Magnetic disk device

Abstract

To provide a magnetic disk device and a prediction method for predicting a head position based on a head position demodulated by a short servo method.SOLUTION: A magnetic disk device according to this embodiment includes: a head position demodulation unit that demodulates a head position by switching between a normal servo demodulation unit that processes servo information written to a servo sector of the disk and a servo demodulation unit that is different from the normal servo demodulation unit and processes the servo information by a short servo method; a head position prediction unit that predicts the head position; and a write prohibition unit that determines to prohibit writing operations of data to the disk based on the predicted head position. The head position prediction unit predicts the head position by using the latest head position demodulated by the head position demodulation unit and the head position demodulated by the normal servo demodulation unit in the past.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] An embodiment of the present invention relates to a magnetic disk drive having a write inhibit process for a head. [Background technology]

[0002] In magnetic disk devices such as hard disk drives (HDDs), tracking control is performed to align the head position with a target track on a rotating disk. In tracking control, the position of the head is detected using servo information written on the disk. A method of predicting the head position is used to prevent the effects of a time lag between the process of detecting the head position and the process of writing data to the disk by the head. On the other hand, head position demodulation using the short servo method, a technology for reducing the occupancy rate of servo information on the disk, may be used to detect the head position. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] U.S. Pat. No. 1,087,2631 [Patent Document 2] U.S. Pat. No. 9,025,269 [Patent Document 3] U.S. Patent No. 7,400,467 Summary of the Invention [Problem to be solved by the invention]

[0004] However, head position demodulation using the short servo method tends to be more affected by head position detection errors than head position demodulation using normal servo information that does not use the short servo method.

[0005] An object of the present invention is to provide a magnetic disk drive and a prediction method for predicting a head position based on a head position demodulated by a short servo system. [Means for solving the problem]

[0006] The magnetic disk device of this embodiment includes a head position demodulation unit that demodulates the head position by switching between a normal servo demodulation unit that processes servo information written to servo sectors of the disk and a short servo demodulation unit that processes servo information using a short servo method different from the normal servo demodulation unit, a head position prediction unit that predicts the head position, and a write prohibition determination unit that decides to prohibit the operation of writing data to the disk based on the predicted head position, and the head position prediction unit predicts the position using the latest head position demodulated by the head position demodulation unit and a head position previously demodulated by the normal servo demodulation unit. [Brief description of the drawings]

[0007] [Figure 1] FIG. 1 is a configuration diagram of a magnetic disk device according to an embodiment. [Diagram 2] FIG. 2 is a diagram showing an outline of the format of servo information in the magnetic disk device according to the embodiment. [Diagram 3] FIG. 3 is a schematic diagram showing the positional relationship between a head of a magnetic disk device and a desired track to be written. [Figure 4] FIG. 4 is a schematic diagram showing a head position prediction calculation method using simple linear interpolation. [Diagram 5] FIG. 5 shows an example of frequency characteristics of position prediction in a magnetic disk device using position prediction by simple linear interpolation. [Figure 6] FIG. 6 is a flowchart showing a processing operation of the servo control unit of the magnetic disk device according to the first embodiment. [Figure 7] FIG. 7 is a schematic diagram showing an example of a head position prediction calculation method associated with the first position prediction unit of the magnetic disk device according to the first embodiment. [Figure 8] FIG. 8 is an example of frequency characteristics of the first position predictor of the magnetic disk device according to the first embodiment. [Figure 9] FIG. 9 is a schematic diagram showing an example of a head position prediction calculation method associated with the second position prediction unit of the magnetic disk device according to the first embodiment. [Figure 10] FIG. 10 is an example of frequency characteristics of the second position predictor of the magnetic disk device according to the first embodiment. [Figure 11] FIG. 11 is a schematic diagram showing an example of a head position prediction calculation method for the magnetic disk drive according to the second embodiment. [Figure 12] FIG. 12 is an example of frequency characteristics of the position prediction unit in the magnetic disk device according to the second embodiment. [Figure 13] FIG. 13 is a diagram showing time history waveforms of demodulated positions and predicted positions in the magnetic disk device according to the second embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0008] Hereinafter, an embodiment will be described with reference to the drawings. Note that the drawings are merely examples and do not limit the scope of the invention.

