Piezo20 probe and piezo kit now available
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Thanks for posting the results. I think the sensor is now as good as the high end microswitches. Its a shame my latest effort with underbed mounts is on a marlin equipped printer as there isn't an easy way to run this test, and marlin only reports to 1 decimal place, as its the most sensitive piezo setup I've seen so far. See if the elusive 1 micron deviation is achievable. Almost worth buying a duet board just to do this test on it.
20 microns is probably not noticeable in a first layer. The heater block and heatbreak (below the heatsink) on a v6 can expand 20 microns when heated from 25 to 130 degrees. So that puts it in perspective. But this is constant if you always probe at the same temperature. I mention it in the Precision Piezo documentation going from 130 degrees recommended probing temperature to 250 degrees printing temperature you'll be 20 microns lower at the nozzle.
Try Russ' other test which moves the head around, then probes the same point, check the gcode first as it sometimes moves to extreme positions depending on your printer. If the sensor is reliable to 2 microns, then you are effectively testing the mechanical accuracy of your printer with the moving test. Try a few different speeds for the moves.
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Will test it tomorrow… What still bugs me is why that first Z is not constant... I changed the homeall to move to the point slowly, wait 5 seconds, do G30, and then do G28 Z (yeah, I know, I'm testing twice Z, one with the homeall and the other with homez), and I got this results:
Bed probe heights: 0.002 0.004 0.006 0.006 0.010 0.008 0.008 0.008 0.006 0.008 0.006 0.010 0.010 0.010 0.011 0.006 0.004 0.009 0.008 0.008 0.008 0.008 0.009 0.009 0.005 0.006 0.009 0.009 0.008 0.008 0.010 0.006 0.008 0.009 0.009 0.006, mean 0.007, deviation from mean 0.002
(here I do a G29 to mesh the bed: 56 points probed, mean error -0.054, deviation 0.057 and all again)Second time:
Bed probe heights: 0.013 0.013 0.009 0.013 0.013 0.016 0.014 0.013 0.011 0.013 0.010 0.011 0.011 0.010 0.010 0.013 0.013 0.013 0.013 0.011 0.013 0.010 0.011 0.011 0.014 0.010 0.009 0.013 0.011 0.011 0.013 0.008 0.014 0.011 0.013 0.014, mean 0.012, deviation from mean 0.002
(here I do again a G29 to mesh the bed: 56 points probed, mean error -0.051, deviation 0.056 and repeat all again)Third time:
Bed probe heights: 0.014 0.011 0.011 0.011 0.010 0.009 0.009 0.009 0.010 0.011 0.010 0.011 0.011 0.011 0.009 0.013 0.009 0.011 0.011 0.009 0.010 0.010 0.011 0.010 0.010 0.011 0.010 0.008 0.010 0.010 0.009 0.009 0.009 0.010 0.011 0.013, mean 0.010, deviation from mean 0.001
(here for the last time I do again a G29 to mesh the bed: 56 points probed, mean error -0.052, deviation 0.058)Always the same deviation (which is awesome), not always the same mean during the gcode execution, which is something I don't understand... So my issue is not with the mean, is with the repeatability of the process itself... I don't care if the prints needs 5 minutes to start because I'm doing 7 mesh and 15 homing if the print is always the same :D.
Please do not misunderstand me, I just don't understand why, seen the awesome precision and repeatability the sensor has, the homing is not always the same... although with my rubbish test it seems I'm getting at least similar values around 0.01 xD
Cheers
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Id say something mechanically not tight on the printer/hotend/sensor even. Maybe a youtube video might help.
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Just got my drop in unit today, just a quick inquiry before i screw something up. Should i losen the rear before tightening the front screws or should i just tighten the front?
I dont want to damage the disc so i figured i would ask, but it isnt level.
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So i just opened it up to check out the disc, while reassembling i noticed that it does not fit inside the middle plate which is what is casuing the mount to be tilted. Is this by design or should i print a new center plate?
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The disc is designed to sit on a flange just inside the outer circular recess. It is not supposed to be inside the deeper recess. The idea is the lower part bends the disc in the centre. Do up the screws gradually and ensure they are all done up the same amount with a little preload on the disc.
Then re-tune the module as per instructions, any change in preload level will affect the precision of it.
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If it's one that I made the disc fitted when I made and tested it. But sure you can print a new one if you want. Might be worth watching my YouTube video series on assembling it. It looks simple but won't work if done wrong.
How to Guides: https://www.youtube.com/playlist?list=PL9g_2J-RjkRCy5Sr5gIVwMYGhI9DrJewq
Sorry for being a while getting back to you I don't check here so often our official support thread is at reprap forum:
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Hi!
As cheap piezo discs are mostly made to build buzzers, why not using them this way?
The idea is to use 2 piezos: one on the head, and one somewhere on the heatbed. One of them is used to generate a vibration, and the other one to detect this vibration, which will be transmitted when the hotend is in contact with the bed.
It should be possible to find a resonant frequency to optimize transmission (far from motor vibrations and other noise…).
