QTPlasmaC with fourth axis - rotary

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26 Jun 2023 16:46 #274262 by mariusl
Replied by mariusl on topic QTPlasmaC with fourth axis - rotary
@LesNewell does the post processor take care of the faster feedrate for the A axis when cutting over the corners? If so by what ratio must the Axis be faster to be able to do a reasonable cut?

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Marius


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27 Jun 2023 04:42 #274294 by phillc54
Replied by phillc54 on topic QTPlasmaC with fourth axis - rotary
The last posted pipe_2023_06_26 appears to work with the current changes albeit it is a little large for my tube. 

There is one issue at the beginning of the circle:
N0100 (o=0, pd=0.5)
N0110 G00 X14.7352 Y3.922 Z50.0 A-90.0
N0120 G38.2 Z15.00 F500.0
N0130 G92 Z[25.0 - #<_hal[plasmac.float-switch-travel]>]
N0140 G00 Z28.0
N0150 M03 $0 S1
N0160 G01 Z26.5 F100.0
N0170 G03 X18.7657 Y5.98 I0.9862 J3.0442 F2000.0
N0180 G01 X21.7803 Y14.0015 A270.0
N0190 X24.7737 Y18.6269 F1607.3831
A is set to -90 in line N0110 and after the lead-in it is set to 270 in line N0180
It may be my setup but it does a complete revolution here so I changed N0110 to 270 and it seems OK.

I have pushed a test branch named phillc54/plasmac-tube with what I have so far which is only the basics. It includes the latest pipe.ngc file in nc_files/plasmac

Warning: Spoiler!

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27 Jun 2023 08:29 #274299 by mariusl
Replied by mariusl on topic QTPlasmaC with fourth axis - rotary
There seems to be a problem with the feed rate of the rotational axis on the last bit of the cutting. It seems to slow down over the corners instead of speeding up.

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Marius


www.bluearccnc.com

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27 Jun 2023 12:03 #274303 by LesNewell
Replied by LesNewell on topic QTPlasmaC with fourth axis - rotary

@LesNewell does the post processor take care of the faster feedrate for the A axis when cutting over the corners? If so by what ratio must the Axis be faster to be able to do a reasonable cut?
 

Yes, SheetCam varies the feed rate when cutting around the corner. The exact speed for each axis depends a lot on the tube corner radius. I generally recommend that the rotary axis be capable of 200RPM and the linear axes 10m/min (400IPM).

Looking at the test run there does seem to be something odd going on with the feed rates. I can see it in simulation here. I'll investigate further.

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27 Jun 2023 12:58 #274304 by LesNewell
Replied by LesNewell on topic QTPlasmaC with fourth axis - rotary
After more testing the feed rates in the code look correct. The slowdown I was seeing in SheetCam's sim is simply the simulator not being able to process movement blocks quickly enough. I need to upgrade the rotary simulation to use the new simulator engine used by 3 axis simulation. According to the code all of the corners apart from the one at 0:11 should be cut at around 20000-25000 units/min (I say units because it is a combination of linear and angular movement). The corner at 0:11 is has a lower feed because a lot of the movement is roughly parallel to the edge, unlike the rest which are closer to perpendicular. 

Phill, I have attached a version of the code that includes feed on every line. It may help you figure out what is going on.
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28 Jun 2023 05:14 - 28 Jun 2023 05:54 #274358 by phillc54
Replied by phillc54 on topic QTPlasmaC with fourth axis - rotary
There seems to be two issues at play here:
  1. My little rotary table is only capable of 150°/sec which is 25rpm
  2. LinuxCNC has poor path planning for axes other than X, Y, or Z
I made an AXIS sim with axes X, Y, and Z having max velocities of 30M/min (500mm/sec) and axis A having a max velocity of 200rpm (1200°/sec) and the result was fairly ordinary as far as I could observe.

EDIT: I have attached a halsampler capture of the A axis velocities for the second cut from the above sim.

File Attachment:

File Name: a_velocity.txt
File Size:145 KB
Attachments:
Last edit: 28 Jun 2023 05:54 by phillc54.

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28 Jun 2023 09:03 #274377 by LesNewell
Replied by LesNewell on topic QTPlasmaC with fourth axis - rotary
I think we need to test this on a machine with a decently fast fourth axis. Marius, it's probably up to you for this.

Phill, just out of interest how do the A axis velocities compare to the first cut?

I found Mach3 works more smoothly with the rotary axis configured for 1 unit per rev instead of 360 units/rev. Do you think this would help here?

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28 Jun 2023 09:35 #274378 by phillc54
Replied by phillc54 on topic QTPlasmaC with fourth axis - rotary

Phill, just out of interest how do the A axis velocities compare to the first cut?

I didn't plot those, I can do tomorrow.

I found Mach3 works more smoothly with the rotary axis configured for 1 unit per rev instead of 360 units/rev. Do you think this would help here?

TBH I don't know if that is possible, I assumed angular joints/axes needed to be degrees.

This is from the docs:
ANGULAR_UNITS = <units> - Specifies the machine units for rotational axes. Possible choices are deg, degree (360 per circle), rad, radian (2*π per circle), grad, or gon (400 per circle). This does not affect the angular units of NC code. In RS274NGC, A-, B- and C- words are always expressed in degrees.

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28 Jun 2023 12:33 #274387 by snowgoer540
Replied by snowgoer540 on topic QTPlasmaC with fourth axis - rotary

  1. My little rotary table is only capable of 150°/sec which is 25rpm
  2. LinuxCNC has poor path planning for axes other than X, Y, or Z


Would inverse time (G93) help with #2 at all? I know it's common on mills to use G93 with 4/5th axis moves.
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28 Jun 2023 13:44 #274389 by LesNewell
Replied by LesNewell on topic QTPlasmaC with fourth axis - rotary

TBH I don't know if that is possible, I assumed angular joints/axes needed to be degrees.

I generally recommend that the 4th axis is defined as a linear axis rather than angular. I'm not sure about LinuxCNC but some other controls treat rotary axes differently to linear axes. Functions such as rotary axis diameter compensation or 360 degree rollover can cause all sorts of unexpected issues.

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