Distance-based and Orientation-based Visual Servoing from Three Points

International audienceThis paper is concerned with the use of a spherical-projection model for visual servoing from three points. We propose a new set of six features to control a 6-degree-of-freedom (DOF) robotic system with good decoupling properties. The first part of the set consists of three invariants to camera rotations. These invariants are built using the Cartesian distances between the spherical projections of the three points. The second part of the set corresponds to the angle-axis representation of a rotation matrix measured from the image of two points. Regarding the theoretical comparison with the classical perspective coordinates of points, the new set does not present more singularities. In addition, using the new set inside its nonsingular domain, a classical control law is proven to be optimal for pure rotational motions. The theoretical results and the robustness to points range errors of the new control scheme are validated through simulations and experiments on a 6-DOF robot arm

Visual servoing with respect to complex objects

International audienceThis paper presents new advances in the field of visual servoing. More precisely, we consider the case where complex objects are observed by a camera. In a first part, planar objects of unknown shape are considered using image moments as input of the image-based control law. In the second part, a pose estimation and tracking algorithm is described to deal with real objects whose 3D model is known. For each case, experimental results obtained with an eye-in-hand system are presented

Visual servoing with respect to complex objects

International audienceThis paper presents new advances in the field of visual servoing. More precisely, we consider the case where complex objects are observed by a camera. In a first part, planar objects of unknown shape are considered using image moments as input of the image-based control law. In the second part, a pose estimation and tracking algorithm is described to deal with real objects whose 3D model is known. For each case, experimental results obtained with an eye-in-hand system are presented

Metabolic profiling identifies trehalose as an abundant and diurnally fluctuating metabolite in the microalga Ostreococcus tauri

© 2017, The Author(s).Introduction: The picoeukaryotic alga Ostreococcus tauri (Chlorophyta) belongs to the widespread group of marine prasinophytes. Despite its ecological importance, little is known about the metabolism of this alga. Objectives: In this work, changes in the metabolome were quantified when O. tauri was grown under alternating cycles of 12 h light and 12 h darkness. Methods: Algal metabolism was analyzed by gas chromatography-mass spectrometry. Using fluorescence-activated cell sorting, the bacteria associated with O. tauri were depleted to below 0.1% of total cells at the time of metabolic profiling. Results: Of 111 metabolites quantified over light–dark cycles, 20 (18%) showed clear diurnal variations. The strongest fluctuations were found for trehalose. With an intracellular concentration of 1.6 mM in the dark, this disaccharide was six times more abundant at night than during the day. This fluctuation pattern of trehalose may be a consequence of starch degradation or of the synchronized cell cycle. On the other hand, maltose (and also sucrose) was below the detection limit (~10 μM). Accumulation of glycine in the light is in agreement with the presence of a classical glycolate pathway of photorespiration. We also provide evidence for the presence of fatty acid methyl and ethyl esters in O. tauri. Conclusions: This study shows how the metabolism of O. tauri adapts to day and night and gives new insights into the configuration of the carbon metabolism. In addition, several less common metabolites were identified

Point-based and region-based image moments for visual servoing of planar objects

International audienceMoments are generic (and usually intuitive) descriptors that can be computed from several kinds of objects defined either from closed contours or from a set of points. In this paper, we present improvements in image-based visual servo using image moments. First, the analytical form of the interaction matrix related to the moments computed from a set of coplanar points is derived, and we show that it is different of the form obtained previously using coplanar closed contours. Six visual features are selected to design a decoupled control scheme when the object is parallel to the image plane. This nice property is then generalized to the case where the desired object position is not parallel to the image plane. Finally, experimental results are presented to illustrate the validity of our approach and its robustness with respect to modeling errors

New decoupled visual servoing scheme based on invariants projection onto a sphere

International audienceIn this paper a new decoupled imaged-based control scheme is proposed from projection onto a unit sphere. This control scheme is based on moment invariants to 3D rotational motion. This allows the control of translational motion independently of the rotational one. First, the analytical form of the interaction matrix related to the spherical moments is derived. It is based on the projection of a set of points onto a unit sphere. From the spherical moment, six features are presented to control the full 6 degrees of freedom. Finally, the results are validated through realistic simulation results

Distance-based and Orientation-based Visual Servoing from Three Points

International audienceThis paper is concerned with the use of a spherical-projection model for visual servoing from three points. We propose a new set of six features to control a 6-degree-of-freedom (DOF) robotic system with good decoupling properties. The first part of the set consists of three invariants to camera rotations. These invariants are built using the Cartesian distances between the spherical projections of the three points. The second part of the set corresponds to the angle-axis representation of a rotation matrix measured from the image of two points. Regarding the theoretical comparison with the classical perspective coordinates of points, the new set does not present more singularities. In addition, using the new set inside its nonsingular domain, a classical control law is proven to be optimal for pure rotational motions. The theoretical results and the robustness to points range errors of the new control scheme are validated through simulations and experiments on a 6-DOF robot arm