Development of High Precision Linear Transfer Platform using Air Floating System for Flat Panel Display Production and Inspection Process

Transcription

1 Development of High Precision Linear Transfer Platform using Air Floating System for Flat Panel Display Production and Department of Mechatronics Engineering, Korea Polytechnic University, Republic of Korea doi : /ijei.vol2.issue2.3 Abstract Recently, there is an increasing requirement for high precision linear transfer platform using for flat panel display production and inspection process such as liquid crystal display, plasma display panel, and organic light-emitting diode. As next generation technology in the area of transfer platform, precision positioning and transfer flatness control under the 10 m is required for inline process such as automatic optical inspection, surface treatment, and marking. As magnetic roller conveyer type is used as transfer platform for flat panel display, there are many problems such as contamination of panel by contact between roller and panel, deterioration of quality, and uncontrollable flatness. The requirements of the high precision linear transfer platform are high positioning accuracy and high transfer flatness. To satisfy these requirements, it has to be designed with the direct drive linear motion system and air floating system. In this work, linear transfer platform having air floating system is proposed, where moving system using linear motor is mounted at the inside of the air floating system, and air floating system is used for floating the flat panel display panel, control system are used for performance requirement. The developed high precision linear transfer platform is verified by performance test in the condition of 50mm step motion for 300mm stroke. From the performance test, positioning accuracy is measured as 4.6μm and repeatability is measured as 0.4μm. Velocity ripple is measured as 0.3% at transfer velocity of 100mm/sec. The transfer flatness is measured as 2.0μm, air gap is measured as 34.5μm in the condition of 1kg payload, and straightness is measured as 9.0μm. From the performance test, developed linear transfer platform is applicable for the flat panel display production and inspection process. Keywords: Transfer Platform, Air Floating, Flat Panel Display, Liquid Crystal Display 1. Introduction Recently, there is an increasing requirement for high precision linear transfer platform using for flat panel display (FPD) production and inspection process such as liquid crystal display (LCD), plasma display panel (PDP), and organic light-emitting diode (OLED). As next generation technology in the area of transfer platform, precision positioning and transfer flatness control under the 10 m is required for inline process such as automatic optical inspection (AOI), surface treatment, and marking. As magnetic roller conveyer type is used as transfer platform for FPD, there are many problems such as contamination of panel by contact between roller and panel, deterioration of quality, and uncontrollable flatness [1]. The requirements of the high precision linear transfer platform are high positioning accuracy and high transfer flatness. To satisfy these requirements, it has to be designed with the direct drive linear motion system and air floating system [2-4]. In this work, linear transfer platform having air floating system is proposed, where moving system using linear motor is mounted at the inside of the air floating system, and air floating system is used for floating the FPD panel, control system is used for performance requirement. The developed high precision linear transfer platform is verified by performance test

2 2. Configuration of linear transfer module The configuration of high precision linear transfer platform using for FPD production and inspection process is as follows, air floating system for floating of FPD panel, moving system using linear motor and mounted in the inside of the air floating system, glass panel gap monitoring system for control of flatness, control system, and pneumatic system as showed in Fig. 1. Figure 1. Configuration of linear transfer platform 3. Development of linear transfer platform 3.1. Air floating system The requirement of air floating system is that air gap is under 50μm in the condition of 1kg payload and transfer flatness is under 10μm. In the design of air floating system, air blowing and vacuum suction type is used as floating method to improve the transfer flatness. Fig. 2 shows the structure of air floating plate, which has air blowing and vacuum holes. (a) (b) (c) Figure 2. Structure of air floating plate; (a) air blowing and vacuum hole size, (b) air blowing section, (c) vacuum hole section By using the finite element analysis tool (FLUENT 6.2), air blowing and vacuum holes of air floating plate are designed. Fig. 3 shows the results of analysis such as static pressure contour on the

3 plane of glass panel, velocity vector on the base plane. Fig. 4 shows the developed air floating system consisted with air floating plate and air blowing and vacuum system. (a) (b) Figure 3. Results of finite element analysis; (a) static pressure contour on the plane of glass panel, (b) velocity vector on the base plane 3.2. Moving system Figure 4. Developed air floating system The moving system is used for transfer of glass panel and driven by linear motor. The requirement of moving system is that velocity ripple is under 0.5% at transfer velocity of 100mm/sec. In the design of moving system, coreless type linear motor is used as driving method to reduce the velocity ripple. Fig. 5 shows the developed moving system with linear motor Glass panel gap monitoring system Figure 5. Developed moving system with linear motor The glass panel gap monitoring system is required to control of flatness of glass panel. Laser displacement meter (LK-2001 of KEYENCE) is used as measuring device as showed in Fig

