Re: Re: X-Y Table, Rotary Table for CNC INFO

Ballendo

The z motion compared to the rotation of the screw is really riding along
an arc or a cam. The leadscrew comp produces a linear compensation
between points. This should be okay for most of the arc but like you say
it would be big as you approached the top.

Till Franitza built a little hexapod using a a crank shaft and connecting
rod to get linear motion. This would be very similar to the motion of
the scissor table. If we get serious about this, I can see if we can get
him to explain it to us.

Ray

On Saturday 18 January 2003 04:56 am, Ballendo wrote:
> Message: 2
>    Date: Sat, 18 Jan 2003 04:18:32 -0000
>    From: "ballendo <ballendo@...>" <ballendo@...>
> Subject: Re: X-Y Table, Rotary Table for CNC INFO
>
> Ray,
>
> Good point.
> But it would be repeatable, and therefore possible to correct in
> software. Possibly even with EMC's leadscrew correction, though the
> error is "squished at one end" of the travel.
>
> Ballendo
>
> --- In CAD_CAM_EDM_DRO@yahoogroups.com, Ray Henry <rehenry@u...>
>
> wrote:
> > 
> > >    From: "ballendo <ballendo@y...>" <ballendo@y...>
> > > Subject: Re: X-Y Table, Rotary Table for CNC INFO
> > <s>
> > > Think scissor lift table. A couple of accurately placed pivots;
>
> ONE
>
> > > screw, lots of force. Problem: Stability in the direction perp. to
> > > the scissor. Fix that with a vertical guidepost (or two. Note that
> > > these DON'T need to be heavy duty linear motion component quality;
> > > they are just keeping the structure stable in one axis(resisting
>
> only
>
> > > side loads).
> > 
> > With a scissor you will need to be a bit careful where you place
>
> the
>
> > screw.  The usual place is in the middle between pivot arms and
> > perpendicular to the motion.  Many car jacks are made this way.  
>
> With
>
> > something like this, z motion would NOT be linearly related to
>
> rotation
>
> > of the screw.
> > 
> > Ray