This article proposes a bioinspired variable stiffness dielectric elastomer actuator (VSDEA) that is inspired by the leaf habit of monocots. The VSDEA is a fully flexible strip with a curved cross section and a tip dielectric elastomer minimum energy structure (DEMES). An arc fixture is used to clamp the strip that imitates the connection mode between the leaf and the cylindrical stem of the monocot. When applying voltage on the tip DEMES, the transverse curvature of the strip is changed, and then, the bending stiffness of the VSDEA can be tuned. Effects of applied voltage and important design parameters on the bending behavior of the VSDEA are experimentally studied in detail. The results show that the bending stiffness of the VSDEA approximately decreases linearly with the increase of applied voltage, which is very advantageous for stiffness control. The load capacity of the VSDEA is enhanced due to the bioinspired clamping mechanism and can be tuned by the applied voltage. It can also be found from the tested VSDEA prototypes that, when the applied voltage ranges from 0 V to 5.6 kV, the maximum relative stiffness and critical load changes reach about 71.8% and 75.6%, respectively. The maximum stiffness and critical load are, respectively, 157.8 N/m and 889.9 mN, which are two orders greater in magnitude than general DEMESs; as a result, this VSDEA can bear a payload 139 times its weight. It demonstrates that the bioinspired VSDEA can be useful for soft robots, vibration control, and morphing applications.
Keywords: curved strip; dielectric elastomer actuators (DEAs); load capacity; variable stiffness.