# Adaptive Control of Active Magnetic Bearing against Milling Dynamics
## 3 Experimental Setup and Results  
The prototype specifications of milling module and ECAMA are as follows:  
* Axial length of milling module: 40 cm.
* Maximum radial length of milling module: 11 cm.
* Total weight of milling module: 7.5 kg.
* Power of drive motor: 1 kW.  
Figure 14: Spindle position deviation in the \(Y\)-axis under various control laws.  
Figure 12: Comparison of required coil current for ECAMA in the \(Y\)-axis under various control laws.  
Figure 13: Spindle position deviation in the \(X\)-axis under various control laws.  
* Maximum speed of drive motor: 24k rpm
* Total weight of ECAMA: 2.8 kg
* Axial length of ECAMA: 12.2 cm
* Maximum radial length of ECAMA: 10 cm
* Maximum power consumption of ECAMA: 60 \(W\) (by an individual I-shape electromagnet)  
The comparison between the ECAMA and traditional AMB is listed in Table 3. It is obvious that the ECAMA is able to provide a much stronger regulation force than that of a traditional design of similar size.  
The test rig, including the milling machine (How-Mau CNC Machinery Co., Ltd., New Taipei City, Taiwan), is depicted in Figure 15. Commercial software MATLAB/Simulink (R2011a, The MathWorks, Natick, MA, USA, 2011) and signal processing interface (DS1104, GPACE, Paderborn, Germany, 2007), have been also employed in the intensive experiments. A HSS (high-speed steel) cutter (Chien Wei Machinery&Hardware Co., Ltd., Taichung City, Taiwan) of 8 mm diameter and four cutting blades is equipped and the cutting path is defined in Figure 16. The operation parameters for milling test are set as follows:  
* Materials of workpiece: acrylic, aluminum and copper (three types of materials).
* Spindle speed (\(\omega\)): 3000 rpm
* Feedrate (\(f\)): 300 mm/min.
* Axial cut depth (\(Da\)): 2.5 mm.
* Radial cut depth (\(D_{r}\)): 1 mm.  
The realistic trajectories of spindle position deviation in \(X\)-\(Y\) plane for three kinds of materials are shown in Figures 17-19 respectively. The maximum spindle position deviations for the three different kinds of workpieces are similar, but the spindle dynamics under acrylic cutting is much more complex than those under other materials. Since acrylic is brittle, the variation of cutting force is possibly more drastic than that of metal cutting. Therefore, the compensative force by the ECAMA during acrylic cutting should be tuned rapidly according to the cutting condition. In addition, though the trajectories of spindle position deviation corresponding to aluminum and copper are similar, the spindle position deviation for copper cutting is smoother than that for aluminum cutting, due to different metal properties (_i.e.,_ copper is more ductile). The photographs of the finished workpiece surface are shown in Figures 20-22. The resulting ridges on aluminum are more significant than those on acrylic and copper. The efficacy of the proposed FMRAC for spindle position regulation is verified by realistic milling.  
Figure 16: Cutting path of milling tests.  
Figure 17: Trajectory of spindle position deviation in \(X\)-\(Y\) plane (workpiece: acrylic).  
Figure 19: Trajectory of spindle position deviation in \(X\)-\(Y\) plane (workpiece: copper).  
Figure 20: Micrograph of finished workpiece (acrylic).  
Figure 18: Trajectory of spindle position deviation in \(X\)-\(Y\) plane (workpiece: aluminum).