Patent Application
20050094303
1. Field of the Invention
The present invention relates to a method for disabling a write element of a hard disk drive by monitoring the flying height of a head through the control signal of an automatic gain control circuit.
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.
The magnetic field detected by the head is inversely proportional to the flying height of the head. Likewise, the strength of the magnetic field written onto the disk is also inversely proportional to the fly height. A larger fly height will produce a weaker magnetic field on the disk.
Due to various reasons the fly height of the heads may vary during operation of the drive. Such a variation in fly height may result in poorly written data on the disk. Weakly written data may create errors during a read routine. It would be desirable to monitor the fly height of the heads to prevent write operations when the height is at an undesirable level. It would also be desirable to provide such a monitoring function without significantly changing the components, cost, or operation of the drive.
A hard disk drive with a controller that monitors a control signal for an automatic gain control circuit of the drive. The controller inhibits a write element of a head if the control signal extends beyond a threshold.
Disclosed is a disk drive that monitors a fly height of a head and disables a write element if the fly height extends beyond a threshold. The head is coupled to an amplifier that is controlled by a control signal from an automatic gain control. The control signal varies proportionally with the fly height of the head. An increase in fly height will reduce the amplitude of the signal read by the head. To compensate for the weaker signal the gain control increases the control signal and the gain of the amplifier. The drive further contains a controller that monitors the control signal generated by the automatic gain control. If the control signal extends beyond a threshold value, indicative of an excessive fly height, the controller inhibits the write element so that data cannot be written onto a disk.
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 gain of the amplifier 80 is adjusted by an automatic gain control circuit 86. The automatic gain control circuit 86 receives as input the digital output of the ADC 84 and provides an analog control signal to the amplifier 80.
The control signal is inversely proportional to the amplitude of the read signal. A weak signal will result in a larger control signal. A larger control signal will increase the gain of the automatic gain control circuit and boost the amplitude of the read signal. The signal read by the head is inversely proportional to the head fly height. Consequently, the control signal is proportional to the fly height. A larger control signal is indicative of an increasing fly height.
The controller 64 monitors the control signal generated by the automatic gain control circuit 86. The controller 64 compares the value of the control signal with a threshold value. If the control signal exceeds the threshold, indicative of an undesirable fly height, the controller inhibits the write gate and write element from writing data onto the disk. This is graphically shown by the timing diagram in
In block 102 the gain control signal is varied to change the gain of the amplifier. The controller reads and compares the adjusted control signal with a threshold value in decision block 104. If the control signal exceeds the threshold then the write gate is inhibited in block 106. If the control signal does not exceed the threshold then the controller allows for a write operation in block 108. The threshold may be set at a value that corresponds to a maximum allowable flying height for the head.
By monitoring the gain control signal the controller can monitor variations in fly height and prevent undesirable write operations without adding components and cost to the disk drive.
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.
