Seek error retry method of a disk device and disk device

In a disk device having a ramp-load mechanism, stable retry operation is performed even upon occurrence of seek errors. A disk device is provided with a ramp to which the head is retracted from the disk, at the time of seek error retry, prior to beginning seek retry, checks whether the head has climbed onto the ramp. And if the head has not climbed onto the ramp, normal seek retry is performed, but if the head has climbed onto the ramp, unloading is first performed before seek retry. Consequently crashes due to climbing onto the ramp due to a seek error in a ramp-load device can be prevented, and improvement of device reliability can be expected.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is based upon and claims the benefit of priority from the prior Japanese Patent Application No. 2005-023548, filed on Jan. 31, 2005, the entire contents of which are incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to a seek error retry method of disk device and its disk device to perform retry control when a seek error has occurred during head seeking, and in particular relates to a seek error retry method of disk device and its disk device, which is suitable for a disk device having a ramp mechanism to retract a head from the disk media.

2. Description of the Related Art

A disk device employing a magnetic disk, magneto-optical disk, optical disk, or other storage media performs a seek operation to position the head at a desired track on the disk. In such a disk device, as the head flying height is reduced, use of the CSS (Contact Start-Stop) method becomes difficult. Moreover, there are demands for disk devices with improved resistance to shocks when not in operation.

Consequently devices adopting a ramp-load method have been proposed. In a ramp-load method, a ramp mechanism is provided on the external perimeter of the disk, and while not in operation the head is retracted from the disk to the ramp mechanism.FIG. 9shows the configuration of a magnetic disk device adopting a conventional ramp-load method.

As shown inFIG. 9, a magnetic disk160is provided on the spindle120of the magnetic disk device. The magnetic head110which reads information on the magnetic disk160moves in the radial direction of the magnetic disk160. A ramp mechanism111is provided at the outermost perimeter of the magnetic disk160. The ramp mechanism111has an inclined portion111-1and a depressed portion111-2.

In a ramp-load method, when operation ends the magnetic head110is moved to the ramp mechanism111, as indicated by the direction of the arrow UL. The magnetic head110rides over the inclined portion111-1of the ramp mechanism111, and is accommodated in the depressed portion111-2(this is called an unload operation). On the other hand, when starting operation the magnetic head110is moved from the ramp mechanism111to the magnetic disk160, as indicated by the direction of the arrow LO. The magnetic head110moves from the depressed portion111-2to the inclined portion111-1of the ramp mechanism111to return to the magnetic disk160(this is called a load operation). At the time of this load operation, for example the velocity is detected based on the back-electromotive force of the VCM (actuator) driving the magnetic head110, and the velocity is controlled at a prescribed velocity to load the magnetic head110and prevent crashes.

In the prior art, when seeking in the outward direction, if a seek error occurs the magnetic head110is immediately stopped, and a current flows in the inward direction (current in the opposite direction), causing motion in the inward direction, to perform a seek error retry (see for example Japanese Patent Laid-open No. 2004-178790).

In recent years, the densities of magnetic disks160have risen and the area up to the outermost perimeter have been used as a data zone, in order to increase storage capacities; and in order not to detract from performance as capacities are increased, there has been a demand for faster seek velocities. For example, in sampled servo operation during seeking, the head moves over 200 to 300 tracks for one sample.

Hence in the prior art, when there is a degree of velocity outward during seek error detection, and when seek error detection is delayed, there is the danger that the head110may ride over the ramp mechanism111. If current in the inward direction is begun in this state, due to high-speed loading action the head110may collide with the magnetic disk160, causing a crash between the magnetic head110and magnetic disk160.

In particular, when the disk storage density is high and the data zone is extended outward for increased storage capacity, if a seek error occurs during outward-direction seeking, the head may readily climb onto the ramp mechanism.

SUMMARY OF THE INVENTION

Hence an object of this invention is to provide a seek error retry method of a disk device and its disk device having a ramp-load mechanism, to safely execute seek error retries.

A further object of this invention is to provide a disk device seek error retry method of a disk device and a disk device to prevent crashes between head and disk during seek error retries.

Still a further object of this invention is to provide a seek error retry method of a disk device and a disk device to prevent crashes between head and disk during seek error retries, without increasing the retry time.

Still a further object of this invention is to provide a seek error retry method of a disk device and a disk device to safely execute seek error retries, and to realize fast operation and large storage capacities.

In order to achieve these objects, a seek error retry method of this invention has a step of judging whether the head has climbed onto the ramp provided to retract the head, in response to seek error detection; a step, when the judgment indicates that the head has not climbed onto the ramp, of again seeking the head to the desired track; a step, when the judgment indicates that the head has climbed onto the ramp, of unloading the head from the ramp and then loading the head from the ramp onto the disk; and a step, after this loading, of again seeking the head to the desired track.

A disk device of this invention has a head which at least reads information on a disk, an actuator which seeks a desired track position on the disk, a control unit which controls the actuator according to output from the head, detects seek errors, and performs retry processing, and a ramp provided to retract the head from the disk. And the control unit judges whether the head has climbed onto the ramp, in response to seek error detection, and if according to the judgment the head has not climbed onto the ramp, again seeks the head to the desired track, but if according to the judgment the head has climbed onto the ramp, after unloading the head from the ramp, loads the head from the ramp onto the disk, and after this loading, again seeks the head to the desired track.

Further, it is preferable that in this invention, the judgment step comprise a step of judging, from the head output, whether the head has climbed onto the ramp.

Further, it is preferable that in this invention, the judgment step comprise a step of judging, from the gain of the AGC circuit performing AGC control of the output of the head, whether the head has climbed onto the ramp.

Further, it is preferable that in this invention, the again seek step further have a step of detecting whether a seek error has occurred, and, when a seek error is detected, a step of again executing the above judgment step.

Further, it is preferable that in this invention, the load step comprise a step of performing velocity control of the head movement to load the head onto the disk.

Further, it is preferable that this invention further have a step of limiting the number of executions of the above repeated execution step.

Further, it is preferable that in this invention, the judgment step comprise a step of judging whether the head has climbed onto the ramp, in response to a seek error due to detection of the absence in the head output of servo information written to the disk.

Further, it is preferable that in this invention, the judgment step comprise a step of judging, from the output of the magnetic head which is the above head which reads servo information written to the magnetic disk which is the above disk, whether the head has climbed onto the ramp.

Further, it is preferable that in this invention, the load step comprise a step of executing unload processing to retract the head to the ramp and load processing.

Prior to beginning seek retry at the time of a seek error retry, a check is performed to determine whether the head has climbed onto the ramp, and if the head has not climbed onto the ramp a normal seek retry is performed, but if the head has climbed onto the ramp, load and unload process is performed again form the unloading before the seek retry. Consequently crashes caused by ramp-climbing due to seek errors in a device adopting the ramp-load method can be prevented, and improved device reliability can be expected. Moreover, unloading and loading are not performed each time during seek errors, so that the retry time can be shortened, and ramp wear and similar can also be prevented. Further, the normal unload/load functions of a device adopting the ramp-load method are used, so that the invention can be realized without adding special functions.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Below, embodiments of the invention are explained, in the order of a disk device, seek error retry processing, and other embodiments.

Disk Device

FIG. 1shows the configuration of the magnetic disk device of a first embodiment of the invention,FIG. 2is a cross-sectional view of the ramp mechanism ofFIG. 1,FIG. 3is a top view of the ramp mechanism ofFIG. 1, andFIG. 4is a block diagram of the control unit in the magnetic disk device ofFIG. 1. As the disk device, the example of a magnetic disk device is shown.

As shown inFIG. 1, the magnetic disk drive10has a magnetic disk12; a spindle motor14which rotates the magnetic disk12; an arm16having at the tip a head slider comprising a magnetic head26; a VCM (Voice Coil Motor)18which moves the arm16, comprising the head slider, in the radial direction of the magnetic disk12; and a ramp20, provided on the outer perimeter of the magnetic disk12, to which the arm16is retracted.

The VCM18comprises a fixed magnet and a driving coil provided at the posterior end of the arm16. The arm16comprises a swing arm which rotates about a rotation axis24. The VCM18is provided with an inner stopper22, which limits the inner-perimeter position of the arm16.

The arm16and ramp20are explained usingFIG. 2andFIG. 3. The ramp20comprises an inclined surface20-1, which rises at an incline from the side of the magnetic disk12; a first level surface20-2which continues from the inclined surface; and a groove portion20-3, continuing from the first level surface20-2, provided between the first level surface20-2and a second level surface20-4.

On the other hand, a lift28(seeFIG. 3) is provided at the tip of the arm16, and a head slider26comprising a magnetic head is provided at the top of the arm16. The magnetic head may be called as sign ‘26’ below. A head unload (retraction) operation is an operation in which, by moving the arm16rightward inFIG. 2andFIG. 3, the lift28of the arm16climbs over the inclined surface20-1of the ramp20, past the first level surface20-2to reach the groove portion20-3, and is stopped by the step portion with the second level surface20-4. By this means the lift28falls precisely into the groove portion20-3and is parked.

