This application is based upon and claims the benefit of priority from the prior Japanese Patent Application No. 2002-380276, filed Dec. 27, 2002, the entire contents of which are incorporated herein by reference.
1. Field of the Invention
The present invention relates to a disk drive that uses a head to read and write data from and to a disk, and in particular, to a disk drive that sets an offset between a track position specified by a command from a host and a target position at which the head is to be actually positioned, as well as a head positioning method used for this disk drive.
2. Description of the Related Art
A hard disk drive is well known as a disk drive that uses disks (disk media) as recording media. In general, a plurality of concentric servo tracks are arranged on a recording surface of a disk. The pitch of the servo tracks on the disk is fixed. Servo information is pre-written in each servo track discretely at equal intervals in the circumferential direction of the disk. The servo information pre-written in the disk is called embedded servo. The servo information is a kind of positional information, also called a servo pattern, and contains address code and burst signals. The address code contains a cylinder code (cylinder number). The cylinder code indicates a cylinder position on the disk at which the corresponding servo information is written. The burst signal is also called a position error signal, and it indicates information (position error) on the position of the head relative to the cylinder (servo track) in which the corresponding servo information is written. The cylinder code in the servo information is a value that varies with the consecutive servo tracks (in general, the respective servo tracks have different values).
If a host utilizing the hard disk drive provides a read/write command to the drive, the position of a target track on the disk specified by this command is calculated. Then, head positioning control is carried out on the basis of the servo information read by the head. This control allows the head to be positioned at the target position (in the radial direction of the disk). In this state, the head reads or writes data from or to the disk. In this case, the tracks in which the head writes data coincide with the servo tracks. The pitch of the tracks (track pitch) is fixed.
The heads of recent hard disk drives are mainly of a composite type. The composite head is composed of a read head (read element) and a write head (write element) separately formed on the same slider. With a hard disk drive comprising such a composite head, the signal to noise ratio of a read signal (reproduction signal) is degraded if the head has a large azimuth angle. This is because crosstalk may occur, in which data recorded in a track on the disk is deleted by writing data in adjacent tracks.
Thus, techniques have hitherto been proposed which suppress the adverse effects of crosstalk. For example, Jpn. Pat. Appln. KOKAI Publication No. 10-255201 describes a technique of dividing the recording surface on the disk into areas with a large azimuth angle and areas with a small azimuth angle. The technique (hereinafter referred to as the prior art) described in this publication arranges servo tracks in each area, the tracks having a track pitch unique to that area. Specifically, in the prior art, servo information is written using different track pitches for the areas with the large azimuth angle and for the areas with the small azimuth angle.
Thus, in the prior art, in order to suppress the adverse effects of crosstalk resulting from the large azimuth angle of the head, it is necessary to write servo information using different track pitches for the respective areas into which the recording surface has been divided on the basis of a difference in azimuth angle. However, the length (known as the head width) of the head in the radial direction of the disk varies with the head. Crosstalk may also occur if the width (write width) over which data is actually written varies owing to the variation in head width. In this case, different track pitches must be used to write servo information in the respective areas on the disk into which the recording surface is divided, also taking the variation in head width into account.
According to an embodiment of the present invention, there is provided a disk drive comprising a disk having a recording surface on which a plurality of concentric tracks are arranged at a fixed pitch, wherein data is read from and written to the disk by a head arranged in association with the recording surface of the disk. The disk drive comprises calculating means, determining means, and executing means. The calculating means calculates a first offset value on the basis of the position of a first target track specified by a command from a host, the first offset value reflecting a track pitch which enables adverse effects of crosstalk to be suppressed. The first offset value indicates an offset of a target position at which the head is to be actually positioned from a predetermined position on the first target track in a radial direction of the disk. The determining means determines a second target track, to which the target position belongs, and a second offset value on the basis of the position of the first target track and the first offset value calculated by the calculating means. The second offset value indicates an offset of the target position from a predetermined position on the second target track in the radial direction of the disk. The executing means executes control to position the head at the target position on the second target track on the basis of the second target track position and second offset value each determined by the determining means.
The accompanying drawings, which are incorporated in and constitute a part of the specification, illustrate embodiments of the invention, and together with the general description given above and the detailed description of the embodiments given below, serve to explain the principles of the invention.
With reference to the drawings, description will be given of an embodiment in which the present invention is applied to a hard disk drive.
Referring back to
The head 12-i is connected to a head IC (head amplifier circuit) 17. The head IC 17 includes a read amplifier (not shown) that amplifies a read signal read by the head 12-i and a write amplifier (not shown) that converts write data into a write current. A head IC 23 is connected to a read/write IC (read/write channel) 18. The read/write IC 18 is a signal processing device that executes various signal processes. These signal processes include a process of subjecting a read signal to an analog-to-digital (A/D) conversion, a process of encoding write data, and a process of decoding digitalized read data. The read/write IC 18 also has a function of pulsing (binarizing) a read signal into a read pulse signal and a function of extracting burst signals (in this case, burst signals A, B, C, and D) from servo information in accordance with a timing signal (burst timing signal) from a gate array 19. The burst signals are transmitted to the CPU 21, which uses them for positioning control (track following control) to settle the head 12-i at a target position on a target track.
