Pablo J. Alsina

Dynamic Modelling of a Quadrotor Aerial Vehicle with Nonlinear Inputs

In this paper the quadrotor dynamic model with nonlinear inputs is presented. Deadzone and saturation nonlinear inputs are considered for the quadrotor reflected to the actuators. The goal is to obtain a faithful mathematical representation of the mechanical system for system analysis and control design, not only in hover as presented in many works, but also in motion when take-off, land and flight for aerial navigation task. The model was implemented in Matlab/Simulink simulation model to optimize the design and to project control. Simulations of the model show that the nonlinear inputs must be considered in the control project.

Dynamic Modeling with Nonlinear Inputs and Backstepping Control for a Hexarotor Micro-Aerial Vehicle

In this paper the hexarotor dynamic model with nonlinear inputs and full state back stepping technique is presented. Dead zone and saturation nonlinear inputs are considered reflected to the rotors. The goal is to obtain a faithful mathematical representation of the mechanical system for analysis and control design, not only in hover, but also in motion when take-off, land and flight for aerial navigation tasks. The model was implemented in Matlab/Simulink to optimize the design of control system. Simulations of the hexarotor model shows the performance of the control law and stabilizes with good tracking.

HYPERPRESENCE-an application environment for control of multi-user agents in mixed reality spaces

The HYPERPRESENCE system proposed in this work is a mix between hardware and software platforms developed for control of multi-user agents in a mixed reality environment. The hardware is basically composed of robot systems that manipulate objects and move in a closed, real environment and a video camera, imaging system. The environment can be any place that provides or needs interactions with virtual environments for showing results or else to allow manipulation in it via a virtual reality interface. The software part is composed of three main systems: an acquisition module for position control, a tower (hardware) communication module for manipulating the robots and a multi user VRML server for managing virtual spaces and to provide synchronism between the real places and the virtual ones. We present the design and implementation solution adopted for the HYPERPRESENCE architecture. We analyze problems with communication protocols, precision of positioning, how to relate physical and virtual objects and show our solutions for these problems.

Ortholeg Project - Development of an Active Orthosis Prototype for Lower Limbs

Currently the increasing number of robotic devices for application in the mobility of people who had suffered some type of spinal cord injury, it is necessary to develop new equipment more adaptable, safe and efficient. Robotic devices that aid in locomotion of paraplegic people can play their function, they must be able to reproduce the lost movements with most of fidelity and security. This paper presents a prototype of an active orthosis for lower limbs developed by the robotic and dedicated systems group of Department of Computing Engineering and Automation (DCA/UFRN) named Ortholeg. The proposed orthosis is an orthopedic device with the main objective of providing walking capacity to people with partial or total loss of limbs movements. The orthosis was projected to reproduce the movements of human gait. The movements of the joints of the orthosis are controlled by DC motors equipped with mechanical reductions, whose purpose is to reduce rotational speed and increase the torque, thus generating smooth movements. An embedded electronic system for sensory data acquisition and motor control was projected.

Gait Cycle Modeling for an Active Orthosis Using Principal Component Analysis

Concerning the human factor and ergonomics in an active orthosis for lower limbs application, it is important to generate an anthropomorphic gait. The objective of this work is to find an anthropomorphic gait model using Principal Component Analysis able to be used in a real orthosis application. The gait was modeled from the perspective of the joint leg angles. In order to find a model close to the human gait behavior, gait experiments from humans were collected. The straight line slow walk was selected to be modeled because it fits the basic walk for an orthosis. The validity of the proposed model was verified through extrapolation and comparison with real human gait cycles, different from the ones used to build the model.

Project of a hardware and software architecture for an Unmanned Aerial Vehicle

This paper describes a simple hardware/software architecture for a micro UAV (Unmanned Aerial Vehicle). This architecture follows the master-slave model and uses the Standard USB as communication interface. The main contribution of this paper is a C++ library, which makes possible communicate an embedded PC with several microcontrollers. Through this interface, it is possible to build a robot using a standard Linux as operational system, and even though, attend to certain time deadlines.

