一种新颖的基于两个特征点的室内移动机器人定位方法

提出了一种新颖的基于两个特征点的室内移动机器人定位方法。与已有的几何位姿估计方法或航标匹配方法不同，该方法不需要人工航标，也不需要准确的环境地图，只需一幅由传统的CCD相机拍摄的图像。从机器人接近的目标上选取相对于地面等高的两个点作为两个特征点。基于这两点建立一个目标坐标系。在相机平视且这两个特征点与相机投影中心相对于地面不是恰好等高的条件下，就可以根据这两个特征点在图像中的坐标确定机器人相对于目标坐标系的位置和运动方向。该方法非常灵活，适用范围广，可以大大简化机器人定位问题。试验结果表明这一新的方法不仅简单灵活而且具有很高的定位精度。     

Self-calibration of environmental camera for mobile robot navigation

An environmental camera is a camera embedded in a working environment to provide vision guidance to a mobile robot. In the setup of such robot systems, the relative position and orientation between the mobile robot and the environmental camera are parameters that must unavoidably be calibrated. Traditionally, because the configuration of the robot system is task-driven, these kinds of external parameters of the camera are measured separately and should be measured each time a task is to be performed. In this paper, a method is proposed for the robot system in which calibration of the environmental camera is rendered by the robot system itself on the spot after a system is set up. Specific kinds of motion patterns of the mobile robot, which are called test motions, have been explored for calibration. The calibration approach is based upon executing certain selected test motions on the mobile robot and then using the camera to observe the robot. According to a comparison of odometry and sensing data, the external parameters of the camera can be calibrated. Furthermore, an evaluation index (virtual sensing error) has been developed for the selection and optimization of test motions to obtain good calibration performance. All the test motion patterns are computed offline in advance and saved in a database, which greatly shorten the calibration time. Simulations and experiments verified the effectiveness of the proposed method.     

Compact laparoscopic assistant robot using a bending mechanism

This paper presents the development of a compact laparoscopic assistant robot. The robot was designed to increase convenience and reduce possible interference with surgical staff by confining the majority of motions inside the abdomen. Its size was miniaturized as much as possible for convenient handling. A bending mechanism composed of several articulated joints was introduced to produce motions inside the abdomen. The proposed assistant robot can generate 3-DOF motion, including 2-DOF internal bending motion and 1-DOF external linear motion. Since the robot itself functions as a laparoscope, a small CCD camera module and a bundle of optical fibers were integrated as part of the system. For accurate control, mathematical modeling of the bending mechanism and a method of hysteresis compensation were introduced and implemented. For the control of the robot, a voice interface and a visual-servoing method were implemented. The performance of the developed system was tested through solo-surgery of in vivo porcine cholecystectomy. It was found that the views generated by the bending mechanism were sufficient throughout the surgery. Since the robot has functions comparable to the previously developed systems, while retaining its compactness, it is expected to be a useful device for human cholecystectomy.     

An adaptive observer for a spacecraft–manipulator system using a camera mounted on its spacecraft

This paper deals with a motion control system for a space robot with a manipulator. Many motion controllers require the positions of the robot body and the manipulator hand with respect to an inertial coordinate system. In order to measure them, a visual sensor using a camera is frequently used. However, there are two difficulties in measuring them by means of a camera. The first one is that a camera is mounted on the robot body, and hence it is difficult to directly measure the position of the robot body by means of it. The second one is that the sampling period of a vision system with a general-purpose camera is much longer than that of a general servo system. In this paper, we develop an adaptive state observer that overcomes the two difficulties. In order to investigate its performance, we design a motion control system that is constructed by combining the observer with a PD control input, and then conduct numerical simulations for the control system. Simulation results demonstrate the effectiveness of the proposed observer.     

一种五自由度视觉伺服机器人的跟踪控制研究

提出了一种基于图像的视觉伺服机器人系统的结构，以及该系统跟踪平面运动目标的算法. 该系统有5个自由度，包括一个3自由度的机器人和一个2自由度的手腕，手腕安装在机器人末端，而摄像机安装在手腕末端. 由于具有较小的运动惯量，手腕可快速旋转，以实现对运动目标的跟踪. 而在需要时，3自由度的机器人可将摄像机移动到适当的位置， 对目标进行更为仔细的观察. 该系统实现了对运动目标的跟踪. 此外，还提出了提高系统性能的方法，实验证实这些方法是有效的.     

