Estimation of the rigid transformation between two cameras from the Fundamental Matrix VS from Homographies.

The 3D reconstruction is an important step for the analytical calculation of the Jacobian of the image in a process of visual control of robots. In a two-camera stereo system that reconstruction depends on the knowledge of the rigid transformation between the two cameras and is represented by the rotation and translation between them. These two parameters are the result of a calibration of the stereo pair, but can also be retrieved from the epipolar geometry of the system, or from a homography obtained by features belonging to a flat object in the scene. In this paper, we make an assessment of the latter two alternatives, taking as reference an Euclidean reconstruction eliminating image distortion. We analyze three cases: the distortion inherent in the camera is corrected, without corrected distortion, and when Gaussian noise is added to the detection of features

A Comparative Study between Analytic and Estimated Image Jacobian by Using a Stereoscopic System of Cameras

This paper describes a comparative study of performance between the estimated image Jacobian that come from taking into account the epipolar geometry in a system of two cameras, and the well known analytic image Jacobian that is utilized for most applications in visual servoing. Image Based Visual Servoing architecture is used for controlling a 3 DOF articular system using two cameras in eye to hand configuration. Tests in static and dynamic cases were carried out, and showed that the performance of estimated Jacobian by using the properties of the epipolar geometry is such as good and robust against noise as the analytic Jacobian. This fact is considered as an advantage because the estimated Jacobian does not need laborious previous work prior to control task in contrast to the analytic Jacobian does

Visual Servoing of Robot Manipulators Part I : Projective Kinematics

Visual servoing of robot manipulators is a key technique where video images, i.e. the visual appearance of an object is used to control the end-effector. Most such methods use robots and cameras that have been calibrated. In this report we suggest a non-metric formulation of visual servoing that works with an uncalibrated stereo rig, i.e. in the projective space associated with it. In consequence, the robot kinematics and the robot Jacobian have to defined projectively, as well. Elementary motions of robot joints are pure rotations and pure translations. Rather than representing them by Euclidean transformations, the uncalibrated stereo rig suggests to represent them by corresponding projective transformations (homographies). They are introduced as projective rotations and projective translations, their algebraic properties and special parameterizations are thoroughly investigated- . This gives raise to the definition of a projectiv kinematic map and a projective Jacobian matrix. Unlike the classical robot Jacobian, which relates joint-velocities to end-effector velocities, we establish a direct relationship between joint-velocities and image-velocities, i.e. the velocitie- s of those images points corresponding to end-effector features. Finally, we provide a practical method to establish the projective kinematics and describe preliminary simulated experiments of stereo-based visual servoing using the non-metric model. Nevertheless, in depth analysis of projective control will be the topic of a forthcoming paper

Uncalibrated visual servo for unmanned aerial manipulation

© 20xx IEEE. Personal use of this material is permitted. Permission from IEEE must be obtained for all other uses, in any current or future media, including reprinting/republishing this material for advertising or promotional purposes, creating new collective works, for resale or redistribution to servers or lists, or reuse of any copyrighted component of this work in other works.This paper addresses the problem of autonomous servoing an unmanned redundant aerial manipulator using computer vision. The overactuation of the system is exploited by means of a hierarchical control law, which allows to prioritize several tasks during flight. We propose a safety-related primary task to avoid possible collisions. As a secondary task, we present an uncalibrated image-based visual servo strategy to drive the arm end-effector to a desired position and orientation by using a camera attached to it. In contrast to the previous visual servo approaches, a known value of camera focal length is not strictly required. To further improve flight behavior, we hierarchically add one task to reduce dynamic effects by vertically aligning the arm center of gravity to the multirotor gravitational vector, and another one that keeps the arm close to a desired configuration of high manipulability and avoiding arm joint limits. The performance of the hierarchical control law, with and without activation of each of the tasks, is shown in simulations and in real experiments confirming the viability of such prioritized control scheme for aerial manipulation.Peer ReviewedPostprint (author's final draft

Image-based Visual Servoing of a Gough-Stewart Parallel Manipulator using Leg Observations

International audienceIn this paper, a tight coupling between computer vision and paral- lel robotics is exhibited through the projective line geometry. Indeed, contrary to the usual methodology where the robot is modeled indepen- dently from the control law which will be implemented, we take into ac- count, since the early modeling stage, that vision will be used for con- trol. Hence, kinematic modeling and projective geometry are fused into a control-devoted projective kinematic model. Thus, a novel vision-based kinematic modeling of a Gough-Stewart manipulator is proposed through the image projection of its cylindrical legs. Using this model, a visual ser- voing scheme is presented, where the image projection of the non-rigidly linked legs are servoed, rather than the end-effector pose

Visual Servoing

The goal of this book is to introduce the visional application by excellent researchers in the world currently and offer the knowledge that can also be applied to another field widely. This book collects the main studies about machine vision currently in the world, and has a powerful persuasion in the applications employed in the machine vision. The contents, which demonstrate that the machine vision theory, are realized in different field. For the beginner, it is easy to understand the development in the vision servoing. For engineer, professor and researcher, they can study and learn the chapters, and then employ another application method

Model free visual servoing in macro and micro domain robotic applications

This thesis explores model free visual servoing algorithms by experimentally evaluating their performances for various tasks performed both in macro and micro domains. Model free or so called uncalibrated visual servoing does not need the system (vision system + robotic system) calibration and the model of the observed scene, since it provides an online estimation of the composite (image + robot) Jacobian. It is robust to parameter changes and disturbances. A model free visual servoing scheme is tested on a 7 DOF Mitsubishi PA10 robotic arm and on a microassembly workstation which is developed in our lab. In macro domain, a new approach for planar shape alignment is presented. The alignment task is performed based on bitangent points which are acquired using convex-hull of a curve. Both calibrated and uncalibrated visual servoing schemes are employed and compared. Furthermore, model free visual servoing is used for various trajectory following tasks such as square, circle, sine etc. and these reference trajectories are generated by a linear interpolator which produces midway targets along them. Model free visual servoing can provide more exibility in microsystems, since the calibration of the optical system is a tedious and error prone process, and recalibration is required at each focusing level of the optical system. Therefore, micropositioning and three di erent trajectory following tasks are also performed in micro world. Experimental results validate the utility of model free visual servoing algorithms in both domains