Idea for high speed machining / trajectory
18 Feb 2013 17:33 #30267
by juwi
Idea for high speed machining / trajectory was created by juwi
Hi
This concerns the problem with lookahead and fast machining...
Just an idea:
If you use G64 without precision The machine will run pretty fast but will only try to catch up every command.
Would it be possible to calculate the distance a specific feed F would be from commanded position and reduce feed as long as it will get into a given tolerance?
The resulting feed for each move then shall be written to a new gcode file which can be run in constant speed mode without obeying tolerance...
This only makes sense for bad gcode, consisting of short moves. But IMHO it would be an enourmous speedup for such code...
This concerns the problem with lookahead and fast machining...
Just an idea:
If you use G64 without precision The machine will run pretty fast but will only try to catch up every command.
Would it be possible to calculate the distance a specific feed F would be from commanded position and reduce feed as long as it will get into a given tolerance?
The resulting feed for each move then shall be written to a new gcode file which can be run in constant speed mode without obeying tolerance...
This only makes sense for bad gcode, consisting of short moves. But IMHO it would be an enourmous speedup for such code...
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18 Feb 2013 21:26 #30274
by alan_3301
Replied by alan_3301 on topic Idea for high speed machining / trajectory
wiki.linuxcnc.org/cgi-bin/wiki.pl?TrajectoryControl
look at the section "path tolerance"
basically g64 p0.005 will stay within 5 thou of programmed path while keeping speed up as much as possible.
no need to rewrite the gcode.
I think thats what you need.
look at the section "path tolerance"
basically g64 p0.005 will stay within 5 thou of programmed path while keeping speed up as much as possible.
no need to rewrite the gcode.
I think thats what you need.
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18 Feb 2013 22:02 #30277
by juwi
No, IMHO the G64 P mode is much slower because it only blends moves but sticks to the "exakt stop on end of next move" limitation making it very slow.
Replied by juwi on topic Idea for high speed machining / trajectory
[...]
basically g64 p0.005 will stay within 5 thou of programmed path while keeping speed up as much as possible.
No, IMHO the G64 P mode is much slower because it only blends moves but sticks to the "exakt stop on end of next move" limitation making it very slow.
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18 Feb 2013 22:18 #30278
by BigJohnT
Replied by BigJohnT on topic Idea for high speed machining / trajectory
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18 Feb 2013 22:28 #30279
by alan_3301
Replied by alan_3301 on topic Idea for high speed machining / trajectory
I see what you mean now.
I know g64 p0 is the default mode, but I feel like my speed is improved with g64 p0.005
Is the naive cam detector enabled with a P word, if the Q is left off?
If i run a complex vcarve with the g64 default, it seems ok speed.
but with g64 p0.005 I swear it speeds up a lot.
I do know that I sped up 3d toolpaths a good bit by jacking up my acceleration as high as my machine could stand.
I use 2 machine profiles, one for generic stuff with reasonable accel.
and another for 3d rastering with 100 acceleration for X and Z
I know g64 p0 is the default mode, but I feel like my speed is improved with g64 p0.005
Is the naive cam detector enabled with a P word, if the Q is left off?
If i run a complex vcarve with the g64 default, it seems ok speed.
but with g64 p0.005 I swear it speeds up a lot.
I do know that I sped up 3d toolpaths a good bit by jacking up my acceleration as high as my machine could stand.
I use 2 machine profiles, one for generic stuff with reasonable accel.
and another for 3d rastering with 100 acceleration for X and Z
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18 Feb 2013 22:44 #30281
by juwi
"Blending without tolerance - The controlled point will touch each specified movement at at least one point. The machine will never move at such a speed that it cannot come to an exact stop at the end of the current movement (or next movement, if you pause when blending has already started). The distance from the end point of the move is as large as it needs to be to keep up the best contouring feed."
Ok, well, it was an idea
sorry for not rtfm...
Replied by juwi on topic Idea for high speed machining / trajectory
Instead of guessing...
linuxcnc.org/docs/html/common/User_Conce...trajectory_control_a
John
"Blending without tolerance - The controlled point will touch each specified movement at at least one point. The machine will never move at such a speed that it cannot come to an exact stop at the end of the current movement (or next movement, if you pause when blending has already started). The distance from the end point of the move is as large as it needs to be to keep up the best contouring feed."
Ok, well, it was an idea
sorry for not rtfm...
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18 Feb 2013 23:38 #30284
by BigJohnT
G64 is default not G64P0. G64Pn turns on the naive cam detector and if your file is full of little moves that can be blended within the tolerance of P then you might see an increase in speed. Variables that affect the speed are acceleration and how much blending can be done. I've found that acceleration is usually 10 - 20 times the velocity for the axis.
John
Replied by BigJohnT on topic Idea for high speed machining / trajectory
I see what you mean now.
I know g64 p0 is the default mode, but I feel like my speed is improved with g64 p0.005
Is the naive cam detector enabled with a P word, if the Q is left off?
If i run a complex vcarve with the g64 default, it seems ok speed.
but with g64 p0.005 I swear it speeds up a lot.
I do know that I sped up 3d toolpaths a good bit by jacking up my acceleration as high as my machine could stand.
I use 2 machine profiles, one for generic stuff with reasonable accel.
and another for 3d rastering with 100 acceleration for X and Z
G64 is default not G64P0. G64Pn turns on the naive cam detector and if your file is full of little moves that can be blended within the tolerance of P then you might see an increase in speed. Variables that affect the speed are acceleration and how much blending can be done. I've found that acceleration is usually 10 - 20 times the velocity for the axis.
John
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18 Feb 2013 23:43 #30285
by BigJohnT
G64 P- Q- - (Blend With Tolerance Mode) This enables the naive cam detector and enables blending with a tolerance.
Naive Cam Detector - Successive G1 moves that involve only the XYZ axes that deviate less than Q- from a straight line are merged into a single straight line. This merged movement replaces the individual G1 movements for the purposes of blending with tolerance. Between successive movements, the controlled point will pass no more than P- from the actual endpoints of the movements.
John
Replied by BigJohnT on topic Idea for high speed machining / trajectory
[...]
basically g64 p0.005 will stay within 5 thou of programmed path while keeping speed up as much as possible.
No, IMHO the G64 P mode is much slower because it only blends moves but sticks to the "exakt stop on end of next move" limitation making it very slow.
G64 P- Q- - (Blend With Tolerance Mode) This enables the naive cam detector and enables blending with a tolerance.
Naive Cam Detector - Successive G1 moves that involve only the XYZ axes that deviate less than Q- from a straight line are merged into a single straight line. This merged movement replaces the individual G1 movements for the purposes of blending with tolerance. Between successive movements, the controlled point will pass no more than P- from the actual endpoints of the movements.
John
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19 Feb 2013 00:14 #30288
by juwi
Replied by juwi on topic Idea for high speed machining / trajectory
My Idea was based on the guess that G64 would accept overshooting and therefore does not need to be stoppable the end of the next move.
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19 Feb 2013 00:47 #30289
by BigJohnT
Replied by BigJohnT on topic Idea for high speed machining / trajectory
G64 just cuts corners to obtain the F speed if possible. If you have long moves it will be as fast as it gets, however if you have thousands of tiny moves it will be painfully slow on a machine with low acceleration.
John
John
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