Showing papers on "Mobile robot published in 1995"

Control of chained systems application to path following and time-varying point-stabilization of mobile robots

Abstract: Chain form systems have recently been introduced to model the kinematics of a class of nonholonomic mechanical systems. The first part of the study is centered on control design and analysis for nonlinear systems which can be converted to the chain form. Solutions to various control problems (open-loop steering, partial or complete state feedback stabilization) are either recalled, generalized, or developed. In particular, globally stabilizing time-varying feedbacks are derived, and a discussion of their convergence properties is provided. Application to the control of nonholonomic wheeled mobile robots is described in the second part of the study by considering the case of a car pulling trailers. >

The focussed D* algorithm for real-time replanning

Abstract: Finding the lowest-cost path through a graph is central to many problems including route planning for a mobile robot If arc costs change during the traverse then the remainder of the path may need to be replanned. This is the case for a sensor-equipped mobile robot with imperfect information about its environment. As the robot acquires additional information via its sensors it can revise its plan to reduce the total cost of the traverse. If the prior information is grossly incomplete the robot may discover useful information in every piece of sensor data. During replanning, the robot must either wait for the new path to be computed or move in the wrong direction therefore rapid replanning is essential The D* algorithm (Dynamic A*) plans optimal traverses ID real-time by incrementally repairing paths to the robots state as new information is discovered. This paper describes an extension to D* that focusses the repairs to significantly reduce the total time required for the initial path calculation and subsequent replanning operations. This extension completes the development of the D* algorithm as a full generalizatin of A* for dynamic environments where arc costs can change during the traverse of the solution path.

The swing up control problem for the Acrobot

Abstract: Underactuated mechanical systems are those possessing fewer actuators than degrees of freedom. Examples of such systems abound, including flexible joint and flexible link robots, space robots, mobile robots, and robot models that include actuator dynamics and rigid body dynamics together. Complex internal dynamics, nonholonomic behavior, and lack of feedback linearizability are often exhibited by such systems, making the class a rich one from a control standpoint. In this article the author studies a particular underactuated system known as the Acrobot: a two-degree-of-freedom planar robot with a single actuator. The author considers the so-called swing up control problem using the method of partial feedback linearization. The author gives conditions under which the response of either degree of freedom may be globally decoupled from the response of the other and linearized. This result can be used as a starting point to design swing up control algorithms. Analysis of the resulting zero dynamics as well as analysis of the energy of the system provides an understanding of the swing up algorithms. Simulation results are presented showing the swing up motion resulting from partial feedback linearization designs. >

Control of a nonholonomic mobile robot: backstepping kinematics into dynamics

Abstract: A dynamical extension that makes possible the integration of a kinematic controller and a torque controller for nonholonomic mobile robots is presented. A combined kinematic/torque control law is developed using backstepping and asymptotic stability is guaranteed by Lyapunov theory. Moreover, this control algorithm can be applied to the three basic nonholonomic navigation problems: tracking a reference trajectory, path following and stabilization about a desired posture. A general structure for controlling a mobile robot results that can accommodate different control techniques ranging from a conventional computed-torque controller, when all dynamics are known, to adaptive controllers.

Cooperative mobile robotics: antecedents and directions

Abstract: There has been increased research interest in systems composed of multiple autonomous mobile robots exhibiting collective behavior. Groups of mobile robots are constructed, with an aim to studying such issues as group architecture, resource conflict, origin of cooperation, learning, and geometric problems. As yet, few applications of collective robotics have been reported, and supporting theory is still in its formative stages. In this paper, the authors give a critical survey of existing works and discuss open problems in this field, emphasizing the various theoretical issues that arise in the study of cooperative robotics. The authors describe the intellectual heritages that have guided early research, as well as possible additions to the set of existing motivations.

