Re: [CAD_CAM_EDM_DRO] Easson DRO with cnc?

Hi Jon & Fortino, thanks for the replies. Fortino, I already have the
scales fitted so no more expense there, and Jon, you make a very good point
about the backlash and "hunting", I hadn't thought about that. I guess I
will have to keep twirling the handles for a while longer yet!

At 2010-01-01 17:32, you wrote:

>
>
>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
>
>
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Cheers, Ken
vk7krj@...
www.vk7krj.com

'It seems hard to sneak a look at God's cards. But that He plays dice and uses
"telepathic" methods .... is something that I cannot believe for a single
moment.' (Einstein's famous quote on Quantum theory)


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