bluuebunny/crossref_metadata_2025 huggingface dataset:
Structural Simplification of Modular Bond-Graph Models Based on Junction Inactivity
Authors: Ersal Tulga , Fathy Hosam K. , Stein Jeffrey L.
Published: April 2008

The modular modeling paradigm facilitates the efficient building, verification and handling of complex system models by assembling them from general-purpose component models. A drawback of this paradigm, however, is that the assembled system models may have excessively complex structures for certain purposes due to the amount of detail of the component models, which is introduced to promote modularity. This work presents a domain-independent structural simplification technique that can detect such unnecessary complexities in a modular bond-graph model and eliminate them from the model without compromising accuracy. To this end, the activity concept in the literature is extended to define "inactivity" for junction elements, and simplification is obtained by detecting and eliminating inactive junction elements and by propagating the implications. It is shown that this simple idea can result in models that are conceptually and computationally more efficient. Some subtleties associated with this approach are highlighted.
Analysis and Optimization of Partial Constrained Damping Layers
Authors: Tang Shing-Jia , Lumsdaine Arnold
Published: April 2008

Topology optimization has been used to maximize the damping performance of constrained damping layer structures with viscoelastic core [1-3]. Studies show that using nanotubes as reinforcements in polymer material might improve the damping and stiffness properties [4,5]. Experimental investigations using nanotube reinforcements in constrained damping layers showed a significant improvement in damping properties of the structure [6]. Optimizing the topology of structures involving nanotube reinforcements can further enhance the damping properties by making optimal use of the nanotubes as reinforcements. In preliminary studies performed with volume fraction of nanotubes as a design variable in the optimization [7,8] substantial improvements in the damping properties were observed. In this work, the topology of a cantilever beam structure involving nanotube reinforced polymer layers is optimized with the objective of maximizing the system loss factor for the first resonance frequency of the base beam. The volume fractions and orientations of the nanotubes in each finite element and the material fraction of the nanotube reinforced polymer (NRP) and the elastic material are the design variables in the optimization process. ABAQUS is used for the finite element modeling and an optimization code NLPQL which uses a sequential quadratic programming algorithm is used for the optimization.
Improving Surface Finish Quality of Rapid Tooling via Surface Contact Infiltration of 3-D Printed Metal Parts
Authors: Godbey Brady B. , Angstadt David C.
Published: April 2008

Solid freeform fabrication technology has shown a great deal of promise for the plastic injection molding industry due to its ability to produce complex geometry tooling relatively quickly. However, one shortcoming of metal-based SFF processes is that they have difficulty producing parts with acceptable surface quality. As such, secondary operations, such as machining, are frequently required thereby increasing fabrication time and cost. In addition, there is variation in the surface quality that is dependent upon the surface orientation during the build process. For example, parts produced using the metal-based 3-D printing process have vertical faces with a typical roughness 52% greater than the horizontal faces. This work investigates the effects on part surface quality resulting from the application of a contact surface "blank" to the part free surfaces during the infiltration stage of a powder metalbased rapid manufacturing process. Specifically, the effects of "blank" surface roughness and contact pressure are studied with respect to resultant surface roughness and uniformity of the infiltrated part. Application of a smooth contact surface on vertical faces resulted in Ra values at least 25% lower than that of vertical free surfaces. It was also revealed that there is a correlation between surface roughness of the blank and the surface roughness of the infiltrated part. Such blanks could be used to impart desired surface finish and texture to critical surfaces of a mold tool.
Dynamic Simulation of Train Derailments
Authors: Paetsch C. R. , Perlman A. B. , Jeong D. Y.
Published: April 2008

This paper describes a planar rigid-body model to examine the gross motions of rail cars in a train derailment. The model is implemented using a commercial software package called ADAMS (Automatic Dynamic Analysis of Mechanical Systems). The results of the ADAMS model are compared with results from other engineering models that were developed from explicit derivation of the equations of motion. The ADAMS model was also used to conduct sensitivity studies. Various assumptions and characteristic values were varied to examine their respective effect on the resulting motion. The variations include: the number of cars in the train make-up, on-and off-track coefficients of friction, coupler characteristics, and initial conditions. Results from the simulations suggest that train speed, on- and off-track coefficients of friction, and coupler characteristics have the most significant influence on the gross motions.
Direct Simulation of Scattering and Absorption by Particle Deposits
Authors: Mackowski Daniel W.
Published: April 2008

