Optical Feedback Galvo ACG (Cambridge and Cambridge Clones made in China)

I get a few requests a year for how AGC works, mainly from PhD students. AGC is a Linearity correction that mainly influences tangent and edge bow errors at the outer edges of the image field.

So, I set Chat GPT loose on a fragment of the schematic and asked for the transfer functions. YMMV and I haven't confirmed all this on the bench yet, but the attached document is better than nothing. It looks about right for a simple explanation.

If you're a grad student, check the math before using this, as sensor flag shape and sensor LED transfer functions matter, and neither is factored into this PDF.

Consider this document an Ab Initio Tutorial.

FOLLOW THE INSTRUCTIONS IN THE FACTORY MANUAL FOR YOUR GALVO PAIR.
IMPROPERLY CALIBRATED POSITION SENSORS CAN RESULT IN SEVERE PERFORMANCE DEGRADATION, OSCILLATION, OR SYSTEM DAMAGE.

The "Volts per Degree" transfer function carries through the whole galvo amp circuit design, do NOT change the potentiometers unless a prior technician totally messed up the position scale, offset, and linearity adjustments. Never touch position scale if there is any possibility that it is still set correctly. In most cases, the Linearity potentiometer never needs more than a fraction of a turn once set at the factory.

Steve