bluuebunny/crossref_metadata_2025 huggingface dataset:
MEDIATOR: A Resource Adaptive Feature Recognizer that Intertwines Feature Extraction and Manufacturing Analysis
Authors: Gaines D. M. , Castan˜o F. , Hayes C. C.
Published: February 2008

A deterrent to practical use of many feature extraction systems is that they are difficult to maintain, either because they depend on the use of a library of feature-types which must be updated when the underlying manufacturing resources change (e.g. tools and fixtures), or they rely on the use of task-specific post processors, which must also be updated. For such systems to become practical, it must be easy for a user to update the system to match the current resources. This paper presents MEDIATOR (Maintainable, Extensible Design and manufacturing Integration Architecture and TranslatOR). MEDIATOR is a resource adaptive feature extraction and early process planning system for 3-axis milling. A resource adaptive system is one that changes its behavior as the manufacturing resources in a shop change. MEDIATOR allows users to select from a standard set of tools and fixtures, and automatically identifies any changes in the features that result. It attains its resource adaptive behavior by blurring the line between feature extraction and process planning; descriptions of the manufacturing resources are used to directly identify manufacturable areas of the part. A non-programmer can easily update MEDIATOR by selecting different shop resources.
The Optimum Quality Index for the Stability of In-Parallel Planar Platform Devices
Authors: Lee J. , Duffy J. , Keler M.
Published: February 2008

The paper investigates primarily the geometrical meaning of the determinant of the Jacobian (det j) of the three connector lines of a planar in-parallel platform device using reciprocity. A remarkably simple result is deduced: The maximum value of det j namely, det jm is simply one-half of the sum of the lengths of the sides of the moving triangular platform. Further, this result is shown to be independent of the location of the fixed pivots in the base. A dimensionless ratio λ = |det j|/det jm is defined as the quality index (0 ≤ λ ≤ 1) and it is proposed here to use it to measure “closeness” to a singularity. An example which determines the optimal design by comparing different shaped moving platforms having the same det jm is given and demonstrates that the optimal shape is in fact an equilateral triangle
Synthesis of Stationary Cams
Authors: Wu L.-I. , Fang P.-H.
Published: February 2008

This paper presents a method for designing stationary cams with constant speed roller followers. A stationary cam is immovable, but it guides its follower to produce a desired motion with the follower being driven by other links. In order to avoid infinite jerk of the follower motion, the pitch curve of a stationary cam should consist of pieces of transition curve, which provide gradual change in curvature and are interposed between straight lines and circular arcs. The general parametric equations of transition curves are derived and the cam design process is demonstrated. This method is applicable for designing the guideways of tool magazine in automatic tool-changing system of the machine center.
Geometric Design of Roller Gear Cam Reducers
Authors: Tsay D. M. , Huang N. J. , Lin B. J.
Published: February 2008

A roller gear cam. reducer, composed of a turret with rollers and a globoidal cam, is often used to provide high positioning precision at low cost. In this study, a simple procedure is given to generate the surface of the cam without solving any contact equations. The method is based on rigid body transformations between the cam and the turret roller. Analyses of the pressure angle and the principal curvature of the surface geometry are also accomplished. In addition, contact forces between the roller and cam, input torque, and the reducer efficiency are evaluated. An example of the procedure is given.
Determination of the Actual Configuration of the General Stewart Platform Using Only One Additional Sensor
Authors: Parenti-Castelli V. , Di Gregorio R.
Published: February 2008

This paper presents a procedure for the determination of the actual configuration of the general geometry Stewart platform (GSP), a fully-parallel manipulator that features two rigid bodies connected to each other via spherical pairs by six controlled-length legs. The six leg length measurements, provided by the displacement sensors incorporated in the leg hardware equipment, do not make it possible to uniquely find the GSP configuration because several configurations are possible for a given set of leg lengths. Several extra sensors in addition to those incorporated in the leg equipment have been proposed in the literature in order to obtain a one-to-one correspondence between the measurements and the actual GSP configuration. The proposed procedure makes use of only one additional displacement sensor and relies upon the analytical results available in the literature for a particular type of Stewart platform. The procedure, which uniquely defines the actual configuration of the GSP, is not intended for on-line implementation. Three different algorithms are proposed for computation and their efficiency compared. A case study is reported that confirms the effectiveness of the procedure.
Closed Form Solution to Workspace of Hexapod-Based Virtual Axis Machine Tools
Authors: Huang T. , Wang J. , Whitehouse D. J.
Published: February 2008

A novel methodology is presented in this paper for the workspace analysis of virtual axis machine tools. The workspace is defined which enables to describe in a unified framework both the position and orientation capabilities of the mobile platform. Given a range of the orientation of the mobile platform, the piecewise closed solution to the workspace boundary is formulated. It is indicated for the first time that the workspace boundary in fact is the cap of twelve envelope surfaces. Two examples are given to illustrate the effectiveness of this approach.
In-Parallel Manipulators: A Framework on How to Model Actuation Schemes and a Study of their Effects on Singular Postures
Authors: Matone R. , Roth B.
Published: February 2008

