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Dissertations / Theses on the topic 'Contact engineering'
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1
Li, Sheng. "Lubrication And Contact Fatigue Models For Roller And Gear Contacts." The Ohio State University, 2009. http://rave.ohiolink.edu/etdc/view?acc_num=osu1234822355.
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Alshahrany, Shaya. "Rolling contact fatigue in heavily loaded gear transmission contacts." Thesis, Cardiff University, 2015. http://orca.cf.ac.uk/90422/.
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This thesis examines the influence of asperities such as found on the teeth of gears and discs, and failure mechanisms associated with rough surface Elastohydrodynamic Lubrication (EHL). The principal outcomes of the research provide a good insight into fatigue life, residual stress effects, damage prediction and surface contact failures. In particular, the study is intended to provide understanding into the residual stress distribution resulting from plastic deformation of surface asperities in the running in process. The residual stress is then added to the asperity elastic stress distribution and examined in detail to see the effects on fatigue damage and fatigue life. So, a theoretical model has been developed to assist design against the residual stress effect and surface contact fatigue, such as micropitting. The technique used in the study starts with developing an elastic plastic model of the rough surface by using the Abaqus Finite Element analysis software package. This is a nonlinear problem and ranges of applied loads have been applied to the as-manufactured surfaces causing the asperity features to experience varying degrees of plastic deformation. The pre and post running roughness profiles are studied in order to assess the level of plastic deformation actually occurring at significant surface asperity features by aligning the pre and post running profiles. This results in a new technique that has helped to identify the level of plastic deformation occurring in the practice, and also to make a comparison with FEA contact analysis for the same asperity features to identify the appropriate residual stress field. The residual stress field associated with the plastic deformation was extracted and evaluated. The extracted residual stress field was transferred to a form that facilitated IV inclusion in stress evaluation code to obtain the stress history for the material subject to loading in an EHL contact. The research carried out considers surface fatigue analysis with and without a residual stress field, so as to establish the influence of asperity plastic deformation on the fatigue properties of the surface. All the work is based on numerical simulation of surface fatigue failure in EHL situations and carried out numerically. The procedure can be applied quickly and gives the opportunity to apply several models and investigate the influence of all the model parameters on material deformation and fatigue life.
3
Webster, Martin Nicholas. "Measurement and contact analysis of engineering surfaces." Thesis, Imperial College London, 1986. http://hdl.handle.net/10044/1/38184.
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Rodriguez, Garcia Alberto. "Shape For Contact." Thesis, Carnegie Mellon University, 2013. http://pqdtopen.proquest.com/#viewpdf?dispub=3575524.
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Given a desired function for an effector, what is its appropriate shape? This thesis addresses the problem of designing the shape of a rigid end effector to perform a given manipulation task. It presents three main contributions: First, it describes the contact kinematics of an effector as the product of both its shape and its motion, and assumes a fixed motion model to explore the role of shape in satisfying a certain manipulation task. Second, it formulates that manipulation task as a set of constraints on the geometry of contact between the effector and the world. Third, it develops tools to transform those contact constraints into an effector shape for general 1-DOF planar mechanisms and general 1-DOF spatial mechanisms, and discusses the generalization to mechanisms with more than one degree of freedom.
We describe the case studies of designing grippers with invariant grasp geometry, grippers with improved grasp stability, and grippers with extended grasp versatility. We further showcase the techniques with the design of the fingers of the MLab hand, a three-fingered gripper actuated with a single motor, capable of exerting any combination of geometrically correct enveloping or fingertip grasps of spherical, cylindrical, and prismatic objects of varying size.
5
McGonnell, John. "Contact Point Detection and Contact History Tracking in Biomimetic Whiskers." University of Akron / OhioLINK, 2011. http://rave.ohiolink.edu/etdc/view?acc_num=akron1306960264.
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Eberman, Brian Scott. "Contact Sensing: A Sequential Decision Approach to Sensing Manipulation Contact." Thesis, Massachusetts Institute of Technology, 1995. http://hdl.handle.net/1721.1/7061.
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This paper describes a new statistical, model-based approach to building a contact state observer. The observer uses measurements of the contact force and position, and prior information about the task encoded in a graph, to determine the current location of the robot in the task configuration space. Each node represents what the measurements will look like in a small region of configuration space by storing a predictive, statistical, measurement model. This approach assumes that the measurements are statistically block independent conditioned on knowledge of the model, which is a fairly good model of the actual process. Arcs in the graph represent possible transitions between models. Beam Viterbi search is used to match measurement history against possible paths through the model graph in order to estimate the most likely path for the robot. The resulting approach provides a new decision process that can be use as an observer for event driven manipulation programming. The decision procedure is significantly more robust than simple threshold decisions because the measurement history is used to make decisions. The approach can be used to enhance the capabilities of autonomous assembly machines and in quality control applications.
7
Schmidt, Aaron Jerome 1979. "Contact thermal lithography." Thesis, Massachusetts Institute of Technology, 2004. http://hdl.handle.net/1721.1/27116.
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Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2004.Includes bibliographical references (p. 65-67).
Contact thermal lithography is a method for fabricating microscale patterns using heat transfer. In contrast to photolithography, where the minimum achievable feature size is proportional to the wavelength of light used in the exposure process, thermal lithography is limited by a thermal diffusion length scale and the geometry of the situation. In this thesis the basic principles of thermal lithography are presented. A traditional chrome-glass photomask is brought into contact with a wafer coated with a thermally sensitive polymer. The mask-wafer combination is flashed briefly with high intensity light, causing the chrome features heat up and conduct heat locally to the polymer, transferring a pattern. Analytic and finite element models are presented to analyze the heating process and select appropriate geometries and heating times. In addition, an experimental version of a contact thermal lithography system has been constructed and tested. Early results from this system are presented, along with plans for future development.
by Aaron Jerome Schmidt.
S.M.
8
Rasheed, Rawand Muzafar. "Non-Contact Distillation." PDXScholar, 2019. https://pdxscholar.library.pdx.edu/open_access_etds/5275.
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Leidenfrost phenomenon has been studied extensively for its role in applications ranging from nuclear reactor cooling, to metals manufacturing, combustion, and other fields. Herein, Leidenfrost phenomenon is pursued towards non-contact distillation processes with hopes of reducing or even eliminating contaminant fouling. In particular, the microgravity environment of a drop tower is exploited to demonstrate the facility with which droplets achieve and sustain the Leidenfrost state. Dynamic Leidenfrost impacts in microgravity are presented for impacts on hydrophilic and superhydrophobic planar substrates, macro-pillar arrays, confined passageways, and others. Nearly ideal elastic non-contact impacts and droplet oscillation modes are observed. Dynamic Leidenfrost impacts in microgravity for uniquely low velocity impacts are investigated analytically and experimentally. We find Leidenfrost vapor layer thicknesses on the order of millimeters for a 1 mL droplet of water with impact velocity 1 mm/s - a 100-fold increase relative to terrestrial vapor layers. Such results are supported by preliminary experimental observations. Further droplet distillation experiments are conducted in a terrestrial gravity environment using a heated tilted rotating hemi-circular track. Droplet evaporation rates and lifetimes are tabulated for the sliding/rolling drops at varying angular velocities and tilt angles. An analytical model for the evaporation rate of a rolling Leidenfrost droplet is developed and compared to the experimental results with good agreement. The empirical and analytical results serve as key design tools for sizing a prototypical non-contact distillation system for terrestrial desalinization or spacecraft water recycling.
9
Qi, Hongsheng. "A contact length model for grinding wheel-workpiece contact." Thesis, Liverpool John Moores University, 1995. http://researchonline.ljmu.ac.uk/5134/.
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10
Chung, Raymond Y. M. "Non-contact surface inspection." Thesis, Liverpool John Moores University, 1992. http://researchonline.ljmu.ac.uk/4944/.
