JP3352715B2 - Head positioning device for magnetic disk drive - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magnetic disk device used as a storage device of a computer or the like, and more particularly to a head positioning device for a small and high-capacity magnetic disk device whose demand has been rapidly increasing in recent years.

[0002]

2. Description of the Related Art Conventionally, in a magnetic disk device, a servo surface servo for positioning a head to a target data track by relying on servo information written on one surface of a recording medium has been widely used. However, in this method, since the data head is positioned based on the reliability of the accuracy of the positional relationship between the servo surface and the data surface, off-track is likely to occur due to various environmental changes, for example, a temperature change in the device. There is a disadvantage that it is difficult to increase the track density.
Therefore, recently, attention has been paid to a data surface servo method for writing servo information on a data surface and improving reliability during recording and reproduction. One of them is a sector servo method. In this method, a positioning servo sector is embedded in advance at the head of each sector on the data surface, and when an arbitrary data track is selected, the head follows each data track based on the servo information of the servo sector. It is a method. According to this method, the servo surface and the data surface are not physically separated from each other as in the conventional servo surface servo method, so that the influence of off-track can be eliminated and the track density can be dramatically increased.

An example of the sector servo system will be described below. FIG. 6 is a block diagram of an example of a magnetic disk drive of the sector servo system. In FIG. 6, reference numeral 1 denotes a rotatable magnetic medium such as a magnetic disk, which is rotated at a constant speed by a spindle motor (not shown). Reference numeral 2 denotes a servo sector in which servo information discretely embedded (recorded) in advance on the surface of the magnetic medium is recorded in the circumferential direction. Reference numeral 3 denotes a data sector for recording data. Reference numeral 4 denotes an information track composed of a servo sector and a data sector, and a plurality of tracks are recorded on concentric circles. 5 is a data head capable of reading and writing information on the information track, 6 is a VCM (voice coil motor) positioner for moving and positioning this data head to the selected information track, and 7 is a magnetic head of the VCM positioner. This is a VCM magnetic circuit that forms a circuit and generates driving torque. 8 is a head amplifier for amplifying a small signal from the data head to a level suitable for processing, and 9 is a servo for detecting a discrete servo signal from the output signal from the head amplifier 8 and extracting the signal. Information demodulator, 10 is head position information recognizing means for recognizing and determining the relative positional relationship of the data head with respect to the information track using the servo pattern formed in the servo sector, 100 is the output of the head position information recognizing means and 100 CPU) 101, the distance in the radial direction of the recording medium between the arbitrarily determined track and head,
A head positioning signal generation device that calculates at a track width resolution and generates a head positioning signal in accordance with the calculated content.11.A track access control for moving (accessing) a data head to a selected information track. A speed commander that gives a target speed command value according to the distance or the number of tracks to the target track, 12
Is a speed detector that generates speed information based on the position information output from the head position information recognizing means 10 each time the data head passes through the servo sector, and 13 calculates an error between the speed commander 11 and the output of the speed detector 12. The output of the error amplifier 13 is supplied to a current driver 17 that supplies a drive current to the VCM positioner 6 via a compensator 14 and a switch 16 to form a speed control loop. Further, after moving to the selected information track, a position control loop for causing the data head to follow the information track includes:
The output of the head positioning signal generator 100 is supplied to a current driver 17 via a compensator 15 and a switch 16.

The operation of the conventional magnetic disk drive head positioning device configured as described above will be described with reference to FIG. First, the central processing unit 101 determines which information track of the magnetic medium 1 the data head 5 should be positioned in accordance with a command from an external device. Next, the central processing unit 101 calculates the radial distance between the current data head position and the target information track in the magnetic medium direction, and furthermore, the central processing unit 101 corresponds to the remaining distance according to the speed profile shown by the solid line in FIG. Speed commander 1
Output to 1 sequentially. The remaining distance to the target track can be easily obtained by subtracting the output of the head position information recognizing means 10 from the target track position. When the remaining distance to the target track reaches a certain distance K, the central processing unit 101 decelerates the speed command value according to the speed profile. Thus, as the speed command value approaches zero, the remaining distance to the target track approaches zero.
The central processing unit 101 determines that the remaining distance to the target track is zero.
Is determined, the switch 16 is switched to the position control, and the data head is controlled to follow the target track in accordance with the position information from the head position information recognizing means 10. As described above, in the head positioning device of the magnetic disk drive, the data head is positioned quickly and accurately from the current position to the target track. Here, as shown in FIG. 7, the time required to move the data head to a position very close to the target position by the speed control is set to the seek time. After the data control is switched from the speed control to the position control, the data head is moved to the track center position. The time required for settling is called the settling time, and the rotation wait time and the access time of the magnetic disk excluding the software overhead are the sum of these two times. In a positioning device of a magnetic disk drive, how to shorten the access time generally becomes a major issue.

