McKibben artificial muscle using shape-memory polymer

When McKibben artificial muscle actuators are used to drive robotic joints, they are typically configured in pairs which act antagonistically to increase joint stiffness. However, this configuration cannot maintain a fixed position without continuous control. The objective of this study is to develop a McKibben artificial muscle which can fix into a rigid shape without the need for continuous control. This is achieved by exploiting the inherent properties of shape-memory polymers (SMPs). SMPs can be deformed above their glass transition temperature (Tg) upon the application of a small load. They can maintain their shape in a rigid form after they have been cooled to below Tg. When heated again above Tg, they return to their predefined shape. Exploiting these characteristics, we impregnate the braided mesh shell of a commercial McKibben artificial muscle with SMP resin. When this new actuator is warmed above Tg, it can be used as a conventional McKibben muscle. When the actuator attains its desirable length, it can be cooled to below Tg and the SMP will fix the structure in a rigid, actuated, state. This state is maintained without the need for any air supply or control system. The enhanced versatility of this new actuator is shown through a series of experiments conducted on a prototype SMP McKibben actuator.