Re: [CAD_CAM_EDM_DRO] Easson DRO with cnc?

Ken , VK7KRJ wrote:

> Hi, I have had a 3-axis Easson dro on my mill for some time, now I am
> retired I am looking at cnc'ing it with mach3 or similar, and it would be
> nice to be able to use the easson scales for position feedback- no backlash
> and position to a tenth of a thou.
>
> Does anyone know if this is possible- what protocol do the easson scales
> use, can they be hooked up to something like mach3 or emc?
>
> It would be a pity (and a step backwards) to have the scales and not be
> able to use them with the cnc software.
>

Most likely the scales are straightforward incremental optical encoders
with digital
(TTL) outputs. But, you should probably check out the signals while
still connected
to the DRO box. If there are two signals that rapidly flicker between
approx. zero
and +4 V or so, then they should work fine with EMC2, using a suitable
encoder
counter board. Mach3 doesn't really close the servo loop itself, you'd
either need
an external servo board or Mach will just use the encoder data to detect
lost steps.

Note that any servo system where there is substantial backlash between
the motor and
the encoder will not work well at all. The problem is the encoder
detects minute
position changes and commands the motor to correct them. So, the motor
ends up
banging back and forth across the backlash, causing a lot of clattering
and quickly
making the wear worse. So, this scheme is really only good when you
have preloaded
ballscrews with minimal wear. Much over .002" backlash starts to become
a big
problem.

"Backlash compensation" is a very bad band-aid that attempts to mask the
problem,
but certainly does not solve it.

Jon