In fact, any kind of transducer can be used on the bed, to generate the frequency, to have more power than a simple piezo, so it can be easily detect by the head.
A friend in our hackerspace wrote, a few months ago, an Arduino routine to detect a single frequency, which can help to analyse the signal: https://gist.github.com/edgar-bonet/0b03735d70366bc05fc6
Just an idea. Let me know if it has already been discussed.
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Thanks, it has been discussed more so on reprap in the general piezo thread http://forums.reprap.org/read.php?1,635075. I've never tried it, but whilst its an alternative approach is it potentially a solution looking for a problem, as the current method works so well adding a second piezo, and possibly adjusting/changing the PCB to search for the frequency outputted by it, would only be worthwhile if we were going to gain some sensitivity or better discrimination between a trigger and a false trigger (with current firmware settings this isn't particularly a big problem). I'm down to 4g of force to trigger on my microdelta with underbed piezos.
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Well, I was trying to find a solution which doesn't need specific mount for the hotend nor the bed…
I will read the reprap thread. Thanks.
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The gold standard (unless you want to calibrate/level manually) is electrical contact, but we don't have conductive printing surfaces, on the whole, so it isn't practical. You can get conductive PEI at eye-watering prices.
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If it's one that I made the disc fitted when I made and tested it. But sure you can print a new one if you want. Might be worth watching my YouTube video series on assembling it. It looks simple but won't work if done wrong.
How to Guides: https://www.youtube.com/playlist?list=PL9g_2J-RjkRCy5Sr5gIVwMYGhI9DrJewq
Sorry for being a while getting back to you I don't check here so often our official support thread is at reprap forum:
It was how it arrived look at the photo, bought one of your drop in units. I only dissasembled to see why it was so lop sided (have not even installed the thing because i dont want a hotend that sits at an angle. the disc does not fit in the outer recess, i will print another and follow the video. or i might just wait and install the bed sensors that you are shipping to me
just giving you a heads up for QA
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That's just very odd, is it installed already? I'm tempted to send you another one and pay you the shipping to return it by regular airmail. I'd like to see what happened.
If it's installed and working then leave it if you're happy to.
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Its not installed, it arrived, i took it out of the package made my post here then left on a fishing trip. Came home to an overheated and fried computer from this heatwave we are having
hopefully ill have my computer up and running by the time your bed piezo sensors arrive. -
Does anyone has a working design for a Diamond hotend? Ian, did you make progress on yours?
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Your best bet here, and quite practical on a delta, for example, is to use underbed piezo sensors. There are designs for mounts, and with a stationary bed it works very well.
Here are some exmaple bed mounts
https://www.thingiverse.com/thing:2446460You add to that the piezo kit:
https://www.precisionpiezo.co.uk/product-page/precision-piezo-z-probe-kitAfter a bit of tuning you should be probing away with high sensitivity and with whatever hotend/nozzle you want.
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Ok, thanks.
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Mmm, I may have another idea… What about having the hotend (any hotend, in fact) mounted on a support which is anchored on one side, but free on the other side. On this free side, it is supported on a piezo disc. In order to have a good sensitivity, a spring put the right force on the piezo (just to maintain the head in its position). Then, once the bed calibration is done, an additional force can be applied (to increase the spring one) to firmly maintain the hotend (it can be a simple servo eccentric)...
In fact, it can be the opposite: a very strong spring firmly maintains the hotend, and the servo releases a little bit the force so the piezo is less strained, and more sensitive. Could work with a FSR too.
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I ordered an assembled kit (screwmount version) and I‘m very curious how it will perform compared to the IR sensor (tilt problems etc.)
I didn’t find a dedicated effector design for my Kossel Mini (Think3DPrint3D). What will be the best way to mount the piezo20, just screw underneath the original effector?
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Thanks for the order.
Compared to the IR sensor (unless you have an evenly reflective (to IR) bed surface, which remains evenly reflective at all times, and no tilt), it will be like breathing fresh air. Tilt isn't a problem in the same way. There is no x or y offset so the nozzle determines the height at any given probing point, whether the entire effector and attached nozzle are tilted or not. In theory, if your tilt is quite minimal this should generate little/no issue with calibration/first layer thickness.
However, if you have a very precise machine (or large one) then tilt is still going to feed into your calibration and reduce its accuracy to some extent, as instead of the trigger height being different relative to the nozzle at different probing points because of tilting that you see when using an offset sensor, its the nozzle height that changes if the effector tilts. So try to get rid of tilt if you can.
As for mounting start off by using the supplied drilling guide (also a natty keyfob) to drill 2 3mm (3.5mm) holes equidistant from your central hole for your filament path, then screw the unit under your effector using m3 screws. This works but absorbs around 18mm of your z printing height.
Once you've determined you are satisfied with the performance of it, consider designing an effector with the upper part of the unit integrated into it (even better if this is raised above the effector, so that just your heater block hangs beneath, this really reduces the effect of any tilt you might still have, but makes cooling the heatsink a little more challenging), to regain the z height you lost.
