Patent Application
20090009904
The instant nonprovisional patent application claims priority to Japanese Patent Application No. 2007-167723 filed Jun. 26, 2007 and which is incorporated by reference in its entirety herein for all purposes.
With a magnetic disk drive, signals for detection of a head position, in numbers ranging from scores to not less than a hundred, per one cycle, are continuously disposed across a whole region in a radial direction on a recording surface (hereinafter referred to as a servo pattern). Work for writing the servo pattern is called servo write, and is generally executed in a process for production of a magnetic disk drive. As one form for executing the servo-write, there is a method called self servowrite, whereby the magnetic disk drive executes positioning of a head, and timing control by reading a pattern written by itself to thereby write the servo pattern.
In the self servowrite, there is repeatedly executed an action (called a self-propagation action) for spreading the pattern by writing a new track while executing the positioning of the head by reading the pattern written by the magnetic disk drive itself. Accordingly, a write element and a read element are disposed on a slider face of a head so as to be radially offset from each other such that a pattern formed by the write element at a stage can be read by the read element later on.
At the initial stage of the self servowrite, however, nothing is written on a recording face of a disk, and consequently, with the disk as it is, a pattern written to the disk by the write element cannot be read by the read element. For this reason, it is necessary to form a pattern (hereinafter referred to as an initial pattern) enabling the self-propagation action to be executed by means of any method at a stage prior to the start of the self-propagation action. With the self-propagation action, because positioning control of the head, in a radial direction, is executed on the basis of a pattern as-read, it is required that the initial pattern is capable of detecting the positioning of the head, in the radial direction, by reading itself, and a pattern formation range is continuously formed over a wide range (in general, corresponding to several tracks) sufficient to cover both the read element, and the write element.
In Japanese Patent Publication No. 2004-185682 (“Patent Document 1”), in order to write such a pattern as described, there is disclosed a method whereby bias current in a given direction is applied to an actuator supporting a head at the stage of starting the self servowrite to thereby firmly press the actuator to an inner peripheral crash-stop so as to hold a head position, and in that state, the current applied to the actuator is gradually decreased, thereby writing the pattern while moving the head little by little toward the outer periphery. With this method, by taking advantage of pressing of the actuator by the agency of the bias current, and elastic deformation of the crash-stop, patterns spread in a radial direction can be written even at a stage where a read signal cannot read.
The above-described method of executing fine shifting of the head in order to write the initial pattern by adjustment of the magnitude of the bias current is based on the premise that an output resolution of a driver circuit for driving the actuator, and a dynamic range can be sufficiently secured against a track pitch of the servo pattern to be written. However, with the latest magnetic disk drive having a high recording density, the width of one track has since decreased to a level as small as 200 nm or less, so that there is no denying the possibility that with the method using the adjustment of the magnitude of the bias current, described as above, if future enhancement in track density is taken into consideration, a problem of insufficient resolution of the driver circuit will arise. Further, there is also a possibility of occurrence of problems such as a change in bias force, due to variation in temperature, and so forth, inability of securing reproducibility of a relationship between applied current and a head position, due to variation in properties of the crash-stop, and so forth.
There is the possibility that the dynamic range of VCM bias current becomes insufficient at the time of forming the initial pattern for the self servowrite. Further, it becomes impossible to secure the reproducibility of the relationship between applied current and a head position, due to variation in properties of the VCM, and the crash-stop, attributable to variation in temperature.
Embodiments of the present invention provide a method of forming an initial servo-pattern for self servowrite, insusceptible to constraints of an output resolution of a driver circuit for driving an actuator, and a dynamic range. According to the embodiment of
a) and 6(b) are views showing a relationship between a radial position of a read element when reading the cluster pattern, and a waveform amplitude as obtained.
a) and 9(b) are views showing a basic concept, based on which adjustment is made on a difference between the waveform amplitude target for positioning on an inner peripheral edge, and that on an outer peripheral edge on the basis of a way in which bursts of the third cluster pattern overlap each other.
Embodiments of the present invention relate to a magnetic disk drive, and in particular, to self servowrite for writing servo signals without the use of an external actuator, and a clock head.
It is an object of embodiments of the present invention to provide a method of forming an initial servo-pattern for self servowrite insusceptible to constraints of an output resolution of a driver circuit for driving an actuator, and a dynamic range.
Another object of embodiments of the present invention is to provide a magnetic disk drive capable of implementing self servowrite by a feedback operation on the basis of a read waveform as-read by a read element.
