NR 57
AN­T RO­P O­M O­T O­R Y­K A
2012
THE MOVEMENT OF A HUMAN BEING
IN THE MEDICAL EXOSKELETON –
THE ANTHROPOMOTORIC ASPECTS
PORUSZANIE SIĘ CZŁOWIEKA W EGZOSZKIELECIE
MEDYCZNYM – ASPEKTY ANTROPOMOTORYCZNE
Emilia Mikołajewska*, Dariusz Mikołajewski**
***PhD, Department of Rehabilitation, 10th Military Clinical Hospital with Polyclinic SPS ZOZ in Bydgoszcz, Poland
***MSc, Department of Informatics, Faculty of Physics, Astronomy and Informatics, Nicolaus Copernicus University
in Toruń, Poland
Key words: rehabilitation, physical therapy, exoskeletons, biomechanics
Słowa kluczowe: rehabilitacja, fizjoterapia, egzoszkielety, biomechanika
SUMMARY • STRESZCZENIE Exoskeletons are mechanical constructions attached to particular parts of a human body, supporting its
movement with the in-built effectors. Exoskeletons are promising solutions as rehabilitation devices and as
tools, supporting patients, medical personnel, families and caregivers in everyday life activities. They may be
particularly helpful for the people with deficiencies and those who suffer from pathology of the central nervous system (CNS) in result of, for instance, a stroke. The aim is to improve the quality of life of such people
by supporting and expanding their motoricity. As for today, the knowledge and understanding in the area of
adaptation of a human being to walking and performing everyday life activities in combination with such robots
as exoskeletons are limited. This article is aimed at estimating to what extent the possibilities in this field are
being exploited.
Egzoszkielety są konstrukcjami mechanicznymi mocowanymi do poszczególnych części ciała człowieka,
wspomagającymi jego ruch za pomocą wbudowanych efektorów. Egzoszkielety stanowią obiecujące rozwiązania
zarówno jako urządzenia rehabilitacyjne, jak i wspierające pacjentów, personel medyczny, rodziny lub opiekunów
w czynnościach codziennego życia. Mogą być szczególnie pomocne u osób z osłabieniami oraz cierpiących z powodu patologii ośrodkowego układu nerwowego, spowodowanych np. udarem. Celem ich funkcjonowania jest
poprawa jakości życia tych osób przez wsparcie i rozszerzenie ich zdolności motorycznych. Aktualny stan wiedzy
oraz zrozumienie zagadnienia adaptacji człowieka do chodzenia i wykonywania czynności życia codziennego
we współdziałaniu z takimi robotami, jak egzoszkielet, są mocno ograniczone. Artykuł jest próbą oceny, w jakim
stopniu wykorzystuje się dziś możliwości w tej dziedzinie biomechaniki.
Introduction
The medical exoskeleton, defined as a power suit at­
tached to particular points of the user’s body, allowing
him to expand his strength and motor capabilities (in­
cluding the lost or limited ones) constitutes a promis­
ing solution in the field of medical robotics (including
rehabilitation robotics) for the people with deficits of the
central nervous system or with the weakened muscle
power. The exoskeleton is an excellent solution for the
disabled, seriously ill and elderly people not only in the
area of their mobility (replacing wheelchair and expand­
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Emilia Mikołajewska, Dariusz Mikołajewski
ing its capabilities) but also as a rehabilitation device
interacting with the user all day long in the course of the
standard exploitation of the device. Therefore, the im­
portant element is the analysis of the exoskeleton and
the interaction between a human being and a machine
both on the bio-cybernetic and biomechanical levels,
which overlap here. It seems particularly significant
also from the viewpoint of introducing the steering of
exoskeletons with brain-computer interface (BCI). One
of the research projects conducted nowadays in this
area is MindWalker [2, 3]. In the market, there are al­
ready first two commercial medical exoskeletons: HAL5
and ReWalk (versions B1/B2); and the consecutive one
– eLegs – is to be available in the middle of 2012 [4, 5].
In the course of clinical trials and the development of
knowledge on the exoskeletons, the dynamic growth of
their clinical applications is predicted.
Two main basic groups of the applications of the
exoskeletons are being under consideration here:
• r e h a b i l i t a t i v e m o d e – the use of the exoskel­
eton in case of severely ill people, the disabled and
the aged as an ultra modern equivalent of a com­
bination of today’s wheelchair with a rehabilitation
robot, and the tele-medical system (for instance,
tele-supervision); the aim of using the exoskeleton
may be here of a dualistic nature: providing the con­
stant support of everyday life activities and mobil­
ity by replacing, strengthening and supplementing
the particular functions’ parameter or else – when
the exoskeleton is used temporarily – training the
above-mentioned functions (e.g. while gradually re­
ducing the support), so that – when the using of the
exoskeleton has been completed – those functions
are performed by a patient in an improved way;
• a s s i s t i v e m o d e – the use of the exoskeleton
as a supporting device for medical personnel and
caregivers of the severely ill people, the disabled
and the aged, particularly in case of the activities
requiring a great physical effort: the change of a po­
sition, moving over, assuming the upright position or
reeducation of walking, bathing etc. [6, 7, 8, 9, 10].
