One of the major challenges in an AFM is making a motion control system that allows moving the probe to the surface before scanning. This must be done such that the probe does not crash into the surface and break. An analogous engineering challenge would be to fly from the earth to the moon in 60 seconds and stop 38 meters from the surface with out overshooting or crashing.

FIGURE 2-20 Motion of probe in the “woodpecker” method for probe approach in an atomic force microscope. The z PZT and Z motor are activated sequentially until the surface is detected.

Typically, probe approach is achieved with a “woodpecker” method, Figure 2-20. In this method, the stepper motor is stepped a small increment, say 1 micron. Then the z piezoelectric ceramic is extended 5 microns to see if the surface is detected. The z piezo is then retracted, the stepper motor engaged.......on and on. A key component here is that when the probe encounters the surface, the feedback is turned on immediately.