myoelectric arm
TRANSCRIPT
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A CKNOWLEDGEMENT:
We take this opportunity to thank Ms. Hetul Gandhi and Mr. Nimit Shah who have guided us through out this seminar and guided us to prepare our presentation effectively. Also our special thanks go to all our friends and others who have directly or indirectly contributed to the success of this seminar.
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A BSTRACT
The motto of new era in medical sciences is “Repair it if you can. Replace it you can’t.”
This motto serves right when we peep into the history of the prosthetic arm. Latest in the field of development is the myoelectric arm, which gives additional gripping facilities along with various degrees of freedom of movements.
The myoelectric arm works under the influence of Electromyographic signals extracted from skin surface. These Electromyographic signals are utilized to run various motors which enables the user (patient) to grip and move is limbs in a much more effective manner.
The myoelectric arms have become extremely popular after the wars which have left several efficient soldiers without their arms. They give them a psychological boon as they very closely resemble their natural arm.
Hence it can be correctly said that technology never puts a full stop to the development and these developments are effectively utilized for the betterment of human life.
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I NDEX:
Sr No CONTENTS PAGE No.
1 Introduction 1
2 Why do we need myoelectric arm? 2
3 Brief history of development of 3orthotic and prosthetic arm
4 What is EMG? 6
5 Upper Extremity Prosthetic Devices 7
6 Block diagram of myoelectric arm 9
7 Construction of myoelectric arm 26
8 Cosmetic gloves for myoelectric arm 32
9 Control systems of myoelectric arm 35
10 How the surgery is performed 40
11 Who is appropriate for myoelectric arm? 41
12 Comparison between prosthetic arm 43and myoelectric arm
13 Future Enhancement 44
14 Conclusion 45
15 Bibliography 46
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I NTRODUCTION
Rehabilitation may be defined as reintegration of an individual with a disability in the
society. Rehabilitation engineering is the application of science and technology to
ameliorate the handicaps of individual with disabilities.
Rehabilitation may be classified into two parts:
(i) Orthosis
(ii) Prosthesis.
O rthosis : It is an appliance that aids an existing function of a limb.
P rosthesis : It is a medical appliance that substitutes a limb both structurally and
functionally.
Rehabilitation of humans with disabilities requires effective usage of assistive
systems for restoration of motor functions. Important features of an effective system are
(i) Reliability
(ii) Minimum increase of energy rate and cost with respect to able bodied
subjects performing the same task.
(iii) Minimum disruption of normal activities when employing the assistive
system;
(iv) Cosmetics and practicability.
These requirements and availability of technology have led to development of externally
powered prostheses that interface directly with the neuromuscular system. These devices
may be battery operated, microprocessor based, or reliable biological sensor.
Some basic requirements of prosthesis are:
(i) The prosthesis must support body weight of amputee like a normal limb
(ii) Body is supported such that undesirable socket or stumps interface
pressures and gait abnormalities due to painful socket/stumps contacts are
prevented.
(iii) Prosthesis should duplicate as nearly as possible the kinematics and
dynamics of the normal gait.
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W HY DO WE NEED A MYOELECTRIC ARM????
Advances in myoelectric technology in recent years have made these upper
extremity prosthetic components far superior to body-powered equivalents. Myoelectric
hand/arm components perform better than conventional prostheses in terms of function,
weight, comfort, and cosmetics. Even small children can learn to create the signals
controlling operation. The single exception may be manual laborers who transport heavy
weights in wet, dirty, and otherwise physically-challenging work environments.
Myoelectric wearers don’t require the bulky, heavy harness of a
body-powered prosthesis.
Improved grip force and proportionate control permit strong grasp as
well as delicate handling.
Improved physiological control of gripping movement through operation
of prehensor by closest muscle groups.
Many users report decreased phantom pain.
Improved cosmetic of myoelectric glove over hook terminal device.
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B RIEF HISTORY OF DEVELOPMENT OF ORTHOTIC AND PROSTHETIC LIMBS:
We know from Egyptian stelae (2500 BCE) and from early Roman
mosaics that prostheses and simple walking aids (orthoses) have been
used during much of recorded history. People in parts of the world still
use a head-high wooden stick to vault over on the side of their non-
functional limb when they walk, much as some disabled Egyptians did
thousands of years ago. Simple wooden canes must be nearly as old as
human kind itself. Wooden peg legs have been effective aids to
walking for thousands of years. Until the 20th Century, wood and
leather were the favorite composite materials in O&P devices.
Paintings of Brueghel from the 16th Century show clearly the plight of
persons without limbs or with dysfunctional limbs as a result of polio or
cerebral palsy. Most of their locomotory aids were fashioned from
wood and leather, perhaps by themselves.
Wars and conflicts have inevitably stimulated developments in O&P
technology, and the
armor makers of the medieval era were early O&P practitioners. The
noble German knight, Götz von Berlichingen, remarked in Goethe’s
play The Iron Hand, that his iron hand had served him better in the
fight than ever did the original of flesh. Ambroise Paré (1510-1590), a
French army surgeon can rightly be called the father of amputation
surgery and prosthetics.
He developed the ligature, which eliminated searing the residual
limb to stop bleeding. He used site selection to try to produce limbs
that were as useful as possible, and he designed prostheses and
followed the outcome of his patients.
Not all warriors wore prostheses. The next time you are in
Trafalgar Square in London, observe the statue of Viscount Horatio
Nelson. Nelson lost his arm above the elbow at Tenerife, lost sight in
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his right eye on Corsica, received a severe head injury at Alexandria,
and watched his greatest naval victory at Trafalgar while propped up
on deck with a fatal spinal cord injury.
His only rehabilitation aid was the “Nelson knife”, now frequently
called a rocker knife, which remains even today one of the best eating
aids for persons with only one arm. The Napoleonic wars played their
part in prosthetics development, mostly in France and in England. Lord
Uxbridge, Wellington’s cavalry officer at Waterloo became the wearer
an above knee prosthesis that became known as the Anglesea Leg
after the island of Anglesea where Uxbridge resided after the war. It
was a unique prosthesis that raised the toe as the knee was flexed in
order to reduce stumbling. The concept is still used today. The
Anglesea prosthesis, after some changes, was used widely in America
by veterans of the Civil War. The enormous number of amputations
resulting from the American Civil War established the prosthetics
industry in the United States during the late 1800s. However, it was
WWI that set the stage for modern prosthetics. Many of the early
advances occurred in Germany.
In Zürich, about 1915, a well-known German surgeon, Ferdinand
Sauerbruch, worked with Aurel Stodola, a famous turbine engineer and professor of
mechanics at the Polytechnic Institute of Zürich to produce a hand prosthesis that was
controlled and powered directly from surgically prepared muscles of the residual limb.
The surgical technique developed to achieve this biological control mechanism was
called muscle tunnel cineplasty. Sauerbruch was one of the first surgeon/physicians to
recommend multidisciplinary scientific and engineering endeavors in the
prosthetics/rehabilitation field. After successfully developing the Sauerbruch hand he
said, “Henceforth, surgeon, physiologist, and technologist will have to work together.”
After WWI, American surgeons studied surgical and prosthetic rehabilitation methods in
Europe, such as Sauerbruch’s tunnel cineplasty and Krukenberg’s surgical fashioning of
the radius and ulna of the limb of long below elbow amputees into two large “fingers”
that could be used effectively for gripping large objects.
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However, no research and development work was fostered in
America after WWI.
World War II mobilized research and development of prostheses all
over the world. In
America this burst of research activity was stimulated partially by
veteran amputees who were languishing in hospitals and who were
disappointed by the state of limb prosthetics in 1945. As a
consequence of their lobbying, the surgeon general of the Army asked
the National Research Council to call a meeting to select which
prostheses would be best for the veterans of WWII. This meeting, held
in Chicago during January of 1945, produced recommendations for
scientific and engineering studies of limb prostheses. From this
meeting the first federal grants were issued to promote the science
and technology of prostheses and amputation. Early investigations
included tours of O&P facilities in many countries. The early studies
and the new research were dramatically successful, and the period
from 1945 to 1975 was perhaps the most productive period ever in
American orthotics and prosthetics. In fact, this period was productive
for O&P technology worldwide. The O&P field is international in scope
and this brief history has
captured only a few happenings in a handful of countries.
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W HAT IS EMG?
Electromyography (EMG) is a medical technique for measuring muscle response
to nervous stimulation. EMG is performed using an instrument called an
electromyograph, to produce a record called an electromyogram. An electromyograph
detects the electrical potential generated by muscle cells when these cells contract.
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The above figure shows the normal EMG graph and the frequency spectrum of an
EMG signal.
S IGNIFICANCE OF EMG IN MYOELECTRIC ARM: The potentials developed by the muscles are used in a myoelectric arm for its
movement. There are two conditions to be satisfied:
(i) The minimum EMG voltage required is 15 micro volts.
(ii) The scar through the EMG potentials are obtained should not break down
under the weight of the prosthetic arm.
U PPER EXTRIMITY PROSTHETIC SYSTEM:
P ASSIVE OR COSMETIC DEVICES:
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These are the conventional type of prosthetic limbs which are
just a psychological consolation to the patient. They are just for name
sake. They can do nothing that a natural limb can do.
B ODY POWERED DEVICES:
They are mainly categorized in the field of orthosis. Here the
prosthetic device is strapped to the shoulder or the trunk of patient
which enables him some degree of freedom of movement. But this
freedom of movement is restricted to only certain positions. Not all
angle of movement is achievable in this method of rehabilitation.
M YOELECTRIC DEVICES:
The myoelectric prosthesis or ‘myo’ was invented in 1948 by
Reihold Reiner. This type of prosthesis uses sensors to detect,
commonly, a threshold of electromyography activity to switch an
electric motor in the artificial ‘hand’, and can also be used to switch
powered wrist and elbow components. Electromyography (EMG)
activity originates from the depolarization and repolarization of the
individual muscle cell membranes during muscle activity. Using surface
electrodes it is possible to measure these potential differences on
surrounding skin. There are many permutations of this control scheme,
however, a salient point is that commercial myoelectric prostheses do
not operate in a ‘volitional’ manner. Rather, the amputee is taught to
achieve the necessary degrees of muscular contraction corresponding
to the threshold levels of electrical activity needed for operation.
Additionally, the myoelectric control method only provides an ‘efferent’
signal to the prosthesis from the amputee. There is no ‘afferent’ signal
returned to the amputee to inform what grip strength is being applied
or what position the fingers are in; unlike the mechanical connection to
the body of the body-powered device. The greatest benefits of
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myoelectric prostheses are their increased grip strength compared to
body-powered devices, and that there is no necessity for the donning
of elaborate control straps combined with the fact that the myo often
has a more hand-like appearance.
T HE ROBOTIC ARM:
Robotic arm is basically a robot in the shape of an arm capable
of performing almost all the task that can be done using a normal limb.
But robotic arm is far too bulky to be attached to the human body. It
can perform all the work like eating lunch with knife and fork or holding
a wine glass and drinking wine. But it cannot be attached to the body
so it is not portable.
Recently interfacing between the brain and robotic arm is trying
to be established and is termed as brain computer interface.
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B LOCK DIAGRAM OF MYOELECTRIC ARM:
B LOCK DIAGRAM FOR WORKING OFMYOELECTRIC ARM:
Figure: Block diagram of myoelectric arm.
E XTRACTION OF EMG SIGNAL:
Electromyographic (EMG) signals, collected at the skin surface, have been used
for the control of upper limb prosthetic devices since 1948; because they provide easy
USER(EMG POTENTIAL)
SIGNAL ACQUISITION AND PROCESSING
CONTROL
ACTUATOR SENSOR
PROSTHESIS
OUTSIDE WORLD
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and noninvasive access to physiological processes that cause the contraction of the
muscles. At present, the process of EMG signals is the most common approach used for
the control of active prosthetic hands.
A CQUISITION AND PROCESSING OF EMG SIGNAL The formal scheme for the acquisition and analysis of the EMG signal for the
control of prosthetic devices is composed of several modules:
• signal conditioning and preprocessing
• feature extraction
• pattern recognition
• offline and online learning.
The first module that is the signal acquisition and processing unit preprocesses the EMG
signal in order to reduce noise artifacts and/or enhance spectral components that contain
important information for data analysis. Moreover, it detects the onset of the movement
and activates all the following modules. During the feature extraction phase, the
SIGNAL ACQUISITION AND PROCESSING
FEATURE EXTRACTION
PATTERN RECOGNITION
OFFLINE AND ONLINE LEARNING
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measured EMG signal is processed in order to emphasize the relevant structures in the
data, while rejecting noise and irrelevant data, producing the so-called “original feature.
Sometimes a reduction of the dimensionality is needed to simplify the task of the
classifier. In this case, a pattern recognition algorithm is used on the (reduced) feature L,
and the measured signal is classified into the output space. The learning modules are used
to adapt the device to the EMG signals generated by the users because of its time-variant
characteristics.
