Raphaël Juston

Miniature curved artificial compound eyes.

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.

Hardware Architecture and Cutting-Edge Assembly Process of a Tiny Curved Compound Eye

The demand for bendable sensors increases constantly in the challenging field of soft and micro-scale robotics. We present here, in more detail, the flexible, functional, insect-inspired curved artificial compound eye (CurvACE) that was previously introduced in the Proceedings of the National Academy of Sciences (PNAS, 2013). This cylindrically-bent sensor with a large panoramic field-of-view of 180° × 60° composed of 630 artificial ommatidia weighs only 1.75 g, is extremely compact and power-lean (0.9 W), while it achieves unique visual motion sensing performance (1950 frames per second) in a five-decade range of illuminance. In particular, this paper details the innovative Very Large Scale Integration (VLSI) sensing layout, the accurate assembly fabrication process, the innovative, new fast read-out interface, as well as the auto-adaptive dynamic response of the CurvACE sensor. Starting from photodetectors and microoptics on wafer substrates and flexible printed circuit board, the complete assembly of CurvACE was performed in a planar configuration, ensuring high alignment accuracy and compatibility with state-of-the art assembling processes. The characteristics of the photodetector of one artificial ommatidium have been assessed in terms of their dynamic response to light steps. We also characterized the local auto-adaptability of CurvACE photodetectors in response to large illuminance changes: this feature will certainly be of great interest for future applications in real indoor and outdoor environments.

A small-scale hyperacute compound eye featuring active eye tremor: application to visual stabilization, target tracking, and short-range odometry

In this study, a miniature artificial compound eye (15 mm in diameter) called the curved artificial compound eye (CurvACE) was endowed for the first time with hyperacuity, using similar micro-movements to those occurring in the flys compound eye. A periodic micro-scanning movement of only a few degrees enables the vibrating compound eye to locate contrasting objects with a 40-fold greater resolution than that imposed by the interommatidial angle. In this study, we developed a new algorithm merging the output of 35 local processing units consisting of adjacent pairs of artificial ommatidia. The local measurements performed by each pair are processed in parallel with very few computational resources, which makes it possible to reach a high refresh rate of 500 Hz. An aerial robotic platform with two degrees of freedom equipped with the active CurvACE placed over naturally textured panels was able to assess its linear position accurately with respect to the environment thanks to its efficient gaze stabilization system. The algorithm was found to perform robustly at different light conditions as well as distance variations relative to the ground and featured small closed-loop positioning errors of the robot in the range of 45 mm. In addition, three tasks of interest were performed without having to change the algorithm: short-range odometry, visual stabilization, and tracking contrasting objects (hands) moving over a textured background.

Hyperacute Edge and Bar Detection in a Bioinspired Optical Position Sensing Device

We present an improved bioinspired optical position sensing device, in which insect-based retinal microscanning movements are used to detect and locate contrasting objects such as edges or bars. The active microvibrations imposed upon the retina endow the sensor with hyperacuity. For the sake of clarity, this is demonstrated here for a two-pixel sensor, but the same principle could be applied to all pairs of neighboring photosensors in a focal plane array. The sensor is able to detect an edge or a bar present within its small field of view ( 4°) and locate it with a resolution ( 0.025°) 160-fold finer than the static resolution imposed by the pixel spacing. The sensor features the novel ability to establish whether it is actually facing an edge or a bar, based on the phase difference between the sinusoidally modulated signals of its two photoreceptors. The visual processing algorithm involves simple linear filtering and purely arithmetic operations requiring few computational resources. The complete theoretical framework is presented here, including an analytical model for the microscanning sensor. This high-performance, low-cost angular position sensing device could have many applications in fields such as metrology, astronomy, robotics, automotive design, and aerospace.

An artificial elementary eye with optic flow detection and compositional properties

We describe a 2 mg artificial elementary eye whose structure and functionality is inspired by compound eye ommatidia. Its optical sensitivity and electronic architecture are sufficient to generate the required signals for the measurement of local optic flow vectors in multiple directions. Multiple elementary eyes can be assembled to create a compound vision system of desired shape and curvature spanning large fields of view. The system configurability is validated with the fabrication of a flexible linear array of artificial elementary eyes capable of extracting optic flow over multiple visual directions.

