bluuebunny/crossref_metadata_2025 huggingface dataset:
Steady-State Response of Periodically Time-Varying Linear Systems, With Application to an Elastic Mechanism
Authors: Farhang K. , Midha A.
Published: February 2008

This paper presents the development of an efficient and direct method for evaluating the steady-state response of periodically time-varying linear systems. The method is general, and its efficacy is demonstrated in its application to a high-speed elastic mechanism. The dynamics of a mechanism comprised of elastic members may be described by a system of coupled, inhomogeneous, nonlinear, second-order partial differential equations with periodically time-varying coefficients. More often than not, these governing equations may be linearized and, facilitated by separation of time and space variables, reduced to a system of linear ordinary differential equations with variable coefficients. Closed-form, numerical expressions for response are derived by dividing the fundamental time period of solution into subintervals, and establishing an equal number of continuity constraints at the intermediate time nodes, and a single periodicity constraint at the end time nodes of the period. The symbolic solution of these constraint equations yields the closed-form numerical expression for the response. The method is exemplified by its application to problems involving a slider-crank mechanism with an elastic coupler link.
Elastodynamic Analysis and Control of Industrial Robotic Manipulators With Piezoelectric-Material-Based Elastic Members
Authors: Choi Seung-Bok , Thompson B. S. , Gandhi M. V.
Published: February 2008

This technical brief addresses the dynamic modeling and control methodology to suppress structural deflections of industrial robotic manipulators featuring elastic members retrofitted with surface bonded piezoelectric actuators and sensors. The dynamic modeling is accomplished by developing a finite element formulation. The governing equation of motion is then modified by condensing the electric potential vectors, and subsequently two different feedback controllers are established: a constantgain feedback controller and a constant-amplitude feedback controller. Computer simulations are undertaken in order to demonstrate the superior performance characteristics, such as smaller deflections at the end-effector, to be accrued from the proposed methodology.
Circuit Rectification for Four Precision Position Synthesis of Stephenson Six-Bar Linkages
Authors: Mirth J. A. , Chase T. R.
Published: February 2008

Circuit rectification ensures that a linkage may reach all precision positions without disassembly. Circuit rectification is crucial to the practical synthesis of Stephenson linkages, which have up to six circuits. Causes of circuit defects that may arise during synthesis are quantified first. A procedure is then developed to identify the segments of Burmester curves which produce mechanisms with all precision positions on the same circuit. The procedure is applicable to any Stephenson linkage.
Planar Motion Synthesis Using an Approximate Bi-Invariant Metric
Authors: Larochelle P. , McCarthy J. M.
Published: February 2008

In this paper we present a technique for using a bi-invariant metric in the image space of spherical displacements for designing planar mechanisms for n (> 5) position rigid body guidance. The goal is to perform the dimensional synthesis of the mechanism such that the distance between the position and orientation of the guided body to each of the n goal positions is minimized. Rather than measure these distances in the plane, we introduce an approximating sphere and identify rotations which are equivalent to the planar displacements to a specified tolerance. We then measure distances between the rigid body and the goal positions using a bi-invariant metric on the image space of spherical displacements. The optimal linkage is obtained by minimizing this distance for each of the n goal positions.
Quadri-directional Air Thrusters for Free-floating Robot Applications
Authors: Batsios N. , Annapragada M. , Agrawal Sunil Kumar
Published: February 2008

This paper describes the operational theory and design of a quadri-directional air thruster ( “quad” ) for propulsion of the free-floating robot of Ohio University. In this design, the air is drawn from a central air tank and routed to four nozzles of a quad thruster via a pressure regulator, a distribution manifold, four solenoid valves, and a quad manifold. The pressure regulator is controlled by a d.c. servomotor and the solenoid valves are turned on/off using the digital output ports of the computer. The performance characteristics of this quad thruster were determined experimentally. The experimental measurement of the thrust as a function of the regulated pressure shows a good match with the data predicted by the supporting theory.
A Simple Technique to Passively Gravity-Balance Articulated Mechanisms
Authors: Rahman T. , Ramanathan R. , Seliktar R. , Harwin W.
Published: February 2008

A simple method to counter the effects of gravity in articulated mechanisms is proposed. The scheme uses kinematics and linear springs to produce a nonlinear restoring force to oppose the gravitational moment. The method equilibrates a rotational mechanism for all postures. A solution for one link is obtained then general equations for n links are derived. The method is simpler than previous schemes and has applications in robotics, orthotics and a host of everyday mechanisms.
Design of an Orthogonal Compliance for Polygonal Peg
Insertion
Authors: Sturges R. H. , Laowattana S.
Published: February 2008

