Linuxcnc - s-curve acceleration? (7176e)

dear all,

I'm planning a Project for using LinuxCNC for a high-end 3-5 axis micromilling machine.
The machine Features high precision and high Dynamics.

1) The communication with the drives uses an Ethernet-based bus (either EtherCAT or TriaLink, a proprietary bus of the drive manufacturer www.trialink.com ).
I know that there has been attempts to integrate realtime Ethernet bus communications to LinuxCNC.
Any hint or information is highly appreciated.

2) Jerk-limited acceleration profiles are essential for my application in order to avoid acceleration jumps.
But this Needs also that the pieces of of trajectories feature "G^2 continuity".
If, e.g., a G01 is followed by a tangential G02, the normal acceleration jumps, which is undesirable (vibrations/surface quality).
Usually, commercial CNC's feature geometrical cornering before doing the time-based motion planning.

Is this the case with LinuxCNC ?

My activity domain is the development of Motion Planning (geometrical preprocessing and feedrate planning), but using high Level languages (Matlab).

I would like to include them to LinuxCNC.
Is this realistic in your view ?

thanks in advance and best regards,

Raoul

Herzog wrote: I know that there has been attempts to integrate realtime Ethernet bus communications to LinuxCNC.
Any hint or information is highly appreciated.

The Mesa ethernet FPGA cards already do this, so it is pretty mainstream in LinuxCNC now.

2) Jerk-limited acceleration profiles are essential for my application in order to avoid acceleration jumps.

Unfortunately jerk-limited trajectory planning is not an option with LinuxCNC. If you absolutely have to have that then I am afraid that LinuxCNC won't work for you.

I was wondering what it would take to make #2 an option in LinuxCNC?

If Raoul has Matlab code for motion planning I/others might be able to help him convert it over to SciPy, which could link up with LinuxCNC via Python.

Is there a high-level block diagram of the LCNC libraries to understand how one could go about plugging in modules like this?

I feel like it could be hugely beneficial to LinuxCNC to make it a go-to option for people in the academic community to test new algorithms. You saw that with Gimp back in the day when it became a popular software to demo new image processing algorithms to the academic community (since Matlab is slow and frustrating to develop UI for).

Making LinuxCNC appropriate for high end applications with high machine dynamics and very high precision would be cool.
For this kind of applications low excitation of vibrational modes is essential, and also low tracking errors in the drive control loops.

Commercial CNC's offer e.g. "bellshaped acceleration profiles" which have a steep drop off in the spectrum avoiding excitation of vibrational modes. Other "standard" features are e.g. "crosstalk compensation".

All this stuff needs time to be developed, time to make it reliable in order to work properly in every situation.
Help from Academia is welcome and needed.

LinuxCNC could be for them an easy to use platform to incorporate new algorithms for trajectory planning (TP) and G^2 cornering.
A better description of the actually implemented TP core algorithms would be helpful.

Let me know what you think about this.

best regards,

Raoul

IMHO
Lack of documentation of linuxcnc's core is probably the main reason it doesn't get developed much. few people have the skill and time to get up to speed.
Only a few people have experience with the core.
The only reason we got a look ahead planner is because Tormach paid someone to do it.
I agree help from Academia would be welcome - detailed documentation would be the first step.

Chris M

I ventured into the source looking for something recently (and went round in circles) and I reviewed the current developer docs today after reading your post Chris. I think what's missing is an overview of the source code files. I know there is some block diagrams in the docs but they are not cross-referenced to the code. Unfortunately, its not really a task a newbie could do.