Open Sourcing the Pegasus

[doobie]

Maybe this link will help a bit:

https://docs.google.com/spreadsheets...it?usp=sharing

[doobie]

The projection of the laser isn't linear, but more spherical based on how the laser bounces off the mirror. I'm going to work on a few gcode files to test my calibration to see how close things are with different algorithms, once I have a few formulas or ideas to try. It's physically possible because FSL3D does it, so just need to figure out this transformation. If we had more points it'd be more accurate, I'm wondering what FSL3D does to make it accurate. I'll have to look into how laser projection systems work to keep their images scaled properly.

[fred_dot_u]

I had hoped to be able to create an image representing your objective in a pseudo-3d manner. I picture a calibration grid projected on the ceiling of a room. The last mirror in the beam travel is the zero point of each triangle. You would need one very precise measurement from the mirror reflection point to any point on the grid. You already know the travel of the beam on the calibration grid, so you have two adjacent triangle edges. I suspect it is possible to determine via code/experimentation the angle created between the first known length measurement and the second point on the grid. Now there's three pieces of data for the triangle. All other calculations can be done with any number of triangle calculators available on the internet. I like this one, as it requires less thought and much less demand on my brain cells: http://www.1728.org/trig4.htm

How does this fit in with your direction?

[doobie]

It might, I'm not sure. I found this link which is interesting:

http://www.open-electronics.org/how-...ampaign=buffer

"In addition, in the printers using galvanometers, if the size of area to be built is very large, an issue is introduced, due to ovality of the spot of the laser beam in the extreme parts, this ‘aberration’ is to be corrected by the manufacturers through software artifices."

Not entirely sure how to properly correct for it. Going to try to ask around.

[fred_dot_u]

I would be very surprised to learn that there is much of an ovality of the spot for the Pegasus Touch printer. My Emblaser laser cutter when well focused provides for a 0.05 mm cut. That would indicate the the laser dot is smaller, as the burn-off of material provides for the increased width of cut. For sake of argument, we could consider that my laser presents a 0.03 spot. Even extending it at an angle sufficient to elongate such a dot by a factor of two, that would mean a 0.06 spot. As the laser cutter creates burn-off increase, so would a resin laser present a burn-on increase in resin, I suppose.

I don't think it's severe, if it's even measurable.

[doobie]

That is very possible the ovality isn't a big deal, but the position is definitely an issue, moving the galvo 500 points in the center is very different that on the outside. I think I have an idea of what to do, just need to figure out how to do it.

[fred_dot_u]

Are you able to calculate or measure the angle of deflection/change of the final galvo? For the sake of argument, I'd prefer to consider that you're objective is to calibrate specific points on a line. That would mean one galvo does not move, while the other moves in a precise manner. I'd also expect that with appropriate trial and error, one could calculate the distance from the mirror to the vat. I'll make a guess that you can do the mirror movement and calculate angles, otherwise my method vanishes instantly.

Another aspect of this task is to determine the three inputs needed for the calculator online. You can get your "top" distance on the calibration paper and the angle of the galvo movement from the electronics (?) but the third measurement appears to be a tricky one. Can you think of a way to measure the distance from the mirror surface to the vat? Are there indications that at a specific point, the laser is directly below the vat and that the beam would form a right angle to the vat? That would provide a second angle to the calculation, rather than a second distance but any three works.

Another thought is that the angle of the laser movement through an arc on the vat creates a chord of a circle, but at that point, the math goes well beyond my comprehension.

[doobie]

I don't have a good way to measure the angle. I'm trying to under stand how the FSL3D software and calibration does it. They user that 25 PT grid to solve how calibrate and align the points.

[fred_dot_u]

Does the method of moving the mirror involve commanding the stepper motor to move a specific number of steps? I'd expect that the grid method takes into account the number of steps executed for movement from one point on the grid to another and calculates an adjustment factor for any movement within the box described by four points.

[doobie]

Not a steeper motor. It is a galvo. It uses a voltage to position itself. I can position it anywhere, but just not accurately yet, unless I move it manually to a specific spot.