Powered exoskeleton

Powered exoskeleton
The exhibit 'future soldier', designed by the US Army

A powered exoskeleton, also known as powered armor, or exoframe, is a powered mobile machine consisting primarily of an exoskeleton-like framework worn by a person and a power supply that supplies at least part of the activation-energy for limb movement.

Powered exoskeletons are designed to assist and protect the wearer. They may be designed, for example, to assist and protect soldiers and construction workers, or to aid the survival of people in other dangerous environments. A wide medical market exists in the future of prosthetics to provide mobility assistance for aged and infirm people. Other possibilities include rescue work, such as in collapsed buildings, in which the device might allow a rescue worker to lift heavy debris, while simultaneously protecting the worker from falling rubble.

Working examples of powered exoskeletons have been constructed but are not currently widely deployed.[1] Various problems remain to be solved, including suitable power-supply. However three companies launched exoskeleton suits for people with disabilities in 2010.[2]

A fictional mech is different from a powered exoskeleton in that the mecha is typically much larger than a normal human body, and does not directly enhance the motion or strength of the physical limbs. Instead the human operator occupies a cabin or pilot's control seat inside a small portion of the larger system. Within this cabin the human may wear a small lightweight exoskeleton that serves as a haptic control interface for the much larger exterior appendages.



The first exoskeleton was co-developed by General Electric and the United States military in the 1960s, named Hardiman, which made lifting 250 pounds (110 kg) feel like lifting 10 pounds (4.5 kg). It was impractical due to its 1,500 pounds (680 kg) weight. The project was not successful. Any attempt to use the full exoskeleton resulted in a violent uncontrolled motion, and as a result it was never tested with a human inside. Further research concentrated on one arm. Although it could lift its specified load of 750 pounds (340 kg), it weighed three quarters of a ton, just over twice the liftable load. Without getting all the components to work together the practical uses for the Hardiman project were limited.[3]


A Hybrid Assistive Limb powered exoskeleton suit, currently in development.

One of the proposed main uses for an exoskeleton would be enabling a soldier to carry heavy objects (80–300 kg) while running or climbing stairs. Not only could a soldier potentially carry more weight, he could presumably wield heavier armor and weapons. Most models use a hydraulic system controlled by an on-board computer. They could be powered by an internal combustion engine, batteries or potentially fuel cells. Another area of application could be medical care, nursing in particular. Faced with the impending shortage of medical professionals and the increasing number of people in elderly care, several teams of Japanese engineers have developed exoskeletons designed to help nurses lift and carry patients.

Exoskeletons could also be applied in the area of rehabilitation of stroke or SCI patients. Such exoskeletons are sometimes also called Step Rehabilitation Robots. An exo-skeleton could reduce the number of therapists needed by allowing even the most impaired patient to be trained by one therapist, whereas several are currently needed. Also training could be more uniform, easier to analyze retrospectively and can be specifically customized for each patient. At this time there are several projects designing training aids for rehabilitation centers (LOPES exoskeleton, LOKOMAT, ALTACRO and the gait trainer, Hal 5.)

Exoskeletons could also be regarded as wearable robots: A wearable robot is a mechatronic system that is designed around the shape and function of the human body, with segments and joints corresponding to those of the person it is externally coupled with. Teleoperation and power amplification were said to be the first applications, but after recent technological advances the range of application fields is said to have widened. Increasing recognition from the scientific community means that this technology is now employed in telemanipulation, man-amplification, neuromotor control research and rehabilitation, and to assist with impaired human motor control (Wearable Robots: Biomechatronic Exoskeletons).[4]

Current Research

Los Alamos Laboratories worked on an exoskeleton project in the 1960s called Project Pitman. In 1986, an exoskeleton prototype called the LIFESUIT was created by Monty Reed, a US Army Ranger who had broken his back in a parachute accident.[5] While recovering in the hospital, he read Robert Heinlein's Starship Troopers and from Heinlein's description of Mobile Infantry Power Suits, he designed the LIFESUIT, and wrote letters to the military about his plans for the LIFESUIT. In 2001 LIFESUIT One (LSI) was built. In 2003 LS6 was able to record and play back a human gait. In 2005 LS12 was worn in a foot race known as the Saint Patrick's' Day Dash in Seattle, Washington. Monty Reed and LIFESUIT XII set the Land Speed Distance Record for walking in robot suits. LS12 completed the 3-mile race in 90 minutes. The current LIFESUIT prototype 14 can walk one mile on a full charge and lift 92 kg (200 lb) for the wearer.[citation needed]

