Abstract
Dielectric elastomers (DEs) consist of highly compliant electrostatic transducers which can be operated as actuators, by converting an applied high voltage into motion, and as sensors, since capacitive changes can be related to displacement information. Due to large achievable deformation (on the order of 100%) and high flexibility, DEs appear as highly suitable for the design of soft robotic systems. An important requirement for robotic systems is the possibility of generating a multi degree-of-freedom (MDOF) actuation. By means of DE technology, a controllable motion along several directions can be made possible by combining different membrane actuators in protagonist-antagonist configurations, as well as by designing electrode patterns which allow independent activation of different sections of a single membrane. However, despite several concepts of DE soft robots have been presented in the recent literature, up to date there is still a lack of systematic studies targeted at optimizing the design of the system. To properly understand how different parameters influence the complex motion of DE soft robots, this paper presents an experimental study on how geometry scaling affects the performance of a specific MDOF actuator configuration. The system under investigation consists of two cone DE membranes rigidly connected along the outer diameter, and pre-compressed out-of-plane against each other via a rigid spacer. The electrodes of both membranes are partitioned in four sections that can be activated separately, thus allowing the desired MDOF actuation feature. Different prototypes are assembled and tested to study the influence of the inner radius as well as the length of the rigid spacer on the achievable motion range. For the first experimental study presented here, we focus our analysis on a single actuation variable, i.e., the rotation of the rigid spacer about a fixed axis. A physics-based model is then developed and validated based on the collected experimental measurements. A model-based investigation is subsequently performed, with the aim of studying the influence of the regarded parameters on the rotation angle. Finally, based on the results of the performed study, a model-based optimization of the prototype geometry is performed.
Highlights
In recent years, the idea of human-robot cooperation, in which robots support human workers by undertaking exhausting or harmful subtasks of their work, is becoming more and more relevant
The performed investigation has shown the influence of geometrical scaling on the motion behavior of the dielectric elastomers (DEs) actuator, expressed in terms of in-plane rotation angle
The maximum angle achieved with the first set of DC-DE actuator (DEA) is 2.2 degrees, corresponding to the smallest of the three radii (8.5 mm) and a start deflection of 9 mm
Summary
The idea of human-robot cooperation, in which robots support human workers by undertaking exhausting or harmful subtasks of their work, is becoming more and more relevant. A potential way of addressing this problem consists of designing soft robots in which conventional metal parts are replaced by highly compliant materials (Albu-Schaffer et al, 2008; Laschi et al, 2017) These soft materials must be able to sustain the structure of the robot, as well as to provide actuation and sensing capabilities. A viable alternative for the design of soft robots is represented by smart materials like shape memory alloys (Laschi et al, 2012; Cianchetti et al, 2015; Villoslada et al, 2015), shape memory polymers (Shen et al, 2016), or electro-active polymers (Shintake et al, 2015; Godaba et al, 2016) Among those materials, dielectric elastomers (DEs) represent a class of electro-active polymers which appear to be suitable for soft robotics applications. This is due to a unique combination of features such as large deformations, high flexibility, lightweight, low power consumption, and self-sensing (Carpi et al, 2008)
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