This paper is concerned with the modeling of actuation schemes and their effects on the singularities of in-parallel manipulators. We begin by presenting a framework on how to incorporate actuator location and drive mechanism into the kinematic model of in-parallel manipulators. We show how to obtain the model in joint (actuator) space given the corresponding representation in actuator (joint) space. Next we show that, for in-parallel manipulators, the locations of actuators can modify singular postures. We present necessary and sufficient conditions on how to transform a singular configuration into a non-singular one by simply changing actuators locations. Finally, we illustrate these concepts with the analysis and design of a five-bar in-parallel manipulator for which transmission ratios and drive mechanisms are selected in order to improve kinematic characteristics. The example illustrates the fact that the choice of actuation schemes influences the size, shape, and direction of the velocity ellipsoid. Consequently, this choice modifies the velocity distribution in the entire workspace.
Singularity Analysis of Closed Kinematic Chains
Authors: Park F. C. , Kim J. W.
Published: February 2008

This paper presents a coordinate-invariant differential geometric analysis of kinematic singularities for closed kinematic chains containing both active and passive joints. Using the geometric framework developed in Park and Kim (1996) for closed chain manipulability analysis, we classify closed chain singularities into three basic types: (i) those corresponding to singular points of the joint configuration space (configuration space singularities), (ii) those induced by the choice of actuated joints (actuator singularities), and (iii) those configurations in which the end-effector loses one or more degrees of freedom of available motion (end-effector singularities). The proposed geometric classification provides a high-level taxonomy for mechanism singularities that is independent of the choice of local coordinates used to describe the kinematics, and includes mechanisms that have more actuators than kinematic degrees of freedom.
Interpolation of Spatial Displacements Using the Clifford Algebra of E4
Authors: Etzel K. R. , McCarthy J. M.
Published: February 2008

In this paper we show that the Clifford Algebra of four dimensional Euclidean space yields a set of hypercomplex numbers called “double quaternions.” Interpolation formulas developed to generate Bezier-style quaternion curves are shown to be applicable to double quaternions by simply interpolating the components separately. The resulting double quaternion curves are independent of the coordinate frame in which the key frames are specified. Double quaternions represent rotations in E4 which we use to approximate spatial displacements. The result is a spatial motion interpolation methodology that is coordinate frame invariant to a desired degree of accuracy within a bounded region of three dimensional space. Examples demonstrate the application of this theory to computing distances between spatial displacement, determining the mid-point between two displacements, and generating the spatial motion interpolating a set of key frames.
Burmester Lines of Spatial Five Position Synthesis from the Analysis of a 3-CPC Platform
Authors: Murray A. P. , McCarthy J. M.
Published: February 2008

This paper presents a new technique for determining the fixed axis for a spatial CC chain that guides a rigid body through five finitely separated positions, termed a Burmester Line. It is known that there can be as many as six Burmester lines for a given set of five spatial positions. Here we show that these six lines can be obtained from the analysis of a 3-CPC platform, constructed from relative screw axes associated with the five specified displacements. The screw axes of the displacement of this platform to each of its assemblies are the desired Burmester lines. Roth’s original example is presented to verify the calculations.
Kinematic Geometry of Wheeled Vehicle Systems
Authors: Sreenivasan S. V. , Nanua P.
Published: February 2008

This paper utilizes a kinematic-geometric approach to study the first-order motion characteristics of wheeled vehicles on even and uneven terrain. The results obtained from first-order studies are compared to those obtained from second order kinematic analyses, and special situations where the first-order analysis is inadequate are discussed. This approach is particularly suited for studying actively actuated vehicles since their designs typically do not include intentional passive compliances. It is shown that if a vehicle-terrain combination satisfies certain geometric conditions, for instance when a wheeled vehicle operates on even terrain or on a spherical surface, the system possesses a singularity—it possesses finite range mobility that is higher than the one obtained using Kutzbach criterion. On general uneven terrain, the same vehicles require undesirable ‘kinematic slipping’ at the wheel-terrain contacts to attain the mobility that it possesses on these special surfaces. The kinematic effects of varying the vehicle and/or terrain geometric parameters from their nominal values are discussed. The design enhancements that are required in existing off-road vehicles to avoid kinematic slipping are presented for a class of vehicles that include two-wheel axles in their designs.
A Geared 2-dof Mechanical Function Generator
Authors: Dooner D. B.
Published: February 2008