Learning by Experience and by Imitation in Multi-Robot Systems

With the increasing number of robots in industrial environments, scientists/technologists were often faced with issues on cooperation, coordination and collaboration among different robots and their self governance in the work space. This has led to the development of systems with several cooperative robotic agents. (Kim et al., 1997b). Generally, a system with several robotic agents (multi-robot system) is composed by two or more robots executing a task in a cooperative way (Arai and Ota, 1992). Coordination, collaboration and cooperation are three terms used without distinction when working with multi-agent and multi-robot systems. In this work, we adopt a definition proposed by Noreils (Noreils, 1993) in which cooperation occurs when several agents (or robots) are gathered together so as to perform a global task. Coordination and collaboration are two forms of cooperation (Botelho and Alami, 2000). Coordination occurs when an entity coordinates its activity with another, or it synchronizes its action with respect to the other entity, by exchanging information, signals, etc. And, collaboration occurs when two or more agents decompose a global task in subtasks to be performed by each specific agent. Generally, the solution for problems using multi-agent and multi-robot systems is divided into stages. When talking about autonomous robots, two of these stages are the task allocation stage and the task execution stage. Task allocation should be done so that all components (agents or robots) in the system are used and the problem is completely solved. The task execution stage itself should be performed so that the agents do not interfere to each other (coordination and/or collaboration) when solving the problem. Traditionally, both stages are carried out independently. In the task allocation stage, it is defined if the agents will collaborate to each other or if they will coordinate their activities. In the task execution stage, collaboration and/or coordination are effectively done. In the literature, each stage is implemented using different techniques. The task allocation stage can be implemented using centralized or decentralized approaches (Le Pape, 1990). Centralized approaches can be implemented as an optimization problem. Decentralized approaches generally use marked based approaches like the contract-net protocol (CNP) (Ulam et al., 2007) or other approaches derived from it (Botelho and Alami, 1999). The task execution stage can be implemented in many ways. It depends of the nature of interactions between agents (Collaboration or coordination) and if agents can modify or not their strategies (Static and dynamic strategies). For example it can be implemented using

Pose estimation of a humanoid robot using images from a mobile external camera

This paper describes an ongoing project to move a simple humanoid robot, without an advanced embedded electronics. We used another wheeled mobile robot which already has a locating system and is equipped with a camera. We will locate the humanoid in the environment based on images, and then take the necessary actions to move it. In the future, we will also move the robot with the camera, so it will take good images of the humanoid.

Point-to-point paths generation for wheeled mobile robots

This paper proposes a point-to-point path generation method consistent with the non-holonomic constraints of a two-wheeled mobile robot. The generated path is described by continuous curves, instead of the traditional chaining of different curves. Parametric polynomials of third degree are used to calculate the robot configuration variables, x(/spl lambda/) and y(/spl lambda/). The orientation angle, /spl theta/(/spl lambda/), is imposed to respect the non-holonomic constraint. The free polynomial coefficients are used to refine the path, avoiding maximal or minimal values of x(/spl lambda/) and y(/spl lambda/) which tends to generate shorter paths, avoiding unnecessary motions.

Powered Orthosis Ortholeg: Design and Development

This paper presents the design and development of a lower limb powered orthosis called Ortholeg. This device was designed to provide lower limb movements (such as walk) to spinal cord injured people unable to move their legs. Ortholeg weights 20kg and can be worn by users within a heights range between 1,55m to 1,70m, and weights up to 65 kg. This robotic device has two actuators for each leg, one at the knee and the other at the hip. Each one of the actuators controls one degree of freedom on the sagittal plane. The device is able to perform movements such as straight walk, sit and stand up. To ensure balance and safety, the user uses a pair of crutches. Ortholeg orthosis has an embedded modular system, motor controllers, sensors and two Human Machine Interfaces (HMI) based on buttons and electroculography.