Fall accidents are one of the most serious problems leading to unintentional injuries and fatalities among older adults. However, it is difficult to assess individuals' fall risk and to determine who are at risk of falls and in need of fall interventions. Therefore, this study was motivated by a need to provide a cogent fall risk assessment strategy that may be conducive to various wireless platforms. It aimed at developing a fall risk assessment method for evaluating individuals' fall risk by providing diagnostic modalities associated with gait. In this study, a "determinants of gait" model was adopted to analyze gait characteristics and associate them with fall risk. As a proof of concept, this study concentrated on slip-induced falls and the slip initiation risks. Two important parameters of determinants of gait, i.e. the pelvic rotation and the knee flexion, were found to be associated with slip initiation severity. This relationship appeared to be capable of differentiating fallers and non-fallers within older adults, as well as differentiating normal walking conditions and constrained walking conditions. Furthermore, this study also leveraged portable wireless sensor techniques and investigated if miniature inertial measurement units could effectively measure the important parameters of determinants of gait, and therefore assess slip and fall risk. Results in this study suggested that pelvic rotation and knee flexion measured by the inertial measurement units can be used as a substitution of the traditional motion capture system and can assess slip and fall risk with fairly good accuracy. As a summary, findings of this study filled the knowledge gap about how critical gait characteristics can influence slip and fall risk, and demonstrated a new solution to assess slip and fall risk with low cost and high efficiency. / Ph. D.

Wearable computers and e-textiles are increasingly prevalent in today's society. Motion capture is one of many potential applications for on-body electronic systems. Self-contained motion capture applications require information from sensors distributed throughout the body on a "smart" garment. Therefore, this thesis presents the design of a flexible hardware platform for e-textile motion capture applications. This thesis also presents software for one such application, namely, tracking the pose or relative position of body limbs. The accuracy of this solution is compared to an industrial optical motion capture system. The combined hardware and software design are successful at collecting and processing motion capture data in the context of an e-textile jumpsuit. / Master of Science

La navigation par système inertiel strapdown est aujourd’hui la plus répandue. L’architecture est bien connue et a été très largement améliorée au cours des dernières décennies. Néanmoins, le principe fondamental n’a subi de bouleversement et reste constitué d’une triplette d’accéléromètres et de gyromètres permettant de revenir aux informations d’attitude et de cap.La précision de l’estimation de position repose principalement sur la gamme de performance des capteurs utilisés. En particulier, des applications telles que des lanceurs spatiaux requièrent une très haute précision et des capteurs d’une technologie éprouvée sont utilisés. L’arrivée sur le marché de capteurs inertiels MEMS de haute précision ouvre une alternative à coût réduits couplée à une réduction de masse, volume et de consommation. Les moyens de production des MEMS ainsi qu’une meilleure connaissance des propriétés des matériaux ont permis l’arrivée d’accéléromètres MEMS pouvant rivaliser avec les technologies éprouvées de gamme tactique. Toutefois, les gyromètres de technologie MEMS existantes restent dans une gamme de performance de type industrielle.La présente étude vise à analyser la possibilité d’utiliser des accéléromètres de haute précision pour améliorer les performances gyrométriques, dans l’objectif de réaliser une solution tout MEMS d’unité de mesure inertielle. Une brève introduction sur les techniques de filtrage de Kalman pour la fusion de données est présentée, ainsi que son implémentation pour notre étude. L’analyse théorique se poursuit avec une présentation des résultats expérimentaux.L’étude conclut que l’utilisation d’une paire d’accéléromètres de haute performance et d’un gyroscope de type consommateur permet d’atteindre les performances d’un gyromètre tactique. Les contraintes de définition et de mesure pour l’implémentation du système sont présentées en détail.Cette étude est menée pour la mesure angulaire autour d’un axe unique de rotation, un complément d’étude est nécessaire à l’extrapolation de cette approche pour une mesure générique en 3D. / Strapdown inertial navigation units are the most popular systems used for navigation. The system architecture is well established and has been extensively improved over the past decades. However, the core idea remains same where a triad of accelerometers and gyroscopes provide the attitude and heading information.The accuracy of the position estimate depends on the performance grade of the sensors employed. For applications like space launchers requiring very high accuracy, high-grade devices using traditional technologies are used. The advent of accurate MEMS based sensors offer an exciting low-cost alternative with expected reduction in size and power consumption. MEMS fabrication technology, assisted by improved understanding of material properties have led to accelerometers that can compete with traditional devices for tactical applications. However, the MEMS based solutions currently available for gyroscopes can replace only industrial grade applications.This study attempts to investigate if the currently available high-grade accelerometers can be used to improve the gyroscope performance, towards the final goal of a complete MEMS based solution for inertial navigation units. The study begins with a literature review of current status of technology. A brief explanation of linear Kalman filtering technique for data fusion is presented, along with its implementation concerning this work. The theoretical discussion is then followed by presentation of experimental results.The study found that using a pair of high-grade accelerometers, a consumer grade gyroscope can have its performance upgraded for tactical applications. The design and sensing constraints for realizing this system are discussed in detail.Since this research work primarily concerns with angular rate estimation around a single axis of rotation, further research is recommended for extrapolating this approach for a more general 3-D sensing case.

Thesis(M.S.)--Auburn University, 2006. / Abstract. Vita. Includes bibliographic references (p.115-120).