A variable-non-circular gear pair is introduced to achieve 2-dof (degree of freedom) function generation. Included is a mechanism where two independent input parameters (angular positions) uniquely determine the angular position of an output axis. Basic kinematic relationships necessary to parameterize the variable noncircular gear pair are presented. The mobility of the mechanism is considered by addressing the kinematic structure of the mechanism. An illustrative example is included where the functional requirements are specified and a graphical display of the corresponding variable-non-circular gears used to satisfy these requirements is presented.
First- and Second-Order Design Sensitivity Analysis Scheme Based on Trefftz Method
Authors: Kita E. , Kataoka Y. , Kamiya N.
Published: February 2008

This paper presents a new scheme for the first- and second-order design sensitivity analysis of the two-dimensional elastic problem by using Trefftz method. In the Trefftz method, the physical quantities are approximated by superposition of regular T-complete functions. Therefore, direct differentiation of the approximate expressions with respect to design parameters leads to the regular expressions of the sensitivities. The present schemes are applied to some examples in order to confirm the validity.
Synthesis of Binary Manipulators Using the Fourier Transform on the Euclidean Group
Authors: Kyatkin A. B. , Chirikjian G. S.
Published: February 2008

In this paper we apply the Fourier transform on the Euclidean motion group to solve problems in kinematic design of binary manipulators. In recent papers it has been shown that the workspace of a binary manipulator can be viewed as a function on the motion group, and it can be generated as a generalized convolution product. The new contribution of this paper is the numerical solution of mathematical inverse problems associated with the design of binary manipulators. We suggest an anzatz function which approximates the manipulator’s density in analytical form and has few free fitting parameters. Using the anzatz functions and Fourier methods on the motion group, linear and non-linear inverse problems (i.e., problems of finding the manipulator’s parameters which produce the total desired workspace density) are solved.
Singularity Analysis of Spatial Mechanisms Using Dual Polynomials and Complex Dual Numbers
Authors: Cheng H. H. , Thompson S.
Published: February 2008

Complex dual numbers wˇ = x + iy + εu + iεv which form a commutative ring are introduced in this paper to solve dual polynomial equations numerically. It is shown that the singularities of a dual input-output displacement polynomial equation of a mechanism correspond to its singularity positions. This new method of identifying singularities provides clear physical insight into the geometry of the singular configurations of a mechanism, which is illustrated through analysis of special configurations of the RCCC spatial mechanism. Numerical solutions for dual polynomial equations and complex dual numbers are conveniently implemented in the CH language environment for analysis of the RCCC spatial mechanism.
Solving the Forward Kinematics of a Planar Three-Legged Platform With Holonomic Higher Pairs
Authors: Hayes M. J. D. , Husty M. L. , Zsombor-Murray P. J.
Published: February 2008

A practical solution procedure for the forward kinematics problem of a fully-parallel planar three-legged platform with holonomic higher pairs is presented. Kinematic mapping is used to represent distinct planar displacements of the end-effector as discrete points in a three dimensional image space. Separate motions of each leg trace skew hyperboloids of one sheet in this space. Therefore, points of intersection of the three hyperboloids represent solutions to the forward kinematics problem. This reduces the problem to solving three simultaneous quadratics. Applications of the platform are discussed and an illustrative numerical example is given.
Integration Method for Input-output Modeling and Error Analysis of Four-bar Polymer Compliant Micromachines
Authors: Chang R. J. , Wang Y. L.
Published: February 2008

A methodology to integrate FEA, pseudo-linkages model, and experimental test for input-output modeling and error analysis of compliant micromachine is developed. A four-bar micromachine fabricated from polyethylene is employed for investigations. The integration of FEA and pseudo-linkages model is simulated through the equivalence of force system and strain energy along with motion estimated under kinematic constraints. The method to integrate linear FEA and experimental test is realized through the information of stress and strain along with the data average and offset compensation of experimental creep-recovery process. Two types of four-bar micro-machines with either convex or concave joint are selected to investigate the effects of variations of compliant joints under loading. Proportional factor and indices of RMS error are defined to help the selection of joint types in the micromachines. The validity of utilizing linear model is finally supported by experimental test through data analysis and processing.
Two Wheels Connected by an Unactuated Variable Length Axle on Uneven Ground: Kinematic Modeling and Experiments
Authors: Choi B. J. , Sreenivasan S. V. , Davis P. W.
Published: February 2008

It has been shown in previous work that when two wheels independently joined by a fixed-length axle are placed on an uneven surface, such that the line joining the wheel contact points is not coplanar with the axle, rolling without slip is possible only if the wheels are driven at the same speed. Otherwise, the wheels must slip against the terrain due to kinematic constraints. Based on analytical kinematics, it is shown in this article that a method to prevent slip on uneven terrain is to use a variable length axle. This research explores the instantaneous and gross motion of two wheels joined by a variable length axle on uneven terrain. Next, the overall range of the axle length change is investigated through numerical simulations. Based on the results from the simulation, a novel variable length axle that possesses no prismatic joints, hence has low friction, and has high stiffness has been designed. Experimental results are obtained for the axle length change as a three wheeled laboratory prototype that includes the variable length axle travels on a smooth uneven surface. These experiments verify the kinematic model. Limitations of using an unactuated variable length axle and related future research topics are also discussed.
Fatigue Damage Prediction in Synchronous Belts
Authors: Iizuka H. , Gerbert G. , Childs T. H. C.
Published: February 2008