A feature of embodiments of the present invention lies in that instead of holding a position of the magnetic head by applying a given bias current at the stage of forming the initial servo-pattern for the self servowrite, a relative position of the magnetic head against the pattern written on the magnetic disk is held by dynamically adjusting current applied to the actuator by a feedback operation based on a read waveform as-read with the read element. By so doing, the initial servo-pattern for the self servowrite is formed without being subjected to the constraints of the output resolution of the driver circuit for driving the actuator, and the dynamic range.
More specifically, a method for forming a servo-pattern according to embodiments of the present invention comprises the steps of writing a cluster pattern made up of pattern blocks, each including a burst pattern, by use of a write element, at the stage of forming an initial servo pattern by pressing a head-support mechanism to a crash-stop with the use of a magnetic head having a read element offset on an inner peripheral side of the write element, and newly writing a pattern block with the read element in states of being positioned at an inner peripheral side edge of the cluster pattern, an outer peripheral side edge thereof, and the center of two burst patterns included in the cluster pattern, respectively, thereby writing a cluster pattern having pattern blocks greater by one in numbers than the pattern blocks of the cluster pattern, wherein by sequentially changing a cluster pattern for use in positioning into a newly written cluster pattern thereafter, an operation for writing a cluster pattern is repeated, and a width of the cluster patterns is increased in stages, thereby forming the initial servo pattern for use in a propagation action.
A magnetic disk drive according to embodiments of the present invention comprises a magnetic disk, a magnetic head having a read element offset on an inner peripheral side of a write element, and a control circuit for controlling an operation for positioning of the magnetic head against the magnetic disk, and write/read operations of the magnetic head, wherein a cluster pattern made up of pattern blocks, each including a burst pattern, is written by use of the write element at the stage of forming an initial servo pattern by pressing a head-support mechanism to a crash-stop under control by the control circuit, a pattern block is newly written with the read element in states of being positioned at an inner peripheral side edge of the cluster pattern, an outer peripheral side edge thereof, and the center of two burst patterns included in the cluster pattern, respectively, to thereby write a cluster pattern having pattern blocks greater by one in numbers than the pattern blocks of the cluster pattern, a cluster pattern for use in positioning is sequentially changed into a newly written cluster pattern thereafter, an operation for writing the cluster pattern is repeated to thereby increase a width of the cluster patterns in stages, and the initial servo pattern for use in a propagation action is formed.
With the embodiments of the present invention, it is possible to provide the method of forming the initial servo-pattern for self servowrite insusceptible to the constraints of the output resolution of the driver circuit for driving the actuator, and the dynamic range.
Further, it is possible to provide the magnetic disk drive capable of implementing the self servowrite by the feedback operation on the basis of the read waveform as-read by the read element.
Described hereinafter are embodiments of a magnetic disk drive, and a method for forming a servo pattern, respectively, according to embodiments of the present invention.
With the magnetic disk drive made up as above, described hereinafter is the function of a control circuit for implementing the write/read operations of the magnetic head, for writing information to, and reading information from the magnetic disk with reference to
An operation procedure of the magnetic disk drive 200 is written as a program to be executed by the microprocessor 236, and the program is stored in regions in the memory 238. The microprocessor 236 executes generation of a write signal against the magnetic disk 202, and demodulation of a read signal via the signal processing circuit 234. Meanwhile, the microprocessor 236 further executes control of the operation of the spindle motor via the motor driver IC 242, and control of positioning of the magnetic head by driving the VCM. The hard disk controller 240 provides the microprocessor 236 with respective accesses to peripheral functions such as the signal processing circuit 234, the motor driver IC 242, and so forth, and an access to a host computer (not shown).
Now, a procedure for self servowrite in common use is first described with reference to
The method for forming the initial servo-pattern according to the embodiments of the invention relates to a startup action (S1003) among series of steps of the procedure described as above. The method has a feature lying in that patterns called cluster patterns, each having servo information, and trigger information, written so as to be connected together to have a width in a radial direction, corresponding to several steps, by aligning in phase with each other, are formed at the stage of the startup action, and a new cluster pattern, having a width spread by one step, is sequentially written while executing positioning against the respective cluster patterns to thereby form the initial servo-pattern for the self-propagation action, greater in width than an offset between the read element, and the write element (hereinafter referred to as an RF offset).
