Karsten Mortier Braided pneumatic muscles for rehabilitation apparatus

79 Pages·2014·12.42 MB·English

Braided pneumatic muscles for rehabilitation apparatus
Karsten Mortier
Supervisors: Prof. dr. Paul Kiekens, Prof. Guido Belforte
Master's dissertation submitted in order to obtain the academic degree of
Master of Science in Textile Engineering
Department of Textiles
Chairman: Prof. dr. Paul Kiekens
Faculty of Engineering and Architecture
Academic year 2013-2014
Acknowledgment
Hereby I would like to thank prof. Guido Belforte for giving me the possibility of doing my thesis in the
Politecnico di Torino. Also my thanks goes to ir. Silvia Sirolli, who helped me at the set-up of the tests
and answered my questions throughout the semester.
Next I would like to thank my friends I met during this two years of international master and my friends
from Belgium. Thanks for all the joy they’re bringing.
I would like to thank especially my two friends Adam and Joeri for the given advice and review of
my work. It was greatly appreciated.
FinallyIwouldliketothankmyparents,sister,StevenandgirlfriendFabiolafortheirsupportthroughout
this master.
Copyright notice
The author gives permission to make this master dissertation available for consultation and to copy parts
of this master dissertation for personal use. In the case of any other use, the limitations of the copyright
havetoberespected,inparticularwithregardtotheobligationtostateexpresslythesourcewhenquoting
results from this master dissertation.
Karsten Mortier
20 July 2014 - Turin
i
Summary
Braided pneumatic muscles are soft in touch, (cid:29)exible, and have a contraction ratio similar to the muscles
ofahumanarm. Butespeciallytheirveryhighpowertoweightratiomakestheminterestingactuators. It
consistsoutofanexpandablebladdersurroundedbyabraidedsheath. Duetoitsdesign,itcontractsand
generates a tensile force when pressurized air is injected. The braided pneumatic muscle is better known
under the name of McKibben muscle. Its main disadvantage is the di(cid:30)culty in accurately controlling the
muscle due to its non-linear behavior.
Currently, the actuation of rehabilitation apparatus is mainly done by electric motors. Due to im-
provements in modern controllers, complex feedback algorithms can be used to control actuators with
non-linear behavior. It should be examined if the braided pneumatic muscles could be a worthy alter-
native for actuating rehabilitation apparatus. When the di(cid:30)culty in accurately controlling is overcome,
variousadvantagesofthebraidedpneumaticmusclecanbeaddedtorehabilitationapparatus. Itcanlead
to a lower cost and a lower overall weight of the apparatus. This is very important due to the increasing
demand for rehabilitation apparatus in our increasing elderly society.
Thisthesisisdividedintofourparts. First,adescriptionofthebraidedpneumaticmuscleisgiven. The
typicalcontractionbehaviorandgeneratedtensileforceinfunctionoftheinjectedpressureareexplained.
In Politecnico di Torino, own braided pneumatic muscles are developed and their tensile and contraction
behavior are examined by several tests. Part two deals with the modeling of the muscles. A distinction
is made between an experimental and physical model. The aim of the described models is to predict the
generated tensile force in function of the muscles contraction and pressure. An accurate model simpli(cid:28)es
the controlling of the muscles in various applications. The results of most important conducted research
are mentioned and is followed by the (cid:28)rst task for this thesis: calculating an own experimental model
for the braided pneumatic muscles. Results of the performed tests and accuracy calculations are given.
The second task for this thesis is explained in part three. A rehabilitation apparatus actuated by braided
pneumaticmusclesisdesignedinMatlab. Thisprototypeshouldrehabilitatetheupperlimpandperform
total three movements: in shoulder, elbow and forearm. The information from previous described parts
is used to select the dimensions of the muscles for their integration in the rehabilitation prototype and an
explanation of the design is given. The fourth and last part gives a conclusion of the thesis.
Keywords: McKibben muscles, experimental modeling, rehabilitation apparatus, upper limp
ii
Braided pneumatic muscles for rehabilitation
apparatus
Karsten Mortier
Supervisor(s): Prof. Guido Belforte, ir. Silvia Sirolli
Abstract - This research examines the contraction and tensile B. Working principle
force behavior of Braided Pneumatic Muscles in function of
The muscle allows an injection of air pressure inside the
injected air pressure. These muscles are often referred as
bladder. An amount of energy is introduced in the muscle. The
McKibben muscles in literature and it's examined if they would
most stable state is wanted by increasing the bladder volume.
be a worthy alternative for the actuation of modern rehabilitation
apparatus. Therefore, a device with 3 degrees of freedom is The braided sheath surrounding the bladder makes an
designed for the rehabilitation of the upper limb. The actuation expansion in axial direction impossible. Instead the muscle
will be done by the Braided Pneumatic Muscles. expands in radial direction and a contraction of the muscle is
Keywords - McKibben muscles, Braided Pneumatic Muscles, observed. The strands of the sheath reposition themselves so
rehabilitation apparatus, upper limb the diameter can increase, leading to a contraction of the
length.
