Magnetic disk device, and method for switching bias voltage and drive voltage of microactuator

Abstract

The present invention provides a magnetic disk drive that improves reliability, and a method for switching the bias voltage and drive voltage of a microactuator. The magnetic disk drive of this embodiment includes: a disk; a head that writes data to and reads data from the disk; an actuator that rotationally drives and controls the movement of the head mounted on the disk; a microactuator mounted on the actuator that minutely oscillates the head in the radial direction of the disk using a piezoelectric element. The piezoelectric element expands and contracts when a drive voltage based on a bias voltage is applied to the piezoelectric element; and a controller that switches the bias voltage according to the state of access processing.

Description

[0001] Related Application

[0002] This application claims the benefit of priority based on Japanese Patent Application No. 2021-145605 (filing date: September 7, 2021), and the present application incorporates all the contents of the basic application by reference. Technical Field

[0003] Embodiments of the present invention relate to a magnetic disk device and a method for switching a bias voltage and a drive voltage of a microactuator. Background Art

[0004] The magnetic disk device includes a plurality of disks rotatably arranged in a housing, at least one head that performs reading and writing processing on the disks, and a head actuator that supports the head so as to be movable relative to the disks.

[0005] The actuator has at least one suspension assembly that supports the head at its tip. The head suspension assembly consists of a base plate with one end fixed to an arm, a load beam extending from the base plate, and a flexible member (wiring component) attached to the load beam and base plate. The flexible member has a freely movable gimbal portion, which supports the head.

[0006] In recent years, head suspension assemblies have been proposed that include multiple (e.g., two) piezoelectric elements to form microactuators. The two piezoelectric elements are mounted on a flexure. The electrodes of the piezoelectric elements are electrically and mechanically connected to a conductive pattern, such as a conductive pad, on the flexure using, for example, a conductive adhesive.

[0007] As a driving method for the microactuator, for example, single-ended driving and bias driving can be cited. Under single-ended driving, the two piezoelectric elements are polarized in opposite directions, and a driving voltage is input with 0V as the center to perform push-pull driving. On the other hand, under bias driving, the two piezoelectric elements are input with driving voltages of opposite phases with the bias voltage as the center to perform push-pull driving. By bias driving, it is possible to prevent the application of a reverse voltage that can depolarize these piezoelectric elements. In the case of using a conductive adhesive such as silver paste as the electrode of the piezoelectric element, if the bias voltage is continuously applied, the risk of a short circuit caused by migration between the positive and negative electrodes will increase. Summary of the Invention

[0008] An object of the embodiment is to provide a magnetic disk device and a method for switching the bias voltage and drive voltage of a microactuator that can improve reliability.

[0009] The magnetic disk device of this embodiment comprises: a disk; a head for writing data to the disk and reading data from the disk; an actuator for rotationally driving and controlling the movement of the head mounted on the disk; a microactuator mounted on the actuator for causing the head to swing slightly in the radial direction of the disk via a piezoelectric element, the piezoelectric element expanding and contracting by being applied with a driving voltage based on a bias voltage; and a controller for switching the bias voltage according to the action state of the access processing. BRIEF DESCRIPTION OF THE DRAWINGS

[0010] Figure 1 This is a block diagram showing the configuration of a magnetic disk device according to an embodiment.

[0011] Figure 2 It is a perspective view showing a configuration example of a suspension assembly.

[0012] Figure 3 This is an exploded perspective view showing an example of a mounting portion of a flexure and a piezoelectric element.

[0013] Figure 4 This is a schematic diagram showing an example of connection of wiring to a microactuator and the ranges of bias voltage and drive voltage.

[0014] Figure 5 This is a schematic diagram showing an example of a waveform of a driving voltage in a normal operation state of this embodiment.

[0015] Figure 6 This is a schematic diagram showing an example of a waveform of a driving voltage in a relaxation operation state according to the present embodiment.

[0016] Figure 7 This is a flowchart showing an example of a method for switching the bias voltage and the drive voltage applied to the piezoelectric element of the microactuator according to the present embodiment.

[0017] Description of labels

[0018] 1…disk device, 10…disk, 10a…user data area, 10b…system area, 12…spindle motor (SPM), 13…arm, 14…voice coil motor (VCM), 15…head, 15W…write head, 15R…read head, 20…driver IC, 30…head amplifier IC, 40…read / write (R / W) channel, 50…hard disk controller (HDC), 60…microprocessor (MPU), 70…volatile memory, 80…non-volatile memory, 90…buffer memory, 100…host system (host), 130…system controller DETAILED DESCRIPTION

[0019] Hereinafter, embodiments will be described with reference to the accompanying drawings. However, the accompanying drawings are merely examples and are not intended to limit the scope of the invention.

[0020] (Implementation Method)

[0021] Figure 1 This is a block diagram showing the configuration of the magnetic disk device 1 according to the embodiment.

[0022] The magnetic disk device 1 includes a head disk assembly (HDA) (described later), a driver IC 20, a head amplifier integrated circuit (hereinafter referred to as a head amplifier IC or preamplifier) ​​30, a volatile memory 70, a nonvolatile memory 80, a buffer memory (buffer) 90, and a system controller 130, which is a single-chip integrated circuit. Furthermore, the magnetic disk device 1 is connected to a host system (hereinafter referred to simply as a host) 100.

[0023] The HAD includes a magnetic disk (hereinafter referred to as a disk) 10, a spindle motor (hereinafter referred to as an SPM) 12, an arm 13 equipped with a head 15, and a voice coil motor (hereinafter referred to as a VCM) 14. The disk 10 is mounted on the SPM 12 and rotated by the drive of the SPM 12. The (head) actuator 16 is composed of the arm 13, an actuator module 18 with a built-in bearing unit 17, and a suspension assembly (sometimes referred to as a head gimbal assembly (HGA)) 19 extending from the arm 13. The head 15 is supported at the top end of the suspension assembly 19. The actuator 16 is rotatably supported by a pivot shaft provided on the bottom wall of the housing of the magnetic disk device 1 via the bearing unit 17. The disk 10, arm 13, head 15, and suspension assembly 19 may be provided in one or more configurations.

[0024] A printed circuit board (not shown) is screwed onto the outer surface of the bottom wall of the housing of the magnetic disk drive 1. The printed circuit board includes a system controller 130. The system controller 130 controls the operation of the SPM 12 and, via a substrate unit (FPC unit) on which electronic components such as a conversion connector are mounted, controls the operation of the VCM 14, actuator 16, and head 15.

