BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 shows the structure of a general magnetic disk device disclosed by Patent reference 1;
FIG. 2 shows the shape of the surface of a main pole disclosed by Non-patent reference 1;
FIG. 3 shows the circuit configuration of the magnetic disk device in the preferred embodiment of the present invention;
FIG. 4 shows the shape of a suspension arm on which the magnetic head 32 is mounted;
FIG. 5 shows a slider mounted at the end of an arm 41;
FIG. 6 shows the structure of the magnetic head 32;
FIG. 7 shows the shape of the surface facing the magnetic disk 33, of a main pole 61a;
FIG. 8 is a graph showing an example of the yaw angle dependence of an optimal track pitch;
FIG. 9 is a graph showing another example of the yaw angle dependence of an optimal track pitch;
FIG. 10 is a graph showing the change of a storage capacity (line storage capacity) per cylinder according to a position in the radius direction;
FIG. 11 is a graph showing the difference of a track pitch according to a position in the radius direction;
FIG. 12 is a graph showing the relationship between the position whose skew angle becomes 0 degree and the storage capacity of the device;
FIG. 13 is the flowchart of a servo signal generation process; and
FIG. 14 is the flowchart of a positioning process.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
The preferred embodiments of the present invention are described in detail below with reference to the drawings.
FIG. 3 shows the circuit configuration of the magnetic disk device in the preferred embodiment of the present invention.
As shown in FIG. 3, the magnetic disk device comprises a controller 30 for controlling the entire device, a voice coil motor (VCM) 31 driven by the controller 30, a magnetic head 32 and a magnetic storage medium (magnetic disk) 33 rotated by a motor, which is not shown in FIG. 3.
The controller 30 comprises a head position control unit 30a, a side write characteristic evaluation unit 30b, a servo information write control unit 30c and a track pitch/layout calculation unit 30d. Each of the units is as follows.
The head position control unit 30a drives/controls the VCM 31 to move the magnetic head 32 in the radius direction of the magnetic disk 33. The side write characteristic evaluation unit 30b evaluates (measures) its side write characteristic by recording data on the magnetic disk 33 by the magnetic head 32, reading the recorded data and analyzing it. The recorded data is read by finely moving its position in the radius direction by the head position control unit 30a. The track pitch/layout calculation unit 30d receives the evaluation result of the side write characteristic from the side write characteristic evaluation unit 30b and calculates an optimal track pitch for each position in the radius direction. The track pitch calculated for each position in the radius direction is a track pitch layout. The servo information write control unit 30c writes servo information on the magnetic disk 33 by the magnetic head 32, according to the track pitch calculated for each position in the radius direction by the track pitch/layout calculation unit 30d.
The evaluation (measurement) of a side write characteristic, the calculation of a track pitch and the writing of servo information are performed to initialize the magnetic disk 33. FIG. 13 is the flowchart of a servo signal generation process performed for the initialization. The measurement of a side write in step S1 is performed by the side write characteristic evaluation unit 30b. The determination of a track pitch layout according to the side write characteristic in step S2 is performed by the track pitch/layout calculation unit 30d. The generation of servo information (signal) on the magnetic disk 33 according to the track pitch layout in step S3 is performed by the servo information write control unit 30c. The units 30a through 30d including them can be actually realized by executing a program stored in ROM built in the controller 30.
As the servo information, a track number, a sector number and the like are written in the magnetic disk 33. Thus, the writing of data or the positioning for moving the magnetic head 32 to a position to move in order to reproduce it can be realized by performing the positioning process shown in FIG. 14.
Firstly, in step S11, a servo signal is read by the magnetic head 32. In step S12, the current position of the magnetic head 32 is calculated based on the read servo information. In step S13, the rotation control of the VCM 31 is started in order to move the magnetic head 32 from the current position up to a target position to move. The movement is continued until the servo information of the target position is read. After the servo information is read, it is determined that the movement (positioning) of the magnetic head 32 is completed and the series of the processes terminate.
FIG. 4 shows the shape of a suspension arm on which the magnetic head 32 is mounted. The suspension arm (hereinafter called “arm”) 41 is driven/rotated around the center 42 by the VCM 31. The magnetic head 32 is mounted at the end 43 of the arm 41.
