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- Type of Document: Ph.D. Dissertation
- Language: Farsi
- Document No: 50743 (08)
- University: Sharif University of Technology
- Department: Mechanical Engineering
- Advisor(s): Vossoughi, Gholamreza; Selk Ghafari, Ali
- Abstract:
- Todays, the exoskeleton is known as a practical device for use in robotic rehabilitation and elderly assistance and has attracted the attention of many researchers. Impedance control is the most widely recognized control strategy in research on exoskeletons. Impedance control can properly handle soft interaction of robots with the environment. Optimal target impedance selection can increase the performance of the overall system and guarantee the stability. The main objective of this research was to introduce a variable impedance control system and verifying the presented control system on an exoskeleton. In this research, an exoskeleton with 4 active DoF and 8 semi-passive DoF is designed and fabricated. A novel torque control as the inner loop of the impedance control is also introduced and evaluated experimentally. Two model-based torque controls is designed and introduced based on the velocity and current commands. Results show good performance of the robot in zero-force control and impedance control during swing phase of motion. Then, a systematic analysis is done to introduce a method to estimate the human stiffness and consequently adjust the robot target stiffness. Then, particle swarm optimization is used to find the damping and inertia parameters of the robot to minimize the peak of the interaction force. Then, experimental results on a lower limb exoskeleton is provided to validate the proposed approach. Finally a adaptive impedance control system is introduced that helps elderly or partially paralyzed individuals. To ensure that a smart and compliant controller, in each cycle of the gait is developed, we adapted the target impedance gains and feed-forward force of the assistive mechanism according to a learning law. A strength metric was defined to determine when the human needs assistance. Then, a cost function was introduced and the gains are modified to reduce the cost function. Applying the proposed controller, the interaction force between patient’s limb and robot was reduced in cases wherein user has sufficient strength for task execution and minimizes the position error in the sub phases where users need assistance. Using the Lyapunov stability theorem, the stability of the closed loop system was proved without and with parameter uncertainty, respectively. The results of simulations and an experiment on an exoskeleton showed that the proposed adaptive impedance control improves performance to a level substantially higher than that achieved with constant impedance control
- Keywords:
- Adaptive Impedance Control ; Lower Limb Exoskeleton ; Exoskeleton ; Interaction Force Control ; Rehabilitation ; Strength Measure ; Assiste-as-needed
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