Efficient exploration of unknown indoor environments using a team of mobile robots

Whenever multiple robots have to solve a common task, they need to coordinate their actions to carry out the task efficiently and to avoid interferences between individual robots. This is especially the case when considering the problem of exploring an unknown environment with a team of mobile robots. To achieve efficient terrain coverage with the sensors of the robots, one first needs to identify unknown areas in the environment. Second, one has to assign target locations to the individual robots so that they gather new and relevant information about the environment with their sensors. This assignment should lead to a distribution of the robots over the environment in a way that they avoid redundant work and do not interfere with each other by, for example, blocking their paths. In this paper, we address the problem of efficiently coordinating a large team of mobile robots. To better distribute the robots over the environment and to avoid redundant work, we take into account the type of place a potential target is located in (e.g., a corridor or a room). This knowledge allows us to improve the distribution of robots over the environment compared to approaches lacking this capability. To autonomously determine the type of a place, we apply a classifier learned using the AdaBoost algorithm. The resulting classifier takes laser range data as input and is able to classify the current location with high accuracy. We additionally use a hidden Markov model to consider the spatial dependencies between nearby locations. Our approach to incorporate the information about the type of places in the assignment process has been implemented and tested in different environments. The experiments illustrate that our system effectively distributes the robots over the environment and allows them to accomplish their mission faster compared to approaches that ignore the place labels.     

Intelligent and Efficient Strategy for Unstructured Environment Sensing Using Mobile Robot Agents

In field environments it is not usually possible to provide robots in advance with valid geometric models of its task and environment. The robot or robot teams need to create these models by scanning the environment with its sensors. Here, an information-based iterative algorithm to plan the robot's visual exploration strategy is proposed to enable it to most efficiently build 3D models of its environment and task. The method assumes mobile robot (or vehicle) with vision sensors mounted at a manipulator end-effector (eye-in-hand system). This algorithm efficiently repositions the systems' sensing agents using an information theoretic approach and fuses sensory information using physical models to yield a geometrically consistent environment map. This is achieved by utilizing a metric derived from Shannon's information theory to determine optimal sensing poses for the agent(s) mapping a highly unstructured environment. This map is then distributed among the agents using an information-based relevant data reduction scheme. This method is particularly well suited to unstructured environments, where sensor uncertainty is significant. Issues addressed include model-based multiple sensor data fusion, and uncertainty and vehicle suspension motion compensation. Simulation results show the effectiveness of this algorithm.     

Concurrent localization of multiple robots

A concurrent localization method for multiple robots using ultrasonic beacons is proposed. This method provides a high-accuracy solution using only low-price sensors. To measure the distance of a mobile robot from a beacon at a known position, the mobile robot alerts one beacon to send out an ultrasonic signal to measure the traveling time from the beacon to the mobile robot. When multiple robots requiring localization are moving in the same block, it is necessary to have a schedule to choose the measuring sequence in order to overcome constant ultrasonic signal interference among robots. However, the increased time delay needed to estimate the positions of multiple robots degrades the localization accuracy. To solve this problem, we propose an efficient localization algorithm for multiple robots, where the robots are in groups of one master robot and several slave robots. In this method, when a master robot calls a beacon, all the group robots simultaneously receive an identical ultrasonic signal to estimate their positions. The effectiveness of the proposed algorithm has been verified through experiments.     

全区域覆盖移动机器人无标识工作环境的边界建立与识别

针对工作在户外环境中的全区域覆盖移动机器人,提出在无人为标识的工作环境中,建立边界和识别边界的新方案. 设计组合传感器定位系统实现工作区域的边界建立和识别. 基于分段策略建立工作边界地图,并对其性能与连续获取策略进行比较分析. 设计RBF神经网络以实时获取精确的定位信息. 实验证明, 定位系统和方案能够保证工作区域边界的准确建立和成功识别,机器人能顺利完成全区域覆盖任务,而且具有一定的工程实用性.     

Deep unsupervised network for multimodal perception,representation and classification

In this paper, we tackle the problem of multimodal learning for autonomous robots. Autonomous robots interacting with humans in an evolving environment need the ability to acquire knowledge from their multiple perceptual channels in an unsupervised way. Most of the approaches in the literature exploit engineered methods to process each perceptual modality. In contrast, robots should be able to acquire their own features from the raw sensors, leveraging the information elicited by interaction with their environment: learning from their sensorimotor experience would result in a more efficient strategy in a life-long perspective. To this end, we propose an architecture based on deep networks, which is used by the humanoid robot iCub to learn a task from multiple perceptual modalities (proprioception, vision, audition). By structuring high-dimensional, multimodal information into a set of distinct sub-manifolds in a fully unsupervised way, it performs a substantial dimensionality reduction by providing both a symbolic representation of data and a fine discrimination between two similar stimuli. Moreover, the proposed network is able to exploit multimodal correlations to improve the representation of each modality alone.     

