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Rakotondrabe M.,CNRS Femto ST Institute | Ivan I.A.,University Valahia of Targoviste
IEEE Transactions on Automation Science and Engineering | Year: 2011

A new microgripper dedicated to micromanipulation and microassembly tasks is presented in this paper. Based on a new actuator, called thermo-piezoelectric actuator, the microgripper presents both a high range and a high positioning resolution. The principle of the microgripper is based on the combination of the thermal actuation (for the coarse positioning) and the piezoelectric actuation (for the fine positioning). In order to improve the performances of the microgripper, its actuators are modeled and a control law for both the position and the manipulation force is synthesized afterwards. A new control scheme adapted for the actuators of the hybrid thermo-piezoelectric microgripper is therefore proposed. To prove the interest of the developed microgripper and of the proposed control scheme, the control of a pick-and-release task using this microgripper is carried out. The experimental results confirm their efficiency and demonstrate that the new microgripper and the control law are well suited for micromanipulation and microassembly applications. © 2011 IEEE.

Baida F.I.,CNRS Femto ST Institute
Optics Express | Year: 2010

The control and localization of light at sub-wavelength scale are theoretically demonstrated with a very simple sub-wavelength dimension structure. This is demonstrated through a peculiar structure that can support localized modes which are not linked to any plasmon resonance. It is based on the acronym "FEMTO" that is designed using 26 sub-wavelength rectangular apertures engraved into perfectly conducting metal screen. A polarization-sensitive guided mode through these nano-apertures is at the origin of the light localization. Consequently, sub-wavelength light spots can be achieved with very simple structures illuminated by temporally shaped plane waves. Three parameters are temporally controlled for this purpose: the polarization, the wavelength and the amplitude of the incident beam. It is also demonstrated that replacing the perfect conductor by a real metal with dispersion leads to accentuate both the light confinement and its localization. These results open the path to the conception of optical nano-structures dedicated to sub-wavelength light addressing. © 2010 Optical Society of America.

Rakotondrabe M.,CNRS Femto ST Institute
Proceedings of the American Control Conference | Year: 2012

This paper presents a new approach to compensate the static hysteresis in smart material based actuators that is modeled by the Prandtl-Ishlinskii approach. The proposed approach allows a simplicity and ease of implementation. Furthermore, as soon as the direct model is identified and obtained, the compensator is directly derived. The experimental results on piezoactuators show its efficiency and prove its interest for the precise control of microactuators without the use of sensors. In particular, we experimentally show that the hysteresis of the studied actuator which was initially 23% was reduced to less than 2.5% for the considered working frequency. © 2012 AACC American Automatic Control Council).

Rakotondrabe M.,CNRS Femto ST Institute
Proceedings of the American Control Conference | Year: 2011

This paper presents the performances inclusion on time and frequency domains of SISO stable interval systems. We demonstrate that an interval transfer function included in another interval transfer function will have its performances also included in those of the second one. While the results may be intuitive, the paper provides an analytical demonstration by using interval arithmetic and related tools. These results are of great interest for robust performances analysis and for controller design in parametric uncertain systems. © 2011 AACC American Automatic Control Council.

Wang Z.,CEA Grenoble | Devel M.,CNRS Femto ST Institute
Physical Review B - Condensed Matter and Materials Physics | Year: 2011

We study the mechanism of wrinkling of suspended graphene, by means of atomistic simulations. We argue that the structural instability under edge compression is the essential physical reason for the formation of periodic ripples in graphene. The ripple wavelength and out-of-plane amplitude are found to obey 1/4-power scaling laws with respect to edge compression. Our results also show that parallel displacement of the clamped boundaries can induce periodic ripples, with oscillation amplitude roughly proportional to the 1/4 power of edge displacement. © 2011 American Physical Society.

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