bluuebunny/crossref_metadata_2025 huggingface dataset:
Design of Planar Nonlinear Springs for Prescribed Load-Displacement Functions
Authors: Jutte Christine V. , Kota Sridhar
Published: May 2009

Nonlinear springs can simplify and improve the performance of a variety of devices, including prosthetics, MEMS, and vehicle suspensions. Each nonlinear spring application has unique load-displacement specifications that do not correspond to one general spring design. This limits the use of nonlinear springs and thus compromises the performance of these applications. This paper presents a generalized methodology, including topology, size, and shape optimization, for creating nonlinear springs with prescribed load-displacement functions. The methodology includes a new parametric model that represents nonlinear springs as a single-plane, ‘fractal’-like network of splines. The parametric model and the objective function are incorporated into a genetic algorithm optimization scheme. Nonlinear finite element analysis evaluates the large displacements of each spring design. Three nonlinear spring examples, each having uniquely prescribed load-displacement functions including a “J”-shaped, an “S”-shaped, and a constant-force function, generate designs that demonstrate the methodology’s effectiveness in designing nonlinear springs.
Applications of the Fractal-Like Finite Element Method to Sharp Notched Plates
Authors: Treifi Muhammad , Tsang Derek K. L. , Oyadiji S. Olutunde
Published: May 2009

The fractal-like finite element method (FFEM) has been proved to be an accurate and efficient method to analyse the stress singularity of crack tips. The FFEM is a semi-analytical method. It divides the cracked body into singular and regular regions. Conventional finite elements are used to model both near field and far field regions. However, a very fine mesh of conventional finite elements is used within the singular regions. This mesh is generated layer by layer in a self-similar fractal process. The corresponding large number of degrees of freedom in the singular region is reduced extremely to a small set of global variables, called generalised co-ordinates, after performing a global transformation. The global transformation is performed using global interpolation functions. The Concept of these functions is similar to that of local interpolation functions (i.e. element shape functions.) The stress intensity factors are directly related to the generalised co-ordinates, and therefore no post-processing is necessary to extract them. In this paper, we apply this method to analyse the singularity problems of sharp notched plates. Following the work of Williams, the exact stress and displacement fields of a plate with a notch of general angle are derived for plane stress and plane strain conditions. These exact solutions which are eigenfunction expansion series are used as the global interpolation functions to perform the global transformation of the large number of local variables in the singular region around the notch tip to a few set of global co-ordinates and in the determination of the stress intensity factors. The numerical examples demonstrate the accuracy and efficiency of the FFEM for sharp notched problems.
SAAST Robotics: An Intensive Three Week Robotics Program for High School Students
Authors: Cappelleri David J. , Keller James F. , Kientz Terry , Szczesniak Peter , Kumar Vijay
Published: May 2009

We have designed an intensive, three-week robotics program for high school students that combines theory with hands-on practical experience in cutting edge technologies. Conventional approaches to engineering education are bottom-up. Students are first taught the basics and are then courses that build on the basics. Most students do not take coursework on engineering applications, particularly design and systems engineering, until the end of the curriculum. This has the disadvantage of not exposing students to the excitement in engineering until late in the curriculum. Our goal is to develop a top-down curriculum in which students are introduced first to the applications and systems concepts which then leads to the teaching of fundamentals. This approach has the potential to recruit and retain students in engineering while making the curriculum more relevant and rigorous.
Analysis and Mitigation of Dead-Zone Effects on Systems Using Two-Impulse ZV Input Shaping
Authors: Sorensen Khalid L. , Cross Patrick W. , Singhose William E. , Prakash Shashvat
Published: May 2009

Input shaping is an effective method for reducing oscillatory motion in linear systems. Many physical systems, however, exhibit discontinuous dynamics, such as saturation, rate limiting, backlash, and dead-zone. These hard nonlinearities can degrade the vibration reducing properties of shaped signals. This paper investigates the detrimental effects of dead-zone on a class of input-shaped commands. A mitigation strategy is proposed for reducing these detrimental effects when the value of the deadzone can be estimated. The robustness of this mitigation approach to uncertainties in the dead-zone width is also determined. Theoretical developments are experimentally verified using an industrial 10-ton bridge crane.
Optimal Design of Sandwich Beam With Frequency Constraints
Authors: Gantovnik Vladimir B. , Lopatin Alexander V. , Shumkova Lubov V.
Published: May 2009

In this paper, we analyze selection of optimal parameters of sandwich beam in the presence of constraints on the frequencies of the transversal vibrations. The employed equations of motion take into account the transverse shear deformations in the core and rotatory inertia of the beam cross-section. The expressions for the transversal vibrations are obtained. The results show that one-dimensional model of the sandwich beam can be used for preliminary vibrational analysis of more complex models of sandwich plates and shells.
A Case Study of Design Process and Development of a Design Enabling Tool for Wright Metal Products
Authors: Kayyar Madhusudan , Summers Joshua D. , Ameri Farhad , Biggers Sherrill
Published: May 2009

