Showing papers on "Obstacle avoidance published in 2001"

RHex: A Biologically Inspired Hexapod Runner

Abstract: RHex is an untethered, compliant leg hexapod robot that travels at better than one body length per second over terrain few other robots can negotiate at all. Inspired by biomechanics insights into arthropod locomotion, RHex uses a clock excited alternating tripod gait to walk and run in a highly maneuverable and robust manner. We present empirical data establishing that RHex exhibits a dynamical (“bouncing”) gait—its mass center moves in a manner well approximated by trajectories from a Spring Loaded Inverted Pendulum (SLIP)—characteristic of a large and diverse group of running animals, when its central clock, body mass, and leg stiffnesses are appropriately tuned. The SLIP template can function as a useful control guide in developing more complex autonomous locomotion behaviors such as registration via visual servoing, local exploration via visual odometry, obstacle avoidance, and, eventually, global mapping and localization.

Posture-based motion planning: applications to grasping.

Abstract: This article describes a model of motion planning instantiated for grasping. According to the model, one of the most important aspects of motion planning is establishing a constraint hierarchy - a set of prioritized requirements defining the task to be performed. For grasping, constraints include avoiding collisions with the to-be-grasped objects and minimizing movement-related effort. These and other constraints are combined with instant retrieval (recall of stored postures) and instance generation (generation of new postures and movements to them) to simulate flexible prehension. Dynamic deadline setting is used to regulate termination of instance generation, and performance of more than one movement at a time with a single effector is used to permit obstacle avoidance. Old and new data are accounted for with the model.

Underwater vehicle obstacle avoidance and path planning using a multi-beam forward looking sonar

Abstract: This paper describes a new framework for segmentation of sonar images, tracking of underwater objects and motion estimation. This framework is applied to the design of an obstacle avoidance and path planning system for underwater vehicles based on a multi-beam forward looking sonar sensor. The real-time data flow (acoustic images) at the input of the system is first segmented and relevant features are extracted. We also take advantage of the real-time data stream to track the obstacles in following frames to obtain their dynamic characteristics. This allows us to optimize the preprocessing phases in segmenting only the relevant part of the images. Once the static (size and shape) as well as dynamic characteristics (velocity, acceleration,...) of the obstacles have been computed, we create a representation of the vehicle's workspace based on these features. This representation uses constructive solid geometry (CSG) to create a convex set of obstacles defining the workspace. The tracking takes also into account obstacles which are no longer in the field of view of the sonar in the path planning phase. A well-proven nonlinear search (sequential quadratic programming) is then employed, where obstacles are expressed as constraints in the search space. This approach is less affected by local minima than classical methods using potential fields. The proposed system is not only capable of obstacle avoidance but also of path planning in complex environments which include fast moving obstacles. Results obtained on real sonar data are shown and discussed. Possible applications to sonar servoing and real-time motion estimation are also discussed.

Motion planning in dynamic environments: obstacles moving along arbitrary trajectories

Abstract: This paper generalizes the concept of velocity obstacles given by Fiorini et al. (1998) to obstacles moving along arbitrary trajectories. We introduce the nonlinear velocity obstacle, which takes into account the shape, velocity and path curvature of the moving obstacle. The nonlinear v-obstacle allows selecting a single avoidance maneuver (if one exists) that avoids any number of obstacles moving on any known trajectories. For unknown trajectories, the nonlinear v-obstacles can be used to generate local avoidance maneuvers based on the current velocity and path curvature of the moving obstacle. This elevates the planning strategy to a second order method, compared to the first order avoidance using the linear v-obstacle, and zero order avoidance using only position information. Analytic expressions for the nonlinear v-obstacle are derived for general trajectories in the plane. The nonlinear v-obstacles are demonstrated in a complex traffic example.

Obstacle avoidance for mobile robots using artificial potential field approach with simulated annealing

Abstract: The artificial potential field methods provide simple and effective motion planners for practical purposes. However, there is a major problem with the artificial potential field approach. It is the formation of local minima that can trap the robot before reaching its goal. The avoidance of local minima has been an active research topic in potential field path planning. As one of the powerful techniques for escaping local minima, simulated annealing has been applied to local and global path planning. In this paper, the authors present and apply the mobile robot path planning technique which integrate the artificial potential field approach with simulated annealing to mobile robots.

