Command functions of open loop galvanometer scanners with optimized duty cycles

Abstract

The paper approaches the problem of the command functions of galvanometer-based scanners (GS) that are necessary to produce the linear plus parabolic scanning function of the GS, which we have proved previously to produce the highest possible duty cycle (i.e., time efficiency) of the device. We have completed this theoretical aspect (which contradicted what has been stated previously in the literature, where it has been considered that the linear plus sinusoidal scanning function was the best) with the experimental study of the most used scanning functions of the GSs (sawtooth, sinusoidal and triangular), with applications in biomedical imaging, in particular in optical coherence tomography, demonstrating that the triangular function is always the best one to be applied, from both an optical and a mechanical point of view. In the present study the input voltage/command function which should be applied to the GS to produce the desired triangular scanning function (with controlled non-linearity for the fastest possible stop-and-turn portions) was determined analytically, in relationship with the active torque that drives the device. This command function is analyzed with regard to the specific, respectively required parameters of the GS: natural frequency and damping factor, respectively scan speed and amplitude. The modeling in an open loop control structure of the GS is finally discussed as a trade-off between using the highest possible duty cycle and minimizing the maximum peaks of the input voltage.