> Date: Tue, 22 Dec 2015 11:18:20 -0600
> From: [email protected]
> To: [email protected]
> Subject: Re: [Emc-developers] jerk limited trajectory
>
> On 12/21/2015 11:59 PM, Chris Morley wrote:
> >
> > That version of jerk-limited just didn't quite work right
> > with spindle-synch. IIRC the person doing it didn't need
> > spindle-synch and got little help - lost interest. Not
> > that i blame him - it looks very difficult!
> Yes, I think combining jerk limiting with spindle synch
> REQUIRES a compromise. There are probably a couple ways to
> do it. One is to just turn off jerk limiting when in
> spindle synch. The other is to warn users that there is
> some initial part of the motion which will not be fully
> synched to the spindle, until the jerk limit has been
> integrated out. This latter scheme will break taps on
> spindle reversal, so doesn't seem like the right approach.
> Maybe somebody else knows a better way?
>
> Jon
>
I've heard this argument before and it just doesn't make sense to me.
I can't figure out why one would not want to have jerk limiting.
jerk limiting allows one to define a machine command that the machine
can actually physically perform. In fact it can allow you to raise acceleration
setting giving you more performance.
If ignoring jerk allowed better performance then ignoring acceleration should be
even better? I don't think that would be very successful.
I mean obviously if your jerk setting is out to lunch that could be just as bad.
but I bet jerk is such a small part of machine movement that it wouldn't break
the tap.
I say this because all linuxcnc machines out there ignore jerk and they don't
break taps
all the time. Though i guess one could argue that the axis has jerk anyways so
it matches
the spindle close enough.
I am not an expert or have done the math on this - it just doesn't make sense
to me.
I'd love to know the answer definitively!
It would be interesting to see the actual motion profile of a spindle tapping
vrs
the actual motion profile of an axis following it vrs the commanded motion
profile.
Interesting !
Chris M
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