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The MEMS, known as microrobots (or microbots) are very small machines (technically, they are electrical/mechanical devices on a micron scale).
In this video, Dr. Bruce Donald intrduces the microscopic robot dance troupe doing a Strauss waltz and explains some of the issues involved when working at such a relatively small scale.
The field of miniature robotics emphasizes mobile robots with characteristic dimensions less than 1 mm or those capable of handling micrometer size components.
Microbots have a the potential for variety of serious applications, especially where the working environment is either too small or too dangerous for human workers. Some of the first applications appear to involve repairs and/or upgrades to the brain.
Researchers face the challenge of using a very limited power supply to achieve motion. Recent advances have seen them use a small lightweight battery source (e.g., coin cell) or scavenging vibration or light energy from the surrounding environment to use as a power source.
Wireless connections (like the Wi-Fi of domestic networks) has expanded microbotic communications, allowing groups of microbots to coordinate their actions and accomplish more complex tasks.
Research by Dr. Bruce Donald, professor of computer science and biochemistry at Duke University, and his colleagues has resulted in self-organized structures composed of microbots that maneuver separately without any obvious guidance.
Each microrobot is shaped something like a spatula but with dimensions measuring in just microns, or millionths of a meter.
Donald and other Duke researchers are now working on how to use the maneuverable microrobots for the insertion of tiny, billionths-of-a-meter electrodes (nanotubes) into neural cells. The research will be supported by the Duke Institute for Brain Sciences.
Durham, NC, USA. Little things that go awry in the brain can have large consequences. What if we could insert tiny electrodes (nanotubes) into neural cells? And how could we get them there? We may be a step closer to answers with the emergence of maneuverable microrobots measured in the mere billionths-of-a-meter. Scientists at Duke University craft microscopic robots that assemble into self-organized structures to maneuver as separate entities without any obvious guidance.
Each microrobot is shaped something like a spatula but with dimensions measuring just microns, or millionths of a meter. They are almost 100 times smaller than any previous robotic designs of their kind and weigh even less.
Planar Microassembly by Parallel Actuation of MEMS Microrobots. B. R. Donald, C. Levey, and I. Paprotny. Journal of Microelectromechanical Systems, In Press. (2008). ISSN: 1057-7157. doi: 10.1109 / JMEMS.2008.xxxxxx [ Download PDF ]
The devices are formally known as microelectromechanical system (MEMS) microrobots. They are of suitable scale for Lilliputian tasks such as performing diagnostics on brain function, moving around the interiors of laboratories-on-a-chip, and inserting tiny nanotubes into neural cells.
"It's marvelous to be able to do assembly and control at this fine a resolution with such very, very tiny things," said Bruce Donald, a Duke professor of computer science and biochemistry.
In videos produced by the team, two microrobots can be seen pirouetting to the music of a Strauss waltz on a dance floor just 1 millimeter across.
In another sequence, the devices pivot in a precise fashion whenever their boom-like steering arms are drawn down to the surface by an electric charge. This response resembles the way dirt bikers turn by extending a boot heel.
New research summaries describe the group's latest accomplishment: getting five of the devices to group-maneuver in cooperation under the same control system. "Our work constitutes the first implementation of an untethered, multi-microrobotic system."
A microassembly experiment using devices from species 1,3,4 & 5. The robots initially arrange along the corners of a 1 x 0.9 mm rectangle. There are three stages: (1) devices 4 and 5 dock together to form the initial stable shape; (2) device 3 docks with the initial stable shape; (3) device 1 docks with the stable shape to form the final assembly.
Microscope image courtesy of Duke University.
Donald's team presented a report during the Hilton Head Workshop on Solid State Sensors, Actuators and Microsystems in South Carolina (1-2 June 2008) [R1]. More comprehensive details on how the scientists achieve this "microassembly" will be published later in their report for the IEEE/ASME Journal of Microelectromechanical Systems [R2].
During the early 1970s, then classified research for U.S. intelligence agencies supported early research and conceptual design of small robots. However, the underlying miniaturization support technologies were not fully developed. The core concepts of building very small robots, and benefiting from MEMS advances was publicly introduced in a seminal paper by Anita M. Flynn in 1987 [R3].
Bruce Donald has been working on various versions of the MEMS microrobots since 1992, initially at Cornell and then at Stanford and Dartmouth before coming to Duke. The first versions were arrays of microorganism-mimicking ciliary arms that could "move objects such as microchips on top of them in the same way that a singer in a rock band will crowd surf," he said. "We made 15,000 silicon cilia in a square inch."
Donald, Paprotny, Levey and others detailed the basics of the current design in the Journal of Microelectromechanical Systems A (February 2006) [R4]. Devices about 60 microns wide, 250 microns long and 10 microns high that each run off power scavenged from an electrified surface.
The microrobots can be so small because they are not encumbered by leash-like tethers attached to an external control system. Built with microchip fabrication techniques, they are each designed to respond differently to the same single "global control signal" as voltages charge and discharge on their working parts. This global control is akin to ways proteins in cells respond to chemical signals, said Donald, who also uses computer algorithms to study processes in biochemistry and biology.
Microrobots propell themselves across such surfaces in an inchworm-like fashion. They are impelled by a scratch-drive motion actuator that advances their movements in steps of 10-20 billionths of a meter, but repeated as often as 20,000 times a second.
At times, the microrobots resemble pivoting dirt bikers.
In their new reports, the team shows that five of the microrobots can be made to advance, turn and circle together in pre-planned ways when each is built with slightly different dimensions and stiffness. Following a choreography mapped out with the aid of mathematics, the microdevices ultimately assemble into group micro-huddles that could set the stage for something more elaborate.