[0025] The disk 10 allocates a user data area 10a, which can be used by users, and a system area 10b, which stores information required for system management, to areas where data can be written. Hereinafter, the direction from the inner periphery toward the outer periphery of the disk 10, or the direction from the outer periphery toward the inner periphery of the disk 10, will be referred to as the radial direction. In the radial direction, the direction from the inner periphery toward the outer periphery will be referred to as the outer direction (or outer side), and the direction from the inner periphery toward the outer periphery will be referred to as the inner direction (or inner side). The circumferential direction corresponds to the direction along the circumference of the disk 10. The radial and circumferential directions are orthogonal to each other. Furthermore, a predetermined position in the radial direction of the disk 10 may sometimes be referred to as a radial position, while a predetermined position in the circumferential direction of the disk 10 may be referred to as a circumferential position. Sometimes, radial positions and circumferential positions are collectively referred to as simply a position. The user data area 10a of the disk 10 can be divided into multiple areas. For example, the user data area 10a can be divided radially into areas (hereinafter sometimes referred to as sections) comprising a predetermined number of tracks. Sections can be divided radially by track.

[0026] In addition, a “track” is a recording area among a plurality of recording areas obtained by dividing the disk 10 in a radial direction, a recording area for one circumference of a predetermined radial position of the disk 10, a predetermined recording area at a predetermined radial position of the disk 10, a recording area extending in the circumferential direction of the disk 10, a recording area corresponding to the path of the head 15 positioned at a predetermined radial position of the disk 10, a path of the head 15 positioned at a predetermined radial position of the disk 10, data written to one of a plurality of recording areas obtained by dividing the disk 10 in a radial direction, a recording area for one circumference of the predetermined radial position of the disk 10, Various meanings are adopted, including data written to a predetermined recording area at a predetermined radial position of the disk 10, data written to a recording area extending in the circumferential direction of the disk 10, data written to a recording area corresponding to the path of the head 15 positioned at a predetermined radial position of the disk 10, data written along the path of the head 15 positioned at a predetermined radial position of the disk 10, data extending in the circumferential direction of the disk 10, data written to a predetermined track of the disk 10, data written for one circle of the predetermined track of the disk 10, a part of the data written to the predetermined track of the disk 10, and / or other various meanings. "Sector" is used to mean one of the multiple recording areas obtained by dividing the predetermined tracks of the disk 10 in the circumferential direction, one of the multiple recording areas obtained by dividing the recording areas extending in the circumferential direction at a predetermined radial position of the disk 10, a predetermined recording area of ​​a predetermined track of the disk 10, a predetermined circumferential position of a predetermined track of the disk 10, a predetermined circumferential position (predetermined position) at a predetermined radial position of the disk 10, data written to one of the multiple recording areas obtained by dividing the predetermined tracks of the disk 10 in the circumferential direction, data written to one of the multiple recording areas obtained by dividing the recording areas extending in the circumferential direction at a predetermined radial position of the disk 10, data written to a predetermined recording area of ​​a predetermined track of the disk 10, data written to a predetermined circumferential position of a predetermined track of the disk 10, data written to a predetermined circumferential position (predetermined position) at a predetermined radial position of the disk 10, data written to a predetermined sector, and / or other various meanings. The “radial width of a track” is sometimes referred to as the “track width.” The “path passing through the center of the track width in a predetermined track” is sometimes referred to as the “track center.” Data written to the user data area 10a and usable by the user is sometimes referred to as user data.

[0027] The head 15 includes a slider as its main body and includes a write head 15W and a read head 15R attached to the slider. The write head 15W writes data to the disk 10. The read head 15R reads data recorded on the disk 10. The "write head 15W" is sometimes referred to simply as the "head 15," the "read head 15R" is sometimes referred to simply as the "head 15," and the "write head 15W and read head 15R" are sometimes collectively referred to simply as the "head 15." The "center portion of the head 15" is sometimes referred to as the "head 15," the "center portion of the write head 15W" is referred to as the "write head 15W," and the "center portion of the read head 15R" is referred to as the "read head 15R." In other cases, the "center portion of the write head 15W" is sometimes referred to simply as the "head 15," and the "center portion of the read head 15R" is sometimes referred to simply as the "head 15." “Positioning the center of the head 15 at the track center of a predetermined track” is sometimes expressed as “positioning the head 15 at the predetermined track”, “arranging the head 15 at the predetermined track”, or “locating the head 15 at the predetermined track”.

[0028] Figure 2 It is a perspective view showing a configuration example of the suspension assembly 19 .

[0029] like Figure 2 As shown, the suspension assembly 19 includes a suspension 124 extending in the longitudinal direction from the arm 13, and the head 15 is mounted on the top end of the suspension 124. The head 15 and the suspension assembly 19 supporting the head 15 are collectively referred to as a head suspension assembly.

[0030] The suspension 124, which functions as a support plate, comprises a rectangular base plate 142 made of a metal plate several hundred microns thick, and a slender, leaf-spring-like loading beam 125 made of a metal plate several tens of microns thick. The base end of the loading beam 125 overlaps the top end of the base plate 142 and is secured to the base plate 142 by welding at multiple locations. The base end of the loading beam 125 is formed to have a width approximately equal to that of the base plate 142. A rod-shaped lug 146 protrudes from the top end of the loading beam 125.

[0031] The suspension assembly 19 includes a thin and long strip-shaped flexible member (wiring member) 140 for transmitting recording and reproduction signals and a driving signal (driving voltage) of the piezoelectric element 150, and a pair of piezoelectric elements (for example, PZT elements) 50 mounted on the flexible member 140. Figure 2 As shown, the top side portion 140a of the flexible member 140 is arranged on the load beam 125 and the base plate 142, and the rear half (protrusion) 140b protrudes outward from the side edge of the base plate 142 and extends along the side edge of the arm 13. The connection end portion (not shown) at the top of the protrusion 140b has multiple connection pads (not shown). These connection pads are connected to the main FPC of the substrate unit.

[0032] The top end of the flexible member 140 is positioned at the top end of the load beam 125, forming a gimbal portion 126 that functions as an elastic support. The head 15 is mounted and fixed on the gimbal portion 126, and is supported by the load beam 125 via the gimbal portion 126. A pair of piezoelectric elements 150, serving as driving elements, are attached to the gimbal portion 126 and positioned on the base end side of the load beam 125 relative to the head 15. Hereinafter, the structure including the piezoelectric elements 150 may be referred to as a microactuator 16M. These piezoelectric elements 150 are used to cause the head 15 to swing more finely in the radial direction of the disk 10 (the seek direction or the track-crossing direction of the head 15) than the swinging performed by the VCM 14 in the radial direction of the disk 10. Furthermore, a microactuator may be referred to as a MA.

