gfu Jin

Decentralized cooperative mean approach to collision avoidance for nonholonomic mobile robots

This paper presents a novel, decentralized, control-theoretic approach to address collision avoidance for multi-robot systems. We create a virtual obstacle at the mean position of the robots. A control is be designed such that each robot will avoid the closest obstacle when a collision is possible. The closest obstacle can be the virtual obstacle or the nearest robot. We present two such control laws. The first assumes perfect knowledge of the velocities of all nearby robots and can allow a saturated velocity input for each robot. In practice, the velocities of the other robots are hard to measure or estimate precisely. Therefore, the second control law removes the assumption of known velocities based on a high-gain, robust control scheme. We prove the first control scheme is globally asymptotically stable, and the robust control law is globally uniformly ultimately bounded. To verify the effectiveness of the proposed approach, Monte Carlo simulations and experiments have been conducted.

A stable switched-system approach to obstacle avoidance for mobile robots in SE(2)

In this paper, we propose a novel approach for obstacle avoidance. The configuration space of a nonholonomic mobile robot in the special Euclidean group SE(2). Therefore, we divide the whole configuration space into two sub-regions (i.e., a safe region and an obstacle avoidance region). We have derived two functions to define the robots behavior in each region, which generate velocity vectors that drive the robot away from the obstacle and always towards the goal. We consider the existence of a switching surface between these two sub-regions, and specifically define this switching surface as a local subset of SE(2), i.e. the switching surface includes orientation, defined by the relative angle between the robot heading and bearing to the obstacle. Two different switching signals are proposed based on the switching surface. Lyapunov stability analysis proves the robot will converge to a goal position. To verify the effectiveness of the proposed approach, several simulations and experiments have been conducted.

Collision-free formation and heading consensus of nonholonomic robots as a pose regulation problem

Abstract This paper presents a novel, decentralized control algorithm to address the problem of controlling of multiple, network connected, nonholonomic mobile robots to achieve a collision-free formation and heading consensus simultaneously. Our approach transforms the formation and heading consensus problem to a pose regulation problem. The pose is derived by a virtual graph, which is an isomorphic mapping of the graph of the network connected systems. If the system is holonomic, traditional consensus on the virtual graph can stabilize the real system to the desired formation. In the case of nonholonomic systems, such as mobile robots, each robot’s pose then is regulated to the known consensus pose by a novel smooth and continuous control law. The control law also induces the real robot systems to achieve not only the desired formation but also heading consensus. We prove the proposed control schemes are globally asymptotically stable. Theoretical analysis, several simulations, and experiments have been conducted to verify the effectiveness of the proposed approach.

A Multi-view camera-projector system for object detection and robot-human feedback

In this paper, we present a novel camera-projector system for assisting robot-human interaction. The system is comprised of a stereo camera pair and a DLP projector. The proposed system provides feedback information indicating the robots perception of the environment and what action a human user desires. Feedback is delivered by iteratively spotlighting objects in the environment using the projector. When the spotlight lands on an object that the human user wants the robot to retrieve, he or she can confirm the object selection, and the robot will perform a grasping task to retrieve the selected object. In this investigation, the proposed camera-projector performs three tasks: 1) Actively detect visually salient objects in the scene from the two camera views using a visual attention model. 2) Locate the detected objects using a trifocal tensor based object matching method, and project a spot of light on the objects to provide information back to the human user. 3) Reconstruct the 3D position of the target to plan robot motion and conduct vision-based control to move a robot manipulator to grasp the object. Experimental results of human-directed object grasping task are presented to demonstrate the functions of the proposed system.

Consensus based attractive vector approach for formation control of nonholonomic mobile robots

A novel, decentralized switched-system approach is proposed to address the problem of controlling multiple nonholonomic mobile robots to achieve a desired formation as well as heading consensus. The formation is induced by each robot following an attractive vector derived using a virtual, isomorphic graph. Then, a novel switching control law is designed such that each robot follows its attractive vector and achieves consensus on the virtual graph, which will result in the multiple robot systems moving to the desired formation and achieving heading consensus. We prove the proposed control scheme is asymptotically stable. To verify the effectiveness of the proposed approach, a simulation and an experimental results are provided.

