Series elastic actuators (SEAs) have numerous benefits for force controlled robotic applications. This thesis presents the design and assembly of a set of compact, lightweight, low-friction linear SEAs for the legs of the Tactical Hazardous Operations Robot (THOR). The THOR SEA pairs a ball screw driven linear actuator with a configurable titanium leaf spring. A removable pivot changes the effective cantilever length, setting the compliance to either 372 or 655 kN/m. Unlike typical SEAs which measure actuator load through spring deflection, an in-line axial load cell directly measures actuator forces up to the commandable peak of 2225 N. The continuous operating range of the actuator is computed, along with an evaluation of the range of motion and torque profiles for the parallel hip and ankle joints. With a focus on a large power-to-weight ratio and small packaging size, the THOR SEAs are well-suited for accurate torque control of the parallel joints on the robot. Linearly actuated joints, especially ones driven through a crank arm, tend to suffer from a loss of mechanical advantage toward the ends of its limited range of motion. To augment the range of motion and mechanical advantage profile on THOR, an inverted Hoeken's linkage straight line mechanism is paired with a linear SEA at the hip and knee pitch joints on the robot. The resulting linkage assembly is capable of delivering nearly constant peak torque of 115 Nm across its 150 degree range of motion. The mechanical advantage profile of the Hoeken's linkage actuator is computed for the nominal case, as well the deviation resulting from maximum deflection of the titanium beam. / Master of Science

The objective of this dissertation is to demonstrate the use of in situ TEM mechanical testing to find mechanical properties of as received, self-ion, and proton irradiated Fe-9%Cr ODS. The desire to work at small scale in the characterization of irradiated materials to reduce costs and improve throughput, require the development of novel methods to assess mechanical properties in volume-limited irradiation damage layers. Yet at these micrometer or nanometer scales, the mechanical properties can begin to be impacted by size effects. In this work micropillar compression, cantilever bending, lamellae indentation, and clamped beam fracture testing is conducted on ion-irradiated Fe-9%Cr ODS to find yield stress, elastic modulus, flow stress, and fracture toughness. Micropillars in compression allow us to define a minimum sample dimension, which approaches the obstacle spacing of the material, at which size effects are observed. This relationship between sample dimension and obstacle spacing defined through micropillar compression is extended to a new testing geometry, cantilever bending, and material property, flow stress. Lessons learned during the cantilever bending informed the clamped beam design for conducting fracture testing on a ductile engineering alloy at micrometer scales. Finally, lamellae indentation was conducted to link qualitative observations of the microstructure under load with literature strength of obstacle values. By combining an understanding of the microstructure of irradiated Fe-9%Cr ODS and the in situ TEM technique, one can find the bulk-like mechanical properties of ion irradiated Fe-9%Cr ODS.

"Health monitoring of structures by experimental modal analysis is typically performed with piezoelectric based transducers. These transducers are usually heavy, large in size, and require high power to operate, all of which reduce their versatility and applicability to small components and structures. The advanced developments of microfabrication and microelectromechanical systems (MEMS) have lead to progressive designs of small footprint, low dynamic mass and actuation power, and high-resolution inertial sensors. Because of their small dimensions and masses, MEMS inertial sensors could potentially replace the piezoelectric transducers for experimental modal analysis of small components and structures. To transfer data from MEMS inertial sensors to signal analyzers, traditional wiring methods may be utilized. Such methods provide reliable data transfer and are simple to integrate. However, in order to study complex structures, multiple inertial sensors, attached to different locations on a structure, are required. In such cases, using wires increases complexity and eliminates possibility of achieving long distance monitoring. Therefore, there is a need to implement wireless communications capabilities to MEMS sensors. In this thesis, two different wireless communication systems have been developed to achieve wireless health monitoring of structures using MEMS inertial sensors. One of the systems is designed to transmit analog signals, while the other transmits digital signals. The analog wireless system is characterized by a linear frequency response function in the range of 400 Hz to 16 kHz, which covers the frequency bandwidth of the MEMS inertial sensors. This system is used to perform modal analysis of a test structure by applying multiple sensors to the structure. To verify the results obtained with MEMS inertial sensors, noninvasive, laser optoelectronic holography (OEH) methodology is utilized to determine modal characteristics of the structure. The structure is also modeled with analytical and computational methods for correlation of and verification with the experimental measurements. Results indicate that attachment of MEMS inertial sensors, in spite of their small mass, has measurable effects on the modal characteristics of the structure being considered, verifying their applicability in health monitoring of structures. The digital wireless system is used to perform high resolution tilt and rotation measurements of an object subjected to angular and linear accelerations. Since the system has been developed based on a microcontroller, programs have been developed to interface the output signals of the sensors to the microcontroller and RF components. The system is calibrated using the actual driving electronics of the MEMS sensors, and it has achieved an angular resolution of 1.8 mrad. The results show viability of the wireless MEMS inertial sensors in applications requiring accurate tilt and rotation measurements. Additional results presented included application of a MEMS gyroscope and microcontroller to perform angular rate measurements. Since the MEMS gyroscope only generates analog output signals, an analog to digital conversion circuit was developed. Also, a program has been developed to perform analog to digital conversion with two decimal places of accuracy. The experimental results demonstrate feasibility of using the microcontroller and the gyroscope to perform wireless angular rate measurements."

