LinuxCNC S-Curve Accelerations

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5 years 4 months ago #211417 by TheRoslyak
Replied by TheRoslyak on topic LinuxCNC S-Curve Accelerations
Hi.
Is it possible to simple import this module in linuxcnc?
It need me for this topic forum.linuxcnc.org/27-driver-boards/4274...-with-stm32-or-esp32
Or can you say another way: How to smooth velocity?

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5 years 4 months ago #211728 by chris@cnc
Replied by chris@cnc on topic LinuxCNC S-Curve Accelerations
I try to find an easier way and stumbled over Sigmoid function. My Idea is to build s-curve gain and multiply to current acceleration. This function get back good result but i am not able to scale the timer. If its possible to define this function with timers could we bend anything to S curve.
What do you thing about this way?

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5 years 4 months ago #211870 by TheRoslyak
Replied by TheRoslyak on topic LinuxCNC S-Curve Accelerations
Hi arvidb,
Can you share how you imported S-Curve Accelerations?
Looking at scope you did it.

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5 years 4 months ago #211876 by arvidb
Replied by arvidb on topic LinuxCNC S-Curve Accelerations
Hi TheRoslyak,

What you see on the scope is just the simplest case of jerk-limited motion: from stationary to stationary with a constant velocity part in between. There are much trickier cases that must work too for the code to be usable.

My code isn't finished yet. Since my last post I've fixed the bug I found during testing with the MPG (and another one), but there is still one corner case that I have to implement, and then integrate the resulting library with the LinuxCNC build system. I've had precious little "leftover energy" to spend on hobby programming lately, but the project is still moving forward, albeit *very* slowly at present.

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5 years 4 months ago #211893 by automata
Replied by automata on topic LinuxCNC S-Curve Accelerations
Hi arvidb,
Nice work with the jerk limited motion.
I am very much interested in helping out and have decent experience in the linuxcnc codebase. ( I coded the original switch kins module to switch between multiple kinematics).
It you share your current branch which looks in good form, the community can move together to solve this long standing missing feature from one of the most flexible and open cnc software.
- automata

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5 years 4 months ago #211917 by chris@cnc
Replied by chris@cnc on topic LinuxCNC S-Curve Accelerations
hello arvidb hello automata, i would also help as far as i can. My approach would be a 2nd acceleration time in the ini that defines the curve. So we can easily decide whether linear or in s-curve. And the curve defines, for example, the sigmoid function. Some servo manufacturers go this route and it works very well. I have no idea how to start this. what do you think of this idea?
Christian

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5 years 4 months ago #211919 by arvidb
Replied by arvidb on topic LinuxCNC S-Curve Accelerations

automata wrote: Hi arvidb,
Nice work with the jerk limited motion.
I am very much interested in helping out and have decent experience in the linuxcnc codebase.

Thanks!

Did you download and compile/run the code that I've already published ? If not, that's a good place to start (for anyone who wants to help).

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5 years 4 months ago #211921 by arvidb
Replied by arvidb on topic LinuxCNC S-Curve Accelerations
Another step forward: I managed to implement that missing corner case yesterday. Here's an oscilloscope plot showing MPG jogging, where jerk limited planning might have its biggest impact:

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A bit more interesting than the last plot, don't you think? :)

There are still a few known bugs in the code, but it's nearing a state where testing might soon become meaningful!

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5 years 4 months ago #211925 by arvidb
Replied by arvidb on topic LinuxCNC S-Curve Accelerations

chris@cnc wrote: hello arvidb hello automata, i would also help as far as i can. My approach would be a 2nd acceleration time in the ini that defines the curve. So we can easily decide whether linear or in s-curve. And the curve defines, for example, the sigmoid function. Some servo manufacturers go this route and it works very well. I have no idea how to start this. what do you think of this idea?
Christian

Hi Christian!

I think a great way to start would be to make your algorithm move a specified distance. Looking at your plot above, your algorithm moves from v = 0.0 to v = 1.0. Add a deceleration stage (from v = 1.0 to v = 0.0) and then scale peak velocity so that your algorithm ends up moving any distance that you specify as an input.

Then check that your peak velocity doesn't violate any "max velocity" (also specified as an input). If it does, insert a constant velocity segment.

Then make it work with initial velocity not zero.

And so on...

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5 years 4 months ago #211954 by chris@cnc
Replied by chris@cnc on topic LinuxCNC S-Curve Accelerations

arvidb wrote: . Add a deceleration stage (from v = 1.0 to v = 0.0) and then scale peak velocity so that your algorithm ends up moving any distance that you specify as an input.

Hi arvidb,
You're right. It's a good idea to climb down the hill. :) But i can't do it.I can't do two calculations in a row. I can now control the length of the curve using a pin. My programming skills are not enough. I should leave it to people who know what they're doing. Try and error no longer leads to the goal.
Maybe someone else can make something of it. I can not...

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