空地协同机器人目标定位方法

针对空地协同机器人中无人机对地面无人车的实时精准定位问题,提出一种红色双圆型定位标记及标记识别与定位方法。引入颜色分割与轮廓提取相结合的方式,减少提取到的轮廓特征数量,排除背景信息干扰以减少误识别;提出一种圆形轮廓快速检测算法,快速识别目标轮廓并准确定位目标像素坐标和方向;基于针孔相机成像模型,根据目标像素坐标和方向,估计出目标在机体坐标系下三维坐标和偏航角。实验结果表明,无人机与地面无人车相对高度1.5 m时,该方法在[x]轴和[y]轴方向定位误差分别为3.9 mm和3.6 mm,每帧图像平均处理耗时为11.6 ms,优于基于核相关滤波的识别定位方法的13.3 mm、14.3 mm和56.3 ms。该方法与无人机控制相结合,可以实现无人机协同跟踪与自主降落功能,提升空地协同机器人作业效率,具有显著的工程意义。     

Decentralized planning and control for UAV–UGV cooperative teams

In this paper we study a symbiotic aerial vehicle-ground vehicle robotic team where unmanned aerial vehicles (UAVs) are used for aerial manipulation tasks, while unmanned ground vehicles (UGVs) aid and assist them. UGV can provide a UAV with a safe landing area and transport it across large distances, while UAV can provide an additional degree of freedom for the UGV, enabling it to negotiate obstacles. We propose an overall system control framework that includes high-accuracy motion planning for each individual robot and ad-hoc decentralized mission planning for complex missions. Experimental results obtained in a mockup arena for parcel transportation scenario show that the system is able to plan and execute missions in various environments and that the obtained plans result in lower energy consumption.     

Federated‐filter‐based unmanned ground vehicle localization using 3D range registration with digital elevation model in outdoor environments

An integrated GPS/INS does not guarantee localization robustness in outdoor environments, because GPS is vulnerable to external disturbances. However, a digital elevation model (DEM) contains 3D data on the terrain over a specified area and hence can provide in‐depth localization information during GPS blockage. This paper proposes federated‐filter‐based localization using three‐dimensional (3D) range registration with a DEM. A no‐reset‐feedback method is used and a 3D LIDAR sensor, magnetic compass, and odometer are used to correct INS errors in GPS blockage. For 3D range registration with DEM, this paper presents a framework based on the weighted registration scheme of two transformations, pairwise registration and registration with DEM, with the INS position and attitude information. The transformation is first determined by comparing the results of two registration methods with the INS position and is then modified to replace the orientation result of 3D registration with the INS attitude. A multilayered DEM approach using the height of the integrated system is also used to constrain the search range of DEM into three layers near the current unmanned ground vehicle (UGV) position when the corresponding point is searched for in the DEM. Experimental results show that the proposed localization algorithm can greatly enhance the robustness and accuracy of UGV localization in outdoor environments. © 2012 Wiley Periodicals, Inc.     

空地正交视角下的多机器人协同定位及融合建图

针对单一机器人在复杂场景下进行同步定位与建图存在的视角局限等问题,本文提出了一种空地正交视角下的空中无人机与地面机器人协同定位与融合建图方法.鉴于无人机的空中视角与地面机器人视角属于正交关系,该方法主要思想是解决空地正交视角的坐标系转换问题.首先,设计了一种空中无人机和地面机器人协同定位与建图的框架,通过无人机提供的全局俯视图像与地面机器人的局部平视图像获得全面丰富的场景信息.在此基础上,通过融合惯性测量单元和图像信息修正偏移并优化轨迹,利用地面机器人上带有尺度信息的视觉标识,获得坐标系转换矩阵以融合地图.最后多组真实场景实验验证了该方法具有有效性,是空地协同多机器人协同定位及融合建图(simultaneous localization and mapping, SLAM)领域中值得参考的方法.     

基于高基尼不纯度的UAV&UGV协作监测系统路径规划

空地异构机器人系统由无人机和地面车组成,通过两者相互协作完成持续监测任务可以提高工作效率、解决无人机续航能力不足的问题.在该异构机器人系统中,地面车可以为无人机进行补能,保证监测任务的持续性.由于周期性的监测路径极易发生监测规律信息的泄露,提高无人机监测路径的随机性具有重要意义.针对此问题,引入基尼不纯度指标来评估监测路径的随机性,以目标点的归一化访问间隔时间及其基尼不纯度的加权之和最小为优化目标,建立无人机和地面车协作系统持续监测路径规划模型,提升监测路径的隐私性.采用蚁群算法对无人机监测路径和地面车补能路径进行优化求解,验证了模型的有效性与合理性.通过与其他算法比较,说明了蚁群算法具有更快的搜索速度和运行效率.     