This paper addresses automatic assembly with passive rather than active compliant devices. Previous work has shown that in an ideal manufacturing environment three assembly primitives (prismatic insertions, threaded fits and general path insertions) exhibit a high level of difficulty. None of these are reliably assemblable under sensor-based force control or with an ordinary remote center compliance (RCC) device. In this paper, we extend the science of part mating and apply dexterity theory to synthesize a passive assembly device for precision fits of three-dimensional prismatic parts. This Spatial Remote Center Compliance (SRCC) obviates sensor-based and force control approaches to precision assembly of nonaxisymmetric parts.
Modeling and Simulation of Assembly in a Free-floating Work Environment by a Free-floating Robot
Authors: Agrawal S. K. , Chen M. Y. , Annapragada M.
Published: February 2008

Freely moving systems in space conserve linear and angular momentum. As moving systems collide, the velocities get altered due to transfer of momentum. The development of strategies for assembly in a free-floating work environment requires a good understanding of primitives such as self motion of the robot, propulsion of the robot due to onboard thrusters, docking of the robot, retrieval of an object from a collection of objects, and release of an object in an object pool. The analytics of such assemblies involves not only kinematics and rigid body dynamics but also collision and impact dynamics of multibody systems. This paper presents analytical models of assembly, built from the models of primitives, and some possible strategies for overall assembly.
Evaluation of Equivalent Spring Stiffness for Use in a Pseudo-Rigid-Body Model of Large-Deflection Compliant Mechanisms
Authors: Howell L. L. , Midha A. , Norton T. W.
Published: February 2008

Compliant mechanisms gain some or all of their mobility from the flexibility of their members rather than from rigid-body joints only. More efficient and usable analysis and design techniques are needed before the advantages of compliant mechanisms can be fully utilized. In an earlier work, a pseudo-rigid-body model concept, corresponding to an end-loaded geometrically nonlinear, large-deflection beam, was developed to help fulfill this need. In this paper, the pseudo-rigid-body equivalent spring stiffness is investigated and new modeling equations are proposed. The result is a simplified method of modeling the force/deflection relationships of large-deflection members in compliant mechanisms. The resulting models are valuable in the visualization of the motion of large-deflection systems, as well as the quick and efficient evaluation and optimization of compliant mechanism designs.
The Synthesis of Follower Motions of Camoids Using Nonparametric B-Splines
Authors: Tsay Der Min , Hwang Guan Shyong
Published: February 2008

This paper proposes a tool to synthesize the motion functions of the camoid-follower mechanisms. The characteristics of these kinds of motion functions are that they possess two independent parameters. To implement the work, this study applies the nonparametric B-spline surface interpolation, whose spline functions are constructed by the closed periodic B-splines and the de Boor’s knot sequences in the two parametric directions of the motion function, respectively. The rules and the restrictions needed to be noticed in the process of synthesis are established. Numerical examples are also given to verify the feasibility of the proposed method.
Performance Quality and Tolerance Sensitivity of Mechanisms
Authors: Ting Kwun-Lon , Long Yufeng
Published: February 2008

This paper presents a general theory to determine the sensitivity of tolerances to the performance quality of mechanisms and a technique to identify a robust design, which is the least sensitive to the tolerances. The method is demonstrated in position synthesis of linkages. The sensitivity Jacobian is first introduced to relate the performance tolerances and the dimensional tolerances. The Rayleigh quotient of the sensitivity Jacobian, which is equivalent to Taguchi’s signal to noise ratio, is then used to define the performance quality and a sensitivity index is introduced to measure the sensitivity of the performance quality to the dimensional tolerances for the whole system. The ideal tolerance distribution is obtained in closed form. It shows how the tolerance specification affects the performance quality and that the performance quality can be significantly improved by tightening a key tolerance while loosening the others. The theory is general and the technique can be adapted easily for other mechanical systems, including multiple-loop linkages.
A Shape Optimization Method Based on Implicit Differentiation and Node Removal Techniques
Authors: Shim P. Y. , Manoochehri S.
Published: February 2008

This paper presents a methodology for the generation of optimal shapes of structural members. This work is based on altering the finite element model of the structure by removing or restoring nodes to generate optimum designs subject to constraints on maximum stress value and maintenance of connectivity in the model. A sequential linear programming algorithm is utilized to determine optimum positions of the boundary nodes. Based on the results, at each iteration a binary decision is performed to determine which nodes should be removed or restored. A correction factor is used in this study to compensate for the error caused by linearization of the stress function.
Helically Curved Unfurlable Structural Elements: Kinematic Analysis and Laboratory Demonstration
Authors: Greschik G. , Park K. C. , Natori M.
Published: February 2008

The concept of the unfurling deployment of helically curved tubular members is proposed and its feasibility is confirmed through kinematic analyses and a demonstration model. The challenge of curved geometry—the varying lengths of longitudinal fiber lines across the member’s constituent strip—is answered by a noncylindrical storage drum shaped not to engender membrane strains in the retracted configuration (for a membrane strain-free unfurled state). The overall kinematics and the involved strains are numerically investigated and the feasibility of the deployment process itself is confirmed via a beryllium copper model.
Geometric Influence of a Molded Part on the Draw Direction Range and Parting Line Locations
Authors: Weinstein M. , Manoochehri S.
Published: February 2008