In January 2007, Newsweek magazine reported that the Pentagon had granted development funds to The University of Texas at Dallas' nanotechnologist Ray Baughman to develop military-grade artificial myomer fibers. These electrically-contractive fibers are intended to increase the strength-to-weight ratio of movement systems in military powered armor.[6]

Current exoskeletons

  • Sarcos/Raytheon XOS Exoskeleton arms/legs. For use in the military and to "replace the wheelchair," weighs 68 kg (150 lb) and allows the wearer to lift 90 kg (200 lb) with little or no effort. Recently, the XOS 2 was unveiled, which featured more fluid movement, increase in power output and decrease in power input.[7]
  • Berkeley Bionics/Lockheed Martin HULC (Human Universal Load Carrier) legs, the primary competitor to Sarcos/Raytheon. Weighs 24 kg (53 lb) [8] and allows the user to carry up to 91 kg (200 lb) on a backpack attached to the exoskeleton independent of the user.[9]
  • Cyberdyne's HAL 5 arms/legs. Allows the wearer to lift 10 times as much as they normally could.[10]
  • Honda Exoskeleton Legs. Weighs 6.5 kg (14 lb) and features a seat for the wearer.[11]
  • M.I.T. Media Lab's Biomechatronics Group legs. Weighs 11.7 kg (26 lb).[12]
  • Rex Bionics' Rex, Robotic Exoskeleton Legs. Weighs 38 kg (84 lb). Enables wheelchair users to stand up, walk, move sideways, turn around, go up and down steps as well as walk on flat hard surfaces including ramps and slopes.[13] It is the only exoskeleton to be sold for personal use instead of renting like HAL exoskeleton or testing. It costs 150,000 USD and is only sold in New Zealand; the price is expected to drop once demand increases. The FDA has yet to approve it for sale in the US.
  • Activelink Co Ltd's PowerLoader Robot. Currently with its PLL(PowerLoader Light) version. Uses Mechanical Feedback and Force Sensors to power the user's legs motion.(PowerLoader Light)

Limitations and design issues

Engineers of powered exoskeletons face a number of large technological challenges to build a suit that is capable of quick and agile movements, yet is also safe to operate without extensive training.

Power supply

One of the largest problems facing designers of powered exoskeletons is the power supply. There are currently few power sources of sufficient energy density to sustain a full-body powered exoskeleton for more than a few minutes. Most research designs are tethered to a much larger separate power source. For a powered exoskeleton that will not need to be used in completely standalone situations such as a battlefield soldier, this limitation may be acceptable, and the suit may be designed to be used with a permanent power umbilical.

Strong but lightweight skeleton

Initial exoskeleton experiments are commonly done using inexpensive and easy to mold materials such as steel and aluminum. However steel is heavy and the powered exoskeleton must work harder to overcome its own weight in order to assist the wearer, reducing efficiency. Aluminum is lightweight but also a brittle metal; it would be unacceptable for the exoskeleton to fail catastrophically in a high-load condition by "folding up" on itself and injuring the wearer.

As the design moves past the initial exploratory steps, the engineers move to progressively more expensive and strong but lightweight materials such as titanium, and use more complex component construction methods, such as molded carbon-fiber plates.

Strong but lightweight actuators

The powerful but lightweight design issues are also true of the joint actuators. Standard hydraulic cylinders are powerful and capable of being precise, but they are also heavy due to the fluid-filled hoses and actuator cylinders, and the fluid has the potential to leak onto the user. Pneumatics are generally too unpredictable for precise movement since the compressed gas is springy, and the length of travel will vary with the gas compression and the reactive forces pushing against the actuator.

