Showing papers on "Obstacle avoidance published in 2000"

VFH/sup */: local obstacle avoidance with look-ahead verification

Abstract: This paper presents an enhancement to the earlier developed vector field histogram (VFH) method for mobile robot obstacle avoidance. The enhanced method, called VFH/sup */ successfully deals with situations that are problematic for purely local obstacle avoidance algorithms. The VFH/sup */ method verifies that a particular candidate direction guides the robot around an obstacle. The verification is performed by using the A/sup */ search algorithm and appropriate cost and heuristic functions.

Recent progress in local and global traversability for planetary rovers

Abstract: Autonomous planetary rovers operating in vast unknown environments must operate efficiently because of size, power and computing limitations. Recently, we have developed a rover capable of efficient obstacle avoidance and path planning. The rover uses binocular stereo vision to sense potentially cluttered outdoor environments. Navigation is performed by a combination of several modules that each "vote" for the next best action for the robot to execute. The key distinction of our system is that it produces globally intelligent behavior with a small computational resource - all processing and decision making are done on a single processor. These algorithms have been tested on our outdoor prototype rover, Bullwinkle, and have recently driven the rover 100 m at a speed of 15 cm/sec. In this paper we report on the extension on the systems that we have previously developed that were necessary to achieve autonomous navigation in this domain.

Kinodynamic motion planning amidst moving obstacles

Abstract: This paper presents a randomized motion planner for kinodynamic asteroid avoidance problems, in which a robot must avoid collision with moving obstacles under kinematic, dynamic constraints and reach a specified goal state. Inspired by probabilistic-roadmap (PRM) techniques, the planner samples the state x time space of a robot by picking control inputs at random in order to compute a roadmap that captures the connectivity of the space. However, the planner does not precompute a roadmap as most PRM planners do. Instead, for each planning query, it generates, on the fly, a small roadmap that connects the given initial and goal state. In contrast to PRM planners, the roadmap computed by our algorithm is a directed graph oriented along the time axis of the space. To verify the planner's effectiveness in practice, we tested it both in simulated environments containing many moving obstacles and on a real robot under strict dynamic constraints. The efficiency of the planner makes it possible for a robot to respond to a changing environment without knowing the motion of moving obstacles well in advance.

Spatial avoidance method and apparatus

Abstract: An obstacle avoidance system, apparatus, and method is described suitable for use on autonomously guided or man-in-the-loop guided vehicles such as aircraft, missiles, cars, and other types of vehicles. The system provides guidance instructions in the situation where the vehicle encounters an obstacle either directly or indirectly in its path while traveling to a desired destination or where vehicles are traveling in formation. The system can be applied not only to obstacle avoidance but also to trajectory shaping by defining obstacles, operational boundaries and/or threats which influence the trajectory of the vehicle.

Controlling a multi-joint robot for autonomous sewer inspection

Abstract: In this paper a multi-joint robot for sewer inspection tasks is presented. In order to increase the operating scope the robot has been designed to run round or over obstacles, to follow sewage branches and is operated with no wire attached to it. As a result of the wireless approach the robot has to carry an energy resource and must be abbe to act autonomously. In this paper we give a short description of the mechanical design and the electronic components used. Then we describe the control system and show sequences and results of in-pipe experiments.

Nonlinear tracking control of kinematically redundant robot manipulators

Abstract: In this study, we consider the nonlinear control of kinematically redundant robot manipulators. Specifically, we use a Lyapunov technique to design a model based nonlinear controller that achieves exponential link position and subtask tracking. We then illustrate how the model based controller can be redesigned as an adaptive full-state feedback controller that achieves asymptotic link position and subtask tracking despite parametric uncertainty associated with the dynamic model. We also illustrate how the model based controller can be redesigned as an exact model knowledge output feedback controller that achieves semi-global exponential link position and sub-task tracking despite the lack of link velocity measurements. We note that the control strategy does not require the computation of inverse kinematics and does not place any restriction on the self-motion of the manipulator; hence, the extra degrees of freedom are available for subtasks (i.e., maintaining manipulability, avoidance of joint limits and obstacle avoidance). Simulation results are included to illustrate the performance of the control law.

Application of fuzzy control to a sonar-based obstacle avoidance mobile robot

Abstract: Describes how fuzzy control can be applied to sonar based obstacle avoidance of the HelpMate mobile robot. Behavior-based fuzzy control for the HelpMate mobile robot was designed. The design and implementation of the fuzzy control system is described. The fuzzy controller provides the mechanism for solving sensor data from all sonar sensors which present different information. The behavior-based approach is implemented as an individual high priority behavior. The highest level behavior is called task-oriented behavior, which consists of two subtasks, wall following and goal following. The lower level is obstacle avoidance behavior. The lowest is an emergency behavior. Visual Basic 6 code was developed for implementation. The fuzzy inference system was created. Helpmate obstacle avoidance was implemented. The result shows that each behavior works correctly. The HelpMate robot can avoid all obstacles that are detected by sonar sensors.

