The Shop > CNC
3D printer bed correction
shipto:
Sorry but I don't have any issues right at this moment with my printer, this isn't to fix an immediate problem. As I said its more of a failsafe in the event of an issue arising say 5 hours into a 6 hour print.
WeldingRod:
It's easy to add an "each layer" script to recheck zero. If you go that way, you should think about two prox sensors rather than the usual mechanical switch.
I did it, and then un-did it when I solved the blobs sticking up problem.
Sent from my SM-G892A using Tapatalk
shipto:
--- Quote from: WeldingRod on December 27, 2020, 11:06:54 AM ---It's easy to add an "each layer" script to recheck zero. If you go that way, you should think about two prox sensors rather than the usual mechanical switch.
I did it, and then un-did it when I solved the blobs sticking up problem.
Sent from my SM-G892A using Tapatalk
--- End quote ---
Thats going to add loads of time to each print when it probably wont be needed 9 times out of 10.
ddmckee54:
I'm not saying this can't be done, because if you try hard enough the software can get around a LOT of hardware limitations. However, as a controls type engineer doing this stuff for 30+ years I can see a lot of gotchyas that you'll need to work around.
1) How accurate do you want this thing to be? You need to realize that most 3D printers are claiming that they can position to within limits that were considered state of the art for integrated circuit dimensions 40 years ago.
2) Your light source, you'll probably want to use a laser. A normal light will spread out in more or less a cone shape once it leaves the source.
3) Are you planning on stopping the bed at what is thought to be the correct position, or at least traveling at the same speed? The hardware will react at a fixed rate and if the bed is traveling at different speeds the "Correct" spot could occur at what seem to be different locations. Been there, done that - got the Tee shirt.
You can try compensating for this, but I wouldn't recommend it. I knew a guy once that was trying to keep a large weight suspended 40' below a traveling car from oscillating when the car slowed down and came to a stop. He worked on that for months and never did get it to work correctly. The calculations can be done, but NOT by an 8 bit Arduino in any reasonable time.
4) It's gonna be a BEAR to align this, and keep it aligned. Think about how much of a shaking the Y axis gets when doing a solid infill on a narrow part.
Again, I'm not saying this can't be done, because my gut feeling is that it can be done. I'm just playing the Devil's Advocate and giving you some things to think about, so you can avoid some dead-ends.
Don
shipto:
--- Quote from: ddmckee54 on December 30, 2020, 03:11:44 PM ---I'm not saying this can't be done, because if you try hard enough the software can get around a LOT of hardware limitations. However, as a controls type engineer doing this stuff for 30+ years I can see a lot of gotchyas that you'll need to work around.
1) How accurate do you want this thing to be? You need to realize that most 3D printers are claiming that they can position to within limits that were considered state of the art for integrated circuit dimensions 40 years ago.
2) Your light source, you'll probably want to use a laser. A normal light will spread out in more or less a cone shape once it leaves the source.
3) Are you planning on stopping the bed at what is thought to be the correct position, or at least traveling at the same speed? The hardware will react at a fixed rate and if the bed is traveling at different speeds the "Correct" spot could occur at what seem to be different locations. Been there, done that - got the Tee shirt.
You can try compensating for this, but I wouldn't recommend it. I knew a guy once that was trying to keep a large weight suspended 40' below a traveling car from oscillating when the car slowed down and came to a stop. He worked on that for months and never did get it to work correctly. The calculations can be done, but NOT by an 8 bit Arduino in any reasonable time.
4) It's gonna be a BEAR to align this, and keep it aligned. Think about how much of a shaking the Y axis gets when doing a solid infill on a narrow part.
Again, I'm not saying this can't be done, because my gut feeling is that it can be done. I'm just playing the Devil's Advocate and giving you some things to think about, so you can avoid some dead-ends.
Don
--- End quote ---
Thank you for the input, what I had in mind was something like the picture below. If for example you had 200mm bed travel every time it got to the point where it should be at 100mm it would check the state of this sensor, if sensor is in correct state then carry on but if not then home that axis. sounds quite simple in my head but as you point out there is much to think about.
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