JP3744725B2 - Magnetic disk unit - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a magnetic disk device, and more particularly to a magnetic disk device having a speed detection unit of an actuator that drives a magnetic head.
[0002]
[Prior art]
The speed control of the magnetic head in the magnetic disk apparatus has been developed as a main technique for recording and transferring a large amount of information at a high speed as well as the positioning of the head. For example, as a technique close to the present invention, Japanese Patent Laid-Open No. Japanese Patent Application Laid-Open No. 7-192413 and Japanese Patent Application No. 10-361605 disclose a technique for estimating speed by measuring a back electromotive force generated in an actuator that drives a magnetic head.
[0003]
2. Description of the Related Art Conventionally, a magnetic disk device having an actuator speed detection circuit estimates a speed by detecting a counter electromotive voltage generated in a voice coil motor (VCM). FIG. 12 is a circuit block diagram of an embodiment of a magnetic disk device having a speed detection circuit. Referring to FIG. 12, the magnetic disk device includes a magnetic disk 1 for recording data, a magnetic head 2 for reading and writing data, a spindle motor 3 for rotating the magnetic disk 1, and an actuator 4 for driving the magnetic head 2. The head amplifier 11 that amplifies the servo reproduction signal 21, the position detection circuit 12 that generates the track information signal 23 and the position error signal 24 from the servo signal 22, the start-up signal 26 of the spindle motor 3 and the digital that drives the actuator 4 CPU 13 for generating control signal 29, spindle motor drive circuit 14 for generating spindle motor drive signal 25, power amplifier 15 for amplifying analog control signal 28, D / A converter 16, and speed for detecting the actuator speed From the detection circuit 17 and the A / D converter 18 It has been made.
[0004]
Conventionally, the speed detection circuit 17 of this type of magnetic disk apparatus has a bridge circuit that detects a voltage including a back electromotive voltage as disclosed in, for example, Japanese Patent Laid-Open No. 7-141803. The back electromotive voltage detection output V1 of the bridge circuit can be expressed as follows from the back electromotive voltage Vb, the driver output VD, the VCM winding resistance RL, and the sense resistance Rs (FIG. 3 and Formula 2 of JP-A-7-141803). .
V1 = Rs / (Rs + RL) · (VD−Vb) (1)
Since the detected voltage V1 includes the back electromotive voltage Vb generated by the movement of the VCM, the VCM speed can be estimated.
[0005]
FIG. 13 shows an embodiment of a back electromotive voltage detection circuit using an operational amplifier. Referring to FIG. 13, the speed detection circuit 17 in FIG. 12 includes an inverting amplifier including a resistor 47 (R1), a resistor 48 (R2), and an operational amplifier 45, a resistor 49 (R3), a resistor 50 (R4), and an operational amplifier 46. An inverting amplifier, a current detection resistor 41, a coil resistance Rm43 of the actuator, a coil inductance Lm44, and a back electromotive voltage Vb42. If the current (current sense current) on the input side of the VCM drive voltage 30 is I and the inductance component is ignored (Lm = 0 as a DC component), the speed estimation voltage Vout31 can be expressed as follows.
Vout =-(Vb + (Rm-Rs.R2 / R1) .I) .R4 / R3 (2)
Therefore, if the ratio of the resistors 47 (R1) and R48 (R2) is R2 / R1 = Rm / RS, the back electromotive voltage Vb multiplied by R4 / R3 to Vout can be taken out, so that the resistance gain R4 / R3 and the back electromotive force are obtained. If the constant Keb 103 is corrected, the speed of the actuator 4 can be obtained.
[0006]
FIG. 14 is a control block diagram of only the speed control system. Referring to FIG. 14, the speed control unit inside the CPU 13 includes a speed controller 130 including an integrator, a phase advance / delay controller, a gain, and the like, and a function or array value expressed by a time function or a position function. A difference between the target speed 230 and the estimated speed 231, a target speed generator 131 that generates a target speed by table lookup such as position pulling or speed pulling, a speed conversion gain 132 that converts the digital speed estimated voltage 32 to the estimated speed 231, And a speed differentiator 133 for calculating The current sense current 205 is the current I shown in FIG.
