Proceedings of the World Congress on Engineering and Computer Science 2017 Vol II
WCECS 2017, October 25-27, 2017, San Francisco, USA
Low Cost Mechatronics Prototype Prosthesis for
Transfemoral Amputation Controled by Myolectric
Signals
Bravo Xavier, Comina Mayra, Tobar Johanna, Danni De La Cruz, David Loza, Jonathan Corella
Abstract— This article presents the development of low cost is difficult to access a prosthesis that helps them walk, for
prototype prosthesis for transfemoral amputation leg, the this reason the social impact of the project, due to be a
prototype has not only low weight but also emulates the functional and economic prosthesis, is highly beneficial [1]
natural movement of a leg. It is activated by myoelectric
signals obtained through the rectus femoris muscle of the
amputated leg stump. Additionally, the prosthesis has a
The socket has a coupling system by pneumatic
constant monitoring system of physiological parameters of compression whose rigidity can be controlled by the Fuzzy
temperature and humidity, this monitoring can be seen system that allows the real-time automation of pressure in
through an application for mobile phones. For this, the specific areas of the socket. [2]
biomechanical analysis of gait was performed, after that the
mechanical and electronic design, and finally test and results. Another of the main parts is the knee, although the
mechanical knees are capable of performing a quite adequate
Keywords—Prosthesis, Transfemoral, Myoelectric, cycle, they present a deficiency adapting to these changes.
Physiological, Monitoring. The article "A Robotic Leg Prosthesis" by Brian E. Lawson
integrates various electronic components, adds and
coordinates the actions of a knee and ankle motor with the
I. INTRODUCTION intention of replicating biomechanics of the healthy limb. [3]
The importance of this work lies in providing a solution to Regarding the feet designs, that have position sensors to
the problem faced by much people in Ecuador who have regulate the angles of foot movement according to the
been affected by a transfemoral amputation, since at present running cycle, are implemented; a clear example of this is
people with physical disabilities in Pichincha province developed in the title article: "Design of foot and ankle
represent the 2.51% of the total population. The vast powered prosthesis By parallel elastic actuators "developed
majority of these people has lack of economic resources so it by Fei Gao, Wei-Hsin Liao, Bing Cehn, Hao Ma, Lai-Yin
Qin. Its design improves the storage efficiency and release
A transfemoral amputation prosthesis consists of three of mechanical energy by reducing the dimensions of the
main parts: the socket, the knee, and the foot. The Socket is device. [4]
the only part of the prosthesis that is in direct contact with
human skin and allows the prosthesis to attach to the body
Research is currently underway on the development of new II. BIOMECHANICAL ANALYSIS OF THE GAIT
styles of sockets in order to improve the people comfort
during the use of this coupling part; one of these innovations A. Analysis of parameters during the gait cycle.
is detailed in the article named "Development of an
immediate automatic lace system for artificial leg and Slow-cycle analysis is performed by placing markers at
modeling of a socket with Fuzzy Control "developed by four reference points along the leg:
Kohuei Najamura, Kazuhiko Sasaki and Kinya Fujita Tokyo
University of Agriculture and Technologies members.
Ing, Bravo Xavier, Universidad de las Fuerzas Armadas - ESPE,
Sangolquí, Ecuador (e-mail: xavieralcivar5555@gmail.com).
Ing, Comina Mayra, Departamento de Ciencias de la Energía y Mecánica.
Universidad de las Fuerzas Armadas - ESPE, Sangolquí, Ecuador (e-mail:
mecomina@espe.edu.ec).
Msc, Johanna Tobar, Departamento de Ciencias de la Energía y Mecánica,
Universidad de las Fuerzas Armadas - ESPE, Sangolquí, Ecuador (e-mail:
jbtobar@espe.edu.ec).
Msc, David Loza, Departamento de Ciencias de la Energía y Mecánica.
Universidad de las Fuerzas Armadas - ESPE, Sangolquí, Ecuador (e-mail:
dcloza@espe.edu.ec).
