You want to use a Position Sensitive Device.
Normally this has been used to track an object that has been illiminated by a modulated laser.
So Lens-Array -PSD.x PSD.y , Demodulation-Amps for selectable channel (15KHz to ?80KHz) - Analog Flight regulator (Takes also Gyro and Gravity) , Flap Servos to Flaps which control the thrust vector of a laser guided missile.

So here you can use the same approach to have laser guided position feedback for a handling controller.
PID is enough.

Cheers

LuJa


On January 26, 2022 11:24:18 AM GMT+01:00, lkcl <luke.leighton@gmail.com> wrote:


On January 26, 2022 6:32:09 AM UTC, "David Lanzendörfer" <leviathan@libresilicon.com> wrote:
Hi
What about just buying a new cheap Chinese laser diode and a photo
diode and
then putting a mirror onto the lense carrier, which reflects the laser
diode 
beam back to the photo diode next to the laser diode?

dc32 used 2 and got a phase differential which increased accuracy. actually, it was infrared but you get the idea.  source is somewhere, uses an ATTINY. mirror not needed, works with any reflective surface.

i saw well over a year ago some maker actually used a DVD sensor (taken from a DVD player) which did 2D phase differential, when it produces a circle instead of an oval the 4 readings in 4 quadrants are equal and you have focus.

the nice thing is, if the oval is squashed one way you are too close, squashed the other way is too far.

l.
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