Journal of Engineering Science and Technology EURECA 2013 Special Issue August (2014) 28 - 39 © School of Engineering, Taylor’s University
28
SINGLE PHASE FLUX SWITCHING DC LINEAR ACTUATOR
ARAVIND CV1,* , KHUMIRA I.
1, R. N. FIRDAUS
2, FAIRUL A.
3
School of Engineering, Taylor’s University, Taylor's Lakeside Campus,
No. 1 Jalan Taylor's, 47500, Subang Jaya, Selangor DE, Malaysia 2Power Electronics and Drives, University Teknikal Melaka, Malaysia
*Corresponding Author: [email protected]
Abstract
A number of variable speed applications require linear actuation such as in linear
compressors, drilling and cutting applications. In this research a flux switching
DC induction actuator with a feedback sensor for operation in closed loop
condition is proposed. The appropriate choice of the permanent magnet
dimensions improves the performance of the PM machines. The linear induction
actuator is chosen by the variations in the height to width of the permanent
magnet through Finite Element Methods. Analysis on the effect of changing the
magnet ratio on the torque and the cogging force is reported in this work. The flux
switching between the adjacent poles is achieved through a control drive circuitry
based on the feedback signal from the sensor. The static characteristic of such a
machine is presented together with the experimental results.
Keywords: linear actuator, Hall sensor, DC machine, Flux switching, Height to
width ratio, Permanent magnet
1. Introduction
Linear actuators are machines that develop the linear force along its length (linear
thrust) [1, 2]. Linear motor covers a wide range of applications from transportations
[3] to its utilization in medical field such as linear actuator syringe pump. Linear
motor is preferred compared to rotary motor due to the relative speed accuracy,
better positioning, and fast acceleration response characteristics [2-3]. This motor
eliminates the mechanical components used to convert the rotation as it requires no
mechanical transmission thereby reducing the flux density. Flux switching
technique is whereby the flux in the coil is switched by varying the operation
through control element thereby changing the direction of the operation through the
feedback element. The control element significantly controls the electro-magnetic
energy inside the machine thereby increasing the thrust. A high power control
Single Phase Flux Switching DC Linear Actuator 29
Journal of Engineering Science and Technology Special Issue 8/2014
module is essential for these types of machines that derive a feedback signal and
then decide the switching pattern.
In this paper the developed linear machine is analysed using Finite Element
methods to choose the best ratio of permanent magnet ratio and then it is analysed
for the static thrust characteristics.
2. Methodology
2.1. Principles of the linear actuator
Linear Induction Actuators are used for short travel and thus their mechanical air-
gap is about 1 mm [3]. Figure 1 shows the flux flow of HDLM with positive,
negative and zero current.
In the unexcited condition, Fig. 1(a), the upper section of the permanent magnet
creates a path for the flux flow like a short circuit in an electrical circuit, so that the
most of the flux flow of the permanent magnet pass through this path and a smaller
flux flow cross from air gap. Whereas the cogging force arises from flux flow of
unexcited condition, in this structure the cogging force is very low. Figures 1(b) and
(c) show the flux flow under the excited condition. With the applied magnetic force
created by the coil energization, the flux of permanent magnets and that of the coils
cross in the air gap. The direction of thrust depends on the direction of magnetic force
developed as shown in Fig. 1(b). The change of the flux direction due to the reverse
polarity excitation, changes the direction of the thrust as shown in Fig. 1(c). The
reverse in polarity by the driver circuit is initiated by the feedback signal so that the
advance excitation is possible thereby improving the thrust value. Thus in this
magnetic circuit, the magnetic fluxes effectively produce thrust at pole (A) and (A’)
with single phase, while the leakage fluxes from the slots are eliminated [4].
Fig. 1. Operational Principle of an HDLM.
N N SS N S N S
N N SS N S N S
N N SS N S N S
(a) unexcited mode
(b) forward excited mode
(c) reverse excited mode
A A’
A A’
A A’
HS HS
HS HS
HSHS
30 Aravind CV et al.
Journal of Engineering Science and Technology Special Issue 8/2014
2.2. Design aspects
The overall research design is a quantitative study derived from the reference [5],
where magneto-static analysis is done on the design through finite element methods.
