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Mohamadabadi K.,Plasma Physics Laboratory | Coillot C.,Plasma Physics Laboratory | Hillion M.,SYSNAV
IEEE Sensors Journal | Year: 2013

In this study we address the cross-axis effect (or error) problem in three-axis Anisotropic Magneto Resistance (AMR) magnetic sensors. We focus on magnetometer calibration in the Earth's magnetic field for low-cost sensors. We propose a self-consistent and practical method based on the cross-axis effect modeling, to compensate for the cross-axis effect without using any high precision magnetic sensors for comparing the results. This method does not depend also to other instruments to provide and measure the magnetic field. The compensation method is implemented in two configurations: direct amplification of an AMR signal and magnetization flipping. We show that the residual error with the compensation method in a non-flipped sensor is similar to that sensor in a using flipping. © 2001-2012 IEEE.


PubMed | Groupe Hospitalier Of La Pitie Salpetriere and SYSNAV
Type: Journal Article | Journal: PloS one | Year: 2016

Measurement of muscle strength and activity of upper limbs of non-ambulant patients with neuromuscular diseases is a major challenge. ActiMyo is an innovative device that uses magneto-inertial sensors to record angular velocities and linear accelerations that can be used over long periods of time in the home environment. The device was designed to insure long-term stability and good signal to noise ratio, even for very weak movements. In order to determine relevant and pertinent clinical variables with potential for use as outcome measures in clinical trials or to guide therapy decisions, we performed a pilot study in non-ambulant neuromuscular patients. We report here data from seven Duchenne Muscular Dystrophy (DMD) patients (mean age 18.5 5.5 years) collected in a clinical setting. Patients were assessed while wearing the device during performance of validated tasks (MoviPlate, Box and Block test and Minnesota test) and tasks mimicking daily living. The ActiMyo sensors were placed on the wrists during all the tests. Software designed for use with the device computed several variables to qualify and quantify muscular activity in the non-ambulant subjects. Four variables representative of upper limb activity were studied: the rotation rate, the ratio of the vertical component in the overall acceleration, the hand elevation rate, and an estimate of the power of the upper limb. The correlations between clinical data and physical activity and the ActiMyo movement parameters were analyzed. The mean of the rotation rate and mean of the elevation rate appeared promising since these variables had the best reliability scores and correlations with task scores. Parameters could be computed even in a patient with a Brooke functional score of 6. The variables chosen are good candidates as potential outcome measures in non-ambulant patients with Duchenne Muscular Dystrophy and use of the ActiMyo is currently being explored in home environment.ClinicalTrials.gov NCT01611597.


Bristeau P.-J.,MINES ParisTech | Callou F.,Parrot | Vissiere D.,SYSNAV | Petit N.,MINES ParisTech
IFAC Proceedings Volumes (IFAC-PapersOnline) | Year: 2011

This paper exposes the Navigation and Control technology embedded in a recently commercialized micro Unmanned Aerial Vehicle (UAV), the AR.Drone, which cost and performance are unprecedented among any commercial product for mass markets. The system relies on state-of-the-art indoor navigation systems combining low-cost inertial sensors, computer vision techniques, sonar, and accounting for aerodynamics models. © 2011 IFAC.


Mohamadabadi K.,Ecole Polytechnique - Palaiseau | Hillion M.,Sysnav
IEEE Sensors Journal | Year: 2014

In this paper, we propose a new indoor magnetometer calibration system using the 3-D Helmholtz coil. In this method, in order to the use two-step calibration algorithm instead of rotating the sensor in a constant magnetic field vector, the vector rotates around the magnetometer. In other words, a three-axis magnetometer can be calibrated by a zero degrees of freedom system while a shielded Helmholtz coil provides and rotates a constant magnetic field vector. The results of this calibration method will be compared with the classical calibration method in the earth's magnetic field as well. We also present evidence that the magnetometer does not need to align with the Helmholtz coil axis; instead, it can be calibrated with any arbitrary direction of the Helmholtz coil. It is shown that this method can be performed easily and fast in order to calibrate the three-axis magnetometer in an indoor environment. Meanwhile, it can provide almost the same calibration parameters and thermal model for the magnetometer, compared with the classical one. © 2001-2012 IEEE.


Mohamadabadi K.,Ecole Polytechnique - Palaiseau | Jeandet A.,Ecole Polytechnique - Palaiseau | Hillion M.,SYSNAV | Coillot C.,Ecole Polytechnique - Palaiseau
IEEE Sensors Journal | Year: 2013

In this paper, we present a zero-cost indoor calibration method for anisotropic magnetoresistive (AMR) sensors. The implemented circuit is designed to calibrate AMR sensors using integrated coils. A microcontroller is used to generate an artificial three-dimensional magnetic field by injecting three separate currents into three offset coils. We show the similarity of the results for residual calibration norm by using this method compared with the calibration of the sensor in free Earth's magnetic field. Furthermore, this method does not need any other instruments such as Helmholtz coils or a platform for rotating the sensor. Here the sensor is placed inside a mu-metal box during calibration, and the calibration process is completely autonomous. © 2001-2012 IEEE.


