Resonant Enhanced Afm Closed-loop Feedback Control System

The principle and work modes of the Atomic Force Microscope(AFM) are analyzed. On the basis of the analysis, a novel non-contact resonance intensifying scheme of AFM close-loop control is advanced and designed. Using the microprobe-sample force curve measured in the open-loop mode, this scheme can judge the most sensitive and linear area and choose the midpoint of this area as the balance point of the feedback. The corresponding signal voltage is used as feedback control signal-Vset.In the close-loop mode, on the one hand the voltage signal containing the sample surface information is sent into the computer as the sampling signal after A/D converter, on the other hand it is compared with the Vset and drives the piezoelectric crystal in Z direction to flex through the integral and high-voltage magnifying circuit. This can keep the distance between microprobe and sample constant. Meanwhile the computer drives the two-dimension piezoelectricity flexible hinge to scan. Then the three dimensions microcosmic shape of the sample surface is obtained.The novelty lies in the combination of resonance intensifying technique and analogue PID feedback control. It give system high sensitivity and feedback speed. The circuit work mainly includes: the design and fabrication of Z-direction PZT high voltage driving and feedback control circuit; parameter adjustment, optimization of the open-loop circuit; the fabrication of PCB board. After small adjustments, this feedback control scheme can be wholly applied to the tapping mode.A four dimensions microcosmic adjusting mechanism is designed. It has high precision, good repeatability and reliability. Meanwhile it is also proposed that it uses one piezoelectricity crystal, which combines the approaching and server approaching section. This will reduce one component and make the system more compact.Because of the close-loop mode, necessary modifications and improvement of scanning and testing program are made. The force curve testing program is also written. To complete the conversion from sampling data to the image, under the frame of VC++, 3D surface displaying program is written using OpenGL.Using the non-contact resonance intensifying scheme of AFM, a number of experiments are carried out and the satisfying force curve and sample surface scanning results are obtained.