This analysis is accomplished with two significant steps - the first one is to design
three different actuators through the height to width ratio of the permanent magnet and
then using finite element tool to analyse the static characteristics. Results of this step
demonstrate the flux flow, magnetic flux density, magnetic field intensity and its
thrust. Data obtained from the initial design [6] is compared with different height-to-
width ratios of its permanent magnet size to study the effect of varying the parameter
to the motor’s performance characteristic.
In the initial design the height to width ratio is 2.5 with the magnet dimensions
as 15 mm height and width of 6 mm. In this research, the ratio is varied to 2.7 and
2.9 by keeping the original width as it is and varying the height of the pole
magnet. This is to increase the torque density accumulations at the surface of the
mover to be higher. The design methodology employed in this investigation is as
shown in Fig. 2. Three different design structures with varied h/w ratio as shown
in Table 1 are analysed. Magneto-static analysis is applied to each design. The
main objective of the analysis is to study the machine static characteristics for
each of the incremental 1 mm distance along its linear movement. The same
simulation is repeated for three different current values; 0 A, 1 A and 5 A. The
thrust values obtained are plotted and compared so that the design with the best
sinusoidal waveform can be sent for fabrication.
Fig. 2. Design Methodology.
Table 1. Dimension of Permanent Magnet.
Specification of the
Machine
Design of Machine
Finite Element
Analysis
Results
Magnetostatic
Analysis
Modelling Tool
Simulation Tool
Flux Flow, Flux
Density, Field
Intensity and Thrust
Design Xplorer
Initial Condition
Forward and Reverse
Condition
Static Thrust
Characteristics
Stack Length = 92.5 mm
Height to Width Ratio
2.5
(initial) 2.7 2.9
Height of permanent magnet, mm 15.00 16.25 17.50
Height of moving yoke, mm 6.50 5.50 4.50
Width of permanent magnet, mm 6.00 6.00 6.00
Width of moving yoke, mm 6.00 6.00 6.00
Single Phase Flux Switching DC Linear Actuator 31
Journal of Engineering Science and Technology Special Issue 8/2014
2.2.1. Structural design
Figure 3 is the structural configuration of the linear actuator brushless type with a
required electronic commutation circuit for controlling the flux switching
operation of the motor [7]. Hence a hall sensor is utilized that usually give signal
for the control circuit. The advancements in the microelectronic field s high
efficient digital driver with MOSFET and controller is utilized.
Moving Part SensorStator Yoke
Permanent
MagnetMoving
Yoke
Fig. 3. Structural Configuration.
Table 2 shows the materials used in the design. The stator yoke and the
moving element is made from silicon core steel. High performance of high energy
rare-earth materials, an NdFeB permanent magnet with a remnant flux density of
1.05T, a coercive force of 750 kA/m, and a relative permeability of 1.08 is
chosen. This minimizes the energy required and maximizes the flux. This help to
achieve a high force per unit volume of the magnet. When a magnet is used as a
field source it becomes biased at an operating point (Bm, Hm) on its
demagnetization curve. The operating point depends on the circuit in which it is
used. It can be determined from the load line of the circuit. This intersects the
demagnetization curve at the operating point (Bm, Hm) as shown Fig. 4.
Table 2. Material Specifications of LFSIA.
Fig. 4. Permanent Magnet Operating Point.
Section Item Material
Stator Stator Yoke Silicon Core Iron Coils Copper Alloy Coil Case Teflon
Mover Permanent Magnet NdFeB Moving yoke Silicon Core Iron Shaft SS304
H -Hc
B
-Hm
Bm
Br
0
Operation point
Demagnetization curve
Load line
32 Aravind CV et al.
Journal of Engineering Science and Technology Special Issue 8/2014
2.2.2. Static analysis
In order to analyse the variation in the machine dimensions the ratio of the
height to width is investigated. The rationale on this is to increase the height of
the permanent magnet and keeping the width as it thereby increase the flux
accumulation and thereby increase the torque density. The parameters varied in
the design are as shown in Fig. 5. Numerous simulations on the ratio are done
however the restrictions on two deviations from the original model are
presented in this work. A detailed analysis on the design variations through
finite element method is available in [8, 9].
