Modelling of dielectric elastomer actuators and application to soft robots

Abstract

A variety of materials of artificial muscles have been widely studied and applied in various fields over the past few decades. Dielectric elastomer (DE), a type of artificial muscle, is famous for its superior electromechanical properties, such as large deformation, fast response, and good flexibility, which exhibit outstanding performance among the other artificial muscles like shape memory alloys and ionic polymer-metal composites. The circular dielectric elastomer actuators (DEAs), a type of simple yet widely-adopted configuration, has been drawn great attention with considerable theoretical analyses and practical applications. The analytical model of DEAs is of great importance to precise control of both DEAs and DEAs-based robots. In this thesis, a novel analytical model of DEAs is proposed to interpret the deformation mechanism and to predict the actuation behavior. The maximum deformation and failure modes of DEAs are studied based on the proposed model. A soft robot driven by circular DEAs is developed. An analytical model is also proposed for the soft robot, and the proposed model enables the robot to track desired trajectories. We first propose an analytical model for DEAs that takes into account both the viscoelastic and inhomogeneous effects. These two factors which are closely related to intrinsic features of the DE material and characteristics of the circular configuration pose a significant impact on the performance of circular DEAs. Subsequently, the algorithm for numerical solutions of the proposed model is developed, with which the required actuation voltage for controlling the circular DEAs to track the desired deformation is proposed. A feedforward controller based on the proposed model is designed to test the accuracy and effectiveness of the theoretical analyses, which paves the way for the later research on the locomotion control of the developed robot driven by circular DEAs. In order to obtain large deformation and to avoid potential failures, failure modes of DEAs are investigated based on the proposed analytical model. A novel 3D figure consisting of multiple surfaces that represent those types of failure modes is presented to give information about the maximum deformation and possible failure modes, which provides guidelines for optimal design of the actuator configuration. Following, a soft robot driven by a circular DEA is developed to achieve the ability of trajectory tracking. In order to solve the vibration resulted from the alternate process of adhesion and release of the robot foot, the foot connectors and electro-adhesive pad are carefully designed and tested. An analytical model presenting a theoretical interpretation of the robot behavior is proposed based on the DEAs model. Not only the inherent attributes of the circular DEAs such as viscoelastic and inhomogeneous effects are considered, but also the dynamics factors such as inertia effect and static friction are well considered in the modified model for the developed soft robot. Subsequently, a locomotion control scheme is designed for the robot to achieve trajectory tracking. Experiments are then carried out to test the trajectory tracking ability of the proposed model, and the effectiveness and robustness are well verified with the experimental results.