The latest popular and promising robotics trend is miniaturization. The latest advances in bots and drones are based not on digital technology but on weight: the smaller the size of sensors, the importance of cameras, and other intelligent equipment, the better.
Microbots
Microbotics is the field of miniature robotics, particularly mobile robots with a characteristic size of less than 1 mm. The terminology can also be used for robots capable of machining micrometer-sized components.
History of the emergence of micro-robots
Microbots were born from the advent of the microcontroller in the last decade of the 20th century and the beginning of miniature mechanical systems. The earliest research and conceptual development of such small robots occurred in the early 1970s in the (then) private study for the U.S. intelligence agencies. At the time, the main goals of the research were to realize the need for organizing prisoner rescue and electronic interception missions. At the time, essential miniaturization support technologies were not fully developed, so no significant progress was made in prototype development. Advances in wireless connectivity, especially Wi-Fi, have significantly increased the communication capability of microbots and thus their capacity to coordinate with other microbots to perform more complex tasks. Indeed, many recent studies have focused on microbot communications, including a robot at Harvard University that assembles into various shapes; and microbot production at SRI International for DARPA's MicroFactory for Macro Products program, which can create lightweight, high-strength structures.
Design Features
Micro-robots are less than 1 mm in size. They differ in this respect from millirobots, smaller than 10 cm (4 inches), small robots smaller than 100 cm (39 inches), and nanorobots, at or below 1 micrometer or in a size range of 1 to 1000 nm. Because of their small size, micro-robots are potentially very cheap and can be used in large quantities (swarm robots) to explore environments that are too small or too dangerous for humans or more giant robots. Micro-robots are especially useful when searching for survivors in collapsed buildings after an earthquake or scanning through the digestive tract. They lack physical and/or computational power, but this can be compensated using groups or micro-robot swarms. The way micro-robots move depends on their purpose, and the size needed. For example, robots functioning in aqueous or other liquid environments often have movable rotating flagella. One of the main problems in moving a micro-robot is achieving this ability using a minimal power source. Micro-robots can use a small, lightweight battery source or can be powered by energy from the environment in the form of vibration. Micro-robots also use biological motors as energy sources, such as flagella, to obtain chemical energy from the surrounding fluid to power the robotic device. A common alternative to an onboard battery is to power robots using external energy. Examples include electromagnetic fields, ultrasound, and light to activate and control micro-robots. To be autonomous, a micro-robot must have:
- Sufficiently efficient sensors (micro- or nanosensors),
- energy autonomy requires efficient low-power micro-batteries or the ability to find and use an external energy source (solar, microwave, hydrogen source, biomimetic ability to extract energy from organic matter, etc.). One way to save energy is to ensure that the various micro-robot functions are activated only when needed and optimally. The rest of the time, they are put on standby, which does not prevent them from moving passively (carried by the wind, current, vehicle, etc.),
- a built-in intelligent system (individual or collective in the case of robots with additional functions working together) and/or communication that allows interaction or remote control,
- the curriculum must be complex enough to respond to the appearance of simple events and changes in the environment (stimuli) and respond to them (individually or collectively) with appropriate reactions.
Applications
Excellent prospects with micro-robots involve dangerous, painful, repetitive, or impossible tasks for humans (in small spaces, in a vacuum) or more accessible functions. Still, robots can perform them better than humans. They can also be used as industrial and technical robots (capable, for example, of making tiny parts or mechanisms, diagnosing or repairing the inside of a machine without disassembling it, inspecting piping from the inside, etc.). They are able to work in a vacuum or an environment with no air, etc. Nowadays, micro-robots have already been developed and applied in the domestic sphere (service robots), for example, robots for vacuum cleaners and games or training robots for programming.
Applications of micro-robots in health care
The year 2018 has seen significant progress in using micro-robots in health care. Researchers at the City University of Hong Kong published a study in the journal Science Robotics claiming that micro-robots can be used to diagnose diseases, administer medications, and even in surgery, all at the cellular level. Researchers have already successfully conducted trial runs, such as delivering cells to the right place in a live mouse. The potential practical application of these technologies is the delivery of beneficial substances to a specific home in the human body, which could become a new kind of non-invasive personalized medicine. Scientists have been developing even smaller robots for more precision medicine for years. The current miniaturization has dramatically helped them create medical micro-robots, the unit of measure that is no longer a millimeter but a micron. These small bots can diagnose and monitor diseases in real-time, measure blood sugar levels for diabetics, or deliver necessary drugs precisely to a target, such as a tumor. Developers have also created floating micro-robots capable of navigating through human body fluids. These bots mimic the body's natural processes; they move forward using metachronal waves, similar to the infusoria in the human body. Scientists are trying to find applications for these technologies, from treating cardiovascular disease to eye surgery. In the future, micro-robots could clean arteries of plaque and break up kidney stones. A medical robot or medical aid in the form of a micro-robot might one day be able to work in a living organism.
