Re: [CAD_CAM_EDM_DRO] Converting Hydrolic copy Milling Machine

You can get a servo valve combination that will take +/-10 volt dc
directly. If you look at what it would cost to replace the hydrolic' with
servo motors it is probably even money.


Harko

On 2/20/06, Jon Elson <elson@...> wrote:
>
> Harko Schwartz wrote:
>
> >I think it is a worthwhile thing to convert. You need to have position
> >feedback which can be done with a tape scale and you can get hydrolic
> servo
> >valves that can control the motion.
> >
> have you priced proportional hydraulic valves? They are REALLY expensive,
> like thousands of $ each!
>
> > You will need to have a CNC that is
> >capable of doing Analog out like the Machinemate CNC.
> >
> >
> It gets much more complicated than that. You need a valve driver that
> adds dither to the output. at several hundred Hz, to keep the valve spools
> floating on a cushion of oil. if you just drive the valve with the plain
> PID output, the stiction of the servo valve will cause the machine to
> have terrible servo hunting problems. It is possible that at a 1 KHz
> update rate, the dither could be added in software, at either 333 or 500
> Hz. But, you still need the servo valve, and a valve driver amplifier.
>
> Jon
>
>
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