JPH0287379A - magnetic disk device - Google Patents

Abstract

PURPOSE:To attain the positioning of a highly accurate data head by detecting an off-track quantity of a data head during seek. CONSTITUTION:The device is so constituted that an off-track of all data heads 2 during seek is detected and stored and the off-track is offset at the changeover of the heads 2. In this case, in order to detect the off-track from an output of the data head 2, a specific pattern for position detection is provided in the data or at a specific position and the position of the head 2 is detected by the amplitude of the pattern. Since the off-track of the data head 2 is discriminated from an output of the data head 2, the data head 2 is positioned with high accuracy without revising a conventional servo face servo system.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a head positioning method for a magnetic disk device.

[Prior Art] Conventional head positioning systems for magnetic disk devices include: 1.
One side of the multiple disks is dedicated to the servo,
2. A servo surface servo system in which the data head is configured to maintain a specific relationship with the servo head using a mechanical system; As in Japanese Patent Application Laid-Open No. 52-80814, the servo signal is configured to coexist on the data surface, and the data head itself
3. data surface servo system for head positioning; Three basic systems are known, including a system that combines the servo surface servo system and the data surface servo system as disclosed in Japanese Patent Application Laid-Open No. 53-95005.

[Problems to be Solved by the Invention] The conventional servo surface servo method described above is the mainstream technology, but since it does not detect changes in the data head itself, it is difficult to maintain positioning accuracy due to thermal displacement, etc. The problem is that it is difficult to improve.

In the sector servo system as disclosed in Japanese Patent Application Laid-Open No. 52-80814, the position signal is intermittent, so there are problems in increasing the seek speed and increasing the servo band. Japanese Patent Publication No. 53-95005
In the combined method of servo surface servo method and data surface servo method, the data area is reduced because the servo signal is written on the data surface, and the servo signal is also written on the data surface.

There were problems such as an increase in manufacturing costs and a time-consuming correction of radical misalignment after head switching.

The present invention aims to eliminate positioning errors caused by data head temperature changes, etc., without making major changes to the conventional servo surface servo system.

[Means for Solving the Problems] In order to achieve the above object, a means is provided for estimating the amount of off-track of the data head from the output of the data head, and a method is provided to offset the servo head in order to correct the amount of off-track. It is composed of

More specifically, in order to detect the amount of off-track from the output of the data head, a specific pattern for position detection is provided in the data or at a specific location, and the head position is detected by the amplitude path of the pattern. It is structured like this.

More specifically, the signal amplitude for position detection by the data head is calibrated using the head output near the target track in order to calibrate differences in output such as track position.

Furthermore, since the off-track amount detection by the data head is performed before arriving at the target track, that is, during seek, the off-track amount is taken into consideration when moving to the following operation in order to shorten the access time of the spatula 1z. It is something.

Furthermore, in order to reduce the head movement time after switching between heads in a device with many heads, the off-track amount of all data heads is detected and saved during seek, and the off-track amount of all data heads is detected and saved when the head is switched. This offsets the amount of off-track.

Furthermore, in devices that use both servo surface servo and data surface servo, the amount of off-track between the data head and the servo head is detected during seek to shorten access time, and when moving from seek mode to following mode, feed It is a forward off-track.

[Operation Co. Since the off-track amount of the data head can be determined from the output of the data head, high-precision positioning can be performed without making any major changes to the conventional servo surface servo system. In addition, by determining a specific location when detecting off-track of the data head, it is possible to take into account adjacent positions, thereby enabling accurate off-track detection. Furthermore, since the off-track amount can be detected during seek, the head settling time can be shortened by feedforward control, and the switching time can also be shortened when switching heads.

[Example code] Hereinafter, one embodiment of the present invention will be described with reference to the drawings.

FIG. 1 is a diagram showing a schematic configuration of an embodiment of the present invention.

One surface of the stacked magnetic disks 1 is a servo-dedicated disk, and the data head 2 is positioned using position information detected by the servo head 3. The data head and servo head are mechanically connected by the carriage 5, but temperature changes.