The gate array 19 has a function of generating various timing signals including a burst timing signal, from a read pulse signal outputted by the read/write IC 18 and a function of extracting cylinder code from servo information. The cylinder code is used for seek control to move the head 12-i to the target track. A disk controller (hereinafter referred to as an “HDC”) 20 is connected to a host (host system) utilizing the HDD. The host is digital electronic equipment represented by a personal computer. The HDC 20 processes read data decoded by the read/write IC 21 in accordance with a control signal from the gate array 19 to generate data to be transmitted to the host. The HDC 20 also transfers write data transferred by the host, to the read/write IC 18 in accordance with a control signal from the gate array 19.
The CPU 21 is a main controller for the HDD. The CPU 21 contains an FROM (Flash Read Only Memory) 22 and a RAM (Random Access Memory) 23. The FROM 22 is a rewritable nonvolatile memory. The FROM 22 pre-stores a control program 221 to be executed by the CPU 17. The control program 221 contains a process routine for determining a target position at which the head 12-i is to be actually positioned, on the basis of positional information on a target track specified by a command from the host. The target position is determined taking the azimuth angle of the head 12-i or the like into account. The FROM 22 also pre-stores an offset table 222, described later. A part of the entire area of the RAM 23 is used by the CPU 21 as a work area.
The offset table 222 indicates the relationship between concentric areas Aj (j=1 to n) (see
The offset value (third offset value) ΔOj indicates the difference (pitch difference) between a servo track pitch STP and a data track pitch DTP. The data track pitch DTP enables the adverse effects of crosstalk to be suppressed. The DTP and the STP have the relationship expressed by the following equation:
DTP=STP+ΔOj (1)
In the prior art, the data track pitch DTP is equal to the servo track pitch STP. That is, ΔOj=0. In this case, the target position TP coincides with the predetermined position on the target track TT1. However, when the data track pitch DTP is equal to the servo track pitch STP, with some HDDs, the adverse effects of crosstalk become more significant. Such HDDs are classified into two types. A first type includes HDDs in which the head 12-i has an azimuth angle varying markedly depending on the position on the disk in its radial direction. With the first type of HDD, owing to the varying azimuth angle of the head 12-i, the width (write width) over which data is actually written by the head 12-i also varies depending on the position on the disk in its radial direction. This is equivalent to the head width of the head 12-i varying depending on the position on the disk in its radial direction. A second type includes HDDs in which the heads 12-0 and 12-1, corresponding to the recording surfaces H0 and H1, respectively, of the disk 11, have greatly different head widths (which depend on the physical shapes of the heads). Thus, in the present embodiment, for each area Aj, a unique data track pitch DTP (DTP>STP) is set which enables the adverse effects of crosstalk to be suppressed. Specifically, a unique offset value ΔOj is set for each area Aj.
The numbers of servo tracks 111 arranged in areas A1 to Aj−1 are assumed to be N1 to Nj−1, respectively. The offset value Oj can be calculated in accordance with the following equation:
Oj=Oj−1 +ΔOj−1(Nj−1−½)+ΔOj/2 (2)
Specifically, the offset value Oj can be calculated from Oj−1, ΔOj−1 and ΔOj, as well as the number of tracks N1 to Nj−1. In this case, O1=ΔO1/2.
Alternatively, the offset value Oj can be calculated using the following equation:
Here, ΣΔOp*Np represents the sum of ΔOp*Np for p=1 to j−1. As is apparent from Equation (3), the offset value Oj can also be calculated from the offset values ΔO1 to ΔOj and the number of tracks N1 to Nj−1. Accordingly, if the time required to calculate the offset value Oj does not matter, information on the offset value Oj need not necessarily be stored in an entry Ej in the offset table 222.
It is assumed that the k+1-th track Tjk in the area Aj is the first target track TT1. In this case, the offset of the target position TP at which the head 12-i is to be actually positioned, from the predetermined position on the target track TT1 (=track Tjk) is expressed by Oj+k(STP+ΔOj)=Oj+k*DTP.
