JPH03160673A - Servo control circuit for disk device - Google Patents

Abstract

PURPOSE:To prevent the output of erroneous position signal even if an amplitude value of a servo signal becomes abnormally large by allowing a charging current to detect the peak value of the servo signal to be the smaller current control value than the current limiting value in the seaking operation time. CONSTITUTION:In the seak operation time a seaking signal is given to peak detecting means (14-1)-(14-4) and a first current source 24 having a large current limiting value is connected to a transistor 22 by a current switching means 28. Consequently, while the servo signal exceeding the charging voltage of a capacitor 20 the transistor 22 is made to be conductive state and is charged to the voltage corresponding to the peak value of servo signal amplitude. On the other hand, in the on track operation the means 28 is connected to a second current source 26, even if abnormal large amplitude change to the servo signal occurs by a medium flaw and an extrinsic noise, the charging current of peak detecting is suppressed. In such a manner, the influence to the position signal is controlled to the minimum and the output of the erroneous position signal is prevented.

Description

[Detailed Description of the Invention] [Summary] This invention relates to a servo control circuit for a disk device that performs a seek operation or an on-track operation using a position signal created based on peak detection of a servo pattern read signal, A current source that supplies a charging current to keep the capacitor charged at the peak value of the servo signal, with the aim of not generating an erroneous position signal even if an abnormally large amplitude change occurs in the servo signal due to a defect or external noise. Two current sources are provided, and during a seek operation with a large amplitude change, the current source is switched to a current source with a large upper limit current limit value, and during an on-track operation, the current source is switched to a current source with a sufficiently small upper limit current limit value.

[Industrial Field of Application] The present invention relates to a disk device that performs seek operations and on-track operations by creating a position signal indicating the position in the disk radial direction based on a head read signal from a disk medium on which a servo pattern is recorded. Regarding servo control circuits.

In a magnetic disk device, when an external access is received, a seek operation (coarse control) is performed to move the head to an access track, and when the seek operation is completed, an on-track operation (fine control) is performed to cause the head to follow the track.

The seek operation and on-track operation of the head in such a magnetic disk device are performed based on a position signal created from a read signal of a disk medium on which a servo pattern is recorded. That is, a servo pattern for creating a position signal indicating the radial position of the head is recorded on one of a plurality of disk media, this servo pattern is read by a dedicated servo head, and the read servo signal is read. Position signal based on peak position, e.g. two-phase position signal POS
N. Creating POSQ.

The peak detection circuit for the servo signal used to create this position signal turns on a switching element such as a transistor when the human servo signal exceeds the charging voltage of a capacitor that charges and holds the peak value. A new peak value is created by supplying a current below a certain upper limit value to charge the capacitor.

Incidentally, during a seek operation, the head moves across the track, so the amplitude change in the servo signal is large, but during an on-track operation, the head follows the track, so the amplitude change in the servo signal is very small. Therefore, in a peak detection circuit for creating a position signal, the current applied to the capacitor is The upper limit value of the source is determined. On the other hand, the amplitude change of the servo signal during on-track is very small, and the capacitor charging current for peak detection only needs to be very small, which is below the upper limit value of the current source.

However, if a large amplitude change occurs in the servo signal due to a media defect, external noise, etc. during on-track operation, the peak value that follows this amplitude change will be incorrectly detected and an incorrect position signal will be output, resulting in on-track operation. There is a problem that the servo signal becomes unstable, and a circuit that does not generate an erroneous position signal due to abnormally large amplitude changes in the servo signal during on-track operation is desired.

[Prior Art] Conventionally, in a peak detection circuit (peak detector) that detects the peak value of a servo signal, the upper limit value of a current source that supplies charging current to a capacitor is set to a constant value.

That is, the peak detection circuit connects the output of the current source to a capacitor that charges and holds the peak value via a transistor switch, and when the servo signal level input to the base of the transistor switch exceeds the capacitor charging voltage, the transistor switch is activated. is turned on, a charging current is supplied from the current source to the capacitor via the transistor switch, and a new peak value is obtained as the charging voltage.

The upper limit value of the current source used in such a peak detection circuit is set so that the capacitor can be charged in a manner that follows the maximum slope (rate of change) of the signal waveform during a seek operation where the amplitude of the servo signal changes significantly. determining the value.