Inertial navigation systems for mobile robots

Abstract: A low-cost solid-state inertial navigation system (INS) for mobile robotics applications is described. Error models for the inertial sensors are generated and included in an extended Kalman filter (EKF) for estimating the position and orientation of a moving robot vehicle. Two different solid-state gyroscopes have been evaluated for estimating the orientation of the robot. Performance of the gyroscopes with error models is compared to the performance when the error models are excluded from the system. Similar error models have been developed for each axis of a solid-state triaxial accelerometer and for a conducting-bubble tilt sensor which may also be used as a low-cost accelerometer. An integrated inertial platform consisting of three gyroscopes, a triaxial accelerometer and two tilt sensors is described. >

Probabilistic robot navigation in partially observable environments

Abstract: Autonomous mobile robots need very reliable navigation capabilities in order to operate unattended for long periods of time. This paper reports on first results of a research program that uses par tially observable Markov models to robustly track a robots location in office environments and to direct its goal-oriented actions. The approach explicitly maintains a probability distribution over the possible locations of the robot taking into account various sources of uncertainly including approximate knowledge of the environment and actuator and sensor uncertainty. A novel feature of our approach is its integration of topological map information with approximate metric information. We demonstrate the robustness of this approach in controlling an actual indoor mobile robot navigating corridors.

Communication in reactive multiagent robotic systems

Abstract: Multiple cooperating robots are able to complete many tasks more quickly and reliably than one robot alone. Communication between the robots can multiply their capabilities and effectiveness, but to what extent? In this research, the importance of communication in robotic societies is investigated through experiments on both simulated and real robots. Performance was measured for three different types of communication for three different tasks. The levels of communication are progressively more complex and potentially more expensive to implement. For some tasks, communication can significantly improve performance, but for others inter-agent communication is apparently unnecessary. In cases where communication helps, the lowest level of communication is almost as effective as the more complex type. The bulk of these results are derived from thousands of simulations run with randomly generated initial conditions. The simulation results help determine appropriate parameters for the reactive control system which was ported for tests on Denning mobile robots.

Social potential fields: a distributed behavioral control for autonomous robots

Abstract: A Very Large Scale Robotic (VLSR) system may consist of from hundreds to perhaps tens of thousands or more autonomous robots. The costs of robots are going down, and the robots are getting more compact, more capable, and more flexible. Hence, in the near future, we expect to see many industrial and military applications of VLSR systems in tasks such as assembling, transporting, hazardous inspection, patrolling, guarding and attacking. In this paper, we propose a new approach for distributed autonomous control of VLSR systems. We define simple artificial force laws between pairs of robots or robot groups. The force laws are inverse-power force laws, incorporating both attraction and repulsion. The force laws can be distinct and to some degree they reflect the ‘social relations’ among robots. Therefore we call our method social potential fields. An individual robot's motion is controlled by the resultant artificial force imposed by other robots and other components of the system. The approach is distributed in that the force calculations and motion control can be done in an asynchronous and distributed manner. We also extend the social potential fields model to use spring laws as force laws. This paper presents the first and a preliminary study on applying potential fields to distributed autonomous multi-robot control. We describe the genetic framework of our social potential fields method. We show with computer simulations that the method can yield interesting and useful behaviors among robots, and we give examples of possible industrial and military applications. We also identify theoretical problems for future studies.

Sensors for Mobile Robots: Theory and Application

Abstract: The author compiles everything a student or experienced developmental engineer needs to know about the supporting technologies associated with the rapidly evolving field of robotics. From the table of contents: Design Considerations * Dead Reckoning * Odometry Sensors * Doppler and Inertial Navigation * Typical Mobility Configurations * Tactile and Proximity Sensing * Triangulation Ranging * Stereo Disparity * Active Triangulation * Active Stereoscopic * Hermies * Structured Light * Known Target Size * Time of Flight * Phase-Shift Measurement * Frequency Modulation * Interferometry * Range from Focus * Return Signal Intensity * Acoustical Energy * Electromagnetic Energy * Optical Energy * Microwave Radar * Collision Avoidance * Guidepath Following * Position-Location Systems * Ultrasonic and Optical Position-Location Systems * Wall, Doorway, andCeiling Referencing * Application-Specific Mission Sensors

Desktop teleoperation via the World Wide Web

Abstract: We built a system that allows a robot manipulator to be teleoperated via the WWW. Although the field of teleoperation dates back over 50 years, the WWW provides a low-cost and widely-available interface that can make teleoperated resources accessible to anyone with a desktop or laptop computer and modem. The "Mercury Project" consists of an industrial robot arm fitted with a CCD camera and a pneumatic system. We placed a sandbox filled with buried artifacts in the robot workspace. Using the ISMAP feature of HTTP, users can remotely move the camera to view desired locations or direct a short burst of compressed air into the sand to view the newly cleared region. To our knowledge, the Mercury Project is the first system to permit WWW users to remotely view and alter the real world. This paper focuses on interface design, robot hardware, and system architecture.

