Correction of Incorrect Anatomic Posture of Cervical Spine
with Biofeedback Method
(Sensory Phase)
M.Ali Khalilzadeh ¹
Elyas Ranjbarian ²
Omid Jahanian ³
Ghasem Karimi ³
Department of Bio-Medical Engineering
Robotic Lab.
Islamic Azad University of Mashhad
Islamic Azad University of Mashhad
Ostadusefi St., Emamieh Blv., Ghasemabad , Mashhad , Khorasan Razavi , Iran
MAKhalilzade@mshdiau.ac.ir
Elyas.Ranjbarian@Gmail.com
Jahanian_o@hotmail.com
Gh_Karimi@hotmail.com
ABSTRACT
Great reduction in physical activities and incorrect anatomic habits in different periods of life and different
places in their rest time or in working at job causes incorrect anatomic posture and skeletal and articulated
diseases. Such problems take long time to get corrected successfully with ordinary methods such as fixing
splints, physiotherapy operations and special exercises. But in our project to solve mentioned anatomic
problems, Biofeedback method was devised. Up to now biofeedback method hasn’t been used for such a
purpose but we have used this technique in order for anatomic posture correction. First step to reach this propose
is the body posture detection. Our target limb in this project is cervical spine. The amount of neck flexion, the
angle between head and trunk and the displacement of posterior parts of cervical spine relative to each other are
the features which describe well enough to judge about the posture of cervical spine. Here in this paper detection
by suggested sensory method will be explained. Sensory phase involves designing, fabricating, experimenting
and optimisation of proposed sensors; the carbon sensor for angular flexion detection, the capacitor sensor for
displacement of posterior parts of cervical spine detection and the combined gravitational sensor for the angle
between head and trunk detection. After detection of target limb posture with our recommended designed
sensors in sensory fusion phase, processing the samples and timed incorrect posture announcing to body
intelligent system occur to complete our devised biofeedback method.
Keywords: cervical anatomic posture, bio feedback systems ,posture correction, combined sensor
1 INTRODUCTION
As the technology has facilitated hard and
dangerous responsibilities of human being in most
aspects of life from industries to social activities
also has caused great reduction in physical
activities, incorrect anatomic posture, skeletal and
articulated diseases because of incorrect anatomic
habits in different periods of life from their
childhood up to old ages and different places in
their rest time at home and also when they are
working at job. Incorrect posture and such
problems are usually uncorrectable (incurable) or it
takes long time to cure
-----------------------------------------------------------1: Assistant professor of BIO-MEDICAL Engineering Dpt. Of
Islamic Azad University of Mashhad.
2: M.S.Student of BIO-MEDICAL Engineering Dpt. Of Islamic
Azad University of Mashhad.
3: B.S. Student of MECHNICAL Engineering Dpt. of Islamic
Azad University of Mashhad.
them so usually they cant be cured (corrected)
successfully .ordinary methods which are used in
order to solve these problems are such as fixing
splints and other anatomic fixtures ,physiotherapy
operations and special exercises . Some methods
like using splints because of non-flexibility and
putting the target limbs under pressure and also
mental pressure due to being continues and long
are not so efficient. The method in our project to
solve mentioned anatomic problems is based on
Biofeedback system in which by sampling from
target limb or limbs posture with our recommended
designed sensors, processing the samples and timed
incorrect posture announcing to body intelligent
system it doesn’t put under pressure the patient
and also doesn’t have the problems of previous
methods because of non-permanent incorrect
posture alarm announcement. up to now
biofeedback method hasn’t been used for such a
purpose but we have used this technique in order
for anatomic posture correction .easy sampling
method from anatomic posture and biofeedback
technique are the principles of our project thus
designing and fabrication of proper data recording
system and processing the data are so important in
order to reach the purposes in our project.
2.2 sensory data fusion:
Due to non-linearity of sensors and different
detected parameters (amount of flexion, angle and
displacement) in order to make understood the
decision maker about sensors out put a fuzzy
sensory data fusion was used.
We expect following results for this research:
Presentation of a biofeedback system for correcting
neck incorrect posture (cervical spine)(spinal cord
situation and its problems are so related to this
posture.) in order to get improved the people who
have neck posture problems in different body
settlement postures (different types of standing,
sitting and lying) without being under physical or
mental pressure. in future it will be tried to analyze
the results of our research according to statistical
method .
