Second order sliding mode control of vehicles with distributed collision avoidance capabilities

Recent research has shown that the longitudinal control of platoons of vehicles is appropriate to improve the traffic capacity of road networks while maintaining the safety distance between vehicles. This paper investigates the possibility of reducing the number of accidents involving pedestrians or other vulnerable road users (VRUs), like cyclists and motorcyclists, by providing the control systems of the vehicles of the platoon with some collision detection and avoidance capabilities. The control system proposed in this paper allows to maintain a desired distance from the preceeding vehicle, and, as a novelty with respect to other proposals, to avoid the collision with VRUs present on the road. The proposed control scheme is realized by means of a supervisor, which makes the decision on which is the appropriate current control mode for each controlled vehicle, and manages the switches among low-level controllers. The adopted control technique is the so-called sliding mode control methodology, which is particularly suitable to deal with the uncertainties and disturbances typical of automotive applications.     

基于ADS-B的飞机防撞算法

面对飞行流量持续快速增长,民航空域资源日益短缺,对冲突飞机进行有效的解脱,是避免飞机间发生碰撞的关键技术。对飞机保护区域进行合理建模,给出一种基于广播式自动相关监视（ADS．B）技术的冲突解脱算法,该算法有效利用ADS．B的数据精度高、更新快的特点,从水平方向上给出“保向变速”与“保速变向”两类解脱策略,从垂直方向上给出“爬升”和“下降”两种解脱策略。把飞机的水平速度、航向和垂直速度作为控制变量,通过计算冲突解脱的边界条件获得控制变量转换时间,从而找到可行的解脱方法。仿真结果表明,对于同一飞行冲突情形,并不是所有的冲突解脱策略都是可行的,但是对于可行的冲突解脱策略,需要由飞行员根据当时的具体情况去决定哪种解脱方式是最优的。     

基于激光与视觉的车辆防撞技术的研究

提出了一种基于视觉与激光测距相结合的车辆防撞技术.首先采用改进的Hough变换对车道标志线进行检测与提取,根据车辆底部的阴影特征搜寻车辆可能出现的位置;利用边缘检测排除非车辆区域;然后结合车辆在图像中的宽度,利用激光测距传感器对前方车辆动态扫描,计算出两车的车距和相对速度;最后用卡尔曼滤波算法连续跟踪检测到的车辆;实验表明:该方法能够实时有效地检测前方车辆,在高精度汽车防撞系统中具有一定的意义.     

地面强激光操控空间碎片避碰的控制策略

日益增长的太空碎片为载人空间站和卫星带来严重的安全挑战。2011年，NASA提出使用地面连续激光照射空间碎片，利用其微弱的光压力效应，通过长期积累，改变其轨道，从而预防其与航天器可能的碰撞。这一碰撞避免方法并不把太空碎片拉回大气层内，而是防止碰撞，由于不需要航天器机动，且光压的温和作用也对激光器发射功率没有太高要求，因此这种避碰方法受到广泛关注。然而，该方法的提出者采用的迎面照射控制律尽管简单但非最优，故需要设计最优控制律。通过建立两点边值问题模型，以两物体之间距离的最大化为控制目标，求解了最优性条件。仿真显示，经优化后控制律的避碰效果提高程度非常显著，提高幅度与初轨有关，通常为25%~125%。     

Development of a Scaled Vehicle With Longitudinal Dynamics of an HMMWV for an ITS Testbed

This paper applies Buckingham's pi theorem to the problem of building a scaled car whose longitudinal and power-train dynamics are similar to those of a full-size high-mobility multipurpose wheeled vehicle (HMMWV). The scaled vehicle uses hardware-in-the-loop (HIL) simulation to capture some of the scaled HMMWV dynamics physically, and simulates the remaining dynamics onboard in real time. This is performed with the ultimate goal of testing cooperative collision avoidance algorithms on a testbed comprising a number of these scaled vehicles. Both simulation and experimental results demonstrate the validity of this HIL-based scaling approach.     