[0009] (Embodiment) Here, the basic configuration and basic principles of the embodiment will be mainly described.

[0010] FIG. 1 is a configuration diagram of a magnetic disk device according to an embodiment.

[0011] The magnetic disk device 1 is a storage device equipped with a magnetic disk 11 (hereinafter sometimes simply referred to as a disk) from which data is read and written, and is equipped with a computer such as a microprocessor. The magnetic disk device 1 outputs data to the host system 2 based on commands received from the connected host system 2, and writes data input from the host system 2 to the disk 11.

[0012] The host system 2 is, for example, a personal computer, and outputs to the magnetic disk device 1 a read command which is an instruction to read data from the disk 11, and a write command which is an instruction to write data together with data to be written to the disk.

[0013] The HDA 10 is called a head disk assembly, and includes a disk 11, a spindle motor (hereinafter sometimes referred to as SPM) 12, a voice coil motor (hereinafter sometimes referred to as VCM) 13, an arm 15 carrying a head 19, and the like, which are stored in a housing. In the HDA 10 of this embodiment, an example is shown in which one disk 11 and one head 19 are installed, but one or more of each may be provided.

[0014] Disk 11 is a rotating disk-shaped magnetic rotating disk storage medium, and has a data area where data can be written (sometimes called writing), which is assigned to a user data area available to users and a system area where information required for system management is written. Hereinafter, the direction perpendicular to the radial direction of disk 11 will be referred to as the circumferential direction. Disk 11 is attached to spindle motor 12, and rotates when driven by spindle motor 12.

[0015] A plurality of tracks are set on the disk 11. In Fig. 1, three tracks TR1, TR2, and TR3 (referred to as tracks TR when no particular distinction is made) are shown as examples, but a plurality of tracks are set concentrically around the spindle motor 12 in the data area. When reading and writing data from the disk 11, the head 19 is moved by seek control, tracking control, etc. to the track TR where the data to be read or written (sometimes referred to as target data) is located, and the head 19 reads and writes the data. The track TR where the target data is located may also be referred to as the target track.

[0016] In addition, servo information is written on the disk 11 and is used for detecting the position of the head 19, etc. The servo information is provided at predetermined positions (called servo areas or servo sectors) in the circumferential direction of the disk 11. The servo information will be described later. In the example of FIG. 1, three servo areas SVA1, SVA2, and SVA3 (called servo areas SVA when no particular distinction is made) are shown as examples of servo areas, but generally, servo areas SVA are provided at equal intervals over the entire circumferential direction of the disk 11, and servo information is written in the servo area SVA of each track TR. The magnetic disk device 1 can detect the current position of the head 19 by the servo information read by the head 19.

[0017] The spindle motor 12 is a support for the disk 11, and is installed in a housing of the magnetic disk, etc. The disk 11 rotates as the spindle motor 12 rotates.

[0018] The VCM 13 is a voice coil motor type actuator, and is used to move the arm 15 etc. The VCM 13 controls the operation of the arm 15 etc. based on an input current or voltage.

[0019] The pivot 14 is a bearing that supports the arm 15 and the like and allows it to perform rotational movements.

[0020] The arm 15 supports a suspension 16, a slider 18, and a head 19, and transmits power from the VCM 13 to the head 19 to move the head 19 to a target track TR.

[0021] The suspension 16 is a portion that supports a slider 18 and a head 19 , and includes a microactuator 17 .

