JP3686271B2 - Magnetic disk unit - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a magnetic disk device capable of correcting a loop gain for positioning control, and more particularly to a device capable of correcting a loop gain for positioning control by estimating a force constant of an actuator that drives a magnetic head. .
[0002]
[Prior art]
Conventionally, an actuator force constant compensation method in a magnetic disk apparatus has been used for the purpose of highly accurate positioning control of a magnetic head, as disclosed in, for example, Japanese Patent Laid-Open No. 6-259900.
FIG. 4 is a circuit block diagram of positioning control showing an example of the prior art, and FIG. 5 is a control block diagram thereof. Each component will be described with reference to FIG. The spindle motor drive circuit 14 performs start-up of the spindle motor 3 and control at steady rotation. The CPU 13 monitors the number of rotations of the spindle motor 3 and calculates the positioning control of the magnetic head 2 of the magnetic disk 1. The head amplifier 11 amplifies the servo reproduction signal 21 output from the magnetic head 2 and outputs a servo signal 22.
[0003]
The position detection circuit 12 outputs a track information signal 23 from the servo signal 22 and a position error signal 24 indicating a position deviation from the track center. The power amplifier 15 supplies a current proportional to the analog control signal 28 to the actuator 4. The DA converter 16 converts the digital control signal 29 from the CPU 13 into an analog control signal 28.
[0004]
The actuator 4 is represented by a gain Kf52 indicating a force constant, a gain 1 / M53 indicating the mass of the actuator, and two integrators 1 / S54 and 1 / S55 in the control block diagram of FIG. The inside of the CPU 13 includes a force constant estimating means 58, a controller 60, an excitation signal generating means 61, a force constant correcting means 62, and an observer 59 for estimating the speed.
In FIG. 4, 25 is a drive signal, 26 is a start-up signal, 27 is a rotation speed signal, 29 is a digital control signal, 30 is a drive signal, 73 is an estimated speed signal, and 77 is an estimation result.
[0005]
Next, the operation will be described. After the power is turned on, the spindle motor 3 is positioned on the target track when the spindle motor 3 is in a steady rotation. In this state, the excitation signal generating means 61 outputs the sine wave data on the memory at every predetermined interval (sampling period), and outputs a sine wave signal having a predetermined frequency over several cycles. The sine wave signal 75 output from the excitation signal generating means 61 is added to the control output 74 at the addition point 63 and sent to the actuator 4 through the force constant correcting means 62 and the drive circuit gain 51.
[0006]
As a result, the actuator 4 is vibrated for several cycles with a sine wave. At this time, the force constant estimation means 58 obtains a transfer gain from the drive circuit gain 51 to the position sensitivity gain 57 by Fourier transform using the control output 76 to which the sine wave signal 75 is added as an input and the position signal 72 as an output. Thereafter, the gain Kf52, which is a force constant, is obtained by multiplying the known drive circuit gain 51, the position sensitivity gain 57, and the inverse of the gain 1 / M53, respectively. The difference between the obtained gain Kf52 and the design value is calculated by the force constant correction means 62, and the correction gain is set.
[0007]
The force constant estimation and correction operations described above are performed on several tracks after the power is turned on to estimate the force constant that varies depending on the position of the magnetic head 2 and is always constant regardless of the position of the magnetic head 2. A control band can be secured. This method can also absorb fluctuations in the force constant due to aging. Even after the correction operation is finished once after the power is turned on, the correction of the correction operation is repeated as appropriate to absorb the fluctuation of the force constant due to the temperature change.
[0008]
However, an NRRO (non-repeatable runout) component and RRO (repeatable runout) component of the spindle motor 3 and a disturbance 71 of the NRRO component due to vibration of the magnetic disk 1 are added to the servo reproduction signal 21 at the addition point 64. Since these disturbances 71 contain a lot of frequency components close to the frequencies used for estimation, there is a problem that the position signal 72 that is output at the time of Fourier transform is affected and the estimation accuracy of the force constant deteriorates. is there. In order to avoid this, a method has been employed in which estimation is performed at several frequencies and the gain Kf52 obtained at each frequency is averaged for estimation.
[0009]
[Problems to be solved by the invention]
The first problem is that disturbance components such as the NRRO component and RRO component of the spindle motor 3 and the vibration component of the magnetic disk 1 are included in the measurement path from the digital control signal 29 to the position signal 72 as shown in FIG. It is to end up. As a result, the position signal that is output at the time of Fourier transform is affected, and high-precision loop gain correction cannot be performed.
[0010]
The second problem is that in order to obtain accuracy with this conventional method, measurement must be performed at various frequencies, so that a large amount of memory is required and the time until the end of correction is lengthened.