[0007]
FIG. 2 is a control block diagram of the actuator 4 and the speed detection circuit 17. Referring to FIG. 2, the actuator 4 includes an arm 101 that supports the magnetic head 2 (not shown), a VCM 102 that drives the arm 101, a counter electromotive force constant Keb 103 that converts the VCM speed 201 into a counter electromotive voltage 202, and The voltage difference unit 104 is configured to take a difference between the VCM drive voltage 30 and the back electromotive voltage 202. The speed detection circuit 17 includes a voltage conversion gain K105 that generates a VCM applied voltage estimated voltage 206 from the current sense current I205, and a voltage difference point 108 that takes a difference between the VCM drive voltage 30 and the VCM applied voltage estimated voltage 206. The The voltage conversion gain K105 is expressed as follows using the resistors R1, R2, and Rs of the speed detection circuit of FIG.
K = Rs + Rs · R2 / R1 (3)
[0008]
FIG. 9 shows frequency characteristics of the speed detection circuit unit shown in FIG. Referring to FIG. 9, the frequency characteristic from the analog control signal 28 to the actual VCM speed 201 is represented by a gain characteristic 80 and a phase characteristic 81 indicated by a broken line. On the other hand, the frequency characteristic from the analog control signal 28 to the speed estimation voltage 31 shows a gain characteristic 84 and a phase characteristic 85. The VCM speed 201 generated by adding some analog control signal 28 to the VCM is generated according to the gain characteristic 80 and the phase characteristic 81, whereas the speed estimation voltage 31 is generated according to the gain characteristic 84 and the phase characteristic 85. To do. At this time, if the frequency characteristic up to the speed estimation voltage 31 is the same as the gain characteristic 80 and the phase characteristic 81, the speed estimation voltage completely detects the VCM speed. However, in the conventional example, the gain characteristics 80 and 82 and the phase characteristics 81 and 83 coincide with each other at a frequency lower than the frequency f5 including the DC component (Lm = 0) at the frequency 0, but at a frequency higher than the frequency f5. When the characteristics are different and the analog control signal 28 includes a component higher than the frequency f5, the VCM speed 201 and the speed estimation voltage 31 do not match.
[0009]
[Problems to be solved by the invention]
A conventional magnetic disk device having a speed estimation circuit using a bridge circuit or an operational amplifier can accurately detect the VCM speed when the coil inductance Lm44 of the VCM can be ignored, but is higher in the frequency range than the frequency at which it starts to be affected by the inductance component. However, since the frequency characteristic from the actuator control signal 28 to the VCM speed 201 is different from the frequency characteristic from the actuator control signal 28 to the speed estimation voltage 31, the speed cannot be estimated accurately, and the control band of the speed control system Could not be high enough.
[0010]
That is, the problems to be solved are summarized as follows.
The first problem is that the VCM speed that changes at a high frequency cannot be estimated.
This is because the frequency characteristic from the analog control signal to the VCM speed is different from the frequency characteristic from the analog control signal to the speed estimation voltage in the frequency region where the inductance component cannot be ignored.
The second problem is that the control band of the speed control system cannot be increased. The reason is that the frequency characteristic from the analog control signal to the estimated speed voltage works like a differential operation in the high frequency range due to the influence of the inductance component, and the stability becomes insufficient when the control band of the speed control system is increased. Because.
A third problem is that approximation of the estimated speed is insufficient only by passing the estimated speed voltage through a low-pass filter that cancels the differential operation in the high frequency region. The reason is that even if the conventional speed estimation voltage is corrected by adding a secondary low-pass filter (FIG. 6) (FIG. 3), the frequency characteristics from the analog control signal to the VCM speed and the speed estimation from the analog control signal are performed. This is because the range in which the frequency characteristics up to the voltage coincide is limited (FIGS. 10 and 11).
[0011]
The purpose of the present invention is to improve the accuracy of the speed that changes at high frequencies by improving the frequency characteristics of the speed estimation circuit, and at the same time, increase the control band of the speed control system to improve the followability to the speed It is an object of the present invention to provide a magnetic disk device.
[0012]
[Means for Solving the Problems]
In order to achieve the above object, a magnetic disk apparatus according to claim 1 includes a magnetic disk and a magnetic head, a spindle motor that rotates the magnetic disk, an actuator that drives the magnetic head, a head amplifier that amplifies a servo reproduction signal, A position detection circuit for generating a track information signal and a position error signal from a servo signal, a CPU for generating a spindle motor start-up signal and a digital control signal for driving an actuator, and a spindle motor drive circuit for generating a spindle motor drive signal; Speed detection for detecting actuator speed by detecting a voltage including a back electromotive voltage generated in a power amplifier, an A / D converter and a D / A converter, and a voice coil motor (VCM) that amplifies an analog control signal in a magnetic disk device having a circuit, the VC Characterized in that it has a speed detecting circuit having a filter that corrects the inductance component.
