Showing papers on "Collision avoidance published in 2008"

Formation Control and Collision Avoidance for Multi-agent Non-holonomic Systems: Theory and Experiments

Abstract: In this paper we present a theoretical and experimental result on the control of multi-agent non-holonomic systems. We design and implement a novel decentralized control scheme that achieves dynamic formation control and collision avoidance for a group of non-holonomic robots. First, we derive a feedback law using Lyapunov-type analysis that guarantees collision avoidance and tracking of a reference trajectory for a single robot. Then we extend this result to the case of multiple non-holonomic robots, and show how different multi-agent problems, such as formation control and leader-follower control, can be addressed in this framework. Finally, we combine the above results to address the problem of coordinated tracking for a group of agents. We give extensive experimental results that validate the effectiveness of our results in all three cases.

Autonomous ship collision avoidance navigation concepts, technologies and techniques

Abstract: This study provides both a spherical understanding about autonomous ship navigation for collision avoidance (CA) and a theoretical background of the reviewed work. Additionally, the human cognitive abilities and the collision avoidance regulations (COLREGs) for ship navigation are examined together with water based collision avoidance algorithms. The requirements for autonomous ship navigation are addressed in conjunction with the factors influencing ship collision avoidance. Humans are able to appreciate these factors and also perform ship navigation at a satisfactory level, but their critical decisions are highly subjective and can lead to error and potentially, to ship collision. The research for autonomous ship navigation may be grouped into the classical and soft computing based categories. Classical techniques are based on mathematical models and algorithms while soft-computing techniques are based on Artificial Intelligence (AI). The areas of AI for autonomous ship collision avoidance are examined in this paper are evolutionary algorithms, fuzzy logic, expert systems, and neural networks (NN), as well as a combination of them (hybrid system).

Artificial potential functions for highway driving with collision avoidance

Abstract: We present a set of potential function components to assist an automated or semi-automated vehicle in navigating a multi-lane, populated highway. The resulting potential field is constructed as a superposition of disparate functions for lane- keeping, road-staying, speed preference, and vehicle avoidance and passing. The construction of the vehicle avoidance potential is of primary importance, incorporating the structure and protocol of laned highway driving. Particularly, the shape and dimensions of the potential field behind each obstacle vehicle can appropriately encourage control vehicle slowing and/or passing, depending on the cars' velocities and surrounding traffic. Hard barriers on roadway edges and soft boundaries between navigable lanes keep the vehicle on the highway, with a preference to travel in a lane center.

Flying Fast and Low Among Obstacles: Methodology and Experiments

Abstract: Safe autonomous flight is essential for widespread acceptance of aircraft that must fly close to the ground. We have developed a method of collision avoidance that can be used in three dimensions in much the same way as autonomous ground vehicles that navigate over unexplored terrain. Safe navigation is accomplished by a combination of online environmental sensing, path planning and collision avoidance. Here we outline our methodology and report results with an autonomous helicopter that operates at low elevations in uncharted environments, some of which are densely populated with obstacles such as buildings, trees and wires. We have recently completed over 700 successful runs in which the helicopter traveled between coarsely specified waypoints separated by hundreds of meters, at speeds of up to 10 m s—1 at elevations of 5—11 m above ground level. The helicopter safely avoids large objects such as buildings and trees but also wires as thin as 6 mm. We believe this represents the first time an air vehicle has traveled this fast so close to obstacles. The collision avoidance method learns to avoid obstacles by observing the performance of a human operator.

