The industrial sector often employs piezoelectric materials as actuators for a variety of uses, some of which requires a precise positioning while being limited by space and cost factors that impede the insertion of external position and force sensors. Piezoelectric Actuators are characterized by strong nonlinearities (hysteresis and creep), badly damped oscillations and sensitivity to the environment, especially temperature variation, that make the measurement of the position mandatory to guarantee the required precision and repeatability of piezoelectric-based positioning systems operating at the micro and nanoscale. Self-Sensing Actuation techniques allow the implementation of precise positioning control of Piezoelectric Actuators without the hindrance of external position sensors. This paper reviews the different Self-Sensing Actuation techniques used for precise positioning control of Piezoelectric Actuators. The principle of Self-Sensing Actuation is defined by the capability of deriving the physical state of a Piezoelectric Actuator (displacement, perceived force,...) without the use of external sensors to directly measure thereof, but rather by estimating it from the measurement of less intrusive and cheaper physical signals produced by the Piezoelectric Actuator itself (throughout current, voltage drop,...). The applicability and constraints of each Self-Sensing Actuation approach are examined in order to help in the determination of the most adequate approach for precise control of Piezoelectric Actuators positioning and handling force control.

Recently, micro-assembly of individual photonic elements has been highly attracting to provide new optical functionalities and products with high performances. This approach requires position control in free space and contact detection in constrained space. In both cases, getting accurate measurements remains a key lock. For this sake, the FP (Fabry-Perot) interferences happening during the active alignment of optical elements is exploited. This 1D displacement measurement is combined with multi-DoF (Degrees-of-Freedom) robotic motions and a compliant structure along a photo-robotic approach to provide high accurate estimation of both multi-DoF position and contact forces during the assembly process. This approach has been applied to the assembly of an optical lamella with respect to a fiber. An original contact detection algorithm has been proposed, which relies on correlations between the interference figure and the expected irradiance deduced from the nano-positioner internal sensors. This contact detection enables to estimate the position of the lamella with respect to the fiber along the optical axis and thus control the UV-adhesive thickness required to achieve high optical performances after assembly. Experimental investigations using this new approach shows that a positioning accuracy of 27.6 nm and 2.1 m° (standard deviation values) are reached for positions and orientations respectively. The contact detection algorithm has also been studied experimentally and results shows that the contact position can be detected with a maximum error of 80 nm, which

This paper introduces an optical 2-axis Micro Electro-Mechanical System (MEMS) micromirror actuated by a pair of electrothermal actuators and a set of passive torsion bars. The actuated element is a dual-reflective circular mirror plate of 1 $\mathrm{m}\mathrm{m}$ in diameter. This inner mirror plate is connected to a rigid frame via a pair of torsion bars in two diametrically opposite ends located on the rotation axis. A pair of electrothermal bimorphs generates a force onto the perpendicular free ends of the mirror plate in the same angular direction. An array of electrothermal bimorph cantilevers deflects the rigid frame around a working angle of 45 ${}^{\circ }$ for side-view scan. The performed scans reach large mechanical angles of 32 ${}^{\circ }$ for the frame and 22 ${}^{\circ }$ for the in-frame mirror. We denote three resonant main modes, pure flexion of the frame at 205 $\mathrm{Hz}$ , a pure torsion of the mirror plate at 1.286 $\mathrm{kHz}$ and coupled mode of combined flexion and torsion at 1.588 $\mathrm{kHz}$ . The micro device was fabricated through successive stacks of materials onto a silicon-on-insulator wafer and the patterned deposition on the back-side of the dual-reflective mirror is achieved through a dry film photoresist photolithography process.