Cross-section of
Permanent Magnet
Height
Width
HeightCross-section of
Moving Yoke
Fig. 5. Parameters Considered for Thrust Improvement.
In order to derive the torque characteristics of the double rotor reluctance
machine it is constructed using the FEA tool [10]. Finite element analysis is a
numerical method of solving linear and non-linear partial differential equations.
FEA tool is used to obtain the magnetic vector potential values due to the
presence of complex magnetic circuit geometry and non-linear properties of the
magnetic materials. The force on the object in the magneto-static field is
calculated from Maxwell’s equation stress [11, 12]:
(1)
(2)
(3)
where H is the magnetic field intensity, J is the source current density, B is the
magnetic flux density, and ν is the magnetic reluctivity. The divergence-free field
B introduces a magnetic vector potential A .
(4)
( ) (5)
In two-dimensional analysis, we can assume that the current density J has only
a z-direction component. Likewise, the magnetic vector potential A has only a z-
direction component. Then, we obtain the following Poisson equation.
( )
( ) (6)
Single Phase Flux Switching DC Linear Actuator 33
Journal of Engineering Science and Technology Special Issue 8/2014
The above equation is solved using the finite element method. From FEA
simulation, the path of flux flow, magnetic flux density, the torque characteristics
are derived. Figure 6 shows the magnetic flux flow, flux intensity inside the of
the stator yoke and mover configuration for a chosen ratio of 2.5. The results
derived from the simulation are presented as next section. A comprehensive
numerical analysis through the finite element is documented in [8]. The three
different models are analysed for their magneto-static analysis and the
comparison is presented in the following section.
(a)
(b)
Fig. 6. Flux Flow inside the Machine.
(a) Flux Density (b) Flux Intensity
2.3. Driver circuit
The operation of the single phase linear actuator required a power electronic drive
system that enables the sequence of operations. Figure 7 shows the flowchart on
the sequence of operation and Fig. 8 shows the circuit configuration on the design.
A comprehensive approach on the drive circuit design is presented in [6, 9]. The
drive circuit comprises an H bridge MOSFET with driver unit that can switch
bidirectional and thereby the forward reverse movement is achieved. The
controller used is the Atmega series and a voltage regulator to power up the unit is
used in the design.
Hall sensor reads current position
Yes
Switching Circuit Reversed
NoDetect
Initiate Drive Circuit
Fig. 7. Drive Control Circuit Flowchart.
34 Aravind CV et al.
Journal of Engineering Science and Technology Special Issue 8/2014
H-Bridge Circuit Driver Driver
(a)
(c)
(b)
Fig. 8. Driver Controller Circuit.
2.4. Experimental setup
Figure 9 shows the experimental setup of the flux switching actuator with a fan
load to derive the thrust characteristics of the machine under investigations. An
LCR meter is used to calculate the passive parameters of the machine. A DC
power supply is used that give controlled voltage based on the switching of the
device. A recording unit through a computer interface using LABVIEW
instrumentation (not shown in picture) is used to capture the data in real time.
Linear
Acutator
Oscilloscope
DC Power
Supply
DriverMultimeter
LCR
Meter
Load
Fig. 9. Experimental Setup.
Single Phase Flux Switching DC Linear Actuator 35
Journal of Engineering Science and Technology Special Issue 8/2014
3. Results and Discussions
3.1. Thrust and cogging characteristics
From Figs. 10(a), (b) and (c), the thrust characteristics of three different ratio
under investigations. The design with 2.9 h/w ratio has the most stable sinusoidal
waveform at all current conditions simulated. All designs at all current conditions
showed a normal pattern of sinusoidal waveform with different thrust values
according to their h/w ratio as well as their current condition. However, design
with h/w ratio of 2.5 at current condition 5 A shows unexpected results at its
1 mm displacement where its thrust dropped significantly.
