Patent Application
20090034109
A disk drive is an information storage device. A disk drive includes one or more disks clamped to a rotating spindle and at least one head for reading information representing data from and/or writing data to the surfaces of each disk. The head is supported by a suspension coupled to an actuator that may be driven by a voice coil motor. Control electronics in the disk drive provide electrical pulses to the voice coil motor to move the head to desired positions on the disks to read and write the data in tracks on the disks and to park the head in a safe area when not in use or when otherwise desired for protection of the disk drive.
Although it is desirable to have zero defects on the surface of a disc, inevitably some level of defects exists. A common solution to managing disc drive operation with media defects is to scan the disc surface for defects, and create a map or defect table containing the defect locations. In this way, the defects can be avoided when reading or writing data to the disc. However, there is always a need to improve defect detection ability to ensure reliable drive operation.
Hereinafter, example embodiments of the present invention will be described with reference to the drawings.
The magnetic disk (discrete track media) 11 is mounted on and rotated by a spindle motor 12. Various digital data are recorded on the magnetic disk 11 in a perpendicular magnetic recording manner. In an example embodiment, the magnetic head incorporated in the head slider 16 is an integrated head including a write head of a single pole structure and a read head using a shielded magneto resistive (MR) read element (such as a GMR film or a TMR film). The suspension 15 is held at one end of the actuator arm 14 to support the head slider 16 to face the recording surface of the magnetic disk 11. The actuator arm 14 is attached to a pivot 13. The voice coil motor (VCM) 17, which drives the actuator, is provided at the other end of the actuator 14. The VCM 17 drives the head suspension assembly to position the magnetic head at an arbitrary radial position of the magnetic disk 11. The circuit board comprises a head IC to generate driving signals for the VCM and control signals for controlling read and write operations performed by the magnetic head.
As the substrate 21, a flat glass substrate may be used. The substrate 21 is not limited to the glass substrate but an aluminum substrate (or any other suitable substrate) may be used. A magnetic material is placed onto the substrate 21 and selectively magnetized to form recording tracks. A magnetic material such as recording track 23, CoCrPt may be used, although the invention is not so limited. Although not shown, a protective film of diamond-like carbon (DLC) may be formed on the surfaces of the media. In one example, lubricant may be applied to the surface of the protective film.
With reference to
As shown in
The preamble section 41 is provided to execute a phase lock loop (PLL) process for synthesizing a clock for a servo signal read relative to deviation caused by rotational deflection of the media, and an AGC process for maintaining appropriate signal amplitude.
The address section 42 may have servo signal recognition codes called servo marks, sector data, cylinder data, and the like formed at the same pitch as that of the preamble section 41 in the circumferential direction using encoding, for example Manchester, or other types of encoding. In particular, since the cylinder data has a pattern exhibiting a data varied for every servo track to provide the minimum difference between adjacent tracks so as to reduce the adverse effect of address reading errors during a seek operation.
The burst section 43 is an off-track detecting region used to detect the amount of off-track with respect to the on-track state for a cylinder address. The burst section 43 includes patterns to locate a read or write head with respect to a desired track center. A pattern in
The principle of detection of a position on the basis of the burst section 43 will not be described in detail. When using the pattern shown, the off-track amount is obtained by calculating the average amplitude value of read signals from the A, B, C, and D bursts. As discussed above, other patterns may be used that do not depend on average amplitude.
As shown in
The head slider 16 may be elastically supported by a gimbal provided on the suspension 15. The suspension 15 is attached to the actuator arm 14, which is rotatably attached to the pivot 13. The VCM 17 generates a torque around the pivot 13 for the actuator arm 14 to move the head in the radial direction of the magnetic disk 11. The HIC is fixed to the actuator arm 14 to amplify input signals to and output signals from the head. The HIC is connected to the PCB 200 via a flexible cable 120. Providing the HIC on the actuator arm 14 may effectively reduce noise in the head signals. However, the HIC may be fixed to the HDA main body.
As described above, the magnetic recording layer is formed on each side of the magnetic disk 11, and the servo zones 19, each shaped like a circular arc, are formed so as to correspond to the locus of the moving head. The specifications of the magnetic disk meet outer and inner diameters and read/write characteristics adapted to a particular drive. The radius of the circular arc formed by the servo zone 19 is given as the distance from the pivot to the magnet head element.
In the illustrated example embodiment, several major electronic components, so-called system LSIs, are mounted on the PCB 200. The system LSIs are a controller 210, a read/write channel IC 220, and a motor driver IC 240. The controller 210 includes a disk controller (HDC) and an MPU, and firmware. In one embodiment, the firmware is configured for defect detection methods as described below. In one embodiment, defect detection is controlled by a system external to the hard disk drive during a stage of the manufacturing and testing of the hard disk drive.