A load applied on the end of the muscle counteracts the
I. INTRODUCTION contraction of the muscle. Then is the introduced energy
converted into a generated tensile force.
Today, strokes are the main reason of full or partial
disability in the upper limb. A long and slow rehabilitation is
C. Design properties of the BPM
needed to retrieve the limbs functionality. It is believed that
the amount of people suffering of strokes will be increased Braided Pneumatic Muscles can be developed in a range of
due to the increasing amount of elderly persons in our society. diameters and lengths. The effects of these properties are:
The demand for a rehabilitation apparatus assisting the 1) Initial length of the muscle
medical personnel keeps increasing. Todays used apparatus An enlargement of the muscles initial length will increase
are actuated by electrical motors. An actuation by Braided the length of contraction when air pressure is injected. The
Pneumatic Muscles can add several advantages to an contraction ratio expresses the contraction displacement in
apparatus. It can lower the cost and increase the mobility of percentage of its initial length. It should be noted that the
the device. contraction ratio is independent of a change in initial length.
A commercial breakthrough of Braided Pneumatic Muscles This value is constant in BPM and has a typical value of 30-
hasn't been achieved in robotic applications. This is due to the 35%. [1]
difficulty of controlling the muscles accurately. The 2) Outer-diameter of the BPM
controlling was complicated by the non-linear behavior of the An enlargement of the muscles outer-diameter will increase
Braided Pneumatic Muscles. It is believed that modern the generated tensile force when air pressure is injected. The
controllers with complex feedback algorithms can solve the pressurized air converts the energy into a larger tensile force
controlling issue. due to the increase of surface area.
For this reason, a rehabilitation apparatus actuated by
Braided Pneumatic Muscles is designed. First several tests are D. Main characteristics of the BPM
conducted on self-assembled muscles to examine their
• contractile force for a given cross-sectional area of
behavior. These muscles are integrated in the mechanical
the muscle can be over 300N/cm² [1]
design of a rehabilitation apparatus for the upper limb
• contraction ratio is typical 30-35 % of the initial
describing 3 degrees of freedom. The data from the tests are
muscle length [1]
analyzed in Matlab and the mechanical design is made in
• very high force to weight ratio ( > 1kW/kg) [1]
SolidWorks.
E. Conducted tests
II. DESCRIPTION BRAIDED PNEUMATIC MUSCLES
Four tests are conducted to examine the muscles behavior.
1. Examining the contraction behavior under influence
A. Parts of the muscles
of injected air pressure and applied loads.
Braided Pneumatic Muscles consist out of three main parts. 2. Examining the generated tensile force under
A bladder is surrounded by a braided sheath which are influence of injected air pressure and predefined
connected in the ends by end-fittings. The bladder is made out contraction ratios.
of a latex rubber and the braided sheath consists out of 3. Examining the hysteresis effect of the generated
inextensible strands. The bladder is sealed off from the tensile force during muscle inflation and deflation
surrounding environment and one of the end-fittings is adapted with no muscle contraction.
to allow an injection of air pressure.
4. Examining the hysteresis effect of the contraction
ratio during muscle inflation and deflation and
examining the effect of applied loads on the
hysteresis.
III. RESULTS OF THE TESTS
In total 10 prototype muscles are assembled (with the
distinction of two sizes in outer-diameter). The tensile and
contraction behavior are examined by the four previously
described tests. The results are given here in 4 figures.
Figures one and two represent information of five muscles
with an outer-diameter of 15mm. The lines represent the
means of the five muscles. The standard deviation, which
represent the location of 95% of the results, is also displayed
in the figures 1 and 2.
Figures three and four represent information for the
hysteresis of one muscle.
