Denis G. wrote:
Sometime recently I read about someone who acquired an older milling
machine that had hydraulic feed on the table. I wondered about how
these tables might be controlled and if any lathes have been designed
using hydraulics to move the carriage or crossfeed instead of lead or
feedscrews. (After all, there are mechanical, hydraulic and pneumatic
linear actuators.)
I don't know if you could control hydraulics as precisely as
feedscrews (with respect to headstock spindle rotation) for cutting
threads, but you'd never have to worry about worn screws and metric/
inch conversions. I imagine that the big problem is in designing the
feedback system and getting it to respond well.
I've seen descriptions of hydraulic systems made by companies like
Enerpac that control the balancing of bridge sections to keep them
level while being positioned with cranes. I know that hydraulics can
be controlled with electronics and proportional or servo valves.
Probably it's difficult to beat mechanical feed and leadscrews because
it's a simple and accurate system, but I was just curious.
I don't think that a hydraulic system could retain anything approaching
the rigidity that you get from lead screws, so I don't see it as being a
good candidate. I think you'd get such a springy feed that you'd be
constantly bouncing off of hard cuts, then digging in too far when the
cuts got light.
Notice that the cited examples (the mentioned tracer machines, the film
of the metal spinning, old old mill with hydraulic feed) were all things
where some fixture provided the rigidity, or where the precision of the
feed wasn't critical.
I'll believe it if I see it, and you can pay me my going rate to do a
feasibility study if you want, but it's not something that I'd recommend
off the cuff.
--
Tim Wescott
Wescott Design Services
http://www.wescottdesign.com
Do you need to implement control loops in software?
"Applied Control Theory for Embedded Systems" gives you just what it says.
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