串列通訊直接姿態回授工具機研發

Development of a EtherCAT Based CNC Machine Tool with Direct Pose Feedback

林宜宏(Lin, Frederick E HUNG)

指導教授 ： 雷衛台

國立清華大學/工學院/動力機械工程學系/碩士(2015年)

摘要

傳統藉由馬達編碼器間接回授之工具機有螺桿節距誤差、背隙誤差、結構變形、組裝誤差等幾何誤差，及馬達生熱、室溫變化造成之熱誤差，本研究以具並聯機構之六維運動量測裝置直接量測工具機工具端相對工件端的姿態，進行即時直接回授控制，以消除機構鏈中所有元件之幾何誤差及熱誤差。

本研究改良現有Hexapod構型之六維運動量測裝置元件設計，以低熱脹係數之石英板材料設計上平板與下平板，以降低其受室溫變化影響造成之熱誤差。另外針對可伸縮量測桿受室溫變化及讀頭熱源影響產生之熱誤差，進行熱誤差實驗，提出補償方法，使六維運動量測裝置能在一定環境室溫變化條件之下，依然能夠維持其量測精度。

本研究研發之直接姿態回授工具機採用EtherCAT串列通訊界面，以之回授六維運動量測裝置與工具機編碼器讀值並驅動伺服馬達，與傳統運動控制卡相比，EtherCAT串列通訊系統有更大彈性及節省配線的優勢。

經定位實驗驗證，工具機在直接姿態回授控制下，能夠將X、Y、Z方向之定位精度分別由±2.6μm、±17.5μm及±8.3μm，大幅提升至±1.7μm、±1.8μm及±0.7μm；經加工實驗驗證，直接姿態回授控制可將主軸熱誤差造成之X及Z方向加工誤差分別由9.5μm及7.7μm，降低至2.2μm及1.7μm之內。

關鍵字

工具機 ； 直接回授 ； 六維運動量測裝置 ； 串列通訊 ； 直接姿態回授

並列摘要

The traditional machine tools with indirect feedback of motor encoders face the accuracy problems caused by geometric errors, like screw pitch error, backlash, structure deformation, assembly errors and thermal errors caused by the change of room temperature and the heat generated by motors. This research uses the Six-Degree Motion Measurement Device (MMD) to measure the pose of the tool relative to the workpiece and to perform the direct pose feedback control. By this way, all geometric and thermal errors within the mechanism chain of the machine tool can be eliminated.

This research improves the original design of the Hexapod-type MMD. The top and bottom plate of the new MMD are made of Invar and Quartz, in order to reduce thermal errors caused by the change of room temperature. Furthermore, experiments are conducted to investigate thermal errors of the telescopic measuring ball bars of the MMD caused by room temperature changes and the heat sources in the read heads of the linear scales. Methods for the compensation of thermal errors are proposed, so that the MMD can maintain its measurement accuracy within a certain range of room temperature changes.

The developed machine tool with direct pose feedback uses the EtherCAT to read the encoder values of the machine tool and the MMD, and to drive the servo motors. In contrast to the traditional motion card system, the EtherCAT CNC system has the advantages of simple wiring and flexible configuration.

Verified by the positioning experiments, the position accuracies on the x, y and z directions of the machine tool with direct pose feedback control are dramatically improved from ±2.6μm, ±17.5μm and ±8.3μm to ±1.7μm, ±1.8μm and ±0.7μm. Verified by the machining experiments, the machining errors on the x and z directions are reduced from 9.5μm and 7.7μm to 2.2μm and 1.7μm.

並列關鍵字

Machine Tool ； Direct feedback ； MMD ； EtherCAT ； Direct Pose Feedback

參考文獻

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