This case study investigates the design process followed by a small to medium scale enterprise (SME) that primarily depends on special expertise in the form of a few key individuals, who design products mainly based on past experience, augmented by trial and error. This is an inefficient, time consuming, and expensive way of designing products and evaluating their performance. This led to development of a specialized and affordable design enabler that facilitates engineering analysis, noticeably absent in SME’s current design process. Further, the design enabler forms the foundation for extending the scope to include rule-based systems, optimization and case based reasoning that would assist designers in efficient product development.
Optimization-Based Digital Human Dynamics: Santos™ Walking Backwards
Authors: Kwon Hyun Jung , Xiang Yujiang , Rahmatalla Salam , Marler R. Timothy , Abdel-Malek Karim , Arora Jasbir S.
Published: May 2009

An objective of this study is to simulate the backward walking motion of a full-body digital human model. The model consists of 55 degree of freedom – 6 degrees of freedom for global translation and rotation and 49 degrees of freedom representing the kinematics of the entire body. The resultant action of all the muscles at a joint is represented by the torque for each degree of freedom. The torques and angles at a joint are treated as unknowns in the optimization problem. The B-spline interpolation is used to represent the time histories of the joint angles and the well-established robotics formulation of the Denavit-Hartenberg method is used for kinematics analysis of the mechanical system. The recursive Lagrangian formulation is used to develop the equations of motion, and was chosen because of its known computational efficiency. The backwards walking problem is formulated as a nonlinear optimization problem. The control points of the B-splines for the joint angle profiles are treated as the design variables. For the performance measure, total dynamic effort that is represented as the integral of the sum of the squares of all the joint torques is minimized using a sequential quadratic programming algorithm. The solution is simulated in the Santos™ environment. Results of the optimization problem are the torque and joint angle profiles. The torques at the key joints and the ground reaction forces are compared to those for the forward walk in order to study the differences between the two walking patterns. Simulation results are approximately validated with the experimental data which is motion captured in the VSR Lab at the University of Iowa.
Sensitivity-Free Approach for Reliability-Based Robust Design Optimization
Authors: Youn Byeng D. , Xi Zhimin , Wells Lee J. , Gorsich David J.
Published: May 2009

This paper attempts to integrate a derivative-free probability analysis method to Reliability-Based Robust Design Optimization (RBRDO). The Eigenvector Dimension Reduction (EDR) method is used for the probability analysis method. It has been demonstrated that the EDR method is more accurate and efficient than the Second-Order Reliability Method (SORM) for reliability and quality assessment. Moreover, it can simultaneously evaluate both reliability and quality without any extra expense. Three practical engineering problems (vehicle side impact, layered bonding plates, and lower control arm) are used to demonstrate the effectiveness of the EDR method.
A Critical Systems Position on Augmented Prototyping Systems for Industrial Design
Authors: Verlinden Jouke , Horva´th Imre
Published: May 2009

In order to assess usability and impact of new Augmented Reality based prototyping technologies in industrial design engineering, we are carrying out a multiple case study. We focus on shortcomings in current (physical) prototypes and bottlenecks in the design process, which might present to cues for new Augmented Prototyping technologies. However, tracking and categorizing these bottlenecks is difficult, attention has to be given on the complete scope of prototyping use and its value towards design. A method was devised to capture bottlenecks in concept uttering, based on Critical Systems Thinking; identifying functionalist, interpretive, emancipatory, postmodern views tunes the researcher’s view to uses of advanced prototyping means that have impact on the complete design process.
Spin Testing of Pneumatic Artificial Muscle Systems for Helicopter Rotor Applications
Authors: Bubert Edward A. , Woods Benjamin K. S. , Sirohi Jayant , Kothera Curt , Wereley Norman
Published: May 2009

This research investigates the feasibility of using Pneumatic Artificial Muscles (PAMs) to drive a rotor blade Trailing Edge Flap (TEF) for primary control and/or vibration reduction. Specifically, this work investigates the effects of operating these compliant, pneumatic actuators under the high CF loading typical of a helicopter rotor blade. A prototype TEF actuation system was designed and built. It was tested in a vacuum whirl chamber over a range of centrifugal accelerations. Bi-directional actuation was performed to track changes in system performance with increasing CF field. Additionally, testing was performed under different levels of torsional spring loading to simulate aerodynamic hinge moment effects. Results of these tests motivated a second experiment wherein the effects of CF loading on the PAMs themselves are isolated from the rest of the system. This was accomplished by fixing the ends of PAM and performing blocked force testing over a range of centrifugal accelerations. Taken together, these tests show that chordwise PAM actuators are capable of operating under high CF loading with only minor losses in performance. Additionally, the need for careful design of actuation and flap system components for operation in this harsh environment is reiterated.
Positive Feedback in Powered Exoskeletons: Improved Metabolic Efficiency at the Cost of Reduced Stability?
Authors: Norris James A. , Marsh Anthony P. , Granata Kevin P. , Ross Shane D.
Published: May 2009