The MPU is a control unit of a driving system and includes ROM, RAM, CPU, and a logic processing unit that implements a head positioning control system according to the present example embodiment. The logic processing unit is an arithmetic processing unit comprised of a hardware circuit to execute high-speed calculations. Firmware for the logic processing circuit is saved to the ROM or elsewhere in the disk drive. The MPU controls the drive in accordance with firmware.
The disk controller (HDC) is an interface unit in the hard disk drive which manages the whole drive by exchanging information with interfaces between the disk drive and a host computer 500 (for example, a personal computer) and with the MPU, read/write channel IC 220, and motor driver IC 240.
The read/write channel IC 220 is a head signal processing unit relating to read/write operations. The read/write channel IC 220 is shown as including a read/write path 212 and a servo demodulator 204. The read/write path 212, which can be used to read and write user data and servo data, may include front end circuitry useful for servo demodulation. The read/write path 212 may also be used for writing servo information in self-servowriting. It should be noted that the disk drive also includes other components, which are not shown because they are not necessary to explain the example embodiments.
The servo demodulator 204 is shown as including a servo phase locked loop (PLL) 226, a servo automatic gain control (AGC) 228, a servo field detector 231 and register space 232. The servo PLL 226, in general, is a control loop that is used to provide frequency and phase control for the one or more timing or clock circuits (not shown in
One or more registers (e.g., in register space 232) can be used to store appropriate servo AGC values (e.g., gain values, filter coefficients, filter accumulation paths, etc.) for when the read/write path 212 is reading servo data, and one or more registers can be used to store appropriate values (e.g., gain values, filter coefficients, filter accumulation paths, etc.) for when the read/write path 212 is reading user data. A control signal can be used to select the appropriate registers according to the current mode of the read/write path 212. The servo AGC value(s) that are stored can be dynamically updated. For example, the stored servo AGC value(s) for use when the read/write path 212 is reading servo data can be updated each time an additional servo zone 19 is read. In this manner, the servo AGC value(s) determined for a most recently read servo zone 19 can be the starting servo AGC value(s) when the next servo zone 19 is read.
The read/write path 212 includes the electronic circuits used in the process of writing and reading information to and from the magnetic disks 11. The MPU can perform servo control algorithms, and thus, may be referred to as a servo controller. Alternatively, a separate microprocessor or digital signal processor (not shown) can perform servo control functions.
As discussed above, the magnetic disk 11 includes regions of magnetic media upon which information is stored. Although a perfect magnetic media surface would be desirable, a number of regions that include defects are inevitable. In embodiments shown, a hard disk drive operates despite the media defects by first detecting defects present on the surface of the magnetic disk 11 and mapping the locations of the defects to a defect table or the like. During data read/write operations, the defect table is checked, and the regions where defects are located are avoided, thus leaving the remaining regions of the magnetic disk 11 fully functional. In one method of defect detection such as a tone scan method, data is written to the magnetic disk and then later read. Differences between the data written and the data read are checked and locations of the differences are mapped.
Defects that are larger than a threshold size are not usable, and therefore the size and location of these defects are mapped to the defect table to be avoided. Some defects are below the threshold size, and while they are detectable as defects, they are not sufficiently large to require avoidance during drive operation. In one embodiment, with such small defects, an error correction system or code (ECC) is employed to enable use of the media region containing the small defect.
However, some regions of the magnetic disk 11 are more sensitive to small defects, and ECC is unable to correct for defects in these regions. For example, a sector pulse region includes information to sync the read/write head to the timing used for data access in a following data region on the magnetic disk. In one example, it is possible for a small defect adjacent to a sync mark to affect drive operation.
One mechanism where a small defect adjacent to a sync mark affects drive operation includes drive motor jitter. The motor that drives the magnetic disk 11 includes a bearing with a small, but measurable, bearing jitter tolerance. At different times during drive operation, the data written on the magnetic disk can be located at slightly different locations within the jitter tolerance. An effect of motor jitter is further illustrated in
The sector pulse region 732 is shown with a window size 734 that encompasses the sector pulse 710. A large defect 720 is shown within the second sector 714 and a small defect 722 is shown within the data region 730 of the first sector 712. As discussed above, in one embodiment, the large defect 720 is larger than a threshold size, and the defect information is cataloged in the defect table. In one embodiment, the threshold defect size is determined by an ECC system present in the drive. In other words, a defect smaller than the threshold size can be compensated for during drive operation using ECC, therefore the defect is not mapped.
