Simpler Design Idea for Delta Printers

I just had a thought and wanted to share it with developers for some feedback on viability and whether or not its already been attempted.
Perhaps if it sounds okay; I'll find time to play with it.

How about a Delta Printer that uses the lead-screws as the connecting joints instead of trying to stick them in the three corners of a triangle?

1) The bed (i.e. Plate) could have over-sized holes drilled
2) The end of the lead-screw could have a hole-drilled marble attached with a couple of nuts holding it up.
3) The (3) lead-screw motors would sit on the the top of the frame with rotational ability ( say; 1-bolt/bearing ) attaching motor to the frame

So the lead-screws would pop-up out the top of the printer and pivot as needed.
The bed would start at the very high/top side and moved down as printing progressed.

I've always liked the idea of having the "tool" permanently mounted since a mill or something would require that extra strength.

Anyways; what do the developers think? Would this be a good approach to eliminating a lot of parts and expense?

I'm not sure I understand, are the leadscrews moving the gantry or the bed? What do you gain by doing this? Perhaps a diagram would explain it better

I don't think there's any need for the bed to move... extending all 3 lead screws simultaneously would move the effector downward.

It would mean that the motors would move with the lead screws, and there would be a lot of weight and inertia in the mechanism, which I gather is a bad thing for delta printers.

I think you would still need some kind of pantograph mechanism (2 lead screws at each corner, driven by the same stepper?) to keep the effector level.

You need 6 leadscrews to fix the position, tilt and rotation of the bed, not 3. Such an arrangement is called a Stewart platform. There has been at least one 3D printer built using this principle.

In the context of FDM printing, moving a heavy bed instead of a much lighter hot end is a significant disadvantage.

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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].

... this type of kinematics is often used for CNC-milling - have seen several different types for wood- and stone-art-works ... or for 6-axis-milling of ultra precise machine parts ...

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Viktor
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Yes, yes.... Thank you so much for this answer. I always wondered why delta printers didn't "tip" the head/bed when moving side to side until you made this statement. Then I noticed all delta printers have 6-links and its not just for extra strength .. Googling stewart platforms actually found about the design I was speaking of - except of course I didn't realize it'd take 6-connections to keep level.

While this isnt simpler it does have stewart platform.

[www.3ders.org]
Though not so simple as they havent got it working.

Edited 1 time(s). Last edit at 02/13/2017 03:28PM by MechaBits.

It's not a Stewart platform because the bed has 3 degrees of freedom not 6, but the combination of the tilting bed and the standard Delta effector gives it almost the same versatility.

The challenge for using a machine like that is that the slicer needs to be rewritten to pass a suggested bed angle in the gcode, based on what overhangs are being printed. Given that information, the motion control firmware wouldn't be difficult. RepRapFirmware already includes bed tilt compensation.

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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].

Quote
dc42
It's not a Stewart platform

Looking at that design; I couldn't help but think a 6-axis bed with a solid top extruder wouldn't have been easier to develop. This of course leads into the thinking that perhaps a Stewart Platform linked directly to the bed like the image 'hexapod' might not only be a little simpler but offer the option of bed tilt. Throw in some cheap 28BYJ stepper motors at $2/ea ( If they prove to be strong enough ) it might be a plan for simpler, 6-axis, cheaper, and with a tilt bed feature design.

I just may play with that idea someday in the real world -- only to realize 1/2 way through its 10x easier to say it than do it ...

Moving the bed of a 3D FDM printer on a Stewart platform has some disadvantages:

- If you move the bed and have the print head fixed, then to get a printable diameter of e.g. 300mm you would need to be able to move the bed 150mm in each direction. So the space it occupies is a disc 600mm in diameter, and the frame needs to be large enough for that.

- You can't have the beck ends of the leadscrews sticking out like you can in your diagram 4 posts up (unless you stand the printer on a table with holes cut into it!). If you use a simple screw-driven linear actuator design, your ratio of max to min length is less than 2:1. This means that if you want 300mm printable height, your platform will have to be around 600mm above the table when you start the print, dropping to around 30mm at the end of a tall print.

Moving the (heavy) bed rather than the print head and using screw-driven actuators also means that you will lose some or all of the speed advantage of a delta printer. OTOH the print head can be as complicated as you like.

Edited 1 time(s). Last edit at 02/19/2017 04:19AM 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].

Quote
dc42
You can't have the beck ends of the leadscrews sticking out like you can in your diagram 4 posts up (unless you stand the printer on a table with holes cut into it!).

Wonder if instead of pushing the bed up from the floor or table top if it couldn't hang the bed from the top - allowing the same setup as diagrammed above??

It would be nice to have the stewart platform control just the head; as it does in this CNC video [www.youtube.com]

But I was thinking that just an angled 3d print head wouldn't obtain much since gravity still points downward.

Quote
tgit23

Quote
dc42
You can't have the beck ends of the leadscrews sticking out like you can in your diagram 4 posts up (unless you stand the printer on a table with holes cut into it!).

Wonder if instead of pushing the bed up from the floor or table top if it couldn't hang the bed from the top - allowing the same setup as diagrammed above??

Yes you could do that. However, you would need to make the bed support larger than the printable area to ensure that the leadscrews are always clear of the print head. So the bed diameter is now something like the printable diameter + the print head diameter + a bit more for the leadscrew nuts in their ball-and-socket joints. Now the frame has to be even larger.

Quote
tgit23
It would be nice to have the stewart platform control just the head; as it does in this CNC video [www.youtube.com]

But I was thinking that just an angled 3d print head wouldn't obtain much since gravity still points downward.

Exactly - the advantage of moving the bed on a Stewart platform is that you can tilt it when printing overhangs.

Another thing I haven't worked out is how to mount the stepper motors in such a way that they can swing with the leadscrews.but resist rotation.

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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].

Quote
dc42
how to mount the stepper motors in such a way that they can swing with the leadscrews.but resist rotation.

I was thinking exactly the way the hexapod cnc did it - looks like it has a swivel 'L' link to the tool fitting and U-Center axis Motor holders.

There was also this project here which was a delta with a movable bed. http://www.diyouware.com/

Found it most interesting for tool changing ability.