[Problems to be Solved by the Invention] However, in the conventional servo control circuit that sets the upper limit of the charging current to a constant value in order to obtain a peak value that follows the amplitude change of the servo signal during a seek operation, In some cases, there is a problem in that an abnormal position signal is generated during the on-track operation after the seek operation is completed.

In other words, the on-track operation is an operation in which the head follows the track on which it is currently positioned, and the same servo pattern repeatedly recorded on the track is read, so even if the head position shifts, the amplitude of the servo signal will not change. is very small, and the charging current that flows through the capacitor for peak detection is also very small.

However, during on-track operation, the amplitude of the servo signal may change significantly due to media defects or external noise, and incorrect detection of the peak value generates an incorrect position signal, making track following operation unstable, and There was a problem in that the recorded data could be destroyed by accidentally writing data to an adjacent track, or the data could be read incorrectly.

The present invention has been made in view of these conventional problems, and aims to provide reliability that does not generate an erroneous position signal even if abnormal amplitude fluctuations appear in the servo signal due to medium defects or external noise during on-track operation. The purpose of this invention is to provide a highly stable servo control circuit for disk devices.

[Means to solve the problem] FIG. 1 is a diagram explaining the principle of the present invention.

First, the present invention provides a disk on which a servo pattern is recorded, in which the same amplitude pattern is repeated in the circumferential direction and different types of amplitude patterns are repeated in the radial direction in units of multiple tracks, as shown in FIG. 1(a). medium 10 and disk medium 1
A servo head 12 that reads a servo pattern recorded in 0 and outputs a servo signal, and a peak detection means 1 that detects the amplitude peak value of the servo signal from the servo head 12.
4-1 to 14-4 and peak detection means 14-1 to 14-
position signal generating means 16-1.16-2 for generating a position signal indicating the radial position of the servo head 12 with respect to the disk medium 10 based on the detected peak value of the position signal generating means 16-1. The present invention is directed to a servo control circuit for a disk device equipped with a head driving means 18 that performs a seek operation to move the head in the radial direction based on a position signal from the head 16-2, and an on-track operation that causes the head to follow a track. do.

In the servo control circuit of such a disk device, as shown in FIG. 1(b), the peak detection means 16-1 to 16-4 include capacitors that charge and hold the peak level of the servo signal. 20, a switching means 22 conducting while the input servo signal exceeds the charging voltage of the capacitor 20, and a first current having an upper current limit value Imaxl for supplying the charging current to the capacitor 20 via the switching means 22; source 24 and a second upper current limit value 1 max2 that is sufficiently smaller than said first upper current limit value 1+11111 for supplying a charging current to the capacitor 20 via the switching means 22.
and a current that connects the output of the first current source 24 to the switching means 22 during the seek operation of the head driving means 18, and connects the output of the second current source 26 to the switching means 22 during the on-track operation. A source switching stage 28 is provided.

Here, the second upper limit current limit value 1 max2 is set to a value of 1710 or less with respect to the lth upper limit current limit value 1 mxxl.

[Function] According to the servo control circuit for a disk device according to the present invention having such a configuration, since a current source with a large upper limit current limit value Imatl is connected during a seek operation, a large amplitude change in the servo signal is prevented. On the other hand, during on-track operation, the current source connection can be changed to a small upper limit current limit value [max 2] that is less than 1/10 of the seek operation, so on-track operation is possible. Even if an abnormally large amplitude change appears in the servo signal due to medium defects or external noise, the charging current for peak detection is suppressed to obtain a peak value with noise components suppressed, minimizing the influence on the position signal. This makes it possible to improve the stability and reliability of on-track tracking operation.

[Embodiment] FIG. 2 is a block diagram showing an embodiment of the present invention.

In FIG. 2, 12 is a servo head that is moved in the radial direction of a disk medium (not shown) by a head motor 42, and the servo head 12 reads a pattern to obtain a position signal recorded on the servo disk. It is output as a servo signal via the AGC amplifier 44. The servo disk read by the servo head 12 has a third F.
! ! A servo pattern shown in J is recorded.

