219 research outputs found
Ein objektorientiertes Modell der menschlichen unteren Extremität zur invers- und vorwärtsdynamischen Simulation der menschlichen Gehbewegung
No full textIm Rahmen dieser Arbeit wird eine offene, objektorientierte Bibliothek zur Modellierung der menschlichen unteren Extremität vorgestellt. Wesentliches Charakteristikum ist die Anwendbarkeit der entwickelten Softwarebausteine in Form eines Baukastensystems.
Die Vorteile der vorgestellten Architektur sind (1) eine einfache Handhabbarkeit der entstehenden Modelle, (2)die Möglichkeit schneller und punktueller Detaillierung von Teilmodellen sowie (3) die Möglichkeit, effizienten und getesteten Programmcode aus anderen Applikationen zu verwenden. Dieser Aspekt bietet insbesondere in Hinblick auf zukünftige Erweiterungen der Bibliothek großes Potential.
Die Anwendung der Softwarebibliothek wird anhand von drei Beispielen im Kontext der klinischcen Ganganalyse illustriert.
Als erste Anwendung wird eine automatisierte Methode zur Reduzierung von systematischen Fehlern bei der z.B. in einem Ganglabor üblichen Bewegungserfassung mittels Markern (motion capturing) vorgestellt. Durch ungenaue Positionierung der Marker auf der Haut sowie Relativbewegungen zwischen Haut und dem darunter liegenden Skelett (skin artefacts) sowie Messrauschen kann die Position der Gelenksmittelpunkte nur ungenau bestimmt werden. Dadurch treten in von diesen Bewegungsdaten abgeleiteten Modellen unrealistische Variationen in den Segmentlängen auf. Die vorgestellte Methode identifiziert Segmentvektoren sowie die Differenzvektoren zwischen den realen (anatomischen) Gelenksmittelpunkten sowie den Gelenksmittelpunkten des biomechanischen Modells unter Verwendung eines Optimierungsansatzes. Durch Anwendung der Methodik konnte die Variation der Segmentlängen zwischen 19% und 32% reduziert werden.
Als zweite Anwendung wurde mit Hilfe der entwickelten Software ein Tool zur Unterstützung bei der Diagnostik spezieller Formen des sog. Spitzfuß bei spastischen Lähmungen entwickelt. Hierdurch kann die komplizierte klinische Methodik durch eine auf einfacher Bewegungserfassung basierende, numerische Prozedur ersetzt werden. Die Übereinstimmung der Diagnose mit der klassischen klinischen Methode beträgt zwischen 71% ud 90%.
Im Rahmen einer dritten Anwendung wird ein Modell zur Identifizierung von Muskelaktivierungsverläufen mittels dynamischer Optimierung vorgestellt. Die hierbei verwendeten Kostenfunktionen basieren ausschließlich auf jeweils patientenindividueller Kinematik. Weiterhin wird ein vereinfachtes Muskelmodell verwendet. Dieses zeichent sich durch eine begrenzte Anzahl von Parametern aus, mit dem Ziel, die mit der Methodik der dynamischen Optimierung verbundenen hohen Berechnungsaufwände zu reduzieren. Um die Empfindlichkeit der Modellierung gegenüber Ungenauigkeiten in den Eingabeparametern zu untersuchen wurde eine Sensitivitätsanalyse durchgeführt. Die Ergebnisse der Untersuchung implizieren, dass die menschliche Gehbewegung allein auf Basis gemessener Bewegungsdaten nicht beobachtbar ist.Within the scope of this thesis, an open-architecture library to set up the model of the human lower extremity has been proposed. As a main characteristic, the library provides a construction kit for stetting up any leg model.
The open-architecture benefits are: (1) model manageability, (2) an easily improved model depth and (3) the possibility of including efficient and tested code. This aspect becomes especially important with respect to future extensions of the library.
The applicability of the proposd library is illustrated by three example investigations related to gait analysis.
In a first example, the adaption of the lower extremity model to patient-specific physiognomy is discussed. To reduce systematic errors in the estimation of joint center locations from marker position, marker placement inaccuracy, skin artefacts and measurement noise in motion capturing, an automated tracking error reduction method was implemented. This method is based on a surrogate mechanism identifying the offsets between the assumed and anatomic joint center locations and the unknown segment vectors. The method lead to reductions in segment vector length variation between 19\% and 32\%.
As a second example, the proposed library was used to diagnose talipes equinus in the context of cerebral palsy. The tool allows to replace anesthesia and a physical test by a purely numerical procedure. The diagnosis given by the proposed method coincides with the medical one between 71\% and 90\% of all considered cases.
