Scavenging a galvo Laser projector - Page 1
Forum section: electronics / projects

author: Kevman
author_rank: Regular Contributor
timestamp: July 11, 2020, 12:23:08 am
content: So my dad works for a machine shop that has some sort of laser inspection system. They were having trouble with it and the manufacturer made them buy a new head for it.He kept the old one and it turns out that it is a wide open, complete laser projection system- 2 Switchmode power supplies to generate +/- 28v, feeding 2 identical laser galvo servo drivers for the and X and Y.So I want to reuse it for... fun stuff... Well, I'd like to show at LASE my local demoparty at least. So I'm hoping for some advice here.There doesn't seem to be any internal protections or shutdowns that need bypassed. It just sorts of works and doesn't notice anything unplugged.The galvo driver boards have little IC-shaped daughter boards plugged into them with an LTC1597 parallel DAC and companion op amp to generate the galvo signal. I've already drawn my own images by tracing the output of the op amp to the correct pin and feeding in my own signal.I was thinking of building small replacements boards with an RCA jack input an a buffer op-amp (the driver boards went more like 5v, so I need a bit of gain), but maybe I could drive the LTC1597 with Rasbperry Pi's GPIO?The only software I can find for this kind of thing is "OpenLASE" which uses JACK, so that might be a tall order, but it seems like a waste to toss such an expensive DAC.Would I need any special sort of op-amp beyond like a TL072 or whatever?Supposedly the manufacturer said the issues leading to its retirement are from the laser diode wearing out... Is that a thing that can happen? I definitely think it needs upgraded, either way. The one that's in it is 5 mW.The laser driver circuit gets feedback from the driver boards and automatically adjust brightness based off of the amount of deflection- even if you create a line by pushing on the galvo and forcing it to servo.. It'd be nice to retain this, I suppose? Could I just replace the diode?

author: LaserSteve
author_rank: Super Contributor
timestamp: July 11, 2020, 04:49:02 pm
content: It just so happens that someplace a few dead laptops ago I have the manuals for those galvo amps.The number 651xx comes to mind for the series, and they are NOT online for free, Cambridge sales doesn't do that , you have to call or email, and that design is very old.You'll need to disable the on-board slew rate limiter with a jumper or turn it down to use those with standard laser show software.Reason being that system is designed for a constant vector slew rate, so the PID loops on the amps are tuned for that, rather then tuning to the International Laser Display Association galvo tuning. Constant Slew gives you very even image intensity, but does not allow for great speed.On mine I got to ILDA 10K at 8' scan angle, measured with the standard test pattern without changing the speed or the limiter, but the limiter does, um, unique things to distort beam show and graphic images..... It needs to be reduced in effect. On the other hand it is there to prevent overdriving the galvos in the frequency domain.So, You'll need to pull the jumper(s) on the amp that connects to the on board D/A converter, turn the limiter down, supply a proper differential input or ground the inverting side of the diff input, clean up the tuning a bit with a scope and you will have, by today's standards, a slow but very useful laser show projector.Give me a while to dig up the manuals... If not, GSI was bought by Cambridge Technologies which was bought by Novantia, so they may still have the PDFs, but I doubt it. I have two pairs of those galvos and amps.Those are scanners for precise, incredibly accurate movement, their huge mirror and shaft inertias are NOT designed for speed. If you detune the PID loops too much, the loop can oscillate and either the amplifier or the galvo could destroy itself.I have both Pangolin and LSX control systems. WARNING, Laser shows are an expensive and addictive hobby, makes the test equipment anonymous thread here look like a lunch money enterprise. You have been warned..Mine were at the local surplus place. BTW, if your ever want to do precision engraving, or stereolithography, you have the right galvo pair. If you just want to do laser shows, get a pair of DT30 off Ebay for 200$.PS, Marcan's stuff is a PITA to use, especially if you want to sync with music. Use wav files and a sound card or sine wave oscillators using a sound card. . Yes, there are sound cards that can run down to DC, but the device driver setup does not like it.You only have enough velocity for about 1/3rd of the stuff in that video, and the wider the angle, the slower the galvos can jump due to device physics.Given your scanners are slow, you might want to take a look at Maxwell software. Grab a Helios DAC and the free version of LaserShowGen.If you want to hack, you have on-board, parallel load, 12 bit DACs on the amps. You have an addressable eight bit parallel interface on the upstream control boards , if yours is identical to mine. Ie some address bits for selecting x high byte, x low byte, Y high byte, y, low Byte, and on/off. These are parallel input, and a latch signal.It also has hardware that blanks the laser till the galvo motion settles using position and velocity feedback signals from the amp.https://bluefang.itch.io/maxwellAbstract images using sine and triangle waves work better on a constant V system. Ie Lissajous patterns.Then come over to Photonlexicon where we can help you set up a single mode diode RGB module at around a a half watt of total power for full color.Aluminum Migration used to be a problem in the laser diode industry. If those are the red model, soldering in a new 35$ diode is an option and the rest of the hardware is fine. If it were a green DPSS laser, the pump diode does wear out over time, and opening up a green and replacing the diode is something most OEMs would dread. Dad might like his laser back.Keep what you have, OEM cost on those galvo scanners was well north of 3000$ a pair in the 90's. They have ultra precise capacitive feedback on the rotors. As opposed to optical feedback which is probably 30% less accurate in that generation of device.I may still even have the diode board if Dad wants his laser projector back. But 35$ gets you a diode rated for 150 mW of single mode red.Steve

