Disk drive head touchdown detection with improved discrimination

DETAILED DESCRIPTION The present invention provides a disk drive that detects head touchdown based on a signal value of a signal related to tracking the head at a discrete frequency.
In an embodiment, the discrete frequency is one-half the disk rotation frequency or an integral multiple (harmonic) of the disk rotation frequency.
In another embodiment, the head includes a heater and the head is heated by turning on the heater at a heater frequency, thereby injecting bias into the servo system that increases the signal value at the heater frequency.
The heater frequency is one-half the disk rotation frequency or an integral multiple of the disk rotation frequency.
In addition, the discrete frequency is the heater frequency or an integral multiple of the heater frequency.
In another embodiment, the servo system has a first transfer function for tracking the head during read and write operations and a second transfer function for tracking the head during head touchdown detection.
The second transfer function has smaller vibration rejection than the first transfer function so that the disk drive is less sensitive to vibration during read and write operations than during head touchdown detection.
In another embodiment, the signal is a position error signal (PES) and a Fourier transform measures the peak magnitude of the PES at the discrete frequency or at multiple discrete frequencies.
These and other objects, features and advantages of the invention will be apparent from the following description taken in conjunction with the following drawings.