Pedro M. Faia

Electronic noses, a different approach to the sensitivity and selectivity issues

Many approaches have been made during the past years to the gas sensing task. It may be addressed using one sensor or a set of arranged sensors. Solid state chemical sensing has been systematically used for the development of gas sensor devices, based on semi conducting metal oxides. There are three major issues related to chemical sensing: sensitivity, selectivity and stability. Selectivity may be improved by the use of sensor arrays (also referred as electronic noses), while the use of additives may improve sensitivity (pure doped materials or porosity control). In this paper we describe our current work about the sensitivity and selectivity issues. A tentative explanation of the observed resistance and impedance changes by porosity control is given.

Hybrid ZnO/TiO2 Loaded in Electrospun Polymeric Fibers as Photocatalyst

Hybrid ZnO/TiO2 nanoparticles were applied as potential photocatalyst agents incorporated into electrospun fibers of enteric block copolymers. The resistance of fibers avoids aggregation and contributes to prolonged action of semiconductor nanoparticles under continuous light irradiation. Such behavior is attributed to the minimal aggregation degree and elevated efficiency of photodegradation of modified nanoparticles in comparison with pristine ones. Hybrid ZnO/TiO2 in nanofibers contributes to the association of different mechanisms such as N-deethylation and cleavage of dye molecules applied in the overall process of photodegradation.

HDL Library of Processing Units for an Automatic LDPC Decoder Design

In this paper we propose an efficient and generic HDL library of processing units which are the key elements of a modular low-density parity check (LDPC) decoder design approach. General purpose, low complexity and high throughput bit node and check functional models are developed. Both full serial and parallel architectures are considered. Also, it is described an automatic HDL code generator for the proposed processing units using Matlab language and synthesis results for a Xilinx FPGA device are documented

Ultrasonic Guided Waves Scattering Effects From Defects in Adhesively Bonded Lap Joints Using Pitch and Catch and Pulse-Echo Techniques

In this article a method to evaluate defect dimensions in adhesively bonded lap joints based on the measurement of scattering effects of ultrasonic guided waves is presented. A simplified theoretical model is proposed which was initially tested in plates with through holes. The experimental results obtained using both pitch-and-catch and pulse-echo techniques for 500 kHz and 1 MHz frequencies confirm the validity of this model. To evaluate the lap joint defects, a set of samples with artificial defects were manufactured and the form and dimensions were confirmed using C-scan ultrasonic images. With the same methodology used in through-hole analysis, scattering effects of defects were measured. The results obtained with the pitch-and-catch technique with 1 MHz transducers allow us to say that an estimate of defect dimensions could be done by using the proposed model with reasonable accuracy and according with the predictions.

Hierarchical architecture for multi-sensor robot cell operation

The authors describe a hierarchical architecture designed to carry out experiments in multisensor integration and sensor-based control in robotics. The hierarchical model is composed of three major levels: a high-level information processing and planning structure at the top, a logic-branching control structure at the intermediate level, and a real-time continuous sensory feedback loop at the bottom level. The two lower control structures are addressed. The principal submodules of the intermediate structure are described, with particular emphasis on communication issues and on the available software mechanisms for configuration and online maintenance of the robot cell. The architecture of the real-time continuous control structure that composes the bottom level is also described. The application of the adaptive self-tuning scheme in controlling position and force, specified in task-space coordinates, is discussed. Practical issues and experimental results are summarized.<<ETX>>

Imaging Particulate Two-Phase Flow in Liquid Suspensions with Electric Impedance Tomography

Different approaches have been followed to model the hydraulic transport of particles, ranging from pure empirical correlations to general models based on fundamental principles. However, these models suffer from uncertainties associated with the parameters in the constitutive equations and scarcity of experimental data in the literature. Nonintrusive techniques such as electric impedance tomography (EIT) can be used to circumvent the difficulties associated with sampling techniques. EIT is an imaging technique for the phase distribution in a two-phase flow field, allowing reconstructing the resistivity/conductivity distribution gradients from electrical data in a medium subjected to arbitrary excitations. Our best efforts were concentrated on the development of a new EIT system that is analogue based, portable, low-cost, and capable of providing high-quality sharp images when used to characterize the flow of particle suspensions. A voltage source was used, rather than a more complex and costly current source, since it provided the EIT system with a more precise and flexible current output. The data acquisition system consists of 16 electrodes equally spaced in the boundary of a tube and a custom dedicated electronic apparatus. The software supplies results in the form of two-dimensional reconstructed images that allow mapping the phase distribution inside the tube.

Sensor-based 3-D autonomous surface-following control

Many industrial operations can be automated using robot arms that, however, require the use of robots being able to perform surface-following in an adaptive way. Surface-following in real-time based on sensor information is a delicate task to overtake, yet very useful in operations like painting, welding, glues administration and surface polishing. The surface-following can be accomplished either by using previous knowledge of the shape of the surface, by executing a sequence of movements point-by-point, or in an adaptive way. In the last case a sensor or a set of sensors for collecting data from the environment is used. Furthermore, the surface-following can be characterized by occur with or without robot-surface contact. The paper describes a 3-D surface-following controller. The surface-following operation is performed in real-time, out of contact using proximity information. Experimental results concerning 3-D surface-following movements performed by a PUMA 560 robot are shown.

Development and control issues in contact and proximity sensing for a robotic system

Flexible robotic systems, for example systems to be used in parts assembly automation, require robot manipulators featuring among other capabilities, the capacity of executing reliable fine motions. This requirement leads to the need of using sensors and so to the need of searching for techniques for efficient processing and integration of sensory data. The paper addresses issues regarding the integration of sensors for flexible robotics, namely, force/torque, tactile and proximity range sensors. The authors are concerned with sensory integration for fine motion control, the following subjects being addressed: the architecture of the control system integrating force/torque, tactile and distance sensors and algorithms for position and force control using task-space sensory feedback.<<ETX>>

CFD simulation of a turbulent fiber suspension flow - a modified near-wall treatment

Turbulent Eucalyptus fiber suspension flow in pipes was studied numerically using commercial CFD software. A pseudo-homogeneous approach was proposed to predict the flow behavior of pulp fiber suspensions for medium consistencies and for Reynolds numbers ranging from 4.7÷65.3·103. Viscosity was introduced into the model as a function of shear rate to represent the non-Newtonian behavior of the pulp suspension. Additionally, the existence of a water annulus was considered at the pipe wall, surrounding the flow core, where viscosity is equal to the water viscosity. The near-wall treatment was modified considering an expression for the logarithmic velocity profile in the boundary layer, similar to the one suggested by Jäsberg (2007). The final model could reproduce the drag-reduction effect resulting from the presence of fibers in the flow. Moreover, the numerical results show that a better fit for pressure drop is obtained when the modified near-wall treatment is used and the Jäsberg adjustable parameters are adapted to take into account the flow conditions.

Sensor-based 3-D autonomous contour-following control

Many industrial operations can be automated using robot arms but, however, require the use of robots being able to perform surface following in an adaptive way. Contour-following in real-time based on sensor information is a delicate task, yet very useful in operations like painting, welding, glues administration and surface polishing. The contour-following can be accomplished either by using previous knowledge of the shape of the surface, by executing a sequence of movements point-by-point, or in an adaptive way. In the last case a sensor or a set of sensors for collecting data about the environment are used. Furthermore, the contour-following can occur with or without contact. The paper describes a 3-D contour-following behavior controller. The contour-following operation is performed in real-time without contact using proximity information. Results of simulations and real-time implementation are presented and discussed.<<ETX>>