True bed levelling using multiple Z leadscrews

Of possible interest to CoreXY printer builders is that the latest release of RepRapFirmware supports bed levelling using 2, 3 or (if you insist) 4 Z leadscrew motors driven from individual stepper drivers. The procedure is described at [duet3d.com]. It uses a least-squares algorithm similar to our famous delta printer auto calibration algorithm.

When multiple motors are used to drive the Z axis it is not uncommon for them to lose sync when the printer is powered off and on again. This feature provides automatic resynchronization.

We had expected to be the first firmware to support bed levelling using multiple leadscrews, but Repetier beat us to it.

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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].

Could this also work for a belt based z-axis? something like one belt on each side of the bed?

Will be interesting to see if anyone goes to the expense of 4 screws just to utilise this feature on a terrible bed! To be honest, the expense of even the 2 motor set up is quite high given you also need an expansion board.

Even so, this is a great option to have and I can see it having a lot of value in industrial spec printers. Great job.

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badrobit
Could this also work for a belt based z-axis? something like one belt on each side of the bed?

Yes, that should work too.

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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].

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Origamib
Will be interesting to see if anyone goes to the expense of 4 screws just to utilise this feature on a terrible bed! To be honest, the expense of even the 2 motor set up is quite high given you also need an expansion board.

Even so, this is a great option to have and I can see it having a lot of value in industrial spec printers. Great job.

Thanks! A Duet 085, Duet Wifi or Duet Ethernet has 5 stepper outputs, so in a single extrusion printer you have 1 spare for the second Z motor without needing an expansion board

I don't normally advise using 4 leadscrews, because (as DD is fond of pointing out), 3 points define a plane. However, I have seen a very large printer that utilised 4 leadscrews and a steel bed frame about 30mm thick, and it had sufficient flexibility that adjusting all 4 leadscrews independently made sense. So I don't discount the notion that 4 independent leadscrews may make sense in some situations. Also we have customers that want to drive 4 leadscrews independently. The maths for 4 leadscrews is complicated (see [github.com] line 131 onwards), but on an ARM processor it takes only a fraction of a second.

Edited 3 time(s). Last edit at 07/19/2017 03:13PM by dc42.

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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].

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dc42

Quote
Origamib
Will be interesting to see if anyone goes to the expense of 4 screws just to utilise this feature on a terrible bed! To be honest, the expense of even the 2 motor set up is quite high given you also need an expansion board.

Even so, this is a great option to have and I can see it having a lot of value in industrial spec printers. Great job.

Thanks! A Duet 085, Duet Wifi or Duet Ethernet has 5 stepper outputs, so in a single extrusion printer you have 1 spare for the second Z motor without needing an expansion board

I don't normally advise using 4 leadscrews, because (as DD is fond of pointing out), 3 points define a plane. However, I have seen a very large printer that utilised 4 leadscrews and a steel bed frame about 30mm thick, and it had sufficient flexibility that adjusting all 4 leadscrews independently made sense. So I don't discount the notion that 4 independent leadscrews may make sense in some situations. Also we have customers that want to drive 4 leadscrews independently. The maths for 4 leadscrews is complicated (see [github.com] line 131 onwards), but on an ARM processor it takes only a fraction of a second.

Yes that's a good point on the 2 Z motor set up, I'm thinking of my own printer at the moment with 2 extruders and making assumptions!