Control Reference Parameter for Stance Assistance Using a Passive Controlled Ankle Foot Orthosis-A Preliminary Study

Featured Application The control reference parameter suggested in this study is implemented in a Passive-Controlled Ankle Foot Orthosis (PICAFO) equipped with magnetorheological (MR) brake on its ankle joint. Previously, the PICAFO has been shown to successfully deal with foot drop by locking the foot ankle position during the swing phase. By adding functions such as stance assistance, the user can get more benefits when using the PICAFO. Abstract This paper aims to present a preliminary study of control reference parameters for stance assistance among different subjects and walking speeds using a passive-controlled ankle foot orthosis. Four young male able-bodied subjects with varying body mass indexes (23.842 +/- 4.827) walked in three walking speeds of 1, 3, and 5 km/h. Two control references, average ankle torque (aMa), and ankle angular velocity (a omega), which can be implemented using a magnetorheological brake, were measured. Regression analysis was conducted to identify suitable control references in the three different phases of the stance. The results showed that a omega has greater correlation (p) with body mass index and walking speed compared to aMa in the whole stance phase (p1(a omega) = 0.666 > p1(aMa) = 0.560, p2(a omega) = 0.837 > p2(aMa) = 0.277, and p3(a omega) = 0.839 > p3(aMa) = 0.369). The estimation standard error (Se) of the aMa was found to be generally higher than of a omega (Se1(aMa) = 2.251 > Se1(a omega) = 0.786, Se2(aMa) = 1.236 > Se2(a omega) = 0.231, Se3(aMa) = 0.696 < Se3(a omega) = 0.755). Future studies should perform a omega estimation based on body mass index and walking speed, as suggested by the higher correlation and lower standard error as compared to aMa. The number of subjects and walking speed scenarios should also be increased to reduce the standard error of control reference parameters estimation.