Headed bed and noise issues
February 13, 2013 04:45PM
I have been having "fun" the last coupple of days trying to get some decent quality out of my new prusa.

Very long story short, I wanted to upgrade the printer, so I ordered a heated bed, and some alu pulleys from T3dP3d. For a start I did the first coupple of test prints with the HBP hooked up to my bench PSU, and the prints looked fine.

Then I took the printer apart, upgraded the belts, and hooked up the HBP to my sanguinololu, and then the fun started. All my prints had a "vinyl record" texture to them, I tried a lot of different things, like slowing the print speed down, adjusting motor current, and different combination of settings, but nothing worked. Though I did found out that I had a problem with filament supply, but that wasn't the main problem. Even reverting to the old T5 belts and printed pulleys didn't made any difference..

Then I thought about my first test prints, wich was done with the HBP hooked up to my bench PSU, so just to try something different I tried that again, with a dramatic increase in print quality as a result.

Then I set out to test things further, and hooked up my oscilloscope the supply for the HBP, and there it all was:

When the HBP FET turned off, the HBP behaved like an inductor, and send noise back to the sanguinololu.

This issue was solved with a capacitor and a diode in parallel with the HBP, and then it looked like this:

However print quality didn't improved, it was still crap, the right one is when the HBP is connected to the sanguinololu

The supply is a decent quality Chieftech hacked ATX supply capable of 12V 17A, I am not 100% sure, but I think that I used it for my first reprap project, also with a heated bed, but of my own design.

Have anyone expeirenced similar problems?
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open | download - withfilter.jpg (21.9 KB)
Re: Headed bed and noise issues
February 13, 2013 07:55PM
Possibly when the Sanguinololu switches the bed on and off the thermal expansion of the heated side causes it to warp up and down making the layers squashed or not. I have seen people report this with kapton heaters direct on glass.

Re: Headed bed and noise issues
February 14, 2013 01:01PM
Spot on.. thumbs up

I measured with a dial indicator, which showed approx 0.1mm movement up and down within the first second after the heater turned on or off.

Reason.. The glass plate I am printing on is missing a corner, so I rearranged the attachment to 3 point instead of 4, and away from the broken corner. Then I set the bed temp check interval to 0.5 sec, and now the movements is in the order 0.01 to 0.02 mm, so now I guess that I'll have some other tolerances taking over.. winking smiley
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