer interface that allows participants to interact naturally with digital objects which are represented as three-dimensional images that occupy positions in a three-dimensional world. Related to problems of engineering design and manufacturing, this new technology offers engineers the ability to work with computer models in a three-dimensional, immersive environment. This paper describes a virtual reality application where the results of a discrete event simulation of a manufacturing cell are integrated with a virtual model of the cell to produce a virtual environment. The program described in this paper, the VRFactory, combines results from a commercial discrete event simulation program, SLAM II, with a virtual environment. This allows the user to investigate, using three-dimensional computer models, how various changes to the manufacturing cell affect part production. This investigation is performed while immersed in a computer-generated three-dimensional representation of the cell. Existing discrete event programming software allows only two-dimensional views of the factory as the parts progress through the simulation. Parts are shown only as primitive geometric shapes on the computer monitor and instantaneously move from one station to the next. The virtual environment implementation of the SLAM II results allows users to experience the simulation in a fully immersive three-dimensional digital environment. The virtual environment used here is a CAVE™-like projection screen-based facility called the C2, which is located at Iowa State University. This paper describes the creation of the VR model of the manufacturing cell, the animation of the environment and the implementation of the results of the discrete event simulation.
Decomposition-Based Assembly Synthesis for In-Process Dimensional Adjustability
Authors: Lee Byungwoo , Saitou Kazuhiro
Published: September 2003

This paper presents a method of assembly synthesis focused on the in-process adjustability, where assembly synthesis is defined as the decomposition of the end product design prior to the detailed component design phase. Focusing on the effect of joint configurations on dimensional integrity of complex assemblies, the method recursively decomposes a product configuration and assigns joint configurations according to simple rules, in order to achieve a designed dimensional adjustability and non-forced fit. The rules employed during the decomposition process are drawn from the previous works of assembly design. An augmented AND/OR graph is utilized to represent a process of assembly synthesis with the corresponding assembly sequences, and the algorithm for generating the AND/OR graph is discussed. The method is applied to two dimensional skeletons of products without moving parts at very early stage of the design process. The relation of the assembly synthesis to Datum Flow Chain [1] is discussed. It is also shown that each final design from the assembly synthesis defines its own Datum Flow Chain.
Sensitivity Analysis of the Conical-Shaped Equivalent Model of a Bolted Joint
Authors: Manring Noah D.
Published: September 2003

In this paper, the conical-shaped equivalent model for a bolted joint is considered. In particular, the governing equations for this model are made non-dimensional for the purposes of conducting sensitivity analysis. From this work, a plot of the dimensionless spring-rate of the clamped material is generated for all reasonable designs for which the conical-shaped equivalent model applies. The sensitivity analysis is then used to discuss the relative importance of estimating the proper model and design parameters and a maximum percent of uncertainty in the spring-rate calculation is also presented. It is shown in this discussion that the calculations are quite sensitive to a proper estimation of the cone angle (a model parameter) and that uncertainty within this calculation can range from 5 to 20%.
The Design of a New Metal Forming Press with Controllable Mechanism
Authors: Du R. , Guo W. Z.
Published: September 2003

Metal forming press is one of the most commonly used manufacturing machines. Every day, millions of parts are produced by metal forming ranging from battery caps to automotive body panels. Therefore, even a small improvement may add to significant corporative gain. Currently, the metal forming presses can be divided into two categories: mechanical presses and hydraulic presses. The former is fast (high speed presses may reach up to several thousand shots per minute) and energy efficient (the large flywheel eases the impulsive force), but lacks flexibility. On the other hand, the hydraulic presses are flexible (their motions can be programmed) and accurate, but are expensive to build and to operate. Recently, there are mechanical presses driven by servomotors. They could perform as flexible as hydraulic presses with high speed. Nevertheless, they are even more expensive to build and to operate. This paper introduces a new design of mechanical press whose performances are programmable, including the trajectory and the velocity of the stroke, and yet, it is relatively inexpensive to build and to operate. The key idea of the new design is a 2-degree-of-freedom seven-bar linkage mechanism driven by a large constant speed motor and a small servomotor. First, the kinetics and kinematics of the design are presented including the feasibility conditions, mechanical advantage, as well as the torque and power distribution between the two motors. Next, a number of simulation results are given. The design (parameter) optimization is also carried out using Genetic Algorithm (GA). Based on computer simulation, it is shown that the new design is indeed very attractive.
Solution Selectors: A User-Oriented Answer to the Multiple Solution Problem in Constraint Solving
Authors: Bettig Bernhard , Shah Jami
Published: September 2003