A broad objective of many lower extremity exoskeletons is to allow the wearer to expend less of their own energy for locomotion. Existing exoskeleton control algorithms are based on positive feedback. Forces are generated to augment movement initiated by the wearer. Positive feedback, however, can have destabilizing effects in dynamic systems. In fact, stability in these lower extremity exoskeletons is achieved by relying on the wearer’s neuromuscular system. Relying on the wearer to maintain stability may increase metabolic demand, which is counter productive to increasing efficiency. Thus, the goal of this study was to measure how a simple form of positive feedback that augments ankle push-off power affects both metabolic efficiency and dynamic walking stability. We developed a pair of powered ankle-foot orthoses (PAFOs) similar in design to Ferris, et al. (J. Appl. Biomech. 21, 189–197, 2005). Nine young healthy adults (23.3±1.6 years) walked on a treadmill in the PAFOs under two conditions: (1) with and (2) without push-off power assistance. Metabolic energy expenditure was calculated using indirect calorimetry. Walking stability was quantified using techniques for studying stability of dynamic system trajectories. The maximum Lyapunov exponent for assessing local dynamic stability, and the maximum Floquet multiplier magnitude for assessing orbital stability were calculated from foot and shank kinematics for each condition. Greater Lyapunov exponents and Floquet multipliers indicate decreased stability. Walking with mechanically generated push-off power increased metabolic efficiency (2.58±0.39 to 2.97±0.38, p<0.01), did not affect local dynamic stability (0.14±0.02 to 0.14±0.02, p = 0.77), but decreased orbital dynamic stability (0.43±0.03 to 0.48±0.06, p = 0.05). This study provides evidence that positive feedback can negatively affect stability. Further investigations into understanding stability of movement will be necessary for the design of controllers for powered lower extremity exoskeletons.
Predicting the Traction Force Requirements of Wheeled Mobile Robots Traversing Obstacles
Authors: Oyadiji S. Olutunde , Lai Eugene
Published: May 2009

The analytical models of a wheeled mobile robot (WMR) are often derived based on the assumption that the surface on which it manoeuvres is free from any irregularities. However, the wheels of a WMR are likely to encounter small but unavoidable obstacles. The interaction between stationary obstacles and the wheels of the mobile robot can adversely affect the stability of the payload as well as the robot’s handling control. The limited understanding of the mechanism of wheel-obstacle interaction and its implication on the overall dynamics of a WMR has hindered the development of control tools that may be used to limit the adverse effects of traversing surface irregularities. In this paper, vectorial mechanics approach is used to model the dynamics of wheeled mobile robots (WMRs) travelling over localised surface irregularities. This model is employed in conjunction with temporal trajectory functions to compute the traction force requirements of WMRs traversing obstacles of specified profiles. The obstacles are in the form of sinusoidal humps which are decomposed into positive and negative sinusoidal ramps. It is shown that a compromise can be obtained between the minimum times requirement for obstacle traversing, the traction force requirements, and the geometrical properties of the obstacles. The traction force can become negative which implies the need to switch to a braking action. This switch between the traction mode and braking mode of the actuators can be prevented if an optimal time for the obstacle traversing is selected a-priori. It is also shown that the relationship between the traction or breaking force magnitude and the manoeuvre time is non-linear and that the traction force requirements are much greater at small manoeuvre times than at big manoeuvre times. In addition, it is shown that the grade of an obstacle, which depend on its length and height, affect the traction requirements.
Variability and Component Criticality in Component Reuse and Remanufacturing Systems
Authors: Pandey Vijitashwa , Thurston Deborah
Published: May 2009

Product take-back and remanufacturing systems are difficult to implement cost-effectively. Two contributing factors to this problem are the complex nature of the interrelationships among components, and their high degree of variability. Legislated take-back mandates have made it imperative for manufacturers to realize when there is value to be recovered in components and when there is not. This paper proposes a component criticality method to help ascertain this remaining value. We also develop a metric that measures the randomness or variability that a reuse alternative imposes on the remanufacturing system. A case study on washing machines illustrates how the two measures can be incorporated into a design decision model, can help reduce the complexity of reuse operations, and result in a superior design solution.
A New Method for Determining Joint Constraint Forces and Moments During Optimal Dynamic Motion of Redundant Manipulators
Authors: Kim Joo H. , Yang Jingzhou , Abdel-Malek Karim
Published: May 2009