The mechanics of cords is analyzed under simple bending to understand the fatigue failure mechanism of synchronous belts. A simplified beam model of synchronous belt bending is then proposed to calculate the amount of curvature under conditions of torque transmission. Especially the effect of friction force at the working flank is taken into account to explain the difference of damage accumulation between the driving-entry and driven-exit partial meshings. Finally, fatigue life prediction is carried out based on the calculated curvature under driving-contact and driven-contact fatigue failure conditions.
Product Architecture Definition Based Upon Customer Demands
Authors: Yu J. S. , Gonzalez-Zugasti J. P. , Otto K. N.
Published: February 2008

The product portfolio architecture developed by a design team will have a tremendous impact upon customer satisfaction and market acceptance of the set of products offered by the firm. Yet most work in architecture centers around cost savings, manufacturability, and other production-driven concerns. Here, we propose a customer need basis for defining the architecture of a portfolio of products. Customer needs analysis provides a list of requirements for a product to sell. At any moment in time, one can assess a market population to establish target values for product features and represent those targets as probability distributions. Similarly, one can also trace the product through its use over time, and establish a separate set of desired target values, also as a set of distributions. Comparing these two distribution sets for every important customer need can point to the type of architecture a market population desires. When population and time distributions match, feature adjustability is required. When these distributions are different but constant in time, a family of product variants is more appropriate. When the population distribution changes over time, the feature must be isolated so it can be upgraded over time. If the distributions across both time and population are narrow, a single offering will supply the needs of the market. An instant film camera product is used as an example of the relationship between customer need distributions and appropriate product architecture.
Design Criteria for Bolted Connection Elements in Aluminum Alloy 6061
Authors: Menzemer C. C. , Fei L. , Srivatsan T. S.
Published: February 2008

Plates frequently find use as connecting elements in structures built from aluminum alloys. Many structural elements employ mechanical fasteners. Design of connections necessitates that due consideration be given to: (a) bolt or rivet failure, (b) progressive bearing distress of material adjacent to the fastener(s), (c) net-section tensile failure, and (d) tear out of the fastener group(s). Current design provisions for block shear failures of bolted and riveted joints in aluminum-based alloys make use of models initially developed for structural steels or, alternatively, fail to address an estimation of joint capacity. Shear failure of aluminum connecting elements is the focus of this paper. An experimental and analytical program was undertaken with the objective of studying block shear failure of aluminum connecting elements. Twenty aluminum alloy 6061-T6 gusset plates, representing four different bolt patterns, were mechanically deformed. Models to estimate the capacity of the joints are examined and compared with experimental results. Strain distribution around the periphery of the connections were measured and compared to finite element predictions. The correlations between the design models and experimental observations are highlighted.
A Framework for Closed-Form Displacement Analysis of Planar Mechanisms
Authors: Almadi A. N. , Dhingra A. K. , Kohli D.
Published: February 2008

This paper presents a closed-form approach, based on the theory of resultants, to the displacement analysis problem of planar n-link mechanisms. The successive elimination procedure presented herein generalizes the Sylvester’s dialytic eliminant for the case when p equations (p ≥ 3) are to be solved in p unknowns. Conditions under which the method of successive elimination can be used to reduce p equations (in p unknowns) into a univariate polynomial, devoid of extraneous roots, are presented. This univariate polynomial corresponds to the I/O polynomial of the mechanism. A comprehensive treatment is also presented on some of the problems associated with the conversion of transcendental loop-closure equations, into an algebraic form, using tangent half-angle substitutions. It is shown how trigonometric manipulations in conjunction with tangent half-angle substitutions can lead to non-trivial extraneous roots in the solution process. Theoretical conditions for identifying and eliminating these extraneous roots are presented. The computational procedure is illustrated through the displacement analysis of a 10-link 1-DOF mechanism with 4 independent loops.
Design of Two-Link, In-Plane, Bistable Compliant Micro-Mechanisms
Authors: Jensen B. D. , Howell L. L. , Salmon L. G.
Published: February 2008

A bistable mechanism has two stable states within its range of motion. Its advantages include the ability to stay in two positions without power input and despite small external disturbances. Therefore, bistable micro-mechanisms could allow the creation of MEMS with improved energy efficiency and positioning accuracy. This paper presents bistable micro-mechanisms which function within the plane of fabrication. These bistable mechanisms, called “Young” bistable mechanisms, obtain their energy storage characteristics from the deflection of two compliant members. They have two pin joints connected to the substrate, and can be constructed of two layers of polysilicon. The pseudo-rigid-body model is used to analyze and design these mechanisms. This approach allows greater freedom and flexibility in the design process. The mechanisms were fabricated and tested to demonstrate their bistable behavior and to determine the repeatability of their stable positions.
Modeling and Control of a Hybrid Locomotion System
Authors: Krovi V. , Kumar V.
Published: February 2008