This Thesis relates to the continually advancing field of microelectromechanical systems (MEMS). With MEMS technology, there are many different areas of concentration available for research. This Thesis addresses analysis and preliminary characterization of a cantilever-type MEMS chemical sensor for detection of chemicals and organic components operating at room temperature (20˚C and sea level pressure of 1 atm). Such sensors can be useful in a wide variety of applications. There currently exist several different types of MEMS chemical sensors. Each is based on a different detection method, e.g., capacitive, thermal, resistive, etc., and is used for specific tasks. Out of all currently available detection methods, the most common is the gravimetric method. The gravimetric sensor works by absorbing the chemical in a special material, usually a polymer, which alters the overall mass of the sensing element that can then be measured, or detected, to identify the chemical absorbed. One of the more exciting developments in the field of gravimetric chemical MEMS has been with the advancement of cantilever-type sensors. These cantilevers are small and usually on the order of only about 300 m in length. In order to utilize the gravimetric method, a cantilever is coated with a polymer that allows an analyte to bond to it and change its mass, which in turn changes the resonant frequency of the cantilever. The change in frequency can then be measured and analyzed and from it, the amount of absorbed mass can be calculated. Current research in the cantilever-type resonating sensors for the detection of hydrogen is developing measurement capabilities of 1 ppm (part-per-million). In this Thesis number of sample cantilevers were qualitatively assessed and their dimensional geometry measured. Based on these measurements, frequency data were obtained. In addition, the overall uncertainty in the resonant frequency results was calculated and the contributing factors to this uncertainty were investigated. Experimental methods that include laser vibrometry, optoelectronic laser interferometric microscopy (OELIM), and atomic force microscopy (AFM), were utilized to measure the frequency responses of the samples. The analytically predicted natural frequencies were compared to the experimental data to determine correlation subject to the uncertainty analysis. Parametric analyses involving chemical absorption processes were also conducted. Such analyses considered different parameters, e.g., damping and stiffness as well as changes in their values, to determine contributions they make to the quality of the frequency data and the effect they have on sensitivity of the MEMS cantilever-type chemical sensors. Once these parametric analyses were completed, it was possible to estimate the sensitivity of the cantilever, or the ability for the cantilever to detect frequency shifts due to absorption of the target chemical. Results of the parametric analyses of the fundamental resonant frequency were then correlated with the sensitivity results based on the chemical absorption. This Thesis correlates many results and ideas and probes problems revolving around the analysis and characterization of a MEMS cantilever-type chemical sensor.

