Exoskeleton is a device designed to increase human muscle strength due to external skeleton. It replicates human biomechanics to scale up efforts in movements and can be integrated into a suit. Actual working models are now developed in Japan and the United States.
The first exoskeleton was co-developed by the General Electric and the United States military in the '60s, and was called Hardiman (Kong and Jeon, 2006). It could lift up to 110kg with a force applied at the lifting of 4.5 kg. However, it was impractical because of its considerable weight up to 680kg. The project was not successful. Any attempt to use the full exoskeleton ended with intense uncontrolled movement, whereby it had never been tested with a person inside. Further investigations were focused on one hand. Although it had to lift 340kg, it weighed three quarters of a ton, which was two times higher than the lifting capacity. Without getting together all the components for work, the practical application of the Hardiman project was limited. Working examples of exoskeletons were built after the Hardiman, but widespread use of such models is not yet possible.
It is also interesting to see how exoskeleton is presented today in fiction. The first concept of exoskeleton armor was described in the novel “Tom Swift and His Jet marine”, published in 1954. In the novel Andromeda by Efremov (1957), star expeditions used to move under gravity larger electromechanical "jumping skeletons" worn over suits. Characters in the novel by Robert A. Heinlein, "Starship Troopers" (1959) used armored fighting suits with integrated exoskeletons, allowing running, jumping to great heights with built rocket engines equipped with a variety of weapons and other equipment. In the novel by Stanislaw Lem "Fiasco" (1987) pilot Angus Parvis is looking for the missing group of people, which includes one of the Lem’s regular characters Pirx pilot. For searches, Parvis uses a giant humanoid exoskeleton - Diglator.
The main focus of the development is military applications of exoskeletons. Goal is the creation of armor, which will combine the firepower and protection of the tank, mobility and speed of man, and by many times increasing the strength of the person who uses the exoskeleton. Another possible area of application of exoskeletons is help to injured people and disabled, older persons, who because of their age have problems with the musculoskeletal system.
Modifications of exoskeletons, and some of their models, can provide considerable assistance to the rescuers when removing the debris of collapsed buildings. At the same time, exoskeleton can protect rescuer from falling debris. Nowadays, the biggest obstacle for the beginning of construction of full exoskeletons is the lack of appropriate sources of energy that could allow the machine to operate autonomously for a long time.
Modern soldiers are forced to bear more and more weapons, systems for protection, terrain reconnaissance and tracking enemy. At the same time, there is a growing number of computing systems, which inform the soldier of the evolving combat environment in real time. Unfortunately, to take all the necessary equipment and gear for soldier is not physically possible. After all, besides the fact that the weight of his armor is limited by his physical capability, the soldier still has to conduct active operations, easily and quickly move on the battlefield. That is why the problem of exoskeleton development becomes very topical.
Currently, another "smart" suit is being created by scientists from the Harvard University. It is expected that it will be able to help soldiers travel for long distances, while carrying on themselves rather heavy load. In the work on the creation of exoskeleton there is involved the Wyss Institute for Biologically Inspired Engineering, a division of the Harvard. Currently, the institute has received a contract from DARPA - DARPA Pentagon.
According to published information, the new suit is made of flexible and soft materials. In order to help the men to move, reducing the burden on their muscular system, there will be used the new flexible sensors that help determine the biomechanics of the body motion. Application of these sensors will eliminate the bulk and solid components, which can be found in other systems of this kind and the exoskeleton, which often significantly hold down movements of a soldier.
In addition to systems with instant response and assisting soldier during movement, as part of the overalls there will be used systems to maintain balance that will produce low-frequency vibrations that coincide with the center of gravity in the process of human movement. At the same time, the project developed by DARPA can be widely used in the civilian sphere. For example, this "smart" clothing can significantly increase the strength and endurance of older people who because of their age already restrict themselves in the movements. In addition, today it is possible to state that these technologies will be used among people suffering from disorders of the musculoskeletal system.
