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DESIGN AND CONSTRUCTION OF AN ELECTRO-RHEOLOGICAL VALVE ACTUATING SYSTEM
A MASTER’S THESIS
in
Mechanical Engineering University of Gaziantep
By Egemen Ramazan TOPÇU
December, 1997
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Approval of Graduate School of Natural and Applied Sciences. Assoc. Prof. Dr. Ali Rýza TEKÝN
Director I certify that I have read this thesis satisfies all the requirements as a thesis for
the degree of Master of Science. Assoc. Prof. Dr. Sedat BAYSEÇ
Chairman of the Department
I certify that I have read this thesis and that opinion it is fully adequate, in scope and quality, as a thesis for the degree of Master of Science.
Assist. Prof. Dr. Sadettin KAPUCU Supervisor
Examining Committee in Charge: Assoc. Prof. Dr. Sedat BAYSEÇ (Chairman) Assist. Prof. Dr. A. İhsan KUTLAR Assist. Prof. Dr. Sadettin KAPUCU
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ABSTRACT
DESIGN AND CONSTRUCTION OF AN ELECTRO-RHEOLOGICAL
VALVE ACTUATING SYSTEM
TOPÇU, Egemen Ramazan M.S. in Mechanical Engineering
Supevisor: Assist. Prof. Dr. Sadettin KAPUCU December 1997, 63 pages
An Electro-Rheological fluid (ERF) is a mixture of finely divided particles
suspended in a non-conducting base fluid. The application of the sufficient electric
field causes polarisation of particles between electrodes and flow resistance is
increased in this way. The study presented here is about to finding out the
performance of shear and flow mode operations of ER fluids, and also to design and
construct an ER valve as an alternative conventional hydraulic valves. To achieve
this, firstly, mineral oil and transformer oil-based ER fluids were prepared by mixing
them with varying mass ratio of corn starch. Then, the effect of the applied electric
field and the concentration of the corn starch on rheological behaviour of these
mixtures were determined by using Rotational viscometer. Viscous behaviour of the
ER fluids were drawn, i.e., the change of yield stress with the applied electric field
was determined. Furthermore, ER valve dimensions were determined by using the
Rotational viscometer results on the basis of desired pressure drop analysis. Then, a
rectangular multi-plate ER valve was designed and manufactured. This ER valve was
directly connected to a hydraulic pump and pressure drops through the ER valve were
measured with respect to the varying pump flow rate as well as the intensity of the
electric fields. Finally, four ER valves were arranged as Wheatstone bridge in
hydraulic circuit to control the hydraulic piston regard in to start, stop and direction
of motion.
Keywords: Electro-rheological fluid, Wheatstone bridge, Rotational Viscometer.
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ÖZET
ELEKTRO-RHEOLOGICAL VALF İLE HAREKETLENDİRİLEN BİR SİSTEMİN
DİZAYNI VE YAPIMI
TOPÇU, Egemen Ramazan Yüksek Lisans Tezi, Makine Müh. Bölümü
Tez Yöneticisi: Yar. Doç. Dr. Sadettin KAPUCU Aralık 1997, 63 sayfa
Elektro-Rheological (ER) akışkan, iletken olmayan parçacıklarla bir temel
akışkanın karışımından oluşur. Yeterli elektrik alanın uygulanması elektrodlar
arasındaki parçacıkların polarize olmasına sebep olur ve böylece akışa karşı direnç
artırılır. Sunulan çalışma, ER akışkanların kesme gerilimi ve akış davranışlarının
tespit edilmesinin tanı sıra halihazırda kullanılan hidrolik valflerin yerini alabilecek
bir ER valfin tasarlanması ve üretilmesi hakkındadır. Bunu yapabilmek için de, İlk
olarak, farklı oranlarda mısır nişastası içeren madeni yağ ve trafo yağı bazlı ER
akışkanlar hazırlanmıştır. Daha sonra, uygulanan elektrik alan ve nişasta oranının, bu
karırışımların rheological davranışları üzerindeki etkileri döner viskosite ölçer
kullanılarak incelenmiştir. ER akışkanların uygulanan değişik elektrik alan altındaki
viskoz davranışları ve akma gerilimi üzerinde yarattığı değişimler grafiksel olarak
belirlenmiştir. Bunların ötesinde, ER valf’in ölçüleri, elde edilen viskosite
sonuçlarını kullanarak, gerçekleşmesi istenen basınç düşüleri analizi temel alınarak
belirlenmiştir. Daha sonra, birden fazla dikdörtgen şeklinde plakaları bulunan ER
valf tasarlanıp üretilmiştir. Hidrolik bir pompaya doğrudan bağlanılan ER valf
üzerinde oluşan düşümler, değişik debi ve elektrik alan şiddetleri uygulanarak
ölçülmüştür. Son olarak, ER valfler hidrolik devre içerisinde Wheatstone köprü
şeklinde dizilerek bir hidrolik pistonun hareketinin başlaması, durması ve hareket
yönü kontrol edilmiştir.
Anahtar Kelimeler: Electro-rheological Akışkan, Wheatstone Köprü,
Döner Viskosite Ölçer.
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ACKNOWLEDGEMENTS
I wish to express my sincere appreciation to my supervisor Assist. Prof. Dr.
Sadettin KAPUCU, for his helpful encouragement throughout all experiments,
especially for his help making this thesis understandable and readable.
I wish to express my warmest gratitude to the Assoc. Prof. Dr. Sedat
BAYSEÇ, Dr. Oðuzhan Koca, Assistant Hüseyin OVAYOLU and all personnels of
the Mechanical Engineering Department.
This study would have never been completed without moral support,
continuous help and encouragement of my dearest family, Çiðdem HAZIR and
Assistant Bircan YILMAZ. Therefore, my special thanks are due to them.