Application of micro-robots in extreme conditions
First, extreme conditions in robotics are dangerous for people or technical devices: high radiation background, chemically aggressive environment, strong electromagnetic fields, high pressure, and temperature. When robots perform various tasks at the scenes of natural or man-made disasters or military conflicts, the non-deterministic environment takes on special significance, where along with extreme external conditions, there is a high degree of uncertainty not only of the parameters of the environment itself but also of the operations to be performed. The resistance of robots to aggressive environmental conditions is ensured mainly by engineering and technical solutions. At the same time, the ability of robots to adequately and timely respond to unforeseen changes in ecological parameters depends primarily on the chosen control strategy, as well as the level of intelligence of the robot. Such robots must be equipped with a powerful onboard computing machine, an ample supply of onboard power resources, and, often, a significant set of working organs. Such "hoarding" leads to increased dimensions and weight of a robot, which, in turn, significantly limits the possible area of application. At the same time, among various tasks solved by extreme robotics, there are several tasks for which a small-sized robot is desirable and sometimes necessary. These include surveillance of territories and water areas under conditions of organized enemy resistance, search for victims in rubble after natural or man-made disasters, search and neutralization of explosive devices in anti-terrorist operations in dense urban settlements, and surface exploration of other planets, etc. Solving such tasks requires micro-robots with small dimensions and mass, which allows moving freely in narrow passages, remaining unnoticed by enemy radars. Such robots are characterized by lower costs of transporting the robotic complex to the place of work. However, the small size of micro-robots imposes some limitations:
- It is difficult to move in an unprepared space because relatively small protrusions and depressions can hinder the movement of the micro-robot,
- the task of moving large bodies (for example, earthquake victims or rock samples) with the help of one micro-robot is difficult. The small dimensions of a micro-robot also impose several indirect limitations:
- The small onboard energy reserve of the micro-robot,
- small size and power consumption of communication means lead to limitations of the maximum radio communication radius,
- the number of working tools available to the robot is significantly limited. All of the above limitations apply to a single micro-robot. Therefore, an obvious solution to these problems could be using a group of micro-robots capable of combining efforts to solve complex tasks. Micro-robots can help each other overcome obstacles and jointly carry out the transportation of a large body. Information exchange in a group of robots makes it possible to expand information about the environment available to each robot. At the same time, some tasks can be distributed between micro-robots and performed in parallel. For example, while some robots in a group are collecting environmental data, others are collecting soil samples. Moreover, group application of micro-robots helps reduce the risk of task failure because the damage of one or several group micro-robots in the general case (primarily in swarming and collective control strategies) does not lead to a task failure. However, it reduces the efficiency of the group. At the same time, damage to individual units of a single robot can disrupt the work it performs and attempts to duplicate the most basic functional units of the robot lead to an increase in the mass, dimensions, and cost of the robot, but do not increase the efficiency of work (even reduce it, given the large size and group).
