Re: servos, steppers, limit switches

--- In CAD_CAM_EDM_DRO@yahoogroups.com, "Brian Sherwood" <lurch@m...>
wrote:

> i'm in the process of converting my taig to servos...and someone

told

> me i don't need limit switches on a servo setup although the

stepper

> setup has one at the max-value of each axis. the wiring diagram

for

> the servo setup shows the limit switches wired in series with the e-
> stop switch.

Brian,
The diagram is correct on limits and E-stop. Servo systems can run
away a max speed if the encoder cable becomes disconnected or an
output transistor fails. On a big machine this is heart stopping. The
Estop/limit switch at least powers down the motors before hitting a
hard stop. If you don't do a power down Estop the servo would
continue to drive against the stop. On a small mini-mill without a
limit I broke my coupling. On a big machine you could break iron.
Don't trust software to stop a run away machine.

The best solution is to use a second set of switches for homing. This
is the way "real" machines do it.

On stepper controlled Bridgeports this wasn't an issue as steppers
can't run away.

Roger S