工具機滑塊預壓監測與主軸適應性切削轉速估測技術之研發

本論文以操作模態分析法(Operational modal analysis, OMA)為基礎，發展兩項工具機關鍵技術；第一項是線性滑軌預壓力自動偵測技術；第二項是主軸適應性切削轉速估測技術。進給系統中若其滑塊預壓消失，則進給系統定位精度與剛性將隨之降低，本研究提出一自動監控線性滑軌之滑塊預壓力是否改變的方法。此法無須拆卸工作台，只須於進給系統之工作台上安裝數顆加速規，並以伺服馬達激振工作台，透過OMA自動鑑別工作台自然頻率與相對應之模態，並經由模態可信度(Modal assurance criteria, MAC)矩陣追蹤偏擺模態(Yawing mode)頻率之變化，透過該頻率變化反估線性滑軌之滑塊預壓力是否消失以達滑塊預壓自動偵測之目的。工件銑削過程中，在某些轉速與切深會引發切削不穩定(例如顫振)，其會使工件表面精度不良與刀具壽命縮減，本研究第二項發展主軸適應性切削轉速估測技術以避免此問題的產生。本研究首先由工具機主軸-刀具系統靜止狀態下之顫振穩定界線，預估切削狀態下之最佳轉速，以此轉速進行切削，但切削時以OMA不斷鑑別切削過程中主軸-刀具系統之動態特徵(自然頻率與阻尼比)，進而以此更新顫振穩定界線與調變其最佳轉速，由於切削過程中進行鑑別，有包含切削時之工件阻抗，其預估之主軸轉速更為準確，亦即透過此技術不斷維持最佳之主軸切削轉速以保持切削穩定性，此技術經實驗驗證不僅能高效率地移除材料且同時獲得良好的切削表面工件品質，其主軸振動與噪音亦能有效降低。

關鍵字

操作模態分析；線性滑軌；模態可信度；顫振穩定界線

並列摘要

Two important techniques of machine tool based on operational modal analysis (OMA) are proposed and realized. The first is an automatic monitoring technique for preload degradation of linear guide ways, and the second is an adaptive spindle cut-ting speed technique. The linear guideway type (LGT) recirculating linear ball bearing abrasion caused by long time operation, eventually leads to preload loss, which however often occurs much earlier than the guide ways fatigue. Therefore, detecting the preload loss be-comes an important issue especially in a machine tool designed for high speed and high accuracy. In this study, a novel methodology of monitoring degradation of linear guideway type recirculating linear ball bearing of an X-Y table is proposed. By simply attaching accelerometers on the worktable of the feed drive system and then exciting the worktable with a pulse from servo motor, the worktable natural frequencies and the corresponding mode shapes are identified based on the method of OMA. Thereaf-ter, tracking the change of yawing mode frequency of worktable using modal assur-ance criteria (MAC), the linear bearing preload degradation can be monitored auto-matically without exciting the worktable manually. The material removal rate (MRR) reflects the machining efficiency, so how to increase the MRR without inducing instability, i.e. chatter, is always an important is-sue in machining. In this study, the natural frequencies, mode shapes and correspond-ing damping ratio of spindle tool system are identified firstly by using OMA. With these information, the stability lobe diagram (SLD) which depicts the machining sta-bility in terms of spindle speed and stiffness ratio can then be created. With this SLD, the optimal spindle speed can be determined. During the machining, an adaptive op-timal spindle speed machining (AOSS) technique is proposed. That is, during the ma-chining process the dynamic characteristic of the spindle tool system and then the SLD are continuously identified and updated using OMA and then the spindle speed changes accordingly. Results show that using AOSS not only increases the MRR but also maintains a good workpiece surface roughness. Moreover, the associated spindle vibration and noise are also effectively reduced.

並列關鍵字

Operational modal analysis ； Linear guideway type ； Modal assurance criteria ； Stability lobe diagram

參考文獻

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工具機滑塊預壓監測與主軸適應性切削轉速估測技術之研發

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