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International audience; In recent years, lower-limb exoskeletons have been marketed to become a possible alternative to wheelchairs for people with walking impairments or paralysis. However, most assistive exoskeletons rely on constraining control strategies based on remote controls or torso tilting events. One approach to build more intuitive control interfaces would be to exploit knowledge on human motor control, and the coordination between upper and lower limb movements during gait events, such as the anticipatory postural adjustments that precede gait initiation. In this study, it was hypothesized that generic trunk and arm movements preceding gait in a free walking setting in able-bodied users can still be retrieved while wearing an assistive lower-limb exoskeleton that constrains their leg movements. This was evaluated on a group of eight unimpaired participants, and analysis of upper-body wearable IMU signals showed similarity of pos-tural adjustments between the free and exoskeleton-constrained settings. Additionally, a classification architecture showed that the walking state of the robot can be correctly triggered based on free-walking data gathered from all participants with an accuracy rate of 95%. This suggests that interlimb coordination still exists in a constrained setting, and could pave the road towards the elaboration of more natural controls for assistive lower-limb exoskeletons.

International audience; — The X-Morf robot is a 380-g quadrotor consisting of two independent arms each carrying tandem rotors, forming an actuated scissor joint. The X-Morf robot is able to actively change in-flight its X-geometry by changing the angle between its two arms. The magnetic and electrical joint between the quadrotors arms makes them easily removable and resistant to crashes while providing the propellers with sufficient power and ensuring high quality signal transmission during flight. The dynamic model on which the X-Morf robot was based, was also used to design an adaptive controller. A Model Reference Adaptive Control (MRAC) law was implemented to deal with the uncertainties about the inertia and the center of mass due to the quadrotors reconfigurable architecture and for in-flight span-adapting purposes. The tests performed with the X-Morf robot showed that it is able to decrease and increase its span dynamically by up to 28.5% within 0.5s during flight while giving good stability and attitude tracking performances.

In this paper, we present: (i) a novel analog silicon retina featuring auto-adaptive pixels that obey the Michaelis-Menten law, i.e. V=V(m) I(n)/I(n)+σ(n); (ii) a method of characterizing silicon retinas, which makes it possible to accurately assess the pixels' response to transient luminous changes in a ±3-decade range, as well as changes in the initial steady-state intensity in a 7-decade range. The novel pixel, called M(2)APix, which stands for Michaelis-Menten Auto-Adaptive Pixel, can auto-adapt in a 7-decade range and responds appropriately to step changes up to ±3 decades in size without causing any saturation of the Very Large Scale Integration (VLSI) transistors. Thanks to the intrinsic properties of the Michaelis-Menten equation, the pixel output always remains within a constant limited voltage range. The range of the Analog to Digital Converter (ADC) was therefore adjusted so as to obtain a Least Significant Bit (LSB) voltage of 2.35mV and an effective resolution of about 9 bits. The results presented here show that the M(2)APix produced a quasi-linear contrast response once it had adapted to the average luminosity. Differently to what occurs in its biological counterparts, neither the sensitivity to changes in light nor the contrast response of the M(2)APix depend on the mean luminosity (i.e. the ambient lighting conditions). Lastly, a full comparison between the M(2)APix and the Delbrück auto-adaptive pixel is provided.

Two bio-inspired guidance principles involving no reference frame are presented here and were implemented in a rotorcraft, which was equipped with panoramic optic flow (OF) sensors but (as in flying insects) no accelerometer. To test these two guidance principles, we built a tethered tandem rotorcraft called BeeRotor (80 grams), which was tested flying along a high-roofed tunnel. The aerial robot adjusts its pitch and hence its speed, hugs the ground and lands safely without any need for an inertial reference frame. The rotorcraft's altitude and forward speed are adjusted via two OF regulators piloting the lift and the pitch angle on the basis of the common-mode and differential rotor speeds, respectively. The robot equipped with two wide-field OF sensors was tested in order to assess the performances of the following two systems of guidance involving no inertial reference frame: (i) a system with a fixed eye orientation based on the curved artificial compound eye (CurvACE) sensor, and (ii) an active system of reorientation based on a quasi-panoramic eye which constantly realigns its gaze, keeping it parallel to the nearest surface followed. Safe automatic terrain following and landing were obtained with CurvACE under dim light to daylight conditions and the active eye-reorientation system over rugged, changing terrain, without any need for an inertial reference frame.