There is a slight deviation due to temperature distribution, etc. (for example, off-track during recording and playback). One object of the present invention is to correct the above-mentioned off-track amount of the data head. The configuration example shown in FIG. 1 will be explained below in sequence, but first, a conventional servo loop will be explained. In the follow-in group, the signal reproduced by the servo head 3 is converted into a position error signal by the position demodulator 6, and after receiving appropriate compensation by the compensator 7, is sent to the power amplifier 12. This constitutes a loop that is fed back to the voice coil motor 4 and performs track following. On the way, a switch 11 is used to switch between the velocity loop and the follow-in loop, and is controlled by a control signal A. A velocity loop is a loop for moving the head from the current track to another track. First, based on a command from a controller (not shown), the number of moving tracks is set in the counter 9, and at the same time, the switch 11 is switched to the speed loop system. Speed guide generator 1 according to the value of counter 9 to control at a speed determined according to the moving distance
0, a speed guide signal is generated, a difference signal from the speed is fed back to the power amplifier, and the target track is moved so that the speed matches the speed guide. The value of counter 9 is decremented every time the vehicle moves one track, and becomes zero when the target track is reached. The track cross pulse generator 13 generates a pulse every time the track moves by one track based on the position error signal. The electronic tachometer 8 detects speed based on the current flowing to the voice coil motor and position information. The outline of the conventional technology has been described above. Next, the present invention will be explained.

The present invention is to detect the amount of off-track of the data head based on the signal from the data head 2, and to offset the servo head in accordance with the amount of error. Therefore,
First, off-track detection of the data head will be described. As shown in Figure 3, the reproduction circuit of the data head is constructed by increasing IJ with a preamplifier 21, adjusting the gain of an AGC (auto gain control) amplifier 22 to maintain a constant amplitude, and then using an LPF (low pass filter). 23 and is input to the signal discrimination system. In the present invention, since the amount of position change is made responsive to the signal amplitude 11, when detecting a position error, A
The GC 22 makes the feedback voltage a constant value of Vc by the control signal C of the switch 24 so that it functions as a simple amplifier. (When detecting data, switch 24 is switched to use the output of envelope circuit 15 as a feedback signal.) Figure 2 shows the position and envelope circuit output (EV
) shows the relationship. At this time, if the signals are written in an arbitrary pattern between tracks, the periodicity will deteriorate, so the pattern used for position error detection should be a regular pattern including between adjacent tracks. This matter will be discussed later. In addition, since position error detection is actually performed during data detection, it is performed intermittently at certain time intervals, but in FIG. 2, it is shown as a continuous signal for the purpose of explanation. The off-track detection of data heads will be described in detail below with reference to FIG. In FIG. 2, in addition to the envelope change (Ev) of the data head, there is also a position error signal (pos) demodulated from the servo head.

) is also described. Now, if the target track of the servo head is XT, (XT-1,) (well, it is one track before the target track.Here, if the off-track amount of the data head is ΔX, the maximum value of the Ev output is from x7. The problem in the figure is to estimate the position of the maximum value of Ev by the time the head arrives at the target trunk.The method for this estimation is shown next. The method of directly detecting the maximum value has poor accuracy because it is insensitive.Also, in order to detect the maximum value on the target track, it is necessary to fob the head back and forth, resulting in poor responsiveness. occurs.

The method presented here does not directly detect the position of the maximum value, but rather estimates ΔX before arriving at the target track, that is, during seek. First, the embodiment shown in FIG. 2 will be described. The focus of this embodiment is that the state of the tracks near the target track is almost the same as the state of the target track. In other words, in the example shown in FIG.
and since the trunk is before the arrival of the target truck, the relationship between position and output can be given without the need for wobbling. When (XE-1) is the position of the maximum value of Ev one track ago, (XE-1
), the output Ev becomes almost symmetrical, so find the same voltage level ff1XBI
)=(XA+XB)/2. XA,X,
B indicates the voltage position of (VH+VL)/2. (X T
-1) is the servo head position, so it can be determined accurately, so as Δx' = (XEl) (xr-1),
The direction and amount of offset can be estimated (in voltage form Δxl=VA+VB). An example of the hardware configuration of the above detection method is shown in FIG. The signals from the envelope circuit 15 and the PO8 demodulator 6 are sampled at appropriate time intervals by the A/D converter 16, and the Ev and PO5 signals for about two tracks are loaded into the register 18 and calculations are performed based on these values. As described above, V HI V L + V B (corresponding to X B),
Calculate v^ (corresponding to XA) and estimate ΔX. The processor 17 is for controlling the above operation when the value of the counter 9 reaches, for example, two tracks before the target track, and normally sets 17, 18, and 19 to 1.
It consists of two microprocessors.