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This thesis describes the development of a non-contact inspection system, used in providing a comparative method for gauging a surface. The purpose of this system is not to measure the 3-D shape of a part. The volume difference between the part to be inspected and a master, is merely part of the decision criteria, where if this difference exceeds a certain threshold value, then the component under inspection is deemed to have failed. The technique involves a combination of fringe projection and image subtraction. The system comprises two sub-systems, a low-cost pc based image processor and a white light, square wave fringe projector. A camera provides the interface between the two sub-systems. Validation of the technique is provided by the simulation of mathematically generated defects, and by means of experiments on samples of known volume. In addition, the effect of the variation of particular set-up constants, on the technique's accuracy are also illustrated. The problems and subsequent solutions associated with the practical inspection, result in an improved method of gauging. The system provides reliable results (within 4%) for surfaces of nominally similar form and reflectivity. Additional results (within 10%) are illustrated, where the images and fringe patterns are mis-aligned. As a result of a selective filtering scheme, precise relocation of the surfaces (used in the comparison) is unnecessary. This is conditional upon the fringes on each surface, being identical in orientation with each other. Further consideration of the technique (within an error analysis) indicates the necessity of an accurate determination of all the set-up constants. The error results cannot be taken too literally, since the worst case values are presented. However, the trends of the effects of these errors are useful. An adapted alternative method is also described that may prove to be (in certain applications) an interesting real-time solution.
11
King, Christopher David S. M. Massachusetts Institute of Technology. "A coupled contact-mechanics computational model for studying deformable human-artifact contact." Thesis, Massachusetts Institute of Technology, 2018. http://hdl.handle.net/1721.1/118672.
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Thesis: S.M., Massachusetts Institute of Technology, Department of Mechanical Engineering, 2018.This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.
Cataloged from student-submitted PDF version of thesis.
Includes bibliographical references (pages 199-205).
Gas-pressurized spacesuits are necessary for human spaceflight, most notably for extravehicular activity (EVA). Legacy EVA suits have been primarily rigid, and operation in such suits can result in significant metabolic expense, or even injury, for the wearer. To reduce these effects, modern spacesuits are more flexible, through the incorporation of more softgood materials and specially designed joint interfaces such as hip bearings. However, modeling the effects of human-suit interaction for these softgood materials is challenging due to the highly deformable nature of the suit coupled with the deformable nature of the human. To enable improved analysis and design of modern spacesuits, a computational model that can resolve the structural deformations of the suit and human resulting from contact interactions is developed. This thesis details the development and validation of a coupled contact-mechanics solver architecture for use in studying the effects of human-artifact interaction, particularly with respect to pressurized softgood exosuit design. To resolve contact and structural mechanics interactions for a deformable human and artifact, a finite element model is developed. First, the SUMMIT computational framework is employed for resolving the structural deformations of the system, and is coupled to an explicit contact mechanics scheme. The explicit contact scheme is implemented so as to resolve both external- and self-contact problems. Next, the model architecture is integrated to enable parallelization of both the structural deformation and contact systems, and computational scaling investigated. A computational trade study is performed to benchmark the coupled contact-mechanics method against a simpler rigid body model employing a penalty method. Following this, the model is validated against experimental data for various artifact contact problems. The explicit coupled contact-mechanics model is found to effectively capture contact interactions of the experimental data, with improved fidelity for deformable contact interactions. With careful tuning of the system properties, the coupled contact-mechanics model enables an architecture for an integrated human-suit analysis and design model.
by Christopher David King.
S.M.
12
JOSHI, PRASAD RAMAN. "AN ELASTIC CONTACT THEORY FOR MODELING VIBRATION TRANSMISSIBILITY THROUGH ROLLING CONTACT BEARINGS." University of Cincinnati / OhioLINK, 2004. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1092882073.
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Poopat, Bovornchok. "Analysis and optimization of contact and non-contact hot plate welding of thermoplastics /." The Ohio State University, 1999. http://rave.ohiolink.edu/etdc/view?acc_num=osu1488192119262064.
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Dai, Hongkai Ph D. Massachusetts Institute of Technology. "Robust multi-contact dynamical motion planning using contact wrench set." Thesis, Massachusetts Institute of Technology, 2016. http://hdl.handle.net/1721.1/107328.
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Thesis: Ph. D., Massachusetts Institute of Technology, Department of Electrical Engineering and Computer Science, 2016.Cataloged from PDF version of thesis.
Includes bibliographical references (pages 127-142).
In this thesis, we seek to plan a robust motion for robot with multiple non-coplanar contact on the environment. When the robot interacts with the environment through contact, it relies on the contact forces to generate the desired acceleration. The contact forces have to satisfy some physical constraints, such as lying within the friction cones. These constraints limit the robot acceleration. The robustness of the motion can be measured as the margin to the boundary of these constraints. By planning motion with a large preserved margin, we enable the robot to withstand large disturbance in the online motion execution. In this thesis, we adopt the notion of contact wrench set to approximate the constraints on the robot dynamics. The margin of such set measures the capability of the motion to perfectly resist external wrench disturbance. We plan robust motion to increase this contact wrench set margin. We present two planners to improve this robustness metric. For the first simple-model planner, we pre-specify the contact locations, and it generates a Center of Mass trajectory and an angular momentum trajectory, by solving a convex optimization problem. We show that this planner has similar output as the widely-used walking pattern generator that relies on Zero Moment Point (ZMP) on flat ground. Moreover, it can plan feasible motion on uneven ground with friction cone limits, while the ZMP planner fails. For the second planner with robot whole-body model, we will search for the contact location and the robot whole-body motion simultaneously. We show that we can improve the robustness metric through certain non-convex optimization techniques. We apply our planner to three problems: 1) force closure grasp optimization, 2) static posture optimization, 3) trajectory optimization, achieving improved performance for all of them.
by Hongkai Dai.
Ph. D.
15
Manuelli, Lucas Ph D. Massachusetts Institute of Technology. "Localizing external contact using proprioceptive sensors : the contact particle filter." Thesis, Massachusetts Institute of Technology, 2018. http://hdl.handle.net/1721.1/115739.
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Thesis: S.M., Massachusetts Institute of Technology, Department of Electrical Engineering and Computer Science, 2018.Cataloged from PDF version of thesis.
Includes bibliographical references (pages 61-65).
In order for robots to interact safely and intelligently with their environment they must be able to reliably estimate and localize external contacts. This paper introduces the CPF, the Contact Particle Filter, which is a general algorithm for detecting and localizing external contacts on rigid body robots without the need for external sensing. The CPF finds external contact points that best explain the observed external joint torque, and returns sensible estimates even when the external torque measurement is corrupted with noise. We demonstrate the capability of the CPF in multiple scenarios. We show how it can track multiple external contacts on a simulated Atlas robot, and also perform extensive simulation and hardware experiments on a Kuka iiwa robot arm.
by Lucas Manuelli.
S.M.
16
Pechrach, Kesorn. "Arc root commutation from the contact region in low contact velocity circuit breakers." Thesis, University of Southampton, 2003. https://eprints.soton.ac.uk/46530/.
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Circuit breakers are widely used in commercial and industrial installations for automatically switching off a short circuit current. Arc motion in low voltage (240VAC) high current (103-104 A.) circuit breakers is dominated by arc root mobility. This study provides a vital step in the development of a consistent arc structure and motion in circuit breakers operating at low contact opening velocity. The experimental investigations focus on the influence of the contact material, arc chamber material, contact velocity, power supply polarity, the gap behind the moving contact and the peak short circuit current level on the arc motion. The gas flows and gas composition effects are inspected. This thesis concentrates on the arc commutation at reduced contact opening velocity down to 1 m/s from a moving contact and in particular the point at which the arc root moves off from the contact region To investigate the arc root motion, the Flexible Test Apparatus (FTA) is used to simulate circuit breaker operation. The Arc Imaging System (AIS) is used to record series of the arc motion. New pressure transducers and a spectrometer are used to observe the gas flow and gas composition in the contact region. This data combination provides a new insight into the arc motion. The studies have observed that the gas flow in the region of the moving contact has been shown to affect the arc root mobility. The spectral emission from the arc gases confirms the presence of electronegative species. Experimental results are presented which include the measurements of pressures in the arc chamber, arc spectrum, and arc root motion. The interrelation of gas dynamic and magnetic forces is investigated further by developing relationships between electromagnetic forces and high temperature gas dynamic flows. New semi-empirical modelling is presented in terms of electrical and thermal energy transfer between the arc and the gas flow.
