AIP Conference Proceedings 1788, 030032 (2017); https://doi.org/10.1063/1.4968285 1788, 030032
© 2016 Author(s).
Performance prediction of serpentine
type compact magnetorheological brake
prototype
Cite as: AIP Conference Proceedings 1788, 030032 (2017); https://doi.org/10.1063/1.4968285
Published Online: 03 January 2017
Ubaidillah, A. Wibowo, D. Adiputra, et al.
ARTICLES YOU MAY BE INTERESTED IN
Wind energy potential assessment to estimate performance of selected wind turbine in
northern coastal region of Semarang-Indonesia
AIP Conference Proceedings 1788, 030026 (2017); https://doi.org/10.1063/1.4968279
The study of the influence of the diameter ratio and blade number to the performance of the
cross flow wind turbine by using 2D computational fluid dynamics modeling
AIP Conference Proceedings 1931, 030034 (2018); https://doi.org/10.1063/1.5024093
Effect of blades number to performance of Savonius water turbine in water pipe
AIP Conference Proceedings 1931, 030046 (2018); https://doi.org/10.1063/1.5024105
Performance Prediction of Serpentine Type Compact
Magnetorheological Brake Prototype
Ubaidillah
1,a)
, A. Wibowo
1
, D. Adiputra
2
, D.D.D.P. Tjahjana
1
, M.A.A. Rahman
2
,
and S.A. Mazlan
2
1
Mechanical Engineering Department, Universitas Sebelas Maret, Surakarta, Jawa Tengah, Indonesia 57126
2
Malaysia-Japan International Institute of Technology, Universiti Teknologi Malaysia, Kuala Lumpur, Malaysia
54100
a)
Corresponding author: ubaidillah@uns.ac.id
Abstract. A magnetorheological brake (MRB) with serpentine flux type for ankle-foot orthosis (rehabilitation device) was
assessed its performance regarding braking torque and dynamic range. This assessment was conducted based on a problem
that the MRB did not generate sufficient braking torque for the orthosis device. The braking capability was appraised
through analytical approached based on the prototype design. The magnetic circuit of the MRB design was firstly
investigated its capability for generating magnetic flux at braking surface area using finite element method magnetic
(FEMM) software. Governing equation was derived to determine the braking performance i.e. braking torque and dynamic
range as a function of applied current. The main factors influencing the braking performance were magneto-induced shear
stress, the clearance between rotor and stator, and braking surface area. Especially for shear stress, this factor was totally
influenced by the magnetic flux generated within the braking area. These all factors were contained within the governing
equation. Furthermore, the braking performances were determined by solving the governing equation according to the
design parameters. As a result, the governing equation can be used for improving the MRB design to get a better braking
performances.
INTRODUCTION
Magnetorheological (MR) fluids have been widely used for smart damping devices such as MR damper, MR brake,
MR engine mounting and MR haptic device[1]. The use of MR fluids in the braking system has been revolutionary
changing mechanical brake to the brake-by-wire system in which it is less employing mechanical parts [2]. The
working principle of MR brake is a dissipation of energy resulted from rotor into another form of energy by
manipulating the shear stress of MR fluids within the gap between rotor and stator. The change of shear stress is
usually accommodated by treating MR fluids with magnetic fields. Meanwhile, the magnetic fields are provided from
electromagnetic parts embedded within the MR brake. Some magnetic fields depend on the electric current generated
by the electromagnet. It is, therefore, the alteration of shear stress can be achieved in the ranges of milliseconds (less
than 10 milliseconds) [3].
