不平滑路徑之五軸循跡控制

Contouring Control for Five-axis Machine Tools with Non-smooth Path

李宗穎(Li,TsungYing)

指導教授 ： 陳世樂

國立中正大學/工學院/機械工程學系/碩士(2012年)

摘要

本論文主要探討考量以五軸工具機循不平滑路徑之設計。由於多了旋轉軸，相較於傳統工具機，五軸工具機要達到高速度與高精度，需要更先進的技術。其主要困難點包括：(1) 五軸工具機之循跡控制器不易設計；(2) 五軸工具機之各軸加減速相互耦合，彼此間關係複雜且不易規劃；因此我們先從雙軸來作不平滑路徑之循跡控制，相較於五軸工具機易分析及規劃，最後再應用於五軸工具機上。
對於循跡控制器設計，本論文採用等效誤差法。此法適用於具非線性動態之多軸運動系統，正適合用於五軸工具機之循跡控制。而等效誤差包括等效輪廓誤差與切線誤差，透過系統所建立的等效誤差模型，再以穩定誤差作為新的控制目標。
本研究重點是從一平滑路徑過渡到另一平滑路徑時，循跡控制器之切換方法，以及對循跡性能之影響。實際上不平滑路徑是由多組平滑路徑串接而成的，如直線接圓弧或不同半徑之圓弧相接等，其中每段路徑相接的點我們稱為轉折點。以NURBS所表示之曲線，若中間包含結點(knots)，在結點位置之平滑性通常有限，故也是屬於此類。我們將以不平滑路徑上的轉折點之切線方向來劃分切換區域來表示各區域之等效輪廓誤差，而切線誤差則跟命令加減速有關，並透過加減速規劃來引導切線方向，以加減速的時間來做切換，來達到我們所規劃不平滑路徑的循跡控制。
最後確保控制器的可行性，首先以兩種五軸工具機分別作系統鑑別及動態推導來得到系統動態方程式，我們再以數值模擬方式來驗證所設計之循跡控制器的切換方法，再連接架設PC-Based控制器透過dSPACE/ControlDesk DS1103即時動態模擬運算，最後與五軸工具機作連結，進行實驗驗證，結果說明我們提出此切換方法是可行的。

關鍵字

五軸工具機 ； 不平滑路徑 ； 等效誤差法

並列摘要

This study investigates the designs of five-axis machine tools in different non-smooth paths. Due to the additional rotation axes, it is more difficult to achieve high speed and high accuracy for 5-axis machine tools, compared to the conventional machine tools. The main difficulties include: (1) the contouring controller is difficult to design; (2) in a 5-axis machine tool, the velocity profile of the machining path possesses complicated relationship with that of each axis, and hence is difficult to design. So we start with the two-axis machine tool to do the contour controlling in non-smooth path because it is easier to analyze. And we apply the results in the five-axis machine tools finally.
For the contouring controller design, the method of equivalent errors is adopted in this thesis. The method can be applied to general multi-axis motion systems with complicated non-linear dynamics, which is perfectly suitable for 5-axis machine tools. The equivalent errors include equivalent contour error and tangent error. The system will build the equivalent error model, and make steady error the new controlling target.
The main contribution is that we study the switching ways of the contour controllers from a smooth path to another smooth path, and the effects of contour controlling performance. In fact, the non-smooth path consists of lots of smooth paths, like straight lines cascaded by an arc or arcs of different radiuses. If a curve indicated by NURBS includes knots, it usually has finite smoothness in the turning points, so it is one kind of path mationed. We will divide the switching regions by the tangent directions to express the equivalent contour errors. While the tangent errors have relations of commands, and we switch it with time to reach the contour controlling in non-smooth paths.
To ensure the practicability of the controller, we get the dynamic equations by system identification of the 5-axis machine tools, and we verify the switching ways of the designed contour controller by numerical simulations. Then we set up the PC-Based controller to simulate immediately by dSPACE/ControlDesk DS1103, and we connect it with the 5-axis machine tools to verify the results. The experiment results show that the switching ways we proposed do work.

並列關鍵字

Five-axis Tool Machine ； Non-smooth PathS ； Equivalent Error

參考文獻

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