Force-Balanced Deltas

[Ryan Carlyle]

Here's an interesting concept. Counterbalances masses can be added to a Clavel Delta in a way that exactly balances the weight and all motions with respect to linear momentum, ie there is no reaction force transmitted to the frame during linear acceleration (although there may still be reaction moments). I don't immediately see how we would apply it in a 3d printer (column delta or other) but I like the premise.

https://www.researchgate.net/publication/225896536_Dynamic_Balancing_of_Clavel's_Delta_Robot

Without worrying about the complex linkages here, the basic idea is that the motor is pushing equivalent masses (ie same reflected inertia) in opposite directions with every movement. So the reaction forces cancel and you get less ringing/overshoot. You get more motor torque load but less frame flex. 

I think you could get the same effect with a column delta where each column has a counter-travelling carriage mass for vertical forces, and there's a second set of arms and effector riding on the carriages to produce opposite horizontal forces. Seems complicated though. Some sort of clever linkage may be able to do it much easier. 

[Whosawhatsis]

By adding mass you're negating forces transmitted outside the mechanism, but you're still moving more mass around inside it, which makes acceleration harder. 3D printers need to maximize acceleration (and deltabots printers are designed specifically for this purpose), so I'm not sure I see the benefit.

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[Ryan Carlyle]

People running full-sized NEMA 17 steppers on a Bowden delta have oodles of available torque compared to their moving mass and typical acceleration levels. So much so that I often see people who don't even know how to set driver currents, or set them so the motors are COOL to the touch. And frame flex is a MAJOR source of ringing in RepRap style deltas (eg Mini Kossels with plastic vertices) and tall deltas where people don't up-scale the vertices and columns properly. So I can see some potential performance gain... although I really doubt it would be enough to be worth the extra design complexity.

In Clavel deltas, the fact that the entire mechanism must be mounted above the work area on some kind of support far removed from the ground means there are more benefits to negating external forces. 

On Monday, July 18, 2016 at 4:02:44 PM UTC-5, Whosa whatsis wrote:

By adding mass you're negating forces transmitted outside the mechanism, but you're still moving more mass around inside it, which makes acceleration harder. 3D printers need to maximize acceleration (and deltabots printers are designed specifically for this purpose), so I'm not sure I see the benefit.

From: Ryan Carlyle <temp...@gmail.com>
Reply: Ryan Carlyle <temp...@gmail.com>
Date: July 18, 2016 at 13:07:18
To: 3DP Ideas <3dp-...@googlegroups.com>
Subject:  [3dp-ideas] Force-Balanced Deltas

Here's an interesting concept. Counterbalances masses can be added to a Clavel Delta in a way that exactly balances the weight and all motions with respect to linear momentum, ie there is no reaction force transmitted to the frame during linear acceleration (although there may still be reaction moments). I don't immediately see how we would apply it in a 3d printer (column delta or other) but I like the premise.

https://www.researchgate.net/publication/225896536_Dynamic_Balancing_of_Clavel's_Delta_Robot

Without worrying about the complex linkages here, the basic idea is that the motor is pushing equivalent masses (ie same reflected inertia) in opposite directions with every movement. So the reaction forces cancel and you get less ringing/overshoot. You get more motor torque load but less frame flex. 

I think you could get the same effect with a column delta where each column has a counter-travelling carriage mass for vertical forces, and there's a second set of arms and effector riding on the carriages to produce opposite horizontal forces. Seems complicated though. Some sort of clever linkage may be able to do it much easier. 

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