Equation of Motion for Galvo

[mixedgas]

This is the baseline equation of motion for a feedback equipped G120 galvo. From a book in my personal library. Dr
Montagu is a Founding Father of the galvo business.
In reality it would have a lot more terms, especially as the torsion bar is virtual, not physical in a modern one.
Those are multi-dimensional qualities, so don't say: "I can solve that in a micro", either.

This is being posted for a certain idealist busybody in Kali who needs to get a grip on what they are saying, or actually run some real numbers.

Its NOT so easy to speed things up from the present physical limits.

You cant just hire Mango from SNL to build the things, either...


Steve

[echelon]

What book is this from, and would you recommend it to a scanning beginner? I do have _some_ Diff EQ and Linear Algebra in my background and I am looking to write positioning algorithms for galvos. If this isn't an ideal book, is there one that you can recommend?

[mixedgas]

The galvo amp does everything in that equation for you.
Laser Beam Scanning, Gerald Marshall, editor, Marcel Dekker, Publisher, is something that you get on University Interlibrary Loan once. Its more for a printer or display engineer the for laser shows, its well written, but more oriented to a grad student. It does not cover MEMs, so it is dated, a bit. It covers AO, EO, and Polygon scanners as well as Galvos. Its for serious systems enginners, and while you could learn much, it is of little relevence for Laser Shows.

An old friend hosts this for me, its a outdated (Late 1990s) mix of useful documents, that you can learn from:

http://www.skywise711.com/lasers/scanner/scanner.html

Then there is this, but the current amps/scanners used for laser shows are quite a bit different then a Minisax:

http://camtech.com/archive/176-25016...X_Manual_G.pdf

In your case, you get the HENE from Jon, a pair of decent 30K scanners, and hook your newly arrived scanners to simple Sine Wave, Square Wave, and Impulse, at SMALL amplitude/small angles, and raise the frequency slowly.
Then look at a FFT of the ac coupled feedback signal on a soundcard, and watch the full feedback on a scope. And in your case, figure out how to look at I and Fdbk on a dual trace scope...

Dont retune your scanners when you get them, other then minor tweeks, unless you can source the ILDA testpattern.
But you can make measurements.

The amps are Classical PID and PII loops. The galvos have a LED in the base, and two Photodiodes. A specially shaped flag blocks the LED light as the shaft rotates.
Dont rip your scanners apart, they are made to .0001" or better tols, and are hard/impossible to put back together.

Look at
US 5,235,180
US 5,671,043 etc

for ideas...

Also you can find Buffo's scanner tuning docs on this forum.

Dont build when you can buy... Spend time on keeping your grades up, because once your out of the educational system, you will wish you were back in... It is a once in a lifetime thing unless you become a grad student.

Peruse, but dont order parts......

http://elm-chan.org/works/vlp/report_e.html

http://www.fab-favreau.com/index.php...ShowController

http://www.fab-favreau.com/index.php...enLaserShowDAC




Steve