Ned Simmons wrote:

On Sat, 10 Jul 2010 01:45:39 -0500, Ignoramus30064
wrote:

... Because it "creeps".

I have only one axis (x) wired right now. When the drive is powered on,
but with no input signal, the table imperceptibly slowly creeps. I
only noticed it because some tools fell off the table as it moved by
perhaps 8 inches in an hour.

There is a "test/offset" pot on the board that, if turned properly,
shifts input signal and makes the table move. I could easily set it so
that the mill does not _visibly_ move. I have not, however, been able
to get rid of the slow creep.

I may call AMC on Monday to find out.

I assume you have no controller attached yet? The offset pot can get
you very close to zero speed, but without the controller you'll always
see a little drift. Remember, the amp has no knowledge of the motor's
position at this point. The controller is needed to close the position
loop and hold an exact position.

There's no problem with the amp.

Exactly. Iggy need to read up a bit more on servo loops, and understand
that the drive is little more than a power amplifier. The fact that the
drives have some features for non CNC applications i.e. simple closed
loop speed control based on tach feedback is confusing him.

Iggy, CNC servo control is not about speed, it is about position. The
CNC control manages the speed through it's control of position and how
quickly it changes that position. Acceleration and deceleration rates
and travel speeds are all controlled by the CNC control, not by the
servo drive. This is different from something like a VFD where those
parameters are controlled by the VFD.