On 23 May 2005 02:14:45 -0700, wrote:

I like JohnM's suggestion. A piezo crystal mounted at every station
near the end of a rod could provide just the right amount, about a
tenth of a degree, of *rotation* (perpendicular to way travel), to
break stiction once per travel clockwise and counterclockwise. Not
quite as perfect as a rotating rod, but sooo much simpler. I think to
move the rod axially would just introduce random errors into way
travel.

Whadda say, is this one patentable? You could sell premade shafting
with piezo ends, in modular lengths. You would lose the infinite
flexibility in design of having yard long shafting that can be cut to
any length, but gain in the fight for smoothness. A simple controller
could be patched to every rod. A controller with capacity for sixteen
rods would be cover pretty much any machine tool situation. Various
other drives are possible, such as an electromagnetic rod end that
merely needs to be hooked to 110 VAC.

Interesting idea.

You wouldn't need to lose the flexibility of yard long shafting cut to
length. Just make rotational dither mounts that accept stock
shafting.

Giant magnetrostrictive devices (as Terfenol D) might work better
than piezo here because they exhibit greater strain, hence more motion
per unit length. However, there are more sources for piezoceramic
materials and structures than for giant magnetostrictive materials.

Google searches on "magnetostrictive" and "piezoceramic" will find
lots of material for you.

Piezo and/or magnetostriction aren't the only possible approaches
here. One might also devise a structure that is constrained against
displacement while compliant rotationally, actuated by an alternating
magnetic field. It could be a variable reluctance structure or one
with a permanent magnet. Resonance could be used to magnify rotation.
The SoniCare toothbrush uses these principles: two supermagnets, a
coil actuated by AC, and a resonant beam.