单目视觉智能车的伺服规律研究

通过分析单目视觉智能车的运动特征,建立其空间约束模型以及与运动控制密切相关的图像坐标系和运动平面坐标系,在此基础上根据摄像头相对位姿的不同推导出2种不同的坐标映射关系,讨论将其应用在单目标跟踪和连续目标跟踪时的车体运动控制规律,形成一个有较强针对性和实用价值的手眼机器人视觉伺服框架。实验验证了单目视觉智能车伺服规律的有效性。     

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.     

基于点线特征的解耦视觉伺服控制方法

针对机器人的自动对准问题,提出一种基于点线特征的解耦视觉伺服控制方法。所提方法以点和直线作为图像特征,并利用图像特征的交互矩阵解耦姿态控制和位置控制,实现六自由度对准。首先利用直线及其交互矩阵设计姿态控制律,以消除旋转偏差;然后利用点及其交互矩阵设计位置控制律,以消除位置偏差;最后实现机器人末端目标的自动对准。在对准控制过程中,基于执行的相机运动量以及相机运动前后特征的变化量,可实现对深度的在线估计。另外,还设计了监督器对相机的运动速度进行调节,从而确保特征一直处于相机视野当中。在Eye-in-Hand机器人平台上,分别用所提方法和传统的基于图像的视觉伺服方法实现了机器人的六自由度对准。所提方法经过16步实现了机器人的自动对准,对准结束时机器人末端位姿的最大平移误差为3.26 mm,最大旋转误差为0.72°。相较于对比方法,该方法的控制过程更加高效,控制误差收敛更快,对准误差更小。实验结果表明,所提方法可以实现快速高精度的自动对准,能够提高机器人操作的自主性和智能化水平,有望应用于目标跟踪、拾取和定位、自动化装配、焊接、服务机器人等领域。     

Wide-baseline stereo vision for terrain mapping

Terrain mapping is important for mobile robots to perform localization and navigation. Stereo vision has been used extensively for this purpose in outdoor mapping tasks. However, conventional stereo does not scale well to distant terrain. This paper examines the use of wide-baseline stereo vision in the context of a mobile robot for terrain mapping, and we are particularly interested in the application of this technique to terrain mapping for Mars exploration. In wide-baseline stereo, the images are not captured simultaneously by two cameras, but by a single camera at different positions. The larger baseline allows more accurate depth estimation of distant terrain, but the robot motion between camera positions introduces two new problems. One issue is that the robot estimates the relative positions of the camera at the two locations imprecisely, unlike the precise calibration that is performed in conventional stereo. Furthermore, the wide-baseline results in a larger change in viewpoint than in conventional stereo. Thus, the images are less similar and this makes the stereo matching process more difficult. Our methodology addresses these issues using robust motion estimation and feature matching. We give results using real images of terrain on Earth and Mars and discuss the successes and failures of the technique.     

新型移动机器人激光测距雷达的研究

研制了一种新型的基于激光结构光三维视觉技术的移动机器人模块化测距雷达样机,并提出了多平面靶标的转轴现场标定方案,为实现其对周围环境的扫描测量,首先标定线激光器与网络摄像头的相对位置,利用三角法测量激光交线到摄像头光心的距离。然后标定舵机转轴与摄像机的相对位置,并将旋转的激光交线坐标,统一到一个世界坐标系下,实现扫描测距。三维测量实验中,相对误差0.31%,系统测量误差小于4%。实验证明该样机测量精度高,成本低,具有广阔的应用前景。     

Robust omnidirectional mobile robot topological navigation system using omnidirectional vision

Robust topological navigation strategy for omnidirectional mobile robot using an omnidirectional camera is described. The navigation system is composed of on-line and off-line stages. During the off-line learning stage, the robot performs paths based on motion model about omnidirectional motion structure and records a set of ordered key images from omnidirectional camera. From this sequence a topological map is built based on the probabilistic technique and the loop closure detection algorithm, which can deal with the perceptual aliasing problem in mapping process. Each topological node provides a set of omnidirectional images characterized by geometrical affine and scale invariant keypoints combined with GPU implementation. Given a topological node as a target, the robot navigation mission is a concatenation of topological node subsets. In the on-line navigation stage, the robot hierarchical localizes itself to the most likely node through the robust probability distribution global localization algorithm, and estimates the relative robot pose in topological node with an effective solution to the classical five-point relative pose estimation algorithm. Then the robot is controlled by a vision based control law adapted to omnidirectional cameras to follow the visual path. Experiment results carried out with a real robot in an indoor environment show the performance of the proposed method.     