Cooperative multi-robot box-pushing

Abstract: This paper deals with the communication in task-sharing between two autonomous six-legged robots equipped with object and goal sensing, and a repertoire of contact and light-following behaviors. The performance of pushing an elongated box towards a goal region is difficult for a single robot and improves significantly when performed cooperatively, but requires careful coordination between the robots. We present and experimentally demonstrate an approach that utilizes cooperation at three levels: sensing, action, and control, and takes the advantage of a simple communication protocol to compensate for the robots' noisy and uncertain sensing.

Evolving mobile robots in simulated and real environments

Abstract: The problem of the validity of simulation is particularly relevant for methodologies that use machine learning techniques to develop control systems for autonomous robots, as, for instance, the artificial life approach known as evolutionary robotics. In fact, although it has been demonstrated that training or evolving robots in real environments is possible, the number of trials needed to test the system discourages the use of physical robots during the training period. By evolving neural controllers for a Khepera robot in computer simulations and then transferring the agents obtained to the real environment we show that (a) an accurate model of a particular robot-environment dynamics can be built by sampling the real world through the sensors and the actuators of the robot; (b) the performance gap between the obtained behaviors in simulated and real environments may be significantly reduced by introducing a "conservative" form of noise; (c) if a decrease in performance is observed when the system is transferred to a real environment, successful and robust results can be obtained by continuing the evolutionary process in the real environment for a few generations.

Control of nonholonomic wheeled mobile robots by state feedback linearization

Abstract: We are concerned in this article with the control of wheeled mobile robots, which constitute a class of nonholonomic mechanical systems. More precisely, we are interested in solving the problem of tracking with stability of a reference trajectory, by means of linearizing ''static'' and ''dynamic'' state feedback laws. We give conditions to avoid possible singularities of the feedback laws.

A sensor-based navigation for a mobile robot using fuzzy logic and reinforcement learning

Abstract: The proposed navigator consists of an avoidance behavior and goal-seeking behavior. Two behaviors are independently designed at the design stage and then combined them by a behavior selector at the running stage. A behavior selector using a bistable switching function chooses a behavior at each action step so that the mobile robot can go for the goal position without colliding with obstacles. Fuzzy logic maps the input fuzzy sets representing the mobile robot's state space determined by sensor readings to the output fuzzy sets representing the mobile robot's action space. Fuzzy rule bases are built through the reinforcement learning which requires simple evaluation data rather than thousands of input-output training data. Since the fuzzy rules for each behavior are learned through a reinforcement learning method, the fuzzy rule bases can be easily constructed for more complex environments. In order to find the mobile robot's present state, ultrasonic sensors mounted at the mobile robot are used. The effectiveness of the proposed method is verified by a series of simulations. >

Geometric Phases and Robotic Locomotion

Abstract: Robotic locomotion is based in a variety of instances upon cyclic changes in the shape of a robot mechanism Certain variations in shape exploit the constrained nature of a robot's interaction with its environment to generate net motion This is true for legged robots, snakelike robots, and wheeled mobile robots undertaking maneuvers such as parallel parking In this paper we explore the use of tools from differential geometry to model and analyze this class of locomotion mechanisms in a unified way In particular, we describe locomotion in terms of the geometric phase associated with a connection on a principal bundle, and address issues such as controllability and choice of gait We also provide an introduction to the basic mathematical concepts which we require and apply the theory to numerous example systems

Mobile robot sonar for target localization and classification

Abstract: A novel sonar array is presented that has applications in mobile robotics for localization and mapping of indoor en vironments. The ultrasonic sensor localizes and classifies multiple targets in tw...

Moving furniture with teams of autonomous robots

Abstract: The authors wish to organize furniture in a room with a team of robots that can push objects. The authors show how coordinated pushing by robots can change the pose (position and orientation) of objects and then they ask whether planning, global control, and explicit communication are necessary for cooperatively changing the pose of objects. The authors answer in the negative and present, as witnesses, four cooperative manipulation protocols that use different amounts of state, sensing, and communication. The authors analyze these protocols in the information invariant framework. The authors formalize the notion of resource tradeoffs for robot protocols and give the tradeoffs for the specific protocols discussed here.