A versatile and safe mobility assistant

Abstract: The Bremen autonomous wheelchair implements obstacle avoidance plus driving and routing assistance in a shared-control system. This article shows how the tasks of reliably detecting obstacles in the environment and safely avoiding these obstructions are solved.

Internet Control Architecture for Internet-Based Personal Robot

Abstract: This paper proposes a novel direct internet control architecture for internet-based personal robot, which is insensitive to the inherent internet time delay. The personal robot can be controlled using a simulator provided at a local site. Since the internet time delay is affected by the number of nodes and the internet loads, it is variable and unpredictable so that a large internet delay makes some control inputs distorted. The proposed control architecture guarantees that the personal robot can avoid obstacles and reduce the path error and the time difference between a virtual robot at the local site and a real robot at the remote site. This architecture is extended for an uncertain environment. Simulations and experimental results in the real internet environment demonstrate the effectiveness and applicability of the proposed internet control architecture.

The effect of obstacle position on reach-to-grasp movements.

Abstract: Numerous everyday tasks require the nervous system to program a prehensile movement towards a target object positioned in a cluttered environment. Adult humans are extremely proficient in avoiding contact with any non-target objects (obstacles) whilst carrying out such movements. A number of recent studies have highlighted the importance of considering the control of reach-to-grasp (prehension) movements in the presence of such obstacles. The current study was constructed with the aim of beginning the task of studying the relative impact on prehension as the position of obstacles is varied within the workspace. The experimental design ensured that the obstacles were positioned within the workspace in locations where they did not interfere physically with the path taken by the hand when no obstacle was present. In all positions, the presence of an obstacle caused the hand to slow down and the maximum grip aperture to decrease. Nonetheless, the effect of the obstacle varied according to its position within the workspace. In the situation where an obstacle was located a small distance to the right of a target object, the obstacle showed a large effect on maximum grip aperture but a relatively small effect on movement time. In contrast, an object positioned in front and to the right of a target object had a large effect on movement speed but a relatively small effect on maximum grip aperture. It was found that the presence of two obstacles caused the system to decrease further the movement speed and maximum grip aperture. The position of the two obstacles dictated the extent to which their presence affected the movement parameters. These results show that the anticipated likelihood of a collision with potential obstacles affects the planning of movement duration and maximum grip aperture in prehension.

Haptically augmented teleoperation

Abstract: Concerns telerobotic microsurgery. Existing systems offer tremor elimination and scaling of motions. This article goes beyond the strict master/slave scheme to the enhancement of the operator's capabilities during teleoperation. It is focused on the implementation of three types of constraints for the operators' movements: constrained movement (along a curve or on a predefined surface); virtual obstacle avoidance; and geometric constraints to limit the robots workspace. Constraints for the operator's movements can be implemented mechanically. Our approach uses a haptic master robot, and consists in adding constraint forces to its control scheme. Constraint forces are computed according to attractive or repulsive potential fields placed around constraints. This article presents the principles of these control enhancements which, we believe, will raise dramatically the level of safety and precision that a surgeon can achieve, but those principles can also be applied to a wide variety of teleoperation applications.

Insect Inspired Visual Control of Translatory Flight

Abstract: Flying insects use highly efficient visual strategies to control their self-motion in three-dimensional space. We present a biologically inspired, minimalistic model for visual flight control in an autonomous agent. Large, specialized receptive fields exploit the distribution of local intensities and local motion in an omnidirectional field of view, extracting the information required for attitude control, course stabilization, obstacle avoidance, and altitude control. In open-loop simulations, recordings from each control mechanism robustly indicate the sign of attitude angles, self-rotation, obstacle direction and altitude deviation, respectively. Closed-loop experiments show that these signals are sufficient for three-dimensional flight stabilization with six degrees of freedom.

Real-time path planning and obstacle avoidance for RAIS: an autonomous underwater vehicle

Abstract: This paper describes a navigation and guidance system (NGS) with real-time path planning and obstacle avoidance capabilities that has been developed for the autonomous underwater vehicle RAIS. The vehicle is designed to accomplish two missions: pre-deployment survey of sea bottom, and visual inspection of pipelines. In the first mission, the NGS must be able to track a predefined path while avoiding the unplanned occurrence of obstacles. In the second mission, the NGS must track a pipeline by locally reconstructing its location from visual information; also in this case, the unplanned occurrence of obstacles must be handled. Furthermore, the NGS must properly take into account the presence of ocean current and some drastic constraints due to sensor and actuator characteristics. Numerical and hardware-in-the-loop simulations have been developed to verify the effectiveness of the proposed NGS.