Zarrouati N.,Directorate General of Armaments | Aldea E.,SYSNAV | Rouchon P.,MINES ParisTech
Proceedings of the American Control Conference | Year: 2012

In this paper, we use known camera motion associated to a video sequence of a static scene in order to estimate and incrementally refine the surrounding depth field. We exploit the SO(3)-invariance of brightness and depth fields dynamics to customize standard image processing techniques. Inspired by the Horn-Schunck method, we propose a SO(3)-invariant cost to estimate the depth field. At each time step, this provides a diffusion equation on the unit Riemannian sphere of R3 that is numerically solved to obtain a real time depth field estimation of the entire field of view. Two asymptotic observers are derived from the governing equations of dynamics, respectively based on optical flow and depth estimations: implemented on noisy sequences of synthetic images as well as on real data, they perform a more robust and accurate depth estimation. This approach is complementary to most methods employing state observers for range estimation, which uniquely concern single or isolated feature points. © 2012 AACC American Automatic Control Council).


Zarrouati N.,Directorate General of Armaments | Hillion M.,SYSNAV | Petit N.,MINES ParisTech
Proceedings of the American Control Conference | Year: 2012

We propose in this paper a method to estimate the velocity of a rigid body, using a novel stereo-vision principle. It is presented and applied in a laboratory test case which is representative of low-cost navigation for ground vehicles. The method exploits the dynamics of a scalar field obtained by weighting and averaging the brightness perceived by two embedded neighboring cameras. To be more specific, the cameras are complemented with a gyrometer to retrieve the curvilinear velocity of the moving rigid body. The proposed method is first tested on synthetic data, then on real data, and shows robustness to poor quality of image data. Significant levels of noise and blur are tested; in addition, this method does not require high resolution images, as opposed to any existing methods based on triangulation and tracking of keypoints. © 2012 AACC American Automatic Control Council).


Bristeau P.-J.,MINES ParisTech | Dorveaux E.,MINES ParisTech | Vissiere D.,SYSNAV | Petit N.,MINES ParisTech
Control Engineering Practice | Year: 2010

This paper reports the design and testing of an embedded system for a low-cost small scaled helicopter (Benzin Acrobatic from Vario TM with a 1.8m diameter rotor). The sensors under consideration are an Inertial Measurement Unit (IMU), a GPS, a magnetometer, a barometer and on-off switches serving as take-off and landing detector. Along with one PC board and one micro-controller, they represent a total cost below USD 3000. By contrast to other experiments reported in the literature, the presented work do not rely on any accurate IMU or GPS systems which costs are, separately, largely above the mentioned amount of USD 3000. To compensate the weaknesses of this low cost equipment, efforts focus on designing a robust, dependable and sufficiently embedded system, which exploits an accurate flight dynamics model. This improves the prediction capabilities of an embedded extended Kalman filter that serves for data fusion. The main contribution of this paper is to detail, at the light of a successful reported autonomous hovering flight, the hardware, software architectures and the derivation of the model along with its calibration. Numerous implementation details are presented and the relevance of some modeling hypothesis is discussed. © 2010 Elsevier Ltd.


Zarrouati N.,MINES ParisTech | Zarrouati N.,Directorate General of Armaments | Aldea E.,SYSNAV | Rouchon P.,MINES ParisTech
Proceedings - International Conference on Pattern Recognition | Year: 2012

The objective of our work is to reconstruct the dense structure of a static scene observed by a monocular camera system following a known trajectory. Our main contribution is representated by the proposition of a TV-L1 energy functional that estimates directly the unknown depth field given the camera motion, thus avoiding to estimate as an intermediate step an optical flow field with additional geometric constraints. Our method has two main interests: we highlight a practical minimal parametrization for the given assumptions (static scene, known camera motion) and we solve the resulting variational problem using an efficient, discontinuity preserving formulation. © 2012 ICPR Org Committee.


Dorveaux E.,MINES ParisTech | Vissiere D.,SYSNAV | Petit N.,MINES ParisTech
Proceedings of the 2010 American Control Conference, ACC 2010 | Year: 2010

We address the problem of the calibration of an array of sensors by investigating theoretically and experimentally the case of 2 three-axis sensors. Our focus is on magnetometers that can be used in a low-cost inertial navigation system. Usual errors (misalignments, non-orthogonality, scale factors, biases) are accounted for. The proposed calibration method requires no specific calibration hardware. Instead, we solely use the fact that, if the sensor is properly calibrated, the norm of the sensed field must remain constant irrespective of the sensors orientation. Several strategies of calibration for an array of sensors are described along with the impact of (unavoidable) field disturbances. Experiments conducted with a couple of magneto-resistive magnetometers and data fusion results illustrate the relevance of the approach. © 2010 AACC.

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