Abstract

MARQUEZ, J. A. et al. Fuzzy logic scheme for tip-sample distance control for a low cost near field optical microscope. J. appl. res. technol [online]. 2013, vol.11, n.6, pp.886-894. ISSN 2448-6736.

The control of the distance between the surface and the tip-sample of a Scanning Near Field Optical Microscope (SNOM) is essential for a reliable surface mapping. The control algorithm should be able to maintain the system in a constant distance between the tip and the surface. In this system, nanometric adjustments should be made in order to sense topographies at the same scale with an appropriate resolution. These kinds of devices varies its properties through short periods of time, and it is required a control algorithm capable of handle these changes. In this work a fuzzy logic control scheme is proposed in order to manage the changes the device might have through the time, and to counter the effects of the non-linearity as well. Two inputs are used to program the rules inside the fuzzy logic controller, the difference between the reference signal and the sample signal (error), and the speed in which it decreases or increases. A lock-in amplifier is used as data acquisition hardware to sample the high frequency signals used to produce the tuning fork oscillations. Once these variables are read the control algorithm calculate a voltage output to move the piezoelectric device, approaching or removing the tip-probe from the sample analyzed.

Keywords : Low-cost SNOM; fuzzy logic; nanometric control; shear-force.

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