On visual servoing based on efficient second order minimization

This paper deals with the Efficient Second order Minimization (ESM) and the image-based visual servoing schemes. In other words, it deals with the minimization based on the pseudo-inverse of the mean of the Jacobians or on the mean of Jacobian Pseudo-inverses. Chronologically, it has been noticed in Tahri and Chaumette (2003) [22] that ESM generally improves the system behavior when compared with the system in which only the simple Jacobian Pseudo-inverses are used. Subsequently, a mathematical explanation has been given in Malis (2004) [12]. In this paper, the proofs given by Malis are discussed and it will be shown that there is a limitation to the validity of the ESM. We will also show that the use of ESM does not necessarily ensure a better system behavior, especially in the situations where large rotational motions are involved. Further, a new appropriate formula of the ESM is proposed and validated using several kinds of features.     

基于视觉伺服的高精度运动控制系统设计

本文针对高速流水线上的机械手特点设计了一种高精度的视觉伺服运动控制系统,详细介绍了控制系统结构,描述了视觉伺服模型的建立以及系统的具体实现。     

Visual servoing for online facilities

Visual servoing for online facilities aims at automated manipulation of instrument control parameters based on visual-scene interpretation. It provides a layer of computing that hides the latency in the Internet environment and simplifies the use of scientific imaging instruments. This approach makes remote real-time imaging experiments feasible over unpredictable wide area networks. The authors' efforts focus on developing a framework for remotely manipulating microscopic objects. Two diverse applications demonstrate the framework's usefulness: microdissection of DNA molecules and in situ examination of crystal formation. Microdissection and subsequent amplification of DNA molecules allow for rapid closure of gaps in the genomic library. In situ experiments reveal information about the thermal and morphological properties of crystal structures     

Visual servoing and CAD-driven microassembly

The authors describe current research and development on a robotic visual servoing system for assembly of LIGA (lithography galvonoforming abforming) parts. The workcell consists of an AMTI robot, precision stage, long working distance microscope, and LIGA fabricated tweezers for picking up the parts. Fourier optics methods are used to generate synthetic microscope images from CAD drawings. These synthetic images are used off-line to test image processing routines under varying magnifications and depths of field. They also provide reference image features which are used to visually servo the part to the desired position. Currently, we can visually servo a 100 micron outside diameter LIGA gear to a desired x,y reference position as determined from a synthetic image of the gear     

Visual servoing for large camera displacements

The first aim of any visual-servoing strategy is to avoid features being lost from the field of view and that the desired location may not be reached. However, avoiding both these system failures turns out to be very difficult, especially when the initial and desired locations are distant. Moreover, the methods that succeed in presence of large camera displacements often produce a long translational trajectory that may not be allowed by the robot workspace and/or joint limits. In this paper, a new strategy for dealing with such problems is proposed, which consists of generating circular-like trajectories that may satisfy the task requirements more naturally than other solutions. Knowledge of geometrical models of the object or points depth is not required. It is shown that system failures are avoided for a calibrated camera. Moreover, necessary and sufficient conditions are provided for establishing tolerable errors on the estimates of the intrinsic and extrinsic parameters, in order to guarantee a robust field of view and robust local asymptotic stability. Several simulation results show that the translational trajectories obtained in presence of large displacements are significantly shorter than those produced by the existing methods, in cases of both correct and bad camera calibration. Very satisfactory results are achieved also in presence of small displacements.     

Visual servoing for an autonomous rendezvous and capture system

Many autonomous space systems are under development to economically extend the lives of space systems, either by orbit modification or replenishment of consumables. This paper explains the theory behind and demonstrates experimentally the terminal control portion of an autonomous rendezvous and capture system. The system will grapple the launch bolt holes of common satellite interfaces in order to minimize the necessary client hardware. This is accomplished using a stereoscopic vision system using an edge detector and Hough transform to locate the target point. This project demonstrated the use of off-the-shelf hardware and open source algorithms to accomplish its objective.     

Binocular visual servoing based on linear time-invariant mapping

We propose a simple visual servoing scheme based on the use of binocular visual space. When we use a hand-eye system which has a similar kinematic structure to a human being, we can approximate the transformation from a binocular visual space to a joint space of the manipulator as a linear time-invariant mapping. This relationship makes it possible to generate joint velocities from image observations using a constant linear mapping. This scheme is robust to calibration error, especially to camera turning, because it uses neither camera angles nor joint angles. Some experimental results are also shown to demonstrate the positioning precision remained unchanged despite the calibration error,     

Robust image-based visual servoing using invariant visual information

This paper deals with the use of invariant visual features for visual servoing. New features are proposed to control the 6 degrees of freedom of a robotic system with better linearizing properties and robustness to noise than the state of the art in image-based visual servoing. We show in this paper that by using these features the behavior of image-based visual servoing in task space can be significantly improved. Several experimental results are provided and validate our proposal.     

