Browsing by Subject "Robust"
Now showing 1 - 6 of 6
Results Per Page
Sort Options
Item A compliant control law for industrial, dual-arm manipulators(2013-05) Zelenak, Andrew J; Landsberger, Sheldon; Pryor, Mitchell WayneMany of the first robots ever built, decades even before the first industrial robots, were humanoids. It seems like researchers have always sought to imitate the human form with their robots, and with good reason. Humans are incredibly flexible; they can perform a huge variety of tasks, from locomotion over rough terrain, to delicate assembly, to heavy lifting. A human’s second arm allows him to lift twice as much weight. His workspace is approximately doubled, and he can perform a broader variety of tasks as items are passed back and forth between hands. We sought to impart some of that same functionality to a strong, rigid, dual-arm robot. Specifically, we developed a control law that allows two robot arms to lift and manipulate an object in cooperation. As opposed to the prior art, our control law is tailored for industrial robots. These robots do not usually allow torque control and their control frequency is generally 60 Hz. Through the use of fuzzy logic, the control law is quite robust at 60 Hz control rates. Its simple structure reduces the computational cost of the algorithm by approximately 75% over Jacobian-based methods. Stability is proven and the controller parameters can be adjusted to handle perturbances of arbitrary magnitude. Since the robots behave as an admittance, torque control is not required. Several experiments were conducted to benchmark and validate the performance of this control law. The controller is able to maintain a clamp force within ± 4N despite a wide variation in trajectory and control frequency. This fine level of force control makes the controller suitable for delicate tasks. The conclusion suggests several extensions that would make this control law more useful. For example, adaptive control would improve the performance. A position feedback controller should be cascaded so that the robot arms’ tracking accuracy is improved. Many tasks (such as co-robotics) require external compliance, and we show how external compliance could easily be incorporated.Item Dynamic and Robust Capacitated Facility Location in Time Varying Demand Environments(2010-07-14) Torres Soto, JoaquinThis dissertation studies models for locating facilities in time varying demand environments. We describe the characteristics of the time varying demand that motivate the analysis of our location models in terms of total demand and the change in value and location of the demand of each customer. The first part of the dissertation is devoted to the dynamic location model, which determines the optimal time and location for establishing capacitated facilities when demand and cost parameters are time varying. This model minimizes the total cost over a discrete and finite time horizon for establishing, operating, and closing facilities, including the transportation costs for shipping demand from facilities to customers. The model is solved using Lagrangian relaxation and Benders? decomposition. Computational results from different time varying total demand structures demonstrate, empirically, the performance of these solution methods. The second part of the dissertation studies two location models where relocation of facilities is not allowed and the objective is to determine the optimal location of capacitated facilities that will have a good performance when demand and cost parameters are time varying. The first model minimizes the total cost for opening and operating facilities and the associated transportation costs when demand and cost parameters are time varying. The model is solved using Benders? decomposition. We show that in the presence of high relocation costs of facilities (opening and closing costs), this model can be solved as a special case by the dynamic location model. The second model minimizes the maximum regret or opportunity loss between a robust configuration of facilities and the optimal configuration for each time period. We implement local search and simulated annealing metaheuristics to efficiently obtain near optimal solutions for this model.Item Harmonic rejection mixers for wideband receivers(2013-05) Rafi, Aslamali Ahmed; Viswanathan, T. R., doctor of electrical engineering; Hassibi, ArjangThis dissertation presents novel Harmonic Rejection (HR) Mixer architectures to obtain a high level of harmonic rejection. This is achieved by reducing the sensitivity to mismatches in devices operating at high frequencies. Consequently, the HR performance for this mixer architecture is primarily determined by resistor and capacitor matching at low intermediate frequencies (IF). Since large resistor areas can be used at relatively less power penalty in the low frequency IF section, superior HR performance is realized. A design fabricated in 110 nm CMOS process, rejects up to the fi rst 14 local oscillator (LO) harmonics and achieves 3rd, 5th and 7th HR ratios in excess of 52, 54 and 55 dB respectively, without any calibration or trimming. This mixer architecture also rejects flicker noise, has improved image rejection (IR) and second-order input-intercept-point (IIP2) performance. By using a clock N times the desired LO frequency, this scheme rejects the (N-1)th LO harmonic only by an amount of 20log(N-1) dB. A new technique is presented that enables better HR for the (N-1)th harmonic while preserving the level of rejection for other harmonics. This mixer fabricated in 55 nm standard CMOS process has a programmable number of 8, 10, 12 or 14 mixer phases and achieves an improvement of 29 dB for the (N-1)th harmonic while achieving 52 