LinuxCNC S-Curve Accelerations

Thanks, a very interesting lecture. Thanks to Robert Ellenberg too for talking!

It was kinda cool to see: the jerk-limited counterpart to parabolic blending is kindof what I called "constant jerk vector" here (i.e. switch as fast as possible from one direction to another). The jerk-limited counterpart to arc blending would then be the clothoid, which, just like the arc, keeps constant velocity.

Clothoids are parameterized by length, too. But they only give constant jerk for something like a train or car, which turns with the curve. For something like a tool in a machine, that keeps a constant heading, there's also jerk needed to rotate the acceleration vector around it, and acceleration to rotate the velocity vector. That can be seen from the jerk and acceleration limit violations in my plot on that same page.

For anybody interested in the topic, maybe this could be informative. It provides a general over view on path blending and proposes a method using clothoids.

dro.deakin.edu.au/eserv/DU:30118119/shah...thsmoothing-2019.pdf

[edit]

Just realized that this looks like the usual spam post. It's not I swear.

There are 2 aspects to this problem.

One thing is the generation of the speed profile. The other one is blending toolpaths under constraints like allowed deviation, allowed acceleration, allowed jerk.

I just resurrected my branch (that only changes the speed profile) and it seems to merge cleanly on master. If you want to play around with it, you need to #define BEZIER for the "smooth" planner or compile with -DBEZIER.

Also, as a memento, if I remember correctly, the MachineKit ppl refactored the trajectory planner into it's own module so you can plug it in at run time. Maybe it's worth taking a look at that.

And thanks for the link to the dissertation, this will make an interesting read.

Aciera wrote: Just realized that this looks like the usual spam post. It's not I swear.

Having your user name at the start of the post makes this "not spam" as you have become a very valuable member of this community willing to help always, and for that we are very thankful.
M.F.G.
Tom.

Aciera wrote:
Just realized that this looks like the usual spam post. It's not I swear.

Don't stress, we know who the good guys are and won't shoot on sight

rodw wrote:

Aciera wrote:
Just realized that this looks like the usual spam post. It's not I swear.

Don't stress, we know who the good guys are and won't shoot on sight

Well, accidents do happen ...