Today there are several developments available for consideration. The first of them is XOS 2 Exoskeleton. This costume allows the holder to carry on himself or in the hands tens of kilograms of various goods without apparent effort. Currently, the U.S. Company Raytheon is working to improve the second model of its XOS 2 exoskeleton (Perry, Rosen and Burns, 2007). Today operator in this suit during loading and transport of loads can replace three soldiers. At the same time, unlike a number of other developments, XOS 2 is capable to rapidly enough process its operator’s motion, so the person inside of the exoskeleton does not feel squeezed in extremely strong, but unhurried and slow pile of hardware. Accuracy of exoskeleton feedback allows its operator even to play with a soccer ball.
The new exoskeleton unlike XOS-1 possesses superior load-carrying capacity and has a high ratio of weight to be lifted by perceived man. Therefore, if in XOS-1 the ratio was 6 to 1, the XOS-2 has 17 to 1. Despite the fact that very little exoskeleton weighs 90 kg (10% less than its predecessor does), for human operator it does not exceed the weight of a conventional jacket. In this new design, there is used less energy – by 50% more resistant to the adverse effects of the environment.
During demonstration of its exemplary work, test engineer Rex Jameson repeatedly put and took away a special heavy-caliber artillery shells weighing 95 kg, feeling the real weight of somewhere around 5.5 kg. All this allows people to perform heavy physical work, spending a minimum of physical effort. Rex Jameson during demonstration of the suit without problems punched with his fist a package of 4 three-centimeter boards. To repeat this trick cannot afford even the most trained martial artist.
As conceived by the Raytheon Company’s specialists, soldiers dressed in such exoskeletons, can significantly accelerate the unloading or loading of ammunition, fuel, water in the rear, and the theater of war. Opportunity to alone without the help of fellow soldiers to transfer tank shell or rocket aircraft means that more people can be used to solve other problems. The first XOS exoskeleton proved to everyone, including the creators, that this idea is workable. Taking into account the experience gained, the Raytheon Company threw all their forces to optimize its structure, starting with a system of sensors and frame and ending all actuators. As a result, in the development of its second version they managed to increase the energy efficiency of the exoskeleton.
Limbs of this suit are powered by high pressure hydraulics, but the power supply is still out of the suit. So today the real Iron Man is still tied to the stationary equipment with long hoses and cables. However, as such, this costume can be quite useful as well, and in the nearest future engineers are going to fully "decouple" the exoskeleton from a separate power source.
According to Fraser Smith, vice president of Raytheon, exoskeletons deployment is inevitable. This product is badly needed, and he considers them as a viable solution for quite a number of the current issues. The creators of this suit suggest that a large military exercise during various storage and transport operations is a negative aspect, which not only reduces the speed of work, but also is more than a risk factor and cause of injury. Proposed exoskeleton can get rid of all these problems. In the future, engineers at the U.S. Company say about development of reinforced armored version of their creation, which will be designed to break the walls and doors in rescue hostages.
Another current development is the HULC exoskeleton. At one time the company Lockheed Martin created versatile exoskeleton, called HULC (Human Universal Load Carrier). Its purpose is to facilitate the movement of fighters who operate in isolation from their main forces. In such circumstances, today's soldiers are sometimes forced to carry on themselves more than 60 kg of various goods, including ammunition, food, electronics and a large number of batteries that are designed to supply various electronic equipment (Bogue, 2009). The initial version of HULC exoskeleton was powered by a lithium-polymer battery, which actuates not only the electro-hydraulic system of the costume, but also other electronics for military use.
This exoskeleton in the nearest future will be quite possible to be met on the field of combat operations. Its basis is the two "legs" made of light, but at the same time durable titanium alloy. The role of "muscle" in this exoskeleton performs hydraulic system, and as a source of energy there is used lithium-ion batteries. The possibilities of this exoskeleton are really unique and able to impress anyone - general lifted weight can reach up to 140 kg. The only condition is that it is necessary to distribute properly the load on the machine. For example, the rear HULC frame can bear a weight of up to 100 kg, and you an additional burden can be placed on the shoulders of the suit (Zoss, Kazerooni and Chu, 2006).
One of the most important parameters of the exoskeleton is the length of its battery life. Here the company Lockheed Martin managed to reach a high enough level. Battery charge is enough for 5 hours of movement at a speed of 4 km/h. Thus, the exoskeleton allows people to make a forced march in full gear at a distance of 20 km. Today this unit is under cultivation. The main direction of the work is associated with improved suit work in extreme conditions.
