Binary Pneumatic Air Muscles (PAM) arranged in an elastically-averaged configuration can form a cost effective
solution for Magnetic Resonance Imaging (MRI) guided robotic interventions like prostate cancer biopsies and
brachytherapies. Such binary pneumatic manipulators require about 10 to 20 MRI-compatible valves to control the
pressure state of each PAM. In this perspective, this paper presents the design of a novel dielectric elastomer actuator
(DEA) driven jet-valve to control the states of the PAMs. DEAs are MRI compatible actuators that are well suited to the
simplicity and cost-effectiveness of the binary manipulation approach. The key feature of the proposed valve design is
its 2 stages configuration in which the pilot stage is moved with minimal mechanical friction by a rotary antagonistic
DEA made with acrylic polymer films. The prismatic geometry also integrates the jet nozzle within the DEA volume to
provide a compact embodiment with a reduced number of parts. The low actuation stretches enabled by the rotary
configuration minimize viscoelastic losses, and thus, maximize the frequency response of the actuator while maximizing
its reliability potential. The design space of the proposed jet valve is studied using an Ogden hyperelastic model and the
valve dynamics is predicted with a 1D Bergstrom-Boyce viscoelastic model. Altogether, the low friction of the pilot
stage and optimized DEA dynamics provide an experimental shifting time of the complete assembly in the 200-300ms
range. Results from this work suggest that the DEA driven jet valve has great potential for switching a large number of
pneumatic circuits in a MRI environment with a compact, low cost and simple embodiment.
Dielectric Elastomer Actuators (DEAs) are a promising actuation technology for mobile robotics due to their high forceto-
weight ratio, their potential for high efficiencies, and their low cost. The preliminary design of such actuators requires
a quick and precise assessment of actuator energy conversion performance. To do so, this paper proposes a simple
thermodynamic model using experimentally acquired loss factors that predict actuator mechanical work, energy
consumption, and efficiency when operating under constant voltage and constant charge modes. Mechanical and
electrical loss factors for both VHB 4905 (acrylic) and Nusil's CF19-2186 (silicone) are obtained by mapping the
performances of cone-shaped DEAs over a broad range of actuator speeds, capacitance ratios, and applied voltages.
Extensive experimental results reveal the main performance trends to follow for preliminary actuator design, which are
explained by the proposed model. For the tested conditions, the maximum experimental brake efficiencies are ~35% and
~25% for VHB and CF19-2186 respectively.
Fundamental studies of Dielectric Elastomer Actuators (DEAs) using viscoelastic materials such as VHB 4905/4910
from 3M showed significant advantages at high stretch rates. The film's viscous forces increase actuator life and the
short power-on times minimize energy losses through current leakage. This paper presents a design paradigm that
exploits these fundamental properties of DEAs called discrete actuation. Discrete actuation uses DEAs at high stretch
rates to change the states of robotic or mechatronic systems in discrete steps. Each state of the system is stable and can
be maintained without actuator power. Discrete actuation can be used in robotic and mechatronic applications such as
manipulation and locomotion. The resolution of such systems increases with the number of discrete states, 10 to 100
being sufficient for many applications. An MRI-guided needle positioning device for cancer treatments and a space
exploration robot using hopping for locomotion are presented as examples of this concept.
Dielectric Elastomer (DE) actuators have been studied extensively under laboratory conditions where they have shown promising performance. However, in practical applications, they have not achieved their full potential. Here, the results of detailed analytical and experimental studies of the failure modes and performance boundaries of DE actuators are presented. The objective is to establish fundamental design principles for DE actuators. Analytical models suggest that DE actuators made with highly viscoelastic films are capable of reliably achieving large extensions when used at high speeds (high stretch rates). Experiments show that DE actuators used in low speed applications, such as slow continuous actuation, are subject to failure at substantially lower extensions and also have lower efficiencies. This creates an important reliability/performance trade-off because, due to their viscoelastic nature, highest DE actuators forces are obtained at low speeds. Hence, DE actuator design requires careful reliability/performance trade-offs because actuator speeds and extensions for optimal performance can significantly reduce actuator life.