advertisement

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 972 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 973 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 974 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 975 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 976 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 977 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 978 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. References [1] M. J. Chung, S. Y. Son and Y. H. Yee, High precision X-Y stage for production and inspection equipment of organic light-emitting diode display, Advances and Applications in Mechanical Engineering and Technology, 1 (2010), 19 - 34. Development of liquid crystal display production equipment 979 [2] M. J. Chung, Development of high-thrust and double-sided linear synchronous motor module for liquid crystal display equipment, Journal of measurement science and instrument, 1 (2010), 114 - 117. [3] M. J. Chung, Development of transfer robot using for small size flat panel display manufacturing process, Applied Mechanics and Materials, 541542 (2014), 1146 - 1149. http://dx.doi.org/10.4028/www.scientific.net/amm.541-542.1146 [4] J. W. Ryu and D. G. Gweon, Optimal design of a flexure hinge based xy-theta wafer stage, Precision Engineering, 21 (1997), 18 - 28. http://dx.doi.org/10.1016/s0141-6359(97)00064-0 [5] M. J. Chung and S. Y. Son, Development of compact auto focus actuator for camera phone by applying new electromagnetic configuration, Journal of Mechanical Science and Technology, 20 (2006), 2087 - 2093. http://dx.doi.org/10.1007/bf02916325 [6] M. J. Chung, Development of high precision linear transfer platform using air floating system for flat panel display production and inspection process, International Journal of Engineering and Industry, 2 (2011), 27 - 34. http://dx.doi.org/10.4156/ijei.vol2.issue2.3 [7] X. Lin, Y. Li, Y. Zhang and J. Xu, Numerical analysis for transient electromagnetic field of permanent magnet brushless DC motor, Electromagnetic Field Problems and Applications (ICEF), 1 (2012), 1 - 4. http://dx.doi.org/10.1109/icef.2012.6310279 [8] S. Ding, Z. Wang and W. Li, Numerical calculation of starting electromagnetic field for salient pole synchronous motor, Large Electric Machine and Hydraulic Turbine, 1 (2005), 19 - 23. [9] B. Zhao, Numerical analysis of the electromagnetic field of a permanent magnet linear synchronous motor using wavelet finite element method , International Journal of Computational Science and Engineering, 8 (2013), 78 - 85. http://dx.doi.org/10.1504/ijcse.2013.052107 Received: August 11, 2015; Published: September 25, 2015