Figure 2: test 2 Contraction ratio vs injected air-pressure
In figure 1, the tensile force is examined under a predefined
contraction ratio of the muscle (0, 5, 10, 15, 20 and 25 %). In figure 3, the hysteresis effect on the tensile force is
The ratios are indicated by different colors. The generated examined. The muscle is inflated to 2 bar and back deflated to
force rises linear proportional with the injected pressure. 0 bar. This test is repeated 3 times in a row. An hysteresis
When a predefined contraction ratio is set, the muscle needs to effect on the tensile force is observed. The size of the
inflate first. The tensile force is generated after the muscle is hysteresis effect is equal in all 3 tests. The hysteresis effect is
inflated (until its predefined contraction ratio). independent on the amount of performed working cycles.
figure 3: test 3 hysteresis effect on the generated tensile force
Figure 1: test 1 Tensile force vs injected air-pressure.
In figure 4, the hysteresis effect on the contraction ratio is
examined. Like previous test, the muscle is inflated to 2 bar
In figure two, the contraction ratio is examined under an
and back deflated to 0 bar. This is performed 11 times while a
applied load (0, 1, 2, 3, 4, 5 kg). The weights are expressed
load was applied and removed. First the muscle was loaded
into their corresponding force and are indicated by different
with 0 kg (indicated with load1), and is risen to 5kg (indicated
colors. After a certain pressure threshold is reached, rises the
with load6) with steps of 1kg. After this sixth load, the weights
contraction ratio logarithmic when air pressure is injected. The
were removed until 0kg (indicated with load11) was reached
contraction ratio approximates a maximum value at a pressure
again. The loads with equal weight are indicated in the same
of 4 bar, around 29% for a muscle diameter of 15 mm, when
color. The solid lines represent the increasing loads, the dotted
the muscle isn't loaded. An increase of loads weight leads to a
lines represent the decreasing loads.
decrease of contraction ratio.
A first conclusion can be drawn when one load cycle is
observed, a hysteresis effect on the contraction ratio is present.
A second conclusion is that an increasing load (0 to 5 kg)
doesn't increase or decrease the hysteresis effect.
Third, no significant effect of the hysteresis was observed
between the load order (load1 to load11) and the contraction
behavior.
contraction when both are injected with a different pressure.
This will move the wire and create a friction force at the
pulley. The pulley will rotate if the friction force is higher than
the gravitational force. The muscles dimensions can be
calculated according to the necessary range of rotation of the
pulley. It is considered that no slippage between the wire and
pulley occurs due to the low weight construction of the
apparatus.
C. Results of the mechanical design
The mechanical design is developed in the CAD software
SolidWorks. The proposed design is showed in figure 6.
figure 4: test 4 hysteresis effect on the contraction ratio
IV. DEVELOPING AN EXPERIMENTAL MODEL
An experimental model can predict the contraction behavior
and tensile force in function of the injected air-pressure. A
model is developed after several performed tests on the
muscles. An accurate model can simplify controlling of
robotic and automatized applications.
A method of developing an experimental model is examined
with the data of test 1 and 2. The acquired models were figure 6: mechanical design of the rehabilitation apparatus
proven inaccurate due to individual differences in the muscles.
It consists out of 4 muscles pairs. The design works for both
This is observed in the standard deviation of figures 1 and 2.
left and right arm without any re-adjustments. The calculated
A large spread of data is observed especially in figure one at
initial length of the muscles actuating the shoulder, elbow and
high pressure area. The spread of data is a result of errors
forearm are respectively 23.17 cm, 13.2cm and 17.67cm (if a
present in the BPM prototypes.
muscle with contraction rate of 30% is considered).
V. DESIGNING OF A REHABILITATION APPARATUS
VI. CONCLUSION
A rehabilitation apparatus for the upper limb is designed.
A. Task of designing an apparatus
This devices is actuated by Braided Pneumatic Muscles. The
Next, a rehabilitation apparatus for the upper limb is
design is kept simple and as light weight as possible. This
designed. This device needs to be actuated by the recent
research should be start of examining if a production of cheap
examined Braided Pneumatic Muscles. By integrating BPM
rehabilitation apparatus is possible.
technology, this will lead to a low cost and low weight
Several tests are conducted to examine the contraction
apparatus with soft touch actuators.
behavior and tensile force in function of the injected pressure.
The apparatus is designed with a total of 3 degrees of
freedom: in shoulder, elbow and forearm.