This paper presents a methodology based on the geometry of the injection molded part to identify the draw direction range and parting line locations. These parameters are shown to be a function of the interaction of the outward normals of the surfaces that have been divided into concave and convex regions of the part. This approach can also be applied incrementally to determine these mold parameters for a part as design features are added. The designer can then select from the choices provided to find the optimum parting line location and draw direction using heuristic rules. An absence of an allowable draw direction indicates the presence of an undercut that complicates the mold by requiring a side action so that the mold cost increases. The designer can either redesign the part or accept the undercut by specifying a side core or cavity. Design examples are provided which illustrate the effectiveness of the developed approach.
The Spanning Line Segments of a Polyhedron
Authors: Ye Wang Jia , Liu Ding Yuan , Chen Xiao Ming , Woo T. C.
Published: February 2008

In a polyhedron, it is observed that line segments arranged in a certain fashion preserve the intersection property: if intersection occurs with the polyhedron, the same also takes place with the line segments, and vice versa. Such line segments are said to be spanning the polyhedron which can be non-convex and non-simply connected. The properties of the spanning line segments in a polyhedron are introduced and an algorithm is presented based on “building blocks” with known solutions.
Surface Curve Design by Orthogonal Projection of Space Curves Onto Free-Form Surfaces
Authors: Pegna Joseph , Wolter Franz-Erich
Published: February 2008

A novel technique for designing curves on surfaces is presented. The design specifications for this technique derive from other works on curvature continuous surface fairing. Briefly stated, the technique must provide a computationally efficient method for the design of surface curves that is applicable to a very general class of surface formulations. It must also provide means to define a smooth natural map relating two or more surface curves. The resulting technique is formulated as a geometric construction that maps a space curve onto a surface curve. It is designed to be coordinate independent and provides isoparametric maps for multiple surface curves. Generality of the formulation is attained by solving a tensorial differential equation formulated in terms of local differential properties of the surfaces. For an implicit surface, the differential equation is solved in three-space. For a parametric surface the tensorial differential equation is solved in the parametric space associated with the surface representation. This technique has been tested on a broad class of examples including polynomials, splines, transcendental parametric and implicit surface representations.
Synthesis of Spatially and Intrinsically Constrained Curves Using Simulated Annealing
Authors: Malhotra A. , Oliver J. H. , Tu W.
Published: February 2008

A general technique is presented for automatic generation of B-spline curves in a spatially constrained environment, subject to specified intrinsic shape properties. Spatial constraints are characterized by a distance metric relating points on the curve to polyhedral models of obstacles which the curve should avoid. The shape of the curve is governed by constraints based on intrinsic curve properties such as parametric variation and curvature. To simultaneously address the independent goals of global obstacle avoidance and local control of intrinsic shape properties, curve synthesis is formulated as a combinatorial optimization problem and solved via simulated annealing. Several example applications are presented which demonstrate the robustness of the technique. The synthesis of both uniform and nonuniform B-spline curves is also demonstrated. An extension of the technique to general sculptured surface model synthesis is briefly described, and a preliminary example of simple surface synthesis presented.
A Deterministic Global Design Optimization Method for Nonconvex Generalized Polynomial Problems
Authors: Lo Chihsiung , Papalambros P. Y.
Published: February 2008

A new design optimization method is described for finding global solutions of models with a nonconvex objective function and nonlinear constraints. All functions are assumed to be generalized polynomials. By introducing new variables, the original model is transformed into one with a linear objective function, one convex and one reversed convex constraint. A two-phase algorithm that includes global feasible search and local optimal search is used for globally optimizing the transformed model. Several examples illustrate the method.
Dynamic Response of Planetary Trains to Mesh Parametric Excitations
Authors: Velex P. , Flamand L.
Published: February 2008

An extended three-dimensional model is used for calculating dynamic tooth loads on a planetary gear set. Time dependent mesh stiffnesses are determined and an original Ritz method aimed at solving large parametrically excited differential systems is proposed. Results from the Ritz method compare favorably with those given by direct integrations for highly reduced computation times. The difference between local critical speeds (for one individual mesh) and global critical speeds (for sun or ring gear-planet meshes) on a sequential spur gear train is pointed out. Finally, it is shown that, for linear behaviors, mesh stiffnesses are largely controlling dynamic tooth loads while the influence of a floating sun or ring gear is less important.
Genetic Algorithm-Based Structural Topology Design With Compliance and Topology Simplification Considerations
Authors: Chapman C. D. , Jakiela M. J.
Published: February 2008