Multi-Sensor-Based Fully Autonomous Non-Cooperative Collision Avoidance System for Unmanned Air Vehicles

Abstract: This paper presents a fully autonomous multi-sensor anti-collision system for Unmanned Aerial Vehicles. This system is being developed by the Italian Aerospace Research Center in collaboration with the Department of Aerospace Engineering of the University of Naples “Federico II”. The research project is entitled TECVOL and is funded in the frame of the National Aerospace Research Program. The system prototype will be initially installed onboard a manned laboratory aircraft equipped for automatic control, therefore flight tests will verify the adequacy of attained performances for supporting fully autonomous flight. The obstacle detection and tracking function is performed by a multi-sensor configuration made up by a pulsed Ka-band radar, two visible (panchromatic and color) video cameras, two infrared video cameras, and two computers. One computer is dedicated to real time sensor fusion and communication with the radar and the flight control computer (by means of a deterministic data bus), the other is devoted to image processing. On the basis of the tracking estimates and of a Collision Avoidance Software, the flight control computer generates and follows in real-time a proper escape trajectory. In order to evaluate the performance of the collision avoidance system, numerical simulations have been performed taking into account the obstacle detection sensors’ accuracy, unmanned aircraft’s and intruder’s flight dynamics, navigation system accuracy and latencies, and collision avoidance logic. The relevant results helped to assess overall system performances and are discussed in depth.

UAV collision avoidance based on geometric approach

Abstract: A method of collision avoidance is described by using simple geometric approach. Two UAVs are dealt with and considered as point masses with constant velocity. This paper discusses en route aircraft which are assumed to be linked by real time data bases like ADS-B. With this data base, all UAVs share the information each other. Calculating PCA (point of closest approach), we can evaluate the worst conflict condition between two UAVs. This paper proposes one resolution maneuvering logic, which can be called dasiavector sharing resolutionpsila. In case of conflict, using miss distance vector in PCA, we can decide the directions for two UAVs to share the conflict region. With these directions, UAVs are going to maneuver cooperatively. First of all, this paper describes some dasia2Dpsila conflict scenarios and then extends to dasia3Dpsila conflict scenarios.

Intersection collision avoidance techniques

Abstract: System and method for preventing accidents between first and second vehicles at intersections in which the absolute position and velocity of the first vehicle are determined, map data relating to edges of lanes of roadways, edges of roadways and the location of traffic control devices is stored in a map database and the status of the traffic control devices is provided to the first vehicle when needed. The absolute position and velocity of the second vehicle are determined and a collision between the first and second vehicles is predicted based on the position and velocity of the first and second vehicles, the map data and the status of the traffic control devices. An action or changing operation is initiated by a reactive component or system in the first and/or second vehicle when a collision is predicted.

Optic-Flow-Based Collision Avoidance

Abstract: Flying in and around caves, tunnels, and buildings demands more than one sensing modality. This article presented an optic-flow- based approach inspired by flying insects for avoiding lateral collisions. However, there were a few real-world scenarios in which optic flow sensing failed. This occurred when obstacles on approach were directly in front of the aircraft. Here, a simple sonar or infrared sensor can be used to trigger a quick transition into the hovering mode to avoid the otherwise fatal collision. Toward this end, we have demonstrated a fixed-wing prototype capable of manually transitioning from conventional cruise flight into the hovering mode. The prototype was then equipped with an IMU and a flight control system to automate the hovering process. The next step in this research is to automate the transition from cruise to hover flight.

A fast Monte Carlo algorithm for collision probability estimation

Abstract: In order to navigate safely, it is important to detect and to react to a potentially dangerous situation. Such a situation can be underlined by a judicious use of the locations and the uncertainties of both the navigating vehicle and the obstacles. We propose to build an estimation of the collision probability from the environment perception with its probabilistic modelling. The probability of collision is computed from integrals of Gaussians and takes into account the uncertain configurations and the volume of both the vehicle and the obstacles.

