Mechanical Engineering Commons^™

Development Of An Advanced Stem Heating Model, Joshua L. Jones

Theses and Dissertations

A new one-dimensional heat conduction model for predicting stem heating during fires is presented. The model makes use of moisture and temperature dependent thermal properties for bark and wood. Also, the thermal aspects of the processes of bark swelling, desiccation, and devolatilization are treated in an approximate fashion. Simulation with a surface flux boundary condition requires that these phenomena be accounted for. Previous models have used temperature-time boundary conditions, which prevents them from being directly coupled to fire behavior models. This model uses a flux-time profile for its boundary condition, making it possible to eventually couple it to fire behavior …

A Self-Retracting Fully Compliant Bistable Micromechanism, Nathan D. Masters, Larry L. Howell

Faculty Publications

A new class of fully compliant bistable mechanisms with the added benefit of integrated self-retraction has been developed (hereafter identified as Self-Retracting Fully compliant Bistable Mechanism or SRFBM). A technique using tensural pivots to manage compressive loading in compliant mechanisms is introduced and implemented in the SRFBM. The elimination of traditional kinematic joints and their associated clearance allows a total displacement between stable positions of 8.5 m, and the mechanism size is less than 300 m square when using 2.0 m minimum line widths. Maximum actuation force is approximately 500 N. The SRFBM's small linear displacement and reasonable actuation force …

Identification Of Macro- And Micro-Compliant Mechanism Configurations Resulting In Bistable Behavior, Brian D. Jensen

Theses and Dissertations

The purpose of this research is to identify the configurations of several mechanism classes which result in bistable behavior. Bistable mechanisms have use in many applications, such as switches, clasps, closures, hinges, and so on. A powerful method for the design of such mechanisms would allow the realization of working designs much more easily than has been possible in the past. A method for the design of bistable mechanisms is especially needed for micro-electro-mechanical systems (MEMS) because fabrication and material constraints often prevent the use of simple, well-known bistable mechanism configurations. In addition, this knowledge allows designers to take advantage …

A Self-Retracting Fully-Compliant Bistable Micromechanism, Nathan D. Masters

Theses and Dissertations

The purpose of this research is to present a class of Self-Retracting Fully-compliant Bistable Micromechanisms (SRFBM). Fully-compliant mechanisms are needed to overcome the inherent limitations of microfabricated pin joints, especially in bistable mechanisms. The elimination of the clearances associated with pin joints will allow more efficient bistable mechanisms with smaller travel. Small travel, in a linear path facilitates integration with efficient on-chip actuators. Tensural pivots are developed and used to deal with the compressive loading to which the mechanism is subject. SRFBM are modeled using the Pseudo-Rigid-Body Model and finite element analysis. Suitable configurations of the SRFBM concept have been …

Development Of In-Plane Compliant Bistable Microrelays, Troy Alan Gomm

Theses and Dissertations

Bistable microrelays have many possible applications and have the potential to reduce the size, weight, power consumption, and cost of products in which they are used. This research outlines the current state of microrelays, presents three new compliant bistable micromechanisms, and characterizes their performance as microrelays. The characterization includes a treatment of a new force-tester, a preliminary contact resistance study, contact-force measurements, switching time measurements, insertion loss, AC isolation, breakdown voltage, and DC isolation. This document also includes recommendations for further research.

Cooperative Path Planning For Timing Critical Missions, Timothy W. Mclain, Randal W. Beard

Faculty Publications

This paper presents a cooperative path planning approach for teams of vehicles operating under timing constraints. A cooperative control approach based on coordination variables and coordination functions is introduced and applied to cooperative timing problems. Three types of timing constraints are considered: simultaneous arrival, tight sequencing, and loose sequencing. Simulation results demonstrating the approach are presented.

