Due to the presence of various vibrations in the hard disk drive (HDD) such as disk wobbling, air-flow induced suspension/slider vibration, spindle vibration and external vibrations, it is a great challenge for servo engineers to work out feasible servo control mechanisms which can keep track mis-registration (TMR) budget and provide a high positioning accuracy in nanometer level for the Read/Write head to maintain off-track capability. An advanced servo control system is developed to improve servo positioning accuracy and system robustness to achieve ultra-high track density needed in future high density magnetic recording.
Block diagram of a servo control loop.
nominal servo control is designed to guarantee stability and robustness, its design is a compromise between performance and robustness, feedforward control is designed to improve positioning accuracy without degradation of robustness, and intelligent algorithms are used for learning and updating of parameters online.
- Develop a universal experimental platform to demonstrate servo performance. advantages with dedicated servo technology at drive level.
- Servo control scheme and algorithms for dual-actuator disk drives.
- High bandwidth control of dual-stage actuation system.
- Identification and control of critical mechanical resonances above Nyquist frequency.
- Active vibration control with self-sensing technology.
- Control design and implementation with different configurations for millactuator and microactuator-based tri-stage actuation system.
1) Vibration rejection
- Narrowband vibrations at certain frequencies: peak filter, H2 optimal control, KYP Lemma, blending control
- High frequency resonance & vibrations: KYP Lemma, phase-stabilized control, blending control
- Known-frequency vibrations: adaptive feedforward, adaptive resonance compensation
- Unknown vibrations: adaptive estimation and compensation
2) Dual-stage control
- High bandwidth control: resonance compensation
- Shaping sensitivity function: H∞ loop shaping
- TMR optimization: LQG/LTR, H2 method
- Reduce position error: peak filtering
- Saturation control: anti-windup; optimal reset
- Active vibration control with sensors: active damping, feedforward compensation
- Uncertain resonances: robust control, adaptive identification and control
- Nonlinearity (friction, bias): modeling, neural network
- Impulse disturbance: nonlinear filtering
- Limited sampling rate: multi-rate control, identification and control of resonances above Nyquist frequency
- Fast and smooth seeking: current profile/reference trajectory, time optimal control, optimal reset control, nonlinear control
- Drive level servo control system