JPH0438778A - Track follow-up controller - Google Patents

Abstract

PURPOSE:To obtain sufficient tracking following-up performance even when the number of servo signal lines is small by removing the noise of track oscillation information by Fourier transform. CONSTITUTION:When a recording medium 15 is rotated and a servo area passes through a head 11, a data signal and a servo signal are transmitted to a position error signal generating means 12. The means 20 generates a position error signal 20 like a sample. This signal 20 is applied to a memory means 16 and a control means 13. For the track oscillation information stored in the means 16, discrete Fourier transform is executed by a Fourier transforming means 17 and inverse Fourier transform is executed by an inverse Fourier transforming means 19. Then, the information is demodulated to a time base data and applied to the control means 13. The means 13 controls the drive of an actuator 14 and controls following-up to the track of the head 11. Before executing this following-up control, however, the means 13 executes compensation calculation based on a head position signal 21 to drive the actuator 14 and to fix the position of the head 11. Then, the medium 15 is rotated in such a state, and the track oscillation information at an arbitrary track is obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a 1-rank tracking control device for a disk device such as a magnetic disk device or an optical disk device.

BACKGROUND OF THE INVENTION In recent years, in flexible magnetic disk devices using floppy disks, research has been conducted on methods of increasing the track density of floppy disks (hereinafter referred to as recording media) in order to increase their recording capacity. In order to increase the track density, it is a prerequisite that a head (magnetic head) for recording and reproducing data on a recording medium is accurately positioned with respect to a data track. Conventionally, this type of head positioning has generally been performed by an open loop control method using a stepping motor.

By the way, in flexible magnetic disk devices,
Track runout (first-order eccentric component) with the same frequency as the rotational frequency of the recording medium occurs due to rotational runout due to chucking misalignment (misalignment of the recording medium) that occurs when the recording medium is loaded into the apparatus.

Further, the recording medium has anisotropy in terms of material because its heath film is rolled in either direction during the manufacturing process. Therefore, due to temperature and humidity expansion, the recording medium tends to elongate in a specific direction, resulting in track runout (secondary eccentric component) having a frequency twice the rotational frequency.

If the amount of track deflection becomes too much to ignore in relation to track pinch, the head will not be accurately positioned on the data track, and recording and playback will be performed while straddling adjacent tracks, resulting in poor data reliability. decreases. Therefore, in order to achieve high track density in a flexible magnetic disk device, servo signals are recorded discretely on the disk surface of the recording medium in advance, and data is sent to the head based on the servo signals reproduced in samples by the head. A track following control device is required that detects a position error signal with respect to the track and positions (follows) the head on a predetermined track in accordance with the detection signal.

On the other hand, in hard disk drives, a track following control called a sector servo method has been conventionally implemented. In this sector servo method, a data surface of a recording medium is divided into a plurality of sectors, a servo signal is recorded in a part of each sector, and the servo signal is reproduced by a head to generate a track position error signal. Then, based on this position error signal, the voltage or current of the head drive actuator is controlled to position the head on the data track.

Recently, research has been conducted to apply this sector servo method to flexible disk devices to achieve higher track density. Hereinafter, a conventional sector servo system in a flexible disk device will be explained with reference to FIGS. 3 to 5. However, FIG. 3 is a drawing showing a conventional track following control device, FIG. 4 is a drawing showing a recording medium on which servo signals are recorded, and FIG. 5 is a drawing showing an outline of a sector.

In FIG. 4, the recording area on one or both sides of the recording medium 15 is divided into a plurality of sectors 41 . . . , and each sector 41 is further divided into a data area 43 and a servo area 42 . As shown in FIG. 5, servo signals S are alternately recorded in the servo area 42 at positions shifted by half a track pitch with respect to the track 44. The recording medium 15 moves in the direction of the track 44 as shown. On the other hand, the head 11 is
It moves in the radial direction of the recording medium 15 and is controlled to be positioned at the center of the track 44.