According to the company Lockheed Martin, to develop a new power source for HULC robotic exoskeleton, Protonex Technology Corporation Company will be engaged. This firm will face the challenge of ensuring autonomous operation, designed for the military, for 72 hours. In order to realize such a long duration of operation, it was decided to apply fuel cell technology. It is assumed that the entire power supply system will be at the exoskeleton, and be able to serve other electronic devices of the fighter. Developing these power sources received much attention, as the existing solution with lithium-ion batteries is clearly inadequate for prolonged combat operations outside the city and available electricity.
It is worth noting that the Protonex Company has extensive experience in creating compact and lightweight fuel cell systems, which are used as mobile battery power in 100-1000 watts. The company's products are in demand in the commercial and consumer markets, as well as in the military sector. Such a solution in the form of fuel cells is necessary for autonomous anthropomorphic mechanism with an electrohydraulic drive such as HULC. Microcomputer exoskeleton detects motion of the operator and then appropriately manages the various parts of the device, which allows the flexibility to crawl, crouch and move loads with a minimum of human strength.
In the recent years, scientists are trying to develop exoskeletons that will be useful in the rehabilitation of patients and be able to return the ability to move normally. The main problem is that most exoskeletons are made of hard and inactive materials, which in itself hinder movements and inferior maneuverability of the healthy parts of the body. A team of U.S. scientists have developed a "soft" exoskeleton design that replicates the muscles, tendons and ligaments of the human body.
Orthopedic device was created through the cooperation of researchers from the Carnegie Mellon University, the Harvard University, the University of Southern California, the Massachusetts Institute of Technology (MIT) and the developer of wearable sensors BioScience. It includes flexible artificial muscles, light sensors and control software. Machine is made of soft elastic polymer.
Currently the prototype can be worn only on the lower part of a leg, wherein the biological structure in the apparatus is painstakingly reproduced. Three of its cylindrical artificial muscles correspond to the front of the shin muscles, and one of the back. Artificial tendons (steel cables) are stretched from the ends of these muscles down to the foot, and are used to move the ankle (Veneman et al., 2006).
Feedback is provided by hyperelastic strain gauges located on the top and side of the ankle. Each sensor consists of a rubber layer, comprising the microchannels filled with liquid metal alloy conductor. The shape of the channel changes when the elastic material is stretched or contracted, thereby changing the electrical resistance of the metal. When the change in resistance is registered, the software can determine the position of the ankle joint.
Mobility is ensured by flexible materials, but the flexibility is a particular problem: the device is much harder to control than the usual exoskeleton of hard materials. Therefore, the sensors should be sensitive here, and ways to control more accurate. Laboratory tests have shown that the device is able to move the ankles of subjects sufficient for normal walking in 27-degree range of motion.
Currently, scientists are trying to improve the design so that patients with the real problems of mobility were more convenient to carry the device. Furthermore, the inventors have yet to ensure the safety of the device. The slightest disruption in the device can lead to the fact that people will fall. Although the current version of the exoskeleton is intended for use by persons with impaired mobility of the foot and ankle, the developers in the future plan to use their development in other areas, for example to improve the mobility of joints of the hands.
References
Bogue, R., 2009. Exoskeletons and robotic prosthetics: a review of recent developments. Industrial Robot: An International Journal, 36(5), pp.421-427.
Kong, K., and Jeon, D., 2006. Design and control of an exoskeleton for the elderly and patients. Mechatronics, IEEE/ASME Transactions on, 11(4), pp.428-432.
Perry, J. C., Rosen, J., and Burns, S., 2007. Upper-limb powered exoskeleton design. Mechatronics, IEEE/ASME Transactions on, 12(4), pp.408-417.
Veneman, J. F., Ekkelenkamp, R., Kruidhof, R., van der Helm, F. C., and van der Kooij, H., 2006. A series elastic-and bowden-cable-based actuation system for use as torque actuator in exoskeleton-type robots. The international journal of robotics research, 25(3), pp.261-281.
Zoss, A. B., Kazerooni, H., and Chu, A., 2006. Biomechanical design of the Berkeley lower extremity exoskeleton (BLEEX). Mechatronics, IEEE/ASME Transactions on, 11(2), pp.128-138.