The genetic algorithm (GA), an optimization technique based on the theory of natural selection, is applied to structural topology design problems. After reviewing the genetic algorithm and previous research in structural topology optimization, we detail the chromosome-to-design representation which enables the genetic algorithm to perform structural topology optimization. Extending our prior investigations, this article first compares our genetic-algorithm-based technique with homogenization methods in the minimization of a structure’s compliance subject to a maximum volume constraint. We then use our technique to generate topologies combining high structural performance with a variety of material connectivity characteristics which arise directly from our discretized design representation. After discussing our findings, we describe potential future work.
Virtual Wedging in Three-Dimensional Peg Insertion Tasks
Authors: Sturges R. H. , Laowattana S.
Published: February 2008

Quasi-static wedging of three point contacts is investigated, wherein the concepts of virtual and redundant wedging due to a resultant force falling into a frictional cone are proposed. We consider the fully started case of a square peg and hole consisting of two point-surface contacts and one line-line contact. An analysis of the wedging diagram for this highly constrained configuration is carried out and compared to the two-dimensional case. An approximate wedging diagram is constructed which shows that wedging of square pegs into square holes is more likely than cylindrical pegs and holes of similar sizes.
The Implications of Arrow’s Impossibility Theorem on Approaches to Optimal Engineering Design
Authors: Hazelrigg G. A.
Published: February 2008

Many modern approaches to engineering design seek to optimize design in order to maximize the value of the system to its customers. These approaches rely on the formulation of a system utility function as a measure of system worth. It is shown here that, under certain circumstances, however, such a measure cannot exist. It is then indicated that these circumstances comprise the rule rather than the exception. Finally it is shown that pursuing the objective of design optimization as defined by the customers via contemporary approaches can lead the designer to highly inappropriate and undesirable designs. As a consequence of this, it becomes apparent that the methods of Total Quality Management (TQM) and Quality Function Deployment (QFD) can lead to highly erroneous results.
Finite Element Incremental Approach and Exact Rigid Body Inertia
Authors: Shabana A. A.
Published: February 2008

In the dynamics of multibody systems that consist of interconnected rigid and deformable bodies, it is desirable to have a formulation that preserves the exactness of the rigid body inertia. As demonstrated in this paper, the incremental finite element approach, which is often used to solve large rotation problems, does not lead to the exact inertia of simple structures when they rotate as rigid bodies. Nonetheless, the exact inertia properties, such as the mass moments of inertia and the moments of mass, of the rigid bodies can be obtained using the finite element shape functions that describe large rigid body translations by introducing an intermediate element coordinate system. The results of application of the parallel axis theorem can be obtained using the finite element shape functions by simply changing the element nodal coordinates. As demonstrated in this investigation, the exact rigid body inertia properties in case of rigid body rotations can be obtained using the shape function if the nodal coordinates are defined using trigonometric functions. The analysis presented in this paper also demonstrates that a simple expression for the kinetic energy can be obtained for flexible bodies that undergo large displacements without the need for interpolation of large rotation coordinates.
New Resolution Scheme of the Forward Kinematics of Parallel Manipulators Using Extra Sensors
Authors: Han Kilryong , Chung Wankyun , Youm Y.
Published: February 2008

This paper presents a new closed-form resolution scheme of the forward kinematics of parallel manipulators based on two concepts, local structurization and mechanism partition. This scheme is applied to 6-DOF Stewart platform manipulators and the effectiveness of this scheme is verified through numerical examples. It is shown that one extra sensor is sufficient for both 3-3 SPM and 6-3 SPM to exactly resolve the forward kinematic problem (FKP) in closed form and two sensors for 6-6 SPM. In previous research, at least three extra sensors were needed for closed-form resolution of the FKP for 6-6 SPM. Consequently, the new resolution scheme is efficient to implement and easy for real-time applications for the control of parallel manipulators.
Conditions for Initiating the Translation of a Rigid Cylinder in a Tube
Authors: de Meester B. , Raucent B. , Dumont E.
Published: February 2008

The conditions on the required forces to initiate the sliding translation of a perfectly rigid cylindrical part inserted in a tube are defined in a model taking into account the effects of gravity. The theory presented can therefore be used to predict the behavior of heavy parts. The model is two-dimensional and restricted to static or quasistatic applications. It takes into account the inclination of the cylinder axis relative to that of the tube. Conditions on the applied forces for the stability of the cylinder with respect to its inclination are established. Jamming and wedging are thoroughly discussed. A short example is given at the end to illustrate how the theory presented can be used to analyze practical cases of application.
Geometry Design of Globoidal Cams With Generalized Meshing Turret-Rollers
Authors: Yan Hong-Sen , Chen Hsin-Hung
Published: February 2008