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TABLE OF CONTENTS
Page
ABSTRACT ........................................................................................... iii
ÖZET ..................................................................................................... iv
ACKNOWLEDGEMENTS .................................................................... v
LIST OF TABLES ................................................................................. viii
LIST OF FIGURES ................................................................................ ix
1. INTRODUCTION ............................................................................. 1
1.1 Electro-Rheological Fluids .............................................................. 1
1.2 Electro-Rheological Effect .............................................................. 2
1.3 Literature Survey and Previous Works ........................................... 3
1.4 Content of This Work .................................................................... 9
2. ELECTRO-RHEOLOGICAL BEHAVIOUR .................................. 11
2.1 Introduction ................................................................................. 11
2.2 Idealised Behaviour of ER Fluids .................................................. 12
2.3 Electro-Rheological Fluids Used in this Study ................................ 13
2.4 Experimental Set-up ..................................................................... 14
2.5 Experimental Results .................................................................... 16
2.6 Conclusion ................................................................................... 22
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3. ELECTRO-RHEOLOGICAL SINGLE VALVE MODEL .......... 24
3.1 Introduction ............................................................................... 24
3.2 Design of an ER Valve ............................................................... 25
3.3 Pressure Analysis of ER Valve ................................................... 27
3.4 Conclusion ................................................................................. 31
4. ER VALVE HYDRAULIC WHEATSTONE BRIDGE
ARRANGEMENT ....................................................................... 33
4.1 Introduction ............................................................................... 33
4.2 ER Valve Wheatstone Bridge Arrangement ................................ 34
4.3 ER Valve Hydraulic Wheatstone Bridge ...................................... 35
5. CONCLUSIONS AND RECOMENDATIONS .......................... 38
5.1 Conclusion ................................................................................. 38
5.2 Recommendations ...................................................................... 40
REFERENCES ............................................................................ 42
APPENDICES
A- ASSEMBLY AND PART DRAWING OF THE DESIGNED
ER VALVE .............................................................................. 44
B- ASSEMBLY AND PART DRAWING OF THE DESIGNED
ROTATIONAL VISCOMETER ............................................... 52
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LIST OF TABLES
Table Page
1.1 Ingredients for ER Fluids ............................................................ 2
1.2 Available Load Pressure on Piston ............................................. 37
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LIST OF FIGURES
Figure Page
1.1 Rheological Effect ...................................................................... 3
1.2 Operation Modes of ER Fluids .................................................... 4
1.3 ER Valve Construction Types ..................................................... 6
1.4 Two Valve Arrangement ............................................................ 6
1.5 Wheatstone Bridge Arrangement ................................................ 7
1.6 Multi-Plate ER Valve .................................................................. 7
2.1 Ideal Behaviour of ER Fluid ...................................................... 12
2.2 Dynamic Viscosity of Mineral Oil-Based ER Fluids .................... 13
2.3 Dynamic Viscosity of Transformer Oil-Based ER Fluids ............. 14
2.4 Rotational Viscometer ................................................................ 15
2.5 Viscous Behaviour of Mineral Oil-Based ER Fluid
Contamining 20% Corn Starch by Weight .................................. 17
2.6 Viscous Behaviour of Mineral Oil-Based ER Fluid
Containing 30% Corn Starch by Weight ................................... 17
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2.7 Viscous Behaviour of Mineral Oil-Based ER Fluid
Containing 40% Corn Starch by Weight .................................. 17
2.8 Viscous Behaviour of Mineral Oil-Based ER Fluid
Containing 50% Corn Starch by Weight ................................... 18
2.9 Viscous Behaviour of Transformer Oil-Based ER Fluid
Containing 20% Corn Starch by Weight .................................. 20
2.10 Viscous Behaviour of Transformer Oil-Based ER Fluid
Containing 30% Corn Starch by Weight .................................. 20
2.11 Viscous Behaviour of Transformer Oil-Based ER Fluid
Containing 40% Corn Starch by Weight ................................... 21
2.12 Viscous Behaviour of Transformer Oil-Based ER Fluid
Containing 50% Corn Starch by Weight .................................... 21
3.1 Parallel Plate Valve .................................................................... 25
3.2 Multi-Plate ER Valve ................................................................ 27
3.3 Single ERValve Pressure Analysis System ................................... 28
3.4.a Valve Pressure Drop Against Pump Flow Rate,
Transformer Oil-Based ER Fluid
Containing 20% Corn Starch by Weight ............ ....................... 29
3.4.b Valve Pressure Drop Against Pump Flow Rate,
Transformer Oil-Based ER Fluid
Containing 30% Corn Starch by Weight ............................... 30
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3.4.c Valve Pressure Drop Against Pump Flow Rate,
Transformer Oil-Based ER Fluid
Containing 40% Corn Starch by Weight ................................ 30
4.1 ER Valve Hydraulic Wheatstone Bridge Arrangement ............... 34
4.2 Valve Actuator System ............................................................... 36
A- Part List of ER Valve ................................................................. 44
Assembly Drawing of The ER Valve .......................................... 45
Nipple ......................................................................................... 46
Front Cover ................................................................................ 47
ER Valve Plate ........................................................................... 48
Isolator Plate ............................................................................... 49
Outer Cover ................................................................................ 50
Bolt ............................................................................................. 51
Isolator Ring ................................................................................ 51
B- Part List of Rotational Viscometer ............................................... 52
Assembly Drawing of The Rotational Viscometer ........................ 53
DC Motor Plate ........................................................................... 54
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Coupler ........................................................................................ 54
Plate Stick ................................................................................... 55
Top Plate Rice Ring .................................................................... 55
Main Top Plate Bearing ............................................................... 56
Isolating Fittings .......................................................................... 56
Main Top Plate ............................................................................ 57
Inner Cylinder ............................................................................... 58
Outer Cylinder ............................................................................. 59
Main Block Stick ......................................................................... 60
Outer Cylinder Isolator Cup ......................................................... 61
Outer Cylinder Fittings ................................................................ 61
Main Bottom Plate ...................................................................... 62
Top Plate Rice Ring ..................................................................... 63
Main Bottom Plate Bearing ......................................................... 63
1
CHAPTER 1
INTRODUCTION
1.1 Electro-Rheological Fluids
When a material dissolves in another material to form a bona-fide solution and
the size of the solute particles are greater than the size of the molecules of the
solvent, the system will term a colloidal dispersion which have a variety of
subgroups. These subgroups include sols which are dispersion of solids in solids, or
solids in liquid; emulsion which are dispersions of liquids in liquids; aerosols which
are dispersion of liquids in gases, or solids in gases; and foams which are dispersions
of gases in liquids, or gases in solids. Electro-rheological (ER) fluids belong to the
sols, [1].
The ingredients of ER fluids have a great diversity of solvent, solute and
additive category as indicated in Table 1.1. This diversity depends upon seven
criteries which must be considered when developing ER fluids. They are electro-
mechanical, electrical, thermal, stability, viscous, solvent and solute characteristics,
[1].
An ER fluid is a mixture of finely divided particles suspended in a non-
conducting base. The application of the sufficient electric field causes polarisation of
the particles which forming chains between the electrodes. When the electric field is
removed, these particle chains are breakdown. The mechanical properties of the ER
fluid in shear, tension, and compression are subject to dramatic variations with
applied electric field. It is often stated in the literature that ER fluids behave like a
Bingham plastic in which the yield strength is a function of the applied electric field,
[9].
The relationship between the shear stress and applied electric field is important
in the design of any ER device. High shear stress should be desired for a relatively
2
low electric field intensity and ER fluids to be characterised by a low viscosity in the
absence of an electric field and be characterised by a high viscosity when an electric
field applied upon the fluid. It should be low volatility, non-toxic, non-corrosive, and
non-flammable.
Table 1.1: Ingredients for ER Fluids.
SOLVENT SOLUTE ADDITIVE Silicone oils Sodium carboxymethyl
cellulose Water
Olive oil Gelatine none Mineral oil Aluminium dihydrogen Water
Transformer oil Carbon Water Dibutyl sebacate Iron oxide Water and surfactant
Mineral oil Lime none P-xylene Piezoceramic Water and glycerol oleates
Silicone oil Copper Phthalocyanine none Transformer oil Starch none
Kerosene Silica Water and detergents Polychlorinated biphenyls Sulphopropyl dextran Water and sorbitan
Hydrocarbon oil Zeolite none
1.2 Electro-Rheological Effect
Modern solid state devices and microprocessor systems meet the
performance/cost criterion of the logic aspect. The ER effect is a method of providing
high performance inexpensive output element that is interfacable with solid state
electronics.
The ER effect is known as the increasing of the resistance of the special fluids
under the applied electric field. When the elements of the ER fluid device are neutral
(no charge on the electrode) the solute particles are free to move in ER fluids. When
the voltage is applied, negative side of the particles are nearest the positive electrode,
positive side of the particles are nearest the negative electrode, at the same time they
attract each other and consequently arrange themselves into chains, thus forming
mechanical bridges across the electrodes, shown in Figure 1.1.
At low field strength the ER fluid is essentially in a liquid state. When the
electric field is 1 to 3 kV/mm, the ER fluid behave more like a solid, [2]. The effect
3
is reversible so that when the electric field removed the ER fluid reverts to begin a
fluid. Under the fast switching of the electric field, the change of the state quickly.
This electro-rheological phenomenon has been exploited in engineering practices for
the development of discrete devices and in hydraulic circuits. Such devices are
clutch, [3,4], damper, [5], beam, [6], valve, [2,7,11], brake, [15], etc.
Electrode
ER particle
V+
(a) (b)
Figure 1.1: Rheological Effect.
1.3 Literature Survey and Previous Works
The addition of the polarizable solid particles causes the resulting emulsion to
undergo a liquid-to-semi-solid phase change on the application of an electric field.
This was first discovered by Winslow who reported the variation of rheological
properties of some fluids when an electric field is applied. But the authorities can not
claim credit for his observation. They explained this effect to under the presence of
electric field, these fluids become solid. Recent reviews on the phenomenon of
electro-rheology and its applications has been presented by Jordan and Shaw, [8].
Survey of the literature on ER fluids reveals there are three possible modes of
operations which are shear, flow and squeeze- flow modes, shown in Figure 1.2.
