Showing papers on "Obstacle published in 1998"

Motion Planning in Dynamic Environments Using Velocity Obstacles

Abstract: This paper presents a method for robot motion planning in dynamic environments. It consists of selecting avoidance maneuvers to avoid static and moving obstacles in the velocity space, based on the cur rent positions and velocities of the robot and obstacles. It is a first- order method, since it does not integrate velocities to yield positions as functions of time.The avoidance maneuvers are generated by selecting robot ve locities outside of the velocity obstacles, which represent the set of robot velocities that would result in a collision with a given obstacle that moves at a given velocity, at some future time. To ensure that the avoidance maneuver is dynamically feasible, the set of avoidance velocities is intersected with the set of admissible velocities, defined by the robot's acceleration constraints. Computing new avoidance maneuvers at regular time intervals accounts for general obstacle trajectories.The trajectory from start to goal is computed by searching a tree of feasible avoidance maneuve...

OBPRM: an obstacle-based PRM for 3D workspaces

Abstract: Recently, a new class of randomized path planning methods, known as Probabilistic Roadmap Methods (prms) have shown great potential for solving complicated high-dimensional problems. prms use randomization (usually during preprocessing) to construct a graph of representative paths in C-space (a roadmap) whose vertices correspond to collision-free con gurations of the robot and in which two vertices are connected by an edge if a path between the two corresponding con gurations can be found by a local planning method.

Reconstruction of a two-dimensional binary obstacle by controlled evolution of a level-set

Abstract: We are concerned with the retrieval of the unknown cross section of a homogeneous cylindrical obstacle embedded in a homogeneous medium and illuminated by time-harmonic electromagnetic line sources. The dielectric parameters of the obstacle and embedding materials are known and piecewise constant. That is, the shape (here, the contour) of the obstacle is sufficient for its full characterization. The inverse scattering problem is then to determine the contour from the knowledge of the scattered field measured for several locations of the sources and/or frequencies. An iterative process is implemented: given an initial contour, this contour is progressively evolved such as to minimize the residual in the data fit. This algorithm presents two main important points. The first concerns the choice of the transformation enforced on the contour. We will show that this involves the design of a velocity field whose expression only requires the resolution of an adjoint problem at each step. The second concerns the use of a level-set function in order to represent the obstacle. This level-set function will be of great use to handle in a natural way splitting or merging of obstacles along the iterative process. The evolution of this level-set is controlled by a Hamilton-Jacobi-type equation which will be solved by using an appropriate finite-difference scheme. Numerical results of inversion obtained from both noiseless and noisy synthetic data illustrate the behaviour of the algorithm for a variety of obstacles.

Vehicle obstacle detecting system

Abstract: A vehicle control system for detecting an obstacle present ahead on the road in the course of travel of a vehicle, comprising a first laser radar mounted on the vehicle which emits an electromagnetic beam to detect the obstacle present ahead on the road, and second and third laser radars which measures distances between the first laser radar and the road surface at different angles. The system determines whether the first laser radar is mounted on the vehicle such that the laser beam central axis is horizontal or inclines upward or downward relative to the road surface or vehicle body, based on the distances, a height of the first laser radar from the road surface, the angles at which the distances are measured and reference values. The system may correct the inclination if determined. With the arrangement, the system ensures detection of an obstacle on the road without fail and conduction of a desired obstacle avoidance control.

Attention in action or obstruction of movement? A kinematic analysis of avoidance behavior in prehension

Abstract: Obstacle avoidance strategies are of two basic but interrelated types: moving around an obstacle to that body parts do not come too close, and slowing down. In reaching-to-grasp, avoidance may involve the transport component, the grasp formation component, or both. There has been little research that has directly examined obstacle avoidance strategies during reaches-to-grasp. Several recent reports describe experiments in which reaches-to-grasp were made when nontarget objects were present in the workspace. The effects of these nontargets were interpreted as being due to their distracting effects rather than their obstructing effects. The results of these studies are reinterpreted as being due to the non-target's obstructing effects. The obstacle interpretation is more parsimonious and better predicts the pattern of results than the distractor interpretation. Predictions of the obstacle interpretation were examined in an experiment in which participants were required to reach to grasp a target in the presence of another object in various locations. The results were exactly in line with the interpretation of the object as an obstacle and the data show how grasp and transport movements are subtly adjusted so as to avoid potential obstacles. It is proposed that people move so as not to bring body parts within a minimum preferred distance from nontarget objects within the workspace. What constitutes the preferred distance in a particular context appears to depend upon the speed of movement and a variety of psychological factors related to the cost that a person attaches to a collision.

