Serge R. Lafontaine

Artificial muscle technology: physical principles and naval prospects

The increasing understanding of the advantages offered by fish and insect-like locomotion is creating a demand for muscle-like materials capable of mimicking natures mechanisms. Actuator materials that employ voltage, field, light, or temperature driven dimensional changes to produce forces and displacements are suggesting new approaches to propulsion and maneuverability. Fundamental properties of these new materials are presented, and examples of potential undersea applications are examined in order to assist those involved in device design and in actuator research to evaluate the current status and the developing potential of these artificial muscle technologies. Technologies described are based on newly explored materials developed over the past decade, and also on older materials whose properties are not widely known. The materials are dielectric elastomers, ferroelectric polymers, liquid crystal elastomers, thermal and ferroelectric shape memory alloys, ionic polymer/metal composites, conducting polymers, and carbon nanotubes. Relative merits and challenges associated with the artificial muscle technologies are elucidated in two case studies. A summary table provides a quick guide to all technologies that are discussed.

A teleoperated microsurgical robot and associated virtual environment for eye surgery

We have developed a prototype teleoperated microsurgical robot (MSR-1) and associated virtual environment for eye surgery. Bidirectional pathways relay visual, auditory, and mechanical information between the MSR-1 master and slave. The surgeon wears a helmet (visual master) that is used to control the orientation of a stereo camera system (visual slave) observing the surgery. Images from the stereo camera system are relayed back to the helmet (or adjacent screen) where they are viewed by the surgeon. In each hand the surgeon holds a pseudotool (a shaft shaped like a microsurgical scalpel) that projects from the left and right limbs of a force reflecting interface (mechanical master). Movements of the left and right pseudotools cause corresponding movements (scaled down by 1 to 100 times) in the microsurgical tools held by the left and right limbs of the micromotion robot (mechanical slave) that performs the surgery. Forces exerted on the left and right limbs of the slave microsurgical robot via the microtools are reflected back (after being scaled up by 1 to 100 times) to the pseudotools and hence surgeon via actuators in the left and right limbs of the mechanical master. This system enables tissue cutting forces to be felt including those that would normally be imperceptible if they were transmitted directly to the surgeons hands. The master and slave subsystems (visual, auditory, and mechanical) communicate through a computer system which serves to enhance and augment images, filter hand tremor, perform coordinate transformations, and perform safety checks. The computer system consists of master and slave computers that communicate via an optical fiber connection. As a result, the MSR-1 master and slave may be located at different sites, which permits remote robotic microsurgery to become a reality. MSR-1 is being used as an experimental testbed for studying the effects of feedforward and feedback delays on remote surgery and is used in research on enhancing the accuracy and dexterity of microsurgeons by creating mechanical and visual telepresence.

Fast reversible NiTi fibers for use in microrobotics

The authors report the experimentally determined characteristics of NiTi fibers which have been modified using a preparation procedure in which the fibers were subjected to brief very large current pulses during forced stretching. The modified fibers contract and relax fast enough to be of use in microrobotics. The modified fibers generate a maximum extrapolated stress of 230 MN/m/sup 2/ and yield a peak measured power/mass approaching 50 kW/kg. The theory of a micro-actuator incorporating the modified fibers is presented.<<ETX>>

Ophthalmic microsurgical robot and associated virtual environment

An ophthalmic virtual environment has been developed as part of a teleoperated microsurgical robot built to perform surgery on the eye. The virtual environment is unique in that it incorporates a detailed continuum model of the anatomical structures of the eye, its mechanics and optical properties, together with a less detailed geometric-mechanical model of the face. In addition to providing a realistic visual display of the eye being operated on, the virtual environment simulates tissue properties during manipulation and cutting and the forces involved are determined by solving a mechanical finite element model of the tissue. These forces are then fed back to the operator via a force reflecting master and so the surgeon can experience both the visual and mechanical sensations associated with performing surgery. The virtual environment can be used to enhance the images produced by the camera on the microsurgical slave robot during surgery and as a surgical simulator in which it replaces these images with computer graphics generated from the eye model.

Application of polypyrrole actuators: feasibility of variable camber foils

A decade of research into electroactive polymer actuators is leading to the exploration of applications. These technologies are not ready to compete with the internal combustion engine and electric motors in high power propulsion systems but are suitable for intermittent or aperiodic applications with moderate cycle life requirements, providing an alternative to solenoids and direct drive electric motors. Polypyrrole, an emerging actuator material, is applied to drive hydrodynamic control surfaces and in particular to change the camber of a foil. The foil is intended for use in the propeller blade of an autonomous underwater vehicle. A scaled prototype is constructed which employs polypyrrole actuators imbedded within the blade itself to vary camber. The kinematics required to generate camber change are demonstrated, with >30/spl deg/ deflections of the trailing edge being observed from both bending bilayer and linear actuator designs. Forces developed in still conditions are five times lower than the 3.5 N estimated to be required to implement variable camber. The observed 70 kJ/m/sup 3/ polypyrrole work density however is more than sufficient to produce the desired actuation from within the limited blade volume, enabling an application that is not feasible using direct drive electric motors. A key challenge with the polypyrrole actuators is to increase force without sacrificing speed of actuation.