An operation for forming the initial pattern according to embodiments of the invention is described hereinafter with reference to
The cluster patterns are sequentially written by increasing the number of stages, such as a first stage, a second stage, and so forth, starting from the inner peripheral side. First, upon writing a first cluster pattern 104-1, positioning of the read element 203b on the top of the first cluster pattern 104-1 is executed, thereby writing a second cluster pattern 104-2. The second cluster pattern 104-2 is positioned on the outer peripheral side further by the RF offset as seen from the first cluster pattern 104-1. At this point in time, writing is executed with the read element 203b at two sites slightly off from the center of the pattern, the cluster pattern in the second stage is formed from the cluster pattern in the first stage. Since writing is executed by triggering against one pattern, consistency in phase of the cluster pattern in the second stage is secured. Similarly, by executing positioning of the read element 203b on the top of the second cluster pattern 104-2, a third cluster pattern 104-3 is written, and by executing positioning of the read element 203b on the top of the third cluster pattern 104-3, a fourth cluster pattern 104-4 is written. By sequentially increasing the number of the stages of the cluster patterns, the pattern spreads in width, and in the case of the embodiment shown in
Further, a makeup of the cluster pattern is described with reference to
At the head of the servo information unit 101, there are provided a preamble 101a for an automatic gain adjustment (Automatic Gain Control: hereinafter referred to as AGC), and detection of a waveform phase, and a servo address marker 101b continuing thereto, to be used for adjustment of a gain of an amplifier in an AGC circuit such that an amplitude of a waveform will be at an adequate level at the time of reading, and for aligning a detector in phase with the waveform. There is provided a track ID code 101c behind the address marker 101b. Behind the servo information unit 101, the burst 102 for detecting a radial position of the head is disposed. A burst pattern is divided into four segments in a circumferential direction, that is, 102a (burst A), 102b (burst B), 102c (burst C), and 102d (burst D), and the bursts in the respective segments, each having a width of the write element 203a, are disposed so as to be offset from each other in the radial direction of the disk.
The trigger block 103 comprises a trigger field 103a for detection of a waveform phase, and a trigger marker 103b. The signal processing circuit 234 can accurately synchronize with the waveform phase of the pattern written on the magnetic disk by reading the trigger block 103. Further, according to embodiments of the present invention, the trigger block 103 is independently disposed behind the servo block, however, if the hard disk controller 240 corresponds to the signal processing circuit 234, the trigger block 103 may be disposed in reverse order thereto, or if the function for synchronization with the waveform phase of the pattern can be shared between the trigger block 103 and the address marker 101b, the trigger block 103 may be omitted by leaving out the address marker 101b only.
A configuration for forming the cluster pattern by combining the pattern blocks shown in
When writing the fourth cluster pattern 104-4 from the third cluster pattern 104-3, a new pattern block is formed by executing positioning of the read element 203b at four sites of an inner peripheral edge 401-1, the center 401-2 of the burst A, and the burst B, the center 401-3 of the burst B and the burst C, and an outer peripheral edge 401-4.
Shown at 402-1, 402-2, 402-3, and 402-4 are respective waveforms of patterns as read when the read element 203b is at respective radial positions 401-1, 401-2, 401-3, and 401-4. A positioning action will be described in detail later in the present specification, but to take the case of the positioning at the center 401-3 between the burst B and the burst C as an example, the positioning is implemented by the microprocessor 236 adjusting current applied to the VCM 206 on the basis of a difference between amplitudes 403b, 403c in the burst.
Upon completion of writing, i_layer is incremented by one (step S508), thereby determining which of i_layer, and i_cluster is greater in value (step S509). If i_layer is smaller in value, the positioning is made at the center of the two bursts (step S513), thereby writing an i_layer-th servo-trigger block (step S514).
On the other hand, if i_layer is greater in value, the positioning at the outer peripheral edge is executed (step S510), thereby writing an i_layer-th pattern block (step S511). Upon completion of the writing, checking is executed on whether or not the cluster pattern formed at the outer peripheral edge has spread to a degree sufficient to enable the self-propagation action to be started (step S512). Such checking can be executed by seeing whether or not the newly written cluster pattern at the position of the outer peripheral edge after the completion of the writing can be read, and if yes, by detecting position information obtainable from the newly written cluster pattern to thereby find out an extent to which the newly written cluster pattern overlaps the cluster pattern at the position already determined, along the radial direction. If such overlapping is found sufficient, the newly written cluster pattern can be used as the initial pattern for the self-propagation action, so that a forming operation is completed, whereupon the procedure proceeds to the next step. On the other hand, if an overlapping width is found insufficient, the procedure reverts to the step S503, and a target for the positioning is changed to the cluster pattern previously written, whereupon operations from the step S503 to the step S514 are repeated to thereby record a new cluster pattern.