FIG. 5 shows a slider mounted at the end of the arm 41. As shown in FIG. 5, the magnetic head 32 is mounted at the end of a slider 50, that is, at the end on the far side when viewed from the rotation direction A of the magnetic disk 33.
FIG. 6 shows the structure of the magnetic head 32. The magnetic head 32 comprises a recording head 61 for recording data and a reproduction head 62 for reproducing recorded data. The recording head 61 comprises a main pole 61a, an auxiliary pole 61b and a coil 61c for generating a magnetic field. The reproduction head 61b comprises two shields 62a and a magnetic resistor device 62b inserted between the two shields 62a. Data recorded on the magnetic disk 33 is read by the resistor device 62b.
FIG. 7 shows the shape of the surface facing the magnetic disk 33, of the main pole 61a. The surface shape is obtained when viewed from the direction of the arrow B shown in FIG. 6.
As shown in FIG. 7, the surface shape is a trapezoid with two sides facing each other in the rotation direction A, that is, in the direction orthogonal to the radius direction of the magnetic disk 33. Taper angles formed by a straight line orthogonal to the longer one of two bases and two sides are 0 and a degrees, respectively. Thus, there is a size relationship in which two angles formed by the shorter one of the two bases and the two sides are 90 degrees and over 90 degrees, respectively. The side whose angle is 90 degrees is located inside in the radius direction of the magnetic disk 33.
It is because the surface on the side is not planed that one of the two angles is 90 degrees. In other words, it is because usually the main pole 61a is fabricated by planning a rectangular member. Thus, the angle can also depend on the shape of a member before being planed. Since usually the angle is 90 degrees, the actual angle becomes 90 degrees or in its neighborhood. The side surface whose angle is 90 degrees, of the two angles can also be located outside in the radius direction, that is, a side surface the reverse of this preferred embodiment.
The magnetic head 32 is mounted at an angle where the direction orthogonal to the radius direction of the magnetic disk 33 and a side the taper angle of the main pole 61a of which is a are parallel in the position whose skew angle becomes 0 degree or at an angle where the orthogonal direction becomes parallel to the side in a position further outside the position. The latter corresponds to the fact that an angle formed by the orthogonal direction and a straight line orthogonal to a base with a core width W in FIG. 7 is larger than the taper angle α. By mounting the magnetic head 32 thus, outside the position whose skew angle becomes 0 degree, a side located outside in the radius direction can be prevented from being located further outside than the base with core width W. On the side located inside, the side located inside in the radius direction can be prevented from being located further inside the base with core width W or a width projected from it can be suppressed at a minimum. Inside the position whose skew angle becomes 0 degree, the side located outside can be prevented from being further outside the base with core width W or a width projected from it can be suppressed at a minimum. On the side located inside, the side located inside in the radius direction can be prevented from being located further inside the base with core width W. thus, the side write of the entire radius direction can be suppressed.
The main pole 61a can be fabricated by planing only one side surface of a member. Therefore, compared with when planning the member from two directions, it can be more easily fabricated. Thus, the yield in the fabrication of the magnetic head 32 can be further improved.
As shown in FIG. 4, in this preferred embodiment, the arm 41 is folded in the shape of a Japanese character “![]()
” between the center 42 and the end 43. This is because the skew angle should be 0 degree in the outer magnetic disk 33. By adopting such a shape, even if the distance between the center 41 and the magnetic head 32 is short, the skew angle can be surely made 0 degree in the outer magnetic disk 33. A position in the radius direction, whose skew angle is 0 degree is made within a third of an area extended from the outermost circumference toward the center (rotation axis) of the magnetic disk 33. More specifically, a third of the area is an outer third of an area in a zone to record data or an area in which the number of recording tracks counted from the outermost circumference of the recording track is a third of the total. The reason why the skew angle should be 0 degree in such an area is described in detail below with reference to the drawings FIGS. 8 through 12.
FIG. 8 is a graph showing an example of the yaw angle dependence of an optimal track pitch. The horizontal axis indicates a yaw angle. The left- and right-side vertical axes indicate a track pitch in arbitrary unit and a normalized track pitch, respectively. As to a polygonal line located in the upper section, the right-side vertical axis indicates the change of an optimal track pitch by the yaw angle (skew angle). As to a polygonal line located under it, the left-side vertical axis indicates the change of an optimal track pitch by the yaw angle (skew angle). A track pitch is normalized to be 1 when the yaw angle is 0 degree.