The Role of Inertial Sensitivity in Motor Planning

Abstract: To achieve a given motor task a single trajectory must be chosen from the infinite set of possibilities consistent with the task. To investigate such motor planning in a natural environment, we examined the kinematics of reaching movements made around a visual obstacle in three-dimensional space. Within each session, the start and end points of the movement were uniformly varied around the obstacle. However, the distribution of the near points, where the paths came closest to the obstacle, showed a strong anisotropy, clustering at the poles of a preferred axis through the center of the obstacle. The preferred axes for movements made with the left and right arms were mirror symmetric about the midsagittal plane, suggesting that the anisotropy stems from intrinsic properties of the arm rather than extrinsic visual factors. One account of these results is a sensitivity model of motor planning, in which the movement path is skewed so that when the hand passes closest to the obstacle, the arm is in a configuration that is least sensitive to perturbations that might cause collision. To test this idea, we measured the mobility ellipse of the arm. The mobility minor axis represents the direction in which the hand is most inertially stable to a force perturbation. In agreement with the sensitivity model, the mobility minor axis was not significantly different from the preferred near point axis. The results suggest that the sensitivity of the arm to perturbations, as determined by its inertial stability, is taken into account in the planning process.

An analytically tractable potential field model of free space and its application in obstacle avoidance

Abstract: An analytically tractable potential field model of free space is presented. The model assumes that the border of every two dimensional (2D) region is uniformly charged. It is shown that the potential and the resulting repulsion (force and torque) between polygonal regions can he calculated in closed form. By using the Newtonian potential function, collision avoidance between object and obstacle thus modeled is guaranteed in a path planning problem. A local planner is developed for finding object paths going through narrow areas of free space where the obstacle avoidance is most important. Simulation results show that not only does individual object configuration of a path obtained with the proposed approach avoid obstacles effectively, the configurations also connect smoothly into a path.

Fast local obstacle avoidance under kinematic and dynamic constraints for a mobile robot

Abstract: This paper presents an efficient approach for reactive collision avoidance taking into account both vehicle dynamics and nonholonomic constraints of a mobile robot. Motion commands are generated by searching the space of actuating variables. Vehicle dynamics are considered by restricting the search space to values which are reachable within the next time step. The final selection among admissible configurations is done by an objective function which trades off speed, goal-directedness and remaining distance until an obstacle is hit when moving along the chosen path. The presented approach differs from previous ones in the selective use of precalculated lookup tables. These are the key to efficiency, and they especially allow the use of any-shaped robot contours. Furthermore, obstacle information from different sources can easily be considered without preprocessing. Extensive experiments on different robots have shown robust operation in dynamic and unprepared indoor environments with speed up to 1 m/s.

Moving obstacle detection from a navigating robot

Abstract: This paper presents a system that detects unexpected moving obstacles that appear in the path of a navigating robot, and estimates the relative motion of the object with respect to the robot The system is designed for a robot navigating in a structured environment with a single wide-angle camera The system uses polar mapping to simplify the segmentation of the moving object from the background The polar mapping is performed with the focus of expansion as the center A vision-based algorithm that uses the vanishing points of segments extracted from a scene in a few 3D orientations provides an accurate estimate of the robot orientation In the transformed space qualitative estimate of moving obstacles is obtained by detecting the vertical motion of edges extracted in a few specified directions Relative motion information about the obstacle is then obtained by computing the time to impact between the obstacles and robot from the radial component of the optical flow The system was implemented and on an indoor mobile robot

Optimal Control of the Obstacle for an Elliptic Variational Inequality

Abstract: An optimal control problem for an elliptic obstacle variational inequality is considered. The obstacle is taken to be the control and the solution to the obstacle problem is taken to be the state. The goal is to find the optimal obstacle from H 1 0 (Ω) so that the state is close to the desired profile while the H 1 (Ω) norm of the obstacle is not too large. Existence, uniqueness, and regularity as well as some characterizations of the optimal pairs are established.

