Changing Z-Height While Maintaining Y Velocity

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08 Aug 2017 16:44 #97185 by PlasmaRemoval
PlasmaRemoval created the topic: Changing Z-Height While Maintaining Y Velocity
I would like to perform multiple moves in the Z axis while maintaining a constant velocity along the Y axis. For example, I would like to be able to execute something similar to:
G1 X1 Y1 Z1
G1 Y3 Z1
G1 Y5 Z2

...without decelerating and then accelerating again in the Y direction.

Is this possible? I am using a Shopbot PRSalpha Buddy with a Mesa 7i76 board and LinuxCNC. I have tried using G64, but still get more acceleration along Y than I would like.

Thanks!
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08 Aug 2017 17:16 #97192 by andypugh
andypugh replied the topic: Changing Z-Height While Maintaining Y Velocity
Is the application plasma torch height adjustment?
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08 Aug 2017 17:55 #97196 by PlasmaRemoval
PlasmaRemoval replied the topic: Changing Z-Height While Maintaining Y Velocity
Yes, although it's a nonstandard torch for which the typical voltage-based adjustments will not work. We plan to probe the surface to measure height changes.
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08 Aug 2017 19:22 #97199 by andypugh
andypugh replied the topic: Changing Z-Height While Maintaining Y Velocity
In that case, you could investigate "probekins"

wiki.linuxcnc.org/cgi-bin/wiki.pl?ProbeKins

Your problem sounds identical.
The following user(s) said Thank You: PlasmaRemoval
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08 Aug 2017 19:50 #97200 by PlasmaRemoval
PlasmaRemoval replied the topic: Changing Z-Height While Maintaining Y Velocity
That module does sound interesting. Do you know where I can find the original source code? The Gitweb link in the wiki is dead. I found an old compiled version on the forum, but I would prefer the source if possible.

Is there no simple G code means to avoid acceleration along one axis between commands affecting a different axis? The module seems like overkill for handling this, but maybe there is no simple solution.

Thanks!
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08 Aug 2017 20:06 #97201 by andypugh
andypugh replied the topic: Changing Z-Height While Maintaining Y Velocity
The advantage of that module is that it doesn't require special G-code, any 2D plasma CAM software will work.

As for the second question, I don't know. I have never needed to worry about the trajectory planner with my slow old machines
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09 Aug 2017 02:16 #97226 by jmelson
jmelson replied the topic: Changing Z-Height While Maintaining Y Velocity
As long as you are not set for exact stop mode, your code should give smooth motion in Y. You may have to experiment with the P and Q parameters of the G64 command to get the results you want.
See linuxcnc.org/docs/html/gcode/g-code.html#gcode:g61-g61.1
for more info.

Jon
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