Additively manufactured unimorph dielectric elastomer actuators: Design, materials, and fabrication

Abstract

Dielectric elastomer actuator (DEA) is a smart material that holds promise for soft robotics due to the material’s intrinsic softness, high energy density, fast response, and reversible electromechanical characteristics. Like for most soft robotics materials, additive manufacturing (AM) can significantly benefit DEAs and is mainly applied to the unimorph DEA (UDEA) configuration. While major aspects of UDEA modeling are known, 3D printed UDEAs are subject to specific material and geometrical limitations due to the AM process and require a more thorough analysis of their design and performance. Furthermore, a figure of merit (FOM) is an analytical tool that is frequently used for planar DEA design optimization and material selection but is not yet derived for UDEA. Thus, the objective of the paper is modeling of 3D printed UDEAs, analyzing the effects of their design features on the actuation performance, and deriving FOMs for UDEAs. As a result, the derived analytical model demonstrates dependence of actuation performance on various design parameters typical for 3D printed DEAs, provides a new optimum thickness to Young’s modulus ratio of UDEA layers when designing a 3D printed DEA with fixed dielectric elastomer layer thickness, and serves as a base for UDEAs’ FOMs. The FOMs have various degrees of complexity depending on considered UDEA design features. The model was numerically verified and experimentally validated through the actuation of a 3D printed UDEA. The fabricated and tested UDEA design was optimized geometrically by controlling the thickness of each layer and from the material perspective by mixing commercially available silicones in non-standard ratios for the passive and dielectric layers. Finally, the prepared non-standard mix ratios of the silicones were characterized for their viscosity dynamics during curing at various conditions to investigate the silicones’ manufacturability through AM.

Characterization of Photocurable IP-PDMS for Soft Micro Systems Fabricated by Two-Photon Polymerization 3D Printing

“…The obtained Young's modulus value is considerably lower than the 15.3 MPa reported on the manufacturer's website, despite using the recommended printing parameters for 2PP fabrication of the tested sample and determining both Young's moduli through nanoindentation [9]. Meanwhile, both values are larger than for the majority of common PDMS compositions in the literature [26][27][28]. Like all elastomers, PDMS is composed of slightly cross-linked polymer chains, and its mechanical properties are sensitive to the degree of polymerization.…”

“…The first conducted dielectric test is a relative permittivity measurement that is performed on 113 µm thick IP-PDMS (spin-coated, cured) films. The measured capacitance is converted to the permittivity value of ε r = 2.63 ± 0.02, which is within the typical range of relative dielectric permittivity for common PDMS formulations [26][27][28]. An attempt was made to measure the dielectric permittivity based on the 2PP-printed cylindrical coupon.…”

Fully inkjet-printed dielectric elastomer actuators

“…23,24 Sikulskyi et al developed a contact dispensing 3D printing process for bending unimorph DEAs (UDEAs). 18 The process is based on a Polydimethylsiloxane (PDMS) membrane with poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS) electrodes. Su et al employed UV-cured extrusion to print acrylic elastomer films for multilayer DEAs.…”

“…However, in the context of eEAP transducers production, AM methods are still in the early stages of development and present non-trivial challenges. These challenges encompass formulating printable inks, [17][18][19] obtaining pairs of conductive, electrically isolated compliant electrodes, [20][21][22] and achieving strong inter-layer adhesion. 23,24 Sikulskyi et al developed a contact dispensing 3D printing process for bending unimorph DEAs (UDEAs).…”