[0022] The microactuator 17 (sometimes referred to as MA 17) performs highly accurate position adjustment, such as tracking control of the head 19, based on the input current or voltage. Although the microactuator 17 has a general function and detailed description is omitted, it performs fine adjustment of the position of the head 19 during settling after seek control and tracking control for the target track after seek control. Settling refers to the time it takes for the positioning error for the target track, including the effect of vibration of the head 19 due to seek control, to settle below a certain threshold value, for example, after the movement of the head 19 due to seek control. After the vibration of the head 19 has settled to a sufficiently small level due to settling, data read / write control and tracking control are executed.

[0023] The slider 18 comprises a suspension 16 which supports the head 19 and floats it above the disk 11, and an arm which supports the slider 18 and the head 19. The slider 18 transmits power from the VCM 13 to the head 19 and moves the head 19 to the target track TR.

[0024] The suspension 16 is a portion that supports the slider 18 and the head 19, and controls the operation of the microactuator 17 connected thereto.

[0025] Head 19 is a component that writes data to disk 11 and reads data recorded on the data tracks of disk 11. When making a particular distinction, a head that writes data to disk 11 is called a write head 19W, and a head that reads data recorded on the data tracks of disk 11 is called a read head 19R.

[0026] The driver IC 20 outputs a current or voltage for driving and controlling the SPM 12, the VCM 13, the microactuator 17, etc., according to the control from the HDC 50, the servo control unit 62, etc.

[0027] The head amplifier IC 30 includes a read amplifier and a write driver. The read amplifier amplifies a read signal read from the disk 11 and outputs it to the R / W channel 40. The write driver outputs a write current to the head 19 according to the signal output from the R / W channel 40.

[0028] The R / W channel 40 receives a read data signal from the head amplifier IC 30 and extracts read data in response to instructions from the HDC 50, main controller 60, etc., or generates a write data signal based on write data instructed to be written and outputs it to the head amplifier IC 30. The R / W channel 40 also has a function of measuring the signal quality of the read data received from the head amplifier IC 30. The R / W channel 40 demodulates the servo information signal received from the head amplifier IC 30 and extracts position information of the head 19. The R / W channel 40 includes a normal servo demodulation unit 401 that performs normal servo demodulation (referred to as normal servo demodulation) to extract head position information (referred to as normal servo position information), and a short servo demodulation unit 402 that performs short servo demodulation to extract head position information (referred to as short servo position information).

[0029] The HDC 50 is an interface between the magnetic disk device 1 and the host system 2, and is a hard disk controller that controls each part of the magnetic disk device 1. The HDC 50 may be configured by a computer such as a CPU, or an IC chip equipped with another computer. The HDC 50 receives commands such as an instruction to write data to the disk 11 or an instruction to read data from the disk 11 from the host system 2. Based on the received commands, the HDC 50 controls each part of the magnetic disk device 1 and transfers data between the host system 2 and the R / W channel 40. The HDC 50 may control reading and writing of data to the volatile memory 70, the buffer memory 90, the non-volatile memory 80, etc.

[0030] The main controller 60 is a main controller that controls each part of the magnetic disk device 1, and may be configured, for example, by a computer such as a microprocessor, or an IC chip equipped with other computer functions. The various processes of the main controller 60 may be executed by a software (including firmware, etc.) program, or may be provided as hardware or a combination of software and hardware.

[0031] The read / write control unit 61 selects the destination to save the write data (e.g., information such as a data sector or track of the disk 11) based on a command received from the host system 2, and controls the operation of writing data to the disk 11. The read / write control unit 61 notifies the servo control unit 62, etc. of the destination to save the read data (e.g., information such as a data sector or track of the disk 11) based on a command received from the host system 2, and operates the head 19 to control the operation of reading data from the disk 11.

[0032] The read / write control unit 61 controls reading and writing of the head 19 based on the head predicted position and the like input from the servo control unit 62. The read / write control unit 61 includes a write prohibition determination unit 611 that determines whether writing of user data to the disk 11 by the head 19 is possible, and a control execution unit 612 that controls reading / writing of the head 19 based on the determination results of the write prohibition determination unit 611 and the like.

