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An optical bed sensor for auto leveling?

An optical bed sensor for auto leveling?
December 13, 2018 07:36AM
Use a laser diode to make submicron measurements from a distance of several cm:

[www.youtube.com]


Son of MegaMax 3D printer: [www.instructables.com]
Ultra MegaMax Dominator 3D printer: [drmrehorst.blogspot.com]
Re: An optical bed sensor for auto leveling?
December 13, 2018 08:35AM
I've looked into this before. Using a laser to detect small amounts of movements over short time periods using interferometry is easy. Using one to measure distances in a reproducible way to the precision needed for bed compensation is not. For example, suppose we decide that from one day to another, a difference in measured height of 30um is acceptable when the actual height is constant. That would mean the timing reproducibility we need is 30um divided by 3e8 m/sec = 0.1 picosecond.

Some time ago I built bed height sensors that used ultrasound to measure bed height. Because the speed of sound is so much slower than light, the timing is much easier. Unfortunately the speed of sound varies too much with temperature for it to be a good solution, even when the height is compensated for changes in bed temperature.



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

Disclosure: I design Duet electronics and work on RepRapFirmware, [duet3d.com].
Re: An optical bed sensor for auto leveling?
December 13, 2018 09:16AM
Saw that too.
Was thinking about a vibration sensor based on that. Don't know if I still have somewhere this kind of diode. Would help here as no contact, no additional mass. Beats the smarphone attached with duct tape to the frame, gantry ....


"A comical prototype doesn't mean a dumb idea is possible" (Thunderf00t)
Re: An optical bed sensor for auto leveling?
May 21, 2019 07:59PM
I just stumbled across the VL6180X Time of Flight optical sensor, and wondering about using it for measuring bed height.

However, the datasheet says the RESULT_RANGE_VAL and RESULT_RANGE_RAW registers only gives the distance in whole mm sad smiley (despite being 16-bit registers). But I'm wondering if one of the other registers (RESULT__RANGE_RETURN_SIGNAL_COUNT perhaps? -- it's 32 bits) gives better resolution?

A comment at Sparkfun's forum says sub-millimetre can't be done, but you can't believe everything you read on the Internet.

There's a Hackaday project to do this.

Has anyone here done any experimentation with this device to get sub-millimetre measurements?
Re: An optical bed sensor for auto leveling?
May 22, 2019 03:36AM
Re. Hackady project: ±0.2mm after 20 minutes warm up and temperature stabilisation.
It may be easier to use a whole bunch of sensors with introduced noise and average the output – there may be a weight penalty however.

Mike
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