Search

Odd-harmonic repetitive control (ORC) has been successfully applied to improve the triangular trajectory tracking performance of nanopositioners. However, the conventional ORC tends to amplify the tracking errors at frequencies other than the odd-harmonic components, mainly the even harmonics of the fundamentals of the intended triangular trajectory to be tracked. Due to the influence from the hysteresis nonlinearity of the piezoelectric actuator, this would result in significant tracking errors. To overcome this limitation, this article proposes an enhanced odd-harmonic repetitive control (EORC) using the spectrum-selection filtering scheme to improve the loop-shaping property of the ORC. This effectively eliminates the problem of amplifying the tracking errors while preserving the advantages of the conventional ORC, such as fast convergence speed and low computation cost. The EORC is combined with a proportional–integral tracking controller to improve the tracking performance. The controller design, stability analysis, and performance evaluation are presented. The experimental results demonstrating the effectiveness of the proposed EORC-based control scheme are presented showing the excellent tracking of triangular trajectories with fundamental frequencies up to 1000 Hz. Moreover, a reduction in rms tracking errors by up to 52% is achieved. Note to Practitioners—The high-speed atomic force microscopy (AFM) plays an increasingly vital role in observing and manipulating objects at the nanoscale. In the raster scanning of AFMs, the most challenging issue is the triangular trajectory tracking of nanopositioning stages with high precision. Although the odd-harmonic repetitive control (ORC) has been successfully applied to improve the tracking performance, the conventional ORC would amplify the tracking errors distributed at the frequencies other than the odd harmonics, especially those at the even harmonics, resulting from the inherent complicated hysteresis nonlinearity. This problem of amplifying the tracking errors would lead to larger tracking errors, deteriorating the performance of AFM imaging. To address this issue, this article proposes an enhanced ORC using the spectrum-selection filtering scheme to improve the loop-shaping property of the ORC, so as to eliminate the problem of amplifying the tracking errors while preserving the advantages of the conventional ORC, such as fast convergence speed and low computation cost. The experimental results show that, with this simple modification, the positioning errors are reduced greatly, all-the-while preserving the benefits of the conventional ORC scheme– fast convergence speed and low computation cost. In terms of tracking accuracy and the simple structure, this development can be easily implemented to other systems that challenge from the tracking accuracy under ORC scheme. [ABSTRACT FROM AUTHOR]

The scanning speed of atomic force microscopes (AFMs) is typically limited by the frequency of the triangular trajectory used in generating the raster scan. This is because the higher harmonics of the triangular trajectory have a tendency to excite the mechanical resonances of the nanopositioners incorporated in the AFM; thereby, introducing significant positioning errors. To address this issue, this article proposes a novel scanning trajectory smoothing method to enable high-speed raster scanning. The proposed method utilizes the acceleration-continuous B-spline to replace the backward path of the triangular trajectory for the fast axis. As a result, the advantage of uniform sampling along the forward path is preserved. The trajectory generation process is described in detail. A hysteresis compensation method is employed to improve the tracking performance of the scanner. Experiments conducted on a commercial piezoelectric tube scanner are presented to demonstrate the performance improvement delivered by the proposed method when compared with the traditional raster scanning method. It is shown that the proposed method enables a five-fold improvement in achievable scanning rate, from 10 to 50 Hz. [ABSTRACT FROM AUTHOR]

During the raster scanning of atomic force microscopes (AFMs), the coupling effect from the fast-axis to the slow-axis is extraordinarily pernicious, especially when the scanning rate is set high. Whilst great efforts have been made in the field of piezo-actuated stages, less attention is paid on control design to mitigate this coupling effect. In this paper, we propose a modified repetitive control based cross-coupling compensation (MRC-CCC) approach for high-speed and high-precision scanning motion control of a piezoelectric tube scanner in AFMs. Based on the experimental observations, we first describe this coupling effect as the periodic disturbance to the output of the slow-axis when the fast-axis is designed to track triangular trajectories. Then, the MRC-CCC controller is developed to remedy the periodic disturbances, which generates the compensation signals targeting the coupling effect. Therefore, the complicated modeling of the cross-coupling effect is avoided, which significantly reduces the complexity of usage. To ensure the high-precision tracking performance for the slow-axis in scanning, we further design a tracking controller that combines with the offline trained MRC-CCC controller. Finally, comparative experiments are conducted on an AFM piezoelectric tube scanner. Experimental results show that the developed MRC-CCC approach significantly compensates for the coupling effect, in which the root-mean-square tracking error is substantially reduced from 172.1 to $3.3\text{ nm}$ at the scanning rate of 40 Hz. We also perform high-speed scanning tests for AFM imaging to verify the effectiveness of the development. [ABSTRACT FROM AUTHOR]

A compliant XY nanopositioner is presented in this brief. The device is designed to have a very low cross-coupling between the X - and Y -axis. Despite this, during high-speed raster scans, the cross-coupling effect can not be ignored. In this brief, a H∞ controller is designed and implemented to minimize the X -to-Y cross-coupling of the nanoscale positioning stage, particularly at its mechanical resonance frequencies. The controller is augmented with integral action to achieve accurate tracking, as well as sufficient damping. Raster scan results over an area of 10 µm 10 µm with small positioning errors are demonstrated. High-speed accurate raster scans of up to 100 Hz, with nanoscale resolution are also illustrated. [ABSTRACT FROM AUTHOR]

We introduce a backside island isolation method for silicon-on-insulator (SOI)-based microelectromechanical systems technology and demonstrate vertical comb drive-based two-dimensional gimbaled micromirrors with large static rotation using the isolation method. The proposed isolation method provides electrical isolation and mechanical coupling of SOI structures without additional dielectric backfill and planarization by utilizing timed etched backside handle wafer structures. The backside island is a hidden layer beneath the gimbal and allows independent application of actuation potentials to the gimbal and inner mirror. We developed the fabrication process that accommodates the backside island isolation structures into an established vertical comb drive process, thereby allowing implementation of two-axis gimbaled structures. The maximum static optical deflections of the gimbal and mirror are 46° and 15°, respectively. [ABSTRACT FROM PUBLISHER]

We describe the design, fabrication, and experimental results of a raster scanning laser display system using micromachined electrostatic scanning micromirror. The micromirror is comprised of a diaphragm mirror plate supported by an array of diamond shaped support frame, and movable comb electrodes. A prototype raster scanning laser display system using the fabricated micromirror, having optical scan angle of 16.9deg at resonance frequency of 19.55 kHz, as the horizontal scanner was developed and tested. To compensate for the nonlinear characteristics of the scanner, a simple image correction method was developed, and the projected image was analyzed and compared with the simulation results [ABSTRACT FROM PUBLISHER]