Microbotics is the field of miniature robotics, in particular mobile robots with characteristic dimensions less than 1 mm. The term can also be used for robots capable of handling micrometer size components.

Microbots were born thanks to the appearance of the microcontroller in the last decade of the 20th century, and the appearance of miniature mechanical systems on silicon (MEMS), although many microbots do not use silicon for mechanical components other than sensors. The earliest research and conceptual design of such small robots was conducted in the early 1970s in (then) classified research for U.S. intelligence agencies. Applications envisioned at that time included prisoner of war rescue assistance and electronic intercept missions. The underlying miniaturization support technologies were not fully developed at that time, so that progress in prototype development was not immediately forthcoming from this early set of calculations and concept design. As of 2008, the smallest microrobots use a Scratch Drive Actuator.

The development of wireless connections, especially Wi-Fi (i.e. in domotic networks) has greatly increased the communication capacity of microbots, and consequently their ability to coordinate with other microbots to carry out more complex tasks. Indeed, much recent research has focused on microbot communication, including a 1,024 robot swarm at Harvard University that assembles itself into various shapes; and manufacturing microbots at SRI International for DARPA’s “MicroFactory for Macro Products” program that can build lightweight, high-strength structures.

Design considerations
While the ‘micro’ prefix has been used subjectively to mean small, standardizing on length scales avoids confusion. Thus a nanorobot would have characteristic dimensions at or below 1 micrometer, or manipulate components on the 1 to 1000 nm size range. A microrobot would have characteristic dimensions less than 1 millimeter, a millirobot would have dimensions less than a cm, a minirobot would have dimensions less than 10 cm (4 in), and a small robot would have dimensions less than 100 cm (39 in).

Due to their small size, microbots are potentially very cheap, and could be used in large numbers (swarm robotics) to explore environments which are too small or too dangerous for people or larger robots. It is expected that microbots will be useful in applications such as looking for survivors in collapsed buildings after an earthquake, or crawling through the digestive tract. What microbots lack in brawn or computational power, they can make up for by using large numbers, as in swarms of microbots.

The way microrobots move around is a function of their purpose and necessary size. At submicron sizes, the physical world demands rather bizarre ways of getting around. The Reynolds number for airborne robots is close to unity; the viscous forces dominate the inertial forces, so “flying” could use the viscosity of air, rather than Bernoulli’s principle of lift. Robots moving through fluids may require rotating flagella like the motile form of E. coli. Hopping is stealthy and energy-efficient; it allows the robot to negotiate the surfaces of a variety of terrains. Pioneering calculations (Solem 1994) examined possible behaviours based on physical realities.

One of the major challenges in developing a microrobot is to achieve motion using a very limited power supply. The microrobots can use a small lightweight battery source like a coin cell or can scavenge power from the surrounding environment in the form of vibration or light energy. Microrobots are also now using biological motors as power sources, such as flagellated Serratia marcescens, to draw chemical power from the surrounding fluid to actuate the robotic device. These biorobots can be directly controlled by stimuli such as chemotaxis or galvanotaxis with several control schemes available. A popular alternative to an on-board battery is to power the robots using externally induced power. Examples include the use of electromagnetic fields, ultrasound and light to activate and control micro robots.

Size and definition
The prefix ” micro ” has been used a lot to subjectively designate small robots, but very variable sizes. A project to standardize names corresponding to size scales avoids confusion. So:

a nanorobot has dimensions equal to or less than 1 micrometer, or allows to manipulate components in the range of 1 to 1000 nm in size.
A micro-robot would have characteristic dimensions of less than 1 millimeter,
a millirobot would have dimensions less than one cm (it is measured in millimeters),
a minirobot would have dimensions less than 10 cm,
a small robot would have dimensions less than 100 cm.

Specific conditions for the development of microrobotics
The development of microbots involves better understanding and control of certain physical phenomena at play at these scales, because a micro-robot is subjected to forces that are of great importance at micrometric scales and that would not disturb an object of larger size;

Van der Waals force,
static electricity,
surface tension,
breath of air,
more exacerbated and brutal effects of solar heat or cold, condensation, etc.).

Microrobotics includes the study of manufacturing processes (micro-systems or even nano-systems, including micro- or nanoelectronics) required for very small scale elements.

The Biomimicry is a discipline that inspires microrobotics,

It must allow the robot to move and interact with its environment, for example:

Of haptics that allow the robot to adhere to a robot, and possibly to grasp objects, to assemble another microrobot, or be anchored to a substrate;
of micromotors enabling mobile elements to move along one or more degrees of freedom;
micro- gyroscopes or alternative devices performing similar functions are searched;
innovative modes of travel; For example, as gerris do, microbots can already move on the water taking advantage of the surface tension of this liquid “substrate”. We also try to mimic the suckers of the geckos, so as to allow a robot of several grams or tens of grams to walk on the ceiling or on any support (Program Geckohair Nanolab of Carnegy Mellon University). Students work on adhesion systems adapting to varying degrees of slope, allowing a suspended walk (on the ceiling, under a sheet…).

