prototype of a human upper limb driven by pneumatic muscles · 2019-12-30 · keywords: pneumatic...

http://www.iaeme.com/IJMET/index.asp 367 [email protected]

International Journal of Mechanical Engineering and Technology (IJMET)

Volume 10, Issue 12, December 2019, pp. 367-379, Article ID: IJMET_10_12_039

Available online at http://www.iaeme.com/ijmet/issues.asp?JType=IJMET&VType=10&IType=12

ISSN Print: 0976-6340 and ISSN Online: 0976-6359

© IAEME Publication

PROTOTYPE OF A HUMAN UPPER LIMB

DRIVEN BY PNEUMATIC MUSCLES

Laura A. Beltrán, Oscar F. Avilés S, Mauricio Mauledoux,

Oswaldo Rivera, Robinson Jiménez

Universidad Militar Nueva Granada, Programa de Ingeniería Mecatrónica, Grupo de

Investigación en Mecatrónica DAVINCI, Cr 11 No. 101-80 Bogotá D.C, Colombia

ABSTRACT

The following document shows in detail the process of design, construction and

operation by applying a mechatronic system to an arm operated with pneumatic

muscles. The arm has 3 degrees of freedom through which movements of flexion,

extension, adduction and abduction are mainly generated, which will be described

inside the document. The prototype designed implements a mechanical, electronic

development and control interface.

Keywords: Pneumatic Muscle, Upper Limb assistive technology, Biomechatronics

Design.

Cite this Article: Laura A. Beltrán, Oscar F. Avilés S, Mauricio Mauledoux, Oswaldo

Rivera, Robinson Jiménez, Prototype of a Human Upper Limb Driven by Pneumatic

Muscles. International Journal of Mechanical Engineering and Technology 10(12),

2019, pp. 367-379.

http://www.iaeme.com/IJMET/issues.asp?JType=IJMET&VType=10&IType=12

1. INTRODUCTION

The number of people who lose an upper limb in Colombia every year due to causes such as

illness, an accident or as a consequence of the armed conflict according to the Colombian

Association of Physical Medicine and Rehabilitation is approximately 200 to 300 people per

100 thousand inhabitants, which is why there is a need to replace the missing members with

biomechatronic elements that resemble real members, either to replace the loss or to replace

dangerous tasks where it is necessary to apply a movement.

In Colombia, the use of robotic devices in health applications is limited due to the high

costs and the lack of availability of modern technologies, as well as the need to search for

mechanisms to solve problems such as those described above.

This work raises the possibility of generating a performance system for upper limb based

on unconventional actuators, as is the case of pneumatic muscles, for this purpose a

characterization of a McKiben type muscle is performed [10], the system is then simulated in

an environment of Matlab and later emulate the movements of the shoulder and elbow in the

upper limb on a physical device in order to validate the functionality of the system.

Laura A. Beltrán, Oscar F. Avilés S, Mauricio Mauledoux, Oswaldo Rivera, Robinson Jiménez


2. THEORETICAL FRAMEWORK

The system of locomotion of the human body is composed mainly of bones, muscles, joints

and tendons, which, together, function as support and protection of the other organs of the

body which allows the human being to interact with the environment that surrounds it.

Broadly speaking, the bones are responsible for maintaining the structure and protecting the

other organs of the body, it is a resistant tissue, which allows movement, support and balance

[8], the muscles are contractile tissues that generate displacements when contracting and / or

relax and which are attached to the bones through the tendons.

Each part of the body is composed of mechanisms that provide the ability to move, such

as the legs, feet, arms, hands, hips, head and shoulders.

The arm is a fundamental organ for the realization of daily activities that have to do with

physical strength, they also intervene in the functions of balance. The muscles of the arms are

among the most powerful in the human body. These being the ones that are located from the

hand to the shoulder blade passing through the humerus [7].

The bones that make up the arm are the humerus, which articulates with the scapula

(shoulder), the ulna and the radius (Forearm), Figure 1.

The basic movements that a human arm can perform are: Abduction, Adduction, Flexion,

Extension and rotation. To explain the types of movements it is necessary to define the planes

in which each one executes since as we know, the human being can move in three

dimensions, but generally each one of the movements that the arm has is executed in two

dimensions, In addition to the elements that intervene in it and generate movement as they are

the bones, muscles and joints [6].

Figure 1. Bone structure of the human arm

The anatomical planes are spatial references that take as reference axes the Cartesian

plane through which they allow to describe the position of the different organs and systems

[9], [7].