[0013]
According to another aspect of the present invention, the filter is a filter A (106 in the embodiment) as a phase lead compensator having a coil inductance Lm of VCM, and a low-pass filter B having a frequency characteristic corresponding to the pole of the filter A. (107 in the embodiment).
[0014]
According to a third aspect of the present invention, the filter A as the phase advance compensator has a phase advance related to the coil inductance of the VCM, the voltage conversion gain of the VCM, and a predetermined set frequency, and the low pass filter B is the predetermined setting. It has the same pole as the phase lead compensator in relation to the frequency, and both have continuous smooth frequency characteristics as shown in FIG. 5 of the embodiment, for example.
[0015]
The magnetic disk apparatus according to claim 4, wherein the phase advance compensator is:
FA (S) = ((Lm / K) · S + 1) · ω1 / (S + ω1)
Identified by
The low-pass filter is
FB (S) = ω1 / (S + ω1)
However, ω1 is a frequency set according to the frequency component of the speed to be estimated,
K has a characteristic specified by a voltage conversion gain.
[0016]
The magnetic disk apparatus according to claim 5, wherein the filter includes a low-pass filter D (120 in the embodiment) for correcting a differential operation in a high frequency region and a coil inductance Lm estimated corresponding to the pole of the filter D in the low frequency region. And a high-pass filter E (121 in the embodiment) that performs a differentiation operation.
[0017]
6. The magnetic disk drive according to claim 6, wherein the low-pass filter D has a frequency characteristic related to a predetermined set frequency, and the high-pass filter E has a frequency characteristic related to a coil inductance of the VCM, a voltage conversion gain of the VCM, and a predetermined set frequency. Both have the same poles, and are characterized by, for example, continuously smooth frequency characteristics as shown in FIG.
[0018]
The magnetic disk device according to claim 7, wherein the low-pass filter is
FD (S) = ω1 / (S + ω1)
With the characteristics specified in
The high-pass filter is
FE (S) = (Lm / K) · S · ω1 / (S + ω1)
However, ω1 is a frequency set according to the frequency component of the speed to be estimated,
K has a characteristic specified by a voltage conversion gain.
[0019]
According to the magnetic disk apparatus having the above configuration, the speed estimation voltage affected by the inductance component is corrected by the filter to detect the VCM speed.
Further, the influence of the inductance component is corrected by passing the VCM applied voltage estimated voltage generated from the current sense current I through the filter A, and the VCM drive voltage in the frequency region that has been changed by the filter A is passed through the filter B. Correct in the same way. Subsequently, the VCM speed is detected by taking the difference between these correction amounts.
Further, the VCM applied voltage estimated voltage generated from the current sense current I affected by the inductance component is advanced by the filter A so that the phase of the frequency component higher than the frequency affected by the inductance component is advanced to amplify the gain. The gain and phase in the frequency domain corrected by the filter A are corrected in the same manner as the filter A by the filter B having low-pass characteristics corresponding to. Subsequently, the VCM speed is detected by taking the difference between these correction amounts.
Further, the speed estimation voltage affected by the differential operation of the conventional speed detection circuit is corrected by the filter D, and the influence of the inductance component not considered by the filter D is corrected by the filter E. Subsequently, the VCM speed is detected by taking the difference between these correction amounts.
Furthermore, the influence of the differential operation of the conventional speed detection circuit is corrected by a filter D having a low-pass characteristic, and the influence of an inductance component that is not corrected by the filter D is extracted by a filter E having a high-pass characteristic. To correct. Subsequently, the VCM speed is detected by taking the difference between these correction amounts.
[0020]
DETAILED DESCRIPTION OF THE INVENTION
Next, a first embodiment of the present invention will be described in detail with reference to the drawings.
FIG. 1 is a control block diagram of the speed detector. Referring to FIG. 1, the speed detection circuit 17 includes a voltage conversion gain 105 that generates a VCM applied voltage estimated value 206 from a current sense current I205 that flows through the VCM 102, a filter A 106 that corrects an inductance component of the VCM 102, and a pole of the filter A. And a voltage difference point 108 that takes the difference between the filter outputs. The filter A is the following phase lead compensator having the estimated coil inductance Lm44 of the VCM.
