Re: mill threading, Acceleration, Axis

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