Modified dual-mode resonant scanning system

Abstract

A dual-mode resonant scanning system comprising an electronic control circuit and a dual-mode resonant mechanical scanner to produce an essentially triangular scan pattern. The dual-mode mechanical scanner is mechanically tuned to simultaneously oscillate at a predetermined third harmonic frequency and the free running fundamental thereof. The electronic control circuit drives the mechanical scanner to oscillate at the exact fundamental frequency of the predetermined third harmonic frequency and phase locks the fundamental oscillation to the third harmonic oscillation. The dual-mode resonant mechanical scanner includes an optical scanning element having a first mass, a second mass, at least one torsion rod, a rotational actuator and a mechanical ground designed and integrated together such that the mechanical scanner is self resonant at the predetermined third harmonic frequency and at or within a few hertz of the exact fundamental frequency of the predetermined third harmonic frequency. The electronic control circuit includes a mirror-position sensing subsystem, a bandpass filter tuned to the predetermined third harmonic frequency, a divider circuit, a summing circuit, a manual phase and amplitude adjustment, a scan angle automatic gain control circuit and a driving circuit. The exact fundamental oscillation in combination with the third harmonic oscillation produces an essentially constant scan rate through a predetermined scan angle.