A switched-system approach to formation control and heading consensus for multi-robot systems

This paper proposes a novel, hybrid and decentralized, switched-system approach for formation and heading consensus control of mobile robots under switching communication topology, including collision avoidance capability. The set of robots consists of nonholonomic wheeled mobile robots and can include a teleoperated UAV. The key feature of this approach is a virtual graph, which is derived by adding a set of relative translation vectors to the real graph of the multiple robots. Our approach results in the robots in the real graph moving to the desired formation and achieving heading consensus while the virtual robots on the virtual graph reach pose consensus. If any robot detects a nearby obstacle or other robot, the robot will temporarily move along an avoidance vector, which is perpendicular and positively projected onto the attractive vector, such that collision is avoided while minimally deviating from its formation control path. Experimental results are provided by two different research groups to demonstrate the effectiveness of our approach. These experiments extend the theoretical development by introducing a teleoperated quadrotor as a leader robot of the multi-robot systems. The same control law works for the extended system, with no modifications.

A Stable Switched-System Approach to Collision-Free Wheeled Mobile Robot Navigation

This paper presents a novel switched-system approach for obstacle avoidance by mobile robots. This approach does not suffer from common drawbacks of existing methods, such as needing prior knowledge of obstacles, or local minima or chattering in control laws. We define an attractive and an avoidance vector in obstacle-free and obstacle-avoidance regions, respectively. Next, we define an unified velocity vector, which represents either the attractive vector or the avoidance vector, and drives the robot away from the obstacle and ultimately towards the goal. The avoidance vector differs from the repulsive vector commonly used in potential field approaches, rather it is defined always perpendicular to such a repulsive vector and projects positively onto the attractive vector. The unified velocity vector enables the use of a common Lyapunov function in analyzing the stability of the system under arbitrary switching. Novel switching rules are proposed for obstacles that can be well bounded by a circle in the local subset of SE(2). To better handle large, non-circular obstacles, a separate switching signal is proposed. Through the choice of switching rule, we investigate the chattering problem that can hinder some switching controllers. We present two control laws, one with bounded inputs and one with no bounds on inputs. We prove both control schemes are asymptotically stable and guide the robot to the goal while avoiding obstacles. To verify the effectiveness of the proposed approach, as well as compare the control laws and switching rules, several simulations and experiments have been conducted.

Camera relative pose estimation for visual servoing using quaternions

Abstract We present a novel approach to estimate the rotation and translation between two camera views from a minimum of five matched points in the images. Our approach simultaneously recovers the 3D structure of the points up to a common scale factor, and is immune to a variety of problems that plague existing methods that are based on the Euclidean homography or Essential matrix. Methods based on homography only function when feature points are coplanar in 3D space. Methods based on the Essential matrix often lose accuracy as the translation between two camera views goes to zero or when points are coplanar. By recovering the rotation and translation independently using quaternions, our algorithm eschews the shortcomings of these methods. Moreover, we do not impose any constraints on the 3D configuration of the points (such as coplanar or non-coplanar constraints). Our method is particularly well-suited for Position-Based Visual Servoing (PBVS) applications. Investigations using both simulations and experiments validate the new method. Comparisons between the proposed algorithm and the existing algorithms establish that our algorithm is robust to noise. A Matlab implementation of our algorithm is available online and free.

A switched-system approach to shared robust control and obstacle avoidance for mobile robots

We propose a shared control structure for nonholonomic mobile robots, in which a human operator can command motions that override autonomous operation, and the robot overrides either the teleoperation or autonomous controller if it encounters an obstacle. We divide the whole configuration, including orientation, space into an obstacle avoidance and an obstacle-free region. This enables a switched-system approach to switch between autonomous and teleoperation mode, or the obstacle avoidance and the obstacle-free region. To reject disturbances or noise present in the error dynamics, two different robust control laws are proposed using a high gain and a variable structure approach. Lyapunov-based stability analysis is provided. To rigorously test the approach under different circumstances, experiments have been conducted by two different research groups. The results from two groups show that the shared control approach works effectively both in the teleoperation mode and autonomous mode with different system settings and environments.Copyright