Paul Diego

Markerless motion capture (MoCap) systems have emerged as a cost-effective alternative to marker-based technologies; however, their accuracy remains highly dependent on acquisition setup. This study aims to provide a systematic evaluation and validation of a multi-camera markerless MoCap system based on ZED 2i devices. A two-phase experimental protocol was implemented. In Phase 1, the influence of acquisition parameters, including the number of cameras, spatial arrangement, subject distance, skeletal model, processing modality, and subject orientation, was evaluated using internal consistency indicators reflecting the stability of the reconstructed kinematics. This enables efficient identification of stable configurations without requiring a gold-standard measuring system. In Phase 2, the selected stable layouts were validated against a gold-standard OptiTrack system, with joint kinematics computed using the OpenSim inverse kinematics solver. Results indicate that, under the experimental conditions evaluated, a two-camera symmetric configuration with moderate viewing angles (30°) and a distance of 3 m provides a favorable trade-off between stability and measurement accuracy. High temporal agreement is observed for simple movements ( r > 0.9). Despite this, absolute errors remain substantial (RMSE up to 20°) and increase markedly during complex dynamic tasks (up to 45° in squat tasks). Validation was performed on controlled laboratory tasks, and the results should not be generalized to more complex functional activities without further investigation. These findings provide practical guidelines for the deployment of multi-camera markerless systems and highlight the need to distinguish between reconstruction stability and actual measurement accuracy when evaluating their performance.

In the study of biomechanical models, balance represents a complex problem due to the issue of indeterminate forces while standing. In order to solve this problem, it is essential to measure the ground reaction forces (GRFs) applied to each foot independently. The present work proposes a methodology for determining the independent GRF applied to each foot while standing when only one forceplate is available. For this purpose, an analytical method is proposed to determine the distribution of vertical GRFs and the position of the independent center of pressure (CoP) in each foot. Concurrently, several neural network (NN) models are trained to improve the results obtained. This hypothesis is experimentally validated by a self-developed device that allows one to simultaneously obtain the vertical GRF and CoP location of each foot at the same time that the GRF and the global CoP location are obtained from a single forceplate. The results obtained achieve a CoP position error of less than 8% and a vertical force error of 2%. The analytical hypothesis is demonstrated to offer a satisfactory level of precision, while the NN is shown to result in considerable improvement in some cases.

Este trabajo de investigación presenta un estudio comparativo de diversos indicadores derivados del centro de presión adquirido mediante la plataforma OREKA que induce perturbaciones controladas y mide la respuesta para el análisis de la función del equilibrio de las personas. OREKA es una plataforma dinamométrica móvil basada en un manipulador paralelo 3-PRS con dos grados de libertad rotacionales alrededor de ambos ejes horizontales y una traslación sobre el eje z. Adicionalmente, está instrumentada con retroalimentación visual en una pantalla. La posición del centro de presión se calcula a partir de las fuerzas de reacción medidas por los sensores de la plataforma dinamométrica. El ensayo se llevó a cabo con un conjunto de 28 voluntarios los cuales realizaron una batería de ejercicios en posición bipedestada bajo dos condiciones, con y sin retroalimentación en la pantalla, con el objetivo de identificar el impacto de dichas condiciones sobre el comportamiento del control postural. Las perturbaciones inducidas por la máquina durante los ejercicios consistieron en seis rotaciones anteroposteriores y tres mediolaterales con diferentes amplitudes y velocidades. Para identificar las diferencias entre ambas condiciones se realizó un estudio comparativo aplicando la prueba t-student a diversos indicadores derivados del centro de presión, los cuales son: distancias y velocidades medias en dirección anteroposterior y mediolateral, área de la elipse de predicción del estatocinesigrama y ejes menor-mayor del diagrama de Poincaré. Los resultados obtenidos permiten identificar que los valores de los indicadores tienden a ser menores cuando la retroalimentación visual en la pantalla se encuentra ausente. Esto se interpreta como que las personas tienden a tener un mejor desempeño en la función del equilibrio cuando se les permite adaptarse naturalmente a las perturbaciones de la máquina. En estudios posteriores se pretende comparar el comportamiento de los indicadores entre personas que han sufrido ictus y personas aparentemente sanas de tal manera que se siga profundizando en las capacidades de la plataforma OREKA para potenciales aplicaciones de entrenamiento y evaluación en el ámbito clínico

