On 2009-06-15, Bob Engelhardt wrote:
Jon Elson wrote:
Of course these can be used for CNC. You just need a servo interface
that puts
out +/- 10 V analog velocity commands. ...

Then this amp would just be a driver, and its tach feedback/servo
circuitry wouldn't be used?

No. The interface described above puts out a voltage somewhere
between -10V and +10V -- proportional to the speed (and direction)
required.

The servo amplifier compares this voltage with the tach feedback
and adjusts the voltage to maintain the speed as commanded -- even as
the load varies. And this is all happening without the computer needing
to get involved until it is near time to change the speed of one or more
axes.

The encoder is used to tell the computer what is happening as a
double-check on the servo amplifier's behavior.

I've hooked up a servo amplifier and servo motor with tach
feedback to a precision power supply which can produce up to 20 volts in
steps of 0.001 V. And there is a pot which will allow adjustment
between any 0.001 V value and then next 0.001V higher.

I've set up the servo amp's pots so the motor spins at its
fastest speed at 10V from the power supply. When I turn it down to
0.001V -- I need to put a piece of tape on the motor's shaft to tell
that it is moving -- and if you time it between full turns, you will
discover that it is maintaining the same speed -- even if you manage to
put a significant load on the motor's shaft.

All of this is with the DC servo motors and amplifiers. I've
never had an AC servo motor running, so I'm not sure how slow it can be
made to go.

Enjoy,
DoN.

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