[0033] like Figure 2 As shown, the flexible member 140 comprises a thin metal plate (metal plate) 144a, such as stainless steel, as a base, and a strip-shaped laminated component 141 adhered or fixed to the thin metal plate 144a, forming an elongated laminate. The laminated component 141 comprises a base insulating layer 144b, the majority of which is fixed to the thin metal plate 144a, and a conductive layer (wiring pattern) 144c formed on the base insulating layer 144b and constituting a plurality of signal wirings, drive wirings, and connection pads. Copper foil, for example, can be used as the conductive layer 144c. At the top end portion 140a of the flexible member 140, the thin metal plate 144a is adhered or spot-welded at multiple welding points to the surface of the load beam 125 and the base plate 142.

[0034] In the universal joint portion 126 of the flexible part 140, the metal sheet 144a has a rectangular tongue portion (support portion) 126a located on the top end side, a roughly rectangular base end portion (base end plate portion) 126b located on the base end side with a space separated from the tongue portion 126a, and a pair of slender brackets (outriggers) (connecting portions) 126c extending from the tongue portion 126a to the base end portion 126b.

[0035] The base end portion 126b is adhered to the surface of the load beam 125 or fixed to the surface of the load beam 125 by spot welding. The tongue portion 126a is formed to a size and shape that can support the head 15, for example, into a roughly rectangular shape. The tongue portion 126a is arranged so that the central axis in the width direction, which intersects (e.g., is perpendicular to) the longitudinal direction, coincides with the central axis in the width direction of the suspension 124 (hereinafter sometimes simply referred to as the central axis of the suspension 124). The tongue portion 126a is elastically deformed by a pair of brackets 126c and can be displaced in various directions. As a result, the tongue portion 126a and the head 15 can flexibly follow the surface changes of the disk 10 in the roll and pitch directions, maintaining a small gap between the surface of the disk 10 and the head 15.

[0036] In the universal joint 126, a portion of the laminated member 141 of the flexible member 140 is bifurcated and positioned on either side of the central axis of the suspension 124. The laminated member 141 includes a base end 147a fixed to the base end 126b of the metal sheet 144a, a tip 147b adhered to the tongue 126a, a pair of first, strip-shaped bridge portions 147c extending from the base end 147a to the tip 147b, and a pair of second, strip-shaped bridge portions 147d extending parallel to the first bridge portions 147c from the base end 147a to the midway portion of the first bridge portion 147c and merging with the first bridge portion 147c. The first bridge portions 147c are positioned parallel to the bracket 126c on either side of the tongue 126a, extending along the length of the load beam 125.

[0037] The head 15 is fixed to the tongue 126a with an adhesive. The head 15 is arranged so that its longitudinal center axis is aligned with the center axis of the suspension 124. The recording element (write head 15W) and the reproducing element (read head 15R) of the head 15 are electrically bonded to a plurality of electrode pads 140d on the tip 147b using a conductive adhesive such as solder or silver paste. Thus, the head 15 is connected to the signal wiring via the electrode pads 140d.

[0038] Figure 3 1 is an exploded perspective view showing an example of the mounting portion 160 of the flexible member 140 and the piezoelectric element 150. Figure 3 As shown, the mounting portion 160 includes a first connection pad 170a and a second connection pad 170b, each formed from a conductive layer 144c. The first connection pad 170a and the second connection pad 170b are each electrically connected to a drive wiring 145b formed from the conductive layer 144c. The first connection pad 170a and the second connection pad 170b are arranged parallel to the central axis of the load beam 125 with a predetermined spacing therebetween. In this embodiment, the first bridge portion 147c of the flexible member 140 is disconnected between the first connection pad 170a and the second connection pad 170b. As a result, the first connection pad 170a and the second connection pad 170b are arranged with a predetermined distance therebetween.

[0039] A rectangular recess 174a is formed in the base insulating layer 144b at a position overlapping the first connection pad 170a. Recess 174a is formed, for example, by half-etching a predetermined portion of the base insulating layer 144b. Recess 174a is formed in a rectangular shape slightly larger than the first connection pad 170a. The first connection pad 170a and recess 174a are formed so as to overlap and be recessed along the length of recess 174a.

[0040] A rectangular recess 174b is formed in the base insulating layer 144b at a position overlapping with the second connection pad 170b. Recess 174b is formed, for example, by half-etching a predetermined portion of the base insulating layer 144b. Recess 174b is formed in a rectangular shape slightly larger than the second connection pad 170b. Second connection pad 170b is formed to overlap recess 174a and to be recessed along recess 174a.

[0041] Furthermore, the base insulating layer 144b is not limited to having a single recess 174a, 174b for each connection pad, and multiple recesses may be provided for each connection pad. The shape of the recesses 174a, 174b is not limited to a rectangle, and various shapes are possible.

[0042] Insulating cover layer 144d, which is stacked on conductive layer 144c, has openings 172a and 172b, respectively, at locations overlapping first and second connecting pads 170a and 170b. Most of first and second connecting pads 170a and 170b are exposed on the outer surface of insulating cover layer 144d through openings 172a and 172b, respectively. In one example, first and second connecting pads 170a and 170b are each rectangular in shape, and openings 172a and 172b are also rectangular in shape, slightly smaller than the connecting pads.

[0043] A cover layer 144e is provided on the cover insulating layer 144d near the opening 172a. The cover layer 144e is provided on the side of the opening 172a facing the drive wiring 145b, i.e., on the side opposite the second connection pad 170b. In one example, the cover layer 144e is formed in a generally rectangular shape and extends substantially the entire width of the first bridge portion 147c. As described later, the cover layer 144e functions as a bank that limits the spread of the conductive adhesive.

[0044] Similarly, a cover layer 144e is provided on the cover insulating layer 144d near the opening 172b. The cover layer 144e is provided on the side of the opening 172b facing the drive wiring 145b, i.e., on the side opposite the first connection pad 170a. In one example, the cover layer 144e is formed in a generally rectangular shape and extends substantially the entire width of the first bridge portion 147c. As described later, the cover layer 144e functions as a bank that limits the spread of the conductive adhesive.

[0045] In one example, cover layer 144e is formed to have approximately the same thickness as cover insulating layer 144d and is made of the same insulating material as cover insulating layer 144d. Furthermore, cover layer 144e is not limited to a rectangular shape and can have any desired shape. Cover layer 144e can also be provided slightly apart from openings 172a and 172b.

[0046] In one example, the piezoelectric element 150 as a driving element includes a piezoelectric body 150a formed of a piezoelectric material into a flat rectangular parallelepiped shape, and a first electrode 151a and a second electrode 151b provided on the outer surfaces of the piezoelectric body 150a. Examples of the piezoelectric material include zinc zirconate titanate and ceramics.

