Feedback Scheme Based on Fuzzy Control for Shear Force Control

Fuzzy logic scheme for tip-sample distance control for a low cost near field optical microscope

“…A PID controller has a quick control response, allowing the processes to fulfil the desire behaviour, but for higher resolution images the scanning rate should be improved. Most strategies to get this resolution have been focused in the modification of the tuning fork features like Q-factor instead of controller design [3]. This Q-factor is defined by ∆ ⁄ , where ∆ means full frequency width at the half-maximum of the tuning fork amplitude resonance, and is the resonance frequency [4].…”

“…In this scheme, a tip-probe is perpendicularly aligned to the sample as it approaches to the surface in a horizontal array. Typically, the device vibrates laterally at one of its fundamental mechanical resonance modes, in the range of 10-100 KHz, in which the vibration is reduced due the presence of shear forces [3].…”

“…This property make the sensing task practical to implement and operate, compared to optical force measurements techniques. Furthermore, it can be designed to work in any frequency between 10 and 150 KHz [3].…”