This paper describes a hybrid mobility system that combines the advantages of both legged and wheeled locomotion. The legs of the hybrid mobility system permit it to surmount obstacles and navigate difficult terrain, while the wheels allow efficient locomotion on prepared surfaces and provide a reliable passive mechanism for supporting the weight of the vehicle. We address the modeling, analysis and control of such hybrid mobility systems using the specific example of a wheelchair with two powered rear wheels, two passive front casters, and two articulated, two-degree-of-freedom legs. We exploit the redundancy in actuation to actively control and optimize the contact forces at the feet and the wheels. Our scheme for active traction optimization redistributes the contact forces so as to minimize the largest normalized ratio of tangential to normal forces among all the contacts. Simulation and experimental results for the prototype are presented to demonstrate and evaluate the approach.
Design and Virtual Prototyping of Rehabilitation Aids
Authors: Krovi Venkat , Kumar Vijay , Ananthasuresh G. K. , Vezien Jean-Marc
Published: February 2008

This paper presents the methodology for user-customized design of a class of one-of-a-kind assistive devices. This class consists of passive, articulated mechanical manipulation aids, which are physically coupled to the user and therefore, must be customized to the user. Geometric and kinematic measurements of the user are used to create a virtual model of the user. The design of the customized product is based on kinematic synthesis and simulation. An integrated virtual environment, with a virtual model of the user interacting with the product, allows the testing, iterative re-design, and evaluation of the product. Geometric and kinematic data acquisition, mechanism design and analysis, CAD/CAM and visualization modules aid the designer in this process. A head-controlled feeding aid for quadriplegics is used to illustrate the approach.
To Injection Mold, to Stamp, or to Assemble? A DFM Cost Perspective
Authors: Hu W. , Poli C.
Published: February 2008

This paper presents a DFM cost comparison of injection molding and stamping, the processes most commonly used in the production of consumer oriented special purpose components. The general guidelines obtained and conclusions drawn in order to determine if a component should be injection molded or stamped, and/or if several components should be combined into a single component or not, are discussed. The cost evaluation and comparison are primarily in terms of the functional equivalence of feature, component, and assembly.
Completely Specified Displacements of a Rigid Body and Their Application in the Direct Kinematics of In-Parallel Mechanisms
Authors: Mavroidis C.
Published: February 2008

In this paper we study the type of completely specified displacements of a rigid body where the distances of six points on the body, between their final and initial positions, have been specified. A method is presented to calculate the screws associated with these displacements. It is shown that there are 24 different screws at the most that will bring the rigid body from the initial to its final position to satisfy the six distances. If the six points are co-planar or symmetrical with respect to a plane then the number of screws reduces to 16. The method to calculate the screws associated with these completely specified displacements, is used to obtain a simple algebraic solution to the direct kinematics problem of a special type of in-parallel mechanisms: the mechanisms where the moving and the fixed platforms are the same.
Kinematic Synthesis of Manipulators Using a Distributed Optimization Method
Authors: Ouezdou F. B. , Re´gnier S. , Mavroidis C.
Published: February 2008

In this paper, the rigid body guidance problem of general 6 degree of freedom manipulators is studied. A new method, called Distributed Optimization Method (DOM), is used to determine the dimensional parameters of general manipulators that are able to reach a finite number of given six degree of freedom position and orientation tasks. It is shown that the global multi-variable optimization problem of kinematic synthesis can be solved as a sequence of local, one variable, optimization problems. The new method allows the possibility to include additional criteria in the manipulator kinematic synthesis such as joint limits, range of dimensional parameters, obstacles avoidance, isotropy and number of configurations to reach a specific end-effector task. Two examples are given to illustrate the validity of the method.
Assessing the Effectiveness of Traditional and Virtual Reality Interfaces in Spherical Mechanism Design
Authors: Evans P. T. , Vance J. M. , Dark V. J.
Published: February 2008

Virtual reality (VR) interfaces have the potential to enhance the engineering design process, but before industry embraces them, the benefits must be understood and documented. The current research compared two software applications, one which uses a traditional human-computer interface (HCI) and one which uses a virtual reality HCI, that were developed to aid engineers in designing complex three-dimensional spherical mechanisms. Participants used each system to design a spherical mechanism and then evaluated the different interfaces. Participants rated their ability to interact with the computer images, their feelings about each interface, and their preferences for which interface device to use for certain tasks. The results indicated that participants preferred a traditional interface for interaction tasks and a VR interface for visual tasks. These results provide information about how to improve implementation of VR technology, specifically for complex three-dimensional design applications.
Spherical Mechanism Synthesis in Virtual Reality
Authors: Furlong T. J. , Vance J. M. , Larochelle P. M.
Published: February 2008