As shown in FIG. 3, the servo signal S recorded in each sector 41 is reproduced by the head 11 and output to the position error signal generating means 32. Position error signal generation means 3
2 generates a position error signal 36 corresponding to the amount of deviation between the head 11 and the track 44 based on the servo signal S reproduced for each sector 41, and outputs it to the control means 33. Then, the control means 33 performs a compensation calculation based on the position error signal 36 and outputs a command signal to the actuator 14. The actuator 14 moves the head 11 according to this command signal, thereby positioning the head 11 on the track 44. In addition, as such a track following control device, for example, Nikkei Electronics 19
87.1.26 No. 413.

Problems to be Solved by the Invention According to the sector servo system as described above, the track following performance improves as the number of servo signals S increases, but in this case, the area occupied by the servo signals S increases, resulting in The drawback is that the area occupied by the data is reduced, and the storage capacity is also reduced. Such a drawback becomes a particularly serious problem in flexible magnetic disk drives.

That is, in a flexible disk device, since the amount of track deviation is larger than that in a hard disk device, more servo signals S are required to obtain sufficient track following performance, and the storage capacity of the recording medium is significantly reduced. This is because it will be put away.

The present invention has been made to solve these problems, and it is an object of the present invention to provide a track following control device that can obtain sufficient track following performance even with a small number of servo signals.

Means for Solving the Problems The present invention provides a recording medium that has a plurality of tracks for recording information and records servo signals discretely along one track, and a recording medium that records the servo signals recorded on the recording medium. It has a head for reproducing, and a position error signal generation means for detecting the servo signal samplewise and generating a position error signal indicating the amount of positional deviation between the target track and the head, A track following control device for positioning a track to the target track, a storage means for obtaining and storing track runout information as a sample from a servo signal of an arbitrary track before performing track following control; Fourier transform means for Fourier transforming runout information; inverse Fourier transform means for inverse Fourier transforming track runout information of a predetermined frequency component that has been Fourier transformed;
The apparatus is characterized by comprising means for feeding rank deviation information to the head as a positioning command in a feedforward manner.

Further, the track following control device according to the present invention performs inverse Fourier transform on the track runout information of a predetermined frequency component that has been Fourier transformed by the Fourier transform means, by advancing the phase.
The feature is that it is given as a positioning command to the head using feedforward.

According to the present invention, track runout information is obtained as a sample from an arbitrary track before starting track following control. By Fourier transforming this track runout information, the amplitude and phase of each frequency component of the track runout information can be found, but since track runout (eccentricity) is dominated by the primary eccentricity component and the secondary eccentricity component, other frequency components can be identified as noise and removed.

Furthermore, since the present invention advances the phase of the primary and secondary components of track runout and performs inverse Fourier transform, it is possible to obtain temporally future track runout information. Therefore, since track shake can be predicted, it is possible to perform good track following control even with a small number of servo signals.

Example An embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 is a drawing showing a schematic configuration of a track following control device according to the present invention.

In the figure, 11 is a head, 12 is a position error signal generating means, 13 is a control means, 14 is an actuator, 15 is a recording medium, 16 is a storage means, 17 is a Fourier transform means, 1
8 is a position detection means, 19 is an inverse Fourier transform means,
The operation of the track following control device configured as described above will be described below. Note that the configuration of the recording medium 15 is the same as that of the conventional example shown in FIGS. 4 and 5, and a description thereof will be omitted. However, in this embodiment, the number of sectors is 32 trees.

In the figure, a recording medium 15 on which servo signals are recorded sector by sector is rotating, and when the servo area passes the head 11, the data signal and the servo signal are reproduced and sent to the position error signal generating means I2.

When the position error signal generation means 12 detects the servo signal, it generates a sample position error signal 20 up to the target track to which the head 11 is to follow. This position error signal 20 is stored in the memory means (storage means) 16 and the control means 1.
given to 3.

