This paper presents a new experimental method for the estimation of hydrodynamic parameters of underwater vehicles, namely the added mass and drag coefficients. The principle is to accurately record the movement of the vehicle in response to a known time-varying actuating force, and find an optimal solution for the parameters that allows simulating a velocity trajectory that fits the recorded trajectory. The optimal solution is obtained using a Numerical Integration Fitting method, which, employing an error minimization algorithm, successively generates velocity trajectories through numerical integration until the parameters converge. This method is applied to determine the hydrodynamic parameters of a torpedo-shaped Autonomous Underwater Vehicle (AUV). The hydrodynamic parameters obtained are compared and found to be close to their theoretical values. In addition, the use of a time-varying force is shown to provide better and more reliable results than the use of a constant or zero external force.

We present the design of a bird-like kinematics model for a biped robot as an alternative to the human model. The starting point of the research consists of analyzing the walking motion of quail birds using biological data obtained by X-ray radiography. The 3-D-motion analysis allows identification of the number of degrees of freedom (DOF) and the rotation mechanism for each leg, especially the main rotation axis. Leg joints are located at the hip, knee, ankle, and foot. The ankle is off the ground. Using this analysis, we have designed a biped kinematics model with a minimum of actuated joints and with the original orientation of hip and ankle main rotary joints, which are not horizontally and vertically oriented as in classical biped robotics. Given a reference-foot trajectory, we carry out simulations to compare internal-joint trajectories with the ones obtained from biological measurements. We show that the proposed model can be used to reproduce the kinematics of bird locomotion with a minimum of four actuated joints per leg, i.e., two at the hip and one at the knee, and one at the ankle, which is less than the usual six joints per leg that drive anthropomorphic legs.

Underwater images are altered by the physical characteristics of the medium through which light rays pass before reaching the optical sensor. Scattering and wavelength-dependent absorption significantly modify the captured colors depending on the distance of observed elements to the image plane. In this paper, we aim to recover an image of the scene as if the water had no effect on light propagation. We introduce SUCRe, a novel method that exploits the scene’s 3D structure for underwater color restoration. By following points in multiple images and tracking their intensities at different distances to the sensor, we constrain the optimization of the parameters in an underwater image formation model and retrieve unattenuated pixel intensities. We conduct extensive quantitative and qualitative analyses of our approach in a variety of scenarios ranging from natural light to deep-sea environments using three underwater datasets acquired from real-world scenarios and one synthetic dataset. We also compare the performance of the proposed approach with that of a wide range of existing state-of-the-art methods. The results demonstrate a consistent benefit of exploiting multiple views across a spectrum of objective metrics. Our code is publicly available at github.com/clementinboittiaux/sucre.

SUMMARY: The goal of this paper is to present a new hybrid system based on the fusion of gaze data and Steady State Visual Evoked Potentials (SSVEP) not only to command a powered wheelchair, but also to account for users distraction levels (concentrated or distracted). For this purpose, a multi-layer perception neural network was set up in order to combine relevant gazing and blinking features from gaze sequence and brainwave features from occipital and parietal brain regions. The motivation behind this work is the shortages raised from the individual use of gaze-based and SSVEP-based wheelchair command techniques. The proposed framework is based on three main modules: a gaze module to select command and activate the flashing stimuli. An SSVEP module to validate the selected command. In parallel, a distraction level module estimates the intention of the user by mean of behavioral entropy and validates/inhibits the command accordingly. An experimental protocol was set up and the prototype was tested on five paraplegic subjects and compared with standard SSVEP and gaze-based systems. The results showed that the new framework performed better than conventional gaze-based and SSVEP-based systems. Navigation performance was assessed based on navigation time and obstacles collisions.

Reluctance coil guns are electromagnetic launchers having a good ratio of energy transmitted to actuator volume, making them a good choice for propelling objects with a limited actuator space. In this paper, we focus on an application, which is launching real size soccer balls with a size constrained robot. As the size of the actuator cannot be increased, kicking strength can only be improved by enhancing electrical to mechanical energy conversion, compared to existing systems. For this, we propose to modify its inner structure, splitting the coil and the energy storage capacitor into several ones, and triggering the coils successively for propagating the magnetic force in order to improve efficiency. This article first presents a model of reluctance electromagnetic coil guns using a coupled electromagnetic, electrical and mechanical models. Four different coil gun structures are then simulated, concluding that splitting the kicking coil into two half size ones is the best trade-off for optimizing energy transfer, while maintaining an acceptable system complexity and controllability. This optimization results in robust enhancement and leads to an increase by $104\%$ of the energy conversion compared to a reference launcher used. This result has been validated experimentally on our RoboCup robots. This paper also proves that splitting the coil into a higher number of coils is not an interesting trade-off. Beyond results on the chosen case study, this paper presents an optimization technique based on mixed mechanic, electric and electromagnetic modelling that can be applied to any reluctance coil gun.