Fig. 10. Thrust Characteristics of the h/w Ratio, (a) 2.5 (b) 2.7 (c) 2.9.
Figure 11 shows a comparison of all the three designs to determine which
design has the least cogging force. Cogging force is a main contributor of force
ripple. Cogging force is the retention magnetic field contained in the actuator
when the current is 0 A. To increase the performance of the actuator, researchers
have been optimizing the actuators structure dimension to reduce the cogging
force. In Fig. 11 it shows that Design 3 has the least cogging force compared to
the other two designs.
Fig. 11. Cogging Thrust Characteristics of the h/w Ratio, (a) 2.5 (b) 2.7 (c) 2.9.
3.2. Electro-mechanical characteristics
Figure 12 shows the pulsed waveforms at the various voltage levels applied to the
actuator to study the performance of the test machine.
Displacement (mm)5-5 -4 -3 -2 -1 0 1 2 3 4
-5 -4 -3 -2 -1 0 1 2 3 4 5Displacement (mm)
-5 -4 -3 -2 -1 0 1 2 3 4 5Displacement (mm)
-5 -4 -3 -2 -1 0 1 2 3 4 5Displacement (mm)
-5 -4 -3 -2 -1 0 1 2 3 4 5Displacement (mm)
-5 -4 -3 -2 -1 0 1 2 3 4 5Displacement (mm)
Thru
st (
N)
-
120
-80
-40
0
40
80
120
Thru
st (
N)
-
120
-80
-40
0
40
80
120
Thru
st (
N)
-
120
-80
-40
0
40
80
120
Thru
st (
N)
-
240
-
160
-80
0
80
160
240
Thru
st (
N)
-
240
-
160
-80
0
80
160
240
Thru
st (
N)
-
240
-
160
-80
0
80
160
240
1 A 5 A
(c)(a) (b)
-5 -4 -3 -2 -1 0 1 2 3 4 5Displacement (mm)
-140-120-100-80-60-40-200
20406080
100120
Th
rust
(N
)
-5 -4 -3 -2 -1 0 1 2 3 4 5Displacement (mm)
-100
-80
-60
-40
-20
0
20
40
60
80
100
Th
rust
(N
)
-5 -4 -3 -2 -1 0 1 2 3 4 5Displacement (mm)
-100
-80
-60
-40
-20
0
20
40
60
80
100
Th
rust
(N
)
(a) (b) (c)
36 Aravind CV et al.
Journal of Engineering Science and Technology Special Issue 8/2014
Fig. 12. Pulsed Waveforms from the Oscilloscope.
The voltage to displacement is shown in Fig. 12. A simple vibration analysis
is also performed to study the impact of use with the load application. With less
than 18 V given to the actuator, it is vibrating very slow and emits slow noise
from the motor. However, as the input voltage increases, the displacement of the
shaft’s position is linearly increases. It also produces louder sound and stronger
vibration as the effect of longer linear motion when high input voltage is given to
the actuator.
Single Phase Flux Switching DC Linear Actuator 37
Journal of Engineering Science and Technology Special Issue 8/2014
Fig. 12. Comparison of the Proposed Structure.
The voltage current characteristic of the machine is as shown in Fig. 13 to see
the effect of manipulation of Vin to the behaviour of the current. The data of
current is acquired from the operating motor when input voltage is varied. The
graph plotted below shows that as the input voltage value is increased, the value
of current is linearly increases as well.
Fig. 13. Comparison of the Proposed Structure.
3.2. Thrust characteristics comparison
Figure 14 shows the investigation on the same force by comparing conventional
design with proposed design. As can be seen the thrust characteristics is
improvised and near to sinusoidal. In other words the cogging force of the model
is reduced. However an optimisation procedure on the machine could further
improve the thrust characteristics value. Figure 15 shows the improvement in the
design through the ratio being 2.9 better than the original design ratio of 2.5 [6].
Hence the performance characteristic of such a machine is improved through the
variations in the magnetic circuit inside the machine.
