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Difference of light intensity along X axis


#1

Hello,
I found a problem while printing narrow and long parts. It seems that light intensity differs significantly along X axis, because close to Z axis linear module resin is not cured enough, however on the other side it’s overcured. When I increase curing time it get better, as whole part is printed, but there are large differences in wall thickness on opposite sides (0,7 mm to 1,2 mm). Is there any way to make it better?
I use HT gery resin with 50 um resolution. Part is 90 mm long, 12 mm wide and 70 mm high.


#2

It’s an unfortunate side effect of lamp-based projectors. When used in the A/V environment, they can get close with light distribution and it doesn’t have a negative effect on the viewing of video material. However, in our case where the amount of light in the near UV range varies, it has a direct impact on the cure performance.

The intensity mask in Creation Workshop is designed to knock down the bright sections to a uniform intensity, however, it is very difficult to build the mask and there is no guarantee how long that mask will last due to the effects of aging on the bulb filament or arc.

LED seems to be the place to be, since the LEDs can be calibrated to create a uniform distribution of light across the whole build space. Custom projectors for printers are around, but cost significantly more than the standard A/V projector.


#3

HI Rkundla

So what can be the solution for this issue, I´m getting a lot of difference in ligh, can it be solved by changing the lamp/bulb of the optoma?

Thanks in advance


#4

Hi Cardano,
the solution is not the change of lamp, but applying suitable printing mask. I did it this way:

  1. find UV meter in range 390-410 nm or build it yourself - it is very easy you need Arduino or it’s clone and the sensor ML8511 (and maybe 5 cables)
  2. make an 8bit (gray scale) image with matrix of dots - for me for printing on 54x96mm was 5 columns and 9 rows of 5 mm dots.
  3. calibrate sensor - make several images with greyscale white dots value from 255 to 100 (best is 10 by step). Find the most intensive spot and lest intensive, check the changes in sensor signal for those two Points with every grayscale (plot them in Excel and find correlation)
  4. With correlation from 3) calculate how much you should decrease intensity of each dot. Then make an average between every dot. Ta dam you unded up with mas which you subtract from every Image of your print (best done in matlab)

#5

May just be easier to decrease the XY resolution by dropping your projector lower. The spherical distortion from the lenses becomes more noticeable when you are printing over a smaller surface area. I mainly print small, high detail models for jewelery casting and this is a big issue for me as well. I either have to orientate the model a specific way so it rises from the area of lowest concentration first and use much higher exposure settings and then dial the settings back as the model moves back into the area of focus. This can be a little bit difficult to get the programing down right for so I suggest that if you aren’t constrained by resolution requirements, just print at a lower XY res…you can get a little bit of resolution back if you cut the z layers a little thinner


#6

Thank you guys, I will follow the advices.
I´m printing right now in the area that I get good results with the parameters I confirmed (many tested until find the bests). Just I´m printing piece by piece, since I cannot use the full area.
Yes, thats a good idea GreatOwl. I will try it :wink:


#7

Thank you Darnok, I will do it


#8

Dear Darnok

ML8511 only lenght goes from 280-390 nm.
It that works?

Thanks
David


#9

Worked well for me :wink: