MODELIRANJE IN OCENJEVANJE SMUČARSKEGA SKOKA IZ PODATKOV NOSLJIVEGA MERILNEGA SISTEMA

Uporaba nosljivih merilnih sistemov je v zadnjih letih zaradi razvoja in miniaturizacije senzornih tehnologij omogočila nastanek nabora novih aplikacij. Informacije, pridobljene z nosljivimi senzorji, so uporabne na področjih, ki se tičejo človeka samega ter njegovih navad: medicina, biomehanika, šport, sociologija, psihologija, tehnika. Za potrebe preučevanja biomehanike gibanja športnikov se za določanje orientacije segmentov telesa v prostoru in času med bolj uporabne nosljive senzorje šteje kombinacija žiroskopa, pospeškometra in magnetometra, ki skupaj sestavljajo inercialno merilno enoto. Vsak senzor meri svojo fizikalno veličino. Z različnimi metodami senzornega združevanja iz več signalov pridobimo znanje o novi, lahko tudi neposredno nemerljivi veličini ali preprosto izboljšamo osnovni merilni rezultat senzorja. Senzorje poleg miniaturnosti odlikuje tudi energetska učinkovitost in so primerni za spremljanje oseb v daljšem časovnem obdobju. V Poglavju 2 so predstavljeni smučarski skoki. Predstavljena je aerodinamika smučarskih skokov, ki ima zelo pomemben vpliv na dolžino skoka. Opisana je tehnična razdelitev skoka na faze in kako aerodinamične sile delujejo na skakalca v določenih fazah skoka. Skakalci izvajajo skoke v različnih vremenskih pogojih in letnih časih, v ta namen smo opisali infrastrukturo poligonov in opreme, ki jo pri tem potrebujejo. Na koncu poglavja so opisani pripomočki za preučevanje biomehanike skokov, s katerimi si pomagajo trenerji. Predstavljene so naprave za zajem kinematičnih in dinamičnih parametrov. Za analizo smučarskih skokov smo v nosljiv merilni sistem, ki je opisan v Poglavju 3, vključili 10 inercialnih merilnih enot. Po namestitvi merilnih enot smo izvedli kalibracijski postopek. Predstavljena metoda združevanja senzornih informacij se razlikuje od ostalih, saj je smučarski skok sestavljen iz oporne in neoporne faze. Za dobro oceno dinamičnih parametrov smo razvili biomehanski model. Model uporablja Newton–Eulerjevo inverzno dinamično analizo. Za dobro oceno sklepnih sil in navorov moramo poznati antropometrične parametre vsakega segmenta telesa skakalca. Model predstavlja večsegmentni sistem togih teles s konstantno maso. Rekurzivni postopek začnemo z izračunom spremenljivk od prvega segmenta do zadnjega segmenta v verigi. Opisan je tudi postopek avtomatske zaznave posameznih časovnih točk skoka, ki skok delijo na faze. V Poglavju 4 so predstavljeni rezultati preizkusa delovanja merilnega sistema v laboratoriju, kjer smo preverili sposobnostmerjenja kinematičnih parametrov. Rezultati inercialnih merilnih enot sovpadajo z referenčnim sistemom. S pritiskovno ploščo, vgrajeno v tla laboratorija, smo preverili uporabo dinamičnega modela ter navedli, kakšen rekurzivni postopek izračuna sklepnih sil in momentov bomo uporabili na skakalnici. Preizkus sistema na skakalnici je opisan v Poglavju 5. Kinematični parametri se ujemajo z literaturo. Vse izračunane sile in navori sovpadajo s prejšnjimi simulacijskimi študijami. Predlagani sistem je poleg kinematičnih parametrov segmentov zmožen posredno podati vrednosti sil in navorov v sklepih smučarskega skakalca ter reakcijsko silo tal med zaletno in vzletno fazo skoka, primerljivo z vgrajeno pritiskovno ploščo v skakalnico. Izračunamo lahko kinematične in dinamične parametre na katerikoli skakalnici ne glede na vremenske pogoje. Ocenjevanje smučarskih skokov opisujemo v Poglavju 6. Iz predstavljenih norm ocenjevanja sloga in izvedbe gibov ter analize smernic sodnikov za določitev velikosti odbitka za posamezno ocenjevalno fazo skoka smo izdelali matematični model ocenjevanja skoka. Posamezno ocenjevalno fazo skoka opišemo z različnimi parametri, ki skupaj tvorijo odbitek in s tem končno sodniško oceno. Na koncu poglavja so predstavljeni rezultati našega poskusa avtomatskega ocenjevanja smučarskih skokov. Zadnji izmed ciljev disertacije je analiza biomehaničnih parametrov iz celotnega skoka in doseženega rezultata z uporabo nosljivega merilnega sistema večih skakalcev. Rezultati so opisani v Poglavju 7. Analiza je izvedena za vsak parameter posebej z namenom povezovanja z dolžino skoka, slogovno oceno skoka in skupno oceno. Progress and minimization of sensory technologies used in wearable systems has enabled