Orientation dans l'espace | EPFL Graph Search

L'orientation d'un objet dans l'espace est une partie de la description de la façon dont un objet est placé dans l'espace. Cette orientation est relative et ne peut être décrite que par rapport à une orientation de référence ; l'orientation est alors la rotation imaginaire que l'objet devrait subir pour être placé de la même façon que la référence. Une rotation n'est pas en général suffisante pour retrouver le placement de référence et il est le plus souvent nécessaire de faire subir une translation à l'objet, ce qui correspond à la position de l'objet dans l'espace. Repère lié à l'objet Pour définir l'orientation d'un objet, la première étape consiste donc à définir deux vecteurs, c'est-à-dire deux axes orientés (c'est-à-dire munis d'un sens) non parallèles et liés à l'objet. Ces axes peuvent être choisis de manière arbitraire, ou bien suivre la forme ou l'anisotropie de l'objet. Par exemple, si l'objet est parallélépipédique, on choisira deux des arêtes de l'objet ; s

Nano-SAW devices for RFID and sensing applications: study of lithium niobate behavior

Seïfeddine Mounir Ben Khelil, Andrea Lozzi

The key element of a SAW device is the piezoelectric material that allows conversion between electrical and mechanical energy. Lithium niobate is an appealing material as it could potentially provide high efficient SAW devices. This material is strongly anisotropic, thus, all the properties of the material are dependent of the orientation on the plane of the device and on the chosen piezoelectric layer cut. An analytical model is built to predict how the electromechanical coupling varies depending on cut and device on plane orientation.

2015

Biomechanical Ambulatory Assessment of 3D Knee Angle Using Novel Inertial Sensor-Based Technique

Kamiar Aminian, Lai Kuan Tham

Three-dimensional (3D) knee angle measurement is one of the key measures in human gait analysis. Inertial sensor capable of measuring joint motion under unconstrained conditions is a practical tool for clinical evaluation and rehabilitation. An inertial measurement unit (IMU) consisting of accelerometer and gyroscope allows orientation measurement in 3D with an additional sensor (i.e., magnetometer). However, ferromagnetic interference negatively affects the performance of magnetometer and thus reduces measurement accuracy. In this study, a technique based on nonlinear autoregressive neural network with exogenous inputs (NARX) is presented to measure 3D segmental orientation during gait without the use of magnetometer. With IMUs attached to the thigh and shank, 3D knee angles in long-distance treadmill walking were computed and validated against an optical motion analysis system as the gold standard. Pseudo-integrator (PI) was also compared to the reference system for benchmarking. The learning capability of NARX was further assessed with the comparison of complementary filter (CF) to the reference system. The proposed NARX model was shown to outperform PI with biases between -3.5 degrees and -0.2 degrees, and root mean square errors between 4.5 degrees and 2.5 degrees. Results demonstrated the capability of NARX in providing accurate estimates of 3D knee joint angle while avoiding interference as encountered in systems incorporating magnetometer, suggesting that NARX is feasible to computing long-term ambulatory measurements of body segment orientation and 3D joint angles.

IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC2021

Augmented Reality to Facilitate a Conceptual Understanding of Statics in Vocational Education

Lorenzo Lucignano

At the core of the contribution of this dissertation there is an augmented reality (AR) environment, StaticAR, that supports the process of learning the fundamentals of statics in vocational classrooms, particularly in carpentry ones. Vocational apprentices are expected to develop an intuition of these topics rather than a formal comprehension. We have explored the potentials of the AR technology for this pedagogical challenge. Furthermore, we have investigated the role of physical objects in mixed-reality systems when they are implemented as tangible user interfaces (TUIs) or when they serve as a background for the augmentation in handheld AR. This thesis includes four studies. In the first study, we used eye-tracking methods to look for evidences of the benefits associated to TUIs in the learning context. We designed a 3D modelling task and compared users' performance when they completed it using a TUI or a GUI. The gaze measures that we analysed further confirmed the positive impact that TUIs can have on the learners' experience and enforced the empirical basis for their adoption in learning applications. The second study evaluated whether the physical interaction with models of carpentry structures could lead to a better understanding of statics principles. Apprentices engaged in a learning activity in which they could manipulate physical models that were mechanically augmented, allowing for exploring how structures react to external loads. The analysis of apprentices' performance and their gaze behaviors highlighted the absence of clear advantages in exploring statics through manipulation. This study also showed that the manipulation might prevent students from noticing aspects relevant for solving statics problems. From the second study we obtained guidelines to design StaticAR which implements the magic-lens metaphor: a tablet augments a small-scale structure with information about its structural behavior. The structure is only a background for the augmentation and its manipulation does not trigger any function, so in the third study we asked to what extent it was important to have it. We rephrased this question to whether users would look directly at the structure instead of seeing it only through a tablet. Our findings suggested that a shift of attention from the screen to the physical object (a structure in our case) might occur in order to sustain users' spatial orientation when they change positions. In addition, the properties of the gaze shift (e.g. duration) could depend on the features of the task (e.g. difficulty) and of the setup (e.g. stability of the augmentation). The focus of our last study was the digital representation of the forces that act in a loaded structure. From the second study we observed that the physical manipulation failed to help apprentices understanding the way the forces interact with each other. To overcome this issue, our solution was to combine an intuitive representation (springs) with a slightly more formal one (arrows) which would show both the nature of the forces and the interaction between them. In this study apprentices used the two representations to collaboratively solve statics problems. Even though apprentices had difficulties in interpreting the two representations, there were cases in which they gained a correct intuition of statics principles from them. In this thesis, besides describing the designed system and the studies, implications for future directions are discussed.

EPFL2018

Augmented Reality to Facilitate a Conceptual Understanding of Statics in Vocational Education

Lorenzo Lucignano

EPFL2018