Micro Selfassembly with Electrostatic Force Fields
Massively Parallel Assembly of Microparts (1996-1998)
Karl F. Böhringer, Michael Cohn, Ken Goldberg, Roger Howe, Al Pisano
Assembly is a fundamental issue in the volume production of products
that include microscopic (submillimeter) parts. These parts are often
fabricated in parallel at high density but must then be assembled into
patterns with lower spatial density. In this paper we propose a new approach
to microassembly using
(1) ultrasonic vibration to eliminate friction and adhesion, and
(2) electrostatic forces to position and align parts in parallel.
We perform experiments on the dynamic and frictional properties of collections
of microscopic parts under these conditions. We first demonstrate that
ultrasonic vibration can be used to overcome adhesive forces; we also
compare part behavior in air and vacuum. Next, we demonstrate that parts
can be positioned and aligned using a combination of vibration and electrostatic
forces. Finally, we demonstrate part sorting by size.
Tribological Experiments: Small particles (sides approximately
0.2 - 0.5 mm) were dropped onto a flat gold-covered silicon substrate,
which was attached to a piezoelectric transducer. When no signal is applied
to the piezo, the particles tend to stick to the substrate and to each
other due static charges, capillary or Van der Waals forces. After applying
sinusoidal voltages, the particles break contact and exhibit random "Brownian
motion" patterns if the surface is carefully leveled. Tilting of the substrate
surface by less than 0.2 percent is sufficient to make the particles move
in a particular direction. This implies that friction is negligible.
|Figure 1: Experimental setup. Piezoelectric
shaker table and Cr-Au substrate. Small surface-mount microparts can
be seen in the front left quadrant of the substrate.
|Figure 2: Parallel microassembly
with electrostatic force fields: Surface-mount capacitors are placed
onto a glass substrate with a 100 nm thin patterned Cr-Au electrode.
Frictional and adhesive forces are overcome by ultrasonic vibration.
||Figure 3: Voltage applied to the
electrode creates an electrostatic field. The parts are attracted
to the apertures in the electrode (dark squares) and are trapped there.
Electrostatic Selfassembly: The substrate from Figure 1 was replaced
by a dielectric plate with a continuous lower electrode and a lithographically
patterned upper electrode which contains one or more small apertures (0.5
mm width). This electrode design results in fringing fields which polarize
neutral particles, so that they are attracted to the apertures and get
trapped there. Once a particle is trapped, it reduces the fringing field,
which prevents attraction of more particles to this location.
- K. F. Böhringer, Ronald S. Fearing, Ken Y. Goldberg, "Microassembly."
In Shimon Nof, editor, The Handbook of Industrial Robotics (2nd edition),
pp. 1045-1066, John Wiley & Sons, February 1999. Paper.
- M. B. Cohn, K. F. Böhringer, J. M. Novorolski, A. Singh, C. G.
Keller, K. Y. Goldberg, R. T. Howe, "Microassembly Technologies for
MEMS." SPIE Micromachining and Microfabrication, Conference on Micromachining
and Microfabrication Process Technology IV, pp. 2-16, Santa Clara,
CA, September 21-22, 1998 (invited
paper / keynote address).
- K. F. Böhringer, K. Goldberg, M. Cohn, R. Howe, and A. Pisano,
"Parallel Microassembly Using Electrostatic Force Fields." IEEE International
Conference on Robotics and Automation (ICRA), p. 1204-1211, Leuven,
Belgium, May 16-20, 1998. Paper.
A complete list of our publications
(many of them available online) can be found here.
- NSF CDA-9726389, IRI-9553197, IRI9157051), IRI- 9531837
- NSF CISE Postdoctoral Associateship in Experimental Computer Science
to Karl F. Böhringer CDA- 9705022
© Karl F. Böhringer, Department of Electrical Engineering, Box
352500, Seattle, WA 98195-2500, USA