E MG ACQUISITION AND PROCESSING:
Precise detection of discrete motor events, such as the onset of voluntary muscle
contractions, is a prerequisite for various psycho physiological approaches in
sensorimotor system analysis. EMG signal for prosthetic applications is generally
acquired by placing one or more differential electrodes on the skin of the user, depending
on his/her level of amputation and on the data that should be extracted from the signal. A
good acquisition of the EMG signal, in fact, is a prerequisite for good signal processing.
In particular, the consortium defined some recommendations about electrode shape
and size, interelectrode distance, electrode material, and sensor construction (where
sensor is defined as the ensemble of electrodes, electrode construction, and integrated
preamplifier, if any)., e use of one or more low-noise, high-input impedance amplifiers to
acquire the EMG signal is suggested.
After the acquisition, the signal is filtered, generally using a band-pass filter with
high CMRR and gain in order to reduce motion artifacts (high-pass filter) and noise (low-
pass filter). Generally, about 95% of the power spectrum of the EMG is accounted for by
harmonics up to 400 Hz, and most of the remaining is electrode and equipment noise. A
low-pass filter, or anti-aliasing, is usually applied to the signal. The cut-off. frequency
varies from 250 to 2000 Hz, the most common choice being around 500 Hz.². A high-
pass filter is also required to attenuate movement artifacts and the instability of the
electrode–skin interface. In the literature, the lower cut-off. frequency varies from 0.1 to
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100 Hz, but generally a value between 10 and 20 Hz is used. In simple on–o. devices a
notch .filter at 50 or 60 Hz (depending on the frequency of the electric power supply)
could be added. However, it is worth noting that this filter could also eliminate some
important information present in the EMG signal and should not be used for
multifunctional hands. At this stage the signal is sampled and converted into a digital
stream of data.
E MG FEATURE EXTRACTION:
Many EMG-based control systems are able to control a single Degree of Freedom
in a prosthetic limb (hand open/close, wrist or elbow flexion/extension). These systems
generally extract the EMG amplitude or rate of change by using two electrodes placed on
two antagonist muscles (e.g., biceps and triceps brachii or flexor and extensor of the
forearm, depending on the level of the amputation), is information is used to defined the
state of the hand and to control its speed or strength in a constant or even proportional
way.
Starting from the late 1970s, the EMG signal was modeled as amplitude
modulated Gaussian noise whose variance was related to the force developed by the
muscle. As a consequence, most commercial myoprocessors used in prosthetic control
are now based only on one dimension of the EMG signal—the variance or mean absolute
value. Two independent measurements and control systems ensure that the hand switches
to grip force mode when an object is gripped and the grip force is proportional to the
muscle signal.
(a) Original EMG signal
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(b) Rectified EMG signal
(c) Low pass filtered EMG signal
(d) Threshold-based detection of movement
Despite some promising results, this method turned out to be sensitive to changes in
signal amplitude. All these systems have been successfully implemented, but they cannot
provide sufficient information to effectively control more than one DoF. Generally, all
commercial myoelectric control systems are based on the common assumption that the
instantaneous value of the myoelectric signal contains no information. Users are trained
to produce a constant level of activation of muscles, and the prostheses are tuned
according to these values. The steady-state EMG signal, however, has very little temporal
structure because of the active modification of recruitment and firing patterns needed to
sustain a contraction. The parameters that could be extracted to quantify its amplitude
(e.g., variance, mean absolute value) or its frequency characteristics. Starting from the
1990s, researchers found that there is useful information in the transient burst of
myoelectric signal.
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O NLINE AND OFFLINE LEARNING:
The online and offline learning are necessary for the adaptation of the device to
the EMG potentials generated by the user or the patient. In the offline phase, the user has
to generate the adequate EMG potentials that are necessary for the proper working of the
myoelectric arm. If the user fails to do so, then he/she has to go to the rehabilitation
centre and get his controller tuned.
On the other hand, in online learning the controller is designed in such a way that
it adjusts to the EMG potential generated by the patient and performs the controlling
operation of the myoelectric arm.
C ONTROL OF MULTIFUNCTIONAL PROSTHETIC HANDS USING EMG:
Replicating the performance of the human hand is beyond current technical capabilities.
In fact, the human hand is extremely complex: it has 22 degree of freedom in rotation and
movement, controlled by about 38 muscles in the hand. Commercial hand prostheses
have a limited number of degree of freedoms (one or two for finger movements and
thumb opposition), and thus they have low grasping functionality. In fact, they do not
allow adequate encirclement of objects, compared to the adaptability of the human
hand. , The main advantage of current prosthetic hand devices is that they can generate
large grasping forces and are simple to implement and control, in particular by using
EMG signal. Electromyographic signal is a simple and easily obtained source of
information on what the users of prosthesis would like to do with their artificial hands.
Surface electrodes are easy to use and manage, and they do not require surgery.
Moreover, there are no harnesses that could limit the movement of the forearm. It is
possible to control an active device with just one differential electrode placed on the
residual limb, even in infants.
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A CTUATORS AND SENSORS: The function of actuators is to trigger the myoelectric arm in accordance with the
EMG which carries the information of the brain. The sensors do the vice versa. They
sense the activity of the outside world and inform the brain.
E LECTRODE AND AMPLIFIER DESIGN The design of the electrode unit is the most critical aspect of the electronics
apparatus which will be used to obtain the signal. The fidelity of the EMG signal detected
by the electrode influences all subsequent treatment of the signal. It is very difficult
(almost impossible) to improve the fidelity and signal-to-noise ratio of the signal beyond
this point. Therefore, it is important to devise an electrode unit that provides minimal
distortion and highest signal-to-noise ratio. The following characteristics are important
for achieving this requirement.
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Figure: A CTUAL BLOCK DIAGRAM OF MYOELECTRIC ARM.
• D ifferential amplification –
In order to eliminate the potentially much greater noise signal from power
line sources, a differential detecting configuration is employed. The differential
amplification technique is shown schematically in Figure. The premise is simple. The
signal is detected at two sites, electronics circuitry subtracts the two signals and then
amplifies the difference. As a result, any signal that is "common" to both detection sites
will be removed and signals that are different at the two sites will have a "differential"
FilterAmplifier
A-D Converters
Windowing
Extracting characteristics
To the stepper motor.
Electrode
Muscle fiber To the DC motor.
