IEEE Robotics & Automation Magazine - June 2013 - 67

made of four distinctive layers. This avoided contamination
magnetic gradients
of dust particles and also allowed quick arena interchange.
above the friction
In 2010, the Nanogram
We noticed that our setup was mostly miniaturized and
threshold, the microroprovided with embedded electronics.
bot can move slowly
Robocup Competition was
Some opposite corners in the arena layers were cut in a
(without electric field),
manner that allowed electrical access to the electrodes
but addition of the elecrenamed as NIST IEEE
[Figure 5(b)]. The layers are as follows:
tric field pulses signifi● A top conductive ITO glass acting as a transparent top
cantly improves speed
Mobile Microrobotics
electrode (high voltage) is bonded to a conductive wire.
as the microrobot loses
● An intermediate glass layer of 155 n m plays the role of a
contact with the base
Challenge and was held in
dielectric isolation that was cut annularly by an ultrasound
surface [see Figure
machine.
4(b)]. This operating
Anchorage, Alaska, during
● An intermediate silicon layer of 110 n m that was micromode provides very
fabricated at both the sides using a clean room process:
high speeds (see the
the IEEE International
Gold and aluminum sputtering, photolithography, and
"Actuation Results" secdeep reactive ion etching (DRIE) techniques. This layer
tion), and was used durConference of Robotics
insured the border walls and the marks of the virtual starting the challenge for the
ing and finish lines.
2-mm dash. The French
and Automation.
● A bottom silicon piece cut from a wafer whose surface was
team won the event
metalized by Cr-Al sputtering. This layer played as the
with an RMS score of 32
ground electrode.
ms and a record of 28 ms.
The internal height of the arena was 255 n m, fairly supe- ● Short impulse driving, when the magnetic force is kept well
rior to the one of the agent (224 n m). The microrobot tracbelow the friction threshold. In this case, small amounts of
tion was performed using a mix of one high-voltage signal
actuation (leaps) are provided for each piezoelectric
and four high-current signals. A series of
high-voltage square pulses (300 V, 400
Hz) provided out-of-plane piezoelectric
strain, while the nickel mass acted inerBtial, making the robot to perform
Field
E-Field
micrometer-range jumps by losing the
adhesion contact with the arena surface.
Simultaneously, the external magnetic
field gradients (between 3 and 30 mT/
Ni-Layer
mm) issued by four orthogonal coils
Ferroelectric
PMN-PT
with iron core insured the attractive
Plezoelectric
translation force and steering. Quick
(a)
breaking could be performed by stopping the electrostatic field impulses and
E-Field Off
E-Field On
B-Field Off
by reversing the magnetic field gradient.
State of Rest
B-Field On
There are two possible operating
Electrodes
strategies:
● Continuous driving, where the magnetic
force is higher, equal, or slightly lower
B-Field
Ferro
than the friction threshold (maximum
Piezoelectric
friction value). The threshold usually
Oscillations
Piezo
corresponds to a gradient from 0.2 to
5 mT/mm depending on the surface
Electrodes
state and humidity. Upon time constant
signals, the resulting actuation is mono(b)
tonically accelerated. Piezoelectric effect
serves to improve the sliding conditions.
Figure 4. (a) An SEM image of a Type II agent combined with a schematic of magnetic
For instance, if we apply a magnetic gra- and electrostatic field directions. The microrobot is 388 # 300 # 224 n m3. (b) The
dient just slightly under the friction mechanism of locomotion: electric field is generated between both the electrodes of top
threshold, the microrobot will not start and bottom surfaces to generate strain in the PMN-PT layer, vertical oscillations can reduce
the adhesion force between the surface and microrobots, the microrobots can move along
moving until the electric field impulses the magnetic field gradient, and, finally, the electric field is cut when the microrobot is
trigger displacement. In the case of reached to the target position (drawing not to scale).
june 2013

IEEE ROBOTICS & AUTOMATION MAGAZINE

Table of Contents for the Digital Edition of IEEE Robotics & Automation Magazine - June 2013