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Metamaterials have attracted wide scientific interest to break fundamental bounds on materials properties. Recently, the field has been extending to coupled physical phenomena where one physics acts as the driving force for another. Stimuli-responsive or 4D metamaterials have been demonstrated for thermo-elasticity, magneto-optics or piezo-electricity. Herein, a soft, ultra-compact and accurate microrobot is described which can achieve controlled motion under thermal stimuli. The system consists of an organized assembly of two functional structures: a rotational and a translational element. Both elements are designed basing upon the principle of the thermoelastic bilayer plate that bends as temperature changes. Samples are fabricated using gray-tone lithography from a single polymer but with two different laser writing powers, making each part different in its thermal and mechanical behaviors. Excellent motion-controllable, reversible and stable features in a dry environment are verified by simulations and experiments, revealing broad application prospects for the designed soft micro actuators. 4D metamaterials offer the additional functionality of being responsive to external stimuli. Here, a metamaterial-based soft robot is composed of bilayer plates that can rotate and translate in response to thermal stimuli, allowing controlled motion.

International audience; This paper deals with the task of autocalibration of scanning electron microscope (SEM), which is a technique allowing to compute camera motion and intrinsic parameters. In contrast to classical calibration, which implies the use of a calibration object and is known to be a tedious and rigid operation, auto- or selfcalibration is performed directly on the images acquired for the visual task. As autocalibration represents an optimization problem, all the steps contributing to the success of the algorithm are presented: formulation of the cost function incorporating metric constraints, definition of bounds, regularization, and optimization algorithm. The presented method allows full estimation of camera matrices for all views in the sequence. It was validated on virtual images as well as on real SEM images (pollen grains, cutting tools, etc.). The results show a good convergence range and low execution time, notably compared to classical methods, and even more in the context of the calibration of SEM.

Recent studies show that the handling of thin wafers in the photovoltaic industry can lead to unacceptable yields due to cell scratching and breaking. This paper presents the concept and design of a novel modular conveyor that is intended for handling planar fragile objects at a high speed without contact. Each element of the conveyor is a square block that is able to generate tilted air jets that lift and push the object in a single direction. Various handling functions can thus be achieved by the assembly of several blocks. To manage the complexity of assembling systems composed of hundreds of blocks, an automatized design methodology is proposed. This process gives the best topology of the conveyor that meets expected specifications such as trajectory, speed, and travel time. The optimization relies on the physical model of the modular system describing the motion of the object pushed by directed air jets. Experimental comparisons show that the simulation predicts accurately the motion of a glass wafer according to the arrangement of the blocks and the volume of air flow. A maximal speed of 0.3 m/s was experimentally observed and, on larger simulated conveyors, the speed of the wafer could theoretically reach 2.9 m/s.

Position measurement at nanoscale currently raises issues such as making significant compromise between range and resolution or as the difficulty to measure several directions with a single sensor. This paper presents a novel visual method to measure displacements at nanometric scale along two axes. This method allows subpixelic measurement of position by using a pseudo-periodic pattern observed by a regular visual setup. This micrometric pattern corresponds to the intertwining of two perpendicular copies of a single-axis pattern made of two frequency carriers with slightly different periods. It was realized in clean room by photolythography of aluminium on glass. The algorithm is based on a twin-scale principle, itself based on direct phase measurement of periodic grids. Experiments are performed at video rate (30 fps) and show a linearity below 0.16% and a repeatability below 14 nm over an unambiguous range of 221 μm. A resolution below 0.5 nm is demonstrated by the use of 2000 images. The method can be adjusted to different ranges, according to the needs.

International audience; With growing trend of miniaturization, new challenges in microrobotics have appeared. In particular, the complexityof microworld comes from the fact that visual sensors such as Scanning Electron Microscope have a very different principles of image formation in contrast with classical cameras, and their field of view stay very limited. Moreover, usually, the kinematic model of the robots used are not well defined. The consequence of both properties is that even a small movement of the robot arm leads to a huge object displacement comparing to the size of the viewed area. This paper develops a procedure allowing to perform object rotation while keeping it at the same 3D-position in open loop. Such performance is achieved by a method of robot calibration based on visual servoing and autofocus inside SEM. This kind of properties is required for manipulation and 3D reconstruction inside SEM.

