Control and Systems Approaches to Atomic Force Microscopy (original) (raw)
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A Tutorial on the Mechanisms, Dynamics, and Control of Atomic Force Microscopes
2007 American Control Conference, 2007
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.
Design and control of atomic force microscopes
Proceedings of the 2003 American Control Conference, 2003., 2003
Models for two atomic force microscope (AFM) designs were presented, namely, cantilever-on-scanner and sample-an-scanner design. It was found that coupling between scanner's bending and extension motion is present in both designs, making the scanner bending mode observable from the output. As a result, the ultimate feedback bandwidth is limited by the lowerfrequency bending mode in contrast to being ideally limited by the extension mode. Simulation and experimentaldata provided insight into pole-zero flipping and changes in the system dynamics as a function of force set-paint and input amplitude. Closed loop performance under integral and PID control were compared. It was found that PID control offers lower bandwidth over integral control if high-frequency rollloff and step response overshoot constraints were to be met. In addition, integral controller has a single gain compared 3 for PID; which makes it easier for parameter tuning by AFM users.
A comparison of control architectures for atomic force microscopes
Asian Journal of Control, 2009
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.
On automating atomic force microscopes: An adaptive control approach
Control Engineering Practice, 2007
In this paper, modeling and experimental results are given to reveal the structure of atomic force microscope (AFM) dynamics and uncertainties which are strongly impacted by the user's choice of scan and controller parameters. A robust adaptive controller is designed to eliminate the need for the user to manually tune controller gains for different sample cantilever combinations and compensate for uncertainties arising from the user choice of different scan parameters. The performance of the designed adaptive controller is studied in simulation and verified through experiments. A substantial reduction in contact force can be achieved with the adaptive controller in comparison with an integral controller.
Architectures for tracking control in atomic force microscopes
2008
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 find that even in the presence of plant uncertainty, the closed-loop-injection architecture yields better tracking performance of a raster scan.
Combined Feedforward/Feedback Control of Atomic Force Microscopes
2007 American Control Conference, 2007
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∞, ℓ1, 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.
Multivariable Control of a Metrological Atomic Force Microscope
2009
Atomic Fore Microscopes (AFMs) are widely used for nanoscale applications. Until recent developments these instruments were controlled in open loop or by a PID type controller. In the last decade model-based control techniques emerged for controlling AFMs, but in almost all cases the multivariable behavior was ignored. In this paper, we present a multivariable control strategy using the standard plant framework, applied to a metrological AFM, used for the calibration of transfer standards. Although this device has a low amount of coupling, we will show that multivariable control has advantages. By using multivariable control, the amount of coupling is reduced compared to decentralized control. Simulations show a significant reduction of the errors in x, y and z directions by applying multivariable control.
Advanced Mechanical Design and Control Methods for Atomic Force Microscopy in Real-Time
2007 American Control Conference, 2007
This article reviews mechanical design and control of atomic force microscopes (AFM) with a special emphasis on high-speed imaging. The mechanical design and the control system determine the achievable imaging speed of the AFM. To enable AFM imaging at video-rates, imaging speed -and thus system performance -has to be increased by at least two orders of magnitude relative to today's commercial AFMs. Methods and results presented in this paper demonstrate how this can be achieved.
Advanced Control of Atomic Force Microscope for Faster Image Scanning
In atomic force microscopy (AFM), the dynamics and nonlinearities of its nanopositioning stage are major sources of image distortion, especially when imaging at high scanning speed. This chapter discusses the design and experimental implementation of an observer-based model predictive control (OMPC) scheme which aims to compensate for the effects of creep, hysteresis, cross-coupling, and vibration in piezoactuators in order to improve the nanopositioning of an AFM. The controller design is based on an identified model of the piezoelectric tube scanner (PTS) for which the control scheme achieves significant compensation of its creep, hysteresis, cross-coupling, and vibration effects and ensures better tracking of the reference signal. A Kalman filter is used to obtain full-state information about the plant. The experimental results illustrate the use of this proposed control scheme.
2009
Abstract This paper presents experimental implementation of a positive position feedback (PPF) control scheme for vibration and cross-coupling compensation of a piezoelectric tube scanner in a commercial atomic force microscope (AFM). The AFM is a device capable of generating images with extremely high resolutions down to the atomic level. It is also being used in applications that involve manipulation of matter at a nanoscale. Early AFMs were operated in open loop.