Generally electronic servomotors are more efficient and power-dense, utilizing high-gauss permanent magnets and step-down gearing to provide high torque and responsive movement in a small package. Geared servomotors can also utilize electronic braking to hold in a steady position while consuming minimal power.

Joint flexibility

Flexibility is another design issue. Several human joints such as the hips and shoulders are ball and socket joints, with the center of rotation inside the body. It is difficult for an exoskeleton to exactly match the motions of this ball joint using a series of external single-axis hinge points, limiting flexibility of the wearer.

A separate exterior ball joint can be used alongside the shoulder or hip, but this then forms a series of parallel rods in combination with the wearer's bones. As the external ball joint is rotated through its range of motion, the positional length of the knee/elbow joint will lengthen and shorten, causing joint misalignment with the wearer's body. This slip in suit alignment with the wearer can be permitted, or the suit limbs can be designed to lengthen and shorten under power assist as the wearer moves, to keep the knee/elbow joints in alignment.

A partial solution for more accurate free-axis movement is a hollow spherical ball joint that encloses the human joint, with the human joint as the center of rotation for the hollow sphere. Rotation around this joint may still be limited unless the spherical joint is composed of several plates that can either fan out or stack up onto themselves as the human ball joint moves through its full range of motion.

Spinal flexibility is another challenge since the spine is effectively a stack of limited-motion ball joints. There is no simple combination of external single-axis hinges that can easily match the full range of motion of the human spine. A chain of external ball joints behind the spine can perform a close approximation, though it is again the parallel-bar length problem. Leaning forward from the waist, the suit shoulder joints would press down into the wearer's body. Leaning back from the waist, the suit shoulder joints would lift up off the wearer's body. Again, this alignment slop with the wearer's body can be permitted, or the suit can be designed to rapidly lengthen or shorten the exoskeleton spine under power assist as the wearer moves.

Power control and modulation

Control and modulation of excessive and unwanted movement is a third large problem. It is not enough to build a simple single-speed assist motor, with forward/hold/reverse position controls and no on-board computer control. Such a mechanism can be too fast for the user's desired motion, with the assisted motion overshooting the desired position.

If the wearer's body is enclosed with simple contact surfaces that trigger suit motion, the overshoot can result the wearer's body lagging behind the suit limb position, resulting in contact with a position sensor to move the exoskeleton in the opposite direction. This lagging of the wearer's body can lead to an uncontrolled high-speed oscillatory motion, and a powerful assist mechanism can batter or injure the operator unless shut down remotely.

A single-speed assist mechanism which is slowed down to prevent oscillation is then restrictive on the agility of the wearer. Sudden unexpected movements such as tripping or being pushed over requires fast precise movements to recover and prevent falling over, but a slow assist mechanism may simply collapse and injure the user inside.

Fast and accurate assistive positioning is typically done using a range of speeds controlled using computer position sensing of both the exoskeleton and the wearer, so that the assistive motion only moves as fast or as far as the motion of the wearer and does not overshoot or undershoot. This may involve rapidly accelerating and decelerating the motion of the suit to match the wearer, so that their limbs slightly press against the interior of the suit and then it moves out of the way to match the wearer's motion. The computer control also needs to be able to detect unwanted oscillatory motions and shut down in a safe manner if damage to the overall system occurs.

Detection of unsafe/invalid motions

A fourth issue is detection and prevention of invalid or unsafe motions. It would be unacceptable for an exoskeleton to be able to move in a manner that exceeds the range of motion of the human body and tear muscle ligaments. This problem can be partially solved using designed limits on hinge motion, such as not allowing the knee or elbow joints to flex backwards onto themselves.

However, the wearer of a powered exoskeleton can additionally damage themselves or the suit by moving the hinge joints through a series of combined and otherwise valid movements which together cause the suit to collide with itself or the wearer.

A powered exoskeleton would need to be able to computationally track limb positions and limit movement so that the wearer does not casually injure themselves through unintended assistive motions, such as when coughing, sneezing, when startled, or if experiencing a sudden uncontrolled seizure or muscle spasm.

