CHAPTER 1 INTRODUCTION
The powered exoskeleton is essentially a wearable robot that amplifies its wearer’s strength, endurance and agility. There is an effective transfer of power
between the human and the robot. Humans and exoskeletons are in close physical interaction. A possible classification of wearable robots takes into account the function they perform in cooperation with the human actor. Thus, the following are instances of wearable robots:
Empowering robotic exoskeletons. These were originally called extenders (Kazerooni, 1990) and were defined as a class of robots that extends the strength of the human beyond its natural ability while maintaining human control of the robot. A specific and singular aspect of extenders is that the exoskeleton structure maps on to the human actor’s anatomy.
Orthotic and prosthetic robots - According to this classification, orthotic wearable robots, e.g. exoskeletons, are those that operate mechanically parallel to the human body. Its purpose is to restore lost or weak functions, whereas prosthetic wearable robots operate mechanically in series with the human body and their chief function is to substitute for lost body limbs, e.g. following an amputation.
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CHAPTER 2 HISTORY
In the early 1960s, the US Defense Department expressed interest in the development of a man-amplifier, a “powered suit of armor” which would augment soldiers’ lifting and carrying capabilities. At the same time, at Cornell Aeronautical
Laboratories work started to develop the concept of man – amplifiers amplifiers – manipulators to enhance the strength of a human operator. In later work, Cornell determined that an exoskeleton, an external structure in the shape of the human body which has far fewer degrees of freedom than a human, could accomplish most desired tasks. General Electric Co. further developed the concept of human – amplifiers amplifiers through the Hardiman project from 1966 to 1971. The Hardiman concept was more of a robotic master – slave configuration in which two overlapping exoskeletons were – slave implemented. The inner one was set to follow human motion while the outer one implemented a hydraulically powered version of the motion performed by the inner exoskeleton. All these studies found that duplicating all human motions and using master – slave systems were not practical. Additionally, difficulties in human sensing – slave and system complexity kept it from walking. Several exoskeletons were developed at the University of Belgrade in the 1960s and 1970s to aid paraplegics. Although these early devices were limited to predefined motions and had limited success, balancing algorithms developed for them are still used in many bipedal robots. “HAL” by Cyberdyne is an orthosis, connected to thighs and shanks that move a patient’s legs as a function of the EMG signals
measured from the wearer. The concept of extenders versus master/slave robots as systems exhibiting genuine information and power transmission between the two actors was coined in 1990 (Kazerooni, 1990).Efforts in the defense and military arena have continued up to the present, chiefly promoted by the US Defense Advanced Research Projects Agency (DARPA).
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CHAPTER 3 PRINCIPLE
The powered exoskeleton is based on the principle of internal force or external force systems. Which of these force interaction concepts is chosen depends chiefly on the application. On the one hand, empowering exoskeletons must be based on the concept of external force systems; empowering exoskeletons are used to multiply the force that a human wearer can withstand, and therefore the force that the environment exerts on the exoskeleton must be grounded: i.e. in external force systems the exoskeleton’s mechanical structure acts as a load-carrying device and only a small
part of the force is exerted on the wearer. The power is transmitted to an external base, be it fixed or portable with the operator. The only power transmission is between the human limbs and the robot as a means of implementing control inputs and/or force feedback.
Fig 3.1. Schematic representation of internal force(left) and external force(right) exoskeleton
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On the other hand, orthotic exoskeletons, i.e. exoskeletons for functional compensation of human limbs, work on the internal force principle. In this instance of a wearable robot, the force and power are transmitted by means of the exoskeleton between segments of the human limb. Orthotic exoskeletons are applicable whenever there is weakness or loss of human limb function. In such a scenario, the exoskeleton complements or replaces the function of the human musculoskeletal system. In internal force exoskeletons, the force is non-grounded; force is applied only between the exoskeleton and the limb. In all, the design consists in using biomechanical data (sEMG) or the contact force between the extender and human from the limbs to determine the configuration of the actuators and actions that are applied at joint level.
