bluuebunny/crossref_metadata_2025 huggingface dataset:
Dynamical Resolution of Redundancy for Robot Manipulators
Authors: Ghosal A. , Desa S.
Published: June 2008

A large class of work in the robot manipulator literature deals with the kinematical resolution of redundancy based on the pseudo-inverse of the manipulator Jacobian. In this paper an alternative dynamical approach to redundancy resolution is developed which utilizes the mapping between the actuator torques and the acceleration of the end-effector, at a given dynamic state of the manipulator. The potential advantages of the approach are discussed and an example of a planar 3R manipulator following a circular end-effector trajectory is used to illustrate the proposed approach as well as to compare it with the more well-known approach based on the pseudo-inverse.
Equilibrators for Planar Linkages
Authors: Streit D. A. , Shin E.
Published: June 2008

This manuscript provides a mathematical basis for comparing the complexity of equilibrator methodologies, extends the applications of those methodologies, and develops new methodologies. Two methodologies exist for spring equilibration of two degree of freedom revolute joint planar linkages. Extensions of both methodologies are now demonstrated for equilibration of all rigid body planar linkages having lower and/or higher order kinematic pairs. Reduction in complexity of these general methodologies is demonstrated when kinematic chains include only revolute joints. A mathematical description of the complexity of each of three equilibration methodologies is introduced to provide a means of comparing the effectiveness of each approach. Examples demonstrate the appropriate equilibrator design choice for particular applications, based on the mathematical description of system complexity. A new approach for equilibration of linkages having higher order planar kinematic pairs (1R1T) is introduced. A solution to the problem of spring mass in equilibrator design is presented. Examples are included to demonstrate the effectiveness of both the 1R1T equilibrator design scheme, and the spring mass equilibration scheme. The 1R1T design represents a first equilibration of pantograph type mechanisms.
Analytical Dynamic Response of Elastic Cam-Follower Systems with Distributed Parameter Return Spring
Authors: U¨nlu¨soy Y. Samim , Tu¨mer S. Turgut
Published: June 2008

An analytical method of solution for the high-speed dynamic response of a lumped/distributed parameter model for cam-follower systems is developed. The model combines the distributed parameter model of the return spring with a viscously damped, single degree-of-freedom, lumped model of the elastic follower train. The cam event is considered as a periodic motion, of period 360 deg, and is represented by its Fourier series approximation. Linear systems approach utilizing four-pole parameter representation of lumped and distributed elements is adopted. The applicability and the accuracy of the method are verified with the aid of the experimental results reported in recent literature on the dynamic response of a high-speed cam-follower system.
Design for Stamping—Analysis of Part Attributes that Impact Die Construction Costs for Metal Stampings
Authors: Poli C. , Dastidar P. , Mahajan P. , Graves R. J.
Published: June 2008

This paper describes an alternative approach to the rules-of-thumb-based design of metal stampings. The design for manufacturing system (DFM) presented here highlights those manufacturing-related features that significantly increase cost so that designers can minimize difficult-to-produce features. The DFM system is not dependent on the creation of a geometric model, and can be used to qualitatively and quantitatively assess a preliminary concept sketch. The system focuses on stampings produced by “hard tooling” and is based on expertise gained from stampers who produce parts for the office automation, computer, electromechanical, and small consumer appliance industries. The application of the system to a real-life part is illustrated.
A General Strategy for the Optimal Design of Reinforced Concrete Footings to Support Wind Loaded Structures
Authors: Hannan M. R. , Johnson G. E. , Hammond C. Reif
Published: June 2008

A strategy to select the minimum volume reinforced concrete footing to support a wind loaded structure is outlined. Practical examples of such structures include highway signs and elevated steam lines. A mathematical design model for these systems is posed with constraints to assure that the structure will not overturn and that stresses in the footing and soil do not exceed the strength of the respective materials. Optimal solutions obtained by a conjugate gradient algorithm with parabolic exterior penalty functions are given and general guidelines for minimum volume footing design are summarized. The results indicate that, for lightly loaded structures, the optimal footing design tends to be a piling (large depth relative to length) while for a relatively heavily loaded structure the optimal design is more “plate like” (large length relative to depth).
Sensitivity Analysis for the Steady-State Response of Damped Linear Elastodynamic Systems Subject to Periodic Loads
Authors: Tortorelli D. A.
Published: June 2008

Adjoint and direct differentiation methods are used to formulate design sensitivities for the steady-state response of damped linear elastodynamic systems that are subject to period loads. Variations of a general response functional are expressed in explicit form with respect to design field perturbations. Modal analysis techniques which uncouple the equations of motion are used to perform the analyses. In this way, it is possible to obtain closed form relations for the sensitivity expressions. This eliminates the need to separately evaluate the adjoint response and psuedo response (these responses are associated with the adjoint and direct differentiation sensitivity problems) over the time domain. The sensitivities need not be numerically integrated over time, thus they are quickly computed. The methodology is valid for problems with proportional as well as nonproportional damping. In an example problem, sensitivities of steady-state vibration amplitude of a crankshaft subject to engine firing loads are evaluated with respect to the stiffness, inertial, and damping parameters which define the shaft. Both the adjoint and direct differentiation methods are used to compute the sensitivities. Finite difference sensitivity approximations are also calculated to validate the explicit sensitivity results.
A Numerically Efficient Algorithm for Steady-State Response of Flexible Mechanism Systems
Authors: Yang Z. , Sadler J. P.
Published: June 2008