[0047] The first electrode 151a is provided from one end of the bottom surface of the piezoelectric body 150a, extending over the side surface of the short side and most of the top surface. The second electrode 151b is provided from one end of the top surface of the piezoelectric body 150a, extending over the side surface of the other short side and most of the bottom surface. On the bottom surface of the piezoelectric body 150a, one end of the first electrode 151a and one end of the second electrode 151b face each other with a gap therebetween. On the top surface of the piezoelectric body 150a, the other end of the first electrode 151a and the other end of the second electrode 151b face each other with a gap therebetween.

[0048] By applying a voltage between the first electrode 151a and the second electrode 151b, the piezoelectric body 150a sandwiched between the first and second electrodes 151a, 151b expands or contracts in the longitudinal direction. In one example, the first electrode 151a serves as a voltage application (Vin) electrode, and the second electrode 151b serves as a ground (GND) electrode.

[0049] The piezoelectric element 150 is arranged on the mounting portion 160 with one longitudinal end (first electrode 151a) of the piezoelectric body 150a facing the first connection pad 170a and the other longitudinal end (second electrode 151b) facing the second connection pad 170b. A conductive adhesive Ad is filled between the first connection pad 170a and the first electrode 151a. Silver paste, solder, or the like can be used as the conductive adhesive. The first electrode 151a is electrically and mechanically connected to the first connection pad 170a via the conductive adhesive Ad. The conductive adhesive Ad is filled in the opening 172a of the cover insulating layer 144d and in the recess of the first connection pad 170a along the recess 174a, adhering to the surface of the first connection pad 170a and the inner surface of the opening 172a (cover insulating layer 144d). Furthermore, the conductive adhesive Ad adheres to the edge of the cover layer 144e and is stopped by the cover layer 144e, thereby limiting leakage toward the driving wiring 145b side.

[0050] When the microactuator 16M is in operation, a driving voltage is applied to the first electrode 151 a via the driving wiring 145 b , the first connection pad 170 a , and the conductive adhesive Ad.

[0051] Similarly, conductive adhesive Ad is filled between the second connection pad 170b and the second electrode 151b. The second electrode 151b is electrically and mechanically connected to the second connection pad 170b via the conductive adhesive Ad. At this time, the conductive adhesive Ad fills the opening 172b of the cover insulating layer 144d and the recessed portion of the second connection pad 170b along the recess 174b, adhering to the surface of the second connection pad 170b and the inner surface of the opening 172b (cover insulating layer 144d). Furthermore, the conductive adhesive Ad adheres to the edge of the cover layer 144e and is blocked by the cover layer 144e, thereby limiting leakage toward the drive wiring 145b.

[0052] In the magnetic disk device 1 constructed as described above, by applying a voltage (driving signal) to the piezoelectric element 150 via the driving wiring 145b, the piezoelectric element 150 expands and contracts along its length direction (a direction parallel to the central axis of the suspension or a direction in which the suspension assembly 19 extends). By driving the two piezoelectric elements 150 in directions opposite to each other, the pair of first bridge portions 147c also move (stroke) in opposite directions. The first bridge portion 147c causes the tongue portion 126a of the universal joint portion 126 and the head 15 to swing. In this way, the head 15 can be slightly displaced by the expansion and contraction action of the piezoelectric element 150. In addition, the swinging direction of the head 15 corresponds to the seek direction (the direction of crossing the magnetic track or the radial direction) of the head 15 on the disk 10.

[0053] The driver IC 20 is connected to the system controller 130 (more specifically, the MPU 60 described later), the SPM 12, and the VCM 14, and controls the driving of the SPM 12 and VCM 14 under the control of the system controller 130 (more specifically, the MPU 60 described later). The driver IC 20 includes a bias voltage control circuit 210 and a drive voltage control circuit 220. The bias voltage control circuit 210 controls the bias voltage applied to the piezoelectric element 150 of the microactuator 16M. For example, the bias voltage control circuit 210 switches to a bias voltage selected from a plurality of pre-set bias voltages under the control of the MPU 60. The drive voltage control circuit 220 controls the drive voltage applied to the piezoelectric element 150 of the microactuator 16M. For example, the drive voltage control circuit 220 controls the drive voltage range under the control of the MPU 60 to prevent the application of an excessive reverse bias voltage.

[0054] The driver IC 20 is also connected to a RV (Rotational Vibration) sensor 21, and transmits a detection value detected by the RV sensor 21 to the MPU 60. The RV sensor 21 can detect vibration amount, displacement amount, velocity, acceleration, and the like.

[0055] The head amplifier IC (preamplifier) ​​30 includes a sense amplifier and a write driver. The sense amplifier amplifies the read signal from the disk 10 and outputs it to the system controller 130 (specifically, the read / write (R / W) channel 40 described later). The write driver outputs a write current corresponding to the write data output from the R / W channel 40 to the head 15.

[0056] Volatile memory 70 is a semiconductor memory that loses stored data if power is disconnected. It stores data required for processing by various components of magnetic disk drive 1. Examples of volatile memory 70 include DRAM (Dynamic Random Access Memory) or SDRAM (Synchronous Dynamic Random Access Memory).

[0057] The nonvolatile memory 80 is a semiconductor memory that records stored data even when power is turned off. The nonvolatile memory 80 is, for example, a NOR-type or NAND-type flash ROM (Flash Read Only Memory: FROM).

[0058] The buffer memory 90 is a semiconductor memory that temporarily stores data exchanged between the magnetic disk drive 1 and the host computer 100. Alternatively, the buffer memory 90 may be integrally formed with the volatile memory 70. Examples of the buffer memory 90 include DRAM, SRAM (Static Random Access Memory), SDRAM, FeRAM (Ferroelectric Random Access Memory), and MRAM (Magnetoresistive Random Access Memory).

[0059] The system controller (controller) 130 is implemented, for example, using a large-scale integrated circuit (LSI) known as a System-on-a-Chip (SoC), in which multiple components are integrated into a single chip. The system controller 130 includes, for example, a read / write (R / W) channel 40, a hard disk controller (HDC) 50, and a microprocessor (MPU) 60. The R / W channel 40, HDC 50, and MPU 60 are electrically connected to one another. The system controller 130 is electrically connected to, for example, the driver IC 20, the head amplifier IC 30, the volatile memory 70, the nonvolatile memory 80, the buffer memory 90, and the host system 100.