[0005]

In the above-described positioning device of the magnetic disk drive of the sector servo system, the servo information is discretely embedded. Therefore, the servo information can be obtained continuously by the servo surface servo. Based on discrete servo information obtained by discretely sampling servo information, a speed control servo loop and a position control servo loop are configured. Therefore, the time delay between samples becomes the phase delay as it is, and it is not possible to increase the phase margin near the gain intersection of the servo loop. On the other hand, VCM
The magnetic material constituting the magnetic circuit of the positioner is made of a material having a very small coercive force in order to obtain a large torque with a small size and a small current and to shorten the seek time. However, magnetic materials having a high coercive force generally have remarkable deterioration in characteristics due to temperature changes, and therefore have the disadvantage that the torque constant of the VCM positioner is greatly reduced due to changes in environmental temperature and self-heating due to coil loss. ing. In addition, the heat generated by the coil itself also increases the resistance of the coil.
This is a major factor in reducing the positioner torque constant. FIG. 5 shows the characteristics of the maximum gap magnetic flux density with respect to the temperature of a neodymium magnet, which is one of the high coercivity magnetic materials.
As can be seen from this figure, when the temperature of the magnetic material increases, VC increases.
Even if a constant current is applied to the M positioner, the generated torque is reduced, and the torque constant is significantly reduced. The coil is composed of ordinary copper wire, copper because it has a resistance temperature coefficient number γ of about 0.00393, the current flowing through the coil by the temperature rise of the coil is briefly reduced. As described above, the characteristics of the magnetic material are degraded due to the temperature rise, and V
When the torque constant of the CM positioner decreases, the overall transmission characteristic of the servo loop decreases, and in the speed servo system, an inrush speed error occurs when switching to position control.
If the stability during settling is impaired and severe,
Accurate positioning cannot be performed. In the position servo system, the followability of the VCM positioner is deteriorated, causing an increase in settling time. Therefore,
If the overall gain of the servo loop is set high to maintain the stability of the servo system and shorten the settling time even if the transfer characteristics decrease, the position margin at room temperature will decrease and the stability will worsen. Time increases.
There is a drawback that it is difficult to shorten the access time to the target track due to these conflicting conditions. An object of the present invention is to solve the above problem, and an object of the present invention is to provide a head positioning device of a magnetic disk drive capable of shortening the access time on average even if the environmental temperature changes.

[0006]

SUMMARY OF THE INVENTION In order to achieve the above object, the present invention provides a rotatable magnetic medium having a plurality of tracks formed of data information and discrete servo information on concentric circles; A data head for reading and writing information, an actuator for moving the data head to an arbitrary track position on a magnetic medium, a magnetic material constituting a voice coil motor used as an actuator, and temperature detection for measuring an environmental temperature near the actuator Means,
Table storage means for storing the variation of the transfer characteristic with respect to the temperature of the magnetic material, servo information demodulation means for separating servo information from an output signal from the data head and demodulating the information into position information, and externally using position information from the servo information demodulation means. Central processing means for outputting a speed command value and a position command value for positioning the data head to a track position corresponding to the command from the actuator to the actuator, wherein the speed command value and the position command value are the output a variable <br/> head positioning device of a magnetic disk device for varying the detects a current value flowing through the voice coil motor by adding a predetermined time constant voltage to a voice coil motor, the central processing unit from the current value Temperature inside the voice coil motor calculated by the above and the ambient temperature near the actuator detected by the temperature detecting means. Using the door, and calculates the temperature of the magnetic material in consideration of the thermal gradients that lead to the temperature detection means from the voice coil motor.

[0007]

According to the present invention, when the environmental temperature rises and the magnetic circuit characteristics of the VCM positioner deteriorate due to the above-described configuration, the overall loop gain of the servo system decreases, and as a result, the following performance deteriorates. By increasing the gain of the transfer characteristic of the electric system, the total loop gain can be increased to suppress the increase in seek time. Also, when the ambient temperature decreases, the magnetic circuit characteristics of the VCM positioner improve, and the overall loop gain of the servo system increases, so that the phase margin near the servo gain intersection becomes insufficient and the stability of the system deteriorates. In addition, it is possible to reduce the gain of the transfer characteristic of the electric system, increase the phase margin near the intersection of the servo gain, and suppress the increase in the settling time. In this way, V
Variations in the characteristics of the magnetic material of the magnetic circuit of the CM can be suppressed, and the access time can be averagely shortened even if the environmental temperature changes.