17
Mehta, Prina. "Advanced engineering of contact lens coatings using electrohydrodynamic atomization." Thesis, De Montfort University, 2018. http://hdl.handle.net/2086/17476.
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While the eye presents numerous opportunities for drug delivery (DD); there are many challenges met by conventional methods. Despite the exponential growth in research to overcome these downfalls and achieve sustained and controlled DD, the anatomical characteristics of the eye still pose formulation challenges. The research presented in this thesis utilises Electrohydrodynamic Atomization (EHDA) to engineer novel coatings for ocular contact lenses. EDHA was selected to develop coatings for the delivery of timolol maleate (TM); with the intention of achieving sustained drug release for treatment of glaucoma. The work presented here is a proof-of-concept; showing the versatility of a promising technique by applying it to a DD remit within which EHDA has not yet been fully exploited: Ocular Drug Delivery (ODD). The first step was to identify a suitable polymeric matrix to act as the vehicle/carrier and see the effects of different polymers on the in vitro release of TM and ex vivo TM permeation. Hereafter, based on the results of this work, 4 different PEs were incorporated to attempt to enhance TM release and permeation through the cornea. Further modification of the formulations saw the effect of integrating chitosan on the release of TM from the electrically atomised coatings. Characterisation of the atomised coatings at each stage demonstrated highly stable matrices, which possessed extremely advantageous morphologies and sizes (within the nanometre range). All coatings also demonstrated adequate to high encapsulation efficiencies (EEs) (>64%) with the highest EE being 99.7%. In vitro release (i.e. cumulative percentage release) steadily increased upon introduction of additives to the base polymeric formulations yielding different release profiles; ranging from biphasic profiles to triphasic profiles. Ex vivo analysis and biological compatibility testing also presented promising results. The use of EHDA has not yet been explored in depth within the ocular research remit. It has shown great potential in the work presented here; engineering on demand lens coatings capable of sustaining both TM release and TM permeation.
18
Koziara, Tomasz. "Aspects of computational contact dynamics." Thesis, University of Glasgow, 2008. http://theses.gla.ac.uk/429/.
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This work summarises a computational framework for dealing with dynamic multi-body frictional contact problems. It is in fact a detailed account of an instance of the Contact Dynamics method by Moreau and Jean. Hence the title. Multi-body systems with contact constraints are common. Some of them, such as machines or arrangements of particulate media, need to be predictable. Predictions correspond to approximate solutions of mathematical models describing interactions within such systems. The models are implemented as computational algorithms. The main contributions of the author are in an improved time integration method for rigid rotations, and in a robust Newton scheme for solving the frictional contact problem. A simple and efficient way of integrating rigid rotations is presented. The algorithm is stable, second order accurate, and in its explicit version involves evaluation of only two exponential maps per time step. The semi-explicit version of the proposed scheme improves upon the long term stability, while it retains the explicitness in the force evaluation. The algebraic structure of both schemes makes them suitable for the analysis of constrained multi-body systems. The explicit algorithm is specifically aimed at the analysis involving small incremental rotations, where its modest computational cost becomes the major advantage. The semi-explicit scheme naturally broadens the scope of possible applications. The semismooth Newton approach is adopted in the context of the frictional contact between three-dimensional pseudo-rigid bodies, proposed by Cohen and Muncaster. The Signorini-Coulomb problem is formulated according to the formalism of Contact Dynamics. Hybrid linearisation, parameter scaling and line search techniques are combined as the global convergence enhancements of the Newton algorithm. Quasi-static simulations of dry masonry assemblies exemplify performance of the presented framework.
19
Slocum, Alexander Henry Jr. "Rolling contact orthopaedic joint design." Thesis, Massachusetts Institute of Technology, 2013. http://hdl.handle.net/1721.1/81736.
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Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2013.This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.
Cataloged from student-submitted PDF version of thesis.
Includes bibliographical references.
Arthroplasty, the practice of rebuilding diseased biological joints using engineering materials, is often used to treat severe arthritis of the knee and hip. Prosthetic joints have been created in a "biomimetic" manner to reconstruct the shape of the biological joint. We are at a disadvantage, however, in that metals and polymers used to replace bone and articular cartilage often wear out too soon, leading to significant morbidity. This thesis explores the use of kinetic-mimicry, instead of bio-mimicry, to design prosthetic rolling contact joints, including knee braces, limb prosthetics, and joint prostheses, with the intent of reducing morbidity and complications associated with joint/tissue failure. A deterministic approach to joint design is taken to elucidating six functional requirements for a prosthetic tibiofemoral joint based on anatomical observations of human knee kinetics and kinematics. Current prostheses have a high slide/roll ratio, resulting in unnecessary wear. A rolling contact joint, however, has a negligible slide/roll ratio; rolling contact prostheses would therefore be more efficient. A well-established four-bar linkage knee model, in a sagittal plane that encapsulates with the knee's flexion/extension degree of freedom, is used to link human anatomy to the shape of rolling cam surfaces. The first embodiment of the design is a flexure coupling-based joint for knee braces. Failure mode analysis, followed by cyclic failure testing, has shown that the prototype joint is extremely robust and withstood half a million cycles during the first round of tests. Lubrication in the joint is also considered: micro- and nano-textured porous coatings are investigated for their potential to support the formation of favorable lubrication regimes. Hydrodynamic lubrication is optimal, as two surfaces are separated by a fluid gap, thus mitigating wear. Preliminary results have shown that shear stress is reduced by more than 60% when a coating is combined with a shear thinning lubricant like synovial fluid. These coatings could be incorporated into existing joint prostheses to help mitigate wear in current technology. This thesis seeks to describe improvements to the design of prosthetic joints, both existing and future, with the intent of increasing the overall quality of care delivered to the patient.
by Alexander Henry Slocum, Jr.
Ph.D.
20
Murarka, Apoorva. "Contact-printed microelectromechanical systems." Thesis, Massachusetts Institute of Technology, 2012. http://hdl.handle.net/1721.1/77080.
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Thesis (M. Eng.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 2012.Cataloged from PDF version of thesis.
Includes bibliographical references (p. 105-107).
Microelectromechanical systems (MEMS) are ubiquitous. Scalable large-area arrays of MEMS on a variety of substrates, including flexible substrates, have many potential applications. Novel methods for additive fabrication of thin (125±15 nm thick) suspended gold membranes on a variety of rigid and flexible cavity-patterned substrates for MEMS applications are reported. The deflection of these membranes, suspended over cavities in a dielectric layer atop a conducting electrode, can be used to produce sounds or monitor pressure. The reported fabrication methods employ contact-printing, and avoid fabrication of MEMS diaphragms via wet or deep reactive-ion etching, which in turn removes the need for etch-stops and wafer bonding. Elevated temperature processing is also avoided to enable MEMS fabrication on flexible polymeric substrates. Thin films up to 12.5 mm2 in area are fabricated. The MEMS devices are electrically actuated and the resulting membrane deflection is characterized using optical interferometry. Preliminary sound production is demonstrated, and further applications of this technology are discussed.
by Apoorva Murarka.
M.Eng.
21
Li, Wei 1967. "Determination of the relationship between thermal contact resistance and contact pressure based on their distributions." Thesis, McGill University, 1994. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=26402.
