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Development and applications of an innovative wearable system based on time-of-flight technology for the measurement of the human movement
Get PDFThe analysis of the human movement is the subject of many research projects. Recently, thanks to the advancement in the development of high performance and low-power electronic components, wearable sensors have given rise to devices and techniques which allow an objective evaluation of different human movement quantities both inside and outside the laboratory setting (e.g. during activities of daily living).
The objectives of the research conducted and reported in this Ph.D. thesis regard the devise, development, validation and applications of an innovative wearable system, named SWING, for the human movement monitoring and analysis.
The SWING system is the result of a design aimed at providing a wireless system-on-board processing capabilities integrating a magneto-inertial measurement unit and a Bluetooth module (main board) and up to three infrared time-of-flight distance sensors (satellite boards). It was specifically devised to take advantage of the positive points of magneto-inertial measurement units, which are capable of measuring the human movement for a long period of time and also during daily life activities with a good level of accuracy, but also to overcome some of their limitations (e.g. drift, ferromagnetic interferences, etc.). Moreover, the SWING system allow the direct measurement of quantities, such as the inter-foot distance and the step width, that magneto-inertial measurement units can only obtained indirectly (high estimation errors).
The advantages of using the infrared time-of-flight technology over other technologies, such as ultrasound and light intensity infrared which have been already investigated in the literature, are that the same or higher performance can be obtained with a simpler experimental setup (only one foot instrumented) and with a higher robustness to the changing of the experimental/environmental conditions (e.g. colour of the shoe, ambient light).
First, a thorough testing protocol for evaluating the infrared time-of-flight distance sensor performances was performed under experimental conditions resembling those encountered during gait.
Second, the SWING system was validated for the inter-foot distance estimation and step detection during walk on sixteen healthy subjects.
Third, the SWING system was tested and validated on a group of subjects characterised by highly abnormal gait patterns (e.g. low speed walks, foot dragging walks, use of walking aids) while performing a six-minute walking test.
Finally, by exploiting the Bluetooth low energy as an alternative solution for indoor-localisation and proximity sensing, a thorough characterisation of the received signal strength indicator and distance relationship under controlled conditions was provided.
The findings of this Ph.D. thesis lead to the conclusion that the SWING system and the proposed methods could be reliably applied to both normal and abnormal gaits obtaining a high level of accuracy while maintaining a very simple experimental setup (only one lower limb instrumented).
Indeed, the mean absolute errors obtained for the measurement of the inter-foot distance on healthy subjects were in the range of 9.3–12.4 mm.
The results of the validation of the SWING system, as step counter, showed an accuracy of 100 % on healthy and between 94.6 % and 98 % on pathological subjects (i.e. multiple sclerosis).
Lastly, the findings of the characterisation of the Bluetooth low energy technology for the inter-distance estimation showed an average percentage error of 25.7 % (0.4 m). Therefore, Bluetooth low energy can be a solution for indoor positioning applications, but cannot be used for proximity sensing applications which require very high accuracy (resolution down to 0.1 m)
A wearable solution for accurate step detection based on the direct measurement of the inter-foot distance
Get PDFAccurate step detection is crucial for the estimation of gait spatio-temporal parameters. Although several step detection methods based on the use of inertial measurement units (IMUs) have been successfully proposed, they may not perform adequately when the foot is dragged while walking, when walking aids are used, or when walking at low speed. The aim of this study was to test an original step-detection method, the inter-foot distance step counter (IFOD), based on the direct measurement of the distance between feet. Gait data were recorded using a wearable prototype system (SWING2DS), which integrates an IMU and two time-of-flight distance sensors (DSs). The system was attached to the medial side of the right foot with one DS positioned close to the forefoot (FOREDS) and the other close to the rearfoot (REARDS). Sixteen healthy adults were asked to walk over ground for two minutes along a loop, including both rectilinear and curvilinear portions, during two experimental sessions. The accuracy of the IFOD step counter was assessed using a stereo-photogrammetric system as gold standard. The best performance was obtained for REARDS with an accuracy higher than 99.8% for the instrumented foot step and 88.8% for the non-instrumented foot step during both rectilinear and curvilinear walks. Key features of the IFOD step counter are that it is possible to detect both right and left steps by instrumenting one foot only and that it does not rely on foot impact dynamics. The IFOD step counter can be combined with existing IMU-based methods for increasing step-detection accuracy