Designing Active Smart Features To Provide Nesting Forces In Exactly Constrained Assemblies, Eric Pearce

Theses and Dissertations

Ever since the design and manufacture of products moved from the craftsman era where individual craftsman designed and manufactured the entire product, to the mass production era, where skilled laborers were crafting interchangeable parts or in some cases single features on interchangeable parts, variation in assemblies has been a major concern to designers, manufacturers, and in a more subtle way, customers. Variation, in the end, affects quality, performance and the cost of products. One particular type of design that is particularly robust to variation is an exactly constrained design.

Several researchers have recently explored the topic of exact constraint design. …

Microstructure Sensitive Design Of An Orthotropic Plate Subjected To Tensile Load, Brent L. Adams, Mark Lyons, Joshua R. Houskamp, Surya R. Kalidindi

Faculty Publications

Financial support for this work was provided by the Army Research Office, Proposal No. 42566-MS, Dr. David Stepp, Program Director and Army Research Lab, Dr. Scott Schoenfeld, Point of Contact. Microstructure Sensitive Design (MSD) is a newly developed mathematical framework that facilitates rigorous solutions to inverse problems in microstructure design of materials. In this paper, this methodology is applied to an orthotropic thin plate containing a circular hole subjected to an in-plane uniaxial tensile load. The primary design objective is to maximize the load carrying capacity of the plate while avoiding plastic deformation in the plate. Making use of the …

The Pseudo-Rigid-Body Model For Dynamic Predictions Of Macro And Micro Compliant Mechanisms, Scott Marvin Lyon

Theses and Dissertations

This work discusses the dynamic predictions of compliant mechanisms using the Pseudo-Rigid-Body model (PRBM). In order to improve the number of mechanisms that can be modeled, this research develops and identifies several key concepts in the behavior of beam segments where both ends are fixed to a rigid body (fixed-fixed flexible segments). A model is presented, and several examples are discussed. The dynamic behavior of several compliant segments is predicted using the PRBM and the results are compared to finite element analysis and experimental results. Details are presented as to the transient behavior of a typical uniform rectangular cross section …

Reconstruction Of The Temperature Profile Along A Blackbody Optical Fiber Thermometer, David Gary Barker

Theses and Dissertations

A blackbody optical fiber thermometer consists of an optical fiber whose sensing tip is given a metallic coating. The sensing tip of the fiber forms an isothermal cavity, and the emission from this cavity is approximately equal to the emission from a blackbody. Standard two-color optical fiber thermometry involves measuring the spectral intensity at the end of the fiber at two wavelengths. The temperature at the sensing tip of the fiber can then be inferred using Planck's law and the ratio of the spectral intensities. If, however, the length of the optical fiber is exposed to elevated temperatures, erroneous temperature …

An Approach To Concept Development For Compliant Mechanisms Possessing High Coefficients Of Restitution, Brandon H. Woolley

Theses and Dissertations

The design of structures and mechanisms subject to impact loading has historically involved designing in such a way as to minimize damage induced by the impact. This has historically been accomplished by absorbing and dissipating the energy of the impact. However, in some applications it is desirable to harness the energy and return it to the impacting object to maximize the coefficient of restitution (COR), resulting in large rebound velocities. The use of traditional rigid-body mechanisms to achieve high-COR mechanisms is limited by issues of friction, durability, poor strain-energy distribution and others. Compliant mechanisms do not possess the same limitations …

On-Chip Actuation Of Compliant Bistable Micro-Mechanisms, Michael S. Baker

Theses and Dissertations

Two compliant bistable micro-mechanisms have been developed which can be switched in either direction using on-chip thermal actuation. The energy storage and bistable behavior of the mechanisms are achieved through the elastic deflection of compliant segments. The pseudo-rigid-body model was used for the compliant mechanism design, and for analysis of the large-deflection flexible segments. To achieve on-chip actuation, the mechanism designs were optimized to reduce their required rotation, allow them to be switched using linear-motion thermal actuators. The modeling theory and analysis are presented for several design iterations. Each iteration was successfully fabricated and tested using either the MUMPs or …

