Galvo Ghosting / Double Image and beam alignment

[evanevery (Ed)]

I recently took delivery of a 65W CO2 Galvo laser from Finnlaser. I have identified a couple of issues which I notified them about. It is the weekend so I’m still waiting to hear back. However, I think its also worth posting/asking here as the forum has such good resources…

Note specifically that this is a Galvo Laser - and not a gantry laser. I have two other Galvo’s (a 5W UV From Finnlaser and a 60W MOPA Fiber from OMTech) as well as an 80W CO2 Gantry from OMTech. All of these are running with Lightburn so I am fairly familiar with the tech and the software. Anyway…

I ran my first job the other day. Its a raster etching on clear acrylic. However, after running the first piece, I noticed I had a double image about a mm or 2 apart in the horizontal direction. Typically, I do my raster scanning as bidirectional at 0 degrees (horizontal). My initial thought was that there was some slop in the horizontal galvo mirror and it was being taken up as the mirror changed direction.

So, I turned off bidirectional scanning and the issue was no longer apparent. But the job obviously took twice as long…

Out of curiosity, I changed the bidirectional scanning mode to 90 degrees (vertical). Now the double image is in the vertical direction by about the same amount.

Its pretty clear (to me), that the galvo mirrors are changing direction out of sync with the laser pulse. Since this is happening identically on both axis, I think its less likely an issue with identical mechanical “slop” in BOTH mirrors. So, its not really a double image, its just that half the image is offfset from the other half. Odd rows/columns to one side, even rows/columns to the other. (I even ran a low LPI test to confirm this.)

So, this kinda points to a controller/config issue with the laser hardware or the software. Maybe the firmware in the controller is not set properly. Maybe Lightburn needs some other setting (which I can not find). As with all my other Galvo’s, I merely imported the EZCad markcfg7 file into Lightburn to configure the device. None of my other galvo’s behave like this.

This is a SinoGalvo 2808 galvonometer. Its a premium unit and it is supposed to be capable of speeds up to 7000 mm/sec. (I wanted a galvo CO2 laser specifically for raster etching to save the wear and tear on my Gantry laser). My initial job was only running at 1500 mm/sec. I have tested at both 1000 and 2000 and the problem gets worse as the speed increases. Again, I think this points to some timing/sync issue between the galvo head and the laser.

However, I’m not sure where that sync should be taking place. I expect it is the responsibility of the laser controller to handle the sync (surely this is not happening over the USB bus…). But maybe Lightburn needs to pass in some sort of config param for the end of line delay/sync? I’m kinda thinking “not”, but this forum is a good place to ask!

My primary goal is to understand which component is likely the one which is misconfigured/failing. I’m guessing its hardware (controller or galvo head) but not sure which. Anyone got any insight?

Also…

Can anyone familiar with Galvo heads tell me if there should be an adjustment inside the galvo head (trim screw, etc) to tweak the mirrors such that the laser shoots straight down through the lens. At a 450mm focal length, I’m off to the left on the X-Axis by about 26mm. (Vertical seems reasonably close though). As I cut fixtures to mount my jobs on the work table, I can’t have my beam wandering as I move the galvo head up and down (changing lenses, etc).

Thanks in advance!
Ed

[evanevery (Ed)]

The manufacturer of the laser tells me I should check/confirm/set this value. Of course they want me to use EZCad. Can anyone tell me where this value might be visible in Lightburn? I can not find it.

Also, here is the markcfg7 file which was provided with the laser and imported into Lightburn:

markcfg7 Finnlaser 60W CO2 300x300.txt (10.1 KB)

I will be on travel for the next couple of weeks so I will not be able to view/reply to this thread until I get back.

Thanks in advance for any insight which might be provided!

[evanevery (Ed)]

I found the settings in Lightburn. I have updated them (“Laser On TC” and “End TC”). But this DID NOT help. Here are what my settings look like now:

[jkwilborn (Jack Wilborn)]

I’ve dealt with these delays on my fiber machine. They tell it how long to wait for the mirrors before they start/end lasing. As far as I know they have nothing to do with your mirror track, only their response time.

@evanevery

adjustment inside the galvo head

I’d suggest you stay out of the galvo head unless the vendor advises otherwise…

After looking, I’m resolving that I will have to learn to live with virtually no documented knowledge about the inner working of these. All of us know how they work… generally… I find no technical data on them such as service.

I’ve looked down mine, but have never seen anything that looks like it’s adjustable.

---

I have 8 markcfg files… 0 through 7 that came with my machine. I was told to use 7. It has the factory lens correction for the lens I ordered.

Are you sure you are supposed to use 7? I wouldn’t think it would be different, but it seems they just ditch 0 through 6… I don’t know if there is a different configuration for these… ???

We’ll all be watching…

Good luck

[evanevery (Ed)]

Just got back from out of the country. (…who drives north from Stockholm to the arctic circle in Feb anyway?)

In any case…

…as mentioned earlier, I tried changing settings as the manufacturer suggested and this did not help. I sent them a a screenshot of my updated settings in Lightburn (2 weeks ago) and specifically told them it did not help. So then they send me a screen shot of what needs to be changed in Lightburn!!! So they are NOT reading my messages and NOT looking at my screen shots. They knew I was was leaving the country and now its Chinese New Year. 3 Weeks lost when something could have been in shipment…

I guess this is what happens when you buy a laser from a company in Europe who appears simply to be a money/order broker for manufacturer(s) in China. Finnlaser tells me I have to work directly with the Chinese manufacturer to get their tech support and return/replacement authorization. Even though I offered up a CC for security, they will also NOT ship a replacement part until I return the original part (AFTER I get approval). So much wasted time… This is so frustrating!

The galvo head is not even shooting straight down through the lens. I keep asking why not simply replace the galvo head and see if the scanning issue clears up as well…

Ugh!