A computational scheme is presented to exactly calculate the electromagnetic field distribution, and associated radiative absorption and scattering characteristics, of large-scale ensembles of spherical particles that are subjected to a focussed incident beam. The method employs a superposition extension to Lorenz/Mie theory, in which the internal and scattered fields for each sphere in the ensemble are represented by vector spherical harmonic expansions, and boundary conditions at the surfaces of the spheres are matched by application of the addition theorem for vector harmonics. The incident field is modeled as a transverse, linearly-polarized wave with a Gaussian amplitude distribution along a fixed focal plane. Application of the method to prediction of the absorption and reflectance characteristics of particle deposits is discussed, and illustrative calculations are presented.
Cooling Heat Transfer and Flow Characteristics of Carbon Dioxide and Lubricant Mixtures in Supercritical Pressure Conditions
Authors: Mori Koji , Shimoki Kunihiro , Shimaoka Hirokazu , Onishi Junji
Published: April 2008

In order to obtain the data for designing and optimizing air conditioning systems using a CO2 refrigerant, the cooling heat transfer characteristics of CO2-lubricant mixtures were experimentally examined. The experiments were carried out under the CO2 mass fluxes of 100 - 500 kg/(m2s) and oil concentrations of 0 - 13 % at the pressure of 9.5MPa. The obtained data revealed that heat transfer coefficients of the mixtures were approximately 0.3 - 0.85 times as much as those of only CO2. In order to clarify the effects of the lubricant, flow visualization experiments were carried out and the obtained information revealed that there appeared two types of flow patterns, stratified flow and annular flow. Furthermore, it was also found that in the lubricant concentration range of 3-5 %, the heat transfer coefficients decreased about 25 % in separated flows, and about 70% in annular flows. For estimating flow pattern, already published well-known flow pattern maps were examined whether those maps were consistent with the measured flow pattern data and it was found that no map was available. A new flow pattern map was proposed for CO2-lubricant mixtures.
Study on Heat Transfer and Flow Behavior of Mini-Tube Bank for Micro Heat Exchanger
Authors: Koizumi Y. , Okuyama T. , Ohtake H.
Published: April 2008

Heat transfer and flow behavior in the mini tube bank were examined. The tube bank was composed of 1 mm diameter nickel wires and a 30 mm wide × 15 mm high flow channel. Experiments were performed in the range of the rod Re = 5 ~ 430 by using water. Numerical analyses were also conducted with the commercial CFD code STAR-CD. The heat transfer coefficient after the second row was lower than first row's one. The flow visualization results indicated that the wake region was stagnant when the Reynolds number was low. This flow stagnation seemed to cause the heat transfer coefficient deterioration in the tube bank. As the Reynolds number was increased, the flow state in the wake region gradually changed from the stagnant condition to the more disturbed condition. The deeper the row was, the more disturbed the wake was. The heat transfer coefficient began to recover to the first row value at certain Reynolds number. The recovery started from the most downstream row; fifth row in the present experiments and was propagated to the upstream row. The Reynolds number when the recovery was initiated decreased as the spacing between rods was increased. The analytical results of the STAR-CD code supported the experimental results. When the wake was stagnant, the heat transfer coefficient distribution around the rear rod, i.e. the rod in the wake, showed a large dip in the front region of the rod. It was considered that this dip caused the heat transfer coefficient decrease after the second row observed in the experiments.
Evaluation of Passenger Vehicle Crashworthiness Using Field Performance Data
Authors: Ray Rose M. , Grossman Helene L. , Murray Steven J. , Lang Robert C.
Published: April 2008

Both state police and the National Automotive Sampling System/Crashworthiness Data System (NASS/CDS) keep automotive collision statistics to varying levels of detail. Some of these details (e.g., collision relative velocity and driver height and weight) are reported in the NASS/CDS, but not in state databases. This article explores whether these details are confounding factors that would bias conclusions based on analysis of state data. To determine this, a methodology was created to predict overall risk based only on the distribution of possible confounding factors experienced by each manufacturer. Relative impact velocity (Delta-V) and driver height and weight are found not to be true confounding factors. Although the distribution of possible confounding factors varies somewhat among manufacturers, the impact on overall expected risk is minimal, and therefore evaluation of risk based on datasets that do not contain information for Delta-V and driver height and weight appears appropriate. The accuracy of match between police reporting and NASS/CDS was also explored and found consistent across manufacturers. Therefore, inaccuracies between police reports and NASS/CDS should not bias comparisons of risk between manufacturers.
Wireless Hydrogen Sensor Self-Powered Using Ambient Vibration and Light
Authors: Nishida Toshikazu , Lin Jenshan , Ngo Khai , Ren Fan , Norton David , Pearton Stephen , Cattafesta Louis , Sheplak Mark , Jun Jerry , Kasyap Anurag , Johnson David , Phipps Alex
Published: April 2008

This paper presents the design, integration, and test of a self-contained wireless hydrogen sensor system powered using ambient vibrations and light. A large number of distributed sensors are required to safely operate hydrogen production, storage, distribution, and fuel cell facilities for aviation, space, and terrestrial applications. Due to cost and reliability issues pertaining to a widespread distributed network, a completely wireless hydrogen sensor system is desirable. For a long (10 year) operating life with minimal maintenance, a wireless system implies both wireless data transmission and local energy mining and/or wireless collection of directed RF energy. Design procedures and issues pertaining to minimizing power consumption for a self-powered hydrogen sensor system are discussed.
A Static Anti-Windup Compensator Design Technique for Robust Regional Pole Placement
Authors: Hencey Brandon , Alleyne Andrew
Published: April 2008

