doktorska disertacija
Matej Tomc (Author), Zlatko Matjačić (Mentor)

Abstract

Gleženjski sklep pri zdravih ljudeh igra ključno vlogo pri ustvarjanju mehanskega dela za propulzijo težišča telesa naprej v smeri hoje. Ljudje po živčno-mišični bolezni ali poškodbi, na primer po možganski kapi, pogosto izgubijo polno zmožnost zavestnega obvladovanja mišic, te pa tudi oslabijo. Niso več zmožni ustvarjati zadostnega navora plantarne fleksije v gležnju in zato ne morejo vzdrževati zdravim podobnega vzorca hoje. Na področju rehabilitacije je bilo v pomoč tem ljudem razvitih že veliko rešitev v obliki gleženjskih eksoskeletov, a zaradi različnih pomanjkljivosti te naprave še niso postale del klinične prakse. V okviru doktorske disertacije smo po korakih zasnovali, razvili in eksperimentalno preizkusili delovanje novega gleženjskega eksoskeleta. Najprej smo predstavili nov koncept gleženjskega eksoskeleta, ki ne vsebuje lastnega aktuatorja, pač pa za delovanje izrablja tekalno stezo, po kateri uporabnik hodi. Med fazo opore energijo shranjuje v elastično tetivo, v podfazi odriva pa jo preko ortoze odda uporabniku in mu s tem olajša odriv. Napravo, ki po tem konceptu deluje, smo poimenovali ANkle EXoskeleton using TReadmill Actuation for Push-off assistance, ali krajše AN-EXTRA-Push. Zastavili smo okvirno zgradbo in delovanje naprave in identificirali parametre načrtovanja, s spreminjanjem katerih bo mogoče voditi napravo in jo prilagajati potrebam uporabnika. Na karakteristiko dodatnega navora plantarne fleksije, ki ga eksoskelet ustvarja za pomoč uporabniku, lahko sproti vplivamo s spremembami naslednjih parametrov: čas vklopa zavore, čas izklopa zavore in togost elastične tetive. Koncept predstavljenega eksoskeleta smo preverili v simulacijski študiji. Izdelali smo 2D dinamični model hodeče osebe, ga opremili z modelom AN-EXTRA-Push in za vse tri parametre izvedli parametrično analizo. Uporabili smo optimizacijo z genetskim algoritmom, da smo simulirali vzorce hoje za širok nabor vrednosti treh parametrov. Rezultati simulacijske študije so določili obseg potencialno primernih vrednosti parametrov, na podlagi katerih smo načrtovali nadaljnje praktične eksperimente. Po iterativnem postopku smo razvili prototip AN-EXTRA-Push. Pozorni smo bili na izzive pri načrtovanju, ki so pomembni ne le za izvedbo eksperimentov ampak tudi za uspešno rabo naprave v kliničnem okolju. Nastavljivo togost elastične tetive smo realizirali s paralelnim vpenjanjem elastičnih vrvi. Pripravili smo dva predloga za vodenje vklopa in izklopa zavore. Naloga vodenja se v veliki meri zreducira na razpoznavanje in predikcijo faz cikla hoje v realnem času. V prvem predlogu smo algoritem prilagodili opremi v moderno opremljenem