Figure 3 shows the magnetic recording state of the servo pattern by extracting five tracks on the servo disk on the left.
From above, servo pattern PI. P2. P3 and P4 are recorded in order, and following servo pattern P4, the same servo pattern P1 as the first one is returned to, and thereafter, these servo patterns P1 to P4 are repeated in the disk radial direction. Also,
Regarding the circumferential direction (track direction) of each servo pattern P1 to P4, magnetic recording unique to each pattern is performed between synchronous patterns in which NS is recorded three times at a fine pitch.
This is repeated in the circumferential direction.

Furthermore, the right side of FIG. 3 shows one pattern of signal waveforms of servo signals obtained when the servo head 12 is positioned at cylinders CYO, CYI, and CY2 as shown. For example, the servo head 12 is attached to the cylinder CYO.
The signal waveform of the servo signal obtained from the read signal when is located has three amplitude patterns in which there are two small amplitude changes and then a large amplitude change during a two-cycle synchronization pattern.

Referring again to FIG. 2, in this embodiment, the servo signal read from the servo disk by the servo head 12 and obtained via the AGC amplifier 44 is a two-phase position signal as shown in FIG. Since this is a servo pattern to obtain 4 peak detectors (peak detection circuits)
14-1. 14-2, 14-3, and 14-4, respectively. Note that the servo signal from the AGC amplifier 44 receives a 5 volt DC bias from a bias circuit (not shown).

The peak detectors 14-1 to 14-4 are activated by wind pulses at timings A, B, C, and D shown in the servo signal in FIG. 3, detect the peak value of the servo signal obtained at that time, and Outputs peak value detection outputs A, B, C, and D.

The position signal generation circuit 16-1 has a differential amplifier 48, and determines the position based on the peak value detection outputs A and B of the peak detectors 14-1 and 14-2 and the reference voltage R from the reference voltage generation circuit 52. Create signal POSN. Further, the position signal detection circuit 16-2 has a differential amplifier 50, and the peak value detection output C of the peak detector 14-3, 14-4.
, D and the reference voltage R to generate another position signal P
Create an OSQ. Two position signals POSN and POSQ
There is a phase difference of one track pitch between them.

Position signal creation circuit 16-1.1 that creates a two-phase position signal
Position signals POSN and POSQ from 6-2 are applied to the head drive circuit 18.

The head drive circuit 18 includes an AD converter 34 and an MPU 3.
6. A DA humbator 38, 46 and a power amplifier 40 are provided, and the output of the power amplifier 40 drives the head motor 42.
is driven to control the movement of the servo head 12 in the radial direction of the disk medium.

A read or write access command is given to the MPU 36 by the host controller, and upon receiving the access command, the MPU 36 calculates the track difference indicating the difference between the target track and the current track, and calculates the track difference to move the head to the target track. Perform a seek operation. This seek operation is performed as speed control (coast control) in which servo control is performed to minimize the deviation between the target speed generated in accordance with the track difference and the head movement speed. When the seek operation by the MPU 36 is completed and the head is positioned on the target track, the MPU 36 performs an on-track operation (fine control) to cause the head to follow the track.

Such seek operation and on-track operation by the MPU 36 are performed by converting the two-phase position signals POSN and POSQ from the position signal generation circuit 16-1, 16-2 to the AD converter 34.
This is done by importing it as digital data.

The calculation of the deviation signal between the target speed and the actual speed for the seek operation is performed by program control within the MPU 36,
The deviation data as a result of the calculation is sent to the DA converter 38.
The signal is converted into an analog signal and supplied to the power amplifier 40. This point is the same during on-track operation, and MP
The positional deviation is calculated in U36, and the positional deviation data is converted into an analog signal by the DA converter 38 and then sent to the power amplifier 4.
By supplying the signal to 0, the head motor 42 is driven.

The DA converter 46 is a peak detector 1 which will be explained later.
Is the capacitor discharged for peak value detection in 4-1 to 14-4? ! Used to control current.

Next, the configuration of the peak detectors 14-1 to 14-4 of the present invention will be explained using the peak detector 14-l as a representative.

The peak detector 14-1 is provided with a capacitor 20 for charging and holding the peak value of the servo signal. Two current sources 24 and 26 can be selectively connected to the capacitor 20 via a transistor 22 as a switching means by means of changeover switches 28-10 and 28-20.