Presented in this work is a numerically efficient algorithm for treating the periodic steady-state response of flexible mechanisms as the solution to separated two-point boundary value problems. The finite element method is applied to discretize continuous elastic mechanisms systems and a set of second-order ordinary differential equations is obtained with periodically time-varying coefficient matrices and forcing vectors. Modal analysis techniques are employed to decouple these equations into a number of single scalar ordinary differential equations in modal basis. The periodic time-boundary conditions at both ends of a fundamental period equal to a cycle of input motion are mathematically separated by introducing auxiliary variables, thus resulting in a so-called almost-block-diagonal matrix for linear algebraic systems of equations. Solving such a system is computationally less expensive than solving a general linear algebraic system. Examples are included to illustrate the procedures applied to a four-bar linkage through which computing time is compared with other approaches.
Body Vibration of a Legged Walking Machine
Authors: Gao Xiaochun , Song Shin-Min
Published: June 2008

Unlike wheeled vehicles, compliance in walking machine systems changes due to the variation of leg geometry, as its body proceeds. This variation in compliance will cause vibration, even if external loads remain constant. A theory is thus developed to predict the body vibrations of a walking machine during walking. On the other hand, dynamic foot forces under body vibrations can be computed by application of the existing numerical methods. As an example, the body vibrations of a quadrupedal walking chair under different walking conditions are simulated in terms of the developed theory. The results show that the influence of body vibrations on the foot force distribution is essential and, in some cases, the walking chair may lose its stability due to its body vibrations, even though it is identified to be stable in a quasistatic analysis. The developed theory can also be extended to other similar multilimbed robotic systems, such as multifingered robot hands.
A Strategy for Determining the Stability of Parts Fixtured Under Three-Point Frictional Constraint
Authors: Linder K. J. , Cipra R. J.
Published: June 2008

Flexible assembly systems require flexible fixtures to constrain parts in a stable fashion in order to perform assembly operations. This paper gives a systematic strategy that uses graphical techniques to determine the stability of parts fixtured under a particular type of three-point frictional constraint. The two inputs into the analysis method are the geometry and frictional properties of the fixturing system. No information about the applied clamping force is necessary for the method to determine stability. The strategy finds all kinematically possible motions of a part based on the existence of instant centers. Then for subsets of these motions it determines if static equilibrium exists in order to find out which of these motions cannot occur. Finally, the method classifies a part into one of three categories: stable, not stable, or unstable. If it is determined that there are no possible unstable motions, then the part is stable. But if it is determined that the part will move in one-point unstable motion then it is unstable. If any two- or three-point unstable motions are determined to be possible, then the part is classified as not stable. Although some of the parts in the not stable category will be unstable, there are other cases in this classification in which it is not known whether one of the unstable modes will occur. These are indeterminate cases in which the stability of the part cannot be determined. However, the method can determine those cases in which the part is stable which makes it a useful fixture analysis tool.
Series-Chain Planar Manipulators: Inertial Singularities
Authors: Agrawal S. K.
Published: June 2008

Often, the dynamic behavior of multi-degree-of-freedom mechanical systems such as robots and manipulators is studied by computer simulation of their dynamic equations. An important step in the simulation is the inversion of a matrix, often known as the inertia matrix of the system. In the configurations, where the inertia matrix is singular, the simulation is prone to large numerical errors. Commonly, it is believed that this inertia matrix is always positive definite (or, nonsingular) no matter what geometric and inertial attributes are assigned to the links. In this paper, we show that the inertia matrix of a multi-degree-of-freedom mechanical system modeled with point masses can be singular at special configurations of the links. We present a way to systematically enumerate some of these configurations where the inertia matrix for planar series-chain manipulators built with revolute and prismatic joints are singular.
A Cross-Sectional Shape Multiplier Method for Two-Level Optimum Design of Frames
Authors: Zhao Wenzhong , Azarm Shapour
Published: June 2008

In this paper, a new method for optimum design of frame structures is presented. The method is based on a hierarchical decomposition of the structure into two-levels, namely, the bottom- and the top-level. The bottom-level consists of several subproblems each dealing with the cross-sectional sizing of a given frame-element. The top-level consists of one subproblem which is formulated for configuration design of the frame structure. Since there may be a large number of frame elements, a new shape multiplier method has been developed to simplify the formulation of the bottom-level subproblems. Furthermore, a two-level solution procedure has been developed which first solves the bottom-level subproblems based on their monotonicity analysis. It then solves the top-level subproblem as it coordinates, based on a linear approximation, the solutions to the bottom-level subproblems. Three examples with increasing degree of difficulty are presented to demonstrate the effectiveness of the method.
Dynamic Collision Detection Using Space Partitioning
Authors: Ganter M. A. , Isarankura B. P.
Published: June 2008