Strategies for managing a micro-robot group
The efficiency of micro-robot groups depends mainly on the chosen control strategy. A difference is made between centralized and decentralized control strategies. In centralized control strategies, some central control device has access to information about the state of all robots in the group and the environment. The control device evaluates the current situation and makes decisions about the actions of the group's robots. The central control device may be located outside the group (e.g., on the operator's control panel) or on board one of the robots in the group. In the latter case, we speak of centralized control "with a master." Centralized control strategies give good results when the number of robots in the group is small. As the group size increases, the load on the communication channel and the computational means of the control device increase. One solution is to use hierarchical control strategies in which a group of robots is divided into subgroups, each with its leader (usually from among the group robots), and the subgroup leaders are controlled by a central control device located on board one of the robots, or, more often, outside the group. Hierarchical control strategies complicate the nature of communications between robots in the group, making severe demands on onboard communication equipment. Interference in the communication channel is highly detrimental to the group operating under centralized control strategies. In addition, the failure of a robot controlling a group or a subgroup leads to severe problems - communication with all robots under its control is lost. Decentralized robot group control strategies include collective, swarm and swarm control strategies. In a collective control strategy, each robot of a group receives information from all other robots in the group and transmits the information it has collected about the environment and its state to the communication channel so that this information is available to all other robots in the group. Thus, information exchange in a group of robots under collective control is carried out according to the "each to all" principle. Due to this, each robot can independently evaluate the current situation and decide on the necessary further actions. Collective control strategies allow the group to maintain operability in case of failure of one or several robots in the group. The load on the communication channel increases in direct proportion to the number of robots in the group. The limitation on onboard computing devices of robots also increases since they need to process the received information. Although the upper limit of permissible group size in collective control methods is, on average, higher than in centralized ways, the "scalability" of these methods leaves much to be desired. In swarm control strategies, there is no dedicated communication channel for information exchange between robots; each robot collects information about the environment independently and independently decides on its subsequent actions to contribute to the group task. The absence of communication between robots in a group under swarm control strategies allows for successfully solving only those tasks that can be easily paralleled into independent unrelated subtasks. The main advantage of swarm control strategies is scalability: the computational complexity of control tasks does not increase with increasing robot group size, allowing swarm strategies to control huge groups of micro-robots. Methods of swarm intelligence, already used for solving many practical problems, can be applied to control large groups of robots, which led to the appearance of a separate direction, the so-called swarm robotics. Each group robot communicates only with some neighboring robots falling within the visibility range limited by the range of its telecommunication devices (or artificially limited). Each robot makes its own decision about further actions based on simple local rules. The robot has access to the information about the environment that is collected on its own, as well as the information about the environment and the state of some robots in the group that was passed to it by neighboring robots. The robot transmits the data collected about the environment and its form to the communication channel. This information becomes available to those robots whose line of sight this robot enters (in the case of the same radius of view, they are the same neighboring robots). This approach gives the robots more information about their environment than in swarm control strategies. The information available concerns the area around them, i.e., is the most relevant. At the same time, scalability is preserved - increasing the group size does not increase the load on the onboard computing devices. Thus, swarm intelligence methods offer excellent opportunities to develop mass-applicable micro-robots, allowing the successful use of large groups of micro-robots. However, the achievements of swarm robotics are limited to a few experimental projects; they are still almost uncommon in practice.
Obstacles in the development of micro-robot group applications
One of the apparent obstacles to the development of swarm robotics is that multiple groups of micro-robots must serve as control objects, which in turn implies relatively inexpensive mass production of micro-robots. The progress in microelectronics, mechatronics, and nanotechnology suggests that the mass production of micro-robots will be possible and economically feasible shortly.
The second obstacle is the lack of general theory and approaches in creating and developing methods of swarm control in groups of robots. To date, much of the research has focused on using natural analogs of swarm intelligence methods to solve technical problems: ants, bees, flocks of birds and schools of fish, and immune systems have served as prototypes for various swarm intelligence methods.
Differences in the tasks and capabilities of natural and technical systems make it challenging to find and adapt natural algorithms to solve technical problems. Several types of research are devoted to creating artificial methods of swarm intelligence, initially intended to solve practical problems. Unfortunately, the lack of a unified approach complicates these studies. In fact, each new issue is solved almost "from scratch" each time. It is expected that using a suitable system to solve several tasks will significantly simplify the task of organizing swarm interaction in groups of mass-applicable micro-robots.
Small robots, significant prospects
Micro-level objects are governed by forces and laws that are very different from those at the macro level, so basic research into these phenomena seems inevitable. A significant challenge in using mobile micro-robots is achieving predictable robot behavior and controllability, including swarming behavior. In addition, micro-robots used for observations with both military and civilian applications need reliable and long-term power sources. Such applications also imply significant challenges for micro-robot design, depending on the application environment of flying, crawling, or floating micro-robots. Communication in micro-robot swarms is also a big challenge in this application. One thing is clear: While many micro-robot projects and ideas are still in their infancy, this industry is poised for enormous growth because the opportunities are plentiful. According to Energias Market Research, the cumulative compound annual growth rate for the global micro-robot market through 2024 will be 65% as various industries find applications for these technologies.