A fuzzy control for high-speed and low-overshoot hopping probe ion conductance microscopy

At present, hopping probe ion conductance microscopy (HPICM) is the most capable ion conductance microscopy for imaging complex surface topography. However, the HPICM controller usually does not begin to stop the pipette sample approach until the ion current reaches a threshold, which results in short deceleration distances. Furthermore, closed-loop piezo actuation usually increases the response time. These problems tend to increase the ion current overshoot and affect imaging speed and quality. A fuzzy control system was developed to solve these problems via ion current deviation and deviation rate. This lengthens the deceleration distance to enable a high-speed approach toward the sample and smooth deceleration. Open-loop control of the piezo actuator is also used to increase sensitivity. To compensate for the nonlinearity of the actuator, a multi-section fuzzy logic strategy was used to maintain performance in all sections. Glass and poly(dimethylsiloxane) samples were used to demonstrate greater imaging speed and stability of the fuzzy controller relative to those of conventional controllers.