Eduardo O. Freire

Corridor navigation and wall-following stable control for sonar-based mobile robots

Abstract In this paper, a mobile robot control law for corridor navigation and wall-following, based on sonar and odometric sensorial information is proposed. The control law allows for stable navigation avoiding actuator saturation. The posture information of the robot travelling through the corridor is estimated by using odometric and sonar sensing. The control system is theoretically proved to be asymptotically stable. Obstacle avoidance capability is added to the control system as a perturbation signal. A state variables estimation structure is proposed that fuses the sonar and odometric information. Experimental results are presented to show the performance of the proposed control system.

On the equalization of keystroke timing histograms

The effect of parametric equalization of time interval histograms (key down-down intervals) on the performance of keystroke-based user verification algorithms is analyzed. Three algorithms are used throughout this analysis: a classic one for static (structured) texts, a second one, also proposed in literature, for both static and arbitrary (free) text, and a new one for arbitrary text based verification. Their performances are reported before and after time interval histogram equalization, and the results corroborate with the hypothesis that the nonlinear memoryless time interval transform proposed here, despite its simplicity, can be a useful and almost costless building block in keystroke-based biometric systems.

Equalization of keystroke timing histograms for improved identification performance

The effect of parametric equalization of time interval histograms (key down-down intervals) on the performance of keystroke-based user verification algorithms is analyzed. Four algorithms are used throughout this analysis: a classic one for static (structured) texts, a second one, also proposed in literature, for both static and arbitrary (free) text, a new one for arbitrary text based verification, and an algorithm recently proposed, where keystroke timing is indirectly addressed in order to compare user dynamics. The algorithms performances are presented before and after time interval histogram equalization, and the results corroborate with the hypothesis that the nonlinear memoryless time interval transform proposed here, despite its simplicity, can be a useful and almost costless building block in keystroke-based biometric systems.

Contributions to empirical analysis of keystroke dynamics in passwords

Keystroke pattern stabilization strongly affects verification performance.Each sequence of symbols induces a rhythmic profile.Rhythm stabilization seems to be a learning/forgetting process.Enrollment with post-habituation samples improves verification rates.EER is consistently lowered as the number of strokes increases. Rhythmic patterns in passwords are addressed through biometric verification tests. Experimental results are obtained through three publicly available databases, whereas experiments are guided by questions Q1: How does a subject develop a stable rhythmic signature associated to a new password? and Q2: How does the number of symbols affect biometric performance? Measurements show that even if subjects are instructed to train themselves before sample acquisition, a clear habituation phenomenon is noticed at the beginning of the first sessions, both for the password .tie5Roanl and the passphrase greyc laboratory, with significant consequences in terms of biometric verification performances. As for Q2, all experiments show that error rates are consistently lowered as password length increases. Additionally, a marginal but potentially useful observation is the stabilization of patterns around a rhythmic profile which seems to be induced by the corresponding sequence of symbols, whose consequences are addressed.

Fillet Weld Identification for Automatic Inspection of Spherical Tanks

In this article the development of a system for fillet weld identification is considered for automatic inspection of storage spheres. Distance sensors based on different physical principles are characterized and selected, thus getting, greater confidence of the acquired data. The data provided from the different types of sensors will be submitted to a fusing process, aiming at to increase the confidence and performance of the system.

Fault-tolerant weld line detection for automatic inspection of storage tanks based on distance and visual information fusion

Quality control, cost reduction and above all, human and environmental safety are great reasons that stimulate the investments in technologies like automatic inspection. The automatic inspection of weld lines in storage tanks is of special interest, due to the fact that such tanks are currently used to store harmful products. For a reliable inspection it is necessary to accurate detect the weld line position. In this paper the development of a system to perform weld line detection in storage tanks is proposed. Two redundant systems, based on different physical principles, distance and visual information, are implemented and tested. Such systems make use of a fault-tolerant estimation process based on the α-β filter. Finally, the outputs of the two redundant systems are fused, aiming at to increase the confidence and performance of the system.

Multimodal biometric fusion — joint typist (keystroke) and speaker verification

Identity verification through fusion of features from keystroke dynamics and speech is addressed in this paper. We experimentally compare performances from identity verification algorithms based on fusion of median pitch (prosodic level information), mel-frequency cepstral coefficients (short-time spectral level information) and keystroke dynamics (down-down intervals). These experimental results are also compared to the corresponding unimodal performances. All experiments are carried out on a small but true multimodal public database. Three fusion strategies are experimentally compared. A nonnegligeable performance improvement is then observed, mainly with a simple linear fusion strategy based on fusion of estimates.

A Model-Based Fault-Tolerant Weld Line Detection for Automatic Inspection of Storage Tanks Using Visual Information and a-ß Filter

Quality control, cost reduction and above all, human and environmental safety are great reasons that stimulate the investments in technologies such as automatic inspection. The automatic inspection of weld lines in storage tanks is of special interest due to the fact that such tanks are currently used to store harmful products. For a reliable inspection it is necessary to accurately detect the weld line position. In this paper the development of a system to perform weld line detection in storage tanks is proposed. The system based on visual information is implemented and tested. Such system makes use of a fault-tolerant estimation process based on the α-β filter and a model-based fault detection method, proposed in this paper.

A Methodology to Designing Strategies for Robot Soccer Based on Discrete Event Systems Formalism

In the robot soccer, a good strategy is essential to the success of a team. It is responsible to define the behavior of each robot on the many game situations and make the team play in a cooperative manner to win the game. To accomplish this, it is proposed in this paper a methodology to designing strategies for robot soccer based on discrete event systems formalism. The main idea is to allow the construction of a game strategy where the behavior of each robot can be dynamically modified, depending on the context of the match. This strategy is modeled based on the discrete events system (DES) theory. The DES formalism enables to implement the interaction between the various behaviors of a system in a simple way, allowing the addition of new behavior without changing the current behaviors already in use, which is the main advantage of the proposed approach.

Execution Monitoring Applied to Data Estimation Processes

This paper presents how execution monitoring can be applied to detect sensor measurements faults and shows how to use this information to improve data estimation processes. Experimental results based on ultrasonic sensors measurement data are presented and the estimation process improvement could be verified.