Pinching and joint fouling

An exoskeleton is typically constructed of very strong and hard materials, while the human body is much softer than the alloys and hard plastics used in the exoskeleton. An exoskeleton typically cannot be worn directly in contact with bare skin due to the potential for skin pinching where the exoskeleton plates and servos slide across each other. Instead the wearer may be enclosed in a heavy fabric suit to protect them from joint pinch hazards.

The exoskeleton joints themselves are also prone to environmental fouling from sand and grit, and may need protection from the elements to keep operating effectively. A traditional way of handling this is with seals and gaskets around rotating parts, but can also be accomplished by enclosing the exoskeleton mechanics in a tough fabric suit separate from the user, which functions as a protective "skin" for the exoskeleton. This enclosing suit around the exoskeleton can also protect the wearer from pinch hazards.

Fictional powered exoskeletons

Iron Man, wearing his characteristic armor.

Powered armor has appeared in a wide variety of fiction, beginning with E. E. Smith's Lensman series in 1937. Since then, it has featured in science fiction movies and literature, comic books, video games, and tabletop role-playing games. One of the most famous early versions was Robert A. Heinlein's 1959 novel Starship Troopers, which can be seen as spawning the entire sub-genre concept of military "powered armor."[14][15]

In addition to heightened strength and protection provided by the exoskeleton, other popular features include internal life support for hostile environments, protection from environmental hazards such as radiation and vacuum, weapons targeting systems, firearms affixed directly to the suit itself, and transportation mechanisms that allow the wearer to fly, make giant leaps, or speed by on ground.

In some portrayals of powered armor, the suit is not much larger than a human. These depictions can be described as a battlesuit with mechanical and electronic mechanisms designed to augment the wearer's abilities. Other power armors are portrayed as being much larger, more like a bipedal vehicle the size of a tank or much larger. These latter are frequently termed Mecha, from the Japanese “メカ” (meka), an adaptation of the English “mechanical”. The line between mecha and power armor is necessarily vague. The usual distinction is that powered armor is form-fitting and worn; mecha have cockpits and are driven,[16] or that powered exoskeletons augment the user's natural abilities, whilst mechas replace them entirely. However, the line between the two can be difficult to determine at times, especially considering that force feedback systems are often included for delicate maneuvers. Even in a larger mecha meant to be driven like a walking tank rather than worn, a realistic control system would have to be either cybernetic or form-fitting[citation needed]: In the BattleTech universe, a cybernetic system is necessary to provide a sense of balance.

Another variation is Bio-Armour, which produces similar strength with organic technology (e.g. Peter F. Hamilton's novel Fallen Dragon, Jim Shooter's X-O Manowar comic book, and the Bio Booster Armor Guyver Japanese manga series). Another example is the Nanosuit worn by Prophet and Alcatraz in the Crysis series, which augments the wearer's speed, strength and stealth, but does not look like traditional powered armor and is powered by advanced nanotechnology.

Most fictional power armors carry an on-board, self-sufficient power source. Masamune Shirow's Landmates in Appleseed used simple internal combustion engines installed into the thigh assembly of the armor. The "hardsuits" of Bubblegum Crisis 2040 have a battery the size of an American football between their shoulderblades, though the underlying technology is never described. More fantastic power sources have been introduced, for example, in the Halo series the Master Chief's MJOLNIR armor is powered by miniaturized fusion power reactors. The Power Armor in the Fallout series, which is usually worn by the Brotherhood of Steel, a techno-religious group, is also described as being fueled by fusion power cells. In Privateer Press' Iron Kingdoms setting, a steam boiler powers pneumatics, which ultimately power the suit through triggers the wearer operates with his limbs. Similarly, in Final Fantasy: The Spirits Within, the suits are powered by single-celled organisms cultured in Ovo Packs while in the "Metroid" series Samus Aran's armour is alien in design and origin and unknown as to how it functions. The HEV suit in the Half-Life series contains small, portable armor batteries to charge up the suit. The Nanosuits from the Crysis series are designed with nano systems. They are powered with fusion energy batteries that almost instantly recharge after drainage and various other systems that collect usable energy from other sources like the sun and ambient radiation.

