Re: [CAD_CAM_EDM_DRO] Low cost limit switch suggestions

Robert Allen & Marsha Camp wrote:

> Jon Elson wrote:
>
> > Robert Allen & Marsha Camp wrote:
> >
> > > If I already have max. travel limits do I need any thing but
> > > a home switch?
> >
> > Probably not. EMC, at least, has software limits that are referenced
> > from the home switch position. The software-sensed limit switches
> > would be pretty redundant.
>
> What happens when you home the machine, then move to some other position on
> the table and reset the axes to zero? Will the software realize that you do
> not have full x or y travel from this point? The machine I have now ain't
> that smart, I've always wondered why but it is a 1983 control.

EMC, at least, keeps track of the machine's position in several completely
different coordinate systems. One is machine position, which is set
when you home the machine. Then, there is a relative offset from that
position, which is set with the G92 command, and establishes a part
coordinate system, aligned with an egde or feature on the part to be machined.
Then, there are 10 work offset systems that can be referenced to the
relative system. These are useful if you have multiple parts located
in a fixture, for instance. Then, the same program can be run on each part.

My 1978 Allen-Bradley 7320 control had pretty much the same scheme, too.

So, professional controls have software limits that work correctly when you
set the part coordinate offset.

Jon