Patent Application
20080291564
1. Field of the Invention
The present invention relates to a system and method for monitoring contact between a head and a disk of a hard disk drive during an off-track operation.
2. Background Information
Hard disk drives contain a plurality of magnetic heads that are coupled to rotating disks. The heads write and read information by magnetizing and sensing the magnetic fields of the disk surfaces. Each head is attached to a flexure arm to create a subassembly commonly referred to as a head gimbal assembly (“HGA”). The HGA's are suspended from an actuator arm. The actuator arm has a voice coil motor that can move the heads across the surfaces of the disks.
The disks are rotated by a spindle motor of the drive. Rotation of the disks creates an air flow within the disk drive. Each head has an air bearing surface that cooperates with the air flow to create an air bearing between the head and the adjacent disk surface. The air bearing eliminates or minimizes the mechanical wear between the head and the disk. The height of the air bearing is commonly referred to as the flying height of the head.
Due to various reasons the heads may make contact with the disks. This contact may cause damage to the head and/or disk. It would be desirable to monitor the system to detect head/disk contact.
Contact or near contact between the heads and disks can be determined by analyzing the read signal generated by the heads. For example, it is known that head contact or near head contact changes the temperature of the head and varies the amplitude of the read signal. For example, head contact can create frictional heat that increases the head temperature. Near contact can cause heat transfer from the head to the disk that lowers the head temperature.
Head contact can be located by determining when the read signal exceeds a certain threshold. Analyzing the read signal amplitude to determine head contact can be effective when the head is following a disk track. These techniques are less accurate when the head is not following a single track. For example, during a seek routine the head moves across the disk to a new track location. The amplitude of the read signal constantly varies as the head moves from track to track during the seek routine. It would be desirable to provide a system and method that allows for head contact detection during an off-track operation such as seeking, ramp loading or head take-off.
A hard disk drive with a head coupled to a disk. The head has a read element and a heater element. The disk drive includes a circuit that moves the head across the disk in a seek routine and drives the heater element to cause contact between the head and the disk. The circuit determines a center frequency of a read signal provided by the head during the seek routine that corresponds to the head contact.
Disclosed is a disk drive that can detect contact between a head and a disk during an off-track operation such as a seek routine, a ramp load or a head take-off. The disk drive includes a circuit that causes the head to move across the disk in a seek routine. A head heater element is driven to move the head into contact with the disk. A read signal provided by the head is filtered through a band pass filter that has a center frequency. The frequency that produces the maximum signal is selected as the center frequency for the band pass filter. The drive can monitor subsequent head contact during an off-track operation by detecting output from the band pass filter.
Referring to the drawings more particularly by reference numbers,
The disk drive 10 may include a plurality of heads 20 located adjacent to the disks 12. As shown in
Referring to
The hard disk drive 10 may include a printed circuit board assembly 38 that includes a plurality of integrated circuits 40 coupled to a printed circuit board 42. The printed circuit board 40 is coupled to the voice coil 32, heads 20 and spindle motor 14 by wires (not shown).
The read/write channel circuit 62 is connected to a controller 64 through read and write channels 66 and 68, respectively, and read and write gates 70 and 72, respectively. The read gate 70 is enabled when data is to be read from the disks 12. The write gate 72 is to be enabled when writing data to the disks 12. The controller 64 may be a digital signal processor that operates in accordance with a software routine, including a routine(s) to write and read data from the disks 12. The read/write channel circuit 62 and controller 64 may also be connected to a motor control circuit 74 which controls the voice coil motor 36 and spindle motor 14 of the disk drive 10. The controller 64 may be connected to a non-volatile memory device 76. By way of example, the device 76 may be a read only memory (“ROM”). The non-volatile memory 76 may contain the instructions to operate the controller and disk drive. Alternatively, the controller may have embedded firmware to operate the drive.
The band-pass filter frequency can be set and adjusted by control signals from the controller. The controller can set the filter to the frequency which generates the largest amplitude. The frequency range for the read signal in a head contact event is typically between 100 and 400 KHz.
The output of the band-pass filter 82 can be provided to the controller. After the band-pass filter is set the controller can monitor the output of the filter to detect head contact. An output from the filter may be indicative of head contact. The controller may also monitor the output of the amplitude detector 84 to determine head contact. A head contact count may be defined as an output from the band-pass filter that exceeds a threshold.
In step 136, the subsequent output of the filter or amplitude detector can be monitored to detect head contact. This head contact can be monitored by the drive even during an off-track operation such as a seek routine. By way of example, the read signal can be monitored to detect and count the number of times the signal exceeds the threshold. A warning signal can be generated if the count exceeds a certain value within a predetermined time interval.
When a head contact is detected, the time, head number, gray code and operating conditions (eg. temperature) can be recorded and saved onto a dedicated track of the disk. An area of a disk that repeatedly creates head contact can cause the generation of a warning signal. The time, head number, gray code and operating condition data can be provided in a log for evaluation. The region with the highest density of track numbers is the region where head contact is most likely to occur.
A method can be implemented to determine whether head contact is created by an actuator movement profile or a head/disk interface. A seek routine can be initiated and head contact is detected while the heads move across different track ranges. The location of head contact is analyzed to determine whether a high contact region moves as a function of seek range. If the high contact region moves with different seek lengths, then the head contact is most likely caused by the seek profile. If the region does not move then the contact is caused by the head/disk interface. If the region disappears then head contact was most likely caused by the combination of the seek profile and head/disk interface.
While certain exemplary embodiments have been described and shown in the accompanying drawings, it is to be understood that such embodiments are merely illustrative of and not restrictive on the broad invention, and that this invention not be limited to the specific constructions and arrangements shown and described, since various other modifications may occur to those ordinarily skilled in the art.
