Control of user-in-charge exoskeletons in the presence of interaction forces and environmental disturbances

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.