MEMS microbots harness insect “know-how”

by R. Colin Johnson
Contributing Editor, MEMS Investor Journal

Microbots based on MEMS have long been sought to collect environmental samples, to search for survivors in collapsed buildings and for other reconnaissance style missions that are ill-suited for people.  Although decades in the making, one major “hang-up” for fully autonomous operation of such microbots remains – a locomotion source.  The tiny mechanisms and electrical circuitry are relatively easy to cast, but currently there are no reliable locomotion sources on such a small scale.

The National Institute of Standards and Technology (NIST) holds an annual microbot contest – the Mobile Microrobotics Challenge co-sponsored by the IEEE – but there power source for the microbots is usually externally applied by either magnetic or electric fields.  The court on which the microbots move around has embedded electrodes and coils that allow changing electric and magnetic fields to alternatively tether and release the microbot to realize locomotion – pull from the front, push from the back.  Unfortunately, if you take the microbot off the court, it can no longer move.

The Insect Cyborg Sentinels Project uses MEMS implants to create cybernetic insects – part biology and part machine – for the purposes of surveillance and reconnaissance.  MEMS implants are set during the pupa stage so that when they emerge from metamophosis as moths, they are integrated into a true cyborg.

The Defense Advanced Research Project Agency (DARPA) has solved this problem by enlisting insects to provide the power.  The concept behind DARPA’s Hybird Insect MEMS (HI-MEMS) project is to use implanted electrodes to trigger the muscles inside an insect, and thus allow an operator in Arizona to fly a moth in Bagdad, while carrying a microphone and radio transmitter for surveillance.  The trickiest part of the project is implanting the MEMS devices inside the insect while it is in the pupae stage so that when it emerges from its cocoon as a full grown moth, all the scars and injury caused by the implantation have been healed by the insect's metamorphosis process.

At the Cornell Lab for Intelligence Machine Systems, the Insect Cyborg Sentinels Project is crafting piezoelectric backpacks for these flying cyborgs that harvest enough energy from the insect's flight motions to power its sensors and radio transmitter.

For those researchers looking for ways to move their MEMS microbots without having to breed insects, look to University of Washington who recently re-purposed an insect-like walking technology to provide locomotion to untethered microbots sans the insect.

Tiny, four-sided cilia-pulsating structures that mimic the hairs that line the human windpipe, are arranged in rows along the underside of the robot.

The system does draw electricity, so either a battery or solar cell is needed, but once so powered the "centipede" locomotion system can move a platform in any direction while carrying a payload seven times its own weight -- enough for a battery, sensor and RF transmitter to send the data back.

The demonstration created by Professor Karl Bohringer at the University of Washington uses technology originally invented at Stanford University for a paper-thin actuator in a printhead and was later adapted for use in a docking mechanism for space satellites.  In its most recent incarnation, the tiny MEMS structures are providing locomotion by acting like the moving cilia on a centipede.

The researchers added paperclips to the microrobot's back to test how much weight it could carry. The robot could carry seven times its own weight.  The microrobot is about the width of a fingernail, significantly slimmer than a dime.  Wires to the center transmit power and directions.  At the front and back are an 8-by-8 grid of tiny, shuffling legs.

The demonstration microbot centipede weighed under half a gram and yet had 512 feet arranged into 128 sets of four.  The sets of four legs allowed repetitive gaits to move the robo-insect in any direction with equal ease.  The legs are operated electrically by heating a resistor for about 20 milliseconds, thereby causing two bonded polymers to expand, but one at a greater rate thereby producing a clawing foot motion.  By cycling the electrical current through the 128 sets of four adjacent feet at 30 times a second, the microbots can effectively crawl like a bug at about three feet per hour.  Funding was provided by the U.S. Defense Advanced Research Projects Agency, the National Science Foundation and General Motors Co.

Copyright 2010 MEMS Investor Journal