Piezo20 probe and piezo kit now available


  • administrators

    Piezo bimorph plate is quite tough, we used to cut circular discs out of them with a hole saw when I was building lasers. Don't let the piezo get hot when cutting or drilling it, because too much heat will destroy the piezoelectric properties.



  • Yeah I drilled two, one with a regular twist drill on a piece of wood that one worked, the other with a diamond core drill, not so successful too much heat.

    It is uncanny how precise the probing is though and how gently it does it.


  • administrators

    I wonder if its possible to get plates made to a custom shape.



  • It would be interesting if a smaller unit with hole already drilled could be made. The 27mm unit is larger than ideal packaging-wise, but works by bending so it might be hard to get the same sensitivity from a smaller disc, although it could be made thinner.


  • administrators

    what would be awesome would be the ability to get them with mounting holes to screw into the top of the hotend (3x3mm m3 for example) and another set of mounting holes to screw into an effector or carriage. does anyone know how they are made?



  • Found a 20mm Dia one at rs (they also have a 12 mm version)

    http://uk.rs-online.com/web/p/piezo-buzzer-components/7214940/


  • administrators

    Interesting to see how well the buzzer works as a sensor, do they manufacture piezo's with different properties ans actuators vs sensors?



  • These are the Murata ones from the same range that was in the original post so should be ok But I think I will get some of the 27mm ones and have a go with this.

    DJ did you go back to the std E3D Cooler with the 30 mm fan?



  • I think a slightly smaller one would work but perhaps not a 12mm, once you've cut away 4mm from the centre you will have not much piezo-electric material left to generate a trigger, and it won't bend as much. I don't think there's any feasible version without cutting a hole in the Piezo.

    I am envisioning a unit with two pieces, one piece with the hot end on, one for mounting to the carriage/effector which slide over one another with perhaps two small bolts to connect them,with the Piezo sandwiched between. For deltas I'd build this into the effector, for cartesians/corexy the best design would be to incorporate this into the x carriage.

    If anyone wants to pick the ball up and see how far they can run with it I'm behind them all the way. It's a promising sensor on account of it being very sensitive and nozzle based plus the Piezo disc can be fairly tightly compressed reducing the compliance of the whole assembly getting rid of the wobbly nozzle issue you get with fsr's, microswitches etc..



  • Doug, I'm using a 30mm fan e3d cooler with adjustable dual 30mm part fans that I co-designed with Jinx from reprap. http://www.thingiverse.com/thing:1692742



  • @T3P3Tony:

    Interesting to see how well the buzzer works as a sensor, do they manufacture piezo's with different properties ans actuators vs sensors?

    My understanding is that they are essentially the same thing. Some produce more voltage, a sharp tap with a tool can get 90v out of one of these things according to Mike (leadinglights) but as I have mine setup on the scope it was producing around 1.5v with a light tap.



  • Have ordered a batch of discs and the board.

    The issue with the 30mm fans is the noise they produce wonder if a redesign of the top of one of DC's 40mm Fan mounts may be in order and attach to the effector by all 6 screws in a radial ring arrangement (Just thinking out loud)



  • Sounds like a good idea. I find the sunon maglev 30mm fans are quiet, reliable and powerful you can get them from Farnell for around £13 each.


  • administrators

    Here's another possible configuration:

    1. Drill and tap the top end of an E3D heatsink with 3 small holes, probably M2.5 or possible M3. I hate groove mounts.

    2. Take a piezo element with the active element about 20mm diameter. Perhaps this one http://www.digikey.co.uk/product-detail/en/murata-electronics-north-america/7BB-27-4L0/490-7714-ND/4358154. Drill a central hole for the Bowden tube and collet, and 3 smaller holes around it.

    3. Attach the disk to the top of heatsink using 3 nylon screws, with a piece of insulation between the piezo and the heatsink. The purpose of the insulation is so that if the heater cartridge develops a short and makes the heatsink live, we don't get a short between the heater and the piezo.

    4. Clamp the brass surround of the piezo disc between the effector (which has a hole in it for the top of the heatsink to pass through) and a printed ring.

    For the electronics, I would take one of my IR sensors, remove the optical components, and feed the piezo into the analog input. Then program it to produce a nice clean pulse when it detects a shock. Piezos produce a good voltage from a very small mechanical shock if the load resistance is very high.

