Browsing by Author "Yaman, Alper."

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    Load independent trajectory control for an artificial muscle
    (Thesis (M.S.)-Bogazici University. Institute of Biomedical Engineering, 2003., 2003.) Yaman, Alper.; Özkan, Mehmed.
    In this study, the hysteretic characteristics of pneumatic McKibben artificial muscle were investigated to develop an alternative trajectory control method to traditional PID (Proportional-Integral-Derivative) controller avoiding feedback delays. Furthermore motion trajectory is intended to be payload independent by developing a physical model that will adapt itself to mass changes. In this study, we focus on only one actuator and evaluate our model experimentally. The contraction of the muscle against different pressure values was measured for several different load masses.The proposed model requires computation of actual forces involved in the motion generation of the muscle. These forces are related to contraction ratio, speed, and acceleration of the actuator. First, the load mass that the muscle lifts is measured by force sensation. The mass assessment is performed by using a friction coefficient model. Next a mathematical model relating actuator pressure with its contraction ratio is established. The coefficients are related to both the load mass and the electrical current speed that controls the servo valve pressure. Because of spring-like characteristics of the muscle, its contraction ratio is different for different loads for the same control signal. To achieve load independent trajectory control, the physical model must contain mass related parameters. In this control system, control signal (input electrical current) and electrical current speed are related to the target trajectory. The control system is open-loop, and has no feedback.
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    MRI assessment of in vivo epimuscular myofascial force transmission
    (Thesis (Ph.D.)-Bogazici University. Institute of Biomedical Engineering, 2014., 2014.) Yaman, Alper.; Öztürk, Cengizhan.; Yücesoy, Can A.
    Recent developments have been evolving magnetic resonance imaging (MRI) to a combined tool in order to assess human anatomy and physiology in vivo. In the present thesis 3D high resolution anatomic and di usion weighted imaging capabilities of MRI were combined with nonrigid registration technique in order to quantify principal strains and ber direction strains locally. The presented method was used to assess the e ects of epimuscular myofascial force transmission (EMFT) and external mechanical load simulating ischemic compression manual therapy technique in human lower leg in vivo. In healthy subjects, global length changes of gastrocnemius muscle-tendon complex were shown to cause sizable and heterogeneous local principal strains and ber direction strains within the all muscles of the limb. It was concluded that EMFT has determinant role in human muscles that a ects the mechanical characteristics of synergistic and antagonistic muscles as changing heterogeneity of ber lengths. Thus it was proven that muscles are not isolated functioning units in vivo. Even all muscles of lower leg were kept isometric, external mechanical load imposed on gastrocnemius muscle caused pronounced and quite heterogeneous principal strains not only within that muscle but also in other muscles of the limb. These ndings may lead therapists to relate the mechanical load and the size and penetration of deformations it creates.|Keywords : Epimuscular myofascial force transmission, manual therapy, magnetic resonance imaging, di usion tensor imaging, nonrigid registration, in vivo biomechanics, motion analysis.