This paper develops a new method of designing anti-windup compensators using the concept of robust pole placement using linear matrix inequality (LMI) regions. The anti-windup problem seeks to minimize the closed loop performance deterioration due to input nonlinearities such as saturation for a given linear time-invariant plant and controller. Existing LMI-based anti-windup synthesis techniques do not explicitly provide a method to account for robust pole placement. This paper suggests a LMI-based method that not only attempts to minimize performance deterioration, but also explicitly restricts the anti-windup closed loop dynamics to an admissible set. Finally, the techniques discussed in this paper are demonstrated on a hydraulic test bed.
Particle Image Velocimetry Measurements of Wake Flows of Various Bridge Sections
Authors: Palombi Emanuela , Kopp Gregory A. , Gurka Roi
Published: April 2008

Using Particle Image Velocimetry (PIV) we investigate the influence of leading and trailing edge geometry on the wake flows of various elongated cylinders in smooth uniform flow. The results present a comparison between the mean wake flows, as well as the vortex shedding activity found to occur in each case. Pressure measurements were recorded on the surface of the cylinders to examine the corresponding fluctuating and mean forces exhibited by each model tested. Significant variations in the wake topology and aerodynamic behaviour of the four cylinder geometries tested were observed.
Boiling Flow Interaction Between Two Parallel Microchannels
Authors: Flynn Roger D. , Fogg David W. , Koo Jae-Mo , Cheng Ching-Hsiang , Goodson Kenneth E.
Published: April 2008

Microchannel heat exchangers predominately use a parallel channel configuration to maximize heat transfer with minimal pump demand. Previous work optimized bulk performance of liquid flow heat exchangers but noted that upon boiling, flow redistributed among parallel channels, and they ultimately found that this instability caused an uncontrollable operating condition. This work predicts and measures fully coupled boiling flow interaction in a simplified two microchannel system. A series of silicon microfabricated devices enable piecewise study of the coupled fluidic and heat transfer interactions, first uniting the fluid inlets of thermally isolated channels, then connecting neighboring channel walls to allow heat transfer between channels. Multiple combinations of boiling and liquid flow, each satisfying system boundary conditions, are identified using flow demand curves assembled from single channel data. Each unique flow condition is experimentally demonstrated and found to be heavily dependent on the prior state of the channels. Connecting channel walls, thermally, is shown to lessen the number of allowed solutions and increase instability in the two channel system, allowing distinction between purely fluidic instabilities and fluidic instabilities coupled to heat transfer between channels. This work in describing interaction between two channels is a necessary step as work continues toward characterizing flow boiling in more complex parallel channel heat sinks.
Nearly Reversible Heat Engines for Thermal Storage of Excess Electric Power
Authors: Levine Jonathan S. , Lackner Klaus S. , Modi Vijay
Published: April 2008

Efficient and affordable energy storage technologies would enable greater use of electricity generation with low operating but high capital cost. Such generating plants must maximize their utilization to spread capital cost over as much output as possible. Without affordable storage capacity their penetration into the market is limited to base load. Intermittent solar and wind power, which at times are simply not available, suffer even more than baseline power plants from the lack of affordable storage technologies. With the exception of pumped hydro-storage, energy storage is too expensive, suffering from low energy density in storage and low round-trip efficiency. Low grade thermal storage with temperature differences of up to about 100°C could achieve storage densities far in excess of that in most pumped storage facilities while avoiding the costs associated with high temperature operations. Roundtrip efficiency, defined as the ratio of the electric output from a heat engine driven by stored thermal energy to the electric input used to drive a heat pump to store the thermal energy, can approach 100% as the heat pump and the heat engine both approach Carnot efficiency. This theoretical limit is independent of the temperature difference between the heat reservoirs. Roundtrip efficiencies of at least 70 to 80% are necessary for energy storage to be economically competitive with higher priced electricity sources. This high round trip efficiency implies that both the heat engine and the heat pump would have to operate at 85 to 90% of the efficiency of a reversible engine. The most promising practical engines for such high efficiency are based on the Stirling cycle. This paper discusses a variation of the Stirling cycle aimed at large, slow units optimized for high efficiency far in excess of the Curzon-Ahlborn efficiency, which results from maximizing the power of the engine. This tradeoff in favor of efficiency over power output demands extreme simplicity in design, as the size of the engine is far larger than that of conventional engines optimized for power throughput. The goal of the paper is to show that low-grade thermal energy storage could provide a viable alternative to regionally limited pumped hydro-storage as long as the design challenges explained in the paper can be overcome. Given the current lack of cost-effective, scalable energy storage systems, thermal storage technology could have a profound impact on future energy infrastructures.
An Investigation of a Micro-Scale Ranque-Hilsch Vortex Tube
Authors: Hamoudi Amar F. , Fartaj Amir , Rankin Gary W.
Published: April 2008

