Re: [CAD_CAM_EDM_DRO] Re: Ball-bar

Hugh Currin wrote:

> Jon:
>
> On Wednesday 09 January 2002 11:34 pm, you wrote:
> >
> > Yes, presumably, you could do without the shaft encoder, but since the
> > Renishaw ballbars are portable instruments moved from machine to
> > machine, they need to be self-contained. They may use LVDTs, I really
> > don't know. Strain gauges would measure force, the idea is to measure
> > displacement.
> >
> Strain gages measure strain which is a displacement. Jon is right that their
> main use is in determining stress and force though. They will work in
> instruments used to measure displacement and the signal conditioning is less
> complicated than an LVDT. Without some "mechanical amplification" (like a
> cantelever beam) the displacements that can be measured are miniscule though.
> If the variations in the ballbar were a few throusands some scheme using
> strain gages might work well. I suspect though that commercial versions use
> LVDTs but I've never seen one. If anyone has one laying around you can send
> it to me so I may study/use/keep it. :-)

LVDT's are fairly simple to use, but to keep things digital, I thought I could
take a dial indicator (of the tenths-reading kind) and replace the pointer with
a
small encoder disc, and have digital readout to 10 uIn or so. Then, I just
have to read 2 encoders and store the results for later plotting or numerical
analysis.

Jon