Selective Combination of Visual and Thermal Imaging for Resilient Localization in Adverse Conditions: Day and Night,Smoke and Fire

Long‐term autonomy in robotics requires perception systems that are resilient to unusual but realistic conditions that will eventually occur during extended missions. For example, unmanned ground vehicles (UGVs) need to be capable of operating safely in adverse and low‐visibility conditions, such as at night or in the presence of smoke. The key to a resilient UGV perception system lies in the use of multiple sensor modalities, e.g., operating at different frequencies of the electromagnetic spectrum, to compensate for the limitations of a single sensor type. In this paper, visual and infrared imaging are combined in a Visual‐SLAM algorithm to achieve localization. We propose to evaluate the quality of data provided by each sensor modality prior to data combination. This evaluation is used to discard low‐quality data, i.e., data most likely to induce large localization errors. In this way, perceptual failures are anticipated and mitigated. An extensive experimental evaluation is conducted on data sets collected with a UGV in a range of environments and adverse conditions, including the presence of smoke (obstructing the visual camera), fire, extreme heat (saturating the infrared camera), low‐light conditions (dusk), and at night with sudden variations of artificial light. A total of 240 trajectory estimates are obtained using five different variations of data sources and data combination strategies in the localization method. In particular, the proposed approach for selective data combination is compared to methods using a single sensor type or combining both modalities without preselection. We show that the proposed framework allows for camera‐based localization resilient to a large range of low‐visibility conditions.     

Vision‐based Localization and Robot‐centric Mapping in Riverine Environments

This paper presents a vision‐based localization and mapping algorithm developed for an unmanned aerial vehicle (UAV) that can operate in a riverine environment. Our algorithm estimates the three‐dimensional positions of point features along a river and the pose of the UAV. By detecting features surrounding a river and the corresponding reflections on the water's surface, we can exploit multiple‐view geometry to enhance the observability of the estimation system. We use a robot‐centric mapping framework to further improve the observability of the estimation system while reducing the computational burden. We analyze the performance of the proposed algorithm with numerical simulations and demonstrate its effectiveness through experiments with data from Crystal Lake Park in Urbana, Illinois. We also draw a comparison to existing approaches. Our experimental platform is equipped with a lightweight monocular camera, an inertial measurement unit, a magnetometer, an altimeter, and an onboard computer. To our knowledge, this is the first result that exploits the reflections of features in a riverine environment for localization and mapping.     

Robust Navigation and Mapping Architecture for Large Environments

This paper addresses the problem of Simultaneous Localization and Mapping (SLAM) for very large environments. A hybrid architecture is presented that makes use of the Extended Kalman Filter to perform SLAM in a very efficient form and a Monte Carlo localizer to resolve data association problems potentially present when returning to a known location after a large exploration period. Algorithms to improve the convergence of the Monte Carlo filter are presented that consider vehicle and sensor uncertainty. The proposed algorithm incorporates significant integrity to the standard SLAM algorithms by providing the ability to handle multimodal distributions over robot pose in real time during the re‐localization process. Experimental results in outdoor environments are presented to demonstrate the performance of the algorithm proposed. © 2003 Wiley Periodicals, Inc.     

Improved visual SLAM: a novel approach to mapping and localization using visual landmarks in consecutive frames

Pathfinding is becoming more and more common in autonomous vehicle navigation, robot localization, and other computer vision applications. In this paper, a novel approach to mapping and localization is presented that extracts visual landmarks from a robot dataset acquired by a Kinect sensor. The visual landmarks are detected and recognized using the improved scale-invariant feature transform (I-SIFT) method. The methodology is based on detecting stable and invariant landmarks in consecutive (red-green-blue depth) RGB-D frames of the robot dataset. These landmarks are then used to determine the robot path, and a map is constructed by using the visual landmarks. A number of experiments were performed on various datasets in an indoor environment. The proposed method performs efficient landmark detection in various environments, which includes changes in rotation and illumination. The experimental results show that the proposed method can solve the simultaneous localization and mapping (SLAM) problem using stable visual landmarks, but with less computation time.     

Robust Navigation and Seamless Localization for Carlike Robots in Indoor‐outdoor Environments

This paper describes a navigation and seamless localization system that permits carlike robots to move safely in heterogeneous scenarios within indoor and outdoor environments. The robot localization integrates different sensor (GPS, odometry, laser rangefinders) information depending on the kind of area (indoors, outdoors, and areas between) or on the sensor uncertainty in such a way that there are no discontinuities in the localization, and a bounded uncertainty is constantly maintained. Transitions through indoor and outdoor environments are thoroughly considered to assure a smooth change in‐between. The paper addresses a navigation technique that combines two well‐known obstacle avoidance techniques, namely the nearness diagram and the dynamic window approaches, exploiting the advantages and properties of both, and integrating the seamless localization technique. The navigation technique is developed for carlike robots by considering their shape and kinodynamic constraints, and the restrictions imposed by the environment. Forward‐backward maneuvers are also integrated in the method, allowing difficult situations in dense scenarios to be managed. The whole system has been tested in simulations and experiments in real large‐scale scenarios.     

