Re: [CAD_CAM_EDM_DRO] replacing feed screw with a hydraulic cylinder

Bill Vance wrote:

>>From the accuracy/resolution standpoint, what about slapping an encoder and
>ballscrew/acme thread/timing chain onto a hydraulic motor, and as a way to
>ditch some of the more complicated servo power supply/amplifier/control issues?
>looks do-able, at least at first glance.
>
>

Many of the really big machines from 20 years ago did this.
Kearney&Trecker, Cincinnatti, etc.
But, you still need the exact same hydraulic power source and the
expensive proportional servo
valves. My Allen-Bradley 7320 CNC was commonly used with
hydraulically-operated machines,
and most used hydraulic motors, not cylinders. They had a special
version of the DAC card to
feed velocity commands to the Moog valves. It had the small linear amp
required, and added
400 Hz dither to the output to keep the spools in the valve floating.

The real killer is that even fairly small machines, like a Series-II
Bridgeport, needed something
like a 15 Hp hydraulic pump, and if it used a constant-displacement
pump, it drew 15 HP all day!
Even with the more expensive variable-displacement pumps, it would draw
several Hp when
idling.

Jon