This review comprises a detailed survey of ongoing methodologies for soft actuators, highlighting approaches suitable for nanometer- to centimeter-scale robotic applications. Soft robots present a special design challenge in that their actuation and sensing mechanisms are often highly integrated with the robot body and overall functionality. When less than a centimeter, they belong to an even more special subcategory of robots or devices, in that they often lack on-board power, sensing, computation, and control. Soft, active materials are particularly well suited for this task, with a wide range of stimulants and a number of impressive examples, demonstrating large deformations, high motion complexities, and varied multifunctionality. Recent research includes both the development of new materials and composites, as well as novel implementations leveraging the unique properties of soft materials.

Soft Actuators for Small-Scale Robotics.

Aim—To recognise automatically the main components of the fundus on digital colour images. Methods—The main features of a fundus retinal image were defined as the optic disc, fovea, and blood vessels. Methods are described for their automatic recognition and location. 112 retinal images were preprocessed via adaptive, local, contrast enhancement. The optic discs were located by identifying the area with the highest variation in intensity of adjacent pixels. Blood vessels were identified by means of a multilayer perceptron neural net, for which the inputs were derived from a principal component analysis (PCA) of the image and edge detection of the first component of PCA. The foveas were identified using matching correlation together with characteristics typical of a fovea—for example, darkest area in the neighbourhood of the optic disc. The main components of the image were identified by an experienced ophthalmologist for comparison with computerised methods. Results—The sensitivity and specificity of the recognition of each retinal main component was as follows:99.1% and 99.1% for the optic disc; 83.3% and 91.0% for blood vessels; 80.4% and 99.1% for the fovea. Conclusions—In this study the optic disc, blood vessels, and fovea were accurately detected. The identification of the normal components of the retinal image will aid the future detection of diseases in these regions. In diabetic retinopathy, for example,an image could be analysed for retinopathy with reference to sight threatening complications such as disc neovascularisation, vascular changes, or foveal exudation. (Br J Ophthalmol 1999;83:902‐910)

https://bjo.bmj.com/content/bjophthalmol/83/8/902.full.pdf

Automated localisation of the optic disc, fovea, and retinal blood vessels from digital colour fundus images.

Reports a method to additively build three-dimensional (3-D) microelectromechanical systems (MEMS) and electrical circuitry by ink-jet printing nanoparticle metal colloids. Fabricating metallic structures from nanoparticles avoids the extreme processing conditions required for standard lithographic fabrication and molten-metal-droplet deposition. Nanoparticles typically measure 1 to 100 nm in diameter and can be sintered at plastic-compatible temperatures as low as 300/spl deg/C to form material nearly indistinguishable from the bulk material. Multiple ink-jet print heads mounted to a computer-controlled 3-axis gantry deposit the 10% by weight metal colloid ink layer-by-layer onto a heated substrate to make two-dimensional (2-D) and 3-D structures. We report a high-Q resonant inductive coil, linear and rotary electrostatic-drive motors, and in-plane and vertical electrothermal actuators. The devices, printed in minutes with a 100 /spl mu/m feature size, were made out of silver and gold material with high conductivity,and feature as many as 400 layers, insulators, 10:1 vertical aspect ratios, and etch-released mechanical structure. These results suggest a route to a desktop or large-area MEMS fabrication system characterized by many layers, low cost, and data-driven fabrication for rapid turn-around time, and represent the first use of ink-jet printing to build active MEMS.

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Ink-jet printed nanoparticle microelectromechanical systems

Design of multiphysics actuators using topology optimization - Part I: One-material structures

INTRODUCTION MEMS and NEMS A Capsule History of MEMS and NEMS Dimensional Analysis and Scaling Exercises A REFRESHER ON CONTINUUM MECHANICS Introduction The Continuum Hypothesis Heat Conduction Elasticity Linear Thermoelasticity Fluid Dynamics Electromagnetism Numerical Methods for Continuum Mechanics SMALL IS DIFFERENT The Backyard Scaling Systems Exercises THERMALLY DRIVEN SYSTEMS Introduction Thermally Driven Devices From PDE to ODE: Lumped Models Joule Heating of a Cylinder Analysis of Thermal Data Storage Exercises MODELING ELASTIC STRUCTURES Introduction Examples of Elastic Structures in MEMS/NEMS The Mass on a Spring Membranes Beams Plates The Capacitive Pressure Sensor Exercises MODELING COUPLED THERMAL-ELASTIC SYSTEMS Introduction Devices and Phenomena in Thermal-Elastic Systems Modeling Thermopneumatic Systems The Thermoelastic Rod Revisited Modeling Thermoelastic V-Beam Actuators Modeling Thermal Bimorph Actuators Modeling Bimetallic Thermal Actuators Exercises MODELING ELECTROSTATIC-ELASTIC SYSTEMS Introduction Devices Using Electrostatic Actuation The Mass-Spring Model Modeling General Electrostatic-Elastic Systems Electrostatic-Elastic Systems - Membrane Theory Electrostatic-Elastic Systems - Beam and Plate Theory Analysis of Capacitive Control Schemes Exercises MODELING MAGNETICALLY ACTUATED SYSTEMS Introduction Magnetically Driven Devices Mass-Spring Models A Simple Membrane Micropump Model A Small-Aspect Ratio Model Exercises MICROFLUIDICS Introduction Microfluidic Devices More Fluidic Scaling Modeling Squeeze Film Damping Exercises BEYOND CONTINUUM THEORY Introduction Limits of Contiuum Mechanics Devices and Systems Beyond Continuum Theory Exercises REFERENCES APPENDICES Mathematical Results Physical Constants INDEX Each chapter also contains Related Reading and Notes sections.