REFERENCES
B. Joint motion by antagonistic muscle pairs
[1] D. Caldwell, N. Tsaragakis, "Soft" exoskeletons for upper and lower
The robotic arms (where the human arm is attached) should body rehabilitation - design, control and testing, International journal
of humanoid robotics, Vol. 4, No. 3, 2007
rotate around the joints. This is done by setting up 2 muscles
[2] S. Eskiizmirliler, N. Forestier, B. Tondu, C. Darlot, A model of the
in agonist and antagonist pair as shown in figure 5.
cerebellar pathways applied to the control of a single-joint robot arm
actuated by McKibben artificial muscles, Biological Cybernetics,
Vol. 86, 2002
figure 5: antagonistic muscle pair [2]
The ends of the muscles are connected with a wire which is
circled around a pulley. The 2 muscles will have a different
Contents
Acknowledgment i
Copyright notice i
Summary ii
Extended abstract iii
Table of contents vi
Nomenclature ix
I Description Braided Pneumatic Muscle 1
1 General information of the Braided Pneumatic Muscle 1
1.1 History of the Braided Pneumatic Muscle . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
1.2 General description of BPM . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2
1.2.1 Contraction behavior of the BPM . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
1.2.2 Parts of BPM and used materials . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
1.2.3 E(cid:27)ect of the braid on the working principle of Braided Pneumatic Muscle . . . . . 4
1.2.4 Characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
1.3 Geometry of the braid . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
1.4 Properties: e(cid:27)ect of muscle length, diameter, braid angle, maximum contraction . . . . . 6
1.4.1 E(cid:27)ect of the length and diameter of the BPM . . . . . . . . . . . . . . . . . . . . . 6
1.4.2 E(cid:27)ect of the weave of the braid . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
1.4.3 E(cid:27)ect of the braid angle . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
1.5 Advantages, disadvantages and why is there interest in BPM . . . . . . . . . . . . . . . . 8
1.6 Braided Pneumatic Muscles from the Politecnico di Torino. . . . . . . . . . . . . . . . . . 9
1.7 Necessary equipment for usage of BPM technology . . . . . . . . . . . . . . . . . . . . . . 11
1.8 Comparison with traditional rod & piston . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
1.9 The state-of-the-art pneumatic muscles. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
1.9.1 Linear tension pneumatic muscles . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
1.9.2 Flexible pneumatic muscles . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
II Experimental and physical modeling 16
2 Literature study: Modeling the behavior of BPM 17
2.1 Purpose and di(cid:30)culties of modeling in process-controlling . . . . . . . . . . . . . . . . . . 17
2.2 Physical models from literature . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
2.2.1 Basic static model of Schulte . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18
2.2.2 Consideration of bladder and braid thickness . . . . . . . . . . . . . . . . . . . . . 19
2.2.3 Consideration of conic shape . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20
2.2.4 Consideration of bladder elasticity . . . . . . . . . . . . . . . . . . . . . . . . . . . 23
2.2.5 Consideration of Elastic energy storage of the actuators bladder . . . . . . . . . . 25
2.2.6 Consideration of (cid:28)ber stretching . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25
2.2.7 Consideration of friction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26
2.3 Conclusion modeling the behavior of BPM . . . . . . . . . . . . . . . . . . . . . . . . . . . 30
vi
3 Practical part: Making experimental model for BPM 31
3.1 Introduction: describing the behavior of own Braided Pneumatic Muscle . . . . . . . . . . 31
3.2 The test bench of Politecnico di Torino . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31
3.3 The set-up of the test bench for the performed tests . . . . . . . . . . . . . . . . . . . . . 34
3.3.1 Set-up of the test bench and procedure for test 1 PL (pressure - length) . . . . . . 34
3.3.2 Set-up of the test bench and procedure for test 2 PF . . . . . . . . . . . . . . . . . 35
3.3.3 Set-upofthetestbenchandprocedurefortest3PFhysteresisandtest4PLhysteresis 35
3.4 Examining the behavior of the BPM . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36
3.4.1 Results of the test 1 PL . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36
3.4.2 Results of the test 2 PF . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37
3.5 Examining the hysteresis e(cid:27)ect of the BPM . . . . . . . . . . . . . . . . . . . . . . . . . . 38
3.5.1 Results of the test 3 PF hysteresis . . . . . . . . . . . . . . . . . . . . . . . . . . . 38
3.5.2 Results of the test 4 PL hysteresis . . . . . . . . . . . . . . . . . . . . . . . . . . . 39
3.6 Calculation of the experimental model of the BPM . . . . . . . . . . . . . . . . . . . . . . 40