Conversely, a head load operation is an operation in which the arm16, parked in the groove portion20-3, is moved leftward inFIG. 2andFIG. 3, so that the lift28climbs over the inclined surface of the groove portion20-3and the first level surface20-2, and slides down the inclined surface20-1, so that the arm16comprising the head is returned to above the magnetic disk12.

This load and unload operation is performed by driving the VCM18. As is well known, during this load operation, the velocity is detected from the back-electromotive force of the VCM (actuator)18driving the arm16comprising the magnetic head, and the VCM18is velocity-controlled so that the magnetic head is loaded onto the magnetic disk12at a prescribed velocity, to prevent crashes.

FIG. 4is a block diagram of the control circuit3of the disk drive inFIG. 1, and in particular shows IC chip units. The HDC (hard disk controller) chip5controls the interface with the host CPU (not shown), including exchange of data and various commands with the host CPU, and generates control signals within the magnetic disk drive to control the recording and reproduction format on the magnetic disk12.

The MCU (microcontroller) chip7comprises a microprocessor (MPU) and similar. The MCU7executes servo control to position the magnetic head26. The MCU7executes a program stored in memory, not shown, recognizes head position signals (servo information recognition and demodulation), and performs computation of control current values for the VCM18and SPM14of the SVC (Servo Combo Driver)11, by means of servo control operations.

Further, the MCU7performs seek control processing and seek error retry processing, described below. The SVC chip11is a driving circuit for the spindle motor (SPM)14and VCM18ofFIG. 1, and has a VCM driver36and spindle driver37.

The read channel chip9is a circuit to perform recording and reproduction. The read channel9has an AGC circuit90comprising a peak hold circuit and an integrated circuit as a circuit for demodulating servo patterns recorded on the magnetic disk12, a modulation circuit to record write data from the host CPU onto the magnetic disk12, and a demodulation circuit to reproduce data from the magnetic disk12.

The preamp19, installed on the arm16, amplifies the reproduced voltage from the magnetic head26and outputs the result to the read channel chip9.

By means of this configuration, the AGC (Automatic Gain Control) circuit90of the read channel chip9controls the reproduced voltage gain according to the reproduced voltage, so that the magnetic head reproduced voltage from the preamp19is held at a prescribed voltage.

Seek Error Retry Processing

FIG. 5is a diagram of the flow of seek processing in the first embodiment of the invention,FIG. 6is a diagram of the flow of seek error retry processing, andFIG. 7andFIG. 8explain seek error retry operation. First, seek processing is explained usingFIG. 5.

(S10) Upon initiating seek, a coarse control velocity curve is formed according to the distance between the current position of the magnetic head26and the seek target position. First the MCU7samples the read output of the magnetic head26via the read channel9and detects servo information.

(S12) The MCU7demodulates the read output servo information to obtain the current position. As stated above, a track number indicated by a gray code and an offset burst pattern A, B, C, D are recorded, as servo information, on each track.

(S14) The MCU7judges whether demodulation has succeeded. For example, there are cases in which servo information cannot be detected from the read output, and the demodulated position cannot be obtained. Moreover, in coarse velocity control, when the error between the current position at the current sample as predicted from the previous sample and the current position detected from the current sample is large, demodulation is judged to have failed.

(S16) Upon judging that demodulation has failed, the MCU7judges whether demodulation failures have been continuous. For example, a judgment is made as to whether demodulation failures have continued for a number n of samples (for example, n=3). If demodulation failures have continued for a prescribed number of times, control is executed to halt operation due to a seek error. If on the other hand demodulation failures have not continued for the prescribed number of times, processing returns to step S10.

(S18) When demodulation is successful, the MCU7judges whether the demodulated current position is the target position. If the demodulated current position is not the target position, coarse control or fine control is executed, according to the position error. For example, if the position error between the target position and the current position is large, control is executed according to the velocity error between the target velocity and the current velocity based on the position error, according to the above-described coarse control velocity curve. This current velocity is obtained by dividing the difference between the current position at the time of the previous sample and the current position at the time of the current sample by the sample interval. If the position error is within a prescribed range (for example, 0.5 tracks), a transition is made to fine control (position control). Processing then returns to step S10. On the other hand, if the demodulated current position is the target position, seeking ends, and fine control (following control) is continued.

Next, seek error retry processing is explained usingFIG. 6, referring toFIG. 7andFIG. 8. In this processing, at the time of occurrence of a seek error, a check is performed to determine whether the magnetic head26has climbed onto the ramp20, and the retry method is changed according to whether the head has or has not climbed onto the ramp20.

