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ABSTRACT: In previous work, we evaluated the performance of two control architectures applied to atomic force microscopes (AFM). Experimental results in indicated that the closed-loop-injection (FFCLI) architecture outperformed the plant-injection (FFPI) architecture when using a specific model-inversion feedforward technique for the tracking of a raster pattern. Empirical work suggested that a nontraditional variation upon the experimentally inferior FFPI architecture may allow it to track a raster pattern at a performance level in the neighborhood of the FFCLI architecture. This variation is manifested as additional delay inserted in the feedforward control system. An online adaptive technique is used to determine the required amount of additional delay. Experimental results show that the performance level of the FFCLI architecture and the adaptive-delay FFPI architecture are comparable.
American Control Conference (ACC), 2010; 08/2010
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ABSTRACT: We evaluate the performance of two control architectures applied to atomic force microscopes (AFM). Feedback-only control is a natural solu-tion and has been applied widely. Expanding on that, combining feedback controllers with plant-injection feedforward filters has been shown to greatly improve tracking performance in AFMs. Alternatively, performance can also be improved by the use of a closed-loop-injection feedforward filter applied to the reference input before it enters the feedback loop. In this paper, we compare the plant-injection architecture with the closed-loop-injection archi-tecture when used in controlling AFMs. In particular, we provide experimen-tal results demonstrating the closed-loop-injection architecture yields better tracking performance of a raster scan.
Asian Journal of Control 04/2009; 11(181). · 1.03 Impact Factor
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ABSTRACT: We evaluate the performance of two control architectures applied to atomic force microscopes (AFM). Feedback-only control is a natural solution and has been applied widely. Expanding on that, combining feedback controllers with plant-injection feedforward filters has been shown to greatly improve tracking performance in AFMs. Alternatively, performance can also be improved by the use of a closed-loop-injection feedforward filter applied to the reference input before it enters the feedback loop. In this paper, we compare the plant-injection architecture with the closed-loop-injection architecture when used in controlling AFMs. In particular, we provide experimental results demonstrating the closed-loop-injection architecture yields better tracking performance of a raster scan. Copyright © 2009 John Wiley and Sons Asia Pte Ltd and Chinese Automatic Control Society
Asian Journal of Control 02/2009; 11(2):175 - 181. · 1.03 Impact Factor
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ABSTRACT: Noncollocated sensors and actuators, and/or fast sample rates with plants having high relative degree, can lead to nonminimum-phase (NMP) discrete-time zero dynamics that complicate the control system design. In this paper, we examine three stable approximate model-inverse feedforward control techniques, the nonmimimum-phase zeros ignore (NPZ-Ignore), the zero-phase-error tracking controller (ZPETC) and the zero-magnitude-error tracking controller (ZMETC), which have frequently been used for NMP systems. We analyze how the discrete-time NMP zero locations in the z-plane affect the success of the NPZ-Ignore, ZPETC, and ZMETC model-inverse techniques. We also provide simulation examples using plants based on the system identification of an atomic force microscope and a hard disk drive, showing the tradeoffs in performance relative to NMP zero locations in these different application systems.
American Control Conference, 2008; 07/2008
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ABSTRACT: The atomic force microscope (AFM) is one of the most versatile tools in nanotechnology. For control engineers this instrument is particularly interesting, since its ability to image the surface of a sample is entirely dependent upon the use of a feedback loop. This paper will present a tutorial on the control of AFMs. We take the reader on a walk around the control loop and discuss each of the individual technology components. The major imaging modes are described from a controls perspective and recent advances geared at increasing the performance of these microscopes are highlighted.
American Control Conference, 2007. ACC '07; 08/2007
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ABSTRACT: The atomic force microscope (AFM) is a powerful imaging and nanofabrication tool that allows the user to observe and manipulate samples at the atomic level. However, one limitation of current AFMs is the long time required to obtain a quality image of a sample. Several researchers have investigated this problem in recent years, and we give an overview of the approaches explored, including H<sub>infin</sub>, lscr<sub>1</sub>, and model-inverse based methods. We compare and discuss advantages and disadvantages of the various approaches, and we end with a summary of open questions to be addressed in improving the control of AFMs.
American Control Conference, 2007. ACC '07; 08/2007