Perception network for the team of indoor mobile robots: concept,architecture, implementation

The concept of perception network with application to the distributed perception processes taking place among mobile robots operating on the shared shop-floor is discussed. Its relationship with the distributed environment modeling is pointed out. The concept of geometrical database is combined with multiple classes of maps generated with particular physical sensors, in order to obtain the world model. The logical and functional structure of the perception network has been proposed to reflect the semantics of the transportation system consisting of the team of indoor mobile robots.     

分布式视觉机器人导航中的定位算法研究

生物启发的无线复眼导航技术是新型的机器人导航方案,将分布在环境中的分布式智能代替了传统的集中式智能。蒙特卡洛定位是近来流行的机器人自主定位算法,将这种算法应用在分布式视觉传感器机器人的定位中,并针对多视觉传感器观测值的最优选择,提出了一种分布式的基于熵的观测量选择方法,目的是选择那些对提高定位精度更有效的观测信息,在保证定位精度的前提下,提高了定位的实时性和可靠性。仿真实验结果证明了这种算法的可行性。     

A team of mobile robots and monitoring sensors—from concept to experiment

This paper describes the underlying concepts, architecture and implementation of a robotic system consisting of heterogenous mobile robots and stationary sensors, cooperating in a task of collective perception and world modeling. The navigation capability of a group of robots can be improved by sharing available information about the state of the environment (the environment model) and information about the relative position estimates. The information sharing can be especially beneficial to the robots when there are also some stationary monitoring sensors (e.g. cameras) available in the environment, which can serve as external navigation aids. In the article, information processing performed by individual members of the team—robots and sensors—is analyzed and a unifying multi-agent blackboard architecture is described. For information sharing between robots and monitoring sensors, a framework based on the idea of the Contract Net Protocol is proposed. The communication backbone provides agents with unified communication interfaces. The experimental set-up is described. The results of tests validating the correctness of the design on the tasks of cooperative localization and world-model building are reported. A discussion and comparison to other multi-robot systems closes the article.     

A Localization Method Based on Map-Matching and Particle Swarm Optimization

This paper presents a novel localization method for small mobile robots. The proposed technique is especially designed for the Robot@Factory, a new robotic competition which is started in Lisbon in 2011. The real-time localization technique resorts to low-cost infra-red sensors, a map-matching method and an Extended Kalman Filter (EKF) to create a pose tracking system that performs well. The sensor information is continuously updated in time and space according to the expected motion of the robot. Then, the information is incorporated into the map-matching optimization in order to increase the amount of sensor information that is available at each moment. In addition, the Particle Swarm Optimization (PSO) relocates the robot when the map-matching error is high, meaning that the map-matching is unreliable and the robot gets lost. The experiments presented in this paper prove the ability and accuracy of the presented technique to locate small mobile robots for this competition. Extensive results show that the proposed method presents an interesting localization capability for robots equipped with a limited amount of sensors, but also less reliable sensors.     

Fast self-localization method for mobile robots using multiple omnidirectional vision sensors

This paper presents a method for estimating position and orientation of multiple robots from a set of azimuth angles of landmarks and other robots which are observed by multiple omnidirectional vision sensors. Our method simultaneously performs self-localization by each robot and reconstruction of a relative configuration between robots. Even if it is impossible to identify correspondence between each index of the observed azimuth angles and those of the robots, our method can reconstruct not only a relative configuration between robots using `triangle and enumeration constraints' but also an absolute one using the knowledge of landmarks in the environment. In order to show the validity of our method, this method is applied to multiple mobile robots each of which has an omnidirectional vision sensor in simulation and the real environment. The experimental results show that the result of our method is more precise and stabler than that of self-localization by each robot and our method can handle the combinatorial explosion problem. Correspondence to:T. Nakamura (e-mail: ntakayuk@sys.wakayama-u.ac.jp)     

A Neuro-Fuzzy Assisted Extended Kalman Filter-Based Approach for Simultaneous Localization and Mapping (SLAM) Problems

