Flávio Garcia Pereira

An approach to avoid obstacles in mobile robot navigation: the tangential escape

An approach to guide a mobile robot from an initial position to a goal position avoiding any obstacle in its path, when navigating in a semi-structured environment, is proposed in this paper. Such an approach, hereinafter referred to as tangential escape, consists in changing the current robot orientation through a suitable combination of the values of the angular and linear velocities (the control actions) whenever an obstacle is detected close to it. Then, the robot starts navigating in parallel to the tangent to the obstacle, regarding the point of the obstacle boundary the robot sensing system identifies as the closest one. The stability of the control system designed according this approach is proven, showing that the robot reaches any reachable goal, with or without a prescribed final orientation. Such a control system is programmed onboard a mobile platform whose sensing system is a laser scanner which provides 181 range measurements, for experimental validation. The results obtained are presented and discussed, allowing concluding that the tangential escape approach is able to guide the robot along trajectories that result in a reduction of the traveling time, thus saving batteries and reducing the motor wearing.

Object transportation task by a human and a mobile robot

This paper addresses the human-robot cooperation problem on object transportation tasks, particularly when a human grasps one side of the object while the other extremity is carried by the robot. The robot is equipped with a pair of infrared sensors used to obtain the loads status and apply it as a feedback to accomplish a specific task. A nonlinear controller is proposed to allow the robot to perform coordinated movements and thus help a human to carry an object from an initial position to a final goal with a defined position and orientation. The controller is proved to be asymptotically stable at the equilibrium point, which guarantees the accomplishment of the task. In contrast to other methods, the approach presented in this paper does not use either force or visual information to estimate the status of the robot and the object. In order to validate the proposed method some experiments are shown.

A nonlinear controller for people guidance based on omnidirectional vision

In the last years there has been an increasing interest in developing robots that are able to perform tasks cooperatively with humans instead of replacing them, for instance a robot which works as a guide in a museum. Until now the developed service guide robots only navigates through the aisles of the museums without concerning the peoples movement. Then, the main purpose of the work presented in this article is to develop a nonlinear controller to allow a robot to guide a person through a specific environment until it reaches a desired point taking into consideration the movement capability of the guided person. Besides the controller a person detection and tracking is also necessary in order to accomplish the guidance task. The person detection and tracking are done by using omnidirectional images. The stability of the proposed controller is proved through the Lyapunov analysis. Some experiments are presented to show the effectiveness of the proposed controller.

O potencial efetivo para uma teoria com quebra espontânea de simetria

In this work we show how to derive the effective potential for a theory with spontaneous symmetry breaking.

O potencial efetivo e sua expansão em "loop'', interpretação e convexidade

In this work we have showed how the effective potential is obtained from the generating functional for the Greens functions of the theory and what is its interpretation. The convexity of the effective potential has been also proved.