2015-11-09 20:16 GMT+02:00 Jon Elson <el...@pico-systems.com>: > On 11/09/2015 02:34 AM, Andrew wrote: > >> there were hydraulic milling machines sold based on Moog hydraulics > >> and Bridgeport iron. I assume those two companies could screw things > >> up, but the world has moved on. To move a long distance takes a lot > >> of power. Small movements with a lot of force behind them are really > >> easy, that's why you see fatigue machines and other shorter stroke > >> machines with hydraulic servo. > >> > >> AFAIK the problem of hydraulic actuators is low efficiency. There should > > be a high pressure high rate pump to provide high velocity and force. But > > when the actuator doesn't move it all goes via baypass just heating the > > fluid. Probably adjustable pump could help but it gets more complicated > > (just a guess). > > > Yes, some systems had fixed displacement pumps and > regulating valves, others had variable-displacement pumps. > Then, you have to provide cooling for the variable > displacement pumps so it doesn't overheat when the machine > is idling. In either case, the drive motor has to be quite > huge, so there is plenty of energy wasted, and they make a > HUGE amount of noise. So much that sound barriers have to > be placed around the hydraulic power pack. > > Talking about hydraulics and CNC... There's an old (~40 years) CNC lathe in our lab https://www.dropbox.com/s/9cxnv0luduo11uf/SAM_2154.JPG?dl=0 It has hydraulic boosters (amplifying valves) for the ballscrews https://www.dropbox.com/s/nnkle9elu8lh90p/SAM_2157.JPG?dl=0 A low-torque stepper motor rotates the valve, then the hydraulics rotates the ballscrew. There's a pretty large hydraulic power unit behind https://www.dropbox.com/s/bqajpxwd8xs4dd7/SAM_2219.JPG?dl=0 It has 7.5KW motor https://www.dropbox.com/s/8ypf3d3yryb3dcq/SAM_2151.JPG?dl=0 We turned the lathe on some time ago, the noise was very bad. Its spindle gearbox with electromagnetic couplings also makes a lot of noise at high speed. The whole CNC with hydraulics was very unreliable, so these lathes had not worked for a long time back then.
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