The results of an experimental investigation of the energy separation performance of a micro-scale Ranque-Hilsch vortex tube are presented in this paper. The micro-scale vortex tube is 2 mm in diameter and constructed using a layered technique from multiple pieces of Plexiglas and aluminum. Four inlet slots, symmetrically located around the tube, form the vortex. The hydraulic diameter of each inlet slot and the orifice diameter for the cold exit are 229 and 800 microns respectively. The working fluid is low pressure, non-dehumidified compressed air at room temperature. The rate of the hot gas flow is varied by means of a control valve to achieve different values of cold mass fraction. The mass flow rates, temperatures and pressures of the supply and outlet flows are measured and the performance of the device presented. The supply channel Reynolds number is varied over a considerable range which extends into the laminar regime in order to determine the operating conditions for cooling. An increase in dimensionless temperature is found in both the cold and hot outlets as supply nozzle Reynolds number increases from zero. Maximum values occur at a Reynolds number of approximately 500 and the cold flow dimensionless temperature becomes negative at about 2500. Although the optimum cold mass ratio is higher than the conventional tubes, the effect on performance of tube length and cold exit diameter is similar to the conventional devices.
Development of a Standard for New Passenger Car Wheel Designs
Authors: Talamini Brandon , Perlman Benjamin , Gordon Jeff
Published: April 2008

The American Public Transportation Association (APTA) is seeking to develop specifications to ensure that wheels used in transit and commuter applications perform safely under the service conditions to which they are exposed. To this end, a design standard has been conceived to ensure that new wheel designs proposed for such applications are not susceptible to fatigue cracking in the wheel plate and hub. Historically, the Association of American Railroads (AAR) Standard S-660 has been applied in the industry for the purposes of qualifying wheel designs for use in passenger applications. The standard stipulates particular loads to apply in a simple finite element analysis of the new wheel design. The basis for approval is an empirical comparison (by an independent third party) of the results with those in a database of previous analysis results of other qualified wheels. The proposed "S-660 equivalent" design standard is envisioned to be self-qualifying, in that results of the analysis will directly determine whether the wheel design will perform safely in service; a review or approval body will not be required. The new standard is needed to overcome limitations embodied in the current wheel qualification process, namely, the assumption of purely elastic material behavior, the omission of residual stresses due to manufacturing, and the use of comparative approval criteria. The Union Internationale des Chemins de Fer (UIC) introduced a wheel design requirement based on finite element analysis, the results of which are subjected to a fatigue criterion in order to achieve acceptance of the wheel design. As in the current S-660 methodology, a set of thermal and mechanical loads are prescribed. This methodology is essentially self-qualifying as the results of the analysis (obtained following a prescribed procedure) determine whether the wheel design will perform safely in service. The proposed design standard is envisioned to be a combination of the current S-660 analysis requirements and the fatigue calculation-based approach of the UIC. The task force developing the standard is still resolving the specific details of the thermal and mechanical loading requirements. This paper explores the underlying methodology behind the developing standard. A finite element calculation forms the basis of the qualification procedure. Initial (asmanufactured) residual stresses present in a new wheel are determined. Mechanical and thermal loading representative of passenger operations are applied. The analysis yields three characteristic stress distributions: as-manufactured, mechanical, and thermal. The Sines criterion, with temperature-dependent material fatigue properties obtained from testing, is applied to infer whether the candidate wheel design is fatigue-prone. Results are presented for a wheel design currently in transit/commuter service. The APTA committee is currently investigating the thermal and mechanical load levels to be prescribed in the proposed standard.
Nano-and Micro-Actuations of Hard Disk’s Head Positioning System: Precision Control and Evaluation
Authors: Han Y. , Tzou H. S.
Published: April 2008

A new piezoelectric micro-actuator with 2-dimensional control, i.e., a track following control and a flying height control, of the head positioning system for high-density hard disk drives (HDD) was previously developed in our lab. In this study, control algorithms for the new 2-degree-of freedom (DOF) micro-actuator are developed to independently control the lateral displacement and the transverse deflection to against various disturbances and system uncertainties. The structure of the piezoelectric micro-actuator is reviewed briefly. Then, the overall control strategy for the micro-actuator system is discussed. Next, controller design schemes for each DOF are presented. The pole placement method is used to design controllers. To obtain compensation for overshoot and settling time, pole and zero locations are carefully chosen. First, the control law is defined for the disturbance rejection. Second, the estimator is designed for noise reduction. Lastly, the reference input is added for the command following. Simulation results show that the proposed controllers in the closed-loop system provide good stability, and compensate for disturbances and noises. The data suggest that the proposed micro-actuator control system considerably improves track following and flying height control of head positioning systems in highdensity HDDs.
Numerical Simulation of Fluid-Induced Vibration and Wall Shear Stress in Fusi/Form Cerebral Aneurysm: Newtonian and Non-Newtonian Fluid
Authors: Kim Yong Hyun , Lee Joon Sand , Wu Xin
Published: April 2008