Prototype of a Human Upper Limb Driven by Pneumatic Muscles


Figure 2. Planes of the human body

Flexion: It is performed in three times, the first reaches 60º, and is given by the deltoid,

the coracobrachial and pectoral muscle, the second reaches 120º and the trapeze intervenes

and the third reaches 180º with the collaboration of the rachis. This movement takes place

around the transverse axis and describes the movement when the arm is raised forward. On

the shoulder, it is measured with the value of the angle that is created between the arm and the

longitudinal axis in the Flexion-Extension plane [11].

Extension: Reaches 50 degrees in a single time, the muscles involved in this movement

are the round, the deltoid and the latissimus dorsi. This movement is opposed to flexion, it

also takes place on the transverse axis, if the arm is in flexion, it is the movement that returns

it to the body again.

Abduction: As in the flexion, the 180º rotation is performed in three times, first at 60º

where the deltoid and supraspinatus intervene, the second at 120º involves the trapezius and

the third the spine. Both Abduction and Adduction take place around the anteroposterior axis

and happens when the arm moves away from the body.

Flexion and extension of the

arm. Flexion and extension of the

shoulder

Abduction and adduction of

the shoulder

Biceps contracted; Triceps

relaxed

Anterior deltoid, Pectoralis

major, biceps and

coracobrachialis muscle

Deltoid, biceps, supraspinatus

Figure 3. Some muscle groups involved in arm movement.



Adduction: Reaches 30º, the muscles intervene: broad dorsal, greater round, subscapular

and pectoral. It occurs when the arm approaches the body. In the shoulder they are measured

with the angle that is formed between the arm and the longitudinal axis

Rotation: The shoulder externally rotates 80 degrees, the infraspinatus and greater round

muscles intervene, and internally 30º intervene dorsal, round, subscapular and pectoral. It

takes place on the longitudinal axis of the member; it is the rotation of the member on its own

axis. The above can be seen in Figure 3.

3. PNEUMATIC MUSCLE

An actuator is defined as a mechanical device capable of generating a force to achieve a

displacement, the force that causes the actuator. Among the conventional ones you can find

pneumatic, hydraulic and motor-electric types.

An alternative to emulate a biological muscle is the pneumatic muscle that has its origin

by the physicist Joseph L. McKibben in the decade of the 50's. The emulation consists in

injecting compressed air to the pneumatic muscle causing a contraction and a linear

movement. The linear movement can be transmitted by means of tendons that are connected

to rigid elements to transmit a movement, in Figure 4 (FESTO, 2019) a muscle with and

without pressure is shown, the difference in length can be observed, these elements are

composed of a tube of rubber covered by a layer of twisted fibers of helical form, closed to

the ends, their characteristics are the dynamic behavior, the lightness, the reduced cost, great

initial strength and versatility.

Figure 4. Festo Pneumatic Muscle

When pressurized air is introduced through the rubber tube, it is inflated, expanding

transversely, which causes the mesh to generate tension in a direction tangential to the tube

and orthogonal to the axis of rotation, which translates into a displacement and force axial.

The nominal length of the muscle is defined to be without pressure or load, this

corresponds to the length of the rubber tube. The muscle expands when subjected to a pulling

force. When pressure is applied shrinkage occurs decreasing its length.

4. DEVELOPMENT AND CHARACTERIZATION OF THE

PNEUMATIC MUSCLE

For the construction of a prototype, materials that meet the characteristics of elasticity,

strength and displacement are taken into account in order to achieve a contraction from an

established pressure [3].

The materials used for the construction of the muscle are: Latex Hose, Braided Mesh,

Mooring, Pressure Hose FESTO ¼ "

Characterization: To perform this procedure, it should be noted that a muscle with the

following dimensions was taken as reference: Length: 20.5 cm, diameter of the hose: 1 cm. A

pressure variation from 0 bar to 4.5 bar is carried out. Figure 5 shows the muscle with load

and no load in real assembly.



Actuator

characterization

without

charge

whit

charge

P

[Bar]

d

[cm]

d

[cm]

0 20,5 20,5

0,5 20,4 20,4

1 20 20,3

1,5 19,9 20,1

2 19,5 19,8

2,5 19,2 19,3

3 18,6 18,7

3,5 18,1 18,3

4 17,9 17,7

4,5 17,3 17,4

Figure 5. Variation of the length of the artificial muscle with variation of pressure.

With the data obtained in Table 1, it is interpolated to determine the equation that defines

the behavior of the unloaded muscle:

(1)

The equation that describes the behavior of the muscle with load is:

(2)

When performing the characterization of the pneumatic muscle with a certain load, it can

be determined that the displacement is evidently reduced, the applied force depends on the

displacement of the muscle when introducing pressure, in Figure 6 the behavior of the loaded

muscle is observed.