A technique termed space partitioning is employed which dramatically reduces the computation time required to detect dynamic collision during computer simulation. The simulated environment is composed of two nonconvex polyhedra traversing two general six-degree-of-freedom trajectories. This space partitioning technique reduces collision detection time by subdividing the space containing a given object into a set of partitions. Using these partitions, all testing can be confined to the local region of overlap between the two objects. Further, all entities contained in the partitions inside the region of overlap are ordered based on their respective minimums and maximums to further reduce testing.
Evaluation of Creep-Fatigue Damage Interaction in HK40 Alloy
Authors: Konosu S. , Koshimizu T. , Iijima T. , Maeda K.
Published: June 2008

In order to establish design criteria for materials which may sustain creep-fatigue damage, the creep rupture and creep-fatigue behavior of a high-carbon centrifugal cast steel was investigated at three different temperatures of 800, 900, and 1000°C, using HK-40 alloy which is a typical furnace tube material for fuel cell plant reformers and so on. The strain waveforms used for the creep-fatigue tests consisted of triangular waveforms—pp waves (fast-fast waves), cc waves (slow-slow waves), pc waves (fast-slow waves), and cp waves (slow-fast waves)—and a trapezoidal waveform holding the peak strain at the tension side. The applicability of various creep-fatigue interaction damage assessment methods were evaluated with particular emphasis on the life fraction rule (LFR) employed in ASME Section III, Boiler & Pressure Vessel Code Case N-47 and the strain range partitioning method (SRP). As it turned out that through the LFR life evaluation of HK-40 alloy subjected to strain cycling with holding at the tension side was well interpreted, design criteria for reformer tubes were established by applying the LFR to creep-fatigue life evaluation.
Electric Resistive Heat Curing of the Fiber-Matrix Interphase in Graphite/Epoxy Composites
Authors: Sancaktar E. , Ma Weijian , Yurgartis S. W.
Published: June 2008

A novel method for tailoring the interphase of carbon fiber-polymer composites by resistive electric heating is presented. The single fiber-epoxy resin tensile test is used to investigate the adhesion and fracture properties of the interphase. Electric resistive heating is shown to increase adhesion and toughness at the interphase region. In analyzing the results, the strength and fracture energy of the interphase are related to the thermal postcure conditions created by resistive electric heating. For this purpose, difference analysis method is used to obtain numerical solution for heat conduction problem in the single fiber test specimen and the temperature distributions are plotted. Improvements obtained using resistive electric heating via carbon fiber are compared with those obtained by postcuring of the whole sample via convective thermal postcuring. The results obtained using these two different postcure methods seem to be similar.
A Stress Based Methodology for the Design of Wire Rope Systems
Authors: Velinsky S. A.
Published: June 2008

Wire ropes have been used extensively in a wide variety of applications for many years. However, detailed analysis capabilities for wire ropes have only been developed in the last several years. Furthermore, these capabilities have not been exploited in the design of actual systems which are still designed in an empirical manner. This paper presents a stress based design methodology for wire rope systems based on these recent analysis capabilities. In addition to wire stress, this methodology allows multiple system properties to be considered during the design process. This is in opposition to current methods which only consider rope strength, and then size other components to match that particular rope. The optimum design problem is formulated for minimum weight design. Finally, examples illustrate the usefulness of the approach and its applicability to the improved design of real systems.
Kinematic Model for Arthropod Legs and Other Manipulators
Authors: Albright S. L. , Fichter E. F. , Fichter B. L.
Published: June 2008

Existing kinematic models for linkages fail to satisfy three criteria important for modeling an arthropod leg: (1) proportionality—changes in parameters should be proportional to changes in leg, (2) similarity—legs with similar appearance should have similar model parameters, (3) expandability—model should accommodate both single- and multi-degree-of-freedom joints since both are usually represented on a single leg. The theoretical basis for a linkage model is examined and a model developed with equations for revolute-revolute, revolute-spherical, and revolute-prismatic links. Parameters for legs of a darkling beetle are presented.
On the Nomenclature, Classification, and Abstractions of Compliant Mechanisms
Authors: Midha A. , Norton T. W. , Howell L. L.
Published: June 2008