Msc, Danni De La Cruz, Departamento de Eléctrica y Electrónica,
Universidad de las Fuerzas Armadas - ESPE, Sangolquí, Ecuador (e-mail:
drde@espe.edu.ec).
Jonathan Corella está en el Departamento de Ciencias de la Energía y
Mecánica, Universidad de las Fuerzas Armadas - ESPE, Sangolquí,
Ecuador (e-mail: jpcorella@espe.edu.ec).
Fig 1. Reference points for gait cycle analysis
ISBN: 978-988-14048-4-8 WCECS 2017
ISSN: 2078-0958 (Print); ISSN: 2078-0966 (Online)
Proceedings of the World Congress on Engineering and Computer Science 2017 Vol II
WCECS 2017, October 25-27, 2017, San Francisco, USA
These reference points are captured by a camera to
generate a series of frames that after being analyzed allow to
obtain the data of: speed, walking time, number of steps, step In the analysis of the movement intervals of human gait
length, and acceleration; so they can be used in the design was observed that the maximum angle reaching the knee is
of parts and pieces. and the minimum angle is , considering at most,
calculate torque shown below:
Table 1 shows the results of the variables analyzed during
the slow gait cycle. C. Angular analysis of the leg during the gait cycle
TABLE I
GAIT CYLLE VARIABLES
A cycle starts when one foot touches the ground and ends
Variables Results when the same foot touches the ground again. The cycle is
Time slow gait 3 seconds
Number steps slow gait 5 steps formed by two main phases: first, the support phase that
Step length slow gait 510 mm starts with the initial contact of the heel and ends with the
Speed slow gait 1.67 m/s takeoff of the fingers after that the swing phase begins; that
Acceleration slow gait 0.55 m/ phase is defined as the time from takeoff to when the foot
Maximum knee angle touches the ground again. (Sanz, 2017) [4]
Minimum knee angle
Next, the angular analysis of the leg without amputation
during the support phase is shown in Figure.3, considering
B. Force analysis the following steps:
Heel contact: Refers to the moment when the heel
The forces analysis in the knee was performed of the reference leg touches the ground.
considering the gait where the person can displaced by a Plantar support: refers to the contact of the forefoot
horizontal plane with a slight inclination, taking into with the floor.
account the angle of variation that happens in the knee Medium Support: occurs when the greater
movement. trochanter is aligned vertically with the center of
the foot, seen from a sagittal plane.
Heel lift: occurs when the heel rises from the floor,
Foot peeling: occurs when fingers rise from the
floor. (Sanz, 2017)
Fig 2. Load-displacement of the human leg
In Figure. 2 we can be observed the decomposition of
the P force in the corresponding axes. y are the
components of the prosthesis weight in the x and y axes
respectively.
This analysis is necessary to find the torque that the
motor should have to simulates the knee movement. For
this, the following parameters are considered: person mass
( , the knee radius ( ), acceleration ( ), gravity ( , the
angle variation that occurs during the gait ( ), the motor
efficiency and the safety factor .
As a result of that previous process the necessary Fig 3. Leg support phase without amputation
torque for the motor is obtained considering a safety factor
of 2 and an efficiency motor of 90% : Then, Figure. 4 shows the angular analysis of the leg
(1) without amputation during the swing phase considering its
next steps:
ISBN: 978-988-14048-4-8 WCECS 2017
ISSN: 2078-0958 (Print); ISSN: 2078-0966 (Online)
Proceedings of the World Congress on Engineering and Computer Science 2017 Vol II
WCECS 2017, October 25-27, 2017, San Francisco, USA
-Acceleration: it is characterized by the rapid acceleration of
the end of the leg immediately after the fingers leave the
ground.