On the other hand, the absolute position of the head 11 is determined by the position detection means 18.
The head position signal 21 is constantly detected and the detected head position signal 21 is supplied to the control means 13.

The memory means 16 stores the position error signal 20 as track runout information, and has at least the same number of areas as the number of sectors (4.1). Track runout information stored in the memory means 16 is read out by the Fourier transform means 17. The Fourier transform means 17 converts the read 1-
The rank fluctuation information is subjected to discrete Fourier transform as described below. The data subjected to the discrete Fourier transform by the Fourier transform means 17 is subjected to inverse Fourier transform by the inverse Fourier transform means 19, and the primary eccentric component and the secondary eccentric component of the track runout are demodulated into time axis data. The demodulated data is given to the control means 13.

Here, the control means 13 finally controls the actuator 1 consisting of a piezoelectric actuator or a voice coil motor.
4 to control the tracking of the head 11 on the track. However, in the present invention, before performing this tracking control, the control means 13 performs compensation calculation based on the head position signal 21 to drive the actuator 14. Head 11
fix the position. Then, in this state, the recording medium 15 is rotated to obtain track runout information at an arbitrary 1-rank. The track runout information obtained in this way is
Since the head 11 is stationary, track runout information is directly shown.

Then, the memory means 16 sequentially stores this track runout information in storage areas corresponding to the sectors.

In addition, at this time, the position error signal 2 of several times of the recording medium 15
If you average 0 for each sector and store it,
This will be preferable for implementation.

That is, the averaging process can reduce noise associated with the rotational movement of the recording medium 15, and accordingly it is possible to perform tracking control operations with high accuracy.

The track runout information stored in the memory means 16 is subjected to a discrete Fourier transform by the Fourier transform means 17.
Here, in the present invention, the track runout information is subjected to Fourier transform to remove noise components other than the first-order eccentricity component and the second-order eccentricity component, that is, third-order or higher harmonics, and as a result, the first-order eccentricity component This is to extract only the second-order eccentric component and perform highly accurate follow-up control.

Here, the harmonic noise components are caused by errors in the format accuracy of the servo signal that occur during the production of the recording medium 15 (deviation in the writing position of the servo signal that should have been written at a location shifted by half a track pitch) and recording. medium 15
This occurs due to rotational fluctuations.

Further, the track runout information stored in the memory means 16 has a direct current component such as a direct current superimposed on a coil component.
This DC component is taken in as a disturbance because the head 11 and the position of the corresponding track are not associated with each other due to track deflection. This DC component can also be removed by Fourier transformation. That is, when Fourier transform is performed, only the first-order and second-order components, which are AC components, are obtained, so that the DC component can be canceled.

Below, details of the discrete Fourier transform for removing harmonic components and extracting only the first-order eccentricity component and the second-order eccentricity component will be explained. Since the track runout information stored in the memory means 16 can be expressed by a periodic function, when expressed as a Fourier series, it is expressed by the following equation (1).

However, the asterisk * indicates multiplication, and specifically, for example, in equation (3), 32 / 2 * al is,
(-32/2)xa. Further, H(K) in equation (1) indicates the track runout information of the sector stored in the memory means 16, a is the amplitude of the i-th harmonic of the track runout, and φ is the track runout information. The phase angle with respect to the first sector of the i-th harmonic is shown.

First, the discrete Fourier transform for the first-order eccentric component will be explained. The Fourier transform means 17 is prepared with a sine/cosine function table shown in equation (2).

Ru.

"-" * 5IN (tφ1) Therefore, it is obtained as 5I--a, * 5IN (φ, ).

C7 can also be found in the same way as in equation (3).

After executing the calculation of equation (3), the Fourier transform means 17 temporarily stores Sl and 01, which are the calculation results, in the memory.

Next, the discrete Fourier transform of the second-order component is executed, and the Fourier transform means 17 prepares a sine/cosine function table shown in equation (4) for the discrete Fourier transform of the second-order component. ing.

This equation (3) is obtained by the following procedure. Below, s1 will be explained as a representative.

