Control of McKibben pneumatic muscles for a power-assist, lower-limb orthosis

In this research, a power-assist, lower-limb orthosis is developed to help the elderly or people suffering sports injuries walk or climb stairs. In the pneumatic muscle used for actuation, it is found that hysteresis phenomenon exists during the inflation–deflation process and such a phenomenon deteriorates the control performance. In order to eliminate the influence of hysteresis on the control system, a hysteresis model is constructed and used to devise an inverse control for feedforward compensation. The inverse control is combined with loop transfer recovery (LTR) feedback control to achieve better tracking performance. Moreover, bumpless switching compensators are also incorporated into the combined control system to ensure smooth switching between different phases of operation. To verify that the developed orthosis can effectively accomplish the assistive function, a human subject wearing the orthosis is asked to walk and to climb stairs. Experiments indicate that the orthosis is indeed helpful in assisting human locomotion.