Penetration of MR brake in some application such as automotive braking system, rotary damper, joystick, and
medical rehabilitation devices has challenged researchers to develop various types and design. Numerous types of MR
brake have been proposed and assessed such as disc type, drum type, T-shaped MRBs, multiple disks, and multiple
coils [4]. These types were proposed based on typical application. Although, the MR brake has been tried to be applied
in the tremendous application, one of the main drawback is less producing braking torque compared to the mechanical
brake. So far, the application of high torque MR brake was conducted by Sohn et al. [5] which utilizing MR brake in
middle size motorcycle. The maximum torque achieved by the optimized design was more than 100 Nm. This excellent
result was achieved after optimization on the MR brake design. Based on the drawback, existing research on MR brake
mostly penetrated low brake application such as haptic and medical rehabilitation devices. Utilization of MR brake
for rehabilitation medical device has been previously conducted. Avraam et al. [4,6] proposed solicitation of MR brake
International Conference on Engineering, Science and Nanotechnology 2016 (ICESNANO 2016)
AIP Conf. Proc. 1788, 030032-1–030032-8; doi: 10.1063/1.4968285
Published by AIP Publishing. 978-0-7354-1452-5/$30.00
030032-1
for wrist rehabilitation device. T-shaped MR brake was adopted for this application. Another application for
rehabilitation medical device was MR brake for controllable ankle-foot orthoses by Kikuchi et al. [7,8]. This
controllable ankle foot orthosis was utilized for ankle rehabilitation. A compact multiple disc type MR brake having
a size of 52 mm total diameter and 32 mm thick which available torque was about 4 Nm. This design was indeed
achieving high torque since it used 18 layers MR fluids with micron sized gap. However, the fabrication of multiple
disks in a compact size would need advanced machining process due to very high tolerances.
All of MR brake designs have mostly the same strategy for reaching optimum braking torque or dynamic ranges
that are improving effective braking area or friction area. As proposed by Senkal and Gurocak [9], a compact
serpentine type MR brake is proposed in this study to achieve maximum braking area in a limited size of MR brake.
For information, this MR brake would be integrated into ankle-foot orthoses for foot drop prevention. This kind of
disorder usually happens in the post-stroke patient. Since the application is for foot swinging, the overall mass of
ankle-foot orthoses should be as light as possible. This paper delivers the first step development of MR brake that is
design and braking performance prediction of the device. The discussion covers design, working principle,
mathematical model, magnetic circuit analysis, finite element method magnetic, and braking torque performance
prediction.
METHODOLOGY
Design of MR Brake
As stated before, the compact MR brake with serpentine flux type was dedicated for ankle-foot orthoses. Therefore,
the size and mass were limited to a constraint that the design has a maximum size of 45 mm and thickness of 30 mm.
The 3D model of MR brake including its cross-sectional view is depicted in Fig. 1. A rotor and a stator construct the
compact MR brake. The rotor consists 6 parts namely: rotor shaft (1 pc, bronze), rotor steel (3 pcs, AISI 1020), and
spacer (2 pcs, bronze). Meanwhile, the stator is constructed of main wall (AISI 1020), o-ring (rubber), rubber seal
(rubber), a spacer (bronze), bobbin (bronze), and wire coil (copper). The structure of rotor steel, stator steel, and
spacers as shown in Fig. 1 is objected to making all surface in the rotor can be magnetized. Hence, the shear stress
occurs optimally. The flow of magnetic flux can be seen in section finite element method magnetic. Based on the
existing structure, we predicted that the spacer could bend the flux flow. Hence, the flow pattern is similar to
meandering shape or for the appropriate term, serpentine pattern. In this device planning, MRF-132DG, Lord Corp.
was utilized as a braking medium. The technical specification and relationship between shear yield stress and flux
density are shown in Table 1 and Fig. 2, respectively.
FIGURE 1. The design of MR brake.
030032-2
TABLE 1. Specification of MR fluids MRF-132DG
Property
Value/limits
Based fluid
Hydrocarbon
Work temperature
-40 to 130°C
Density range
2.98 to 3.18݃ܿ݉
ଷ
Τ
Solid percentage weight
80.98%
Specific heat @ 25°C
0.79 ܬ݃ιܥ
Τ
FIGURE 2. The relationship between shear yields stress and magnetic fields.
