Piezo20 probe and piezo kit now available
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Have been probing away and changing things for the last few hours now.
Setting it as digital M558 P5 for me anyway is not working. If I leave it set to analogue M558 P1 I1, inverted output and set the piezo board by turning VR2 until the LED is just on with sensitivity fairly high (VR1), but use a trigger value of 600 it works. Its also worth setting a probing speed of 500mm/min M558 F500 so that the nozzle gives the bed a fairly sharp tap rather than descends very slowly which sometimes doesn't trigger.
My probe settings currently are
M558 P1 I1 F500 X0 Y0 Z0 ;analogue piezo sensor output falls on contact, probing speed, not used to home axes
G31 X0 Y0 Z0 P600 ;sensor is nozzle and trigger value.You can monitor the "analogue" output on web interface. Setup as I have mine the value shows approx 215 when head is stationary, during normal travel moves it goes up to 400-500, on a sharp tap with the bed it goes above 600 often to 1000 (max - essentially digital ON). At this setting on the piezo board I can get reliable and sensitive triggers.
Of course having faster probing speed is risky its harder to pull the power in case of a head crash there is less time to do so, suggest setting your stepper motor current to as low as you can go whilst still moving, so that these are less severe if they happen. However faster probing speed will show false triggers requiring slightly less sensitivity (VR1), so its useful in that respect.
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My bed.g if it helps:
[[language]] ; Auto calibration routine for delta printers M906 X500 Y500 Z500 E800 I60 ; Set low motor currents (mA) and increase idle current to 60% M561 ; clear any bed transform, otherwise homing may be at the wrong height G28 ; home the printer G28 ;home again in case of endstop problem ;slow down movement to delineate bed touch from travel moves M201 X250 Y250 Z250 E1000 ; Accelerations (mm/s^2) M203 X15000 Y15000 Z15000 E3600 ; Maximum speeds (mm/min) M566 X100 Y100 Z100 E1200 ; Maximum instant speed changes mm/minute G30 P0 X0.00 Y120.00 Z-99999 H0 G30 P1 X75.20 Y89.63 Z-99999 H0 G30 P2 X109.80 Y19.36 Z-99999 H0 G30 P3 X95.08 Y-54.89 Z-99999 H0 G30 P4 X38.37 Y-105.43 Z-99999 H0 G30 P5 X-40.44 Y-111.11 Z-99999 H0 G30 P6 X-103.92 Y-60.00 Z-99999 H0 G30 P7 X-118.18 Y20.84 Z-99999 H0 G30 P8 X-77.13 Y91.93 Z-99999 H0 G30 P9 X0.00 Y60.00 Z-99999 H0 G30 P10 X46.66 Y26.94 Z-99999 H0 G30 P11 X43.81 Y-25.29 Z-99999 H0 G30 P12 X0.00 Y-54.74 Z-99999 H0 G30 P13 X-51.96 Y-30.00 Z-99999 H0 G30 P14 X-51.96 Y30.00 Z-99999 H0 G30 P15 X0 Y0 Z-99999 S6 ;restore speed settings to normal printing speeds M201 X3000 Y3000 Z3000 E1000 ; Accelerations (mm/s^2) M203 X15000 Y15000 Z15000 E3600 ; Maximum speeds (mm/min) M566 X1200 Y1200 Z1200 E1200 ; Maximum instant speed changes mm/minute G29 S1 ;load grid levelling mesh M376 H10 ;taper off compensation after 10mm M906 X1100 Y1100 Z1100 E800 I60 ; Set normal motor currents (mA) and increase idle current to 60% G1 X0 Y0 Z75 F3000 ; get the head out of the way of the bed M500 ;save calibration to config_override.gRemove the G29 if you aren't using grid levelling, and the M500 unless you want auto-save of results to config_override.g and obviously replace the G30 points with your preferred probing locations and number of factors.
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Its weird. Both P1 and P5 do more a less the same thing for me but get slightly less crashed heads with P5. When I send the command to probe and it tap the nozzle it will register the tap .
It's like seems to be a delay between the trigger of the sensor and duet reading the probe point before it pushes though the bed. I don't think its a sensitivity problem because sometimes it will trigger from just the movement of the effector.
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Sounds like you've got everything there, its just a case of finding the sweet spot where it triggers well. I might do a few videos later showing how I have it setup. You might have the clamp/piezo assembly tightened too much, try loosening it off a tiny bit. There is a zone where you find the optimum between a tight assembly/less sensitivity/firm nozzle, and a loose assembly/high sensitivity/wobbly nozzle. I say this as there is no delay as I have it setup the lightest touch of the nozzle gives an above threshold trigger.
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A question. Why all this trouble and not use a simple conductive touch plate with an known thickness? Same like most DIY CNCs use? Hot end could be wired constantly , led could be implemented for visual check if working, prior to test. Costs absolutely nothing. Plate could be moved sequentially manually to predefined places on heat bed. Is this possible with the Duet board?
