Re: [CAD_CAM_EDM_DRO] CNCing a big surface grinder ?

So do you think that it would be feasible to replace the hydraulic drive
system with a high speed servo system ? This is quite interesting
because most of these units even today are hydraulic drive...

On Fri, 2003-11-07 at 11:27, Jon Elson wrote:
> Ejay Hire wrote:
>
> >Alternately, what's the feasibility of spending a few bucks on
> >electrical hydraulic valves? You'd still need some form of encoder for
> >positional feedback, but no need to tear into the treadmills.
> >
> >
> Ugh! A bad choice. Back in the relatively early days of CNC, many
> machines were made with hydraulic motors for brute force, and
> proportional servo valves as the amplifiers. This required a hydraulic
> pump running into a pressure relief valve, so that the system drew
> maximum electrical power all the time, and dissipated the heat from
> the fluid in big coolers. (Why they didn't use variable-displacement
> pumps, I don't know.) The noise, power consumption and maintenance
> headaches were huge, and as soon as power electronics got to the point
> that large electric motors could be controlled with electronic servo
> amps, all these machines were retrofitted or scrapped.
>
> If you want a "project" to keep you busy for the rest of your life, go
> ahead and do it this way. But, you'll be sorry!
>
> First, good Moog proportional servo valves will run somewhere
> around $5000 each. Used and repairable ones have a core charge
> of something like $1000! Then, there are all sorts of hairy problems
> when using some tyoe of servo driver to operate a servo valve-controlled
> load. there are dynamic effects like fluid compressibility (actually,
> I think it is the hoses that bulge) and sticktion in the servo valve
> spool that really confound servo amps that expect linear performance
> like an electric motor. The sticktion is dealt with by adding electronic
> dither to keep the spool floating on oil. But, this wears out the valve
> faster. The dynamic effects are dealt with mostly by lowering gain and
> bandwidth a great deal.
>
> Jon
>
>
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