Dr. Pierre J. Brosens of GSI

[lasermaster1977]

From the CYGN-B thread reference to Dr. Brosens:

I've only found three of his GSI papers, two of which are co-written with Edward P. Grenda.

They are from the two of them:
Applications of Galvanometers to Laser Scanning and Closing The Loop On Galvo Scanners

And from Brosens' only:
Fast Retrace Optical Scanning

EDIT: If there is any interest for me to post these let me know. I'll add to another post some integrator/differentiator and a simplified GSI open-loop scanner math analysis documents my brother did when he was tutoring me later as well. It does not take into account the torsion physics of the armature of the early GSI optical scanners.

[djeric68]

I would enjoy reading those if you were to post them.

Thanks!

[lasermaster1977]

I would enjoy reading those if you were to post them.

Thanks!

Here are three of them. The "Fast Retrace Optical Scanning.pdf" is missing one or more pages. I'm guessing they wound up in some other related file folder in my file cabinet. I'll keep looking and append it to my existing pdf when I find it, then repost the updated file.

[masterpj]

Thanks for sharing! Will give these a read! Never enough to read about galvos!

[lasermaster1977]

Regarding the open-loop GSI galvo scanners and their response plot here is a crude drawing I did back in the late 70's of the G-115 galvo showing resonant frequency under varying load conditions:
No mirror mount
Mirror mount only
7 x 7mm mirror and mount
7 x 14mm mirror and mount

The feedback loop gain reference is when using the GSI method of backEMF feedback that I've posted somewhere on this forum earlier.



And here are some simple Laplace transform equations for op amp intergrator/differentiator circuits.

[Greg]

Thanks for making this information available. The articles are great reads full of history and nostalgia as well as getting right to the foundation of the current consideration regarding an understanding of why the harshly clipped KQO signal looks so good on open loop galvos, and, thence, an approach to a circuit that would emulate a given open loop galvo position response.

I'm not sure my technical proficiency is sufficient to build the bridge with this info. If I understood Steve's comment regarding a narrow bandpass pulse being added to the position signal, that is about trying to get the mirror to the desired position at the right time. Somehow, from that I guess it may be determined where the mirror actually is given the drive conditions. Anyway, sorry for rambling.

[lasermaster1977]

Thanks for making this information available. The articles are great reads full of history and nostalgia as well as getting right to the foundation of the current consideration regarding an understanding of why the harshly clipped KQO signal looks so good on open loop galvos, and, thence, an approach to a circuit that would emulate a given open loop galvo position response.

I'm not sure my technical proficiency is sufficient to build the bridge with this info. If I understood Steve's comment regarding a narrow bandpass pulse being added to the position signal, that is about trying to get the mirror to the desired position at the right time. Somehow, from that I guess it may be determined where the mirror actually is given the drive conditions. Anyway, sorry for rambling.

I could be wrong but my impression of Steve's statement:
"There was a method in the paper of taking a specified width pulse at 1/2 the amplitude of the command signal, inverting it, and adding it to command to put the brakes on any resonance and thus stop the motion quicker."

The graph I posted below that shows the effect of the "backEMF feedback loop" on open-loop galvos. I've posted the circuitry of this in other posts and again here. Steve, if I'm incorrect, please step in and comment.

Our discussing this has made me (once again as many, many time before this past decade) want to build a replica of my original XY open-loop amps for my G-115 galvos, and take photos of the cool ringing effects when driven by Lissajous square waves in the 1:1 and 1:2 ratio ranges, then do the same take the same photos using my backEMF feedback G-115 drive amps which I still have. The u791 power op-amp was perfect for my first open-loop drive amp version because using the current limiting feature of the 791 and 7812 and 7912 voltage regulators as the regulated power source provided extra protection from accidently frying my galvos as they provided 1amp current limiting.

My backEMF drivers used the 7815 and 7915 regulators and Darlington transistors drivers.

[mixedgas]

The paper entitled "Closing the Loop" talks about
the non-back EMF way of "Hitting the Brakes" with two pulses. That is the paper I remember from 1990 or so.

Thank You for posting that. Damn, I wish understood how to use Laplace's definitions. I know it results in "Yet another transfer function" in the form of a substitution, but its a half year class at the College I work at. While I find I don't suck at math as bad as I used to, for me the only way I'd pass that class is an Act of God.

For those who are wondering how this applies to modern galvos without torsion return spings aka the T-Bar, there is a simple answer. The feedback loop drives the coil to produce a centering aka "Restoring" force.

Steve

[lasermaster1977]

The paper entitled "Closing the Loop" talks about
the non-back EMF way of "Hitting the Brakes"

Thank You for posting that. Damn, I wish understood how to use Laplace's definitions. I know it results in "Yet another transfer function" in the form of a substitution, but its a half year class at the College I work at. While I find I don't suck at math as bad as I used to, for me the only way I'd pass that class is an Act of God.

Steve

Thank you, sir. I wish I could find the "Closing the Loop" paper. I've searched and searched with no luck.

Sounds like we're kindred math spirits. My brother taught me the 1st and 2nd order transforms for low, high and band pass transforms. From that I learned I don't have to derive these transforms just use their simplified derivations, but I haven't had need to do that for, I don't know, 30 years.