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Effect of mechanical parameters on dielectric elastomer minimum energy structures

  • Authors: Shintake, Jun; Rosset, Samuel; Floreano, Dario; Shea, Herbert

Soft robotics may provide many advantages compared to traditional robotics approaches based on rigid materials, such as intrinsically safe physical human-robot interaction, efficient/stable locomotion, adaptive morphology, etc. The objective of this study is to develop a compliant structural actuator for soft a soft robot using dielectric elastomer minimum energy structures (DEMES). DEMES consist of a pre-stretched dielectric elastomer actuator (DEA) bonded to an initially planar flexible frame, which deforms into an out-of-plane shape which allows for large actuation stroke. Our initial goal is a one-dimensional bending actuator with 90 degree stroke. Along with frame shape, the actuation performance of DEMES depends on mechanical parameters such as thickness of the materials and pre-stretch of the elastomer membrane. We report here the characterization results on the effect of mechanical parameters on the actuator performance. The tested devices use a cm-size flexible-PCB (polyimide, 50 μm thickness) as the frame-material. For the DEA, PDMS (approximately 50 μm thickness) and carbon black mixed with silicone were used as membrane and electrode, respectively. The actuators were characterized by measuring the tip angle and the blocking force as functions of applied voltage. Different pre-stretch methods (uniaxial, biaxial and their ratio), and frame geometries (rectangular with different width, triangular and circular) were used. In order to compare actuators with different geometries, the same electrode area was used in all the devices. The results showed that the initial tip angle scales inversely with the frame width, the actuation stroke and the blocking force are inversely related (leading to an interesting design trade-off), using anisotropic pre-stretch increased the actuation stroke and the initial bending angle, and the circular frame shape exhibited the highest actuation performance.

Posted on: April 22, 2013

HYPER-FLEXIBLE 1-D SHAPE SENSOR

  • Authors: Dobrzynski, Michal; Vanderparre, Hugues; Pericet Camara, Ramon; L"Eplattenier, Géraud; Lacour, Stéphanie; Floreano, Dario

Here we describe a sensor capable of perceiving complex one-dimensional (1-D) shape of an underlying substrate in a static and dynamic manner. The sensor consists of seven, serially connected, hyper-flexible strain gauges, manufactured using stretchable-gold-conductordeposited-on-PDMS technology. The custom designed read-out scheme allows decoupling strain-sensitive resistances of the strain-gauges from the parasitic pressure- and temperature-sensitive resistances of the connectors. The developed prototype device confirms full operation within the tested deflections ranging from 0 o to 35 o, showing an average sensitivity of 36 !/o and an average resolution of 0.22 o. The read-out frequency of 100 Hz allows quick scanning of the whole sensor array.

Posted on: February 20, 2013

Variable stiffness material based on rigid low-melting-point-alloy-microstructures embedded in soft poly(dimethylsiloxane) (PDMS)

  • Authors: Schubert, Bryan Edward; Floreano, Dario

Materials with controllable stiffness are of great interest to many fields, including medicine and robotics. In this paper we develop a new type of variable stiffness material based on the combination of a rigid low-melting-point-alloy (LMPA) microstructure embedded in soft poly(dimethylsiloxane) (PDMS). This material can transition between rigid and soft states by controlling the phase of the LMPA through efficient, direct Joule-heating of the LMPA microstructure. The devices tested demonstrate a relative stiffness change of > 25x (elastic modulus is 40 MPa when LMPA is solid and 1.5 MPa when LMPA is liquid) and a fast transition from rigid to soft states (< 1 s) at low power (< 500 mW). Additionally, the material possesses inherent state (soft and rigid) and strain sensing (GF = 0.8) based on resistance changes.

Posted on: October 10, 2013