author: LaserSteve
author_rank: Super Contributor
timestamp: July 11, 2020, 10:56:15 pm
content: Ps, I just checked, the LD is socketed on mine, so no problem changing laser diodes, and no need to press the diode into the mount, as is common.Steve

author: Kevman
author_rank: Regular Contributor
timestamp: July 12, 2020, 02:52:04 am
content: Yeah, after googling the names on the galvos after reviewing the photos, I realized that such a precise thing miggghhhht not be super fastI don't suppose these drivers would run a higher speed, less precise set of galvos, would they?Out of curiosity, Do you know what does the actual sensing on these things? I didn't see any sort of optical sensor to pick up the returned beam. Is it sensed using the laser diode itself?The diode is red, but they already installed the replacement, so I doubt the company would want this back. I'll send him this thread though.

author: LaserSteve
author_rank: Super Contributor
timestamp: July 12, 2020, 11:41:31 am
content: The sensor is co-axial with the LD optics. There is a hole drilled in the lens glass to pass the LD beam. The rest of the lens collects the reflected light, and the old manual said there was an external sensor option.G120 is not much of an upgrade, and it has a torsion rod to provide the centering force. But it would work with those amps..12-14K ILDA with the tiny mirrors. It was the galvo that invented the laser show. Improvements in position sensors eliminated the need for the t-bar. T-bars have a habit of breaking, so buying used is risky.Hang onto this thing if you can... You might be surprised what you can do with it. other then Lightening Twos or Scannermax Saturn, there are no new products with that level of accuracy on the market. Well, there is Cannon or Aerotech, but those are not affordable even used and have even larger shaft inertia.I've got two complete sets of those, if the unit goes back I don't see why one can't go into a box and be shipped for the cost of postage. The other I will keep if I ever need that level of accuracy, and considering what I do for the day job, some day I just might. Other then the fact the switching PSUs are needlessly physically huge for their amperage by today's standards, that is still a good setup for a beginner who is willing to write own code. Especially since with the limiter on, you can't kill them with an accidental microprocessor code error. That is not so true on a cheap clone set made in China with a type 1 PID loop, you have a type 0.Speed goes way, way up if you change the mirrors to ones with less inertia and retune. Easier then G120...https://github.com/DeltaFlo/LaserProjectorI'll have time this afternoon after Church to find the manual. But for now, here is a manual for a similar amp for units two generations later... The PID tuning chapter is relevant to you.Steve

author: Kevman
author_rank: Regular Contributor
timestamp: July 14, 2020, 01:19:39 pm
content: Hmm, I have everything mentioned in that manual except for a frequency counter... But I don't really see why I would need that? Can I get away without it?Seems like upgrading to lighter mirrors is my best bet. Is there some place I can get lighter mirrors, or should we try to add lightness to the existing?

author: Kevman
author_rank: Regular Contributor
timestamp: August 16, 2020, 12:13:47 am
content: Hey, LaserSteve, did you find those manuals?Also, is there a recommended sound card for this type of thing?

author: LaserSteve
author_rank: Super Contributor
timestamp: August 25, 2020, 01:43:34 pm
content: Here ya go, had to sort through the hard drives from dead computers box.See attached..I would strongly, strongly, suggest never touching the position sensor calibration when the factory has done it for you.Steve

author: tggzzz
author_rank: Super Contributor
timestamp: August 25, 2020, 04:31:50 pm
content: Quote from: Kevman on July 11, 2020, 12:23:08 amForget about learning how to make it work until after youfullyunderstandallof the ways it canfail, and the effect that might have on random strangers at a party.Compare the laser power output with the power that can instantly and permanently blind someone. Be aware that cheap lasers often outputmorepower than their specification.Do not rely on insurance covering you unless you are operating the equipment in accordance with the manufacturers specifications. If you aren't doing that and someone is injured, expect to be hammered into the ground by various people and government organisations. "I didn't mean to" is not regarded as a defence!

author: Kevman
author_rank: Regular Contributor
timestamp: August 25, 2020, 06:44:39 pm
content: Quote from: LaserSteve on August 25, 2020, 01:43:34 pmThank you very much! There's a lot to parse here, I hope we'll be able to figure out a way to lighten the mirrors. Are all the images in the tuning PDF missing for you as well?The party I was hoping to show this at just went virtual for this year because of COVID, though. Oh well.

author: LaserSteve
author_rank: Super Contributor
timestamp: August 25, 2020, 09:06:30 pm
content: Yeah, but I can dig up some tuning images when I get home.Steve