Measure stepper motor torque/resistance

I was looking to upgrade my Prusa i3 to auto level and then I had an idea, is there anyway to measure the resistance of a stepper, so when the extruder touches the bed, the motor will generate resistance that can be detected? If this is possible, then any printer can potentially auto level/auto end.

I am still new to the world of 3d printing, so I might be missing something obvious. Can someone much smarter then me comment on this idea?

Edited 1 time(s). Last edit at 09/25/2015 04:55PM by GreatGrizzly.

You can´t measure stepper torque or current to identify nozzle/bed contact.

Also on my Prusa it wouldn´t be possible, because the X-carrier only rests on the Z-leadscrews by gravity.

I´ve seen Delta Effectors where the nozzle is used as Z-probe with a switch on the effector.
Don´t know, if this has been tried on a Prusa? ( Same gravity problem )
-Olaf

There are some newer stepper driver chips that have built-in sensing to detect stalled drives, so that might become practical eventually. The problem I see is how to know exactly at what point the motor started skipping steps.

There are designs that put a microswitch or FSR in the hot end mount, to detect when the nozzle is in contact with the bed. This seems to me to be an easier approach to detecting contact.

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Large delta printer [miscsolutions.wordpress.com], E3D tool changer, Robotdigg SCARA printer, Crane Quad and Ormerod

Disclosure: I design Duet electronics and work on RepRapFirmware, [duet3d.com].