Compliant mechanisms, unlike rigid-body mechanisms, gain some or all of their mobility from the flexibility of their members. Complaint mechanisms are desirable since they require fewer parts, and have less wear, noise, and backlash than their rigid-body counterpart mechanisms. The field of compliant mechanisms is expected to continue to grow as materials with superior properties are developed. Inasmuch as evolution of efficient design techniques is viewed as an essential research activity, a parallel, systematic development of appropriate vocabulary (nomenclature, classification, etc.) is of primary importance. This paper proposes a standard nomenclature for the components of compliant mechanisms and discusses the relevant issues involved in this process. Definitions for components, such as “links” and “joints,” remove ambiguity that has been associated with these terms in the past. Names and diagrams are discussed, and are shown to be similar because they represent “abstractions” of the same mechanisms. The concept of “levels of abstraction” is introduced, and common levels of abstraction are identified. A concerted effort is made to be consistent with current literature on both rigid-body mechanisms and compliant mechanisms whenever possible.
Linearized Inverse Dynamic Models for Robot Manipulators With Varying Link Parameters
Authors: Li Chang-Jin , Sankar T. S.
Published: June 2008

In this paper, two fast computational algorithms are developed for effective formulation for the linearized inverse dynamic robot models with varying (kinematic and dynamic) link parameters. The proposed algorithms can generate complete linearized inverse dynamic models for robot manipulators, taking variations (e.g., inexactness, inconstancy, or uncertainty) of the kinematic and dynamic link parameters into account. They can be applied to any robot manipulator with rotational and/or translational joints, and can be utilized. The computational complexity of these algorithms is only of order O(n), where n is the number of degrees-of-freedom of the robot manipulator.
The Bayesian Compromise Decision Support Problem for Multilevel Design Involving Uncertainty
Authors: Vadde S. , Allen J. K. , Mistree F.
Published: June 2008

In this paper we present an extension to the traditional compromise Decision Support Problem (DSP) formulation. In this formulation we use Bayesian statistics to model uncertainties associated with the information being used. In an earlier paper we have introduced a compromise DSP that accounts for uncertainty using fuzzy set theory. In this paper we describe the Bayesian Decision Support Problem. We use this formulation to design a portal frame structure. We discuss the results and compare them with those obtained using the fuzzy DSP. Finally, we discuss the efficacy of incorporating Bayesian statistics into the traditional compromise DSP formulation and describe some of the pending research issues.
Constrained Optimization of Multi-Degree-of-Freedom Mechanisms for Near-Time-Optimal Motions
Authors: Sundar S. , Shiller Z.
Published: June 2008

This paper presents a method to design multi-degree-of-freedom mechanisms for near-time optimal motions. The design objective is to select system parameters, such as link lengths and actuator sizes, that will minimize the optimal motion time of the mechanism along a given path. The exact time-optimization problem is approximated by a simpler procedure that maximizes the acceleration near the end points. Representing the directions of maximum acceleration with the acceleration lines, and the reachability constraints as explicit functions of the design parameters, we transform the constrained optimization to a simpler curve-fitting procedure. This problem is formulated analytically, permitting the use of efficient gradient-based optimizations instead of the zero order optimization that is otherwise required. It is shown that with the appropriate choice of variables, the reachability constraints for planar mechanisms are linear in the design parameters. Consequently, the reachability of the entire path can be guaranteed by satisfying the reachability of only two extreme points along the path. This greatly simplifies the optimization problem since it reduces the dimensionality of the constraints and it permits the use of efficient projection methods. Examples for optimizing the dimensions of a five-bar planar mechanism demonstrate close correlation between the approximate and the exact solutions and better computational efficiency of the constrained optimization over previous penalty-based methods.
A New Probabilistic Method for the Performance Evaluation of Manipulators
Authors: Rastegar J. , Singh J. R.
Published: June 2008

A new probabilistic method is introduced which can be used to obtain a global map of the distribution of the velocity and force transmission characteristics of robot manipulators. The method yields the global distributions of volumes of the velocity and force ellipsoids. It utilizes the most basic definition of the properties of the mapping functions between the joint coordinates and the Cartesian (task) coordinates. The method is extremely simple, numerical in nature, and readily implemented on a computer. It requires very simple and limited analytical formulations. No inverse calculations are involved. The method can be utilized for optimal positioning of task spaces within workspaces of manipulators. Velocity and force transmission (alone and in combination) may be used as optimality criteria. Complex task space and manipulator workspace geometries are readily handled. The tasks, velocity, and force transmission requirements may assume any arbitrary, even conditional, distributions within the task space. These distributions, especially conditional distributions, are extremely difficult, if not impossible, to handle using other methods. The application of the method to task planning and optimal manipulator synthesis is discussed. Several examples are presented.
Towards an Objective Evaluation of Alternate Designs
Authors: Iyengar G. , Lee Chun-Liang , Kota S.
Published: June 2008