a rich development development of new applications. Information acquired with wearable sensors can be used in different areas such as medicine, biomechanics, sport, sociology, psychology, and engineering. A combination of gyroscope, accelerometer, and magnetometer as an inertial measurement unit is considered to be the most useful for the assessment of orientation of the body segments and study of the biomechanics of an athlete’s movement. The raw signals measured by each sensor are processed using sensory fusion to assess the orientation of the sensor, or simply improve the basic measurement of the sensor’s physical quantity. In addition to a small size, which makes them wearable, sensors are also energy efficient and therefore suitable for monitoring athletes over longer periods of time. Chapter 2 is describing the aerodynamics of a typical ski jump. The technical division of the jump into stages is described along with aerodynamic forces interacting with the jumper, and more importantly, their influence on the ski jump length. A brief description of infrastructure and equipment used for ski jumping is given. Tools and instruments used to study the biomechanics of the ski jumps and assist the trainers are presented at the end of the chapter. A special emphasis is given to devices used for measuring the kinematic and dynamic parameters of the jump. The proposed measuring system can be used in different weather conditions and seasons. Chapter 3 describes the wearable measurement system used to analyse the ski jump. The measurement system consists of 10 inertial measurement units. After attaching the measurement units to different spots on athlete’s body, the calibration procedure is carried out. The implemented sensory fusion differs from other applications, since the ski jumper has ground contact during in–run and does not have the ground contact during different phases of flight. To estimate the dynamic parameters, a biomechanical link–segment model was developed. The model uses the Newton–Euler inverse dynamic analysis. The model is composed as a multi–segment rigid body with constant mass. The recursive procedure sequentially calculates the variables form the first to the last segment in the chain. An automatic procedure for detection timing of the ski jump is presented. Chapter 4 presents the results of the experiment, where the ability to measure the kinematic parameters was verified. The wearable measuring system was used in laboratory environment. The results obtained from inertial measurement units coincide with the results of the reference system. The dynamic model was verified using a built–in pressure plate in the laboratory. This way, different recursive procedures for calculating the joint forces and moments were tested. The evaluation of the measurement system and algorithms were carried out on a ski hill, and the results are presented in Chapter 5. Obtained kinematic parameters match those from the literature. All calculated forces and torques comply with previous simulation studies. The proposed system is capable of indirectly providing the values of joint forces and torques during the ski jump. In addition, the ground reaction forces during in–run and take–off phases of the jump are provided with comparable precision to the force platform built in the take off table. This way it is possible to calculate the kinematic and dynamic parameters at any ski hill, regardless of weather conditions and season. Chapter 6 presents the possibility of automatic judging of the ski jump performance. Analysis of the judges guidelines for deduction of points for each jump stage was a starting point for a mathematicalmodel that can judge the ski jumpers performance. Each stage of the jump is described and assessed using different parameters, which together give a deduction sum and thus a final judge rating. At the end of the chapter the results of automatically determined sum of deduction points for three groups are presented. The last goal of the dissertation is presenting an analysis of a full set of biomechanical parameters of the entire jump acquired with wearable measurement system during several jumps. The results are described in Chapter 7. The analysis is performed for each separate parameter with correlation to the length of the jump, judge rating and the total score.