4
Motion Direction ER Plate
ER Fluid
SHEAR MODE
ER Plate
Flow ER Fluid
FLOW MODE
Fixed Plate
ER Fluid
Moving Plate
Motion Direction
SQUEEZE-FLOW MODE
Figure 1.2: Operation Modes of ER Fluids.
In shear mode, the electrodes of the ER fluid devices are free to rotate or
translate in relation to each other. Control of the shear properties of the fluid leads to
application torque transmission such as clutches, brakes, shock absorbers and
vibration dampers, etc. Increasing of the shear stress with the applied electric field is
the important performance characteristics of the ER fluids and it was detected by
using Rotational viscometer and Oscillatory viscometer. Donalds L. Klass and
Thomas W. Martinek have used Rotational viscometer to observ the increase in
5
viscosity with electric field, [12]. But the stiffening and consequent ability of ER
fluids to transmit forces is due to rheological characteristics and not due to a viscosity
change. Detailed discussions of these rheometers are undertaken by many
researchers, [8].
N.G. Stevens, J.L. Sproston and R. Stanway designed ER clutches for torque
transmission by using shear mode principle, [10]. They describe the test facility and
presents the results of a series of experiments to determine the torque transmission
characteristics as a function of voltage and fluid temperature. They designed first
clutch in 1984. It had a vertical shaft with the ER fluid contained in an open reservoir
and the clutch plate was fixed. The transmission torque obtained was 0.007 Nm
upon the application of 1 kV/mm electric field. Second clutch was designed by these
researchers in 1988 [3]. This new design involved a horizontal shaft with a totally
enclosed reservoir for the ER fluid and the clutch plates were easily adjustable which
allowed opportunity to study the effect of the clutch plates distance.
N. Martis, S. A. Burton, D. Hill and M. Jordan investigated the mechanical
behaviour of a silicon oil based ER fluid by using oscillatory viscometer and
designed an ER damper, [5]. The modification of the damping resistance is obtained
by varying the mechanical properties of the ER fluid within the damper by applying
an electric field. Their damper consists of an outer cylinder and a double-ended
piston rod that pushes the ER fluid through a stationary annular duct.
In the flow mode, the electrodes of the ER devices are assumed fixed. The ER
devices can be constructed in which the flow rate-pressure characteristic is controlled
by varying the applied electric field. This leads to the concept of ER actuators in
which ER valves control the fluid flow in a hydraulic circuit.
D.A. Brooks explained the ER valve and different types of constructions
which are cylindrical and rectangular, shown in Fig 1.3, [11]. His rectangular valve
consist of pair of flat electrodes which are isolated with insulator material. The yield
stress obtained is 7 kPa when 3 kV/mm electric field is applied. The yield value is
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controllable from 0 to 7 kPa by voltage from 0-1.5 kV and the no-field pressure loss
can be reduced by having multiple flow paths or increasing the gap.
Flow Flow insulator length length
width plate electrode width
(a) (b)
Figure 1.3: ER Valve Construction Types.
Two valve arrangement of the Brooks is shown in Figure 1.4. If a voltage
applied across the valves, the resulting differential pressure can cause the ram to
move.
Supply Pressure
ER Valve
Exhaust
Figure1.4: Two valve arrangement
Single valve has limited uses in itself. Four ER valves are arranged to form a
Wheatstone bridge by Brooks, shown in Figure 1.5. Opposing valves are connected
to the same power supply and bi-directional movement effected by upsetting the
balance of the bridge. The flow resistance to one side of the ram is raised and the
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other side reduced and fluid flows into the ram chamber. The available thrust is a
product of the ER pressure drop and the piston area and the ram speed as a function
of the flow rate.
Supply Pressure
ER Valve
Exhaust
Figure 1.5: Wheatstone Bridge Arrangement.
A. J. Simmonds designed ER valve which operate in flow mode operation, [2].
His valve plate geometry is similar to the Brooks’s valve plate, but he uses multi-
plate in a valve to increase the surface area, shown in Figure 1.6.
ER Fluid Length
Flow Width
Length
Flow
HV
8
Figure 1.6: Multi-plate ER valve.
The ER fluid which is used in his experiments obtained by mixing of the 40%
cornflour and 60% silicon oil by weight. It has advantages in that it is cheap,
available in quantity and it is not biologically hazardous etc.
Firstly, he explained the pressure drop characteristics of the single valve with
the electric field and the flow rate of the fluid . Maximum pressure drop obtained
was 160 kPa with the application of 3.2 kV/mm as 19.3 lt/min from his single valve
was flowing.
Another ER valve study was presented by S. B. Choi, C. C. Cheong, J. M. Jung
and Y. T. Choi, [7]. They tested the Bingham property of the silicone oil-based ER
fluid as a function of electric field. The ER valve with multi-channel plates is
manufactured. Pressure drops of the ER valve are evaluated with respect to the
number of electrodes and the intensity of the electric field. The ER valve-cylinder
system is formulated and equations of motion for the system are derived to achieve
the position control of the cylinder system.
In squeeze-flow mode, the ER fluid is sandwiched between two electrodes, one
fixed and one moving in a direction normal to its own plate. In this mode, the
variation of the transmitted pressure with the applied electric field on the upper plate
are investigated.
J.L. Sproston, S.G. Rigby, E.W. Williams and R. Stanway have investigated
the compressive squeeze performance of an ER fluid sandwiched between two
circular electrodes,[13]. They explained the variation of transmitted force through the
ER fluid on the upper plate with the electrode distance, frequency of oscillation and
applied electric field.
9
1.4 Content of This Work
Electrohydraulic servovalves have been used in hydraulic control systems.
However, this type valves are complex and expensive, [16]. ER valves are designed
instead of servovalves to control the hydraulic system by using the ER effect. They
are desirable to introduce an alternative means of reversible and fast control since
they have no moving parts.
The aim of this work is to find out the rheological characteristics of the ER
fluids and to manufacture a valve by using this phenomenon. Mineral oil and
transformer oil-based ER fluids were produced by mixing with corn starch in
different weight ratios. Shear mode and flow mode operations of this ER fluids were
investigated.
Rotational viscometer was designed and constructed. Bingham property of the
ER fluids were tested as a function of electric field intensity. The relationship
between shear stress, shear rate and electric-field magnitude on such a devices was
obtained in order to determine geometrical dimensions of an ER valve.
After setting the dimensions, an ER valve was manufactured. Single ER valve
was connected directly to a pump. Then, pressure against flow characteristics under
the electric field for a Bingham plastic flow through an ER valve was obtained.
Four ER valves were arranged to form a hydraulic wheatstone bridge. Pump
and hydraulic actuator were connected to this bridge. Opposing pairs of valves were
connected to the same voltage supply and bi-directional movement effected by
upsetting the balance of the bridge.
• Chapter 2 presents the concentrations of the ER fluids and relationship
between shear stress, shear rate and electric-field magnitude on ER fluids. This part
of the investigation shear mode type of operation of the ER fluids.
10
• Chapter 3 presents the method of determination of the multi-plate ER valve
dimensions and pressure against flow characteristics of the multi-plate single ER
valve. This part of study is flow mode type of operation of the ER fluid.
• Chapter 4 describes wheatstone bridge arrangement of the multi-plate ER
valves. The performance characteristics of the bridge in hydraulic circuit was
explained and available load on piston were determined.
• Chapter 5 presents conclusions and recommendations for future research.
11
CHAPTER 2
ELECTRO-RHEOLOGICAL BEHAVIOUR
2.1 Introduction
The influence of the electric field on the deformation of the materials has
been investigated by many researchers over the years. Electro-rheological effect is
main part of these studies. If an external electric field applied on an ER fluid, the
particles of the ER fluid is charged and arrange themselves like chains, between
electrodes. In this way, flow resistance and applied stress on electrodes can be
increased. This effect is proportional to the electric field applied, and it is reversible
and fast acting.
This special characteristic of the ER fluids allow some potential applications.
Flow, squeeze-flow and shear modes are three major application methods of the ER
effect in practical devices. The fluid is pumped through a valve which consists of
fixed electrodes in flow modes. The ER fluid is sandwiched between two electrodes
in squeeze-flow mode. In shear mode, shearing the fluid by moving one electrode
relative to another. Rotational viscometer test is the type of shear mode operation.