FA (S) = ((Lm / K) · S + 1) · ω1 / (S + ω1) (4)
However, ω1 is a frequency set according to the frequency component of the speed to be estimated,
K is voltage conversion gain 105
The filter B is the following low-pass filter corresponding to the pole of the filter A106.
FB (S) = ω1 / (S + ω1) (5)
[0021]
FIG. 5 shows the frequency characteristics of the filter used in the embodiment of the present invention. Referring to FIG. 5, filter A shows gain characteristic 70 and phase characteristic 71, and filter B shows gain characteristic 72 and phase characteristic 73.
[0022]
The operation of the present invention will be described below with reference to the drawings. Referring to FIG. 5, the gain characteristic 70 and the phase characteristic 71 of the filter A 106 gain in a frequency region higher than the frequency f5 of FIG. 9 in which the VCM coil inductance Lm44 starts to affect the component of the VCM applied voltage estimated voltage 206. And the phase are changed to generate the VCM applied voltage correction voltage 207. At the same time, the VCM drive correction voltage 208 is generated by the gain characteristic 72 and the phase characteristic 73 of the filter B 107 corresponding to the frequency component changed at the pole of the filter A. Subsequently, the difference between the VCM applied voltage correction voltage 207 and the VCM drive correction voltage 208 is taken to output the speed estimation voltage 31a.
[0023]
FIG. 8 shows the frequency characteristics of the speed detection circuit improved by the present invention. Referring to FIG. 8, the frequency characteristic from the analog control signal 28 to the speed estimation voltage 31 of the speed control circuit unit of the present invention shows a gain characteristic 82 and a phase characteristic 83. Comparing the gain characteristics 80 and 82 and the phase characteristics 81 and 83, both are the same at a frequency lower than the frequency f4. Further, compared with the conventional example, the characteristics match up to the frequency f4 higher than the frequency f5, so that the speed can be estimated with higher accuracy than the conventional example, and the differential operation in the high frequency region seen in the gain characteristic 84 and the phase characteristic 85 is eliminated. .
[0024]
Next, another embodiment of the present invention will be described. When a filter is added to the conventional speed estimation detection circuit 17, refer to the VCM applied voltage correction voltage for the speed estimation voltage with insufficient correction of the inductance component obtained by adding the filter only to the speed estimation voltage 31. It is also possible to generate an output for correcting the inductance component and estimate the VCM speed.
[0025]
FIG. 4 is a control block diagram showing another embodiment of the present invention. Referring to FIG. 4, the configuration includes a conventional filter D120 for the estimated speed voltage 31, a filter E121 that extracts an inductance component from the VCM applied voltage estimated value 206, and a voltage difference point 122 that takes a difference between these filter outputs. is there. The filter D120 is the following low-pass filter that corrects the differential operation in the high frequency region.
FD (S) = ω1 / (S + ω1) (6)
The filter E121 is the following high-pass filter including the estimated coil inductance Lm44 corresponding to the pole of the filter D.
FE (S) = (Lm / K) · S · ω1 / (S + ω1) (7)
The filter D120 outputs a speed estimation voltage 220 with insufficient correction for the inductance component. The filter E121 generates a speed estimation correction voltage 221 that cancels the influence of the inductance component included in the filter D120 from the VCM applied voltage estimation voltage. Subsequently, the voltage difference point 122 takes the difference between the speed estimation voltage 220 and the speed estimation correction voltage to generate a speed estimation voltage 31c.
[0026]
FIG. 7 shows the gain characteristic 74 and phase characteristic 75 of the filter D120, and the gain characteristic 76 and phase characteristic 77 of the filter E121. Referring to FIG. 7, the differential operation is canceled by the filter D120, and the influence of the inductance component Lm44 of the VCM that is not corrected by the filter D120 is extracted from the VCM application estimated voltage 206 by the gain characteristic 76 and the phase characteristic 77, and the speed estimation correction voltage is extracted. 221 is removed from the speed estimation voltage 220. As a result, the frequency characteristic from the analog control signal 28 to the speed estimation voltage 31c is the same as the gain characteristic 82 and the phase characteristic 83 in FIG.
[0027]
【The invention's effect】
The first effect is that the VCM speed changing at high frequency can be estimated. The reason is that by adding a filter that corrects the inductance component of the VCM, the frequency characteristic from the analog control signal to the VCM speed and the frequency characteristic from the analog control signal to the speed estimation voltage coincide with each other. This is because it was possible to increase the height.