Static and dynamic interaction mechanism of the retained soil-compressible geofoam buffer and yielding retaining structures requires further investigation. The present study, initiated on this motive, discusses the results of 1-g physical model tests and numerical analyses of cantilever retaining walls with and without deformable geofoam buffers between the wall and cohesionless granular backfill. 0.7m high walls with various wall thicknesses were utilized in the physical modeling. Dynamic tests were carried out by using a laminar container placed on a uni-axial shaking table. Influence of buffer thickness, geofoam type and wall flexibility as well as base excitation characteristics on the lateral earth pressures and flexural wall deflections were under concern. Outcomes of the analyses performed with FLAC-2D (v6.0) finite difference code were validated against the results of the physical model tests. It was observed that the arching effect induced in the retained soil by the lateral compression of the lower half of the geofoam buffer has a positive effect, as this zone is able to absorb a portion of the total unbalanced lateral force exerted by the backfill thus causing a reduction in the static and seismic lateral wall pressures. Relative thickness and stiffness of the geofoam buffer appear to be the most dominant factors affecting the reduction in earth thrust. Lateral earth pressure coefficients determined from physical model tests were compared with those calculated using methods available in the literature. Good agreement was observed between the predictions. Graphs were provided to estimate the static and dynamic lateral earth pressure coefficients for various combinations of wall stiffness and buffer characteristics. Analysis of a 6m high prototype cantilever wall subjected to an excitation recorded in August 17, 1999 Kocaeli earthquake by finite difference method exhibited the contribution of geofoam buffers on seismic performance of cantilever earth retaining walls. It was observed that the presence of an EPS geofoam inclusion provides a reduction of the permanent flexural wall deflections as well as total seismic thrust likely to be experienced by the wall during an earthquake.

A new type of cantilever beam gyroscope is introduced, modeled, and analyzed. The main structure includes a cantilever beam and a rigid body attached to the free end of the beam. The model accounts for the eccentricity, that is the offset of the center of mass of the rigid body relative to the beam's free end. The first and second moments of mass and the rotary inertia appear in the equations of motion and boundary conditions. The common mechanism of electrostatic actuation of microgyroscopes is used with the difference of computing the force at the center of mass resulting in the electrostatic force and moment in the boundary conditions. By using the extended Hamilton's principle, the method of assumed modes, and Lagrange's differential equations, the equations of motion, boundary conditions, and the discretized model are developed. The generalized model simplifies to other beam gyroscope models by setting the required parameters to zero. Considering the DC and AC components of the actuating and sensing methods, the response is resolved into the static and dynamic components. The static configuration is studied for an increasing DC voltage. For the uncoupled system of equations, the explicit equation relating the DC load and the static configuration is computed and solved for the static configuration of the beam-rigid body in each direction. Including the rotation rate, the stationary analysis is performed, the stationary pull-in voltage is identified, and it is shown that the angular rotation rate does not affect the static configuration. The modal frequencies of the beam-rigid body gyroscope are studied and the instability region due to the rotation rate is computed. It is shown that the gyroscope can operate in the frequency modulation mode and the amplitude modulation mode. To operate the beam-rigid body gyroscope in the frequency modulation mode, the closed-form relation of the observed modal frequency split and the input rotation rate is computed. The calibration curves are generated for a variety of DC loads. It is shown that the scale factor improves by matching the zero rotation rate natural frequencies. The method of multiple scales is used to study the reduced-order nonlinear dynamics of the oscillations around the static equilibrium. The modulation equations, the ``slow'' system, are derived and solved for the steady-state solutions. The computational shooting method is employed to evaluate the results of the perturbation method. The frequency response and force response plots are generated. For combinations of parameters resulting in a single-valued response, the two methods are in excellent agreement. The synchronization of the response occurs in the sense direction for initially mismatched natural frequencies. The global stability of the system is studied by drawing phase-plane diagrams and long-time integration of response trajectories. The separatrices are computed, the jump phenomena is numerically shown, and the dynamic pull-in of the response is demonstrated. The fold bifurcation points are identified and it is shown that the response jumps to the higher/lower branch beyond the bifurcation points in forward/backward sweep of the amplitude and the excitation frequency of AC voltage. The mechanical-thermal (thermomechanical) noise effect on the sense response is characterized by using a linear approximation of the system and the nonlinear "slow" system obtained by using the method of multiple scales. To perform linear analysis, the negligible effect of Coriolis force on the drive amplitude is discarded. The second-order drive resonator is solved for the drive amplitude and phase. Finding the sense response due to the thermal noise force and the Coriolis force and equating them computes the mechanical-thermal noise equivalent rotation rate in terms of system parameters and mode shapes. The noise force is included in the third-order equation of the perturbation and equation to account for that in the reduced-order nonlinear response. The numerical results of linear and reduced-order nonlinear thermal noise analyses agree. It is shown that higher quality factor, higher AC voltage, and operating at lower DC points result in better resolution of the microsensor.

