【正文】 disturbance observer helps the servo control loop recovering fast from the disturbed status. In the experiment, the disturbance observer takes a half of time pared to the time which the H∞ controller alone takes for disturbance rejection. Crosscoupled Control In machining applications, one of the most important issues is the elimination of machining error to ensure the quality of the final product. The dimensional accuracy of the final product is one important measure of product quality. Contouring error directly describes the dimensional accuracy. Two major approaches have been adopted to reduce contouring errors. In the first approach, reduction of axis of tracking errors can reduce contour errors indirectly. The applications of feedforward control and disturbance rejection techniques are included in this area. The other approach explicitly estimates contour errors in real time and perform control against them. Koren introduced the crosscoupled controller6 and other work done in crosscoupled control can be found ,8 In Fig. 16, we pare contour errors with and without the crosscoupled control. It clearly shows that crosscoupled control added to H∞ controller reduces the peak of the contour error occurred at around 0 degree, which is caused by friction of the air cylinder in the yaxis. The maximum peak of the contour error diminishes from 50 μm to 20 μm. In our 3axis milling machine, feedforward control does not show any significant improvement in reducing the large peak of the contour error but on the contrary, crosscoupled control does. 5. Conclusions In the paper, a 3axis desktop size milling machine and a CNC system are presented. The milling machine utilizes two voicecoil motors for XY stage and a linear motor for the zaxis and a 160,000 rpm air turbine spindle. Through finite element analysis and impact hammer test, we verified that the 3axis milling machine has highstructural stiffness and high natural frequencies. A CNC system, which was developed for the 3axis milling machine, was also discussed. The CNC system consists of two programs: a user interface program under Microsoft Windows and a DSP program running on a Daytona DSP board. Two programs municate through a dual port RAM and process user inputs and Gcode mands. We presented and pared a few control techniques to improve control performance of the desktop size 3axis milling machine. The H∞ controller intentionally designed with double integrators showed better performance than PID control in terms of tracking error and stiffness for the zaxis, which is equipped with a linear motor and air bearing. But H∞ control and PID control are similar when they are applied for voice coil motor driven x and yaxes. The input shaping control is useful when high acceleration is required, but it should be used with caution for multiple axes because it may destroy the synchronization of coordinated reference trajectories for each axis. The disturbance observer showed its usefulness in counteracting disturbances. The closedloop servo system recovered from sudden impulselike disturbances parably fast when it has a disturbance observer on top of a feedback controller. The disturbance observer may help preserving machining accuracy when large cutting forces apply to the tool stage. Crosscoupled control appears to be very effective to improve not only contour error but also tracking error when a significant friction exists. In our testbed machine, a crosscoupled controller added to H∞ control servoloop showed remarkable reduction in contour errors and it gave better tracking error than a feedforward controller. 三軸工作臺銑床及運用先進現(xiàn)代控制算法 的數(shù)控系統(tǒng)的研發(fā) 1. 簡介 隨著新的領域如 IT(信息技術 )、 BT(生物技術 ) 和 NT(納米技術 ) 的出現(xiàn)及其對工業(yè)發(fā)展的帶動，人們對微型工廠系統(tǒng)的興趣與日俱增。在第三部分中，我們討論了基于 PC的用于三軸 銑床的數(shù)控系統(tǒng)。圖 4和表 1顯 示了測得的固有頻率和三軸銑床相應的頻率響應函數(shù)，可以看出而本以為因空氣軸承可能會有較低的剛度的 Z軸的固有頻率范圍為 250~390Hz。如果 G指令行是關于圓弧運動的，用戶界面程序將會計算圓弧的中心、正方向、起止角。兩部分共享一個雙向 RAM，并通過它進行信息傳遞。它的工作臺體積為 200 300 200 mm3，加工范圍為 20 20 20 mm3。它的尺寸為 200 300 200 mm3，作為我們的測試機床。這個三軸銑床作為一個微型工廠模塊用來生產(chǎn)高精度零件。圖 1顯示了該三軸銑床及其規(guī)格。 DSP部分每秒接受成千上萬的時鐘脈沖，譯成實時指令用于機床的每個軸并執(zhí)行伺服控制循環(huán)。 所有的預程序信息輸入 DPRAM然后遞給了 DSP程序。 XY軸的固有頻率大約為 400710 Hz，且其背部結構大約為 440640 Hz。第四部分討論了一些現(xiàn)代控制方法如 H∞控制、成型控制、擾動觀測器和非門控制的優(yōu)缺點。 微型工廠是一個小型柔性制造系統(tǒng)，它所用的空間和能量相對傳統(tǒng)工廠要小得多，而且它適宜生產(chǎn) IT、 BT 和 NT產(chǎn)業(yè)中所需的微型 /中型尺寸的機械部件。 數(shù)控系統(tǒng)用于操作三軸工作臺銑床，它包括一個 G指令譯碼器，能實時編輯基本的 G指令和 M指令。 圖 1 三軸銑床及其參數(shù) 圖 2 三軸銑床圖 本文運用了有限元模型對設計的三軸銑床進行了有限元分析用以研究其靜態(tài)和動態(tài)性能，如圖 3所示。成一個單一的平滑的運動不間斷地每一個終端。目前，可供執(zhí)行的 G指令和 M指令有 G00（快速移動 ),G01(直線運動 ),G02(順時針圓弧運動）、 G03（逆時針圓弧運動）、 G04（暫停）、 G17（選擇 x y平面 ),G18(選擇 ZX平面 ),G19(選擇 YZ平面）、 M21（輪廓開啟）、 M22（輪廓關閉）、 M30（程序結束和重置）。當把 10N的力加載到 Z方向的加工位置處時， 數(shù)值計算結果表明 ,工作臺處位移改變量大約為 ,而背面的 Z方向偏差 小于 。這兩部分通過一個雙向 RAM（隨機讀取存儲器）傳遞信息，兩部分的工作分配在這里進行詳細的討論。 Reset). When a user click the Open Gcode button, a whole Gcode file is read in and saved in a memory area, and then the Gcodes appear at the bottom left list box. When the Start Gcode button is clicked, the user interface program takes out a line from the memory and checks its syntax and identifies all the meaningful tokens. During preprocessing a Gcode line, the user interface program is supposed to pute, a motion plane, a driving axis, maximum allowable velocity and acceleration, the starting position of the deceleration, directional cosines. If the Gcode line is about circular motion, the center point of the arc, the normal direction of the arc, and start and end angles are also puted by the user interface program. All the preprocessed information is entered in the DPRAM and handed to the DSP program. A circular buffer in the DPRAM has rooms for only 4 lines of Gcodes, so the user interface pr