采用全景相机的移动机器人视觉伺服

为了解决机器人上装置传统相机而产生的视野域有限的问题,采用了全景相机,并且针对采用近似线性输入输出反馈控制模型中近似与假设过多的情况,提出了一种使用极线几何与三角几何相结合的方法,更简便地实现基于图像的视觉伺服运用于移动机器人的情况.由于是基于图像的视觉伺服,该方法不需要预先知道三维场景的结构知识.实验仿真结果表明了该方法的有效性.     

基于仿人智能控制的无标定视觉伺服

设计了无标定视觉伺服的仿人智能控制器,仿真完成了无标定双目视觉下机械臂的五自由度运动空间定位。选取点特征作为双目视觉图像特征,设计了视觉特征模型与多模态视觉伺服控制器,并在Matlab平台下设计了五自由度运动空间的视觉定位仿真实验,验证了方法的有效性。     

Visual servoing in the task-function framework: A contour following task

We describe an approach to contour following unknown objects using a handeye robotic system. Relevant and sufficient feature points providing optical flow data are extracted from the edges of the target object. The desired motion of the end-effector is computed with the objective of keeping the visual features always at the same target location in the image plane. A cartesian PD controller is used to perform the desired motion by the robot's end-effector. To address thecontrol issues, we take advantage of the unifying robot control theory stated in the literature as thetask-function approach [21]. To validate our approach, we restricted our experiments to motionless objects positioned in a plane parallel to the image plane: three degrees of freedom (two of translation, one of rotation) are thus controlled.     

A low-frequency construction watermarking based on histogram

Multimedia Tools and Applications - The robust watermarking scheme has very broad application scenarios. For robust watermarking methods, the transform domain based watermarking algorithms are...     

Visual servoing tracking control of uncalibrated manipulators with a moving feature point

The paper is concerned with the problem of uncalibrated visual servoing robots tracking a dynamic feature point along with the desired trajectory. A nonlinear observer and a nonlinear controller are proposed, which allow the considered uncalibrated visual servoing robotic system to fulfil the desired tracking task. Based on this novel control method, a dynamic feature point with unknown motion parameters can be tracked effectively along with the desired trajectory, even with multiple uncertainties existing in the camera, the kinematics and the manipulator dynamics. By the Lyapunov theory, asymptotic convergence of the image errors to zero with the proposed control scheme is rigorously proven. Simulations have been conducted to verify the performance of the proposed control scheme. The results demonstrated good convergence of the image errors.     

Visual servoing of redundant manipulator with Jacobian matrix estimation using self-organizing map

Vision based redundant manipulator control with a neural network based learning strategy is discussed in this paper. The manipulator is visually controlled with stereo vision in an eye-to-hand configuration. A novel Kohonen’s self-organizing map (KSOM) based visual servoing scheme has been proposed for a redundant manipulator with 7 degrees of freedom (DOF). The inverse kinematic relationship of the manipulator is learned using a Kohonen’s self-organizing map. This learned map is shown to be an approximate estimate of the inverse Jacobian, which can then be used in conjunction with the proportional controller to achieve closed loop servoing in real-time. It is shown through Lyapunov stability analysis that the proposed learning based servoing scheme ensures global stability. A generalized weight update law is proposed for KSOM based inverse kinematic control, to resolve the redundancy during the learning phase. Unlike the existing visual servoing schemes, the proposed KSOM based scheme eliminates the computation of the pseudo-inverse of the Jacobian matrix in real-time. This makes the proposed algorithm computationally more efficient. The proposed scheme has been implemented on a 7 DOF PowerCube? robot manipulator with visual feedback from two cameras.     

A new formulation of visual servoing based on cylindrical coordinate system

Image-based visual servoing is a flexible and robust technique to control a robot and guide it to a desired position only by using two-dimensional visual data. However, it is well known that the classical visual servoing based on the Cartesian coordinate system has one crucial problem, that the camera moves backward at infinity, in case that the camera motion from the initial to desired poses is a pure rotation of 1800 around the optical axis. This paper proposes a new formulation of visual servoing, based on a cylindrical coordinate system that can shift the position of the origin. The proposed approach can interpret from a pure rotation around an arbitrary axis to the proper camera rotational motion. It is shown that this formulation contains the classical approach based on the Cartesian coordinate system as an extreme case with the origin located at infinity. Furthermore, we propose a decision method of the origin-shift parameters by estimating a rotational motion from the differences between initial and desired image-plane positions of feature points.