Braking Torque Model
The design of compact MR brake was firstly predicted its capability for generating the braking torque. As can be
seen in Fig. 3, the braking torque results from the summation between viscous (off state) and magneto-induced torques
(on state). Based on Figure 3, the both annular and radial area contribute to the braking torque. Each torque value can
be calculated based on equations stated in Table 2. On state torque depends on the shear yield stress values which are
influenced by a number of magnetic fields. The shear yields stress ߬
௬
is obtained from the MR fluids characteristics
as depicted in Figure 2 and the polynomial relationship is governed based on the shear yield stress data. The
polynomial equation representing shear yield stress characteristic can be viewed in Fig. 2.
TABLE 2. List of equation used for braking torque calculation
Torque value, radial (off state)
ࢴ
ࣁ࢘ࢇࢊࢇ
ൌ
࣊ࣁࣂ
ሶ
ࢍ
ൣࡾ
࢘
െࡾ
൧
Torque value, annular (off state)
ߒ
ఎ௨
ൌʹߨ݄ߟ
ߠ
ሶ
݃
ܴ
ଷ
Total torque (off state)
ߒ
ఎ
ൌ
ߨߟߠ
ሶ
݃
ሾ
ܴ
ସ
െܴ
ସ
ሿ
ʹߨ݄ߟ
ߠ
ሶ
݃
ܴ
ଷ
Torque value, radial (on state)
ߒ
ఛௗ
ൌ
ʹ
͵
ߨ߬
௬
ሺ
ܴ
ଷ
െܴ
ଷ
ሻ
Torque value, annular (on state)
ߒ
ఛ௨
ൌʹߨ݄߬
௬
ܴ
ଶ
Total torque (on state)
ߒ
ఛ
ൌߒ
ି௦௧௧
ߒ
ି௦௧௧
The value of shear yield stress is proportional to the generated magnetic flux flow through the MR fluids. The
magnetic flux enhanced when the current applied to the coil increases. Therefore, there are two strategies capable of
߬
ݕ
ሺ
ܤ
ሻ
ൌͷʹǤͻʹܤ
Ͷ
െ ͳǤͷͳܤ
͵
ͳͷͺǤͻܤ
ʹ
ͳ͵ǤͲͺܤ ͲǤͳͶͶʹ
030032-3
increasing magnetic flux those are either increasing the electric current on the coil or choosing thinner copper wire
size to get a larger amount of coil winding. Increasing current is not a good choice for limited space of coil winding
since it will generate heat. Thus, the appropriate alternative for limited space of MR brake is choosing thin copper
wire diameter. In this study, the diameter of the copper wire is 0.45 mm (AWG26). The thinner size can be selected.
However, it will limit the maximum chassis current transmitted through the copper wire. Whereas, this design required
maximum current applied about 2 A.
The base dimensions used for braking torque performance calculation are detailed in Table 3. The radial and
annular gap were initially set to 0.65 and 0.5 mm. The calculation of MR brake performance will also cover the
changes of both annular and radial gaps size. This step is necessary for knowing the effect of gap turning to the MR
brake performance.
FIGURE 3. The configuration of rotor and stator.
TABLE 3. MR brake dimension.
No
Symbol
Description
Value
1
ߨ
Phi/constant
22/7
2
ߟ
Viscosity of base fluid (Pa.s)
0,112
3
ߠ
ሶ
Rotational velocity (rad/s)
1,046
4
݃
Radial gap (mm)
0,45
Angular gap (mm)
0,3
5
ܴ
Outer rotor radius (mm)
7,7
6
ܴ
Inner rotor radius (mm)
4,0
7
݄
Angular channel length 1 (mm)
3,7
Angular channel length 2 (mm)
3,3
Angular channel length 3 (mm)
3,3
Angular channel length 4 (mm)
3,7
Angular non-magnetic area/spacer (mm)
0,7
8
߬
௬
Shear yield stress of the MR fluids (MPa)
Magnetic Circuit
It is important to establish the magnetic circuit of the designed MR brake. The magnetic circuit will confirm the
flux flow along the circuit and it can also be used for initial prediction of magnetic field density generated by the
electromagnet. Besides, material selection can be firstly determined by considering the magnetic circuit. Kirchhoff
Laws is useful to derive the magnetic circuit in one loop system. Based on the design configuration, there are 13
030032-4