Vascular techniques have been used for curing the aneurysm, but the reason for the occurrence of aneurysms can not be known using these techniques. These techniques are usually used for preventing a significant situation such as rupture of an aneurysm. In our study, blood flow effects with or without vascular techniques inside an aneurysm were analyzed with computational fluid dynamics (CFD). Important hemodynamic quantities like wall shear stress and pressure in vessel are difficult to measure in-vivo. Blood flow is assumed to be Newtonian fluid. But it actually consists of platelets, so it is also considered a non-Newtonian fluid in this study. Results of the numerical model were used to compare and analyze fluid characteristics with experimental data. Using the flow characteristics (wall shear stress (WSS), wall shear stress gradient (WSSG)), the rupture area was identified to be located in the distal area. However, the rupture area, in vivo studies, was observed to be present at a different location. During pulsatile flow, vibration induced by flow is implicated by weakening of the artery wall and affects more than shear stress. After adapting the fluid-induced vibration, the rupture area in aneurysm is found to be located in the same area as the in-vivo result. Since smaller inflow and low WSS provide the effect of the distal neck, the vibration provides more effects in dome area. In this study it has been found that the effect of shear stress on the rupture of aneurysm is less than the effect of vibration. In the case of non-Newtonian fluid, vibration induced by flow also has more effects than WSS and WSSG. The simulation results gave detailed information about hemodynamics under physiological pulsatile inlet condition.
Clearing the Way: Using Turbines to Reclaim or Remediate Acid Mine Drainage
Authors: Miller Amy L. , Stegman Alyson
Published: April 2008

Pennsylvania has a long history of coal mining. Unfortunately, it has left many scars. The Pennsylvania Department of Environmental Protection (PA DEP) is looking at the potential of using micro hydro turbines in acid mine drainage streams. They hope to make it profitable for business to "clean-up" the streams by providing seed money to initiate the hydro turbine projects. It is believed that businesses can profit from both the energy created by the turbines and the extraction of the acid mine drainage (AMD) minerals. The minerals and concentrations vary with each stream. Some possess precious metals, others contain minerals that are used in paint pigment, and still others are being researched for use in powder metallurgy. The paper outlines an undergraduate research project done at the University of Pittsburgh at Johnstown. The study is to create a comprehensive diagnostic spreadsheet to be used by the PA DEP to determine viable economical turbines based on waterway conditions. The study has parallel phases: one addressing issues related to turbine parameters and a second dealing with waterway variables. Also to be discussed in the paper is the use of the project as an undergraduate research study for technology students. For students interested in research or graduate school, it is immensely important to introduce them to research. By guiding them through the process they are better prepared for their future.
De-Tethering of Metallic and Polymeric MEMS/NEMS Parts for the Direct Pick-and-Place Assembly of 3D Microsystem
Authors: Colinjivadi Karthik S. , Cui Yonghao , Ellis Matthew , Lee J.-B. , Skidmore George
Published: April 2008

We report our study on several de-tethering methods for various metallic and polymeric MEMS and NEMS parts including thick (30~100μm) metallic (nickel and its alloys) MEMS parts, sub-micron (350 nm) feature size 1 μm thick metallic NEMS parts, and thick polymer/metal bi-layer (polymer ~50μm, metal ~2μm) MEMS parts. The conventional stress-based de-tethering used in silicon would not be effective for all of these three types of devices. High current injection through narrow tethers was found to be effective and reproducible means of de-tethering thick metallic MEMS parts. But such a method could not be applied for metallic NEMS and polymer/metal bi-layer MEMS parts, as large areas near tethers were burned even with significantly reduced amount of currents. In order to de-tether these NEMS and polymer/metal bi-layer devices, we performed the milling of tethers using a focused ion beam. Very low current (20 pA) ion beam was found to be very effective means of de-tethering the metallic NEMS parts. Relatively larger current (0.3 nA) was found to be good for the polymer/metal bi-layer parts. We demonstrated 3D assembly and/or complete packaging of some of the de-tethered MEMS parts.
Calculating the System Efficiency of the NETL Gas-Turbine/Fuel-Cell Hybrid System Using a Fully Coupled Lumped Parameter System Model
Authors: VanOsdol John , Tucker Dave
Published: April 2008

