壓電式液晶滴注器及高精度液滴體積線上量測系統研製

Development of a LCD droplet generator and precision in situ droplet volume measurement system

陳智遠(Jhih-Yuan Chen)

指導教授 ： 范光照

共同指導教授 ： 王興華

國立臺灣大學/工學院/機械工程學研究所/博士(2009年)

https://doi.org/10.6342/NTU.2009.00324

摘要

傳統的平面顯示器液晶充填技術均屬於真空注入液晶方式，對愈作愈大的基板而言，於注入液晶的步驟會耗費許多時間，而採用單滴填充技術(one drop filling, ODF)，可有效縮短製程時間。ODF不同於以往利用壓力差將液晶注入基板間隙的方式，ODF首先需先瞭解液晶面板的構造，利用光學量測方式測量Spacer的高度以決定所需滴注液晶的體積，再以液晶滴注器與其控制裝置來控制滴入的液晶量、最後使用框膠與壓合等技術封裝成液晶面板。
本研究成功的研製出一壓電式液滴產生器，滴注器的設計則以低成本、拆卸與清洗的便利性為考量重點，整體結構為可拆卸式，避免使用完後液體材料殘留於縫隙而產生污染，滴注器運作原理為利用壓電片上下反覆震動推出液體，驅動波形以脈衝波為主，探討各種參數條件對滴注穩定性的影響，如噴嘴品質、電壓訊號與液體性質，控制滴注器可長時間維持穩定滴注狀態。為求加快滴注製程速度，本研究開發多滴頭滴注系統，配合重量校正程序，針對不同滴注器調整滴注量，使多顆滴注器之滴注量一致，另外藉由加大噴嘴孔徑，單顆液滴重量可達1.14mg，能有效提升製程速度。
於滴注過程中可使用頻閃法觀測液滴之滴注以及飛行過程，並以此原理開發液滴體積線上量測系統即時量測液滴體積。本研究開發之線上量測系統是以CCD為取像裝置，利用閃頻法所攫取到的液滴靜態影像，經由影像處理取得所要的液滴邊緣資訊後，以旋轉對稱體積模型計算液滴體積，由於此法的計算精度取決於液滴截面分割數與橫截面圓的直徑精度，因此本研究使用次像素技術增加影像解析度，以多項式曲線擬合重建液滴邊緣輪廓曲線，細分曲線後所得到次像素點則以點分群法與雜湊法的概念建立次像素點資料結構，加快影像資料處理時間。單張影像處理時間約0.4秒，量測結果與精密電子秤比較之誤差在±0.3%的範圍內，可符合ODF線上量測的需求。本系統亦可即時監控任何單滴液滴體積的變動量，以期能精確的控制液晶滴注總量，符合液晶面板製程的需求。

關鍵字

單滴充填 ； 液滴產生器 ； 頻閃法 ； 體積量測 ； 影像處理

並列摘要

Traditional liquid crystal injection method of TFT/LCD will face fierce challenge when the display size becomes larger and larger, because of its long process time. The advanced one drop filling (ODF) technique will become a key process trend to overcome. The amount of liquid crystal depends on the gap between two liquid crystal panels. Therefore, the height of spacer is the key point of determining the gap. Initial works will focus on the literature survey and optical measurement technique to realize the actual height of each spacer. A micro dropping dispenser using DOD technique will also be studied at the second stage. Variation in LC volume control will yield surface defect of the display.
This paper presents the design, fabrication and tests of a piezoelectric type droplet generator, which can be used for liquid dispensing system. At the end of each liquid filling process, the remaining liquid has to be drained out and the parts have to be cleaned. A Teflon gasket is particularly designed to connect the main body and the nozzle holder. This design helps the dismantling process to be done easily and ensures the assembled structure to be fully sealed. The principle is to actuate a disk type PZT by a function generator to push the liquid out of the droplet generator and form a near-spherical droplet due to surface tension. In our research, we investigated the phenomenon of dispensing, in order to improve the accuracy and reliability of the droplet generator. There are three process parameters to be kept under control, namely, the quality of the nozzle, the voltage signals and the liquid properties. We expected to find out the best control parameters of the actuator in order to precisely control the total amount of the liquid crystal material. This research develops a multi-dispenser system to provide a method for dispensing liquid that enables increased efficiency by applying liquid from a plurality of liquid dispensing devices. Then, we could utilize the developed calibration procedure to achieve a goal by controlling the weight of drops. It is very useful that each time when the target weight of droplet was changed, the calibration procedure was not necessary to repeat again. In addition, the single drop weight can reach 1.14 mg by increasing the nozzle size.
In addition to exciting the PZT, the signal generator also drives a light emitting diode LED that is used to observe the droplet formation phenomenon by means of stroboscopic technique. An online droplet volume measurement system is applied to the One Drop Fill (ODF) process of the liquid crystal display (LCD) manufacture. The developed system utilizes the stroboscopic technique to synchronize the triggering of the strobe light and the CCD camera. A steady image of the droplet can be captured online by the CCD camera. The method of precise volume estimation is based on the rotationally symmetric model of the droplet's shape. Polynomial fitting is used to reconstruct the droplet profile. The image resolution can thus be enhanced by the sub-pixel technique. Compared to a precision electronic balance, the total weight measured by this system has an error being within ±0.3% and the computation time for each droplet is about 0.4 s. This all together fits the actual ODF requirements.

並列關鍵字

One Drop Fill, ； droplet generator ； volume measurement ； image processing

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