V2V Wireless Communication Protocol for Rear-End Collision Avoidance on Highways

Abstract: More than 23% of annual vehicle accidents are rear-end collisions, which provides an important test-case for enhanced collision avoidance approaches based on v2v wireless communications. In this work, we propose and study the impact of a 802.11 based multi-hop MAC protocol that propagates an emergency warning message (EWM) down a platoon of cars on a highway. The design objective is to ensure reception of this message with stringent (low) delay constraints so as to provide drivers with requisite available maneuver time (AMT) to avoid rear-end collision. We provide realistic simulation studies of protocol performance within ns-2 environment for various topology (1 lane and 3 lanes) and background traffic scenarios, as well as different protocol parameter settings, to highlight the potential of this approach for effective collision avoidance or mitigation.

Real-time (self)-collision avoidance task on a hrp-2 humanoid robot

Abstract: This paper proposes a real-time implementation of collision and self-collision avoidance for robots. On the basis of a new proximity distance computation method which ensures having continuous gradient, a new controller in the velocity domain is proposed. The gradient continuity encompasses no jump in the generated command. Included in a stack of tasks architecture, this controller has been implemented on the humanoid platform HRP-2 and experienced in a grasping task while walking and avoiding collisions with the environment and auto-collisions.

Decentralized cooperative collision avoidance for acceleration constrained vehicles

Abstract: Safety must be ensured in the deployment of multi-agent vehicle systems. This paper presents decentralized collision avoidance algorithms for systems with second order dynamics and acceleration constraints, using a switching control law. The technique augments existing multi-agent control laws with the capability to switch to provably safe collision avoidance maneuvers when required. Two algorithms with low computational cost are presented, one for two vehicles and one for more vehicles. In both methods, each vehicle computes avoid sets with respect to every other vehicle. When one or more vehicles are on the boundary of their avoid sets, collision avoidance action is taken. These algorithms are applied in simulation scenarios for which existing techniques either fail or are computationally expensive, and used for information theoretic control of a mobile sensor network to reduce the computational complexity. Finally, they are demonstrated in quadrotor helicopter flight experiments.

Decentralized reactive collision avoidance for multiple unicycle-type vehicles

Abstract: This paper addresses a novel approach to the n-vehicle collision avoidance problem. The vehicle model used is a planar constant-speed unicycle, chosen for its wide applicability to ground, sea, and air vehicles. An algorithm is developed which guarantees all vehicles remain free of collisions while attempting to attain their trajectory goals (given certain restrictions on their initial conditions). This controller is reactive and decentralized, making it well suited for real time applications, and explicitly accounts for actuation limits. Results are demonstrated in simulation.

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

Abstract: 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.

The MIT–Cornell collision and why it happened

Abstract: Midway through the 2007 DARPA Urban Challenge, MIT's robot “Talos” and Team Cornell's robot “Skynet” collided in a low-speed accident. This accident was one of the first collisions between full-sized autonomous road vehicles. Fortunately, both vehicles went on to finish the race and the collision was thoroughly documented in the vehicle logs. This collaborative study between MIT and Cornell traces the confluence of events that preceded the collision and examines its root causes. A summary of robot–robot interactions during the race is presented. The logs from both vehicles are used to show the gulf between robot and human-driver behavior at close vehicle proximities. Contributing factors are shown to be (1) difficulties in sensor data association leading to an inability to detect slow-moving vehicles and phantom obstacles, (2) failure to anticipate vehicle intent, and (3) an overemphasis on lane constraints versus vehicle proximity in motion planning. Finally, we discuss approaches that could address these issues in future systems, such as intervehicle communication, vehicle detection, and prioritized motion planning. © 2008 Wiley Periodicals, Inc.

UAV formation flight using 3D potential field

Abstract: The paper presents a solution for formation flight and formation reconfiguration of unmanned aerial vehicles (UAVs). Based on a virtual leader approach, combined with an extended local potential field, it is universal applicable by driving the vehiclepsilas auto pilot. The solution is verified, using a group of UAVs based on a simplified small-scale helicopter, which is simulated in MATLABtrade/Simulinktrade. As necessary for helicopters, the potential field approach is realized in 3D including obstacle and collision avoidance. The collision avoidance strategy could be used separately for the sense and avoid problem.