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CHAPTER 4 EXOSKELETON DESIGN ARCHITECTURE
Fundamental to designing a lower extremity exoskeleton is selecting the overall structural architecture of the limbs. Many different layouts of joints and limbs can combine to form a functioning body part e.g. a leg, but any architecture generally falls into one of a few categories:
Fig 4.1. Anthropomorphic exoskeleton
Fig 4.2. Non-anthropomorphic
exoskeleton
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4.1. Anthropomorphic Architecture
Anthropomorphic architectures attempt to exactly match the human limb. By kinematically matching the human degrees of freedom and limb lengths, the exoskeleton’s leg position exactly follows the human leg’s position. This greatly
simplifies many design issues. For example, one does not have to be concerned with human/exoskeleton collisions. However, one major difficulty is that the joints in human legs cannot be duplicated using the common state of technology in designing joints. For instance, the human knee does not exhibit a pure rotation and duplicating all its kinematics will result in a complicated (and perhaps non-robust) mechanical system. Another major point of concern in this architecture is that the exoskeleton limb lengths must be equal to the human limb lengths. This means that for different operators to wear the exoskeleton, almost all the exoskeleton limbs must be highly adjustable. In general, the anthropomorphic architecture is erroneously regarded to be the preferred choice because it allows the exoskeleton to attach to the operator wherever desired.
4.2. Non-anthropomorphic Architecture
While not as common in exoskeleton designs, many non-anthropomorphic devices are highly successful, such as bicycles. Non-anthropomorphic architectures open up a wide range of possibilities for the limb design as long as the exoskeleton never interferes or limits the operator. Often it is difficult to develop architecture significantly different from a human leg that can still move the foot through all the necessary maneuvers (e.g. turning tight corners and deep squats). Safety issues become more prominent with non-anthropomorphic designs since the exoskeleton must be prevented from forcing the operator into a configuration they cannot reach. Another problem with this architecture is that the exoskeleton legs may collide with the human legs or external objects more often because the exoskeleton joints are not located in the same place as the human joints.
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4.3. Pseudo-anthropomorphic Architecture
For maximum safety and minimum collisions with the environment, architecture is chosen that is almost anthropomorphic. This means, for example the leg is kinematically similar to a human’s, but does not include all of the degrees of
freedom of human legs. Additionally, the degrees of freedom are all purely rotary joints. Since the human and exoskeleton leg kinematics are not exactly the same (merely similar), the human and exoskeleton are only rigidly connected at the extremities (feet and torso). Any other rigid connections would lead to large forces imposed on the operator due to the kinematic differences. However, compliant connections, allowing relative motion between the human and exoskeleton, are tolerable. Another benefit of not exactly matching the human kinematics is that it is easier to size for various operators.
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CHAPTER 5 EXOSKELETON COMPONENTS
Any biomechatronic system must have the following types of components: 5.1. Biosensors
Biosensors detect the user's "intentions." Depending upon the impairment and type of device, this information can come from the user's nervous and/or muscle system. The biosensor relates this information to a controller located either externally or inside the device itself. Biosensors also feedback from the limb and actuator (such as the limb position and applied force) and relate this information to the controller or the user's nervous/muscle system. Biosensors detect electrical activity such as galvanic detectors (which detect an electric current produced by chemical means on the skin).
Fig 5.1. Biosensor
5.2. Mechanical sensors
Mechanical sensors measure information about the device (such as limb position, applied force and load) and relate to the biosensor and/or the controller. There are mechanical devices such as force meters and accelerometers.
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Fig 5.2. Cutaway view of LVDT
5.3. Controller
The controller interfaces the user's nerve or muscle system and the device. It relays and/or interprets intention commands from the user to the actuators of the device. It also relays and/or interprets feedback information from the mechanical and biosensors to the user. The controller also monitors and controls the movements of the bio mechatronic device.
Fig 5.3. A network architecture to monitor/control a lower limb exoskeleton
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5.4. Actuator
The actuator is an artificial muscle that produces force or movement. In selecting actuators for a particular application, a number of requirements may arise. These include power or force density, efficiency, size and weight, and cost. In general, actuators in wearable robot applications are used under dynamic operating conditions. Dynamic operation usually produces changing conditions in the amount of power flow. The actuator can be a motor with cable-drive system, pneumatic or a hydraulic system that aids or replaces the user's native muscle depending upon the device. In wearable robotics, traditional actuator technologies, e.g. pneumatic, hydraulic and electromagnetic actuators, are commonly used. Hydraulic and pneumatic actuators are known for their high force density and high force or torque characteristics, and have been used in a number of applications .
