Piezo20 probe and piezo kit now available
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I have been following the discussion with great interest and have tried a 27 mm disc with my E3D Lite hotend on my coreXY machine.
I soon discovered that the inner wire soldered position on the disc would be in the way of the top of the E3D so the contact would not be flat.
I tried to move the wire further out to the edge of the active sensor but the mechanical bond was very weak and after a short time the wire came off, bringing with it some of the coating. I tried another position and the same thing happened. I now have a piezo disc with very little coating so I am unable to solder a wire to the piezo surface.While the wire was attached I was able to get good readings by tapping the hotend, without the bowden tube fitted. Pleased with this I drilled a hole in the centre of the disc to clear the bowden connector but this left only a small amount of the piezo in contact with the E3D because of this I could not obtain consistent readings, in fact they seemed quite random.
So:-
1. how have you all resolved the fact that the wired soldered joint is in contact with the E3D? I assume you have the active piezo surface in contact with the hotend as opposed to the brass side.
2. How are you finding such a small area of piezo in contact with the E3D is sufficient to obtain good readings?Any help and advice would be great.
Paul -
So in my design there is a cut out for the solder pad and wire in the rim of the lower part (which clamps around the e3d groove mount). Place the piezo with the side with solder/wires/active element downwards towards the hot end and then sandwich it between the upper and lower parts. I get very normal triggering despite cutting a 5mm hole in the middle, but unless you have a better approach use a spur point wood drill on a wood surface and drill few seconds at a time with plenty of breaks to let heat dissipate.
The trick has been to tune the recess above the piezo and the contact area of the hot end clamp to allow just enough flex in the piezo to get the signal above the noise, but not so much that the nozzle is wobbly. If you set it up with the piezo flat between two surfaces its not sensitive enough, if you have it so that it can bend dramatically, i.e. a very narrow rim to the lower part, you get amazing sensitivity but wobbly nozzle. Its optimising it between the two.
Assuming the rods Doug sent me arrive today, I will see if the latest revision eliminates the residual nozzle wobble enough to consider it the Beta version.
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I like the idea of no moving parts, just a little flex in the system. That might be a good way to reach the compromise between flex and no wobble. Of course, the problem here is that the wobble and the flex go in the same direction, sort of. It would be nice if one was vertical and the other horizontal.
I will have a look at a different effector design that will locate the hot end with a little up flexibility. If we tune it right, we might use the force of the extruder to keep the hot end down against the stops. Can't wait for the Peizo, so I can have a look at the actual forces happening on a hot end.
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Had the same problem with the thin wires pulling off the Piezo. Not solved that problem yet…. As my mount for the hotend allows laterally movement so I used a spacer between the flat part of my e3d and Pieso. This allows space for the wires too. Only problem at the moment is sensitivity but Im pretty sure I can fix this with a design different design for the clamp. Was going to print this but got a clog in my hotend.... so need to strip that down first when I get a chance. Bah!
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Lykle in most ways the nozzle wobble is lateral and comes from the clamp resting against the piezo which is compliant - and the 2 screw fixing system is the line about which it pivots, the triggering force is vertical and is the whole hot end plus clamp pushing up into the piezo. This is why I am keen to test the design with the four rods to slide the clamp up and down on. Or as you said use a version with 4 screws (like the mk I but smaller). Its no problem for the nozzle to move upwards by 0.15mm, its equivalent to having a sprung bed (but only very slightly sprung), its the lateral movement which can cause issues with squashed down first layers which are uneven when the nozzle passes over them on the second layer and curling edges of overhangs etc…
Sakey - If I might be so bold to suggest a strategy start with my mk5 design and try it then tell me where you changed it, if this is feasible. It seems silly to design from the ground up when my version works albeit needs refining to reduce lateral nozzle movement without eliminating vertical (upwards) nozzle movement.
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Not taking anything away from DJ's work, was just trying to mount it into onto a Rostock with a machined mount to hold the hotend already (it seems to lets it slide up and down and then is clamped via 3 points at the top already which is seemed a good platform to start with for a piezo. I wanted to use this with as little modification as possible. My temp spacer is just a nut with a cut out in . Ill post a picture and stl when I re-assemble and get it working somewhat reliably.
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That makes sense, it will be nice if these can be fitted between two existing parts without much change but my experience so far shows they need to be able to flex on probing contact, by an amount (around 0.15mm if my z resulting offset is anything to go by) to trigger clearly above the noise they generate.
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Hmm, if the hot end can slide up and down in the clamp, you might be able to avoid sideways wobble.
Only trouble I see here is tolerances. You have to get it exactly right so that there is no sideways play but just enough space to slide up and down. That will be very hard to achieve with printed parts. So it will have to be post processed.But I like the idea of a sliding hot end, A little like the Auto lift hot ends but then for calibration.