Figure 6. Pneumatic Muscle

Finally, the behavior of the muscle in terms of the force that it exerts is presented in

Figure 7.

17

17.5

18

18.5

19

19.5

20

20.5

21

0 0.5 1 1.5 2 2.5 3 3.5 4 4.5



P

[Bar]

F

[N]

0 0

0,5 1,4

1 2,8

1,5 5,6

2 9,8

2,5 16,8

3 25,5

3,5 30,8

4 39,2

4,5 43,4

Figure 7. Variation of force versus variation of pressure

5. ANTHROPOMORPHIC ARM

For the realization of the CAD model of the arm, the bone structure of the arm is taken into

account, since this is going to be the support of the muscles, as it is handled in the real

environment.

It was exported to SolidWorks to work the arm with Simmechanics and to control the

rotation angles of each of the joints from Matlab®.

Figure 8: CAD design in SolidWorks

5.1. Muscular behavior Analysis by Opensim

Opensim is an open source software that allows to build and analyze models of the skeletal

muscle system of the human being, in addition to the dynamic simulations of movements, it

has a graphical user interface where the work that is being performed is visualized. It is

implemented in a large number of applications such as biomechanical research, medical

device design, orthopedics, rehabilitation, ergonomic analysis, robotic research and education

mainly.

Having the point of reference as the thorax, we proceed to define the movements that will

make the shoulder and arm, taking into account the degrees of freedom that a human arm is

able to rotate and / or move.

0

5

10

15

20

25

30

35

40

45

0 1 2 3 4 5



For the forward-backward movement (adduction) of the shoulder, degrees of freedom are

taken from -90 ° to 130 °, shoulder elevation (flexion) is handled from 0 ° to 180 ° (shoulder

movement from top to bottom) in orientation perpendicular to the axis of the torx, rotation of

the shoulder is between -90 ° to 20 °. In the case of the arm, a range of 0 ° to 130 ° is used for

bending.

Next in Figures 9, Figure 10 and Figure 11 is shown as from the software and the

movements made by the shoulder and elbow, it can be determined how the muscles are

coupled to the bone structure, this in order to perform an adequate emulation.

Figure 9. Shoulder Flex Movement.

Figure 10. Shoulder Adduction movement

Figure 11. Elbow flexion movement

5.2. Bend Elbow Movement

Shown in Figure 12 of the behavior of the muscles involved in the movement of flexion, such

as biceps and triceps, for the taking of the curves was determined the position of the arm at

130 ° which is the maximum angle of flexion.



It can be observed that, in the movement of the flexed arm, the triceps muscle lengthens

approximately 4 mm, while the biceps contracts 7 mm.

Figure 12. Graph OpenSim Flexion

5.3. Shoulder Flexion

It is known all the muscles mentioned above, it should be noted that it depends on the position

where the arm is, if it is in flexion or extension, its muscle groups are extended or contracted.

Figure 13.

Figure 13. Graphical Shoulder Flexion in OpenSIm

5.4. Shoulder Adduction

Figure 14. Graphical Shoulder Adduction in OpenSim



5.5. Interface Development in Matlab®

In order to implement the CAD model developed in MATLAB, it is necessary to use

Simmechanics, the SolidWorks model is exported in XML format, then after having installed

the necessary complements, it opens in Matlab which converts it to SLX (Simulink) format.

Under the block diagrams that are generated, the rotations and movements linked to the

GUIDE interface are worked and manipulated, Figure 15.

Figure 15. Model Simmechanics MATLAB

For the development of the interface, three sliders were implemented that vary the angle

of the three rotations; Elbow flexion, and rotation up-down and left-right of the shoulder.

The interface shows the value of the elongation of each muscle implemented for the

movements, in addition to the state in which it is, for example, if the arm is decreasing the

angle means that it is in extension while if it increases it is in flexion, and finally, according to

the equations, the necessary pressure is determined so that the muscle is able to move to the

desired angle.

For example, for the calculation of movement of the biceps and triceps muscle, Eq. (1)

was used, where the behavior of the muscle was determined when the angle of rotation was

changed, then Eq. (2) was used to establish the muscle behavior with load to elongation

changes, and thus determine the pressure required to achieve the desired movement.



Figure 16. Graphical Interface Matlab

The Biceps and Triceps muscles are analyzed at the 90 ° angle. For the movement of

Flexion and Extension of the Elbow

Figure 17. Elongation-pressure chart

In the case of Triceps at 90 ° the muscle is elongated approximately 0.175 cm, as the

elongation increases, the pressure increases because the muscle is contracting.