[0011]
[Means for Solving the Problems]
In order to solve the above-described problems, the invention described in claim 1 includes a magnetic disk (for example, the magnetic disk 1 in the embodiment) and a magnetic head (for example, the magnetic head 2 in the embodiment), and an actuator for moving the magnetic head. In a magnetic disk device having a positioning control mechanism for positioning the magnetic head to a target track (for example, the actuator 4 in the embodiment) (for example, the power amplifier 15 in the embodiment). ), An excitation signal generating means for outputting an excitation signal for exciting the actuator to the drive circuit (for example, the excitation signal generating means 61 in the embodiment), and an inverse for detecting the speed of the actuator when the actuator is vibrated. An electromotive voltage detection circuit (for example, the counter electromotive voltage detection circuit 17 in the embodiment); Force constant estimation means for estimating the force constant of the actuator from the vibration signal and the speed signal of the back electromotive voltage detection circuit (for example, the force constant estimation means 58 in the embodiment), and the loop gain of the positioning control is corrected from the estimated force constant. It has a force constant correction means (for example, the force constant correction means 62 in the embodiment).
[0012]
Therefore, to correct the force constant of the actuator, an excitation signal is sent from an excitation signal generator such as an excitation signal generator to the drive circuit, and the drive circuit passes a current proportional to the excitation signal to the actuator. At this time, the counter electromotive voltage generated in the actuator is detected by a reverse voltage detection circuit, and the speed of the actuator is detected. The force constant of the actuator is estimated by force constant estimating means by Fourier transform from the speed signal and the vibration signal. Then, the gain is corrected by the force constant correcting means so that the positioning control band of the magnetic head becomes a desired value from the estimated force constant.
The invention described in claim 2 is characterized in that the excitation signal for exciting the actuator is a sine wave signal (for example, the sine wave signal 75 in the embodiment).
With such a configuration, it is possible to smoothly perform arithmetic processing during Fourier transform.
[0013]
DETAILED DESCRIPTION OF THE INVENTION
Next, an embodiment of the present invention will be described with the same reference numerals assigned to the same parts as the prior art. FIG. 1 is a circuit block diagram of one embodiment of the present invention.
In the figure, a magnetic disk apparatus 1 includes a spindle motor drive circuit 14 that controls the spindle motor 3 to be started and controlled at a regular rotation, and a CPU 13 that monitors the rotation speed of the spindle motor 3 and calculates the positioning control of the magnetic head 2. A head amplifier 11 that amplifies the servo reproduction signal 21 output from the magnetic head 2 and outputs a servo signal 22, a track information signal 23 from the servo signal 22, and a position error signal 24 indicating a positional deviation from the track center. An output position detection circuit 12; a DA converter 16 that converts a digital control signal 29 from the CPU 13 into an analog control signal 28; a power amplifier 15 that supplies a current proportional to the analog control signal 28 to the actuator 4; The reverse signal which detects the back electromotive voltage from the driving signal 30 and outputs the speed signal 31 A voltage detection circuit 17, and a AD converter 18 for converting the speed signal 31 is an analog signal into a digital speed signal 32.
[0014]
Next, the control block of FIG. 2 will be described in correspondence with the circuit block diagram of FIG.
The actuator 4 is represented by a force constant gain Kf52, a mass gain 1 / M53, and two integrators 1 / S54 and 1 / S55.
The position sensitivity gain 57 is obtained by multiplying the transmission gains of the head amplifier 11 and the position detection circuit 12. The drive circuit gain 51 is obtained by multiplying the DA converter 16 and the transmission gain of the power amplifier 15. The speed conversion gain 56 is obtained by multiplying the back electromotive voltage detection circuit 17 and the transmission gain of the AD converter 18. The CPU 13 has a force constant estimating means 58, a controller 60, an excitation signal generating means 61, a force constant correcting means 62, and an observer 59 for estimating the speed.
[0015]
Further, the back electromotive voltage detection circuit 17 will be described with reference to FIG. The back electromotive voltage detection circuit 17 includes an inverting amplifier including a resistor 47 (R1), a resistor 48 (R2), and an operational amplifier 45, an inverting amplifier including a resistor 49 (R3), a resistor 50 (R4), and an operational amplifier 46, and a current detection. A resistor 41, an actuator coil resistance 43 (Rm), an actuator coil inductance 44 (Lm), and a back electromotive voltage 42 (Vb).
Assuming that the current on the input side of the drive signal 30 is I, the voltage Vout on the output side of the speed signal 31 is as follows. (As DC component, Lm = 0)
Vout = − (Vb + (Rm−Rs * R2 / R1) * I) * R4 / R3
Therefore, if the ratio of the resistors 47 (R1) and R48 (R2) is R2 / R1 = Rm / RS, the counter electromotive voltage multiplied by R4 / R3 to Vout can be taken out, and the speed of the actuator 4 can be obtained.