This paper derives the generalized surface equation for cylindrical, conical, and hyperbolic meshing turret-rollers. Based on the generalized equation of meshing turret-rollers, generalized mathematical expressions of surface geometry for globoidal cams with cylindrical, conical, and hyperbolic meshing turret-rollers are derived using theory of conjugate surfaces, differential geometry, and coordinate transformation. A design example is presented for demonstrating procedures of surface generating of the globoidal cam. The result of this work is necessary for the computer-aided design and manufacturing of roller gear cams for industrial applications.
A Variable-Speed Method for Improving Motion Characteristics of Cam-Follower Systems
Authors: Yan Hong-Sen , Tsai Mi-Ching , Hsu Meng-Hui
Published: February 2008

A cam is often assumed to be operated at a constant speed in designing a cam-follower system. The motion characteristics of the follower are determined once the cam displacement curve is designed. The traditional design method for improving the motion characteristics is to find a new displacement curve which has better motion characteristics. This paper, however, presents an alternative approach by varying the speed of the cam to reduce the peak values of the follower output motion characteristics. Constraints and design criteria for selecting suitable cam speed trajectories are then developed. Finally, examples are given to illustrate the design procedure and also to show its feasibility.
Axial Force Test and Modelling of the V-Belt Continuously Variable Transmission for Mopeds
Authors: Ferrando F. , Martin F. , Riba C.
Published: February 2008

This article discusses the experiments and modelling carried out on a V-belt continuously variable transmission (CVT) of the type that is used in mopeds. Our aim was to characterize the forces which determine how the system functions. A test bench was designed for them to be determined experimentally and a series of tests which cover the variable conditions of speed, torque, transmission ratio and tension of a CVT are carried out. Estimates of the principal existing models are compared and an empirical model for assessing these forces is discussed.
Displacement Analysis of an Actively Articulated Wheeled Vehicle Configuration With Extensions to Motion Planning on Uneven Terrain
Authors: Sreenivasan S. V. , Waldron K. J.
Published: February 2008

This manuscript presents a displacement analysis of actively articulated wheeled vehicles on uneven terrain. These vehicles are distinct from traditional wheeled systems since they have the ability to actively adapt to variations in the terrain and they can actively influence the forces at the wheel-terrain contact locations. They also possess special mobility capabilities such as obstacle climbing and self-recovery from an over-turn failure. The problem of solving for the configuration of these vehicles on uneven terrain has been addressed in detail. The displacement analysis leads to multiple solutions due to the inherent nonlinearity in the position kinematic equations. Geometric reasoning has been used to identify the particular configuration that represents the “correct” vehicle geometry on the terrain. Applications of the displacement analysis algorithms to vehicle planning on uneven terrain have been discussed. An obstacle climbing maneuver of a three-module actively articulated wheeled vehicle has been described.
Updated Stress Concentration Factors for Filleted Shafts in Bending and Tension
Authors: Tipton S. M. , Sorem J. R. , Rolovic R. D.
Published: February 2008

Published elastic stress concentration factors are shown to underestimate stresses in the root of a shoulder filleted shaft in bending by as much as 21 percent, and in tension by as much as forty percent. For this geometry, published charts represent only approximated stress concentration factor values, based on known solutions for similar geometries. In this study, detailed finite element analyses were performed over a wide range of filleted shaft geometries to define three useful relations for bending and tension loading: (1) revised elastic stress concentration factors, (2) revised elastic von Mises equivalent stress concentration factors and (3) the maximum stress location in the fillet. Updated results are presented in the familiar graphical form and empirical relations are fit through the curves which are suitable for use in numerical design algorithms. It is demonstrated that the first two relations reveal the full multiaxial elastic state of stress and strain at the maximum stress location. Understanding the influence of geometry on the maximum stress location can be helpful for experimental strain determination or monitoring fatigue crack nucleation. The finite element results are validated against values published in the literature for several geometries and with limited experimental data.
Isotropic Design of Tendon-Driven Manipulators
Authors: Ou Yeong-Jeong , Tsai Lung-Wen
Published: February 2008

This paper deals with the synthesis of mechanical transmission structures for tendon-driven manipulators. Based on static force analysis, necessary conditions are developed for the synthesis of tendon-driven manipulators with isotropic transmission characteristics. It is shown that an n degree-of-freedom (dof) manipulator will possess the isotropic transmission characteristics, if it satisfies two isotropic conditions. Furthermore, a design equation is derived for the construction of isotropic transmission structure matrices and a three-dof spatial manipulator is synthesized to demonstrate the methodology. It is shown that the isotropic design leads to a more uniform tendon force distribution.
Freedom Analysis of Planar Kinematic Chains Using the Concept of Distance
Authors: Yadav J. N. , Pratap C. R. , Agrawal V. P.
Published: February 2008

A computer-aided method, based on the concept of distance, has been developed for identifying planar kinematic chains with fractionated freedom. Algorithms have also been developed for detecting the presence of any k-bar independent loop, and any f-degree-of-freedom sub-chain in a multi-degree-of-freedom planar kinematic chain, leading to the characterization of partial freedom of two- and three-degree-of-freedom kinematic chains.
Rectified Synthesis of Six-Bar Mechanisms With Well-Defined Transmission Angles for Four-Position Motion Generation
Authors: Bawab S. , Kinzel G. L. , Waldron K. J.
Published: February 2008