基于似然域背景差分的行人检测和跟踪方法

基于激光雷达的室内机器人行人检测、跟踪容易受到复杂背景的影响。针对这种情况,提出一种基于似然域背景差分的行人检测、跟踪和跟随系统。利用即时定位与地图构建算法获得陌生环境的二维栅格地图,通过蒙特卡洛定位获得机器人在地图中的后验位姿,利用似然域模型分割出前景对应的激光雷达数据后,进行行人的检测、跟踪以及跟随。实验结果表明,该系统使行人检测准确率提升3.49%,平均检测时间缩短近32%,有效降低复杂背景对多行人检测与跟踪的影响,实现机器人对目标行人的实时跟随。     

Path planning in GPS-denied environments via collective intelligence of distributed sensor networks

This paper proposes a framework for reactive goal-directed navigation without global positioning facilities in unknown dynamic environments. A mobile sensor network is used for localising regions of interest for path planning of an autonomous mobile robot. The underlying theory is an extension of a generalised gossip algorithm that has been recently developed in a language-measure-theoretic setting. The algorithm has been used to propagate local decisions of target detection over a mobile sensor network and thus, it generates a belief map for the detected target over the network. In this setting, an autonomous mobile robot may communicate only with a few mobile sensing nodes in its own neighbourhood and localise itself relative to the communicating nodes with bounded uncertainties. The robot makes use of the knowledge based on the belief of the mobile sensors to generate a sequence of way-points, leading to a possible goal. The estimated way-points are used by a sampling-based motion planning algorithm to generate feasible trajectories for the robot. The proposed concept has been validated by numerical simulation on a mobile sensor network test-bed and a Dubin’s car-like robot.     

Vehicle Localization in Outdoor Mountainous Forested Paths and Extension of Two-Dimensional Road Centerline Maps to Three-Dimensional Maps

This paper presents an approach for vehicle three-dimensional (3-D) localization in outdoor woodland environments where a previously available two-dimensional road centerline map is used in combination with a loosely coupled multi-sensor system to estimate the vehicle position in mountainous forested paths. The localization system is composed of a wheel encoder, an inertial measurement unit, a DGPS, a laser sensor and a barometer. An extended Kalman filter is used for sensor data fusion and pose estimation. When available, DGPS is used for 3-D dead reckoning accumulated error correction. During DGPS blackouts, the laser sensor is used for road extraction and measurement of the displacement of the vehicle to the road centerline, then the position is corrected towards the map. Moreover, the barometer that measures the height difference towards a reference is used to correct the estimated height in absence of DGPS 3-D data. The estimated height is added to the available road map to obtain a 3-D road centerline map that includes the road width measured with the laser sensor. Experimental results in large-scale real mountainous woodland environments show the robustness and simplicity of the proposed approach for vehicle localization and 3-D map extension.     

Underwater place recognition using forward‐looking sonar images: A topological approach

Autonomous underwater vehicles are a prominent tool for underwater exploration because they can access dangerous places avoiding the risks for the human beings. However, the autonomous navigation still a challenge due to the characteristics of the environment that decrease the performance of the sensor and the robot perception. In this context, this paper proposes a loop closure detector addressed to the simultaneous localization and mapping problem at semistructured environments using acoustic images acquired by forward‐looking sonars. The images are segmented by an adaptative approach based on the acoustic beams analysis. A pose‐invariant topological graph is build to represent the relationship between image features. The loop closure detection is achieved using a graph comparison. The approach is evaluated in a real environment at a marina. The results reveal all loop closures of the data set are detected with a high precision and present an invariant to image rotation.     

Real-time hierarchical POMDPs for autonomous robot navigation

This paper proposes a new hierarchical formulation of POMDPs for autonomous robot navigation that can be solved in real-time, and is memory efficient. It will be referred to in this paper as the Robot Navigation–Hierarchical POMDP (RN-HPOMDP). The RN-HPOMDP is utilized as a unified framework for autonomous robot navigation in dynamic environments. As such, it is used for localization, planning and local obstacle avoidance. Hence, the RN-HPOMDP decides at each time step the actions the robot should execute, without the intervention of any other external module for obstacle avoidance or localization. Our approach employs state space and action space hierarchy, and can effectively model large environments at a fine resolution. Finally, the notion of the reference POMDP is introduced. The latter holds all the information regarding motion and sensor uncertainty, which makes the proposed hierarchical structure memory efficient and enables fast learning. The RN-HPOMDP has been experimentally validated in real dynamic environments.     