biomehanskem laboratoriju, v katerem smo izvedli eksperimentalne študije. Izkoristili smo meritve reakcijske sile podlage pod pohodno površino tekalne steze z ločenima pohodnima površinama za vsako nogo. Drugi predlog ponuja rešitev za primer, ko tekalna steza ni opremljena s senzorji sile. Faze cikla hoje lahko razpoznavamo z algoritmom, osnovanim na bazenu oscilatorjev z adaptivno frekvenco. Vhod v ta algoritem bi lahko bile meritve najmanj ene inercialne merilne enote, pritrjene na nogo z eksoskeletom. Izvedli smo raziskavo vpliva AN-EXTRA-Push na hojo zdravih ljudi. V raziskavi je sodelovalo dvanajst prostovoljcev. Pri različnih nastavitvah časov vklopa zavore in togosti tetive smo merili časovno-prostorske parametre, kinematiko in kinetiko hoje ter mišično aktivnost z elektromiografijo. Predstavili smo tudi novo metriko za ovrednotenje sinhronosti delovanja uporabnikovega mišično-kitnega sistema in eksoskeleta. AN-EXTRA-Push je najbolj vplival na gleženjski sklep, v katerem je neposredno ustvarjal navor plantarne fleksije. Večinoma se koti, navori in moči v vseh sklepih noge niso veliko spremenili, prispevek eksoskeleta pa je povzročil zmanjšanje prispevka bioloških struktur k navoru v gležnju. S povečano pomočjo je upadla aktivnost mišic plantarnih fleksorjev gležnja. Glede na literaturo je AN-EXTRA-Push dosegal zadovoljiv nivo pomoči za potrebe rehabilitacije, sinhronost delovanja eksoskeleta in bioloških struktur pa je bila primerljiva najsodobnejšim eksoskeletom z vodenjem s človekom v zanki. Zmožnosti AN-EXTRA-Push v zahtevnejšem primeru močno variabilne hoje osebe po možganski kapi smo preverili v študiji primera. Da bi se izognili napakam pri vodenju, smo napravo še bolj poenostavili. Prednji del tetive smo namesto začasne zaustavitve z zavoro trajno pritrdili. Preiskovanec zaradi posledic možganske kapi ni bil zmožen zdravim podobnega odriva. Ob pomoči naprave sta njegov lastni navor in moč v gležnju ostala približno enaka, pomoč eksoskeleta pa je prispevala k skupnemu dvigu navora in moči v gležnju, s čimer smo izpolnili cilj po močnejšem odrivu. Naprava AN-EXTRA-Push je v eksperimentalnih študijah tako na zdravih osebah kot na pacientu dajala rezultate, ki so zelo primerljivi sodobnim gleženjskim eksoskeletom. Hkrati je od sodobnih eksoskeletov mnogo enostavnejša, zlasti z vidika vodenja. Posebno pozornost smo pri razvoju posvetili tudi praktičnim vidikom uporabe v klinični praksi. Na podlagi izsledkov študij zato ocenjujemo, da je AN-EXTRA-Push naprava, ki bi lahko bila primerna za rabo v rehabilitaciji. Pred dokončnim prebojem iz raziskovalnega v klinično okolje so sicer nujno potrebne študije vpliva AN-EXTRA-Push na večjem vzorcu oseb po preboleli možganski kapi.

