Enhanced actuation frequency in actuators using twisted and coiled SMA artificial muscles

Artificial muscles powered by shape memory alloys (SMAs) or highly twisted artificial muscles offer promising alternatives to conventional actuators, particularly in applications requiring lightweight, compliant or biomimetic motion. However, these high-force actuators suffer from reduced actuation frequency due to passive cooling constraints limiting their widespread adoption. This paper presents the design, modeling, and experimental evaluation of a novel twisted and coiled SMA (TCAM) actuator. This actuator offers both enhanced force outputs and actuation frequency, overcoming the inherent trade-off between strength and speed of SMAs. Compared to a commercial SMA spring using the same material mass, the TCAM configuration achieved a 186% increase in force output while also showing a 11.5% improvement in actuation frequency. Analytical modeling attributed these improvements to the increased stiffness from the twisted configuration. Experimental validation confirmed the TCAM's superior performance under identical thermal and electrical conditions, highlighting its potential for high force output, lightweight, and high frequency artificial muscle applications in robotics and biomedical devices.