[0033] The servo control unit 62 controls the data head 19 based on, for example, commands received from the host system 2. For example, the servo control unit 62 executes seek control and tracking control for controlling the VCM 13 via the driver IC 20 to move the head 19 to a target position (target track). The servo control unit 62 also controls the microactuator 17 via the driver IC 20 to execute tracking control of the head 19.

[0034] More specifically, the servo control unit 62 determines an input current value or an input voltage value as a control value for seek control and tracking control of the head 19 based on the target position of the head 19 determined based on commands received from the host system 2 and the current position of the head 19 received from the R / W channel 40, and outputs the determined input current value or input voltage value to the VCM 13 and the microactuator 17.

[0035] The servo control unit 62 includes a first position prediction unit 621 and a second position prediction unit 622 that predict the position of the head 19 from normal servo position information and short servo position information input from the R / W channel 40. The operations of the first position prediction unit 621 and the second position prediction unit 622 will be described later.

[0036] The volatile memory 70 is a semiconductor memory in which stored data is lost when the power supply is cut off. The volatile memory 70 stores data necessary for processing in the magnetic disk device 1. The volatile memory 70 is, for example, a dynamic random access memory (DRAM) or a synchronous dynamic random access memory (SDRAM).

[0037] The non-volatile memory 80 is a semiconductor memory that records stored data even if the power supply is cut off. The non-volatile memory 80 is, for example, a NOR type or NAND type flash ROM (Flash Read Only Memory: FROM).

[0038] The buffer memory 90 is a semiconductor memory that temporarily records data transmitted and received between the magnetic disk device 1 and the host system 2. The buffer memory 90 may be integrated with the volatile memory 70. The buffer memory 90 is, for example, a DRAM, a static random access memory (SRAM), a SDRAM, a ferroelectric random access memory (FeRAM), or a magnetoresistive random access memory (MRAM).

[0039] The buffer memory 90 represents a working memory of the main controller 60. The buffer memory 90 may be included in the volatile memory 70 or the non-volatile memory 80.

[0040] FIG. 2 is a diagram showing an outline of the format of servo information in the magnetic disk device according to the embodiment.

[0041] 2(a) is a diagram showing an outline of the data format in one track TR on the disk 11. On the track TR, servo areas (SVA1, SVA2, SVA3) are periodically allocated between user data areas (UDA1, UDA2, UDA3). Servo information SVI is written in advance in the servo areas SVA.

[0042] FIG. 2(b) is a diagram showing the format of the servo information SVI in more detail, in which servo data SVD1 including a preamble, servo data SVD2 including a servo mark, servo data SVD3 including a burst, and servo data SVD4 including an address are written.

[0043] 2(c) is a diagram showing the demodulation timing of servo information (referred to as normal servo information) by the normal servo demodulator 401. When the normal servo demodulator 401 detects the preamble SVD1, it starts demodulating the servo information, demodulates the position of the head 19 from data including SVD2, SVD3, and SVD4, and outputs the position information of the head 19 to, for example, the servo control unit 62. When the normal servo demodulator 401 demodulates SVD4 including the address, it detects that the servo information has ended and ends the demodulation process. When the normal servo demodulator 401 detects the preamble SVD1 of the next servo sector, it similarly starts demodulation process, demodulates the position information of the head 19, and thereafter performs the same process for each servo sector.

[0044] FIG. 2(d) is a diagram showing the demodulation timing of servo information (referred to as short servo information) by the short servo demodulator 402. The short servo demodulator 402 processes short servo information (SVD3, SVD4 in FIG. 2(b)) which is a part of the servo information processed by the normal servo demodulator 401. The short servo demodulator 402 does not detect servo marks for the servo information of the short servo sector, but opens a gate at a certain timing based on the servo mark detected in the immediately previous normal servo sector, captures a servo burst signal (corresponding to SVD3 in FIG. 2(b)), and demodulates the head position. Therefore, when the short servo method is adopted, the demodulation position of the short servo sector does not detect servo marks, so that the position demodulation error of the head 19 by the short servo demodulator 402 tends to increase due to the influence of the jitter of the burst SVD3.

