Re: servo question

> From: "emconut" <muz2000nz@...>
>
> If a servo system is basicaly DC motors controlled by positional
> feedback
> could you not use DRO's for this to drive DC motors or is there a
> fundimental flaw in my thinking?
> If I am right is there a particular software/hardware system that
> would facilitate this best
> Could I still get a visible readout?
> Would a particular DRO be better to facilitate this
> waiting your answers with baited breath
> emconut

Most of the DRO's that I deal with are limited to 0.0005 resolution. If
that's enough for your setup you should be in range of the target. You
should also note that resolution is not the same as accuracy or
repeatability. A good servo system can come close (2 * resolution) but
often they do not.

Many DRO's do not update fast enought to keep up with a servo system. The
standard update rate required by the EMC is 1000 Hz but this could be
dumbed down if the DRO was close.

Those DRO's that have an external connection may only connect using a
serial port. You will also need to check the rate at which it can
present it's data to whatever host is connected.

If the DRO you find refreshes this fast, and has adequate interface to get
positions into a PC, an EMC driver could be written to read those
signals. From there you would need to find a digital to pwm or analog
board or box that can put out signals to the servo motor drive amps and
write a driver for it. Once you get that far, the BDI (Brain Dead
Install for EMC) has all of the programs that you would need for a servo
drive system. You can download and burn a copy of this program without
cost from www.sherline.com/emc.

On the down side, the EMC's backlash compensation will not work for
encoders that are not connected to the motor. You will get proper
position because the scale is connected to the axis but you'll need to
set acceleration way down and use some integral component in the PID loop
or backlash will cause hunting by an axis around the setpoint (commanded
position).

Ray