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Author Topic: Trajectory planer/CV Mode - Does it use/make estimates?  (Read 253 times)

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Trajectory planer/CV Mode - Does it use/make estimates?
« on: January 28, 2020, 10:11:59 PM »
Hello,

I had a "discussion" about Mach3, its Trajectory planer and the CV Mode.
I'm quite sure it's an algorithm or what not and relies strictly on calculations based on inputs, meaning velocity, acceleration and CV settings and the Gcode it is processing.

He is adamant and claims that: "CV is predicting the excel and decel characteristics of your machine due to weight and velocity."
"CV is the estimated prediction of the characteristics of the mass in motion as for as excel decel and change of direction." The spelling is his, not mine.
And I removed the insults, of course.

So, could someone, preferably from Artsoft or a respected knowledgeable person, shed some light on this?
It doesn't make sense to me at all and he got me very, very mildly confused.

I thought the trajectory planer just takes in data, processes them according to the given limits set by the user and puts out the corresponding step/dir signals.
If the machine can or can not follow them is of no concern to the TP and it doesn't estimate anything about the inertias and so forth.
I mean, that's the job of the user to find settings that produces signals the machine can follow without stalling or stopping with error from too high following error.

Tl;dr:
Does the trajectory planer in CV mode make any kind of estimates like guessing the inertia of the moving components?
Can someone elaborate a bit on how the TP and the CV Mode work internally without giving trade secrets away?

Any links that explain in depth but understandable how TPs and contouring modes work would be interesting as well.

Thanks a lot,
Stefan F.
Re: Trajectory planer/CV Mode - Does it use/make estimates?
« Reply #1 on: January 29, 2020, 12:53:41 AM »
Hi,
Mach3's CV does not make any estimate about inertia, it has the motor tuning max acceleration/deceleration to go on and that's it.

In fact Mach3's CV adjustments to the planned trajectory are fairly simplistic. They are somewhat more refined in Mach4 and in particular
there are some calculations that can be done to set max error bounds and so on. You might be interested in Chaoticones contributions
in this field.

https://www.machsupport.com/forum/index.php?topic=35860.msg245507#msg245507

Craig
My wife left with my best friend...
     and I miss him!