A novel optical diffraction based technique is proposed and demonstrated to measure deflections of the order of ~1nm in microcantilevers (MC) designed for sensing ultra-small forces of stress. The proposed method employs a double MC structure where one of the cantilevers acts as the active sensor beam, while the other as a reference. The active beam can respond to any minute change of stress, for example, molecular recognition induced surface stress, through bending (~1nm) relative to the other fixed beam. Optical diffraction patterns obtained from this double slit aperture mask with varying slit width, which is for the bending of MC due to loading, carries the deflection profile of the active beam. A significant part of the present work explores the possibility of connecting diffraction minima (or maxima) to the bending profile of the MC structure and thus the possibility to measure induced surface stress. To start with, it is also the aim to develop double MC sensors using PHDDA (Poly – Hexane diol diacrylate) because this material has the potential to achieve high mechanical deformation sensitivity in even moderately scaled down structures by virtue of its very low Young’s modulus. Moreover, the high thermal stability of PHDDA also ensures low thermally induced noise floors in microcantilever sensors. To demonstrate the proposed optical diffraction-based profiling technique, a bent microcantilever structure is designed and fabricated by an in-house developed Microstereolithography (MSL) system where, essentially one of the microcantilevers is fabricated with a bent profile by varying the gap between the two structures at each cured 2D patterned layer. The diffraction pattern obtained on transilluminating the fabricated structure by a spherical wavefront is analyzed and the possibility of obtaining the deflections at each cross section is ascertained. Since the proposed profiling technique relies on the accurate detection and measurement of shifts of intensity minima on the image plane, analysis of the minimum detectable shift in intensity minima for the employed optical interrogation setup with respect to the minimum detectable contrast and SNR of the optical measurement system is carried out, in order to justify the applicability of the proposed minima intensity shift measurement technique. The proposed novel diffraction based profiling technique can provide vital clue on the origins of surface stress at the atomic and molecular level by virtue of the entire bent profile due to adsorption induced bending thereby establishing microcantilever sensor technology as a more reliable and competitive approach for sensing ultra-low concentrations of biological and chemical agents.

The presented work aims to optimize the performance of piezoresistive cantilevers in cases where the output signal originates either from a static deflection of the cantilever or from the dynamic (resonance) characteristic of the beam. Based on a new stress concentration technique, which utilizes silicon beams and wires embedded in the cantilever, the force sensitivity of the cantilever is increased up to 8 fold with only about a 15% decrease in the cantilever stiffness. Moreover, the developed stress-concentrating cantilevers show almost the same resonance characteristic as conventional cantilevers. The focus of the second part of the present work is to provide guidelines for designing rectangular silicon cantilever beams to achieve maximum quality factors for the fundamental and higher flexural resonance at atmospheric pressure. The applied methodology is based on experimental data acquisition of resonance characteristics of silicon cantilevers, combined with modification of analytical damping models to match the measurement data. To this end, rectangular silicon cantilever beams with thicknesses of 5, 7, 8, 11 and 17 um and lengths and widths ranging from 70 to 1050 um and 80 to 230 um, respectively, have been fabricated and tested. To better describe the experimental data, modified models for air damping have been developed. Moreover, to better understand the damping mechanisms in a resonant cantilever system, analytical models have been developed to describe the cantilever effective mass in any flexural resonance mode. To be able to extract reliable Q-factor data for low signal-to-noise ratios, a new iterative curve fitting technique is developed and implemented. To address the challenge of frequency drift in (mass-sensitive) resonant sensors, and especially cantilever-based devices, the last part of the research deals with a novel compensation technique to cancel the unwanted environmental effects (e.g., temperature and humidity). This technique is based on exploring the resonance frequency difference of two flexural modes. Experimental data show improvements in temperature and humidity coefficients of frequency from -19.5 to 0.2 ppm/˚C and from 0.7 to -0.03 ppm/%RH, respectively. The last part of the work also aims on techniques to enhance or suppress the flexural vibration amplitude in desired overtones.

