The application of robotic manipulators in machining systems has gained a great interest in manufacturing because of their lower prices, higher kinematic flexibility and larger workspace compared to conventional CNC machine tools. However, their performance is limited due to the much lower structural rigidity which makes them more susceptible to excessive and unstable vibrations, known as chatter, during the machining process. Highly effective chatter modeling and avoidance methods that have been developed for CNC machining in the past decades are now being used by the industry to design high-performance chatter-free machining operations. The available methods, however, face major difficulties when applied to robotic machining, mainly due to the high flexibility and pose-dependency of the vibration response in robots. High flexibility leads to high-amplitude vibrations which affect the process dynamics and excite structural nonlinearities. The existing approaches to modeling machining vibrations assume linearity of the structural dynamics of the robotic manipulator. This assumption, considering the inherent nonlinearities in the robot’s revolute joints, may cause considerable inaccuracies in predicting the stability of vibrations during the process. This thesis studies the high flexibility and nonlinearity of the robot’s structural dynamics and their effects on chatter vibrations. The research starts with investigating the effects of high flexibility of robot's structure in the process dyamics by considering the modulation of cutting forces by axial vibrations, which is normally ignored in CNC milling due to high rigidity of the machine in this direction. The results of chatter prediction considering this effect are shown and discussed. The rest of the thesis focuses on the structural nonlinearity. Firstly, an experimental study is presented to investigate the extent of nonlinearity in structural dynamics of the robot. The results confirm that structural nonlinearities in robotic machining systems can be effectively excited in the presence of high-amplitude vibrations due to milling forces, such that they cause remarkable differences in chatter prediction. The following step is modeling the structural nonlinearities. For this purpose, the variation of restoring forces with the dynamic response (displacement and velocity) are observed when the robot is subjected to harmonic excitation. Based on the experimental observations, the nonlinear effects are modeled by cubic stiffness and damping characteristics. Parameters of the nonlinear model are then identified using Higher-order Frequency Response Functions (HFRF) extracted from measurements. The identified model can predict the vibration behavior of the robotic machining system when subjected to periodic loads such as milling forces. The developed model of nonlinear structural dynamics is then coupled with the chatter model. Consequently, the system is described by nonlinear Delay Differential Equations (DDE) with periodic coefficients. Bifurcation diagrams for the forced vibrations in the described system are developed using the numerical continuation method. The effects of cutting parameters such as feedrate as well as the nonlinear parameters are studied. The thesis is concluded by proposing the use of in-process FRF in the linear model of chatter stability for quick prediction of stability limits. In this approach, the exact characteristics of the nonlinear mechanisms are not studied; instead, the measured FRF during the milling process are used, which are assumed to represent the nonlinear structural dynamics that are linearized about the applied operational conditions. Two methods of measuring in-process FRF are proposed and employed in the robotic milling system. The measured FRF are then used in the linear chatter model to develop the Stability Lobes Diagram (SLD) which shows the combination of cutting parameters that lead to stable or unstable vibrations. Experimental chatter tests show that better agreement with predictions can be achieved by using in-process FRF instead of FRF measured at the idle state of the system. The results of this thesis contribute to better characterization of vibrations in robotic machining with high-amplitude forces and selecting suitable strategies to enhance productivity of the operation. / Graduate

Vibration within the vocal tract during speech is transmitted through body tissue to the skin surface and can be used to transmit speech. Achieving quality speech signals using skin vibration is desirable but problematic, primarily due to the different sources of sound during speech. The objective of this study was to characterize the frequency content of speech signals at various locations on the head and neck. Signals were recorded using accelerometers attached to 15 locations on the heads and necks of 14 males and 10 females as well as a microphone to record audible speech. The subjects produced several isolated phonemes and one phrase. The power spectral densities (PSDs) of the phonemes were used to determine a quality ranking for each location and sound. A spectrogram of the phrase was used to compare the response at selected locations. A perceptual listening test was conducted and compared to the PSD rankings. The PSD rankings were also calculated for signals recorded with background noise in order to identify locations that are least sensitive to external noise. With background noise, the frequency response of the skin was also used to study how the skin itself responds to external noise. The signal-to-noise ratio (SNR) was found for various sounds and locations with and without the presence of background noise. The frequency response of a concentrated area of the neck was also studied. Notably, while high frequency content was found to be attenuated at locations on the throat near the thyroid cartilage, it was detectable at some other locations. The best locations for speech transmission were found to be generally common to males and females in quiet environments but varied with background noise. During speech in the presence of background noise, the accelerometers performed better than the microphone when compared to the PSD of a clean microphone recording of the same sound. All SNR of all locations were influenced somewhat by external noise, some considerably more than others. Some neck locations may be better suited for contact microphone placement other than directly over the thyroid cartilage (where many commercial contact microphones are currently worn) if the neck is the preferred location for contact microphone placement.

