Design and analysis of a knee prosthesis with (MR) magnetorheological damper

In this thesis, an electronically controlled, semi-active, above-knee prosthesis, which can adapt to environmental conditions, has been designed to restore natural mobility to people who have lost their legs above the knee. The prosthesis designed in this study contains magnetorheological damper as an actuator. Due to its short response time, this damper, which can be controlled by a current, is found suitable for continuous time control. The damping control of the torque produced during the gait from the user's hip provides a movement close to the natural knee motion. The first condition for successful control is to obtain the theoretical models of the gait and damper dynamic behaviour. Then the performance analysis of measurement phase are carried out by utilizing the obtained models and control block into the simulation environment. Kinematic and kinetic behavior were examined separately during the derivation of theoretical model. For the kinematic analysis of the gait, a leg and foot were regarded as a robot manipulator with three revolute joints and three prismatic joints. Forward and inverse kinematics, velocity kinematics and trajectory generation topics were discussed on the manipulator frame. The kinetic behavior is determined by the analysis of dynamic equations derived from the relationship of the leg and foot with the ground plane during walking. Differential equations establish a link between the kinematic (displacement, velocity and acceleration) and dynamic (forces and torques) variables of gait. The performances of analytical models were examined in a simulation environment by using kinetic and kinematic measurements obtained from natural gait trials. The theoretical model obtained from the priori stage was evaluated in the simulation environment considering the input-output relations and the control of desired gait scenarious. Theoretical models, validated using real gait measurements, are examined in the closed loop control structure and the results are observed. This part provides the analysis giving an idea about which extent the differential equations can express prosthetic gait and their controllability. Given results presented that stance phase errors introduced by the double pendulum can be corrected by the inverse double pendulum model. Therefore, an important improvement has been presented by proposing inverse pendulum model to the control problems when both swing and stance phases of the gait were used in the unified model. In the control stage carried out on the embedded system, control parameters obtained from the simulation environment via the continuous-time control algorithm that adjusts the current driving the damper, and a variable torque are generated for the knee joint according to the measured and estimated kinematic variables. Based on the difference between the measured knee angle and the reference knee angle, the controller adjusts the stiffness level of the damper in real time. One of the most important expectations of the application is to give a proper reference knee angle according to the gait phases. Based on this purpose, knee angle was estimated by using inertial sensors attached onto the prostesis. Under the light of the results of experiments and analyzes conducted, the suitability of the magnetorheological damper for continuous time control has been verified and the results are reported.