[0008]

FIG. 1 shows a block diagram of a head positioning device of a magnetic disk drive according to an embodiment of the present invention. In FIG. 1, 1 is a magnetic medium, 2 is a servo sector, 3 is a data sector, 4 is an information track composed of a servo sector and a data sector, 5 is a data head for reading and writing information on the information track, and 6 is an arbitrary data head. VC that moves to the information track and performs positioning
M positioner, 7 is a VCM magnetic circuit, 8 is a head amplifier, 9 is a servo information demodulator for detecting a servo signal, and 10 recognizes a relative position of a data head with respect to an information track using a servo pattern formed in a servo sector. Head position information recognition means for discriminating, 11 is a speed commander,
12 is a speed detector, 13 is an error amplifier that outputs an error between the speed command value of the speed commander and the speed detection value of the speed detector, 14, 15
Is a compensator, 16 is a switch for switching the servo loop between the speed control system and the position control system, and 17 is a current driver for driving the VCM positioner, which is the same as in the conventional example. Reference numeral 18 denotes a temperature sensor (for example, a thermistor) for detecting an ambient temperature near the VCM magnetic circuit, and a temperature information output is input to the central processing unit 101. Reference numeral 19 denotes a current detection circuit which detects the amount of current for driving the VCM positioner 6 by the current driver 17 and inputs the result to the central processing means 101. Numeral 100 denotes a head positioning signal generator, which uses a head central processing unit (CPU) 101 to generate a signal for correctly positioning a data head on a target information track. Reference numeral 102 denotes a table storage unit which stores data corresponding to the temperature information detected by the temperature sensor 18 described above.

Hereinafter, the operation will be described in detail. First, when the position information of the target information track is input from the outside to the head positioning signal generator 100, the central processing unit 101 determines the position information of the information track where the current data head is located, and the position of the target information track. The distance information to be moved is calculated from the information. The position information is stored in the servo sector 2 as binarized information. This position information is discretely written on the magnetic medium (disk) 1.
(Embedded) and data head 5 is in servo sector 2
Every time it passes above, it is discriminated from the data information written in the data sector 3 by the servo information demodulator 9 and detected discretely. Based on the current position information (P _N ) obtained here, the central processing means 101 generates distance information (D _N ) indicating how far the current data head position is away from the target track position (P _D ). calculate. D _N can be easily calculated by the equation (1).

[0010]

[Number 1] _{D N} = P D - P _N as described in the prior art, the speed command unit 11 the distance information
(D _N) incorporates a speed profile as shown in FIG. 7 corresponding to, VC in accordance with the velocity profile
Sequentially outputs a speed command value V _C so as to drive the M. Further, at this time, the central processing means 101 outputs the detected current position information (P _N ) and the position information (P _N ) obtained from the immediately preceding servo sector.
_The present data head moving speed between tracks (V _N ) is calculated from _N-1 ) according to the equation ( ₂ ).

[0011]

V _N = P _N -P _N-1 / T _N -T _N-1 (where T _N is the current time and T _N-1 is the time at which the previous servo sector was detected) Command value (V _C ) and speed detection value
(V _N ) is input to the error amplifier 13 and the difference between the speed command value V _C and the speed detection value V _N that is the actual speed, that is, the speed error _VE is output, and passes through the compensator 14 and the current driver 17 at the subsequent stage. VC
The speed error is fed back so that the M positioner 6 cancels the speed error and moves at the speed according to the command value. In such a speed system, the VCM is speed-controlled, and the distance D
_The data head is moved so that _N becomes zero. Here, when the distance (D _N ) to the target track approaches 0, the speed commander 11 gradually reduces the speed according to the speed profile shown in FIG. When the distance (D _N ) approaches 0 and the speed command value (V _N ) decreases, the central processing means 101 switches.
At 16 the system is switched from speed control to position control, and a more accurate positioning operation is started. In the position control servo loop, the central processing unit 101 determines the target track position (P _D ).
The track burst signals α and β written in the servo sector 2 are fetched by built-in A / D conversion, and the position error signal (P _E ) is calculated according to the equation (3).

[0012]

[Number 3] _{P E = K · (α-} β) where K is a constant.

Further, the position error signal (P _E ) is sent to the central processing unit 101.
Is converted into a position error signal by a D / A converter incorporated in the compensator 15 and output to the compensator 15.
The current is fed back via the current driver 17 so that the VCM positioner 6 moves so as to cancel the position error to zero. With such a position-based servo control, V
The CM positioner 6 realizes position control for accurately following the center of the track where the data head 5 is targeted.