This paper describes a rectified synthesis method where a rigid body of a six-bar linkage with well-defined transmission angles is guided to pass through four precision positions. The procedure includes the elimination of circuit, branch, and order defects. This is achieved by decomposing the six-bar mechanism into groups of vector pairs called dyads and groups of three vectors called triads. The algebraic method of synthesis can be applied to rectify those chains. Although these defects can be eliminated, it has been a challenging task in the past. The procedure has been implemented for a Watt I crank-driven six-bar linkage in the interactive synthesis package RECSYN.
Construction of a Surface Model and Layered Manufacturing Data From 3D Homogenization Output
Authors: Marsan A. L. , Dutta D.
Published: February 2008

A homogenization method has been recently developed to optimize the topology of a structure. This method will suggest a structural topology, but the results will be in finite element form. Most engineering applications, however, require smooth structures, whether the faces of the structures be planar or curved. Given the topology of a three-dimensional structure as suggested by the homogenization method, an algorithm is developed to interpret the structure and generate a smooth, manufacturable surface representation of the structure. Structures designed by the homogenization method can be quite complex and traditional manufacturing technique may not be well suited for constructing them. Layered manufacturing is adopted for producing such structures and it is shown how to generate the necessary data for this novel manufacturing technique from the surface model of the structure. Some steps of the algorithm require designer inputs. Examples are given which demonstrates this algorithm.
Belt Slip—A Unified Approach
Authors: Gerbert G.
Published: February 2008

Slip measurements on thick flat belts, V-belts and V-ribbed belts running on small pulleys reveal that the slip is much higher than can be predicted with classical creep theory. Shear creep plays an important role and special care must be taken when analyzing the shear deflection of the V-belt and the ribs of the V-ribbed belt. Other mechanisms are present as well. The behavior in the seating and unseating regions changes the direction of the frictional forces in these regions on the driver pulley. A unified slip theory is presented for flat belts, V-belts and V-ribbed belts considering creep, shear, seating/unseating and compliance. Measurements and theory fit very well for practical tension levels. At low tension the measured slip is higher than the predicted one for V-belts and V-ribbed belts, which probably depends on the poor fit between the belt and the grooved pulley.
Effect of Contact Ratio on Spur Gear Dynamic Load With No Tooth Profile Modifications
Authors: Liou Chuen-Huei , Lin Hsiang Hsi , Oswald F. B. , Townsend D. P.
Published: February 2008

This paper presents a computer simulation showing how the gear contact ratio affects the dynamic load on a spur gear transmission. The contact ratio can be affected by the tooth addendum, the pressure angle, the tooth size (diametral pitch), and the center distance. The analysis presented in this paper was performed by using the NASA gear dynamics code DANST. In the analysis, the contact ratio was varied over the range 1.20 to 2.40 by changing the length of the tooth addendum. In order to simplify the analysis, other parameters related to contact ratio were held constant. The contact ratio was found to have a significant influence on gear dynamics. Over a wide range of operating speeds, a contact ratio close to 2.0 minimized dynamic load. For low-contact-ratio gears (contact ratio less than two), increasing the contact ratio reduced gear dynamic load. For high-contact-ratio gears (contact ratio equal to or greater than 2.0), the selection of contact ratio should take into consideration the intended operating speeds. In general, high-contact-ratio gears minimized dynamic load better than low-contact-ratio gears.
Geometrically Approximated Rotatability Conditions for Spatial RSRC Mechanisms With Joint Angle Limitations
Authors: Rastegar J. , Tu Q.
Published: February 2008

For closed-loop spatial RSRC mechanisms, input-output rotatability conditions, i.e., conditions for the existence of crank-rocker and drag-link types of mechanisms, are derived using geometrical approximation. The rotatability conditions are derived in the presence and absence of joint angle limitations. The mechanism has two branches. By including joint angle limitations, the rotatability conditions become different for each configuration of the mechanism. The rotatability conditions eliminate the possibility of changeover.
Curvature Optimization of a Cam Mechanism With a Translating Flat-faced Follower
Authors: Yu Q. , Lee H. P.
Published: February 2008

The radius of curvature of a cam profile is an important factor that affects the working life of cam mechanisms. Based on flexible motion curves using parametric polynomials developed earlier, a method for maximizing the minimum radius of cam curvature using a nonlinear programming technique is presented. The relation between the radius of curvature of a cam and the kinematic features of the corresponding motion curves is discussed. Examples are presented to illustrate the method.
Modeling Relationships Among Design Activities
Authors: Belhe U. , Kusiak A.
Published: February 2008