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Loading conditions in a machine structure usually cause the contact pressure at the joints to take the form of a distribution, which in turn causes thermal contact resistance to be position-dependent also.In the experiments described in this thesis, two thin-plate specimens of steel under plane-stress loading conditions generating contact pressure distributions of various profiles at the interface, were subjected to a thermal field. Temperature measurements served as reference for the finite element modelling which, through consecutive iterations, provided the values for the thermal contact resistance distributions. Combined mechanical contact pressure and thermal contact stress distributions were considered at the interface.
The function representing the relationship between thermal contact resistance and contact pressure for various distributions was defined using the least squares method. It was revealed that although this relationship can be expressed by the single function for the whole experimental range, the deviations experienced for different slopes and forms of distributions (convex and concave), particularly noticeable for steep slopes at high contact pressure levels, could indicate the effect of macro-constriction resistance, however small its values according to the theoretical calculations might be.
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Maissa, Cecile A. "Biochemical markers and contact lens wear." Thesis, Aston University, 1999. http://publications.aston.ac.uk/9627/.
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The project objective was to develop a reliable selection procedure to match contact lens materials with individual wearers by the identification of a biochemical marker for assessment of in-eye performance of contact lenses. There is a need for such a procedure as one of the main reasons for contact lens wearers ceasing wearing contact lenses is poor end of day comfort i.e. the lenses become intolerable to the wearer as the day progresses. The selection of an optimal material for individual wearers has the potential benefit to reduce drop Qut, hence increasing the overall contact lens population, and to improve contact lens comfort for established wearers. Using novel analytical methods and statistical techniques, we were able to investigate the interactions between the composition of the tear film and of the biofilm deposited on the contact lenses and contact lens performance. The investigations were limited to studying the lipid components of the tear film; the lipid layer, which plays a key role in preventing evaporation and stabilising the tear film, has been reported to be significantly thinner and of different mixing characteristics during contact lens wear. Different lipid families were found to influence symptomatology, in vivo tear film structure and stability as well as ocular integrity. Whereas the symptomatology was affected by both the tear film lipid composition and the nature of the lipid deposition, the structure of the tear film and its stability were mainly influenced by the tear film lipid composition. The ocular integrity also appeared to be influenced by the nature of the lipid deposition. Potential markers within the lipid species have been identified and could be applied as follows: When required in order to identify a problematic wearer or to match the contact lens material to the contact lens wearer, tear samples collected by the clinician could be dispatched to an analytical laboratory where lipid analysis could be carried out by HPLC. A colorimetric kit based on the lipid markers could also be developed and used by clinician directly in the practice; such a kit would involve tear sampling and classification according to the colour into "Problem", "Border line" and "Good" contact lens wearers groups. A test kit would also have wider scope for marketing in other areas such as general dry-eye pathology.
23
Gibbins, Josh. "Thermal Contact Resistance of Polymer Interfaces." Thesis, University of Waterloo, 2006. http://hdl.handle.net/10012/2856.
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In this study an experimental program was carried out to determine the thermal contact resistance at polymer interfaces. Specifically, a polycarbonate to stainless steel interface along with a polycarbonate to polycarbonate interface were investigated. The thermal contact resistance at a stainless steel to stainless steel interface was also investigated for comparison purposes. Experimental data was obtained over a pressure range of approximately 600 - 7000 kPa, in a vacuum environment. The experimental data was compared to the CMY plastic contact model, the Mikic elastic contact model and the SY elasto-plastic contact model to investigate the ability of such established thermal contact models to predict the thermal contact resistance at polymer interfaces. Based upon predictions made in regards to the mode of deformation of the asperities on the contacting surfaces the appropriate contact model showed good agreement with the experimental data for the stainless steel-stainless steel data set and the polycarbonate-stainless steel data sets. There was poor agreement between the all three contact models and the experimental data for the polycarbonate-polycarbonate data sets. It was determined that uncertainties in the proposed experimental method prevented an accurate measurement of the thermal contact resistance values for the polycarbonate-polycarbonate data sets.
The purpose of this investigation was to extend the use of established thermal contact models to polymer interfaces and to provide a comparison between the thermal contact resistance values of metal and polymer interfaces.
Thermal contact resistance for the polymer to metal interface was shown to be predicted by the Mikic elastic contact model in comparison to the metal to metal interface which was shown to be predicted by the CMY plastic contact model. The thermal contact resistance for a polymer interface was found to be on the same order as a metal interface.
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El-Rifai, Khalid 1979. "Control of AFMs in contact mode." Thesis, Massachusetts Institute of Technology, 2003. http://hdl.handle.net/1721.1/17597.
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Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2003.Includes bibliographical references (leaves 71-74).
The Atomic Force Microscope (AFM) is a high precision surface characterization tool commonly used in Nano-technology, Bio-technology, semiconductors, MEMS, and life sciences' applications. As most versatile systems, AFM offers little guarantees on achieving repeatable satisfactory operation. This is the case as AFMs are not used to perform a single predictable task. AFM systems are feedback regulators, which rely on photodiode detector (PSD) sensing and piezoelectric actuation. The change in probe-surface contact is a disturbance created by scanning across a surface. This disturbance is to be rejected to maintain probe-surface contact and thus allow proper surface characterization. AFM feedback systems are not only required to maintain a nominal PSD output but also guarantee that the control signal used is representative of the rejected disturbance. This is due to the fact that the image of the scanned surface is created from this control voltage. These characteristics impose severe limitations on the system's operation bandwidth, repeatability, and precision. In this effort, the key characteristics and limitations of AFM operation are analyzed. Challenges due to surface variations, plant dynamics, and contact nonlinearity are presented. The closed loop response of AFM systems in single actuator as well as in dual actuator configurations is evaluated. The emphasis is on the underlying structure corresponding to each configuration and not on a particular system tuning. In this regard, the bounds on achievable performance in each configuration are contrasted for operation within the system's overall objectives.
by Khalid El-Rifai.
S.M.
25
Forsberg, Johan. "Mobile robot navigation using non-contact sensors." Doctoral thesis, Luleå tekniska universitet, EISLAB, 1998. http://urn.kb.se/resolve?urn=urn:nbn:se:ltu:diva-26184.
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This thesis concerns localization and control of mobile robots using range measurements from optronic sensors, in particular scanning time-of-flight lasers. The thesis covers the localization algorithms, on-line sensor calibration and tele-operation for semi-autonomous control of mobile robots. A real-world application of an autonomous mobile robot equipped with an arm for surface finishing operations is also developed. The Range Weighted Hough/Radon transform is introduced for robust detection of walls and extraction of geometric parameters. Thus a robot can automatically create a map of its environment and update it using an extended Kalman filter. The required association of observations with the map features uses a Bayesian classifier. New walls are added to the map as they are observed and classified as new. Navigation is performed with typical fluctuations of 1 cm and 1 degree (standard deviation) at speeds of 0.5 m/s. The navigation is robust even in cluttered environments and with several persons moving around. Sheet-of-light range cameras have also been tested for mobile robot navigation. A calibration algorithm for simultaneous calibration and localization integrates the calibration into the localization system. The only absolute reference needed by the calibration algorithm is the relative motion of the robot. The resulting system performs calibration during normal operation without lowering the localization performance. The algorithms above were applied to two applications: - A mobile robot capable of autonomously spray-plastering the walls and ceiling of a room. The prototype was successfully tested at construction sites. - A semi-autonomous robot tele-operated using tele-commands. The tele- commands include navigation along corridors, through open doors, following walking persons and automatic map generation of the remote site.Godkänd; 1998; 20061122 (haneit)
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Mahvash, Mohammadi Mohsen. "Haptic rendering of tool contact and cutting." Thesis, McGill University, 2002. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=38501.
