Alberto Traslosheros

Uncalibrated visual servoing using the fundamental matrix

This paper describes a new algorithm for visual control of an uncalibrated 3 DOF joint system, using two weakly calibrated fixed cameras. The algorithm estimates on-line the Image Jacobian, a matrix which linearly relates joint velocity and image feature velocity. In our experiments we prove that by using the fundamental matrix, robustness of the estimation in the presence of noise is significantly increased with respect to already existing algorithms in specialized literature.

An Inexpensive Method for Kinematic Calibration of a Parallel Robot by Using One Hand-Held Camera as Main Sensor

This paper presents a novel method for the calibration of a parallel robot, which allows a more accurate configuration instead of a configuration based on nominal parameters. It is used, as the main sensor with one camera installed in the robot hand that determines the relative position of the robot with respect to a spherical object fixed in the working area of the robot. The positions of the end effector are related to the incremental positions of resolvers of the robot motors. A kinematic model of the robot is used to find a new group of parameters, which minimizes errors in the kinematic equations. Additionally, properties of the spherical object and intrinsic camera parameters are utilized to model the projection of the object in the image and thereby improve spatial measurements. Finally, several working tests, static and tracking tests are executed in order to verify how the robotic system behaviour improves by using calibrated parameters against nominal parameters. In order to emphasize that, this proposed new method uses neither external nor expensive sensor. That is why new robots are useful in teaching and research activities.

Vision-Based Control of the RoboTenis System

In this paper a visual servoing architecture based on a parallel robot for the tracking of faster moving objects with unknown trajectories is proposed. The control strategy is based on the prediction of the future position and velocity of the moving object. The synthesis of the predictive control law is based on the compensation of the delay introduced by the vision system. Demonstrating by experiments, the high-speed parallel robot system has good performance in the implementation of visual control strategies with high temporary requirements.

One camera in hand for kinematic calibration of a parallel robot

The main purpose of robot calibration is the correction of the possible errors in the robot parameters. This paper presents a method for a kinematic calibration of a parallel robot that is equipped with one camera in hand. In order to preserve the mechanical configuration of the robot, the camera is utilized to acquire incremental positions of the end effector from a spherical object that is fixed in the word reference frame. Incremental positions of the end effector are related to incremental positions of encoders of the motors of the robot. A kinematic model of the robot is modified in order to take into account possible errors of kinematic parameters. The solution of the model utilizes incremental positions of the resolvers and end effector, the new parameters minimizes errors in the kinematic equations. Spherical properties and intrinsic camera parameters are utilized to model sphere projection in order to improve spatial measurements. The robot system is designed to carry out tracking tasks and the calibration of the system is finally validated by means of integrating the errors of the visual controller.

Image Based Visual Servoing: Estimated Image Jacobian by Using Fundamental Matrix VS Analytic Jacobian

This paper describes a comparative study of performance between the estimated image Jacobian that come from taking into account the geometry epipolar of a system of two cameras, and the well known analytic image Jacobian that is utilized for most applications in visual servoing. Image Based Visual Servoing architecture is used for controlling a 3 d.o.f. articular system using two cameras in eye to hand configuration. Tests in static and dynamic cases were carried out, and showed that the performance of estimated Jacobian by using the properties of the epipolar geometry is such as good and robust against noise as the analytic Jacobian. This fact is considered as an advantage because the estimated Jacobian does not need laborious previous work prior the control task in contrast to the analytic Jacobian does.

A method for kinematic calibration of a parallel robot by using one camera in hand and a spherical object

The main purpose of robot calibration is the correction of the possible errors in the robot parameters. This paper presents a method for a kinematic calibration of a parallel robot that is equipped with one camera in hand. In order to preserve the mechanical configuration of the robot, the camera is utilized to acquire incremental positions of the end effector from a spherical object that is fixed in the word reference frame. The positions of the end effector are related to incremental positions of resolvers of the motors of the robot, and a kinematic model of the robot is used to find a new group of parameters which minimizes errors in the kinematic equations. Additionally, properties of the spherical object and intrinsic camera parameters are utilized to model the projection of the object in the image and improving spatial measurements. Finally, the robotic system is designed to carry out tracking tasks and the calibration of the robot is validated by means of integrating the errors of the visual controller.

A comparative study between analytic and estimated image Jacobian by using a stereoscopic system of cameras

This paper describes a comparative study of performance between the estimated image Jacobian that come from taking into account the epipolar geometry in a system of two cameras, and the well known analytic image Jacobian that is utilized for most applications in visual servoing. Image Based Visual Servoing architecture is used for controlling a 3 DOF articular system using two cameras in eye to hand configuration. Tests in static and dynamic cases were carried out, and showed that the performance of estimated Jacobian by using the properties of the epipolar geometry is such as good and robust against noise as the analytic Jacobian. This fact is considered as an advantage because the estimated Jacobian does not need laborious previous work prior to control task in contrast to the analytic Jacobian does.

Visual servoing for the Robotenis system: A strategy for a 3 DOF parallel robot to hit a Ping-Pong ball

This article describes a new visual servo control and strategies that are used to carry out dynamic tasks by the Robotenis platform. This platform is basically a parallel robot that is equipped with an acquisition and processing system of visual information, its main feature is that it has a completely open architecture control, and planned in order to design, implement, test and compare control strategies and algorithms (visual and actuated joint controllers). Following sections describe a new visual control strategy specially designed to track and intercept objects in 3D space. The results are compared with a controller shown in previous woks, where the end effector of the robot keeps a constant distance from the tracked object. In this work, the controller is specially designed in order to allow changes in the tracking reference. Changes in the tracking reference can be used to grip an object that is under movement, or as in this case, hitting a hanging Ping-Pong ball. Lyapunov stability is taken into account in the controller design.

High-speed Visual Servoing of PKMs

In this paper a visual servoing architecture based on a parallel robot for the tracking of faster moving objects with unknown trajectories is proposed. The control strategy is based on the prediction of the future position and velocity of the moving object. The synthesis of the predictive control law is based on the compensation of the delay introduced by the vision system. Demonstrating by experiments, the high-speed parallel robot system has good performance in the implementation of visual control strategies with high temporary requirements.

Homography-Based Tracking Control for Mobile Robots

This work presents a control strategy that allows a follower robot to track a target vehicle moving along an unknown trajectory with unknown velocity. It uses only artificial vision to establish both the robots position and orientation relative to the target. The control system is proved to be asymptotically stable at the equilibrium point, which corresponds to the navigation objective. Experimental results with two robots, a leader and a follower, are included to show the performance of the proposed vision-based tracking control system.