Vectors have no “overscan”. The mirrors move from any direction, an attempt at a straight line from the end of whatever the last vector was.
Just picture where it comes from 90 deg off- or the opposite direction. It will basically begin at a standstill- or even overshoot- and start firing.
A CO2 laser like a Ruida controller throttles back the beam power proportionately when it’s not able to go at the commanded speed.
Galvos current do not. The way the galvo interface controls power is serial comm and it doesn’t work as well as it could to adjust power on the fly. The tech isn’t perfect yet.
So, vectors are going to overburn at starts/stops/corners. On the other hand, the acceleration on a galvo is much much faster than a CO2 gantry laser and these acceleration zones are usually very small.
You can’t adjust this out. That’s not what Ton/Toff do, or anything else. You can reduce it by limiting speed. Because if you ask for a very high speed, and give it a power appropriate for that speed, there’s a big long runway in the starts where it’s getting up to speed and overburning.
If you asked for 1/4 of that speed, the acceleration zone goes down to 1/4 of what it was. You’d be taking your power (or freq) down to 1/4 of what you’d use for the higher speed to get the same new burn.
Yeah, this limitation of the tech annoys me. I’m not 100% clear if this could or couldn’t be fixed if Lightburn did “overscan”- start along the same line the vector is going to be, but go there and start accelerating few mm ahead of the start point with the beam off to get up to speed, and turn on the beam as it passes the start point at a constant velocity. That would be nice.
There’s another flaw with that strategy though- I studied this and saw the beam actually doesn’t start instantly. It gets a fire command and puts out a few weak pulses before it reaches a constant power. Overscan won’t fix that and it could make it worse.
Rasters don’t overscan either on galvo. A Ruida CO2 controller does- it pads the sides, past what your job said to burn, with enough turnaround room that it will always be at a constant speed when it does your content.
Lightburn COULD fix that by inserting that sort of overscan. It’s more straightforward than trying to do it for vectors. But, right now it is what it is.
There IS a workaround. Why is there a vertical bar on the left and right of the Ton/Toff blocks, anyways?
That is forcing Lightburn and the BJJCZ galvo card to start the scan line outside the area you need to have right. It may have artifacts in like the first 2mm of a line at high speed- but that’s outside the timing blocks so just ignore it.
So, the timing test really should be done with the raster layers.
Can I do this fix IRL? Well, say you’re doing a coin. There’s no technological reason LB shouldn’t just pretend like the image starts a few mm outside the first nonzero pixel, start the scan line in whatever direction it is, and be up to speed when it reaches the edge of the image and edge of the coin and fire there.
OK, that’s the way LB could fix it (and maybe they have, I haven’t done tests on mine for a few updates, apologies if I have it wrong). Can *I* fix it? Well, AFAIK you can’t force LB to see the image as larger than it is with white space (actually, I need to confirm that now).
But you COULD make a ring outside your coin image, a ring a few mm larger dia but only one black pixel wide. LB would have to start the line further out and it will be at constant velocity by the time it reaches the coin edge. But it will etch into your holding jig. You could just tolerate it, or put spoil there, or put something there that the fiber laser won’t have any effect on.
The more I used it, the lack of overscan wasn’t all that bad. It’s a small artifact at lower speeds, but can be a limiting factor for running it really fast. And I noticed that because I have a 300W machine so I’d like it to go really fast. And all these machines can actually go faster than advertised- considerably so- WHEN you get Ton/Toff set with precision. Even the mfgs don’t seem to know how to do that- but this test absolutely will.
So, you can run much, much faster with no loss of quality mid-line when Ton/Toff are exact. Huge improvement at no cost. But, then the lack of overscan causes significant issues on the edges unless you add in your own.
