Levente Tamas

Modeling and simulation of an induction drive with application to a small wind turbine generator

Among renewable energies the solution of utilizing wind energy conversion systems is now in a growing trend. A valid choice for operation of such systems may be the use of the induction machine. This study presents modeling and simulation of a stand-alone induction drive with application to a small wind turbine generator system. The model of the induction machine is written in terms of fluxes as state variables and is used to design an estimator model that can provide the correct feedback signals for the vector control of a wind energy conversion system. The estimation of magnetic flux and electromagnetic torque is based on stator currents and stator voltages. Simulation results are provided indicating good estimator design and operation.

Targetless Calibration of a Lidar - Perspective Camera Pair

A novel method is proposed for the calibration of a camera - 3D lidar pair without the use of any special calibration pattern or point correspondences. The proposed method has no specific assumption about the data source: plain depth information is expected from the lidar scan and a simple perspective camera is used for the 2D images. The calibration is solved as a 2D-3D registration problem using a minimum of one (for extrinsic) or two (for intrinsic-extrinsic) planar regions visible in both cameras. The registration is then traced back to the solution of a non-linear system of equations which directly provides the calibration parameters between the bases of the two sensors. The method has been tested on a large set of synthetic lidar-camera image pairs as well as on real data acquired in outdoor environment.

Classification of surface electromyographic signals for control of upper limb virtual prosthesis using time-domain features

The development of a training system in the field of rehabilitation has always been a challenge for scientists. Surface electromyographical signals are widely used as input signals for upper limb prosthetic devices. The great mental effort of patients fitted with myoelectric prostheses during the training stage, can be reduced by using a simulator of such device. This paper presents an architecture of a system able to assist the patient and a classification technique of surface electromyographical signals, based on neural networks. Four movements of the upper limb have been classified and a rate of recognition of 96.67% was obtained when a reduced number of features were used as inputs for a feed-forward neural network with two hidden layers.

State estimation based on Kalman filtering techniques in navigation

This paper tackles the problem of the position measurement and estimation techniques in the robot navigation field based on Kalman filters. It presents the problem of the position estimation based on odometric, infrared and ultrasonic measurements. Further on deals with the theoretical and practical aspects of the state estimation based on Kalman filtering techniques. From the wide range of derivatives of the Kalman filtering technique there are detailed the extended Kalman filter and the one based on unscented transformation. In the second part of the paper is concluded with the results of the comparison between the different filtering algorithms and the further perspectives regarding this subject.

Railway track following with the AR.Drone using vanishing point detection

Unmanned aerial vehicles are increasingly being used and showing their advantages in many domains. However, their application to railway systems is very little studied. In this paper, we focus on controlling an AR.Drone UAV in order to follow the railway track. The method developed relies on vision-based detection and tracking of the vanishing point of the railway tracks, overhead lines, and other related lines in the image, coupled with a controller that adjusts the yaw so as to keep the vanishing point in the center of the image. Simulation results illustrate that the method is effective, and are complemented by vanishing-point tracking results on real images.

Relative pose estimation and fusion of omnidirectional and Lidar cameras

This paper presents a novel approach for the extrinsic parameter estimation of omnidirectional cameras with respect to a 3D Lidar coordinate frame. The method works without specific setup and calibration targets, using only a pair of 2D-3D data. Pose estimation is formulated as a 2D-3D nonlinear shape registration task which is solved without point correspondences or complex similarity metrics. It relies on a set of corresponding regions, and pose parameters are obtained by solving a small system of nonlinear equations. The efficiency and robustness of the proposed method was confirmed on both synthetic and real data in urban environment.

3D Laser scanning system and 3D segmentation of urban scenes

This paper dwells upon the promising 3D technology for mobile robots and automation industry. The first part of the paper describes the design details of our own 3D Time of Flight (TOF) scanning system based on 2D laser range finder. The second part presents a specific segmentation technique for 3D outdoor urban environments by the common detection of plane models. In a few words, the technique separates the raw data into sparse and dense points, followed by the segmentation of the dense points into urban background and foreground objects. In the end we present some experimental results of real-world data-sets taken from the repository1,2 of the Leibniz University in Hannover, Germany.

3D graphical simulation of an articulated serial manipulator based on kinematic models

This paper presents a portable 3D graphical simulator for a Fanuc M-6iB/2HS articulated robot. The mechanical structure is modeled using OpenGL functions implemented in Qt Framework. The robot motions are simulated based on the direct and inverse kinematics equations also presented in this paper. The simulator features include quick motion, step-by-step simulation, 3D scene control functions, objects selection functions and motion algorithms like joint interpolated motion and linear interpolated motion.

3D map building with mobile robots

This paper presents a feature-based registration for 3D environments using mobile robots. The developed 3D laser scanner with custom hardware setup is able to scan both indoor and outdoor. For the map registration a nonlinear variant of the Iterative Closest Point (ICP) algorithm was used with initial alignment from the correspondences given by the features of the scenes. The initial alignment was determined using a set of key-points and the features of the keypoints in order to reduce the computational time and to ensure a robust estimation. Considering the increasing interest in 3D navigation for mobile robots, our aim was to use the created maps for both indoor and outdoor navigation purposes. Several maps were built by merging point clouds while our method was tested for a wide range of datasets including urban and office environments.

Communication delay and jitter influence on bilateral teleoperation

One of the most challenging problems during the design of bilateral teleoperation systems implemented over Wide Area Networks is to assure the stability and transparency in the presence of time varying communication delay between the master and the slave. In this work the influence of the delay and jitter on the passivity controller - passivity observer type stabilizers is analyzed. This control design approach does not require the explicit knowledge on the communication delay. In spite of this fact in this work it is shown that time varying the delay influences the teleoperation performances. Firstly, the relation between the delay and the dissipated energy by the controller was studied. Secondly, it was shown that in the presence of jitter the passivity controller can induce undesired oscillations into the received signals, affecting the transparency of the teleoperation. To handle this problem an extended passivity controller was proposed which assures better performances in the presence of jitter. Experimental measurements, including teleoperation experiments between two universities situated in different countries, are performed to validate the theoretical results.