Human-robot contactless collaboration with mixed reality interface

A control system based on multiple sensors is proposed for the safe collaboration of a robot with a human. New constrained and contactless human-robot coordinated motion tasks are defined to control the robot end-effector so as to maintain a desired relative position to the human head while pointing at it. Simultaneously, the robot avoids any collision with the operator and with nearby static or dynamic obstacles, based on distance computations performed in the depth space of a RGB-D sensor. The various tasks are organized with priorities and executed under hard joint bounds using the Saturation in the Null Space (SNS) algorithm. A direct human-robot communication is integrated within a mixed reality interface using a stereo camera and an augmented reality system. The proposed system is significant for on-line, collaborative quality assessment phases in a manufacturing process. Various experimental validation scenarios using a 7-dof KUKA LWR4 robot are presented.     

Vision-based interception of a moving target with a nonholonomic mobile robot

A novel vision-based scheme is presented for driving a nonholonomic mobile robot to intercept a moving target. The proposed method has a two-level structure. On the lower level, the pan–tilt platform carrying the on-board camera is controlled so as to keep the target as close as possible to the center of the image plane. On the higher level, the relative position of the target is retrieved from its image coordinates and the camera pan–tilt angles through simple geometry, and used to compute a control law which drives the robot to the target. Various possible choices are discussed for the high-level robot controller, and the associated stability properties are rigorously analysed. The proposed visual interception method is validated through simulations as well as experiments on the mobile robot MagellanPro.     

基于立体视觉的串联机器人跟踪检测系统

建立一种六自由度串联机器人视觉跟踪检测系统框架,包括图像采集、摄像机标定、机器臂跟踪检测、机器臂位姿建模与计算等。提出利用CamShift算法对机器人进行在线粗跟踪,搜寻和画定出机器臂操作器在当前窗口的区域位置。对跟踪到的机器臂按照SURF算法进行特征提取与立体匹配。该方法被用于对串联机器人位姿检测进行实验。实验结果表明,2种算法的结合适用于六自由度串联机器人在空间复杂运动的跟踪检测。     

Adaptive position and orientation regulation for the camera‐in‐hand problem

This paper considers the camera‐space position and orientation regulation problem for the camera‐in‐hand problem via visual serving in the presence of parametric uncertainty associated with the robot dynamics and the camera system. Specifically, an adaptive robot controller is developed that forces the end‐effector of a robot manipulator to move such that the position and orientation of an object are regulated to a desired position and orientation in the camera‐space, despite parametric uncertainty throughout the entire robot‐camera system. An extension is also provided that illustrates how slight modifications can be made to the camera‐in‐hand control law to achieve adaptive position and orientation tracking of the end‐effector in the camera‐space for a fixed‐camera configuration. Simulation results are provided to illustrate the performance of the adaptive, camera‐in‐hand controller. © 2005 Wiley Periodicals, Inc.     

A point and distance constraint based 6R robot calibration method through machine vision

This paper proposes a 6R robot closed-loop kinematic calibration method to improve absolute position accuracy with point and distance constraints though machine vision. In the calibration process, a camera attached to the mounting plate of the robot is used to capture a fixed reference sphere as a point constraint and to record robot joint angles and gauge block lengths that are used as a distance constraint. A first-order difference quotient is used to calculate the Jacobian matrix in the joint parameter identification process. The Staübli TX60 robot is successfully calibrated using the proposed method. After calibration, the average distance error of robot motion is decreased from 2.05 mm to 0.24 mm.     

Maintaining a common co-ordinate system for a group of robots based on vision

This work presents a novel approach to the problem of establishing and maintaining a common co-ordinate system for a group of robots. A camera system mounted on top of a robot and vision algorithms are used to calculate the relative position of each surrounding robot. The watched movement of each robot is compared to the reported movement which is sent over some communication link. From this comparison a co-ordinate transformation is calculated. The algorithm was tested in simulation and is at the moment being implemented on a real robot system. Preliminary results of real world experiments are being presented.     

Scrub Nurse Robot for Laparoscopic Surgery

During laparoscopic surgeries, changing forceps is a relatively simple procedure that requires a nurse or another surgeon; however, most hospitals lack a scrub nurse in the operating room. Therefore, we have developed an assisting robot for laparoscopic surgery that is able to pass or receive forceps under the voice control of the surgeon. This robot system consists of a magazine that holds all forceps to be used in one operation and a robot arm that passes or receives forceps between the magazine and surgeon. These two components are located side by side and have a linear actuator for height adjustment. A bar code is attached to the forceps to identify the forceps. This system utilizes speech recognition software and can select the forceps requested by the surgeon. After the robot hand grasps the forceps from the magazine, the arm and the wrist turn to hand the forceps to the surgeon. When the surgeon lays the used forceps on the return holder, the robot returns the forceps to the magazine in a similar motion as when passing the forceps to the surgeon. This robot can, thus, compensate for the shortage of scrub nurses required for surgery.