This paper presents a new approach to using virtual reality (VR) to design spherical mechanisms. VR provides a three-dimensional (3-D) design space where a designer can input design positions using a combination of hand gestures and motions and view the resultant mechanism in stereo using natural head movement to change the viewpoint. Because of the three-dimensional nature of the design and verification of spherical mechanisms, VR is examined as a new design interface in this research. In addition to providing a VR environment for design, the research presented in this paper has focused on developing a “design in context” approach to spherical mechanism design. Previous design methods have involved placing coordinate frames along the surface of a constraint sphere. The new “design in context” approach allows a designer to freely place geometric models of movable objects inside an environment consisting of fixed objects. The fixed objects could either act as a base for a mechanism or be potential sources of interference with the motion of the mechanism. This approach allows a designer to perform kinematic synthesis of a mechanism while giving consideration to the interaction of that mechanism with its application environment.
Algebraic Motion Approximation With NURBS Motions and Its Application to Spherical Mechanism Synthesis
Authors: Ge Q. Jeffrey , Larochelle P. M.
Published: February 2008

In this work we bring together classical mechanism theory with recent works in the area of Computer Aided Geometric Design (CAGD) of rational motions as well as curve approximation techniques in CAGD to study the problem of mechanism motion approximation from a computational geometric viewpoint. We present a framework for approximating algebraic motions of spherical mechanisms with rational B-Spline spherical motions. Algebraic spherical motions and rational B-spline spherical motions are represented as algebraic curves and rational B-Spline curves in the space of quaternions (or the image space). Thus the problem of motion approximation is transformed into a curve approximation problem, where concepts and techniques in the field of Computer Aided Geometric Design and Computational Geometry may be applied. An example is included at the end to show how a NURBS motion can be used for synthesizing spherical four-bar linkages.
The Design of a Novel Mechanical Transmission for Speed Reduction
Authors: Gonza´lez-Palacios M. A. , Angeles J.
Published: February 2008

The design of a novel transmission for speed reduction is reported in this paper. The transmission is based on the layout of pure-rolling indexing cam mechanisms, for it is intended to eliminate backlash and friction, which are the main drawbacks of gear transmissions. The design relies on a unified methodology for indexing cam mechanisms, whereby the same procedure is used to design planar, spherical, and spatial mechanisms. Two versions of the speed reducer, that we term Speed-o-Cam, are described here, namely, planar, to couple shafts of parallel axes, and spherical, to couple shafts of intersecting axes. By means of a cascade of two planar versions of Speed-o-Cam, moreover, coaxial shafts can be coupled. Moreover, contrary to other alternatives to gear transmissions, such as harmonic drives or epicyclic transmissions, Speed-o-Cam caters to shafts with either parallel or intersecting axes; in the latter case, moreover, the angle at which the axes intersect can vary from 0° to 180° continuously. The design with shaft axes at 0° leads to an internal cam, i.e., one with its axis external to the axes of the follower and the roller in contact; for shaft axes at 180°, the design leads to an external cam, i.e., one with its axis lying between those of the follower and the roller in contact.
Optimal Variable Transmission Ratio and Trajectory for an Inertial Load With Respect to Servo Motor Size
Authors: Van de Straete H. J. , De Schutter J. , Leuven K. U.
Published: February 2008

This paper addresses the selection of the optimal trajectory and transmission ratio for a servo motor driving a purely inertial load. Both aspects are studied with respect to the required motor torque and are formulated in a dimensionless fashion. Consequently, the results are generally valid and answer the following questions. What is the gain in terms of required motor torque by optimising the trajectory for minimal motor torque given a required smoothness? What is the corresponding optimal trajectory? What is the gain in terms of required motor torque by inserting a mechanism (variable transmission) between the motor and the load? What is this optimised variable transmission ratio? The final example shows how a realistic mechanism can approximate this theoretically optimised variable transmission ratio and, hence, the corresponding reduction in required motor torque.
A New Study on Reliability-Based Design Optimization
Authors: Tu J. , Choi K. K. , Park Y. H.
Published: February 2008

This paper presents a general approach for probabilistic constraint evaluation in the reliability-based design optimization (RBDO). Different perspectives of the general approach are consistent in prescribing the probabilistic constraint, where the conventional reliability index approach (RIA) and the proposed performance measure approach (PMA) are identified as two special cases. PMA is shown to be inherently robust and more efficient in evaluating inactive probabilistic constraints, while RIA is more efficient for violated probabilistic constraints. Moreover, RBDO often yields a higher rate of convergence by using PMA, while RIA yields singularity in some cases.
Experimental and Analytical Study of Aerospace Spiral Bevel Gear Tooth Fillet Stresses
Authors: Handschuh R. F. , Bibel G. D.
Published: February 2008