There is also another algorithm for the detection of (XE-1). Especially when the waveform of Ev becomes asymmetric, E with X A + X8
An effective method is to draw tangents to V and estimate the intersection of Y as (XE-1).

The above has described an example of data head off-track detection, but a similar method will also be explained. Figure 7 shows how the envelope changes when the data head is off-track. In the figure, the solid line shows the position of the servo head, and the dotted line shows the off-track position of the data head, and the lower figure shows the state of the envelope corresponding to the code.

■ is the case where there is no off-track of the data head, and ■
, ■ is off-track to one side, and ■ is off-track to the + side. In this method, for example, an envelope output is detected at an appropriate position i before the servo head reaches the target track, and the off-track i is determined from the magnitude of the output. Figure 8 corresponds to Figure 7, and at the location A, the off-track amount and output V
This shows that E corresponds one-to-one. Therefore, if the relationship between the envelope output position and the output is known in advance (measured in advance and stored in memory), the amount of off-track can be detected by determining the measurement point (for example, A).

However, what is important in this case is that the envelope output must be standardized so that it is constant regardless of the disk position and head. As a method for this, it is preferable to normalize using the output near the target track, for example, the maximum output of the envelope before the 11-rack. The method described above is
Although this method uses the magnitude of the output of the data head, that is, the envelope, it can also be applied to methods other than detecting the envelope of the output of the data head. As an example of this, a system using both servo surface and data surface servo will be explained using FIG. 5. In the case of this method.

As for the position of the data surface head, a position signal is obtained in the same way as for the servo head, so the relative positional relationship between the servo head and the data heel 1- is as shown in FIG. 5, and .DELTA.X is determined as the difference in zero cross position. (D-PO3 represents the position signal of the data surface head, and 5-pos represents the position signal of the servo head.) Therefore, this ΔX includes the amount of relative positional deviation between the servo disk and the data surface servo signal when writing the servo signal.

This is because it is assumed that data is written based on the data surface servo signal. Therefore, considering the servo plane as a reference, D-PO3 and 5- in the steady state
If the difference in pos is detected in advance and this state is considered as the initial state of the servo head and the data head, then the newly generated error will be the one obtained by subtracting the above initial error. Expressed in a formula, if X is in the initial state and ΔX is the measurement result, the newly generated error ΔXN=ΔX−ΔX.

The advantage of knowing the amount of off-track of the data head when it arrives at the target track using the combined method of servo surface servo and data surface servo will be described later.

Next, the relationship between the area and data format for envelope detection will be described.

FIG. 4 is an example of a format used in a disk device. Usually, the address area and data area are one
repeated on the track in sets of two. However, some data storage formats have fixed lengths for the address area and data area, while others have variable lengths for the data area.

First, in the case of a fixed-length format, the address area and data area are fixed based on the index, so they can be easily identified from the positions of PLO-A and PLO-D and the servo disk clock in Figure 4, for example. . PLO-A,
The part indicated as PLO-D is P L 0 (Pho
This is the tuning section of the SE Locle 0scillator), and the address section and data section are distinguished by -A and -D. Now, this PLO-A part is also used as an envelope detection part (the same goes for PLO-D, the PLO part is suitable for envelope detection because it has a periodic pattern like a sine wave, and Since the envelopes appear at regular intervals, the above-mentioned position detection can be easily performed. However, an improvement is needed here. In order to detect the envelope across the track with sensitivity to position. It is desirable that the phases of adjacent tracks differ by 180 degrees or that there is no pattern in the adjacent portions.

This magnetization state is shown in FIGS. 6(1) and (2). Since the writing timing is based on the clock from the servo disk, it is easy to match the timing. Therefore, it is necessary to newly provide phase management for odd and even tracks.

This write data management is performed on the disk controller. (Not described.) Next, we will discuss the variable tone type. In this case, unlike the fixed length format, the position of the PLO is not fixed, and if the PLO section is used as an envelope detection section, the accuracy of detecting one position may deteriorate as the data length increases. Therefore, in the case of the variable tone format, a plurality of specific parts on the track are designated as envelope detection areas, and a recording pattern as shown in FIG. 6 described above is created.

(For example, an envelope detection area is provided at part E in FIG. 4.) However, this area is rewritten at the same time when data is rewritten. The envelope detection area has been described above, but even in the fixed length format, it is not necessary to use both the envelope detection area and the PLO area, and a new envelope detection area may be provided, and the invention is not limited to the embodiment.

