Fluids functions range from thermal management in buildings to blood circulation in animals. To date the use of fluids in soft and wearable robots has been limited by the need for hard and noisy external pumps. Here we report soft pumps, a class of electrically-driven pumps with an entirely flexible or even stretchable body. These pumps rely on ElectroHydroDynamics, a solid-state mechanism that accelerates liquid molecules using electric fields, resulting in silent bi-directional operation. These elastomer pumps can be integrated into untethered soft robots, soft exoskeletons driven by fluidic muscles, and smart textiles with active temperature management.
Dielectric elastomer actuators (DEAs) are usually composed of elastomeric membranes and electrodes, which are separately fabricated and patterned. In this contribution, we describe a method to monolithically fabricate DEAs that combines molding and microfluidic technologies. In our process, microfluidic channels having desired electrode geometry are formed in a single, monolithic elastomeric matrix, and then liquid conductive material is injected into it. This fabrication method is expected to be effective for making DEAs with multiple sets of electrodes as they can be formed at once. In addition, it potentially enables easy fabrication of DEAs with complicated shapes. We prove the concept through the fabrication and characterization of a DEA that contains a single set of electrodes. A PDMS (Dow Corning, Sylgard 184) and a liquid metal (EGaIn) are chosen as the materials for the elastomeric matrix and the electrodes, respectively. Polylactic acid (PLA) is used as the molding parts made by a commercial FDM 3D printer. After curing the PDMS matrix with microfluidic channel, EGaIn is injected using a vacuum filling method, forming a monolithic DEA ready to be tested. The fabricated DEA has an active electrode area of 10 mm × 10 mm with a gap between the electrodes of 0.5 mm. During the characterization, the device exhibited actuated deformation of 13.2 um at applied electric field of 9 V/um.
Slide ring materials (SRMs), a novel type of elastomer recently developed, are a promising material for dielectric elastomer actuators (DEAs), because of their unique properties such as high dielectric permittivity and low hysteresis. However, limited information is available on the electromechanical characteristics of SRMs. Here, we report on preliminary results of our ongoing study that is intended to clarify the electromechanical performance of SRMs, while comparing with other commercial elastomers (VHB 4905 and CF19-2186). Characterizations are performed using DEA samples with an aspect ratio of 10 (length:width = 1:10) that are mounted on a universal testing machine measuring the actuated force and strain. All the elastomers were processed into the same DEA sample geometry, and were tested under identical experimental conditions. The results show advantageous features of the SRMs, such as, much larger actuated force and strain compared to the other commercial elastomers under the same electric field.
Current drones are developed with a fixed morphology that can limit their versatility and mission capabilities. There is biological evidence that adaptive morphological changes can not only extend dynamic performances, but also provide new functionalities. In this paper, we present different drones from our recent developments where folding is used as a mean of morphological adaptation. First, we show how foldable wings can enable the transition between aerial and ground locomotion or to fly in different aerodynamic conditions, advancing the development of multi-modal drones with an extended mission envelope. Secondly, we show how foldable structures allow to transport drones easily without sacrificing payload or flight endurance. Thirdly, we present a foldable frame that makes drones to withstand collisions. However, the real potential of foldable drones is often limited by the use of conventional design strategies and rigid materials, which motivates to use smart, functional materials. Lastly, we describe a dielectric elastomer based foldable actuator, and a variable stiffness fiber using low melting point alloy for drones. The foldable actuator acts as an active compliant joint with folding functionality and mechanical robustness in drones, thanks to the compliance of dielectric elastomer, a class of smart materials. We also show re-configuration of a drone enabled by the variable stiffness fiber that can transition between rigid and soft states.
We introduce a soft actuator for grippers using DEA capable of bending actuation. The actuator is also able to generate the electro-adhesion by the fringe field formed at the edges of the electrodes. The adhesion improves the holding force and ensures the conformation of the structure to the object. After the characterization of the actuator, we develop a 2-finger soft gripper capable of holding various objects. The gripper has a mass of around 1 g, and consists of a few cm long actuation parts, realizing simple open-close movement. The compliance of the gripper leads to conformation of the structure against the object surface, which is proven by successful handling of objects with different geometries such as a toothbrush, a flat paper, and a ping pong ball. The effect of the electro-adhesion is visible when the paper is held with its flat shape meaning that an adhesion force against gravity exists. Also, by the fact that the conformed structure increases the contact area, the holding force is improved while avoiding damaging the object, which is highlighted by the ability to hold a raw egg weighing around 60 g. This soft gripper, combining both actuation and electro-adhesion, illustrates the potential use of DEA for soft robotics.
Dielectric Elastomer Actuators (DEAs) are an emerging actuation technology which are inherent lightweight and
compliant in nature, enabling the development of unique and versatile devices, such as the Dielectric Elastomer
Minimum Energy Structure (DEMES). We present the development of a multisegment DEMES actuator for use in a
deployable microsatellite gripper. The satellite, called CleanSpace One, will demonstrate active debris removal (ADR) in
space using a small cost effective system. The inherent flexibility and lightweight nature of the DEMES actuator enables
space efficient storage (e.g. in a rolled configuration) of the gripper prior to deployment. Multisegment DEMES have
multiple open sections and are an effective way of amplifying bending deformation. We present the evolution of our
DEMES actuator design from initial concepts up until the final design, describing briefly the trade-offs associated with
each method. We describe the optimization of our chosen design concept and characterize this design in terms on
bending angle as a function of input voltage and gripping force. Prior to the characterization the actuator was stored and
subsequently deployed from a rolled state, a capability made possible thanks to the fabrication methodology and
materials used. A tip angle change of approximately 60° and a gripping force of 0.8 mN (for small deflections from the
actuator tip) were achieved. The prototype actuators (approximately 10 cm in length) weigh a maximum of 0.65 g and
are robust and mechanically resilient, demonstrating over 80,000 activation cycles.
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.