Does Centroid have S curves or jerk control in motion planning?

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cnckeith
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Re: Does Centroid have S curves or jerk control in motion planning?

Post by cnckeith »

martyscncgarage wrote: Wed Dec 01, 2021 3:32 pm
cncsnw wrote: Wed Dec 01, 2021 3:09 pm Not correct. At least from 1993 - 2009 (all versions of CNC7 and CNC10) axis motion profiles were trapezoidal. S-curve accel/decel was introduced with the MPU11 family ca. 2009.
So bottom line. In today's MPU11 Centroid motion controllers (Including Acorn), running the latest software, S-Curve trajectory is employed.
Is that a fair statement?

Marty
yep!
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Re: Does Centroid have S curves or jerk control in motion planning?

Post by Cncninja »

That's awesome thanks for the info... I won't waste time fiddling with other controllers. I was also looking @ clearpath servos that use RAZ where the servo applied some basic S curve functions, now I can stick with my TMC drives. This Project has a Jagger 100k RPM spindle so hi feeds and smoothness matter on this one.
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Re: Does Centroid have S curves or jerk control in motion planning?

Post by cnckeith »

cool. what kind of molds are you making? do you have a sample of the g code you use? photos of the machine?
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Re: Does Centroid have S curves or jerk control in motion planning?

Post by Cncninja »

TPU injection molds for watch straps and cases. G code is made with Mastercam and F360/HSM depending on the 4th axis. I have a build log on my Youtube channel.

Thanks for your input I have already ordered a Ver4 from Amazon.
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Re: Does Centroid have S curves or jerk control in motion planning?

Post by drdennis »

This subject piqued my interest, mostly because I have no experience with, and would love to learn more about control specific to CNC machining. So I hooked up my signal analyzer (to the Acorn X axis) to examine the velocity profile. Indeed there is an S-curve. Very interestingly (at least to me) it is implemented through some pretty course dithering. I suspect the dithering is fine, given the inertia in the system, but I would love to hear some reasoning behind it. Thanks.

Enclosed is a velocity profile computed from the X axis pulse train. You can't really see what's happening due to the dithering, so I included a zoomed-in view that should help visualizing the S-curve.

Cheers
Attachments
10mm_full.png
10mm_dithering.png
cnckeith
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Re: Does Centroid have S curves or jerk control in motion planning?

Post by cnckeith »

Cncninja wrote: Thu Dec 02, 2021 11:23 am TPU injection molds for watch straps and cases. G code is made with Mastercam and F360/HSM depending on the 4th axis. I have a build log on my Youtube channel.

Thanks for your input I have already ordered a Ver4 from Amazon.
cool. did i miss the link to the youtube channel?
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Cncninja
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Re: Does Centroid have S curves or jerk control in motion planning?

Post by Cncninja »

acorn.JPG
@ drdennis

What were your sample rate and bit resolution? I found there is a Centroid command 228 to turn it on and off it would be interesting to see both profiles. it will be a few days before mine shows up and I can throw an accelerometer on one and plot
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Re: Does Centroid have S curves or jerk control in motion planning?

Post by cnckeith »

cncninja,
how about some data on the machine? photos? machine construction? way type? ballscrew type and pitch? axis motors and drives being used? PC specs? preparing a machine mechanically for fast smooth precision work is much more important than fretting about CNC12's motion. :-)
Acorn uses the same motion algorithms found in the $400K 5 axis cnc machine tools that we sell that are doing high speed short vector 3d work. In order for you to get similar results lots of details about the machine tool have to be "designed/built/tuned" in the sweet spot. Will be glad to guide you in this regard.
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cnckeith
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Re: Does Centroid have S curves or jerk control in motion planning?

Post by cnckeith »

related videos.



Need support? READ THIS POST first. http://centroidcncforum.com/viewtopic.php?f=60&t=1043
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and here viewforum.php?f=61
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drdennis
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Re: Does Centroid have S curves or jerk control in motion planning?

Post by drdennis »

@cncninja
The parameter 228 didn't make any difference in my test. Its default setting in my software (CNC12 Acorn Mill v4.64) is 0 (S-curve off), which is what it was when I took the measurement you saw. It clearly does not control the S-curve I saw. But to see what would happen, I set it to 1 restarted the CNC software and re-ran the test, and got exactly the same profile.

I wanted to make sure my measurement error was less than 0.1% so the test parameters were:
Stepper pulse frequency 2kHz, (5x microstep == 1000 per rev with 5mm/rev lead screw)
fed into logic analyzer with 2MHz clock to get the desired 1e-3 precision
Cheers
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