Next, a method of applying the present invention will be described. In the case of data heno 1 (which uses a method to determine the value of ΔX from the envelope of the reproduced signal), the envelope detection section is also rewritten, so if there is an error in off-track amount detection, there is a risk that the off-track amount will increase each time it is rewritten. There are three methods to prevent this risk: 1. Offset only during playback, not during recording. 2. Offset by the detected off-track amount (or even less) during playback. However, during recording, it is offset by an amount smaller than the detected off-track amount.

3. Offset using methods 1 and 2 above only when the off-track amount exceeds a certain value.

The above-mentioned problem does not occur in the combination of data surface servo and servo surface servo because the position signal can be obtained from the data surface servo signal regardless of recording or reproduction.

Finally, referring back to FIG. 1, the processing after detecting the off-track i of the data head before reaching the target track will be described.

The arithmetic unit 19 detects the rank amount to OFF 1 of the data head, and the D/A converter 20 converts it to an analog amount and adds it to the follow-in group. As a result, at the same time as the velocity loop is switched to the follow-in loop, it is offset in a feed-forward manner, so that the settling time can be shortened. Since the offset is made more aggressively, the settling time can be shortened. In order to offset more aggressively, the offset voltage is changed at appropriate time intervals as shown in FIG. Furthermore, by detecting the off-track amount of each of a plurality of data heads before the head arrives at the target track, it is possible to offset in a feedforward manner when switching heads, as shown in Figure 9. Therefore, the offset settling time when switching heads can be shortened.

[Effects of the Invention] According to the present invention, the positional deviation of the data head can be corrected even in a servo surface servo type disk device.
High-precision data head positioning is possible.

In addition, since the amount of offset of the data head can be detected during seek, feed forward can be performed to remove offsets, so the settling time can be shortened.

Furthermore, since the amount of offset can be detected in advance during switching, the offset settling time can be shortened.

[Brief explanation of the drawing]

Fig. 1 is a schematic configuration diagram of an embodiment of the present invention, Fig. 2 is a diagram showing an example of a data format, Fig. 5 is a diagram showing an example of off-track detection of a data and servo combination device, and Fig. 6 is a diagram showing an example of envelope detection. FIG. 7 is a diagram showing the relationship between off-track and envelope output, FIG. 8 is a diagram showing the relationship between the envelope output position at the off l-rank of FIG. 7, and FIG. The figure is a diagram showing an example of feed forward offset voltage for off-track removal. 1. Disk, 2. Data head, 3. Servo head, 4. Voice coil motor, 5. Carriage, 6. Position demodulator, 7. Compensator.
8... Speed detector, 9... Counter, 10... Speed guide generator, 11... Analog switch, 12...
・Power amplifier, 13...)・Rank cross pulse generation layer, 14・Amplifier, 15...Envelope circuit, 16
... A/D converter, 17... Processor, 18 ・
Register 19...Arithmetic unit, 20...D/A converter. PLθ-A PLtl-D 7th

Claims (1)

[Scope of Claims] 1. A magnetic disk device having a magnetic disk exclusively for servo, characterized in that an off-track amount of a data head is detected during a seek. 2. The magnetic disk device according to claim 1, wherein the magnetic disk device is offset in accordance with a detected off-track amount during a following operation. 3. A magnetic disk device according to claim 2, characterized in that offset is performed only during reproduction. 4. The magnetic disk device according to claim 2, wherein during recording, the magnetic disk device is offset by an amount smaller than the detected off-track amount. 5. A magnetic disk device according to claim 3 or 4, wherein the magnetic disk device is offset when an off-track amount exceeds a certain amount. 6. A magnetic disk device according to claim 1, wherein the method for detecting off-track of a data head includes estimating an off-track amount based on a recording pattern output, an envelope output, or the like. 7. A magnetic disk device according to claim 6, characterized in that the amount of off-track of the target track is estimated using an output or an envelope of a track near the target track. 8. A magnetic disk device according to claim 1, characterized in that it has a data surface servo signal and performs feedforward control during following. 9. A magnetic disk device according to claim 1, wherein the off-track amount of each data head is detected during seek, and offset is performed in a feed-forward manner when switching heads. 10. In a magnetic disk drive having a servo head position signal demodulator and a demodulator that demodulates the data head position signal using a signal from the data head, registers are provided to store position information of the data head and servo head, respectively. A magnetic disk device comprising: