Development of a 3-Axis Fast Tool Servo with Low Interference Motions

[[abstract]]近年來，隨著光學裝置的小型化和多功能化，其元件形狀由原來為軸對稱非球面進 展為非軸對稱之自由曲面；而且，具有大量微細溝槽之背光模組或繞射格子等光學元件 的需求亦不斷增加。目前，大量生產這些光學元件的超精密模仁，仍需藉助切削加工或 研磨加工。一般，對於這些非軸對稱形狀的加工，必須計算各個加工點以形成加工點群， 工具再依所定目標點群一邊移動一邊進行加工。這種加工方式，受限於原加工機台之循 跡移動的速率，加工時間極為冗長，以致無法提升加工效率。另外，又如微鏡片陣列的 超精密／微細加工，乃僅以單一刀具進行龐大面積的加工，隨著時間的長久流逝，不論 刀具磨耗、破損或加工環境產生變化，均會產生加工精度劣化的問題。因此，如何縮短 加工時間，為當前的重要課題。 有鑑於此，本研究計畫提出「低干涉運動3軸向快速刀具伺服裝置之研發」以增進 光學元件模仁之加工效能。此刀具伺服裝置的構成，包含XY奈米定位平台及Z軸向微進 給刀座。所提出之快速刀具伺服裝置，乃以壓電致動器驅動，並妥善配合撓性鉸鍊的應 用，其性能與現存之3軸向快速刀具伺服裝置相比較，具有優異之低干涉運動、高剛性， 以及快速響應的優點。 在預期兩年時程的計畫中，將設計及建構完成新型之刀具伺服裝置，且在四軸超精 密加工機上將驗證刀具伺服裝置的切削性能。第一年度(101)的目標，在於設計及建構具 三軸向運動之奈微米進給之快刀伺服裝置，並驗證其靜態特性（位移、剛性、干涉運動）、 動態特性（步階響應、頻率響應），及控制性能（循跡控制、驅動振動波形）等，以期 能達成進給精度在10 nm 以下之超精密快刀伺服裝置。第二年度(102)的目標，在於將所 建構之快刀伺服裝置與原加工機台進行系統整合，並進行加工實驗。首先，規劃包含可 程式規劃邏輯陣列(FPGA)之即時控制系統，可擷取光學尺信號及輸出指令至壓電致動 器，以提供刀具伺服功能。接著，進行切削實驗，內容包含自由曲面加工、微溝槽加工、 微鏡片陣列加工等，以確認本研究計畫的成效。本研究計畫之執行，預期將可提升國內 在超精密加工領域的技術層次，並具學術研究與產業應用價值。[[abstract]]Due to performance progresses and miniaturized sizes of optical devices, features of optical components are with a trend from symmetric aspheric surface to asymmetric free form surface. In addition, the needs for such as back light modules and holograph elements featuring with massive micro grooves are increasingly presented recently. Usually, the productions of optical components are largely relied on dies and molds, which are mainly produced by cutting and/or grinding processes. In the machining process of an asymmetric component, uncountable points are grouped together for the tool to trace in sequence and to perform machining. This kind of machining requires huge time to operate since the travelling speed of a machine tool is restricted. In addition, as to the case using only a single tool to machining a micro lens array, the cutting environment is subject to vary and the cutting tool is prone to wear or break due to lasting operation, thus resulting in a deterioration in machining quality. Therefore, how to improve productivity in ultraprecision machining is an important issue in current industry. In this project, a three axis fast tool servo is proposed to improve the machining performance for molds and dies of optical components. The 3-axis tool servo is consisted of an XY nano positioning stage and a Z-axis feeding tool holder. The proposed fast tool servo actuated by piezoelectric (PZT) actuators well incorporated with flexural hinges is expect to feature excellent low interference motions, high stiffness, and fast response compared to an existing device. In this two years’ project, a newly designed fast tool servo will be implemented, and the experimental examinations for the fast tool servo based on 4-axis CNC ultraprecision machining works will be performed. In the first (2012) year’s works, design and implementation of the fast tool servo is made. Fundamental experiments are performed to examine steady characteristics (displacement, stiffness, interference motions), dynamic characteristics (step response, frequency response), and control performance (contour tracking, vibration actuation) of the fast tool servo. The control performance under 10 nm is expected. In the second (2013) year’s works, the fast tool servo is installed to an existing ultraprecision machine for examining cutting performances. In the beginning, a real time control system embedded with a FPGA (Field Programmable Gate Array) module is configured. The control system capable of acquiring the information of optical encoders and sending commands to the PZT actuators is used to provide tool servo function. In the next, machining experiments are performed for asymmetric free form surface, micro lens array, and micro grooves. Through these experimental examinations, the effectiveness of the project is verified. It is expected that the technology level in ultraprecision machining can be upgraded, and the research results are enriched with academic valuation and industrial applications, with the fulfillment of the proposal.[[note]]NSC101-2221-E327-00