This paper presents a systematic method for the objective evaluation of different product designs that perform the same function. Functional representation is used as a tool for competitive benchmarking of physical systems irrespective of physical implementation of subfunctions. In a top-down design framework, a domain independent functional configuration serves as a skeletal design, and independent subfunctions are mapped to physical components, taking all the prescribed constraints into consideration. On the other hand, in a “bottom-up” evaluation process, the functional representation could serve as a common semantic model for comparing various physical systems, that are composed of components from multiple domains. It is a “bottom-up” process in the sense that we begin with an existing design and proceed to abstract some measure of its performance. There are several differences between top-down design and the bottom-up evaluation process. The concept of “connectors” is introduced as an attempt to resolve some of these differences. Connectors are used to represent the interaction between adjacent components and to explicitly account for function sharing in design. A simple example is also presented to illustrate the process of systematic evaluation of alternate designs.
Incorporating End-User’s Attitudes Towards Uncertainty into an Expert System
Authors: Tian Yun Qi , Thurston D. L. , Carnahan J. V.
Published: June 2008

Uncertainty is a real and unavoidable part of the design process. Uncertainty in the area of manufacturing cost estimation can have a negative impact on the desirability of design alternatives, and some might be deemed “too risky” for further consideration in spite of potential benefits. Expert designers obtain a sense of what level of risk is acceptable for different types of applications. Expert systems for design thus might include a set of necessary and reasonable assumptions which reflect a particular expert’s attitude towards risk and uncertainty. These assumptions may not be applicable for all users. In this paper we present an expert system for design which explicitly addresses the individual user’s attitude towards uncertainty. We have developed a spreadsheet user-interface for assessing this attitude through a utility function, and for linking those results to a heuristic rule base. The heuristic rule base contains only technical expertise used to determine a set of feasible alternatives, while the process of evaluating and ranking these feasible alternatives is driven by the user’s individual preferences and risk-taking profile.
Dynamic Analysis of a Rotary Compressor
Authors: Padhy S. K.
Published: June 2008

The rotary compressor is used in room air conditioners and refrigerators. Although a number of papers have been published on rotary compressors, in the area of dynamics only a few are found, and they lack a complete analysis. In this paper the rotary compressor dynamics is modeled in detail and experimental validation is presented. The effects of some variables on the dynamics are also described.
Residual Vibration Reduction Using Vector Diagrams to Generate Shaped Inputs
Authors: Singhose W. , Seering W. , Singer N.
Published: June 2008

This paper describes a method for limiting vibration in flexible systems by shaping the input to the system. Unlike most previous input shaping strategies, this method does not require a precise system model or lengthy numerical computation; only estimates of the system natural frequency and damping ratio are required. The effectiveness of this method when there are errors in the system model is explored and quantified. Next, an algorithm is presented, which, given an upper bound on acceptable residual vibration amplitude, determines a shaping strategy that is insensitive to errors in the estimate of the natural frequency. Finally, performance predictions are compared to hardware experiments.
A Programmable RCC Hand
Authors: Gershon D.
Published: June 2008

Automated assembly by robots is plagued by two central problems—grasping and insertion. Assembly robots require an array of specialized grippers, each one designed to grasp only one or two specific objects, and they must automatically exchange grippers during an assembly task. General purpose dexterous hands, that imitate the human hand, are far more versatile but they are too complex for industrial automation. The insertion problems refers to wedging or jamming that can occur during an assembly process due to the robot’s poor positioning capability. The Remote Center of Compliance is a simple wrist-mounted compliance device that enables high speed assembly by inaccurate robots without jamming or wedging. However, the RCC must be designed for a particular peg-hole geometry and its compliance characteristics cannot be modified by the robot program. This paper proposes a single device that alleviates both grasping and insertion problems by integrating passive compliance into a three-fingered two d.o.f. hand. A kinematic model of the hand is presented that exhibits RCC properties. By modulating the angle of the fingers, the programmer can obtain different RCC characteristics. Despite the hand’s simplicity, its compliance provides considerable grasping versatility as well as a programmable RCC capability.
A Drift-Free Navigation System for a Mobile Robot Operating on Unstructured Terrain
Authors: Sreenivasan S. V. , Waldron K. J.
Published: June 2008

The orientation and the angular rates of the body of a robotic vehicle are required for the guidance and control of the vehicle. In the current robotic systems these quantities are obtained by the use of inertial sensing systems. Inertial sensing systems involve drift errors which can be significant even after the vehicle has traversed only short distances on the terrain. A different approach is suggested here which guarantees accurate, drift-free sensing of the angular position and rates of the vehicle body. A camera system consisting of two cameras in fixed relationship to one another is made to continuously track two stationary objects (stars or the sun). The camera system is mounted on the vehicle body through an actuated three-degree-of-freedom joint. The angular positions and rates of these joints can be used to evaluate the angular positions and rates of the vehicle body. An estimate of the absolute position of the vehicle on the terrain can also be obtained from this sensing system. This can serve as the primary system for estimating the position of a vehicle on a planet, or as an inexpensive alternative/backup to a more accurate Global Positioning System (GPS) for estimating the position of a vehicle on earth.
Kinematic Analysis and Design of Articulated Manipulators with Joint Motion Constraints
Authors: Dwarakanath T. A. , Ghosal A. , Shrinivasa U.
Published: June 2008