The second effect is that the control band of the speed control system can be increased. The reason is that by adding a filter that corrects the inductance component of the VCM, the frequency characteristic in the high frequency region that worked like a differential operation with the frequency characteristic from the analog control signal to the estimated speed voltage due to the influence of the inductance component can be obtained. This is because it has been improved.
The third effect is that the approximation of the estimated speed, which has been insufficient only by adding a low-pass filter to the estimated speed voltage, has been improved. This is because the frequency characteristic in the high frequency region caused by the inductance can be improved by adding a filter for correcting the influence of the inductance component of the VCM in addition to the filter for correcting the differential operation.
[Brief description of the drawings]
FIG. 1 is a control block diagram of a speed detection unit of the present invention.
FIG. 2 is a control block diagram of a conventional speed detection unit.
FIG. 3 is a control block diagram of a first embodiment for a conventional speed detection unit;
FIG. 4 is a control block diagram according to another embodiment of the present invention.
FIG. 5 is a diagram illustrating frequency characteristics of a filter A106 and a filter B107 according to an embodiment of the present invention.
FIG. 6 is a diagram showing frequency characteristics of a filter C110 in the first and second embodiments with respect to a conventional speed detection unit.
FIG. 7 is a diagram illustrating frequency characteristics of a filter D120 and a filter E121 according to another embodiment of the present invention.
FIG. 8 is a diagram showing frequency characteristics from an analog control signal 28 to estimated speed voltages 31a and 31c in the embodiment of the present invention.
FIG. 9 is a diagram showing frequency characteristics from an analog control signal 28 to a speed estimation voltage 31 in a conventional example.
FIG. 10 is a diagram showing frequency characteristics from an analog control signal 28 to a speed estimation voltage 31b in the first embodiment relative to the conventional embodiment.
FIG. 11 is a diagram showing frequency characteristics from an analog control signal 28 to a speed estimation voltage 31b in the second embodiment relative to the conventional embodiment.
FIG. 12 is a circuit block diagram showing an embodiment of a magnetic disk device having a speed detection circuit.
FIG. 13 is a circuit diagram of a conventional speed detection circuit.
FIG. 14 is a control block diagram showing a speed control system of a magnetic disk device having a speed detection circuit.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Magnetic disk 2 ... Magnetic head 3 ... Spindle motor 4 ... Actuator 11 ... Head amplifier 12 ... Position detection circuit 13 ... CPU
14 ... Spindle motor drive circuit 15 ... Power amplifier 16 ... D / A converter 17 ... Speed detection circuit 18 ... A / D converter 21 ... Servo reproduction signal 22 ... Servo signal 23 ... Track information signal 24 ... Position error signal 25 ... Spindle motor drive signal 26 ... Start-up signal 27 ... Rotational speed signal 28 ... Analog control signal 29 ... Digital control signal 30 ... VCM drive voltage 31 ... Speed estimated voltage 32 ... Digital speed estimated voltage signal 41 ... VCM current detection resistor Rs
42 ... Back electromotive voltage Vb
43 ... VCM coil resistance Rm
44 ... VCM coil inductance Lm
45, 46 ... operational amplifiers 47-50 ... resistors R1-R4
60 ... First gain characteristic 61 of filter C110 ... First phase characteristic 62 of filter C110 ... Second gain characteristic 63 of filter C110 ... Second phase characteristic 70 of filter C110 ... Used in the embodiment of the present invention Gain characteristic 71 of filter A106 ... Phase characteristic 72 of filter A106 used in the embodiment of the present invention ... Gain characteristic 73 of filter B107 used in the embodiment of the present invention ... Phase characteristic of filter B107 used in the embodiment of the present invention 74: Gain characteristic 75 of filter D120 used in other embodiments of the present invention ... Phase characteristic of filter D120 used in other embodiments of the present invention ... Gain of filter E121 used in other embodiments of the present invention Characteristic 77 ... Phase characteristic 80 of filter E121 used in another embodiment of the present invention ... From analog control signal 28 to VCM speed 201 Gain characteristic 81 until ... Phase characteristic 82 from analog control signal 28 to VCM speed 201 ... Gain characteristic 83 from analog control signal 28 to speed estimation voltages 31a and 31c in the embodiment of the present invention ... Analog in the embodiment of the