Identification of a time-varying mechanical system using the Akaike information criterion

Cet article démontre l'intérêt du critère d'information d'Akaike pour les méthodes d'identification contenant une étape de projection de signaux de mesure sur des bases spécifiques. On s'intéresse particulièrement au problème d'identification de paramètres mécaniques variant dans le temps. La méthode est testée expérimentalement avec succès sur un système à un degré de liberté, constitué d'une inertie et d'une poutre à longueur variable travaillant en torsion. Les variations de cette longueur rendent les paramètres du système dynamique changeant. Une approche par moindre carré combinée à une projection des signaux mesuré sur une base polynomiale permet de reconstruire aisément les fluctuations des paramètres mécaniques. Cependant le choix de l'ordre de troncature de la base de projection est toujours un problème clef dans ce genre de méthode inverse et reste bien souvent une question ouverte. On propose ici d'utiliser le critère d'information Akaike permettant ainsi une sélection robuste et automatique de cet ordre de troncature. L'étude présentée ici ainsi que l'expérimentation montrent la pertinence et l'intérêt de ce type de critère associé aux méthodes d'identification

Measuring Multi-Joint Stiffness during Single Movements: Numerical Validation of a Novel Time-Frequency Approach

This study presents and validates a Time-Frequency technique for measuring 2-dimensional multijoint arm stiffness throughout a single planar movement as well as during static posture. It is proposed as an alternative to current regressive methods which require numerous repetitions to obtain average stiffness on a small segment of the hand trajectory. The method is based on the analysis of the reassigned spectrogram of the arm's response to impulsive perturbations and can estimate arm stiffness on a trial-by-trial basis. Analytic and empirical methods are first derived and tested through modal analysis on synthetic data. The technique's accuracy and robustness are assessed by modeling the estimation of stiffness time profiles changing at different rates and affected by different noise levels. Our method obtains results comparable with two well-known regressive techniques. We also test how the technique can identify the viscoelastic component of non-linear and higher than second order systems with a non-parametrical approach. The technique proposed here is very impervious to noise and can be used easily for both postural and movement tasks. Estimations of stiffness profiles are possible with only one perturbation, making our method a useful tool for estimating limb stiffness during motor learning and adaptation tasks, and for understanding the modulation of stiffness in individuals with neurodegenerative diseases

肘関節粘弾性特性分析に基づいた可変粘弾性握手マニピュレータの開発

【学位授与の要件】中央大学学位規則第4条第1項【論文審査委員主査】中村　太郎　（中央大学理工学部教授）【論文審査委員副査】平岡　弘之（中央大学理工学部教授）、新妻　実保子（中央大学理工学部准教授）、諸麥　俊司（中央大学理工学部准教授）、万　偉偉（大阪大学准教授）博士(工学)中央大

ANTHROPOMORPHIC ROBOTIC ANKLE-FOOT PROSTHESIS WITH ACTIVE DORSIFLEXION- PLANTARFLEXION AND INVERSION-EVERSION

The main goal of the research presented in this paper is the development of a powered ankle-foot prosthesis with anthropomorphic characteristics to facilitate turning, walking on irregular grounds, and reducing secondary injuries on bellow knee amputees. The research includes the study of the gait in unimpaired human subjects that includes the kinetics and kinematics of the ankle during different types of gait, in different gait speeds at different turning maneuvers. The development of a robotic ankle-foot prosthesis with two active degrees of freedom (DOF) controlled using admittance and impedance controllers is presented. Also, a novel testing apparatus for estimation of the ankle mechanical impedance in two DOF is presented. The testing apparatus allows the estimation of the time-varying impedance of the human ankle in stance phase during walking in arbitrary directions. The presented work gives insight on the turning mechanisms of the human ankle and how they can be mimicked by the prosthesis to improve the gait and agility of below-knee amputees