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Because the end of a hot end nozzle is not a good contact, it's frequently coated in a layer of gunky/charred plastic.
Moriquendi
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Boytan
It would be possible as it could be setup as a switch, and the firmware will accept any sort of trigger as an endstop. (The signal needs to be within the 3.3V range however that is manageable).
One issue is as Moriquendi described - inconsistant conductivity due to plastic buildup on the nozzle. The other issue is that many(most) bed surfaces are non conductive to you have to have the manual intervention of applying a conductive sheet to the bed.
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Yes I'd love to use a electrified nozzle and at one point I used to print onto aluminium and considered it. Plastic on the nozzle isn't really an issue if you probe hot. But now I print onto printbite which is super convenient and permanent and about as conductive as ceramic. I'd say most people are using glass or polymer surfaces of some sort.
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Updated the tuning guide (long post) above and included a video of how I have it setup which might make it easier to see what I'm on about. https://www.youtube.com/watch?v=F3vi6BOi6sA
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Awesome! I linked your post and the video from the Tutorials page:
https://duet3d.com/wiki/Tutorials#Experimental_FeaturesAlthough at the rate this is progressing it wont be experimental for much longer.
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Next iteration is to make the nozzle wobble disappear almost completely, I had in mind attaching the upper part of the piezo sensor module to the lower with small smooth rods (or delrin rods?) which would slide into the lower clamp part, and if metal, could be greased. This would result in a very firm nozzle constrained laterally but free to move upwards by a small amount to flex the piezo disc.
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DJ
PTFE rod is quite cheap and would probably be a better choice than Delrin or steel (Has self Lubricating properties IIRC).
a 500mm length of say 10mm Diam is about £2.50 from one of my local suppliers it is available in 4,5,6,8,10 mm diam plus a lot bigger as well.
https://www.directplastics.co.uk/ptfe-rodLook forward to seeing your design for it lol
Doug
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Well here's a preview:
I've modded Lykles version as he did his in proper CAD with all the holes geometrically correct etc..
Its pretty simple just 4 rods (in the only places they can go without redesigning the clamp (which is a bit beyond my cad skills TBH). Bonded at the top piece or interference fit, and then initially adapted to the clamp by manually filing the holes in the clamp lightly to achieve a fit that allows vertical movement but not lateral movement. Either that or drill the top holes to 4mm and the lower ones to 4.2mm or something like that. I'd grease them if it were steel but maybe won't need to with PTFE. My concern is maybe the PTFE will flex a little and reduce the stiffening effect I'm hoping for, which is why I was thinking delrin if not steel, which is also self-lubricating (although much more expensive and harder to get hold of).
What do you think? Very much open to ideas for a better way to do this.
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Hmm, would the wobble be decreased if we used a bigger peizo sensor?
In other words, have a wider base where the hot end is pressed into.Related, how big is the wobble and how does it show up in your printing quality?
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Problem with Delrin is getting anything smaller than 10 mm Diam.
a 500mm long piece of 10mm delrin is about £1.25 so is about half the price of PTFE but I can pop in and get it of the shelf so to speak
Would it help if I went and got a length of each and sent you say 100mm of each to try.
I would be tempted to drill the top at 10 but the bottom at 10.1.
Doug
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Doug. Thanks for the offer but 10mm is way too big for what I've got in mind. The whole assembly shown above is only 40mm in diameter and its convenient that it is, it fits inside an effector quite easily. It could be a little bigger but not to accommodate 10mm dia. rods. I'd also be concerned the friction would be quite high with that much surface area to try to slide on. I take your point about the drilling this is why I'd hand file it its easier to control the fit.
Lykle no the wobble would be less with a smaller piezo sensor, but then the sensor would flex less and be less sensitive. This might work with an FSR if there is one with a 4-5mm hole in the middle?
My first attempt at this version is going to be steel as Im sure I've got some thin rod lying around, doesn't need to be very stiff as they are only 15-20mm long.
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OK So would you like me to get some 4mm PTFE rod it could be stiffened with some bigger stuff round it maybe
Doug
Tell you what I need to print the parts so if you could send me the files (If you haven't put them on TV Yet) I will get some 4mm PTFE Rod and give it a try?
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I haven't put this one on TV yet as its totally untested. but here they are:
https://1drv.ms/u/s!Apv79JfGbPIwgu08dlMg3WjnTvCcQAI'll host them there for a while until they go on thingiverse.
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If you have some PTFE rod spare, I'd try it if you're having success with it. Just found some nice chromed steel 4mm rods lying around at work.
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I wonder whether you're over engineering this? The movement of the hot end is tiny, less than 0.5mm and probably less than 0.1mm. I would suggest that a compliant mechanism would allow the necessary movement with minimum weight while maximising lateral rigidity. I've got a pic but nowhere to host it, what's the best way round that?
Moriquendi
