IEEE Robotics & Automation Magazine - September 2013 - 32

Table 3. Test results.
Data

Model

Real Device

Output power (W)

12.2

12.5

Efﬁciency (%)

18

+16

Current (A)

1.3

1.4

Voltage (V)

9

9.5

Resistor ( X )

6.4

6.5

Capacitor ( n F)

-

67

Phase correction (°)

-

+151

Dimensions (mm)

Q52 # 68

Q52 # 68

Metal core diameter (mm)

Q1.3

Q1.3

Turns

530

+530

are strictly related to the low efﬁciency of the device compared
with the traditional transformers that can achieve a very high
efﬁciency up to 95%. The air/water gap, the low working frequency, and the manufacturing process reduce the efﬁciency
to 16%. This value is acceptable for our application in which
external power is not an issue. Furthermore, the concept and
the design are still valid, although applications would require
higher performance and efﬁciency.
Another important feature is the hollow shape of the
secondary core section. Using this design, electronics can
be placed into the secondary coil magnetic core, thus limiting any wasted space. This design also reduces the weight,
which is an important parameter in underwater applications when a neutral trim is required.
The secondary coil ﬁnal mass is 200 g. Considering the
total length (and volume) of the artifact, this low weight
enables the buoyancy of the robot to be designed, thus not
having to take into account the weight of the secondary coil.
Finally, the expected self-docking feature has been
observed. The secondary coil is attracted into the primary
coil with a delicate force of about 0.5 N. This function is not
mandatory for our application, where we have locomotion
capability; however, it is still useful as additional self-guidance while docking.
Conclusion
We have successfully developed a low-weight system for battery charging by proposing a new design for wireless power
transfer devices. Our design is useful in situations when
there are constraints regarding: small dimensions, a cylindrically shaped robot, low weight, and high electrical insulation.
Another advantage is that only one primary coil is needed to
charge different robots equipped with individual secondary
coils. Robot docking is critical and our device provides a neat
solution with self-guidance. All these features highlight that
our device would work well in AUV applications.
During the tests, the device did not cause any damage to
the electronics when the magnetic ﬁeld was applied. The
device will be shortly integrated into the whole system.

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september 2013

Acknowledgment
This work is primarily being carried out under the European Project LAMPETRA (Life-like Artifacts for MotorPostural Experiments and Development of new Control
Technologies inspired by Rapid Animal locomotion) Project Reference: 216100 through the Seventh Frame Program
research area: ICT-2007.8.3-FET "Bio-ICT Convergence." It
also comes under the European Project ANGELS (ANGuilliform robot with ELectric Sense) Project Reference:
231845 through the Seventh Frame Program, research area:
ICT-2007.8.5-FET "Embodied intelligence."
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Tareq Assaf, Scuola Superiore Sant'Anna, Pontedera 56025,
Italy. E-mail: t.assaf@sssup.it.
Cesare Stefanini, Scuola Superiore Sant'Anna, Pontedera
56025, Italy. E-mail: c.stefanini@sssup.it.
Paolo Dario, Scuola Superiore Sant'Anna, Pontedera 56025,
Italy. E-mail: paolo.dario@sssup.it.
http://www.ncbi.nlm.nih http://adb.sagepub.com/
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