For an articulated manipulator with joint rotation constraints, we show that the maximum workspace is not necessarily obtained for equal link lengths but is also determined by the range and mean positions of the joint motions. We present expressions for sectional area, workspace volume, overlap volume and work area in terms of link ratios, mean positions and ranges of joint motion. We present a numerical procedure to obtain the maximum rectangular area that can be embedded in the workspace of an articulated manipulator with joint motion constraints. We demonstrate the use of analytical expressions and the numerical plots in the kinematic design of an articulated manipulator with joint rotation constraints.
Motion Planning for Cooperative Robotic Systems Performing Contact Operations
Authors: Tabarah E. , Benhabib B. , Fenton R. G.
Published: June 2008

Two algorithms are developed in this paper for the optimal motion coordination of a pair of industrial robots engaged in contact operations such as part machining or deburring. In the first algorithm the two robots jointly grasp a tool, and move it in such a way that it performs a prescribed contact operation along the surface of a workpiece. In the second algorithm, one robot grasps the tool while a second robot grasps and maneuvers the workpiece; both robots move simultaneously relative to each other so that the tool maintains contact with the workpiece while tracking a prescribed trajectory along its surface at a constant speed.
Surface Roughness and Lubricant Depletion on a Magnetic Storage Disk
Authors: Ma F. , Hwang J. H.
Published: June 2008

It is widely believed that surface roughness of magnetic storage disks plays an important role in retaining the lubricant layers on the disks. Descriptions of the surface asperities of the disks, however, are so complex that it would be necessary to draw upon statistical techniques for an adequate representation. The purpose of this investigation is to evaluate the effect of surface roughness on lubricant retention by methods of stochastic simulation. It is found that surface roughness markedly enhances the retention of a thin liquid film on a rotating disk; the thinner the lubricant layer the more dominant is the effect of surface roughness. Moreover, different topographic structures of the surface roughness lead to different asymptotic limits of liquid retention.
On the Significance of the Inlet Pressure Build-Up in the Design of Tilting-Pad Bearings
Authors: Rodkiewicz Cz. M. , Kim K. W. , Kennedy J. S.
Published: June 2008

An operating tilting-pad thrust bearing generates a fore-region which is responsible for maintaining, at the bearing entrance, a pressure which is higher than the ambient pressure. This entrance pressure, in the presented analysis, is obtained by applying to the fore-region the momentum integral theorem. The solution of the lubricating film region is then obtained by using this modified inlet pressure. This solution yields the pressure distribution, the load carrying capacity, the film ratio and the frictional force for several values of the modified Reynolds number and various pivot positions. The analysis shows that there is a significant influence of the fore-region pressure on the bearing performance and that to properly design efficient tilting-pad bearing this effect should be taken into consideration.
Adhesion of Contacting Rough Surfaces in the Presence of Sub-Boundary Lubrication
Authors: Stanley H. M. , Etsion I. , Bogy D. B.
Published: June 2008

An improved DMT adhesion model is used in conjunction with an elastoplastic contact model to analyze the adhesion of contacting rough solid surfaces covered with extremely thin layers of a lubricant having a very high affinity for the surfaces. This we call sub-boundary lubrication. The paper investigates the effects of the solid surface topography and the film thickness of the lubricant on the adhesion and pull-off forces. A roughness-dependent critical thickness phenomenon is predicted: very rough surfaces may exhibit low adhesion for a wide range of lubricant thicknesses, while for smooth surfaces adhesion may increase dramatically even for a film thickness t below the standard deviation of surface heights σ. The increased adhesion could cause the surfaces to stick together to the extent that sensitive tribological systems may be damaged.
Operating Conditions of Multi-Lobe Journal Bearings Under High Thermal Loads
Authors: Mittwollen N. , Glienicke J.
Published: June 2008

The governing equations for the performance prediction of oil film journal bearings in high speed turbomachinery are elaborated. The lubricant temperature and viscosity are admitted to vary in all three dimensions and a possible reverse flow is allowed for. Laminar-turbulent flow transition, thermal groove mixing and film rupture are taken into account with refined models. The computational methods are assembled in a corresponding computer code. A successful verification is accomplished by comparing the theoretical results with recent experimental data. The calculation of the running performance of technically important multi-lobe bearing designs shows the significance of the maximum film temperature as failure criterion in severe operating conditions; flow transition and hot oil carry-over have considerable effects.
Advanced Multilevel Solution of the EHL Line Contact Problem
Authors: Venner C. H. , ten Napel W. E. , Bosma R.
Published: June 2008

The application of multilevel multi-integration to the calculation of the elastic deformation integrals and the use of an alternative relaxation process in the multilevel solution of the governing equations have resulted in an algorithm solving the EHL line contact problem in O(n ln n) operations, also for highly loaded situations. The reduction in computing time thus obtained was used to solve the problem using large numbers of nodal points and to study the pressure spike. The presented algorithm will enable fast and accurate solution of surface roughness and transient problems.
Performance Characteristic Analysis of Sector-Shaped Pad Thrust Bearings in Turbulent Inertial Flow Regime Under Three Types of Lubrication Conditions
Authors: Hashimoto H.
Published: June 2008