The kinematic representations of general open-loop chains in many robotic applications are based on the Denavit-Hartenberg (DH) notation. However, when the DH representation is used for kinematic modeling, the relative joint constraints cannot be described explicitly using the common formulation methods. In this paper, we propose a new formulation of solving a system of differential-algebraic equations (DAEs) where the method of Lagrange multipliers is incorporated into the optimization problem for optimal motion planning of redundant systems. In particular, a set of fictitious joints is modeled to solve for the joint constraint forces and moments, as well as the optimal dynamic motion and the required actuator torques, of redundant manipulators described in DH representation. The proposed method is formulated within the framework of our earlier study on the generation of load-effective optimal dynamic motions of redundant manipulators that guarantee successful execution of given tasks, in which the Lagrangian dynamics for general external loads are incorporated. Some example tasks of a simple planar manipulator and a high-degree-of-freedom digital human model are illustrated, and the results show accurate calculation of joint constraint loads without altering the original planned motion. The proposed optimization formulation is equivalent to solving DAEs without integration.
Fatigue Load Equivalent to Distribution of Loads From the US Population
Authors: Tibbits Patrick
Published: May 2009

In seeking to simplify fatigue life calculations for components of fitness equipment, this paper develops a general expression for the user weight Le which, in NT cycles, generates the same fatigue damage as a set of user weights {Li} described by a probability density function fi = Ni/NT, where each Li gets applied for Ni cycles and Σ Ni = NT. The derivation of the method goes beyond the textbook development of equivalent load by retaining geometric, material, and loading parameters throughout the derivation. The expression allows exploration of the effect of the geometry of the mechanical component, material properties, and loading on the value of the user weight Le which simulates the set of user weights {Li}. The paper explores a range of stress-life exponent b typical of common steels. The paper explores the complete range of stress ratio R ∈ (-1, 1). The paper explores the combined effect of the component’s ultimate tensile strength and the ratio between applied load and stress. These last two parameters determine the user weight Lb which causes single-cycle fracture of the component. The results indicate a strong dependence of Le on stress ratio R, stress-life exponent b, and on breaking weight Lb. The paper proposes guidelines for assignment of Le in the special case where the {Li} arise from body weights of the US population.
A Co-Simulation Environment for Virtual Prototyping of Ground Vehicles
Authors: Datar Makarand , Tercha Michael , Pergantis Charles , Manesh Ali , Negrut Dan
Published: May 2009

The use of virtual prototyping early in the design stage of a product has gained popularity due to reduced cost and time to market. The state of the art in vehicle simulation has reached a level where full vehicles are analyzed through simulation but major difficulties continue to be present in interfacing the vehicle model with accurate powertrain models and in developing adequate formulations for the contact between tire and terrain (specifically, scenarios such as tire sliding on ice and rolling on sand or other very deformable surfaces). The proposed work focuses on developing a ground vehicle simulation capability by combining several third party packages for vehicle simulation, tire simulation, and powertrain simulation. The long-term goal of this project is to promote the Digital Car idea through the development of a reliable and robust simulation capability that will enhance the understanding and control of off-road vehicle performance. To this end we concentrate our attention on two main aspects: (1) development of a family of tire and contact models suitable for simulations ranging from high accuracy to real time for on/off-road conditions and extreme environments, and (2) investigation of co-simulation techniques suitable from a numerical standpoint to support long simulations of heterogeneous models that contain vehicle, tire, terrain, powertrain, and controls subsystems.
An Investigation on Information and Gender-Based Power in Product Design Decision-Making
Authors: Okudan Gu¨l E. , Mutluer Can E.
Published: May 2009

The goal of the designed experiment and subsequent analyses presented in this paper was to investigate the power distributions especially with regards to gender in mixed-gender groups engaged in product design decision-making. The task involved determining the set of design criteria pertaining to consumer products with varying gender orientations, and rating the criteria for their importance according to various stakeholder interests. Results indicate that group level acceptance of the contributions was indeed impacted by the type of the product that the decision-making focused on, and that this impact can be attributed to the perceived knowledge levels of the individuals due to their expected familiarity with the product.
On the Design and Control of a Squeeze-Flow Mode Magnetorheological Fluid Mount
Authors: Ciocanel Constantin , Nguyen The , Schroeder Christopher , Elahinia Mohammad
Published: May 2009

The paper presents the design and control of a magnetorheological (MR) fluid based mount that combines the squeeze and flow modes in operation. The proposed design yields a high static stiffness and a low dynamic stiffness in the working frequency range of the mount, enhancing the vibration isolation capabilities of the mount compared to existing hydraulic mounts. Vertical vibrations, namely displacement/force transmissibility, can be isolated or significantly reduced, in real time, by controlling the fluid yield stress through an applied electric current. The mount governing equations have been derived and the effect of system parameters on its performance was analyzed. Preliminary results on the implementation of skyhook, groundhook and hybrid control strategies are also presented.
Diagonal Dominance and the Decoupling Approximation in Damped Discrete Linear Systems
Authors: Morzfeld Matthias , Ajavakom Nopdanai , Ma Fai
Published: May 2009