As a third example, a simulation for forward dynamics prediction of muscle activation time histories is described. The applied objective functions are based on kinematic measurements (motion capturing). To reduce model complexity, a simplified model of muscle activation proposed. The approach limits the number of design variables for each muscle and hence facilitates the optimization process due to a limited search space dimension. To analyze the effects of model perturbations to the predicted muscle activation profiles, a sensitivity investigation was performed. The results of this thesis seem to indicate that the gait dynamics are not observable from kinematic measurements only
Human Gait, Stumble and...fall? Mechanical limitations of the recovery from a stumble.
No full textThe goal of this thesis was to find the limitations in the recovery reactions to avoid a fall. These limitations can be roughly classified as mechanical, neurological and psychological. This thesis has focused on the study of the mechanical limitations of the recovery reaction to a stumble during gate
Explore Pole Vaulting Strategies by control optimization: A biomechanical model based exploration
No full textThe development of the pole vaulting record is only improved by 1 centimeter over the last 25 years. Multiple studies show signs of different control strategies in elite pole vaulters, without pointing out what the cause of the differences is The aim of this research is to explore pole vaulting strategies by a control torque optimization. The optimization is performed for a simplified biomechanical model. The vaulter contains three segments: arms, a trunk including the head and legs. The joints are represented by torque actuators, located at the hands, shoulder joint and hip joint. The torque profile of each actuator is optimized. The optimization starts just after the pole is planted. It ends when the vaulter releases the pole. The pole length, pole stiffness, the vaulter’s length, the vaulter’s mass and the take-off angle are varied to discover the influence of these parameters on the control strategy. Three control strategies are found, as well as two power management strategies. Global trends are found. An increased pole stiffness, a decrease in length and mass of the athlete and a decreased take-off angle improved the performance. A possible optimal pole length is found.Mechanical Engineering | BioMechanical Design | Sports Engineerin
Inertia compensation for perturbations on instrumented treadmills: Optimization and validation
No full textInstrumented treadmills and perturbations of the treadmill are commonly used for gait analysis and can provide real time biomechanical information and feedback of gait patterns and abnormalities. Force plates in the treadmill are combined with motion capture data and fed into a musculoskeletal model. High accuracy of the force plates is needed to give reliable feedback for gait analysis. The accuracy still needs to be tested under dynamic conditions, with the belt running. Also, inertial and gravitational forces are measured during perturbations as a result of the rotation and translation of the platform in which the force plates are positioned. This results in an error in the forces and moments as measured by the force plates, which is added up to the forces exerted by a subject. Inertia compensation models have been developed and showed promising results but have not been validated extensively. This study aimed to optimize and validate an inertia compensation model for perturbations on instrumented treadmills and validate the force measurements under dynamic conditions. It was shown that the treadmill can accurately measure the center of pressure (error = 1-6 mm), forces (error = 1-7 N) and moments (error = 0.5-4 Nm). A new calibration trial was found with higher sway accelerations which improved the inertia compensation model and left residuals forces and moments below 2 N(m). Moreover, it showed that using this inertia compensation model for pitch and sway trials led to a reduction of the kinetic residuals of up to 96% and values close to baseline measurements.Biomedical Engineerin
Design of a flat dynamic hand orthosis finger for DMD patients
No full textPeople with Duchenne muscular dystrophy (DMD) will suffer from a limited hand function. Therefore, a dynamic hand orthosis could be one of the solutions to improve their hand function and quality of life. However, at this moment, none of the obtainable hand orthoses fits their special needs. The goal of this research is to design a flat dynamic hand orthosis finger for DMD patients with Brooke scale grades 4, 5, or 6 and to test its functioning. The design consists of a silicone outer part, and an inner part from polylactic acid. The presented prototype is small, can generate a flexion movement and has a finger mass of 20 g. Output forces were tested in horizontal and vertical direction and different designs were compared in relation to the bending angle. The reached output forces in horizontal and vertical direction with a certain pressure were 3.4 N (10.5 N target) at 1.75 bar and 0.6 N at 2 bar, respectively. The bending angles were 35◦ for the MCP joint, 78◦ for the PIP joint, and 58◦ for the DIP joint. To conclude, this paper presented a new design of a finger for a hand orthosis. The prototype is flat, can generate flexion movements and has a finger mass of 20 g. Except for the MCP joint, the bending angles meet the requirements. Only the output forces were too low. An outer structure of another material might solve this.Biomedical Engineerin
Modelling Short-Range Stiffness: Comparison Between Hill- and Huxley-type Muscle Models