The development of solid modeling to represent the geometry of designed parts and the development of parametric modeling to control the size and shape have had significant impacts on the efficiency and speed of the design process. Designers now rely on parametric solid modeling, but often are frustrated by a problem that unpredictably causes their sketches to become twisted, contorted, or take an unexpected shape. Mathematically, this problem, known as the “multiple solution problem” occurs because the dimensions and geometric constraints yield a set of non-linear equations with many roots. In practice, this situation occurs because the dimensioning and geometric constraint information given in a CAD model is not sufficient to unambiguously and flexibly specify which configuration the user desires. This paper first establishes that only explicit, independent solution selection declarations can provide a flexible mechanism that is sufficient for all situations. The paper then describes the systematic derivation of a set of “solution selector” types by considering the occurrences of multiple solutions in combinations of mutually constrained geometric entities. The result is a set of eleven basic solution selector types and two derived types that incorporate topological information. In particular, one derived type “concave/convex” is user-oriented and may prove to be particularly useful.
Constraint Singularities of Force Transmission in Nonredundant Parallel Robots With Less Than Six Degrees of Freedom
Authors: Zoppi Matteo , Bruzzone Luca E. , Molfino Rezia M. , Michelini Rinaldo C.
Published: September 2003

The analysis of the workspace singularities is one of the fundamental aspects in the design of parallel robots. The architecture singularities are generally studied analysing the local properties of the Jacobian matrix. Nevertheless, for limited-DOF parallel robots, there is a category of singularities (constraint or constructive singularities), relating to the constraint force transmission, which are not described by this matrix. This paper deals with a general approach to the analysis of these singularities, used in the synthesis of a Linear Delta robot to suitably modify its geometry, remarkably improving the structural behavior. Details and numerical results are provided.
Dynamic Analysis of a Nonlinear Torsional Flexible Coupling With Elastic Links
Authors: Bert Charles W. , Wu Shiyuan
Published: September 2003

Torsional oscillations in mechanical power transmission systems are a significant source of dynamic loads which are harmful to the system performance. The effects can cause a drive shaft to become unstable and self-destructive at critical speeds. This research focuses on dynamic analysis of a nonlinear torsional flexible coupling with elastic links. The equations of motion are derived by means of Lagrange’s equation. These equations are used to obtain the quasi-static performance of torque vs. angular displacement at constant rotational velocity. An exact solution is also found for the phase-plane representation for free oscillation torque. The fluctuation ratios of input velocity vs. output velocity of the system are obtained for determining the system performance. The results of the analyses of steady running and transient oscillation performance are applied to the determination of optimum proportions of the couplings. Results are compared with those of rigid-link couplings to show the influence of elasticity of the link on dynamic behavior of the system.
On the Bases of Wrench Spaces for the Kinematic and Dynamic Analysis of Mechanisms
Authors: Sugimoto Koichi
Published: September 2003

The aim of this paper is to find out a computational procedure for the kinematic and dynamic analysis of a mechanism with multiple loops having motion spaces of a Lie algebra or Lie algebras. The basis of a motion space of the loop is determined such that it consists of passive joints axes in a loop, and a basis of a wrench space is determined to be its dual basis. The analysis of a closed loop mechanism can be done by selecting loop-cut-joints and computing values of wrenches acting on these joints from the condition that virtual works of passive joints are zero. By expressing these wrenches in the coordinate vectors on the dual bases, the concise analysis procedure can be obtained. Because a formulation for the analysis is developed based on the bases consisting of passive joint axes and their dual bases, the computational procedure can be applied to a mechanism with any Lie algebras.
Design of Shaving Cutter for Plunge Shaving a Topologically Modified Involute Pinion
Authors: Radzevich Stephen P.
Published: September 2003

