Closed-loop Frequency Tracking and Rejection

This paper develops an adaptive controller for active vibration control. The method is based on the LQG approach via disturbance modelling given in De Nicolao [1]. This approach to the narrow band disturbance rejection problem is then applied to the problem of eliminating the effects of roll eccentricity in steelstrip rolling mills

Adaptive Disturbance Rejection Using ARMARKOV/Toeplitz Models

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/57792/1/RaviARMARKOVAdaptiveTCST2000.pd

Advances In Internal Model Principle Control Theory

In this thesis, two advanced implementations of the internal model principle (IMP) are presented. The first is the identification of exponentially damped sinusoidal (EDS) signals with unknown parameters which are widely used to model audio signals. This application is developed in discrete time as a signal processing problem. An IMP based adaptive algorithm is developed for estimating two EDS parameters, the damping factor and frequency. The stability and convergence of this adaptive algorithm is analyzed based on a discrete time two time scale averaging theory. Simulation results demonstrate the identification performance of the proposed algorithm and verify its stability. The second advanced implementation of the IMP control theory is the rejection of disturbances consisting of both predictable and unpredictable components. An IMP controller is used for rejecting predictable disturbances. But the phase lag introduced by the IMP controller limits the rejection capability of the wideband disturbance controller, which is used for attenuating unpredictable disturbance, such as white noise. A combination of open and closed-loop control strategy is presented. In the closed-loop mode, both controllers are active. Once the tracking error is insignificant, the input to the IMP controller is disconnected while its output control action is maintained. In the open loop mode, the wideband disturbance controller is made more aggressive for attenuating white noise. Depending on the level of the tracking error, the input to the IMP controller is connected intermittently. Thus the system switches between open and closed-loop modes. A state feedback controller is designed as the wideband disturbance controller in this application. Two types of predictable disturbances are considered, constant and periodic. For a constant disturbance, an integral controller, the simplest IMP controller, is used. For a periodic disturbance with unknown frequencies, adaptive IMP controllers are used to estimate the frequencies before cancelling the disturbances. An extended multiple Lyapunov functions (MLF) theorem is developed for the stability analysis of this intermittent control strategy. Simulation results justify the optimal rejection performance of this switched control by comparing with two other traditional controllers

VISIR Upgrade Overview and Status

We present an overview of the VISIR upgrade project. VISIR is the mid-infrared imager and spectrograph at ESO’s VLT. The project team is comprised of ESO staff and members of the original VISIR consortium: CEA Saclay and ASTRON. The project plan is based on input from the ESO user community with the goal of enhancing the scientific performance and efficiency of VISIR by a combination of measures: installation of improved hardware, optimization of instrument operations and software support. The cornerstone of the upgrade is the 1k by 1k Si:As AQUARIUS detector array (Raytheon) which has been carefully characterized in ESO’s IR detector test facility (modified TIMMI 2 instrument). A prism spectroscopic mode will cover the N-band in a single observation. New scientific capabilities for high resolution and high-contrast imaging will be offered by sub-aperture mask (SAM) and phase-mask coronagraphic (4QPM/AGPM) modes. In order to make optimal use of favourable atmospheric conditions a water vapour monitor has been deployed on Paranal, allowing for real-time decisions and the introduction of a user-defined constraint on water vapour. During the commissioning in 2012 it was found that the on-sky sensitivity of the AQUARIUS detector was significantly below expectations and that VISIR was not ready to go back to science operations. Extensive testing of the detector arrays in the laboratory and on-sky enabled us to diagnose the cause for the shortcoming of the detector as excess low frequency noise (ELFN). It is inherent to the design chosen for this detector and can’t be remedied by changing the detector set-up. Since this is a form of correlated noise its impact can be limited by modulating the scene recorded by the detector. We have studied several mitigation options and found that faster chopping using the secondary mirror (M2) of the VLT offers the most promising way forward. Faster M2 chopping has been tested and is scheduled for implementation before the end of 2014 after which we plan to re-commission VISIR. In addition an upgrade of the IT infrastructure related to VISIR is planned in order to support burst-mode operations. The upgraded VISIR will be a powerful instrument providing close to background limited performance for diffraction-limited observations at an 8-m telescope. It will offer synergy with facilities such as ALMA, JWST, VLTI and SOFIA, while a wealth of targets is available from survey work (e.g. VISTA, WISE). In addition it will bring confirmation of the technical readiness and scientific value of several aspects of potential mid-IR instrumentation at Extremely Large Telescopes

A Set-Based Methodology for White Noise Modeling

This paper provides a new framework for analyzing white noise disturbances in linear systems: rather than the usual stochastic approach, noise signals are described as elements in sets and their effect is analyzed from a worst-case perspective. The paper studies how these sets must be chosen in order to have adequate properties for system response in the worst-case, statistics consistent with the stochastic point of view, and simple descriptions that allow for tractable worst-case analysis. The methodology is demonstrated by considering its implications in two problems: rejection of white noise signals in the presence of system uncertainty, and worst-case system identification