Sliding mode control for gradient tracking and robot navigation using artificial potential fields

Abstract: This paper introduces a sliding mode control strategy for tracking the gradient of an artificial potential field. The control methodology is applicable to fully actuated holonomic robotic systems with n-degrees of freedom. The controller yields exact tracking of the gradient lines and is invariant with respect to parametric uncertainty and disturbances in system dynamics. A detailed case study for mobile robots introduces the equilibrium point placement method for designing harmonic planar potential fields for circular obstacle security zones. Diffeomorph mappings can be utilized for more complex obstacle security zones. The gradient of the harmonic potential field is shown to always lead away from the obstacle security zone and to continuously approach the goal point. >

Building, registrating, and fusing noisy visual maps

Abstract: This paper deals with the problem of building three-dimen sional descriptions (we call them visual maps) of the environ ment of a mobile robot using passive vision. These maps are local (i.e., attached to specific frames of reference). Since noise is present, they incorporate information about the ge ometry of the environment and about the uncertainty of the parameters defining the geometry. This geometric uncertainty is directly related to its source (i.e., sensor uncertainty). We show how visual maps corresponding to different positions of the robot can be registered to compute a better estimate of its displacement between the various viewpoint positions, as suming an otherwise static environment. We use these esti mates to fuse the different visual maps and reduce locally the uncertainty of the geometric primitives which have found correspondents in other maps. We propose to perform these three tasks (building, registrating, and fusing visual maps) within the general framework of extended Kalman filter...

The Mobile Robot Rhino

Abstract: Rhino was the University of Bonn's entry in the 1994 AAAI Robot Competition and Exhibition. rhino is a mobile robot designed for indoor navigation and manipulation tasks. The general scientific goal of the rhino project is the development and the analysis of autonomous and complex learning systems. This article briefly describes the major components of the rhino control software as they were exhibited at the competition. It also sketches the basic philosophy of the rhino architecture and discusses some of the lessons that we learned during the competition.

Development of an omni-directional mobile robot with 3 DOF decoupling drive mechanism

Abstract: A new driving mechanism for holonomic omnidirectional mobile robots is designed, which enables 3 DOF motion control by three correspondent actuators in a decoupled manner with no redundancy A prototype of the omnidirectional mobile robot with the driving mechanism is developed including a parallel link suspension mechanism The kinematics of the omnidirectional mobile robot is also analyzed, and simulation for velocity control of the robot is performed by a method for velocity modulation with interpolation to achieve the given target position and velocity

Error eliminating rapid ultrasonic firing for mobile robot obstacle avoidance

Abstract: This paper introduces error eliminating rapid ultrasonic firing (EERUF), a new method for firing multiple ultrasonic sensors in mobile robot applications. EERUF allows ultrasonic sensors to fire at rates that are five to ten times faster than those customary in conventional applications. This is possible because EERUF reduces the number of erroneous readings due to ultrasonic noise by one to two orders of magnitude. While faster firing rates improve the reliability and robustness of mobile robot obstacle avoidance and are necessary for safe travel at higher speed (e.g., V>0.3 m/sec), they introduce more ultrasonic noise and increase the occurrence rate of crosstalk. However, EERUF almost eliminates crosstalk, making fast firing feasible. Furthermore, ERRUF's unique noise rejection capability allows multiple mobile robots to collaborate in the same environment, even if their ultrasonic sensors operate at the same frequencies. The authors have implemented and tested the EERUF method on a mobile robot and they present experimental results. With EERUF, a mobile robot was able to traverse an obstacle course of densely spaced, pencil-thin (8 mm-diameter) poles at up to 1 m/sec. >

Robot hand-eye coordination based on stereo vision

Abstract: This article describes the theory and implementation of a system that positions a robot manipulator using visual information from two cameras. The system simultaneously tracks the robot end-effector and visual features used to define goal positions. An error signal based on the visual distance between the end-effector and the target is defined, and a control law that moves the robot to drive this error to zero is derived. The control law has been integrated into a system that performs tracking and stereo control on a single processor with no special-purpose hardware at real-time rates. Experiments with the system have shown that the controller is so robust to calibration error that the cameras can be moved several centimeters and rotated several degrees while the system is running with no adverse effects. >