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A haptic display is capable of representing the virtual interaction between a tool and a deformable body in order to simulate the contact between them. This capability requires computations to be performed in real time in order to generate the force of the virtual interaction that closely resembles the force applied to the tool during actual mechanical interaction. Reasonable approximations must be made to make this possible.This thesis presents an algorithm for real time calculation of tool force-displacement response of contact interaction with a deformable body, during which the body is locally deformed and cut.
The tool responses of contact interaction with a simulated body (with no cutting) are evaluated by interpolation of pre-calculated force-deflection responses each representing the response of contact interaction between a given tool and the body itself. The pre-calculated responses are prepared and stored during a preprocessing step. The interpolation approach ensures continuity of the rendered forces although these are obtained from pre-calculated responses at a set of discrete surface points.
The process of cutting is reduced to three possible interaction modes: deformation, rupture, and cutting. During deformation the tool work is fully recoverable. The tool force is evaluated by pre-calculated responses obtained by measurements from tests performed on the body used in conjunction with reasonable approximations. During cutting, the tool work equals to energy spent on crack formation. The tool force is calculated from the fracture toughness of the body and the area of a crack extension defined by the tool motions. During rupture, the tool work is zero. The crack extension in the body is evaluated from the pre-calculated tool responses.
Concerning the stability of contact interaction, a multi-rate multi-process strategy is introduced in which a high rate process computes the rendered forces from a buffered passive force-deflection model while a variable rate process updates the buffer such that the potential strain energy does not increase at the moment of buffer update.
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Ayers, George Harold. "Cylindrical thermal contact conductance." Thesis, Texas A&M University, 2003. http://hdl.handle.net/1969/88.
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Najjar, Ismail M. R. I. "Investigation of contact of metrological probe tips with rough engineering surfaces." Thesis, University of Warwick, 2002. http://wrap.warwick.ac.uk/3044/.
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This investigation explores the behaviour of contact interaction between probe tips of indicators (displacement gauges) and rough engineering surfaces, in order to gain new insights into uncertainty in industrial precision gauging. The conditions of interest are contact of a mm-scale hard sphere at 0.1 to 5 N force with metallic surfaces, Rq < 2 mm. The motivation arises from the growing demand of modern industries for higher machining processes and for finer inspection capabilities. In the near future, such a demand is likely to require careful analyses of the measurement error budget of these instruments with a greater consideration of the potential errors induced by the complex behaviour of contact, which is currently assumed to be negligible. A preliminary experimental study was carried out on an existing test-rig of limited accuracy. It raised several concerns related to the effects of surface roughness and material on the resulting contact deflection at the load regimes of indicators’ probes. It stimulated the need for more reliable data. So, a new test-rig of advanced capabilities was designed to perform a comprehensive study of a wider range of contact parameters to simulate real situations of industrial gauging processes. This advanced study confirms the consistent effects of roughness, material and probe tip size not only on the surface deflections but also on the probe rotations. Roughness variability across the same surface caused some inconsistencies in the deflection behaviour and repeatability, and surface contamination gave additional unsystematic effects on these relations. Re-establishing contact on the same position of a contaminated surface appeared to contribute errors of the order of those of a clean surface. Based on the results of this investigation, systematic errors of contact can exceed the 1 mm level with uncertainty up to at least 0.4 mm in many measurement processes with precision indicators. Such figures reveal that the contact cannot any longer be considered a negligible source of errors, and precision metrology must account for these induced errors in the budget of displacement gauges.
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Wang, W. "Rolling contact fatigue of silicon nitride." Thesis, Bournemouth University, 2010. http://eprints.bournemouth.ac.uk/17764/.
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Silicon Nitride has traditionally been used as rolling contact bearing material owing to its superior performance compared to bearing steels. Its successful application as a bearing element has led to the development of Silicon Nitride in other rolling contact applications in the automotive industry and the power industry. However, a major limitation of its wider application is its high material and machining cost, especially the cost associated with the finishing process. In the present study, a low cost sintered and reaction-bonded Silicon Nitride is used to study the surface machining effects on its rolling contact fatigue performance. Studies have been carried out to link the surface strengths of Silicon Nitride derived from half-rod and C-Sphere flexure strength specimens to the rolling contact lives of Silicon Nitride rod and ball specimens. The rolling contact fatigue tests were carried out on ball-on-rod and modified four-ball machines. Three types of surface with coarse, fine and RCF-conventional finishing conditions were examined. Flexure strength tests on half-rod and C-Sphere showed an increasing surface strength from specimens with coarse, fine to RCF-conventionally machined conditions. During rolling contact fatigue tests of as-machined specimens, no failures were observed on either ball-on-rod or four-ball tests after 100 million stress cycles. However, a trend of decreasing wear volumes was measured on the contact path of rods and balls with coarse, fine and RCF-conventional conditions. In four-ball tests, spall failures were observed on pre-cracked specimens. There was a trend of increasing rolling contact fatigue lifetime from pre-cracked specimens with coarse, fine to RCF-conventional machining conditions. The study of Silicon Nitride machining was also carried out using an eccentric lapping machine to investigate the effect of eccentricity on the finishing rate of hot isostatically-pressed and sintered and reaction-bonded Silicon Nitride. The eccentricity had no significant impact on finishing rate as concluded in this study. The effect of lubricant viscosity and chemistry on the rolling contact fatigue performance of Silicon Nitride was also studied. The result is inconclusive.
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Rashid, Asim. "Finite Element Modeling of Contact Problems." Doctoral thesis, Linköpings universitet, Mekanik och hållfasthetslära, 2016. http://urn.kb.se/resolve?urn=urn:nbn:se:liu:diva-124572.
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Contact is the principal way load is transferred to a body. The study of stresses and deformations arising due to contact interaction of solid bodies is thus of paramount importance in many engineering applications. In this work, problems involving contact interactions are investigated using finite element modeling. In the first part, a new augmented Lagrangian multiplier method is implemented for the finite element solution of contact problems. In this method, a stabilizing term is added to avoid the instability associated with overconstraining the non-penetration condition. Numerical examples are presented to show the influence of stabilization term. Furthermore, dependence of error on different parameters is investigated. In the second part, a disc brake is investigated by modeling the disc in an Eulerian framework which requires significantly lower computational time than the more common Lagrangian framework. Thermal stresses in the brake disc are simulated for a single braking operation as well as for repeated braking. The results predict the presence of residual tensile stresses in the circumferential direction which may cause initiation of radial cracks on the disc surface after a few braking cycles. It is also shown that convex bending of the pad is the major cause of the contact pressure concentration in middle of the pad which results in the appearance of a hot band on the disc surface. A multi-objective optimization study is also performed, where the mass of the back plate, the brake energy and the maximum temperature generated on the disc surface during hard braking are optimized. The results indicate that a brake pad with lowest possible stiffness will result in an optimized solution with regards to all three objectives. Finally, an overview of disc brakes and related phenomena is presented in a literature review. In the third part, a lower limb donned in a prosthetic socket is investigated. The contact problem is solved between the socket and the limb while taking friction into consideration to determine the contact pressure and resultant internal stress-strain in the soft tissues. Internal mechanical conditions and interface stresses for three different socket designs are compared. Skin, fat, fascia, muscles, large blood vessels and bones are represented separately, which is novel in this work.
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Andersson, Victor. "Thermal Contact Conductance in Aircraft Applications." Thesis, Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, 2018. http://urn.kb.se/resolve?urn=urn:nbn:se:ltu:diva-72512.
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Sariri-Khayatzadeh, Reyhaneh. "Tear protein interaction with hydrogel contact lenses." Thesis, Aston University, 1995. http://publications.aston.ac.uk/9747/.