A source of inspiration for robotics is Nature itself which tested very many mechanisms and behaviors, some interested robotics. Mimicking the functioning of neural networks and nerve centers and central generators of the spinal cord of primitive animals can already imitate certain mechanisms such as walking, swimming, running, crawling. The muscle groups are replaced by servomotors, but they are animated by reproducing the movements and the rhythm of walking, swimming, crawling or running according to the pulses distributed to computer microcircuits that mimic the nervous network.

Imitation sometimes goes even further. for example:

Nanolab works to identify and reproduce some highly adhesive colloidal molecules synthesized by animals (snails, slugs, some Coleoptera can strongly but temporarily adhere to a support thanks to such molecules). It develops an instrumentation adapted to the measurement of the performances of this type of adhesive.
the nanolab has produced a small tank-shaped robot with adhesive caterpillars that can climb onto the walls by sticking to it;
Nanolab has also developed Adhesive micro-Fibers allowing a very reinforced adhesion on a non horizontal plane, but a performance that is far from being able to reproduce is the capacity of living systems to heal, feed and reproduce, capacities who also pose new ethical questions that go beyond the usual field of bioethics.
A robot inspired by the salamander evolves easily from an aquatic to terrestrial environment; A chicken may continue to run reflexively with his head cut off, showing that the spine and spinal cord contain the essential motor centers.
Robots (salamander or snake) mimic crawling 8. On this principle, Joseph Ayers (Northeastern University in Boston) has also developed robots that mimic the movements of lamprey and lobster.

Risks and limitations
One of the risks of biomimetics is that robots too much like animals are confused with their models and hunted by real predators.

The microprocessor allows the execution of computer software giving autonomy to the robot. Very low power microprocessors are needed for microbots because they have to stay light and can not carry a significant source of energy with them.

Researchers have managed to animate a robot, or more precisely to react the robot to obstacles or light through cultures of rat neurons.

Micro- or nano-sensors
They must allow the robot to situate itself (or locate it) in its environment;
These are, for example, light-reacting cells, temperature sensors, pressure sensors, wave sensors, radio antennas, and so on. even a micro- camera.

Possible uses
It is hoped that they can automatically perform tasks that are dangerous, painful, repetitive or impossible for humans (in small spaces, in a vacuum), or tasks that are simpler but that perform them better than a human being would do.

Prospectivists imagine that they can be used as

industrial and technical robot (able for example to build very small parts or mechanisms, to diagnose or repair the inside of a machine without disassembling it, to inspect a piping from the inside, etc. One imagines them possibly capable of work in a vacuum or in the absence of air, etc.)
robot vacuum cleaner or household smaller and more discreet than those that currently exist
playful robot (teaching robots to program… For the moment, they exist only in the form of toys with the image of robots, but which are not themselves) or pedagogical robots type BEAM (acronym “Aesthetic and Mechanical Electronic Biology”) are robots that are not very intelligent, without a microcontroller or embedded program of any kind; A spring or a simple elastic can be a source of mechanical energy for small experimental projects.
Medical robot or medical assistance. a micro-robot could perhaps one day operate in a living organism.
Spatial micro-probes or micro-robots to be sent into space to save the volume occupied and the take-away load in space exploration

To be autonomous, the micro-robot must have:

sufficiently efficient sensors (micro or nanosensors)
energy autonomy that requires efficient micro-batteries, low energy consumption or the ability to find and exploit an external source of energy (solar, microwave beam, hydrogen source supplying its hydrogen fuel cell, biomimetic ability to extract energy from organic matter..). One way to save energy is to ensure that the various functions of a microrobot are activated only when necessary, and optimally. The rest of the time they are put in standby, which does not possibly prevent it from moving in a passive way (carried by the wind, the current, a vehicle..)
an embedded intelligence system (individual or collective in the case of robots with complementary functions working in concert, in the manner of ants of an ant hill) and / or communication allowing interactions or remote control.
The instructional program must be sophisticated enough to respond to the occurrence of simple events and changes in the environment (stimuli) and respond to them (individually or collectively, as would be done for example by ants in an anthill) by appropriate reactions..

Microbots in literature and cinema
Various authors of science fiction and cinema use in their novels, news or films micro or even nanobots, for example in the form of micro-drones.

Source from Wikipedia