- freely available
Appl. Sci. 2016, 6(2), 52; https://doi.org/10.3390/app6020052
1.1. Active Magnetic Bearing (AMB)
1.2. Milling Dynamics
1.3. Embedded Cylindrical-Array Magnetic Actuator (ECAMA)
2. Control Strategy for ECAMA against Milling Dynamics
2.1. Control Goal
2.2. Fuzzy Model-Reference Adaptive Control (FMRAC)
2.3. Performance of the FMRAC
|Nominal air gap between spindle and yoke|
|Distance between flexible coupling and top yoke|
|Distance between flexible coupling and bottom yoke|
|Distance between flexible coupling and gap self-sensing module|
|Distance between flexible coupling and cutter tip|
|Transverse mass moment of inertia of spindle|
|Polar mass moment of inertia of spindle|
|Stiffness of current|
|Stiffness of displacement|
|Spinning speed of spindle||10k rpm|
3. Experimental Setup and Results
- 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.
- 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)
|Specifications||ECAMA||Modified Radial Design AMB|
|Axial Length (mm)||122||81|
|Coil Turns||1200 (on each individual I-shape silicon steel core)||220 (on each individual pair of electromagnetic poles)|
|Max Induced Magnetic Force (N)||224 |
(1.5 A coil current supplied)
(3 A coil current supplied)
- Materials of workpiece: acrylic, aluminum and copper (three types of materials).
- Spindle speed (ω): 3000 rpm
- Feedrate (f): 300 mm/min.
- Axial cut depth (Da): 2.5 mm.
- Radial cut depth (Dr): 1 mm.
- The ECAMA is a potential solution for milling applications of AMB. It is designed to deal with the issues of magnetic force intensity and overall AMB size at the same time. That is, the regulation force by AMB can be much enhanced under a reasonable size. However, for regular industrial machinery, the size of the ECAMA should be much larger than that in this work to achieve the requirements of industrial applications.
- Since the dynamics of milling processes and magnetic force are both highly nonlinear, estimation errors of the cutting force or magnetic force are definitely met. These force dynamics are investigated by experiments in this work instead of parameters analysis by theoretical methods. The accuracy of experimental models is highly determined by the experiment design. Therefore, the test rig design and the selection of analysis method should be addressed carefully.
- A fuzzy compensator is designed to achieve the adaptive gain control. As previously mentioned, the estimation errors are hard to be avoided. A fine-tuning scheme for control gain is, therefore, embedded to diminish the degree of estimation error. For further applications, such as chatter suppression, the membership functions and the decision rules have to be modified to make the regulation behavior faster and more efficient.
Conflicts of Interest
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