Real time method to measure head disk spacing variation under vibration conditions

Three readback signal detection methods are presented for real-time head disk spacing variation measurement under vibration conditions. The proposed PW₅₀ parameter estimation method is not restricted by the isolated readback pulse signal requirement, thus can be used for spacing variation measurement in normally operated hard disk drives, especially for low frequency variations. Amplitude detection and thermal signal detection methods, on the other side, are more effective for high frequency spacing variation measurement. Theoretical analysis and experimental results are given to illustrate the effectiveness of the methods