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Today, rope access systems (RASs) and fall arrest systems (FASs) incorporate significant technological innovations. This research aims to determine the safest knot to be used in RASs. The most secure knots are those that leave the most resistance in the rope. Static laboratory tests, followed by an extensive statistical analysis of the obtained data, were carried out under controlled conditions. Five types of anchor knots were selected and studied using three rope models with similar diameters, and we analysed the symmetrical versions in the dextrorotational direction. Thirty break tests were performed for each rope model. The total number of breakage tests was 90. The double overhand knot proved to be the safest knot with an average efficiency of 61.82%. A better understanding of the behaviour of knots and their correct use in FASs will be key to accident prevention.

The use of natural targets is one of the obstacles to the extensive use of digital image cross-correlation for measuring movements in civil structures. Long distance measurement through image and without access to the structure itself, brings results in an improvement in accessibility, being the procedure cheaper and safer than common methods that require direct access to the measuring point. One of the most used materials in construction is concrete. Therefore, it is important to analyze its performance when using image cross-correlation. In this work, we have made a series of concrete probes with different production characteristics to have a representative variety of concrete surfaces. With them, we have studied their floor error in a cross-correlation procedure using different illumination and blur conditions, to evaluate the influence of those parameters on the results. All results are compared to those obtained using the conventional texture for image cross-correlation techniques, that is a pseudo-speckle target. All experiments are done in laboratory conditions to control all variables involved and to avoid the influence of other variables linked to open air conditions, such as atmospheric disturbances. As a result, we have determined the best conditions to use the natural concrete texture and we have quantified that using this texture leads to a decrease in the accuracy of the results from two to three times the one obtained with a typical pseudo-speckle texture.

Many applications in physics and engineering require non-invasive, precise object tracking, which can be achieved with image processing methods at very good cost-efficiency ratios. The traditional method for measuring displacement with subpixel resolution involves cross-correlation between images and interpolation of the correlation peak. While this method enables target tracking with a resolution of thousandths of a pixel, it is computationally intensive and susceptible to peak-locking errors. Recently, a new method based on discrete subtraction between images has been presented as an alternative to cross-correlation to improve computational efficiency, which also results in being free of peak-locking errors. This manuscript presents an experimental evaluation of the performance of the discrete subtraction method (DSM) and compares it with the cross-correlation method in terms of subpixel accuracy and deviation errors. Four different targets were used with apparent displacements as small as 0.002 px, which approaches the theoretical digital resolution limit. The results show that the discrete subtraction method is more sensitive to noise but does not suffer from peak-locking error, thus being a reliable alternative to the correlation method, mainly for calibration processes.

Many applications in physics and engineering require non-invasive, precise object tracking, which can be achieved with image processing methods at very good cost-efficiency ratios. The traditional method for measuring displacement with subpixel resolution involves cross-correlation between images and interpolation of the correlation peak. While this method enables target tracking with a resolution of thousandths of a pixel, it is computationally intensive and susceptible to peak-locking errors. Recently, a new method based on discrete subtraction between images has been presented as an alternative to cross-correlation to improve computational efficiency, which also results in being free of peak-locking errors. This manuscript presents an experimental evaluation of the performance of the discrete subtraction method (DSM) and compares it with the cross-correlation method in terms of subpixel accuracy and deviation errors. Four different targets were used with apparent displacements as small as 0.002 px, which approaches the theoretical digital resolution limit. The results show that the discrete subtraction method is more sensitive to noise but does not suffer from peak-locking error, thus being a reliable alternative to the correlation method, mainly for calibration processes.

En esta memoria se presenta el trabajo realizado durante el curso ’21-’22 dentro de la RED de docencia que se solicitó para ello. El objetivo de este trabajo era transmitir algunas de las técnicas más sencillas utilizadas en un grupo de investigación de la Universidad de Alicante a estudiantes de grados inferiores a los estudios de doctorado. Las técnicas de investigación utilizadas permiten medir con precisión el movimiento de algunas estructuras sencillas, de forma que la experiencia realizada ha permitido que estos estudiantes tengan una experimentalidad dentro del mundo real que dentro de sus propias titulaciones es muy difícil de conseguir. Los resultados muestran que la satisfacción general del estudiantado ha sido muy elevada y que los objetivos de transmisión de conocimientos se han logrado con facilidad. Por ello creemos que estas actividades deberían estar incluidas en los planes de estudios de las titulaciones relacionadas; no obstante, la rigidez y densidad de los contenidos de la gran mayoría de las asignaturas en estas titulaciones relacionadas con la construcción dificulta enormemente la puesta en práctica de experiencias como esta.

Se conocen como técnicas de resolución subpíxel aquellas que son capaces de detectar objetos o movimientos capturados por una cámara digital con una resolución superior a la definida por un único sensor. Dado que estas técnicas son capaces de detectar información por encima de la resolución límite teórica del sistema, se engloban dentro de los llamados métodos superresolventes (“Superresolución,” 2019). Las técnicas subpíxel para medidas no invasivas se utilizan desde que se empezó a considerar insuficiente la resolución de la imagen digital para ciertas aplicaciones. Esto ocurre porque en una imagen digital, a priori, no es posible distinguir detalles entre dos puntos del objeto de interés si ambos coinciden dentro del mismo píxel en la imagen, ya que cada píxel proporciona una información única y uniforme para toda su superficie. Originalmente, se comenzaron a utilizar técnicas de correlación para obtener una resolución ampliada (Pearson et al., 1977) y seguidamente, empezaron a aparecer trabajos que trataban de aprovechar las limitadas posibilidades de los sistemas digitales de imagen. Al aumentar el desarrollo tecnológico, empieza a ser más fácil la implementación de métodos de detección de objetos. La mayoría de estudios que utilizan estas técnicas intentan detectar dianas específicas con formas conocidas que se utilizarán como referencia para centrar y guiar sistemas de detección y posicionamiento de objetos con precisión subpíxel. La tecnología de la imagen digital se ha expandido y mejorado enormemente en las últimas décadas, perfeccionando tanto la capacidad de los sistemas de captación y procesado como la calidad de las imágenes obtenidas. Actualmente, los sensores digitales de imágenes están muy extendidos y sus resoluciones espaciales igualan e incluso mejoran la resolución esperada con las películas analógicas tradicionales, aunque, a pesar de estas mejoras, las técnicas subpíxel siguen siendo necesarias ya que muchas limitaciones prácticas permanecen.