J.A. Cancelas

Speed measurement using rotary encoders for high performance AC drives

Most high performance speed control methods for electrical motors, such as AC vector control, use rotary encoders. Accuracy in obtaining the rotor speed from encoder signals is an essential requirement to achieve good dynamic response, but usually implies a delay in the speed control loop, which can cause stability problems. In this paper, the authors present alternatives for obtaining rotor speed from an encoder, highlighting their advantages and disadvantages, and ratifying them by means of simulation. They also show some experimental results obtained with an induction motor, controlled in field coordinates, using the proposed methods.<<ETX>>

Vision Based Measurement System to Quantify Straightness Defect in Steel Sheets

A non-uniform distribution of rolling pressure during steel lamination may produce flatness asymmetries in the steel sheets, causing a certain curvature on its edges. This deformation may cause stoppages in the rolling process, and damages in the machinery. A computer vision system for measuring this straightness defect is presented. This system shows the adaptation of well-known computer vision techniques to fit precision and real-time constraints. Some problems that arise during the implementation phase are also described, and the correspondent solutions outlined.

Face recognition using binary thresholding for features extraction

The paper deals with a system for the analysis and automated identification of a human face. A face can be recognized when the details of individual features are resolved. The idea is to extract the relative position and other parameters of distinctive features such as eyes, mouth, nose and chin. The overall geometrical configuration of face features can be described by a vector of numerical data representing position and size of main facial features. At first, from sequential images, eye coordinates are extracted by detecting eye winking. The interocular distance and eye position can be used to determine size and position of the areas of search for face features. In these areas binary thresholding is performed, the system modifies the threshold automatically to detect features. To find their coordinates, discontinuities are searched for in the binary image. Experimental results show that the proposed method is robust, valid for numerous kind of facial images in real scenes, works in real time with low hardware requirements and the whole process is conducted automatically.

Optical Flow Calculation Using Look-Up Tables

Abstract This work presents a new approach to optical flow calculation from an image sequence. Previously published methods were characterised by their high computational cost and complexity, limiting their applicability. This approach is characterised by avoiding floating point calculations or its emulation using integer arithmetic. Instead of this, starts with a previous off-line calculation of some LUT containing the resulting values of all the necessary operations for flow calculation. In the on-line phase of the method, the LUT is directly accessed using the gray-level of the point neighbourhood in one frame and the corresponding search space in the next frame. The vector formed by the gray levels of both neighbourhoods is interpreted as a number in a numerical base equal to image depth. Those numbers are the indexes to access the LUT and obtain the correct displacement value directly. In order to have some preliminary results, the test of the algorithm was performed with Matlab 5.0, and the results were compared with traditional correlation based methods. This implementation performed nine times faster than the simple correlation based algorithm. Despite of the reduction in the number of gray levels of the image, achieved precision is equal to the one from correlation. According to these results, near real-time optical flow computation can be achieved, with no special hardware requirements.

Toward extended range sub-micron conoscopic holography profilometers using multiple wavelengths and phase measurement

Conoscopic Holography proved to be a very adequate solution for in-situ optical measurement in industrial inspection and quality control systems, offering high-precision with a wide range of standoff distances, while being quite insensitive to the harsh environmental conditions often encountered in industry, as it is a common-path technique. With the aim of extending their applicability, we have already addressed, with good results, several issues that improve sensors based on this technology which include: the use of phase information to obtain one-shot profile measurements at frame rate with higher precision; new signal processing techniques; and speckle reduction to diminish measurement errors. However, the undesirable effect of using the phase information is that it reduces the maximum steep that can be measured without ambiguity, which becomes an issue when working with high precisions. In this article we present our ongoing work towards using the concepts of multiple-wavelength interferometry to extend the measurement range, something that, to our knowledge, has not been done for this technology before.

Design of AC drives with position and speed dynamic control using DSP

A field orientation scheme for current fed induction motor drives is presented. The first part of this work gives a short introduction about principles of field orientation. After this the authors describe the used hardware. The control is implemented on a TMS320C30 DSP with new digital signal processors with which it is possible reduce the sampling time for the control loop and use floating point arithmetic. At last, some experimental results are shown where the prototype performances are shown.<<ETX>>

Collaborative subjects for embedded systems learning in the EHEA frame: A practical approach

This paper presents a teaching experience related to the learning methodology in embedded systems within the European Higher Education Area (EHEA) frame. A Problem Based Learning (PBL) methodology has been applied for combining two courses of a bachelor degree in computer systems. The objectives are the integration and application of previously acquired and new knowledge to create an application for the supervision and control of a mobile robot. Technologies used during the development of the project include real-time programming using Ada language, digital control theory and communications.

A syntactic and contextual edge detector and application of a rewriting rules set to improve detection

This paper presents an image segmentation method which may be applied to various tasks as natural segmentation of monochromatic, colored and even three dimensional images. This algorithm is based on syntactic recognition. The particular novelty of this algorithm lies in the use of an efficient grammar to find edge models with an unknown a priori context. In order to improve and eventually to correct the detection, a set of rules is applied on the edges image. Experimental results are shown.<<ETX>>

A Syntactic and Contextual Edge Detector

Abstract This paper present an image segmentation method which may be applied to various tasks as natural segmentation of monochromatic, colored and even three dimensional images. This algorithm is based on syntactic recognition. The particular novelty of this algorithm lies in the use of an efficient grammar to find edge models with an unknown a priori context In order to improve and eventually to correct the detection, a set of rules is applied on the edges image. Experimental results are shown.

Development of a Computer Vision System to Tridimensional Measure of Lamination Steel Profiles

Abstract We measure all the dimensions of one H profile of a rolling mill, reposed and cold, by means of using two matricial video cameras and a software package developed for this application. The software package develped identifies the intersection of the profile edges with a thin line drawn by a laser beam. We made the integral calibration of the system, and we get, in the worst case, an accuracy of millimetre tenths. The designed prototype has been validated for real applications in Ensidesa company. On the basis of this project we can attempt the measurement of these profiles, when hot and on the rolling mill.