D. L. Klass and T. W. Martinek presented the influence of shear rate, field
strength, composition and temperature on rheological behaviour of special fluids in
1966, [12]. They plotted the apparent viscosity against shear rate under the electric
field and temperature by using rotational viscometer. Since that time, numerous
investigators have studied rheological behaviour by same method.
In this chapter, the shear mode application of ER fluids is presented.
Ingredients of the ER fluid and different mixture ratios are explained. Experimental
results showing the relations between shear stress, shear rate and electric field
12
magnitude are given in graphical form. Besides, Bingham property of the ER fluids is
briefly explained.
2.2 Idealised Behaviour of ER Fluids
Understanding of the ER fluid’s behaviour is the key to design ER devices.
The relationship between shear stress and shear rate is the most important parameter
in understanding this behaviour and it depends on some criteria. Increasing weight
ratio of the polarised particles, field strength and temperature increase ER effect, but
increasing shear rate and frequency decrease this effect, [12].
ER fluids have been modelled as Bingham plastics which means that flow is
observed only after exceeding a minimum yield stress. Idealised behaviour of the ER
fluid is shown in Figure 2.1.
Shear Stress
b η p
τ y
Newtonian Fluid
a ηN
Shear Rate
Figure 2.1: Ideal Behaviour of ER Fluid.
Line “a” shows the characteristics of Newtonian fluids and line “b” shows
the characteristics of Bingham plastics. Slopes of these lines are the dynamic
viscosities of fluids. With no electric field applied an ER fluid behaves like a
Newtonian fluid and the applied stress will cause the liquid to flow. Eq.2.1 is a first
order model approximating the behaviour of a Newtonian fluid.
τ µ ∂ ∂= N u y/ (2.1)
13
Where µ N is the Newtonian viscosity in Pa.s, ∂ ∂u y/ is the shear rate in s-1 and the τ
is the shear stress in Pa.
Flow only occurs for a stress greater than the yield stress in Bingham plastics.
Below the yield stress, applied stress will strain the plastic but not cause it to flow.
The equation for a Bingham body is:
τ τ µ ∂ ∂= +y p u y/ (2.2)
Where τ is the shear stress in Pa, τ y is the yield stress in Pa, µ p is the plastic
viscosity in Pa.s. The yield stress increases proportional to the applied electric field
while the plastic viscosity unchanged, [2].
2.3 Electro-Rheological Fluids Used in This Study
The ER fluids used in rotational viscometer tests comprised of mineral oil and
transformer oil containing corn starch. Dynamic viscosity and density of mineral oil
are 0.041 Pa.s and 900 kg/m3, respectively. 0.0074 Pa.s is the dynamic viscosity and
840 kg/m3 is the density of transformer oil. These fluids are mixed with corn starch in
different weight ratios. Figure 2.2 and Figure 2.3 show the effect of mixing ratios on
dynamic viscosity of mineral oil and transformer oil-based ER fluids, respectively.
0
0,2
0,4
0,6
0,8
0 20 30 40 50% of Polarised Particles by Weight
Dynamic Viscosity ( Pa.s)
Figure 2.2: Dynamic Viscosity of Mineral Oil-Based ER Fluids.
14
0
0,2
0,4
0,6
0,8
0 20 30 40 50% of Polarised Particles by Weight
Dyamic Viscosity (Pa.s)
Figure 2.3: Dynamic Viscosity of Transformer Oil-Based ER Fluids.
The comparison is rather good for weight ratios up to about 50% both mineral
oil-based and transformer oil-based ER fluids. The dynamic viscosities increase
drastically above 50%, even ER fluids lose their fluid properties. Increasing the
weight ratio of particles increases the electro-rheological effect. That is why ER
particle should be maximum in possible range.
2.4 Experimental Set-up
Viscous behaviour of the ER fluids can clearly be seen by plotting the change
in shear stress with respect to shear rate. And this curve are clearly describe the
rheological behaviour of the ER fluids in detail. Flow curves are obtained by using
rotational viscometer which comprises of two concentric cylinders with 0.8 mm
radial separation of two faces as shown in Figure 2.4. An ER fluid is filled in this
space. With no electric field present, rotating the inner cylinder creates the shear
stress but littler or no motion and torque on the outer cylinder. When the electric field
is applied, the ER fluid stiffen with field strength and stress is transferred to the outer
cylinder as a torque. When the electric field great enough, the ER fluid turns out to
be like a solid and the cylinders behave as tough, they were pressed together with no
fluid between them.
15
Figure 2.4: Rotational Viscometer.
The electric field between two concentric cylinders is obtained from a high
voltage power supply capable of providing voltages from 0-1000 Volts. Outer
cylinder of the viscometer is connected to a cantilever beam on which two strain
gauge were stuck. Transmitted stress is determined by using a strain indicator. The
flow curves of the ER fluid were drawn by using a plotter. X direction on the plotter
DC motor
Inner cylinder
Plotter
Outer cylinderER fluid
Strain Gauge
High voltage Pover S l
Power supply
Strain indicator
16
corresponds to the DC motor speed which is proportional to the shear rate and Y
direction corresponds to the voltage of the strain indicator which is proportional to
the transmitted stress. The speed of the inner cylinder is transformed to the shear rate
and the voltage of the strain indicator is transformed to the shear stress. Thus, the
output graph of the plotter is arranged with these new values.
2.5 Experimental Results
The variation of the transmitted torque or shear stress with electric field was
investigated in these experiments. The effect of mixture ratios on ER behaviour was
examined. Increase of the yield stress under the application of different electric
fields on mineral oil and transformer oil-based ER fluids which contain corn starch in
different weight ratios are presented.
Rotational viscometer results of the mineral oil-based ER fluids are given in
Figures 2.5 to 2.8. The shear stress was measured by applying the electric Voltages
from 250 to 1000 V, while the shear rate up to 160 s-1. In order for the experimental
data to be credible, measurement was repeated four or five times at the same
operating conditions.
These graphs present both Newtonian and Bingham property of the ER fluids
and the effect of concentration of polarised particles together with the intensity of
applied electric field on ER behaviour.
17
18
Investigation of Figures 2.5 to 2.8 under the application of electric field show
the effect of concentration of the corn starch on the shear stress. These curves reflect
Bingham plastic characteristics, i.e. under an applied electric field flow only occurs
for a stress greater than the yield stress. Application of 1 kV can cause an increase in
yield stress approximately 6 Pa, 10 Pa, 18 Pa and 110 Pa corresponding to the weight
ratios of 20%, 30%, 40% and 50% corn starch in mineral oil, respectively. It is clear
19
that yield stress increases exponentially depending on the concentration of cornstarch
in mineral oil. Slopes of viscous behaviour curves for the mineral oil-corn starch ER
fluid under the applied different electric fields are almost the same with the slope of
curve for the ER fluid without no electric field applied. Also, it can be deducted from
these curves that shear stress difference between with and without electric field does
not change at any shear rate. It has a constant value which is approximately equal to
the yield stress.
The slope of the flow curves indicate the Newtonian viscosity of mixtures. To
validate the results obtained from Rotational viscometer, some are cross checked
with the results obtained from a saybolt viscometer. It is seen that slope of the fluid
under consideration is about 0.057 in Fig. 2.5 and saybolt viscometer result is the
0.052 Pa.s. This difference may be emerged from the measurement errors and it may
be tolerable according to the nature of the work, but nevertheless, a consistent
method is set to determine viscous behaviour of ER fluids.
Figures 2.7 and 2.8, depicting viscous behaviour under the electric field show
humps within the small region of shear rate around 2 s-1. Where the fluid behaves as
a solid. It is realised that the torque motor used to rotate the inner cylinder of the
viscometer can not overcome the yield stress created by the ER fluid resistance and
the bearing friction force. When the inner cylinder starts its motion initially formed
chains break suddenly. This phenomenon causes a sudden in shear stress. This region
can be assumed as a transitional region and the results obtained within this small
region should not be relied on. Figure 2.8 indicates also that with increasing the
electric field, yield stress increases linearly. Obviously, there is a directly
proportional relationship between them.
