Meanwhile, empowered by artificial intelligence technology, special-purpose robots have become even more powerful. In the future, special-purpose robots will be more widely used in fields such as space exploration, military reconnaissance, and emergency rescue, better meeting the mission requirements of various sectors.
I. Definition and Classification of Special Robots
Special-purpose robots, also known as dedicated service robots, are a type of service robot. According to the International Federation of Robotics (IFR), a service robot is a semi-autonomous or fully autonomous robot (excluding production equipment) that performs tasks beneficial to humans. Service robots can be divided into two categories: dedicated service robots and household service robots. Dedicated service robots operate in special environments and are also called special-purpose robots, such as underwater robots, space exploration robots, disaster relief robots, anti-terrorism and riot control robots, military robots, agricultural robots, medical robots, and other special-purpose robots. Household service robots, on the other hand, are robots that serve humans, such as cleaning robots and rehabilitation robots.
Early research on special-purpose robots focused on the military field. Remote-controlled robots for military purposes first appeared during World War II. The German-made "Goliath" remote-controlled bomb is considered the ancestor of modern remote-controlled military robots. Robots of this period were mainly used for mine detection and removal, as well as military reconnaissance missions. With continuous technological advancements, special-purpose robots have gradually begun to be widely used in the civilian sector. For example, underwater robots can perform maintenance and reconnaissance tasks in waters inaccessible to humans, significantly improving human work efficiency.
The classification of special-purpose robots is quite complex, and different classification methods can be used based on different factors. This article classifies special-purpose robots according to the space in which they are used (land, water, air, space, and multiple spaces), and introduces and analyzes the latest research results on special-purpose robots.
II. Current Status of Research
With the development of technology and the growth of demand, the application fields of special robots continue to expand, and new types of special robots can be found on land, sea and space.
(a) Land-based robots
(1) Self-destructing reconnaissance robot
In August 2023, researchers at Seoul National University in South Korea developed a self-destructible robot that leaves no trace. Made of a flexible silicone resin, this robot releases fluoride ions when exposed to ultraviolet light, heating the material and causing it to rapidly degrade, leaving only an oily liquid. The robot is also equipped with an array of temperature sensors, strain sensors, and photodetectors. The temperature sensors and photodetectors monitor conditions to determine when to trigger the robot's self-destruction. This technology ensures that sensitive data carried by the robot during surveillance, reconnaissance, and transport missions cannot be accessed by the enemy or unauthorized personnel. Once the mission is completed or the robot is discovered by the enemy, the operator can trigger a built-in ultraviolet LED, causing the robot to self-decompose into an irreversible form in less than two hours. Furthermore, these robots can be used for search and rescue missions in dangerous areas, offering a wide range of applications.
(2) Multifunctional reconnaissance robot
In December 2023, researchers at the Military Academy of Logistics and Technical Support of General Khrulev in Russia developed a multi-functional robot capable of performing technical reconnaissance, mine clearance, casualty evacuation, drone launches, and drone charging. This lightweight unmanned platform utilizes a Kevlar fuselage and is equipped with a robotic arm, a PKT machine gun, a smoke screen system, a retractable launch platform and charging device, a location launcher, and a mine detection system. The robot's main functions include weapon and terrain reconnaissance, maintenance work, and casualty evacuation. After a drone lands on the robot, its battery is charged via magnetic contacts located at the bottom of the platform and on the drone's legs. Therefore, this invention simplifies design and improves the reliability of technically intelligent robots, providing the ability to detect mines and other explosive devices, enabling full-duplex communication, and charging drones.
(ii) Aquatic Robots
(1) Multifunctional underwater exploration robot "Jellyfish-Bot"
In April 2023, scientists at the Max Planck Institute for Intelligent Systems (MPI-IS) in Germany, inspired by jellyfish, developed a multifunctional underwater robot—Jellyfish-Bot. Jellyfish-Bot is small, energy-efficient, and almost completely silent. It uses electro-hydraulic actuators as artificial muscles, driving the robot with electric current, and also features air cushions and waterproof components for stability. This design allows the robot to swim gracefully and rapidly, its movements resembling those of a real jellyfish.