A study of the frequency response and gain of Solid-state the Impact-ionization Multiplier (SIM). The SIM generates current gain via impact ionization also known as avalanche gain. The SIM provides low noise amplification from an arbitrary current source. In the case of this study, current sources consisted of photodiodes optimized for a particular wavelength of light. The SIM is fabricated from silicon and enjoys the low noise, low carrier transit time advantages of conventional silicon impact ionization devices while amplifying current from a photodiode of a different material. This is advantageous because ideal detection and multiplication regions cannot always be grown on the same wafer. Furthermore a photodiode fitted to a SIM allows absorption and multiplication regions to be independently optimized. The SIM exhibits a current dependant input resistance. This resistance in combination with field effects from the SIM collector is the limiting factor in the frequency response of the SIM. Frequency response is improved to the extent that this floating voltage at the input can be minimized. Higher AC gains are realized in the device with the incorporation of 3-dimensional geometries. These improvements allow for improved device breakdown and reduced space-charge resistance at high input currents. Frequency response can also be improved by increasing the current flowing into the SIM, this current is most often in the form of DC current such that it can be filtered off at a the output and not interfere with the input signal.

Bilindustrin är i ständig utveckling och är väl medvetna om de ökande kraven från kundermed avseende på körkomfort och körupplevelse. Lastbilar med tunga laster är ofta utrustademed en påbyggnad, till exempel en låda för pallar och gods, en sopsamlare eller en stödram förbärning av timmer. SCANIA Bodybuilding Center utvecklar riktlinjer för val av olika typer avkarosseri, dvs typ av stödram och antal , fästpunkter. Målet med detta arbete är att utvecklaen bättre förståelse för hur det stödjande ramverket och dess infästningar i en lastbil påverkarrammens dynamik och sedan föreslå förbättringar till dessa riktlinjer.Viktiga parametrar som påverkar chassisdynamiken identifierades och beskrivs från början.Fysisk vibrationstestning av chassiet och påbyggnadsram med fasthållningsfäste utfördes vidi testrigg på Scania R&D. Frekvensresponsfunktionerna från mätningarna användes för attbestämma modala parametrar. Olika test utfördes genom att ändra parametrarna och upptagningenav mätningarna. Testresultaten användes för att studera egenfrekvenser egna frekvenser,modifieringsformer och dämpning i systemet. Även en ny metod för att bygga en dynamiskfinit element (FE) modell eller chassi och påbyggnadsram är presenterad i denna undersökning.Modalanalys av chassi-påbygnadsramssystemet gjordes för att studera FEMs egna frekvenseroch modeformer. Den föreslagna metoden för koppling av chassit och delramen i FEM är kritisktbedömd genom att korrelera FE-simuleringen med de experimentella resultaten. Baserat på deutförda experimenten och den numeriska simuleringen föreslås från experiment och numerisksimulering, föreslås nya rekommendationer med avseende på påbyggnadsanslutningarnas konfigurationi lastbil. / The automotive sector is continuously evolving and the companies are well aware of therising demands from customers with regard to driving comfort and experience. Trucks carryingheavy loads are often equipped with on-built bodywork, for example a box for pallets and goods, agarbage collector device or a supporting frame for carrying timber. SCANIA bodybuilding centredevelops guidelines for selecting different types of bodywork, i.e. the type of supporting frame,design and number of attachment brackets, attachment points. The purpose of this master thesisis to develop a better understanding of how the supporting frame and its attachments in a truckinfluence the chassis frame dynamics and to propose improvements to these guidelines.Major parameters influencing the chassis dynamics were identified and described from theoutset. Physical vibration testing of the chassis-subframe assembly was carried out at roadsimulator. The frequency response functions from the measurements were used to determinethe modal parameters. Several tests were performed by altering the parameters and recordingthe measurements. The results from the test cases were used to study and analyse the eigenfrequencies, mode shapes and damping in the system. Also, a new method to build a dynamicfinite element (FE) model of chassis and subframe is presented in this study. Modal analysisof the chassis-subframe assembly was done to study the eigen frequencies and mode shapes byFEM. The proposed method of coupling the chassis and the subframe is critically assessed bycorrelating the results from FE simulation with the experimental results. Based on the resultsfrom experiment and numerical simulation, new recommendations are proposed with regard tothe bodywork attachments’ configuration in the truck.