Super-powered armor suits (super-suits) also appear in fiction. Super-suits have fantastic abilities and powers and are generally unique or very rare compared to "basic" powered armor (for example, Booster Gold's suit which does not even look like powered armor). Super-suits tend to be used in settings with superheroes, such as Iron Man.

Many variations of exoskeletons can be found in science fiction and gaming (e.g. Warhammer 40,000). It was first popularized in Robert A. Heinlein's 1959 novel Starship Troopers where powered armor was used by the Mobile Infantry. Powered armor also is a central feature in the science fiction novels The Forever War by Joe Haldeman, Armor by John Steakley and Dominant Species by Michael E. Marks.

While a realistic visual depiction of powered armor had long been a challenge for practical (live actor in a suit) filming, advances in computer animation have opened the door for several powered armor-centric movies including the film Iron Man, its sequel, and G.I. Joe: The Rise of Cobra. Science fiction video games such as Metroid, Crysis, Fallout, Halo, Warhammer 40,000, Vanquish and StarCraft focus on elaborate representations of powered armor. Several cartoons and Japanese animation have also depicted similar concepts for powered exoskeletons such as ground troops in Exosquad (American series) and Appleseed (Japanese series). In the game Shadow Complex, the character finds the Omega XOS-7 armor, a prototype powered exoskeleton. Powered exoskeletons called AMP Suits also feature prominently in the film Avatar.

While these technologies are clearly over the horizon in terms of current machine and material science, DARPA is actively pursuing a multi-million dollar program "Concepts of Operations for Exoskeletons for Human Performance Augmentation (EHPA)" to develop them.[17]

See also


  1. ^ "BLEEX Project". http://bleex.me.berkeley.edu/bleex.htm. Retrieved 2008-10-15. 
  2. ^ "Exoskeleton Suits For Wheelchair Users". http://www.newdisability.com/exoskeletonsuit.htm. Retrieved 2010-09-04. 
  3. ^ Exoskeleton
  4. ^ Pons, J. L.. "Wearable Robots: Biomechatronic Exoskeletons". http://eu.wiley.com/WileyCDA/WileyTitle/productCd-0470512946.html. Retrieved 2008-02-10. 
  5. ^ TheyShallWalk.org
  6. ^ Spiegel.de
  7. ^ Building the Real Iron Man
  8. ^ http://www.engadget.com/2010/07/21/hulc-exo-skeleton-ready-for-testing-set-to-hit-the-ground-runni
  9. ^ Lockheed Unleashes 'HULC' Super-Strength Gear
  10. ^ "Real-Life Iron Man: A Robotic Suit That Magnifies Human Strength", April 30, 2008, by Larry Greenemeier, Scientific American
  11. ^ "Trouble walking? Try Honda's new exoskeleton legs", November 10, 2008 by Larry Greenemeier, Scientific American.
  12. ^ "The Future of Exoskeletons: Lighter Loads, Limbs and More" by Larry Greenemeier, Scientific American, September 21, 2007
  13. ^ "Exoskeleton could benefit troops with spinal injuries" August 8, 2010 by Seth Robson, Stars and Stripes (newspaper)
  14. ^ Erik Sofge (April 8, 2010). "A History of Iron Men: Science Fiction's 5 Most Iconic Exoskeletons". Popular mechanics. http://www.popularmechanics.com/technology/digital/fact-vs-fiction/SciFi-most-iconic-exoskeletons. 
  15. ^ Noah Shachtman (December 12, 2004). "Exoskeleton Strength". The New York Times. http://select.nytimes.com/gst/abstract.html?res=FB0D11FF38550C718DDDAB0994DC404482. 
  16. ^ Ramsay, David (2005-02-09). "Armored Fighting Suit". TrooperPX.com. http://www.trooperpx.com/AFS/AFS00.html. Retrieved 2007-09-26. 
  17. ^ Concepts of Operations for Exoskeletons for Human Performance Augmentation (EHPA) IAC.dtic.mil

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