The speed servo system of the present embodiment will be described in more detail with reference to FIG. FIG. 2A shows a block of the speed servo system. Here, the transfer function of the VCM positioner can be expressed as Km / 1 + Tm · S. Where Km
Is a torque constant, and Tm is a mechanical time constant. The K ₁ is false
Gain constants of differential amplifier 13, K ₂ is the gain constant of the VCM driver. The loop transfer function of the entire system is as follows. That is, if Ka = K ₁ · K ₂ , a first-order lag system represented by the equation (4) is obtained.

[0015]

(Equation 4)

The stability of the system at this time can be explained using a Bode diagram. The gain characteristic of the Bode diagram in this speed servo system attenuates by -20 db / Dec at 1 / Tm as shown in FIG. 2 (b). The phase characteristic is ideally constant at -90 °, but in actuality, as shown in FIG. 2 (c), because of the sampling delay of the embedded servo, the position is further delayed by 90 ° at half the sampling period. The 180 ° phase goes around. Therefore, in order to ensure the stability of the speed servo system, it is necessary to secure a frequency at which the gain is 0 db, that is, a phase margin at the gain intersection, which is usually about 40 °. Therefore, it is necessary to reduce the gain in the speed system to an appropriate level. On the other hand, if the gain is reduced, the followability of the speed system is reduced, and the steady-state error is increased. Therefore, it is necessary to keep the overall gain in this speed system at an appropriate value.

Next, the position servo system will be described in detail. FIG. 3A shows a block of the position servo system.
As in the description of the velocity servo system, the transfer function of the VCM positioner can be expressed as Km / 1 + Tm · S. The gain constant of the position command value outputted from the central processing unit 101 of K _1,
K ₂ is the gain constant of the VCM driver. The loop transfer function of the entire system is as shown in Expression 5.

[0018]

(Equation 5)

It can be seen from this that if the gain Ka is increased in order to increase the responsiveness of the system, the damping factor 小 さ く becomes smaller and the stability of the system is impaired. This can be specifically explained using a Bode diagram. FIGS. 3B and 3C show Bode diagrams of this system. Wc is usually 4 at gain intersection
It is taken to about 00Hz. The phase delay at this gain intersection is 1
As the temperature approaches 80 °, the stability of the system gradually decreases. Therefore, the compensator 14 performs phase lag compensation in the low frequency range, gains gain in the low frequency range, improves responsiveness,
In the high frequency range, phase lead compensation is performed to reduce the phase lag in the frequency range above the gain intersection Wc, thereby increasing the servo stability. Here, if the magnetic characteristics of the VCM magnetic circuit change due to the temperature characteristics of the magnetic material shown in FIG. 5 due to an increase in ambient temperature and self-heating due to coil loss, the torque constant Km of the VCM positioner becomes Km.
_It changes from ₁ to Km ₂ . In general, when the temperature of a magnetic circuit rises, its characteristics deteriorate and the torque constant decreases. Here, the central processing means 101 detects the temperature near the magnetic body of the VCM positioner by a temperature sensor located near the VCM magnetic circuit. Furthermore, in order to detect the coil temperature rise during VCM port Jishona continuous operation, providing by the central processing unit 101 the current driver 17 a constant voltage by a pulse width of an extent that does not adversely affect the VCM positioner 6 at the right time.
At this time, the central processing means 101 can input the current value of the current detection circuit 19 and detect the resistance value of the coil of the VCM positioner 6. Further, since the resistance value at normal temperature is detected and stored in advance by the central processing means 101, the resistance value obtained by the thermal resistance method is given by
The current temperature of the coil can be known according to the following equation.

[0020]

[6] _{T 2 - T 1 = (R} 2 - R 1) / (γ × R 1) where, T ₁ room temperature of temperature, R ₁ is the coil resistance value at normal temperature,
T ₂ are a current temperature, R ₂ is the current of the coil resistance.

