Head control unit in a disk apparatus

Details Head control unit in a disk apparatus Head control unit in a disk apparatus

1999-10-12

2003-08-12

Hudspeth, David (Department: 2751)

Dynamic magnetic information storage or retrieval

Automatic control of a recorder mechanism

Controlling the head

C369S044280

Reexamination Certificate

active

06606217

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to head control units for controlling a head such that the head seeks information at the center of the target track on a disk, such as a floppy disk (FD), during a reproduction operation.
2. Description of the Related Art
In a conventional floppy-disk drive apparatus, a step driving mechanism employing a stepper motor is used as a head feed unit for moving a head to a track where recording is to be performed concentrically on a recording plane of a disk. With a mechanical step operation of this head feed unit, the head is positioned at the track. Instead of the step driving mechanism, a head feed unit having a linear-motor drive is provided for some floppy-disk drive apparatuses to move the head continuously.
In a disk apparatus of such a type, a detection section detects a return of the head to the origin and reports it to the host computer. To move the head to the target track of a disk, the host computer sends seek instruction pulses formed of STEP pulses one for one track and a seek request direction to the disk apparatus. According to this seek instruction pulses, the disk apparatus moves the head by the number of tracks corresponding to the seek instruction pulses.
In apparatuses such as the conventional floppy-disk drive apparatus, a screw shaft driven by a stepper motor is engaged with a head base and the head is fed by the rotation of the screw shaft. Since the mechanical connection determines the relationship between the rotation of the stepper motor and the movement position of the head, the head is moved to the target track just by driving the stepper motor according to the seek instruction pulses sent from the host computer.
On the other hand, in apparatuses employing a head feed unit having a linear-motor drive, since a head base has flexibility in the head feed unit, a detection section for always detecting the movement position of the head needs to be provided.
Such a head feed unit having a linear-motor drive is, for example, included in a disk apparatus in which a high-density-recording disk on which a servo signal is recorded for tracking and a floppy disk (FD) having a capacity of 2 megabytes (MB) can be loaded. The high-density disk to be loaded into this type of a disk apparatus is also a flexible disk. In the following description, a flexible disk having a capacity of 2 MB is called a floppy disk and it is discriminated from the high-density disk.
When the high-density disk is loaded, the head is moved by a linear-motor drive. When the head reads the servo signal, it is determined that the head has been positioned at a track. On the other hand, when a floppy disk is loaded, the head feed position is controlled according to the detection output of the detection section and the head is positioned at the track.
FIG. 14A
shows an example detection output of the detection section provided for the disk apparatus. This type of detection section is formed, for example, of a scale having fixed-interval slits provided for one of the moving side and the fixed side and a pair of optical detection devices provided for the other side. As the head base moves, phase-A and phase-B detection outputs having a relative phase difference of one-fourth the period (90 degrees) are obtained from the pair of the optical detection devices.
In
FIG. 14A
, the horizontal axis indicates the head movement position in the radial direction of the disk and the phase of the phase-B detection output, and the vertical axis indicates the strength (voltage) of the detection outputs. As shown in
FIG. 14A
, the phase-A detection output and the phase-B detection output have the relationship of the sine curve and the cosine curve, or curves approximating to these trigonometric functions.
As shown in
FIG. 14A
, detection data to be used is switched from the phase-A detection output to the phase-B detection output and vice versa at intersections of both detection outputs. As a result, the movement position of the head is detected with the use of a part of the detection outputs, which shows linearity and is indicated by a solid line in FIG.
14
A.
FIG. 14B
shows head positions calculated according to the detection data, shown by the solid line in FIG.
14
A. The horizontal axis indicates the phase of the phase-B detection output and the vertical axis indicates the detected value of the head position.
As shown in
FIG. 14A
, with the alternate use of the parts of the detection outputs, which show strong linearity, the relationship between the detection outputs and the head position is obtained with a high precision as a relationship approximating to a linear function, as shown in FIG.
14
B. When the position of the detection section is adjusted such that the positions corresponding to phases of 0 degrees, 360 degrees, 720 degrees, . . . of the phase-B detection output match the centers of tracks, the positional deviation from the head position to a track center is always obtained positively.
When the output value of the detection section is abruptly shifted due to the movement of the head caused, for example, by an external impact, since the detection output linearly relates to the head position as shown in
FIG. 14B
, it is easily determined whether the head has been moved toward the center of the disk or toward the outside.
In the detection section, described above, which uses the scale having the slits and the pair of optical detection devices, the machining tolerance of the slits in the scale or an error in the relative positions of the pair of the optical detection devices cannot be eliminated. An error in the phase difference between the phase-A detection output and the phase-B detection output cannot be avoided as shown in FIG.
14
A. In an actual apparatus, it is possible that the phase difference between the phase-A and phase-B detection outputs is shifted by about ±30 degrees from a reference of 90 degrees.
FIG. 15A
shows a case in which the phase-A detection output is shifted from the phase-B detection output by 30 degrees measured from an original phase difference of 90 degrees.
The position of the detection section is adjusted such that the head is positioned at the centers of tracks on the disk when the phase-B detection output is 0 degrees, 360 degrees, 720 degrees . . . . Under this condition, when detection data to be used is switched from the phase-A detection output to the phase-B detection output and vice versa at the same timing as that in
FIG. 14A
, the detection data to be used has steps at the switching points of both phase detection outputs, as shown in FIG.
15
A.
FIG. 15B
shows the relationship between the phase (horizontal axis) of the phase-B detection output and the detection value (calculated value) of the head position. Since a phase tolerance is formed between the phase-A and phase-B detection outputs as shown in
FIG. 15B
, the detected position includes incontinuous points.
While the head is gradually approaching the center of the target track and the head-movement speed is decreasing, for example, when the head reaches an incontinuous point shown in
FIG. 15B
, speed control servo responds sensitively in head seek control and the head is likely to become uncontrollable or a seek error is likely to happen such as a to-and-fro repeated movement of the head.
On the other hand, it is possible that a one-phase detection output is obtained from the detection section and the head position is detected according to the one-phase detection output. In this case, around the peaks of the one-phase detection output, detection-output linearity cannot be obtained. While the detection output is around its peak, if the head is moved by an external impact and the detection output exceeds its peak point, it becomes impossible to determine the direction in which the head has been moved. As a result, a track counting error occurs.
SUMMARY OF THE INVENTION
The present invention has been made to solve the above conventional drawbacks. Accordingly, it is an object of the present invention

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