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Well unfortunately the rods Doug sent to me have not appeared, so lost in the post might be the issue, but I have now got some 4mm steel rods (wood screws shanks cut down with a dremel). I am printing a version now with holes for these rods. I intend to bond/heatpress the rods into the top piece, and then hand file the clamp piece so the rods fit and slide. This might be difficult due to the fact that the clamp will have to be tightened around the hot end exactly the right amount or these holes won't line up.
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Okay so this latest version with rods to support the assembly is working extremely well. Almost no nozzle-wobble and calibration deviation at 0.02mm. It seems to be the optimum between sensitivity and nozzle wobble.
If you intend to make something like this, and are not planning to design your own (or if you are making your own, consider downloading this one and perhaps copy the salient features to your design - to save you time) this is the version to make. I am now calling this the beta version.
I have yet to test it with acetal or PTFE rods instead of steel but 4mm smooth steel rods work.
It's now on Thingiverse - http://www.thingiverse.com/thing:2069480
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DJ I'll put some more in the post tomorrow mate
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Glad to see it is working so well.
It was a pleasure working on this, even tho it was just a small part. -
That's way too kind Doug, the post is a constant source of irritation.
This version does seem quite solid. I've done one to fit Lykle's (congrats on getting the nimble on sale ordered mine already) effector and the other generic one to bolt onto underside of an effector or carriage.
I might make one up for the corexy (and a new x carriage to fit it to) be nice to try it on a ramps setup for the benefit of the majority who haven't got a duetwifi.
Also along the same lines thinking if I can make it fit a clone hotend bowden with the much larger push fit bowden couplers, might be tricky can't cut a 12mm hole in the Piezo…
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I am really impressed by your works guys!!! great to see such projects.
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Thanks on behalf of all who are contributing, it's been a very encouraging collaboration. 3d printing needs a z probe that's cheap, accurate and reproducible, that minimises the effects of tilt because it has no offsets.
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Dj
Another package on it's way you should get it tomorrow sent it first class handed in at the PO desk
Doug
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Awesome, much obliged. I've printed another one with the rod supported version on the kossel Xl and came out looking awesome and a mount for my corexy so hopefully I can use those rods and test the setup on ramps with marlin. I'm aware it's all been very DuetWifi so far. Rods have turned up so thank you very much.
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Okay so made another one this time with 4mm wide 15mm long acetal rods (thanks Doug). Works fine nozzle is quite firm, sensor triggers normally.
Have attached it to my corexy (ramps/mega/Marlin RCbugfix 31-01-07 on). The usual messing around with Marlin and uploading firmware. However it will home nicely and entering a z offset of 0.2mm means the nozzle is nicely positioned just above the bed at z=0 on the lcd. It will do grid levelling if auto_bed_levelling_bilinear is enabled.
I have added instructions for configuration of Marlin on ramps/mega or compatible in the thingiverse listing http://www.thingiverse.com/thing:2069480
Interestingly Marlin allows the M48 probe repeatability test the result is:
Recv: Mean: -2.492500 Min: -2.510 Max: -2.475 Range: 0.035
Recv: Standard Deviation: 0.009014So hitting a standard deviation of 10 probes at just below 0.01mm repeatability.
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Been chatting with Moriquendi about making it safer in terms of a wire break. Currently you'll just get a head crash.
Current thinking is that putting two Piezo transducers back to back into the unit (might need slight adjustments to the top part), would enable redundancy as well as potentially stiffening the system. The second Piezo has to be wired in parallel but with black and red reversed so they don't cancel one another out. If one Piezo is disconnected the other will still function. However you won't know it's failed potentially unless it begins triggering differently,which it might not given the way the comparator works in the signal board.
Any thoughts?
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First of all, VERY COOL idea. I presently have FSRs on my bed. I'm following this thread with lots of interest.
One thought on redundancy, using your idea of back to back transducers… Maybe set it up such that both sensors are handled separately with signal conditioning, then the outputs are logically "AND"ed together. Then, if both don't trigger as expected (maybe after an RC time constant??), the ANDed output stays triggered (or is somehow latched triggered), which will signal an issue to the Duet's firmware.
Or similarly, have a second output from the signal conditioning board that would change states if the outputs don't behave as expected (i.e. last time, only one triggered). This signal could be monitored by the Duet firmware to identify a fault condition.
In either of these cases, you would probably have to match the gain and offset of the signal conditioning/comparator for each sensor such that they trigger at the same time. Or get really slick about it and let a tiny PIC automatically configure gain/offset for each side and also have it drive the triggered output with a buffered signal.
Hope that all makes sense. I don't know if what I suggest is feasible, but I thought I'd throw it out there.
