Powered Exoskeleton
Special thanks to google, wiki
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.
History
The earliest exoskeleton-like device was a set of walking, jumping and
running assisted apparatus developed in 1890 by a Russian named Nicholas Yagin.
As a unit, the apparatus used compressed gas bags to store energy that would
assist with movements, although it was passive in operation and required human
power.[3] In
1917, US inventor Leslie C. Kelley developed what he called a pedomotor, which
operated on steam power with artificial ligaments acting in parallel to the
wearers movements.[4] With
the pedomotor, energy could be generated apart from the user.
The first true exoskeleton in the sense of being a mobile machine integrated
with human movements was co-developed by General Electric and the United States military in the 1960s. The suit was
named Hardiman, and made lifting 250 pounds (110 kg)
feel like lifting 10 pounds (4.5 kg). Powered by hydraulics and electricity, the
suit allowed the wearer to amplify their strength by a factor of 25, so that
lifting 25 pounds was as easy as lifting one pound without the suit. A feature
dubbed force feedback enabled the wearer to feel the forces and objects being
manipulated.
While the general idea sounded promising, the actual Hardiman had major
limitations.[5] It was
impractical due to its 1,500-pound (680 kg) weight. Another issue was the fact
it is a slave-master system, where the operator is in a master suit which is in
turn inside the slave suit which responds to the master and takes care of the
work load. This multiple physical layer type of operation may work fine, but
takes longer than a single physical layer. When the goal is physical
enhancement, response time matters. Its slow walking speed of 2.5 ft/s further
limited practical uses. 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.[6]
Exoskeleton being developed by
DARPA
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.[7] 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.[8]
[edit] Applications
A Hybrid
Assistive Limb powered exoskeleton suit, commercially available
in Japan.
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
Spinal cord injury 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).[9]
[edit] Current exoskeletons
[edit] Limitations and design issues
This section needs
additional citations for verification. Please help improve this article by adding citations to reliable sources. Unsourced
material may be challenged and removed. (September 2012)
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.
[edit] Power
supply
One of the largest problems facing designers of powered exoskeletons is the
power
supply.[17] There
are currently few power sources of sufficient energy density to sustain a
full-body powered exoskeleton for more than a few hours.
Non-rechargeable primary cells tend to have more energy density
and store it longer than rechargeable secondary cells, but then replacement cells must
be transported into the field for use when the primary cells are depleted, of
which may be a special and uncommon type. Rechargeable cells can be reused but
may require transporting a charging system into the field, which either must
recharge rapidly or the depleted cells need to be able to be swapped out in the
field, to be replaced with cells that have been slowly charging.[18]
Internal combustion engine power supplies offer
high energy output, but they also typically idle, or continue to operate
at a low power level sufficient to keep the engine running, when not actively in
use which continuously consumes fuel. Battery based power sources are better at
providing instantaneous and modulated power; stored chemical
energy is conserved when load requirements cease. Engines which do not idle are
possible, but require energy storage for a starting system capable of rapidly
accelerating the engine to full operating speed, and the engine must be
extremely reliable and never fail to begin running immediately.
Engines which are small and lightweight typically must operate at high speed
to extract sufficient energy from a small engine cylinder volume, which both can
be difficult to silence and induces vibrations into the overall system. Internal
combustion engines can also get extremely hot, which may require additional
weight from cooling systems or heat shielding.
Electrochemical fuel cells such as solid
oxide fuel cells (SOFC) are also being considered as a power
source since they can produce instantaneous energy like batteries and conserve
the fuel source when not needed. They can also easily be refueled in the field
with liquid fuels such as methanol. However they require high temperatures
to function; 600 °C is considered a low operating temperature for SOFCs.
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.
[edit] Strong but lightweight skeleton
(Section reference [19])
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. The aluminium alloys used are
lightweight, but fail through fatigue quickly; 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.
[edit] 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.
[edit] Joint
flexibility
Flexibility is another design issue, and which
also affects the design of unpowered hard shell space suits. 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 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.
[edit] NASA AX-5 hard shell space suit
The NASA Ames research center experimental AX-5 hard-shell
space suit (1988), had a flexibility rating of
95%, compared to what movements are possible while not wearing the suit. It is
composed of gasketed hard shell sections joined with free-rotating mechanical bearings that spin around as the person
moves.