The principal coordinates of a non-classically damped linear system are coupled by nonzero off-diagonal element of the modal damping matrix. In the analysis of non-classically damped systems, a common approximation is to ignore the off-diagonal elements of the modal damping matrix. This procedure is termed the decoupling approximation. It is widely accepted that if the modal damping matrix is diagonally dominant, then errors due to the decoupling approximation must be small. In addition, it is intuitively believed that the more diagonal the modal damping matrix, the less will be the errors in the decoupling approximation. Two quantitative measures are proposed in this paper to measure the degree of being diagonal dominant in modal damping matrices. It is demonstrated that, over a finite range, errors in the decoupling approximation can continuously increase while the modal damping matrix becomes more and more diagonal with its off-diagonal elements decreasing in magnitude continuously. An explanation for this unexpected behavior is presented. Within a practical range of engineering applications, diagonal dominance of the modal damping matrix may not be sufficient for neglecting modal coupling in a damped system.
Simulation of Nanomanipulation Using Compliance-Based Contact Dynamics Modeling Technique
Authors: Ma Ou , Diao Xiumin , Zhang Mingjun
Published: May 2009

This paper describes dynamics modeling and simulation of AFM-based manipulation of a nano-scale object using the compliance-based contact dynamics modeling technique (also referred to as the penalty method). Such a modeling technique has been well developed and widely applied in macro-scale applications. Its applicability to nano-scale cases is, however, relatively new and thus, requires more investigation. The dynamics model developed in the paper includes the Van der Waals forces, electrostatic forces, contact forces (for modeling repulsion), and friction forces with consideration of contact geometry, stiffness, and friction properties of all the physically interacting objects. The model can simulate the dynamic behavior of interactions between nano-scale objects and its environment. For demonstration, the dynamic simulation results of an AFM-based manipulation process are presented. To provide confidence of the model fidelity, a simulation example which matches some published data is presented.
Diagnosing Subsynchronous Vibrations: Unstable or Benign
Authors: Rajagopalan Vinayaka N. , Vance John M.
Published: May 2009

Rotordynamic instability, commonly observed as subsynchronous vibration, is a serious problem that can cause heavy damage to a turbomachine or make it incapable of operation due to high vibration levels. However, all subsynchronous vibrations are not necessarily unstable. If the amplitude of the subsynchronous vibration is large, it can cause damage to seals, bearings, or process wheels. If it is small, the question arises as to whether it has the potential to grow larger (“instability”) or whether it is benign and harmless. A way to know would be helpful. The objective of this study is to signal-analyze subsynchronous vibration in turbomachinery and distinguish benign subsynchronous vibration from true rotordynamic instability. Effort is also made to identify unique signatures to a cause, thereby aiding in faster diagnosis. A computer simulation study is conducted on four rotors, including two gas-reinjection compressors that went unstable, to examine the possibility of using the change in synchronous phase angle as a possible indicator of impending instability. Two other rotors in laboratory test rigs were also studied, both experimentally and with computer simulations of the phase angle response. The computer simulations and experimental results agree very closely on the test rigs. Measured signals from another rotor, with bearings having a dead-band clearance are studied as an example of a benign cause that can result in subsynchronous vibration. The effect is studied with the rotor in both horizontal and vertical positions and clear indicators are discovered that confirm the subsynchronous vibration to be benign in nature. Signatures from another rotor with internal friction are also presented. The experimental data clearly shows indicators that distinguish it as a genuine instability. Dry friction whip is also experimentally produced on a test rig. The measurements show that dry friction whip defies all general rules of thumb for diagnosing a true instability and at the same time is a very violent one as well.
Polymer Composite-Based Vibration and Noise Emission Controls for Hand-Struck Impact Tools
Authors: Griffith Matthew , Brisach Daniel , Konchar Janelle , Petfield Stephen , Popper Peter , Glancey James
Published: May 2009

Exposure to high noise levels may be the most common occupational hazard. Recent estimates suggest that as many as 30 million Americans are exposed to noise levels greater than the current safe limits for workplaces. At current durations of exposure, it is expected that 25% of these workers will develop permanent, noise-induced hearing loss. In many of these industrial environments, high levels of vibration also exist that can lead to several injuries and ailments. To address the adverse effects associated with the use of high noise emission impact tools, a study was initiated to develop and evaluate alternate tool designs that reduce the potential for hearing loss and vibration-related injuries. Recent work has focused on integrating advanced engineering polymers (composites) into tool designs for the purpose of eliminating direct metal-to-metal impact. This approach has several significant performance advantages including reduced operator discomfort due to hand-arm mechanical shock, reduced noise, and less danger from flying metal fragments. To quantify sound emission characteristics of these new designs, continuous sound pressure, maximum sound pressure, and maximum sound pressure level were measured using an array of five precision microphones each located 1 meter from the tool. Data was sampled at 40 kHz while test subjects operate both pneumatic tools and hand-struck tools. Frequency spectra of the sound pressure signals were examined for all tool treatments, and indicate that the addition of a polymer insert between metal impact components significantly reduces noise emission, especially at higher frequencies. Similar reductions were observed in vibration transmission in the hand and arm. As a result, tools that integrate polymer-based components may be operated for longer daily exposure times without inducing hearing loss or vibration-related injuries. Data from this study may also help auditory and ergonomic specialists in understanding impulse noise characteristics and exposure.
Kinematic Variability, Local, and Orbital Stability as Predictors of Falls in Passive Dynamic Walking
Authors: Dingwell Jonathan B. , Su Jimmy Li-Shin
Published: May 2009

Falls that occur during walking are a significant health care problem. However, there is as yet no generally accepted way to quantify walking stability. While clinicians often use variability as a proxy for stability, such measures do not quantify how systems respond to perturbations. Our goal was to determine how small-to-moderate perturbations affect both walking variability and stability. We applied random perturbations to a simple passive dynamic model of walking to simulate walking down a bumpy slope. Because the model’s global basin of attraction remained fixed, applying larger perturbations directly increased the risk of falling in the model. We generated 10 simulations of 300 consecutive strides of walking at each of 6 perturbation amplitudes up to the maximum level the model could tolerate without falling. We quantified “orbital stability” by calculating the maximum Floquet multipliers for the model. We quantified “local stability” by calculating local exponential rates of divergence of neighboring state space trajectories. As perturbation amplitudes increased, orbital stability and long-term local instability did not change. These measures reflected the fact that the model never actually “fell” during any of our simulations. Conversely, the mean variability of the walker’s kinematics increased exponentially and measures of short-term local instability increased linearly. These measures thus predicted the increased risk of falling exhibited by the model. For all simulated conditions, the walker remained orbitally stable, while exhibiting substantial local instability. This was because very small initial perturbations diverged away from the limit cycle, while larger initial perturbations converged toward the limit cycle. These results provide insight into how these different proposed measures of walking stability are related to each other and to risk of falling.
Simulation Based Optimal Tolerancing for Multibody Systems
Authors: Arenbeck Henry , Missoum Samy , Basudhar Anirban , Nikravesh Parviz E.
Published: May 2009

This paper introduces a new methodology for probabilistic optimal design of multibody systems. Specifically, the effects of dimensional uncertainties on the behavior of a system are considered. The proposed reliability-based optimization method addresses difficulties such as high computational effort and non-smoothness of the system’s responses, for example, as a result of contact events. The approach is based on decomposition of the design space into regions, corresponding to either acceptable or non-acceptable system performance. The boundaries of these regions are defined using Support Vector Machines (SVMs), which are explicit in terms of the design parameters. A SVM can be trained based on a limited number of samples, obtained from a design of experiments, and allows a very efficient estimation of probability of failure, even when Monte Carlo Simulation (MCS) is used. A modularly structured tolerance analysis scheme for automatic estimation of system production cost and probability of system failure is presented. In this scheme, detection of failure is based on multibody system simulation, yielding high computational demand. A SVM-based replication of the failure detection process is derived, which ultimately allows for automatic optimization of tolerance assignments. A simple multibody system, whose performance usually shows high tolerance sensitivity, is chosen as an exemplary system for illustration of the proposed approach. The system is optimally designed for minimum manufacturing cost while satisfying a target performance level with a given probability.
Embracing Product Design Engineering
Authors: Jack Hugh , Farris John , Choudhuri Shabbir , Anyalebechi Princewill , Standridge Charlie
Published: May 2009

A Product Design and Manufacturing (PDM) Engineering emphasis has been designed to update a Manufacturing Engineering program at Grand Valley State University. While the program continues to include a major focus on manufacturing it also emphasizes crossing disciplinary boundaries for product design. Graduates of the program are educated to work in all phases of the product development process from concept to customer. The program includes a blend of courses from a variety of disciplines, tieing these together using a sequence of product design courses. Within the courses students are exposed to course work that encourages product oriented design including prototyping. The program redesign described in the paper could also be applied to Mechanical Engineering programs.
Incorporating Energy Variations Into Controlled Sagittal Plane Locomotion Dynamics
Authors: Schmitt John M.
Published: May 2009

