Finite Element Model for Investigating the Thermo-Electro-Mechanical Response of Inhomogeneously Deforming Dielectric Elastomer Actuators

Among the available soft active materials, Dielectric elastomers (DEs) possess the capability of achieving the large actuation strain under the application of high electric field. The material behavior of such elastomers is affected significantly by the change in temperature. This paper reports a 3-D finite element framework based on the coupled nonlinear theory of thermo-electro-elasticity for investigating the thermal effects on the electromechanical performance of inhomogeneously deforming dielectric elastomer actuators (DEAs). The material behavior of the actuator is modeled using the neo-Hookean model of hyperelasticity with temperature dependent shear modulus. An in-house computational code is developed to implement the coupled finite element framework. Firstly, the accuracy of the developed FE code is verified by simulating the temperature effects on the actuation response and pull-in instability of the benchmark homogeneously deforming planar DE actuator. Further, the influence of temperature on the electromechanical responses of complex bi-layered bending actuator and buckling pump actuator involving inhomogeneous deformation is investigated. The numerical framework and the associated inferences can find their potential use in addressing the effect of temperature in the design of electro-active polymer based actuators.

Legless soft robots capable of rapid, continuous, and steered jumping

Jumping is an important locomotion function to extend navigation range, overcome obstacles, and adapt to unstructured environments. In that sense, continuous jumping and direction adjustability can be essential properties for terrestrial robots with multimodal locomotion. However, only few soft jumping robots can achieve rapid continuous jumping and controlled turning locomotion for obstacle crossing. Here, we present an electrohydrostatically driven tethered legless soft jumping robot capable of rapid, continuous, and steered jumping based on a soft electrohydrostatic bending actuator. This 1.1 g and 6.5 cm tethered soft jumping robot is able to achieve a jumping height of 7.68 body heights and a continuous forward jumping speed of 6.01 body lengths per second. Combining two actuator units, it can achieve rapid turning with a speed of 138.4° per second. The robots are also demonstrated to be capable of skipping across a multitude of obstacles. This work provides a foundation for the application of electrohydrostatic actuation in soft robots for agile and fast multimodal locomotion.

Design and Simulation of a Flexible Bending Actuator for Solar Sail Attitude Control

This paper presents the design of a flexible bending actuator using shape memory alloy (SMA) and its integration in attitude control for solar sailing. The SMA actuator has advantages in its power-to-weight ratio and light weight. The bending mechanism and models of the actuator were designed and developed. A neural network based adaptive controller was implemented to control the non-linear nature of the SMA actuator. The actuator control modules were integrated into the solar sail attitude model with a quaternion PD controller that formed a cascade control. The feasibility and performance of the proposed actuator for attitude control were investigated and evaluated, showing that the actuator could generate 1.5 × 10−3 Nm torque which maneuvered a 1600 m2 CubeSat based solar sail by 45° in 14 h. The results demonstrate that the proposed SMA bending actuator can be effectively integrated in attitude control for solar sailing under moderate external disturbances using an appropriate controller design, indicating the potential of a lighter solar sail for future missions.

Design of sensing system for experimental modeling of soft actuator applied for finger rehabilitation

Safe interaction and inherent compliance with soft robots have motivated the evolution of soft rehabilitation robots. Among these, soft robotic gloves are known as an effective tool for stroke rehabilitation. This research proposed a pneumatically actuated soft robotic for index finger rehabilitation. The proposed system consists of a soft bending actuator and a sensing system equipped with four inertial measurement unit sensors to generate kinematic data of the index finger. The designed sensing system can estimate the range of motion (ROM) of the finger’s joints by combining angular velocity and acceleration values with the standard Kalman filter. The sensing system is evaluated regarding repeatability and reliability through static and dynamic experiments in the first step. The root mean square error attained in static and dynamic states are 2 $^\circ$ and 3 $^\circ$ , sequentially, representing an efficient function of the fusion algorithm. In the next step, experimental models have been developed to analyze and predict a soft actuator’s behavior in free and constrained states using the sensing system’s data. Thus, parametric system identification methods, artificial neural network—multilayer perceptron (ANN-MLP), and artificial neural network—radial basis function algorithms (ANN-RBF) have been compared to achieve an optimal model. The results reveal that ANN models, particularly RBF ones, can predict the actuator behavior with reasonable accuracy in the free and constrained state (<1 $^\circ$ ). Hence, the need for intricate analytical modeling and material characterization will be eliminated, and controlling the soft actuator will be more practical. Besides, it assesses the ROM and finger functionality.

Underwater Bending Actuator Based on Integrated Anisotropic Textile Materials and a Conductive Hydrogel Electrode

Electroactive polymers (EAPs), especially dielectric elastomer actuators (DEAs), belong to a very promising and emerging class of functional materials. While DEAs are mostly utilized to rely on carbon-based electrodes, there are certain shortcomings of the use of carbon electrodes in the field of soft robotics. In this work we present a fish-like bending structure to serve as possible propulsion element, completely avoiding carbon-based electrodes. The presented robot is moving under water, using a particularly tailored conductive hydrogel as inner electrode and a highly anisotropic textile material to manipulate the bending behavior of the robot. The charge separation to drive two DEAs on the outsides of the robot is provided by the conductive hydrogel while the surrounding water serves as counter electrode. To characterize the hydrogel, tensile tests and impedance spectroscopy are used as measurement methods of choice. The performance of the robot was evaluated using a digital image correlation (DIC) measurement for its bending deflections under water. The developed fish-like robot was able to perform a dynamic bending movement, based on a tri-stable actuator setup. The performed measurements underpin the sufficient characteristics for an underwater application of conductive hydrogel electrodes as well as the applicability of the robotic concept for under water actuations.

Design, modeling and evaluation of a millimeter-scale SMA bending actuator with variable length

Millimeter-scale continuum bending actuators are useful in minimally invasive surgery to allow distal visualization and manipulation outside the line of sight. This paper presents a new continuum bending actuator based on shape memory alloy (SMA) with variable bending length. It consists of two SMA wires antagonistically configured to produce bidirectional bending under Joule heating. A linearly actuated rigid tube along the longitudinal axis enables continuous bending length adjustment, thus enhancing its workspace and force range. The proposed fabrication method tackles the challenging assembly tasks of maintaining the antagonistic configuration of long SMA wires, and robust electrical and mechanical connection during actuation. A quasi-static model of the actuator based on beam model and SMA constitutive model is presented and verified. The bending actuator was evaluated comprehensively for its workspace, blocked force, and trajectory tracking capability at different bending lengths and under different cooling conditions. It is the first work that demonstrates real-time continuous bending length adjustment in SMA-based bending actuator, leading to the potential development of compact and compliant robotic end effectors with improved distal workspace and force.