Geneviève Miron

Design of a MRI-compatible dielectric elastomer powered jet valve

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.

Design and Manufacturing of Embedded Pneumatic Actuators for an MRI-Compatible Prostate Cancer Binary Manipulator

Magnetic Resonance Imaging (MRI) compatible robots can assist physicians in precisely inserting biopsy needles or therapeutic instruments directly into millimeter-size tumors using MR imaging feedback. MRI systems although present a challenging environment, including high magnetic fields and limited space, making the development of MRI-compatible robots complex. This paper presents an MRI-compatible pneumatic actuation technology consisting of molded polymer structures with embedded air-muscle, operated in a binary fashion. While having good positioning accuracy, the technology presents advantages of compactness, perfect MRI-compatibility, simplicity, and low cost. Here we specifically report the design and validation of a transperineal prostate cancer manipulator prototype having 20 embedded air-muscles distributed in four star-like polymer structures. Structures are made of silicone elastomer, using lost-core injection molding. The molded compliant joints of the muscles eliminate sliding surfaces, for low motion hysteresis and good repeatability. A simple and effective two-level design method for polymer air-muscles is proposed, using a manipulator model and three muscle models: geometrical, finite elements and uniaxial analytic. Binary control of each air-muscle assures stability and accuracy with minimized costs and complexity. The manipulator is tested MRI-compatible with no effects on the signal-to-noise ratio and, with appropriate image feedback, reaches targets with repeatability and accuracy under 0.5 mm. The embedded approach reveals to be a key feature since it reduces hysteresis errors by a factor of 6.6 compared to a previous non-embedded version of the manipulator. The successful validation of this binary manipulator opens the door to a new design paradigm for low cost and highly capable pneumatic robots, specifically for the intra-MRI manipulation.© 2012 ASME

Design of a Durable Air-Muscle With Integrated Sensor for Soft Robotics

Soft robotics integrates compliant actuators and sensors that expand design possibilities beyond classic robotics based on rigid modular components. In particular, deformable elastomer-based actuators used in soft robots, such as air-muscles, offer the possibility of having large numbers of embedded degrees of freedom. However, air-muscles fatigue life and strain capability call for a tradeoff, limiting their practical use in demanding applications such as physical rehabilitation, medical robotics, and mobile robots. This paper presents the design of a durable high-strain air-muscle composed of a silicone tube and an axially elastic sleeve (radially rigid), which integrates a flexible Dielectric Elastomer (DE) position sensor. The uniformity of the sleeve, by opposition to usual braids, makes for a reinforcement without local stresses that cause membrane failure. Designed based on fatigue failure principles, this air-muscle withstands 145 000 cycles at 50 % elongation, which demonstrates its potential as a durable high-strain actuator. Performance maps of the air-muscle confirm good linearity between force, pressure and strain and demonstrate bi-directional force capability. Furthermore, the integration of a DE sensor allows for accurate position control of the air-muscle (0.17 mm), making the air-muscle/sensor unit a relevant building block for complex soft robotics systems. The all-polymer high-strain actuator/sensor unit proves to be accurate and durable as well as cost-effective, thus making it ideal for soft robotics applications requiring large numbers of actuators and integrated sensing.Copyright