Figure 1: The multi-functional underwater exploration robot "Jellyfish-Bot"
Jellyfish-Bot has broad application potential, particularly in cleaning up marine debris. It can search for and transport debris in complex marine environments and collect fragile biological samples, such as fish eggs. Furthermore, Jellyfish-Bot operates almost silently, without negatively impacting the surrounding environment, allowing it to interact gently with aquatic species and becoming an ideal assistant for marine biological research. Jellyfish-Bot represents a revolutionary innovation in the field of underwater robotics, providing a new solution to global environmental problems such as marine plastic pollution.
(2) Mantis Shrimp-like Robot
In November 2023, researchers from Zhejiang Sci-Tech University in China and the University of Essex in the UK collaborated to develop a biomimetic robot inspired by the mantis shrimp, designed to explore and monitor confined underwater environments. The robot's structure, referencing the mantis shrimp, features a flat body and streamlined tail fork design to effectively reduce water resistance. A rigid-flexible coupling design minimizes the impact of water on the robot, improving its stability during underwater movement. The robot consists of five pairs of artificial ventral legs and a flexible body; by adjusting the movement frequency, amplitude, and phase difference of the ventral legs, a balance between speed and stability is achieved. Prototype testing showed the robot performed excellently underwater, achieving a maximum speed of 0.28 m/s and a minimum turning radius of 0.36 m, demonstrating its potential for exploration in confined and complex underwater environments. The research team plans to further optimize the robot's structure, shape, and hardware system design to achieve autonomous movement in confined underwater environments and add information acquisition equipment to achieve more precise closed-loop motion control. Future applications of this technology include marine environmental monitoring and rescue.
(III) Aerial Robots
(1) Insect-level robots capable of regaining flight function after being damaged
In March 2023, researchers at MIT developed a resilient "artificial muscle" that allows insect-sized aerial robots to effectively regain flight performance after severe damage. Experiments showed that this insect robot could still fly even after being pierced by 10 needles or having 20% of one wing clipped. Researchers used a flexible material called a "dielectric elastomer actuator" as the "artificial muscle," which converts electrical energy into mechanical energy to power the robot's wings. Crucially, this "artificial muscle" material has a self-cleaning mechanism that disconnects electrodes from minor damage areas, allowing the device to continue operating. For larger damage, researchers developed a laser repair technology that allows insect robots that would previously have to be scrapped to be put back into service. Assessments show that repaired insect robots can regain 87% of their flight capability. Researchers stated that this robot has high robustness and adaptability and can be used for various tasks, such as environmental monitoring, disaster relief, and biological observation.
(2) A "bee" robot capable of stable flight in all directions
In May 2023, researchers at Washington State University developed a bee-like robot (Bee++) capable of stable flight in all directions. Weighing only 95 milligrams and with a wingspan of 33 millimeters, the Bee++ prototype is larger than a real bee weighing about 10 milligrams, yet it fully achieves the six degrees of freedom of movement typical of flying insects. Bee++ has four wings made of carbon fiber and polyester film, along with four lightweight actuators to control them, and can fly autonomously for up to five minutes at a time, making it the world's first prototype capable of stable flight in all directions. The research team first created a lightweight, take-off-capable quadruped robot in 2019, but struggled to control its complex yaw motion. To address this, researchers drew inspiration from insects, improving the robot's physical design and inventing a new controller. They adjusted the robot's wings to flap in an inclined plane and increased the number of flaps per second from 100 to 160. This robot could be used for various applications, including artificial pollination, search and rescue in confined spaces, biological research in various environments, and environmental monitoring.
(iv) Space Robots
(1) Extraterrestrial Life Detector (EELS)
In May 2023, NASA's Jet Propulsion Laboratory (JPL) tested a snake-like robot designed for traversing extreme terrain. Called the "Exobiology Extant Life Surveyor" (EELS), the 100-kilogram, 4-meter-long robot consists of 10 identical, rotating components that use threads for propulsion, traction, and gripping. The EELS snake-like robot can autonomously map, traverse, and explore previously inaccessible destinations without real-time human intervention. One of its goals is to search for signs of life that may be hidden beneath the icy shell of Enceladus. According to available information, EELS possesses many groundbreaking and powerful capabilities, primarily in its high adaptability. EELS has already been tested in sandy, snowy, and icy environments, demonstrating remarkable adaptability. It can choose safe routes on Earth, the Moon, and beyond, including undulating sandy and icy terrain, cliffs, craters too steep for a rover, underground lava tubes, and the interior spaces of glaciers. On the other hand, the robot is highly autonomous. Due to the communication lag between Earth and deep space, EELS was designed as a robot capable of autonomously sensing its environment, calculating risks, and moving around.