Thermodynamic efficiency must be considered in the effective analysis of gas turbine fuel cell power generation system performance. In most numerical simulations of hybrid systems, the use of compressor maps and turbine maps are neglected. It is assumed that the design criterion generated by the system model can be met by the manufacturer of these items. These system models may use partial information from a compressor map, or a turbine map, but they fail to match all the operating conditions of both maps in a hybrid configuration. Also, to simplify the calculations that are performed by the complex hybrid system models, the effects of heat transfer and fluid dynamic drag are often decoupled. When system calculations are done in this way, the resulting calculations for system efficiency may suffer error. Hybrid system designers need a simple method to calculate the system performance directly from the maps of real compressors and real turbines that currently exist, and that would be part of a hybrid system. In this work, a simple procedure is illustrated where a coupled analysis of the various system components is performed and included as part of the system model. This analysis is done using the compressor and turbine maps of the hybrid performance project hardware at the U.S. Department of Energy, National Energy Technology Laboratory (NETL). Model parameters are tuned using experimental conditions and results are obtained. The results show the importance of aerodynamic coupling in system models, and how this coupling affects the system efficiency calculations. This coupling becomes important especially for the variable density flows that are typically found in combustors, heat exchangers and fuel cells.
Three-Degree-of-Freedom Parallel Robot Arm
Authors: Hosek Martin , Valasek Michael , Moura Jairo
Published: April 2008

This paper presents single- and dual-end-effector configurations of a planar three-degree of freedom parallel robot arm designed for automated pick-place operations in vacuum cluster tools for semiconductor and flat-panel-display manufacturing applications. The basic single end-effector configuration of the arm consists of a pivoting base platform, two elbow platforms and a wrist platform, which are connected through two symmetric pairs of parallelogram mechanisms. The wrist platform carries an end-effector, the position and angular orientation of which can be controlled independently by three motors located at the base of the robot. The joints and links of the mechanism are arranged in a unique geometric configuration which provides a sufficient range of motion for typical vacuum cluster tools. The geometric properties of the mechanism are further optimized for a given motion path of the robot. In addition to the basic symmetric single end-effector configuration, an asymmetric costeffective version of the mechanism is derived, and two dual-end-effector alternatives for improved throughput performance are described. In contrast to prior attempts to control angular orientation of the end-effector(s) of the conventional arms employed currently in vacuum cluster tools, all of the motors that drive the arm can be located at the stationary base of the robot with no need for joint actuators carried by the arm or complicated belt arrangements running through the arm. As a result, the motors do not contribute to the mass and inertia properties of the moving parts of the arm, no power and signal wires through the arm are necessary, the reliability and maintenance aspects of operation are improved, and the level of undesirable particle generation is reduced. This is particularly beneficial for high-throughput applications in vacuum and particlesensitive environments.
Optimality of Synergetic Controllers
Authors: Nusawardhana Antonius , Zak Stanislaw H.
Published: April 2008

Optimality properties of synergetic controllers are analyzed using the Euler-Lagrange conditions and the Hamilton-Jacobi-Bellman equation. First, a synergetic control strategy is compared with the variable structure sliding mode control. The synergetic control design methodology turns out to be closely related to the methods of variable structure sliding mode control. In fact, the method of sliding surface design from the sliding mode control are essential for designing similar manifolds in the synergetic control approach. It is shown that the synergetic control strategy can be derived using tools from the calculus of variations. The synergetic control laws have simple structure because they are derived from the associated first-order differential equation. It is also shown that the synergetic controller for a certain class of linear quadratic optimal control problems has the same structure as the one generated using the linear quadratic regulator (LQR) approach by solving the associated Riccati equation.
Surface Friction Guiding for Reduced High Frequency Lateral Vibration of Moving Media
Authors: Kartik V. , Wickert J. A.
Published: April 2008

The free and forced vibration of a moving medium is examined in an application where distributed friction guiding is used to control lateral position passively. Sub-ambient pressure features formed in the guides intentionally modify the naturally occurring self-pressurized air bearing and increase the contact force between the medium and the guide's surface. These features increase friction to a level beyond that achievable based on the nominal wrap pressure. The moving medium is modeled as a beam that is transported over frictional regions and that is subjected to prescribed boundary disturbances arising from runout of a cartridge or pack. For axial transport at a speed that is high compared to the vibration velocity, Coulomb friction between the guides and the moving medium can be well-approximated by a derived expression for equivalent viscous damping. The equation of motion is developed for the cases of a single cylindrical guide, and of a multiplicity of guides having arbitrary placement. The level of equivalent damping for each mode decreases with transport speed, and critical speeds exist where each vibration mode transitions between the overdamped and underdamped regimes. Parameter studies in the contact pressure, transport speed, and guide geometry identify preferred design configurations for maximizing dissipation in particular modes and for attenuating high frequency response.
Development of a Simplified Load-Cycle Model for Wheel Loader Design
Authors: Worley Michael D. , LaSaponara Valeria
Published: April 2008