International audience; Flying insects excellently master visual motion sensing techniques. They use dedicated motion processing circuits at a low energy and computational costs. Thanks to observations obtained on insect visual guidance, we developed visual motion sensors and bio-inspired autopilots dedicated to flying robots. Optic flow-based visuomotor control systems have been implemented on an increasingly large number of sighted autonomous robots. In this chapter, we present how we designed and constructed local motion sensors and how we implemented bio-inspired visual guidance scheme on-board several micro-aerial vehicles. An hyperacurate sensor in which retinal micro-scanning movements are performed via a small piezo-bender actuator was mounted onto a miniature aerial robot. The OSCAR II robot is able to track a moving target accurately by exploiting the microscan-ning movement imposed to its eye's retina. We also present two interdependent control schemes driving the eye in robot angular position and the robot's body angular position with respect to a visual target but without any knowledge of the robot's orientation in the global frame. This "steering-by-gazing" control strategy, which is implemented on this lightweight (100 g) miniature sighted aerial robot, demonstrates the effectiveness of this biomimetic visual/inertial heading control strategy.

International audience; Optic flow based autopilots for Micro-Aerial Vehicles (MAVs) need lightweight, low-power sensors to be able to fly safely through unknown environments. The new tiny 6-pixel visual motion sensor presented here meets these demanding requirements in term of its mass, size and power consumption. This 1-gram, low-power, fly-inspired sensor accurately gauges the visual motion using only this 6-pixel array with two different panoramas and illuminance conditions. The new visual motion sensor's output results from a smart combination of the information collected by several 2-pixel Local Motion Sensors (LMSs), based on the \enquote{time of travel} scheme originally inspired by the common housefly's Elementary Motion Detector (EMD) neurons. The proposed sensory fusion method enables the new visual sensor to measure the visual angular speed and determine the main direction of the visual motion without any prior knowledge. By computing the median value of the output from several LMSs, we also ended up with a more robust, more accurate and more frequently refreshed measurement of the 1-D angular speed.

Insects flying abilities based on optic flow (OF) are nice bio-inspired models for Micro Aerial Vehicles (MAVs) endowed with a limited computational power. Most OF sensing robots developed so far have used numerically complex algorithms requiring large computational power often carried out offline. The present study shows the performances of our bio-inspired Visual Motion Sensor (VMS) based on a 3×4 matrix of auto-adaptive aVLSI photoreceptors pertaining to a custom-made bio-inspired chip called APIS (Adaptive Pixels for Insect-based Sensors). To achieve such processing with the limited computational power of a tiny microcontroller (μC), the μC-based implementation of the “time of travel” scheme requiring at least a 1kHz sampling rate was modified by linearly interpolating the photoreceptors signals to run the algorithm at a lower sampling rate. The accuracy of the measurements was assessed for various sampling rates in simulation and the best tradeoff between computational load and accuracy determined at 200Hz was implemented onboard a tiny μC. By interpolating the photoreceptors signals and by fusing the output of several Local Motion Sensors (LMSs), we ended up with an accurate and frequently refreshed VMS measuring a visual angular speed and requiring more than 4 times less computational resources.

International audience; In previous studies, we described how complicated tasks such as ground avoidance, terrain following, takeoff and landing can be performed using optic flow sensors mounted on a tethered flying robot called OCTAVE. In the present study, a new programmable visual motion sensor connected to a lightweight Bluetooth module was mounted on a free-flying 50-gram helicopter called TwinCoax. This small helicopter model equipped with 3 IR-reflective markers was flown in a dedicated room equipped with a VICON system to record its trajectory. The results of this study show that despite the complex, adverse lighting conditions, the optic flow measured onboard matched the ground-truth optic flow generated by the free-flying helicopter's trajectory quite exactly.

International audience; Considerable attention has been paid during the last decade to navigation systems based on the use of visual optic flow cues, especially for guiding autonomous robots designed to travel under specific lighting conditions. In the present study, the performances of two visual motion sensors used to measure a local 1-D angular speed, namely (i) a bio-inspired 2-pixel motion sensor and (ii) an off-the-shelf mouse sensor, were tested for the first time in a wide range of illuminance levels. The sensors' characteristics were determined here by recording their responses to a purely rotational optic flow generated by rotating the sensors mechanically and comparing their responses with an accurate rate gyro output signal. The refresh rate, a key parameter for future optic flow-based robotic applications, was also defined and tested in these two sensors. The bio-inspired 2-pixel motion sensor was found to be more accurate indoors whereas the mouse sensor was found to be more efficient outdoors.

International audience; Insects can accurately navigate and track sound sources in complex environments using efficient methods based on highly appropriate sensory-motor processing systems. It is proposed here to describe, model and test these methods, by designing them for a micro-flying device. For this purpose, a new bio-mimetic acoustic sensor inspired by the cricket's auditory system was developed and tested. The sound sensor consists of two tiny omnidirectional microphones weighing only 0.1g, equipped with acoustic resonators and a biomimetic temporal processing system. The hearing system was tuned to the carrier frequency of the sound source, which is 4.7kHz (the frequency of crickets' song). The performances of the directional sound sensor were tested and described in terms of their linearity and accuracy, and their robustness to sound disturbances and dynamic sound source movements.

