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

Folks!
May me this is the way to do it!
There is a thing, called mechanical amplifier - developed in Russia
in seventies.
This is nothing else but a worm reducer. This is how it works -
you apply a large moment to a worm gear shaft, however it wont turn
until you rotate a worm, which requiree a very small effort. So small
movement of the worm
will allow a huge moment to be transmitted through the worm gear shaft.
Now , in our case, the worm can be turned by a small stepping motor, which
are cheap and have all the software and interfaces. Hydraulic motor can
be coupled to the shaft of the worm gear. This way small stepping motor can
control a large moments generated by the hydro.
Regards, Alex Likhterman

----- Original Message -----
From: Jon Elson <elson@...>
To: <CAD_CAM_EDM_DRO@yahoogroups.com>
Sent: Wednesday, November 06, 2002 12:21 PM
Subject: Re: [CAD_CAM_EDM_DRO] Re: replacing feed screw with a hydraulic
cylinder


>
>
> Van Der Sandt Coert wrote:
>
> >What if you had one big pump to keep up the pressure and some kind of a
> >rotary valve on each axis that just lets a metered amount of fluid
through
> >every time its activated.
> >
> >Alternatively you could have a pump on every axis and calculate the pump
> >speed so that every axis reaches its goal at the same time.
> >
> >
> And, what is going to drive those pumps? Electric motors? Clutches?
> How can this be better
> than just driving the machine directly with the motor? If you are going
> to hook a servo motor
> to a reversible hydraulic pump, then drive the table with a cylinder,
> that has to be the
> Rube Goldberg method of replacing a leadscrew!
>
> Just as a reference point, hydraulic systems, especially hydraulic
> motors driving a leadscrew,
> was a VERY common system on larger CNC machines, in the 1970s. I
> believe it was the
> most common axis drive system on the larger ones, in fact. Direct
> electric drive cam in
> VERY quickly after larger power transistors became available. The
> makers of big machines
> never looked back, and you'll be VERY hard pressed to find any larger
> CNC machine with
> hydraulic drive today. The only machines still using hydraulic drive
> that I can think of are
> surface grinders, where they just have a steady back and forth feed
> between limit switches.
>
> The buyers of these machines must have a REAL good reason for making
> this choice.
> The reason, of course, is they had HORRIBLE experiences with the high
> maintenance
> costs of hydraulic systems! Another side light, the commercial aircraft
> industry is trying
> to desing their way away from hydraulics, for the same reason - high,
> VERY high, maintenace
> costs.
>
> Jon
>
>
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