auto-height (not auto-level)

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AJM
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Joined: Tue May 02, 2017 11:20 pm

auto-height (not auto-level)

Postby AJM » Wed May 17, 2017 11:30 pm

I use various print surface, so the height has to be adjusted every time.
It would be good if the Z-stop switch is moved to above the actual print surface so that it automatically adjusts for the difference in plate thickness. Right now, it measures Z-height of the bottom of the plate which does not take the actual surface thickness into account. That would be OK for printers with non-removable bed surface, but not for Raise3D.

Moving the switch would be a relatively easy hardware change and it can be retrofit.
Auto-level would solve the problem as well, but it is not necessary for a rigidly-built printer.

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Michael.P@Raise3D
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Re: auto-height (not auto-level)

Postby Michael.P@Raise3D » Wed Jun 21, 2017 12:46 am

Placing the Z-Endstop on the build plate would be a more of a task than just "getting it done". The build plate is being measured from the bottom of the plate but it is offset from the Z-Screw. In order to adjust automatically we would need to place a Z-Sensor onto the print head as the sensor would need to contact the bed before the nozzle. At that point we might as well have an auto level system. The only problem with that is when you implement more electronics and more software you could get more problems. I own a number of printers including the Zortrax M200, It has a Z-Height detection system. It has plowed into the bed 5 times over two years, each time damaging the perforated plate, buildtak, and nozzle. The cause of which was just software error, and one time part failure.

If you mean to move the Z sensor closer to the build plate and have it physically touch the bed plate them we could do that. The one thing to remember is that the build volume on our machines starts at the home position (technically off the bed plate by a few mm) then placing the sensor on the front or left side could impede the path of printing or homing.

Just my thoughts on the matter.
Michael Petitclerc, Technician
Tel: +888 963 9028
Web: http://www.raise3d.com

AJM
Posts: 9
Joined: Tue May 02, 2017 11:20 pm

Re: auto-height (not auto-level)

Postby AJM » Sat Sep 23, 2017 5:49 pm

If your controller can measure the electrical current then there is an easier way.
Why not just lower the head slowly onto the build plate and measure the increase in current when it hits.
That requires no switches or physical modifications. Just a small software change.
As for software errors, you could put in many sanity checks to avoid damaging the hardware. And, of course, have peer reviews to re-check.

You may need to add an option to match bed and extruder temperature, though, for people using cheap non-heatproof glass. Lowering hot head onto cheap glass can shatter it from thermal stress.

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Julia Truchsess
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Re: auto-height (not auto-level)

Postby Julia Truchsess » Sun Sep 24, 2017 1:09 pm

You can't detect a stepper motor stall condition by measuring current drain like you can with a brushed DC motor. There are some "exotic" stepper controller ICs that can detect stall conditions by measuring back-EMF at specific times during the drive pulse waveforms, but it is not trivial.

AJM
Posts: 9
Joined: Tue May 02, 2017 11:20 pm

Re: auto-height (not auto-level)

Postby AJM » Sun Sep 24, 2017 1:22 pm

Ah, so it looks this cannot be done without production change. If hardware change is needed anyway, then perhaps strain gauge can be used. That will detect Z-stop and has an added benefit of detecting object collision and displacement during printing.


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