雙曲軸異相位機構開發應用於高密度微光學結構陣列快速成形研究

Abstract

本研究旨在開發一「雙曲軸異相位平衡驅動機構」，應用於往復式進給系統，以便快速製作「高密度光學微結構模仁陣列」。研究先以曲柄連桿式、偏心凸輪式、斜盤凸輪式及橢圓凸輪式等四種驅動機構進行設計、分析與探討，並發現曲柄連桿機構能在高頻驅動下，快速且確動地進行往復直線運動，而其他凸輪機構，在高頻運動下，刀具「跟隨性(Following performance)」低，易造成定位誤差。研究首先設計並建構一部「三軸CNC類高頻往復式進給系統工具機」，並提出「雙曲軸異相位平衡驅動機構」設計，利用互成180º的雙偏心輪，進行同向等速轉動，可抵消單偏心輪驅動所引發的系統振動問題，所以刀具在任何位置均可獲得平穩運動。經由實驗分析與測試得知，單曲軸驅動的刀具最大驅動頻率至12.5Hz時，系統振幅便已超出1.0µm；而雙曲軸驅動的刀具最大驅動頻率可至40Hz。實驗以雙曲軸異相位驅動機構搭配單晶鑽石刀具加工高密度微凹坑結構陣列進行驗證。於無氧銅上，工件速度480 mm/min，刀具驅動頻率30 Hz下，類高頻往復式進給系統可在6×8 mm2面積內，快速加工出27×40的高密度微凹坑陣列結構，時間僅需320秒，表面粗糙度可達Ra0.023µm；於鎳磷合金上，工件速度480 mm/min，刀具驅動頻率37.5 Hz下，類高頻往復式進給系統可在5×5 mm2面積內，快速加工出23×50的高密度微凹坑陣列結構，時間僅需320秒，表面粗糙度可達Ra0.024µm，顯示「雙曲軸異相位驅動機構」著實能有效抑制系統振動，使往復式進給系統獲得類高頻穩定切削效果。This paper presents the development and application of a dual-crankshaft balance mechanism with out of phase drive for rapidly fabricating high-density optical microstructure mold-core arrays. Four kinds of different drive-mechanisms involving crank-linkage, eccentric-cam, swash-plate-cam, and elliptical cam are devised and analyzed. The crank-linkage is employed as the driving mechanism for the reciprocating feed-tool system since it has an excellent positivity for speedily reciprocating motion, while the rest create the inferior tool following performance leading to a positioning errors occurred under high-frequency motion. In this study, a 3-axis CNC machine tool with quasi-high frequency reciprocating feed-tool system is first designed and constructed. A dual-crankshaft balance mechanism with out of phase drive, in which a pair of eccentric cams reveal a relationship of 180º symmetry with each other and rotation in co-direction and constant velocity, is designed and employed to counterbalance the system vibration. Hence, the tool can be kept in a steady state at any position. Via experimental analysis and trial, in the case of with 'a single crankshaft drive', the system vibrational amplitude is more than 1.0 m once the tool work frequency has arrived at 12.5 Hz. On the contrary, a tool work frequency of 40 Hz can be realized in the case of with 'a dual-crankshaft drive'. Based on the dual-crankshaft driving mechanism and the designed monocrystalline diamond tool, experimental verifications are conducted to rapidly machine high-density optical microstructure mold-core arrays. In the case of 'oxygen free copper', a microdimple array of 27×40 is promptly finished at a work frequency of 30 Hz, workpiece speed of 480 mm/min, cutting area of 6×8 mm2, processing time of 320 seconds and surface roughness of Ra0.023 µm can be achieved. In the case of 'nickel-phosphorous plated alloy', experimental results demonstrate that a high-density microdimple array of 23×50 can be accomplished within 320 seconds at a cutting area of 5×5 mm2, work frequency of 37.5 Hz, and workpiece speed of 480 mm/min. These approaches and conditions generated high-density optical microstructure mold-core arrays with highly consistent micro features confirming that the developed dual-crankshaft balance mechanism is well suited to the high reproducibility of consistently precise machined dense microstructure arrays.