Este trabajo de investigación presenta una metodología para el cálculo y la caracterización del espacio de trabajo de una familia novedosa de manipuladores paralelos capaces de realizar 2 traslaciones (2T) y 2 rotaciones (2R) requeridas en un amplio abanico de aplicaciones del ámbito industrial, aeronáutico y de la rehabilitación. Debido a su similitud cinemática, la metodología da lugar a resultados análogos para cada uno de los manipuladores que conforman la familia, por ende, a lo largo del trabajo se toma como ejemplo ilustrativo un único manipulador. En concreto, uno de topología simétrica y novedosa hasta la fecha (2RRU-2RSS).En primer lugar, se describen las variables cinemáticas de entrada-salida asociadas al manipulador objeto de estudio, y se plantean las coordenadas de sus pares cinemáticos en función de estas. Posteriormente, se enumeran las diferentes variantes topológicas que dan lugar a los mecanismos cinemáticamente equivalentes que conforman esta familia y para los cuales son extrapolables las conclusiones alcanzadas. A continuación, se propone una metodología con un enfoque de carácter geométrico para obtener el espacio de trabajo individual de cada cadena, a partir de las expresiones analíticas del lugar geométrico de sus singularidades. Finalmente, haciendo uso de dichas expresiones y aplicando un método analítico-gráfico de desarrollo propio en MATLAB, se obtiene el espacio de trabajo del mecanismo completo. Además de que el método presenta un coste computacional inferior a aquellos de uso habitual, el hecho de calcular individualmente el espacio de trabajo de cada cadena, no sólo permite observar la influencia o el efecto de cada una de ellas en las fronteras del espacio de trabajo resultante, sino que posibilita caracterizar geométricamente el tamaño y la forma del mismo en función de todos los parámetros dimensionales y la orientación del elemento terminal, lo que resulta de gran utilidad para el proceso de síntesis dimensional y optimización.

This paper presents a novel parallel manipulator capable of generating two translations (2T), inside a vertical plane, and two rotations (2R), about horizontal axes, which are required in aerospace, manufacturing and rehabilitation fields. These four degrees of freedom are reached by means of a unique RRU and three RSS kinematic chains connected to a rhomboid-shaped mobile platform. The kinematic analysis of the new manipulator is provided, which includes the resolution of the inverse position problem and the velocity equations relating to input and output variables. Additionally, a methodology is proposed for obtaining the workspace free of singularities, collisions and kinematic joint range limitation. This systematic methodology allows designers to identify the critical factors affecting the workspace and, thus, to rearrange the mechanical design accordingly for optimum path planning. We represent the workspace using its two-dimensional subspaces (i.e., translational and rotational workspace). The results are analyzed for different working modes of the manipulator to see its potential use in applications wherein 2T2R motion is necessary.

Gait and balance have a direct impact on patients’ independence and quality of life. Due to a higher life expectancy, the number of patients suffering neurological disorders has increased exponentially, with gait and balance impairments being the main side effects. In this context, the use of rehabilitation robotic devices arises as an effective and complementary tool to recover gait and balance functions. Among rehabilitation devices, end effectors present some advantages and have shown encouraging outcomes. The objective of this study is twofold: to propose a general classification of devices for gait and balance rehabilitation and to provide a review of the existing end effectors for such purposes. We classified the devices into five groups: treadmills, exoskeletons, patient-guided systems, perturbation platforms, and end effectors. Overall, 55 end effectors were identified in the literature, of which 16 were commercialized. We found a disproportionate number of end effectors capable of providing both types of rehabilitation (2/55) and those focused on either balance (21/55) or gait (32/55). The analysis of their features from a mechanical standpoint (degrees of freedom, topology, and training mode) allowed us to identify the potential of parallel manipulators as driving mechanisms of end effector devices and to suggest several future research directions.

Poly(ε-caprolactone) (PCL) was mixed with submicron particles of barium sulfate to obtain biodegradable radiopaque composites. X-ray images comparing with aluminum samples show that 15 wt.% barium sulfate (BaSO₄) is sufficient to present radiopacity. Thermal studies by differential scanning calorimetry (DSC) show a statistically significant increase in PCL degree of crystallinity from 46% to 52% for 25 wt.% BaSO₄. Non-isothermal crystallization tests were performed at different cooling rates to evaluate crystallization kinetics. The nucleation effect of BaSO₄ was found to change the morphology and quantity of the primary crystals of PCL, which was also corroborated by the use of a polarized light optical microscope (PLOM). These results fit well with Avrami–Ozawa–Jeziorny model and show a secondary crystallization that contributes to an increase in crystal fraction with internal structure reorganization. The addition of barium sulfate particles in composite formulations with PCL improves stiffness but not strength for all compositions due to possible cavitation effects induced by debonding of reinforcement interphase.