An influence of lubrication conditions on the performance characteristics of sector-shaped pad thrust bearings, which are subjected to the effects of both turbulence and fluid film inertia, is investigated theoretically and experimentally. The momentum equations in terms of pressure and stream function are solved by applying a numerical calculation technique combining control volume integration and the Newton-Raphson linearization method, under three kinds of inlet boundary conditions in relation to three types of lubrication conditions, namely: the flooded condition, the over flooded condition, and the starved condition. Sample numerical results pertaining to the pressure distribution, load carrying capacity and inlet flow rate are obtained for θ = 60 deg, R1 = 0.5, Re = 2000, Re* = 0 to 1.6 and A = 1.0 to 2.0, and the results of the load-carrying capacity are compared with experimental results. From the theoretical and experimental results, the relationships between the lubrication conditions and the static performance characteristics of the bearings are clarified.
Deformation and Strain Fields in Pin Specimens in Sliding Contact by Laser Speckle and Metallographic Techniques
Authors: Seif M. A. , Mohr P. J. , Moslehy F. A. , Rice S. L.
Published: June 2008

This paper describes the application of laser speckle photography to the measurement of deformations associated with sliding wear. The deformations and the associated strains are those which occur on the “side” of a rectangular-sectioned pin which is in sliding contact against a counterface disc. The side of the pin is exposed to a pulsed ruby laser beam, and a double exposure specklegram is made to record deformations which occur between laser pulses. Strain fields are obtained from displacement data by use of the Lagrangian description, and neglecting out-of-plane displacement gradients. By appropriately sequencing pulses, deformation histories can be obtained, in situ. And since the exposed side of the thin pin specimen represents the “cover” layer under which subsurface sections lie, the deformation history observable through the laser speckle method reflects the deformation behavior which is occurring on subsurface planes. By post-test metallography on planes close to this side face, the degree of correspondence between surface and subsurface deformation fields is demonstrated. The paper discusses the materials, apparatus and experimental techniques employed, and presents results obtained with several metallic specimens. Of particular interest is the extent of the plastically deformed subsurface zone, and its development as a function of time.
A Thermohydrodynamic Analysis of Large Tilting-Pad Journal Bearing in Laminar and Turbulent Flow Regimes With Mixing
Authors: Taniguchi S. , Makino T. , Takeshita K. , Ichimura T.
Published: June 2008

This paper describes a thermohydrodynamic analysis of the 19 in. diameter tilting-pad journal bearing for steam turbine in comparison with experimental data. The three-dimensional thermohydrodynamic analysis is performed in both laminar and turbulent flow regimes considering mixing inlet temperature. The linearized turbulent flow model derived by Ng and Pan (1965) is applied. Generally good agreement is obtained for bearing surface temperatures, frictional losses, and minimum film thicknesses between the theoretical and experimental results.
A Generalized Reynolds Equation for Non-Newtonian Thermal Elastohydrodynamic Lubrication
Authors: Peiran Yang , Shizhu Wen
Published: June 2008

A new generalized Reynolds equation, which can incorporate most of the rheological laws found in the literature, is derived in this paper. A number of numerical solutions of the line contact thermal elastohydrodynamic lubrication problem has been obtained by using five rheological laws. The results show that, the influence of the non-Newtonian behavior of lubricant is not as important as that of the thermal one, when Roelands’ viscosity is used in the study.
The Complete Determination of Squeeze-Film Linear Dynamic Coefficients From Experimental Data
Authors: Ellis J. , Roberts J. B. , Hosseini Sianaki A.
Published: June 2008

This paper describes the use of the State Variable Filter (SVF) method of parametric identification to estimate the complete set of twelve linear hydrodynamic coefficients for a squeeze-film bearing system. Simulated force and displacement data are used to assess the algorithm and issues such as noise tolerance, the influence of sample time interval and input signal complexity are investigated. Real experimental data from a squeeze-film rig are processed by the SVF method and the technique used to derive linearized model coefficients is explained. For the first time, all twelve coefficients in the general linear model are estimated from experimental data. Tables and graphs are used to present the coefficient values. Sixteen parameters (including four parameters relating to initial conditions) are identified in each experiment. The direct coefficients show the same trends and orders of magnitude reported in earlier and simpler tests, relating to a single-degree-of-freedom system. The damping cross-terms are found to be virtually zero whereas the inertial and stiffness cross-terms appear to be significantly nonzero.
The Effects of Wear on the Rotordynamic Coefficients of a Hydrostatic Journal Bearing
Authors: Scharrer J. K. , Hecht R. F. , Hibbs R. I.
Published: June 2008