Extended Kalman filter (EKF) has been a popular choice to solve simultaneous localization and mapping (SLAM) problems for mobile robots or vehicles. However, the performance of the EKF depends on the correct a priori knowledge of process and sensor/measurement noise covariance matrices (Q and R, respectively). Imprecise knowledge of these statistics can cause significant degradation in performance. The present paper proposes the development of a new neurofuzzy based adaptive Kalman filtering algorithm for simultaneous localization and mapping of mobile robots or vehicles, which attempts to estimate the elements of the R matrix of the EKF algorithm, at each sampling instant when a ldquomeasurement updaterdquo step is carried out. The neuro-fuzzy based supervision for the EKF algorithm is carried out with the aim of reducing the mismatch between the theoretical and the actual covariance of the innovation sequences. The free parameters of the neuro-fuzzy system are learned offline, by employing particle swarm optimization in the training phase, which configures the training problem as a high-dimensional stochastic optimization problem. By employing a mobile robot to localize and simultaneously acquire the map of the environment, under several benchmark environment situations with varying landmarks and under several conditions of wrong knowledge of sensor statistics, the performance of the proposed scheme has been evaluated. It has been successfully demonstrated that in each case, the neuro-fuzzy assistance is able to improve highly unpredictable, degrading performance of the EKF and can provide robust and accurate solutions.     

Cooperative swarm control for multiple mobile robots using only information from PSD sensors

Recently, many studies on swarm robotics have been conducted in which the aim seems to be the realization of an ability to perform complex tasks by cooperating with each other. Future progress and concrete applications are expected. The objective of this study was to construct a cooperative swarm system by using multiple mobile robots. First, multiple mobile robots with six position-sensitive detector (PSD) sensors were designed. A PSD sensor is a type of photo sensor. A control system was considered to realize swarm behavior, such as that shown by Ligia exotica, by using only information from the PSD sensors. Experimental results showed interesting behavior among the multiple mobile robots, such as following, avoidance, and schooling. The controller of the schooling mode was designed based on subsumption architecture. The proposed system was demonstrated to high school students at OPEN CAMPUS 2010, held in Tokyo University of Science, Yamaguchi.     

基于声音的分布式多机器人相对定位

提出了一种基于声音的分布式多机器人相对定位方法.首先,每个机器人通过声源定位算法估计发声机器人在其局部坐标系下的坐标;然后,每个机器人（不含发声机器人）通过无线通信方式将发声机器人在其坐标系下的坐标广播给所有其他机器人,通过坐标变换每个机器人可计算出所有其他机器人在其坐标系下的坐标,从而实现分布式相对定位.理论推导及实验证明只要两个机器人先后发声,通过本文所提方法即可实现多机器人相对定位.室内外环境中采用6个自制小型移动机器人实验表明,所提方法在3米的范围内可实现16厘米的相对定位精度.     

传感器网络中利用反演集合估计的机器人定位方法

针对大型协作环境中移动机器人的全局定位问题,提出根据机器人车载传感器、环境传感器以及其他机器人的实时数据估计移动机器人的位置。首先,提出的方法整合大量不同类型传感器,从最简单传感器到最复杂传感器;然后,考虑了测量值数量可变、通用测角测量、受容错约束的测量统计知识等约束条件,将非线性边界误差估计问题看作一种反演集合。最后处理特定类型的异常值和不精确环境下的模型误差。完成了误差和异常值的处理,就基本上获得了定位图,解决了移动机器人的定位问题。提出的方法利用实物实验进行验证。测试区域装备有多个传感器、固定在墙顶部的摄像机以及位于机器人上的可见标记。实验结果表明提出的方法在协作环境中具有明显优势,处理异常值更加可靠。     

基于二维码视觉与激光雷达融合的高精度定位算法

为解决以蒙特卡罗定位算法为代表的激光室内定位算法存在的定位精度差和抗机器人绑架性能差的问题,以及传统二维码定位算法环境布置复杂且对机器人运行轨迹有严格要求的问题,提出了一种融合二维码视觉和激光雷达数据的移动机器人定位算法。机器人首先利用机器视觉技术搜索检测环境中的二维码,然后将检测出二维码的位姿分别转换至地图坐标系下,并融合生成先验位姿信息。而后以此作为初始位姿进行点云对准以得到优化后的位姿。同时引入里程计-视觉监督机制,从而有效解决了包括二维码信息缺失、二维码识别错误等由环境因素带来的问题,并保证了位姿的平滑性。基于移动机器人的实验结果表明,所提算法比经典的自适应蒙特卡罗定位（AMCL）算法的雷达采样点平均误差下降了92%,单次位姿计算时间减少了88%,可有效解决机器人绑架问题,并应用于以仓储机器人为代表的室内移动机器人。     

