CN1755799A - Micro-driver, magnetic head folding sheet combination with micro-driver and magnetic disk driver - Google Patents

Abstract

The present invention discloses a head-flip assembly including a slider; a micro-actuator for horizontally rotating the slider with the center of the slider as the rotation center; and a suspension for supporting the slider and the micro-actuator; wherein the micro-actuator includes a support frame, the support frame includes a base, a movable sheet, a lead column connecting the base and the movable sheet; and at least one piezoelectric sheet connecting the base and the movable sheet; wherein the lead column includes a pivot part for assisting the horizontal rotation of the slider. The pivot part is smaller than the width of the lead column. The suspension includes a support bar formed on the tongue of the suspension for abutting against the base of the support frame. The present invention also discloses a hard disk drive structure using the head-flip assembly.

Description

Microdrive, head gimbal assembly provided with the microdrive, and magnetic disk drive

technical field

The invention relates to a disk drive, in particular to a micro drive and a magnetic head gimbal assembly using the micro drive.

Background technique

A disk drive is an information storage device that uses magnetic media to store data. With reference to Fig. 1 a, the existing typical disk drive (Disk Drive) comprises a magnetic disk and a driving arm for driving a head gimbal assembly 277 (Head Gimbal Assembly, HGA) (the head gimbal assembly 277 is provided with a magnetic head 203 cantilever (not shown)). Wherein, the magnetic disk is mounted on a spindle motor for driving the magnetic disk to rotate, and a Voice-Coil Motor (Voice-Coil Motor, VCM) is used to control the movement of the driving arm, thereby controlling the magnetic head 203 to move from a magnetic track to a magnetic disk surface on the magnetic disk surface. next track to read or write data from the disk.

However, during the travel of the magnetic head 203, due to the inherent tolerance (Tolerance) of the voice coil motor (VCM) and the suspension, the magnetic head 203 cannot perform good position control, thus affecting the magnetic head 203 to read or write from the magnetic disk. data.

In order to solve the above problems, a piezoelectric (PZT) micro-actuator is used to adjust the displacement of the magnetic head 203 . That is, the piezoelectric micro-actuator adjusts the displacement of the magnetic head 203 in a small range to compensate for the tolerance of the voice coil motor (VCM) and the suspension. In this way, the track width can be made smaller, and the TPI value ('tracks per inch' value) of the disk drive can be increased by 50% (ie, its surface recording density is increased).

Referring to FIG. 1 b , a conventional piezoelectric micro-actuator 205 has a U-shaped ceramic frame 297 . The U-shaped ceramic frame 297 includes two ceramic arms 207, wherein each ceramic arm 207 is provided with a piezoelectric piece (not shown) on one side thereof. 1a and 1b, the piezoelectric micro-actuator 205 is physically connected to the cantilever 213, wherein, on one side of each ceramic arm 207, there are three electrical connection balls 209 (gold ball bonding (gold ball bonding, GBB) or solder ball bonding) (solder bump bonding, SBB)) connects the microdrive 205 to the HGA cable 210. In addition, there are four electrical connection balls 208 (GBB or SBB) for realizing the electrical connection between the magnetic head 203 and the suspension 213 . FIG. 1 c shows the detailed process of inserting the magnetic head 203 into the microdrive 205 . Wherein, the magnetic head 203 is bonded to the two points 206 on the two ceramic arms 207 through the epoxy glue point 212 , so that the movement of the magnetic head 203 depends on the ceramic arms 207 of the micro-driver 205 .

When current is applied to the micro-driver 205 through the suspension cable 210, the piezoelectric sheet of the micro-driver 205 will expand or contract, thereby causing the deformation of the two ceramic arms 207 of the U-shaped ceramic frame 297 to make the magnetic head 203 move on the track of the disk. . In this way, a good head position adjustment can be achieved.

However, since the piezoelectric micro-actuator 205 and magnetic head 203 are mounted on the cantilever tongue (not shown), when the piezoelectric micro-actuator 205 is excited, it will act as Simply translational motion to oscillate the head 203 will generate a resonance of the suspension at the same frequency as the vibration induced by exciting the base of the suspension. This will limit the disk drive's servo system bandwidth and increase in capacity. As shown in FIG. 2 , reference numeral 201 represents the resonance curve when the cantilever substrate is excited, and reference numeral 202 represents the resonance curve when the micro-actuator 205 is excited, which clearly shows the above problems.

Furthermore, since the micro-actuator 205 includes an additional mass, it not only affects its static performance, but also affects the dynamic performance of the cantilever 213, such as resonance performance, thereby reducing the resonant frequency of the cantilever 213 and increasing its gain.

Meanwhile, since the U-shaped ceramic frame 297 of the micro-actuator 205 is very fragile, its shock resistance is also a problem.

Therefore, it is necessary to provide a microdrive, a HGA, and a disk drive to solve the above-mentioned problems.

Contents of the invention

Based on the deficiencies of the prior art, the main purpose of the present invention is to provide a combination of a micro-drive and a head gimbal, which can achieve good head position adjustment and has good resonance performance when the micro-drive is excited.