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The design and synthesis of biomaterials covers a growing number of biomedical applications. The use of biomaterials in biological environment is associated with a number of problems, the most important of which is biocompatabUity. If the implanted biomaterial is not compatible with the environment, it will be rejected by the biological site. This may be manifested in many ways depending on the environment in which it is used. Adsorption of proteins takes place almost instantaneously when a biomaterial comes into contact with most biological fluids. The eye is a unique body site for the study of protein interactions with biomaterials, because of its ease of access and deceptive complexity of the tears. The use of contact lenses for either vision correction and cosmetic reasons or as a route for the controlled drug delivery, has significantly increased in recent years. It is relatively easy to introduce a contact lens Into the tear fluid and remove after a few minutes without surgery or trauma to the patient. A range of analytical techniques were used and developed to measure the proteins absorbed to some existing commercial contact lens materials and also to novel hydrogels synthesised within the research group. Analysis of the identity and quantity of proteins absorbed to biomaterials revealed the importance of many factors on the absorption process. The effect of biomaterial structure, protein nature in terms of size. shape and charge and pH of the environment on the absorption process were examined in order to determine the relative up-take of tear proteins. This study showed that both lysozyme and lactoferrin penetrate the lens matrix of ionic materials. Measurement of the mobility and activity of the protein deposited into the surface and within the matrix of ionic lens materials demonstrated that the mobility is pH dependent and, within the experimental errors, the biological activity of lysozyme remained unchanged after adsorption and desorption. The study on the effect of different monomers copolymerised with hydroxyethyl methacrylate (HEMA) on the protein up-take showed that monomers producing a positive charge on the copolymer can reduce the spoilation with lysozyme. The studies were extended to real cases in order to compare the patient dependent factors. The in-vivo studies showed that the spoilation is patient dependent as well as other factors. Studies on the extrinsic factors such as dye used in colour lenses showed that the addition of colourant affects protein absorption and, in one case, its effect is beneficial to the wearer as it reduces the quantity of the protein absorbed.
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Peach, Helena C. "The tear film and contact lens wear." Thesis, Aston University, 2003. http://publications.aston.ac.uk/9651/.
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Contact lenses have become a popular method of vision correction for millions of people globally. As with all devices designed for use within the body, interactions occur between the implanted material and the surrounding biological fluid. A common complaint of lens wearers is that they often experience symptoms of dry eye whilst wearing lenses. This sensation is often heightened towards the end of the day. Through the course of this study, various analytical techniques have been utilised including one dimensional electrophoresis and Western Blotting to study the protein profiles of tear samples. By studying the tears of non-contact lens wearers, it was possible to analyse what could be considered normal, healthy, individuals. A clinical study was also undertaken which followed a population of individuals from the neophyte stage to one whereby they were accustomed lens wearers. Tears were monitored at regular intervals throughout the course of this study and worn contact lenses were also analysed for proteins that had been deposited both on and within the lens. Contact lenses disrupt the tear film in a physical manner by their very presence. They are also thought to cause the normal protein profile to deviate from what would be considered normal. The tear film deposits proteins and lipids onto and within the lens. The lens may therefore be depriving the tear film of certain necessary components. The ultimate aim of this thesis was to discover how, and to what extent, lenses affected tear proteins and if there were any proteins in the tear fluid that had the potential to be used as biochemical markers. Should this be achievable it may be possible to identify those individuals who were more likely to become intolerant lens wearers. This study followed the changes taking place to the tear film as an effect of wearing contact lenses. Twenty-eight patients wore two different types of silicone hydrogel lenses in both a daily wear and a continuous wear regime. The tear protein profiles of the lens-wearers were compared with a control group of non-lens wearing individuals. The considerable amount of data that was generated enabled the clearly observable changes to the four main tear proteins to be monitored.
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Lum, Choong Kead. "On the solution of frictional contact problems." Thesis, Massachusetts Institute of Technology, 1990. http://hdl.handle.net/1721.1/14282.
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Reshamwala, Chetak M. (Chetak Mahesh) 1979. "Contact resistance in RFID chip-antenna interfaces." Thesis, Massachusetts Institute of Technology, 2001. http://hdl.handle.net/1721.1/8193.
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Thesis (S.B.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2001.Includes bibliographical references (p. 21).
The purpose of this study was to determine a force-deflection relationship and a force-contact area relationship between a flat planar solid and a spherical solid in terms of material and surface properties of the two bodies. This relationship was determined and it was discovered that the force was directly proportional to both the deflection and contact area. This information is useful in the design and performance of RFID chips. The RFID chip-antenna interface is the area of greatest power loss in the system, and by determining a relationship to increase the contact area in that region, the power loss to the antenna can be reduced. Moreover, an analysis including asperities on the micro scale geometry of the solids was conducted. In the final approach to the problem, a random distribution of asperity types was analyzed. An expression was derived for the total force applied in terms of a given deflection and a range of asperity radii of curvature. A three-dimensional graph was created to show how each of these variables depends on the each other when asperities exist. This relationship is very significant, because it can be used to improve current RFID chip technology to achieve better performance. This expression can also be used to determine specifications in the manufacturing process to achieve a certain deflection or area of contact between the contacting bodies, thereby improving the current manufacturing process.
by Chetak M. Reshamwala.
S.B.
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Salgado-Bierman, Andrés. "In-process measurement of micro-contact printing." Thesis, Massachusetts Institute of Technology, 2016. http://hdl.handle.net/1721.1/105681.
Full textAbstract:
Thesis: S.B., Massachusetts Institute of Technology, Department of Mechanical Engineering, 2016.Cataloged from PDF version of thesis.
Includes bibliographical references (pages 42-43).
In micro contact printing, a polymer stamp with sub micron features is use to pattern a substrate. Micro contact printing has many applications including micro machined circuits and miniaturized biological test kits. Success in printing has been achieved in limited batch processing of plate to plate printing. The physics and chemistry of stamp contact and ink transfer has been studied. To make micro contact printing economically viable developments have been made to advance a roll to roll configuration. Roll to roll processing offers the potential of high volume low cost micro manufacturing similar to the high volume achieved by roll to roll processing for traditional lithography. Roll to roll micro contact printers have been built at the lab scale. The process has been demonstrate to have the potential for rapid high volume production. The current limitation is in the quality of the print. Features on the stamp are printed with defects such as breaks or undesired patterning. The source of failure lies with the contact of the stamp; the stamp either breaking contact or collapsing to allow areas outside of the features to make contact. A barrier to better understanding and controlling contact during the printing process has been a lack of in-process measurement. This thesis examines the use of a new optical set-up to monitor stamp contact in-process on a lab level roll to roll micro contact printer. Image based measures of stamp contact quality are presented.
by Andrés Salgado-Bierman.
S.B.
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Sung, Edward S. M. Massachusetts Institute of Technology. "Horizontal non-contact slumping of flat glass." Thesis, Massachusetts Institute of Technology, 2013. http://hdl.handle.net/1721.1/81717.
Full textAbstract:
Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2013.Cataloged from PDF version of thesis.
Includes bibliographical references (p. 99).
This paper continues the work of M. Akilian and A. Husseini on developing a noncontact glass slumping/shaping process. The shift from vertical slumping to horizontal slumping is implemented and various technologies required for the horizontal slumping process are developed. In the horizontal slumping process, a thin sheet of glass is placed in between two horizontal ceramic air bearings with a bearing to glass gap of about 50 pm, and the assembly is heated up to 600*C. The glass is unconstrained in the horizontal plane and must be positioned without any solid contact. Specifically, the technologies developed are: an optical distance sensor for positioning of the glass, glass position control via air bearing fluid shear force and tilt of device, and device mechanisms for operation in 600*C. Glass was slumped horizontally with bearing-to-glass gaps of >50 [mu]m, 36±2.5 pm, and 30.5±2.5 [mu]m. The best flatness achieved was 6.7/3.6+0.5 [mu]m for front/back of the glass sheet, with a gap of 36+2.5 [mu]pm. It was discovered that 600*C is hotter than necessary and that 550*C is still too hot for optimal slumping conditions. In addition, an important shift is made from using an oven, which heats the entire device, to using in-line pipe heaters, which supply heated air. This allows for much quicker heating and cooling times, which decreases slumping time to less than 30 minutes (10 minutes heating, 5 minutes slumping, 10 minutes cooling).
by Edward Sung.