-Medium swing: the balanced leg passes to the other leg,
moving forward of the same leg, since it is in the support As observed the ultimate strain is 36.55 MPa, value
phase which was higher in relation to Von Mises' efforts than was
-Deceleration: the leg stops quickly when it approaches the obtained in the finite element analysis performed on each of
end of the interval. (Sanz, 2017) the elements of the prosthesis. Which allowed to verify using
a real data that the prototype will support the efforts for
which it was designed
B. CAD Model
The knee and the foot are the main elements of the
prototype. On the knee a mechanical brake was incorporated
to a servomotor that allowed to control the return of the
prosthesis, this because the inertia that is generated during
its operation emulating the movement of a human leg. The
foot is formed by a simple articulation that allows to
regulate the angles with which it moves, improving stability
when walking. Figure 5 shows the CAD model of the
prototype
Fig 4. Swing phase of the leg without amputation.
III. DISEÑO MECÁNICO
A. Traction Test – Material Compression
The material used in the prosthesis is Aluminum. This
material was subjected to tensile and compression tests, in
order to determine if the material will support the 80 kg of
the person, who will use the prosthesis. Fig 5. CAD Model Fig 6. Real prototype.
The tensile and compression tests were performed in a
universal test machine, in which the following results were
obtained: maximum compression value of 9000 kg and
traction of 120 kg. With these data, it was possible to C. CAE Analysis
conclude that the 120 kg that the molten aluminum specimen The finite element analysis was performed in a software to
supported in the tensile test is the critical value in relation to observe the behavior of the parts under static and fatigue
the 9000 kg that are supported in the compression test. So the loads as seen in Figure. 7
ultimate strain is then calculated as shown in equation 2.
(2) The safety factor against fatigue based on finite life was
calculated by applying Modified Goodman's equation.
Then the values are replaced assuming that the specimen (3)
had an initial diameter of 6.40 mm.
These values were used in the mechanical design phase for
static load and fatigue analysis, obtaining the safety factors
specified in the Table II.
ISBN: 978-988-14048-4-8 WCECS 2017
ISSN: 2078-0958 (Print); ISSN: 2078-0966 (Online)
Proceedings of the World Congress on Engineering and Computer Science 2017 Vol II
WCECS 2017, October 25-27, 2017, San Francisco, USA
TABLE II
CAE ANALYSIS RESULTS
Parts Tension Displacement Unitary Minimum
(GPa) (mm) Strain Safety
Factor
Socket coupling 14.5 1.097 x 10-2 1.635 x 10-4 1.9
joint
Knee coupling 16.2 1.445 x 10-3 1.741 x 10-4 1.7
joint
Knee 2.55 1.906 x 10-3 2.823 x 10-5 1.7
Steam 11.3 6.973 x 10-4 1.133 x 10-4 2.5
Ankle 9.58 1.058 x 10-2 9.042 x 10-5 2.9
Foot 19.9 1.066 x 10-2 2.085 x 10-4 1.4
Knee axle 10.6 6.356 x 10-3 3.832 x 10-4 1.62
Foot axle 0.37 1.083 x 10-5 1.44 x 10-6 1.62
Fig 7. FEA Analysis IV. ELECTRONIC DESIGN
In order to activate the prosthesis, we obtained the signals
from the anterior rectus muscles and the vastus external,
with the purpose of selecting the muscle that generates
better biopotentials, as can be seen in Figure. 9, there is
greater repeatability in the measurements of the anterior
rectus muscle, whereby this was selected to give the signal
of activation to the prosthesis
The prosthesis was activated by the myoelectric signals
obtained through the anterior rectus muscle of the
amputated leg stump, thus this way the microcontroller can
send the signals to the knee and hell servomotors to start the
movement when it detects a potential difference when
contracting the muscle.
Fig 8. Stem FEA Analysis
Fig 9. Comparison of vastus external and rectus muscle signals during gait cycle.