[0045] Fig. 2(e) shows an example of the format of the TR of a track when normal servo sectors NSV and short servo sectors SSV are alternately allocated. In this embodiment, the servo sectors are alternately processed as normal servo sectors and short servo sectors as shown in Fig. 2(e). For example, even sectors are normal sectors and odd sectors are short servo sectors.

[0046] The servo information signal read from head 19 is input to R / W channel 40 via head amplifier IC 30. In R / W channel 40, normal servo demodulator 401 and short servo demodulator 402 extract position information alternately for each normal servo sector and short servo sector from the servo information signal input from head amplifier IC 30, and input it to servo control unit 62.

[0047] When head 19 is performing a write operation on disk 11, a write fault process may be executed using the position information of head 19 obtained from the servo information to stop the write operation. The write fault process is outlined below.

[0048] 3 is a schematic diagram showing the positional relationship between a head of a magnetic disk device and a desired track to be written to. The horizontal axis indicates time, and a trajectory HT shows an example of the time transition of the head HD position. On the disk, tracks adjacent to TR2 are TR1 and TR3, and servo information is written between the data areas in the order SVI, SVI2, and SVI3. p(k) indicates the position of the head HD at a discrete point in time k.

[0049] As shown by the locus HT, the head HD shifts its position relative to the desired track TR2 due to vibrations generated in the magnetic disk drive. When the head HD is performing a write operation on the track TR2, if the positional relationship between the head HD and the center of the desired track TR (center in the figure) shifts significantly, data on the adjacent tracks TR1 or TR3 may be destroyed. Therefore, in such a case, write inhibition processing is processing that inhibits the head HD from writing data to the track TR2. TH_HD1 and TH_HD2 are examples of thresholds for the position of the head 19. For example, when the desired track is TR2, if the demodulated position information of the head 19 exceeds TH_HD1 or TH_HD2, write inhibition processing is performed.

[0050] There are several conditions for write inhibition processing, one of which is write inhibition processing (Write Fault) based on predicted position. Since there may be a time lag between the process of acquiring head position information based on servo information and the process of writing data to the disk by the head, for example, at time point k, the position p(k+1) at time point k+1 is predicted, and in the write inhibition processing, the execution of data write processing from time point k+1 onwards is judged based on the predicted value of p(k+1). The calculation of the predicted position can be done by simple linear interpolation or linear regression coefficient optimization. For example, the simplest implementation of the predicted position is by linear interpolation, which is outlined below.

[0051] FIG. 4 is a schematic diagram showing a head position prediction calculation method using simple linear interpolation.

[0052] If p(k-2), p(k-1), and p(k) are obtained as the positions of the head HD from the servo information, the predicted position p{hat}(k+1) of the head HD at time point k+1 is expressed as in Equation 1. In the text, p{hat} indicates that there is a hat mark symbol (also called a circumflex accent or caret) above the p.

[0053]

number

[0054] The purpose of inhibiting writes based on the predicted position is to reduce the possibility of overrunning the write-inhibited slice and encroaching on data in adjacent tracks (TR1, TR3).

[0055] Since the head position error signal can only be obtained at discrete times, and there is a time delay between the head position demodulation process and the write inhibit process, even if the write inhibit process is performed at a certain threshold, there is a possibility that data may actually be written beyond that threshold. In order to prevent the data on adjacent tracks from being erased, it is necessary to keep this amount of overhang below a certain level, and for this reason, write inhibit decisions are made based not only on the current position (demodulated head position information) but also on the predicted position.

