Re: Z axis drive

--- In CAD_CAM_EDM_DRO@yahoogroups.com, "skykotech" <rick@s...> wrote:

>
> > All the commercial VMCs I've worked on use hydraulic or pneumatic
> > counterbalencing on the Z axis, usually hydraulic and with the
> > cylinder in a 2:1 compound arangment with chains like on a

forklift.

> > Reduces the inertia problem since the counterballance is some

chain

> > and a piston as opposed to a giant weight.
> >
> > Pete C.
> >
>
> Hmmm, my Shizuoka B-3V bedmill does not use a counterweight for the

Z

> axis, and the z axis alone probably weighs 1000lbs. I wonder why?
>
> I think it has some clutch arrangement to prevent the z axis from
> falling when the servo is off.
>
> I wonder if adding a counterweight would be beneficial to my
> mill...hmmm....
>

Are you sure there isn't a counterballance system hidden in there
somewhere? A hydraulic counterballance setup for a modest weight like
1,000# can be pretty small and easily hidden.

Without a counterballance system of some sort, any machine with a
heavy head will cause a massive imballance in the servo load between
up and down which I would expect would hurt performance.

As someone else noted, without a counterballance the servo could end
up driving in the up direction to move the head up, and driving in
the up direction (just less force) to move the head down as the
weight of the head backdrives the ballscrew.

Pete C.