4 3.4. Control system Figure 6. Developed glass panel gap monitoring system The control system is constructed with motion controller, servo amplifier, linear encoder, and control panel. As motion controller, YASKAWA controller having functions such as Ethernet protocol and 10Mbps data transfer rate is used. As servo amplifier, YASKAWA amplifier is used. As linear encoder, electronic reflective scanning linear encoder (RSF) having functions such as grating pitch 40μm and maximum velocity 4m/sec. As control panel, double sealed control cable (UL20276-SX) is used to reduce the noise effect. Fig. 7 shows developed control system Pneumatic system Figure 7. Developed control system The pneumatic system is required to control the air gap of glass panel. Fine pressure regulating system is used to adjust the air pressure. Fig. 8 shows the developed pneumatic system. Figure 8. Developed glass panel gap monitoring system

5 4. Experimental results The performance test is conducted with developed linear transfer platform as showed in Fig. 9. In the performance test, laser interferometer (ML10) having 1nm resolution is used to measure the displacement of the moving system in the condition of forward and backward 50mm step motion for 300mm stroke as showed in Fig. 10. From the performance test, positioning accuracy is measured as 4.6μm and repeatability is measured as 0.4μm as showed in Fig. 11. Velocity ripple is measured as 0.3% at transfer velocity of 100mm/sec as showed in Fig. 12. Figure 9. Developed linear transfer platform Figure 10. Experimental setup for performance test Figure 11. Measured positioning accuracy and repeatability

6 Figure 12. Measured velocity ripple Fig. 13 shows the experimental setup for transfer flatness and air gap test. Transfer flatness is measured as 2.0μm as showed in Fig. 14 and air gap is measured as μm as showed in Fig. 15. Figure 13. Experimental setup for transfer flatness test Figure 14. Measured transfer flatness Figure 15. Measured air gap Fig. 16 shows the experimental setup for straightness test. Straightness is measured as 9.0μm as

7 showed in Fig. 17. Figure 16. Experimental setup for straightness test 5. Conclusions Figure 17. Measured straightness Table 1. Measured specifications of developed transfer module Parameter Value Positioning accuracy Repeatability Velocity ripple Transfer flatness Air gap Straightness 4.6μm 0.4μm 0.3% 2.0μm 34.5μm 9.0μm In this work, linear transfer platform having air floating system is proposed, where guide system using linear motor is mounted in the inside of the air floating system, and air floating system is used for floating the FPD glass, control system are used for performance requirement. The developed high precision linear transfer platform is verified by performance test in the condition of 50mm step motion for 300mm stroke. From the performance test, positioning accuracy is measured as 4.6μm and repeatability is measured as 0.4μm. Velocity ripple is measured as 0.3% at transfer velocity of 100mm/sec. The transfer flatness is measured as 2.0μm, air gap is measured as 34.5μm in the condition of 1kg payload, and straightness is measured as 9.0μm. From the performance test, developed linear transfer platform is applicable for the flat panel display production and inspection process

8 9. Acknowledgement This work is financially supported by the Ministry of Education, Science and Technology (MEST), the Ministry of Knowledge Economy (MKE) through the fostering project of HUNIC. 10. References [1] J. H. Shim, Design and analysis of a clean non-contact type conveyor s driving mechanism for vertical transfer of FPD glass, Journal of the Semiconductor & Display Equipment Technology, vol. 8, no. 4, pp.71-76, [2] 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, vol. 1, no. 1, pp.19-34, [3] M. J. Chung and D. G. Gweon, Nano-positioning system using trajectory following control method with cogging force model, In Proceeding of the Int. Symposium on Nanomanufacturing, pp.74-74, [4] M. J. Chung, Development of High Precision Linear Transfer Module using Air Floating System for Flat Panel Display, In Proceeding of the Int. Conference on Control, Automation and Systems, pp ,