Development and Modeling of a Soft Array Actuator for Elderly Assistive Robotic Exoskeleton

The global elderly population is increasing rapidly, and more and more countries are stepping into the aging society. Because of deterioration in gait-related functions, such as muscle activity, most elderly people have difficulty walking, which is one of the most basic activities of daily living. A wearable lower limb robot exoskeleton offers a viable solution to this issue. Rigid exoskeletons usually have fewer degrees of freedom and require a quite big power supply for actuation, resulting in difficulties during wearing and motion. Soft exoskeletons could be an alternative choice for elderly assistance, due to their advantages of lighter weight, simpler mechanism, and compliance. Therefore, this research proposed a soft array actuator for a lower limb assistive exoskeleton for elderly people. The fully compliant actuation mechanism was designed using flexible Thermoplastic Polyurethane fabric to power the soft exoskeleton, making it compact, light, and comfortable to wear. The proposed array actuator was modeled on kinematics, contacting force, output torque, and dynamics. Mechanical performance of the compliant actuation mechanism during inflation/deflation at different air pressures and during static force testing has been evaluated. The internal air pressure of the soft array actuator reaches 100 kPa in 0.2 s and fully deflates in 0.48 s. It can generate 53.7–55.7 N to output 8.1–11.2 N·m of torque at the endpoint, which is 13.5% –18.7% of the maximum human hip joint torque during natural walking. The proposed soft actuation mechanism, with good wearability and performance, could be a good fit for a robot exoskeleton that improves natural gait and reduces human metabolic consumption during walking among the elderly. Its lightweight design, good invisibility, and high power-to-weight ratio enable the proposed soft array actuator to provide compliant, continuous, and consistent gait assistance without imposing a psychological burden on the elderly.