ISBN: 978-988-14048-4-8 WCECS 2017
ISSN: 2078-0958 (Print); ISSN: 2078-0966 (Online)
Proceedings of the World Congress on Engineering and Computer Science 2017 Vol II
WCECS 2017, October 25-27, 2017, San Francisco, USA
extension of the leg. Figure. 11 and Figure. 12 shows the
V. TEST AND RESULTS extension and flexion of the stump, respectively
The protocol of tests is made with the collaboration of the
“prosthetist”, establishing the guidelines and requirements
of a standard prosthesis.
A. Bank alignment
In the test, the prosthesis parts were assembled on a
work station without the patient, the dimensions, alignment
and stability of the prosthesis were checked and the foot was
aligned horizontally. The dimensions were verified
comparing them with those of the healthy limb; it was
achieved alignment and stability in the prosthesis when
checking that the load line is below the axis, with this it was
possible to determine that the prosthesis is perfectly armed
for patient use. Fig 11. Extension of the Fig 12. Flexed prosthesis
B. Static alignment prosthesis.
In the test, the patient is standing with the prosthesis in
which heights, rotations, inclinations, and others parameters D. Gait angular analysis
were verified to obtain a stable standing and a level support Fig. 13 shows the walking cycle analysis during the
on the surface of the floor. It was also verified that the support phase and the swing phase in which angular
patient was aligned, So that it distributes its weight displacements of the knee and foot were verified.
symmetrically, 50% to its affected extremity and 50% to its
healthy extremity as shown in Figure.10.
Fig 13. Angular analysis of the prosthesis during the gait cycle
VI. RESULTS
Fig 10. Standing patient.
The angles were obtained from the analysis of the gait
C. Dynamic alignment cycle of the leg without amputation and the prosthesis, as
presented in Figure 14 y 15
In the test the patient performed his first steps and The Table V below shows a comparison between
started walking, after that the following aspects were measurements taken on the leg without amputation and the
verified: that the passage length is correct, that the patient is prosthesis. The angles correspond to the knee, ankle and
treading on the surface of the floor as flat as possible, that it foot.
does not have many inclinations. Two main views were As can be seen in the table the error rate do not exceed
valued: 5%, allowing to affirm that the operation of the prosthesis
- Front view or back view: In this view the stump resembles the natural movement of a human leg and that can
inclination was determined, in which two main cases can be be verified in the development of the patient's gait. Results
observed: the adduction which is an internal deviation of the guarantee the high efficiency of the prosthesis that improves
stump and the abduction is an external deviation of the stability when walking allowing you to have greater
stump relative to the neutral line. confidence and safety to carry out your activities.
- Side view: In this test the patient is standing sideways Regarding the acquisition of temperature and
in the sagittal plane, in this view the flexion or extension of humidity signals, different conditioning circuits were
the stump was evaluated since these parameters modify the performed, based on the results shown in Table VI and VII,
alignment of the prosthesis. Ideally, the flexion degrees The most suitable circuits for its implementation were
should be equal to the extension degrees during the selected.
ISBN: 978-988-14048-4-8 WCECS 2017
ISSN: 2078-0958 (Print); ISSN: 2078-0966 (Online)
Proceedings of the World Congress on Engineering and Computer Science 2017 Vol II
WCECS 2017, October 25-27, 2017, San Francisco, USA
VII. CONCLUSION
A prototype of leg prosthesis for transfemoral amputation
was made using low cost mechanical and electronic
components. The design requirements were obtained from
the gait cycle analysis, from which the angular
displacements that were produced when walking were
acquired and compared with the angles of the leg without
amputation obtaining an error of between 0% and 5%,
allowing having a natural movement in the gait. The
temperature and humidity monitoring allows the prosthetics
to be kept under constant control, so as not to exceed 37 ° C
and 70% humidity, parameters that will be displayed in a
mobile phone application and keep the patient informed,
avoiding alterations in the skin of the stump.
Fig 15. Prosthesis angle REFERENCES
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ISBN: 978-988-14048-4-8 WCECS 2017
ISSN: 2078-0958 (Print); ISSN: 2078-0966 (Online)