"Initially, we wanted to build something like a car that could drive around at the microscopic scale," Donald said. "Now what we've been able to do is create the first microscopic traffic jam."
He said it took him and various colleagues from 1997 to 2002 to create a microrobot that can operate without a tether, three more years to make the devices steer under global control, and another three to independently maneuver more than one at a time. "The hard thing was designing how multiple microrobots can all work independently, even while they receive the same power and control," he said.
Donald and other Duke researchers are now thinking of trying to enlist the maneuverable microrobots to insert tiny, billionths-of-a-meter electrodes called nanotubes into neural cells. The research will be supported by the Duke Institute for Brain Sciences.
Igor Paprotny is with the Department of Computer Science, Dartmouth College (Hanover, NH), and with the Department of Computer Science, Duke University (Durham, NC), and Bruce Donald's graduate student.
Physicist Christopher Levey. C. Levey is with the Thayer School of Engineering, Dartmouth College (Hanover, NH).
[R1] Planar Microassembly by Parallel Actuation of MEMS Microrobots. B. R. Donald, C. Levey, and I. Paprotny. Journal of Microelectromechanical Systems, In Press. (2008). ISSN: 1057-7157. doi: 10.1109 / JMEMS.2008.xxxxxx
[ Download PDF ]
Abstract
We present designs, theory and the results of fabrication and testing for a novel parallel microrobotic assembly scheme using stress-engineered MEMS microrobots. The robots are 240–280 μm × 60 μm × 7–20 μm in size, and can be controlled to dock compliantly together, forming planar structures several times this size. The devices are classified into species based on the design of their steering arm actuators, and the species are further classified as independent if they can be maneuvered independently using a single, global control signal. In this work we show that microrobot species are independent if the two transition voltages of their steering arms, i.e. the voltages at which the arms are raised or lowered, form a unique pair. We present control algorithms that can be applied to groups of independent microrobot species to direct their motion from arbitrary non-deadlock configurations to desired planar microassemblies.
We present designs and fabrication for four independent microrobot species, each with a unique transition voltage. The fabricated microrobots are used to demonstrate directed assembly of five types of planar structures from two classes of initial conditions. We demonstrate an average docking accuracy of 5 μm, and use selfaligning compliant interaction between the microrobots to further align and stabilize the intermediate assemblies. The final assemblies match their target shapes on average 96%, by area.
[R2] Assembly of Planar Structures by Parallel Actuation of MEMS Microrobots. The Technical Digest of the 2008 Hilton Head Solid-State Sensors, Actuators and Microsystems Workshop, in press. 1-5 June 2008. [ Download PDF ]
[R3] Gnat Robots (and How They Will Change Robotics). Anita M. Flynn. Proceedings of the IEEE Micro Robots and Teleoperators Workshop, Hyannis, MA, November 1987.
[R4] An untethered, electrostatic, globally controllable MEMS micro-robot. Donald, B.R.; Levey, C.G.; McGray, C.D.; Paprotny, I.; Rus, D. Journal of Microelectromechanical Systems 15(1): 1-15. ISSN: 1057-7157. INSPEC: 8771667. doi: 10.1109 / JMEMS.2005.863697.
Abstract
We present an untethered, electrostatic, MEMS micro-robot, with dimensions of 60 /spl mu/m by 250 /spl mu/m by 10 /spl mu/m. The device consists of a curved, cantilevered steering arm, mounted on an untethered scratch drive actuator (USDA). These two components are fabricated monolithically from the same sheet of conductive polysilicon, and receive a common power and control signal through a capacitive coupling with an underlying electrical grid. All locations on the grid receive the same power and control signal, so that the devices can be operated without knowledge of their position on the substrate. Individual control of the component actuators provides two distinct motion gaits (forward motion and turning), which together allow full coverage of a planar workspace. These MEMS micro-robots demonstrate turning error of less than 3.7/spl deg//mm during forward motion, turn with radii as small as 176 /spl mu/m, and achieve speeds of over 200 /spl mu/m/sec with an average step size as small as 12 nm. They have been shown to operate open-loop for distances exceeding 35 cm without failure, and can be controlled through teleoperation to navigate complex paths. The devices were fabricated through a multiuser surface micromachining process, and were postprocessed to add a patterned layer of tensile chromium, which curls the steering arms upward. After sacrificial release, the devices were transferred with a vacuum microprobe to the electrical grid for testing. This grid consists of a silicon substrate coated with 13-/spl mu/m microfabricated electrodes, arranged in an interdigitated fashion with 2-/spl mu/m spaces. The electrodes are insulated by a layer of electron-beam-evaporated zirconium dioxide, so that devices placed on top of the electrodes will experience an electrostatic force in response to an applied voltage. Control waveforms are broadcast to the device through the capacitive power coupling, and are decoded by the electromechanical response of the device body. Hysteresis in the system allows on-board storage of n=2 bits of state information in response to these electrical signals. The presence of on-board state information within the device itself allows each of the two device subsystems (USDA and steering arm) to be individually addressed and controlled- . We describe this communication and control strategy and show necessary and sufficient conditions for voltage-selective actuation of all 2/sup n/ system states, both for our devices (n=2), and for the more general case (where n is larger.).
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Each microrobot is shaped something like a spatula but with dimensions measuring in just microns, or millionths of a meter. 
"It's marvelous to be able to do assembly and control at this fine a resolution with such very, very tiny things," said Bruce Donald, a Duke professor of computer science and biochemistry. 
Donald, Paprotny, Levey and others detailed the basics of the current design in the 
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