Bharath Bhikkaji

Atomic Force Microscopes (AFM) are used for generating surface topography of samples at micro to atomic resolutions. Many commercial AFMs use piezoelectric tube nanopositioners for scanning. Scanning rates of these microscopes are hampered by the presence of low frequency resonant modes. When inadvertently excited, these modes lead to high amplitude mechanical vibrations causing the loss of accuracy, while scanning, and eventually to break down of the tube. Feedback control has been used to damp these resonant modes. Thereby, enabling higher scanning rates. Here, a multivariable controller is designed to damp the first resonant mode along both the x and y axis. Exploiting the inherent symmetry in the piezoelectric tube, the multivariable control design problem is recast as independent single-input single-output (SISO) designs. This in conjunction with integral resonant control is used for damping the first resonant mode. © 2013 American Institute of Physics.

A XYZ scanner is designed for fast and high resolution atomic force microscopy. The objective of this paper is to achieve a large scanning bandwidth along the X and Y axis of the scanner. Finite element analysis of the designed scanner is reported along with the experimental determination of the dynamics. Both suggest the presence of first resonant modes around 8.8 kHz and 8.9 kHz along the X and Y axis respectively. Actuating the scanner at frequencies beyond 1% of the first resonance causes mechanical vibrations and hence degradation of the images generated. Controllers are designed, using the Integral Resonant Control methodology, to damp the resonant modes, to enable fast actuation. Due to the large bandwidth of the designed scanner, a Field Programmable Analog Array (FPAA) is used for analog implementation of the controllers. High resolution images are generated at faster scanning rates in closed loop. © 2011 IEEE.

Most AFMs use piezoelectric tube nanopositioners for scanning. Fast actuation of piezoelectric tubes are restricted due to the presence of low mechanical resonant modes. These resonances, when excited, set off vibrations that cause loss of precision and repeatability of the scans. Thereby restricting the scanning frequencies to less than 1% of the first resonance frequency. Here, an innovative multivariable control design methodology for damping the resonant modes of the tube is presented. This methodology exploits the symmetry present in transfer-functions relating the input and output, and converts the multivariable control design problem into independent SISO designs. This methodology in conjunction with Integral Resonant control is used for damping the first resonant mode of the tube, and enables scans upto 10% of the first resonant mode. The proposed methodology can be applied to a large class of parallel kinematics nanopositioners used in scanning probe microscopes and probe-based data storage systems. © 2011 IFAC.