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 – 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

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

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

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.

CHAPTER 4

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

4.1. Anthropomorphic Architecture

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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.

4.3. Pseudo-anthropomorphic Architecture

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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.

CHAPTER 5

7

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

CHAPTER 6

11

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 pre-

programmed 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

The working phases of a bio mechatronic exoskeleton are:

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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.

3. Actuation – Moving the robotic arm

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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

CHAPTER 7

14

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

CHAPTER 8

15

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.

CHAPTER 9

16

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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