Contemporary Engineering Sciences, Vol. 8, 2015, no. 21, 971 - 979
HIKARI Ltd, www.m-hikari.com
http://dx.doi.org/10.12988/ces.2015.57223
Development of Liquid Crystal Display Production
Equipment Consisting of Linear Motor Having
High-thrust and Low-cogging Force
Myung-Jin Chung
Department of Mechatronics Engineering, Korea Polytechnic University
237, Sangidaehak-Ro, Siheung-Si, Geyonggi-Do, Republic of Korea
c 2015 Myung-Jin Chung. This article is distributed under the Creative
Copyright Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
Abstract
Recently, there has been an increasing requirement for controlling
linear motion up to a few hundred millimeter strokes in the area of the
liquid crystal display (LCD) production equipment. The requirements
of the motion system for LCD production equipment are high acceleration with positioning accuracy and trajectory following accuracy. To
satisfy these requirements, motion system has to be designed with highthrust and low-cogging force. In this work, the design method of linear
synchronous motor (LSM) having high-thrust and low-cogging force is
proposed. Electromagnetic analysis using the finite element method is
applied to maximize the thrust force and minimize the cogging force.
The developed LSM is verified by a performance test and is applied to
the LCD production equipment.
Keywords: High-Thrust; Low-Cogging; Linear Synchronous Motor; LCD
Production Equipment
1
Introduction
Recently, there has been an increasing requirement for controlling linear motion up to a few hundred milimeter strokes in the area of the liquid crystal display (LCD) production equipment [1-3]. Linear positioning system with direct
driving method such as piezoelectric drive and permanent magnet (PM) motor
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Myung-Jin Chung
Figure 1: Configuration of the LSM having high-thrust and low-cogging forces
could offer significant advantages over conventional linear actuation technologies [4, 5]. Among these direct driving methods, motion system using linear
motor is a proper method for long stroke and high accuracy [6]. PM motor
can be designed by using the magnetic field analysis such as numerical method
and reluctance network method. As numerical method, many researchers have
used the finite element method for the analysis of magnetic field [7-9]. The
requirements of the motion system for LCD production equipment are high
acceleration with positioning accuracy and trajectory following accuracy [3].
To satisfy these requirements, motion system has to be designed with the highthrust and low-cogging force.
In this work, the design method of linear synchronous motor (LSM) having
high-thrust and low-cogging force is proposed. Electromagnetic analysis using
the finite element method is applied to maximize the thrust force and minimize
the cogging force. The developed LSM is verified by a performance test and is
applied to the LCD production equipment.
2
Configuration and Design Method
LSM having high-thrust and low-cogging force is consists of a mover and stator
as shown in Figure 1. The mover using a coil block and core is assembled with
2∼8 coil block module according to thrust force. The stator utilizing a magnet
and yoke is fixed with a guide rail. By using the assembling reference bump,
the core gap between coil blocks can be adjusted in the assembling process of
a coil block. Flux path is constructed with the double side of core.
The required specifications of LSM having high-thrust and low-cogging force
for LCD production equipment are listed in Table 1. In the design of LSM,
the shape of the mover and stator are design variables as shown in Figure
2. The design variables describing the shape of the mover and the stator are
Development of liquid crystal display production equipment
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Table 1: Requred specifications of the LSM for LCD production equipment
Parameters
Value
Unit
Input voltage
440
Volt
2,500
N
Rated thrust force
Max. thrust force
5,000
N
1.0
m/sec
Max. Velocity
Figure 2: Design variables of LSM(A is a tooth cutting height, B is a tooth
cutting width, C is an air gap, and D is a mover length pitch)
determined by the electromagnetic analysis using the finite element method.
Figure 3 shows the finite element model of the mover and stator at front,
middle, and rear parts. In Figure 3, the core shape of the mover is designed
to minimize the cogging force generated by magnet and core. Figure 4 shows
the air gap flux density distribution according to slot number per pole and per
phase. In Figure 4, air gap flux density distribution is similar to sine waveform
according to increasing slot number. The LSM having more slot number has
good performance in the motor characteristics such as force ripple, efficiency,
and vibration. The thrust force and cogging force distribution according to
mover moving distance for one pole pitch can be calculated by finite element
analysis as shown in Figure 5. Table 2 lists the specifications of LSM designed
by finite element analysis.
