Re: [CAD_CAM_EDM_DRO] encoder help

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