An aerospace-quality spiral bevel gearset was analytically and experimentally rolled through mesh to investigate tooth bending stress. A nonlinear finite element model utilized multiple teeth from the pinion and gear to simulate three-dimensional multitooth contact. The results were compared to those obtained experimentally with strain gages. A total of five strain gages, mounted in the root/fillet region of three teeth, were used. Effects of changing speed and load were measured. Tests were conducted from static (slow roll) to 14,400 rpm at power levels up to 537 kW (720 hp).
Computerized Design and Generation of Worm Gear Drives with Stable Bearing Contact and Low Transmission Errors
Authors: De Donno M. , Litvin F. L.
Published: February 2008

The authors propose a new approach for design and generation of low-noise, stable bearing contact gear drive with cylindrical worm. The approach is based on application of an oversized hob and varied plunging of worm generating tool. It is discovered that without plunging positive transmission errors occur (that are unacceptable for favorable conditions of force transmission). A predesigned parabolic function is provided that is able to absorb transmission errors caused by misalignment and reduce the level of vibrations, especially in the case of application of multi-thread worms. The developed approach is tested by computerized simulation of meshing and contact by the developed computer program. The investigation is accomplished for a worm-gear drive with the Klingelnberg type of the worm that is ground by a circular cone, but the proposed approach may be applied for other types of worm gear drives with cylindrical worms.
Deviation-Function Based Pitch Curve Modification for Conjugate Pair Design
Authors: Yang D. C. H. , Tong S.-H. , Lin J.
Published: February 2008

In this paper a method for generating new conjugate kinematic pairs is developed. This method, called the “Deviation-Function ” method, is to use deviation functions to reshape the original pitch pairs so that the desired profiles of generated pairs can be obtained. A deviation function is defined as the distance between contacts and their corresponding instant centers of two conjugate pairs. In other words, a deviation function measures the amount of deviation of a point on the generated profile from its corresponding point on the original pitch profile. As demonstrated, this new method is applicable to any type of pitch pairs including circular or noncircular and identical or nonidentical. In addition, by using this method, it is relatively easier to realize desired geometrical and mechanical properties into the design.
A Theoretical Study of the Effect of Pinion Offset on the Dynamics of Hypoid Geared Rotor System
Authors: Lim T. C. , Cheng Y.
Published: February 2008

A new 3-dimensional coupled rotational-translational vibratory model of a high-speed loaded hypoid geared rotor system has been formulated to analyze the dynamic effect of pinion offset. This model includes the effective shaft and bearing flexibilities, and gear mesh induced dynamic couplings of the lateral, axial, torsional and rotational motions. The proposed formulation is also capable of simulating drive and coast operating cases. Its effective mesh point and line of action are assumed stationary for a given steady-state condition, and they are defined by the theoretical pitch point vector and corresponding normal vector at the point of contact respectively. The proposed analytical model is applied here to compute the modal response functions of a typical automotive drivetrain design for a selected range of pinion offset. The calculations revealed interesting frequency-dependent effects of pinion offset on the generation of dynamic mesh force and bearing reaction loads.
Natural Convection of a Liquid Metal in Vertical Circular Cylinders Heated Locally From the Side
Authors: Selver R. , Kamotani Y. , Ostrach S.
Published: February 2008

An experimental study is made of natural convection in gallium melts enclosed by vertical circular cylinders with localized circumferential heating. Heating is done in an axial band at the mid-height, and both ends of the cylinder are cooled. In the present study, the cylinder aspect (Ar = height/diameter) ratio ranges from 2 to 10, and the Rayleigh number (Ra) ranges from 9.0 × 104 to 3.0 × 107. The Prandtl number is 0.021. Temperature measurements are made at six axial levels around the circumference of the cylinder to study thermal convection in the melt. A numerical analysis is also conducted to supplement the experimental information. When Ra is small, the melt is in steady toroidal motion. Above a certain Ra, the flow becomes nonaxisymmetric as a result of a thermal instability, in the case of Ar larger than 3. With increasing Ra, the motion becomes oscillatory, mainly in the upper half. When Ar is smaller than 3, the toroidal flow becomes nonaxisymmetric and oscillatory at the same time beyond a certain Ra. The conditions for the appearance of oscillations and the oscillation frequencies are investigated in detail.
Stability of Mixed Convection in a Differentially Heated Vertical Channel
Authors: Chen Y.-C. , Chung J. N.
Published: February 2008