A Resilient and Scalable Flocking Scheme in Autonomous Vehicular Networks

Vehicular Ad hoc NETworks (VANET) is emerging as a highly promising technology, which aims to provide road safety, environment protection and personal-oriented services. The vehicle ad hoc wireless communications form an indispensable part of truly ubiquitous communications networking. VANET is formed by spontaneously moving autonomous vehicles with the self-organization and self-management capability. In this paper, we focus on the decentralized coordination of multiple unmanned vehicles such that they can freely move and adaptively cooperate in a complex environment. During this procedure, flocking is one of the key operations and requirements. Here, flocking refers to the formation and maintenance of a desired pattern by a group of mobile vehicles without collision during movement. We propose a resilient and scalable flocking scheme for a group of vehicles, which follows the leader–followers moving pattern. In the absence of obstacles, a collision avoidance algorithm is presented to maintain a desired distance among vehicles. This will ensure information completeness and is significant in certain mission critical situations without collision between a unmanned vehicle and its neighboring vehicles. In the presence of obstacles in an environment, this algorithm is able to avoid collision between a vehicle and its neighbor (either a neighboring vehicle or a neighboring obstacle). Theoretical proof has been presented to demonstrate the effectiveness and correctness of the algorithm to guarantee collision-free. In addition, with increasing number of vehicles, the performance of the proposed flocking scheme performs without increasing the processing overhead, which demonstrates the desirable scalability.     

Longitudinal control of a platoon of vehicles with no communicationof lead vehicle information: a system level study

The paper considers the problem of longitudinal control of a platoon of automotive vehicles on a straight lane of a highway and proposes control laws in the event of loss of communication between the lead vehicle and the other vehicles in the platoon. After discussing the main design objectives for the proposed control laws, the authors formulate these objectives as a constrained optimization problem. By solving this optimization problem, they obtain longitudinal control laws for a platoon of vehicles which does not use any communication from the lead vehicle to the other vehicles in the platoon. Comparison between these control laws and the control laws which use such a communication link to transmit lead-vehicle information to the other vehicles in a platoon shows that, in the case of loss of communication between the lead vehicle and the other vehicles, the performance of the longitudinal control laws degrades; however, this degradation is not catastrophic     

A Wireless MAC Protocol with Collision Detection

The most popular strategies for dealing with packet collisions at the medium access control (MAC) layer in distributed wireless networks use a combination of carrier sensing and collision avoidance. When the collision avoidance strategy fails, such schemes cannot detect collisions and corrupted data frames are still transmitted in their entirety, thereby wasting the channel bandwidth and significantly reducing the network throughput. To address this problem, this paper proposes a new wireless MAC protocol capable of collision detection. The basic idea of the proposed protocol is the use of pulses in an out-of-band control channel for exploring channel condition and medium reservation and achieving both collision avoidance and collision detection. The performance of the proposed MAC protocol has been investigated using extensive analysis and simulations. Our results show that, as compared with existing MAC protocols, the proposed protocol has significant performance gains in terms of node throughput. Additionally, the proposed protocol is fully distributed and requires no time synchronization among nodes.     

Vision-Based Target Tracking and Collision Avoidance for Two Autonomous Robotic Fish

A new type of vision-based autonomous robotic fish capable of 3-D locomotion is developed in this paper. Based on our robotic fish prototype, the forces and moments acting on its fins and body are analyzed, and the governing motion equations are derived. We further investigate a decentralized control method in target-tracking and collision-avoidance task for two autonomous robotic fish. Most of previous work on the task strategies of autonomous robots is focused on terrestrial robots and seldom deals with underwater applications due to the uncertainties and complexity in a hydro environment. To address this challenge in such an underwater task, a situated-behavior-based decentralized control is employed on each robotic fish according to its visual data. On dealing with motion planning of the fish during target tracking and collision avoidance, a control law by a combination of an attractive force toward a target and a repulsive force for collision avoidance is utilized. Experimental results of the task performed by two autonomous robotic fish validate the effectiveness of the proposed method.     

基于红外的障碍场中集群微机器人的控制方法

对多障碍物环境下微机器人集群运动的控制问题进行了研究.结合微机器人尺寸小的特点,采用低功耗的红外传感器感知外界环境.设定机器人的安全区域,根据机器人运动过程中避障和路径规划所要满足的边界条件,提出了基于人工蜂群问题优化的路径规划控制模型,实现了微机器人的避障和路径规划.仿真结果验证了该控制方法的有效性.     

