Re: mill threading, Acceleration, Axis

Mariss,

I wasn't quite sure how to get the motor torque curve into the table,
but I can put a linear table in easily enough. I can HEAR my staircase,
so that's not good. Almost sounds like I could "slide" the delay time
down linearly between my steps, which might help. The "shortest" wasn't
really my goal, but the top of my 'S' is gone anyway.

Alan

Mariss Freimanis wrote:

>
> Hi,
>
> Alan, Actually "door #2" gets you the shortest time to speed.
> Secondarily it rounds off somewhat at the terminal speed. The main
> purpose of the S shaped profile is it should have shortest settling
> time since little ringing is induced.
>
> My experience has been that the touted advantages of these profiles
> over a linear ramp aren't as great as one would hope. The major
> detractor is the inevitable "staircasing" that results from software
> generated acceleration ramps. Each is an infinite impulse and will
> pump the motor resonance.
>
> A while ago I built a test circuit that generated a sigmoid voltage
> ramp using analog piecewise linear approximation which then fed a
> voltage controlled oscillator. This gave very nice results, which I
> used as a baseline for comparing digital implementations of same. The
> results were the staircase frequency had to be above 3kHz to accrue
> real benefit. This was beyond the capability of the CPU I was using
> by an order of magnitude.
>
> Mariss
>
> --- In CAD_CAM_EDM_DRO@egroups.com, Alan Marconett KM6VV <KM6VV@a...>
> wrote:
> > Mariss,
> >
> > Again, very infighting! Looks like Door #3. "S-shaped curve (sine
> from
> > -pi/2 to pi/2 + 1)" gives the Sigmoid curve then? And this should
> be
> > the least likely to loose steps? I've used linear ramps before,
> seems
> > like they run out too fast.
> >
> > I generated v/t from my acceleration calc routine, and generated PLC
> > code which I "pasted" into Vector. And yep, if I take it to the max
> > velocity, it's an 'S'. But, for my limited "top end", it's fairly
> > abrupt on the top! The 'S' shape is cut off (truncated) for slower
> > terminal velocities. And if I understand what I'm reading in the
> CY-545
> > doc's, It's true there too! So perhaps Dave's comment about
> generating
> > Sigmoid curves on the fly are the only way to fix it. Oh well.
> >
> > I like the car analogy, except, don't you just HIT THE GAS? Oops!
> that
> > would be a REAL JERK!
> >
> > Thanks,
> > Alan
>
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