The spring loaded inverted pendulum template has been shown to accurately model the steady locomotion dynamics of a variety of running animals. While the template models the leg dynamics by an energy-conserving spring, insects and animals have structures that dissipate, store and produce energy during a stance phase. Recent investigations into the spring-like properties of limbs, as well as animal response to drop step perturbations, suggest that animals use their legs to manage energy storage and dissipation, and that this management is important for gait stability. In this paper, we extend our previous analysis of control of the spring loaded inverted pendulum template via changes in the leg touch-down angle to include energy variations during the stance phase. We incorporate energy variations through leg actuation that varies the force-free leg length during the stance phase, yet maintains qualitatively correct force and velocity profiles. In contrast to the partially asymptotically stable gaits identified in previous analyses, we find that incorporating energy and leg angle variations in this manner enables the system to recover from perturbations similar to those that might be encountered during locomotion over rough terrain.
The Performance Effects of Squeeze Film Stiffness on Non-Resonate Interferometric Inertial Sensors
Authors: Perez Maximillian A. , Shkel Andrei M.
Published: May 2009

This paper studies the nonlinear effects of squeeze film stiffening on the performance of a high resolution MEMS nonresonant inertial sensor. It is shown that these effects introduce a surprising dynamic response that extends the operational frequency range of the devices by retarding the resonate response. In addition, this performance advantage will occur without the traditional gain trade-off associated with linear systems of this type. A method is introduced to experimentally characterize the squeeze film stiffness of a passive inertial sensor through the resonant characterization of a Fabry-Pe´rot interferometric accelerometer under reduced pressure. Such passive devices are uniquely suited for the study of squeeze films and, due to the dependence of both the sensitivity and bandwidth on the device structural stiffness, variation of the stiffness with frequency must be considered to accurately predict sensor performance. The characterization confirms established analytical squeeze film stiffness theory in the continuous gas regime for conditions of Knudsen numbers less then one. As the Knudsen number equal to one is approached, it is shown that ideal kinetic gas theory and continuous squeeze film theory converge yielding a simplified stiffness estimate under the resonant response under reduced pressure. These analytical results are used to predict the performance gains due to the nonlinear, frequency dependent total stiffness of the sensor during non-resonant operation.
Closed Loop CNC Manufacturing: Connecting the CNC to the Enterprise
Authors: Venkatesh S. , Morihara R. , Michaloski J. , Proctor F.
Published: May 2009

Closed Loop manufacturing describes the use of feedback from a Computer Numerical Control (CNC) to the Enterprise Resource Planning (ERP) to help in business operations. Although conceptually simple, many obstacles make CNC-ERP connectivity difficult — incompatibilities of various generations of systems supplied by multiple vendors, differing personnel mindsets and objectives, and outright complexity of ERP. A long journey starts with a single step, and this paper describes a successful pilot project that detected scrap on a CNC during production of the Boeing 737 Leading Edge panels and then automatically entered a scrap reorder into the ERP Supply Chain Management (SCM) Reorder System. The pilot leveraged three major technologies, including open-architecture CNC, OLE for Process Control (OPC) integration technology, and supply chain Web Services. Overall, the pilot project successfully established that integration of CNC into SCM can be straightforward as we automated 90% of one manual step within the scrap Supply Chain Reorder process to impart a leaner manufacturing operation.
Imbalance Vibration Suppression of Supercritical Shafts With Automatic Balancing Devices
Authors: DeSmidt Hans
Published: May 2009

This research explores the use of automatic balancing devices (autobalancers) for imbalance suppression of flexible shafts operating at supercritical speeds. Essentially, autobalancers are passive devices consisting of several balls free to roll within an oil-filled circular track mounted on a rotor or shaft to be balanced. At certain speeds, the stable equilibrium positions of the balls is such that they reduce or cancel the rotor imbalance. This “automatic balancing” phenomena occurs as a result of the non-linear dynamic interaction between the balancer balls and the rotor transverse vibrations. Thus, autobalancer devices can passively compensate for unknown imbalance without the need for a control system and naturally adjust for gradually changing imbalance conditions. Single-plane autobalancers are widely utilized for imbalance correction of computer hard-disk drives and CD-ROM drives as well as for balancing machine tools. While autobalancers can effectively compensate for imbalance of planar disk-type systems and rigid rotors, the use of autobalancing devices on flexible shafts has not been fully considered. This study explores the dynamics and stability of an imbalanced flexible shaft-disk system equipped with a dual ball autobalancer by solving a coupled set of nonlinear equations to determine the fixed-point equilibrium conditions in rotating coordinates. Stability is assessed via eigenvalue analysis of a perturbed system about each equilibrium configuration. It is determined that regions of stable automatic balancing occur at supercritical shaft speeds between each flexible mode. Additionally, the effects of bearing stiffness, autobalancer/imbalance-plane axial offset distance, and relative ball-track viscous damping are each explored. This investigation yields valuable analysis methods and insights for the application of automatic balancing devices to flexible shaft and rotor systems operating at supercritical speeds.
Numerical Geometry of the Coupler Motion of a Planar 4R Closed Kinematic Chain
Authors: Trujillo Carlos A. , Ge Q. J.
Published: May 2009

