CNC剛性攻牙製程之同步運動控制器設計與實現

Abstract

本論文發展以間接向量控制架構，實現感應馬達之速度及位置閉迴路控制。並針對感應馬達的重要轉子時間常數，設計一套自動調整方法，找到最接近的數值使響應達到最好。另外，為了克服馬達在高速時被反電動勢限制的問題，在110 V電源下，本研究使用了弱磁控制，將轉速達成由900 rpm提升到4000 rpm。 在整合感應主軸馬達與伺服馬達為CNC剛性攻牙系統上，因為兩軸馬達的響應差異甚大，導致同動誤差也大，使得加工出來的螺紋並非我們所要的，更嚴重者會有發生崩牙的危險。因此，我們導入了交叉耦合控制器 (cross-coupled control, CCC)，藉著補償器所產生的補償訊號，協調兩軸並消除同動誤差。而當攻牙至孔底時，馬達會遇到最大靜摩擦力的問題，兩軸所受到的摩擦力不同使同動誤差變大，在此，我們加入了非線性摩擦力補償器 (nonlinear friction compensation, NFC)，根據建立好的非線性摩擦力曲線決定補償值。此外，機台在運轉時會受到各種原因的干擾，導致機台抖動的現象，在此我們加入了擾動觀測器 (disturbance observer, DOB)，可以在不需要知道干擾的原因下,即可補償相對應的擾動量。其同動誤差可由132 um 改善至 4.4 um. 最後，本研究發展將原始的交叉耦合控制器架構做重新推導，提出新的位置模式交叉耦合控制器 P_type CCC，使其架構更容易在一般市售的驅動器上實現。並且和原有的速度型交叉耦合控制器 V_type CCC做比較，新的架構對網路時間延遲的容忍度較高，不易發散。因此，新發展的位置型耦合式控制器更適用於網路系統之高速精密CNC攻牙機。

Closed-loop control in both position and velocity loops for induction motors (IM) applying the indirect field oriented control scheme is implemented in this study. For its rotor time constant which is an important parameter but cannot be directly measured, a practical auto-tuning strategy to estimate its value is proposed in this Thesis. Furthermore, limitation of the motor speed due to the back electromagnetic force is overcome by applying the field weakening control to increase its maximum speed from 900 rpm to 4000 rpm as 110 V was provided. In general CNC rigid tapping machines, performance of the spindle axis implemented with an induction motor and the Z axis implemented with a servo motor are not matching well in dynamic responses; thus, significant synchronized motion error exists. Therefore, the tapping tool is broken easily and its machining quality is seriously degraded due to the significant error. In this study, the cross-coupled control (CCC) was applied to coordinate these two axes in tapping machining procedures. When the tapping tool reaches the bottom of the hole, maximum static friction will then deteriorate control performance. A nonlinear friction compensator (NFC) is then proposed to generate a suitable compensated value which is determined according to the nonlinear friction curve. Moreover, as the machine vibration and other undesirable external disturbance and modeling error are significant, a disturbance observer (DOB) is then applied to estimate and compensate for the lumped disturbance. Thus, the taping precision is greatly improved by applying the proposed advanced motion control. Results indicate that the synchronized motion error is thus greatly reduced from 132 um to 4.4 um by applying the proposed motion controller. Finally, the newly proposed positional type CCC (P_type CCC) is developed in this Thesis. This newly developed CCC control structure is easier to be implemented on industrial motor drives with more tolerance in network delays. Consequently, the proposed P_type CCC is more applicable in high-speed-high-precision CNC rigid tapping machines under real network implementation.