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To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.robot.2009.06.001 Byline: Josep M. Font-Llagunes, Joaquim A. Batlle Abstract: Localization is a fundamental operation for the navigation of mobile robots. The standard localization algorithms fuse external measurements of the environment with the odometric evolution of the robot pose to obtain its optimal estimation. In this work, we present a different approach to determine the pose using angular measurements discontinuously obtained in time. The presented method is based on an Extended Kalman Filter (EKF) with a state-vector composed of the external angular measurements. This algorithm keeps track of the angles between actual measurements from robot odometric information. This continuous angular estimation allows the consistent use of the triangulation methods to determine the robot pose at any time during its motion. The article reports experimental results that show the localization accuracy obtained by means of the presented approach. These results are compared to the ones obtained applying the EKF algorithm with the standard pose state-vector. For the experiments, an omnidirectional robotic platform with omnidirectional wheels is used. Author Affiliation: Department of Mechanical Engineering, Universitat Politecnica de Catalunya, Av. Diagonal 647, 08028 Barcelona, Catalunya, Spain Article History: Received 17 April 2008; Revised 3 June 2009; Accepted 12 June 2009

The utilization of Clarke's transformation in the estimation of power system frequency provides the classical single-phase methods with more robustness because the estimated frequency is computed using the information provided by the three-phase voltage. This approach is particularly important when asymmetric sags generate zero voltage in one of the three phases. In addition, the proposed algorithm exhibits good behavior during dynamic conditions. The Clarke components of the voltage signals are then used to compute the frequency of the system following an iterative approach based on a proportional-integral-derivative controller. The inverse component of the voltage is also used in order to detect unbalanced conditions. The proposed algorithm has been put to the test with distorted three-phase voltage supplied by an arbitrary waveform programmable power supply and with different signals generated with an Alternative Transients Program-Electromagnetic Transients Program model. Index Terms--Frequency measurement, power quality (PQ).

A set of theoretic formulations enables the derivation of the adaptive regularized constrained displacement vector field (DVF) estimation algorithm. A group of recursive gradient displacement estimation algorithms are unified by this algorithm. The algorithm's performance is enhanced due to this adaptivity, without an increase in the size of the spatial mask. The enhanced performance is essential for the regions around the occlusion areas of the image sequence. The algorithm is experimentally compared with the other existing algorithms in the estimation of the DVF of the synthetic and standard video conference images.