Re: encoder help

Jon
I haven't been able to check posts for a while. New baby came a
little early, but everyone is finally home! Your reply was very
helpfull. I'm still curious if the marker on the encoder is only for
home position, or is it used in positioning also?
gunmaker

--- In CAD_CAM_EDM_DRO@yahoogroups.com, Jon Elson <elson@p...> wrote:
>
>
> thefinegunmaker wrote:
>
> >I recently bought a small Milltronics Vertical CNC and am having a
> >problem homing the machine. The Z goes first then the X and Y,
When
> >the X hits the limit switch and backs off, it then travels forward
> >again looking for the marker on the encoder. Sometimes it finds
it,
> >but it usually takes 6 or 8 tries. It E stops every time it
misses,
> >and I have to start over. Does anybody know if the accuracy will
be
> >affected when I run it after it finally finds the home, could it
> >forget where it is, or is it just a problem during homing? I
talked
> >to the factory and the price of a new encoder is more than $300,
and
> >they said my old one couldn't be fixed. Are they filling me full
of
> >BS, or are the encoders really a "sealed unit"?
> >
> >
> Most encoders can be opened up with care. Some miniature ones are
quite
> difficult
> to open, like the 1" Sumtak units that have the case crimped
closed.
> Some plastic
> encoders are glued shut, and it can be tricky to open them without
> poking something
> in the wrong spot. But, even if you got it open, would you be able
to
> determine
> the problem and fix it? The index is usually made with a grating
with
> several
> irregularly spaced lines that match up with a similar pattern on
the
> disc. These
> patterns are designed so that only one line lines up at a time
until the
> patterns are in
> perfect alignment when all the lines line up at once. this
alignment
> allows enough
> light through (or blocks enough on some models) to trigger the
> photodetector.
> Very old encoders will have pots to adjust the trip point. Most
newer
> ones do not
> have any adjustments you can tinker with. You might be able to
change
> the series
> resistor on the LED light source to a slightly lower value to make
the LED
> brighter. This is most likely the problem, the LED has dimmed over
time.
>
> Anyway, if the encoder is dying, you are not going to lose much by
> trying to fix
> it. You might also be able to figure out who makes the encoder,
and buy a
> compatible unit, possibly a newer series that is a cheaper drop-in
> replacement
> directly from the manufacturer. Machine makers always charge a
hefty markup
> on spare parts.
>
> Jon