The purpose of this paper is to solve the problem of designing a shaving cutter for plunge shaving a topologically modified involute pinion. Application of topologically modified pinion allows noise reduction. Due to the desired topologically modified pinion tooth surface is determined not analytically, and discretely by a grid of points, the problem under consideration cannot be solved by direct application of methods developed in theory of enveloping surfaces. A modified kinematical approach is developed to establish one-to-one correspondence between points that determine tooth surface of a pinion to be machined, and points that determine tooth surface of a shaving cutter to be applied. The developed approach is based on ideas, which could be traced back to publications by E. Buckingham. The following three considerations are essential: a) tooth surface of an initial nonmodified pinion, b) desired deviations of the topologically modified pinion tooth surface relatively to the nonmodified pinion tooth surface, and c) relative motion that shaving cutter performs in gear finishing operation. Consequently, the algorithm, and software for computing coordinates of points, which determine the modified gear-shaving cutter tooth surface is developed.
Backlash Compensation in Gear Trains by Means of Open-Loop Modification of the Input Trajectory
Authors: Warnecke Martin , Jouaneh Musa
Published: September 2003

This paper presents an approach to reduce the effect of the backlash nonlinearity in systems with relative cyclic motion. A compensation approach is developed to calculate a modified course of input motion for a desired velocity profile in systems with known backlash. The modified input trajectory contains accelerating and decelerating motion features to traverse the backlash area in minimal time. The method was proved with a dc-motor driven gear train. Results show that the output motion delay could be remarkably reduced. The time to overcome the backlash gap depends upon the desired velocity and the amount of backlash introduced to the system. Time savings between 43% and 74% could be measured with the utilized experimental setup. The proposed velocity compensation method is most efficient for low operating speeds and large mounting allowance between gears.
Multi-Speed Gearbox Design Using Multi-Objective Evolutionary Algorithms
Authors: Deb Kalyanmoy , Jain Sachin
Published: September 2003

Optimal design of a multi-speed gearbox involves different types of decision variables and objectives. Due to lack of efficient classical optimization techniques, such problems are usually decomposed into tractable subproblems and solved. Moreover, in most cases the explicit mathematical expressions of the problem formulation is exploited to arrive at the optimal solutions. In this paper, we demonstrate the use of a multi-objective evolutionary algorithm, which is capable of solving the original problem involving mixed discrete and real-valued parameters and more than one objectives, and is capable of finding multiple nondominated solutions in a single simulation run. On a number of instantiations of the gearbox design problem having different complexities, the efficacy of NSGA-II in handling different types of decision variables, constraints, and multiple objectives are demonstrated. A highlight of the suggested procedure is that a post-optimal investigation of the obtained solutions allows a designer to discover important design principles which are otherwise difficult to obtain using other means.
Are dose calculations during dose optimization in brachytherapy necessary?
Authors: Lahanas M. , Baltas D.
Published: September 2003

We consider the problem of anatomy based dose optimization in brachytherapy. A calculation method for some objective functions and their derivatives is proposed which significantly reduces the number of required operations. The optimization in some cases, ignoring a preprocessing step, is independent of the number of sampling points. The idea is that some of the objectives and their derivatives used for dose optimization do not require the explicit calculation of dose values. Dose optimization with the new modified computation method for the objectives and derivatives is, depending on the number of sampling points, up to 100 times faster than the conventional method with dose calculation.
Three‐dimensional dose reconstruction of breast cancer treatment using portal imaging
Authors: Louwe R. J. W. , Damen E. M. F. , van Herk M. , Minken A. W. H. , Törzsök O. , Mijnheer B. J.
Published: September 2003

In this study, we present an algorithm for three‐dimensional (3‐D) dose reconstruction using portal images obtained with an electronic portal imaging device (EPID). For this purpose an algorithm for 2‐D dose reconstruction, which was previously developed in our institution, was adapted. The external contour of the patient was used to correct for absorption of primary photons, but the presence of inhomogeneities was not taken into account. The accuracy of the algorithm was determined by irradiating two anthropomorphic breast phantoms with 6 MV photons. The dose values derived from portal images were compared with results from 3‐D dose calculations, which, in turn, were verified with data obtained with an ionization chamber and film dosimetry. It was found that the application of contour information significantly improves the accuracy of 2‐D dose reconstruction. If the total dose at the isocenter plane resulting from all treatment beams is reconstructed, the average deviation from the planned dose is 0.1%±1.7% (1 SD). If contour information is not available, the differences increase up to ±20% for the individual beams. In that case, the dose can only be reconstructed with reasonable accuracy when (nearly) opposing beams are used. The average deviation of the 3‐D reconstructed dose from the planned dose in the irradiated volume is 1.4%±5.4% (1 SD). If the irradiated volume is enclosed by planes less than 5 cm distant from the isocenter plane, then the average deviation is only 0.5%±3.4% (1 SD). It can be concluded that the proposed algorithm for a 3‐D dose reconstruction allows a determination of the dose at the isocenter plane and the dose–volume histogram with an accuracy acceptable for an independent verification of the treatment.
Monte Carlo calculation of effective attenuation coefficients for various compensator materials
Authors: du Plessis F. C. P. , Willemse C. A.
Published: September 2003

