Level sets and stable manifold approximations for perceptually driven non-holonomically constrained navigation

This paper addresses problems of robot navigation in the presence of non-holonomic motion constraints arising from kinematics as well as holonomic constraints arising from perception. We consider the theoretical problem of visually registering a unicycle with respect to camera images of a known, persistent landmark. We propose a general hybrid procedure that adapts to this constrained motion setting the standard feedback controller arising from a navigation function in the fully actuated case. The algorithm switches back and forth between moving down and across the associated gradient field toward the stable manifold it induces in the constrained dynamics. Guaranteed to avoid obstacles in all cases, after the introduction of some technical (and not easily verified) additional assumptions, the algorithm can be readily shown to converge to an arbitrarily small neighborhood of the goal. We then introduce a more realistic, 'relaxed' version of the algorithm that appears to result in asymptotic convergence to the goal. Illustrative simulations are provided for two different perceptual models appropriate to environments with visual beacons.     

Mechanisms of Adsorption from Aqueous Solutions: Some Basic Problems

Despite its wide occurrence and practical importance, adsorption at the interface between a solid and an aqueous solution still presents one of the most complicated problems in surface chemistry. Some of the factors known to influence adsorption processes are pointed out and the present need for more thorough investigation of well-characterized systems is emphasized.     

Effects of camera calibration errors on static-eye and hand-eye visual servoing

Effects of camera calibration errors for the point-to-point task are investigated in static-eye and hand-eye visual servoing realized with position-based and image-based control laws. For these four configurations, the effect of uncertainty on intrinsic and extrinsic parameters is analyzed. The results show local stability for all configurations under small calibration errors. However, a steady-state error is found in the hand-eye position-based configuration. Simulations have been carried out in order to confirm the theoretical results and evaluate the effects of the uncertainty in terms of the stability region. Another contribution of the paper consists of providing a method for estimating the stability region robust against uncertainty directions for the static-eye position-based case with uncertainty on the camera centers.     

Comparison of Two Sequencing Techniques to Perform a Vision-Based Navigation Task in a Cluttered Environment

We address the problem of multi-sensor-based navigation in a cluttered environment for a non-holonomic robot. To perform such a successful and safe navigation, three controllers realizing, respectively, nominal vision-based navigation, obstacle bypassing and occlusion avoidance have been designed using the task function approach. Then it suffices to sequence them to realize the complete mission. To guarantee the control continuity when switching between two successive controllers, two sequencing approaches have been used and compared. Simulation results validate our work.     

Visual Control of Robots with Delayed Images

This research develops a control scheme for visual servoing that explicitly takes into account the delay introduced by image acquisition and processing. For this purpose, a predictor block, i.e., an estimator that predicts several samples ahead of time, is properly included in the scheme. The proposed approach is analytically analyzed in terms of dynamics and steady-state errors, and compared to previous approaches. Furthermore, several simulations are comparatively shown in order to illustrate the benefits and limitations of the proposed control scheme. Finally, some experimental results using a turntable and a 3-d.o.f. Cartesian robot are provided in order to validate the analytical and simulation results.     

利用AUTOCAD 2002开发冷弯型钢孔型设计软件

叙述了利用VISUAL BASIC 6．0同AUTOCAD 2002进行连接以及用VB编程对AUTOCAD 2002的图形对象进行操作的方法,并简要介绍了自行开发的孔型设计软件(KongXingTools 1．0)的三个基本功能。     

Hiding a secret colour image in two colour images

Abstract

Visual cryptography is different from traditional cryptography. That is, neither time-consuming computation nor complex cryptographic knowledge is needed. Stacking is the only operation required to recover a secret image, and the individual image does not give the hackers any information about the secret image. None of researches tried to deal with meaningful colour share transparencies. Hence, two methods are proposed for hiding a colour image in two meaningful colour share transparencies in this paper. To achieve this goal, the colour decomposition approach and halftone technology are first applied to cope with secret colour images. Then the concept of the human visual system is utilized to generate two colour meaningful sharing transparencies. To support various applications, two variants are presented. The first proposed method, method-1, is suitable for simple colour images, and the second, method-2, provides better visibility of complex colour images.     

Visual control of two aerial micro-robots by insect-based autopilots

In the framework of our research on biologically inspired microrobotics, we have developed two novel Automatic Flight Control Systems (AFCs): OCTAVE ( Optical flow Control sysTem for Aerospace VEhicles) and OSCAR ( Optical Scanning sensor for the Control of Autonomous Robots), both based on insects' visuomotor control systems. OCTAVE confers upon a tethered aerial robot (the OCTAVE robot) the ability to perform terrain following. OSCAR gives a tethered aerial robot (the OSCAR robot) the ability to fixate and track a contrasting target with a high level of accuracy. Both OCTAVE and OSCAR robots are based on optical velocity sensors, the principle of which is based on the results of previous electrophysiological studies on the fly's Elementary Motion Detectors (EMDs) performed at our laboratory. Both processing systems described are light enough to be mounted on-board Micro-Air Vehicles (MAVs) with an avionic payload small enough to be expressed in grams rather than kilograms.     

Collision dynamics of a visual target marker for small-body exploration

MUSES-C mission is the world first sample and return attempt to or from a near-Earth asteroid. In deep space, it is hard to navigate, guide and control a spacecraft on a real-time basis remotely from the earth, mainly due to the communication delay. Thus, autonomy and robotics technologies are required for final approach and landing to an unknown body. In the final descent phase, cancellation of the horizontal speed relative to the surface of the landing site is essential. During the touchdown and sampling phase, the spacecraft will be navigated relative to the asteroid surface using an optical target marker (TM) placed on the asteroid surface. By using the TM as a reference point, navigation during the landing phase will be much more reliable and precise. Thus, it is important to design a TM with as small a coefficient of restitution as possible to reduce the settling time. To develop a small coefficient of restitution of less than 0.1 in vertical direction, the authors propose a novel TM, which is constructed out of a shell with beads stored internally. To better predict the performance of such a TM, analytical and numerical investigations are performed. The validity and the effectiveness of the proposed method are confirmed and evaluated by numerical simulations and flight results.