S.M.
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Jurko, Adam. "Concussion preventative head-gear in contact sports." Thesis, Massachusetts Institute of Technology, 2019. https://hdl.handle.net/1721.1/123286.
Full textAbstract:
Thesis: S.B., Massachusetts Institute of Technology, Department of Mechanical Engineering, 2019Cataloged from PDF version of thesis.
Includes bibliographical references (pages 23-24).
This thesis explores the concussion preventative head-gear used in four contact sports: football, baseball, soccer, and basketball. The most effective head-gear from each sport is presented along with the reasons behind their success. Football and baseball organizations have regulations set in place for players to be required to wear helmets, while soccer and basketball organizations do not require players to wear any sort of head-gear. This thesis presents the reasons why soccer and basketball organizations do not require players to wear head-gear, but it also shows the equipment that have been used by players in the past to prevent further head injuries. This paper includes a personal anecdote as well as a recommendation for soccer organizations to require head-gear during competition and for basketball organizations to fund research into protective equipment specific to basketball players.
by Adam Jurko.
S.B.
S.B. Massachusetts Institute of Technology, Department of Mechanical Engineering
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Park, Seonghwa 1968. "An evaluation of contact solution algorithms." Thesis, Massachusetts Institute of Technology, 2003. http://hdl.handle.net/1721.1/85729.
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Tong, Angela 1983. "Nano-contact printing of DNA monolayers." Thesis, Massachusetts Institute of Technology, 2005. http://hdl.handle.net/1721.1/32856.
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Thesis (S.B.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 2005.Includes bibliographical references (leaf 23).
Technology today is directed towards building smaller devices. To accommodate this development, printing methods are needed. Some printing methods that are used include lithography, micro-contact printing, and inkjet printing. These methods all require specialized instrumentation, hazardous chemicals, and complicated and tedious steps that increase cost of manufacturing. Nano-contact printing is an alternative solution which relies on the specificity of DNA to direct molecules into precise patterns. This study attempts to find the limitations of nano-contact printing through the printing of oligonucleotide monolayers. Eight pattern transfers were made with one master copy and the oligonucleotide surface coverage was analyzed using tapping mode atomic force microscopy (AFM). The percent coverage of oligonucleotide was then calculated from the tapping mode AFM phase images. Two general trends were found. The oligonucleotide surface coverage on the master increased slightly, while the surface coverage on the pattern transfers decreased. One possible explanation for the trends is that the decrease in contact between master and secondary substrate is due to both the accumulation of dirt and the wear and tear of' the master. By improving the contact between master and secondary substrate, the printing method can be expanded from printing monolayers to high resolution patterns.
by Angela Tong.
S.B.
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Conner, Brett P. (Brett Page) 1975. "Contact fatigue : life prediction and palliatives." Thesis, Massachusetts Institute of Technology, 2002. http://hdl.handle.net/1721.1/16866.
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Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 2002.Includes bibliographical references (p. 125-135).
This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.
Fretting fatigue is defined as damage resulting from small magnitude (0.5-50 microns) displacement between contacting bodies where at least one of the bodies has an applied bulk stress. The applicability and limits of a fracture mechanics based life prediction is explored. Comparisons are made against highly controlled experiments and less controlled but more realistic experiments using a novel dovetail attachment fixture. Surface engineering approaches are examined from a mechanics perspective. Using a new tool, depth sensing indentation, the mechanical properties of an aluminum bronze coating are determined. Fretting fatigue experiments are performed on specimens coated with aluminum bronze and on specimens treated with low plasticity burnishing. Low plasticity burnishing is a new method of introducing beneficial compressive residual stresses without significant cold work at the surface. A mechanics based approach to the selection of palliatives is addressed.
by Brett P. Conner.
Ph.D.
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Anisetti, Anusha. "On the Thermal and Contact Fatigue Behavior of Gear Contacts under Tribo-dynamic Condition." Wright State University / OhioLINK, 2017. http://rave.ohiolink.edu/etdc/view?acc_num=wright149363918488722.
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Yunus, Pg Hj Md Esa Al-Islam bin Pg Hj Md. "Carbon nanotube surfaces for low force contact application." Thesis, University of Southampton, 2009. https://eprints.soton.ac.uk/67624/.
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This thesis focuses on developing a testing method to estimate the mechanical and electrical characteristics of CNT-based contact surfaces. In particular the use of gold thin films deposited on a CNT forest has potential to offer a very effective contact surface. Two different pieces of experimental apparatus were used in this research to determine the mechanical and electrical properties of gold/multi-walled carbon nanotube (Au/MWCNT) composites: 1) a modified nano-indentation; and 2) a PZT actuator test rig. These apparatuses were used to mimic force-displacement and contact behaviour of the MEMS relay‟s contact at a maximum load of 1 mN with dry-circuit and hot-switched conditions. The surfaces were compared with reference Au-Au and Au-MWCNT contact pairs studied under the same experimental conditions. In the modified nano-indentation experiment, tests of up to 10 cycles were performed. The results showed that the Au-MWCNT pair electrical contact resistance improved when the Au-Au/MWCNT pair was used. Additionally the Au-Au/MWCNT pair electrical contact resistance (Rc) was comparable with the Au-Au contact pair. When the Au-Au/MWCNT composite surface is in contact with the Au hemispherical probe it provides a compliant surface. It conforms to the shape of the Au hemispherical probe. For a higher number of cycles, a PZT actuator was used to support Au/MWCNT planar coated surfaces. This surface makes electrical contact with a gold coated hemispherical probe to mimic the actuation of a MEMS relay‟s contact at higher actuation frequencies. This apparatus allows the performance of the contact materials to be investigated over large numbers of switching cycles. Different current loads were used in this experiment, 1mA, 10mA, 20mA and 50mA at 4V supply. The Rc of these surfaces was investigated as a function of the applied force under repeated cycles. Under current loads of 1mA and 10mA the Au/MWCNT composite surface provides a stable contact resistance of up to more than a million cycles and no degradation was observed on the surface. Compared with Au-Au contact pair, degradation occurred after 220 cycles. The Au-Au contact pair shows delamination of the Au surface on the probe. The possible reason is the softening or melting of the Au surface. Furthermore, under higher current loads of 20mA to 50mA, degradation had occurred after 50 million cycles (at 20mA) and degradation had occurred at around 45 to 150 cycles for 50mA to 30mA respectively. This is because of the softening or melting of the Au and Au fatigue after a large number of cycles. This study is the first step to show the potential of CNT surfaces as an interface in low force electrical contact applications. With this research, current trends in materials used on contacts and fabrication methods can be explored and even modified or adopted. The use of CNT‟s and their composites for contacts can be tested using the available apparatus to look at their performance and reliability in terms of mechanical and electrical properties. This is useful for MEMS contacts that form part of MEMS relay devices.
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Siegel, David Mark. "Contact Sensors for Dexterous Robotic Hands." Thesis, Massachusetts Institute of Technology, 1986. http://hdl.handle.net/1721.1/6848.
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This thesis examines a tactile sensor and a thermal sensor for use with the Utah-MIT dexterous four fingered hand. Sensory feedback is critical or full utilization of its advanced manipulatory capabilities. The hand itself provides tendon tensions and joint angles information. However, planned control algorithms require more information than these sources can provide. The tactile sensor utilizes capacitive transduction with a novel design based entirely on silicone elastomers. It provides an 8 x 8 array of force cells with 1.9 mm center-to-center spacing. A pressure resolution of 8 significant bits is available over a 0 to 200 grams per square mm range. The thermal sensor measures a material's heat conductivity by radiating heat into an object and measuring the resulting temperature variations. This sensor has a 4 x 4 array of temperature cells with 3.5 mm center-to-center spacing. Experiments show that the thermal sensor can discriminate among material by detecting differences in their thermal conduction properties. Both sensors meet the stringent mounting requirements posed by the Utah-MIT hand. Combining them together to form a sensor with both tactile and thermal capabilities will ultimately be possible. The computational requirements for controlling a sensor equipped dexterous hand are severe. Conventional single processor computers do not provide adequate performance. To overcome these difficulties, a computational architecture based on interconnecting high performance microcomputers and a set of software primitives tailored for sensor driven control has been proposed. The system has been implemented and tested on the Utah-MIT hand. The hand, equipped with tactile and thermal sensors and controlled by its computational architecture, is one of the most advanced robotic manipulatory devices available worldwide. Other ongoing projects will exploit these tools and allow the hand to perform tasks that exceed the capabilities of current generation robots.