[0056] Here, (p(k)-p(k-1)) represents the difference from the previous sample, i.e., the velocity component, but the velocity estimation based on the position difference has a large error. Therefore, in the write prohibition judgment based on the predicted position error using Equation 1, a threshold (th2) larger than the write prohibition judgment threshold (th1) based on the current position is used. The judgment condition at this time is expressed by the following inequality.

[0057]

number

[0058]

number

[0059]

number

[0060] FIG. 5 is an example of the frequency characteristic of position prediction in a magnetic disk device using position prediction by simple linear interpolation, which is obtained from Equation 4.

[0061] It can be seen that the gain is particularly high in the high frequency range. Therefore, if the predicted position is calculated using Equation 1, the error in (p(k)-p(k-1)), which corresponds to the velocity component, will be large, and there is a possibility that writing will be prohibited more than necessary, resulting in a decrease in performance.

[0062] (First embodiment) In this embodiment, an example of a magnetic disk drive in which the calculation method of the head predicted position is switched between short servo sectors and normal servo sectors is shown. For example, even sectors are normal servo sectors and odd sectors are short servo sectors, and the calculation method of the head predicted position is different between even sectors and odd sectors.

[0063] The operation of this embodiment will now be described in detail.

[0064] FIG. 6 is a flowchart showing a processing operation of the servo control unit of the magnetic disk device according to the first embodiment.

[0065] When the servo sector being processed is a normal servo sector, the R / W channel 40 inputs the position information demodulated by the normal servo demodulation unit 401 to the first position prediction unit, and when the servo sector being processed is a short servo sector, the R / W channel 40 inputs the position information demodulated by the short servo demodulation unit 402 to the second position prediction unit (step S101).

[0066] FIG. 7 is a schematic diagram showing an example of a head position prediction calculation method associated with the first position prediction unit of the magnetic disk device according to the first embodiment.

[0067] If the sector processed at time k is a normal servo sector (even sector), the sector processed at time k-1, which is one sector before, is a short servo sector (odd sector), so if the difference from the sector before is taken, the speed estimation error will be large. This is because the position information demodulated from the short servo sector tends to have a large error. Therefore, the first position prediction unit calculates the speed from the difference from the position information obtained in the normal servo sector (even sector) processed at time k-2, which is two sectors before. In other words, the first position prediction unit always calculates the speed term from the difference between the nearest normal servo sectors. More specifically, the first position prediction unit calculates the predicted position p{hat}(k+1) as shown in Equation 5.

[0068]

number

[0069]

number

[0070] FIG. 8 is an example of frequency characteristics of the first position predictor in the magnetic disk device according to the first embodiment.

[0071] The frequency characteristics GC01 and PC01 are frequency characteristics of the position prediction process according to equation 1, and it can be seen that the gain in the high frequency range is reduced in the frequency characteristics GC101 and PC101 of the position prediction process according to equation 5.

[0072] FIG. 9 is a schematic diagram showing an example of a head position prediction calculation method associated with the second position prediction unit of the magnetic disk device according to the first embodiment.

[0073] If the sector being processed at time k is a short servo sector (odd sector), the speed is calculated from the difference in position information obtained at the normal servo sector one sector before (time k-1) and three sectors before (time k-3). That is, the second position prediction unit always calculates the speed term from the difference between the nearest normal servo sectors. More specifically, the second position prediction unit calculates the predicted position p{hat}(k+1) as shown in Equation 7.

[0074]

number

[0075]

number

[0076] FIG. 10 is an example of the frequency characteristic of the second position prediction unit of the magnetic disk device according to the first embodiment, and shows the frequency characteristic of the position prediction process according to Equation 8.

[0077] In comparison with the frequency characteristics GC101 and PC101 in FIG. 8, the frequency characteristics GC102 and PC102 have the advantage of being more resistant to noise, since the gain at high frequencies can be suppressed.