An indispensable part of the off-road construction equipment industry, the front-end-loader (FEL) is a classic example of a working machine, having complex—often nonlinear—interaction between its hydraulic, mechanical, and electrical subsystems [1]. Current state-of-the-art in dynamic simulation of these machines employs full-scale vehicle models and an event-based operator model to quantify the overall system performance, efficiency, and operability. Quantifying these machine parameters is further complicated by the variability in the machine's working environment and task profile. It is recognized that full-scale simulations may offer the most insight into the machine performance and system efficiency; however, even simplified models can yield useful information for structural design, rapid prototyping, and local optimization. This paper explores developing a sub-scale dynamic model for the boom and bucket manipulator system on a FEL that will adequately characterize the system response for the purposes of design and optimization. The equations of motion for the multi- rigid body model of the manipulator system are derived using Kane's method. State equations governing the hydraulic flow to the cylinders and reaction forces on the bucket are employed to model the manipulator system's interaction with the machine and work-pile, respectively. Output from the dynamic simulation is correlated and compared to data gathered during field test operation of the machine.
Restoring Force Surface Analysis of Nonlinear Vibration Data From Micro-Cantilever Beams
Authors: Allen Matthew S. , Sumali Hartono (Anton) , Epp David S.
Published: April 2008

The responses of micro-cantilever beams, with lengths ranging from 100-1500 microns, have been found to exhibit nonlinear dynamic characteristics at very low vibration amplitudes and in near vacuum. This work seeks to find a functional form for the nonlinear forces acting on the beams in order to aide in identifying their cause. In this paper, the restoring force surface method is used to non-parametrically identify the nonlinear forces acting on a 200 micron long beam. The beam response to sinusoidal excitation contains as many as 19 significant harmonics within the measurement bandwidth. The nonlinear forces on the beam are found to be oscillatory and to depend on the beam velocity. A piecewise linear curve is fit to the response in order to more easily compare the restoring forces obtained at various amplitudes. The analysis illustrates the utility of the restoring force surface method on a system with complex and highly nonlinear forces.
New Bond Graph Primitive Elements for Modeling Systems Modeled by Practical Derivatives
Authors: Connolly Thomas J. M. , Contreras Jaime A.
Published: April 2008

This paper describes our work in creating and using new bond graph primitive elements to represent time-varying and/or frequency-dependent effects in engineering systems. These phenomena can be mathematically represented by fractional-order differential and integral operators. Equations with such operators arise from the analysis and application of several classes of partial differential equations [1]. Previous researchers (Bagley, Torvik, et. al.) have used this approach to further the modeling of fluid-structure interactions, heat transfer, and related control systems [3–6]. These new primitive elements represent visco-inertial and visco-elastic phenomena, whose constitutive laws are dictated by half-order derivatives and integrals. After a brief overview of the fractional derivative, we continue with a formalized mathematical development of these new primitive elements using an impedance-based approach, which provides further support in the argument for their necessity. This approach provides the system modeler with new tools to widen the range of systems that he can accurately model using a lumped-parameter bond graph approach. We illustrate the application and utility of the approach with an example problem in fluid-structure interactions by presenting bond graph models and corresponding simulations. The simulations reveal that the use of these new elements accurately captures the frequency-dependent behavior of the physical system.
Software Enabled Variable Displacement Pumps: Experimental Studies
Authors: Rannow Michael B. , Tu Haink C. , Li Perry Y. , Chase Thomas R.
Published: April 2008

The majority of hydraulic systems are controlled using a metering valve or the use of variable displacement pumps. Metering valve control is compact and has a high control bandwidth, but it is energy inefficient due to throttling losses. Variable displacement pumps are far more efficient as the pump only produces the required flow, but comes with the cost of additional bulk, sluggish response, and added cost. In a previous paper [1], a hydromechanical analog of an electronic switch-mode power supply was proposed to create the functional equivalent of a variable displacement pump. This approach combines a fixed displacement pump with a pulse-width-modulated (PWM) on/off valve, a check valve, and an accumulator. The effective pump displacement can be varied by adjusting the PWM duty ratio. Since on/off valves exhibit low loss when fully open or fully closed, the proposed system is potentially more energy efficient than metering valve control, while achieving this efficiency without many of the shortcomings of traditional variable displacement pumps. The system also allows for a host of programmable features that can be implemented via control of the PWM duty ratio. This paper presents initial experimental validation of the concept as well as an investigation of the system efficiency. The experimental apparatus was built using available off-the-shelf components and uses a linear proportional spindle valve as the PWM valve. Experimental results confirm that the proposed approach can achieve variable control function more efficiently than a valve controlled system, and that by increasing the PWM frequency and adding closed-loop control can decrease system response times and of the output ripple magnitude. Sources of inefficiency and their contributions are also investigated via modeling, simulation and are validated by experiments. These indicate design parameters for improving inefficiency.
Impact of Valve Plate Design on Noise, Volumetric Efficiency and Control Effort in an Axial Piston Pump
Authors: Seeniraj Ganesh Kumar , Ivantysynova Monika
Published: April 2008