In this project we have tried to help all people who
have problems and diseases that originated from
incorrect anatomic habits and also who in their jobs
are obliged to have Special anatomic posture for a
long time.
2 ARCHITECTURE
The project path is as followed
2.3 processing and analyzing of
anatomic neck posture:
In this section processing and analyzing of neck
posture; feature extraction, intelligent decision
maker system (preferably fuzzy); base on cervical
spine anatomy and also out put of sensory data
fusion section is designed and the made decisions
are sent to biofeedback system.
2.4 biofeedback:
Using of biofeedback technique in posture
correction process is a new scientific suggestion in
this field. In this research feedback parameters such
as location, time and type of feedback have been
studied which are related to job and habits of
patients.
2.5 system evaluation:
Fig 1. Block diagram of posture correction system
As the last section of this project (posture
correction) effectiveness of biofeedback technique
must be evaluated.
The Procedures in order to evaluate the rate of
cervical posture improvement are:
Long time data record, feature extraction for
evaluation and clustering .
The explained subject in this paper is the sensory of
the project.
2.1 sensory and instrumentation:
In order to detect incorrect cervical posture and
analyzing this situation we need proper sensor,
sensors which can give the amount of neck flexion,
the angle between head and trunk and the
displacement of posterior parts of cervical spine
relative to each other.
All this sensors due to their applications must have
easy installation, light weight and small
dimensions.
According to necessity of having a mobile system
the data recording set which contains transducers,
processor, data communication module and power
also must have characteristics which were
mentioned for sensors.
3 SENSORY
3.1 Carbon sensor:
We have designed this type of sensor in order to
quantitate the amount of flexion of neck.
This sensor is constructed from a 15 centimeter
rubber tube with diameter of 1 mm. which is full of
carbon particles with same dimensions (0.05 mm).
There are two electrodes at two sides of the tube
which are situated inside the carbon particles to
5mm depth
Fig 2. designed Carbon sensor
One head of the sensor must be installed on C2
vertebrae. The operation of this sensor is like that
with flexion of tube the distance between carbon
particles is reduced so the impedance between two
electrodes decreases. It is considerable that the
As the other parameters in the formula are constant
(K: capacitor constant, B: width of sheets and d:
distance between metal sheets) the relation between
capacity and the displacement is linear.
Fig 3. Designed Planar capacitor sensor
location of flexion in this sensor doesn’t effect on
impedance and just existence of flexion influences
on it.
There are some problems in using this type of
sensor such as non-directional flexion sensing
which was solved by putting this sensor on a
flexible strip in which the sensor is constrained in
one direction that with flexion of strip in one
direction the carbon particles close to each other
and in the other direction get far from each other so
the impedance increases. The other problem is
dynamic response of sensor as during ohm
metering, sensor out put decreases. An excuse for
this problem is polarization of carbon particles and
getting close to each other. In order to solve this
problem we experienced two solutions; one AC
metering in which a sinusoidal current with
frequency of 40 KHz prevent from polarization of
carbon particles and fade dynamic response of the
sensor, the mere problem of this method is
decreasing of sensitivity of the sensor because of
capacitor behavior of carbon particles. The second
solution is timed sampling; as we don’t need
continues sampling; we put a thirty second interval
after each ohm metering in order for depolarization
of carbon particles.
There are some noticeable advantages for this
sensor type such as proper size and dimension, easy
installation on neck, good sensitivity and
repeatability.
The disadvantage of this sensor is non-linearity
response.
3.2 Planar capacitor sensor:
In order for quantitating displacement of posterior
parts of cervical spine relative to each other (c1-c5
) capacitor sensor was designed which is
constructed from two flexible sheet metal and a
dielectric plan between them which are constrained
to somehow that can move on each other easily. By
displacing the plans (change in L parameter) the
capacity of the capacitor changes according to the
following formula.
C=K(B.L)/d
One fixture must be fixed on C2 vertebrae and the
other one on . From advantages of this sensor,
linearity and simplicity are considerable and the
disadvantage of it is the difficulty during
installation which because of the existence of two
fixtures in order for installing on body.
3.3 Combined gravitational sensors :
We have designed this type of sensors in order to
measure the angle between head and trunk and each
one separately. This sensory device is constructed
form two gravitational sensors, one on head and the
other one on trunk that each one gives the angle of
horizontal plan and installation location. The angle
between head and trunk is our favorite which can
be cultivate by subtracting the response of two
sensors on head and trunk
Of course the response of each sensor separately
can be use in order for determining the body
settlement posture types (different types of
standing, sitting and lying).