    I'd have a go at this myself, but I don't have a drill press for drilling the top of the E3D heatsink.



  • That's a good approach and neatens the design. As long as the area of contact between the heatsink and the piezo is fairly small it will flex enough. Maybe a small washer with 4mm ID and 6-8mm OD between the heatsink and the piezo transducer. Good idea with the ir board it seems logical it would work. The board Moriquendi came up with is probably very similar to it but has two pots to adjust the sensitivity to suit various piezo discs. But as a finished product using a known and tested piezo this would be unnecessary. I'm fairly sure these boards can only be supplied in fairly small numbers at present.

    My only concern would be the whole hotend is suspended from the piezo unless I'm not visualising what you mean correctly. This might reintroduce the wobbly nozzle issue. My rough design doesn't look nice but it does work and the nozzle is quite firm I think I'll work on making this smaller and neater for now.

    Agreed re. groove mounts they are useless. The 90 deg tee I based mine on clamps the hot end hard and effectively turns a groove mount into a flat mount with m4 bolts.



  • That David sounds like a plan although don't quite get how you would fasten the Hotend to the Effector with this arrangement any chance of a quick Sketch.

    I am sure I could drill and tap 3 holes in the top of a heatsink at M3 and maybe use a piece of Bare PCB G10 board as the insulator.

    Doug


  • administrators

    @Dougal1957:

    That David sounds like a plan although don't quite get how you would fasten the Hotend to the Effector with this arrangement any chance of a quick Sketch.

    I am sure I could drill and tap 3 holes in the top of a heatsink at M3 and maybe use a piece of Bare PCB G10 board as the insulator.

    Doug

    See https://dl.dropboxusercontent.com/u/19369680/Scan029.pdf (sorry about the poor drawing, I flunked Art at school).

    A is the top of the hot end heatsink
    B is the insulator
    C is the piezo transducer. The thicker part is where the element is, the thinner part is where the brass substrate extends beyond the element all round.
    D is the effector
    E is the printed ring. It will need a small tunnel in it to make room for the wires attached to the piezo element.
    F are screws. The two (actually 3) inner ones at least are Nylon to avoid shorting the piezo element out or connecting the piezo to the hot end metalwork.

    If the 27mm O.D element I found proves too insensitive, we could use a 35mm one instead.

    PS - RS also sells a 27mm OD piezo element, see http://uk.rs-online.com/web/p/piezo-buzzer-components/7243162/. They also sell M2.6x6 nylon screws.



  • OK I get that the bit that worries me is if 3 Nylon screws will be substantial enough to hold the hotend especially should it contact anything.

    How about using Mica washers as in the type used to attach 7405 type things to heatsinks and use std Stainless screws would need to drill the Piezo disc a little larger tho and I wonder if there is enough space to get it all in.



  • It's worth trying but I wonder if the Piezo will flex enough, and whether the hotend will wobble but I'm happy to be proved wrong.


  • administrators

    I think it's a question of getting the balance right. If the piezo disc is large (i.e. inner diameter of F is much larger than outer diameter of A), it will produce a large output but the head may wobble. If it is small (inner diameter of F not much larger than outer diameter of A), it will be much more rigid but produce a smaller output. I think the same will apply to any design, except for designs that use some other means to constrain the relative movement of the hot end and the effector to be in the Z direction only.

    The diameter A is about 16mm on my E3Dv6 and I expect the arrangement to be very sensitive because of the direct contact between the hot end and the piezo. That's why I think a piezo for which the outer diameter of the element (which should be slightly smaller than the inner diameter of F) is 20mm may be large enough. But I could be completely wrong.

    There is also the risk that a high-speed head crash could break the piezo element. I don't think this is very likely because of the brass backing. However, the ring F could be made to come over the top of the inner 3 screws so that it acts as a stop if the hot end gets pushed too high.

    I guess another option that avoids tapping the E3D and drilling more than 1 hole in the piezo is to epoxy the brass substrate of the piezo to the top of the insulator, and epoxy the bottom of the insulator to the top of the hot end heatsink. Bonding epoxy to aluminium can be tricky, but I have read that sanding followed by wiping with IPA helps, so does sanding followed by etching in citric acid.

    PS - thinking about it some more, it may be acceptable to bond or screw the piezo element directly to the top of the hot end heatsink, and design the electronics to survive a short between the piezo and +24V.


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