When i ≠ 1, it becomes 8-0, and when i = 1, it becomes as follows.

The Fourier transform equation for the second-order component is executed using equation (5).

After executing the calculation of formula (5), the calculation result Sl and 0
2 is stored in memory.

The above operations are performed by the Fourier transform means 17, and as the calculation results, Sl, CI, 'S2, and C2 are stored in a memory (not shown).

Next, as described above, the inverse Fourier transform means 19 demodulates only the first-order eccentricity component and the second-order eccentricity component of the track runout information into track runout data on the time axis, and the details of this operation will be explained below. do.

It should be noted that when demodulating the primary and secondary eccentric components of the track runout information stored in the memory means 16, it is possible to advance the phase and demodulate. Let the advance amounts be ψ1 and ψ2, respectively. The inverse Fourier transform means 19 is provided with function tables such as equations (6) and (7).

Discrete inverse Fourier transform is performed using the following equation (8) and stored in a memory (not shown) as the track runout amount Z (K)] 9 When the above operations are completed, track following control is activated for the first time. The details will be explained below with reference to FIG. However, FIG. 2 is a block diagram showing details of the control means 13. As shown in the figure, this control system has a minor servo loop for positioning the head 11 by negative feedback using the position detection means 18. There is. The position error signal 20 obtained for each sector is compensated for by the deviation compensator 25, but since the position error signal 20 is obtained sample-wise for each sector, the output of the deviation compensator 25 between sectors is The position error signal 20 is held by the circuit 26 until the next position error signal 20 is input. Held position error signal 2
0 is then subjected to stabilization processing by a stabilization compensator 27 and then output to the actuator 14.

Further, the track runout amount Z (
K) is applied to an adding means 28, as shown in FIG. 2, through which the head 11 is currently passing.

From the above equation (8), it can be seen that Z (K) is the track runout information of the first-order eccentric component and the second-order eccentric component whose phase in the sector is advanced.

The output of the deviation compensator 25 is added to the output of the deviation compensator 25 in synchronization with the sector. As described above, the output of the holder 26 serves as a position command for the minor servo loop, but in the present invention, since the track runout amount Z (K) is output to the minor servo loop in a feedforward manner, The positioning accuracy of the throat 11 can be dramatically improved.

By the way, since the control band of the minor servo loop which is the position control system is limited, the head 11 in response to the position command
In addition to a phase delay occurring in the response, the phase is further delayed due to friction of the actuator 14 and the like. Therefore,
If this continues, there is a possibility that the feed throat 11 will operate with a delay in response to the track runout information that is fed forward due to the phase delay of the holder 26 and the minor servo loop.

Therefore, in this embodiment, the phase delay of the frequency component of the track runout of the first-order eccentric component and the second-order eccentric component in the holder 26 and the minor servo loop is estimated in advance, and the phase is advanced when performing the inverse Fourier transform as described above. The axis track runout information will be demodulated. In other words, by doing so, it is possible to obtain temporally future track runout information.
The phase delay of the holder 26 and the minor servo loop can be compensated for, and the positioning accuracy of the head 11 can be further improved.

Of course, since the positioning accuracy of the head 11 can be dramatically improved without providing the inverse Fourier transform means 19 as described above, the present invention can also be implemented without the inverse Fourier transform means 19.

In addition, since the discrete Fourier transform and discrete inverse Fourier transform of this embodiment are performed before starting the track following control, the time required for these calculations has no bearing on the stability of the control system. Furthermore, during track following control, the track deflection information that has been subjected to inverse Fourier transform is stored in the memory corresponding to each sector, so the computation time is short. Therefore, this method can be fully realized with a one-chip microcomputer.

Note that although the above embodiment has been explained using a flexible disk device, it can also be applied to hard disks, optical disks, etc. Further, although the number of sectors is 32 in the embodiment, the present invention is not limited by the number of sectors as long as it is 4 or more.