Keywords

gleženjski eksoskelet;biomehanika;hoja;rehabilitacija;možganska kap;doktorati;

Data

Language: Slovenian
Year of publishing:
Typology: 2.08 - Doctoral Dissertation
Organization: UL FE - Faculty of Electrical Engineering
Publisher: [M. Tomc]
UDC: 615.82/.84(043.3)
COBISS: 219932163 Link will open in a new window
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Other data

Secondary language: English
Secondary title: Ankle exoskeleton with treadmill actuation for push-off assistance
Secondary abstract: In healthy human gait, the ankle joint plays a key role in generating the mechanical work needed for propulsion. People who suffer from neuromuscular impairments, such as those occurring post-stroke, often struggle with voluntary muscle control and muscle weakness. Compared to healthy individuals, their ankle plantarflexion moment is often insufficient for a proper push-off, leading them to adopt an altered gait pattern. In the field of rehabilitation, many solutions have been developed to help these people in the form of ankle exoskeletons, but due to various shortcomings these devices have not yet been widely adopted in clinical practice. As part of this PhD work, a new ankle exoskeleton was designed, developed and experimentally tested step by step. We presented a novel concept of an ankle exoskeleton that does not contain its own actuator, but instead uses a treadmill on which the user walks to function. During the stance phase of gait, it stores the energy in the elastic tendon, and during the push-off sub-phase, it transfers the energy to the user via the orthosis, thus facilitating push-off. We named the device that works according to this concept the ANkle EXoskeleton using TReadmill Actuation for Push-off assistance, or AN-EXTRA-Push for short. We set out a framework for the structure and operation of the device, and identified design parameters that, when modified, will allow the device to be controlled and adapted to the user's needs. The following design parameters: brake engagement time, brake disengagement time, and elastic tendon stiffness, can be used to modify the assistance torque profile in real time. We checked the validity of the concept of the proposed exoskeleton in an in-silico study. We developed a 2D dynamic model of healthy human gait, added AN-EXTRA-Push to the simulation and performed a parameter sweep analysis. We used a genetic algorithm to solve an optimization problem of simulated walking for a large solution space defined by our three parameters. The results of the study were appropriate value ranges for each parameter that served as the basis for future in-vivo experiment designs. Following an iterative approach, we developed an AN-EXTRA-Push prototype. During development, we considered both our needs for future experimental work and eventual realities of clinical practice. The adjustable stiffness of the elastic tendon was implemented by clamping up to three elastic cords in parallel. Two proposals for the control of the brake engagement and disengagement were developed. The control task can in large part be reduced to the real-time detection and prediction of the phases of the gait cycle. In the first proposal, we adapted the algorithm to the equipment in a modern biomechanical laboratory, where experimental studies were carried out. We made use of measurements of the ground reaction force under the walking surface of a split-belt instrumented treadmill. The second proposal offers a solution for situations where only a normal, not an instrumented, treadmill is available. Gait phases can be identified by an algorithm based on a pool of adaptive frequency oscillators. The input to this algorithm could be the measurements of at least one inertial measurement unit attached to the leg with an exoskeleton. We conducted a study on the effects of AN-EXTRA-Push use on healthy human gait. Twelve volunteers participated in the study. Brake engagement time and elastic tendon stiffness were varied across the experimental conditions. We measured spatio-temporal parameters, kinematics, and kinetics of gait, as well as muscle activity using electromyography. We also introduced a new measure to quantify the synchrony between the user’s muscle-tendon complex and the exoskeleton. Most of the effects were constrained to the ankle joint, where AN-EXTRA-Push directly assisted with plantar flexion moment creation. Total angles, moments and powers across all joints remained substantially similar. The addition of exoskeleton torque resulted in a reduction in moment generation by the biological structures around the ankle joint. The activity of the ankle plantar flexor muscles was reduced with increased assistance. Compared to the relevant literature, AN-EXTRA-Push was generating sufficient assistance for use in rehabilitation. The synchrony between the biological structures and the exoskeleton was comparable to the state-of-the-art exoskeletons that employ human in the loop optimization to tune their control schemes. We carried out a case study on a person that suffered a stroke, in which we tested the operation of AN-EXTRA-Push under the challenging conditions of highly variable hemiparetic gait. Looking to avoid any mistakes that have to do with control, we decided to further simplify the device. Instead of using the brake, we permanently fixed the anterior end of the elastic tendon in place. Due to movement impairment that resulted from the stroke, the subject was unable to walk with a healthy-like gait pattern. When assistance was applied, his biological ankle moment and power remained similar. The applied exoskeleton torque helped the subject reach higher total ankle moment and power values, which resulted in stronger push-off. AN-EXTRA-Push has produced results in experimental studies on both healthy subjects and patients that are highly comparable to state-of-the-art ankle exoskeletons, while being much more simplistic, especially in terms of control. The practical aspects of use in clinical practice have also been given special consideration in the development of AN-EXTRA-Push. Based on the results of the studies, we therefore consider that the AN-EXTRA-Push is a device that could be suitable for use in rehabilitation. However, further studies on the effects of assisting push-off with AN-EXTRA-Push in a larger sample of stroke survivors are necessary before it is ready to move from the research to the clinical setting.
Secondary keywords: ankle exoskeleton;biomechanics;gait;rehabilitation;stroke;
Type (COBISS): Doctoral dissertation
Study programme: 1001057
Embargo end date (OpenAIRE): 1970-01-01
Thesis comment: Univ. v Ljubljani, Fak. za elektrotehniko
Pages: XXII, 126 str.
ID: 25518687