In this study, the linear stability of mixed convection in a differentially heated vertical channel is investigated for various Prandtl numbers. The results indicate that this fully developed heated flow can become unstable under appropriate conditions. It is found that both the Prandtl number and Reynolds number hold very important effects on the critical Grashof number, wave number, wave speed, and instability mechanism for higher Prandtl numbers. For low Prandtl numbers, the effects from the Prandtl number and Reynolds number are relatively small. The most significant finding is that the local minimum wave numbers can be as high as eight for Pr = 1000, which is substantially higher than those found before for other heated flows. The existence of multiple local minimum wave numbers is responsible for the sudden jumps of the critical wave number and wave speed and the sudden shift of instability type for higher Prandtl numbers. The energy budget analysis shows that the thermal-shear and shear instabilities dominate at both low and high Reynolds numbers for Pr = 0.7 and 7. It is the thermal-buoyant instability for Re < 1365 and shear instability for Re ≥ 1365 for Pr = 100. The thermal-buoyant and mixed instabilities are the possible instability types for Pr = 1000. In general, for mixed convection channel flows, the instability characteristics of differentially heated flows are found to be substantially different from those of uniformly heated flows.
Wavelets in the Solution of Nongray Radiative Heat Transfer Equation
Authors: Bayazitoglu Y. , Wang B. Y.
Published: February 2008

The wavelet basis functions are introduced into the radiative transfer equation in the frequency domain. The intensity of radiation is expanded in terms of Daubechies’ wrapped-around wavelet functions. It is shown that the wavelet basis approach to modeling nongrayness can be incorporated into any solution method for the equation of transfer. In this paper the resulting system of equations is solved for the one-dimensional radiative equilibrium problem using the P-N approximation.
Flow Boiling in Horizontal Tubes: Part 2—New Heat Transfer Data for Five Refrigerants
Authors: Kattan N. , Thome J. R. , Favrat D.
Published: February 2008

A summary of a comprehensive experimental study on flow boiling heat transfer is presented for five refrigerants (R134a, R123, R402A, R404A, and R502) evaporating inside plain, horizontal, copper tube test sections. The test data were obtained for both 12.00 mm and 10.92 mm diameters using hot water as the heating source. Besides confirming known trends in flow boiling heat transfer data as a function of test variables, it was also proven that the heat flux level at the dryout point at the top of the tube in annular flow has a very significant downstream effect on heat transfer coefficients in the annular flow regime with partial dryout.
Experimental Study and Modeling of the Intermediate Section of the Nonisothermal Constrained Vapor Bubble
Authors: Karthikeyan M. , Huang J. , Plawsky J. , Wayner P. C.
Published: February 2008

The generic nonisothermal constrained vapor bubble (CVB) is a miniature, closed heat transfer device capable of high thermal conductance that uses interfacial forces to recirculate the condensate on the solid surface constraining the vapor bubble. Herein, for the specific case of a large length-to-width ratio it is equivalent to a wickless heat pipe. Experiments were conducted at various heat loads on a pentane/quartz CVB to measure the fundamental governing parameter fields: temperature, pressure, and liquid film curvature. An “intermediate” section with a large effective axial thermal conductivity was identified wherein the temperature remains nearly constant. A one-dimensional steady-state model of this intermediate section was developed and solved numerically to yield pressure, velocity, and liquid film curvature profiles. The experimentally obtained curvature profiles agree very well with those predicted by the Young-Laplace model. The operating temperature of the CVB was found to be a function of the operating pressure and not a function of the heat load. Due to experimental design limitations, the fundamental operating limits of the CVB were not reached.
Condensation in Smooth Horizontal Tubes
Authors: Dobson M. K. , Chato J. C.
Published: February 2008

An experimental study of heat transfer and flow regimes during condensation of refrigerants in horizontal tubes was conducted. Measurements were made in smooth, round tubes with diameters ranging from 3.14 mm to 7.04 mm. The refrigerants tested were R-12, R-22, R-134a, and near-azeotropic blends of R-32/R-125 in 50 percent/50 percent and 60 percent/40 percent compositions. The study focused primarily on measurement and prediction of condensing heat transfer coefficients and the relationship between heat transfer coefficients and two-phase flow regimes. Flow regimes were observed visually at the inlet and outlet of the test condenser as the heat transfer data were collected. Stratified, wavy, wavy annular, annular, annular mist, and slug flows were observed. True mist flow without a stable wall film was not observed during condensation tests. The experimental results were compared with existing flow regime maps and some corrections are suggested. The heat transfer behavior was controlled by the prevailing flow regime. For the purpose of analyzing condensing heat transfer behavior, the various flow regimes were divided into two broad categories of gravity-dominated and shear-dominated flows. In the gravity dominated flow regime, the dominant heat transfer mode was laminar film condensation in the top of the tube. This regime was characterized by heat transfer coefficients that depended on the wall-to-refrigerant temperature difference but were nearly independent of mass flux. In the shear-dominated flow regime, forced-convective condensation was the dominant heat transfer mechanism. This regime was characterized by heat transfer coefficients that were independent of temperature difference but very dependent on mass flux and quality. Heat transfer correlations that were developed for each of these flow regimes successfully predicted data from the present study and from several other sources.