Sonar behavior-based fuzzy control for a mobile robot

Abstract: This paper describes how fuzzy control can be applied to a sonar-based mobile robot. Behavior-based fuzzy control for HelpMate behaviors was designed using sonar sensors. The fuzzy controller provides a mechanism for combining sensor data from all sonar sensors which present different information. The behavior-based approach is implemented as an individual high priority behavior. The highest level behavior is called the task-oriented behavior, which consists of two subtasks, wall following and goal seeking. The middle level behavior is obstacle avoidance. The lowest level is an emergency behavior. Each behavior was built as an atomic agent based on the intelligent machine architecture (IMA). The results demonstrate that each behavior works correctly. The HelpMate robot can follow the wall, go to the goal, and avoid obstacles detected by the sonar sensors.

Detection and avoidance of simulated potholes in autonomous vehicle navigation in an unstructured environment

Abstract: In the navigation of an autonomous vehicle, tracking and avoidance of the obstacles presents an interesting problem as this involves the integration of the vision and the motion systems. In an unstructured environment, the problem becomes much more severe as the obstacles have to be clearly recognized for any decisive action to be taken. In this paper, we discuss a solution to detection and avoidance of simulated potholes in the path of an autonomous vehicle operating in an unstructured environment. Pothole avoidance may be considered similar to other obstacle avoidance except that the potholes are depressions rather than extrusions form a surface. A non-contact vision approach has been taken since potholes usually are significantly different visually from a background surface. Large potholes more than 2 feet in diameter will be detected. Furthermore, only white potholes will be detected on a background of grass, asphalt, sand or green painted bridges. The signals from the environment are captured by the vehicle's vision systems and pre-processed appropriately. A histogram is used to determine a brightness threshold to determine if a pothole is within the field of view. Then, a binary image is formed. Regions are then detected in the binary image. Regions that have a diameter close to 2 feet and a ratio of circumference to diameter close to pi are considered potholes. The neuro-fuzzy logic controller where navigational strategies are evaluated uses these signals to decide a final course of navigation. The primary significance of the solution is that it is interfaced seamlessly into the existing central logic controller. The solution can also be easily extended to detect and avoid any two dimensional shape.© (2000) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Motion planning in the presence of directional and obstacle avoidance constraints using nonlinear, anisotropic, harmonic potential fields

Abstract: The authors (1998) suggested a new class of intelligent motion controllers, called evolutionary, hybrid PDE-ODE controllers (EHPCs). A controller of such a class is designed for the special task of guiding an agent in a fully unknown environment to a target set along an obstacle-free trajectory. The authors briefly described an extension that would allow an EHPC to jointly condition a motion trajectory with both directional and region avoidance constraints. In this paper, an in-depth investigation of the proposed extension is provided. Also, mathematical proofs of both convergence, and the ability to enforce directional and region avoidance constraints are supplied.

Feature Tracking in Video and Sonar Subsea Sequences with Applications

Abstract: This paper deals with automatic target tracking in video and sonar subsea sequences, an essential capability for automating tasks currently performed by remotely operated vehicles under pilot control. We describe two trackers, one for video sequences, the other for sector scan sonar sequences. No assumptions are made about the images, scene, or motion observed. To illustrate applications, we report results of our systems for 3-D structure reconstruction and panoramic mosaic building from video sequences and describe in some detail our path planning and obstacle avoidance system using sonar sequences.

Obstacle avoidance control for redundant manipulators using collidability measure

Abstract: We present an efficient obstacle avoidance control algorithm for redundant manipulators using a new measure called collidability measure. Considering moving directions of manipulator links, the collidability measure is defined as the sum of inverse of predicted collision distances between links and obstacles: This measure is suitable for obstacle avoidance since directions of moving links are as important as distances to obstacles. For kinematic or dynamic redundancy resolution, null space control is utilized to avoid obstacles by minimizing the collidability measure: We present a velocity-bounded kinematic control law which allows reasonably large gains to improve the system performance. Also, by clarifying decomposition in the joint acceleration level, we present a simple dynamic control law with bounded joint torques which guarantees tracking of a given end-effector trajectory and improves a kinematic cost function such as collidability measure. Simulation results are presented to illustrate the effectiveness of the proposed algorithm.

