Fixed, non-mechanical probe idea: Inductive Proximity Sensors

Here's an idea for a z-probe that I think might be pretty cool.

I ordered a few of these (LJ12A3-4-Z/BX Inductive Proximity Sensor Switch NPN DC6-36V).

My plan is to try and mount it in a fixed manner right next to the hot-end. I think it will wire in just like a hall-effect end-stop.

I'll need to abandon the glass print bed, but I hear DiBond makes for a pretty good surface as well.

If this works, I think its a pretty great combination of accuracy, repeatability, and cheapness. If it doesn't work, I'll use them on my mill.


Any advice?

Is anybody printing on DiBond with hairspray? (I'd like to avoid blue tape if I can.)

I've used these type of sensors as end-stops in CNC machines. They can be triggered with aluminium but then it has to be pretty close. Iron or steel gets detected at 3 or 4mm if thick enough (an M8 nut for example). Dibond aluminium layers being so thin I reckon detection will happen only if it is practically kissing the surface ... just my guess.

Hi

Another thing to consider - they are temperature sensitive. Get them close to a heated bed and the sense distance will change.

Bob

I'll not be using a heated bed, so that won't be too much of a consideration for me.

Thanks for the feedback guys!

Hi

The CNC guys seem to have abandoned them for probes and just use them for limit / out of range sensors. I played with a couple of the parts you mentioned. They don't seem to trigger as reliably as a microswtich.

Bob

Any news about this ? I also thought about a similar solution but couldn t figure out where to put the sensor...and because anything with magnet field does not work well with heat, I didn t want to go further in this direction...

What about this: the hotend and the alu plate are connected to the same low electrical circuit.....for example the plate is (-) and the hotend is (+) and when they touch each other we cause a short circuit...like a switch, now the circuit is closed the electronic register it and proceed to the next point....

Just an idea....I am not an expert, so forgive it is no sence !

Update: talking about sence here is an example of what I mean:

CapSense: Capacitive Switch and CapacitiveSensor Arduino Library, Demo on Teensy 2.0

Update: Arduino Capacitive Sensing Library and Native Capacitive Sensors without additional Hardware

I don t know if it works metal against metal but if it doesnt, one could use a ceramic hotend....

Update:

Because I don t have a resistor, I made another test....and it works not as Capacitive Switch but as a Contact Switch...like the endstops. One pin to the alu bed and one pin to the hotend....The change can be read out on the screen. So if the Capacitive Switch does not work....the contact solution seems to work.

Edited 5 time(s). Last edit at 04/06/2014 01:57PM by zacbot.

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video of my 3DR

I tried an inductive NO proximity sensor switch. Those switches work like the other endstops. If using a Ramps, just plug it at the Zmin endstop connector. You don´t need any extra code.

The sensor I have is triggeredl from a max. distance of about 4mm. It was very cheap (around 7$). It was listed on e-bay as "capacitive sensor", but it's inductive (chinese sellers... you know...)
The detection works ok if there is a metal sheet under my printing platform (an Ikea mirror), As I don't want to add that metal sheet and I'm using and mechanical switch-based alutolevel system which works great, so I won't use the "inductive system", but my experiments looked promising.

@Funkymonk: some of the ones I have tested did not work ok at 5V so I have to power them from 12V (actually mine are spec'd 6-30V DC). If powering them at 12V be careful on how you connect it to the input (NPN one I connect it with a diode, with catode to the probe and anode to the RAMS signal pin).