[0060] The R / W channel 40 performs signal processing for data transferred from the disk 10 to the host 100 (e.g., read data) and data transferred from the host 100 (e.g., write data) based on instructions from the MPU 60, described later. The R / W channel 40 includes circuitry or functionality for measuring the signal quality of read data. The R / W channel 40 is electrically connected to, for example, the head amplifier IC 30, the HDC 50, and the MPU 60.

[0061] The HDC 50 controls data transfer. For example, the HDC 50 controls data transfer between the host 100 and the R / W channel 40 based on instructions from the MPU 60 (described later). The HDC 50 is electrically connected to, for example, the R / W channel 40, the MPU 60, the volatile memory 70, the nonvolatile memory 80, and the buffer memory 90.

[0062] The MPU 60 is a main controller that controls various components of the magnetic disk drive 1. The MPU 60 controls the VCM 14 via the driver IC 20 and performs servo control to position the head 15. The MPU 60 controls the SPM 12 via the driver IC 20 to rotate the disk 10. The MPU 60 controls writing data to the disk 10 and selects data transferred from the host 100, such as the storage address for write data. The MPU 60 controls reading data from the disk 10 and controls data transferred from the disk 10 to the host 100, such as the processing of read data. Furthermore, the MPU 60 manages the area where data is recorded. The MPU 60 is connected to various components of the magnetic disk drive 1. For example, the MPU 60 is electrically connected to the driver IC 20, the R / W channel 40, and the HDC 50.

[0063] The MPU 60 includes a read / write control unit 610 and an MA control unit 620. The MPU 60 executes processing of each unit, such as the read / write control unit 610 and the MA control unit 620, in firmware. Alternatively, the MPU 60 may include each unit, such as the read / write control unit 610 and the MA control unit 620, as a circuit. The read / write control unit 610 may also be included in the R / W 40 or the HDC 50.

[0064] The read / write control unit 610 controls the read process of reading data from the disk 10 and the write process of writing data to the disk 10 according to commands from the host computer 100. The read / write control unit 610 controls the VCM 14 via the driver IC 20 to position the head 15 at a predetermined position on the disk 10 to perform the read process or the write process. In other words, the read / write control unit 610 positions the head 15 at a predetermined position on the disk 10 according to the MA control unit 620 to perform the read process or the write process. Hereinafter, the term "access" may be used to include recording or writing data to a predetermined area (or writing process), reading or reading data from a predetermined area (or reading process), and moving the head 15 to a predetermined area.

[0065] The MA control unit 620 controls the microactuator 16M. The MA control unit 620 controls the microactuator 16M using bias drive. When using bias drive to control the microactuator 16M, the MA control unit 620 inputs drive voltages of opposite phases, centered around (or referenced by) the bias voltage Vb, to the two piezoelectric elements 150 that form the microactuator 16M pair, performing push-pull drive. This bias drive prevents the application of a reverse voltage that could depolarize the polarized piezoelectric elements 150. Hereinafter, a voltage applied to a polarized piezoelectric element 150 to cause it to expand is referred to as a positive voltage, and a voltage applied to a polarized piezoelectric element 150 to cause it to contract is referred to as a negative voltage. Alternatively, a voltage applied to a polarized piezoelectric element 150 to cause it to expand may be referred to as a negative voltage, and a voltage applied to a polarized piezoelectric element 150 to cause it to contract may be referred to as a positive voltage.

[0066] The MA control unit 620 controls the bias voltage applied to the piezoelectric element 150 of the microactuator 16M via the bias voltage control circuit 210. The MA control unit 620 switches the bias voltage Vb applied to the piezoelectric element 150 according to the operating state of the access process (hereinafter sometimes simply referred to as the operating state).

[0067] When the MA control unit 620 determines that the device is in the operating state where normal access processing is being performed (hereinafter sometimes referred to as the normal operating state), it applies a bias voltage Vb = Vb1 to the piezoelectric element 150. In other words, when the MA control unit 620 determines that the device is in the normal operating state, it sets the bias voltage Vb = Vb1. In other words, the MA control unit 620 switches the bias voltage to Vb = Vb1.

[0068] When the MA control unit 620 determines that the operating state is one in which control performance requirements (e.g., accuracy and size) such as positioning of the head 15 or the bit error rate during access processing are relaxed compared to those during normal access processing (hereinafter sometimes referred to as the relaxed operating state), the MA control unit 620 applies a bias voltage Vb=Vb2 having an absolute value smaller than the absolute value of the bias voltage Vb=Vb1 applied to the piezoelectric element 150 when the normal operating state is determined (|Vb2| < |Vb1|) to the piezoelectric element 150. In other words, when the MA control unit 620 determines that the operating state is relaxed, the MA control unit 620 sets the absolute value of the bias voltage Vb=Vb2 to be smaller than the absolute value of the bias voltage Vb=Vb1 set when the normal operating state is determined (|Vb2| < |Vb1|). That is, when the MA control unit 620 determines that the state is the relaxation operation state, it switches from the absolute value of the bias voltage Vb=Vb1 set when the state is the normal operation state to the absolute value of the bias voltage Vb=Vb2 smaller than the absolute value of the bias voltage Vb=Vb1 (|Vb2|<|Vb1|).

[0069] If the absolute value of the bias voltage Vb=Vb1 applied to the piezoelectric element 150 during the normal operation state is greater than 0, and the device is determined to be in a relaxing operation state such as the background media scanning state, the MA control unit 620 applies a bias voltage Vb=Vb2=0 to the piezoelectric element 150. In other words, if the absolute value of the bias voltage Vb=Vb1 set during the normal operation state is greater than 0, and the device is determined to be in a relaxing operation state such as the background media scanning state, the MA control unit 620 sets the bias voltage Vb=Vb2=0. Specifically, if the absolute value of the bias voltage Vb=Vb1 set during the normal operation state is greater than 0, and the device is determined to be in a relaxing operation state such as the background media scanning state, the MA control unit 620 switches from the bias voltage Vb=Vb1 to the bias voltage Vb=Vb2=0, which is smaller than the absolute value of the bias voltage Vb=Vb1.