Effective attenuation coefficients for 6, 8, and 15 MV photon beams were derived and studied for various compensator materials for square beams with side lengths of 0.5, 1.0, 2.0, 3.0, and 5.0 cm. Calculations were based on depth dose data in water obtained from EGS4 based DOSXYZ Monte Carlo simulations. Depth dose data were calculated using different compensator materials as attenuators of variable thickness. The absorbed dose varied exponentially as a function of absorber thickness at any depth in water on the beam axis for all materials. The effective attenuation coefficient data were compared with measurements for wax, aluminum and brass with values from the literature. Theoretical narrow beam linear attenuation coefficients were calculated and compared with the Monte Carlo data. The effective attenuation coefficient data for all materials were parametrized as functions of field size and depth in water. The effective attenuation coefficient was also parametrized as a function of atomic number. It was found that the effective attenuation coefficients calculated from the DOSXYZ data using a simple source model correspond to measured data for wax, aluminum and brass and published data for lead.
A new algorithm for the registration of portal images to planning images in the verification of radiotherapy, as validated in prostate treatments
Authors: Jobse Mark , Davelaar Jaap , Hendriks Emile , Kattevilder Rob , Reiber Hans , Stoel Berend
Published: September 2003

The manual verification of a radiotherapy treatment, where a portal image is matched onto a planning image, is very time consuming and subject to inter‐ and intraobserver variability. Therefore, a fully automatic matching procedure (image registration) is required. Existing automatic matching algorithms are confounded, however, by irrelevant information in the portal images (i.e., air in the intestines). Therefore, we have developed a new method, which is an extension of chamfer matching and uses, apart from the distance to the nearest edge, additional information on the correspondence of the gradient angle and magnitude of the edges, making the method less sensitive to confounding information in the images. To validate the automatic matching procedure in clinical practice, we applied the new method on 157 images of 29 randomly selected patients treated for carcinoma of the prostate. Three experts manually matched these images in consensus. Subsequently, the same observers assessed the results of the automatic registration. When regular chamfer matching is used for the fully automatic matching procedure, only 5% of the image pairs could be matched correctly, whereas the new method successfully registered 80% by using additional information on the angle of the edges. From the results of the validation study it can be concluded that a significant reduction in workload for the physicians and technicians can be achieved with this method.
Detection of prostate cancer by integration of line‐scan diffusion, T2‐mapping and T2‐weighted magnetic resonance imaging; a multichannel statistical classifier
Authors: Chan Ian , Wells William , Mulkern Robert V. , Haker Steven , Zhang Jianqing , Zou Kelly H. , Maier Stephan E. , Tempany Clare M. C.
Published: September 2003

A multichannel statistical classifier for detecting prostate cancer was developed and validated by combining information from three different magnetic resonance (MR) methodologies: T2‐weighted, T2‐mapping, and line scan diffusion imaging (LSDI). From these MR sequences, four different sets of image intensities were obtained: T2‐weighted (T2W) from T2‐weighted imaging, Apparent Diffusion Coefficient (ADC) from LSDI, and proton density (PD) and T2 (T2 Map) from T2‐mapping imaging. Manually segmented tumor labels from a radiologist, which were validated by biopsy results, served as tumor “ground truth.” Textural features were extracted from the images using co‐occurrence matrix (CM) and discrete cosine transform (DCT). Anatomical location of voxels was described by a cylindrical coordinate system. A statistical jack‐knife approach was used to evaluate our classifiers. Single‐channel maximum likelihood (ML) classifiers were based on 1 of the 4 basic image intensities. Our multichannel classifiers: support vector machine (SVM) and Fisher linear discriminant (FLD), utilized five different sets of derived features. Each classifier generated a summary statistical map that indicated tumor likelihood in the peripheral zone (PZ) of the prostate gland. To assess classifier accuracy, the average areas under the receiver operator characteristic (ROC) curves over all subjects were compared. Our best FLD classifier achieved an average ROC area of and our best SVM classifier achieved an average ROC area of . The T2W ML classifier, our best single‐channel classifier, only achieved an average ROC area of . Compared to the best single‐channel ML classifier, our best multichannel FLD and SVM classifiers have statistically superior ROC performance and 0.0017, respectively) from pairwise two‐sided t‐test. By integrating the information from multiple images and capturing the textural and anatomical features in tumor areas, summary statistical maps can potentially aid in image‐guided prostate biopsy and assist in guiding and controlling delivery of localized therapy under image guidance.
High precision film dosimetry with GAFCHROMIC® films for quality assurance especially when using small fields
Authors: Mack Andreas , Mack Günther , Weltz Dirk , Scheib Stefan G. , Böttcher Heinz D. , Seifert Volker
Published: September 2003