Manipulation and dynamic mechanical testing of microscopic objects using a tele-micro-robot system

A microrobot having two high-performance parallel drive limbs which has been developed for manipulation, surgery, and dynamic mechanical testing of very small objects such as single living cells is described. The end points of each limb move in overlapping spherical workspaces of 1-mm diameter with minimum open- and closed-loop movements of 1 nm and 10 nm, respectively. The displacement bandwidth of all six microrobot axes exceeds 1 kHz for small displacements. A three-dimensional laser vision system with a resolution of 50 to 100 nm has been developed to provide the microrobot with volume images containing magnitude, phase, polarization, and spectral information. A macro version of the microrobot has been built to permit force-reflecting teleoperation of the microrobot. The telemicrorobot system permits both microscopic objects and continuum models to be felt. A high-performance parallel computer has been designed, and partially constructed, to meet the substantial computational and control requirements of the telemicrorobot system.<<ETX>>A microrobot having two high-performance parallel drive limbs has been developed for manipulation, surgery, and dynamic mechanical testing of very small objects such as single living cells. The end-points of each limb move in overlapping spherical workspaces of 1 mm diameter with minimum open- and closed-loop movements of 1 nm and 10 nm, respectively. With optimal nonlinear model-based controllers the limbs can move at up to 2 m/s relative to each other. A variety of end effectors, including ferroelectric polymer microgrippers, may be attached to the limbs to permit cell manipulation. A 3D laser vision system with resolution of 50 to 100 nm has been developed to provide the microrobot with volume images containing magnitude, phase, polarization, and special information. A macro version of the microrobot has been built to enable force-reflecting teleoperation of the microrobot. The telemicrorobot system permits both microscopic objects and continuum models to be felt. A high-performance parallel computer has been designed to meet the substantial computational and control requirements of the system.<<ETX>>

Integrating a complex electronic system in a small-scale autonomous instrumented robot: the NanoWalker project

The NanoWalker project is an attempt to explore a new approach in the development of various instruments. The idea is to build a small autonomous robot capable of nanometer range motions that will provide a standard platform for new miniaturized embedded instruments. This modular approach will allow easy expansion in instrumentation capability through the use of an arbitrary number of NanoWalkers which would perform similar or different measurement simultaneously on various samples. To do so, a fair amount of electronics must be embedded for infrared wireless communication, processing, support for the embedded instrument, and accurate control and drive capability for the piezo-actuated motion system. Miniaturization of the whole assembly is also a key characteristic to allow more robots to operate simultaneously within smaller surface areas. As such, new assembly techniques applicable to small volume production must be used to achieve the smallest possible implementation. The integration phase within the technological constraints is complicated by the fact that several factors such as the weight and weight distribution of the electronic assembly will have a direct impact on the very sensitive motion behavior of the robot. The NanoWalker is briefly described with the integration phases and the requirements that must be met by the assembly process.

Fabrication by electrodeposition: building 3D structures and polymer actuators

Electrochemical deposition has traditionally been employed to grow metal coatings (plating) and to fill molds (electroforming). However, by localizing electric field or inducing local convection on a conducting substrate it is possible to write patterns without employing masks or molds. Here we present techniques capable of depositing high aspect ratio, truly 3D structures such as columns and helical springs. Conducting polymers such as polyaniline, polyacetylene, and polypyrrole are routinely employed to fabricate batteries, capacitors, colour displays, and transistors. Here we demonstrate the electrodeposition of polypyrrole films to form bilayer actuators.

A tele-microrobot for manipulation and dynamic mechanical testing of single living cells

A high-performance parallel-drive microrobot has been developed for manipulation, surgery, and dynamic mechanical testing of single living muscle cells. The microrobot has two limbs which more in overlapping spherical workspaces of 1 mm diameter with minimum open-loop and closed-loop movements of 1 nm and 10 nm, respectively. Under nonlinear model-based control the limbs can move at up to 2 m/s relative to each other. Ferroelectric polymer microgrippers have been fabricated to facilitate cell manipulation. The microrobot has a three-dimensional laser vision system with a resolution of 50 to 100 nm. Volume images containing magnitude, phase, polarization, and spectral information can be acquired. The microrobot incorporates facilities to keep single living cells alive for long periods. A macro version of the microrobot has been built to allow force-reflecting teleoperation of the microrobot. The tele-microrobot system constitutes a mechanical microscope in which microscopic objects can be felt. The macro-interface also enables the operator to feel mechanical continuum models. A parallel computation and control computer has been designed to meet the substantial numerical requirements of the tele-microrobot system.<<ETX>>

Characterization and use of a novel optical position sensor for microposition control of a linear motor

The performance of an optical reflective position sensor is evaluated as the position feedback element in the microposition control of a linear electromagnetic motor. The open loop position sensor characteristics are first measured to determine the analog controller design parameters. The performance of the controller, evaluated using an integrated Michelson interferometer, measures the control loop bidirectional accuracy, hysteresis, long‐term stability, and position linearity. Compensation of the small nonlinearity measured required linearization of the input command signal and a practical application is demonstrated with a constant velocity scan of one of the interferometer mirrors. A final result is the submicron square wave modulation of the interferometer output with its scan mirror under closed‐loop control using feedback from the reflective position sensor.