Figures 2.9 to 2.12 show the mechanical stress/strain relationship for
transformer oil-based ER fluids. These curves are obtained by using the same
experimental set-up and measurement techniques.
20
21
The curves which are obtained under 0 V/mm electric field have Newtonian
fluid characteristics. When the slope of this curves are investigated, it is seen that
they are approximately the same with Saybolt viscometer measurements given in
Figure 2.3. For example, Newtonian viscosity of the ER fluid which contains 30%
corn starch and 70% Transformer oil is 0.02 Pa.s and the slope of the flow curve of
this ER fluid is 0.02. Under the application of an electric field, these fluids behave
like a Bingham body. When the viscous behaviour of transformer oil-corn starch ER
fluids given in Figures 2.9 to 2.12 are examined, it is seen that the slopes of the
curves under electric field are not parallel to the slopes of the curves without
electrical field. It can be stated that shear stress difference between the with and
without electric field is reduced by increasing the shear rate. At certain shear rate it
would be very small or zero. The yield stress of the fluids in the same figures are 7,
18, 62 and 158 Pa for the weight ratios of 20, 30, 40 and 50% corn starch particle in
transformer oil respectively. As in the case of mineral oil-starch ER fluid, yield stress
22
increases exponentially depending on the concentration of corn starch in transformer
oil. And also yield stress is linearly proportional to the applied electric field.
2.6 Conclusion
Selection of a suitable base fluid and a mixture ratio can be made on the basis
of observation of the rheological characteristic of a mixture. The experimental results
show that ER properties of the both base fluid under consideration are these:
� Yield stress increases linearly with increasing the electric field.
� Increase of concentration of dielectric particles causes the exponential yield stress
increase.
� Newtonian viscosity exponentially increases with increasing the concentration of
dielectric particles
Transformer oil-based ER fluid have some advantages over the mineral oil-
based ER fluid. These are:
� Newtonian viscosity of the transformer oil-based ER fluid is low. Low no-field
viscosity property of this fluid provides low pressure drop passing through an
orifice.
� The sedimentation of the dielectric particles in transformer oil takes long time.
� Increase of yield stress of the transformer oil-based ER fluids under the applied
electric field is always higher than mineral oil-based ER fluids yield stresses at all
weight ratios.
One of the major disadvantage of the transformer oil is the decrease of the shear
stress between the no-electrical field and under electrical field, while increasing the
shear rate.
24
CHAPTER 3
ELECTRO-RHEOLOGICAL VALVE
SINGLE MODEL
3.1 Introduction
Directional control valves are important elements of an hydraulic system. The
task of the control valve is to connect various hydraulic lines to one another, and
continuously make a variety of cross linkage connection between different hydraulic
lines. Using such valves, it is possible to influence the direction of the effect of
pressure and volumetric flow, and therefore to control the cylinders or hydraulic
motors regard in to start, stop and direction of motion. In order to increase both
accuracy and speed of the system response, servovalves have been used in hydraulic
control systems, but they are highly non-linear, complex, expensive and their
response is limited by moving parts. ER valves are desirable to introduce an
alternative means of fast and simple control since they have no moving parts.
While designing an ER valve, a common requirement is that the ER fluid
have a high ratio between applied field shear stress and no-field shear stress. Power
requirement and solid content of the ER fluids should be known before designing ER
devices. Since, they are important controlling factor of yield strength. Other fluid
characteristics for the device design are the dispersion stability to sedimentation and
no-field viscosity.
Previous chapter presents the performance characteristics of mineral oil and
transformer oil-based ER fluids. Bingham property of the ER fluids were tested as a
function of applied electric field in order to determine geometrical parameters of the
ER valve. The main objective of this study is to determine the controlling factors of
the pressure drop on ER valve and the possibility of using the ER valve for
25
controllable hydraulic systems. The valve dimensions were determined on the basis
of desired pressure drop analysis by using the Rotational viscometer results. Then, a
rectangular multi-plate ER valve was designed and manufactured. This valve was
directly connected to a hydraulic pump and pressure drop over ER valve was
measured with respect to the pump flow rate as well as the intensity of the electric
fields.
3.2 Design of an ER Valve
To analyse an ER valve it is necessary to have some understanding of an ER
fluid’s idealised behaviour. This can be done by using the stress against shear rate
diagram obtained from Rotational viscometer.
When we consider an ER valve which has a single flow path, in the absence
of the electric field the pressure drop produced only by the Newtonian viscosity of
the ER fluid and it is proportional to the flow rate of the ER fluid pumped through
the gap. Assuming that the flow between two plates is laminar, then the pressure drop
becomes, [2,7];
P lQ whN N G= 12 3µ / ( ) (3.1)
where QG is the flow passing through a single gap valve without electric field, in
m3/s,
µ N is the Newtonian viscosity, in Pa.s,
l is the length of valve electrode, in m,
w is width of the valve electrode, in m,
h is the gap between two plates, in m.
w l
h
26
Figure 3.1: Parallel Plate Valve.
Upon applying electric field, a pressure drop due to the yield stress of the ER
fluid is additionally generated. Resistance force on a single plate caused by yield
stress can be written as;
F lwy Y= τ (3.2) Where τ y is the yield stress, in Pa.s. Since there are two plates, this equation must be multiplied by 2 .
F lwy Y= 2τ (3.3) This resistance yields a pressure drop across the gap then, force on the fluid body
contained between the plates becomes;
F P hwf ER= ∆ (3.4)
Equating these forces each other; the pressure drop due to the yield stress becomes;
∆P l hER y= 2τ / (3.5)
Total pressure drop of the ER valve with single path in the presence of the electric
field is obtained by adding the pressure drop due to the Plastic viscosity to the
pressure drop due to the yield stress. This is given by,
∆P lQ wh l hP y= +12 23µ τ/ ( ) / (3.6)
When we consider the ER valve which has a multi-flow path, the contribution
of shear resistance and the pressure drop due to the yield stress increase with number
of flow path. The total pressure drop of the ER valve with multi-channels under the
application of applied electric field can be obtained as:
∆P m l h m Q l why P G= +2 12 3τ µ/ / ( ) (3.7)
27
where m is the number of energised paths by electric field.
Eq. 3.7 reveals that the total pressure drop over an ER valve increases directly
as the number of the energised paths increases. In the absence of electric field,
number of energised paths are zero so that the total pressure drop of the ER valve is
produced by only the Newtonian viscosity of the ER fluid. Eq. 3.7 also implies that
the performance of the ER valve is dependent on the number of energised paths,
rheological behaviour of the ER fluid and design parameters such as the electrode
width, w, length, l , and height, h . Rheological behaviour of ER fluids are controlled
with the electric field intensity applied and the concentration of polarised particles.
Consequently, they directly affect the ER valve performance.
Figure 3.2 shows a rectangular multi-plate ER valve, which was designed on
the basis of desired pressure drop analysis. The material of the electrode is carbon
steel and is isolated from each other by rubber plates. The fluid gasket is applied
between the valve and rubber plates to prevent the leakage of the ER fluid. The
number of electrodes is 6 and they form five flow paths. The gap spacing is 0.7 mm.
The length and width of each electrode is 100 and 25 mm, respectively.
Figure 3.2: Multi-Plate ER valve.
28
3.3 Pressure Analysis of ER Valve
While designing an ER valve-actuating system, it is necessary to known the
pressure drop characteristics of an ER valve. The experimental set-up used in this
study is shown in Figure 3.2.
4 3 2
5
1
8
9
6
7
1- Multi- plate ER Valve 6- Personal Computer
2- 0-1000 V High Power Voltage Supply 7- Pump Driver
3- 0-1000 Psi Pressure Transducer 8- Hydraulic Pump
4- Multimetre 9- ER Fluid Reservoir
5- Amplifier
Figure 3.3: Single ER Valve Pressure Analysis System.