Another object of the present invention is to provide a disk drive with larger servo system bandwidth and capacity.

In order to achieve the above object, the present invention discloses a head gimbal assembly comprising: a slider; a micro-actuator for horizontally rotating the head with the central part of the head as the center of rotation; and a slider for supporting the slider. Suspension of the magnetic head and micro-actuator described above. Wherein, the microdrive includes a support frame, which includes a base, a movable piece, a guide post connecting the base and the movable piece; and at least one piezoelectric piece connecting the base and the movable piece; the guide post includes an auxiliary magnetic head level Pivot to rotate. In the present invention, the pivot portion is smaller than the width of the guide post. In one embodiment, the cantilever member includes support means formed on the tongue of the cantilever for abutting against the base of the support frame. The at least one piezoelectric sheet is sandwiched between the cantilever tongue and the support frame of the micro-driver, and an anisotropic conductive film (ACF) connects the at least one piezoelectric sheet and the cantilever physically and electrically.

In one embodiment of the present invention, the magnetic head part is installed on the movable piece of the supporting frame, and the supporting device is integrally formed with or connected with the suspension. Wherein, the supporting device is made of polymer or metal. In one embodiment, the cantilever member includes a load bar provided with a small protrusion for supporting the cantilever tongue, and the pivot portion is formed at a corresponding position of the small protrusion. At the same time, a parallel gap is formed between the support frame and the cantilever tongue. In the present invention, the at least one piezoelectric sheet is a thin film piezoelectric sheet or a ceramic piezoelectric sheet. The at least one piezoelectric sheet is a single-layer structure or a multi-layer structure including a base layer and a piezoelectric layer. The piezoelectric layer is a single-layer piezoelectric structure or a multi-layer piezoelectric structure, and the base layer is made of metal, ceramic or polymer.

In one embodiment of the present invention, the base and the movable piece are connected in parallel at predetermined positions through guide posts, and both the base and the movable piece are cuboids. The two ends of each piezoelectric sheet are respectively connected with the base and the movable sheet, and a plurality of electrode contacts are arranged on each piezoelectric sheet.

A hard disk drive of the present invention includes a HGA, a drive arm connected to the HGA, a disk; and a spindle motor used to rotate the disk. Wherein, the head gimbal assembly includes a slider, a micro-actuator for horizontally rotating the head with the central part of the head as a rotation center, and a suspension for supporting the head and the micro-actuator. Wherein said microdrive comprises a supporting frame, which includes a base, a movable piece, a lead column connecting the base portion and the movable piece; and at least one piezoelectric piece connecting the base portion and the movable piece; wherein, the guiding column includes an auxiliary magnetic head Pivot for horizontal rotation.

Compared with the prior art, the micro-driver of the present invention uses the piezoelectric sheet to rotate the movable sheet of the support frame, and the magnetic head is partially installed on the movable sheet, so that the magnetic head can be rotated. At the same time, the lead post provided with the pivot portion can prevent the magnetic head from moving laterally, but only allows it to rotate around the pivot portion. Since the pivot portion corresponds to the center line of the magnetic head, the magnetic head can operate without swinging the head gimbal assembly. That is, the trailing side and the leading side of the magnetic head can rotate in different directions at the same time, so that the magnetic head can obtain a larger moving range. Because the head rotates along its center, a greater position stroke adjustment capability and wider servo system bandwidth can be obtained. Generally, the working efficiency of the micro-driver that adjusts the magnetic head through rotation is three times that of the micro-driver that adjusts the magnetic head through translation (such as the prior art). The micro-driver of the present invention adjusts the magnetic head through rotation, so the work efficiency equivalent to 3 times of the prior art can be obtained. In addition, compared with the prior art that needs to provide a driving voltage of 40V for piezoelectric operation, the present invention only needs to provide a driving voltage of 10V because the sway mode of the micro-driver is omitted, correspondingly, it saves energy and can for better performance. In addition, since a supporting device is formed on the cantilever tongue to bear against the base of the support frame, a parallel gap is formed between the cantilever tongue and the support frame, so that when the micro-actuator is activated, the movable piece will move more freely and Rotate the head over a wide range. In addition, the cantilever resonance phenomenon does not occur in the low frequency band, but only the pure micro-drive resonance phenomenon occurs in the high frequency band, which will increase the servo system bandwidth of the disk drive and the disk drive capacity. Finally, compared with the existing U-shaped ceramic frame, the structure of the micro-actuator of the present invention will obtain better anti-seismic performance.

In order to make the present invention easier to understand, the specific embodiments of the microdrive, the HGA and the hard disk drive of the present invention will be further described below in conjunction with the accompanying drawings.