[0078] By the above procedure, the head position can be predicted using the velocity term calculated from the position information of the nearest normal servo sector. Second Embodiment In this embodiment, when the sector processed at time k is a short servo sector (odd sector), a speed term is calculated from normal servo position information obtained at the nearest normal servo sector and short servo position information obtained at the short sector at time k in head position prediction at time k+1. More specifically, the speed term is obtained by taking a weighted average of the difference obtained from two normal servo position information and the difference obtained from the normal servo position information and the short servo position information.

[0079] FIG. 11 is a schematic diagram showing an example of a head position prediction calculation method for the magnetic disk drive according to the second embodiment.

[0080] Specifically, when the sector being processed at time point k is a short servo sector (odd sector), the second position prediction unit 622 calculates the predicted position p{hat}(k+1) of the head at time point k+1 by taking a weighted average of the difference with the sector one sector before (which is a normal servo sector) and the differences between the sector one sector before and three sectors before (both of which are normal servo sectors) to take into account the immediately preceding speed.

[0081] For example, as in Equation 11, the weights may be parameters such as a:b, which can be arbitrarily set by the user.

[0082]

number

[0083] By changing the ratio of a and b, the frequency characteristics of the discrete-time transfer function from p to p{hat} can be adjusted, and the high-frequency gain and phase delay balance can be adjusted. The weights can be designed arbitrarily, but for example, if the weights are set to 1:2, the equation will look like the one below, and the p(k-1) term will be canceled and the calculation formula will be simplified to Equation 10. In this equation, the error contained in the difference term (velocity term) of the predicted position is affected by the error in the position information demodulated from the short servo sector, but the degree of influence is suppressed to √(1 / 3) (indicating the square root of 1 / 3).

[0084]

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[0085]

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[0086] FIG. 12 is an example of frequency characteristics of the second position predictor in the magnetic disk device according to the second embodiment.

[0087] It can be seen that the frequency characteristics GC201 and PC201 are intermediate between the frequency characteristics GC101 and PC101 in FIG. 8 and the frequency characteristics GC102 and PC102 in FIG.

[0088] 13 is a diagram showing time history waveforms of demodulated position and predicted position in the magnetic disk device according to the embodiment, where the horizontal axis indicates time (corresponding to time point k) and the vertical axis indicates position error.

[0089] POS indicates the case of the demodulated head position (corresponding to p(k) in FIG. 4, etc.). Even indicates the case of the predicted head position when normal servo information (corresponding to p(k) in FIG. 7) is obtained as the latest position information (corresponding to p{hat}(k+1) in FIG. 7). Odd indicates the case of the predicted head position when short servo information is obtained as the latest position information (corresponding to p(k) in FIG. 9) (corresponding to p{hat}(k+1) in FIG. 9). Conventional indicates the conventional case of the predicted head position (corresponding to p{hat}(k+1) in FIG. 4). Proposed indicates the case of the predicted head position shown in the second embodiment (corresponding to p{hat}(k+1) in FIG. 11). In FIG. 13, in the cases of Even and Odd, the position error tends to be smaller than in the case of Conventional, and in the case of Proposed, an example of obtaining intermediate characteristics between Even and Odd is shown.

[0090] By the above procedure, the head position can be predicted using the velocity term calculated from the position information of the nearest normal servo sector. Also, a weighted average can be calculated by weighting the velocity calculation between the normal servo sector and the short servo sector.

[0091] In this embodiment, an example is shown in which, at time point k when the latest position information is obtained, two velocity terms are calculated using past normal servo position information up to time point k-3. However, it is also possible to use even more past normal servo position information to increase the number of velocity terms and weight them to predict the head position for time point k+1.

[0092] According to at least one of the embodiments described above, it is possible to provide a magnetic disk device and a prediction method for predicting a head position based on a head position demodulated by a short servo system.

