In order to permit faster scanning of the image, it is necessary to eliminate any artifacts caused by the reversal of the scanner direction.
If a triangular waveform is applied to the PZT, the scanner will oscillate at its horizontal frequency when the waveform reverses direction. This increases in amplitude as the scan frequency increases, since the slope of the waveform increases in proportion to the scan frequency. The turn around problem is dealt with in other systems by merely rounding the ends of the waveform. This uses some of the available scan amplitude since the scan voltage must exceed the useful scan range. This also causes the scan speed to decrease because of the time lost to the rounded portion of the waveform.

        Quesant has taken a slightly different approach to the problem. The waveform below (figure 1) shows the reason for the ringing. The step function is the velocity profile due to the triangular scan voltage. The scanner has a new equilibrium velocity after the reversal, and is not at the correct position or speed to match it. The result is a high Q ringing that persists for most of the scan.

        Through software control of the scan waveform, the Quesant "ringkiller" works by applying half of the step for a time of half the period of the scanner (each type of head is calibrated). At the exact time at which the scanner has reached the maximum overshoot, and matches the velocity for the reverse scan, the second half step is applied. This leaves the scanner at the correct position, and speed to completely eliminate ringing.