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that will be amplified. Any signal that originates far away from the detection sites will
appear as a common signal, whereas signals in the immediate vicinity of the detection
surfaces will be different and consequently will be amplified. Thus, relatively distant
power lines noise signals will be removed and relatively local EMG signals will be
amplified. This explanation requires the availability of a highly accurate "subtractor". In
practice, even with the wondrous electronics of today, it is very difficult to subtract
signals perfectly. The accuracy with which the differential amplifier can subtract the
signals is measured by the Common Mode Rejection Ratio (CMRR). A perfect subtractor
would have a CMRR of infinity. A CMRR of 32,000 or 90 dB is generally sufficient to
suppress extraneous electrical noises. Current technology allows for a CMRR of 120 dB,
but there are at least three reasons for not pushing the CMRR to the limit:
1) Such devices are expensive.
2) They are difficult to maintain electrically stable, and
3) the extraneous noise signals may not arrive at the two detection surfaces in phase, and
hence they are not common mode signals in the absolute sense.
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• I nput impedance –
The source impedance at the junction of the skin and detection surface may range
from several thousand ohms to several megohms for dry skin. In order to prevent
attenuation and distortion of the detected signal due to the effects of input loading, the
input impedance of the differential amplifier should be as large as possible, without
causing ancillary complications to the workings of the differential amplifier. Present day
electronics devices easily provide input impedances of the order of 1012 ohms in parallel
with 5 picofarads. In addition to the magnitude of the input impedance, the balance
between the impedances of the two detection sites is also of great importance. This
consideration requires careful circuit design.
• A ctive electrode design –
The requirement for a high input impedance introduces a problem known as capacitance
coupling at the input of the differential amplifier. A small capacitance between the wires
leading to the input of the differential amplifier and the power When an electrode is
placed on the skin, the detection surfaces come in contact
with the electrolytes in the skin. A chemical reaction takes place which requires some
time to stabilize, typically in the order of a few seconds if the electrode is correctly
designed. But, more importantly, the chemical reaction should remain stable during the
recording session and should not change significantly if the electrical characteristics of
the skin change from sweating or humidity changes.
Even with the above considerations, the EMG signal will be contaminated by some noise.
The signal to noise ratio can be increased by judicious filtering between 20-500 Hz with a
roll-off of 12 dB/oct. (Strict design characteristics could consider 400 Hz as the upper
bandwidth cut-off. The 500 Hz value allows for a safety margin in the design of the
circuitry.) This filtering is generally accomplished at the amplifier stage located outside
the active electrode. television signal strength to increase when one places ones hand near
the antenna input, but does not touch it. The solution is to place the differential amplifier
as close as possible to the detection surfaces of the electrode. This solution has become
known as the "active electrode". One other advantage of this configuration is that the
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output impedance of the differential amplifier can be made to be very low, on the order of
10 ohms.
Therefore, any movement of the cable from the output of the electrode will not generate
significant or even notable noise signals in the cable which feeds into the subsequent
amplifier line will introduce a power line noise signal into the amplifier. This
phenomenon is similar to that which causes a television signal strength to increase when
one places ones hand near the antenna input, but does not touch it. The solution is to
place the differential amplifier as close as possible to the detection surfaces of the
electrode. This solution has become known as the "active electrode". One other
advantage of this configuration is that the output impedance of the differential amplifier
can be made to be very low, on the order of 10 ohms.
Therefore, any movement of the cable from the output of the electrode will not generate
significant or even notable noise signals in the cable which feeds into the subsequent
amplifier.
• F iltering –
Even with the above considerations, the EMG signal will be contaminated by some noise.
The signal to noise ratio can be increased by judicious filtering between 20-500 Hz with a
roll-off of 12 dB/oct. (Strict design characteristics could consider 400 Hz as the upper
bandwidth cut-off. The 500 Hz value allows for a safety margin in the design of the
circuitry.) This filtering is generally accomplished at the amplifier stage located outside
the active electrode.
• E lectrode stability –
When an electrode is placed on the skin, the detection surfaces come in contact
with the electrolytes in the skin. A chemical reaction takes place which requires some
time to stabilize, typically in the order of a few seconds if the electrode is correctly
designed. But, more importantly, the chemical reaction should remain stable during the
recording session and should not change significantly if the electrical characteristics of
the skin change from sweating or humidity changes.
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• P referred method of use –
Given the high performance and small size of modern day electronics, it is possible to
design active electrodes that satisfy the above requirements without requiring any
abrasive skin preparation and removal of hair.
E LECTRODE GEOMETRY
Throughout the history of electromyography, the shape and the layout of the
detection surface of the electrode have not received much attention. Most likely because
past users of electromyography have been interested only in the qualitative aspects of the
EMG signal. The advent of new processing techniques for extracting quantitative
information from the EMG signal requires greater focus on the configuration of the
electrode. The major (but not all) points to consider are:
1.) the signal to noise ratio of the detected signal,
2.) the bandwidth of the signal,
3.) the muscle sample size, and
4.) the susceptibility to crosstalk.
• S ignal-to-noise ratio – The signal-to-noise ratio is a function of complicated interactions between the
electrolytes in the skin and the metal of the detection surfaces of the electrode. This is an
involved subject that is beyond the scope of this short treatise. Suffice it to say that there
are several approaches for reducing the noise, such as using large surface areas for the
detection surfaces, employing conductive electrolytes to improve the contact with the
skin, and removing dead (less conductive) dermis from the surface of the skin. Through
trial and error we have found that detection surfaces made of pure (>99.5%) silver in the
form of bars 1 cm in length and 1 mm in width provide a sufficiently good medium for
the detection surface. The amplitude of the EMG signal is directly proportional to the
distance between the detection surfaces. Hence, this distance should be maximized. But,
increasing this distance introduces undesirable characteristics to the electrode design. As
the electrode becomes larger, it becomes unwieldy and cannot be used to detect EMG
signals from relatively small (in width as well as in length) muscles such as those found
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in the hand, forearm and the leg. Additionally, as the distance increases the filtering
characteristics of the differential amplification decreases in bandwidth. Thus, a
compromise is necessary. We have found by calculations and by heuristics that an inter-
detection surface spacing of 1 cm provides an acceptable compromise.
• B andwidth –
The bandwidth of the EMG signal is affected by the inter-detection surface spacing and
the conduction velocity of the action potentials along the muscle fibers. The differential
configuration possesses a spatial filtering feature that can be expresses as a band pass
filter in the spectral frequency region of the EMG signal. For an average conduction
velocity of 4.0 m/s and an inter-detection surface distance of 1.0 cm, the pass frequency
is 200 Hz and the null point is at 400 Hz. This bandwidth captures the full frequency
spectrum of the EMG signal and suppresses noise at higher frequencies.
