A New Approach to Active Q Control of an Atomic Force Microscope Micro-cantilever Operating in Tapping Mode

When imaging in tapping mode, scan speed and image quality may be improved by modification of the Atomic Force Microscope (AFM) micro-cantilever quality (Q) factor. The most commonly applied method of Q control uses velocity feedback with an estimate of the cantilever tip velocity obtained by phase shifting the displacement signal. System performance may be degraded and stability can not be guaranteed using this control technique as the control action affects unmodeled cantilever dynamics. In this paper a resonant controller is presented as a new method of controlling the cantilever Q factor which guarantees closed loop stability in the presence of unmodeled cantilever dynamics. AFM images are presented to demonstrate the effectiveness of this control technique.