Fascination of down scaling — Alice the sugar cube robot

Abstract: Design of mobile micro-robot (MMR) is still a challenge due to the restricted availability of basic components. However, the number of highly integrated microelectronic and micromechanical components is growing fast. Nevertheless, its integration to a micro-system requires a good knowledge of all the interactions between sensor, actuator, computation and energy source. Often compromises between performance and power consumption have to be found. This paper gives the basic considerations for building mobile micro-robots. The major scaling effects are presented and their impact on micro-system design is discussed. The mobile micro-robot Alice (Fig. 1), having the size of a sugar cube, is presented and discussed in the context of scaling laws. It has an autonomy of around 10 hours and is able to navigate based on simple behaviors like obstacle avoidance or wall following.

A cooperative driving system with automated vehicles and inter-vehicle communications in Demo 2000

Abstract: Describes the technologies of cooperative driving with automated vehicles and inter-vehicle communications in the Demo 2000 cooperative driving. Cooperative driving, aiming at the compatibility of safety and efficiency of road traffic, here means that automated vehicles drive by forming a flexible platoon over a couple of lanes with a short inter-vehicle distance while performing lane changing, merging, and leaving the platoon. The vehicles for the demonstration are equipped with automated lateral and longitudinal control functions with localization data by the DGPS and the inter-vehicle communication function with 5.8 GHz DSRC designed for dedicated use in the demonstration. In order to show the feasibility and potential of the technologies, the demonstration was held in November, 2000 on a test track with 5 automated vehicles. The scenario included stop and go, platooning, merging and obstacle avoidance.

Method for working out an avoidance path in the horizontal plane for an aircraft to resolve a traffic conflict

Abstract: The invention concerns the production of an avoidance path in the horizontal plane enabling an aircraft to resolve a route conflict with another aircraft bringing about a risk of collision in the next 5 to 10 minutes and which minimises the negative consequences, on the aircraft flight plan, of the resulting diversion. The invention concerns a method for working out an avoidance path comprising two parts: a first jinking part with an initial heading such that the threatening aircraft adopts a path relative to the threatened aircraft tangent, on one side or the other, to the edges of the angle under which the threatening aircraft sees a protective circle drawn around the threatened aircraft with a radius equal to an accepted minimum distance, and a second part for returning to the initial route. Said method for working out an avoidance path can be carried out by a flight management computer which, once the evasive course has been accepted by the aircraft crew, continues to monitor said avoidance path by the automatic pilot system.

Radar-assisted collision avoidance/guidance strategy for planar flight

Abstract: We propose a radar-assisted collision avoidance/guidance strategy (RACAGS) for flight vehicles on low altitude missions. The task of obstacle avoidance and guidance are integrated in a single collision avoidance/guidance strategy. The avionic aids and computational requirements are modest as the strategy mainly depends on range-map and inertial system information. The strategy is first implemented in a planar scenario and then extended to three-dimensional and nominal trajectory following flight scenarios. Several simulation studies are presented for illustration.

Semi-autonomous obstacle avoidance of omnidirectional wheelchair by joystick impedance control

Abstract: An omnidirectional wheelchair is highly maneuverable in narrow or crowded areas such as residences, offices and hospitals. A semi-autonomous control method for omnidirectional wheelchairs is proposed. In addition to allowing the normal joystick commands of the wheelchair operator, this method provides a collision avoidance function using external sensors. The proposed method does not employ unexpected autonomous movements conflicting with the operator's joystick commands, because this tends to create discomfort for users and can be dangerous for infirm patients. Instead, the proposed method merely alerts the operator to the presence of an obstacle; this is accomplished by changing the impedance of the joystick essentially creating resistance against moving the joystick in the dangerous. direction. The wheelchair's motion remains controlled only by the operator's joystick commands, while a collision is avoided successfully. The effectiveness of the proposed method is shown by experiments with an onmidirectional wheelchair.

