Automatic adjustment of initial drop speed of foot for intelligently controllable ankle foot orthosis

We have developed intelligently controllable ankle-foot orthoses (i-AFOs) that control their ankle motions with compact and high torque magnetorheological fluid brakes and those sensor systems. The i-AFO was applied to hemiplegic patients and a patient suffering from flaccid paralysis in his ankles. In the previous study, the i-AFO successfully identified the three different gait states, i.e. the initial contact, loading response, and swing phase, and also successfully achieved the avoidance of the abnormal drop foot in the swing phase. However, we did not accomplish the optimal control of the drop speed of foot in the initial contact (initial drop speed of foot, or IDSF in this paper). This report aims to investigate new control method of the i-AFO that focuses on the IDSF. The control model was developed on the basis of the experimental results of the healthy subjects, and the effect of the new controller was evaluated by a post-Guillain-Barre syndrome patient. The performance was evaluated with the kinematic information of the motion sensor installed in the i-AFO and estimated muscle activation simulated by inverse-dynamics software with mathematical models of human body. According to the results, the IDSF control at the initial contact successfully generated the virtual muscle activation of anterior tibial muscle and seemed to reduce the extra muscle activation of rectus femoris muscle.