This paper studies the problem of analyzing the motion of the coupler link of a planar 4R closed kinematic chain from the viewpoint of constrained motion interpolation. The kinematics of the planar 4R chain is formulated using planar quaternions. The four-point interpolatory subdivision scheme for curves in the field of Computer Aided Geometric Design (CAGD) is extended to planar quaternions for the generation of an inbetween candidate position of the coupler link from a given set of four key positions. The candidate position is then checked and modified according to the kinematic constraints of the planar 4R chain. The resulting new inbetween position that satisfies the kinematic constraints is then inserted into the given set of key positions. In the early stage of this refinement process, each new inbetween position must be made to satisfy the 4R kinematic constraints exactly to ensure the correct motion. When there is sufficient number of coupler positions, one can use the unconstrained four-point interpolatory scheme to generate the inbetween positions to allow for fast animation of the coupler motion.
Structural Design Trade-Offs for MEMS Vibratory Rate Gyroscopes With 2-DOF Sense Modes
Authors: Schofield Adam R. , Trusov Alexander A. , Shkel Andrei M.
Published: May 2009

Our previous work demonstrated the advantages of MEMS vibratory gyroscopes with 1 degree of freedom (DOF) drive and 2-DOF sense modes which were shown to be robust to temperature drifts. These devices were designed with frequencies below 1 kHz; many applications, however, require gyroscopes with operational frequencies above 1 kHz for the rejection of ambient vibrations. This paper discusses the design trade-offs associated with increasing the frequency of the 3-DOF gyroscope design concept. Lumped parameter models were used to simulate the effects of frequency increases on the device, focusing on the 2-DOF sense mode. The simulations showed that the sense mode peak spacing increases with frequency which ultimately causes a decrease in sensitivity. A series of 3-DOF gyroscope prototypes with diferent operational frequencies ranging from 0.7 kHz to 5.1 kHz were designed, fabricated, and characterized.
Vibration Analysis of Axially Loaded Euler-Bernoulli Beams With Guided Mass
Authors: Hassanpour P. A. , Cleghorn W. L. , Esmailzadeh E. , Mills J. K.
Published: May 2009

Vibration analysis of an axially loaded beam with an attached mass, as the model of many systems in the macro and micro scales, has been carried out. The axially loaded beam is assumed as an Euler-Bernoulli one with clamped-clamped boundary conditions that carries a lumped mass, which is attached to it at an arbitrary position. The attached lumped mass is guided to only move in the transverse direction. It has been shown that the tensile axial force will increase the natural frequencies of the beam as well as the amplitude of oscillation of the comb-drive at the first mode of vibration. Depending on the position of guided mass, the natural frequencies may either increase or decrease when compared with those found for the same clamped-clamped beam with no attached mass. The natural frequencies and the corresponding natural mode shapes are presented.
A Cost Model for the Metal Inert Gas (MIG) Welding Process
Authors: Tipaji Pradeep Kumar , Allada Venkat , Mishra Rajiv
Published: May 2009

A cost model is an important tool for product design and material selection. An efficient and effective cost estimation tool is necessary for early design evaluations. In this paper, a cost estimation model is presented that estimates the production cost for metal inert gas (MIG) welded joints. This model determines the cost incurred in fabricating each joint with a detailed explanation of each cost component / driver. Each cost component has been closely analyzed and the major cost components have been included in the cost model. We used this cost model to predict the cost of the forty two different joints joined using MIG welding technique. The results predicted by the MIG welding cost model have been compared to that quoted by an expert welder. Initial results show that the cost model and the expert cost estimates follow a similar general trend. Further study is needed to refine the MIG cost model.
Design for Disassembly With High-Stiffness, Heat-Reversible Locator-Snap Systems
Authors: Shalaby Mohammed , Saitou Kazohiro
Published: May 2009

Recent legislative and social pressures have driven manufacturers to consider effective part reuse and material recycling at the end of product life at the design stage. One of the key considerations is to design and use joints that can disengage with minimum labor, part damage, and material contamination. This paper presents a unified method to design high-stiffness reversible locator-snap system that can disengage non-destructively with localized heat, and its application to external product enclosures of electrical appliances. The design problem is posed as an optimization problem to find the orientations, numbers, and locations of locators and snaps, and the number, locations and sizes of heating areas, which realize the release of snaps with minimum heating area and maximum stiffness, while satisfying any motion and structural requirements. Screw Theory is utilized to pre-calculate a set of feasible orientations of locators and snaps, which are examined during optimization. The optimization problem is solved using Multi Objective Genetic Algorithm (MOGA) coupled with structural and thermal FEA. The method is applied to two-piece enclosure of a DVD player with a T-shaped mating line. The resulting Pareto-optimal solutions exhibit alternative designs with different trade-offs between structural stiffness during snap engagement and area of heating for snap disengagement. Some results require the heating of two areas at the same time, demonstrating the idea of a lock-n-key.