Safe joint mechanism based on nonlinear stiffness for safe human-robot collision

Abstract: In recent years, collision safety has been one of the most important issues for service robots. To ensure collision safety assurance, a passive compliance method is preferred to an active one because it can provide faster and more reliable responses to dynamic collision. Since both positioning accuracy and collision safety are equally important, a robot arm should have very low stiffness when subjected to a collision force greater than the one causing human injury, but maintain very high stiffness otherwise. In order to realize these ideal features, a novel safe joint mechanism (SJM) composed of linear springs and a modified slider-crank mechanism is proposed in this paper. The SJM has the advantages of variable stiffness which can be achieved only by passive mechanical elements. Various experiments on static and dynamic collisions show the high stiffness of the SJM against an external force of less than the critical impact force, but an abrupt drop in the stiffness when the external force exceeds this critical force, which guarantees positioning accuracy and collision safety. Furthermore, the critical impact force can be set to any value depending on the application and the environment.

Onboard Measurement and Warning Module for Irregular Vehicle Behavior

Abstract: This paper develops an onboard decision module for issuing appropriate warnings when the equipped vehicle's traveling trajectory is irregular. Potential vehicle accidents exist if the driver is distracted by fatigue, drowsiness, food, phone use, and talking or is under the influence of alcohol or drugs, etc. Usual freeway accidents include lateral and rear-end collisions. Detecting vehicle behavior is a good way to measure the security of driving. This paper presents two modules. An unexpected lane departure avoidance module is utilized to prevent lateral collision. This module issues warnings when the vehicle approaches an irregular departure from the middle of the lane. Radial basis probability networks are applied to distinguish between normal lane change and lane departure. A rear-end collision avoidance module is used to issue warnings to avoid longitudinal accidents. This module reflects driver perceptions of environmental influence with a warning value and the warning threshold by neural networks and fuzzy membership functions, respectively. The proposed modules are satisfactory according to simulations and field tests.

On synchronization and collision avoidance for mechanical systems

Abstract: The current interest in coordinating nonlinear dynamical systems with safety guarantees is driven by emerging practical applications. One of the primary objectives in coordination of multiple mechanical systems (agents) is velocity synchronization with guarantees for collision avoidance among the agents. However, previous results in this direction assume point models for the agent, allow only linear dynamics and neglect delays in communication between the agents. In this paper we demonstrate that velocity synchronization and collision avoidance are simultaneously achievable in non-point, nonlinear mechanical systems in the presence of communication delays and switching interconnection topologies. A numerical example is presented to justify the proposed results.

Angiography device and associated recording method with a mechanism for collision avoidance

Abstract: The present invention involves an angiography device for examining vessels of patients having an x-ray emitter and an associated detector, having an image processing unit, an image display unit, a control unit, a collision computer and sensors. The sensors, which are fastened to the angiography device, are designed to scan the outer dimensions of the patient prior to the actual examination and during the examination. The data obtained in this way can be fed into a memory of the collision computer and the system is controllable by a software of the collision computer such that the movement of the system when the system and patient become too close can be automatically slowed down or completely stopped by means of a the control unit.

Forward Collision Avoidance Assistance System

Abstract: An object of the present invention is to provide a forward collision avoidance assistance system that attains the reduction of driver's uncomfortable feeling and the improvement in drivability while ensuring the collision avoidance performance during operation for avoiding contact with an object. A collision avoidance calculation unit 3 determines a risk of collision between a host vehicle and an object detected in the host vehicle traveling direction based on information about the host vehicle detected by a host vehicle information detection unit 1 and information about the object detected by an object information detection unit 2, and calculates control information for object avoidance to be output to an actuator 5 based on a result of collision risk judgment. The collision avoidance calculation unit 3 uses a collision-avoidable limit distance Δxctl2 determined based on a physical limit that can avoid collision with the object, and a jerk-limited collision avoidable distance Δxctl1 determined based on the acceleration and jerk generated on the host vehicle by object avoidance movement, to control the brake force generated on the host vehicle by a brake actuator 5.