1st Trial 2nd Trial 3rd Trial Average Displacement
5 10 15 20 25 30 35 40
Voltage Input (V)
-0.5
0.0
0.5
1.0
1.5
2.0
2.5
3.0
3.5
4.0
Dis
pla
cem
ent
(mm
)
1st Trial 2nd Trial 3rd Trial Average Current
5 10 15 20 25 30 35 40
Voltage Input (V)
1.0
1.5
2.0
2.5
3.0
3.5
4.0
4.5
Cu
rren
t (A
)
38 Aravind CV et al.
Journal of Engineering Science and Technology Special Issue 8/2014
Fig. 14. Static Thrust Characteristics Comparison of the Model.
Fig. 15. Comparison of the Proposed Structure.
4. Conclusions
Single phase flux switching DC pulsed actuator is investigated to improve the
thrust characteristics from its conventional design. A comparison on the original
design with the height to width ratio of 2.5 is done with other variations through
numerical tool. Three different ratios including the original design are used for
comparative investigations. Induction actuator with height to width ratio of 2.9
has the best thrust characteristics where it is shown through the almost perfect
sinusoidal. Further work involves in the use of optimization tool through either
numeric and analytical is to be presented in its continuing research.
References
1. Boldea, I.; and Nasar S.A. (2005). Linear electric actuators and generators.
Cambridge University Press.
2. Nasar, S.A.; and Boldea, I. (1976). Linear motion electric machines. (2nd
Ed.)
John Wiley & Sons Inc.
Design 1 (original)
Design 2
Design 3 (proposed)
-5 -4 -3 -2 -1 0 1 2 3 4 5
Displacement (mm)
-200
-150
-100
-50
0
50
100
150
200
Thru
st (
N)
-5 -4 -3 -2 -1 0 1 2 3 4 5
Displacement (mm)
-150
-100
-50
0
50
100
150
Th
rust
(N
)
Proposed (numerical)
Initial Model
Proposed (experimental)
Single Phase Flux Switching DC Linear Actuator 39
Journal of Engineering Science and Technology Special Issue 8/2014
3. Gieras, J.F.; and Piech, Z.J.; and Tomczuk, B. (2011). Linear synchronous
motors: Transportation and automation systems. (2th
Ed.) CRC Press.
4. Osawa, S.; Wada, M.; Karita, M.; Ebihara, D.; and Yokoi, T. (1992). Light-
weight type linear induction motor and its characteristics. IEEE Transactions
on Magnetics, 28(2), 3003-3005.
5. Takano, Y.; Yaezaki, S.; Matsumoto, K.; Nishizawa, N.; and Yamada, H.
(1997). Thrust simulation of linear oscillatory actuator. IEEE Transactions
on Magnetics, 33(2), 2085-2088.
6. Fairul, A. (2008). Design of linear oscillatory actuator for oil palm
mechanical cutter. Master of Science Thesis, University Putra Malaysia.
7. Chen, Y.-R.; Wu, J.; and Cheung, N.C. (2003). Lyapunov’s stability theory-
based model reference adaptive control for permanent magnet linear motor
drives. Journal of South China University of Technology, 31(6), 31-35.
8. Khumira, I. (2013). Linear flux switching induction actuator. Bachelors
Thesis, School of Engineering, Taylor’s University, Malaysia.
9. Khumira, I.; Aravind, CV.; Raja, R.N.; and Fairul, A. (2013). Computations
of thrust characteristics of flux switching induction actuator with different
height to width ratio. Proceedings of Engineering Undergraduate Research
Catalyst Conference (eureca 2013), School of Engineering, Taylor’s
University, Kuala Lumpur, Malaysia.
10. Binns, K.; Lawrenson, P.J.; and C.W. Trowbridge (1992). The analytical
and numerical solution of electric and magnetic fields. John Wiley & Sons.
11. Kameari, A. (1993). Local force calculation in 3D FEM with edge elements.
International Journal of Applied Electromagnetics in Materials, 3(1), 231-240.
12. Kameari, A.; and Niikura, S. (1993). Magnetic force calculation by nodal
force method in FEM using edge elements. Proceedings of Compumag
Conference, Part A, 2-13.