Treatment units for radiosurgery, brachytherapy, implementation of seeds, and IMRT generate small high dose regions together with steep dose gradients of up to 30%–50% per mm. Such devices are used to treat small complex‐shaped lesions, often located close to critical structures, by superimposing several single high dose regions. In order to test and verify these treatment techniques, to perform quality assurance tasks and to simulate treatment conditions as well as to collect input data for treatment planning, a GAFCHROMIC® film based dosimetry system for measuring two‐dimensional (2‐D) and three‐dimensional (3‐D) dose distributions was developed. The nearly tissue‐equivalent radiochromic GAFCHROMIC® film was used to measure dose distributions. A drum scanner was investigated and modified. The spectral emission of the light source and the filters together with the efficiency of the CCD filters for the red color were matched and balanced with the absorption spectra of the film. Models based on refined studies have been developed to characterize theoretically the physics of film exposure and to calibrate the film. Mathematical descriptions are given to calculate optical densities from spectral data. The effect of darkening has been investigated and is described with a mathematical model. The influence of the scan temperature has been observed and described. In order to cope with the problem of individual film inhomogeneities, a double irradiation technique is introduced and implemented that yields dose accuracies as good as 2%–3%. Special software routines have been implemented for evaluating and handling the film data.
Quantitative imaging of bromine‐76 and yttrium‐86 with PET: A method for the removal of spurious activity introduced by cascade gamma rays
Authors: Beattie Bradley J. , Finn Ronald D. , Rowland Douglas J. , Pentlow Keith S.
Published: September 2003

Positron Emission Tomography of bromine‐76 and yttrium‐86 results in the detection of coincident events that are not strictly associated with annihilation photon pairs. Instead, these coincidences occur because prompt gamma rays emitted by these nuclides result in cascades of photons that are emitted within the timing window of the PET scanner. Pairs of detected photons from these cascades are not angularly correlated and therefore contain little information regarding the location of their source. Furthermore, these coincidences are not removed by correction procedures (e.g., randoms, scatter) routinely applied to PET data. If left uncorrected, the cascade coincidences will result in spurious apparent activity within the PET images. A correction, applied within projection space, that removes the cascade coincidence signal from septa‐in (i.e., two‐dimensional) datasets is proposed and tested on phantom data.
ROC analysis for assessment of lesion detection performance in 3D PET: Influence of reconstruction algorithms
Authors: Glatting Gerhard , Werner Christoph , Reske Sven N. , Bellemann Matthias E.
Published: September 2003

Image quality in positron emission tomography (PET) can be assessed with physical parameters, as spatial resolution and signal‐to‐noise ratio, or using psychophysical approaches, which include the observer performance and the considered task (ROC analysis). For PET in oncology, such a task is the detection of hot lesions. The aim of the present study was to assess the lesion detection performance due to adequate modeling of the scanner and the measurement process in the image reconstruction process. We compared the standard OSEM software of the manufacturer with a sophisticated fully 3D iterative reconstruction technique (USC MAP). A rectangular phantom with 6 oblique line sources in a homogeneous background (2.6 kBq/ml was imaged dynamically with an ECAT EXACT HR+ scanner in 3D mode. Reconstructed activity contrasts varied between 15 and 0, as the line sources were filled with (3.2 MBq/ml). Measured attenuation and standard randoms, dead time, and scatter corrections of the manufacturer were employed. For the ROC analysis, a software tool presented a cut‐out of the phantom to two observers. These cut‐outs were rated (5 classes) and the area under the ROC curve was determined as a measure of detection performance. The improvement for with USC MAP compared to the OSEM reconstructions ranged between 0.02 and 0.23 for signal‐to‐noise ratios of the background between 2.8 and 3.1 and lesion contrast between 2.1 and 4.2. This study demonstrates that adequate modeling of the measurement process in the reconstruction algorithm improves the detection of small hot lesions markedly.