Piezo20 probe and piezo kit now available
-
It would need to be split into two parts like DjDemonDs, I just knocked it together to demonstrate that you don't need dedicated bearings and shafts, you can achieve the same thing by arranging for flex in specific areas. I've been using a similar mechanism to support my bed with piezo sensors for months with no issues.
Moriquendi
-
I am quite certain that the design for this can be simplified and improved, and it will be, its been a very engaging collaboration so far.
But this is where I'm coming from: my printer was never better in terms of precision than when my hotend was clamped rigidly in a metal clamp, in a metal effector (with magnet arms and metal carriages on linear rails) and had literally zero play whatsoever. Now I know I am not going to get to that level of precision as I am now using a printed effector and carriages, and my hotend is attached to a compliant mechanism. But I do want to limit that compliance to 0.15mm of vertical movement, enough to trigger the piezo, and no lateral movement at all. If this would work with the piezo clamped firmly between two flat parts I would go down that route but it doesn't bend enough to have high sensitivity in this configuration.
I have noticed the nozzle move laterally as it slides over a slightly squashed down first layer, I don't like that at all.
All I'm talking about are 4 short rods pushed through some holes, I wouldn't consider that over engineering it, I'm just pushing to see if I can achieve the aims above. I'll leave the wobblier version available for anyone who wants to settle for that, it works.
I used to be very much a "that's good enough" pragmatist, but since building this large kossel and striving for a lot more precision I'm very much bitten by the bug. I'm only developing this way of using the sensor, as I was not happy with the precision I got from the IR sensor, which is to be fair fairly precise.
BTW the easiest way to image share for this forum is https://postimage.io just upload image and you get all types of links, and they host in perpetuity.
-
I use Photobucket but it is the same Idea
I'll drop into my Plastics place tomorrow for the rods I will get a length of PTFE and a Length of Acetal (Which is a form of Delrin) total cost for 500mm of each is £0.51.
DJ Drop my a Mail with your Address and ill get some of each of to you tomorrow if I get chance (If I can find a PO Open)
Doug
-
BTW the easiest way to image share for this forum is https://postimage.io just upload image and you get all types of links, and they host in perpetuity.
Much obliged.
Moriquendi
-
DJ no prbs mate you have done much to help least I can do to send you some bits of Plastic
-
Thank you. I;d love to get printing this new version but I've a whole heap of parts to print for a customer. Maybe Ill print it on the microdelta.
-
DJ Rods are in the post mate u shud get them tomorrow
-
Thanks mate, I did slightly rework that top sensor holder for 5.5mm rods which I scavenged from work but they are too big the piezo wont fit. The version I sent to you was Lykles original top plate for his effector but I modded it with an extra recess to improve piezo sensitivity. Ive hosted my version here: https://1drv.ms/u/s!Apv79JfGbPIwgu1TAuVGDSUBP5ecuA you need to add holes for the new rods.
-
I will wait till you have tried it out I think you will find 2 pieces in the package one PTFE good to 260 degrees and acetal which is good to 100 the acetal is the stiffer of the 2but I think if you can make the max exposed part of the rods to be about 1-2mm both will be plenty stiff enough. The PTFE also absorbs moisture much better at 0.03% acetal can by 0.3 IIRC.
Let me/us know how you get on
-
DJ
This looks interesting wonder if same idea could be utilised with Piezo's
http://www.robotdigg.com/product/885/Auto-leveling-force-sensitive-resistor-sensor
A fitting that will fit on the nozzle temporarily whilst the Cal/bed mesh is done then remove and the Z Hight set manually would mean not doing it for each print tho?
Hope the rods arrived ok
Doug
-
Hi Doug,
That looks interesting, not sure how it handles a hot bed, and certainly won't handle a hot nozzle, plus the sensing area is a big pad on the end however as an idea a clip on piezo module for probing would certainly eliminate the nozzle wobble issue and the need to change effectors etc…
I will try it, its not that difficult to do is it? The only thing I can't immediately visualise is how it attaches. That being said if we were going to develop a clip-on sensor is piezo the way forward or might FSR be better? Or maybe even a very precise microswitch or optosensor with spring loaded trigger flag a bit like Nebbians deployable touch probe http://www.thingiverse.com/thing:1517363
Haven't got the rods yet but the post in Bristol is notoriously slow.
Lol no pressure but David mentioned that he's developing a PCB/glass/epoxy effector and carriages and has a piezo version in mind but is waiting on the prototype… better get on with it then
Should get them tomorrow I am sure.
-
I've had great success in the past with a tactile switch clipped to the tip of the nozzle, simple, cheap and surprisingly accurate. The disadvantage is convenience and eventually you're guaranteed to forget to take it off before heating the nozzle.
Moriquendi
-
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.
-
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.
-
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!
-
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.
-
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.
-
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.
-
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.