Reynolds equation is solved for the turbulent flow of liquid hydrogen through an orifice compensated hydrostatic bearing with a worn stator element. The clearance function for the worn bearing is defined by the depth and circumferential location of wear and the resulting intersection of the journal and housing radii. Analytical results are presented for stiffness, damping and leakage as a function of bearing wear. The results show that the performance of the bearing degrades steadily for wear amounts greater than 5 percent of the radial clearance and is relatively insensitive to the geometrical location of the wear.
Lubricant Performance in Magnetic Thin Film Disks With Carbon Overcoat—Part I: Dynamic and Static Friction
Authors: Streator J. L. , Bhushan B. , Bogy D. B.
Published: June 2008

Static and dynamic friction coefficients are presented for an Al2O3·TiC slider in contact with 130 mm carbon-coated rigid thin film disks lubricated with several different perfluoropolyether lubricants. The lubricants tested include three nonpolar liquid lubricants and one polar liquid lubricant with dihydroxyl end groups. The effects of lubricant film thickness, disk surface topography, sliding speed and lubricant viscosity are investigated. In many cases, the interfaces exhibited a sharp increase in the dynamic and static friction coefficients after a certain film thickness was reached, due to strong adhesion in the interface. In most cases, the lubricant thickness for the onset of high friction forces was found to increase with increasing disk surface roughness, lubricant viscosity and sliding speed. Under certain conditions stick/slip of the slider occurred during which the static friction increased with time of contact. The various data suggest that the rate at which strong adhesion develops depends on the lubricant viscosity.
Rotordynamic Coefficients for Partially Tapered Annular Seals: Part II—Compressible Flow
Authors: Scharrer J. K. , Nelson C. C.
Published: June 2008

The basic equations are derived for compressible flow in an annular seal with a partially tapered clearance. The flow is assumed to be completely turbulent in the axial and circumferential directions with no separation, and is modeled by Moody’s equation for roughness. Linearized zeroth and first-order perturbation equations are developed for small motion about a centered position by an expansion in the eccentricity ratio. The zeroth-order continuity and momentum equations are solved exactly, yielding the axial and circumferential velocity components and the pressure distribution. The first-order equations are reduced to three ordinary, complex, differential equations in the axial coordinate Z. The equations are integrated to satisfy the boundary conditions and yield the perturbation pressure distribution. This resultant pressure distribution is integrated along and around the seal to yield the force developed by the seal and the corresponding dynamic coefficients. Since no component test data exist for this type of seal, the results of a parametric study on the effect of the taper length/seal length ratio on the seal leakage and rotordynamic coefficients are presented.
Thermal Analysis of Elastohydrodynamic Lubrication of Line Contacts Using the Ree-Eyring Fluid Model
Authors: Wang Shao , Cusano C. , Conry T. F.
Published: June 2008

A thermal Reynolds-Eyring equation is derived for elastohydrodynamic lubrication of line contacts. A control volume approach is used to analyze the inlet region where back-flow occurs. Numerical results are obtained and used to develop a formula for the thermal and non-Newtonian (Ree-Eyring) film thickness reduction factor. Results for maximum temperatures and traction coefficients are also presented. The pressure dependence of lubricant thermal conductivity is found to significantly affect the maximum lubricant temperature.
A Finite Element Cavitation Algorithm
Authors: Kumar A. , Booker J. F.
Published: June 2008

A mass-conserving model is presented for the transient evolution of cavitation in lubrication analysis. Algorithms are given for its finite element implementation in both direct problems (specified motion) and indirect problems (specified load). Numerical examples demonstrate capabilities and applications of the model and algorithm (s).
Traction Coefficients for Coated Bearing Races Lubricated With Teflon Transfer Films
Authors: Dareing D. W.
Published: June 2008

The paper evaluates different soft metal coatings for use in conjunction with teflon transfer films. The work was directed at angular contact bearings. The overall goal was to reduce friction within the bearings and thus increase operation time between engine maintenance beyond current time levels. The paper gives a mathematical model which accounts for elastic deflections in coating, film, and substrates. Predicted traction forces are in agreement with published data. Calculations show that traction coefficients reduce when the coefficient of friction is reduced and surface flexibility is increased. Teflon has a low coefficient of friction (f ≈ 0.10) against nearly all metallic surfaces and is relatively flexible even at cryogenic temperatures. In order to reduce traction coefficients with surface coatings in parallel with teflon transfer films, the coating must bring about a lower coefficient of friction or increase surface flexibility.
Three-Dimensional Laser Anemometer Measurements in an Annular Seal
Authors: Morrison G. L. , Johnson M. C. , Tatterson G. B.
Published: June 2008

The flow field inside an annular seal with a 1.27 mm clearance is investigated using a 3-D laser Doppler anemometer system. Through the use of this system, the mean velocity vector and the entire Reynolds stress tensor distributions are measured for the entire length of the seal (37.3 mm). The seal is operated at a Reynolds number of 18,600 and a Taylor number of 4500. The annular seal is found to produce anisotropic turbulence since the Reynolds stress measurements show the flow entering the seal with isotropic turbulence but exiting the seal with anisotropic turbulence.