A novel variable stiffness actuator composed of a dielectric elastomer actuator (DEA) and a low-melting-pointalloy (LMPA) embedded silicone substrate is demonstrated. The device which we call variable stiffness dielectric elastomer actuator (VSDEA) enables functional soft robots with a simplified structure, where the DEA generates a bending actuation and the LMPA provides controllable stiffness between soft and rigid states by Joule heating. The entire structure of VSDEA is made of soft

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... s with an elastic modulus of less than 1 MPa providing a high compliance when the LMPA is active. The device has the dimension of 40 mm length × 10 mm width × 1 mm thickness, with mass of ∼1 g. We characterize VSDEA in terms of the actuation stroke angle, the blocked force, and the reaction force against a forced displacement. The results show the controllable actuation angle and the blocked force up to 23.7 • and 2.4 mN in the soft state, and 0.6 • and 2.1 mN in the rigid state. Compared to an actuator without the LMPA, VSDEA exhibits ∼90× higher rigidity. We develop a VSDEA gripper where the mass of active parts is ∼2 g, which is able to successfully hold an object mass of 11 g, exhibiting the high performance of the actuator.