The following is from EE Times, CMP Publications. It reminds me very
much of Tim Cranmer's talk at the technology conference.
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"Microbots" aid shift to 3-D fabrication
By Sunny Baines
LAUSANNE, Switzerland -- Microlithography has been successfully
adapted to building a variety of micromechanical systems, from airbag
sensors to micromirror imaging chips. Nevertheless, some researchers
are growing impatient with the limitations of lithography's inherently
planar nature.
Moving in new directions in microfabrication, beyond the layered
structures and limited materials of lithography-based batch
processing, many scientists are looking to "microbots"--small robots
that can operate with micron or better precision--to do the
construction work.
A process that can make mechanical, optical and electronic parts
separately and then put them together after fabrication will be
essential for truly three-dimensional microrobotic systems. Several
groups of researchers--including teams at the University of Tokyo,
Carnegie-Mellon University in Pittsburgh and the Swiss Federal
Institute of Technology, here--are looking into the problems
associated with this emerging technology.
Assembling truly microscopic systems on microfabrication lines will
push basic robotic functions--sensing, actuation and control--to their
limits. In sensing, for example, conventional optical machine-vision
techniques are not good enough for microassembly tasks that require
nanometer precision, because the wavelength of light only allows
resolution to about 1 micron. Likewise, traditional robots are simply
too clumsy to make precise movements at nanometer scales. The actuator
backlash--the slight oscillation caused by inertia when a robot arm
stops moving--alone is enough to destroy a delicate micropart.
On top of that, the mechanics of picking and placing components is
completely different at microscales. Overcoming the force of gravity
becomes irrelevant compared with dealing with the Van der Waals forces
between microscopic particles and such other physical effects as
humidity.
Another barrier to building fully integrated micromachines is
economic, said Jean-Marc Breguet, a senior researcher at the Institute
of Micro Engineering, part of the Swiss Federal Institute of
Technology (EPFL) in Lausanne. "We must consider two different market
segments," he said: "mass production and small to medium production."
In mass production, "large investments are acceptable for production
lines, such as in the IC industry," Breguet said. In small to medium
production environments, "a pragmatic approach is required."
"Pragmatic" here means a small, relatively cheap system that's
flexible enough to be operated by non-specialists. One way of keeping
things flexible and cheap is to cut out one of the three major
problems in building an assembly system: control. That's the tack
being taken by scientists at the University of Tokyo's Research Center
for Advanced Science and Technology (RCAST) in a system that's
operated by telecommunications.
Having a human operator gives researchers one big advantage: It allows
them to concentrate on sensing and actuation rather than on
programming the robot to do specific tasks. On the other hand, the
person using the system must be able to see what he or she is doing,
one way or another.
For vision, therefore, the Japanese system uses two microscopes, one
optical and the other a scanning electron microscope. Although the
electron scope requires that the setup be confined to a vacuum
chamber, it has the advantage of supplying resolution--almost down to
nanometer dimensions--when required. For its part, the optical
microscope is needed to orient the user to the work space: Searching
an area as small as a square centimeter can take a long time when
using a window only a few microns wide.
Depth perception becomes another issue. In order to allow the user to
understand the space in three dimensions, the work area can be rotated
with respect to the microscopes. Showing different angles lets the
operator pick up parallax information that the eye requires to make
sense of a 3-D scene.
To increase the realistic feel of macroscopic objects, the human
controller uses a pencil with force feedback to move objects.
Supplying the nervous system with scaled-up force information has
proven vital for dealing with such tiny, delicate objects. As in
everyday situations, touch is able to fill in when vision is not quite
adequate. Thus, even if the operator cannot see precisely, it is still
possible to make contact with the part or determine if the force is
too great.
This level of interaction is particularly important given the kind of
applications the RCAST team aims to tackle. Tomomasa Sato, the senior
researcher in the group, calls microassembly techniques "indispensable
for realizing real, functional three-dimensional microsystems."
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-- Lloyd Rasmussen
Senior Staff Engineer, Engineering Section
National Library Service for the Blind and Physically Handicapped
Library of Congress 202-707-0535
(work) lras@loc.gov www.loc.gov/nls/
(home) lras@sprynet.com
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