Jean-Sébastien Plante

On the properties of dielectric elastomer actuators and their design implications

Dielectric elastomer actuators (DEA) 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 DEAs are codified into design principles for these actuators. Analysis shows that the performance of DEAs made with highly viscoelastic polymer films is governed by four key mechanisms: pull-in failure, dielectric strength failure, viscoelasticity and current leakage. Design maps showing the effect of these four mechanisms on performance under varying working conditions are proposed. This study shows that the viscous nature of DEA is very important in their performance/reliability trade-offs. A proper balance of performance and reliability is key to successful design of DEAs.

Manipulation in MRI devices using electrostrictive polymer actuators: with an application to reconfigurable imaging coils

MRI (magnetic resonance imaging) is a powerful medical diagnostic tool. Its value would be greatly increased if it were possible to physically manipulate objects within the MRI during imaging. However, the extraordinarily strong magnetic fields used by the MRI make conventional electromagnetic components, such as actuators and sensors, unusable. In this paper, it is shown that devices constructed using binary polymer based actuators, called electrostrictive polymer actuators (EPAM) are able to function effectively within the MRI without degrading its imaging performance. These actuators eliminate the need for conventional electromagnetic actuators and their associated electronics. The binary nature of the actuators eliminates the need for feedback sensors to control the devices motion. The basic concept called digital mechatronics is briefly summarized in this paper. Its application to a reconfigurable MRI surface-imaging coil (RMIC) is also presented. Experimental results are presented that show the EPAM RMIC is completely compatible in the MRI and can be used to enhance the diagnostic capabilities of MRI. The paper also suggests other applications of binary EPAM based actuators for use in MRI systems.

Bistable Antagonistic Dielectric Elastomer Actuators for Binary Robotics and Mechatronics

Binary systems can lead to simple and efficient robotic and mechatronic systems since such systems use a large number of simple bistable actuators to affect its state. Dielectric elastomer actuators (DEAs) are prime candidates for use in binary systems since they are simple, low cost, and lightweight. However, previously proposed bistable DEAs (flip-flop) have relatively low volumetric energy density that limits their use in practical devices. This paper investigates the potential of improving the energy density of bistable designs by employing DEAs in compact antagonistic configurations. To do so, two antagonistic configurations (linear and rotating) are designed and studied using an experimentally validated Bergstrom–Boyce viscoelastic material model. The proposed antagonistic configurations show up to ∼10× higher volumetric energy densities than flip-flop designs. This represents a significant advantage for DEA reliability, since, based on volumetric energy density, antagonist actuators require the manufacturing of significantly less film layers than flip-flop designs. This study also reveals that, in the design of antagonistic DEAs, limiting the polymer films actuation stretch minimizes viscoelastic losses and allows higher actuation speeds and power outputs for a given actuator stroke and size.

A road to practical dielectric elastomer actuators based robotics and mechatronics: discrete actuation

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 films 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.

The experimental study of a precision parallel manipulator with binary actuation: With application to MRI cancer treatment

In this paper the performance of a high-precision parallel robot manipulator with bistable actuation is experimentally evaluated. The manipulator is for performing prostate cancer biopsy and treatment within the bore of a magnetic resonance imaging (MRI) system. The analysis and simulations have shown that this bistable manipulator is able to perform well with dielectric elastomer actuators that have been shown to be compatible with the high magnetic fields of an MRI. In this work an experimental prototype system was developed and tested. The results show that it provides the precise needle placement required by the medical task.

A Concept Mission: Microbots for Large-Scale Planetary Surface and Subsurface Exploration

This paper presents a new mission concept for planetary exploration, based on the deployment of a large number of small spherical mobile robots (“microbots”) over vast areas of a planet’s surface and subsurface, including structures such as caves and near‐surface crevasses (see Figure 1). This would allow extremely large‐scale in situ analysis of terrain composition and history. This approach represents an alternative to rover and lander‐based planetary exploration, which is limited to studying small areas of a planet’s surface at a small number of sites. The proposed approach is also distinct from balloon or aerial vehicle‐based missions, in that it would allow direct in situ measurement. In the proposed mission, a large number (i.e. hundreds or thousands) of cm‐scale, sub‐kilogram microbots would be distributed over a planet’s surface by an orbital craft and would employ hopping, bouncing and rolling as a locomotion mode to reach scientifically interesting artifacts in very rugged terrain. They would be...

Mobility and Power Feasibility of a Microbot Team System for Extraterrestrial Cave Exploration

Planetary scientists are greatly interested in the caves present on the Moon and Mars, however these areas present major challenges to current space robots. A new space robotics concept, microbots, is presented and a possible reference mission to Mars is discussed. The feasibility of the mobility and power systems of the microbot are analyzed within the context of the reference mission. The results of this analysis are that the microbot system is a feasible concept for a development timeline of approximately 10 years.

On the nature of dielectric elastomer actuators and its implications for their design

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.

Soft Two-Degree-of-Freedom Dielectric Elastomer Position Sensor Exhibiting Linear Behavior

Soft robots could bring robotic systems to new horizons, by enabling safe human-machine interaction. For precise control, these soft structures require high-level position feedback that is not easily achieved through conventional one-degree-of-freedom (DOF) sensing apparatus. In this paper, a soft two-DOF dielectric elastomer (DE) sensor is specifically designed to provide accurate position feedback for a soft polymer robotic manipulator. The technology is exemplified on a soft robot intended for MRI-guided prostate interventions. DEs are chosen for their major advantages of softness, high strains, low cost, and embedded multiple-DOF sensing capability, providing excellent system integration. A geometrical model of the proposed DE sensor is developed and compared to experimental results in order to understand sensor mechanics. Using a differential measurement approach, a handmade prototype provided linear sensory behavior and 0.2 mm accuracy on two-DOF. This correlates to a 0.7% error over the sensors 30 mm × 30 mm planar range, demonstrating the outstanding potential of DE technology for accurate multiDOF position sensing.

Compliant Bistable Dielectric Elastomer Actuators for Binary Mechatronic Systems

In this paper, a new all-polymer actuation approach for binary mechatronic systems is demonstrated. The technology consists of using Dielectric Elastomer actuators in a binary fashion by coupling them with a properly designed compliant structure. Here, a bistable actuator based around the “flip-flop” concept is implemented in which two antagonistic actuators switch a compliant truss between two stable positions. This prototype shows promising performance with output forces ranging from 1 to 3.5 N and displacements of 30% of the actuator dimension.© 2005 ASME