[0070] In the normal operating state, when the absolute value of bias voltage Vb=Vb1 applied to piezoelectric element 150 is greater than 0, and the MA control unit 620 determines that the piezoelectric element 150 is in a relaxed operating state (i.e., an operating state in which external vibration is low, such as an operating state in which the detection value of RV sensor 21 is less than a threshold indicating that external vibration is greater than an allowable magnitude (hereinafter, sometimes referred to as a vibration detection threshold), or an operating state in which the positioning error is less than a threshold indicating that external vibration is greater than an allowable magnitude (hereinafter, sometimes referred to as a vibration accuracy threshold), the MA control unit 620 applies bias voltage Vb=Vb2=0 to piezoelectric element 150. In other words, in a relaxed operating state such as an operating state in which external vibration is low, the MA control unit 620 sets bias voltage Vb=Vb2=0. That is, in a case where the absolute value of the bias voltage Vb=Vb1 set in the normal operation state is greater than 0 and it is determined to be a relaxed operation state, such as an operation state with small external vibration, the MA control unit 620 switches from the bias voltage Vb=Vb1 to the bias voltage Vb=Vb2=0 which is smaller than the absolute value of the bias voltage Vb=Vb1.

[0071] The MA control unit 620 also controls the range of the driving voltage applied to the piezoelectric element 150 of the microactuator 16M via the driving voltage control circuit 220. The MA control unit 620 switches the range of the driving voltage applied to the piezoelectric element 150 according to the operating state.

[0072] If the normal operating state is determined, the MA control unit 620 applies a bias voltage Vb=Vb1 to the piezoelectric element 150 and sets the driving voltage Vd applied to the piezoelectric element 150 to the range Vb1-V1≤Vd≤Vb1+V1. In other words, if the normal operating state is determined, the MA control unit 620 sets the bias voltage Vb=Vb1 and sets the driving voltage Vd applied to the piezoelectric element 150 to the range Vb1-V1≤Vd≤Vb1+V1. In other words, if the normal operating state is determined, the MA control unit 620 switches the bias voltage to Vb=Vb1 and switches the driving voltage Vd to the range Vb1-V1≤Vd≤Vb1+V1. Here, Vb1-V1 is designed to ensure the lower limit of the reverse bias voltage. For example, Vb1-V1 corresponds to the lower limit of the reverse bias voltage that allows normal operation. Regarding the maximum range of the driving voltage, the combination of the maximum range of the DAC and the amplifier gain can be switched circuitically, or the range of the output to the DAC can be limited by software.

[0073] When it is determined to be in a easing action state, the MA control unit 620 applies a bias voltage Vb=Vb2 (|Vb2|<|Vb1|) to the piezoelectric element 150, and sets a range of the driving voltage Vd applied to the piezoelectric element 150 to Vb2-V2≤Vd≤Vb2+V2, which is narrower than (or smaller than) the range of the driving voltage Vd applied to the piezoelectric element 150 when it is determined to be in a normal action state, Vb1-V1≤Vd≤Vb1+V1. In other words, when determining that the state is the relaxation operation state, the MA control unit 620 sets the bias voltage Vb to Vb2 (|Vb2| < |Vb1|) and sets the driving voltage Vd applied to the piezoelectric element 150 to a range of Vb2-V2 ≤ Vd ≤ Vb2+V2, which is narrower than (or smaller than) the range of the driving voltage Vd applied to the piezoelectric element 150 (Vb1-V1 ≤ Vd ≤ Vb1+V1) when determining that the state is the normal operation state. In other words, when determining that the state is the relaxation operation state, the MA control unit 620 switches from the bias voltage Vb=Vb1 to the bias voltage Vb=Vb2 (|Vb2| < |Vb1|), and switches from the driving voltage Vd range of Vb1-V1 ≤ Vd ≤ Vb1+V1 to the driving voltage Vd range of Vb2-V2 ≤ Vd ≤ Vb2+V2. Here, |Vb2-V2| ≤ |Vb1-V1|.

[0074] In the normal operation state, when the absolute value of the bias voltage Vb=Vb1 applied to the piezoelectric element 150 is greater than 0 and the device is determined to be in a relaxed operation state such as the background media scanning state, the MA control unit 620 applies a bias voltage Vb=Vb2=0 to the piezoelectric element 150, for example, and sets the range of the drive voltage Vd applied to the piezoelectric element 150 to 0-V2≤Vd≤0+V2. In other words, in the normal operation state, when the absolute value of the bias voltage Vb=Vb1 applied to the piezoelectric element 150 is greater than 0 and the device is determined to be in a relaxed operation state such as the background media scanning state, the MA control unit 620 sets the bias voltage Vb=Vb2=0, for example, and sets the range of the drive voltage Vd applied to the piezoelectric element 150 to 0-V2≤Vd≤0+V2. That is, when the absolute value of the bias voltage Vb=Vb1 applied to the piezoelectric element 150 in the normal operation state is greater than 0 and it is determined to be a mild operation state such as the background medium scanning state, the MA control unit 620 switches from the bias voltage Vb=Vb1 to the bias voltage Vb=Vb2=0, and switches from the range of the driving voltage Vd Vb1-V1≤Vd≤Vb1+V1 to the range of the driving voltage Vd Vb2-V2≤Vd≤Vb2+V2.

[0075] In the normal operating state, when the absolute value of the bias voltage Vb=Vb1 applied to the piezoelectric element 150 is greater than 0 and the piezoelectric element 150 is determined to be in a relaxed operating state, the MA control unit 620 applies a bias voltage Vb=Vb2=0 to the piezoelectric element 150, for example, and sets the range of the drive voltage Vd applied to the piezoelectric element 150 to 0-V2≤Vd≤0+V2. The relaxed operating state is an operating state in which external vibration is small, such as an operating state in which the detection value of the RV sensor 21 is determined to be smaller than the vibration detection threshold, or an operating state in which the positioning error is smaller than the vibration accuracy threshold. In other words, in the normal operating state, when the absolute value of the bias voltage Vb=Vb1 applied to the piezoelectric element 150 is greater than 0 and the piezoelectric element 150 is determined to be in a relaxed operating state, such as an operating state in which external vibration is small, the MA control unit 620 sets the bias voltage Vb=Vb2=0, for example, and sets the range of the drive voltage Vd applied to the piezoelectric element 150 to 0-V2≤Vd≤0+V2. That is, in the case of a normal operation state, when the absolute value of the bias voltage Vb=Vb1 applied to the piezoelectric element 150 is greater than 0 and it is determined to be an operation state with a small external vibration, or in a moderate operation state, the MA control unit 620 switches from the bias voltage Vb=Vb1 to the bias voltage Vb=Vb2=0, and switches from the range of the driving voltage Vd of Vb1-V1≤Vd≤Vb1+V1 to the range of the driving voltage Vd of Vb2-V2≤Vd≤Vb2+V2.

[0076] Figure 4 This is a schematic diagram showing an example of connection of wiring to a microactuator and the ranges of bias voltage and drive voltage. Figure 4 and Figure 3 Corresponding. Figure 4 A piezoelectric element 150 ( 150 x ) and a piezoelectric element 150 ( 150 y ) are shown. Figure 4 A driving voltage Vdx applied to the piezoelectric element 150x and a driving voltage Vdy applied to the piezoelectric element 150y are shown.