International audience; Autopilots for micro aerial vehicles (MAVs) with a maximum permissible avionic payload of only a few grams need lightweight, low-power sensors to be able to navigate safely when flying through unknown environments. To meet these demanding specifications, we developed a simple functional model for an Elementary Motion Detector (EMD) circuit based on the common housefly's visual system. During the last two decades, several insect-based visual motion sensors have been designed and implemented on various robots, and considerable improvements have been made in terms of their mass, size and power consumption. The new lightweight visual motion sensor presented here generates 5 simultaneous neighboring measurements of the 1-D angular speed of a natural scene within a measurement range of more than one decade [25 °/s; 350°/s]. Using a new sensory fusion method consisting in computing the median value of the 5 local motion units, we ended up with a more robust, more accurate and more frequently refreshed measurement of the 1-D angular speed.

Considerable attention has been paid during the past decade to navigation systems based on the use of visual optic flow cues. Optic flow--based visuomotor control systems have been implemented on an increasingly large number of sighted autonomous robots designed to travel under specific lighting conditions. Many algorithms based on conventional cameras or custom-made sensors are being used nowadays to process visual motion. In this paper, we focus on the reliability of our optical sensors, which can be used to measure the local one-dimensional angular speed of robots flying outdoors over a visual scene in terms of their accuracy, range, refresh rate, and sensitivity to illuminance variations. We have designed, constructed, and characterized two miniature custom-made visual motion sensors: (i) the APIS (adaptive pixels for insect-based sensors)-based local motion sensor involving the use of an array custom-made in Very-Large-Scale Integration (VLSI) technology, which is equipped with Delbruck-type autoadaptive pixels, and (ii) the LSC-based (LSC is a component purchased from iC-Haus) local motion sensor involving the use of off-the-shelf linearly amplified photosensors, which is equipped with an onchip preamplification circuit. By combining these photodetectors with a low-cost optical assembly and a bioinspired visual processing algorithm, highly effective miniature sensors were obtained for measuring the visual angular speed in field experiments. The present study focused on the static characteristics and the dynamic responses of these local motion sensors over a wide range of illuminance values, ranging from 50 to 10,000 lux both indoors and outdoors. Although outdoor experiments are of great interest to equip micro-air vehicles with visual motion sensors, we also performed indoor experiments as a comparison. The LSC-based visual motion sensor was found to be more accurate in a narrow, 1.5-decade illuminance range, whereas the APIS-based visual motion sensor was more robust to illuminance changes in a larger, 3-decade range. The method presented in this study provides a new benchmark test for thoroughly characterizing visual motion and optic flow sensors designed to operate outdoors under various lighting conditions, in unknown environments where future micro-aerial vehicles will be able to navigate safely. © 2011 Wiley Periodicals, Inc. © 2011 Wiley Periodicals, Inc.

International audience; CURVACE aims at designing, developing, and assessing CURVed Artificial Compound Eyes, a radically novel family of vision systems. This innovative approach will provide more efficient visual abilities for embedded applications that require motion analysis in low-power and small packages. Compared to conventional cameras, artificial compound eyes will offer a much larger field of view with negligible distortion and exceptionally high temporal resolution in smaller size and weight that will fit the requirements of a wide range of applications.

In most animal species, vision is mediated by compound eyes, which offer lower resolution than vertebrate single-lens eyes, but significantly larger fields of view with negligible distortion and spherical aberration, as well as high temporal resolution in a tiny package. Compound eyes are ideally suited for fast panoramic motion perception. Engineering a miniature artificial compound eye is challenging because it requires accurate alignment of photoreceptive and optical components on a curved surface. Here, we describe a unique design method for biomimetic compound eyes featuring a panoramic, undistorted field of view in a very thin package. The design consists of three planar layers of separately produced arrays, namely, a microlens array, a neuromorphic photodetector array, and a flexible printed circuit board that are stacked, cut, and curved to produce a mechanically flexible imager. Following this method, we have prototyped and characterized an artificial compound eye bearing a hemispherical field of view with embedded and programmable low-power signal processing, high temporal resolution, and local adaptation to illumination. The prototyped artificial compound eye possesses several characteristics similar to the eye of the fruit fly Drosophila and other arthropod species. This design method opens up additional vistas for a broad range of applications in which wide field motion detection is at a premium, such as collision-free navigation of terrestrial and aerospace vehicles, and for the experimental testing of insect vision theories.