The base of the transistor 22 includes diodes D1, D2,
Further, a servo signal from the AGC amplifier 44 is input via D3. Therefore, when the input servo signal exceeds the charging voltage Vc of the capacitor 20, the transistor 22 receives a forward bias and becomes conductive, charging the capacitor 20 with the charging current l1 from the current source 24 or 26, and charging the capacitor 20.
0 is charged to a value corresponding to the peak value of the input servo signal at that time.

The transistor 22 is enabled to operate by a bias circuit provided on the base side via the diode D3. That is, the resistor R1 and the selector switch 28- are connected via the window switch 32 between the connection point of the diodes D2 and D3 and the power supply.
21 series circuit, resistor R2 and selector switch 28-21
series circuits are connected in parallel.

The changeover switch 28-10.11 is an interlocking switch, and the changeover switch 28-20.21 is an interlocking switch.

These changeover switches 28-10.11 and 28-20.
21 is controlled on and off by an on-track/seek switching signal from the MPU 36. That is, when the MPU 36 performs a seek operation, the selector switch 28-10 is pressed as shown in the figure.
．． 11 is on, and 28-20.21 is off. on the other hand,
Conversely, during on-track operation by the MPU 36, the changeover switch 28-10.11 is turned off, and the changeover switch 28-20 is turned off.
．． 21 is turned on.

The wind switch 32 provided in the bias circuit of the transistor 22 is turned on and off by a wind pulse created based on the synchronous component included in the servo signal, and the wind switch 32 of the peak detector 14-1 is controlled to turn on and off.
In this case, it is turned on as shown at timing A in the servo signal waveform of FIG.

A first current source 2 provided on the collector side of the transistor 22
4 and the second current source 26 have an upper current limit value Imsxl and I
+ut2 is different.

That is, the first current source 24 is connected to the transistor 22 when the changeover switch 28-10 is turned on during on-track operation, and the servo signal input at the timing when the window switch 32 is turned on changes to the charging voltage Vc of the capacitor 20.
The charging current I1 is supplied when the voltage exceeds the current value and becomes conductive. At this time, the changeover switch 28-11 on the bias circuit side is also turned on, and the base current 12 determined by the resistor R1 also flows, and eventually the capacitor 20 is charged for peak detection by supplying the charging current (Il +12).

The upper limit value 1maxl of the first current source 24 used during on-track operation is determined as follows.

First, taking as an example the servo signal shown in (a) of the timing chart in FIG. 4, that is, the servo signal obtained by reading the cylinder CYo in FIG. 3, the timing of A-D that exists between the synchronization patterns A slew rate greater than the maximum slope of the amplitude waveforms generated at A, B, and D is required. Specifically, a slew rate of 10V/μS or more is required.

Therefore, the charging voltage Vc of the capacitor 20 and the charging current (N
+12), the following relationship holds true.

II +12 = C-d (Vl) /d t Kokote,
When d・(Vl)/dt=10V/μs and capacitor 20 capacitance ffic=200pF, (II +12 )
=2mA. Accordingly, the upper limit current limit value 1maxl of the l-th current source 24 used during the seek operation is lI
Set Ilxxl=2 mA. Here, in order to set the value of the resistor R1 so that the base current summer 2 is sufficiently smaller than the original charging current I1, by limiting the upper limit current value 1111111 of the current source 24 to 2 mA, the charging current of the capacitor 20 can be limited to approximately 2 mA or less.

Next, the second current source 2 used during on-track operation
The upper limit current limit value 1+11112 of 6 is the upper limit current limit value 1 in the first current source 24 used during the seek operation.
111! ! It is set to a value sufficiently smaller than I, for example, 1710 or less. For example, in the case of 1/10, since the upper limit current limit value 1maxl of the first current source 24 is 2 mA, the upper limit current limit value 1max2 of the second current source 26 is
=0. It will be limited to 2mA.

Furthermore, a current source 30 for discharging is connected in parallel with the capacitor 20. The current source 30 for discharging is always kept in an operating state regardless of the seek operation by the MPU 36, the on-track operation, and even the wind pulse that puts the peak detector into an operating state, and the current is less than 1/10 of the charging current of the capacitor 20. A small discharge current is flowing. Therefore, even in the peak value holding state where the wind switch 32 is opened by the wind pulse and charging is stopped by turning off the transistor 22, the capacitor 20 is slowly discharged by the discharge current I3 from the current source 30.