[0077] When it is determined to be in the normal operation state, the MA control unit 620 switches from the bias voltage Vbx=Vb2 to the bias voltage Vbx=Vb1, applies the bias voltage Vbx=Vb1 to the piezoelectric element 150x, and switches from the range of the driving voltage Vdx Vb2(=0)-V2≤Vdx≤Vb2(=0)+V2 to the range of the driving voltage Vdx Vb1-V1≤Vdx≤Vb1+V1.

[0078] When it is determined to be in the normal operation state, the MA control unit 620 switches from the bias voltage Vby=Vb2 to the bias voltage Vby=Vb1, applies the bias voltage Vby=Vb1 to the piezoelectric element 150y, and switches from the range of the driving voltage Vdx Vb2(=0)-V2≤Vdx≤Vb2(=0)+V2 to the range of the driving voltage Vdy Vb1-V1≤Vd≤Vb1+V1.

[0079] When it is determined to be in the normal operation state, the MA control unit 620 applies a driving voltage Vdx to the piezoelectric element 150x, for example, to extend the piezoelectric element 150x in the longitudinal direction, and applies a driving voltage Vdy that is based on the bias voltage Vb1 and is inversely proportional to the driving voltage Vdx to the piezoelectric element 150y, to contract the piezoelectric element 150y in the longitudinal direction.

[0080] When it is determined to be a easing action state, the MA control unit 620 switches from the bias voltage Vbx=Vb1 to the bias voltage Vbx=Vb2, applies a bias voltage Vbx=Vb2 (|Vb2|<|Vb1| and |Vb1|>0)=0 to the piezoelectric element 150x, and switches from the range of the driving voltage Vdx Vb1-V1≤Vdx≤Vb1+V1 to the range of the driving voltage Vdx Vb2(=0)-V2≤Vdx≤Vb(=0)+V2.

[0081] When it is determined to be a easing action state, the MA control unit 620 switches from the bias voltage Vby=Vb1 to the bias voltage Vby=Vb2, applies a bias voltage Vby=Vb2 (|Vb2|<|Vb1| and |Vb1|>0)=0 to the piezoelectric element 150y, and switches from the driving voltage Vdy range of Vb1-V1≤Vdx≤Vb1+V1 to the driving voltage Vdy range of Vb2(=0)-V2≤Vd≤Vb2(=0)+V2.

[0082] When it is determined to be a relaxation action state, the MA control unit 620 applies a driving voltage Vdx to the piezoelectric element 150x, for example, to extend the piezoelectric element 150x in the longitudinal direction, and applies a driving voltage Vdy that is based on the bias voltage Vb2 and is inversely proportional to the driving voltage Vdx to the piezoelectric element 150y, to contract the piezoelectric element 150y in the longitudinal direction.

[0083] Figure 5 Schematic diagram showing an example of the waveform of the driving voltage Vd in the normal operation state of this embodiment. Figure 5 and Figure 4 Corresponding. Figure 5 In the figure, the horizontal axis represents time and the vertical axis represents voltage. Figure 5The upper diagram shows a waveform Wxn of the driving voltage Vdx applied to the piezoelectric element 150 x when the bias voltage Vb1 is applied to the piezoelectric element 150 x in the normal operation state. Figure 5 The lower figure shows a waveform Wyn of the driving voltage Vdy applied to the piezoelectric element 150y when the bias voltage Vb1 is applied to the piezoelectric element 150y in the normal operation state.

[0084] The waveforms Wxn and Wyn are in opposite phases with respect to the bias voltage Vb1. The waveforms Wxn and Wyn vary within the range of the drive voltage Vdx (Vb1-V1≤Vdx≤Vb1+V1) and the drive voltage Vdy (Vb1-V1≤Vdx≤Vb1+V1), respectively.

[0085] Figure 6 Schematic diagram showing an example of the waveform of the driving voltage Vd in the relaxation operation state according to the present embodiment. Figure 6 and Figure 5 Corresponding. Figure 6 In the figure, the horizontal axis represents time and the vertical axis represents voltage. Figure 6 The upper figure shows a waveform Wxr of the driving voltage Vdx applied to the piezoelectric element 150x when the bias voltage Vb2 (=0) is applied to the piezoelectric element 150x in the relaxation operation state. Figure 6 In the figure above, the range of the driving voltage Vdx applied to the piezoelectric element 150x when the bias voltage Vb2 (=0) is applied to the piezoelectric element 150x in the relaxation state is indicated by the solid line: Vb2-V2≤Vdx≤Vb2+V2. Figure 6 In the above figure, for comparison, the range of the driving voltage Vdx applied to the piezoelectric element 150x when the bias voltage Vb1 is applied to the piezoelectric element 150x in the normal operation state is indicated by a dotted line: Vb1-V1≤Vdx≤Vb1+V1. Figure 6 The lower figure shows the waveform Wyr of the driving voltage Vdy applied to the piezoelectric element 150y when the bias voltage Vb2 (=0) is applied to the piezoelectric element 150y in the relaxation operation state. Figure 6 In the figure below, the range of the driving voltage Vdy applied to the piezoelectric element 150y when the bias voltage Vb2 (=0) is applied to the piezoelectric element 150y in the relaxation state is indicated by a solid line: Vb2-V2≤Vdy≤Vb2+V2. Figure 6 In the figure below, for comparison, the range of the driving voltage Vdy applied to the piezoelectric element 150y when the bias voltage Vb1 is applied to the piezoelectric element 150y in the normal operation state is indicated by a dotted line: Vb1-V1≤Vdy≤Vb1+V1. Figure 6 In the equation, |Vb1-V1|=|Vb2-V2|.

[0086] The waveforms Wxr and Wyr are in opposite phases with respect to the bias voltage Vb2. The waveforms Wxr and Wyr vary within the range of the drive voltage Vdx (Vb2-V2≤Vdy≤Vb2+V2) and the drive voltage Vdy (Vb2-V2≤Vdy≤Vb2+V2), respectively. Figure 5 The range of the driving voltage Vdx of the waveform Wxn shown is Vb1-V1≤Vdy≤Vb1+V1, while the range of the driving voltage Vdx is narrower than that of the waveform Wxn shown in FIG. 1 , which is Vb2-V2≤Vdy≤Vb2+V2. The waveform Wxr varies with the bias voltage Vb=Vb2=0 as a reference. The variation ratio of the waveform Wxr is Figure 5 The waveform Wxn shown has a small change. Figure 5 The range of the driving voltage Vdy of the waveform Wyn shown is Vb1-V1≤Vdy≤Vb1+V1, while the range of the driving voltage Vdy is narrower than that of Vb2-V2≤Vdy≤Vb2+V2. The waveform Wyr varies with the bias voltage Vb=Vb2=0 as a reference. The variation ratio of the waveform Wyr is Figure 5 The fluctuation of the waveform Wyn shown is small. That is, the absolute value of the driving voltage Vd applied to the piezoelectric element 150 is smaller in the relaxation operation state than in the normal operation state.

