Browsing by Subject "Saturation"
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Item Controller Design and Analysis of Dual-stage Hard Disk Drives in the Presence of Micro-Actuator Stroke Limitation(2022-11) Chakraborty, ManashWith the continuous increase in storage capacity, the width of a hard disk drive (HDD) data track is decreasing, and the traditional single-stage actuation system is insufficient for such high-precision actuation. Hence, a secondary high-bandwidth piezoelectric (PZT) type micro-actuator is widely used to enhance HDD's precision servo tracking capability. However, the micro-actuator is typically prone to actuator saturation, which limits the achievable closed-loop sensitivity performance of a controller design. Hence, any undesired high-magnitude disturbance might cause an aggressive controller to demand high stroke usage from the actuator system, which can lead to saturation of the micro-actuator. This work presents an analysis method to predict the micro-actuator stroke usage for a given controller by taking advantage of the stochastic interpretation of H2 system norm. Measured data from a Seagate HDD are used to model several disturbance environments and calibrate the proposed prediction model. Then the idea of predicting the micro-actuator stroke usage is used to explore a mixed H2/H-infinity controller synthesis method to avoid saturation of the micro-actuator in a dual-stage actuator system while maximizing the closed-loop disturbance rejection performance. Finally, a two-step nonlinear analysis method is also discussed to determine the worst-case disturbance rejection performance under micro-actuator saturation by utilizing the concept of bounded nonlinearity. Necessary mathematical proofs are provided to support the proposed analysis method and a numerical example is discussed with a validation process via numerical simulation.Item Global saturation of regularization methods for inverse ill-posed problems(University of Minnesota. Institute for Mathematics and Its Applications, 2008-07) Spies, Ruben D.; Temperini, Karina G.Item Mobility, access, and choice: A new source of evidence(Journal of Transport and Land Use, 2013) Metz, DavidThe availability of a large national data set of accessibility indicators allows investigation of the relationship between mobility and access to, and choice of, key destinations for the population of England. The destinations considered are primary and secondary schools, further education colleges, family doctors, hospitals, food stores, and places of employment. For the populations of 353 local authorities, the average extent of choice of these destinations is estimated as a function of travel time and mode. It is concluded that high levels of access and choice are available to the large part of the population that has available a car or good public transport. This finding is consistent with the suggestion that the demand for daily travel has saturated.