Modelling and control of dynamic platelet aggregation under disturbed blood flow

Diagnosis of platelet function is fundamental for identifying blood disorders of patients, assessing the impact of antiplatelet agents, and enabling the appropriate titration of individual antithrombotic treatments. Following the advancement of new technologies such as microfluidic devices and the use of control engineering methods, new devices have the potential to offer new opportunities in point-of-care diagnosis of platelet function. Such new devices may have significant utility in the development of more tailored antiplatelet therapies. The aim of this thesis is to investigate modelling and control systems which support the study of the dynamic relationship between newly discovered mechanisms of platelet aggregation and disturbed blood flow, using state-of-the-art micro-engineered technologies. In order to observe the dynamics of platelet aggregation under disturbed blood flow, blood perfusion experiments carried out on a device mimicking a scenario of severe vessel narrowing are presented. The resulting biological response, that is the aggregation of platelets, is monitored in real-time and synthesised through novel measures developed using image processing techniques. A mechanistic model identifying four distinct stages observed in the formation of the aggregate is formulated, describing the nonlinear relationship between blood flow dynamics and platelet aggregation. The observed effect of disturbed blood flow on the aggregation of platelets is then modelled mathematically employing System Identification methods. A detailed account of a novel approach for the generation of experimental data is presented, as well as the formulation of tailored mathematical model structures and the calculation of their parameters using collected data. The proposed models replicate experimental results with low variation, and the reduced number of model parameters is suggested as a novel systematic measure of platelet aggregation dynamics in the presence of blood flow disturbances. In order to stabilise, optimise, and automate the measurement of platelet function in response to disturbed blood flow, custom-made control algorithms based on principles of Sliding Mode Control and Pulse-Width Modulation are developed. Moreover, the control algorithms are developed to handle the large variability of the aggregation responses from blood types with platelet hyper- and hypo-function. Simulation results illustrate the robustness of the control algorithms in the presence of time-varying nonlinearities and model uncertainty, and indicate the possibility to regulate the extent of aggregation in the device through modulation of the blood flow rate in the microchannel. The main contribution of this thesis is the development of dynamic models and control systems that allow a systematic measurement of platelet function in response to rapid changes in the blood flow (shear rate micro-gradients), in a microfluidics device containing a scenario of disturbed blood flow. Analysis of the platelet aggregation dynamics revealed that although the aggregate growth appears to be constant at times, measuring its mean fluorescence intensity indicates an increase in the dynamics of platelet density. This densification process appears fundamental for the development of an amplification phase in the aggregation response. The proposed mathematical models and control algorithms facilitate the systematic measurement of platelet function in vitro, pioneering the development of a novel framework for automated blood disorder diagnosis

Quantitative characterization of multi-variable human ankle mechanical impedance

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2013.Cataloged from PDF version of thesis.Includes bibliographical references (p. 222-230).Ankle mechanical impedance, which is a dynamic relationship between angular displacement and the corresponding torque at the ankle joint, plays a key role in natural interaction of the lower-extremity with the environment. The human ankle is a biomechanically complex joint consisting of three bones with non-intersecting anatomical axes, and its motions under normal motor control and function are predominantly in multiple degrees-of-freedom (DOF). This thesis provides a quantitative characterization of multivariable ankle mechanical impedance of young healthy subjects in two DOF, both in the sagittal and the frontal planes. Multi-variable studies provide several important characteristics of the human ankle, unavailable from single DOF studies, which have mostly been in the sagittal plane. Three characterization methods were developed to study ankle mechanical impedance in different conditions: 1) steady-state static, 2) steady-state dynamic, and 3) transient dynamic. First, steady-state static ankle mechanical impedance, which is a non-linear torque and angle relationship at the ankle, was characterized in two coupled DOFs over the normal range of motion. Robust vector field approximation methods based on thin-plate spline smoothing with generalized cross validation showed that static ankle impedance is highly direction dependent, being weak in the inversion-eversion direction. Activating a single muscle or co-contracting antagonistic muscles significantly increased static ankle impedance in all directions but more in the dorsiflexion-plantarflexion direction than the inversion-eversion. Static ankle behavior in both relaxed and active muscles was close to that of a passive elastic system. Second, steady-state dynamic ankle mechanical impedance was characterized based on linear time-invariant multi-input multi-output stochastic system identification methods. A highly linear relationship between muscle activation and ankle impedance was identified in all movement directions in the sagittal and frontal planes. Furthermore, small coupling between 2 DOF and energetic passivity were observed at different levels of muscle activation and over a wide frequency range. Third, transient dynamic ankle mechanical impedance was characterized during walking on a treadmill, across the gait cycle from the end of stance phase through swing and to early stance phase. Modified linear time-varying ensemble based system identification methods enabled reliable identification of transient behavior of the ankle. In both DOF, damping and stiffness decreased at the end of stance phase before the toe-off, remained relatively constant during the whole swing phase, and substantially increased around the heel-strike. Quantitative characterization of multi-variable ankle mechanical impedance of young healthy subjects will shed light on its roles in lower-extremity motor function. It will serve as a baseline for clinical studies in patients, especially those with neurological disorders, as well as studies of elderly subjects, whose biomechanical and neurological properties may be altered due to impairments and/or aging. Finally, the methods presented in this thesis are intended to be sufficiently general to be applicable to any multi-joint system or single joint having multiple DOF.by Hyunglae Lee.Ph.D