Scientific research on exoskeletons focuses primar­
ily on the understanding of biomechanics, nervous con­
trol, and energetic cost of the movement of a human
being in the exoskeleton and without it. It may supple­
The Alternative for a Wheelchair:
The two-limb alternative (the exoskeletons only for lower limbs)
The four-limb alternative (the exoskeletons for both lower and
upper limbs)
Supporting many
everyday life activities
Necessity to develop safety
and emergency systems
Reducing energy cost
of a movement
(e.g. in case of enfeeblement)
Possibility of compensation
(also temporary)
of the OUN deficits
Complex procedure of the
user’s adaptation
and training
Advantages
Disadvantages
Adjusting the steering
to the kind and level
of a deficit
The possibility of steering
with the help of the brain-computer
interface (e.g. the MindWalker project)
Individual
choice
Not fully examined
long-term effects
of the exploitation
Exoskeleton is a
mobile rehabilitation
device and
a platform for telemedical equipment
Figure 1. Advantages and disadvantages of using exoskeletons in rehabilitation
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The movement of a human being in the medical exoskeleton – the anthropomotoric aspects
ment the knowledge and experience already acquired
in this area through, among others, reeducation of the
function (walking, the function of upper limbs) lost in the
result of neurological deficits in the course of rehabilita­
tion and neurological physiotherapy, through the impact
of repetitive exercises on the effectiveness, through the
speed of the return of the above-mentioned function, or
through the use of the rehabilitation robots.
Steering of the exoskeleton
From cybernetic viewpoint, the healthy people while
attempting to make a movement – depending on the
intention to make a movement and the conditions of the
environment – modulate the patterns of the activation
of muscles. Various functional tasks require develop­
ment of a set of various patterns, including the sequen­
Number
of articles
625
tial activation of particular patterns, and stepping up
the power of muscles and its direction. Some disabled
people (e.g. in result of a stroke or damage of the spi­
nal cord) have limited capabilities in this area or even
their total absence, as far as particular muscles are
concerned. It is most often caused by the damage of
the nervous system in the way that prevents the patient
from conducting the above-mentioned modulations in
a controlled way.
Exoskeletons are being equipped with an inter­
face of the user, in traditional understanding of that
concept, although exoskeletons ReWalk, eLegs and
HULC possess partial interfaces for the choice of the
work module. The user is steering the exoskeletons in
the process of an interaction between a human being
and a machine, cooperating with the exoskeleton via
human-machine interface. HMI interface, working in
Comparison of the frequency of the phrases’
appearances
76
50
23
exoskeleton
7
robotic
robotic
robotic
robotic
exoskeleton exoskeleton + exoskeleton exoskeleton
biomechanics
+
+
rehabilitation
physical
therapy
Figure 2. Results of investigation of the PubMed database (U.S. National Library of Medicine) [11]
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name of
the
phrase
Emilia Mikołajewska, Dariusz Mikołajewski
real time on neuro-muscle level, may lead to intuitive
steering of the exoskeleton and the user’s full integra­
tion with it. The user perceives the exoskeleton then,
as an extension (expanding the capabilities) of his own
body [12].
In the simplest sense of the term, the full cycle of
the steering of the exoskeleton covers the following
stages realized in the real time:
• reading from sensors the intention of the user to
make a movement,
• interpretation of that intention while taking into ac­
count the up-to-date behavior and the programmed
patterns of movement,
• interaction of the exoskeleton movement with the
user’s movement while simultaneously strengthen­
ing the power, reducing the support or even replac­
ing the deficient part of the user’s body (according
to needs),
• analysis of the final position, and launching the suc­
cessive cycle [6, 7, 8].
The proper realization of the above-mentioned al­
gorithm is being fulfilled by the subordinated detailed
functioning of the whole (most often doubled) exoskel­
eton steering system. It ensures at the same time:
• maintenance of the movement and particular po­
sitions within the frames of natural patterns or the
patterns close to natural for a particular user – the
most interesting aspect from biomechanical point of
view,
• comfortable and bearable use of the exoskeleton in
a long period of exploitation, at altered effort, and
multiple repetitions [8].
