Piezo20 probe and piezo kit now available
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That's actually very helpful, DjDemonD.
Made me realize I need to change my mount idea a little bit.
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Idris - Haven't tried them yet, though I will. The first and second options sound good but, you/we will have to supply and pretest the piezo discs, the sensitivity etc shouldn't be a problem we'll just find the optimum for whichever Piezo can be reliably sourced into the future. Same as opto/IR sensor they're pre-calibrated.
Option 3 sounds less exciting but currently we all have long wires running to each endstop terminating at the controller. So it would be a case of using the same wires just terminating them at the 3-Piezo board which can be installed next to the controller. So that's less change for existing machines.
Just some thoughts which will probably change after I've tried them, I wondered about supporting the disc at one side and having my carriages hit the other side for maximum flex (and signal).
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That's actually very helpful, DjDemonD.
Made me realize I need to change my mount idea a little bit.
Maybe but if it's not too difficult try it then change it if it doesn't work, as these things are very versatile, most designs work but some are slightly better signal to mechanical noise ratio. Let us know either way.
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Will do. Trivial to change either way.
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Option 2 sounds the most appealing to me.
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Idris could you possibly use individual screened 2 core cable to try and reduce the Capacitance effect or even screened single core cable routed the opposite way round the frame.
Just random thoughts
Rapid online is a good source of Cheap Piezo discs in all sorts of sizes and I will be experimenting with mine at the weekend once I have finished my Callout week
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Just a thought about the endstops. How do we test them? Is there a gcode for test endstop repeatability? I can install them and then autocalibrate and measure the precision? Or do repeat endstop calibrations and measure the spread, compared to my opto's I have now?
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Ok, got my pcb, mounted up the piezo, ready to go… connected to the duet, and no matter what it shows a signal of 1000 on the Z-Probe value.
I'm using either of the two configurations below:
M558 P5 I1 F500 X0 Y0 Z0 ; Z probe is a piezo sensor
G31 X0 Y0 Z0 P100 ; zprobe height and threshold - piezo;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 P700 ;sensor is nozzle and trigger value.Shows 1000 for a value if the signal line is connected. I have the LED wired up, and it's off. What am I missing?
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Using a multimeter, it's putting out 3.3v on the signal line all the time, regardless of if the LED is lit or not.
Hmm.
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I take that back, when the LED is lit, the signal stops. if I trigger it rapidly enough, the z-probe value falls to 0.
Switching the I1 to I0 to invert it did the trick. Should be ready to rock now.
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Go easy at first lower your motor currents during probing, to the minimum needed to move the axes, mine are at 500. Then any head crashes are fairly low impact. A little finesse on the signal conditioning board is required.
The digital config above M558 P5 …. is the one to try first. Lower the debounce value if you get false triggers.
Any issues with that, switch to the analogue one and use the analogue value as a guide for fault finding, use low jerk/accel values with this mode.
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I think screened cable probably has more capacitance per meter than unscreened, we're not talking about electromagnetic interference but rather the capacitance of the cable absorbing the signal.
My current piezos come from rapid but I don't really trust them as a long term source of parts. If I design and calibrate for one particular piezo disk I want to be sure I can get hold of them in a few months or years. I've seen rapid pull parts or replace them with something equivalent but not identical. Rapid is also the only supplier of Kepo piezos I can find, murata elements are much more widespread.
Option 2 is the most versatile but my current designs for option 2 are about 50mm/2" long which may make mounting difficult, width is about 14mm or just over 1/2".
On a delta, option 3 would allow you to pit the endstop board in the top of the printer and route the signals down to the controller using the existing wiring, all you'd need to do is run wires to power the board.
Idris
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The Farnell own-brand (Multicomp) piezos might be made by Kepo too, because I know that their own-brand piezo sounders that I use in PanelDue are made by Kepo.
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Ok, so I'm calibrating succesfully with the piezo now. Some tuning to do, but it's definitely functional and working. Thanks for the help, and guide, and thanks Moriquendi for the board!
I'll post some pictures of my setup, but essentially it's just my hotend mount I already had + $1 in nylon washers from the hardware store.
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I think screened cable probably has more capacitance per meter than unscreened, we're not talking about electromagnetic interference but rather the capacitance of the cable absorbing the signal.
On a delta, option 3 would allow you to pit the endstop board in the top of the printer and route the signals down to the controller using the existing wiring, all you'd need to do is run wires to power the board.
Idris
Idris
On the New delta I intend to put the Controller and motor's at the top of the towers anyway (This will be a slightly taller than normal Delta) And my idea was to use single core screened cable but route it so one leg went down one side and the other down the opposite side to the triangle (This would of course only work if it was at the top).
Could the Control board be placed in the upper part of the Delta (For a traditional type build) and then the signals from the board to the Duet etc be routed down in one bunch as then twisted screened cable should be ok for that?
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It's only the signals from the piezo elements to the endstop board that are delicate, the signals from the endstop board to the controller are as robust, if not more so, than a normal microswitch signal, I don't think you need to take any special precautions with them. To answer your question, yes, for a traditional delta the best arrangement would probably be to have the endstop board in the top of the machine near the endstop piezos.
Idris
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Ok, so I'm probing. So far the only real issue I've hit is I can't probe if the hotend is heating or even hot. No biggie, I calibrated the Z offset for the probe, and I'm good to go.
To mount it, as I noted earlier I use the 713maker hotend mount for my v6. This made it extremely simple.
First, I put a locking right on the collet for the bowden (I have a stub of a bowden to my Y adapter for filament switching). I had to chop the lock ring down to be really small - no bigger than the collet itself. Around the collet / bowden I put a 3.2mm tall nylon washer (12.7mm OD, 8.2mm ID) I got at the hardware store for 23 cents. It's just taller than the collet when locked, and just barely fits around it. Above that I put the piezo with a hole drilled in it (I also filed down the solder some), with the coated side facing up. On top of the coated side I put a bigger nylon washer. 1.6mm thick, 25.2mm OD, 18.5mm ID - also from the hardware store for 50 cents. I cut a small bit out of it to allow the wires to pass out. Then I simply put the locking ring from my hotend mount on top as usual.
Pictures are here if they help - total additional cost for mounting was 73 cents. http://imgur.com/a/tYFXb
Edit to say I did hit some early issues beyond those noted above for inverting the probe. Turned out I had a bearing that failed fairly catastrophically and was causing enough vibration I couldn't calibrate the piezo for all the noise. Replacing that and tightening the belts up took care of things from there.
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This is great feedback kraegar. Do you think the piezo disc is heating up with the hot end? At around 50-60 deg C they are meant to stop working.
Micro-locking ring is a good idea too.
(Not Piezo related but… I've got one of those y splitters on order I'll have to pick your brains about how to set it up on RRF)
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I'll put a temp sensor near the piezo to check the temp. It's odd - it looks like electrical interference, except just turning the heater off doesn't help. It doesn't work reliably again until the temperature drops < 40c.
I was considering re-trying the tuning of the piezo with the heater on, to see if I could get it to filter out the noise. Not sure if I want to bother.
I'll make a separate post on the Y adapter.
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I am still occasionally seeing it register the tap at my Y tower a tad late - I can see the effector "tip" a bit. It's only at the Y tower, and I'm not sure what's causing it. I can't adjust the sensitivity without affecting the other probe points negatively, so I suspect it's something about either the bed there, or that tower / belt. Adjusting belt tension didn't help it. This is the tower that had a bad bearing, and I'd hoped that would fix it. It seemed to improve, but is not 100% resolved.