多移动机器人路径规划仿真系统的设计与实现

该文提出了一种多移动机器人路径规划仿真系统的设计方案，并在设计的基础上实现了仿真系统OpenSim。该仿真系统由GUI、业务处理层和存储层组成。GUI是图形用户界面，将仿真系统的各种功能提供给用户；业务处理层进行仿真数据的处理，由仿真平台和各个COM组件服务器组成，机器人传感器、控制器和协调器在COM组件中实现；存储层存储仿真过程中的数据，程序通过在存储层数据库中读写数据来获得和发布信息。该系统具有很好的通用性、分布式运行能力和强大的与用户的交互能力，极大地方便了对多移动机器人路径规划算法的研究。     

A Probabilistic Approach to Collaborative Multi-Robot Localization

This paper presents a statistical algorithm for collaborative mobile robot localization. Our approach uses a sample-based version of Markov localization, capable of localizing mobile robots in an any-time fashion. When teams of robots localize themselves in the same environment, probabilistic methods are employed to synchronize each robot's belief whenever one robot detects another. As a result, the robots localize themselves faster, maintain higher accuracy, and high-cost sensors are amortized across multiple robot platforms. The technique has been implemented and tested using two mobile robots equipped with cameras and laser range-finders for detecting other robots. The results, obtained with the real robots and in series of simulation runs, illustrate drastic improvements in localization speed and accuracy when compared to conventional single-robot localization. A further experiment demonstrates that under certain conditions, successful localization is only possible if teams of heterogeneous robots collaborate during localization.     

分布式视觉机器人导航中的定位算法研究

生物启发的无线复眼导航技术是新型的机器人导航方案,将分布在环境中的分布式智能代替了传统的集中式智能。蒙特卡洛定位是近来流行的机器人自主定位算法,将这种算法应用在分布式视觉传感器机器人的定位中,并针对多视觉传感器观测值的最优选择,提出了一种分布式的基于熵的观测量选择方法,目的是选择那些对提高定位精度更有效的观测信息,在保证定位精度的前提下,提高了定位的卖时性和可靠性。仿真实验结果证明了这种算法的可行性。     

Identification and tracking of robots in an intelligent space using static cameras and an XPFCP

This paper tackles the problem of identification and tracking of multiple robots in an intelligent space using an array of cameras placed in fixed positions within the environment. Several types of agent can be found in an intelligent space: controlled agents (mobile robots) and uncontrolled ones (users and obstacles). The information transferred between the controlled agents and the intelligent space is limited to the control commands sent to the robots and the measurements of the odometers received from the robots. The proposed solution allows the localization of mobile agents, even if they are not robots; however, we have focused on the controlled agents. The proposal does not require prior knowledge or invasive landmarks on board the robots. It starts from the segmentation of different agents in motion that allows obtaining the boundaries of all robots and an estimation of all 3D points that define those boundaries. Then, the identification of the robots is obtained by comparing the components of the linear velocity estimated by the motion segmentation algorithm and received from the odometers. In order to track the robots, an eXtended Particle Filter with Classification Process (XPFCP) is employed. Several experimental tests have been carried out, and the results obtained validate the proposal.     

Generalized measuring-worm algorithm: high-accuracy mapping and movement via cooperating swarm robots

Recently, many extensive studies have been conducted on robot control via self-positioning estimation techniques. In the simultaneous localization and mapping (SLAM) method, which is one approach to self-positioning estimation, robots generally use both autonomous position information from internal sensors and observed information on external landmarks. SLAM can yield higher accuracy positioning estimations depending on the number of landmarks; however, this technique involves a degree of uncertainty and has a high computational cost, because it utilizes image processing to detect and recognize landmarks. To overcome this problem, we propose a state-of-the-art method called a generalized measuring-worm (GMW) algorithm for map creation and position estimation, which uses multiple cooperating robots that serve as moving landmarks for each other. This approach allows problems of uncertainty and computational cost to be overcome, because a robot must find only a simple two-dimensional marker rather than feature-point landmarks. In the GMW method, the robots are given a two-dimensional marker of known shape and size and use a front-positioned camera to determine the marker distance and direction. The robots use this information to estimate each other’s positions and to calibrate their movement. To evaluate the proposed method experimentally, we fabricated two real robots and observed their behavior in an indoor environment. The experimental results revealed that the distance measurement and control error could be reduced to less than 3 %.