(S20) When, in step S16ofFIG. 5, a seek error is detected, seek error retry processing is begun.

(S22) The MCU7judges whether the magnetic head26has climbed onto the ramp20, as inFIG. 8. As the method of checking for climbing onto the ramp, MCU7monitors the raw waveform of the magnetic head26output from the head IC (preamp)19, and if the waveform vanishes (the AC component is substantially “0”), MCU7judges that the head26has climbed onto the ramp20. For example, if the waveform vanishes, when the AGC circuit90of the read channel9attempts to amplify the waveform, the gain continuously becomes at maximum gain. The firmware of the MCU7then monitors whether sticking (the continue of the maximum gain) of the gain of the AGC circuit90occurs. As shown inFIG. 7, when as a result of this check MCU7judges that the head26not have climbed onto the ramp20, processing advances to step S26.

(S24) If on the other hand the magnetic head26is judged to have climbed onto the ramp20, the MCU7executes the above unload control. That is, the MCU7drives the VCM18to move the arm16rightward inFIG. 8. By this means the lift28of the arm16climbs onto the inclined surface20-1of the ramp20and over the first level surface20-2to reach the groove portion20-3, and stops at the step portion with the second level surface20-4. As a result, the lift28falls precisely into the groove portion20-3and is parked. Next, the MCU7performs the above-described load operation. That is, the MCU7drives the VCM18to move the arm16, which is parked in the groove portion20-3, leftward inFIG. 8. By this means the lift28climbs over the inclined surface of the groove portion20-3and the first level surface20-2, and slides down the inclined surface20-1, so that the arm16comprising the head26is returned to above the magnetic disk12. As is well known, at the time of this load operation the velocity is detected from the back-electromotive force of the VCM (actuator)18driving the arm16comprising the magnetic head, and the VCM18is velocity-controlled to load the magnetic head onto the magnetic disk12at a prescribed velocity, to prevent crashing.

(S26) The MCU7drives the VCM18to move the magnetic head26in seek movement inward over the magnetic disk12, and tracks to the prescribed track. The MCU7takes the tracking position as the current position, and causes the magnetic head26to seek to the target track through the seek processing of the above-describedFIG. 5.

(S28) The MCU7judges whether seeking has ended normally. The MCU7judges, for example, whether the above-described seek error has occurred. If seeking has ended normally, seek error retry ends. On the other hand, if seeking does not end normally, a judgment is made as to whether the number of retries is within a stipulated number. If the number of retries is within the stipulated number, processing ends with an error, and processing returns to step S22. If the number of retries exceeds the stipulated number, processing ends anomalously.

In this way, immediately before beginning inner servo operation (seeking to an inner track) when seek error retry, a check is performed to determine whether the head26has climbed onto the ramp20. If the head26has not climbed onto the ramp20, normal inward servo operation is executed; if the head26has climbed onto the ramp20, unloading is performed before restarting (unload→load→inward servo seek).

Consequently in a ramp-load device, crashes due to the head climbing onto the ramp as a result of seek errors can be avoided, and improved device reliability can be expected. Further, unload and load operations are not performed each time a seek error occurs, so that the retry time can be shortened, and wear of the ramp20and similar can be prevented.

Moreover, because the normal unload/load functions of a ramp-load device are utilized, this embodiment can be realized without adding special functions. Further, the gain of the AGC circuit is monitored for sticking to judge whether the head has climbed onto the ramp20, so that judgment can be performed simply by the firmware without providing a special mechanism.

OTHER EMBODIMENTS

In the above-described embodiment, the AGC gain is used to judge whether the head has climbed onto the ramp; but judgment may also be made based on the raw waveform of the magnetic head, or another mechanism to detect climbing onto the ramp may be provided.

Further, in addition to a magnetic disk device, application to an optical disk device, magneto-optical disk device, or similar is also possible. Also, application to ramp mechanisms with other shapes and arbitrary configurations is possible.

In the above, this invention has been explained through an embodiment, but various modifications can be made within the scope of the invention, and these modifications are not excluded from the scope of the invention.

At the time of seek error retry, prior to beginning seek retry a check is performed to determine whether the head has climbed onto the ramp, and if the head has not climbed onto the ramp normal seek retry is performed, but if the head has climbed onto the ramp an unload operation is first performed before the seek retry. Consequently crashes due to the head climbing onto the ramp as a result of a seek error in a ramp-load device can be prevented, and improvement of the device reliability can be expected, contributing to higher device recording densities and faster operation.