A kinetic coefficient of friction is always lower than the
static one. This difference may be utilized to provide motion of one
bearing mounted (rotating or sliding) component in relation to a moving prawl which pushes when moved slowly (in static mode) or slips
when pulled rapidly (in kinetic mode). The resulting motion can be
made fine in resolution, down to some tens of nanometers per stroke, at
the contact surface. The motion can be realized in either direction
by reversing the direction of the high speed vs. the low speed
stroke. The motion, although finely resolved, is not true
"step" motion, and is only repeatable in a stochastic sense.
This type of prime mover offers much in cryogenic applications, where
greases and oils freeze. Bearing surfaces of engineering plastics
such as Vespel (TM) perform well in this application, and are wholly
suitable for the friction prawl on this type of drive.
The Inventors and Developers
Concept & Design: Robert
Chave & Chris Lindensmith Motor Development: Jason Graetz, JPL / Caltech
HTSC Coil Development John Voccio, America Superconductor
NASA Tech Brief & New Technology Award
NASA New Technology Award, NPO-20275: "Filter Wheel for Use
at Cryogenic Temperatures from 4 K to 77 K and at Room Temperature with
High Resolution and Simple, Low-heat Load, Magnetostrictive Actuation
Systems with Polycrystalline Actuator." 1998
Patent Claims
United States Patent entitled " Magnetostrictive Actuation",
Serial Number 09/183,387, R. Chave, C. Lindensmith, J. Dooley, B. Fultz,
and M. Birsan, Application filed, Oct. 29, 1998 claiming the benefit of
U.S. Provisional Application No. 60/063, 991, filed Oct. 29, 1997
The photo above shows a rotary motor running at
the
bottom of a dewar of liquid helium. The cylinder is an
Etrema Corporation linear actuator casing designed for
room temperature use, employing low temperature TbDy
actuator materials. The small disk in the center is the
driven component.