The CPU 21 in
Now, with reference to the flow chart in
Once the CPU 21 identifies the position of the first target track TT1 (step S2), it identifies the area Aj on the disk 11 to which the target track TT1 (=Tjk) belongs (step S2). The area Aj is one of the areas A1 to An (see
Then, on the basis of the target track TT1 (=Tjk) and the offset value {Oj+k(STP+ΔOj), CPU 21 determines the position of the second target track TT2 and the offset value (second offset value) ΔOj′ (step S6). As described previously, the offset value Oj can also be calculated in accordance with Equation (3) on the basis of the offset value ΔO1 to ΔOj. Therefore, the position of the second target track TT2 and the offset value ΔOj′ can be determined from the first target track TT1 (Tjk) and the offset values ΔO1 to ΔOj.
As described previously, the head 12-i is to be actually moved to the second target track TT2. Specifically, the target position TP (at which the head 12-j is positioned) that is offset from the predetermined position on the leading track Tj0 in the area Aj by the offset value {Oj+k(STP+ΔOj) belongs to the second target track TT2 (servo track 111). On the other hand, the offset value ΔOj′ indicates the offset of the target position TP on the second target track TT2 from predetermined position on the target track TT2.
Then, the CPU 21 executes seek control to move the head 12-i to the target track TT2 determined in step S6 (step S7). This seek control is executed on the basis of a cylinder code extracted from the gate array 19. When the head 12-j is moved to the second target track TT2, the CPU 21 executes positioning control. (tracking control) to position (settle) the head 12-i at the target position TP on the target track TT2 (step S8). This positioning control is based on burst signals extracted by the read/write IC 18. The target position TP at which the head 12-i is to be positioned in this positioning control is offset from the predetermined position on the second target track TT2 in the radial direction of the disk 11 by the offset value ΔOj′. When the head 12-i is positioned within a predetermined error range from the target position TP (in this case, the target position for a write) on the second target track TT2, the CPU 21 proceeds to step S9. In step S9, the CPU 21 causes the head 12-i to execute a read/write (in this case, a write).
Thus, in the present embodiment, the target position TP at which the head 12-i is to be positioned is determined to be a position on the target track TT2 instead of the predetermined position on the first target track TT1 specified by a command from the host. The position on the second target track TT2 is offset from the predetermined position on the first target track TT1 in the radial direction of the disk 11 by the offset value (first offset value) {Oj+k(STP+ΔOj}. This offset value reflects a track pitch that enables the adverse effects of crosstalk to be suppressed. Accordingly, by positioning the head 12-i at the determined target position TP and executing a read/write, it is possible to achieve a data track pitch DTP that enables the use of the disk 11 in which the servo tracks 111 are arranged at a fixed pitch (servo track pitch) STP, with the adverse effects of crosstalk suppressed.
In the above embodiment, the areas A1 to An on the recording surfaces H0 and H1 of the disk 11 and the offset values O1 to On and ΔO1 to ΔOn for the respective areas A1 to An are determined taking into account a difference in the azimuth angle of the heads 12-0 and 12-1 at each position on the disk in the radial direction, as well as a difference in head width between the heads 12-0 and 12-1. However, only one of these two differences may be taken into account. For example, if only the difference in azimuth angle is taken into account, each of the recording surfaces H0 and H1 of the disk 11 may be similarly divided into a plurality of concentric areas. In this case, the adverse effects of the difference in head width between the heads 12-0 and 12-1 may remain. These adverse effects are eliminated by determining the offset values O1 to On and ΔO1 to ΔOn on the basis of the upper limit value in the appropriate standard for the head widths of the heads 12-0 and 12-1.
If only the difference in head width between the heads 12-0 and 12-1 is taken into account, the entire recording surfaces H0 and H1 of the disk 11 may correspond to the areas A0 and A1, respectively. Here, the offset values Oi and ΔOi (or ΔOi) may be set for each recording surface Hi (i=0, 1). The offset values Oi and ΔOi can be determined (calculated) from the head width of the head 12-i by measuring the head width during the manufacture of the HDD (or the head 12-i). The offset values Oi and ΔOi (or ΔOi) determined may be stored in the FROM 22, for example, in a format similar to that for the offset table 222, shown in
Furthermore, if only the difference in head width is taken into account, the heads are classified into, for example, first heads having a head width meeting a first standard and second heads having a head width which is outside the first standard but which meets a second standard. This classification serves to provide HDDs such as those described below. First, the upper limit value of the head width in the first standard is defined as HWUL1. The upper limit value of the head width in the second standard is defined as HWUL2 (HWUL2>HWUL1). Then, the heads are classified into the first heads having a head width meeting the first standard, the second heads having a head width which is outside the first standard but which meets the second standard, and third heads having a head width that is also outside the second standard. The third heads are treated as defectives that cannot be mounted in HDDs. On the other hand, the first heads are mounted in a first HDD that realizes a first data track pitch DTP (first track density). The second heads are mounted in a second HDD that realizes a second data track pitch DTP (second track density) larger than the first data track pitch DTP (first track density). The offset value O1 (=ΔO1/2) determined from the head width HWUL1 is stored in a predetermined position in the FROM 22 in the first HDD, as shown in
Now, a process of determining the offset values Oj and ΔOj for each area Aj will be described with reference to the flow charts in
Then, the CPU 21 executes control to position the head 12-i corresponding to the recording surface Hi on which the area Aj exists, at a predetermined position on the track Tjk (step S13). In step S13, the CPU 21 executes seek control to move the head 12-i to the track Tjk. The CPU 21 also executes positioning control to position the head 12-i moved to the track Tjk, at a predetermined position on the track Tjk.