• M uscle sample size –
The muscle sample size need not be large because the muscle fibers of motor units are
distributed throughout most of the muscle cross-section. Therefore, it is not necessary to
cover a large portion of the muscle with the detection surface of the electrode to obtain a
representative sample of the EMG signal for a particular set of active motor units.
• C ross-talk susceptibility –
The susceptibility to cross-talk is an often overlooked design aspect of EMG electrodes.
The greater the width and length of the detection surfaces and the greater the
interdetection surface distance the closer the electrode will be to adjacent muscles. Thus,
larger electrodes are more susceptible to detecting signals from adjacent (lateral and
below) muscles. In situations where this issue is of concern, it is advisable to reduce the
size of the electrode.
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E MG ELECTRODE PLACEMENT :
• L ocation and orientation of the electrode –
The electrode should be placed between a motor point and the tendon insertion or
between two motor points, and along the longitudinal midline of the muscle. The
longitudinal axis of the electrode (which passes through both detection surfaces) should
be aligned parallel to the length of the muscle fibers. Figure provides a schematic
representation of the preferred electrode location.
• N OT on or near the tendon of the muscle –
As the muscle fibers approach the fibers of the tendon, the muscle fibers become
thinner and fewer in number, reducing the amplitude of the EMG signal. Also in this
region the physical dimension of the muscle is considerably reduced rendering it difficult
to properly locate the electrode, and making the detection of the signal susceptible to
crosstalk because of the likely proximity of agonistic muscles.
• N OT on the motor point –
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During the past one-half century it has been taught that for the purpose of
detecting a surface EMG signal the electrode should be located on a motor point of the
muscle. The motor point is that point on the muscle where the introduction of minimal
electrical current causes a perceptible twitch of the surface muscle fibers. This point
usually, but not always, corresponds to that part of the innervation zone in the muscle
having the greatest neural density, depending on the anisotropy of the muscle in this
region. Presumably, the motor points have been used as landmarks because they were
identifiable and provided a fixed anatomical landmark. Unfortunately from the point of
view of signal stability, a motor point provides the worst location for detecting an EMG
signal. In the region of a motor point, the action potentials travel caudally and rostrally
along the muscle fibers, thus the positive and negative phases of the action potentials
(detected by the differential configuration) will add and subtract with minor phase
differences causing the resulting EMG signal to have higher frequency components. In
the time domain, the signal appears as more jagged and with more sharp peaks. The loss
of stability occurs from the fact that a minor displacement ( 0.1 mm) will affect in an
unpredictable fashion the amount of change in the frequency characteristics of the signal.
A note of caution about the motor points and innervation zones. Most muscles have
multiple innervation zones throughout the muscle. They can be identified by applying
electrical stimulation to the skin above the surface of the muscle or by other more
technically complicated surface mapping techniques. If neither procedure is convenient,
then place the electrode in the middle of the muscle between the origin and insertion
point.
• N OT at the outside edges of the muscle –
In this region, the electrode is susceptible to detecting crosstalk signals from
adjacent muscles. It is good practice to avoid this situation. For some applications,
crosstalk signals may be undesirable.
• Orientation of the electrode with respect to the muscle fibers –
The longitudinal axis of the electrode (which passes through both detection surfaces)
should be aligned parallel to the length of the muscle fibers. When so arranged, both detection
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surfaces will intersect most of the same muscle fibers. Hence, the spectral characteristics of the
EMG signal will reflect the properties of a fixed set of muscle fibers in the region of the
electrode. Also, the frequency spectrum of the EMG signal will be independent of any
trigonometric factor that would provide an erroneous estimate of the conduction velocity. The
resultant value of the conduction velocity affects the EMG signal by altering the temporal
characteristics of the EMG signal, and consequently its frequency spectrum.
R EFERENCE ELECTRODE PLACEMENT
The reference electrode (at times called the ground electrode) is necessary for providing a
common reference to the differential input of the preamplifier in the electrode. For this purpose,
the reference electrode should be placed as far away as possible and on electrically neutral tissue
(say over a bony prominence). Often this arrangement is inconvenient because the separation of
the detecting electrode and reference electrode leads requires two wires between the electrodes
and the amplifier. It is imperative that the reference electrode make very good electrical contact
with the skin. For this reason, the electrode should be large (2 cm x 2 cm). If smaller, the material
must be highly conductive and should have strong adhesive properties that will secure it to the
skin with considerable mechanical stability. Electrically conductive gels are particularly good for
this purpose. Often, power line interference noise may be reduced and eliminated by judicious
placement of the ground electrode.
E LECTRICAL SAFETY CONCERNS
The failure of any electrical instrumentation making direct or indirect galvanic contact with the
skin can cause a potentially harmful fault current to pass through the skin of the subject. This
concern is less relevant in devices that are powered exclusively by low voltage (3-15 V) batteries.
To ensure safety, the subject should be electrically isolated from any electrical connection (to the
power line or ground) associated with the power source. This isolation is generally achieved in
one of two ways: either through the use of optical isolators or through the use of isolation
transformers. Both approaches are satisfactory, but both require careful consideration for not
distorting the EMG signal. This is especially true when a transformer is used. This isolation
provides the added benefit of reducing the amount of radiated power line noise at the electrode
detection surfaces.
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E MG SIGNAL PROCESSING
For several decades it has been commonly accepted that the preferred manner for
processing the EMG signal was to calculate the Integrated Rectified signal. This was
done by rectifying (rendering the signal to have excursions of one polarity) the EMG
signal, integrating the signal over a specified interval of time and subsequently forming a
time series of the integrated values. This approach became widespread and it was
possible to make these calculations somewhat accurately and inexpensively with the
limited electronics technology of earlier decades. The advances made in electronics
devices during the past decades have made it possible to conveniently and accurately
calculate the root-mean-squared (rms) and the average rectified (avr) value of the EMG
signal. The avr value is similar to the integrated rectified value, if the calculations
are made correctly and accurately. Both these variables provide a measurement of the
area under the signal but do not have a specific physical meaning. On the other hand, the
rms value is a measure of the power of the signal, thus it has a clear physical meaning.
For this reason, the rms value is preferred for most applications
T HE ANALOG TO DIGITAL CONVERTERS:
They convert the analog signal into coded digital pulsed which are fed into the stepper motors.
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C ONSTRUCTION OF MYOELECTRIC ARM:
Various motions like pronation & supination are achieved with the help of various
motors and gears. These motors may be either stepper motor or DC motors. Let’s see
how these are selected.