At the present stage as described, since i_cluster is 1 while i_layer is 2 in the step S509, positioning at the outer peripheral edge is executed, thereby writing a 12th pattern block of the second cluster pattern. At a point in time when the writing is completed, the first and second cluster patterns do not overlap each other in the radial direction, so that the procedure reverts to the step S503 to execute positioning at the second cluster pattern 104-2, thereby executing an operation for writing the third cluster pattern 104-3. Thereafter, an operation for similarly writing a new cluster pattern is repeated, and an operation for forming the initial pattern is completed at a point in time when overlapping between the cluster patterns is obtained in the step S512.
Next, there are described hereinafter operations for positioning toward the cluster patterns, executed in the steps S505, S510, and S513, respectively, in
a) is a view showing a state in which a read waveform amplitude undergoes a change depending on a relationship between the first cluster pattern and the read element when the read element passes over the pattern. The amplitude of the waveform of the pattern read by the read element will have a profile shown at 601 depending on a positional relationship between the read element 203b, and the pattern. However, when reading a pattern with a width corresponding to several tracks at most, as in the case of the cluster pattern, a gain of the AGC circuit, at the edge, will vary from that at the center, so that, in order to obtain a relationship of the read waveform amplitude against a read position, as indicated at 601, either the amplitude of the burst is detected by fixing the gain of the AGC circuit, or the reciprocal of the gain of the AGC circuit after adjustment is used as a substitute of the waveform amplitude. In the following description, it is assumed that the reciprocal of the gain of the AGC circuit is used.
In the case where the positioning of the read element 203b at a position of the inner peripheral side edge 602-1 is executed in a state of an amplitude profile indicated at 601 in
Updating of an output current value of the VCM may be executed on the sector-by-sector-basis, however, since the head-support mechanism 204 is in contact with the crash-stop 207 in this stage, there is not much change in position of the magnetic head within a time range substantially corresponding to an interval between the sectors, updating cycles may be reduced without any problem.
In the case of positioning at the outer peripheral edge, the positioning can be implemented by the same operations as described above although there has to be a change in deviation from the target value, and in polarity for causing the VCM current to undergo variation. In
Meanwhile, referring to
Referring to
The initial pattern for the self-propagation action can be formed by executing a series of the operations described as above. However, in order to form the servo pattern with fewer errors in track pitch, it is also required to accurately control the shift pitch of the initial pattern.
Now, a method for controlling the pitch of the initial pattern is further described with reference to
What is the adequate order of magnitude of a set difference between respective waveform amplitude target values on the inner periphery, and on the outer periphery is dependent on the characteristics of individual magnetic heads, so that write/read operations are preferably tried first with a magnetic head to be actually used in the process of the self servowrite operation, thereby setting the difference on the basis of results of such a trial operation.
Accordingly, referring to
For example, if a pre-set difference between the respective waveform target values is too large, a position determined on the basis of the edge on the outer peripheral side will end up on a side of the pattern, inner than the inner side edge thereof. An example of such a case is shown in
In the case of executing the above-described operation in the process of forming the initial pattern, the cluster patterns up to the third cluster pattern are formed by use of a pre-set initial value to thereby compare the amplitude value 903-1 with the amplitude value 903-2, and if a difference therebetween is found inadequate, the difference between the respective waveform amplitude target values on the inner and outer peripheries is adjusted on the basis of results of determination to thereby erase the cluster pattern as formed, whereupon writing of the cluster patterns may be started again.
If the difference between the respective waveform amplitude target values on the inner and outer peripheries is set to the adequate value, the amplitude value 903-1 at a position 902-1 coincides with the amplitude value 903-2 at a position 902-2 as shown in
The operation for forming the initial pattern for the self servowrite with the magnetic disk drive according to embodiments of the present invention has been described in the foregoing. With the present embodiments, the positioning of the head after writing of a first pattern is all executed by a feedback operation using the waveform amplitudes of the pattern as written, so that it is possible to relax resolution required of the motor driver, and conditions of the dynamic range, as compared with the conventional case where the bias current for pressing the head-support mechanism to the crash stop is applied by use of open-loop control. Further, even if there exist variation in characteristics of the VCM and the crash stop, and variation in bias force, due to variation in temperature, and so forth, it is possible to provide a stable operation. Furthermore, since a circuit configuration for controlling the servo write work of the magnetic disk drive according to the present embodiments is in common with that of a control circuit for a magnetic disk drive as a common product, this can contribute to inexpensive means provided for the servo write.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2007-167723 | Jun 2007 | JP | national |