present invention Phase characteristic 84 from control signal 28 to speed estimation voltage 31a, 31c ... Gain characteristic 85 from analog control signal 28 to speed estimation voltage 31 in the conventional embodiment ... Speed estimation voltage 31 from analog control signal 28 in the conventional embodiment Phase characteristic up to 86 ... Gain characteristic 87 from the analog control signal 28 to the speed estimation voltage 31b when the first filter is added to the conventional embodiment 87 ... Add the first filter to the conventional embodiment Phase characteristic 88 from the analog control signal 28 to the speed estimation voltage 31b in the case of the conventional ... Gain characteristics 89 from the analog control signal 28 when the second filter is added to the embodiment to the speed estimation voltage 31b ... From the analog control signal 28 when the second filter is added to the conventional embodiment Phase characteristics 101 up to speed estimation voltage 31b ... Head arm 102 ... Voice coil motor (VCM)
103 ... VCM back electromotive force constant Keb
104, 108, 122 ... Voltage difference point 105 ... Voltage conversion gain 106 ... Filter A
107 ... Filter B
110 ... Filter C
120 ... Filter D
121 ... Filter E
130 ... Speed controller 131 ... Target speed generator 132 ... Speed conversion gain 133 ... Speed differentiator 201 ... VCM speed 202 ... Back electromotive force Vb
203 ... VCM applied voltage 204 ... VCM generation torque 205 ... Current sense current I
206 ... VCM applied voltage estimated voltage 207 ... VCM applied voltage correction voltage 208 ... VCM drive voltage correction voltage 220 ... Speed estimated voltage 221 ... Speed estimated correction voltage 230 ... Target speed 231 ... Estimated speed 232 ... Speed error

Claims (7)

Magnetic disk and magnetic head, spindle motor that rotates the magnetic disk, actuator that drives the magnetic head, head amplifier that amplifies the servo reproduction signal, and position detection that generates a track information signal and a position error signal from the servo signal Circuit, CPU for generating spindle motor start-up signal and digital control signal for driving actuator, spindle motor driving circuit for generating spindle motor driving signal, power amplifier for amplifying analog control signal, and A / D converter And a D / A converter and a speed detection circuit for detecting an actuator speed by detecting a voltage including a back electromotive voltage generated in a voice coil motor (VCM).
The magnetic disk apparatus, wherein the speed detection circuit has a filter for correcting an inductance component of the VCM.   2. The magnetic disk according to claim 1, wherein the filter is a filter A as a phase lead compensator having a coil inductance Lm of VCM and a low-pass filter B having a frequency characteristic corresponding to the pole of the filter A. apparatus.   The filter A as the phase lead compensator has a phase lead related to the coil inductance of the VCM, the voltage conversion gain of the VCM, and a predetermined set frequency, and the low-pass filter B is related to the predetermined set frequency, and the phase lead compensation 3. The magnetic disk apparatus according to claim 2, wherein the magnetic disk apparatus has the same pole as the disk and both have continuously smooth frequency characteristics.   The phase lead compensator is specified by FA (S) = ((Lm / K) · S + 1) · ω1 / (S + ω1), and the low-pass filter is FB (S) = ω1 / (S + ω1) where ω1 is 4. The magnetic disk drive according to claim 2, wherein the frequency set according to the frequency component of the speed to be estimated, K has a characteristic specified by a voltage conversion gain.   The filter is a high-pass filter E that includes a low-pass filter D that corrects a differential operation in a high-frequency region and a coil inductance Lm estimated corresponding to a pole of the filter D and that performs a differential operation in a low-frequency region. Item 2. The magnetic disk device according to Item 1.   The low-pass filter D has a frequency characteristic related to a predetermined set frequency, and the high-pass filter E has a frequency characteristic related to a coil inductance of the VCM, a voltage conversion gain of the VCM, and a predetermined set frequency, and both have the same pole. 6. The magnetic disk apparatus according to claim 5, wherein the magnetic disk apparatus has continuous and smooth frequency characteristics.   The low-pass filter has a characteristic specified by FD (S) = ω1 / (S + ω1), and the high-pass filter has FE (S) = (Lm / K) · S · ω1 / (S + ω1) where ω1 7. The magnetic disk apparatus according to claim 5, wherein a frequency set according to a frequency component of a speed to be estimated and K has a characteristic specified by a voltage conversion gain.

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