Method of determining resonant frequency

A method for operating a torsion oscillator of a scanner having a memory and a mirror disposed on the torsion oscillator and a laser beam being reflected by the mirror to scan the laser at a desired scan amplitude, comprising:

• (a) performing an open-loop resonant frequency sweep to determine at least an open-loop resonant frequency;
• (b) performing a closed-loop resonant frequency sweep to determine at least a closed-loop steady-state resonant frequency;
• and
• (c) driving the torsion oscillator at the closed-loop steady-state resonant frequency in closed-loop amplitude control at the desired scan amplitude.

A method for determining parameters for operating a torsion oscillator of a scanner having a mirror disposed on the torsion oscillator and a laser beam being reflected by the mirror, where the torsion oscillator is driven at a selected drive frequency and a drive level controlled to result in a desired scan amplitude of the laser beam, the method also for minimizing an effect of changes in ambient environmental conditions including temperature and air density on an accuracy of the torsion oscillator, the method comprising:

• (a) determining a plurality of nominal operation parameters including a nominal resonant frequency, a nominal frequency overshoot, and a nominal drive level in a first environment;
• (b) storing the nominal operation parameters in a non-volatile memory;
• (c) when the scanner powers-up, reading the nominal operation parameters from the non-volatile memory;
• (d) using the nominal resonant frequency less a fixed amount as a starting frequency for performing an open-loop resonant frequency sweep to determine an open-loop resonant frequency, the open-loop resonant frequency sweep being performed by driving the torsion oscillator at the nominal drive level and at a plurality of test frequencies
• (e) finding a peak amplitude and storing the test frequency corresponding to the peak amplitude as the nominal resonant frequency;
• (f) driving the scanner at a drive frequency equal to the nominal resonant frequency less the overshoot and determining a drive amplitude at the drive frequency,
• (g) when the drive amplitude at the drive frequency is within an acceptable difference value of the desired scan amplitude, proceeding to step (i);
• and
• (h) when the open-loop amplitude at the open-loop resonant frequency is not within the acceptable difference value of the desired scan amplitude, modifying the nominal drive level and repeating steps (d)-(h);
• (i) driving the torsion oscillator with closed-loop scan amplitude control;
• (j) determining a closed-loop steady-state resonant frequency by sweeping a number of frequencies and determining a minimum controller feedback corresponding to the closed-loop steady-state resonant frequency;
• and
• (k) determining a frequency overshoot by subtracting the closed-loop steady-state resonant frequency from the open-loop resonant frequency and storing the frequency overshoot in the memory as the nominal frequency overshoot.