Indoor distance estimated from Bluetooth Low Energy signal strength: Comparison of regression models
No full textBluetooth Low Energy (BLE) is a wireless technology for exchanging data, over short distances, designed for the Internet-of-Things era. As widely supported by wearable devices, BLE has the potential to become an alternative for indoor-localization and proximity sensing. The aim of this work was to perform a thorough characterization of the RSSI-distance relationship under controlled conditions using two BLE devices. Four calibration models underwent to a comparative evaluation analysis. The best results were obtained using a polynomial model with a mean distance percentage error equal to 25.7% (0.4 m) in the range 0-3 m. An overall improvement of 14.3% (0.24 m) in the distance estimate compared to the exponential model commonly adopted in the literature was reported
Comparison of regression models for interdistance estimate between two BLE devices based on RSSI
No full textDevelopment of a novel wearable system for real-time measurement of the inter-foot distance during gait
Get PDFThe combination of magneto-inertial measurement unit (MIMU) and distance sensor (DS) represents smart solution for evaluating the distance between feet during various daily-life activities. In particular, when analyzing gait, the latter technology can be used for estimating the instantaneous or average distance between selected points of the feet (IFD) during mid-swing and mid-stance phases. The aim of this preliminary work is twofold: a) to develop and validate a novel wearable system for the measurement of the IFD during gait; b) to investigate the optimal positioning of the DS on the foot. Preliminary results showed that the innovative wearable system can be effectively used for accurately measuring the IFD during gait. Interestingly, the accuracy of the IFD estimation is highly affected by the position of the DS on the foot
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Get PDF“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Get PDFWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Static and Dynamic Accuracy of an Innovative Miniaturized Wearable Platform for Short Range Distance Measurements for Human Movement Applications
Get PDFMagneto-inertial measurement units (MIMU) are a suitable solution to assess human motor performance both indoors and outdoors. However, relevant quantities such as step width and base of support, which play an important role in gait stability, cannot be directly measured using MIMU alone. To overcome this limitation, we developed a wearable platform specifically designed for human movement analysis applications, which integrates a MIMU and an Infrared Time-of-Flight proximity sensor (IR-ToF), allowing for the estimate of inter-object distance. We proposed a thorough testing protocol for evaluating the IR-ToF sensor performances under experimental conditions resembling those encountered during gait. In particular, we tested the sensor performance for different (i) target colors; (ii) sensor-target distances (up to 200 mm) and (iii) sensor-target angles of incidence (AoI) (up to 60 ∘ ). Both static and dynamic conditions were analyzed. A pendulum, simulating the oscillation of a human leg, was used to generate highly repeatable oscillations with a maximum angular velocity of 6 rad/s. Results showed that the IR-ToF proximity sensor was not sensitive to variations of both distance and target color (except for black). Conversely, a relationship between error magnitude and AoI values was found. For AoI equal to 0 ∘ , the IR-ToF sensor performed equally well both in static and dynamic acquisitions with a distance mean absolute error <1.5 mm. Errors increased up to 3.6 mm (static) and 11.9 mm (dynamic) for AoI equal to ± 30 ∘ , and up to 7.8 mm (static) and 25.6 mm (dynamic) for AoI equal to ± 60 ∘ . In addition, the wearable platform was used during a preliminary experiment for the estimation of the inter-foot distance on a single healthy subject while walking. In conclusion, the combination of magneto-inertial unit and IR-ToF technology represents a valuable alternative solution in terms of accuracy, sampling frequency, dimension and power consumption, compared to existing technologies
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