FIG. 10 is a graph showing the change of a storage capacity (line storage capacity) per cylinder according to a position in the radius direction. The horizontal and vertical axes indicate a position in the radius direction and a storage capacity, respectively.
The range of the yaw angle is determined based on the relationship between a position in the radius direction and a storage capacity per cylinder. As shown in FIG. 8, an optimal track pitch increases as the absolute value of the yaw angle increases. In other words, the optimal track pitch is minimized when the yaw angle is 0 degree, that is, the track density is maximized. The line storage capacity increases as the position in the radius direction is located further outside. Thus, a position whose yaw angle (skew angle) in which the track density is maximized becomes 0 degree is located outside in the radius direction. By increasing the track density in an area with a high line storage capacity, the storage capacity of the entire device can be effectively improved.
FIG. 11 is a graph showing the difference of a track pitch according to a position in the radius direction. The horizontal and vertical axes indicate a position in the radius direction and a track pitch (relative value), respectively. The relative value of a track pitch in a position whose yaw angle (skew angle) is 0 degree is normalized to be 1. As to the change in the radius direction of a track pitch, solid and broken lines indicate the preferred embodiment of the present invention and the prior art respectively.
Since a side write characteristic can be suppressed, as shown in FIG. 11, in this preferred embodiment, a track pitch is made to vary depending on a position in the radius direction assuming that a track pitch is optimized in a position in the radius direction. Thus, compared with the prior art in which a track pitch is constant, the track pitch is further narrowed in a position whose yaw angle (skew angle) is 0 degree and its neighborhood. Thus, the storage capacity of the entire device can also be greatly improved. As described above, a track pitch (track pitch layout) is determined by the track pitch/layout calculation unit 30d shown in FIG. 3.
FIG. 12 is a graph showing the relationship between the position whose skew angle becomes 0 degree and the storage capacity of the device. The horizontal and vertical axes indicate a position in the radius direction, whose skew angle is 0 degree and the storage capacity of the entire device, respectively. As clearly seen from FIG. 12, by locating the position outside, the storage capacity of the entire device can be increased.
For the reason described above, it is preferable for the position in the radius direction, whose skew angle is 0 degree to be within a third of an area extended from the outermost circumference toward the center (rotation axis). By making the skew angle 0 degree in such an area, the storage capacity of the device can be more easily improved. Since by adopting the main pole 61a with the surface shape shown in FIG. 7, side write can be effectively suppressed, the storage capacity of the device can be more easily improved.
FIG. 9 is a graph showing another example of the yaw angle dependence of an optimal track pitch. As in FIG. 8, the horizontal axis indicates a yaw angle and the left- and right-side vertical axes indicate a track pitch in arbitrary unit and a normalized track pitch, respectively. As to one located in the upper section of two polygonal lines, the right-side vertical axis shows the change of an optimal track pitch by the yaw angle (skew angle). As to one located under it, the left-side vertical axis shows the change of an optimal track pitch by the yaw angle (skew angle).
Most of magnetic heads have the characteristic shown in FIG. 8. However, a part of them have the characteristic shown in FIG. 9. In the characteristic shown in FIG. 9, a track pitch by the position in the radius direction can be obtained by reversing the left/right side of the graph shown in FIG. 11 at the center of the radius position, that is, making the axial symmetry of it by assuming a line parallel to the vertical axis at the radius position. The relationship between the position whose skew angle is 0 degree and the storage capacity of the device can be obtained by reversing the inclination of the graph shown in FIG. 12, that is, its inclination becomes negative. Thus, in the characteristic shown in FIG. 9, the position in the radius direction, whose skew angle is 0 degree can be made within a third of an area extended from the innermost circumference toward the outside of the magnetic disk 33.
Although in this preferred embodiment, the surface shape of the main pole 61a is trapezoidal, the surface shape can also contain a trapezoid. For example, the inclination of a side forming the taper angle a can change on the way.
Patent Application
20070247745