Trajectory planning of robot manipulators by using algebraic and trigonometric splines

Abstract: In this paper, the use of algebraic and trigonometric splines for the trajectory planning of robot manipulators is discussed. First, the two methods are analyzed and compared in detail; then, a strategy, which involves a combined use of the two schemes to perform sudden changes in a predefined trajectory (e.g. in case of obstacle avoidance) is proposed. Results show that the main interest in using trigonometric splines lies especially in the task of connecting two separate pieces of cubic splines, as overshoots are significantly reduced, although the continuity of velocity, acceleration and (in case) jerk is guaranteed.

Industrial Robot Navigation and Obstacle Avoidance Employing Fuzzy Logic

Abstract: This paper proposes a novel conceptual approach based on fuzzy logic to solve the local navigation and obstacle avoidance problem for industrial 3-dof robotic manipulators. The proposed system is divided into separate fuzzy units, which control individually each manipulator link. The fuzzy rule-base of each unit combines a repelling influence, which is related to the distance between the manipulator and the nearby obstacles, with the attracting influence produced by the angular difference, between the actual and the final manipulator configuration, to generate a new actuating command for each link. It can be considered as an on-line local navigation method for the generation of instantaneous collision-free trajectories. The strategy has been successfully applied to manipulators in different simulated workspace environments providing collision-free paths. Some of the simulation results obtained are included.

Using the Time Petri Net Formalism for Specification, Validation, and Code Generation in Robot-Control Applications:

Abstract: The main objective of this paper is to show the advantages of using the time Petri net formalism for specification, validation, and code generation in robot-control applications. To achieve this objective, the authors consider as application the development of a control system for a mobile robot with a rotating rangefinder laser sensor with two degrees of freedom to be used in navigation tasks with obstacle avoidance. It is shown how the use of the time Petri net formalism in the shole development cycle can fulfill the reliability requirement of real-time systems, make the system development easy and quick, strongly reduce the time for the testing and tuning phases and, therefore, reduce the development cost significantly. It allows verification of functional and temporal requirements, error detection in the early stages of the development cycle, and automatic code generation, avoiding coding mistakes. Experimental tests show that the theoretical results obtained from the analysis of formal system models match the real-time behavior of the robotic system.

Two novel approaches for unmanned underwater vehicle path planning: constrained optimisation and semi-infinite constrained optimisation

Abstract: In this paper, two novel approaches to unmanned underwater vehicle path planning are presented The main idea of the first approach, referred to as Constrained Optimisation (CO) is to represent the free space of the workspace as a set of inequality constraints using vehicle configuration variables The second approach converts robot path planning into a Semi-infinite Constrained Optimisation (SCO) problem The function interpolation technique is adopted to satisfy the start and goal configuration requirements Mathematical foundations for Constructive Solid Geometry (CSG), Boolean operations and approximation techniques are also presented to reduce the number of constraints, and to avoid local minima The advantages of these approaches are that the mature techniques developed in optimisation theory which guarantee convergence, efficiency and numerical robustness can be directly applied to the robot path planning problem Simulation results have been presented

Path finding for human motion in virtual environments

Abstract: This paper presents an efficient and robust technique for generating global motion paths for a human model in virtual environments Initially, a scene is discretized using raster hardware to generate an environment map An obstacle-free cell path sub-optimal according to Manhattan metric is generated between any two cells Unlike 2D techniques present in literature, the proposed algorithm works for complex 3D environments suitable for video games and architectural walk-throughs For obstacle avoidance, the algorithm considers both physical dimensions of the human and actions such as jumping, bending, etc Path smoothening is carried out to keep the cell path as closely as possible to Euclidean straight-line paths

Dynamic Approach to Behavior-based Robotics: Design, Specification, Analysis, Simulation and Implementation

Abstract: Tese de doutoramento em Electronica Industrial, ramo de Automacao e Controlo. Guimaraes : Universidade do Minho, 1999.

Practical Structure and Motion from Stereo When Motion is Unconstrained

Abstract: This paper describes a system which robustly estimates motion, and the 3D structure of a rigid environment, as a stereo vision platform moves through it. The system can cope with any camera motion, and any scene structure and is successful even in the presence of large jumps in camera position between the capture of successive image pairs, and when point matching is ambiguous. The system was developed to provide robust obstacle avoidance for a partially sighted person. The process described attempts to maximise use of the abundant information present in a stereo sequence. Key features include the use of multiple stereo match hypotheses, efficient motion computation from three images, and the use of this motion to ensure reliable matching, and to eliminate multiple stereo matches. Points are reconstructed in 3D space and tracked in a static coordinate frame with a Kalman Filter. This results in good 3D scene reconstructions. Structure which is impossible to match with certainty is absent, rather than being incorrectly reconstructed. As a result, the system is appropriate for obstacle detection. The results of processing some indoor and outdoor scenes, are given in the paper, and practical issues are highlighted throughout.