In
As discussed above, selected regions are more sensitive to small defects. For example, small defect 724 is illustrated in
If a sensitive piece of data, for example a sync mark is written close to the small defect 724, it is possible for the drive to operate normally if the small defect 724 is avoided. However, if a mechanism such as motor jitter moves the data written on the magnetic disk 11 slightly, then the sync mark can fall within the small defect 724 causing drive errors in reading the adjacent data region 730.
In one embodiment, small defects such as defect 724 are detected and mapped due to their potential contribution to drive error. In one example the first sector 712 associated with the defect 724 is mapped and avoided. In one embodiment, a first defect detection standard is applied to a first region such as the data region 730. In the first region, a threshold for defect detection includes an ECC threshold above which ECC cannot correct. If ECC can correct the read error, generally there is no defect. In one embodiment, once a defect is found, the entire sector is mapped out as a unit to the defect table and the entire sector is avoided in the future.
In one embodiment, a second defect detection standard is applied to a second region such as the sector pulse region 732. Under the second defect detection standard, the small defect 724 is detected and mapped. In one embodiment, the sector pulse region 732 is centered around the sector pulse 710, although the invention is not so limited. In one example the sector pulse region 732 is centered around a sync mark adjacent to the sector pulse 710. Centering the sector pulse region 732 around the sector pulse 710 is useful because it accounts for an amount of drive motor tolerance, as will be discussed in more detail below. In one embodiment, the window size 734 is equal to or larger than a drive motor jitter tolerance.
Using methods as described above, defects of different sizes that can affect drive operation are all detected and mapped. More magnetic disk area is utilized by employing ECC in regions where it is effective.
Although a data region and a sector pulse region are discussed as examples, the invention is not so limited. Other types of regions on a magnetic disk benefiting from different standards of defect detection are also within the scope of the present disclosure.
In one embodiment, a falling edge 812 of the servo gate pulse 810 is used to trigger assertion of the read/write gate. As shown in
In one embodiment, the read/write gate assertion 820 is triggered using the servo gate pulse 810, and further as described above, more than one standard of defect detection is employed over the magnetic disk 11 to detect defects of varying sizes in different regions. In one embodiment methods of triggering of the read/write gate assertion 820 using the servo gate pulse 810 are only used during defect detection. Selected methods use sector pulses to trigger read/write gates during normal drive operation.
Using methods as described above, in one embodiment, the defect table 916 includes one or more defects larger that a first threshold size such as an ECC threshold. As discussed above, large defects are not correctable during drive operation using ECC therefore, their locations and sizes are mapped to the defect table 916. In one embodiment, small defects below the ECC threshold that are within the user data region 912 are not mapped because ECC can compensate for them.
In one embodiment, the defect table 916 includes one or more defects of a second size smaller than the ECC threshold size and larger than a second threshold size. In one embodiment, a second threshold size includes a detectability limit. In one embodiment, the second threshold size includes a more stringent size that is acceptable in a sector pulse region. As discussed above, smaller defects below the ECC threshold size are mapped when they fall into more sensitive regions that are searched with a higher defect detection standard. Because two defect detection standards are used, both defects above the ECC threshold and selected defects below the ECC threshold will be recorded in the defect table 916.
Although the defect table 916 is shown located on the magnetic disk 910, the invention is not so limited. Other locations such as RAM/ROM 920 located external to the magnetic disk 910 but within the drive 900 can also hold the defect map.
A block diagram of a computer system that executes selected methods as described is shown in
Computer-readable instructions stored on a computer-readable medium are executable by the processing unit 602 of the computer 610. A hard drive, CD-ROM, and RAM are some examples of articles including a computer-readable medium. The computer program may also be termed firmware associated with the disk drive. In some embodiments, a copy of the computer program 625 can also be stored on the disk 11 of the disk drive.
The foregoing description of the specific embodiments reveals the general nature of the invention sufficiently that others can, by applying current knowledge, readily modify and/or adapt it for various applications without departing from the generic concept, and therefore such adaptations and modifications are intended to be comprehended within the meaning and range of equivalents of the disclosed embodiments.
The Abstract is provided to comply with 37 C.F.R. §1.72(b) to allow the reader to quickly ascertain the nature and gist of the technical disclosure. The Abstract is submitted with the understanding that it will not be used to interpret or limit the scope or meaning of the claims.
It is to be understood that the phraseology or terminology employed herein is for the purpose of description and not of limitation. Accordingly, the invention is intended to embrace all such alternatives, modifications, equivalents and variations as fall within the spirit and broad scope of the appended claims.
