Fast Large-Stroke Sheath-Driven Electrothermal Artificial Muscles with High Power Densities

摘要

Electrothermal carbon nanotube (CNT) yarn muscles can provide largestrokes during thermal cycling. However, the slow cooling rate of thermalmuscles limits their applications, since large diameter prior-art thermal musclescannot be rapidly cycled. Herein, a fast thermally powered sheath-drivenyarn muscle that uses a hybrid CNT sheath and an inexpensive polymer core,is reported. The stroke recovery rate for the hybrid muscle is much lower atall frequencies than for about the same diameter sheath-driven muscle, whichmeans that the full cycle contractile mechanical power is much higher thanfor comparable prior-art hybrid muscle. More specifically, the coiled sheathdrivenmuscle contracts 14.3% at 1 Hz and 7.3% at 8 Hz in air when poweredby a square-wave electrical voltage input, which is 2.9- and 11.4-times thestroke of the coiled hybrid muscle at these respective frequencies. An averagepower density of 12 kW kg~(?1) is obtained for a sheath-driven muscle, whichis 42-times that for human skeletal muscle. These high-performance resultssince the heating that drives fast actuation cycles are largely restrictedto the muscle sheath, and this sheath is in direct contact with ambienttemperature air.