Thermal Microactuators For Microelectromechanical Systems (Mems), Rebecca Cragun

Theses and Dissertations

Microactuators are needed to convert energy into mechanical work at the microscale. Thermal microactuators can be used to produce this needed mechanical work. The purpose of this research was to design, fabricate, and test thermal microactuators for use at the microscale in microelectromechanical systems (MEMS). The microactuators developed were tested to determine the magnitude of their deflection and estimate their force. Five groups of thermal microactuators were designed and tested. All of the groups used the geometrically constrained expansion of various segments to produce their deflection. The first group, Thermal Expansion Devices (TEDs), produced a rotational displacement and had deflections …

An Investigation Of Compliant Over-Running Ratchet And Pawl Clutches, Gregory Mark Roach

Theses and Dissertations

This thesis proposes that compliant mechanism theory can be used to design over-running ratchet and pawl clutches with reduced part count, lower assembly and manufacturing time while maintaining functionality. An extension of the theory to the micro regime is also briefly addressed. The results of the research show that the ratchet and pawl type of over-running clutch is a good choice for the use of compliance, and the clutch pawls should be loaded in compression to get the largest amount of output torque. It was found that com-pliant mechanism theory can be used to design ratchet and pawl clutches with …

Advances In Experimental Method And Analysis For Estimation Of Geometrically-Necessary Dislocations, Brent L. Adams, Bassem S. El-Dasher, Anthony D. Rollett

Faculty Publications

The authors wish to thank The Alcoa Technical Research Center for supplying the specimens and performing the compression tests. This work was supported by the MRSEC program of the National Science Foundation under DMR-0079996 as well as Lawrence Livermore Laboratory DOE/DoD Joint Program. An behavior of grain boundaries of the polycrystalline materials over a wide range of length scales during plastic deformation is considered. Electron backscattering diffraction and orientation imaging microscopy provide automated scanning measurements of the lattice orientation near grain boundaries. These methods are useful to set the necessary length scales. The data are presented for directionally-solidified pure Al …

A Joint Trajectory Generator For Motion Recovery, Edward Red, Wei Li

Faculty Publications

This paper describes an adaptive S-curve used to recover a tool path upon a system crash in the Windows operating system (OS). For a mechanism such as a robot or machine tool, the joint values, being delivered as setpoints to the servo-controller, are dynamically recorded by the real-time operating system also residing on the computer. The real-time OS can control the abort and record pertinent motion data after Windows OS crash.

Time Aliasing Methods Of Spectrum Estimation, Jason F. Dahl

Theses and Dissertations

Time aliasing methods of spectrum estimation alter the time representation of a signal for the purpose of improving its frequency domain representation. Time aliasing allows characteristics of longer time window functions to be used with shorter DFT length. Windows designed specifically for use with time aliasing have improved properties compared to conventional windows. Many previous uses of time aliasing, including overlap-and-add methods of digital filtering, have focused on the elimination of time aliasing effects in the frequency domain in order to improve the representation of reconstructed signals in the time domain and have not addressed the issues associated with spectrum …

Tools And Metrics For Evaluating Modular Product Concepts Based On Strategic Objectives, Matthew Bailey Strong

Theses and Dissertations

The design of modular products has recently become the focus of significant research in the area of design theory and methodology. This focus is the result of increased awareness of the potential power of modularity to achieve certain product objectives. However, there continues to be a gap between the results of academic research and industrial application. The refinement, consolidation, and extension of this academic research would help design teams who are charged with developing modular products to use these academic findings in real world, industrial applications. The research presented in this document focuses on developing design tools, based on past …

On-Chip Actuation Of An In-Plane Compliant Bistable Micromechanism, Michael S. Baker, Larry L. Howell

