On Sat, 24 May 2008 22:11:47 -0500, you wrote:
>I have set up lathe-type threading on my mini-mill, with a real
>quadrature encoder on the spindle. It has 1728 lines, for 6912
>quadrature counts/revolution. So, at 100 RPM, it provides
>11,520 counts/second, or 11.52 counts/servo period, assuming a
>1 KHz servo update cycle. I didn't think I needed that kind of
>resolution or count rate, it was just a one-of-a-kind encoder I
>had laying around. I did also see some of this "hunting"
>behavior when I first started setting this up several years ago.
Jon - I know nothing on how EMC works with spindle index, but hunting
that decreases in amplitude and then steadies out in other controls is
usually a sign of over correction with too aggressive correction factors
in PID controls. Random hunting is usually a poor connection.
>Also, if your Z axis is asked to sync to the
>spindle in too short a distance, it will reach its accel limit
>and suffer some hunting.
Shouldn't happen, should be NO hunting in a properly implemented and set
up system - it's overcorrecting. It should get up to speed and stay
there.
The norm is to allow a short pause for the spindle to get to speed
before the Z axis moves, that could either be set in the controller
(EMC) or in Gcode. A short lead in is normal to allow the Z axis to get
to velocity, but how much is machine dependant.
Steve Blackmore
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