M OTOR CHOICE:
S TEPPER MOTOR VS DC MOTORS:
When considering which type of motor should be used, the most
important
criteria was the size of the motor, the torque produced by the motor,
as well as the
requirement for variable speed control.
The motor of choice would need to be mounted onto the robotic arm. A
large
motor would be both cumbersome and impractical. The load, which
comprised of the
lower arm and the hand of the robotic arm, weighed a total mass of
approximately 220
grams. The motor chosen would need to be able to output torque
capable of lifting such a
load.
As mentioned earlier, as a visual aid, the robotic arm is to flex
and extend
according to the RMS value of the EMG signal being read and
processed from the
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amputated arm. As such, an increase in the RMS value causes the arm
to flex at a faster
rate and vice versa. For this reason, it was imperative that the chosen
motor have the
capability of variable speed.
S TEPPER MOTORS:
Stepper motors do as their name suggests, they "step" a little bit
at a time. The
stepper motor is controlled by a series of pulses. Though the stepper
motor operates
using pulses, it cannot simply respond to a clock signal. Instead,
several windings need
to be energized in the correct sequence before the motor's shaft will
rotate. Reversing the
order of the sequence will cause the motor to rotate in the opposite
direction. If the
control signals are not sent in the correct order, the motor will not turn
properly. A
circuit, called a translator, is responsible for converting step and
direction signals into
winding energization patterns. The stepper motor control systems also
includes a driver,
as shown in Figure, to handle the current drawn by the motor's
windings.
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FIGURE: Translator and Driver of Stepper Motor
As mentioned above, the stepper motor operates by a sequence
of pulses.
Therefore, by varying the speed at which the sequence of pulses is
sent to the motor, the
speed of rotation is easily varied. Increasing the speed of the sequence
increases the
rotational speed of the shaft. The opposite is true for decreasing the
speed of the
sequence. With that established, the stepper motor met the criterion of
variable speed.
The stepper motor is particularly suited for precise positioning because
by its very
structure it steps a predetermined angle. Taking 360 degrees and
dividing by the number
of steps the motor will make for one rotation will give the step angle.
In terms of torque, the stepper motor produces the highest levels of
torque at low
speeds and lower levels of torque at high speeds. Stepper motors also
have another
characteristic of holding torque, which is not present in DC motors.
Holding torque
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allows a stepper motor to hold its position firmly when not turning. This
can be useful
for applications where the motor will be starting and stopping, while
the force acting
against the motor remains present. This eliminates the need for a
mechanical brake
mechanism.
The stepper motors acquired were that of an appropriate size.
Unfortunately,
through testing, it was determined that the stepper motors in the
appropriate size range
were unable to produce the required amount of torque to lift a load of
220 grams.
Though stepper motors of a larger size were considered, it was
established that motors
which would output the required torque would be impractical in size.
Therefore, the DC
motor was found to be the most suitable motor for the required
application.
T HE DC MOTORS:
DC motors function using direct current power supply. The
operation of the DC
motor can be observed below in Figure. To allow the rotor to spin
without twisting
the wires, the ends of the coil is connected to a set of contacts called
the commutator,
which rubs against a set of conductors called the brushes. The brushes
make electrical
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contact with the commutator as it spins, and are connected to the
positive and negative
leads of the power source, allowing electricity to flow through the loop.
The electricity
flowing through the loop creates a magnetic field that interacts with
the magnetic field of
the permanent magnet to make the loop spin.
DC motors have a gradual acceleration and deceleration curve
which causes slow
stabilization. The addition of gearing to the motor will to reduce this
problem, but
overshoot is still present and will throw off the anticipated stop
position. A
potentiometer, which acts as a feedback mechanism, is also attached
to determine the
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exact positioning of the motor. In addition, a control circuit, which
compares the position
of the motor with the desired position, moves the motor accordingly.
DC motors differ from stepper motors in their torque-speed
relationship. DC
motors generally do not produce high torque levels at low speeds
without the aid of a
gearing mechanism. However, the DC motor is capable of producing
quite high levels of
torque at higher speeds. With the need for variable speed, it was
established that a gear
box was required for gear reduction.
T HE GEAR BOX:
With the rps of the DC motor determined, it was decided that
gearbox would be
required to provide gear reduction for the motor driving the robotic
arm. With a gear
reduction, the output speed can be reduced while the torque is
increased.
When constructing the gear box, the desired output rps was decided to
be
approximately one revolution per second at maximum voltage of +15
V. To decrease the
speed to one rps, a gear reduction in the range of 1:90 was needed. In
order to
accomplish this, spur gears were utilized. Spurs gears have straight
teeth and are
mounted on parallel shafts. In addition, a worm gear was included to
provide the
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appropriate level of holding torque. Worm gears are often used when
large gear
reductions are required. Worm gears possess a uniqueness unlike any
other gears as the
worm can easily rotate the gear, but the gear cannot rotate the worm.
This is because the
angle on the worm is of such a shallow depth that when the gear
attempts to spin it, the
friction between the gear and the worm holds the worm in place.
Typical metal spur
gears and worm gear can be seen in Figure
Examples of Spur Gears (left) and Worm Gear (right)
T HE POTENTIOMETER:
One major advantage of the stepper motor over the DC motor is
the latter requires
the addition of a potentiometer for position detection. Since the
movement of the stepper
motor is controlled by pulses, the exact position of the robotic arm can
be determined by
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observing the number of pulses sent to the motor5. With the DC motor
chosen, it was
determined that a potentiometer would need to be affixed to the
robotic arm to provide
feedback on positioning. This positioning detection is imperative for
the protection of the
gears being used by the motor.
15 volts is applied into one terminal while the terminal at the
other end of the
resistor is connected to ground. The resulting voltage output is read
through the middle
terminal. Voltages were read at various positions of the potentiometer.
At the fully
flexed position, the voltage at the output of the potentiometer was
found to be -2.8 V. At
the fully extended position, the output was -4.3 V. Therefore, at any
angles that produced
an output voltage between the range of -2.8 and -4.3 V were within the
region of safe
operation. However, any output voltages lower than -2.8 V and higher
than -4.3 V,
required a breaking algorithm to stop the motor from running any
further.
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Model of Modified Myoelectric Arm with Potentiometer
C OSMETIC GLOVES FOR MYOELECTRIC ARM:
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C USTOM MADE GLOVES:
They are usually made of silicone, and are sculpted in the presence of the patient
to match the shape and size of the intact hand as closely as possible. The prosthesis is
painted with details including half moons of the fingernails, age spots, freckles, hair,
veins, etc. The patient is sometimes required to stay near the facility where the glove is
fabricated for several days while the prosthesis is being made. At the high end of cost.
