What is the name of this cartesian / hbot hybrid kinematics?
August 29, 2020 01:06PM
There is an obvious type of kinematics that would almost certainly be terrible for a 3D printer because of its asymmetry, but might be good for a laser cutter, and there's a lot of overlap in technology between the domains.

But I don't know what it's called, and it's sufficiently obvious that I expect it to have a real name.

Here's a simple schematic diagram.



The Y motor has normal cartesian motion. It's moving a gantry back and forth. The X motor is moving a head/effector, and it needs to compensate for any Y motion by composing the inverse of the Y motion.

  • If only the X axis is moving, only the X motor turns.
  • If only the Y axis is moving, the X and Y motors need to turn equally in opposite directions.
  • To move on one 45⁰ diagonal, the X motor would stop and the Y motor would turn.
  • To move on the other 45⁰ diagonal, the X motor would turn twice as fast and in the opposite direction as the Y motor.

It's not one of the kinematics supported by RepRapFirmware, Marlin, Smoothieware, or Klipper as far as I can tell.

If anyone knows an established name for this, I'd be grateful to learn.
Re: What is the name of this cartesian / hbot hybrid kinematics?
August 29, 2020 01:15PM
It's commonly called MarkForged kinematics. It's supported by the standard builds of RepRapFirmware, along with every other kinematics for which the movement of every axis is a linear function of the motion of the motors.



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].
Re: What is the name of this cartesian / hbot hybrid kinematics?
August 29, 2020 05:00PM
Thank you! ☺

I just read the docs for M669 and that's wonderfully general.

Edited 1 time(s). Last edit at 08/29/2020 05:13PM by mcdanlj.
Re: What is the name of this cartesian / hbot hybrid kinematics?
August 30, 2020 12:28AM
much better if you rotate the arrangement 90 degrees smiling smiley


[mechabits.co.uk]
Re: What is the name of this cartesian / hbot hybrid kinematics?
August 30, 2020 03:40AM
Quote
MechaBits
much better if you rotate the arrangement 90 degrees smiling smiley

To make the middle axis shorter? Exactly what I thought. It cuts the deviation on the end point of the axis in half at least.


http://www.marinusdebeer.nl/
Re: What is the name of this cartesian / hbot hybrid kinematics?
August 30, 2020 08:50AM
I think it makes sense when the axes are already very asymmetric, as is typical in a laser engraver/cutter. X is typically longer, possibly much longer, than Y, and rastering/engraving is typically done X-major. (Cutting is slow enough that intertia mostly vanishes as a concern relative to motor torque.)

In at least the case where I've been lightly considering it (for a laser cutter), the Y axis is actually driven at both ends, coupled by a torsion rod; that was just unnecessary detail for the schematic. I would think the same could make sense for a high aspect ratio 3D printer perhaps, if it was long enough belt length started to become a concern for CoreXY? Or for any other reason you didn't want to use CoreXY and still wanted to avoid stacking one of the X/Y axis motors?

But mostly it was intellectual curiosity, which many thanks to dc42 for satisfying. ☺
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