A miniature bio-inspired position sensing device for the control of micro-aerial robots

Here we present an example of a novel bio-inspired active vision system with a vibrating eye that can rotate freely by means of a miniature rotary piezo motor. Active micro-vibrations were applied to the eye by using an innovative micro-mechanism based on a tiny stepper motor. The hyperacuity of this inexpensive position-sensing device, which results from the active micro-vibrations, makes it capable of measuring the angular position of a contrasting edge. Among the many miniature rotary actuators available, piezomotors are often used when small size, low mass, great accuracy and high dynamics are required. The newly off-the-shelf miniature ultrasonic piezomotor presented in this study along with its position servo control system is supplied ready-integrated into a printed circuit board (PCB). The PCB Piezomotor (or PCBMotor) has many advantages, such as high torque (it requires no reducer), fast dynamics (the mechanical time constant is 3 ms), a low mass (1 gram) and a compact size (it is only 20 mm in diameter and 2.6 mm thick). The results of the tests conducted show that the performances of the PCBmotor connected to a custom-made miniature electronic driver make it a good alternative to the actuators classically used in robotic applications. In addition we present a simple visual processing, implemented onto a tiny microcontroller, composed of simple linear filtering and arithmetic operations. We show that our visual scanning sensor is a genuine position sensing device able to measure the relative angular position of a visual object with only two pixels and very few computational resources.

HyperCube: A Small Lensless Position Sensing Device for the Tracking of Flickering Infrared LEDs.

An innovative insect-based visual sensor is designed to perform active marker tracking. Without any optics and a field-of-view of about 60°, a novel miniature visual sensor is able to locate flickering markers (LEDs) with an accuracy much greater than the one dictated by the pixel pitch. With a size of only 1 cm3 and a mass of only 0.33 g, the lensless sensor, called HyperCube, is dedicated to 3D motion tracking and fits perfectly with the drastic constraints imposed by micro-aerial vehicles. Only three photosensors are placed on each side of the cubic configuration of the sensing device, making this sensor very inexpensive and light. HyperCube provides the azimuth and elevation of infrared LEDs flickering at a high frequency (>1 kHz) with a precision of 0.5°. The minimalistic design in terms of small size, low mass and low power consumption of this visual sensor makes it suitable for many applications in the field of the cooperative flight of unmanned aerial vehicles and, more generally, robotic applications requiring active beacons. Experimental results show that HyperCube provides useful angular measurements that can be used to estimate the relative position between the sensor and the flickering infrared markers.

High performance optical angular position sensing at low-cost: A bio-inspired approach

Accurate remote contactless angular sensing at high accuracy often requires emissive sensors with high energy consumption, complex processing and high cost. Thanks to active micro-vibrations applied to its elementary retina, our low-cost bio-inspired optical position sensing device is able to measure the angular position of a contrasting edge at low cost with hyperacuity. This sensor is able, for example, to estimate the elevation of a real edge such as the horizontal roof of a distant building with a resolution (0.025°) at least 160-fold better than the sensorss static resolution (4°), despite any changes in the contrast and illuminance. The visual processing algorithm is based on just a few linear filters and arithmetic operations, which require few computational resources. The high performances and low cost of this novel position sensing device make it suitable for applications in the fields of metrology, astronomy, robotics, automotive and aerospace.

Decoupling the Eye: A Key toward a Robust Hovering for Sighted Aerial Robots

Inspired by natural visual systems where gaze stabilization is at a premium, we simulated an aerial robot with a decoupled eye to achieve more robust hovering above a ground target despite strong lateral and rotational disturbances. In this paper, two different robots are compared for the same disturbances and displacements. The first robot is equipped with a fixed eye featuring a large field-of-view (FOV) and the second robot is endowed with a decoupled eye featuring a small FOV (about ±5°). Even if this mechanical decoupling increases the mechanical complexity of the robot, this study demonstrates that disturbances are rejected faster and the computational complexity is clearly decreased. Thanks to bio-inspired visuo-motor reflexes, the decoupled eye robot is able to hold its gaze locked onto a distant target and to reject strong disturbances by profiting of the small inertia of the decoupled eye.

CURVACE - CURVed Artificial Compound Eyes

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.