In designing an axial piston pump, lot of attention is given to the design of the valve plate. A well designed valve plate can reduce both flow pulsations as well as oscillating forces on the swash plate. In the presented study, a computational tool, CASPAR, has been used for investigating the effect of valve plate design on flow ripple (fluid borne noise), oscillating forces (structure borne noise) and volumetric efficiency. The impact of various valve plate design parameters such as precompression grooves, cross port, indexing and additional precompression volume will be presented using simulation results from CASPAR. The study also details how rate of pressurization and decompression inside the displacement chamber directly relate to the flow ripple, forces applied on swash plate and the control effort needed to stroke the swash plate. The effect of noise reduction techniques on volumetric efficiency will also be presented with simulated results.
Developing Beliefs About the Cost of Systems in a Conceptual Design Phase
Authors: Takai Shun
Published: April 2008

In a conceptual design phase, engineers need to estimate, as accurately as possible, the cost of system developed from each concept (cost of concept). If engineers overestimate cost, engineers may be forced to unnecessarily cancel system development. On the other hand, if engineers underestimate cost, the final system may not be as profitable as initially expected. When engineers make a critical decision to select a concept, the dilemma is that there is typically no or limited information to accurately estimate cost of concept. This paper proposes a belief-based approach for estimating a cost of system in a conceptual design phase. In the proposed approach, engineers benchmark existing systems in the market that are similar to the new system. For these benchmarked systems, engineers estimate costs by subtracting profit margins from observed prices. Engineers develop a distribution of cost for the new system from these estimated costs.
Saturation Effects on Performance and of a Compliant Actuator Force Control System
Authors: Ghorbani Reza , Wu Qiong
Published: April 2008

A novel mechanism for changing the stiffness of a series elastic actuator over a wide range is briefly explained. The series elastic actuator's mathematical modeling, control method and physical limitations are addressed in this work as extension of our previous work. Two remaining issues of the previous work have been studied in this paper: 1 - A new nonlinear compensator is developed to improve the force tracking performance of the actuator. 2- Performance of the control system is studied by substitution of the saturation operator with equivalent gain. Finally, simulations are performed to show the ability of the controller to track desired force commands.
An Investigation of the Dynamic Behavior of a Piezoceramic Vibrator Clamped With a Resonate Amplifier Using Equivalent Circuits
Authors: Wen Fuhliang , Hsu Ichien , Lin Hsiucheng
Published: April 2008

Using equivalent circuit analysis, the dynamic behavior of ultrasonic wave propagation in solid metals is investigated in this study, particularly in Langevin vibrators clamped with a resonant amplifier to enlarge the vibrating magnitude. For piezoelectric static feature, the piezoceramic impedance and equivalent circuits were obtained for the parameter model of the vibrator via the impedance analyzer. To analyze piezoceramic dynamic feature, the characteristic of motional current relative to frequency response was measured under practical operating voltage for the vibrator. Both static and dynamic features of a piezoceramic vibrator were compared to realize the difference and to build the dynamic equivalent circuit. The vibration measurement module of optical fiber was also employed to detect the maximum displacement of a vibrator with a resonant amplifier. The measured results demonstrate that the resonant frequency is moved to the lower frequency band. The new equivalent circuit model is proposed to further match the dynamic response and the stepped horn increases the vibrating amplitude by about seven times. This is the more efficient mechanical output for a vibrator.
Panel Deployment Using Ultrafast SMA Latches
Authors: Barnes Brian , Brei Diann , Luntz Jonathan , Browne Alan , Strom Kenneth
Published: April 2008

Advanced material systems are continuously being sought for energy absorption during impact, but these materials still tend to be heavy and expensive. An alternative approach is to actively increase the crush distance using deployable panels. Depending on the closing speed of "bullet" and "target" objects and the detection range of the pre-impact sensor, for a deployable panel to be effective in energy management, as little as 30-50 ms may be available for releasing, deploying, and in some applications stopping the panel. This paper presents the development of a stored energy panel deployment approach that meets this challenging time regime through a combination of traditional and smart materials technologies selected via a thorough downselection process. In the chosen approach, a light, compact, and inexpensive ultra-fast SMA latch releases energy from traditional compressed springs to deploy a panel which is stopped with integrated shock absorbers. A full-scale integrated prototype was designed, built and experimentally characterized for two bounding cases: 30 ms deploy demanding high force/power and a 50 ms deploy with associated lower force/power requirements. In both cases, the proof-of-concept shows promising performance metrics well within these two specified target deployment times. Given this, when coupled with advanced sensing technology, this system provides a promising alternative mechanism useful for military applications such as projectile interception on vehicles, ships and combat quarters as well as civilian applications such as commercial vehicles and structural terrorist threats.