This work presents a novel actuator system consisting of a combination of shape memory alloy (SMA) wires with electrostatic clutches. The proposed combination of smart material systems stems from the need to reduce the energy consumption of SMA based actuators while leveraging their high energy densities in compact actuation systems. To this end, large actuation forces provided by SMA wires are combined with the highly energy-efficient actuation of electrostatic clutches. The actuation of the SMA wire generates the desired motion after which the activation of the clutch and deactivation of the SMA wire ensures that the desired position is held in an energyefficient manner. A retractable electro-adhesive tubular clutch was chosen for our testing due to its enclosed nature and ease of fabrication. A characterization setup is also developed and used to demonstrate the feasibility of our new actuator concept. The tests show that a 254 μm SMA wire has an energy consumption rate of about 850.7 mJs−1 as compared to less than 31.3 mJs−1 for the clutch, which results in an energy savings rate of over 800 mJs−1 for position holding tasks.
The actuation performance of dielectric elastomers (DE) is determined by the electric field when voltages are applied. As the field-dependence is quadratic, higher voltage leads to more efficient actuation. The limiting factor, however, is dielectric breakdown. Due to early-stage and complex manufacturing processes, thin films at present may still contain local imperfections, limiting the overall breakdown field and sometimes causing early breakdown in DE actuators. In particular, when manufacturing multi-layer actuators, a premature breakdown in only one layer causes failure of the entire actuator system. To overcome this problem and to increase the yield of functional actuators, this paper presents a novel method to test and repair DE layers. In a first step, a DE layer is tested for required breakdown voltage in a specially designed breakdown tester and the location of early breakdown spots is identified. In a second step, a method for the repair of these breakdown spots is introduced. A final validation of the repaired DE layer for quality control concludes the process, hence ensuring higher yield of functional actuators in an early manufacturing stage. The testing process using a specially designed breakdown box is described as well as the subsequent repair method of a patch/glue combination. Results about the influence of the repaired spots on the stress/strain behavior of a silicone thin film w/o electrode as well as the performance of the DE prepared with screen-printed carbon black electrodes are included in the presentation.
This work presents a novel and innovative design for a dielectric elastomer-based pump with a focus on resonance optimization. Dielectric elastomer pumps are increasingly relevant in fluid transport applications, but their efficiency and control remain critical challenges. This study presents a novel approach to addressing these issues. The proposed design leverages the concept of resonance optimization, a cutting-edge approach that enhances the performance of dielectric elastomer pumps by exploiting their inherent resonant frequencies. The mechanical design is systematically chosen to ensure that the system's resonance matches the pump's working frequency, and when an appropriate electric field is applied, it significantly enhances the pump's efficiency through resonance enhancement. To demonstrate the effectiveness of this approach, a fully functional dielectric elastomer-based pump demonstrator is built and tested. The demonstrator showcases how the systematic selection of mechanical design elements, including pump chamber, pump membrane geometry, biasing mechanism and dielectric elastomer design, combined with resonance optimization, results in an optimized pump adapted to handle different loads effectively. Dielectric elastomers (DEs), known for their exceptional properties such as high-frequency operation, high energy efficiency and the ability to freely tailor geometries to suit specific applications, serve as a keystone in achieving these improvements. By exploiting these characteristics, this innovative approach opens up new possibilities for fluid transport technologies, making it an ideal candidate for applications demanding reliability and low energy consumption. In conclusion, this design approach for DE-based pumps with resonance optimization holds promise for overcoming existing limitations in dielectric elastomer technology in the field of pump applications, presenting a pathway towards more efficient and versatile pump systems.
With the characteristics of lightweight, low driving voltage and biocompatibility, ionic polymer-metal composites have attracted much attention in the field of soft-robotics and artificial muscles. This paper introduces the development of a novel design of a segmented tubular ionic-polymer metal composite (IPMC) actuator. This configuration allows a large bidirectional movement, paving the way for the development of intelligent and adaptable structures. In this study, the IPMC actuator is manufactured from a 40-mm long prefabricated Nafion polymer tube with an inner diameter of 1.3 mm and an outer diameter of 1.6 mm. The outer surface is plated via an electroless-plating process. The proposed tubular IPMC design consists of an additional inner electrode and two outer isolated segments, setting it apart from existing approaches. It includes a new coating method of the inner electrode, offering a more efficient and versatile solution for actuation and sensing applications. Preliminary experimental investigation is employed to characterize the electromechanical performance of the actuator, as well as to quantify the maximal angular bending. Furthermore, the presented results establish the operational principles of the innovative design and validate the proof-of-concept. The experimental results show improved performance compared to the state-of-the-art.