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Yu, Kuan-Ting Ph D. Massachusetts Institute of Technology. "Realtime state estimation for contact manipulation." Thesis, Massachusetts Institute of Technology, 2018. http://hdl.handle.net/1721.1/120369.
Full textAbstract:
Thesis: Ph. D., Massachusetts Institute of Technology, Department of Electrical Engineering and Computer Science, 2018.This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.
Cataloged from student-submitted PDF version of thesis.
Includes bibliographical references (pages 133-140).
In this thesis, we develop a real-time state estimation system to recover the pose and contact state of an object relative to its environment. The capability to make such estimations is important for a controller to adequately react to uncertainties in a manipulation task. We propose a framework that combines tactile and visual sensing to improve the accuracy and robustness. Visual sensing is versatile and non-intrusive but suffers from occlusions and limited accuracy, especially with regard to tasks involving contact. Tactile sensing (including contact and force) is local but provides accuracy and robustness to occlusions. The framework uses online estimation techniques to fuse kinematic measurements made by a robot, contact geometry of the object and the environment, and visual measurements. In a complex contact task such as insertion, the contact formations are hard to resolve directly. We propose a data-driven method to assess the contact formation, which is then used in real time by the state estimator. We apply our framework to two iconic tasks in robotic manipulation: planar pushing and object insertion. We evaluate the algorithm in a setup instrumented to provide ground truth. The experiments show that our approach provides an accurate and robust estimation for the studied manipulation tasks.
by Kuan-Ting Yu.
Ph. D.
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Hearle, Adrian Donald. "Deformation, shakedown and fatigue in rolling contact." Thesis, University of Cambridge, 1985. https://www.repository.cam.ac.uk/handle/1810/250858.
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Martin, Michael. "The Effect of Geometrical Contact Input to Wheel-Rail Contact Model." Thesis, KTH, Spårfordon, 2018. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-239735.
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Wheel-rail contact is an important aspect of railway, the forces transferred between the wheel and rail are the one that guide, brake, or accelerate the train, and that is why the understanding of the contact between wheel and rail is an interesting research topic. In this master thesis wheel-rail contact model named ANALYN is used to see the effect of the different geometrical input, like undeformed distance, relative longitudinal curvature, and relative lateral curvature calculation affect the contact patch estimation formed at the wheel-rail contact. In the process, a geometrical contact search code is made to find the contact point between wheel and rail for certain lateral displacement, yaw angle, and roll angle of the wheelset. The codes used to calculate the three geometrical inputs are also prepared, with two methods are prepared for each input. The results that generated from combination of the geometrical contact search and geometrical input preparation are used as the input to ANALYN. The results showed that different geometrical input calculations do affect the shape of the contact patch, with the calculation of lateral curvature being the most important since it affects the shape of the contact patch greater than other geometrical inputs. It is also shown that taking yaw angle into account in the contact search will affect the shape of the contact patch.
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Abu, Sharkh Suleiman Mahmoud. "Influence of contact dynamics and point-on-wave switching on arc and contact phenomena in medium duty switches." Thesis, University of Southampton, 1994. https://eprints.soton.ac.uk/47625/.
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Investigations are made into the effect of contact opening velocity on arc energy and contact erosion in both ac and dc medium duty switches. In addition investigations are carried out into the effect of point-on-wave switching on the erosion of contacts in ac circuits. Theoretical and experimental research is also made into the modelling of the impact event during contact closure. The impact model is used to develop a mathematical model of the dynamics of a contact mechanism which is used in the investigations. The phenomena of pre-impact arcing during contact closure is also studied. The investigations into the effect of contact opening velocity and point-on-wave switching on arc energy and erosion were carried out using a computer controlled experimental apparatus which enables the control of contact opening velocities in the range of medium duty switches (up to 1 m/s). The investigations into the impact and bounce phenomena were made using an existing experimental apparatus. In dc circuits, using currents up to 10 A, the molten bridge length was found to be unaffected by opening velocity indicating that the bridge remains in steady state. For dc currents below 7 A a stepped increase of the arc voltage was observed. The presence of a fourth step and a fifth step are reported in this thesis for the first time. These steps are explained to be due to the quantized nature of the electron energy in the arc which manifests itself at low current. The arc voltage in dc circuits is found to become either higher or lower than its steady state value when the contact velocity increases which was explained to a direct consequence of the energy conservation equation. Arc energy and erosion for a given arc current are found to be inversely proportional to contact opening velocity. Material transfer due to arc erosion was shown to change direction from cathodic to anodic when the circuit current increases above 7A. In ac circuits the arc is observed to extinguish near current zero at all velocities which results in the increase of arc energy and length with opening velocity. This is shown to be predictable from quasi-static arc characteristics. Opening the contacts further from the start of the ac current cycle, i.e. at large point-on-waves is shown to increase the erosion from the anode resulting in the change of the direction of material transfer to become from anode to cathode at a point-on-wave which decreases with the increase of the electrical current. This is explained to be due to the increase of anodic erosion with the increase of arc current. Increasing opening velocity is shown to increase the erosion from anode to cathode for given point-on-wave and current (below 10A)which is due to the increase of the arc length and the anode fall voltage. For currents higher than 10 A erosion due to melting increases significantly with increasing opening velocity leading to material loss from both contacts. Erosion due to random switching of rectified ac current is shown to correlated well with that of fixed point-on-wave switching. It is shown in this thesis that it is possible to model the impact event by a single process of plastic deformation which enables the calculation of impact force and duration. To reduce contact bounce the contact closing velocity has to be reduced. However, the contact velocity has to be high enough to reduce the damage caused by the pre-impact arc whose duration is shown to be inversely proportional to closing velocity. This arc is shown to be caused by field emission breakdown.
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Hoeffel, Elizabeth Marie. "Gender Bias in Engineering: Does More Contact with Female Engineers Reduce Bias?" Thesis, Virginia Tech, 2007. http://hdl.handle.net/10919/31846.
Full textAbstract:
Status Characteristics Theory and Contact Theory are tested to measure gender bias in engineering students, and to determine if contact with female engineers helps reduce gender bias. To assess this, two versions of a resume, one with a femaleâ s name and one with a maleâ s name, were given to senior mechanical engineering students (n=225) to establish if they would rate the male applicant better than the female applicant. Respondents were asked how qualified they thought the respondent was, how much they would want the respondent on their team, and whether or not they would hire the applicant. Respondents were also questioned about contact with female engineering faculty, having female engineers in the family, and having female engineering co-workers. Results showed that all of the effects that were expected to occur were not significant, except one. The interaction between having a female engineer in the family and the applicant sex of the resume significantly impacted malesâ desire to have the applicant on their senior design team. Therefore, overall there is very little support for Status Characteristics Theory and Contact Theory. Only one result supports both Status Characteristics Theory and Contact Theory â having a female engineer in the family seems to reduce gender bias toward team members among males.Master of Science
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Bastola, Ebin. "CdTe Back Contact Engineering via Nanomaterials, Chemical Etching, Doping, and Surface Passivation." University of Toledo / OhioLINK, 2020. http://rave.ohiolink.edu/etdc/view?acc_num=toledo1596813646708798.
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