However, the free-rotating hard sections have no limit on rotation and can
potentially move outside the bounds of joint limits. It requires high precision
manufacturing of the bearing surfaces to prevent binding, and the bearings may
jam if exposed to lunar dust.[20]
[edit] 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. (An underdamped servo typically exhibits oscillations like
this.)[21]
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. (This is known as an overdamped servo.)[21]
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 is called a
critically damped servo.)[21] 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.
[edit] Detection of unsafe/invalid motions
A fourth issue is detection and prevention of invalid or unsafe motions,
which is managed by an on-board realtime computational Self-Collision
Detection System.[22]
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.
[edit] 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.
[edit] In
fiction
This section needs
additional citations for verification. Please help improve this article by adding citations to reliable sources. Unsourced
material may be challenged and removed. (September 2012)
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."[23][24]
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,[25] 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, instead forming a bullet proof,
tight fitting artificial muscle suit.
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). Powered armor also is a
central feature in the science fiction novels The
Forever War by Joe Haldeman, Armor by John Steakley, Old Man's War by John Scalzi, 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, Metal Gear, Halo, Vanquish, StarCraft, and X-COM: UFO Defense 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 OVA).
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.[26]
A realistic and practical representation of a power-assist suit as it might
actually develop can be seen in both the 1967 spy-spoof film The
Ambushers and the 1986 sci-fi film Aliens: both films depict a female
protagonist commandeering a power-assist forklift-like utility suit (in both
films, a full-sized practical prop) as a means to fight an antagonist
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.
History
The earliest exoskeleton-like device was a set of walking, jumping and
running assisted apparatus developed in 1890 by a Russian named Nicholas Yagin.
As a unit, the apparatus used compressed gas bags to store energy that would
assist with movements, although it was passive in operation and required human
power.[3] In
1917, US inventor Leslie C. Kelley developed what he called a pedomotor, which
operated on steam power with artificial ligaments acting in parallel to the
wearers movements.[4] With
the pedomotor, energy could be generated apart from the user.
The first true exoskeleton in the sense of being a mobile machine integrated
with human movements was co-developed by General Electric and the United States military in the 1960s. The suit was
named Hardiman, and made lifting 250 pounds (110 kg)
feel like lifting 10 pounds (4.5 kg). Powered by hydraulics and electricity, the
suit allowed the wearer to amplify their strength by a factor of 25, so that
lifting 25 pounds was as easy as lifting one pound without the suit. A feature
dubbed force feedback enabled the wearer to feel the forces and objects being
manipulated.
While the general idea sounded promising, the actual Hardiman had major
limitations.[5] It was
impractical due to its 1,500-pound (680 kg) weight. Another issue was the fact
it is a slave-master system, where the operator is in a master suit which is in
turn inside the slave suit which responds to the master and takes care of the
work load. This multiple physical layer type of operation may work fine, but
takes longer than a single physical layer. When the goal is physical
enhancement, response time matters. Its slow walking speed of 2.5 ft/s further
limited practical uses. 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.[6]
Exoskeleton being developed by
DARPA
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.[7] 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.[8]
[edit] Applications
A Hybrid
Assistive Limb powered exoskeleton suit, commercially available
in Japan.
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
Spinal cord injury 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).[9]
[edit] 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.[10] - Ekso
Bionics/Lockheed Martin HULC
(Human Universal Load Carrier) legs, the primary competitor to Sarcos/Raytheon.
Weighs 24 kg (53 lb) [11] and
allows the user to carry up to 91 kg (200 lb) on a backpack attached to the
exoskeleton independent of the user.[12] - Cyberdyne's HAL
5 arms/legs. Allows the wearer to lift 10 times as much as they
normally could.[13] - Honda
Exoskeleton Legs. Weighs 6.5 kg (14 lb) and features a seat for the wearer.[14] - M.I.T. Media Lab's Biomechatronics Group legs.
Weighs 11.7 kg (26 lb).[15] - 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.[16] It is
the only exoskeleton to be sold for personal use instead of renting like HAL
exoskeleton or testing. It costs 150,000 NZD (based in New Zealand) and
international sales started 2011; the price is expected to drop once demand
increases. The FDA has yet to approve it for sale in the US as a personal
device, though it is available to rehabilitation centres. - 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. - Argo Medical Technologies
ReWalk
The ReWalk has two versions, ReWalk "I" for institutions to use for research or
for ReWalking therapy. It is designed for use under the supervision of a
healthcare professional, like a physical therapist. Many health benefits have
been reported for paraplegics who stand erect, and in robotic devices that
mechanically move their legs. These benefits and more are expected when a
patient is ReWalking. The other version is the ReWalk "P" personal unit. The
ReWalk P is intended for personal use by patients at home or in the community.