29
Multi-plate ER valve is connected directly to a pump which has the
proportional flow rate with pump speed. The nominal displacement of the pump is
50 10 6 3× − m rev/ and it is driven between 0-100 rpm. Pressure transducers which
have the range of 0-1000 Psi were calibrated by using Dead Weight Tester and
mounted at the inlet and outlet of the ER valve. Transducer signals are conditioned
by a 5 kHz frequency amplifier. 0-1000 Volt high power voltage supply was used to
create electric field between valve plates.
Experimental results are given in Figure 3.4.a-3.4.c which present the field-
dependent pressure drop with respect to the pump flow rate. The agreement between
measured and theoretical values is important for valve design, thus the validation of
the proposed pressure analysis is proved.
30
The pressure drop characteristics of a single valve with respect to the flow rate is
given in Figures 3.4.a, b and c under the applied 1 kV electric voltage. As it can be
seen from these figures, pressure drop due to yield stress shows similar trend as the
shear stress curves obtained from the rotational viscometer. The electro-rheological
pressure drop decreases with the pump flow rate, when using ER fluids containing
20% and 30% corn starch, shown in Figures 3.4.a and b. Shear rate increases with the
31
pump flow the valve effects the yield stress. The particle chains are destroyed, when
the fluid flow exceeds the 4 l/min and the effect of the yield stress on the rheological
pressure drop disappeares. Increase of the concentration of the dielectric particles in
mixtures partially prevent the chain breakdown. And the pressure drop due to yield
stress are additionally generated up to high fluid flow, shown in Figure 3.4.c.
The pressure drop due to yield stress is approximately 85 kPa at a flow of 5
l/min under the application of the 1 kV high voltage and the total pressure drop is
approximately 850 kPa, when using the ER fluid contaminated 40% dielectric
particles by weight, Figure 3.4.c and the theoretical pressure drop due to yield stress
is 75 kPa at the same conditions. Considering the pressure drop due to concentration
of the polarised particles in Fig. 3.4, the pressure drop increases with the
concentration of the corn starch. This results and conclusions are observed some
researchers before that. Brooks designed an ER valve which has the length is 100
mm, electrode spacing is 0.5 mm, width is 155 mm and number of flow path is 1,
[11]. The pressure drop due to Newtonian viscosity is 5.2 bar at a flow of 10 l/min.
Maximum yield stress is 7 kPa and additional pressure drop is 30 bar when the
application of 3 kV/mm. Simmonds designed a multi-flow ER valve, [2]. His valve
has seventeen valve plates, the width of each being 36 mm, length of 102 mm and
gap height 1mm. The maximum pressure drop is obtained 160 kPa when the
application of 3200 V/mm and the pump flow rate is 19.3 l/min. S.B. Choi, C.C.
Cheong, J.M. Jung and Y.T. Choi developed a valve which has five pairs of flow
paths, [7]. Geometrical dimensions of the gap, length and width of each electrode
space are 0.8, 200 and 20 mm, respectively. They obtain the 400 kPa pressure drop
across the valve upon the application of 4 kV/mm when all gaps are energised.
3.4 Conclusion
This chapter presented the flow mode operation of the ER fluids. Design
parameters of the ER valve was determined. A multi-channel plate for the ER valve
was designed and manufactured on the basis of the field depended Bingham model.
The pressure drop of the ER valve was evaluated experimentally and theoretically
32
with respect to the intensity of the electric field and the concentration of polarised
particles.
Eq. 3.7 implies that the performance of the ER valve dependent on the
number of energised paths, rheological behaviour of the ER fluid and design
parameters such as the electrode width, w, length, l , and gap height, h . No-field
viscosity effects can be reduced by increasing the gap between the electrodes, but
required voltage must be very high. Figure 3.7 presents the effect of concentration of
polarised particles and intensity of applied electric field on valve pressure drop.
These results are proved each other and they are verified with the other researches
from literature. Experimental results also shows that the pressure drop due to yield
stress decreases with the increase of the pump flow rate which is directly affected by
the shear rate in the ER valve. The reason for this behaviour is the yield stress
decrease by increasing of the shear rate.
33
CHAPTER 4
ER VALVE HYDRAULIC WHEATSTONE BRIDGE
ARRANGEMENT
4.1 Introduction
The basic concepts behind the hydraulic power and hydraulic control systems
have changed little over the past decades. In designing a hydraulic control system, the
limiting element in performance is often the mechanical stage. The performance of
dynamic system is characterised by the dynamic response. It is largely governed by
the mass, stiffness and energy dissipation characteristics of the system. The electro-
rheological effect is a new method of providing high performance element that is
directly interfecable with solid state electronics. ER phenomena results from the
effect of a electrical field over the contaminated fluid across two electrodes. Thus,
dielectric particles form chains to produce a force that resist the fluid motion.
Single ER valve and two valve actuator system have limited performance for
controlling the load pressure on hydraulic actuators. This type of constructions are
estimated in Reference 11. Four identical ER valves should be arranged to form a
Wheatstone bridge to control the fluid flow in hydraulic circuits. A. J. Simmonds and
D. A. Brooks have used Wheatstone bridge arrangement to control the fluid flow in
an hydraulic circuit, [2,11]. They present the effects on flow resistance of ER fluid in
this circuit.
34
In this study, four identical multi-plate ER valves were designed and they are
arranged to form a Wheatstone bridge. The performance characteristics of this bridge
on fluid flow control are presented. Moreover, the control factors of the available
thrust on hydraulic piston are explained.
4.2 ER Valve Wheatstone Bridge Arrangement
A wheatstone bridge circuit adapted for ER fluids is shown in Figure 4.1.
Four identical ER valves are arranged in pairs 1 through 4 and they are normally
open. Opposing pairs of the valves (1-4 and 2-3) are connected to the same voltage
supply and bi-directional movement effected by upsetting the balance of the bridge.
The flow resistance to one side of the ram is raised and the other side reduced and
fluid flows into the actuator. The available thrust is the product of the pressure drop
and the piston area. Actuator speed depends on the flow rate into the chamber.
P Qp P,
P1,Q1 P2 ,Q2 1 2 3 4 P2 P1
PL ,QL
Figure 4.1: ER Valve Hydraulic Wheatstone Bridge Arrangement.
When a high voltage applied on the valve pairs which are valves in 1 and 4,
available pressure drop P1 is obtained by adding the pressure drop due to the plastic
viscosity to the pressure drop due to the yield stress, P2 is the pressure drop due to
35
Newtonian viscosity. Thus, P1 is greater than P2 and the flow rate Q1 is less than the
Q2. Using the equivalent hydraulic law’s, the following equations can be written,
P P PP P PQ Q QQ Q Q
L
p
L
p
= −= +
= −= +
1 2
1 2
2 1
1 2
(4.1)
Flow rate through the valves can be found,
Q Q QQ Q Q
p L
p L
2
1
22
= +
= −
( ) /( ) /
(4.2)
Eqs. 4.1 and 4.2 hold true for any hydraulic valve. Pump pressure and load pressure
on actuator for ER valve bridge is calculated by using Eq. 4.3, given below
P lQ wh lQ wh m l h
P m l h lQ wh lQ wh
p p N y
L y p N
= + +
= + −
12 12 2
4 12 12
13
23
13
23
µ µ τ
τ µ µ
/ ( ) / ( ) /
/ / ( ) / ( ) (4.3)
Eq. 4.3 implies that, the load pressure decrease with increasing load flow. This is
because as, when the application of applied electric field is increased; P1 is increased
across the valve pairs 1 and 4, P2 is decreased across the valve pairs 2 and 3.
Consequently, the flow Q1 decreased as Q2 increased.
4.3 ER Valve Hydraulic Wheatstone Bridge
Valve-actuator system is shown in Fig. 4.2. This circuit can be operated as a
symmetrical balanced bridge. Each pair of valves must be similar and they are
controlled by a high voltage power supply. When operated of this bridge, the constant
flow is required from the pump. The fluid in the pipe from tank to actuator does not
36
need to be accelerated. Only small reservoir tank is required. Pipes from tank to
bridge and bridge to actuator should be as short as possible. Some care has to be
taken in choosing circuit components because of nature of the fluid mixture.
