Ultrasound bed levelling on UM1

[anon4321 16]

You need to get that super-high-ultra-premium Z-stage done!!!! and shared!!!!!!1!11111one.

I was thinking of a printed two piece bracket with one piece attached to the head and a microswitch to the other piece and have magnets in the right spots to repeatability and accurately "click" the two together (as long as the magnet surfaces are clean).

 

[jonnybischof 60]

It's all in my head. Just have to beat it out of there and into reality (where hopefully it won't turn to total BS because of the new environmental variables...)

One thing against the microswitch:

Could the force required to trigger the switch already be enough to push down the platform? Not sure, but I think the original wooden platform could actually give in a little, even to such a small force...

 

[anon4321 16]

Regarding the force, yes that is a concern. But I don't know of any other way of doing it. Are there non contact sensors out there could be used and that have the resolution required that would work through alu and glass or steel if the UM1 heated bed is released?

 

[jonnybischof 60]

With an inductive sensor you can sense a metallic object just before touching it.

These sensors can't really sense the distance, but afaik you tune them to always switch at the very same distance. So the repeatability should be good.

I've seen RepRap inductive sensors (Hall-O Endstop), but haven't used one of these before. I used some industrial sensor, but it's been some time ago. Would need to look into it more closely. However I still believe it can be made with much lower tech.

I think actual electrical contact is the most exact way to measure, because it's just the simplest one. If you want to use an inductive sensor with multiple different counterparts, then I'm not sure if these counterparts all have to be exactly the same in order to achieve the same sensing distance. Maybe not, but maybe yes. I'm no expert here..

There should be microswitches available which don't require much actuation force. Standard push buttons often come in different actuation forces.

 

[anon4321 16]

Interesting summary of the current state here: http://forums.reprap.org/read.php?340,333301,346258#msg-346258

 

[jonnybischof 60]

I think you're just overengineering things here... A simple electrical contact probe will do the job just fine.

But there are good points on that page. The conclusion is: All of these "advanced" sensing technologies aren't something you just quickly throw together.

Inductive or capacitive sensing seems to be the most interesting thing here, but there's one more thing to consider:

There are 4 completely unshielded stepper motors and two PWM-driven heaters in the machine. Both capacitive and inductive sensors are sensitive to EMI and would most likely not get accurate readings, even if they'd be well designed and tuned.