Linuxcnc - s-curve acceleration? (7176e)

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05 Aug 2018 23:23 #115654 by grijalvap
Is anybody we can pay for, if yes maybe we can start a donation campaign or even a Kickstarter campaign to get money to pay for this development.
what do you think?

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17 Aug 2018 00:06 #116189 by grijalvap
No comments?

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15 Apr 2019 23:53 #130949 by warreng
Sorry, my post is not any kind of update. But instead a question. I'm curious about how many of the "advantages" of limited jerk acceleration processing can be compensated with G-code. I'm sure my naivety is showing...
When I first started using Fusion360 to write toolpaths for an older commercial CNC router (instead of ArtCam) I immediately noticed a different personality to the motion. I would think that if your G-code is coarse then your only hope for smooth motion and optimized acceleration is for your controller to manipulate the situation. But if the G-code is more data dense then I can imagine that the bigger acceleration booboos can be handled right at the start. Any comments that might help me understand this more completely?

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16 Apr 2019 16:09 #130985 by PCW
CAM and the actual chosen shape of machined surfaces can have a direct effect on the acceleration and jerk profiles.

If you consider constant surface speed machining, the actual curve you are machining
entirely determines the acceleration and jerk , as long as you don't exceed machine
constraints, the CNC's trajectory planners jerk/acceleration limits have no real effect.

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16 Apr 2019 17:13 #130989 by cmorley
That is the whole point of the planner... you can ask for impossible profiles and it makes them possible by clipping them to as close as the machine is capable.
The better it is at this, then the more aggressive you can be with speed, acceleration and jerk.
Whether your machine needs/can use this performance is a good question.

Chris M

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16 Apr 2019 19:21 - 16 Apr 2019 19:21 #130999 by PCW
Sure, just pointing out that many time the profile determine these values, not the machine,
though of course the machine determines the tangential acceleration when changing velocity.
Last edit: 16 Apr 2019 19:21 by PCW.

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07 Jun 2019 22:26 #136257 by ihavenofish
The only time jerk is meaningful i find is in exact stop linear moves. Many arcs and constant velocity moves have what is effectively built in jerk control as mentioned above. Machining a square at high speed and high acceleration with G64 on is smooth as butter. With it off, the floor shakes :)

So... how hard is it to do jerk control ONLY for G0 and G1 exact stop moves as a starting point? This would cover most real life cases of bad jerk, and only leave a handful of special cases to be dealt with later. It sounds to me many of the previous tries got hung up on trying to cover all motion. I think we should be more incremental about it.

I have a 2000ipm machine with 0.5G acceleration, so jerk control is an important topic for me as the machine endures a lot of stress.

The cases where we will still have significant jerk ( the start and end of some g64 mode moves, shallow arcs in exact stop, etc) are a fair compromise to leave off.

You will still have to tune your aces for the worst case motion situations, but having smooth rapids and linear moves would be at least for me a vast improvement.

Yes, no, maybe?

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