This thesis is part of the on going work at BTH (Blekinge Technical University) to develop a remote lab for Sound and Vibration Experiments. The aim of this undertaking is to develop a Spectrum Analyzer that can simultaneously take inputs from 10 sensors and be able to measure the Power Spectral Density, Cross correlation, Frequency Response Functions (FRF) and coherence. The Interface and analysis algorithms are developed inLabview programming language. The thesis starts by introducing the overall aim of the project and its scope, the place of this particular thesis in the whole picture and the algorithms used for analysis are introduced. In the second part of the thesis the development of the software is explained and the main aim is to thoroughly document the software. This part of the thesis explains Labview programming concepts in detail to make it easier for other students who want to undertake theses to continue this work and who may not have experience of Labview programming.Two versions of the spectrum analyzer were developed. The third part explains theexperimental set up and results obtained and compares measurements to those obtained using other spectrum analyzers. An accurate Spectrum Analyzer Virtual Instrument has been developed and tested during this thesis project and it can be used as a component of the proposed Sound and vibration analysis laboratory and also for general Spectral Analysis tasks. / Good guide to learn Labview and sound and vibration analysis.. / fkul08@gmail.com Is my email and i can be contacted via messenger usually at farooq_kifayat@hotmail.com And i can also be contacted via skype using farooqkifayat as my name. I move around a lot so i have no permanent address that stays longer than half a year .

Micromachined biosensors are used in chemical and biological applications. A biosensor which uses mass based transduction is called a mass sensor. Mass sensors are used to detect extremely small mass of biomolecules such as proteins, viruses or even parts of DNA in the range of femtograms (10-15 gm) to zeptograms (10−21 gm). Highly effective and reliable microcantilevers are used for detecting the mass of biomolecules using either static deflection or dynamic resonant peak shifts. The main objective of our work is to investigate the effect of elasticity of the attached mass on the shift in the resonant frequency and examine the validity of the rigid mass assumption used in the literature. The natural frequencies of a resonator are either found by solving the governing differential equation or approximately using Rayleigh-Ritz method. The mass of a body, attached to a resonator beam is determined using resonant frequency shift method. In our study, we derive an analytical expression for ‘δm’ based on the shift in frequency ‘δf’ that accounts for the elasticity of the added mass and the location of the mass on the beam. We study the simplest model to incorporate these effects where the added mass is itself modeled as a single degree of freedom spring-mass system. The entire system is represented as a 2-DOF lumped model of cantilever and the attached elastic mass. The natural frequencies are obtained using eigenvalue analysis. We study the mass estimation of Escherichia Coli (E. Coli), a food borne pathogen, using experimental results reported in the literature. We treat E.Coli as an elastic mass and model it as a single degree of freedom system to account for its elasticity. We use the elastic model as well as the rigid mass model to check the results available in the literature and point out the difference that results in mass estimation using the two models. To demonstrate the effect of elasticity on mass sensing using the resonant peak shift technique, we conduct mesoscale experiments. Since the fundamental principle does not depend on any phenomenon exclusively dependent on micro scales, the mesoscale experiments are justified. For this purpose, an experimental set-up with metallic cantilevers and flexible rubber strands as attached masses are used. We also use our experimental set-up to study the effect of positional inaccuracy of the added mass (rigid) in the computation of its mass from the shift in the resonance frequency. The results obtained show that elasticity of the added mass as well as its position on the resonator affect the computed mass but this effect is dependent on the relative stiffness and mass of the resonator and the added mass. We also observe the limitations of the experiments in carrying out studies over the desired range of parameters. We also create a computational model of the system and carry out simulations to explore a larger range of parameter values. In particular, we create an FEM model of our system in ANSYS, and carry out modal analysis for the cantilever beam resonator with and without the added mass, varying the relative stiffness and mass of the two components (the cantilever beam and the added mass). We compare the results of shift in the resonant frequency with those obtained from the rigid mass model. The results show the effect of elasticity clearly in certain ranges of relative stiffness and mass.