Human-machine interaction
Below a description of the chosen solutions to the area
of human-machine interaction used in the contempo­
rary exoskeletons is placed.
Myoprocessors [12] are realized in the course of
HMI computationally as the real time models of all the
muscles covered by support. These models, work­
ing in combination with the functioning muscle, allow
conducting the anticipatory identification of which of
the muscles – and in what way – will be successively
activated. By that means, one can – on the basis of ki­
nematics of the joints and levels of the activation on the
neuronal level – anticipate, for instance, the moments
in joints. It is also possible, due to the fact that each
user has at his disposal the source of natural move­
ment patterns, either fairly limited or relatively close to
the natural. The set is also learning in the process of
adjusting the exoskeleton to the user’s needs and in
the process of its entire exploitation. These patterns
enable creating the internal database for the needs of
HMI, which allow the calculation, for example of the ini­
tial stages of each movement and the assessment and
eventual correction of the supporting of the movement
by the exoskeleton. These procedures are quite com­
plicated and they require the involvement of artificial
intelligence (for instance GA – genetic algorithms, and
such complex muscle models as Hill phenomenological
muscle model). The recent studies have indicated high
effectiveness of that kind of solutions, as sufficient tools
for practical use [12].
For the time being, the most common type of con­
trol is steering of the exoskeleton with simultaneous ap­
plication of all solutions or the ones chosen from the
following solutions:
• electro-myographic sensors,
• gyroscopic sensors of the position,
• sensors of the power of pressure on the founda­
tion,
• sensors of acceleration,
• sensors of the angles of bending the joints of
limbs,
• ultimately (during the research): brain-computer in­
terface and steering of the exoskeleton as the com­
prehensive and advanced neuroprosthetics [1, 2, 3,
13].
Conducting electromyography [14] is commonly
used, due to the fact that EMG signals reflect directly
the intention of the user to make a movement. Various
solutions are examined in this respect:
• the exoskeletons for lower limbs with various levels
of the freedom of movement (from level one up­
wards) in the knee joint, less frequently also in the
ankle joint (although it is very important for the prop­
er walk) – mostly used for supporting the movement
of the disabled people,
• the exoskeletons for lower limbs ankle-knee-hip
with the artificial (according to needs) substitutes of
all important muscles – mostly used for re-educa­
tion of walk, including the patients with hemiplegia
with the regulated relieve of both the paralyzed and
the healthy sides,
• the exoskeletons supporting also the movement of
the upper limbs: the movement of an arm and the
movement in the elbow joint, less frequently in the
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The movement of a human being in the medical exoskeleton – the anthropomotoric aspects
wrist joint – used mostly to support the movement
of the disabled people,
• the advanced exoskeletons equipped with the sup­
port of a palm, including 16 joints – four for each
finger – used in the reeducation of the everyday
activities, also after surgeries.
In steering the exoskeletons, particularly the pro­
totype ones [15], the steering devices equipped with
neuro-fuzzy controllers can be helpful since their easy
adaptation to the EMG signals of the user [14, 15].
Optimizing the power [16] is still a matter of interest
since the values obtained from experimental research,
however useful, require additional modeling. A very pre­
cise reflection of the natural power is not necessary here
but its optimization in the given application is important.
It concerns all the muscles and functions, walking includ­
ed. To calculate the optimal powers in the real time, one
needs to follow quite complicated operational mathema­
tical procedures, often solving the problem of numerous
contradictions and inter-relations with the simultaneous
movement of other muscles. One of the methods allow­
ing the assessment of the muscle power on the basis of
the EMG signal analysis, the Bogey’s and co-workers’
method [17] is often used in different variants.
The presupposition of involuntary reduction in hu­
man strength in the human-machine interface [18] is
reflected in the hypothesis formulated by Lewis and
Ferris that users cooperating in the human-machine
interface involuntarily lower the power of muscles and
the moments in joints, which influences the resultant
moments of the user-exoskeleton interface. In effect,
these values may differ from the natural ones achieved
by the same human being. As for today, the research in
this field is being conducted and the initial results do not
confirm the above hypothesis, however, the effective
implementation of commercial exoskeletons requires
full explanation of that problem.
The improvement of the exoskeletons’ inertia [19] as
one of the means aimed at providing the exoskeleton
movements with the agility natural for a human being,
particularly in the area of the upper limbs movements,
has caught the researchers’ attention. It is believed
that the exoskeleton numbness disturbs naturalness
(also lowering the natural frequency) of the exoskeleton
movements of the human-user. Particular role may be
played here by great accelerations given to some ele­
ments of the exoskeleton, among others, in the substi­
tutes of the hip and knee joints which can sometimes
cause the so called jerky movements of the exoskeleton
while attempting a quick acceleration of a walk by the
user. Hence, the attempts to create the compensation
algorithms in that area are in interest [19].
