Centroid Community CNC Support Forum

Hello,

I'm looking at switching to an acorn for a project that will do a lot of mold work, I have Mach3, UCcnc, Pathpilot(Linuxcnc), and 2 Standalone controllers DDCSV and SMC5-5 and 3 Grbl hall 32 bit systems.

I want smooth motion but most of these controllers us trapezoidal acceleration profiles vs S-Curves (jerk control). I tried a Grbl fork called G2core and it ran on a 32bit controller it uses jerk control motion planning and it was the best control out of the bunch for path planning but the project died but almost all of the 3d printer world and forks of Grbl have implemented there version of it. I see Centroid has a smoothing option could someone explain how this is implemented and if it does any Jerk control or s curve acceleration profiling. I have read a few post saying the Acorn system gets slow and jerky on sweeping moves. I just want to make sure this is a good fit for my new project

Thank you.

hello. there are a large number of factors that make a machine tool "get slow and jerky on sweeping moves" our motion software is not one of them.
Most every time i investigate a complaint like this it turns out to be any number of problems not related to software....keep in mind that no amount of smoothing can make up for a machine tool that is not "geared" correctly, appropriate motor sizing (power, speed, power supplies, operating voltage etc), rigid, low lash, no sticktion, etc...etc..

share your design specs and we can guide you in making a fast smooth cnc mold making machine.

you may be interested in this link.
viewtopic.php?p=22541#p22541

Thanks for the reply,

Yes I'm aware of all those factors and have built many dedicated CNC machines. I'm just focusing on the trajectory planning side now. I know there is Smoothing out there like CV etc, it creates a more flowing path at the cost of precision. where S curves deal with acceleration and jerk control but the motion path remains the same. I have a Multicam CNC router that the control died on and I set up Uccnc on it and wow it was smoother, I then tried G2core on the same router and it was a whole different machine faster smoother, and had even better tolerances. The difference was trapezoidal acceleration profiles vs S curve and jerk profiles. I'm just trying to figure out how centroid handles it to see if it's a good fit.

Here is a video for ref



Thanks

Keith is 100% right, there are a large number of factors that make a machine tool "get slow and jerky on sweeping moves" and the Centroid software is not one of them.

Smoothing is a feature in the Acorn control software and you can read about it in the manual. There's a document that just explains smoothing and it can be found on the Acorn manual page found here:

viewtopic.php?f=60&t=3397

Smoothing has it's place for some tool paths but I would not use it all the time. It's certainly not needed if the CAD/CAM was done properly and the machine is setup properly. Is your CAD software actually drawing an arc or hundreds of straight lines made to look like an arc?

Smoothing has it's place for some tool paths but I would not use it all the time. It's certainly not needed if the CAD/CAM was done properly and the machine is setup properly. Is your CAD software actually drawing an arc or hundreds of straight lines made to look like an arc?

You are missing the question. @cncninja is asking about jerk (time derivative of acceleration) control. For example in its simplest form, when Acorn moves only the X axis (i.e., in a straight line) what is the velocity profile?

I am not a skilled machinist, and I have not looked at what Acorn does yet. But I have designed enough motion control systems to know how important the S-curve profile is. We use it in machines where the jerky motion characteristic to the common trapezoid profiles would disturb fluid dynamics in the jets. It (S-curve) is a common requirement in machines where smooth motion is really important, and as such a very reasonable question to ask.

drdennis wrote: ↑Tue Nov 30, 2021 11:52 pm You are missing the question. @cncninja is asking about jerk (time derivative of acceleration) control. For example in its simplest form, when Acorn moves only the X axis (i.e., in a straight line) what is the velocity profile?

I am not a skilled machinist, and I have not looked at what Acorn does yet. But I have designed enough motion control systems to know how important the S-curve profile is. We use it in machines where the jerky motion characteristic to the common trapezoid profiles would disturb fluid dynamics in the jets. It (S-curve) is a common requirement in machines where smooth motion is really important, and as such a very reasonable question to ask.

The OP also asked about smoothing as an option with the Acorn so I pointed him to the smoothing manual for his reading pleasure. That's the question I answered.

hello. yep S curve has been employed in Centroid motion systems since around 2009?.
the G code smoothing feature works differently as it takes ratty g code and lofts smooth arcs thru a saw tooth pattern of short vectors pumped out by a CAD/CAM system. the G code smoothing feature has cool user editable parameters so user can edit the effect to meet the application, values used often depend on the g code being processed, the geometry and the machine itself.

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.

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

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.

bear trap memory! thanks, i edited my post.