Study And Design On The Digital Control System Of Hard Disk Drive Active Magnetic Bearings

Active magnetic bearing (AMB), which levitates a rotor steadily by magneticforce is a new type of bearing. With the application of AMB to support to the harddisk drive (HDD) rotor, it can be avoided to appear the contact between bearings andHDD rotors. This application not only improves the speed of the HDD rotor a lot,also creates some new functions, such as high precision, low vibration, and no noises,and even provides the possibility of increasing capacity of HDD in the further.Firstly, the basic work principles of AMB and the mechanism structures of theprincipal axis are introduced in this thesis, and the expressions of electromagnetismforce in AMB system is analyzed. With the proper predigest and hypothesis, thesingle-degree-of-freedom (1-DOF) mathematic model of AMB is deduced, whichoffers an academical theory for designing the control system.Then, with the study of AMB control algorithm, the calibration principles of PIDparameters and the anti-integration saturation PID algorithms are presented, andcarriy on the dynamic simulation, compares and evaluates the performance of them.Then in order to enhance the robustness and improve the control characteristic ofHDD-AMB system, the equivalent-switch and the exponent-tendency sliding modecontrollers (SMC) are designed and simulated particularly.Under the feasible premise of the theoretical analysis and according to the needsof HDD-AMB for digital signal processing (DSP) controller, an experiment setup isdesigned. The hardware circuit is designed base on the DSP TMS320F2812. Themodules of filter, analog-digital conversion, digital-analog conversion, and power areall designed particularly, and the debug methods of the hardware are introduced. Thedetailed flow chart of software is also introduced.Finally, suspending experiment on the experiment setup are done with the PIDalgorithm and anti-integration saturation PID algorithm respectively, the experimentalresults are given and analyzed. The figures of the rotor suspending effect traced out,according to the experimental data, are presented to illustrate the control systemperformance. The results show that the control characteristic, no matter the dynamic performance or the control precision of the anti-integration saturation PID algorithm,is much superior to the PID controller, and the control precision is 3μm.The experimental results indicate that the digital controller based on DSP canwork steadily with better performance for HDD-AMB, and the control precision hasreached the anticipation.