Furthermore, the discharge current I3 by the current source 30 is increased or decreased according to the output voltage of the DA converter 46 obtained under the control of the MPU 36. Specifically, the discharge current 13 is determined depending on the head speed during seek. That is, when the head speed during seek is high, that is, when the change in the output of the peak detector 14-1 is large, the discharge current I3 is increased, and conversely, when the head speed during seek is slow,
That is, when the change in the output of the peak detector l4-1 is small, the discharge current I3 is controlled to be small.

The configuration of the peak detector 14-1 is the same for the remaining three peak detectors 14-2, 14-3, and 14-4.
The only difference is the control timing of the window switch 32 provided at No. 4.

Furthermore, a position signal generation circuit 16 generates two-phase position signals POSN and POSQ based on the peak value detection outputs A, B, C, and D of the peak detectors 14-1 to 14-4.
-1.16-2 The position signal is generated as follows.

First, for the position signal 16-1, the peak value detection output A and the reference voltage R are input to the non-inverting input terminal via resistors R12 and R13, and the peak value detection output A and the reference voltage R are input to the inverting input terminal via the resistor R10. The output B is input manually and fed back through R11, and as a result, the output P of the differential amplifier 48 is
As OSN, it outputs a position signal where POSN=A-B+R. On the other hand, position signal generation circuit 1
6-2, a resistor R16.6-2 is similarly connected to the non-inverting input terminal of the differential amplifier 50. The peak value detection output C and the reference voltage R are inputted through R17, and the peak value detection output D is inputted to the inverting input terminal through the resistor R14, and the output is fed back through R15. As a result, the differential amplifier As the output POSQ of 50, a position signal that satisfies POSQ=C-D+R is output.

Next, the operation of the embodiment shown in FIG. 2 will be explained.

First, during a seek operation by the MPU 36, a seek signal is given to the peak detectors 14-1 to 14-4.
．． 11 is turned on, the changeover switches 28-20.21 are turned off, and the first current source 24 is connected to the transistor 22.

In this state, for example, if the servo signal shown in FIG.
As shown in Figures (b) to (e), the peak detector 1 is
4-1 to 14-4.

For example, looking at the wind pulse WA in FIG. 4(b),
In response to the fall of the wind pulse WA (window open), the window switch 32 provided in the peak detector 14-1 is turned on as shown in the figure, and the transistor 22 is turned on via the resistor R1 and the changeover switch 28-11 which is in the on state.
A bias condition is created that enables the . When the amplitude change shown by 8 of the servo signal occurs at the timing of this wind pulse WA, the charging voltage of the capacitor 20 V
While the servo signal exceeds c, the transistor 22 conducts, and a charging current (I1+12) consisting of the sum of the current ■1 from the current source 24 and the base current ■2 flows to the capacitor 20, and the servo signal amplitude of A increases. The capacitor 20 is charged to a charging voltage Vc corresponding to the peak value.

Thereafter, similar peak detection operations are performed at the timing of the wind pulses WB, WC, and WD.

In this way, along with the seek operation, the peak detector 14-
The peak value detection outputs A-D outputted from 1 to 14-4 are given to the position signal generation circuit 16-1.
The two-phase position signals POSN and POSQ shown in the figure are output.

Position signal P from position signal generation circuit 16-1.16-2
OSN and POSQ are connected to the MPU via the AD converter 34.
The head movement speed can be obtained by dividing one track pitch Tp by the cross interval period with respect to the reference voltage of the position signal shown in FIG. The access difference will now be subtracted.

When the seek operation by the MPU 36 is completed and the head reaches the target track, the operation is switched to an on-track operation, and an on-track signal is output to the peak detectors 14-1 to 14-4. This on-track signal causes the changeover switch 28- of the peak detectors 141 to 14-4 to
10.11 is off, the changeover switch 28-20.21 is turned on, and the second current source 26 is connected to the transistor 22.

In on-track operation, the servo head 12 is located on a specific track of any of the servo patterns P1 to P4 shown in FIG. Therefore, even if the servo signal exceeds the charging voltage Vc of the capacitor 20 and the transistor 22 becomes conductive, the current I1 from the second current source 26 and the base current
Only a very small charging current flows as the sum of 2.