Collision Probability Assessment for Speed Control

Abstract: In order to navigate safely, it is important to detect and to react to a potentially dangerous situation. Such a situation can be underlined by a judicious use of the locations and the uncertainties of both the navigating vehicle and the obstacles. We propose to build an estimation of the collision probability from the environment perception with its probabilistic modelling. Then this probability is used for updating a braking order applied to our vehicle either to avoid or to mitigate a collision. The probability of collision is computed from a product of integrals of a product of Gaussians. The integrals take into account the uncertain configurations and the volume of both the vehicle and the obstacles.

A leader-follower formation flight control scheme for UAV helicopters

Abstract: In this paper, we present a control system design and a collision avoidance scheme for the formation flight of multiple UAV helicopters. We adopt the leader-follower pattern to maintain a fixed geometrical formation while navigating the UAVs following certain trajectories. More specifically, the leader is commanded to fly on some predefined trajectories, and each follower is controlled to maintain its position in formation using the measurement of its inertial position and the information of the leader position and velocity, obtained through a wireless modem. In order to avoid possible collisions of UAV helicopters in the actual formation flight test, a collision avoidance scheme based on some predefined alert zones and protected zones is employed. Simulations and experimental results are presented to verify our design.

Reactive Collision Avoidance for Unmanned Aerial Vehicles Using Doppler Radar

Abstract: Research into reactive collision avoidance for unmanned aerial vehicles has been conducted on unmanned terrestrial and mini aerial vehicles utilising active Doppler radar obstacle detection sensors. Flight tests conducted by flying a mini UAV at an obstacle have confirmed that a simple reactive collision avoidance algorithm enables aerial vehicles to autonomously avoid obstacles. This builds upon simulation work and results obtained using a terrestrial vehicle that had already confirmed that active sensors and a reactive collision avoidance algorithm are able to successfully find a collision free path through an obstacle field.

A situation and threat assessment algorithm for a rear-end collision avoidance system

Abstract: Rear-end collisions are common accident scenarios and a frequent cause of these accidents is driver distraction. This paper presents a situation assessment (SA) algorithm that estimates driver distraction by continuously assessing the steering actions of the driver. A collision avoidance (CA) system is proposed, which combines the SA with a threat assessment (TA) algorithm that estimates the effort needed to avoid a collision. It is shown that the SA algorithm proposed enables the CA system to initiate earlier brake interventions when the driver is assessed as being distracted, without significantly increasing the risk of false interventions in real traffic. The CA system has been evaluated in both collision situations on a test track and during 200 driving hours in real traffic conditions.

Robots with collision avoidance functionality

Abstract: A robot is provided with a motion control unit that avoids collision between segments of the robot or between segments of the robot and other objects. The motion control unit of the robot comprises a distance computing module, a whole body control module, a collision avoidance module, and a blending control unit. The distance computing module calculates two closest points of different segments of the robot connected to each other via at least one joint or a segment of the robot and another object. The collision avoidance module is provided with the information about the two closest points. The blending control unit combines the weighted output control signals of the whole body control module and the collision avoidance control module. The weight of the whole body control output signal is higher when the risk of collision is lower. The weight of the collision avoidance control output signal is higher when the risk of collision is higher. The collision avoidance module is designed to control a collision avoidance action only in the direction parallel to a line connecting between the two closest points.

Decentralized feedback controllers for multi-agent teams in environments with obstacles

Abstract: We propose a method for synthesizing decentralized feedback controllers for a team of multiple heterogeneous agents navigating a known environment with obstacles. The controllers are designed to drive agents with limited team state information to goal sets while avoiding collisions and maintaining specified proximity constraints. The method, its successful application to nonholonomic agents in dynamic simulation, and its limitations are presented in this paper.