Novel Collision Detection and Avoidance System for Midvehicle Using Offset-Based Curvilinear Motion

In recent days, the manufacture of automotive vehicles is dramatically enhanced worldwide. Most vehicle crashes are due to the drive distraction on the real highway roads and traffic-density. In this proposed method, a novel collision detection and avoidance algorithm are coined for Midvehicle Collision Detection and Avoidance System (MCDAS), addressing two scenarios, namely, (a) A rear-end collision avoidance with host vehicle under no front-end vehicle condition and (b) offset-based curvilinear motion under critical conditions, while, suitable parallel parking manoeuvring also addressed using offset-based curvilinear motion. The Monte Carlo analysis of the proposed MCDAS is demonstrated using the Constant Velocity (CV) manoeuvring strategy and simulated with real-time data using the NGSIM database.

     

Cluster based emergency message broadcasting technique for vehicular ad hoc network

Broadcasting is one of the major emergency services of Vehicular ad hoc network, since the number of vehicles increases every day. Because of the high density of the vehicles, it is necessary to broadcast emergency messages to all the vehicles to avoid traffic jam and vehicle accidents. Reliable broadcasting of messages in self-organizing Ad hoc networks is a promising research field. In this paper a cluster based emergency message broadcasting algorithm is proposed. In this regard we have proposed cluster based architecture for emergency message dissemination and collision avoidance in VANET. In this paper, first the formation of cluster is done in such a way that it avoids any kind of collision. Once cluster head is selected it takes the responsibility of intra cluster management to avoid interference between the clusters. To increase the reliability during emergency message dissemination two MAC layer broadcasts protocol is used. This assures that message is delivered on time without any hazards. The proposed model is simulated for DSDV, AODV, and DSR protocols with the standards 802.11 and 802.11p in SHWM, Manhattan and freeway mobility models.     

A bandwidth-efficient and fair CSMA/TDMA based multichannel MAC scheme for V2V communications

Designing QoS-aware medium access control (MAC) scheme is a challenging issue in vehicular ad hoc networks. Proportional fairness and bandwidth utilization are among the significant requirements that should be taken into account by a MAC scheme. In this paper, a bandwidth-efficient and fair multichannel MAC protocol is proposed to address these two requirements, specifically in vehicle-to-vehicle communications. The proposed scheme is based on clustering of vehicles and exploits time division multiple access (TDMA) method alongside the carrier sense multiple access with collision avoidance mechanism to allocate DSRC-based resources in a different manner from IEEE 802.11p/IEEE 1609.4 protocols. It divides each channel into aligned dynamic-sized time frames. In each time frame, in a fully TDMA-based period, transmission opportunities are assigned to vehicles letting them have dedicated transmissions on the service and control channels. The maximum number of transmission opportunities per each frame is determined by the cluster head (CH) based on a defined optimization problem which aims at maximizing both proportional fairness and bandwidth utilization. Furthermore, the bandwidth utilization is assumed to be enhanced more through reallocation of unused transmission opportunities in each time frame, using a proposed reallocation algorithm. The proposed MAC protocol is treated as a lightweight scheme such that various types of unicast, multicast and broadcast communications are possible within the cluster without involving the CH. Evaluation results show that the proposed scheme has more than 90 % achievement in terms of proportional fairness and bandwidth utilization simultaneously, and in this case, has a considerable superiority over TC-MAC. In addition, using the proposed scheme, the satisfaction level of vehicles is preserved appropriately.     

Nonlinear brake control for vehicle CW/CA systems

A brake control law for vehicle collision warning/collision avoidance (CW/CA) systems has been proposed in the paper. The control law has been designed for optimized safety and comfort. A solenoid-valve-controlled hydraulic brake actuator system for the CW/CA systems has been investigated. A nonlinear computer model and a linear model of the hydraulic brake actuator system have been developed. Both models were found to represent the actual system with good accuracy. Uncertainties in the brake actuator model have been considered in the design of the control law for the robustness of the controller. The effects of brake control on CW/CA vehicle response has been investigated via simulations. The simulations were performed using a complete nonlinear vehicle model. The results indicate that the proposed brake control law can provide the CW/CA vehicles with an optimized compromise between safety and comfort     

Virtual environments for Internet-based robots. II. Path planning

For pt.I. see ibid., p.383-8. This paper addresses the issue of path planning in a virtual environment (VE) for the control of an Internet-based robot manipulator. A hybrid method is proposed in which the dimension of the path-planning problem is reduced by separating the problem of planning the position of the gripper from that of planning the pose of the gripper. A global configuration-space technique is used for the former and a local operational-space technique is used for the latter. Particular attention is paid to fundamental issues such as mapping the graphical model into configuration space, on-line collision detection and obstacle avoidance in the VE.     