(2) Lizard-like robots exploring Mars
Image: A lizard-like robot exploring Mars
In February 2023, researchers at Nanjing University of Aeronautics and Astronautics in China developed a new lizard-inspired quadruped robot to aid in Mars exploration. The robot features a flexible body structure that replicates the movements and locomotion of desert lizards, enabling it to overcome challenges such as moving on soft soil and climbing rocks. Researchers created a series of kinematic models to determine the robot's motion and evaluated them in simulations and prototype tests. The team is currently working on machine learning models to adapt the robot's movements to different terrains and plans to add a continuous power supply system.
(v) Multi-space robots
In March 2023, researchers at Carnegie Mellon University developed a new type of soft robot that can change its shape and movement under different environmental conditions, enabling rapid transfer from land to the ocean without reconfiguration.
Figure 4: A soft robot capable of adaptive movement on land and in water.
The soft robot, about the size of a mobile phone, consists of two bistable actuators and a curved actuator at each of its four corners. The bistable actuators are the key components enabling seamless switching between walking, crawling, jumping, and swimming modes. These actuators are made of 3D-printed soft rubber containing shape memory alloy springs, which contract in response to electrical current, causing the actuators to bend. On land, the four curved actuators act as legs for walking. In water, the bistable actuators change the robot's shape, positioning the curved actuators to ideally act as propellers, enabling swimming. Researchers say the soft robot is highly flexible and adaptable, making it suitable for various scenarios, such as marine rescue missions and interacting with marine animals.
III. Development Trends of Special Robots
Compared to general industrial robots and household service robots, special-purpose robots operate in more complex environments and under more complex conditions, placing higher demands on their structure and functionality. Therefore, the field of special-purpose robots will see more innovation and development in the future.
First, miniaturization. Currently, the application scenarios for robots are becoming increasingly precise, narrow, and complex. These demands are accelerating the miniaturization of special-purpose robots. Miniature robots are characterized by high flexibility and stealth, enabling them to perform tasks in confined, dangerous, or inaccessible environments. In May 2022, Tsinghua University in China developed a pipe-detecting robot capable of efficient movement within sub-centimeter-level pipes, applicable to fields such as aircraft engine pipeline maintenance. Furthermore, in military applications, miniaturized robots can infiltrate enemy positions to perform reconnaissance, surveillance, and sabotage missions; in the medical field, they can enter the human body for precise treatment and surgery. Miniaturization has become an emerging research branch in the field of special-purpose robots and is currently one of the research hotspots.
Secondly, they will become more intelligent. With the further development of artificial intelligence and autonomous system technologies, special-purpose robots will become more intelligent and autonomous, able to adapt more flexibly to various task environments. Simultaneously, technologies such as multimodal perception and collaborative control will enable special-purpose robots to play a greater role in multi-domain collaborative operations. In June 2023, Google DeepMind released the RoboCat AI model, demonstrating the enormous potential for robot self-learning and providing a new direction for robotics research. Intelligent special-purpose robots can not only perceive their environment and make decisions, but also adapt to complex and ever-changing task scenarios. By integrating technologies such as deep learning and machine learning, special-purpose robots can learn from experience, continuously improving their adaptability and intelligence.
Thirdly, biomimicry. Over millions of years of evolution, living organisms have developed highly adaptable structures and functions, which have long been a source of inspiration for researchers developing new specialized robots. By mimicking living organisms, robots can achieve greater adaptability and perform tasks in complex and uncertain environments. Biomimicry helps robots complete tasks more covertly and safely in specific environments. In July 2023, researchers at the University of California, San Diego, inspired by baby sea turtles, developed a new type of robot that can swim under sand and use its large, flipper-like forelimbs, mimicking those of a sea turtle larva, to dig itself out. This robot became the only one capable of navigating in sand up to 5 inches deep and can be used in various fields such as environmental monitoring, grain silo inspection, and disaster response.
IV. Conclusion
Thanks to advancements in artificial intelligence, bionics, and new materials, the application areas of special-purpose robots are constantly expanding, and their functions are becoming increasingly powerful. Technologies such as machine learning and deep learning enable robots to better perceive their environment, make decisions, and execute tasks. Looking to the future, special-purpose robots will possess more powerful artificial intelligence, higher autonomy, longer endurance, and broader application prospects, continuing to be a powerful tool for solving various complex tasks and challenges.