[0016]
The operation will be described with reference to FIGS.
When the magnetic disk device 1 is powered on, the CPU 13 sends a startup signal 26 to the spindle motor drive circuit 14.
When the spindle motor drive circuit 14 receives the start-up signal 26, the spindle motor 3 is activated by the drive signal 25 and performs a control operation at a steady rotational speed.
When the CPU 13 confirms that the rotation is steady by the rotation speed signal 27 output from the spindle motor drive circuit 14, the CPU 13 next performs the positioning operation of the magnetic head. PID compensation is used for positioning compensation.
[0017]
The controller 60 calculates PID compensation from the estimated speed signal 73 and the position signal 72 output from the observer 59. When the positioning to the target track is completed, the force constant of the actuator 4 is estimated. The excitation signal generating means 61 outputs the sine wave data stored in the memory in the excitation signal generating means 61 at every servo sampling period, and the sine wave signal having a preset frequency is spread over several periods. Generate.
The servo sampling period is a period for reading the servo information discretely written on the track of the magnetic disk 1.
[0018]
The sine wave signal 75 output from the vibration signal generating means 61 is added to the control output 74 at the addition point 63 to become the control output 76, and the force constant correcting means 62 and the drive circuit gain 51 are applied to the actuator 4 . As a result, the actuator 4 is vibrated for several cycles with a sine wave.
At this time, the force constant estimating means 58 obtains a transfer gain from the drive circuit gain 51 to the speed conversion gain 56 by Fourier transform using the control output 76 to which the sine wave signal 75 is added as an input and the digital speed signal 32 as an output. The force constant gain Kf52 can be obtained by multiplying the calculated result, that is, the drive circuit gain 51, the speed conversion gain 56, and the reciprocal of the gain 1 / M53, which are known from the transmission gain .
[0019]
According to this estimation method, as apparent from FIG. 2, disturbance 71 such as the NRRO component and RRO component of the spindle motor 3 and the NRRO component due to vibration of the magnetic disk 1 does not enter the measurement path at the time of estimation. The digital speed signal 32, which is the output at the time, includes only the excited frequency component, and high-precision estimation is possible.
Since the transmission gain of the gain Kf 52 has been obtained, the force constant estimating means 58 sends this estimation result 77 to the force constant correcting means 62. The force constant correction means 62 calculates the difference between the estimation result 77 and the design value and sets it as a correction gain.
As a result, the loop gain of the positioning control can be kept constant.
[0020]
【The invention's effect】
As described above, according to the first aspect of the present invention, the NRRO (non-repeatable runout) component of the spindle motor, the RRO (repeatable runout) component, and the vibration of the magnetic disk are included in the measurement path when estimating the force constant. Therefore, the force constant can be estimated with high accuracy and the reliability can be improved.
Since there is no need to measure at various frequencies, there is an effect that the memory of the excitation signal generating means can be reduced, and there is an effect that the time until the correction of the force constant is completed can be shortened.
According to the invention described in claim 2, there is an effect that the arithmetic processing at the time of Fourier transform can be smoothly performed.
[Brief description of the drawings]
FIG. 1 is a circuit block diagram of an embodiment of the present invention.
FIG. 2 is a control block diagram of one embodiment of the present invention.
FIG. 3 is a back electromotive force detection circuit diagram according to an embodiment of the present invention.
FIG. 4 is a circuit block diagram of the prior art.
FIG. 5 is a control block diagram of the prior art.
[Explanation of symbols]
1 Magnetic disk 2 Magnetic head 4 Actuator 15 Power amplifier (drive circuit)
17 Back electromotive voltage detection circuit 51 Drive circuit gain 52 Gain Kf
53 1 / M gain 54 Integrator 1 / S gain 56 Speed conversion gain 58 Force constant estimation means 61 Excitation signal generation means 62 Force constant correction means 75 Sine wave signal (excitation signal)

Claims (2)

In a magnetic disk device having a magnetic disk and a magnetic head, an actuator for moving the magnetic head, and a positioning control mechanism for positioning the magnetic head on a target track, a drive circuit for supplying current to the actuator, and an actuator are added. From the vibration signal generating means for outputting the vibration signal to be driven to the drive circuit, the back electromotive voltage detection circuit for detecting the speed of the actuator when the vibration is applied, and the speed signal of the vibration signal and the back electromotive voltage detection circuit A magnetic disk device comprising force constant estimating means for estimating a force constant of an actuator and force constant correcting means for correcting a loop gain of positioning control from the estimated force constant. 2. The magnetic disk apparatus according to claim 1, wherein the excitation signal for exciting the actuator is a sine wave signal.

Images