A Technique to Analytically Formulate and to Solve the 2-Dimensional Constrained Trajectory Planning Problem for a Mobile Robot

Abstract: A new technique for trajectory planning of a mobile robot in a two-dimensional space is presented in this paper. The main concept is to use a special representation of the robot trajectory, namely a parametric curve consisting in a sum of harmonics (sine and cosine functions), and to apply an optimization method to solve the trajectory planning problem for the parameters (i.e., the coefficients) appearing in the sum of harmonics. This type of curve has very nice features with respect to smoothness and continuity of derivatives, of whatever order. Moreover, its analytical expression is available in closed form and is very suitable for both symbolic and numerical computation. This enables one to easily take into account kinematic and dynamic constraints set on the robot motion. Namely, non-holonomic constraints on the robot kinematics as well as requirements on the trajectory curvature can be expressed in closed form, and act as input data for the trajectory planning algorithm. Moreover, obstacle avoidance can be performed by expressing the obstacle boundaries by means of parametric curves as well. Once the expressions of the trajectory and of the constraints have been set, the trajectory planning problem can be formulated as a standard mathematical problem of constrained optimization, which can be solved by any adequate numerical method. The results of several simulations are also reported in the paper to show the effectiveness of the proposed technique to generate trajectories which meet all requirements relative to kinematic and dynamic constraints, as well as to obstacle avoidance.

Online Suboptimal Obstacle Avoidance

Abstract: This paper presents an online planner for suboptimal obstacle avoidance. It generates near-shortest paths incrementally by avoiding obstacles optimally one at a time. In known environments, obstacles are avoided in an order determined by a global criterion. In unknown environments, obstacles are avoided as they are detected by on-board sensors. This avoidance strategy is guaranteed to reach the goal regardless of the order in which the obstacles are avoided. The method is demonstrated in several examples for an omnidirectional point robot moving among planar polygonal obstacles.

Reactive mobile manipulation using dynamic trajectory tracking

Abstract: A solution to the trajectory tracking problem for mobile manipulators is proposed, that allows for the base to be influenced by a reactive, obstacle avoidance behavior. Given a trajectory for the gripper to follow, a tracking algorithm for the manipulator is designed, and at the same time the base motions are generated in such a way that the base is coordinated with the gripper. Furthermore, it is shown that the method allows arbitrary upper and lower bounds on the gripper-base distance to be set and this can be achieved without introducing deadlocks into the system. The solution also ensures that the control effort, spent on slow base motions, is kept small.

Coupled Oscillator Control of Autonomous Mobile Robots

Abstract: This paper introduces a nonlinear oscillator scheme to control autonomous mobile robots. The method is based on observations of a successful control mechanism used in nature, the Central Pattern Generator. Simulations were used to assess the performance of oscillator controller when used to implement several behaviors in an autonomous robot operating in a closed arena. A sequence of basic behaviors (random wandering, obstacle avoidance and light following) was coordinated in the robot to produce the higher behavior of foraging for light. The controller is explored in simulations and tests on physical robots. It is shown that the oscillator—based controller outperforms a reactive controller in the tasks of exploring an arena with irregular walls and in searching for light.

Development of teleoperated six-legged walking robot for mine detection and mapping of mine field

Abstract: Our project has developed and studied high instrumentation technologies for mine detection and mine disposal using measuring equipment mounted on a six-legged teleoperated walking robots. This robot is called COMET-1 which is a full-autonomous obstacle avoidance robot or a semi-autonomous obstacle avoidance robot that requires the operator's intervention. When detecting a mine, the robot will lower each leg onto the ground safely and stably without stepping on a mine. For the simulations and experiments in the present study, the authors created a simulation model by attaching an optical proximity sensor on the foot of each leg and designed a walking algorithm using compliance control. Also, they verified the efficiency by means of walking experiments.

Autonomous collision avoidance: the technical requirements

Abstract: Autonomous collision avoidance is necessary if Unmanned Aerial Vehicles (UAVs) are to "blacken the sky" in massed attacks, accompany manned fighters on combat missions, and transition civil airspace. These vehicles will, in some manner, have to "see and avoid" other aircraft. An automated air collision avoidance system will fulfill a part of this need. It will automatically maneuver an aircraft, at the last instant, to avoid an air-to-air collision. It will function in a manner similar to a pilot avoiding a collision. It is a system that must be reliable, verifiable, and partially redundant, forming the last line of defense against collisions. It must provide nuisance free operation and allow safe interoperability. The requirements for such a system will be discussed in detail. Of particular interest are criteria to enable a safe, nuisance free system that will have embedded rules of the road for all encounters. Autonomous control of unmanned aerial vehicles is a goal for the US Air Force in the future. However, flying multiple unmanned vehicles in the same tactical airspace with manned fighters presents very challenging problems. Autonomous collision avoidance is a necessary step in moving toward this goal.