Fig 5.4. Actuator designed for thigh
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5.5. Portable storage
They could be powered by an internal combustion engine, batteries or, potentially, fuel cells. Different types of batteries are commercially available as portable energy solutions. The main issue with battery technologies is the ability to meet power and energy requirements while minimizing the weight of the energy storage device. This requirement will be a major factor in the selection of a given actuation technology and in the practical application of the WR for interaction with a human being. Battery systems range from reliable technologies, such as lead – acid, that have been proven and developed over many years, to various newer designs that are currently under development. Commercial solutions include lithium – ion, sodium – sulfur and sodium – nickel chloride.
Fig 5.5. A figure showing portable storage
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CHAPTER 6 WORKING
In these devices, the operator force on the device is sensed and amplified electronically by use of a computer to drive the device actuator. In other words, these devices extend the workers physical power by adding mechanical power to the maneuvering task. The correct amount of power to add is calculated instantaneously in the device computer. The result is that the intelligent assist device lifts a preprogrammed larger percentage of the total force of the load while the operator lifts the remaining much smaller percentage. This smaller percentage is sensed physically by the operator, so the operator has a feel of the load weight and inertia.
Fig 6.1. An Upper-Limb exoskeleton
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The working phases of a bio mechatronic exoskeleton are: 1. Data acquisition – The measurement of angular position or linear displacements of a given joint or segment using various force and pressure sensing technologies like LVDT, accelerometer, biosensors etc.
Movement and position of limbs are controlled by electrical signals traveling back and forth between the muscles and the peripheral and central nervous system. Electromyography (EMG) is the registration and interpretation of these muscle action potentials.
Surface EMG (sEMG) is produced when ions flow in/out of muscle cells. Nerve sends signal to initiate muscle contraction. This signal is acquired using a high sensitive Ag/AgCl electrode lead in wet condition attached to the skin.
More is the muscle contraction level more is the amplitude of the sEMG signal. This signal is transduced into electronic circuit.
Fig 6.2. A figure showing data acquisition
2. Classification – Estimating the muscle force based on the acquired signal.
Signal is amplified to take full advantage of input after filtering out the noise prior to A/D conversion.
Muscle force is then estimated from above amplified data.
The input to the robot can also be derived from the contact forces between the robot and the human.
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3. Actuation – Moving the robotic arm
The estimated force is sent via an interface circuit to the robotic arm.
In case of contact force, the contact force is measured, appropriately modified, and used as an input to the robotic arm control, in addition to being used for actual maneuvering. So that the human arm feels a scaled down version of the actual forces on the robot without a separate set of actuators.
The actuator arm moves to position corresponding to estimated force.
Fig 6.3. A figure showing actuation
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CHAPTER 7 FEATURES
Some of the features and advantages of exoskeleton are as follows:
Strength augmentation
Endurance augmentation
The system provides its pilot(i.e. wearer) the ability to carry significant payloads with minimal effort
Can operate in any type of terrain
Human provides an intelligent control system for the exoskeleton
Control algorithm ensures that the exoskeleton moves in concert with the pilot with minimal interaction force between the two
exoskeleton’s kinematic chain maps on to the human limb anatomy
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CHAPTER 8 CHALLENGES
Followings are some of the challenges for the development of wearable exoskeleton technologies that DARPA has outlined:
Structural materials - The exoskeleton will have to be made out of composite materials that are strong, lightweight and flexible.
Power source - The exoskeleton must have enough power to run for at least 24 hours before refueling.
Control - Controls for the machine must be seamless. Users must be able to function normally while wearing the device.
Actuation - The machine must be able to move smoothly so it's not too awkward for the wearer. Actuators must be quiet and efficient.
Biomechanics - Exoskeletons must be able to shift from side to side and front to back, just as a person would move in battle. Developers will have to design the frame with human-like joints.
Energy consumption - Energy consumption is a critical issue for wearable robots. It must be optimized. For example, developments of robot capable of walking down a gentle slope without any control or actuation.
Degrees of freedom – The Degree of freedom must be optimized so as to reduce kinematic redundancy that occurs when more degrees of freedom (DoFs) are available than are required to perform a given task.