ENHANCED AIR-GAP CONTROL FOR HIGH-SPEED PLASMONIC LITHOGRAPHY USING SOLID IMMERSION LENS WITH SHARP-RIDGE NANOAPERTURE

INTRODUCTION Recently, plasmonic nanolithography is studied by many researchers (1, 2 and 3). This presented a low-cost and highthroughput approach to maskless nanolithography technique that uses a metallic sharp-ridge nanoaperture with a high strong nanometersized optical spot induced by surface plasmon resonance. However, these nanometer-scale spots generated by metallic nanoapertures are formed in only the near-field region, which makes it very difficult to pattern above the photoresist surface at high-speeds. To overcome this problem, we have designed and developed another type plasmonic nanolithography method that uses a metallic sharp-ridge nanometer-scale aperture and a solid immersion lens (SIL) based near-field recording technology. A plasmonic SIL optical head that consists of a metallic nanoaperture deposited on a SIL can fly ~20 nm above a photoresist (PR)-coated Si-wafer that moves in the linear direction at high speed that is several hundred times faster than existing plasmonic nanolithography methods. Because wafer size is small with several inches, moving velocity and acceleration of lateral stage should be fast to achieve high-speed plasmonic lithography. However, as moving velocity and acceleration are higher, disturbances are dramatically greater. This leads that maintaining gap between SIL and PR coated wafer and line-width is unstable. With existing control method, the residual gap error is over 8 nm at 200 mm/s. To maintain stable line-width, the residual gap error is should be under 2 nm. In this paper, to maintain stable gap and line-width at several hundred mm/s in linear direction, we propose enhanced air-gap control for high-speed plasmonic lithography using SIL. Firstly, we designed the base controller (lead and lag compensator), disturbance observer (DOB) and narrow band disturbance filter (NBDF) that is used to enhance the performance of the air-gap controller under repeatable and nonrepeatable disturbances (4, 5). And, through experiments, the feasibility of the proposed air-gap controller has been verified and checked that the stable gap and line-width are maintained at several hundred mm/s. EXPERIMENTAL SETUP AND CONTROLLER DESIGN EXPERIMENTAL RESULTS CONCLUSIONS To improve the control performance for high-speed plasmonic lithography using solid immersion lens, the control algorithm was designed with narrow-band disturbance filter (NBDF). As the experimental results indicate, the dominant frequency components in the system, which are due to vibration and resonance, are sufficiently eliminated by the proposed integrated control algorithm for the highspeed plasmonic lithography using SIL. Additionally, the nano-gap controller with the NBDF and the double DOB is proposed. In cases where the NBDF-based controller was used together with the double DOB, the air-gap controller performance was improved to avoid disturbance. ACKNOWLEDGMENT

System Identification, Diagnosis, and Built-In Self-Test of High Switching Frequency DC-DC Converters

abstract: Complex electronic systems include multiple power domains and drastically varying dynamic power consumption patterns, requiring the use of multiple power conversion and regulation units. High frequency switching converters have been gaining prominence in the DC-DC converter market due to smaller solution size (higher power density) and higher efficiency. As the filter components become smaller in value and size, they are unfortunately also subject to higher process variations and worse degradation profiles jeopardizing stable operation of the power supply. This dissertation presents techniques to track changes in the dynamic loop characteristics of the DC-DC converters without disturbing the normal mode of operation. A digital pseudo-noise (PN) based stimulus is used to excite the DC-DC system at various circuit nodes to calculate the corresponding closed-loop impulse response. The test signal energy is spread over a wide bandwidth and the signal analysis is achieved by correlating the PN input sequence with the disturbed output generated, thereby accumulating the desired behavior over time. A mixed-signal cross-correlation circuit is used to derive on-chip impulse responses, with smaller memory and lower computational requirement in comparison to a digital correlator approach. Model reference based parametric and non-parametric techniques are discussed to analyze the impulse response results in both time and frequency domain. The proposed techniques can extract open-loop phase margin and closed-loop unity-gain frequency within 5.2% and 4.1% error, respectively, for the load current range of 30-200mA. Converter parameters such as natural frequency (ω_n ), quality factor (Q), and center frequency (ω_c ) can be estimated within 3.6%, 4.7%, and 3.8% error respectively, over load inductance of 4.7-10.3µH, and filter capacitance of 200-400nF. A 5-MHz switching frequency, 5-8.125V input voltage range, voltage-mode controlled DC-DC buck converter is designed for the proposed built-in self-test (BIST) analysis. The converter output voltage range is 3.3-5V and the supported maximum load current is 450mA. The peak efficiency of the converter is 87.93%. The proposed converter is fabricated on a 0.6µm 6-layer-metal Silicon-On-Insulator (SOI) technology with a die area of 9mm^2 . The area impact due to the system identification blocks including related I/O structures is 3.8% and they consume 530µA quiescent current during operation.Dissertation/ThesisDoctoral Dissertation Electrical Engineering 201

Robust structural feedback linearization based on the nonlinearities rejection

International audienceIn this paper, we consider a class of affine control systems and propose a new structural feedback linearization technique. This relatively simple approach involves a generic linear-type control scheme and follows the classic failure detection methodology. The robust linearization idea proposed in this contribution makes it possible an effective rejection of nonlinearities that belong to a specific class of functions. The nonlinearities under consideration are interpreted here as specific signals that affect the initially given systems dynamics. The implementability and efficiency of the proposed robust control methodology is illustrated via the attitude control of a PVTOL