Re: servos, steppers, limit switches

Yep--the 'home' switches are there on teh diagram...shows how much
I know about how little I know <chuckle>

--- In CAD_CAM_EDM_DRO@yahoogroups.com, "vrsculptor" <vrsculptor@h...>
wrote:

> --- 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