Design and control of atomic force microscopes (original) (raw)
Related papers
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.
Improved Control of Atomic Force Microscope for High-Speed Image Scanning
2012
In this paper the design and experimental implementation of an observer based model predictive control (OMPC) scheme for accurate tracking and fast scanning of an atomic force microscope (AFM) is presented. The design of this controller is based on an identified model of the AFM piezoelectric tube (PZT) scanner. A Kalman filter is used to obtain full-state information in the presence of position sensor noise. To evaluate the performance improvement using the proposed control scheme an experimental comparison has been made with scanned images between the proposed controller and the existing AFM PI controller. The experimental results verify the efficacy of the proposed controller.
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.
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.
Semi‐automatic tuning of PID gains for atomic force microscopes
2009
The control of a typical commercial Atomic Force Microscope (AFM) is through some variant on a Proportional, Integral, Derivative (PID) controller. Typically, the gains are hand tuned so as to keep the bandwidth of the system far below the first resonant frequency of the actuator. This paper shows a straightforward method of selecting PID gains from the actuator model so as to allow considerably higher bandwidths.
Modeling, identification and control of a metrological Atomic Force Microscope with a 3DOF stage
Proceedings of the American Control Conference, 2008
Atomic Force Microscopes (AFMs) are widely used for the investigation of samples at nanometer scale. In this paper, we present the modeling, the identification and the control of a metrological AFM. The metrological AFM is used for the calibration of transfer standards for commercial AFMs. Therefore, the focus of the presented work is on scanning accuracy rather than on scanning speed. The contribution of this paper is the combination of 3 degree-of-freedom (DOF) control, including position feedforward, with an AFM with fixed cantilever and a piezo-stack driven stage. The amount of coupling between all DOFs is assessed by a non-parametric MIMO identification of the AFM. Since the dynamics appear to be decoupled in the frequency range of interest, feedback controllers are designed using loopshaping techniques for each DOF separately. Position feedforward is added to the stage in x and y direction, which improves the tracking performance by a factor two. The controlled stage is able to track scanning profiles within the sensor bound of 5 nm. With the proposed control method, the metrological AFM can produce images of the transfer standards with a sensor bound of 2 nm. Furthermore, real-time imaging of the sample is possible without the need for a-posteriori image correction. Finally, it is shown that the proposed control method almost completely compensates the hysteresis in the system.
Design and input-shaping control of a novel scanner for high-speed atomic force microscopy
Mechatronics, 2008
A novel design of a scanning unit for atomic force microscopy (AFM) is presented that enables scanning speeds three orders of magnitude faster than compared to conventional AFMs. The new scanner is designed for high mechanical resonance frequencies, based on a new scanner design, which is optimized using finite element analysis. For high-speed scanning a new controller, based on input-shaping techniques, has been developed that reduces imaging artifacts due to the scanner's dynamics. The implementation of the new AFM system offers imaging capabilities of several thousand lines per second with a scanning range of 13 lm in both scanning directions, and the freedom to choose the fast scan-axis in any arbitrary direction in the X-Y-plane.
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.
Development, analysis and control of a high-speed laser-free atomic force microscope
Review of Scientific Instruments, 2010
This paper presents the development and control of a laser-free atomic force microscopy ͑AFM͒ system for high-speed imaging of micro-and nanostructured materials. The setup uses a self-sensing piezoresistive microcantilever with nanometer accuracy to abolish the need for a bulky and expensive laser measurement system. A basic model for the interaction dynamics of AFM tip and sample in the high-speed open-loop imaging mode is proposed, accounting for their possible separation. The effects of microcantilever and sample stiffness and damping coefficients on the accuracy of imaging are studied through a set of frequency-domain simulations. To improve the speed of operation, a Lyapunov-based robust adaptive control law is used for the AFM XY scanning stage. It is shown that the proposed controller overcomes the frequency limits of the PID ͑Proportional-Integral-Derivative͒ controllers typically used in AFM. Finally, the paper presents a set of experiments on a standard calibration sample with 200 nm stepped topography, indicating accurate imaging up to the scanning frequency of 30 Hz.
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.