Here, the reason why four or more sectors are required is that if four or more sectors are arranged at equal intervals in the circumferential direction of the recording medium, the adverse effects of anisotropy and center runout of the recording medium 15 can be physically eliminated. In addition, mathematically, according to the sampling theorem, if one attempts to obtain the frequency spectrum of the first-order eccentric component and the second-order eccentric component by Fourier transform, four or more sectors are required.

Further, in the above embodiment, a sine function table and a cosine function table are used, but if the number of sectors is even, one can be used to generate the other. In addition, if there is a sine or cosine function table in which one period is divided sufficiently finely compared to the number of sectors, the above (
2) (4) (6) The function table used in equations (7) is unnecessary because it can be generated from a finely divided function table.

Furthermore, in the above embodiment, the servo information is recorded for each sector, but since the present invention is effective for servo signals arranged discretely, the servo information is not necessarily arranged for each data sector. It's obvious that you don't have to.

Furthermore, in the above embodiment, the track runout amount Z(K) is fed forward before the holder 26, but it can also be fed forward after the holder 26.

Effects of the Invention According to the track following control device as set forth in claim (1), since noise in track runout information can be removed by Fourier transformation, head positioning accuracy can be dramatically improved. Therefore, even when the track runout is large, there is no need to increase the number of sectors, and sufficient tracking performance can be obtained even with a small number of servo signals, so the area occupied by the servo signals on the recording medium can be reduced. Therefore, it is extremely convenient for increasing the capacity of recording media.

In particular, according to the track following control device according to claim (2), track runout information of a predetermined frequency component that has been subjected to Fourier transform is inversely Fourier transformed by advancing the phase, and temporally future track runout information is obtained. This has the advantage that the phase delay of the control system can be compensated for and the track following accuracy can be further improved.

In particular, according to the track following control device according to claims (4) and (5), since the structure includes a function table, there is an advantage that Fourier transform and inverse Fourier transform can be performed quickly. .

[Brief explanation of the drawing]

FIG. 1 is a drawing showing the configuration of a track following control device according to the present invention, and FIG. 2 is a block diagram showing details of the control means. Fig. 3 is a drawing showing a conventional track following control device;
Figure 5 shows a recording medium on which servo signals are recorded.
The figure is a diagram showing an overview of sectors. 11...Head, 12...Position error signal generation means 1
3... Control means, 14... Actuator, 15.
...Recording medium, 16.. Storage means, 17.. Fourier transform means, 18.. Position detection means, 19.. Inverse Fourier transform means.

Claims (5)

[Claims] (1) A recording medium having a plurality of tracks for recording information and recording servo signals discretely along the tracks, a head for reproducing the servo signals recorded on the recording medium, and a head for reproducing the servo signals recorded on the recording medium; track tracking, which includes a position error signal generating means for detecting in a sample manner and generating a position error signal indicating the amount of positional deviation between the target track and the head, and positioning the head to the target track based on the position error signal; In the control device, a storage means for obtaining and storing track run-out information as a sample from a servo signal of an arbitrary track before performing track following control, and a Fourier transform means for Fourier-transforming the track run-out information stored in the storage means. , comprising inverse Fourier transform means for inverse Fourier transforming track runout information of a predetermined frequency component that has been Fourier transformed, and means for feeding forward the track runout information that has been subjected to inverse Fourier transform to the head as a positioning command. Features a track following control device. (2) The track following control device according to claim 1, wherein the track runout information of a predetermined frequency component that has been subjected to Fourier transform is inversely Fourier transformed by advancing the phase thereof. (3) Track following according to claim (1), characterized in that the head position of the head is fixed, and track runout data obtained from a servo signal of an arbitrary track is determined based on a position error signal obtained at that time. Control device. (4) Claim (1) characterized in that the Fourier transform means has a function table of a sine function and/or a cosine function.
) track following control device. (5) Claim characterized in that the inverse Fourier transform means has a function table of a sine function and/or a cosine function (
1) Track following control device as described.