3.6.1 Step 1: Calculating the averages of PF and PL tests for diameter 15 and 22 . . . . 42
3.6.2 Step 2: Combining data from PF and PL tests . . . . . . . . . . . . . . . . . . . . 43
3.6.3 Step 3: Calculating the average of the PF and PL tests . . . . . . . . . . . . . . . 43
3.6.4 Step 4: The results for the experimental models. . . . . . . . . . . . . . . . . . . . 43
3.6.5 Determining the accuracy of the Models . . . . . . . . . . . . . . . . . . . . . . . . 44
3.6.6 Conclusion of the experimental model . . . . . . . . . . . . . . . . . . . . . . . . . 45
3.7 Conclusion experimental modeling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45
III Designing Rehabilitation apparatus 47
4 Literature study: Reviewing of existing rehabilitation apparatus and technology 48
4.1 Forearm anatomy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 48
4.2 Currently used rehabilitation apparatus . . . . . . . . . . . . . . . . . . . . . . . . . . . . 49
4.2.1 Kinetec Centura Shoulder & Elbow CPM Machine . . . . . . . . . . . . . . . . . . 49
4.2.2 Biodex System 4 Pro . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 50
4.3 Use of Braided Pneumatic Muscles in rehabilitation apparatus . . . . . . . . . . . . . . . 51
4.3.1 Why use braided pneumatic technology in rehabilitation apparatus? . . . . . . . . 51
4.3.2 The (cid:28)rst historically apparatus in the medical sector actuated by BPM technology 51
4.4 Rehabilitation apparatus prototypes actuated by pneumatic technology . . . . . . . . . . 51
4.4.1 iPam . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 52
4.4.2 RUPERT . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 52
4.4.3 PNEU-WREX . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 54
4.4.4 SRE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 54
4.4.5 Conclusion State-of-the-Art rehabilitation apparatus . . . . . . . . . . . . . . . . . 54
5 Practical part: Designing own Rehabilitation Prototype 55
5.1 Decisions, characteristics and choice of technology for apparatus . . . . . . . . . . . . . . 55
5.1.1 Joint motion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 55
5.1.2 Linking the BPM to the joints . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 56
5.1.3 Exoskeleton or static apparatus . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 56
5.1.4 Location of the BPM on the apparatus. . . . . . . . . . . . . . . . . . . . . . . . . 56
5.1.5 Conclusion of the made design decisions . . . . . . . . . . . . . . . . . . . . . . . . 57
5.2 Mechanical design of the Prototype . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 57
5.2.1 Prototype sketch phase one . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 57
5.2.2 Prototype sketch phase two . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 59
5.2.3 Prototype sketch phase three . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 59
5.2.4 Prototype sketch phase four . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 59
5.2.5 Calculation of Braided Pneumatic Muscles dimensions . . . . . . . . . . . . . . . . 59
5.3 Range of motions of the rehabilitation apparatus . . . . . . . . . . . . . . . . . . . . . . . 60
5.4 Conclusion of the mechanical design of the rehabilitation apparatus. . . . . . . . . . . . . 61
vii
5.5 Electro-pneumatic Circuits . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 61
5.6 Conclusion designing rehabilitation prototype . . . . . . . . . . . . . . . . . . . . . . . . . 63
IV Conclusion 64
List of (cid:28)gures 65
List of tables 66
References 67
viii
Nomenclature
ε contraction ratio of the muscle
b strand length (length of one strand following the helix of the braid)
b minimum strand length (when the muscle is de(cid:29)ated)
min
D diameter of the actuator (or diameter braided sheath)
D theoretical diameter of the muscle when the braid angle is 90(cid:176)
0
D diameter of the end cap (= the end (cid:28)tting)
cap
D strand diameter
s
D initial diameter of the muscle (diameter at de(cid:29)ated state)
zero
F generated tensile force of the muscle
f dynamic friction coº(cid:30)cient
f maximum kinetic dry friction coº(cid:30)cient
k
f static dry friction coº(cid:30)cient
s
G Node separation or pic (distance between 2 nodes opposite of each other on radial direction of the
actuator)
K sti(cid:27)ness per unit pressure
g
K linearized radical actuator elasticity
r
L length of the actuator (only the length of the braid between the two end-(cid:28)ttings)
l Inter strand separation (or the distance between 2 adjacent nodes)
L length of the muscle in de(cid:29)ated state
0
L the straight length of one strand in the braided sheath
h
n number of turns a strand circles the actuator (number of turns the helix spins around the axis of the
actuator)
N number of nodes in one circumference of the actuator (where nodes are the cross points of strands
c
criss-crossing)
P absolute injected air pressure
P(cid:48) relative injected air pressure
P threshold pressure needed to overcome radial elasticity
th
t thickness of the bladder and braided sheath
k
W thickness of one strand
b
ix