S TANDARD GLOVES:
They are made from existing molds to fit standard hands to save costs. They may
be made of silicone or PVC. They are usually not customized specifically to the patient,
but some manufacturers add basic “generic” details like veins and shading to give the
glove a more realistic look.
M AERIALS:
S ILICONE GLOVES:
Lifelike look and feel.
Durability- about 4 years for myoelectric hands, depending on use and care. If
used in a harsh environment, for example, an industrial setting, silicone gloves
will tear easier than PVC.
Flexible. Holds objects better than PVC.
Color stability- the basic material is intrinsically colored.
Resistant to stains like newsprint and ink.
Some gloves may fit directly over metal parts, so no inner hand shell is needed.
Also can serve as a high-quality protective cover for the vulnerable hand
mechanism and electronics of a myoelectric prosthesis.
P VC GLOVES:
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- Cheaper than silicone.
- Stain easily from ballpoint ink and newsprint.
- Durability- Typically will need to be replaced every 4-6 months due to discolorations, but they are much more resistant to tearing than silicone.
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Figure: Fully constructed myoelectric arm
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Sensor hand
Elbow and hand circuits.
Interface with control system
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T HE CONTROLSYSTEM:
S YSTEM OVERVIEW:
The control system designed was named AmpuProTM. A flowchart
of this system
is depicted in Figure. It is made up of three main sections: input signal
processing,
motor control algorithms and motor driver sections. The input signal
processing contains
a real-time data retrieval section, and history buffer section. These are
used in
combination to capture and measure EMG signals from the subject’s
bicep muscles and
produce a stream of steady RMS values. This array of RMS values is
then used to
determine the next movement of the arm. Subsequently, it is
converted into the motor
control output voltage by the motor device drivers and is amplified to
control the
movement of the arm. Using the proper selection of threshold and
fitness levels, any type
of workout may be achieved for the subject.
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Control System Flow Chart
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A MICROPROCESSOR-BASED MULTIFUNCTION MYOELECTRIC CONTROL SYSTEM
I NTRODUCTION:
Myoelectric prostheses are well accepted by below elbow
amputees but less well by those with higher level amputations. The
primary limitation at present lies in the control system. Although these
systems have been successful for single device control (hand or
elbow), the extension to the control of more than one device (either
simultaneously or sequentially) has been difficult. It is the control
systems which now limit the performance and, at times, the
acceptance of the prosthetic fitting. For the high-level amputee
(above-elbow or higher) and especially for the bilateral amputee, the
need for improved control systems for multifunction prostheses is
critical. Over the past several years the Institute has been developing a
myoelectric control system which is easy to operate, yet provides
control of many independent prosthetic limb functions.
S YSTEM DESIGN:
The control scheme developed in this research [1,2] uses information collected
from the amputee to train a pattern classifier in the control system to recognize the
contraction patterns specific to each amputee. The basic operation of the control system is
illustrated in Figure. The classifier uses features extracted from the first 200ms of
myoelectric activity following the initiation of a contraction to determine the intent of the
amputee. The classifier matches this feature set with the features sets obtained from the
amputee during the initial system calibration. The closest match is used to select which
device (hand/elbow/wrist) is to be controlled. Control of this device continues until the
signal level returns to a predetermined low level.
As shown in Figure 2, the controller can operate in two modes: (a) PC-interface
(training & configuration) and (b) Prosthetic control ( normal operation). The first mode
is used to train the control system to recognize the myoelectric control inputs for each
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individual and requires a host computer for off-line processing. This control system-to-
PC host interface serves several functions:
Configure Control Parameters: specify myoelectric control parameters.
Collect Patterns: collect an ensemble of MES patterns, extract features, and store for subsequent training of the ANN.
Train the ANN: from the features of the collected MES patterns, train the ANN to obtain a set of weights.
Download Weights: send the ANN weights to the control unit, and store permanently in nonvolatile memory.
Virtual Arm: simulate the interactive control of a prosthesis by controlling a three-dimensional “virtual arm” on the PC screen.
Figure: Block diagram of Microprocessor based multifunction myoelectric arm.
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Figure: Control System Operation.
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H OW IS THE SURGERY PERFORMED?
Myoelectric arm is intended to transmit the instructions to the brain via unused
nerves to the point outside the body. This is done by surgically moving the nerves that
once led to arm and transplanting them to the chest. The nerves take around six months to
take the root. Once they took root, sensors are placed over the nerve endings to amplify
the electrical signals still coming from the brain. In case the amputation is below the
elbow the grafting of nerves is not necessary.
If the patient thinks to close his hand, then the nerve that used to close his
hand made a little slip of his chest muscle contract. This slip can be detected because
every time the muscle contracts, it emits a certain action potential. Therefore, two little
antennas are fitted over that muscle, which now could tell when it contracted and then tell
the artificial hand to close. So when he thinks "close hand," muscle contracts, artificial
hand closes. The muscle is used as a biological amplifier of his nerve signal. Like the
switches on his mechanical arm, the antennas are inside the supporting vest. The device
senses the movement and translates it into mechanical motion of the pincer and the
elbow.
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W HO IS APPRORIATE FOR MYOELECTRIC ARM?
(i) E VALUATION OF CANDIDATE:
The Myoelectric Arm 3 offers several control choices including EMG (myoelectric
control) by one or two muscles, as well as 3 harness-mounted sensors (linear
potentiometer, force sensor and touch pads [1 or 2]). Evaluation of the muscular as well
as the remnant shoulder anatomy is one of the first steps in evaluation for an electric
prosthesis.
For myoelectric control, at least one muscle EMG signal is required, measuring 5
microvolts for hand control and 15 microvolts for the elbow. Careful probing with a
sensitive EMG tester is necessary to identify all potential control sites, since fitting
considerations may rule out some sites. The evaluator should be thoroughly familiar with
the anatomy of the arm and shoulder so that the remnant musculature can be accurately
identified and the patient properly instructed to contract the muscle being tested.
(ii) M OTIVATION AND PSYCHOLOGICAL ADJUSTMENTS:
It almost goes without saying that the success of any prosthesis depends a great
deal upon the patient's own motivation. Motivation is difficult to assess, and many
clinics feel that merely participating in the fitting steps, such as muscle training,
demonstrates adequate motivation. Others require consistent use of a conventional
prosthesis before a myoelectric limb will be fit. That strategy, indeed, resolves many
questions about the patient's motivation (and provides a backup prosthesis as well), but
risks denying a myoelectric limb to some who could use it, but cannot or prefer not to use
a conventional prosthesis.