Reactive navigation of an intelligent robotic walking aid

Abstract: This work presents the intelligent walking aid system Care-O-bot. Care-O-bot is the prototype of a multifunctional home care system, to be used by elderly people in order to live independently in their homes. In order to enable easy manipulation of the robot platform, the way to use it as a walking aid has been adapted to conventional walking aid systems. The robot drives in reaction to input forces given by the user, for example if the user "pushes" the robot forward, it will start moving in the required direction. As an improvement to conventional walking aid systems, intelligent behaviours, as for example autonomous obstacle avoidance and path planning are included.

Using coded signals to benefit from ultrasonic sensor crosstalk in mobile robot obstacle avoidance

Abstract: One problem oftentimes observed with arrays of multiple ultrasonic sensors (sonars) in obstacle detection and avoidance systems is crosstalk. The paper presents a method in which data generated by crosstalk is actually used to generate more reliable and accurate object detection. This is accomplished by assigning a unique code to the signals emitted by each sonar, so that the source sonar can be identified even if its signal's echo is received by another sonar. Using geometric interpolation between the various sonars increases the accuracy of the measurements, overcoming their limited resolution. Experimental results show the potential of our system for mobile robotics obstacle detection and avoidance, as well as for localization using map-matching techniques.

Computerized obstacle avoidance systems for the blind and visually impaired

Abstract: This chapter gives an overview of existing devices for the guidance of visually impaired pedestrians and discusses the properties of the white cane and of conventional electronic travel aids. Also described are the disadvantages of using a standard mobile robot for this purpose. Next follows a description of the NavBelt, a computerized travel aid for the blind that is based on advanced mobile robot obstacle avoidance technology. The NavBelt is worn by the user like a belt and, via a set of stereo earphones, provides acoustic signals that guide the user around obstacles. One limitation of the NavBelt is that it is exceedingly difficult for the user to comprehend the guidance signals in time to allow fast walking. This problem is effectively overcome by a newer device, called GuideCane. The GuideCane uses the same mobile robotics technology as the NavBelt but it is a wheeled device pushed ahead of the user via an attached cane. When the GuideCane detects an obstacle it steers around it. The user immediately feels this steering action and can follow the GuideCane's new path easily and without any conscious effort. This chapter describes the GuideCane system, including the mechanical, electronic, and software components, followed by a description of the intuitive user-machine interface. The chapter ends with a discussion of the GuideCane's novel information transfer approach and its advantages and disadvantages in practical term.

Nonholonomic stabilization with collision avoidance for mobile robots

Abstract: This paper presents a motion planner and nonholonomic controller for a mobile robot, with global collision avoidance and convergence properties. An appropriately designed (dipolar) potential field is combined with discontinuous state feedback. A new class of Lyapunov functions is introduced and used for nonholonomic navigation. The obstacle avoidance and global asymptotic stability properties are verified through simulations.

Fast optical flow estimation and its application to real-time obstacle avoidance

Abstract: This paper presents a novel fast optical flow estimation algorithm and its application to real-lime obstacle avoidance of a guide-dog robot. The function of the laboratory-developed robot is to help blind or visually impaired pedestrians to move safely among obstacles. The proposed algorithm features a combination of the conventional correlation-based principle and the differential-based method for optical flow estimation. Employing image intensity gradients as features for pattern matching, we set up a brightness constraint to configure the search area. The merit of this scheme is that the computation load can be greatly reduced and in the mean time the possibility of estimation error is decreased. The vision system is installed on-board the robot to provide depth information of the immediate environment. The depth data are transformed to a safety distribution histogram and used for real-time obstacle avoidance. Experimental results demonstrate that the proposed method is effective for a guidance robot in a dynamic environment.

Evolutionary programming-based univector field navigation method for past mobile robots

Abstract: Most of navigation techniques with obstacle avoidance do not consider the robot orientation at the target position. These techniques deal with the robot position only and are independent of its orientation and velocity. To solve these problems this paper proposes a novel univector field method for fast mobile robot navigation which introduces a normalized two dimensional vector field. The method provides fast moving robots with the desired posture at the target position and obstacle avoidance. To obtain the sub-optimal vector field, a function approximator is used and trained by evolutionary programming. Two kinds of vector fields are trained, one for the final posture acquisition and the other for obstacle avoidance. Computer simulations and real experiments are carried out for a fast moving mobile robot to demonstrate the effectiveness of the proposed scheme.