3
Manufacturing
The manufacturing of LSM is consists of the assembly of mover and stator,
driving circuit for driving the assembled LSM, and driving program for control
of driving circuit. The mover having coil block and core is assembled with 6 coil
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Myung-Jin Chung
Figure 3: Flux distribution according to finite element model of LSM: (a) front
part (b) middle part (c) rear part
Figure 4: Air gap flux density distribution according to slot number per pole
and per phase
Development of liquid crystal display production equipment
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Figure 5: Force distribution for one pole pitch: (a) thrust force (b) cogging
force
Table 2: Specifications of LSM designed by finite element analysis
Parameters
Value
Unit
Input voltage
440
Volt
48
A
Continuous current
Peak current
96
A
Thrust force constant
52.5
N/A
Rated thrust force
2,520
N
Max. thrust force
5,040
N
Force ripple
±15
N
Max. Velocity
1.02
m/sec
Mover weight
34.3
kg
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Myung-Jin Chung
Figure 6: Parts for assembling LSM: (a) core (b) coil (c) magnet and yoke (d)
assembled mover
block module, and the stator having magnet and yoke is fixed with a guide rail
as shown in Figure 6. The driving circuit is manufactured with TMS320F1812
DSP, which has 440V input voltage, resolver input, high-speed computing
function of 150MIPS having 32bit, I/O function, and motor drive function.
Figure 7 shows the process block diagram of developed driving circuit. Instant
variation of input voltage having 440V is protected by regulation module. DCDC converter and SMPS are used as electric power source of controller and
gate driver. Current and position feedback are used for current and velocity
control. Thrust force control is conducted by control of current. To drive the
LSM by using resolver input, driver control program using sinusoidal driving
signal is developed.
4
Experiments and Results
To verify the applicability of developed LSM to the LCD production equipment, the performance test is conducted with developed LSM as shown in
Figure 8. The thrust force is measured by using the load cell. The measured
thrust force and thrust force constant according to applied current is shown
in Figure 9. In Figure 9, measured thrust force constant is converged to one
value according to increasing current. The measured thrust force constant is
54.8N/A, the rated thrust force for rated current (48A) is 2,630.8N, and the
maximum thrust force for peak current (96A) is 5,261.8N for operating velocity
range. Measured thrust force constant deviats from calculated value by 4.4%.
Table 3 lists the specifications of LSM measured by experiment.
Development of liquid crystal display production equipment
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Figure 7: Process block diagram of developed driving circuit
Table 3: Specifications of LSM measured by experiment
Parameters
Value
Unit
Input voltage
440
Volt
48
A
Continuous current
Peak current
96
A
54.8
N/A
Thrust force constant
Rated thrust force
2,630.8
N
Max. thrust force
5,261.8
N
±16.1
N
Force ripple
1.02
m/sec
Max. Velocity
Mover weight
35
kg
5
Conclusion
By applying the electromagnetic analysis using the finite element method, the
design variables of LSM is obtained for the high-thrust and low-cogging forces.
The designed thrust and cogging forces are 2,520N and ±15N respectively.
The LSM is manufactured with designed variables and the performance test is
conducted to verify the applicability of developed LSM to the LCD production
equipment. The measured thrust and cogging forces are 2,630.8N and ±16.1N
respectively. The specifications of the LCD production equipment having the
developed manufactured LSM are a maximum velocity of 1.02m/sec, mover
weight of 35kg, and positioning accuracy of 1µm.
From the study on the design method of LSM, it was found that electromagnetic analysis using the finite element method is applicable and useful. The
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Myung-Jin Chung
Figure 8: Experimental setup for performance test with developed LSM
Figure 9: Measured thrust force and thrust force constant
error between designed and measured value are 4.2% in thrust force and 6.8%
in cogging force.
Acknowledgements. This work is financially supported by the ministry
of education, science technology [MEST] and the ministry of knowledge economy [MKE] through the fostering project of the industrial-academic cooperation centered university.
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Received: August 11, 2015; Published: September 25, 2015