[0087] Figure 7 This is a flowchart showing an example of a method for switching the bias voltage and the drive voltage applied to the piezoelectric element 150 of the microactuator 16M according to the present embodiment.

[0088] The MPU 60 executes access processing according to a command from the host 100 or the like (B701), and determines whether the operation is in a relaxed state or a non-relaxed state (B702). In other words, the MPU 60 determines whether the operation is in a relaxed state or a normal state.

[0089] If it is determined that the operation is not in the relaxation state, that is, in the normal operation state (No in B702), the MPU 60 applies a bias voltage Vb = Vb1 to the piezoelectric element 150 (B703). The MPU 60 switches the driving voltage Vd applied to the piezoelectric element 150 from the range of Vb2-V2≤Vd≤Vb2+V2 to the range of Vb1-V1≤Vd≤Vb1+V1 (B704), and the process ends.

[0090] When it is determined that the operation is in a relaxation state ("Yes" in B702), the MPU 60 applies a bias voltage Vb=Vb2 to the piezoelectric element 150 that is smaller than the bias voltage Vb=Vb1 applied to the piezoelectric element 150 in the case of the normal operation state (B705). When it is determined that the operation is in a relaxation state, the MPU 60 switches the range of the drive voltage Vd applied to the piezoelectric element 150 from Vb1-V1≤Vd≤Vb1+V1 to Vb2-V2≤Vd≤Vb2+V2, which is narrower than (or smaller than) the range of the drive voltage Vd Vd Vb1-V1≤Vd≤Vb1+V1 (B706), and ends the processing.

[0091] According to this embodiment, when the magnetic disk device 1 is determined to be in a normal operating state, the MPU 60 applies a bias voltage Vb=Vb1 to the piezoelectric element 150, and switches the driving voltage Vd applied to the piezoelectric element 150 from a range of Vb2-V2≤Vd≤Vb2+V2 to a range of Vb1-V1≤Vd≤Vb1+V1. When the magnetic disk drive 1 determines that the operation is in the relaxed state, it applies a bias voltage Vb=Vb2 to the piezoelectric element 150 that is smaller than the bias voltage Vb=Vb1 applied to the piezoelectric element 150 when the operation is in the normal state. This switches the range of the driving voltage Vd applied to the piezoelectric element 150 in the normal state from Vb1-V1≤Vd≤Vb1+V1 to a range of the driving voltage Vd applied to the piezoelectric element 150 that is narrower (or smaller) than the range of the driving voltage Vd Vb1-V1≤Vd≤Vb1+V1. The magnetic disk drive 1 can reduce the bias voltage applied to the piezoelectric element 150 when the operation is in a relaxed state compared to the normal state. Furthermore, the magnetic disk drive 1 can reduce the range of the driving voltage Vd when the operation is in a relaxed state compared to the normal state. Therefore, the magnetic disk drive 1 can suppress the migration of the conductive adhesive Ad that bonds the piezoelectric element 150 to the first and second connection pads 170a and 170b. Furthermore, by setting an amplitude limit on the drive voltage (waveform), the risk of depolarization of the piezoelectric element 150, which has been polarized by the application of a reverse voltage, can be reduced. Consequently, the magnetic disk drive 1 can improve reliability.

[0092] While several embodiments of the present invention have been described, these embodiments are presented as examples and are not intended to limit the scope of the invention. These novel embodiments may be implemented in various other ways, and various omissions, substitutions, and modifications may be made without departing from the gist of the invention. These embodiments and their variations are intended to be within the scope and spirit of the invention and are intended to be within the scope of the invention as set forth in the claims and their equivalents.

Claims

1. A magnetic disk device comprising: plate; a head for writing data to and reading data from the disk; an actuator for rotationally driving and controlling the movement of the head mounted on the disk; a microactuator mounted on the actuator, which causes the head to oscillate minutely in the radial direction of the disk via two piezoelectric elements, wherein the two piezoelectric elements expand and contract when drive voltages having opposite phases relative to a bias voltage are applied; A bias voltage control circuit, configured to control the bias voltage; as well as The controller switches the bias voltage from a first bias voltage to a second bias voltage that is lower than the first bias voltage according to an operation state of an access process.

2. The magnetic disk device according to claim 1, The controller switches the range of the driving voltage according to the operating state.

3. The magnetic disk device according to claim 1, The controller switches from a first driving voltage range to a second driving voltage range that is lower than the first driving voltage range.

4. The magnetic disk device according to claim 3, The controller switches from the first bias voltage to the second bias voltage and switches from a first driving voltage range to a second driving voltage range that is lower than the first driving voltage range during background operation.

5. The magnetic disk device according to claim 3, When external vibration is small, the controller switches from the first bias voltage to the second bias voltage, and switches from the first driving voltage range to a second driving voltage range that is smaller than the first driving voltage range.

6. The magnetic disk device according to claim 5, When the positioning error is smaller than a threshold indicating that the external vibration is larger than an allowable value, the controller switches from the first bias voltage to the second bias voltage, and switches from the range of the first drive voltage to the range of the second drive voltage below the range of the first drive voltage.

7. The magnetic disk device according to claim 5, A sensor having detection values ​​for detecting rotation and vibration; The controller switches from the first bias voltage to the second bias voltage and from the range of the first drive voltage to the range of the second drive voltage below the range of the first drive voltage when the detection value is smaller than a threshold value indicating that the external vibration is larger than an allowable magnitude.

8. A method for switching bias and drive voltages of a microactuator, applicable to a magnetic disk device, the magnetic disk device comprising: a disk; a head for writing data to and reading data from the disk; an actuator for rotationally driving and controlling the movement of the head mounted on the disk; a microactuator mounted on the actuator, configured to cause the head to finely oscillate in a radial direction of the disk via two piezoelectric elements, the two piezoelectric elements expanding and contracting when a drive voltage having a phase inverted relative to a bias voltage is applied to the two piezoelectric elements; and a bias voltage control circuit for controlling the bias voltage; In the switching method, The bias voltage is switched from a first bias voltage to a second bias voltage that is lower than the first bias voltage according to an operation state of access processing.

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