Experimental studies on kinematics and kinetics of walking with an assistive knee brace

Assistive knee brace is a species of wearable lower extremity exoskeletons. Such assistive equipment can enhance people's strength and provide desired locomotion to have advantages over wheelchairs, which are commonly used for patients with mobility disorders. However, the integration between the assistive knee brace and the user is challenging as inaccurate alignments may adversely affect the biomechanics of the knee joint. The goal of this study is to evaluate the changes between normal walking and walking with an assistive knee brace in "off" mode. The assistive knee brace was developed by integrating a multifunctional actuator with a custom-made knee-ankle-foot orthosis in order to minimize excessive shifting and to improve alignment to the knee joint. Spatial and temporal gait parameters, joint kinematics and joint kinetics parameters were compared. In general, the observed results showed that most of the gait parameters were not affected when walking with the knee brace. The only significant differences were found in knee flexion and knee rotational motions. These results indicated that walking with the developed knee brace provided minimal hindrance to the user and assured that assistive torque can be applied to the knee joint

Finite Element Studies of Colloidal Mixtures Influenced by Electric Fields

A further understanding of colloidal mixture behavior under applied electric fields would greatly benefit the design of smart material systems such as electrorheological fluidic devices and microfluidic reconfigurable antennas. This thesis presents a finite element analysis of colloidal mixture electrokinetic behavior. Computations of particle forces as a function of applied frequency and particle shape were performed. An effective medium property method was also studied. Fluidic and electric forces were obtained with various applied excitation frequencies throughout three locations in a coplanar microelectrode domain. This domain consists of two 50 nanometers thick gold electrodes separated by a 30 micrometers gap. The three locations are 1.2 micrometers, 40 micrometers, and 90 micrometers from the gap center. Total force vectors were computed by integrating Maxwell and Cauchy stress tensors to determine whether the particles are pushed toward or away from the electrode gap at frequencies of 10 Hz, 1 kHz, and 100 kHz. It was determined that particles were pushed outside the gap at median frequencies of 1kHz (indicating ac electroosmotic force domination) and began to be pushed back toward the gap at higher frequencies of 100 kHz (indicating dielectrophoretic force intensification). Particle shape effects were examined by calculating the electrical interparticle force between two particles at various incidences with respect to a uniform electric field. Particle attraction occurs when the line between the particle centers is aligned with the electric field; repulsion occurs when this center line is perpendicular. The incidence angle at which the particles switch from attraction to repulsion is defined as θcr. The aspect ratio and particle edge separation distances used in this study were 1, 5,12.92 and 0.25 micrometers, 0.50 micrometers, 2.0 micrometers, respectively. The results indicate that higher aspect ratio particles tend to have smaller θcr values and larger interparticle force magnitudes for given separation distances. Finally, effective dielectric constant simulations utilizing periodic crystalline arrangements of colloidal structure were performed. The results show good agreement with the Maxwell Garnett mixing rule at volume fractions above 30 percent. Less canonical structures of cubic particles were also modeled

Tunable shear thickening in suspensions.

Shear thickening, an increase of viscosity with shear rate, is a ubiquitous phenomenon in suspended materials that has implications for broad technological applications. Controlling this thickening behavior remains a major challenge and has led to empirical strategies ranging from altering the particle surfaces and shape to modifying the solvent properties. However, none of these methods allows for tuning of flow properties during shear itself. Here, we demonstrate that by strategic imposition of a high-frequency and low-amplitude shear perturbation orthogonal to the primary shearing flow, we can largely eradicate shear thickening. The orthogonal shear effectively becomes a regulator for controlling thickening in the suspension, allowing the viscosity to be reduced by up to 2 decades on demand. In a separate setup, we show that such effects can be induced by simply agitating the sample transversely to the primary shear direction. Overall, the ability of in situ manipulation of shear thickening paves a route toward creating materials whose mechanical properties can be controlled.I.C. and N.Y.C.L. gratefully acknowledge the Weitz Laboratory at Harvard University, School of Engineering and Applied Sciences for generous use of their rheometry facility. I.C. and N.Y.C.L. were supported by National Science Foundation (NSF) CBET-PMP Award 1232666 and continued support from NSF CBET-PMP Award 1509308. C.N. and J.S. acknowledge funding from the Engineering and Physical Sciences Research Council (EPSRC), EP/N025318/1. M.E.C. is supported by the Royal Society and EPSRC Grant EP/J007404. This work also made use of the Cornell Center for Materials Research Shared Facilities, which are supported through the NSF Materials Research Science and Engineering Centers Program (DMR-1120296).This is the author accepted manuscript. The final version is available from the National Academy of Sciences via http://dx.doi.org/10.1073/pnas.160834811

Comparison of DC Motors and Dielectric Elastomer Actuators For Wearable Wrist Exoskeletons

