This paper proposes a structure for the decoupling and performance improvement of a hybrid control system. Additionally, the application of this system to a motion-copying system (MCS) is introduced. MCSs are proposed as a means of preserving human-skilled techniques. In the motion-saving phase, a bilateral controller (a type of position/force hybrid control system) is utilized. A decoupling controller is required for bilateral control, for realizing precise force and position reproduction. A conventional hybrid controller for bilateral control systems has been developed, based on a force controller, by using a modal space disturbance observer (DOB). However, deterioration in the system performance during changes in the configuration of the manipulator is observed in force controllers based on workspace DOBs. It is also found that another conventional bilateral controller based on a hybrid matrix generates an interference term in the force control system, if there is a difference between the masses of the master and slave systems. This study shows that an acceleration controller can also realize decoupling control in the modal space. Furthermore, a novel DOB for enhancing the performance of an acceleration controller is proposed. Additionally, it is shown that a saved human motion can be reproduced accurately, while maintaining the high transparency of the bilateral control, by implementing a structure based on a hybrid controller and using the proposed DOB. The validity of the proposal is confirmed through analyses and experiments.
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