Re: Limit switches revisited

--- In CAD_CAM_EDM_DRO@yahoogroups.com, Alan Rothenbush <alan@s...> wrote:

<snip>
> But I use slotted optical switches for Home. While I've heard all sorts of
> good things about the repeatability of mechanical switches, the opticals are
> just about as easy to use (for a guy with a wee bit of electronics skill) and
> just _have_ to be more repeatable, long term.
>
> Last ones I bought were
>
> Omron EE-SX4009-P1
>
> cheap, easy to mount.
>
> While perhaps not as reliable as a good-ole mechanical switch, should they
> fail, they are more likely to fail entirely, causing a limit switch to
> activate. This is, to my mind, preferable to a slow drift in Home position
> that a mechanical switch _might_ be prone to.
<snip>

I also use a slotted optical switch for home, and for the same reasons as above. I measured the repeatability of this arrangement once, over about 20 "homes", and it was < .001", more like 1/2 a thou. I did notice that the slew rate into the home switch affected the repeatability. These measurements were taken while running EMC with the default slew rate (can't remember the speed right now). I'm sure a lot of factors affect this repeatability, but I wanted to throw out a measured repeatability for at least one system.

As far as using a home switch or not, I found it was more convenient to have it when running EMC. Without a switch, the system can be made to go into "home" wherever the home button is pushed. While that's OK sometimes, it plays havoc with the max/min travel and max/min command settings in the .ini file. Since "homeing" zeros the position counter at the spot you push the button, there's no telling how far the real max and min travel are from this "zero". It's easy to command into a limit that way.

My two cents worth also...
Irby