[0093] In the above embodiment, an example of the short servo method in which normal servo information is written in all servo sectors is shown, but there are various types of short servo methods, such as writing different servo information as normal servo information and short servo information for each servo sector. In general, short servo technology reduces the servo occupancy rate on the medium by making the servo information less than the normal servo information. Even in these cases, the normal servo demodulation unit 401 and the short servo demodulation unit 402 read the normal servo information and the short servo information at their respective timings, demodulate the position information of the head 19, and output the position information to the servo control unit 62, making it possible to apply this embodiment.

[0094] In addition, in this embodiment, as shown in Fig. 2 (e), the example of alternating normal servo sector and short servo sector is shown, but it is not limited to this case.For example, even if it is not alternating like normal servo sector, normal servo sector, short servo sector, normal servo sector, normal servo sector, it can obtain the same effect as this embodiment by using past normal servo position information to obtain the speed term at the time when latest position information is obtained.

[0095] Although several embodiments have been described, these embodiments are presented as examples and are not intended to limit the scope of the invention. These novel embodiments can be implemented in various other forms, and various omissions, substitutions, and modifications can be made without departing from the gist of the invention. These embodiments and their modifications are included in the scope and gist of the invention, and are included in the scope of the invention and its equivalents described in the claims. In addition, the processes shown in the flowcharts, sequence charts, etc. may be realized by hardware such as a CPU, an IC chip, a digital signal processor (Digital Signal Processor or DSP), or software (such as a program) operated by a computer including a microcomputer, or a combination of hardware and software. In addition, the device of the present invention is applied even when the claims are expressed as control logic, expressed as a program including instructions to execute a computer, or expressed as a computer-readable recording medium containing the instructions. In addition, the names and terms used are not limited, and other expressions are included in the present invention as long as they have substantially the same content and the same meaning. [Explanation of symbols]

[0096] 1...magnetic disk device, 2...host system, 10...HDA, 11...disk, 12...SPM, 13...VCM, 14...pivot, 15...arm, 16...suspension, 17...microactuator, 18...slider, 19...head, 20...driver IC, 30...head amplifier IC, 40...R / W channel, 50...HDC, 60...main controller, 61...read / write control unit, 62...servo control unit, 70...volatile memory, 80...non-volatile memory, 90...buffer memory, 401...normal servo demodulation unit, 402...short servo detection unit, 601...write inhibition determination unit, 602...control execution unit, 621...first position prediction unit, 622...second position prediction unit.

Claims

1. a head position demodulation unit which demodulates the head position by switching between a normal servo demodulation unit which processes servo information written in a servo sector of the disk and a short servo demodulation unit which processes servo information by a short servo method different from the normal servo demodulation unit; a head position prediction unit for predicting a head position; a write prohibition determination unit that determines whether to prohibit a head from writing data to the disk based on the predicted head position (predicted head position); The head position prediction unit predicts the position using the latest head position demodulated by the head position demodulation unit and a head position previously demodulated by a normal servo demodulation unit.

2. a first position prediction unit that calculates a predicted position by a first calculation formula when the latest head position is a head position demodulated by the normal servo demodulation unit (normal head position); A magnetic disk device as described in claim 1, further comprising a second position prediction unit that calculates the predicted position using a second calculation formula different from the first calculation formula when the latest head position is a head position (short head position) demodulated by the short servo demodulation unit.

3. The magnetic disk drive according to claim 2 , wherein the head position prediction unit switches between the first position prediction unit and the second position prediction unit.

4. 3. The magnetic disk drive according to claim 2, wherein the first position prediction unit obtains the predicted position of the head by using a velocity term of a position obtained from a difference between two immediately previous normal head positions.

5. 3. The magnetic disk drive according to claim 2, wherein the second position prediction unit obtains the predicted position of the head by using a velocity term of a position obtained from a difference between two immediately previous normal head positions.

6. 6. The magnetic disk drive according to claim 5, wherein the second position prediction unit obtains a plurality of differences between past normal head positions, and obtains a predicted position of the head using a weighted average of the plurality of differences.

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