I don't see why it has be this way. Running a pump at full power past a valve sounds daft. That's why the new pressbrakes, presses and injection moulding machines use servo hydraulics.
Simply put, you have a gear pump, and both ends go to a cylinder. Turn one way, rod extends. Turn other way, rod retracts. Of course it's more complex than that, but the idea is that if there's no work to be done, the motor isn't turning. I think the idea is great in that you can have a monster motor on the floor, and small cylinders inside a machine. But I think movements in the 10's of Hz would cause too much oil heating, so better to just put a ballscrew on the motor for a CNC machine. Regards Roland On 9 November 2015 at 20:16, Jon Elson <el...@pico-systems.com> wrote: > On 11/09/2015 02:34 AM, Andrew wrote: > > 2015-11-09 8:49 GMT+02:00 Eric Keller <eekel...@psu.edu>: > > > >> 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. > > Jon > > > ------------------------------------------------------------------------------ > Presto, an open source distributed SQL query engine for big data, initially > developed by Facebook, enables you to easily query your data on Hadoop in a > more interactive manner. Teradata is also now providing full enterprise > support for Presto. Download a free open source copy now. > http://pubads.g.doubleclick.net/gampad/clk?id=250295911&iu=/4140 > _______________________________________________ > Emc-users mailing list > Emc-users@lists.sourceforge.net > https://lists.sourceforge.net/lists/listinfo/emc-users > ------------------------------------------------------------------------------ Presto, an open source distributed SQL query engine for big data, initially developed by Facebook, enables you to easily query your data on Hadoop in a more interactive manner. Teradata is also now providing full enterprise support for Presto. Download a free open source copy now. http://pubads.g.doubleclick.net/gampad/clk?id=250295911&iu=/4140 _______________________________________________ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