Faculty Publications

A compliant bistable micromechanism has been developed which can be switched in either direction using on-chip thermal actuation. The energy storage and bistable behavior of the mechanism is achieved through the elastic deflection of compliant segments. The Pseudo-Rigid-Body Model was used for the compliant mechanism design, and for analysis of the large deflection flexible segments. To achieve on-chip actuation, the mechanism design was optimized to allow it to be switched using linear motion thermal actuators. The modeling theory and analysis are presented for three design iterations, with two iterations fabricated in the MUMP's process and the third in the SUMMiT …

Development And Design Of Constant-Force Mechanisms, Brent Lewis Weight

Theses and Dissertations

This thesis adds to the knowledge base of constant-force mechanisms (CFMs). It begins by reviewing past work done in the area of CFMs and then develops new nondimensionalized parameters that are used to simplify the calculations required to design a CFM. Comparison techniques are then developed that utilize these non-dimensionalized parameters to compare mechanisms based on stiffnesses, percent constant-force, actual lengths, normal displacements, and feasible design orientations. These comparison techniques are then combined with optimization to define new mechanisms with improved performance and range of capabilities. This thesis also outlines a design process, methods to identify mechanisms that are suitable …

Mapping The Mesoscale Interface Structure In Polycrystalline Materials, Brent L. Adams, C. L. Bauer, D. Casasent, A. Morawiec, S. Ozdemir, A. Talukder, Chialin T. Wu

Faculty Publications

This work was supported primarily by the MRSEC Program of the National Science Foundation under Award Numbers DMR-9632556 and DMR-0079996. A new experimental approach to the quantitative characterization of polycrystalline microstructure by scanning electron microscopy is described. Combining automated electron backscattering diffraction with conventional scanning contrast imaging and with calibrated serial sectioning, the new method (Mesoscale Interface Mapping System, MIMS) recovers precision estimates of the 3-dimensional idealized aggregate function G(x). This function embodies a description of lattice phase and orientation (limiting resolution ~ 1 degree) at each point x (limiting spatial resolution ~ 100 nanometers), and therefore contains a complete …

Modeling The Thermal Behavior Of A Surface-Micromachined Linear-Displacement Thermomechanical Microactuator, Christian D. Lott, Timothy W. Mclain, John N. Harb, Larry L. Howell

Faculty Publications

Thermomechanical microactuators possess a number of desirable attributes including ease of fabrication and large force and displacement capabilities relative to other types of microactuators. These advantages provide motivation for improving thermomechanical microactuator designs that are more energy efficient and thus better suited for low-power applications. To this end, this paper describes the development and experimental validation of a finite-difference thermal model of a thermomechanical in-plane microactuator (TIM). Comparisons between the model and experimental results demonstrate the importance of including the temperature dependence of several parameters in the model. Strategies for reducing the power and energy requirements of the TIM were …

Viewpoint: Experimental Recovery Of Geometrically Necessary Dislocation Density In Polycrystals, Brent L. Adams, Bassem S. El-Dasher, Anthony D. Rollett

Faculty Publications

The authors wish to thank The Alcoa Technical Research Center for supplying the specimens and performing the compression tests. This work was supported primarily by the MRSEC program of the National Science Foundation under DMR-0079996. Application of electron backscattering diffraction methods to recover estimates of the geometrically necessary dislocation density is described. The limitations of the method arising from the opacity of crystalline materials and the spatial and angular resolution limits are discussed.

Experimental Demonstration Of Multiple Robot Cooperative Target Intercept, Timothy W. Mclain, Randal W. Beard, Jed M. Kelsey

Faculty Publications

This paper presents experimental results for the simultaneous intercept of preassigned targets by a team of mobile robots. The robots are programmed to mimic the dynamic behavior of unmanned air vehicles in constant-altitude flight. In proceeding to their targets, robots must avoid both known static threats and pop-up threats. An overview of the cooperative control strategy followed is given, as well as a description of the robot hardware and software used. Experimental results demonstrating simultaneous intercept of targets by the robot team are presented.

