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Z- Probing Inductive Sensor

Posted by Nate523 
Z- Probing Inductive Sensor
February 11, 2017 01:37AM
So I decided to add a inductive proximity sensor to my Delta printer. I use Repetier host and its firmware, 0.92. I have the sensore triggering just fine, powered by 12V.

I try going through this demonstration, [www.repetier.com] to no avail. I get close at times, but for some reason my inductive sensor will not level the bedd accurately. I constantly have an uneven first layer.

A note about my heated bed, it is the buildtak flex plate system so there is a metal plate that gets magnetized to the bed, I was wondering if this would be a problem and if that might cause an issue as far as the inductive sensor goes?
Re: Z- Probing Inductive Sensor
February 11, 2017 06:37AM
If you are using repetier firmware i suggest upgrading to the latest dev version, severall updates have happened recently to improve auto bed levelling
Re: Z- Probing Inductive Sensor
February 11, 2017 10:29AM
The inductive sensor works by generating a small magnetic field and sensing when something metallic changes that field. I can imagine that it would get confused if it comes down into a strong magnetic field generated by something else.
Re: Z- Probing Inductive Sensor
February 11, 2017 02:04PM
Would a capacitive sensor have the same issues?
Re: Z- Probing Inductive Sensor
February 11, 2017 02:04PM
I have the latest 0.92 version is that the dev one you are talking about?
Re: Z- Probing Inductive Sensor
February 11, 2017 02:35PM
no. 0.92 is the stable release version,
On the firmware config tool page [www.repetier.com]

click on the green 'switch to development' button
then go thru the tool settings and download the complete firmware
Re: Z- Probing Inductive Sensor
February 11, 2017 02:37PM
Would a capacitive sensor have the same issues?
yes, works on the same principle, just make sure bed heater is turned off while probing
Re: Z- Probing Inductive Sensor
February 11, 2017 08:40PM
Allright Thanks for the updated informatio on repetier, it does work better with the development version.

On the z probing, maybe I don't understand it properly.

Is autoleveling only to set the height? Because that would mean that I really need to calibrate my printer still to spot on in order for it to work properly.

The reson I ask, is because I do everything, I calibrate my printer as best as I can, then I do repetiers z probing instructions, minus the endstop correction deal. Then I get a probe that will semi level the bed, meaning the lower side of my bed seems to be at the right height, but th eupper side is always higher.

Is this a Z-probing issue? Or is this a calibration issue? Basically, if my calibration i snot spot on, is autoleveling useless?
Re: Z- Probing Inductive Sensor
February 12, 2017 02:12AM
I have never used a delta , but from what i have read on the repetier forums ,they are more tricky to get set up properly.
But after you home all axis with G28 then run G32 S2 this should probe the bed and compensate Z for a unlevel bed.
Re: Z- Probing Inductive Sensor
February 12, 2017 11:43PM

The inductive sensor seems to be pretty repeatable in a way. The problem is that I couldn't get it to stop making the plane tilted a little bit. Found a setting in repetier eeprom though, z probing bending correction. Just outta curiosity looked into it, and decided to adjust the values and see what happens. Turns out I was able to adjust for whatever the probe was doing and now it levels the bed pretty well. Id say at least within .1m. The problem is that the height varies, so I am assuming that it because of two things, either the sensor itself is causing it because of some sort of interference from the magnets. Or There is slop in my build somewhere that is causing the height difference, just did a second print and the first layer seemed about .1 higher than the last one. but at least it keeps it in the ball park.

Still need to tweak something though I just don't know what yet, I'll have to investigate my delta frame and such to see if there is some sort of play that would mess the probing up.

Edited 1 time(s). Last edit at 02/12/2017 11:48PM by Nate523.
Re: Z- Probing Inductive Sensor
February 13, 2017 12:44AM
Is your delta printer tilting the effector plate as it goes round the bed? The reason I ask is that I had a similar problem on my delta - as the probe was separate from the nozzle it would end up a different height on different parts of the bed.

This sounds suspiciously like your problem... if so, you might find it easier to use a probing method that uses the nozzle tip itself to find the height, like this one.

Note: I got so fed up trying to get this right I scrapped the delta and used the electronics and motors to make a CoreXY!
Re: Z- Probing Inductive Sensor
February 13, 2017 02:30AM
Magnets and inductive probes are not a good mix, can you remove the magnets and test the probing without them?
Re: Z- Probing Inductive Sensor
February 16, 2017 12:19AM
Not without destroying the 125 dollar kit they gave me, the magnets are manufactured into the base plate, and the base plate is now seriously adhered to the borosilicate glass plate. If I had an extra glass plate I suppose I could test it but I don't have one of those handy, they are kinda pricey.

From what I gather about auto leveling, it seems like I still have to have my printer calibrated and spot on. Correct me if I'm wrong but the reason I am thinking is that the auto level feature does not level the bed in the sense that it will make my head move flat across the bed, all it does is take the 3 points or grid that you probe, and define an oriented plane based on those three points. That plane though I think relies heavily on the fact that the printer actually moves in a flat horizontal manner when calibrated. Otherwise things are out of wack and when it tries to correct the head position according to the plane that has been oriented with the matrix, its unsuccessful because the printer head doesn't move the way it is predicting it will. So auto leveling not only can't correct for bad calibration, but if your calibration is even a little off it will manifest itself even with z probing I think.

This is why I have spent a bit of my free time re evaluating my frames build, I found interestingly enough that my plate is flat and that it is mounted as flat as I can tell measuring with a ruler from a flat surface to the plate. I did find that my towers were not very parrallel to the build plate, so I suspect there is a problem there and corrected it, now there are at least pretty parallel according to my L scale to the bed. Now I just need to calibrate it again and test to see if it made a difference, I suspect it will.

Before doing these build corrections though, I re calibrated the printer being really anal about it, got it to be within .05 to .1 in all 10 points that I was checking with the Escher 3D calibration tool, tested some prints adjusting that Bed Bending Correction values, and it got pretty close to flat every time I operated the G32 S2 command. I couldn't get a perfect first layer though, always had some errors in some spots, I am hoping that was because I still had some parts of my build that were off that I corrected. I also am going to calibrate using a dial indicator to get as close as I can get this time around.

I suspect because of the magnets and such I will always have a .1 or so error with the probe, I am tempted to install the capacitive sensor I bought at some point to try it out and see if there is a difference, otherwise the only real solution I think is to install a z probing mechanical switch that I can manually extend or put on, but I wanted to avoid the extra step if I could and I supect that it will have the same amount of error in it being a mechanical switch. More experimentation to come!
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