Re: [CAD_CAM_EDM_DRO] Re: Prox switches

If you use a hall-effct sensor, you have a lot of say over both the sensing
distance and the length over which the switch stays 'tripped' (so it the
switch won't reverse in the time it takes your axis to stop). You just have
to choose the appropriate sensor and magnet.strength. You will also probably
end up with something quite insensitive to the random metal chips flying in
the proximity of the sensor, which is a plus. Of course, depending on your
setup and the kind of material you work with, you may end up having small
ferric shavings sticking to the magnet. If this is your home switch, this is
definitely a minus. But if this is your limit switch, then this is probably
OK - the switch will still trip. It just may do so a fraction of a
millimeter sooner than when it's clean.

In my setup I ended up using a fairly insensitive hall-effect sensor and a
very strong small magnet that moves parallel to the face of the sensor (so,
in effect, the pole of the magnet is perpendicular to the surface of the
sensor when the magnet is directly above it). The sensor 'trips' reliably
(probably <.1 mm repeatability, though I have not actually measured it)
about 4 mm away from the magnet, and stays 'tripped' until the magnet moves
4mm past the sensor for a total of about 15 mm of travel. It's a bit
cumbersome to setup because this is not some prepackaged ready-to-install
solution, but it works.

Vlad

On 3/4/06, Paul Kelly <tech@...> wrote:
>
>
> > That is definitely true. For some reason when you approach
> > most proximity sensors "head on" the point at which they
> > "trip" isn't always exactly the same.
>
> Interesting, its <1 step in my set up. I'm looking forward to testing the
> other orientation.
> I have to change to that setup because my motors can't decelerate the axis
> in the sensing distance (2mm)
> Not much point in a limit switch that can't stop a crash.
>
> PK
> >
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> If you wish to post on unlimited OT subjects goto:
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> if you have trouble.
> http://www.metalworking.com/news_servers.html
>
> http://groups.yahoo.com/group/jobshophomeshop I consider this to be a
> sister site to the CCED group, as many of the same members are there, for OT
> subjects, that are not allowed on the CCED list.
>
> NOTICE: ALL POSTINGS TO THIS GROUP BECOME PUBLIC DOMAIN BY POSTING
> THEM. DON'T POST IF YOU CAN NOT ACCEPT THIS.....NO EXCEPTIONS........
> bill
> List Mom
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--
Vlad's shop
http://www.krupin.net/serendipity/index.php?/categories/2-metalworking


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