Here, assuming that the coil resistance at room temperature is 20Ω, the current coil resistance is 30Ω, and the room temperature is 20 ° C., the current coil temperature difference is about 127 ° C. according to the above formula.
It can be seen that it is. The temperature sensor 18 detects the ambient temperature of the VCM magnetic circuit at this time, and calculates the temperature rise of the magnetic body itself from the previously detected coil temperature and the thermal gradient of the magnetic body. At this time, the characteristic deterioration due to the temperature rise of the magnetic material can be easily calculated since the temperature characteristics shown in FIG. 5 are stored as a table. The torque constant of the VCM positioner 6 thus decreases due to an increase in resistance due to a rise in temperature of the coil itself and a rise in temperature of the magnetic body, and the result is stored in the table storage means 102 storing the above calculation and a temperature characteristic table of the magnetic body. By reference, the central processing unit 101 detects the information. As described above, the VCM
The central processing means 101 detects the temperature rise of the magnetic material of the positioner 6 and the temperature rise of the coil, and infers a decrease in the torque constant of the VCM positioner 6 due to the temperature rise. Based on the inferred value, the central processing unit 101 determines the phase margin at the gain intersection of the loop transfer function of the speed servo system described above.
The gain constant K ₁ of the error amplifier 13 is maintained so as to maintain the angle at about 40 °.
Is increased or decreased to vary the output of the speed command value. In the position servo system as well as in the speed servo system, the central processing unit 101 is used.
In order to keep the phase margin at the point of gain crossover of the loop transfer function of the position system constant, the above equation P _E = K · (α−β)
Operating the conversion gain K to increase or decrease this conversion gain ,
The output of the command value Ru is varied. FIG. 4 shows the result of the embodiment of the positioning operation according to the present invention. Compared with the conventional example, the rush speed error when shifting from speed control to position control is reduced even when the magnetic conversion characteristics of the magnetic circuit are greatly deteriorated as shown in FIG. 5 due to the ambient temperature and self-heating of the VCM positioner. In addition, since the stability after the shift to the position control is increased, the settling time is shortened. As a result, the positioning operation can be performed stably and the access time can be shortened.

[0022]

As described above, in the prior art, the characteristics of the magnetic circuit of the VCM are deteriorated due to an increase in the ambient temperature and self-heating, and when the resistance of the coil increases, the response becomes poor, resulting in a seek time. Inevitably increases, and a steady-state error in the control of following the track increases. In addition, when the ambient temperature decreases, the VCM magnetic characteristics improve, and as a result, the overall gain of the system increases too much, thereby deteriorating the stability of the system and increasing the settling time. Had increased. However, as is apparent from the embodiment, the use of the head positioning device according to the configuration of the present invention makes it possible to keep the total gain of the entire system constant even when the temperature fluctuates. The servo system can be adjusted to the best point, and there is an effect that it is possible to provide a small and high-density magnetic disk device capable of always performing a stable operation with a high access time.

[Brief description of the drawings]

FIG. 1 is a block diagram of a head positioning device of a magnetic disk drive according to an embodiment of the present invention.

FIG. 2 is a diagram illustrating a speed servo in one embodiment of the present invention.

FIG. 3 is a diagram illustrating a position-based servo in one embodiment of the present invention.

FIG. 4 is a diagram for explaining an actual positioning operation in one embodiment of the present invention.

FIG. 5 is a diagram illustrating an example of a temperature characteristic of a high coercive force magnetic body.

FIG. 6 is a block diagram of a conventional head positioning device for a magnetic disk drive.

FIG. 7 is a diagram showing a positioning operation of a conventional magnetic disk drive.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Magnetic medium, 2 ... Servo sector, 3 ... Data sector, 4 ... Information track, 5 ... Data head, 6 ...
Voice coil motor (VCM) positioner, 7 ... VCM
Magnetic circuit, 8: Head amplifier, 9: Servo information demodulator, 10: Head position information recognition means, 11: Speed commander, 12: Speed detector, 13: Error amplifier, 14, 15 ...
Compensator, 16… Switch, 17… Current driver, 18…
Temperature sensor, 19: current detection circuit, 100: head positioning signal generator, 101: central processing means, 102: table storage means.

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁷ , DB name) G11B 21 / 08,21 / 10

Claims (1)

(57) [Claims] 1. A rotatable magnetic medium having a plurality of tracks formed of data information and discrete servo information on concentric circles, a data head for reading and writing information on the tracks, and a data head mounted on the magnetic medium. An actuator for moving to an arbitrary track position, a magnetic material constituting a voice coil motor used as the actuator, a temperature detecting means for measuring an environmental temperature near the actuator, and a transfer characteristic of the magnetic material for temperature. Table storage means for storing the fluctuation, servo information demodulation means for separating the servo information from the output signal from the data head and demodulating it into position information, and responding to an external command by the position information from the servo information demodulation means. The speed command value and the position command value for positioning the data head at the track position are described above. Comprising a central processing unit for outputting to the actuator, a head positioning device of a magnetic disk apparatus for varying the output of the speed command value and position command value by the data in the table storage means, a predetermined time to the voice coil motor A current value applied to the voice coil motor by applying a constant voltage is detected, a temperature inside the voice coil motor calculated by the central processing unit from the current value, and an ambient temperature near the actuator detected by the temperature detection unit. Wherein the temperature of the magnetic body is calculated in consideration of a thermal gradient from the voice coil motor to the temperature detecting means.