Proportional myoelectric control [20] intensifies the
process of the user’s adaptation, both the one with
deficits, and the healthy one to steer the exoskeleton
also in case of the necessity to reduce and to diminish
the energy consumption. It is what makes the above
method the leading one in the market. In this method,
the value of powers of the particular muscles is pro­
portional to the amplitudes of the equivalent EMG sig­
nals. It should be noted that EMG signals have to be
processed here in the real time. It is suspected that
the precision of movements in this method may not be
an effect of a certain specific action of the descending
stimuli but may rather depend on the long-lasting exer­
cises, proprioceptive feedback or mechanics of joints
(e.g. the movement in the elbow may be less precise
since the associated movement in the wrist will expand
it) [20, 21, 22].
The control of an individual muscle [23] is realized
mainly by the “individual muscle-force control” sup­
ported by the exoskeleton which allows obtaining much
broader spectrum of data than with the help of such
conventional methods as gripping or pushing the han­
dles. In the controlling of groups of muscles, there may
arise problems with coordination of the movements
of the synergistic muscles both in case of the healthy
people and the people with movement deficits in that
sphere. Although in exoskeletons the issue of the arti­
ficial “muscles” construction as such is of a secondary
importance, the choice of the appropriate pneumatic or
hydraulic elements as well as electric actuator may sig­
nificantly influence the algorithms of steering itself and
the construction of the steering system, e.g. in the field
of the energetic optimization or using the numbness of
the limbs movement.
In accordance with all above-mentioned, two cru­
cial problems should be taken under consideration:
1. Education and coordination of the user-exoskeleton
interaction in the situation of a temporary using of
the exoskeleton (e.g. for the time of convalescence
in case of weakening of the user, and also while us­
ing the exoskeleton as the support of the weakened
muscles with its gradual reduction) as well as the
estimation of the influence of the exoskeleton’s pe­
riod of exploitation upon the possibility of returning
to the natural (self-reliant) patterns of movement.
2. Not sufficiently examined effects of a long-time stay
in the exoskeleton in case of using it as an alterna­
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Emilia Mikołajewska, Dariusz Mikołajewski
tive for a wheelchair (i.e. even 11–14 hours a day)
resulting primarily from:
• enforced repetition of the movement patterns,
• the lack of natural reflexes implemented in the
exoskeleton software,
• the effect close to the human being lost in vir­
tual reality: will the too profound trust in the ma­
chine not make the user too much dependent
on the machine, hampering or even preventing
him from functioning without it? Nowadays, for
instance, the stabilization of the balance of the
human-exoskeleton set is entrusted to a human
being, since the proper automatic realization of
that function is complicated. On the other hand,
it is not known whether, for example, the auto­
mation of keeping the balance by the exoskel­
eton will not contribute to the weakening of this
function in the exoskeleton’s user.
Moreover, the significant part of the research is con­
ducted on the population of the healthy people, also in
the area of a possible influence of the exoskeleton upon
the changes in the movement patterns. It is caused, in­
ter alia, by the fact that the origins of the research upon
exoskeletons were of a military nature, focusing on the
use of exoskeletons for expanding the endurance and
lifting the capacity of individual soldiers. Additionally, in
case of research on people with deficiencies, there is
a whole range of types and levels of deficits, to which
the tested exoskeleton would have to be individually
adjusted. Also the research is being conducted on the
development of the reliable indicators in the area of
compliance of the cooperation of the exoskeleton set
with the elements of limbs while making a movement,
both in the form of a simple 3D analysis of the move­
ment and the coordination, speed and chronology of
the rotation in the joints for whole limbs. One of the pos­
sible solutions is the registration and the measuring of
the position of a limb and the forces while making the
specific movement [24]. That research is particularly
important also for further development of the stationary
rehabilitation robots. An interesting solution for getting
rid of some of those problems is an attempt to develop
HAL exoskeleton for one leg (hemiplegic) – particularly
for patients with hemiplegics [25].
Conclusions
In the coming years, one can expect the results of the
European clinical trials on the use of the HAL 5 exoskel­
etons in rehabilitation, launched in 2010 in (among oth­
ers) Odense University Hospital in Denmark [26]). Apart
from the progress in therapy, particularly of neurologi­
cal disorders, the research may bring the improvement
in understanding of physiology, biomechanics, nervous
control and the energetic cost of the human movement
both in case of the healthy people, and the ones with
deficits. Nonetheless, taking into account the coming
implementation of the commercial exoskeletons, one
has to identify and analyze today, the problems and po­
tential threats, particularly in the area of biomechanics.
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