IR Probe improvements (e.g. selectable sensitivity ) ?
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What you are missing is that the sensor isn't just looking for the IR to exceed a particular threshold. It is looking for the reflected light reaching the phototransistor from the two IR diodes to have equal intensities,
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Thanks that's what I missed indeed… Now I have to think about it .....
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Dear David,
I got my oscilloscope to monitor sig after returning to the original values of the resistors.
with white paper under the glass both signals increase at the about same rate until I am about 1mm away and it takes another 0.7 mm for near to catch on, only to equate when I am close to contact ~0.3mm. Finally near overtakes far only at contact
It is about the same with black paper although with lower intensity.I checked the leds alignement and the photodiode and they are as coplanar, parallel and as close to 45° as a binocular and my eyes could see.
Also all the other materials I have checked (wood, black smooth, black matt, 2mm glass) give close to 2.5mm trigger distance and would be usable as beds… but this damn piece of 5mm glass doesn't want to collaborate. I just ordered some buildtak so it won't be a problem anymore soon.I understand now that the 2 spots are supposed to be of equal intensities (because the difference in resistor values compensate for spot size due to the increased distance of the far led) and that the trigger zone is when the overlapped area of these 2 spots align with the photodiode detection cone.
I think I have been unlucky with my choice of glass thickness as the back reflection must cause the total reflected far led intensity to be larger than intended in the overlapped area. Not sure what happens with the paper but I suspect it is not affecting the 2nd reflection too much as black paint would.I guess that's all the feedback I can give you and hope it could be as much help to design/debug next gen as the number of characters in my posts...
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I agree with your diagnosis. As the target gets closer, the received intensity of the near beam should rise faster than the received intensity of the far beam. I suspect that as the surface reflection of the near beam reaches maximum intensity at the phototransistor, so does the back reflection of the far beam, with that particular thickness of glass. I'll do the sums when I get some spare time.
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Tried to draw this to scale in geometrical optics and yes the far back reflection alignes almost 1to 1 with the near led.
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Hope you don't mind me jumping in here but just wanted to say that I've started commissioning my printer, complete with David's probe. I have 6mm glass on top of black painted aluminium but the glass is sandblasted. This is the first time I've used the probe so I just followed David's instructions and it's worked "straight out of the box". I'm getting a trigger height of 1.47mm which seems to be repeatable (but it's early days yet). Maybe the sandblasting is doing the trick?
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Yes this would surely help; you mean the backside only is sandblasted. Not the front side.
I received my Buildtak yesterday applied it to the glass and it works like a charm it's black and works at about 2.2 mm. Perfect adhesion right from the start. The Duetwifi and sensor are so easy to learn. I am having a lot of pleasure using it!!!Since it is my first printer. I am going through the learning process right now. I am getting 5 perfect PLA layers but I think I need blowers because after that the whole top surface gets so soft (heat from the underlayers). I tried with a handheld blower but then I had hadened curled corners on overhangs and my head crased into them….. Not sure what to do next.. (sry it's out of topic)
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Hi sga,
Nope, it's the top side that's sand blasted (and also "Brite Guard" coated). It's experimental and I haven't yet tried it but if it works, I may be able to print directly on to the (heated) glass without any tape, glue, paste, or other sticky stuff. The surface finish is almost smooth - a bit like the very finest abrasive paper that one can buy - the sort of stuff used between coats of varnish is that means anything to you. The glass just looks opaque like it's been etched but not rough.
If it doesn't work, I can always resort to some other method and/or turn the glass over. I've got 3 pieces of glass so I could potentially have 6 different pre-prepared print surfaces.
It is normal to use print cooling fans with pla but I've found it only necessary with small objects. Larger objects seem to have enough time to set before the next layer gets printed. You could try printing more slowly. I have my Slicer set so that the minimum layer time is 20 seconds. What then happens is that if a layer would normally take say 10 seconds, then the printer will slow down by about 50% so that it always takes 20 seconds to print. If you have no fan, you could experiment with that setting,
Sorry we've gone off topic.
Ian
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Interesting, I guess that you won t have adhesion problems. Or maybe too much of it… let us know, it would be very intersting to know how well it works.
Yes small part-no fans is certainly the problem I think. The layer to layer is too quick to properly set. Plus they get a lot of convection/radiation from the hotend... -
Some time go I tried 4mm glass that was ground on one side. With the ground side up, adhesion was terrible, whereas I often print PLA on plain glass with no problems. With the ground side down, the IR sensor wouldn't work.
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Some people swear by it (sandblasted glass that is) I'll let you know how I get on. I haven't tried printing on plain glass - it's just that the instructions for my original RRP Mendel recommended Kapton tape and I've become fairly proficient at fitting it, so I've carried on. That's with a 200mm square bed and as the new one is 400mm square, I think I'll need to do something different.
I tried your probe with ground side up and ground side down. The trigger height is different but it works OK for me. Maybe it's the extra thickness (mine is 6mm)??