There has been increasing interest in the use of Very Small Aperture Terminals (VSATs) in satellite communication links operating in the Ku and Ka bands. Such systems offers the advantage of low signal margins and therefore, low cost. For the same reason, however, VSATs links can be strongly impaired by tropospheric scintillations. The VA Tech OLYMPUS propagation experiment which includes 12, 20, 30 GHz beacon receivers at an elevation angle of 14° provides us with valuable multi-frequency scintillation data. This dissertation focuses on the characterization of tropospheric scintillations on earth-space paths. Tropospheric scintillations are rapid fluctuations of signal caused by multiple scattering from the sma11 scale turbulent refractive index inhomogeneities in the troposphere. Analysis of the scintillation results from the VA Tech OLYMPUS experiment for both short term and long term studies is presented. The results include spectral characteristics, frequency scaling and statistics of the scintillation intensity, statistics of scintillation fading, diurnal and meteorological trends as well as a comparison with the current CCIR predictive model. Sma11 scale spatial diversity is a potential means to counteract tropospheric scintillation fading; it can be cost effective because of the low cost of VSATs. The VA Tech experiment includes 12, 20, 30 GHz beacon receivers and colocated 20 and 30 GHz diversity receivers that allows us to study this restoration technique. In this dissertation the effects of spatial diversity are studied through a cross-correlation analysis. Experimental results are compared to a theoretical model in which the atmosphere is characterized by an "anisotropic" Kolmogorov spectrum. A method to determine minimum vertical spacing between terminals to achieve good diversity performance is introduced. / Ph. D.

An experimental and analytical investigation was conducted to gain insight and ultimately predict the dynamic flow response of a fan rotor with inlet flow distortion. Rotor exit total pressure circumferential profiles were accurately predicted using frequency response functions derived from experimental rotor response data. Using these predicted profiles, an initial attempt was made at predicting the dynamic (distorted) stage characteristics of the test machine with promising results. The first step of this research was an experimental investigation to gather unsteady rotor response data. The steady three-dimensional inlet flow of an isolated rotor subjected to inlet distortion was obtained using a five-hole pneumatic prism probe. Exit flow dynamic wake data were obtained using a piggyback steady/unsteady total pressure probe in non-nulling mode. Inlet and exit data were collected for eighteen different combinations of distortion level, operating point, and measurement span. Frequency response functions were generated and then averaged for each operating regime, span, and distortion intensity, assuming the data to be stationary and ergodic. These 'generalized' FRF's were used to predict the rotor exit total pressure profile. These pressure profiles were then used in an initial attempt to predict the dynamic stage (distorted) characteristics of the test machine. Best predictions resulted when an FRF was used for individual operating regimes, defined with respect to rotor blade mean aerodynamic loading. / Master of Science

Global Navigation Satellite Systems (GNSS) are vital tools for accurate navigation and timing for both civil and military use. Due to the low power of the GNSS signals, these systems are sensitive to interference attacks. For wideband GNSS jamming, adaptive antenna arrays are commonly used to suppress interference.  This thesis focuses on how distortions induced by adaptive antenna arrays can affect the performance of a GNSS receiver and how prone different beamforming algorithms are to suffer from such distortions. To investigate this, simulations in software have been performed for static scenarios with two different beamforming algorithms and four different antenna arrays. The results show that the method for interference suppression that uses constraints in direction and frequency achieves a higher signal-to-interference-plus-noise ratio, more stable acquisition over the hemisphere, and less fluctuating code delay error than the method that only minimizes the power of the output signal.

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