An ankle-foot orthosis powered by artificial pneumatic muscles

Abstract

We developed a pneumatically powered orthosis for the human ankle joint. The orthosis consisted of a carbon fiber shell, hinge joint, and two artificial pneumatic muscles. One artificial pneumatic muscle provided plantar flexion torque and the second one provided dorsiflexion torque. Computer software adjusted air pressure in each artificial muscle independently so that artificial muscle force was proportional to rectified low-pass-filtered electromyography (EMG) amplitude (i.e., proportional myoelectric control). Tibialis anterior EMG activated the artificial dorsiflexor and soleus EMG activated the artificial plantar flexor. We collected joint kinematic and artificial muscle force data as one healthy participant walked on a treadmill with the orthosis. Peak plantar flexor torque provided by the orthosis was 70 Nm, and peak dorsiflexor torque provided by the orthosis was 38 Nm. The orthosis could be useful for basic science studies on human locomotion or possibly for gait rehabilitation after neurological injury.

Figure 1

Powered ankle-foot orthosis. The carbon fiber shell has an artificial pneumatic dorsiflexor (maximally inflated) and artificial pneumatic plantar flexor (relaxed) attached via titanium fittings.

Figure 2

Comparison of muscle activation patterns and joint kinematics for no-orthosis (black lines) and passive orthosis (grey lines) conditions. EMG graphs include mean profiles of both conditions. Joint angle graphs include mean profiles of the no-orthosis condition (±1 SD) and of the passive orthosis condition. Zero degrees represents standing posture. Flexion is positive for knee and hip joint graphs. Plantar flexion is positive for ankle joint graph.

Figure 3

Comparison of muscle activation patterns and joint kinematics for passive orthosis and powered plantar flexor orthosis conditions. Powered condition in A is after 1 minute of wearing the orthosis; powered condition in B is after 30 min of wearing the orthosis (both black lines). Passive condition in both A and B is after 6 min of wearing the orthosis (grey lines). EMG graphs include mean profiles of both conditions. Control signal, artificial muscle force, and joint angle graphs include mean profiles of powered orthosis condition (±1 SD) and of passive orthosis condition. Zero degrees represents standing posture. Flexion is positive for knee and hip joint graphs. Plantarflexion is positive for ankle joint graph.

Figure 4

Comparison of muscle activation patterns and joint kinematics for passive orthosis and powered dorsiflexor orthosis conditions. Powered condition in A is after 1 minute of wearing the orthosis; powered condition in B is after 30 min of wearing the orthosis (both black lines). Passive condition in both A and B is after 6 min of wearing the orthosis (grey lines). EMG graphs include mean profiles of both conditions. Control signal, artificial muscle force, and joint angle graphs include mean profiles of powered orthosis condition (±1 SD) and of passive orthosis condition. Zero degrees represents standing posture. Flexion is positive for knee and hip joint graphs. Plantar flexion is positive for ankle joint graph.