I know what they mean. I have the third or fourth largest collection of galvo documents in the user world and know where the patents and journal articles are,.
Issue is achieving Automatic Gain Control for the feedback sensor and some circuits which achieve linearity correction.
The Galvo is part of a system, and the individual Galvo does not mean much unless you characterize the scanner driver amplifier PID tuning. In most cases the differential amplifier that processes the photodiode currents is set to N volts per degree, which is kept constant with changeable components on the driver board. This way the same driver can be used with different Galvos with minimal changes.
M+ galvo Coil
M- galvo Coil
Ia sensor output current (one photodiode)
Ib sensor output current (other photodiode)
DC From AGC circuit to drive sensor LED
Common cathode for PDs and LED
AN = LED anode in some cases.
Some Galvos have 4 PDs operating in an opposed pair, some have two, some have dual LEDs.
Some have shaped sensor flags, some have butterfly flags, some (Chinese copy clones) have simple rectangular flaps on the end of the shaft.
Some end users have more or less pins brought out, what you see above could be considered stripped down compared to what may be brought out on a confocal Galvo with separated coil and sensor grounds etc.
Then there is Bill Benner's designs for Scannermax with shaped PDs and DSP amplifiers which are a whole new world.
Give me a day, but you are barking up the wrong tree unless you characterize the whole system (papers by Duda, Et AL are great but skip the amplifier details, which is tragic)
Then there are systems with capacitive sensors and digital encoders.
I'm a former confocal operator as well as light show guy.
Unless you know the design constants for a given amp, swapping parts can be high risk unless you access some check points and test. I do it on a regular basis, but I measure the volts per degree deflection (optical) on my amps long before the galvo dies. I also have a master chart of parts changes for the most popular maker's old stuff.
Tell me more about your plans before you even consider publishing anything. This is NOT easy, and in the hands of a hurried grad student with poor reading comprehension, will result in smoking hardware. Which happens with amazing regularity considering the number of graduate students and laser show folks who have sought my help over the years. You also have shaft resonances and notch filters to consider.
The designs are often copied overseas, with parts cost reductions and omitted components, which makes matters worse.
How you measure is important, for laser shows we have standard test patterns. Marking and Confocal users use proprietary test patterns and square waves. Problem is, what is a great test waveform for one setup is a disaster if overdriven or used elsewhere. There are also various tuning methods which trade off speed, jump size, accuracy etc. There is also strategic shaping of the command waveforms.
So again, tell me what you plan to do before I consider helping you open a huge can of worms for an academic user who reads your work, is in a hurry and skips the details of the PID and PII loop, oscillates or slams their scanners, and smokes them.
Yeah I know there is a backlog since the MBAs took over company X to maximize shareholder value and stopped stocking common parts,
The laser show common test patterns are of little help to you. I'd ignore the term PPS when you encounter if for confocal use. Small jump size, settling time, large jump size, position sensor constants, there are a ton of measurements the light show side often ignores on the data sheet.
And the choice of mirror inertia to shaft inertia ratio is even more complex.
Drop me a PM with your position details and phone number, email, etc if you want to discuss. And I know where the two principal designers of modern Galvo amps reside, one is semi retired, the other shifted companies.
Once upon a time I took the factory tuning course at an industry conference with hands on. Access to that was restricted to persons who could show a modest amount of analog and PID knowledge, and whom were unlikely after vetting to blow up 3000$ systems. the instructor was at the time the foremost analog closed loop amplifier designer at his company.
Forgive me if I sound arrogant, but over the years I've found a little knowledge of Galvo amps and the resulting Transfer Functions is often TOO little.
Show me a willingness to be careful and learn, and you may end up with a pile of half dead galvos and drivers of various brands and sizes to dissect.
Most major makers of Galvo Systems currently ignore academic users due to the smoking unit phenomena, and the immense amount of time and product support required. I was actually told that by the president of one company. That person will sell to me as a Laser Show customer whenever I want, and nearly whatever I want. IF I called from my former academic position sales and service would be politely declined. Hence your difficulty in finding information.
I'll gladly explain why I am so finicky on the phone.
Steve
Last edited by mixedgas; 04-02-2025 at 17:27.
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