On the other hand, even if a servo signal with a large amplitude change is input due to external noise or medium defects during on-track operation, the upper current limit value Imax is applied to the transistor 22.
Since the second current iiA26 limited to 2=0.2mA is connected, the upper limit current limit value 1max2-0.2
A charging current exceeding mA does not flow, and the charging voltage of the capacitor 20, that is, the peak value detection output does not change much even if the servo signal receives abnormal amplitude changes due to external noise or medium defects. In this way, since the peak value detection outputs A-D are limited by the charging current to minimize the influence of the servo signal on external noise and medium defects, the peak value detection outputs A-D are position signal POSN
, POSQ does not change significantly, stable on-track operation can be maintained against external noise and medium defects during on-track operation, and reliability of read and write operations can be guaranteed.

Note that the first and second current sources 24.
Upper current limit value in 26 1nuxl, 1max
The value of 2 is merely an example, and it goes without saying that an appropriate current limit value may be set as necessary.

[Effects of the Invention] As explained above, according to the present invention, the charging current for detecting the peak value of the servo signal is set to a current limiting value that is sufficiently smaller than the current limiting value during the seek operation. Even if the amplitude value of the servo signal becomes abnormally large due to a disk media defect or external noise, it reliably prevents the output of an incorrect position signal, and tracks tracking by outputting an incorrect position signal due to an abnormal amplitude of the servo signal. It is possible to prevent unstable operation, destruction of data by accidentally writing data to a track adjacent to the track that should be positioned, and errors in reading data incorrectly, making it possible to realize a more reliable disk device. .

[Brief explanation of the drawing]

Fig. 1 is an explanatory diagram of the principle of the present invention; Fig. 2 is a configuration diagram of an embodiment of the invention; Fig. 3 is an explanatory diagram of the servo pattern and successive signals of the present invention; Fig. 4 is an operation timing chart of the present invention; FIG. 5 is an explanatory diagram of the position signal of the present invention. In the figure, 10: disk medium 12: servo heads 14-1 to 4 peak detection means (peak detector) 1
6-1.16-2: Position signal generating means (circuit) l8: Head driving means (circuit) 20: Capacitor 22: Switching means (transistor) 24: First current source 26: Second current source 28: Current Source switching means 28-10. 11. 20. 21: Selector switch 30: Current source (for discharging) 32: Window switch 34: AD converter 36: MPU 38.46: DA converter 40: Power amplifier 42: Head motor 44: AGC amplifier 48.50: Differential amplifier

Claims (2)

[Claims] (1) A disk medium (10) recording a servo pattern in which the same amplitude pattern is repeated in the circumferential direction and different types of amplitude patterns are repeated in the radial direction in units of multiple tracks.
a servo head (12) that reads a servo pattern recorded on the disk medium (10) and outputs a servo signal; and a peak detection means (12) that detects the amplitude peak value of the servo signal from the servo head (12). 14-1 to 14-4); and a position indicating the radial position of the servo head (12) relative to the disk medium (10) based on the peak value detected by the peak detection means (14-1 to 14-4). position signal generating means (16-1, 16-2) for generating a signal; and a seek operation for moving the head in the radial direction based on the position signal from the position signal generating means (16-1, 16-2). In a servo control circuit for a disk device, the servo control circuit for a disk device includes: a head drive means (18) for performing an on-track operation for causing the head to follow the track;
-1 to 14-4) include a capacitor (20) that charges and holds the peak level of the servo signal; a switching means (22) that conducts while the input servo signal exceeds the charging voltage of the capacitor (20); a first upper limit current limit value (Imax1) that supplies a charging current to the capacitor via the switching means (22);
); a first upper current limit value (Imax1) that supplies a charging current to the capacitor (20) via the switching means (22);
Second upper limit current limit value (Imax2) that is sufficiently smaller than
a second current source (26) comprising; an output of the first current source (24) is connected to the switching means (22) during a seek operation of the head driving means (18); current source switching means (22) for connecting the output of the second current source (26) to the switching means (22);
(28) A servo control circuit for a disk device, comprising: and; (2) Servo control of a disk device according to claim 1, characterized in that the second upper limit current limit value (Imax2) is set to a value of 1/10 or less of the first upper limit current limit value (Imax1). circuit.