Motion Planning in Environments with Low Obstacle Density

Abstract: We present a simple and efficient paradigm for computing the exact solution of the motion planning problem in environments with a low obstacle density. Such environments frequently occur in practical instances of the motion planning problem. The complexity of the free space for such environments is known to be linear in the number of obstacles. Our paradigm is a new cell decomposition approach to motion planning and exploits properties that follow from the low density of the obstacles in the robot's workspace. These properties allow us to decompose the workspace, subject to some constraints, rather than to decompose the higher-dimensional free configuration space directly. A sequence of uniform steps transforms the workspace decomposition into a free space decomposition of asymptotically the same size. The approach leads to nearly optimal O(n \log n) motion planning algorithms for free-flying robots with any fixed number of degrees of freedom in workspaces with low obstacle density.

Camera-based observation of obstacle motions to derive statistical data for mobile robot motion planning

Abstract: Mobile robots for advanced applications have to act in environments which contain moving obstacles. Motions of obstacles (e.g. humans) usually are not precisely predictable, but neither they are completely random. Long-term observation of obstacle behavior may yield knowledge about prevailing motion patterns. This paper presents concepts and results of an experimental system. Using cameras mounted at the ceiling, the workspace is observed. The image data is processed and transformed into a compact statistical representation of motion patterns. Mobile robot motion planning benefits from such additional knowledge: trajectories are rated in terms of collision probability and expected time for reaching the goal; planning yields efficient paths which are adapted to obstacle behavior.

Obstacle alarming device for vehicle

Abstract: PROBLEM TO BE SOLVED: To provide an obstacle alarming device for vehicle which supplies proper information in accordance with the condition of the running lane around a vehicle. SOLUTION: An HUD 13 changes intensities of the display of segment arrays 13a and 13b in accordance with the positions of obstacles on the left rear side and the right rear side and the traffic volume, which are detected by a control unit, and lights up 8 segments S1 to S8, which can be individually lit and extinguished, while changing their colors to blue, yellow and red colors in accordance with distances D between obstacles on the left rear side and the right rear side and user's vehicle.

Obstacle detector for vehicle

Abstract: PROBLEM TO BE SOLVED: To provide an obstacle detector which gives an alarm in the case of the existence of an obstacle with which it is truly necessary to avoid collision. SOLUTION: A shift position sensor 1 which discriminates whether a vehicle will go forward or backward, a steering angle sensor 2 which discriminates the going direction of the vehicle, a vehicle speed sensor 3 which discriminates the running speed of the vehicle, a course discrimination means 4 which predicts the course of the vehicle in accordance with signals from the shift position sensor 1, the steering angle sensor 2, and the vehicle speed sensor 3, an obstacle position detection means 5 which can detect the positions of obstacles existing around the vehicle, and a collision discrimination means 6 which discriminates a dangerous area of a high possibility of collision in the case of the existence of obstacles and a safe area of a low possibility of collision in spite of the existence of obstacles in accordance with signals from the course discrimination means 4 and the obstacle position detection means 5 and outputs a collision detection signal in the case that obstacles exist in the dangerous area are provided. COPYRIGHT: (C)2000,JPO

Stereo Vision-Based Obstacle Detection for Partially Sighted People

Abstract: Obstacle avoidance is a major requirement for any technological aid aimed at helping partially sighted (TAPS) people to navigate safely. In this paper, a stereo vision-based algorithm (Ground Plane Obstacle Detection) is extended to detect small obstacles for TAPS using RANSAC dynamic recalibration and Kalman Filtering. Obstacle detection and false alarm are investigated probabilistically. Furthermore, a technique is developed to find objects by matching their edges with some heuristic criteria. Experiments show that obstacle edges are extracted much better with our dynamic recalibration approach and that objects can be found successfully by the edge matching technique.

Method and apparatus for in path target determination for an automotive vehicle using a gyroscopic device

Abstract: The present invention concerns a method, an apparatus and an article of manufacture that satisfies the need for determining whether or not an obstacle vehicle is in the path of a host vehicle. Specifically, the present invention satisfies the above stated regardless of whether or not the host vehicle is moving in a straight path or along a curved path. Preferably, input data ('input') is collected from instruments mounted to a host vehicle. The input is used to calculate for the host vehicle the average turn rate, the radius of curvature of the path being traveled, the velocity, and a range from the host vehicle to an obstacle vehicle. Additionally, the input is used to determine the deviation of an obstacle vehicle. Additionally, the input is used to determine the deviation of an obstacle from a 0° reference azimuth extending through the center of a radar beamating from a radar unit mounted to the host vehicle. An obstacle azimuth angle αi, is calculated and used to determine whether or not the obstacle is in the path of the host vehicle. After a determination is made as to whether or not the obstacle is in the path of the host vehicle, the results of that determination are sent to and displayed by sensors and displays which designate the results.

