Development of Hexagonal Pyramid-Shaped Flexible Actuator with Anisotropic Stiffness for Upper-Limb Rehabilitation Device

Rehabilitation devices for passive exercise have been actively researched and developed in accordance with Japan's aging society. A previous study proposed and tested an extension-type flexible pneumatic actuator (EFPA) with reinforced stiffness that could achieve passive exercise in patients. In addition, a rehabilitation device for shoulder joints with an embedded controller and small valves was proposed and tested. Joints such as the shoulder and scapula were subjected to passive exercise utilizing the tested device. However, it is difficult for patients with contractions to perform the same exercise because the reinforced EFPA can buckle. Here, to realize an EFPA with a higher stiffness, a flexible actuator in the shape of a hexagonal pyramid is proposed and tested. The hexagonal pyramid shape of a flexible actuator has a high stiffness in the direction of motion and flexibility in other directions; hereafter, this characteristic is called anisotropic stiffness. The characteristics of the hexagonal pyramid shape of the EFPA are described and compared with those of a previously reinforced EFPA. An analytical model was proposed to predict and design the shape of the hexagonal pyramid EFPA. The validity of the model is also described.