Modeling MEMS and NEMS

Electro-thermal (E-T) actuators have been developed to complement the capabilities of electrostatic actuators. The thermal actuators presented here can be arrayed to generate high forces. Equally significant is that the single actuators and arrays of actuators operate at voltages and currents that are directly compatible with standard microelectronics. This paper demonstrates how combinations of two or more electro-thermal actuators can be applied to a variety of basic building-block micromechanical devices: array of ten lateral actuators; array of ten vertical actuators; vertically actuated two-axis tilting mirror; corner-cube retroreflector actuated by lateral array; grippers over the die edge with flip-over wiring; rotary stepper motor; flip-up optical grating on rotary stepper motor; linear stepper motor; and a linear stepper motor for assembly of hinged structures.

Applications for surface-micromachined polysilicon thermal actuators and arrays

Provided is a movable micromirror assembly wherein a mirror is mounted on, e.g. four flexible support arms, which are mounted in turn on a center support post. The post and arms resiliently support such mirror over, e.g. four address electrodes. The micromirror device is actuated like a parallel-plate capacitor by applying an address potential to the electrodes, which draw a part or all of the mirror toward same, countered by the spring force of the proximate support arms. Motion of the micromirror can be achieved along two axes since the device can be tilted and retracted according to the varying potentials applied to each of the four electrodes and the attractive force applied in turn to various portions of the micromirror in spaced proximity therewith. The support system of the micromirror is positioned beneath the mirror so that no reflective service area is lost to these features. Accordingly individual micromirror assemblies can be placed close to each other, in side by side array, to maximize the active surface area of such array. Thus each such micromirror can be tilted on two axes to scan one or more fields of regard and also can simultaneously be retracted or elevated to a desired depth to remove phase aberrations in the incident image by discreetly lengthening or shortening the optical path of the image reflected therefrom.

Multi-motion micromirror

Microelectromechanical systems must include large-deflection actuators to create devices which can interact mechanically with their surroundings. Electrostatic actuators with large nonresonant motion require high voltages and large surface areas to produce useful forces. Large-deflection thermal actuators have been fabricated in electroplated metal processes, but the choice of materials is limited, and the high conductivity of metal means these devices need a high current to generate the required heat. Thus, there is a need for a low voltage actuator with a large nonresonant deflection which can be fabricated in integrated circuit compatible surface-micromachining processes. The device described in this paper has a simple, flexible, and reliable design which overcomes the limitations of other actuators. It is a low voltage, medium current thermal actuator which can be designed to move laterally in a controllable, nonresonant motion. Typical actuators are 200 micrometers long, 18 micrometers wide, and deflect 10 micrometers at the tip with a drive current of 5 mA at 5 volts. A wide range of layout geometries allows this type of actuator to be fabricated in any surface-micromachining process that includes a releasable, current-carrying layer. An empirical model is presented to describe the devices fabricate in a commercially available surface-micromachining process. Arrays of actuators were fabricated to test the effect of different device dimensions on maximum achievable deflection as a funciton of applied current. Actuators can be combined to produce more force and have been integrated with other micromechanical structures. Applications of these actuators include linear and rotating motors, compliant micromechanisms, latches, micro-relays, variable capacitators and tweezers.

Thermal microactuators for surface-micromachining processes

Vertically and laterally moving surface-micromachined polysilicon microelectromechanical gratings have been designed for optical switching and modulation applications. Analytical models for the gratings are developed using optical diffraction theory. Example gratings have been fabricated in the ARPA sponsored Multi-User MEMS Process (MUMPS), and test results of the fabricated gratings are shown to have good agreement with the model. The vertically moving grating achieved an 18.1 dB contrast ratio between maximum and minimum intensity of the first diffracted order with a drive voltage of only 3 V at modulation rates up to 110 kHz, making it an excellent candidate for an optical switch. The laterally moving grating is demonstrated as a switch for transferring energy between the first and second diffracted orders, achieving modulation intensities of 6.4 dB for the m = 1 and 9.0 dB for the m = 2 diffraction orders.

Polysilicon micromechanical gratings for optical modulation

Surface micromachined polycrystalline silicon thermal micro- actuators provide large deflections while requiring low drive voltages and occupying small device areas. The force provided by thermal actuators is not currently known. Therefore, force testers have been designed and fabricated. The force testers were used to measure the force of individual actuators over a range of design parameters including flexure length, hot arm width, arm separation,and actuator thickness. The force testers have also been connected to arrays of 2 to 20 actuators coupled together. Measurements of force tester deflection versus actuator drive power have been taken. The data shows that individual actuators are capable of generating greater than 4.8 micronewtons of force with less than 15 milliwatts of power. The test also show that coupling the actuators together successfully combines the force of individual actuators. These measurements allow the creation of a general set of design rules for efficient thermal actuators.© (1996) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

John H. Comtois

Papers

Applications for surface-micromachined polysilicon thermal actuators and arrays

Multi-motion micromirror

Thermal microactuators for surface-micromachining processes

Polysilicon micromechanical gratings for optical modulation

Force measurements of polysilicon thermal microactuators