Multimodal localization: Stereo over LiDAR map

In this paper, we present a real‐time high‐precision visual localization system for an autonomous vehicle which employs only low‐cost stereo cameras to localize the vehicle with a priori map built using a more expensive 3D LiDAR sensor. To this end, we construct two different visual maps: a sparse feature visual map for visual odometry (VO) based motion tracking, and a semidense visual map for registration with the prior LiDAR map. To register two point clouds sourced from different modalities (i.e., cameras and LiDAR), we leverage probabilistic weighted normal distributions transformation (ProW‐NDT), by particularly taking into account the uncertainty of source point clouds. The registration results are then fused via pose graph optimization to correct the VO drift. Moreover, surfels extracted from the prior LiDAR map are used to refine the sparse 3D visual features that will further improve VO‐based motion estimation. The proposed system has been tested extensively in both simulated and real‐world experiments, showing that robust, high‐precision, real‐time localization can be achieved.     

通信时延下UAV/UGV混合编队控制系统的稳定性分析

针对通信时延下的高维异构无人机(UAV,unmanned aerial vehicle)/无人车(UGV,unmanned ground vehicle)混合编队控制系统,对系统稳定的充分必要条件和准确时延边界的计算方法进行了研究;具体地,为了处置UAV/UGV工作空间、运动学模型的差异,建立考虑异构特性的UAV/UGV混合编队模型;并针对UAV群组、UGV群组,分别设计基于信息一致性的分布式控制器;利用矩阵相似变换,将高维异构的UAV/UGV混合编队控制系统降维拆分为若干等价的低维子系统,极大地降低了稳定性分析的解析难度和运算量;在此基础上,利用辅助特征函数法推导准确的时延边界,得到系统稳定的充要条件;最后通过仿真验证了所提出稳定性分析方法的有效性。     

Feature extraction for outdoor mobile robot navigation based on a modified Gauss–Newton optimization approach

This paper discusses the problem of feature detection for semi-structured outdoor environments such as campuses and parks using laser range sensors. In these environments, commonly encountered natural features that can be very useful for mobile robot navigation include edges (large discontinuity) and circles (e.g., trees, pillars). The term feature is used to denote objects which are “likely” to be detectable when the sensor is moved to new locations. Note that there has been no systematic approach for feature detection in outdoor environments. In this paper, we present an algorithm for feature detection. The algorithm consists of data segmentation and parameter acquisition. A modified Gauss–Newton method is proposed for fitting circle parameters iteratively. Experimental results show that the proposed algorithm is efficient in detecting features for semi-structured outdoor environments and is applicable to real time simultaneous localization and mapping.     

Nonlinear robust adaptive Cartesian impedance control of UAVs equipped with a robot manipulator

In this paper, a new nonlinear robust adaptive impedance controller is addressed for Unmanned Aerial Vehicles (UAVs) equipped with a robot manipulator that physically interacts with environment. A UAV equipped with a robot manipulator is a novel system that can perform different tasks instead of human being in dangerous and/or inaccessible environments. The objective of the proposed robust adaptive controller is control of the UAV and its robotic manipulator’s end-effector impedance in Cartesian space in order to have a stable physical interaction with environment. The proposed controller is robust against parametric uncertainties in the nonlinear dynamics model of the UAV and the robot manipulator. Moreover, the controller has robustness against the bounded force sensor inaccuracies and bounded unstructured modeling (nonparametric) uncertainties and/or disturbances in the system. Tracking performance and stability of the system are proved via Lyapunov stability theorem. Using simulations on a quadrotor UAV equipped with a three-DOF robot manipulator, the effectiveness of the proposed robust adaptive impedance controller is investigated in the presence of the force sensor error, and parametric and non-parametric uncertainties.     

Localization of mobile robots: Development and comparative evaluation of algorithms based on odometric and inertial sensors

An autonomous mobile robot must be able to elaborate the measures provided by the sensor equipment to localize itself with respect to a coordinate system. The precision of the location estimate depends on the sensor accuracy and on the reliability of the measure processing algorithm. The purpose of this article is to propose a low cost positioning system using internal sensors like odometers and optical fiber gyroscopes. Three simple localization algorithms based on different sensor data processing procedures are presented. Two of them operate in a deterministic framework, the third operates in a stochastic framework where the uncertainty is induced by sensing and unmodeled robot dynamics. The performance of the proposed localization algorithms are tested through a wide set of laboratory experiments and compared in terms of localization accuracy and computational cost. © 2005 Wiley Periodicals, Inc.