Polarised particles can cause same problems on sliding seals. That is why the solid
particles should be wholly solute in base fluids. Double acting hydraulic cylinder
should be taken to obtain similar thrusts on both sides of the actuator.
1
2
1 2 3
3 4 4
5
6
7 8
1- Hydraulic Actuator 5- Amplifier
2- ER Valve Wheatstone Bridge 6- ER Fluid Reservoir
3- Pressure Transducer 7- Hydraulic Pump
4- Multimeter 8- Pump Driver
Figure 4.2: Valve Actuator System.
37
The ER valves used were the same as the prototype used to determine the
experimental results. Double acting cylinder has a low coefficient of friction and the
effective actuator area of both sides is 2 34 10 3 2. × − m . Pressure transducers were
located at the input and output of the actuator to determine the load pressure under
the application of 1 kV/mm. The nominal pump displacement is 50 10 6 3× − m rev/ and
it produces constant flow.
The ER fluid used in these tests comprised of a transformer oil containing
corn starch particles. The weight fraction of the particles was about 40 % and there
was no any other additive material. The Newtonian viscosity of this mixture is
approximately 0.042 Pa.s.
Experiments were carried out with different pump flow rates under the
application of 1 kV voltage. The results are shown in Table 4.1. It indicates that the
load pressure on the both sides of the piston are not the same. It means that valves are
not identical and pressure drop are not identical and for this reason it is drastically
effected.
Table 4.1: Available Load Pressures on Piston.
Q Load Pressure (kPa) l/min First Pairs Second Pairs
1.6 35.53 179.72
2.1 30.72 141.27
2.6 25.92 122.05
3.1 25.02 102.82
In spite of these inconsistent results of the load pressure, hydraulic actuator
motion was controlled by the application of the electric field on the valve pair 1-4
cylinder was moved to leftwards. Removing electric field from this pair and applying
to the other pair it was moved to the rightwards.
38
CHAPTER 5
CONCLUSIONS AND RECOMMENDATIONS
5.1 Conclusions
The mechanical properties of the ER fluids in shear, tension, and compression
are subject to dramatic variations with applied electric field. If the intensity of
electric field is 1-3 kV/mm, an ER fluid turns to a solid, [2]. This effect is fast and
fully reversible.
This electro-rheological phenomenon has been exploited in engineering
practices for the development of discrete devices. The ER devices can be constructed
in which the flow rate-pressure characteristic is controlled by varying the applied
electric field in flow mode. This leads to the concept of ER actuators in which ER
valves control the fluid flow in a hydraulic circuit. In shear mode, the electrodes of
the ER fluid devices are free to rotate and/or translate in relation to each other.
Control of the shear properties of the fluid leads to torque transmission applications
such as clutches, brakes, shock absorbers, and vibration dampers, etc.
The study presented here is investigated the shear and flow mode operations
of ER fluids. The aim of this study was to make the initial step in gathering the
knowledge and the technology of an ER effect in actuating systems which will lead to
design of an ER valve as an ultimate purpose of this study. Firstly, the effect of the
applied electric field and the concentration of the polarised particles on rheological
behaviour were investigated by using Rotational viscometer. Flow curves of the ER
fluids were drawn and the increase of the yield stress with the applied electric field
was determined. Secondly, The valve dimensions were determined on the basis of
desired pressure drop analysis. Then, rectangular multi-plates ER valve was designed
and it was directly connected to a hydraulic pump. Pressure drop over an ER valve
was determined with respect to the pump flow rates and applied electric fields.
39
Finally, the ER valves to form a Wheatstone bridge in a hydraulic circuit and the
available thrust on actuator was determined.
ER fluids which used in hydraulic circuits should be available in quantity,
non-corrosive and biologically non-hazardous. In this study, mineral oil and
transformer oil are used as base fluids and corn starch as an additive. The Bingham
property of the mineral oil and transformer oil-based ER fluids were investigated by
using Rotational viscometer. Experimental results of these fluids show that
concentration of the polarised particles and the intensity of the electric field are the
most important controlling factors. Yield stress increase with the increase of the
applied electric field and the concentration of the corn starch. Experimental results
also show that transformer oil-based ER fluids have some advantages over the
mineral oil-based ER fluids. Newtonian viscosity of the transformer oil-based ER
fluids are low and the sedimentation time of the polarised particles is high. Low
no-field viscosity property of this fluid provides low pressure drop due to Newtonian
viscosity in ER valve. Other advantage of this fluid is the increase of in yield stress
with applied electric field under the same electric field. Consequently, these two
important properties provide a high available thrust force in a hydraulic circuit.
To illustrate the interplay between fluid characteristics and design of an ER
device, an ER fluid must have a high ratio between applied-field stress and no-field
stress. Control factors of the ER effect which are power requirement and solid
content must be determined before designing of an ER device. Under these
considerations, ER devices designed and their dimensions were determined.
Examination of Eq. 3.7 shows that the performance of an ER valve is dependent on
the number of energised paths, rheological behaviour of the ER fluid and dimensions
of valve gap. The pressure drop increases with increasing electrode length and
decreasing electrode height. The pressure drop due to Newtonian viscosity decreases
with increasing of the gap height. Pressure drop-flow rate characteristics show the
effects of rheological behaviour on valve pressure drop. The pressure drop due to
yield stress increase with increasing applied electric field and concentration of
40
polarised particles. It is decrease with increasing pump flow rate. Because, the yield
stress decrease with increasing shear rate.
Single valve has limited uses in itself. Four ER valves were arranged to form
a Wheatstone bridge for controlling actuator in hydraulic circuit. Opposing valves are
connected to the same power supply and bi-directional movement is affected by
upsetting the balance of the bridge. The available thrust is a product of the ER fluid
pressure drop and the piston area. Experimental results show that, the available thrust
on both sides of the actuator are not same. This results from the difference of valve
dimensions and flow in wheatstone bridge. To obtain similar pressure drop the
valve dimensions must have been identical.
5.2 Recommendations
1. ER fluid used in hydraulic circuit must be available in quantity and non-
corrosive. It must have low-no field viscosity for low pressure drop due to
Newtonian viscosity on ER valve. Sedimentation of the polarised particles
must be prevented.
2. Increase of the yield stress under the application of the electric field must
be maximum. The ER fluids must have a high ratio between
applied-field stress and no-field stress.
3. Materials of the circuit component must be selected carefully. Fluid
composition can cause some problems on sliding seals. That’s why, the
solid particles must be wholly solute in base fluids.
4. During the design, manufacturing methods to be used must be kept in
mind. The shape and dimensions of the valve must be determined due to
desired pressure drop. Dimensions and pressure drop of the ER valves
must be similar which used in wheatstone bridge arrangement to obtain
41
similar pressure drop on both sides of the actuators. Only small dimension
differences between the valves can cause unbalanced thrust on hydraulic
piston.
42
LIST OF REFERENCES
1. M. V. Gandhi and B. S. Thompson, 1992, “ Electro-Rheological Fluids”,
Smart Materials & Structures, Chapman and Hall Ltd., pp 137-173.
2. A. J. Simmonds, 1991, “Electro-Rheological Valves in a Hydraulic
Circuit”, IEE Proceedings-D, Vol. 138, No. 4, pp 400-404.
3. N. G. Stevens, J. L. Sproston, R. Stanway, 1988, “ An Experimental Study
Of Electro-Rheological Torque Transmission”, Transactions of the
ASME, Vol. 110, pp 182-188.
4. G. J. Monkman, 1997, “ Exploitation Of Compressive Stress In
Electrorheological Coupling”, Mechatronics, Vol. 7, No. 1, pp 27-36.
5. N. Markis, S. A. Burton, D. Hill and M. Jordan, 1996, “Analysis And
Design Of ER Damper For Seismic Protection Of Structures”, Journal of
Engineering Mechanics, Vol. 122, No. 10, pp 1003-1001.
6. S. B. Choi and Y. K. Park, 1994, “ Active Vibration Control Of A
Cantilevered Beam Containing An Electro-Rheological Fluid”, Journal of
Sound and Vibration, Vol. 173, pp 428-430.
