Re: [CAD_CAM_EDM_DRO] EMC Home and Limit Wiring

Hi Alan

Answers mixed in below....

On Monday 11 Mar 2002 10:35 pm, beer@... wrote:
> I have some questions about the Home and Limit switch wiring for EMC. (
> I'm a CNCPro user )
>
> From what documentation I can find, it seems that three switches are
> envisioned for any single axis; one for Home, one for "Near" Limit and
> one for "Far" limit.
>
> In the case of a three axis system, then, it looks like nine switches
> are expected.

For a three axis machine, this is indeed correct.

>
> It also appears as if the switches are designated for a series
> connection .. a Home loop, and two Limit loops.

For stepper motor systems using the parallel ports, yes. If you have a Servo
To Go card, then there is plenty of spare IO to use one IO pin for each
switch.

> I GUESS I can understand how this might work when the HOME setting is
> asked for.
>
> Move X only until HOME is triggered, then back a bit until it's not
> triggered.
>
> Move Y only until HOME is triggered, then ...
>
> Move Z only ...

And this is how EMC homes each axis - Although You decide which order to home
them in.

> But I don't understand the logic behind the -Limit and +Limit. Why
> should EMC care WHICH direction things are going when a Limit switch is
> activated. Just stop !

EMC needs to know which limit switch was activated so that you don't try to
jog off in the wrong direction.

> And finally, is there no provision for an EStop switch ? Or is this a
> double-pole switch to be added to both Limit switch loops.

Provision is made for an Estop - A second parallel port is needed for this,
and it is also a very good idea to use a double pole switch. One pole for
EMC, and the other to kill the power to your motors.

Regards, Paul.