Figure 18. Simulation angle variation

For the other muscle groups we proceed in the same way



5. CONSTRUCTION AND COMPARISON OF THE MODEL PHYSICAL

IN FRONT OF THE SIMULATION OF THE ARM

ANTHROPOMORPHIC

For the construction of the anthropomorphic arm it was established before it had the

measurements of the body of a person of 1.60 m in height, therefore, its dimensions are: The

humerus, the radio cube, and trunk height. In the OpenSim model the torx was established as

earth and the movements were defined around its axis, in this case also the thoracic region

works as the base of the system. The physical model has a head, Toraxica region, and both

arms, but only in one of them is the muscular system implemented as a check.

The design of the pneumatic muscles went through several stages of improvement, since,

when handled with air, it is very prone to leakage.

Finally, the final model has the muscle groups mentioned in the document, one muscle

makes up the triceps, another the biceps, another the muscle group pectoral, the dorsal, the

Latissimuss and the trapeze, each one was implemented one by one to characterize the

movement expressed.

5.1. Flexion and Extension of the Elbow

It shows the prototype designed to check the movements of the arm by implementing

pneumatic muscles, as for this first movement, the arm does not reach the level of 130 °

flexion because it is necessary to develop more muscles complementary to the system, the

arm reaches a maximum flexion of 90 °, as far as the extension of the same the movement is

immediate.

Figure 22: Flexion Extension Prototype

The movements of flexion (Left), the state of the normal arm (center) and the extension to

the back (Right) are minimized, the flexion angle is approximately 20 ° maximum due to the

design of the prototype, with which it was sought simulate a muscle group such as pectoral,

which is a large muscle in size, in two muscle strips, things that influenced the handling of the

positions of the same.

Figure 23: Flexion Shoulder Extension Prototype



5.2. Adduction and Abduction of the Shoulder

The manner in which adduction is followed in a reduced manner is shown and then abduction

of the shoulder, the elevation angle was 30 °, emphasizing the aforementioned problem

regarding the structure.

Figure 24: Shoulder Adduction Prototype

6. CONCLUSIONS

The development of a homemade pneumatic muscle as an actuator is a very viable solution if

one looks for strength and economy, its construction is elementary for its correct functioning,

since it is necessary to take into account the minor losses of pressure for the muscle to be able

to do more route, at the time of its characterization should be taken into account the values of

length, cross-sectional area, pressure and load that will be handled, making tests with

maximum force, and minimum necessary for the muscle to contract.

When implemented as a muscle group that simulates the movements of the human arm, is

not very accurate in terms of position requirements, it is due to the way the muscles were

coupled, its coupling was made with a thread called Hactan, which is Rigid enough, in the

first measurement the coupling was made with Nylon, but since the muscle generates an

approximate force of 10 N it was able to yield. With the thread, the movement was generated,

but it was quite brusque and not very exact.

Another aspect that stands out in terms of accuracy is mentioned above, the lack of

muscles to achieve a more stable and similar movement.

A prototype of an anthropomorphic robot with three degrees of freedom and rotating

articulations was designed and built in order to show in a general way the application of

pneumatic muscles for this purpose. In addition to this, an analysis and simulation tool was

developed that allows to verify the mathematical foundations with the real application.

The analysis developed by OpenSim, was necessary to define the behavior of each muscle

with the respective movements, in addition to the muscle groups required for each of the

movements that were allowed in the arm, push-ups, extensions, abductions and adductions.

The development of the simulation under the MATLAB Software has the necessary

indications to understand how arm movement develops, which are the antagonistic muscles

and the pressures necessary to achieve, under ideal conditions, the control of angular position,

in addition to a visual feedback to identify the position to which the arm leads with the

variation of the angles.

According to the analysis of art states, the developed anthropomorphic arm has lightness,

strength and economy to those developed previously, it is clearly necessary to make the model

more stable, it is a first prototype of an excellent option to work as a prosthesis or as a

manipulator distant.



Finally, it is important to highlight the differences between the pneumatic muscle and the

real one, the main ones are the speed of movement, the elongation of each one, and in my

opinion one of the most important, the coupling to the bone system.

ACKNOWLEDGEMENTS

This work was financially supported by the Vice presidency for Research of Universidad

Militar Nueva Granada, through the project ING-2657.

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prototype of a human upper limb driven by pneumatic muscles · 2019-12-30 · keywords: pneumatic...

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