dB of rejection for the 3rd harmonic. It also rejects flicker noise and has an IIP2 performance of 68 dBm. The mixers presented in this dissertation set the state-of-the-art in HR performance for single-stage mixers with configurable number of phases without using any calibration or trimming.Item Robust Ensemble Kalman Filters and Localization for Multiple State Variables(2014-05-23) Roh, SoojinEnsemble Kalman filters (EnKF) is a statistical technique used to estimate the state of a nonlinear spatio-temporal dynamical system. This dissertation consists of three parts. First, we develop a methodology to make EnKF robust, based on the employment of robust statistics. This methodology is necessary, since current EnKF algorithms tend to be sensitive to gross observation errors caused by technical or human errors during the data collection process, resulting in large biases or error variances. Second, we discuss the localization in the EnKF algorithms for simultaneous estimation of multiple state variables. The localization of the background-error covariance has proven to be an efficient method in reducing the sampling errors and compensating with the underestimation of the background error covariance terms. For a system of multiple state variables, the localization should be carefully applied in order to guarantee positive-definiteness of the matrices of the filtered background-error covariances. Rigorous localization methods for the case of multiple state variables, however, have rarely been considered in the literature. We introduce a number of localization filters that ensure that the background-error covariance matrix is positive-definite. Lastly, we extend the proposed robust method to both linear and nonlinear dynamical systems of multiple state variables.Item Robust Framework for System Architecture and Hand-offs in Wireless and Cellular Communication Systems(2010-01-14) Varma, Vishal V.Robustness of a system has been defined in various ways and a lot of work has been done to model the robustness of a system, but quantifying or measuring robustness has always been very difficult. In this research, we develop a framework for robust system architecture. We consider a system of a linear estimator (multiple tap filter) and then attempt to model the system performance and robustness in a graphical manner, which admits an analysis using the differential geometric concepts. We compare two different perturbation models, namely the gradient with biased perturbations (sub-optimal model) of a surface and the gradient with unbiased perturbations (optimal model), and observe the values to see which of them can alternately be used in the process of understanding or measuring robustness. In this process we have worked on different examples and conducted many simulations to find if there is any consistency in the two models. We propose the study of robustness measures for estimation/prediction in stationary and non-stationary environment using differential geometric tools in conjunction with probability density analysis. Our approach shows that the gradient can be viewed as a random variable and therefore used to generate probability densities, allowing one to draw conclusions regarding the robust- ness. As an example, one can apply the geometric methodology to the prediction of time varying deterministic data in imperfectly known non-stationary distribution. We also compare stationary to non-stationary distribution and prove that robustness is reduced by admitting residual non-stationarity. We then research and develop a robust iterative handoff algorithm, relating generally to methods, devices and systems for reselecting and then handing over a mobile communications device from a first cell to a second cell in a cellular wireless communications system (GPRS, W-CDMA or OFDMA). This algorithm results in significant decrease in amount of power and/or result is a decrease of break in communications during an established voice call or other connection, in the field, thereby outperforming prior art.Item Satellite Formation Design in Orbits of High Eccentricity for Missions with Performance Criteria Specified over a Region of Interest(2012-10-15) Roscoe, ChristopherSeveral methods are presented for the design of satellite formations for science missions in high-eccentricity reference orbits with quantifiable performance criteria specified throughout only a portion the orbit, called the Region of Interest (RoI). A modified form of the traditional average along-track drift minimization condition is introduced to account for the fact that performance criteria are only specified within the RoI, and a robust formation design algorithm (FDA) is defined to improve performance in the presence of formation initialization errors. Initial differential mean orbital elements are taken as the design variables and the Gim-Alfriend state transition matrix (G-A STM) is used for relative motion propagation. Using mean elements and the G-A STM allows for explicit inclusion of J2 perturbation effects in the design process. The methods are applied to the complete formation design problem of the NASA Magnetospheric Multiscale (MMS) mission and results are verified using the NASA General Mission Analysis Tool (GMAT). Since satellite formations in high-eccentricity orbits will spend long times at high altitude, third-body perturbations are an important design consideration as well. A detailed analytical analysis of third-body perturbation effects on satellite formations is also performed and averaged dynamics are derived for the particular case of the lunar perturbation. Numerical results of the lunar perturbation analysis are obtained for the example application of the MMS mission and verified in GMAT.