Re: Ball-bar

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. :-)

Thanks.

--
Hugh Currin
Klamath Falls, OR