7. S. B. Choi, C. C. Cheong, J. M. Jung and Y. T. Choi, 1996, “ Position
Control Of An ER Valve-Cylinder System Via Neural Network
Controller”, Mechatronics, Vol. 7, No. 1, pp 37-52.
43
8. Therese C. Jordan and Montgomery T. Shaw, 1989, “ Electrorheology”,
IEEE Transactions on Electrical Insulation, Vol. 2, No. 5, pp 849-879.
9. R. Stanway and J. L. Sproston, 1994, “ Electro-Rheological Fluids: A
Systematic Approach to Classifying Modes of Operation”, Transactions of
the ASME, Vol. 116, pp 498-504.
10. N. G. Stevens, J. L. Sproston and R. Stanway, 1985, “ The Influence Of
Pulsed D.C. Input Signals On Electrorheological Fluids”, Journal of
Electrostatics, Vol. 17, pp 181-191.
11. D.A. Brooks, 1982,“ Electro-Rheological Devices”, Chart Mechanical
Engineering, pp 91-93.
12. D. L. Klass and Thomas W. Martinek, 1967,“ Electroviscous Fluids. I.
Rheological Properties”, Journal of Applied Physics, Vol. 38, pp 67-74.
13. J. L. Sproston, S. G. Rigby, E. W. Williams and R. Stanway, 1994, “ A
Numerical Simulation of Electrorheological Fluids in Oscillatory
Compressive Squeeze-Flow”, J. Phys. D: Applied Physics, Vol. 27, pp
338- 343.
14. S. B. Choi, C. C. Cheong, J. M. Jung and G. W. Kim, 1997, “Feedback
Control Of Tension In A Moving Tape Using An ER Brake Actuator”,
Mechatronics, Vol. 7, No. 1, pp 53-66.
15. T. G. Duclos, Debra N. Acker and J. David Carlson, 1988, “ Fluids That
Thicken Electrically”, Machine Design, vol. 1000, pp 56-61.
16. S. Kapucu, “ Design and Construction of a Two Stage Electrohydraulic
Servovalve With Force Feedback ”, M.S. Thesis, METU.
44
PART LIST OF ER VALVE Name of Part Quantity Materials Drawing No 1- Nipple 2 Iron 2
2- Front Cover 2 Iron 3
3- ER Valve Plate 6 Stainless Steel 4
4- Isolator Plate 10 Rubber 5
5- Outer Cover 2 Iron 6
6- Bolt 16 Iron 7
7- Isolator Plate 8 Rubber 8
45
A A
1 2 3 4 5 6 7
SECTION A-A
Drawing Name ASSEMBLY DRAWING OF THE ER VALVE GAZIANTEP
Drawn By Egemen Ramazan Topçu Drawing No 1 UNIVERSITY
46
M14 D5 D24
16 22 16
Drawing Name NIPPLE GAZIANTEP Drawn By Egemen Ramazan Topçu Drawing No 2 UNIVERSITY
47
60 15 30
16 14 12 5 30 Drawing Name FRONT COVER GAZIANTEP Drawn By Egemen Ramazan Topçu Drawing No 3 UNIVERSITY
48
100 20 20 20 20 20 45 60 6 D8 Thickness 2 mm. Drawing Name ER VALVE PLATE GAZIANTEP Drawn By Egemen Ramazan Topçu Drawing No 4 UNIVERSITY
49
20 80 7 11 D8 Thickness 0.7 mm Drawing Name ISOLATOR PLATE GAZIANTEP
Drawn By Egemen Ramazan Topçu Drawing No 5 UNIVERSITY
50
100 45 20 20 20 20 20 60 D8 8 Drawing Name OUTER COVER GAZIANTEP Drawn By Egemen Ramazan Topçu Drawing No 6 UNIVERSITY
51
M8 45 Drawing Name BOLT GAZIANTEP Drawn By Egemen Ramazan Topçu Drawing No 7 UNIVERSITY 5 D8 30 Drawing Name ISOLATOR RING GAZIANTEP Drawn By Egemen Ramazan Topçu Drawing No 8 UNIVERSITY
PART LIST OF ROTATIONAL VISCOMETER
52
Name of Part Quantity Materials Drawing No
1- DC Motor 1 ---- ----
2- DC Motor Plate 1 Iron 2
3- Coupler 1 Rubber 3
4- Plate Stick 4 Iron 4
5- Top Plate Rice Ring 1 Rice 5
6- Main Top Plate Bearing 2 Steel 6
7- Isolator Fittings 1 Rubber 7
8- Main Top Plate 1 Iron 8
9- Inner Cylinder 1 Aluminium 9
10- Outer Cylinder 1 Aluminium 10
11- Main Stick 4 Iron 11
12- Outer Cylinder Isolator Cup 1 Fiberglass 12
13- Outer Cylinder Fittings 1 Iron 13
14- Main Bottom Plate 1 Iron 14
15- Strain Gauge 2 --- ----
16- Main Bottom Plate Bearing 2 Steel 15
17- Main Bottom Plate Rice Ring 1 Rice 16
53
1 2 3 4 6 5 7 8 9 10 11 12 13 14 15 16 17 Drawing Name ASSEMBLY DRAWING OF THE ROTATIONAL VISCOMETER GAZIANTEP Drawn By Egemen Ramazan Topçu Drawing No 1 UNIVERSITY
54
D5 15 55 75 8 Drawing Name DC MOTOR PLATE GAZIANTEP Drawn By Egemen Ramazan Topçu Drawing No 2 UNIVERSITY D5 25 D25 Drawing Name COUPLER GAZIANTEP Drawn By Egemen Ramazan Topçu Drawing No 3 UNIVERSITY
55
M8 D10 15 45 Drawing Name PLATE STICK GAZIANTEP Drawn By Egemen Ramazan Topçu Drawing No 4 UNIVERSITY D20 D12 18 Drawing Name TOP PLATE RICE RING GAZIANTEP Drawn By Egemen Ramazan Topçu Drawing No 5 UNIVERSITY
56
D12 D6 6 Drawing Name MAIN TOP PLATE BEARING GAZIANTEP Drawn By Egemen Ramazan Topçu Drawing No 6 UNIVERSITY M20 40 10 20 D20 D5 Drawing Name ISOLATING FITTINGS GAZIANTEP Drawn By Egemen Ramazan Topçu Drawing No 7 UNIVERSITY D10
57
110 D20 135 18 20 95 Drawing Name MAIN TOP PLATE GAZIANTEP Drawn By Egemen Ramazan Topçu Drawing No 8 UNIVERSITY 5 10
58
15 45 20 D45 D35 D40 M20 Drawing Name INNER CYLINDER GAZIANTEP Drawn By Egemen Ramazan Topçu Drawing No 9 UNIVERSITY
59
45 3 D50 D41.4 Drawing Name OUTER CYLINDER GAZIANTEP Drawn By Egemen Ramazan Topçu Drawing No 10 UNIVERSITY 20
60
68 D25 M8 Drawing Name MAIN BLOK STICK GAZIANTEP Drawn By Egemen Ramazan Topçu Drawing No 11 UNIVERSITY D60 D50 5 10 5
61
30 Drawing Name OUTER CYLINDER ISOLATOR CUP GAZIANTEP Drawn By Egemen Ramazan Topçu Drawing No 12 UNIVERSITY 20 5 D30 D6 Drawing Name OUTER CYLINDER FITTINGS GAZIANTEP Drawn By Egemen Ramazan Topçu Drawing No 13 UNIVERSITY D10 110
62
D20 145 20 25 95 Drawing Name MAIN BOTTOM PLATE GAZIANTEP Drawn By Egemen Ramazan Topçu Drawing No 14 UNIVERSITY
63
D20 D12 20 Drawing Name TOP PLATE RICE RING GAZIANTEP Drawn By Egemen Ramazan Topçu Drawing No 15 UNIVERSITY D12 D6 6 Drawing Name MAIN BOTTOM PLATE BEARING GAZIANTEP Drawn By Egemen Ramazan Topçu Drawing No 16 UNIVERSITY