The ReWalk I is now available for sale to rehab centers in Europe and USA. It is
listed with the FDA. The ReWalk P has been submitted to the FDA, and clearance
is pending. The ReWalk P is CE marked, and can be sold in Europe when it becomes
available, which is expected in 2012. The ReWalk P will not be available for
sale in the US until it is cleared by the FDA. There are several sites in the US
that have, and will soon have the ReWalk I.
[edit] Limitations and design issues
This section needs
additional citations for verification. Please help improve this article by adding citations to reliable sources. Unsourced
material may be challenged and removed. (September 2012)
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.
[edit] Power
supply
One of the largest problems facing designers of powered exoskeletons is the
power
supply.[17] There
are currently few power sources of sufficient energy density to sustain a
full-body powered exoskeleton for more than a few hours.
Non-rechargeable primary cells tend to have more energy density
and store it longer than rechargeable secondary cells, but then replacement cells must
be transported into the field for use when the primary cells are depleted, of
which may be a special and uncommon type. Rechargeable cells can be reused but
may require transporting a charging system into the field, which either must
recharge rapidly or the depleted cells need to be able to be swapped out in the
field, to be replaced with cells that have been slowly charging.[18]
Internal combustion engine power supplies offer
high energy output, but they also typically idle, or continue to operate
at a low power level sufficient to keep the engine running, when not actively in
use which continuously consumes fuel. Battery based power sources are better at
providing instantaneous and modulated power; stored chemical
energy is conserved when load requirements cease. Engines which do not idle are
possible, but require energy storage for a starting system capable of rapidly
accelerating the engine to full operating speed, and the engine must be
extremely reliable and never fail to begin running immediately.
Engines which are small and lightweight typically must operate at high speed
to extract sufficient energy from a small engine cylinder volume, which both can
be difficult to silence and induces vibrations into the overall system. Internal
combustion engines can also get extremely hot, which may require additional
weight from cooling systems or heat shielding.
Electrochemical fuel cells such as solid
oxide fuel cells (SOFC) are also being considered as a power
source since they can produce instantaneous energy like batteries and conserve
the fuel source when not needed. They can also easily be refueled in the field
with liquid fuels such as methanol. However they require high temperatures
to function; 600 °C is considered a low operating temperature for SOFCs.
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.
[edit] Strong but lightweight skeleton
(Section reference [19])
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. The aluminium alloys used are
lightweight, but fail through fatigue quickly; 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.
[edit] 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.
[edit] Joint
flexibility
Flexibility is another design issue, and which
also affects the design of unpowered hard shell space suits. 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 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.
[edit] NASA AX-5 hard shell space suit
The NASA Ames research center experimental AX-5 hard-shell
space suit (1988), had a flexibility rating of
95%, compared to what movements are possible while not wearing the suit. It is
composed of gasketed hard shell sections joined with free-rotating mechanical bearings that spin around as the person
moves.
However, the free-rotating hard sections have no limit on rotation and can
potentially move outside the bounds of joint limits. It requires high precision
manufacturing of the bearing surfaces to prevent binding, and the bearings may
jam if exposed to lunar dust.[20]
[edit] 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. (An underdamped servo typically exhibits oscillations like
this.)[21]
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. (This is known as an overdamped servo.)[21]
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 is called a
critically damped servo.)[21] 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.
[edit] Detection of unsafe/invalid motions
A fourth issue is detection and prevention of invalid or unsafe motions,
which is managed by an on-board realtime computational Self-Collision
Detection System.[22]
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.
[edit] 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.
[edit] In
fiction
This section needs
additional citations for verification. Please help improve this article by adding citations to reliable sources. Unsourced
material may be challenged and removed. (September 2012)
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."[23][24]
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,[25] 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, instead forming a bullet proof,
tight fitting artificial muscle suit.
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). Powered armor also is a
central feature in the science fiction novels The
Forever War by Joe Haldeman, Armor by John Steakley, Old Man's War by John Scalzi, 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, Metal Gear, Halo, Vanquish, StarCraft, and X-COM: UFO Defense 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 OVA).
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.[26]
A realistic and practical representation of a power-assist suit as it might
actually develop can be seen in both the 1967 spy-spoof film The
Ambushers and the 1986 sci-fi film Aliens: both films depict a female
protagonist commandeering a power-assist forklift-like utility suit (in both
films, a full-sized practical prop) as a means to fight an antagonist