Oscillator-based transparent control of an active/semiactive ankle-foot orthosis

Transparency, defined as the ability of a robot to exert nil interaction force on the user, is a key requirement for any wearable robot for assistance, rehabilitation, or functional augmentation. In this study, we propose a new controller to improve the transparency of a powered orthosis. The proposed controller takes advantage of the cyclic nature of human walking to predict the upcoming undesired interaction forces and compensate them in real time. Results from validation tests with a group of N=12 healthy subjects who walked with a powered ankle-foot orthosis indicate that the proposed controller can reduce undesired interaction torques by 19.1% at slow speed and 17.43% at fast speed, compared to a conventional zero-torque controller. When the same controller was implemented in a semiactive actuation mode, these figures increased to 20.06% and 19.59%, respectively, proving the versatility of the proposed approach.