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CHAPTER 9 APPLICATION
In defense establishment where Soldiers could carry heavy loads across rugged terrain without fatigue. Similarly, military medics could carry injured victims off the battlefield.
Fire and rescue workers could carry heavy gear or supplies great distances where vehicles could not travel.
In industries for material handling purposes.
For construction worker for their safety.
In space applications
They can provide improved motor function that better mimic normal biological function to impaired individuals. They can also be used to train individuals with impaired motor function
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CHAPTER 10 FUTURE SCOPES
“Future is Machine”
Superhuman strength has always been confined to science fiction, but advances in human-performance augmentation systems could give a person the ability to lift hundreds of pounds using the effort they would usually use to lift a fraction of that weight. With this added strength, soldiers will be able to mount weapons directly to the uniform system. The Future Force Warrior concept envisions the radical use of technologies such as nanotechnology, powered exoskeletons etc. to provide the infantry with significantly higher force multiplier than the opposing force. The U.S. military hopes to develop a fully realized end product sometime in 2032, incorporating research from U.C. Berkeley’s BLEEX exoskeleton project and the Massachusetts Institute of Technology's Institute for Soldier Nanotechnologies into a final design. It is clear that technology will not remain confined in the Hollywood blockbusters. We will see that impaired one will be able to walk properly. Workers in industries will work more with less fatigue and our soldiers will be more resilient and powerful than what is now.
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CHAPTER 11 CONCLUSION
Humans aren't the swiftest creatures on Earth, and most of us are limited in the amount of weight that we can pick up and carry. These weaknesses can be fatal on the battlefield, and that's why the U.S. Defense is investing $50 million to develop an exoskeleton suit for ground troops. This wearable robotic system could give soldiers the ability to run faster, carry heavier weapons and leap over large obstacles. Imagine a battalion of super soldiers that can lift hundreds of pounds as easily as lifting 10 pounds and can run twice their normal speed. Exoskeleton research and development has been ongoing for the past few years. Efforts have been hindered by a number of challenges, such as developing a system design that does not interfere with the way a wearer would normally walk and can run on a small battery-powered pack rather than fuel. M.I.T.'s research is no exception. During test runs, researchers found that although the loads on their backs were lighter, walking required more exertion, causing the wearer to use 10 percent more oxygen than if he or she was not wearing the exoskeleton. Currently, researches for the development of Exoskeletons are:
UC Berkeley/Lockheed Martin HULC legs, the primary competitor to Sarcos/Raytheon. Allows the user to carry up to 200 lbs on a backpack attached to the exoskeleton independent of the user.
Cyberdyne's HAL 5 arms/legs. Allows the wearer to lift 5 times as much as they normally could.
Honda Exoskeleton Legs. Weighs 14.3 lbs and features a seat for the wearer.
M.I.T. Media Lab's Biomechatronics Group legs. Weighs 11.7 kilograms (26 lbs).
Sarcos/Raytheon XOS Exoskeleton arms/legs. For use in the military and to "replace the wheelchair", weighs 150 lbs and allows the wearer to lift 200 lbs with little or no effort.
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In India, although the study and research on mechatronics have been here from some time, still overall progress in the biomechatronic field is way back when compared to the research work going on other organizations outside the country. Scientists and engineers should consider putting their effort in such field so that in future our country may stand at least comparable to the developed one. “A tool is but the extension of a man's hand, and a machine is
but a complex tool. He that invents a machine augments the power of man and the well- being of mankind.” - Henry Ward Beecher
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REFERENCES
A. Zoss, Kazerooni, H, A. Chu, “ On the Biomechanical Design of the
Berkeley Lower Extremity Exoskeleton (BLEEX)”, IEEE/ASME Transactions on Mechatronics, Volume 11, Number 2, pp. 128-138, April 2006
H. Kazerooni, J. Guo, "Human Extenders," ASME J. of Dynamic Systems, Measurements, and Control, vol. 115, no. 2(B), June 1993.
Jacob, Moshe, Arcan, “A Myosignal-Based Powered Exoskeletons Systems”
IEEE Transactions on Systems, Man And Cybernetics, Volume 31, Number 2,pp. 3132-3139, May 2001
Joel, Jacob, “Upper -Limb Powered exoskeleton Design” IEEE Transactions on Mechatronics, Volume 12, number 4, pp. 408-417, August 2007
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