New technique of mobile robot navigation using a hybrid adaptive fuzzy-potential field approach

Abstract: This paper presents a summary of the research aimed at developing a new reliable methodology for robot navigation and obstacle avoidance. This new approach is based on the artificial potential field (APF) method, which is used extensively for obstacle avoidance. The classical APF is dependent only on the separation distance between the robot and the surrounding obstacles. The new scheme introduces a variable, which is used to determine the importance that each obstacle has on the robot's future path. The importance variable is dependent on the obstacles position, both angle and distance, with respect to the robot. Simulation results are presented demonstrating the ability of the algorithm to perform successfully in simple environments.

Multisensor obstacle detection and tracking

Abstract: This paper describes a multisensor obstacle detection and tracking system for an autonomous vehicle. The key sensors for obstacle detection are a stereo vision sensor and a laser scanner system. Output from the sensors are fed into a sensor fusion unit which then provides information to the controller.

System and method for avoiding collisions between vector and solid objects

Abstract: An apparatus for analyzing a specified path A-B with respect to a specified obstacle determines if the path intersects the obstacle and determines a collision avoidance path when the path is determined to intersect the obstacle. The apparatus is preferably a dedicated path analyzer that provides high speed path analysis support to a host computer performing navigation functions. The path analyzer includes a collision detector and a collision avoidance path generator. The path analyzer receives from the host computer coordinates representing the specified path's first and second endpoints (A and B) in three-dimensional space and the specified obstacle's physical extent. The collision detector generates a preliminary result signal indicating whether the specified path does not intercept the specified obstacle, unavoidably intercepts the specified obstacle, or avoidably intercepts the specified obstacle. When the preliminary result signal indicates that the specified path avoidably intercepts the specified obstacle, the collision avoidance path generator selecting a vertex (C) of a parallelepiped corresponding to the specified obstacle's physical extent, such that a modified path A-C-B from the first specified path endpoint to the selected vertex to the second specified path endpoint circumnavigates the obstacle. The path analyzer returns signals to the host computer representing the preliminary result signal and, when the preliminary result signal indicates that the specified path avoidably intercepts the specified obstacle, the selected vertex.

Obstacle detection and mapping system

Abstract: This paper presents an obstacle detection algorithm developed to support obstacle detection and rough terrain conditions. The algorithm is described as a hybrid of grid-based and sensor-based obstacle detection and mapping techniques. The sensors and the 4D- Realtime Control System (RCS) autonomous driving system are described. The obstacle detection algorithm and an evaluation of its performance on artificial and natural obstacles are discussed. The obstacle mapping module is then described, followed by a conclusion and a discussion of future plans.

Numerical solutions of third-order obstacle problems

Abstract: It is known that a class of odd order obstacle problems in physical oceanography can be studied in the framework of variational inequality theory. In this paper, we show that variational inequalities related with third-order obstacle problems can be characterized by a system of variational equations without constraints, which are solved using modified finite difference technique. A comparison between our and other available results is also presented.

Control device for vehicle

Abstract: PROBLEM TO BE SOLVED: To provide a vehicle control device for realizing vehicle control suitable to road situation SOLUTION: This control device changes a vehicle characteristic according to situation around own vehicle In this case, the device is provided with cameras 7a, 7b for detecting an obstacle in a given range before the own vehicle and an image processing device 8, and a control unit 9 calculates residual road width at a position where the obstacle exists, and changes the vehicle characteristic based on the calculated residual road width Thus, when the obstacle exists before the own vehicle, the vehicle characteristic is changed according to the residual road width at the position where the obstacle exists, and control matching to feeling of a driver is allowed COPYRIGHT: (C)1999,JPO

