Hi:
> I like to think of what happens when I apply the breaks on a car. It
slows down, and if I do not let up a little near the end it grabs... I
think that is technically jerk.<
Good example! Absolutely that is jerk as the curve for acceleration has a
step function in it. The higher derivative curves would have a step in them
also. They are frequently named Snap, Crackle & Pop. While I don't know the
exact significance of them in regards to machine tools, when it comes to
rotating cams, if all the derivatives through Pop are smooth or at least have
no step in them, you can pretty much turn as fast as you want without
developing unintended motions and deflections. Sine waves and their
derivatives pass this test very well but there are other motions that can as
well.
Just easing off the brakes as the car comes to a stop would be a big
improvement for fast moving machinery. That potentially solves the overshoot
problem.
Pete Gruendeman
--------------------------------------------
On Tue, 12/22/15, EBo <[email protected]> wrote:
Subject: Re: [Emc-developers] jerk limited trajectory
To: [email protected]
Date: Tuesday, December 22, 2015, 10:44 PM
On Dec 22 2015 8:33 PM,
andy pugh wrote:
> On 23 December 2015 at
02:02, Jon Elson <[email protected]>
> wrote:
>> So,
the spindle's
>> rotational
inertia makes jerk MECHANICALLY impossible.
>
> I don't think
that there is a mechanical limit on jerk.
>
> This is why you
stumble when a tube train stops hard.
I like to think of what happens when I apply
the breaks on a car. It
slows down, and
if I do not let up a little near the end it grabs... I
think that is technically jerk. As for
applying gas, if you pop the
clutch...
Seriously though. The VLA
example, they installed two motors (each
feeding the opposite way, and would feed them
propositionally to control
jerk, and
possibly higher order derivatives). They told me that when
they originally had one motor on the
system, the initial impulse would
send a
shock through the entire antenna. I could have the story
wrong,
but that is what I remember.
Back to LCNC land... I can
see this being useful for most cases, but
not critically necessary unless I was spinning
something less than a 24"
chuck. I
only had a chance to run a machine that large once, and that
was decades ago.
EBo --
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