KEYWORDS: Dielectric elastomer actuators, Robotics, Robots, Manufacturing, Electrodes, Silicon, 3D modeling, Visual process modeling, Bistability, Model based design
Soft robotic technology offers the potential for enhanced safety in human-robot collaboration. Our research introduces a compact robotic arm segment, actuated by silicone-based rolled dielectric elastomer actuators (RDEAs), in combination with a ball joint, showcasing large-angle multi-directional bending. A simplified kinematic, quasistatic model is presented. The segment was built utilizing PCBs as structural components a custom, low friction ball joint, and 3 groups of 3 RDEAs. Two different modes of operation are identified in the model as well as in experiments. One mode with smaller bending angles of 0° to 7°, and one mode with a larger, but constant angle of 25°. The results demonstrate significant bending capabilities in a compact form-factor, laying the foundation for the development of multi-segment RDEA-actuated soft robotic tentacle arms.
Dielectric Elastomer Actuators (DEAs) are known for their outstanding properties such as low weight, high energy density and self-sensing capability. Compared to conventional magnetic actuators, they are manufactured from generally inexpensive and widely available polymer materials, making the technology particularly attractive for developing actuator systems that are potentially low-cost and serve a wide range of applications. This advantage can be further enhanced by developing scalable and standardized system designs that use identical parts in order to reduce product variation and enable high volumes in a mass production process. Following this approach, this paper introduces a low-profile and compact linear actuator design, which provides a configurable force and stroke transmission in order to serve different load-profiles without changing shape and dimension of the DEA itself. The design is based on rectangular-shaped, in-plane operating DEAs coupled to a unibody linkage mechanism, which is likewise flat and based on compliant joints and rigid links. A negative rate stiffness mechanism enables to increase the performance output of the actuator system in terms of cyclic converted energy in quasi-static operation. By configuring the lever ratios of the input and output sides accordingly, it can either behave stroke-magnifying or force-magnifying. Thus, as an example, a system with negative and one with positive transmission ratio are realized and characterized with respect to their force and their stroke behavior.
In recent years, dielectric elastomers (DEs) have found novel applications in the field of soft robotics, where compliant and compact actuators with high energy densities are needed. Rolled DEs can be effectively used to achieve muscle-like actuators for soft robots, eliminating the need for external motors while providing at the same time a lightweight structure with self-sensing capabilities. In this paper, we propose a large deformation, energy-based model for rolled DEs which permits to describe the actuator behavior in a lumped-parameter fashion. The model is intended for control and self-sensing applications. After presenting the model equations, a parameter identification is performed and discussed based on experimental data.
In this work we present a new concept for scalable and tightly rolled dielectric elastomer actuators (DEA). The proposed solution is motivated by the need for designing soft, high energy density, and compact actuators for soft robotics and artificial muscle applications. Each rolled DEA is made starting from a 50 μm thin silicone film (Wacker Elastosil 2030) with flexible carbon-black based electrodes screen-printed on one side. Two of those printed films are first stacked and subsequently tightly rolled, leading to the final DEA design. At first, the systematic development of the rolled DEA concept is presented. Electrical and mechanical contacts are provided by off-the-shelf wire end ferrules. The roll manufacturing process is described subsequently. Finally, an experimental evaluation of mechanical and electrical characteristics of the developed DEAs is performed. Our measurements show a change of blocking force of 0.18 N under constant load conditions and we predict a stroke of 2.5% at 2 N.
Dielectric Elastomers (DEs) represent a class of soft electro-mechanical transducers, which is promising compared to conventional actuation technologies due to features such as lightweight, high energy efficiency, and low operational noise. Despite several prototypes have been proposed in the recent literature, only very few of them have been commercialized yet. To further DE technology towards real-life applications, it is of great importance to quantify the long-term performance of theses transducers in terms of electrical and mechanical fatigue under controllable environmental conditions. In order to investigate these properties, this paper introduces a modular electro-mechanical testing device that is designed in order to determine the long-term and fatigue characteristics of rectangular shaped DE actuator (DEA) membranes working under in-plane loading conditions. Each module permits to arbitrarily program mechanical stroke and applied voltage, and also enables simultaneous testing of five samples. Quantities of measurement are force and current. The modules are placed inside of a climate chamber which provides testing environments with constant temperature and humidity. To ensure uninterrupted 24/7-operation, the setup provides safety-equipment with remote control and remote monitoring. First test results are presented in this work.
Dielectric Elastomer Actuators (DEAs) represent a promising alternative technology for common small- and micro-drives, due to their lightweight, high energy density, high design flexibility, and silent operations. In order to obtain a stroke, membrane DEAs need to be preloaded with mechanical biasing elements. The use of negative stiffness mechanisms results in a relatively large stroke, in comparison with conventional biasing systems based on masses or linear springs. Centrally loaded, pre-stressed buckled beams show this negative stiffness behavior in a well-defined range. In particular, their force-displacement characteristics is highly nonlinear and depends on the beam geometry and axial pre-compression.
This paper provides a fast model-based design approach for large stroke DEA systems biased with pre-stressed and centrally loaded buckled beams. The method is based on a Finite Element model of a buckled beam, implemented in COMSOL Multiphysics®. Large deformations are considered in order to accurately design compact DEA systems with highly compressed beams. Stroke optimization is achieved by combining nonlinear beam elements with linear spring mechanisms. This method allows the calculation of the required beam geometry and pre-compression in order to achieve the desired characteristics of the preloading mechanism. The proposed methodology is validated by numerous simulations.
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