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Realistic orientation (with all appropriate optimism) is also important, and if the
patient is not aware of the details of the fitting process, then he should be informed of
both the capabilities and the limitations of the prosthesis. If available, experienced
prosthesis users who are willing to talk with a new amputee can give a realistic point of
view and can offer inspiration to a new amputee who may have doubts about his future.
Counseling or therapy to aid amputees in their adjustment may be helpful, especially if
the amputee does not communicate well with the other fitting team members. If the
clinic team or fitting center does not have training in psychology or counseling,
adjustment problems can be particularly baffling. Typically; we may see the technical
aspects of the fitting progressing, but the patient is not making the expected progress in
his rehabilitation. The patient may need professional help in working through their
adjustment problems, or perhaps just more time to solve their problems themselves or
with their families. In any case, the fitting process may be blocked indefinitely until the
patient is psychologically ready to progress.
(iii) S KIN CONDITIONS:
Myoelectric signals can be obtained even through scar tissue. However, care
must be taken to ensure that the scar tissue does not break down either under the weight
of the prosthesis or from pressure under the electrodes (Low profile electrodes are
supplied with the Utah Arm for use in such cases.)
(iv) S IZE AND STRENGTH OF AN INDIVIDUAL:
The Myoelectric arm has been fitted to patients as young as 13 years old and may
be suitable for some even younger, but the forearm length cannot be shortened beyond 8
inches (20.32 cm). The finished weight of a Utah Arm is about three to four pounds,
depending on the terminal device and wrist used, and the individual should be capable of
supporting this amount of weight.
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Neuromas and phantom limb pain may be complications in some patients and
should be carefully evaluated if they are exacerbated with the use of the prosthesis.
Higher level amputees, e.g., shoulder disarticulation, may experience muscle cramping in
the trapezius due to weight or suspension forces. Muscle strengthening with exercise
and/or redesign of the socket may make the weight more tolerable.
The questions that arise in the evaluation of a patient often cannot be answered by
physical examination alone. For some patients, a trial fitting is the only way to assess
questions such as the comfort of wearing a prosthesis day-to day, or the motivation to
utilize the prosthesis regularly. In short, the trial fitting can be used to verify the
tendency of a patient for the Utah Arm or for a particular TD. Also, if the patient proves
to be inappropriate for the first components tried, other components may be substituted,
usually using the original trial socket with several different components.
(V) T HE TRIAL FITTING AS AN EVALUATION DEVICE:
Trial fittings typically involve the fitting of a temporary socket, which should be
substantial enough to be used for several months. (We presently fabricate above-elbow
temporary sockets with vacuum-formed plastic like Surlyn, with a reinforcing outer layer
of fiberglass casting tape.) The trial period also includes the initial training period and
should be continued long enough to allow the patient to adapt to using a prosthesis in
daily life, which in our experience suggests a 1- to 6- month trial period.
(vi) F UNDING DEVICES
A candidate for a myoelectric prosthesis must also have adequate funding to pay
several times the cost of a body-powered prosthesis. Experience shows, however, that
health insurance, or other third-party payers, will fund a myoelectric prosthesis if
properly prescribed and justified to the insurer. We recommend that if the patient's
policy includes prosthetic benefits, the physician's prescription and a detailed letter of
justification be submitted to the insurer, along with the estimate for the costs of the
prosthesis.
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We have found that insurers appreciate the "success guaranteed" nature of the trial
fitting process. A fitting center or clinic can perform such a trial fitting (using rental of
"spare" components) and apply most of the trial fitting costs towards the purchase, even if
the trial indicates a different prosthesis is necessary.
C OMPARISON BETWEEN CONVENTIONAL PROSTHETIC ARM AND MYOELECTRIC ARM:
(i) The low grasping capabilities, because current prosthetic hands have no more than
two active DoFs (and act like a simple gripper).
(ii) The noncosmetic and unnatural appearance of the grasping movement resulting
from the low number of DoFs. On the other hand, cosmetic devices have no active
functionality and can be used only as a passive support.
(iii) The lack of sensory information given to the user. , ere is no feedback except
visual from the outside, so the user has to judge by sight when to stop moving the
hand.
(iv) The lack of a “natural,” intuitive, nonfatiguing command interface, to enable
practical long-term use of a multifunctional prosthetic hand.
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F UTURE ENHANCEMENT:
The future of myoelectric arm is the High Speed sensor hand of Otto Bock health
care, which adjusts to the grip automatically and is the claimed to be the first to open and
close quickly to allow patients to catch and throw a ball.
DARPA (Defense Advanced Research Projects Agency) is seeking to advance the bionic
arm extensively to the point that a person with a bionic arm can play musical instruments
and type on a computer. They have proposed a program called Prosthesis 2007. By the
year 2007, this program plans to have a working bionic arm that functions like a real
human arm. It will have a full range of motion like the human arm. Fingers, hands,
arms, shoulders will all move more naturally. They plan to develop something that can
pick up neural signals directly from the nerves without grafting the nerves onto the chest
muscles and then taking the EMG readings. Instead a device will read neural signals.
The arm translates it and then would send out directions to the arm. This would improve
the response time. As a result the bionic arm would operate more naturally. Here are a
few dramatic improvements they believe the current bionic. It needs to improve upon:
neural sensing
control systems
power storage & distribution
neural control
sensory feedback
transmission design
signal processing
information science
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They plan to have a working bionic arm that function like the human arm control directly
by the human brain directly with the neural sensory from the brain by the year 2007.
Then for the next two years after, they plan to perfect their bionic arm prototype. After
fours from today, a bionic will hopefully be out on the market for amputees. These are
the goals of DARPA.
C ONCLUSION :
Technology never puts a full stop. It is always finding new ways to improve the existing
devices. In order to make the life of people with a malfunctioning limb or without a limb
comfortable to certain extent, the myoelectric arm was developed from earlier prosthetic
devices. Hence it is totally justified to conclude that the myoelectric arm have surely
made the life of amputee easier and convenient.
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B IBILIOGRAPHY:
(1) Rehabilitation engineering, science and technology-
Charles.J.Robinson.
(2) The biomedical engineering handbook- Second edition
(3) Reader’s digest February 2006
(4) Website www.bionicarm.com
(5) Website www.neuroscience.com
(6) Website www.google.co.in/myoelectric arm/ transcarpal
myoelectric prosthesis
(7) Website www.google.co.in/ scholars/ myoelectric arm.
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