Sliding-Mode Formation Control for Cooperative Autonomous Mobile Robots

This paper considers the control of a group of autonomous mobile robots. A coordinated control scheme based on a leader–follower approach is developed to achieve formation maneuvers. First and second order sliding-mode controllers are proposed for asymptotically stabilizing the vehicles to a time-varying desired formation. The latter controller, based on the relative motion states, eliminates the need for measurement or estimation of the leader velocity. It enables formation stabilization using a vision system carried by the followers and ensures the collision avoidance from the initial time instance. Experimental investigation has been conducted using a test bench made of three nonholonomic mobile robots in order to demonstrate the effectiveness of the proposed strategy.      

A position control differential drive wheeled mobile robot

For more accurate path tracking of a four-wheeled two-degrees-of-freedom mobile robot (WMR), a position control algorithm is proposed with two separated feedback loops, a velocity feedback loop and a position feedback loop. In the most conventional position control system of a WMR, internal error is mainly considered, while external error has, as yet, hardly been treated, although it plays an important role in accurate position control. This external error is caused by unexpected environmental situations. The proposed control algorithm is designed to compensate for both internal error and external error. This algorithm makes it possible to accurately follow the designed trajectory     

一种低复杂度立体视频错误隐藏新方法

针对立体视频流传输中右视 点整帧丢失,提出 了一种低复杂度的错误隐藏算法。首先,为了高效地感知立体视频的时域质量和视点间质量 ,定义了时域相似尺度(TSM)、 视间相似尺度(ISM)的概念;将前一时刻右视点图像进行时域和视点间匹配,分别求取 其以像素为单位的TSM和 ISM映射图;然后,计算前一时刻右视点图像当前宏块的TSM和ISM值,通过比较得 到当前宏块的预测模式;最后,根据视频序列的时域一致性,将前一时刻右视点图像宏块 的预测模式作为丢失图像宏 块的预测模式,从而使用运动补偿预测(MCP)或者视差补偿预测(DCP )的方法恢复丢失信息。研究结果表明,与已有错误隐藏 算法相比,本文算法获得更好主客观视觉效果;同时与基于图像结构相似度(SSIM)的错误隐藏算法相比,在保持主观视觉质量情况下,错误隐藏时间节省20%左右。     

A novel method for tracking and counting pedestrians in real-timeusing a single camera

This paper presents a real-time system for pedestrian tracking in sequences of grayscale images acquired by a stationary camera. The objective is to integrate this system with a traffic control application such as a pedestrian control scheme at intersections. The proposed approach can also be used to detect and track humans in front of vehicles. Furthermore, the proposed schemes can be employed for the detection of several diverse traffic objects of interest (vehicles, bicycles, etc.) The system outputs the spatio-temporal coordinates of each pedestrian during the period the pedestrian is in the scene. Processing is done at three levels: raw images, blobs, and pedestrians. Blob tracking is modeled as a graph optimization problem. Pedestrians are modeled as rectangular patches with a certain dynamic behavior. Kalman filtering is used to estimate pedestrian parameters. The system was implemented on a Datacube MaxVideo 20 equipped with a Datacube Max860 and was able to achieve a peak performance of over 30 frames per second. Experimental results based on indoor and outdoor scenes demonstrated the system s robustness under many difficult situations such as partial or full occlusions of pedestrians     

基于多信道的自组织网络功率控制方法

为解决自组网中功率控制引发的碰撞问题,通过引入多信道技术,结合网络层最小功率路由策略,实现了基于多信道功率可控的自组织网络架构MCBPC。该架构控制了拓扑结构的频繁变化,降低了因功率控制带来的碰撞机率,并实现了节省能量的目的。通过NS-2仿真实验验证,相比基于802.11的AODV架构,MCBPC在成功递交分组数、网络生存时间上均提高了90%以上,分组成功递交率也提高达30%以上。