International audience; Force sensors are often required in order to work at the microscale, but existing ones rarely meet all expectations, particularly in terms of resolution, range, accuracy, or integration potential. This paper presents a novel microforce measurement method by vision, based on a twin-scale pattern fixed on a compliant structure. This approach enabled subpixelic measurement of position by the use of a micromachined pattern based on the Vernier principle. This method also presents flexibility, insensitivity to electronic noise, fast operating time, and ease of calibration. The major contribution consists in the large range-to-resolution ratio of the measurement system. With an experimental range of 50 mN and a resolution below 50 nN, a range-to-resolution ratio of 10^6 is obtained. A repeatability under 7.8 μN and a trueness under 15 μN have been experimentally measured. Finally, the method can be applied to other specifications and applications in terms of range.

International audience; Using pseudo-periodic patterns on the observed target releases usual computer-vision constraints by allowing sub-pixel resolutions together with supra field-of-observation absolute measurement ranges. The allowed range of working distances is also tremendously extended using digital holography.

Working at micro-scale efficiently requires accurate and integrated force feedback implemented with a sensor adapted to the scale. This paper presents a 3D-printed vision-based micro-force sensor intended to be used inside the chamber of a Scanning Electron Microscope (SEM). The combination of 3D printed elastic structures with a highly effective vision based measurement method allows to design integrated sensors at the cutting edge of the state of the art. Moreover the presented design respects the Abbe's alignment principle. The paper presents the general design, manufacturing and experimental characterization in SEM environment of the proposed sensor. Images of periodical patterns are used to measure the differential displacement between the two parts of the compliant structure. By the knowledge of its stiffness, the force applied on it is measured. The stiffness of the elastic structure has been measured to be 15.3 N.m−1, leading to a force range of 25 µN.

International audience; This paper presents a visual measurement method able to sense 1D rigid body displacements with very high resolutions, large ranges and high processing rates. Sub-pixelic resolution is obtained thanks to a structured pattern placed on the target. The pattern is made of twin periodic grids with slightly different periods. The periodic frames are suited for Fourier-like phase calculations—leading to high resolution—while the period difference allows the removal of phase ambiguity and thus a high range-to-resolution ratio. The paper presents the measurement principle as well as the processing algorithms (source files are provided as supplementary materials). The theoretical and experimental performances are also discussed. The processing time is around 3 μs for a line of 780 pixels, which means that the measurement rate is mostly limited by the image acquisition frame rate. A 3- repeatability of 5 nm is experimentally demonstrated which has to be compared with the 168 μm measurement range.

Recently, high resolution visual methods based on direct-phase measurement of periodic patterns has been proposed with successful applications to microrobotics. This paper proposes a new implementation of direct-phase measurement methods to achieve 3-DoF (degrees of freedom) visual servoing. The proposed algorithm relies on a single frequency tracking rather than a complete 2D discrete Fourier transform that was required in previous works. The method does not require any calibration step and has many advantages such as high subpixelic resolution, high robustness and short computation time. Several experimental validations (in favorable and unfavorable conditions of use) were performed using a XYδ microrobotic platform. The obtained results demonstrate the efficiency of the frequency-based controller, this in term of accuracy (micrometric error), convergence rate (30 iterations in nominal conditions) and robustness.

International audience; This paper presents recent results obtained with a visual method allowing absolute position measurements at nanoscale. Based on the direct phase analysis of pseudo-periodic patterns, this approach enabled fast measurements of position with large range-to-resolution ratios. Applications include microrobotic manipulators calibration and visual servoing but also microforce measurement by using a compliant structure. Rangeto-resolution ratio of 105 are typically overcome. For instance, the experiments have demonstrated a sub-nanometric resolution over a range of 168 µm, as well as a resolution below 50 nN for a 50 mN range for force measurement

International audience; In the photovoltaic solar cell industry as in the semiconductor industry, efforts to reduce the thickness of silicon wafers are in progress. Wafer damage and breakage during handling can lead to unacceptable yields and alternative solutions have to be proposed. This paper presents a modular contact-free wafer handling system that responds to the industrial requirements in terms of throughput and flexibility. The system is based on simple unidirectional modules that can be assembled together to form the desired trajectory. A complete and accurate physical model of the modular system describing the motion of the wafer transported by directed air-jets is proposed. A decentralized control at the block level is realized to damp the object motion. The experimental results show a great reduction of the response time compared to free motion and a standard deviation of the servo error below the millimeter. In addition, simulations show that a 150 mm wafer could reach a speed up to 2.9 m/s on large conveyors.