No full textMusculoskeletal models often use Hill-type models to study and simulate muscle behaviour. Due to fast simulation time and ability to simulate large and slow movements Hill-type models have remained largely unchanged throughout recent years. Large and slow movements spend a large part in steady state behaviour and thus experience limited influence of transitional behaviour. However, during small and fast movements, transitional behaviour has more influence and causes inaccuracies in Hill-type models, which can cause an overestimation of muscle force. One characteristic of transitional behaviour is short-range stiffness (SRS). This property is a result of crossbridge dynamics and causes an increase in stiffness when muscle velocity changes. Huxley-type models are capable of simulating transitional behaviour, but are computationally expensive. The goal of this article is to identify the optimal parameter values for two Hill- and one Huxley-type model using a surrogate optimization algorithm and determine if these models can simulate general behaviour and SRS. The parameters are fitted to one soleus and medial gastrocnemius muscle of a cat. All models were able to simulate the experimental data with an average RMS of 6.6N and 4.8N for the Hill models and 5.5N for the Huxley model. However, all three models were not capable of predicting SRS during isometric contractions and the method of determining SRS during non-isometric contractions proved unusable. Thus, the Huxley model that was used had no advantage over the used Hill-type muscle models. Furthermore, it was concluded that the simplest Hill was the only model viable for real-time application
Finite element eye model with retinal detachment, investigating head and eye movements as progression factors
No full textRhegmatogenous retinal detachment (RD) is a sight threatening condition. In this type of RD a break in the retina allows liquefied vitreous to enter the subretinal space and the retina to detach. The prognosis concerning the patients' visual ability is better if the RD has not progressed to the macula. The patient is given a posturing advice of bed rest and semi-supine positioning (with the RD as low as possible) to allow the utilisation of gravity in preventing progression of the RD. It is, however, unknown what loads on the eye contribute the most to the progression of a retinal detachment. The goal of this exploratory study is to elucidate the role of saccadic eye movements and head movements on the progression of an RD. A finite element model is produced and evaluated in this study. The model is based on geometric and material properties found in literature. The model shows that a mild head movement and a severe eye movement produce similar loads on the retina. This implies that head movements---and not eye movements---are able to cause loads that can trigger and progress an RD. These preliminary results suggest that head movements have a larger effect on the progression of an RD than saccadic eye movements. This study is the first to use numerical analysis to investigate the development and progression of RD and shows great promise for future work
Parameter Scaling Protocol for Upper-limb Musculoskeletal Models
No full textGeneric musculoskeletal models are not reliable predicting inter-individual variations in muscle forces. Scaling the model parameters is necessary to represent the muscle characteristics of the subjects and thus to pinpoint the differences in force capacity. Optimal Fiber (OFL) and Tendon Slack Length (TSL) have been identified as the two most influential parameters in muscle force generation. The goal of the current study is adjusting a lower-limb scaling algorithm for OFL and TSL to the Delft Shoulder and Elbow Model (DSEM). Furthermore, we evaluate the effect on the preservation of model consistency and muscle force production. Firstly, we scaled the DSEM geometrically. That drove twenty-two muscles to work out of the physiological range in the F-L curve up to 41% of the shoulder ROM. Moreover, the consistency of the model dropped by 78%. We tested three approaches to scale OFL and TSL. The constrained method delivered the best results reducing these percentages to 8% and 2.9%, respectively. It also increased the muscle force production of the DSEM 1.2%BW compared to the geometrically scaled version. The adaptation of the constrained scaling algorithm to the DSEM provides consistency values in the same range observed in lower-limb models. Therefore, we state that it is necessary to scale OFL and TSL whenever the dimensions of the DSEM are modified to obtain reliable muscle force estimations. We recommend further validation of the procedure developed in this article, for example, against data from instrumented endoprosthesis
De rol van het labrum glenoïdale in de actieve stabiliteitsregeling van het schoudergewricht
No full textNociceptive SSEPs induced using multisine frequency modulated pulse trains: An exploratory study in inducing multi-frequency SSEPs
No full textSteady state evoked potentials (SSEPs) using multiple frequency inputs are a well-known method to study the underlying dynamics in the visual, auditory and somatosensory system. Multi-frequency SSEPs provide insight into system dynamics such as delay, non-linearities, and frequency response function. Despite extensive research, little is known about the nociceptive system and its dynamics. Previous research showed the possibility to evoke single frequency nociceptive SSEPs using block wave stimulation. In the present study, we explored the feasibility of evoking multi-frequency nociceptive SSEPs using a multisine frequency modulated pulse train. The novel electrical stimulation technique using a frequency pulse train composed of 3, 7 and 13 Hz can stimulate multiple frequencies simultaneously. For the first time, we were able to induce multi-frequency SSEPs indicated by a contralateral maximal signal to noise ratio EEG response for 3 and 7 Hz. The power in 3 and 7 Hz showed significantly higher power compared to all other frequencies up until 40 Hz. The novel stimulation technique offers a unique opportunity to measure multi-frequency SSEPs related to nociceptive processing, allowing better localization of nociceptive signal processing and possible insight into the dynamics of the nociceptive regulation system
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