Thesis(M.S.)--Auburn University, 2006. / Abstract. Includes bibliographic references (p.105-107).

Thesis--Auburn University, 2009. / Abstract. Vita. Includes bibliographic references (p.75-76).

Inertial measurement units (IMUs) are being recognized as a portable and cost-effective alternative to motion analysis systems and have the potential to be introduced into clinical settings for the assessment of functional movement quality of the spine in patients with low back pain. However, uncertainties regarding sensor accuracy and reliability are limiting the widespread use and acceptance of IMU-based assessments into routine clinical practice. The objective of this work was to assess the performance of inexpensive wearable IMUs (Mbientlab MetaMotionR IMUs; Mbientlab Inc., San Francisco, USA; product specifications available in Appendix C) relative to conventional optical motion capture equipment (Vicon Motion Systems Ltd., Oxford, UK) in: 1) a controlled environment, and 2) an uncontrolled environment. The first study evaluated the performance of 2 IMUs in a controlled environment during simulated repetitive spine motion carried out by means of a motorized gimbal. Root mean square error (RMSE) and mean absolute measurement differences between cycle-to-cycle minimum, maximum, and range of motion values, as well as correlational analyses within IMUs and between IMUs and Vicon, in all movement directions (i.e., simulated flexion-extension (FE), lateral bending (LB), and axial twisting (AT)), were compared. Measurement error was low in all axes during all tests (i.e., ≤ 1.54°); however, low-to-moderate correlational results were found in one non-primary axis, and this axis changed depending on the direction of the movement (i.e., LB during FE-motion (0.244 ≤ R ≤ 0.515), AT during LB-motion (0.594 ≤ R ≤ 0.795), and FE during AT-motion (0.002 ≤ R ≤ 0.255)). The second study was designed to assess the performance of the IMUs in an uncontrolled environment during repetitive spine FE in human participants. Absolute angles and local dynamic stability were compared for individual IMUs (which were placed over T10-T12 spinous processes, and the pelvis) as well as for relative motion between IMUs. Maximum finite-time Lyapunov exponents (λmax) were used to quantify local dynamic stability and were calculated using both FE and the sum of squares (SS) from measured spine kinematics. It was found that the IMUs have acceptable performance in all axes when tracking motion (RMSE ≤ 2.43°); however, low-to-moderate correlational results were found in one non-primary axis (0.987 ≤ RFE ≤ 0.998; 0.746 ≤ RLB ≤ 0.978; 0.343 ≤ RAT ≤ 0.679). In addition, correlations between λmax estimates were high; therefore, local dynamic stability can be accurately estimated using both FE and SS data (0.807 ≤ 〖ICC〗_2,1^FE ≤ 0.919; 0.738 ≤ 〖ICC〗_2,1^SS ≤ 0.868). Correlation between λmax estimates was higher when using FE data for individual sensors/rigid-body marker clusters; however, correlation was higher when using SS data for relative motion. In general, the results of these studies show that the MetaMotionR IMUs have acceptable performance in all axes when considering absolute angle orientation and motion tracking, and measurement of local dynamic stability; however, there is low-to-moderate correlation in one non-primary axis, and that axis changes depending on the direction of motion. Future research will investigate how to optimize performance of the third axis for motion tracking; it will also focus on understanding the significance of the third axis performance when calculating specific outcome measures related to spine movement quality.

Inertial measurement units (IMUs) are devices that sense accelerations and angular rates in 3D so that vehicles and other devices can estimate their orientations, positions, and velocities. While traditionally large, heavy, and costly, using mechanical gyroscopes and stabilized platforms, the recent development of micro-electromechanical sensor (MEMS) IMUs that are small, light, and inexpensive has led to their adoption in many everyday systems such as cell phones, video game controllers, and commercial drones. MEMS IMUs, despite their advantages, have major drawbacks when it comes to accuracy and reliability. The idea of using more than one of these sensors in an array, instead of using only one, and fusing their outputs to generate an improved solution is explored in this thesis.

Yes / The mechanical output at the ankle provides key contribution to everyday activities, particularly step/stair ascent and descent. Age-related decline in ankle functioning can lead to an increased risk of falls on steps and stairs. The rising up-on-the-toes (UTT) 30-second test (UTT-30) is used in the clinical assessment of ankle muscle strength/function and endurance; the main outcome being how many repetitive UTT movements are completed. This preliminary study describes how inertial measurement units (IMUs) can be used to assess the UTT-30. Twenty adults (26.2 ± 7.7 years) performed a UTT-30 at a comfortable speed, with IMUs attached to the dorsal aspect of each foot. Use of IMUs’ angular velocity signal to detect the peak plantarflexion angular velocity (p-fAngVelpeak) associated with each repeated UTT movement indicated the number of UTT movements attempted by each participant. Any UTT movements that were performed with a p-fAngVelpeak 2SD below the mean were deemed to have not been completed over a sufficiently ‘full’ range. Findings highlight that use of IMUs can provide valid assessment of the UTT 30-second test. Their use detected the same number of attempted UTT movements as that observed by a researcher (average difference, -0.1 CI, -0.2 – 0.1), and on average 97.6 ± 3.1% of these movements were deemed to have been completed ‘fully’. We discuss the limitations of our approach for identifying the movements not completed fully, and how assessing the consistency in the magnitude of the repeated p-fAngVelpeak could be undertaken and what this would indicate about UTT-30 performance.

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