以EtherCAT實現CNC伺服控制低頻補償器

Abstract

在CNC工具機的控制器上，除了原有的P控制以外，本研究整合了分別屬於高頻域及低頻域的控制補償器，提昇CNC的運動精密度，除了原有屬於改善高頻域控制範圍的控制器，包含 (1)提昇穩定性的PD(比例-微分)控制器，及 (2)改善追跡誤差的位置迴路前饋控制器外，本研究並提出在CNC工具機控制器上可具體實現的低頻補償器，包含(3) 利用CNC的G指令達成pseudo chirp sine鑑別方式，設計數位式擾動觀測器DDOB，以及 (4) 提出具判斷功能之一階低頻F filter 摩擦力補償器。本研究在東台TC-2000的CNC機台上，透過工研院所開發的以INtime即時環境之EtherCAT網路化CNC控制介面，實現整合式精密運動控制器，經由實驗證實，取樣時間可快速至0.25ms。本研究證明整合了(1)至(4)之伺服控制架構後，可以確實提升整體運動精密度，其真圓度和原始P控制比較，由23.1 改善至8.6 ，改善率達62.77%。本研究並以循圓測試儀量測機械端精密度，由27.4 改善至11.1 ，最後透過調整驅動器剛性及工研院控制器step背隙補償，改善背隙誤差帶來的失運動(lost motion)現象，機械端真圓度可再改善至6.6 ，前述實驗結果說明本研究成果可凸顯EtherCAT於實現彈性的CNC控制架構與運動精密補償器之應用。

In CNC controllers, in addition to the basic P controller, other controllers mainly in the high-frequency range mainly are as (1) proportional-derivative (PD) control to stabilize its performance and (2) the feedforward control greatly improving the tracking performance in the position loop. Furthermore, two more advanced compensators are proposed in this paper as: (3) the digital disturbance observer (DDOB) based on a linear model obtained from the presently proposed pseudo chirp sine CNC G code and (4) the 1st-order low-frequency F filter for friction compensation. With the real-time INtime operating system based on EtherCAT and the ITRI CNC control interface, experimental results indicate that the sampling time can be operated at 0.25ms without data dropout. All above four controllers/compensators can be flexibly integrated and efficiently implemented on the CNC controller through the EtherCAT interface. Experimental results on the Tongtai TC-2000 CNC Lathe indicate that the roundness measured from the encoder is improved form 23.1 to 8.6 . Roundness measured from the double ball bar is also significantly reduced from 27.4 to 11.1 , and is reduced to 6.6 by tuning its servo control gain and step type backlash compensation to further decrease the lost motion effect on the CNC machine tool.