Then, the CPU 21 executes control to shift the position of the head 12-i from the track Tjk (the predetermined position on the track Tjk) in a radially outward direction of the disk 11 by the amount STP+(h−1)*ΔO (step S16).
In the state shown in
Here, it is assumed that ER2−ER1≦TH. In this case, the CPU 21 determines that the writes of the second test data in steps S17 and S19 adversely affects the first test data written in the track Tjk. That is, the CPU 21 determines that the adverse effects of crosstalk cannot be eliminated even by writing data while shifting the head 12-i from the track Tjk in the radially outward or inward direction of the disk 11 by the amount STP+(h−1)*ΔO. Then, the CPU 21 executes step S23, described later, in order to suppress the adverse effects of crosstalk. Specifically, the CPU 21 increments a variable h by 1 in order to increase the value of the offset of the head 12-i from the track Tjk (step S23). Then, the CPU 21 uses the incremented variable h to execute steps S14 to S22, described later. That is, the CPU 21 repeats steps S14 to S22 while incrementing the variable h by 1 until ER2−ER1<TH (step S23).
It is assumed that ER2−ER1<TH. In this case, the CPU 21 determines that the current value of the offset of the head 12-i from the track Tjk is the minimum offset value required to eliminate the adverse effects of crosstalk. Then, the CPU 21 determines whether or not the pointer j is 1 (initial value) (step S24). If the pointer j is 1, the CPU 21 determines the offset values ΔOj and Oj unique to the area Aj in accordance with the following equation (step S25):
ΔOj=2(h−1)*ΔO Oj=ΔOj/2 (4)
On the other hand, if the pointer j is not 1, the CPU 21 determines the offset values ΔOj and Oj unique to the area Aj in accordance with the following equation (step S26):
ΔOj=2(h−1)*ΔO Oj=Oj−1+ΔOj−1(Nj−1−½)+ΔOj/2 (5)
Then, the CPU 21 stores information indicative of the leading track Tj0 in the area Aj and information indicative of the offset values Oj and ΔOj determined, in the entry Ej in the offset table 222, retained in the FROM 22 (step S27). Then, the CPU 21 determines whether or not the pointer j is n, indicating the final area An (step S24). If the pointer j is not n, the CPU 21 increments the pointer j by one and sets the variable h at 1 (initial value) (step S29). Then, the CPU 21 executes the process starting with step S12 in order to determine the values ΔOj and Oj unique to the area Aj indicated by the incremented pointer j. That is, the CPU 21 repeats the process starting with step S12 until the pointer j becomes n and the values ΔOj and Oj unique to the area An are determined. Then, if it is determined at step S28 that the pointer j is n, the CPU 21 ends the process of determining the offsets Oj and ΔOj.
In the above described process of determining the Oj and ΔOj, for simplification of description, the process from steps S13 to S21 is executed only once for a certain h. However, for measurement accuracy, the process from steps S13 to S21 may be repeated a predetermined number of times r. In this case, it may be determined whether or not the value ({Σ(ER2)−Σ(ER1)}/r) is smaller than the threshold TH. The value ({Σ(ER2)−(ER1)}/r) is obtained by subtracting the average of error rates ER1 (Σ(ER1)/r) from the average of error rates ER2 (Σ(ER2)/r).
In the above embodiment, the heads 12-0 and 12-1 are each of a composite type. However, the heads 12-0 and 12-1 may each be of an inductive type that uses a common element to execute read/write. In this case, the head width of the heads 12-0 and 12-1 has only to be taken into account. The recording surfaces H0 and H1 of the disk 11 may be managed as areas A0 and A1, respectively.
In the description of the above embodiment, the present invention is applied to the HDD (Hard Disk Drive). However, the present invention is applicable to disk drives other than HDDs, such as magneto-optical disk drives provided that their heads read and write data from and to a disk.
Additional advantages and modifications will readily occur to those skilled in the art. Therefore, the invention in its broader aspects is not limited to the specific details and representative embodiments shown and described herein. Accordingly, various modifications may be made without departing from the spirit or scope of the general inventive concept as defined by the appended claims and their equivalents.
Number | Date | Country | Kind |
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2002-380276 | Dec 2002 | JP | national |
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0 387 018 | Sep 1990 | EP |
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Number | Date | Country | |
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20040136109 A1 | Jul 2004 | US |