Application of Segmented Shape-Memory Polymer and Alloy Composite Sheet to Pneumatic Artificial Rubber Muscles

In aging societies, soft multi-degree-of-freedom actuators are required for power-assist devices and welfare robots. Therefore, we previously developed a pneumatic artificial rubber muscle that uses shape-memory polymer (SMP) sheets with embedded electrical heating wires, which utilize the large difference in the elastic modulus below and above the glass transition temperature, shape fixity, and shape recovery of SMPs. Moreover, we increased the bending motion range of the actuators by segmenting the SMP sheet with embedded nichrome wires. We also improved the fabrication repeatability and shape recovery of the SMP sheets by using a shape-memory alloy (SMA) electric heating wire. In this study, we combine our previous improvements and propose a segmented shape-memory composite (SMC) sheet that consists of segmented SMP sheets with embedded SMA wires. We compare the shape, thermal images, and mechanical properties of the previously developed SMP sheets and the proposed segmented SMC sheets. The mechanical properties of the sample sheets are evaluated using a shape fixity and recovery test, a bending test, and a tensile test on prototypes. We also evaluate the motion of artificial muscles to which SMP sheets with embedded nichrome or SMA wires were attached using an isometric test and bending angle measurements. The experimental results confirm that the segmentation of the sheets improved muscle performance. Moreover, the use of the SMA wire improved fabrication repeatability and shape recovery, confirming that we successfully combined our previous improvements for SMP sheets with embedded heating wires.