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The aim of this paper is to investigate a new control algorithm of gait rehabilitation robots that simultaneously provides more freedom for the patients and corrects their walking trajectory. The controller utilizes a gait-phase dependent reference trajectory and a gait-phase detection algorithm to determine the desired position and velocity of joints based on of their actual positions and velocities. Moreover, the controller uses two separate control blocks for the correction of the path and the cadence of walking of the patient. Since the reference trajectory is time independent, the patient can change the cadence of his/her walking. Furthermore, the separate control structure enables the controller to provide different levels of freedom and assistive force to be delivered to the patients. The control method has been implemented through ARMan , a gait rehabilitation robot and its effectiveness is evaluated on the walking trajectory of three healthy subjects and one stroke patient. The results of the experiments demonstrate that the proposed control method corrects the gait pattern of the subjects as good as impedance control method. In addition, this method provides more freedom for the patients to walk based on their desired cadence.

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In this paper, a method of tri-axial gravity gradient stabilization of satellite in circular orbit is proposed and investigated. In this method, only one actuator is employed. A satellite with varying-length boom is considered consisting of two rigid bodies having the freedom of moving in the boom direction. The only control input is the force between these two bodies to control the varying-length boom. The gravity gradient torque is considered as the only external torque acting on the satellite. The system is under-actuated and has Hamiltonian structure. So, the port-Hamiltonian approach is utilized. The equations of motion of the system are obtained in Hamiltonian formulation. The equilibrium points and their required control inputs are determined. The linearization around the equilibria is carried out and it can be seen that the linear dynamics of pitch-boom and roll-yaw are decoupled. Therefore, the roll-yaw dynamics is linearly uncontrollable. The method of energy shaping and damping injection is used for controller design. The conditions on the energy shaping control law to stabilize the system are determined. Further, the resulting closed-loop system is analyzed. The closed-loop system has center manifolds. Finally, the performance of the closed-loop system, convergence of state trajectory to the center manifold and its non-exponential convergence is shown by simulation.

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In this paper, a new design approach for an admittance control method is presented to deal with the environmental disturbances for user-in-charge exoskeletons. Since the challenge of maintaining the stability of the robot and the human is met by the user, environmental disturbances as a set of external forces should be considered. However, the proposed control methods have already ignored the issue and focused on presenting a desired dynamic relation between the interaction forces and the robot motion. This paper aims to find a control solution to maintain the desired behavior of the classical controllers in response to the interaction forces as well as to deal with disturbances properly. For this purpose, a control structure is developed by substituting an impedance control method for the low-level layer of an admittance controller. A simulation on an exoskeleton leg is conducted to evaluate the performance of the proposed controller in comparison with the classical control methods for user-in-charge exoskeletons. In contrast to conventional control methods, the results shows that the proposed controller can deal with both the interaction forces and the disturbances properly as the consequence of establishing different dynamic mappings for each of them.