Goal-Directed Navigation of an Autonomous Flying Robot Using Biologically Inspired Cheap Vision

Abstract: In nature, flying insects are capable of surprisingly good navigation, despite the small size and relative simplicity of their brains. Recent experimental research in biology has uncovered a number of different ways in which insects use cues derived from optical flow for navigational purposes, such as obstacle avoidance, safe landing and dead-reckoning. Inspired by the visual navigation of flying insects, this paper presents a model of vision-based navigation using Elementary Motion Detectors (EMDs). The performance tests with an autonomous flying robot successfully demonstrate goal-directed navigation in an unstructured environment, as well as obstacle avoidance and course stabilization behaviors. Further investigation in the simulation shows that goal-directed navigation can be potentially achieved by simple visual processing, and that the design flexibility of this approach leads to high adaptivity to the given task-environment.

Near-time-optimal trajectory planning for wheeled mobile robots with translational and rotational sections

Abstract: We derive a near-time-optimal trajectory for wheeled mobile robots (WMRs) satisfying the following: 1) initial and final postures/velocities; and 2) battery voltage and armature current constraints, under assumptions of simplified dynamics and constant translational/rotational velocity sections. We use a simplified dynamic model for WMRs, neglecting inductances of motor armatures and divide our trajectory generation algorithm for cornering motion into three sections. We specify a path-deviation requirement for obstacle avoidance. Transforming dynamics into uncorrelated form with regard to translational and rotational velocities, we make extreme control possible. By separating the rotational section with translational sections and determining the velocity scale factor a near-time-optimal trajectory can be obtained. Simulation results along with inverse control of path-following are given to validate the generated trajectory.

Trajectory Modeling of Robot Manipulators in the Presence of Obstacles

Abstract: This paper presents two different strategies for the problem of the optimal trajectory planning of robot manipulators in the presence of fixed obstacles. The first strategy is related to the situation where the trajectory must pass through a given number of points. The second strategy corresponds to the case where only the initial and final points are given. The optimal traveling time and the minimum mechanical energy of the actuators are considered together to build a multiobjective function. The trajectories are defined using spline functions and are obtained through offline computation for online operation. Sequential unconstrained minimization techniques (SUMT) have been used for the optimization. The obstacles are considered as three-dimensional objects sharing the same workspace performed by the robot. The obstacle avoidance is expressed in terms of the distances between potentially colliding parts. Simulation results are presented and show the efficiency of the general methodology used in this paper.

Planning reaching and grasping movements: the problem of obstacle avoidance.

Abstract: In this article, we review a model of the movement-planning processes that people use for direct reaching, reaching around obstacles, and grasping, and we present observations of subjects' repeated movements of the hand to touch 2 target locations, circumventing an intervening obstacle. The model defines an obstacle as a posture that, if adopted, would intersect with any part of the environment (including the actor himself or herself). The model finds a trajectory that is likely to bring the end-effector to the target by means of a one-or two- stage planning process. Each stage exploits the principles of instance retrieval and instance generation. In the first stage, a goal posture is identified, and the trajectory of a direct transition to that posture is tested for collision. If the direct movement has no collision, the movement to the target is immediately executed in joint space. If, however, the direct movement is foreseen to result in a collision, a second planning stage is invoked. The second planing stage identifies a via posture, movement through which will probably avoid the collision. Movement to and from the via posture is then superimposed on the main movement to the target so that the combined movement reaches the target without colliding with intervening obstacles. We describe the details of instance retrieval and instance generation for each of these planning stages and compare the model's performance with the observed kinematics of direct movements as well as movements around an obstacle. Then we suggest how the model might contribute to the study of movements in people with motor disorders such as spastic hemiparesis.

Collision avoidance by observing pedestrians' faces for intelligent wheelchairs

Abstract: With the increase in the number of senior citizens, there is a growing demand for human-friendly wheelchairs as mobility aids. One of the main issues in the robotic wheelchair research is autonomous obstacle avoidance for safety. However, this is difficult because most moving obstacles in the real world are human beings. They sometimes change their motion abruptly. The paper presents an intelligent wheelchair that can avoid collisions with such human pedestrians safely and comfortably for each other. We assume that the information whether or not a pedestrian has noticed the wheelchair and which direction he/she wants to go can appear in the face direction. Thus our intelligent wheelchair is continuously observing the pedestrian's face in its front area, realizing smooth passing by changing its collision avoidance strategy based on the face information and the range data from the ultrasonic sensors. Experimental results show the effectiveness and comfortableness of the proposed method.