Each sensor constructed from a rotary shaft
encoder which is fixed to the installation location
(head or trunk), its shaft is unbalanced by adding
non-centric mass to it. Due to installation by
changing the angle of head or trunk relate to
horizontal plan the position of shaft doesn’t change
(in relate to horizontal plan) but this us the encoder
which its position changes according to the change
of the head or trunk position so there is an angular
change between shaft and the encoder which can be
registered as the angular displacement of head or
trunk in relate to horizontal plan.
The amount of unbalancing added mass time the
arm of the unbalancing mass (m× r) is so effective
on precision and sensitivity of this sensor.
Detection of tiny angular changes necessitate
increase of mass or arm but this increase causes
some problems such as creating pendulum cyclic
motion in speedy movements which cause incorrect
out put so it was necessary to make some changes
in order to damp the cyclic motion. Fist we work
on the mechanical design of shaft and the mass
moment of inertia but because of limitations which
we had in dimensions and weight of the sensor in
order to install on head it was not so effective thus
different types of dampers were experienced to
damp the cyclic motion to somehow not to loose
tiny angular motion data.
magnetic pendulum can be coupled with added
mass and move it but in fast movements of body
because of light weight of our additional mass the
pendulum oscillation motion is negligible and also
oscillation of magnetic pendulum because of its
heavy weight is so much thus its magnetic effects
on unbalancing added mass motion is negligible.
Fig 4. Schematic of sensor instruction
In order for data recording we installed one sensor
on ear and the other one on 5th vertebrae thoracicae
(T5) .
Fig 6. Schematic of magnetic damping
3.3.2 mechanical damping
Another damper which we designed was
constructed from a leaf torsion spring and torque
gear reduction module in which the pendulum
oscillation of unbalancing added mass was damped.
Unbalancing added mass and encoder shaft are
installed on a gear which is contacted to a
constrained gear by a leaf spring. In order to damp
the oscillation pendulum motion in fast movement
effectively the constrained gear must have smaller
radius for increasing the angular displacement and
decreasing the torque of oscillation that is exerted
on the leaf torsion spring.
Fig 5. Combined gravitational sensors installation
location
3.3.1 Magnetic damping
The first damper that we used was the magnetic
one which is constructed from a pendulum with the
same length with the arm of added unbalancing
mass but heavier than it, which is from a magnetic
substance but we must take in to consideration that
the unbalancing mass must be made up of
ferromagnetic materials. The magnetic pendulum
must be centric with the encoder shaft but free from
that.
In fast motions in order to prevent from cyclic
pendulum motion lighter mass is necessary but in
reverse heavier weight was necessary in order to
detect tiny angular displacements so we used the
magnetic pendulum as a variable mass which can
vary by changing distance between magnetic and
ferromagnetic mass. It means that in slow motions
the nature of encoder shaft and encoder shaft and
unbalancing encoder mass is to somehow that it
doesn’t move because of light weight so the
Fig 7. Combined gravitational sensor installed on the ear
Another way to prevent from oscillation pendulum
motion was using the dynamic vibration absorber
(D.V.A.) which can absorbs the oscillation,
because of complexity of this system and the
limitation in weight and dimension we didn’t use it.
In order to damp the oscillation pendulum motion
we chose mechanical damper according to its better
damping response in compare to the others.
3.3.3 Shaft encoder
We experienced different types of encoder in
order to detect the angular variations and we came
to this conclusion that the best encoder is noncontact encoders because in contact encoders their
moment of inertia and internal mechanical
resistance affect on the angular displacement of
shaft. We used AM256 8 bit angular magnetic
encoder chip which is a compact solution for
angular position sensing. The IC senses the angular
position of a permanent magnet placed above the
chip. The permanent magnet must be diametrically
polarized and of cylindrical shape.
Fig 8. AM256 8 bit angular magnetic encoder chip
4 CONCOLUSION
We designed, fabricated and experienced different
sensors for measuring amount of neck flexion, the
angle between head and trunk and the displacement
of posterior parts of cervical spine relative to each
other and according to the observed problems we
optimized these sensors. Now we are working on
data recording and sesory data fusion phase in
order to fulfill our purposes in this project which is
correction of incorrect anatomic posture of
cervical spine with biofeedback method.
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Angular Magnetic Encoder IC