Accelerometers for bed leveling

I notice that accelerometers have become the sensors of choice for for nozzle contact detection and bed leveling on several printers. I was wondering if any RepRappers have any experience with them.
The one video that I have seen [www.youtube.com] seems to show contact occurring at a very high speed - is this normal?

Mike

No experience at all...

I suppose they have to hit the bed fairly hard to get them to trigger.

I'll stick to the IR sensor.

Noisy motors too.

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Simon Khoury

Co-founder of [www.precisionpiezo.co.uk] Accurate, repeatable, versatile Z-Probes
Published:Inventions

True dc42s IR sensor is very sweet although for myself I am very happy with piezoelectric disk sensors; but surely the RepRap movement is more about making than about buying.
The cost of the most common accelerometer ICs can be under $1 each and it is possible that there is not a lot other than the IC and as PCB with some wiring needed. The only complexity may be in the software.

Mike

I like your piezo electrics I read that thread and enjoyed it. If my fsrs die on my mini I might try them. Yes reprap is about making things for sure.

Hopefully someone knows something about them.

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Simon Khoury

Co-founder of [www.precisionpiezo.co.uk] Accurate, repeatable, versatile Z-Probes
Published:Inventions

Certainly seems worth exploring. I wonder what else we could do with an accelerometer on the head? Would it be possible to compare the actual head acceleration with the commanded acceleration and detect missed steps?

3 axis accelerometers are usefully accurate and quite cheap but I would be surprised if they could be used to create a closed loop positioning system. Having said that, they probably could be the basis of a system that takes action - like putting everything on pause and sending out a text message to a smartphone if the accelerations seen were too different to what was called for.

Mike

After some initial trials it no longer looks as though accelerometers are worth pursuing for nozzle contact detection. I used a 12mm piezoelectric disk with a 1 gram brass weight connected to it with output to a charge amplifier but even with careful filtering it was not possible to extract a nozzle contact signal with adequate positional accuracy. Although there are many things that could be done to improve the response (using a MEMS sensor, FIR filtering etc.) this is big-budget stuff.
Accelerometers having been excluded along with various sucky ways of bed leveling I think the only ones left at the moment are - in my opinion of course.

The only extendible switch worth considering is the Bltouch and clones of it. Switches which are extended by servos are just too klunky.
The best proximity switch is the IR type typified by those from dc42.
The best nozzle contact method uses piezoelectric disks. FSRs are quite sucky as well as being expensive.

Mike