Autonomous Hierarchical Control Of Multiple Unmanned Combat Air Vehicles (Ucavs), Timothy Mclain, Randal W. Beard, Sai-Ming Li, Jovan D. Boskovic, Sanjeev Seereeram, Ravi Prasanth, Jayesh Amin, Raman K. Mehra

Faculty Publications

In this paper we present a hierarchical control scheme that enables multiple UCAVs to achieve demanding missions in hostile environments autonomously. The objective is to use a swarm of UCAVs for a SEAD type mission: fly the UCAVs in a formation to an enemy territory populated with different kinds of threats, collect enemy information or destroy certain targets, and return to the base, all without human intervention. The scheme is an integration of four distinct components, including: (1) high level Voronoi diagram based path planner to avoid static threats; (2) low level path planner to avoid popup threats; (3) differential …

Elasticity In Microstructure Sensitive Design Through The Use Of Hill Bounds, Benjamin L. Henrie

Theses and Dissertations

In engineering, materials are often assumed to be homogeneous and isotropic; in actuality, material properties do change with sample direction and location. This variation is due to the anisotropy of the individual grains and their spatial distribution in the material. Currently there is a lack of communication between the design engineer, material scientist, and processor for solving multi-objective/constrained designs. If communication existed between these groups then materials could be designed for applications, instead of the reverse. Microstructure sensitive design introduces a common language, a spectral representation, where both design properties and microstructures are expressed.

Using Hill bounds, effective elastic properties …

In-Plane Linear-Displacement Bistable Microrelay, Troy Gomm, Larry L. Howell, Richard H. Selfridge

Faculty Publications

This paper investigates the Linear Displacement Bistable Mechanism (LDBM) for use in microrelays. The LDBM, thermal actuators, and contacts are integrated to demonstrate a relay design. The performance of the relay is characterized using relay performance metrics, including size (1.92 mm2), contact force (23.4 μN), switching time (340 μs), breakdown voltage (> 475 V), and isolation (> 235 V). The actuation voltage and current are 11 V and 85 mA, respectively. AC characteristics, including contact-to-contact crosstalk and AC isolation are also measured. The testing results demonstrate that it is feasible to use the LDBM as a microrelay and that it …

Surface Micromachined Force Gauges: Uncertainty And Reliability, Jonathan W. Wittwer, Troy Gomm, Larry L. Howell

Faculty Publications

Surface micromachining of micro-electro-mechanical systems (MEMS), like all other fabrication processes, has inherent variation that leads to uncertain material and dimensional parameters. By considering the effects of these variations during the design of micro force gauges, the gauge uncertainty and reliability can be estimated. Without means of calibrating micro gauges, these effects are often significant when compared to experimental repeatability. The general force gauge model described in this paper can be used to measure a wide range of forces, and simple design changes can lead to improved accuracy in measurement. A method of probabilistic design is described that is not …

Spectral Integration Of Microstructure And Design, Brent L. Adams, B. Henrie, M. Lyon, H. Garmestani, Surya R. Kalidindi

Faculty Publications

Support of the Army Research Office is greatly appreciated. Mechanical design can be conducted in a framework where consideration of microstructure as a continuous design variable is facilitated by the use of a Fourier space. Selection of the mechanical framework for the problem (e.g., mechanical constitutive model and homogenization relations) dictates the dimensionality of the pertinent microstructure representation. Microstructure is comprised of basic elements that belong to the local state space. Local state includes crystallographic phase and orientation, and other parameters such as composition. The local state space is transformed into an isomorphic set in Fourier space. The universe of …

Ortho-Planar Linear-Motion Springs, John J. Parise, Larry L. Howell, Spencer P. Magleby

Faculty Publications

This paper presents an ortho-planar spring design that operates by raising or lowering its platform relative to the base with no rotation. The compact nature of the design, and its non-rotating motion, eliminates the problem of rotation against adjoining surfaces and is less sensitive to variation in assemblies than many current compact springs. Nomenclature is presented to identify different configurations, mathematical equations are provided that accurately model the force-defection relationships, and a pneumatic valve positioner application is demonstrated.