Reconstruction of a 2-D binary obstacle by controlled evolution of a level-set

Abstract: We are concerned with the retrieval of the unknown cross-section of a homogeneous cylindrical obstacle embedded in a homogeneous mediumand illuminated by time-harmonic electromagnetic line sources. The dielectric parameters of the obstacle and embedding materials are known and piecewise constant. That is, the shape (here, the contour) of the obstacle is su cient for its full characterization. The inverse scattering problem is then to determine the contour from the knowledge of the scattered eld measured for several locations of the sources and/or frequencies. An iterative process is implemented: given an initial contour, this contour is progressively evolved such as to minimize the residual in the data t. This algorithm presents two main important points. The rst one concerns the choice of the transformation enforced on the contour. We will show that this involves the design of a velocity eld whose expression only requires the resolution of an adjoint problem at each step. The second one concerns the use of a level-set function in order to represent the obstacle. This level-set function will be of great use to handle in a natural way splitting or merging of obstacles along the iterative process. The evolution of this level-set is controlled by a Hamilton-Jacobi-type equation which will be solved by using an appropriate nitedi erence scheme. Numerical results of inversion obtained from both noiseless and noisy synthetic data illustrate the behavior of the algorithm for a variety of obstacles. Short title: Reconstruction of a 2-D binary obstacle by controlled evolution of a level-set

Vehicle guide device

Abstract: PROBLEM TO BE SOLVED: To surely detect an obstacle and to guide a vehicle so as to evade the obstacle in a working site where the obstacle changes in real time. SOLUTION: When an obstacle 74 is detected, the position of the obstacle 74 is stored in a storage means as an obstacle 74 common to plural vehicles 2. In accordance with the traveling of these vehicles 2, the stored contents of the storage means are updated. When the positional data of respective target points 72 are applied in each of plural vehicles 2, respective vehicles 2 are guided up to respective target points 72 so as not to interfere with the obstacle 74 based on the stored contents of the storage means.

Obstacle avoiding control device for vehicle

Abstract: PROBLEM TO BE SOLVED: To enhance avoiding performance of an obstacle to a maximum limit, by permitting avoiding action of the obstacle based on a vehicle behavior control means assisting steering operation when an avoidance right or wrong decision means decides the obstacle avoidable. SOLUTION: An avoidance right or wrong decision means M6 decides a driver to have an intention avoiding an obstacle when operation of a steering wheel 2 by the driver is detected by a steering operation detection means M4 during an automatic brake by an automatic brake means M3, and decides whether the obstacle can be avoided or not by turn round ability increasing control through a vehicle behavior control means M5 assisting steering operation of the driver. In the case of the obstacle avoidable, the avoidance capable or not decision means M6 permits execution of the turn round ability increasing control. Then the vehicle behavior control means M5 increases turn round ability of a vehicle in order to avoid the obstacle. As a result, abutting to the obstacle is prevented with obstacle avoiding operation in preference by intention of the driver. COPYRIGHT: (C)1999,JPO

Avoidance of moving obstacles through behavior fusion and motion prediction

Abstract: We propose a novel approach of fusing the fuzzy control actions of the obstacle avoidance, goal seeking and steering behaviors, in which the steering behavior is derived from motion prediction. As such, the navigator is more capable to steer clear of the zone of high collision probability. Through simulation, it has been confirmed that the navigator having this steering behavior can tackle multiple moving obstacles successfully at much higher speed compared with those without. Furthermore, it does not require any a priori knowledge of the obstacle motion.

On-line Planning for Collision Avoidance on the Nominal Path

Abstract: In this paper a solution to the obstacle avoidance problem for a mobile robot moving in the two-dimensional Cartesian plane is presented The robot is modelled as a linear time-invariant dynamic system of finite size enclosed by a circle and the obstacles are modelled as circles travelling along rectilinear trajectories This work deals with the avoidance problem when the obstacles move in known trajectories The robot starts its journey on a nominal straight line path with a nominal velocity When an obstacle is detected to be on a collision course with the robot, the robot must devise a plan to avoid the obstacle whilst minimising a cost index defined as the total sum squared of the magnitudes of the deviations of its velocity from the nominal velocity The planning strategy adopted here is adjustment of the robot’s velocity on the nominal path based on the time of collision between the robot and a moving obstacle, and determination of a desired final state such that its Euclidean distance from the nominal final state is minimal Obstacle avoidance by deviation from the nominal path in deterministic and random environments is based on the work presented here and is investigated in another paper

Collision avoidance by a ship with a moving obstacle: computation of feasible command strategies

Abstract: A ship moving from a point A to a point B detects a moving small obstacle at close range. Hence, the ship has to perform a maneuver to avoid collision with the moving obstacle. Using a realistic model of a tanker ship, a method is proposed for computing feasible rudder command strategies for performing the collision-avoidance maneuver.