A complete navigation system for goal acquisition in unknown environments

Abstract: Most autonomous outdoor navigation systems tested on actual robots have centered on local navigation tasks such as avoiding obstacles or following roads. Global navigation has been limited to simple wandering, path tracking, straight-line goal seeking behaviors, or executing a sequence of scripted local behaviors. These capabilities are insufficient for unstructured and unknown environments, where replanning may be needed to account for new information discovered in every sensor image. To address these problems, the authors developed a complete system that integrates local and global navigation. The local system uses a scanning laser rangefinder to detect and avoid obstacles. The global system uses an incremental path planning algorithm to optimally replan the global path for each detected obstacle. A control arbiter steers the robot to achieve the proper balance between safety and goal acquisition. This system was tested on a real robot and successfully drove it 1.4 kilometers to find a goal given no a priori map of the environment.

A fuzzy logic based extension to Payton and Rosenblatt's command fusion method for mobile robot navigation

Abstract: Payton and Rosenblatt (1990) have proposed a command fusion method for combining outputs of multiple behaviors in a mobile robot navigation system such that information loss due to command fusion can be reduced. Using linguistic fuzzy rules to explicitly capture heuristics implicit in the Payton-Rosenblatt approach, we have extended their approach to a fuzzy logic architecture for mobile robot navigation in dynamic environments, which is simpler and easier to understand and modify. We have also developed and empirically tested a new defuzzification technique for alleviating difficulties in applying existing defuzzification methods to mobile robot navigation control. >

Travel control method, travel control device, and mobile robot for mobile robot systems

Abstract: In the travel control method in the mobile robot system including a plurality of mobile robots and the control station for controlling these mobile robot, the control station directs one of a plurality of mobile robots to the destination robot, responding to the direction, searches the route to the destination directed by the control station and sends the result to the control station. The control station which receives this in formation checks if the travel path searched by the mobile robot is already reserved by other mobile robots or not by the reservation table. If not, the control station informs the reserve completion to said mobile robot. The mobile robot which received the information of the reservation completion travels automatically along the travel path which is already reserved. In addition, said control station, when there are other mobile robots which disturb the travel of each mobile robot, directs the robot to wait or to take an alternate route according to the situation, or directs other mobile robots that disturb the travel to halt.

Divergent stereo in autonomous navigation: from bees to robots

Abstract: This article presents some experiments of a real-time navigation system driven by two cameras pointing laterally to the navigation direction (Divergent Stereo). Similarly to what has been proposed in (Franceschini et al. 1991; Coombs and Roberts 1992), our approach (Sandini et al. 1992; Santos-Victor et al. 1993) assumes that, for navigation purposes, the driving information is not distance (as it is obtainable by a stereo setup) but motion and, more precisely, by the use of qualitative optical-flow information computed over nonoverlapping areas of the visual field of two cameras.

Coordinated motion planning for multiple car-like robots using probabilistic roadmaps

Abstract: Presents a new approach to the multi-robot path planning problem, where a number of robots are to change their positions through feasible motions in the same static environment. The approach is probabilistically complete. That is, any solvable problem is guaranteed to be solved within a finite amount of time. The method, which is an extension of previous work on probabilistic single-robot planners, is very flexible in the sense that it can easily be applied to different robot types. In this paper the authors apply it to non-holonomic car-like robots, and present experimental results which show that the method is powerful and fast.

MapBased Navigation for a Mobile Robot with Ominidirectional Image Sensor COPIS

Abstract: We designed a new omnidirectional image sensor COPIS (Conic Projection Image Sensor) to guide the navigation of a mobile robot. The feature of COPIS is passive sensing of the omnidirectional image of the environment, in real-time (at the frame rate of a TV camera), using a conic mirror. COPIS is a suitable sensor for visual navigation in a real world environment. We report here a method for navigating a robot by detecting the azimuth of each object in the omnidirectional image. The azimuth is matched with the given environmental map. The robot can precisely estimate its own location and motion (the velocity of the robot) because COPIS observes a 360/spl deg/ view around the robot, even when all edges are not extracted correctly from the omnidirectional image. The robot can avoid colliding against unknown obstacles and estimate locations by detecting azimuth changes, while moving about in the environment. Under the assumption of the known motion of the robot, an environmental map of an indoor scene is generated by monitoring azimuth change in the image. >