Paralysis or loss of strength resulting from stroke requires patients to undergo extensive rehabilitation therapy. It is known that intensive therapy contributes significantly to recovery, but as the number of surviving stroke patients increases, it is difficult for clinics to provide patients with the optimal level of therapy. Robotic devices for wrist rehabilitation have been developed to lessen these problems, but at the moment they are physically large and must be used within a clinical setting. More benefit could be obtained if the devices were portable, so that they could be used by the patients on a daily basis. To reduce the size of these devices, other means of actuation need to be considered, as currently DC motors and the required transmission are too large and heavy. Dielectric elastomer actuators (DEAs) may provide a solution to the actuation problem. The focus of this thesis was to compare DC motors with DEAs for use in a wearable wrist exoskeleton to assist with stroke rehabilitation. A simple setup of the forearm, wrist, and hand was developed for testing DC motors and DEAs. For testing the DC motors, kinematic and dynamic models of the arm were created to develop an inverse dynamics controller used to control the movement of the hand. DEAs were fabricated and tested to determine their capabilities in terms of force and range of motion. Based on the data collected, an electromechanical model was optimized to characterize the behavior of the DEAs. The results show that a single DEA strip is not capable of providing the force or range of motion required for a wearable wrist exoskeleton. Future work can be done to improve DEA design so that they may actuate a wearable wrist exoskeleton or could also be considered for use in other wearable rehabilitation devices

Disseny mecànic d’una ortesi activa per a lesionats medul·lars a partir de l’anàlisi dinàmica de la marxa humana

Premi al millor Projecte de Fi de Carrera presentat durant l'any 2013 en l'àmbit de Mecànica que atorga la CÀTEDRA ALSTOMEn aquest projecte es presenta el disseny mecànic d’una ortesi activa tipus SCKAFO (Stance Control Knee Ankle Foot Orthosis) pensada per assistir la marxa de lesionats medul·lars incomplets, amb una classificació C o D segons ASIA (American Spinal Injunry Associaton). Per comprendre el mecanisme seguit per les persones al caminar, s’inclou una breu explicació sobre la biomecànica de la marxa humana. També es descriuen quines són les mancances dels lesionats medul·lars que es poden beneficiar de la tecnologia dissenyada. A més, es realitza una recerca bibliogràfica sobre l’estat de l’art de les ortesis i de l’anàlisi de la marxa, aspecte fonamental per al disseny de dispositius exosquelètics. Per a la realització del disseny cal conèixer les especificacions mecàniques, que són els esforços articulars que realitza una persona sana quan camina. Per a tal fi, es fa una anàlisi dinàmica de la marxa humana. Coneixent la cinemàtica i les forces de contacte amb el terra d’un subjecte sa caminant, es resol un problema de dinàmica inversa. S’utilitzen les equacions de Lagrange amb multiplicadors per trobar els esforços desitjats. Les dades de moviment i de força necessàries per a l’anàlisi s’obtenen a partir d’una captura realitzada al laboratori de biomecànica de l’ETSEIB. Al llarg del projecte es fa una explicació de la metodologia seguida per fer la captura i es presenten i discuteixen els resultats obtinguts, tant a nivell cinemàtic com a nivell dinàmic. Un cop es coneixen les especificacions, es realitza el disseny mecànic del dispositiu sota la hipòtesi que els esforços necessaris per a la marxa assistida d’un lesionat són aproximadament els mateixos que els necessaris per a la marxa d’un subjecte sa (Kao et al., 2010). L’ortesi es dissenya seguint les recomanacions d’un metge i un tècnic ortopeda. El resultat és una ortesi que actua de forma passiva, amb una molla, sobre el turmell i de forma activa sobre el genoll. L’actuació sobre el genoll es realitza amb un motor elèctric i un reductor -col·locats en paral·lel a la cuixa per tal d’estalviar espai- durant la fase de balanceig i amb un sistema de bloqueig comercial durant la fase de recolzament. El funcionament es troba automatitzat gràcies a un sistema de control. Finalment, es fa una anàlisi de viabilitat del projecte per al cas que es vengués l’ortesi durant 7 anys a l’estat espanyol i que la seva producció fos seriada. Aquesta anàlisi dóna per suposada la viabilitat tècnica de la solució per la que s’ha optat i estudia la viabilitat a nivell social, econòmic i ambiental. A nivell social, es fa una hipòtesi dels clients que es tindran a partir de dades estadístiques de lesionats medul·lars. A nivell ambiental, es justifica un ús racional dels recursos i s’explica breument quin seria el procés a seguir per tractar els residus. A nivell econòmic, es realitza un estudi de la viabilitat de comercialització del producte i es dóna una estimació del preu de vendaAward-winnin