Biomedical Engineering Reference
In-Depth Information
The high power density of piezoelectric actu-
ators (around 400 W/kg) compared to insect
muscle (around 80 W/kg)
[10]
has motivated the
development of piezoelectrically actuated flap-
ping-wing mechanisms. Wood
[10]
developed a
robotic insect with a wingspan of 3 cm and a
mass of 60 mg. This insect was powered by pie-
zoceramic bimorph actuators and had wings
with 1.5
μ
m polyester membranes. The body of
the insect, constructed from a laser-microma-
chined sandwich of carbon fiber and polymer,
featured a flapping mechanism similar to that of
an insect thorax. The robotic insect was powered
from an external source and demonstrated a
thrust greater than its weight.
The Micromechanical Flying Insect (MFI)
[53]
is another piezoelectrically actuated robotic insect
with a body constructed from sandwiched com-
posites and flexure hinges. The wingspan is 25 mm
and the wing-flapping frequency is 275 Hz. Efforts
are underway to increase the lift produced by this
mechanism.
Cox
et al
.
[54]
developed several versions of
a piezoelectrically driven flapping-wing mecha-
nism based on four-bar and five-bar linkages.
These had wingspans on the order of 15 cm and
total mass around 7 g. Mechanisms based on
piezoelectric actuators typically operate at reso-
nance to obtain the largest amplitude of flap-
ping. Although they have demonstrated good
benchtop performance, the size of the power
supply required for the piezoelectric actuators
can be considerable, and no microflyer powered
by piezoelectric actuators has achieved free
flight to date.
FIGURE 5.11
Nano hummingbird prototype, with fuse-
lage cut away to show enclosed electronics
[51]
. By kind
permission of M. Keennon.
5.5.3 Samara Type Microflyers
The term
samara
is a generic term for a winged
seed. The seeds of many plants are dispersed
by means of autorotation in wind, and there
are several microflyers that have been inspired
by this concept. The basic idea is to combine
the simplicity of an autorotating samara with a
source of thrust to sustain rotation, thus creating
FIGURE 5.12
DelFly Micro prototype
[52]
. The wing
span is 10 cm and total mass is 3.07 g. Credits: G. C. H. E. de
Croon, K. M. E. de Clerq, R. Ruijsink, B. Remes, and C. de
Wagter. Design, Aerodynamics, and Vision-Based Control of
the Delfly. International Journal of Micro Air Vehicles,
1(2):71-97, 2009.