In this paper, a graph theoretic approach for transformation and analysis of a network of design activities with different types of logical relationships is presented. In addition to the AND type relationship, OR and EXCLUSIVE OR relationships may exist between design activities. This relationship is captured using the IDEF3 notation. The algorithm generates various alternative precedence networks and clusters of design activities in each of these precedence networks. These alternative transformations are further used to analyze the risk of violating the due date of the design activity network. The concepts introduced in this paper are illustrated with an example.
A Genetic Algorithm for Scheduling and Decomposition of Multidisciplinary Design Problems
Authors: Altus Stephen S. , Kroo Ilan M. , Gage Peter J.
Published: February 2008

Complex engineering studies typically involve hundreds of analysis routines and thousands of variables. The sequence of operations used to evaluate a design strongly affects the speed of each analysis cycle. This influence is particularly important when numerical optimization is used, because convergence generally requires many iterations. Moreover, it is common for disciplinary teams to work simultaneously on different aspects of a complex design. This practice requires decomposition of the analysis into subtasks, and the efficiency of the design process critically depends on the quality of the decomposition achieved. This paper describes the development of software to plan multidisciplinary design studies. A genetic algorithm is used, both to arrange analysis subroutines for efficient execution, and to decompose the task into subproblems. The new planning tool is compared with an existing heuristic method. It produces superior results when the same merit function is used, and it can readily address a wider range of planning objectives.
Parametric Continuous and Smooth Motion Interpolation
Authors: Srinivasan L. N. , Ge Q. J.
Published: February 2008

This paper deals with the synthesis of a second order parametrically continuous (C2) motion that interpolates through a given set of configurations of an object. It derives conditions for blending two motion segments with C2 continuity and develops an algorithm for constructing a C2 composite Be´zier type motion that has similarities to Beta-splines in the field of Computer Aided Geometric Design. A criterion for evaluating the smoothness of a motion is established and is used to synthesize a “globally smooth” motion. The results have applications in trajectory generation in robotics, mechanical systems animation and CAD/CAM.
Computation of Shortest Paths on Free-Form Parametric Surfaces
Authors: Maekawa T.
Published: February 2008

Computation of shortest paths on free-form surfaces is an important problem in ship design, robot motion planning, computation of medial axis transforms of trimmed surface patches, terrain navigation and NC machining. The objective of this paper is to provide an efficient and reliable method for computing the shortest path between two points on a free-form parametric surface and the shortest path between a point and a curve on a free-form parametric surface. These problems can be reduced to solving a two point boundary value problem. Our approach for solving the two point boundary value problem is based on a relaxation method relying on finite difference discretization. Examples illustrate our method.
Bernstein-Be´zier Harmonics and Their Application to Robot Trajectory Synthesis With Minimal Vibrational Excitation
Authors: Ge Q. J. , Rastegar J.
Published: February 2008

For a given high-speed machinery, a significant source of the internally induced vibrational excitation is the presence of high frequency harmonics in the trajectories that the system is forced to follow. This paper presents a Bernstein-Be´zier form of harmonic trajectory patterns for synthesizing low-harmonic trajectories. Similar to Bernstein-Be´zier polynomial curves, Bernstein-Be´zier harmonic trajectories can be defined either explicitly using Bernstein-Be´zier basis harmonics or recursively using the harmonic deCasteljau algorithm. The second part of the paper demonstrates how a Bernstein-Be´zier trajectory can be combined with the inverse dynamics of a robot manipulator for synthesizing a joint trajectory that demands “minimal” dynamic response from its actuators. An example involving a planar 2R robot is also presented.
Passing a Central Axis Congruence Through Six Arbitrary Lines in Space
Authors: Murray A. P. , McCarthy J. M.
Published: February 2008

The design theory of a spatial 4C linkage to move a rigid body through four specified spatial positions determines a congruence of lines that may be used as fixed axes of the linkage, called the central axis congruence. In this paper, we locate a central axis congruence in space by identifying six arbitrary lines that it is to contain; we do not specify the positions of a rigid body or the associated relative displacement screws. We find that this yields at least one and as many as five different central axis congruences through a given set of six lines. Having defined the congruence without identifying any positions, we then show how to determine sets of four spatial positions that generate the given central axis congruence.
Singularity Analysis of Serial Robot-Manipulators
Authors: Karger A.
Published: February 2008

This paper is devoted to the description of the set of all singular configurations of serial robot-manipulators. For 6 degrees of freedom serial robot-manipulators we have developed a theory which allows to describe higher order singularities. By using Lie algebra properties of the screw space we give an algorithm, which determines the degree of a singularity from the knowledge of the actual configuration of axes of the robot-manipulator only. The local shape of the singular set in a neighbourhood of a singular configuration can be determined as well. We also solve the problem of escapement from a singular configuration. For serial robot-manipulators with the number of degrees of freedom different from six we show that up to certain exceptions singular configurations can be avoided by a small change of the motion of the end-effector. We also give an algorithm which allows to determine equations of the singular set for any serial robot-manipulator. We discuss some special cases and give examples of singular sets including PUMA 560.
Application of Finite Element Analysis for Determination of Load Share, Real Contact Ratio, Precision of Motion, and Stress Analysis
Authors: Litvin F. L. , Chen J.-S. , Lu J. , Handschuh R. F.
Published: February 2008

