Re: Homebrew STG card

[Jon Elson <jmelson-at-artsci.wustl.edu>]

Matt Shaver wrote:

> > From: Paul Corner <Paul.Corner-at-tesco.net>
> > You asked about including analog inputs -
> > How many inputs, resolution, and bufferd or not ?
>
> I don't really know. That must sound strange, but I brought it up since the
> STG card has it. The only uses I can think of for this feature would be:
>
> 1. Some servo amps output a voltage proportional to motor current, and this
> could be useful for a system that tracked tool wear (or some other
> application I haven't yet imagined)

This would be much more useful for a spindle drive, rather than an axis
drive.

> 2. Some variable frequency drives have an analog output for motor speed. This
> might seem to be redundant except that they also do soft starts where the
> RPM's ramp up over time.

Another thing you could do with analog input is make a VERY good joystick
jog control.  You put a wide deadband around the center position, maybe
20% of the range.  Then, that leaves 80%, or 40% on each side of zero.
You then make this 40% on each side respond logarithmically, so just into
the active range gives .0001"/sec jog rate, 10% into the active range gives
.001"/sec, 20% => .01"/sec, 30% => .1"/sec, and full travel gives 1"/sec.
This would be a GREAT feature for a pendant control.  You would have
to enable the stick with a button, first, to prevent unintended moves by
just bumping the stick.  You could use a pot with a centering spring for
jogging the Z axis.

Jon