| dc.description.abstract | The objective of this research was to demonstrate the capability of a novel design of a high-speed spindle using combination active magnetic bearings (AMBs) with a nonlinear time-frequency controller. The spindle modeled for this research was a five degree of freedom system with a fixed constant rotational velocity in the z-direction of 192,000 RPMs. The spindle was also considered a flexible shaft with static and dynamic eccentricities. The AMBs used in this research were a homopolar design that included both the radial and thrust components in one AMB. These AMBs also used permanent magnets to levitate the system. One combination AMB, along with another radial AMB, was used to support the system.
The controller algorithm was based on discrete wavelet transformations (DWT) and filtered-x least-mean-square (FXLMS) algorithm. The logic of this controller implements DWT and FXLMS adaptive filters to perform a feedforward control, online identification and to construct parallel adaptive filter banks. The use of DWT allows the controller to simultaneously control time and frequency of the system, and the transformation between the two domains is a lossless transformation.
For test purposes the controller was brought online at the same time the system was turned on. Once the system was under control an impulse force of 250 kN was applied to the system to see if the controller was capable of bringing the system back under control. The controller demonstrated control in both the time and frequency domain. The controlled system had a maximum controlled displacement of 2.85x10^-5 meters with an allowable displacement of 0.55x10^-3 meters. In the frequency domain, instantaneous frequency shown using the Hilbert-Huang Transformation (HHT) was used. The frequency response was a highly nonlinear broadband response that was brought under control, and the frequency bandwidth was reduced to a quasiperiodic and predictable response. The bandwidth of the system was reduced to 1.5% of the original bandwidth.
Overall this high-speed spindle design demonstrated the capability of running and being controlled at a speed of 192,000 RPMs. The next step is to validate the controller and AMBs using a physical system. | |
