Plasma - Adjust / Limit Corner Feedrate Automatically

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Plasma - Adjust / Limit Corner Feedrate Automatically

Postby Robertspark » Sat Oct 21, 2017 5:15 pm

This is a bit of a brain storming topic, and it only really applies to plasma

The advice I've always read and stuck to is lower the feedrate to ~60% in the corners or when cutting circles of less than ~ 25mm dia (32mm in this article).

This then got me thinking about adjusting Corner Error Max automatically...

If the Corner Error Max is set too low to the feedrate, it will mean that the tradjectory planner will have to lower the feedrate to meet the requirements of the Corner Error Max setting, and this may lead to over-burn in the corners

Looking at the Corner Error Max another way and considering it in relation to centripetal acceleration it is possible that we could adjust it correctly to limit the drop in velocity to no less than 60% of the programmed linear feedrate

Lets say you have a macroloop which monitors the programmed feedrate, and when it detects a change in the programmed feedrate it corrects / changes the Corner Error Max relative to that feedrate so that the velocity when changing direction never drops below 60% of the linear feedrate.

This would be done by using the lower of the X or Y acceleration settings, to calculate the corrected Corner Error Max.

Simply:
( Feedrate * 0.6 / 60 )^2 / acceleration = Corner Error Max
Simplified to (feedrate * 0.01) ^2 / acceleration = Corner Error Max

Therefore at a high feedrate of 10200mm/min, and acceleration of 3,000mm/s/s, the Corner Error Max would be 3.468mm
Or at a more run of the mill feedrate of 6000 mm/min, same accel, corner Error Max would now be 1.2mm
Or at a lower feedrate of 4000 mm/min, same accel, corner error max would now become 0.53r mm

My point is of this idea that the default corner error max is 0.03mm, meaning even with a very high acceleration of 0.3G ~3000mm/s/s, the feedrate MUST drop to ~570mm/min in the corners hence possibly creating excessive overburn.

At a lower acceleration (say 0.1G), the feedrate MUST drop to 329mm/min!


Long and the short do you think this would lead to a better cut and better control of the cut?
Rob

Einstein ― “If you can't explain it to a six year old, you don't understand it yourself”
UC400eth, UC300eth, UCCNC v1.2104, Neuron Lite.
UCCNC v1.2104 Macro Manual
Robertspark
 
Posts: 668
Joined: Sat Sep 03, 2016 4:27 pm
Location: Nr Liverpool, England

Re: Plasma - Adjust / Limit Corner Feedrate Automatically

Postby Robertspark » Sat Oct 21, 2017 8:24 pm

Working Macroloop Attached, now need to try it out....

Guess this may be now closer to constant velocity, given the velocity can never drop less than 60% (editable) in a change of direction which will happen if you set the Max Corner Error too low relative to your machines feedrate and acceleration

(note: this macro is only setup to work with an XY axis, so will need modification if you are using more than those two axis)
Attachments
M2010.txt
(2.92 KiB) Downloaded 95 times
Rob

Einstein ― “If you can't explain it to a six year old, you don't understand it yourself”
UC400eth, UC300eth, UCCNC v1.2104, Neuron Lite.
UCCNC v1.2104 Macro Manual
Robertspark
 
Posts: 668
Joined: Sat Sep 03, 2016 4:27 pm
Location: Nr Liverpool, England


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