Wei Xi

A Robust Servo Demodulation Algorithm to Compensate for Head Velocity Induced Error

The fast growing areal density and continuous increasing demand of IOPS and throughput in hard disk drive present great challenges to servo systems on the performance of the track-follow accuracy and seek time. A high bandwidth servo system is required to meet the demand. However, the performance of the servo systems is ultimately limited by the resolution of the position signal which is demodulated form embedded servo sector. Inside the servo sector, the servo track address combining with the servo bursts provide a global position signal of read/write head. The servo track address, which is commonly encoded as gray code, provides coarse position information. Whereas the servo bursts carries the position error signal (PES) to determine the fine position information. There are multiple servo pattern schemes that have been used in hard disk drive, for example, amplitude based servo pattern, phase pattern, and dual frequency pattern [1]. The servo track address and servo bursts span multiple magnetic cycles. The head position is assumed to be unchanged when it travels through the servo sector. The assumption is valid when head is track-following or seeking at low velocity. However, when the head seeks with high velocity, the assumption induces large PE demodulation error, since the head can move as much as a few tracks when it travels through the servo sector. Thereby, it prevents us to use high servo bandwidth for pushing seeking performance. To tackle this problem, we proposed a robust PE demodulation algorithm which can eliminate the head velocity introduced error. The new demodulation algorithm can be generally applied to any servo pattern schemes. The paper is organized as follows. The servo burst modeling and problem formulations are introduced in section I. The velocity based PE demodulation algorithm is presented in section II. The paper concludes with simulation and experiment results.Copyright