A loaded gear drive with point contact between tooth surfaces is considered. The principal curvatures and directions at a current point of tangency, the contact paths on tooth surfaces, and the transmission errors caused by misalignment we consider as known. In this paper the following topics are covered: (1) Determination of the contact force and its distribution over the contact ellipse; (2) Determination of the tooth deflection, the load share, and the real contact ratio; and (3) Stress analysis by application of the finite element method. The discussed approach is illustrated with a numerical example.
A Method for Thermal Analysis of Spiral Bevel Gears
Authors: Handschuh R. F. , Kicher T. P.
Published: February 2008

A modelling method for analyzing the three-dimensional thermal behavior of spiral bevel gears has been developed. The model surfaces are generated through application of differential geometry to the manufacturing process for face-milled spiral bevel gears. Contact on the gear surface is found by combining tooth contact analysis with three-dimensional Hertzian theory. The tooth contact analysis provides the principle curvatures and orientations of the two surfaces. This information is then used directly in the Hertzian analysis to find the contact size and maximum pressure. Heat generation during meshing is determined as a function of the applied load, sliding velocity, and coefficient of friction. Each of these factors change as the point of contact changes during meshing. A nonlinear finite element program was used to conduct the heat transfer analysis. This program permitted the time- and position-varying boundary conditions, found in operation, to be applied to a one-tooth model. An example model and analytical results are presented.
A Flexible Optimization Procedure for Mechanical Component Design Based on Genetic Adaptive Search
Authors: Deb K. , Goyal M.
Published: February 2008

A flexible algorithm for solving nonlinear engineering design optimization problems involving zero-one, discrete, and continuous variables is presented. The algorithm restricts its search only to the permissible values of the variables, thereby reducing the search effort in converging near the optimum solution. The efficiency and ease of application of the proposed method is demonstrated by solving four different mechanical design problems chosen from the optimization literature. These results are encouraging and suggest the use of the technique to other more complex engineering design problems.
A Computer-Aided Optimization Approach for the Design of Injection Mold Cooling Systems
Authors: Tang L. Q. , Pochiraju K. , Chassapis C. , Manoochehri S.
Published: February 2008

A methodology is presented for the design of optimal cooling systems for injection mold tooling which models the mold cooling as a nonlinear constrained optimization problem. The design constraints and objective function are evaluated using Finite Element Analysis (FEA). The objective function for the constrained optimization problem is stated as minimization of both a function related to part average temperature and temperature gradients throughout the polymeric part. The goal of this minimization problem is to achieve reduction of undesired defects as sink marks, differential shrinkage, thermal residual stress built-up, and part warpage primarily due to non-uniform temperature distribution in the part. The cooling channel size, locations, and coolant flow rate are chosen as the design variables. The constrained optimal design problem is solved using Powell’s conjugate direction method using penalty function. The cooling cycle time and temperature gradients are evaluated using transient heat conduction simulation. A matrix-free algorithm of the Galerkin Finite Element Method (FEM) with the Jacobi Conjugate Gradient (JCG) scheme is utilized to perform the cooling simulation. The optimal design methodology is illustrated using a case study.
Designing NURBS Cam Profiles Using Trigonometric Splines
Authors: Neamtu M. , Pottmann H. , Schumaker L. L.
Published: February 2008

We show how to design cam profiles using NURBS curves whose support functions are appropriately scaled trigonometric splines. In particular, we discuss the design of cams with various side conditions of practical interest, such as interpolation conditions, constant diameter, minimal acceleration or jerk, and constant dwells. In contrast to general polynomial curves, these NURBS curves have the useful property that their offsets are of the same type, and hence also have an exact NURBS representation.
Dynamical Simulation of Planar Systems With Changing Contacts Using Configuration Spaces
Authors: Sacks E. , Joskowicz L.
Published: February 2008

This paper presents a contact analysis algorithm for pairs of rigid, curved, planar parts based on configuration space computation. The algorithm is part of a dynamical simulator for planar systems with changing contact topologies. The configuration space of a pair of parts is a data structure that encodes the contact configurations for all pairs of part features. The configuration spaces of the interacting pairs in the mechanical system are constructed before the simulation. At each time step, the simulator queries the configuration spaces for contact changes instead of performing collision detection. The simulator demonstrates the efficacy of the configuration space approach to contact analysis. It achieves real-time performance on systems with complex contact geometry, curved parts, and changing contacts.