Description of drawings

FIG. 1a is a perspective view of a conventional head gag assembly (HGA);

Figure 1b is an enlarged partial view of Figure 1a;

Figure 1c shows the detailed process of inserting the magnetic head into the microdrive of the head gag assembly (HGA) in Figure 1a;

Figure 2 shows the resonance curve (resonance curve) of the head gimbal combination in Figure 1a;

3 is a perspective view of the first embodiment of the head gag assembly (HGA) of the present invention;

Fig. 4 is a partial enlarged view of the magnetic head flap assembly in Fig. 3;

FIG. 5 is an exploded perspective view of the magnetic head flap assembly in FIG. 3;

6 is a partial sectional view of the head gimbal assembly along line A-A in FIG. 4;

Figure 7 shows the initial state of the micro-driver of the present invention when no voltage is applied;

Figures 8 and 9 show two different modes of operation of the microdriver in Figure 7 when activated;

Figure 10a shows the electrical connection relationship between the two piezoelectric sheets of the micro-driver shown in Figure 7, according to an embodiment of the present invention, the two piezoelectric sheets have the same polarization direction;

Figure 10b shows the electrical connection between the two piezoelectric sheets of the micro-driver shown in Figure 7, according to another embodiment of the present invention, the two piezoelectric sheets have opposite polarization directions;

Figure 10c shows the waveform diagrams of the two voltages respectively applied to the two piezoelectric sheets shown in Figure 10a;

Figure 10d shows the waveforms of the voltages applied to the two piezoelectric sheets shown in Figure 10b respectively;

Figure 11 shows the resonance curves of the head gimbal combination in Figure 3; and

Figure 12 is a perspective view of one embodiment of the disk drive of the present invention.

Detailed ways

Referring to FIG. 3 , a HGA 3 according to the present invention includes a magnetic head 31 , a micro-driver 32 and a suspension member 8 for carrying the magnetic head 31 and the micro-driver 32 .

Also referring to FIG. 3 , the cantilever member 8 includes a load beam (load beam) 17 , a flexible member (flexure) 13 , a hinge member (hinge) 15 and a base plate (base plate) 11 . A plurality of small protrusions 329 are disposed on the load bar 17 (refer to FIG. 6 ). A plurality of electrode contacts 308 are provided on the flexible member 13 , one end of the plurality of electrode contacts 308 is connected to a control system (not shown), and the other end is connected to a plurality of cables 309 , 311 . 4 and 5, the flexure 13 also includes a cantilever tongue (suspension tongue) 328, the cantilever tongue 328 is used to support the micro-driver 32 and the magnetic head 31, and make the bearing force always pass through the load bar 17 A small protrusion 329 is applied to the central area of the magnetic head 31 . A plurality of electrode contacts 113 and 328a are provided on the cantilever tongue 328 . One end of the magnetic head 31 is provided with a plurality of electrode contacts 204 corresponding to the electrode contacts 113 on the cantilever tongue 328 .

Referring to FIGS. 4-5 , according to an embodiment of the present invention, the micro-driver 32 includes a support frame 320 and two piezoelectric sheets 321 , 322 . Corresponding electrode contacts 328a on each piezoelectric sheet 321,322 are provided with plural electrode contacts (for example, the piezoelectric sheet 321 is provided with two electrode contacts 321a, and the piezoelectric sheet 322 is provided with two electrode contacts 322a ). The supporting frame 320 may be made of metal (eg, stainless steel), ceramic or polymer. It includes a bottom arm 392 , a top arm 390 , and a lead post 393 connecting the bottom arm 392 and the top arm 390 in parallel at predetermined positions. In one embodiment, both the bottom arm 392 and the top arm 390 are cuboid. A pivot portion 394 is formed on the guide post 393 , and the width of the pivot portion 394 is smaller than that of the guide post 393 . The bottom arm 392 includes two free ends 392a, 392b and the top arm 390 includes two free ends 390a, 390b. Referring to FIG. 6 , in one embodiment, the pivot portion 394 is formed corresponding to the position of the small protrusion 329 on the load lever 17 . Thus, the support frame 320 and the cantilever tongue 328 have the same rotation center, and a parallel gap 400 is formed between the support frame 320 and the cantilever tongue 328 . In the present invention, the piezoelectric sheet 321 is connected to the support frame 320 by connecting its two ends to the two free ends 392 b and 390 b of the support frame 320 . Similarly, the piezoelectric sheet 322 is connected to the support frame 320 by connecting its two ends to the two free ends 392 a and 390 a of the support frame 320 . Wherein, the connection between the piezoelectric sheets 321 and 322 and the support frame 320 may be a conventional connection, such as epoxy glue connection, anisotropic conductive film connection.

In the present invention, the piezoelectric sheets 321, 322 are preferably made of thin-film piezoelectric materials, and the piezoelectric sheets 321, 322 may be single-layer piezoelectric elements or multi-layer piezoelectric elements. In one embodiment, the piezoelectric sheets 321 and 322 can both be a multi-layer structure including an inner base layer and an outer piezoelectric layer. The inner base layer can be made of ceramics, polymers or metals, and the outer piezoelectric layer can be a single-layer piezoelectric element or a multi-layer piezoelectric element.

Referring to FIGS. 5 and 6 , a support bar 300 is formed on the cantilever tongue 328 to support the support frame 320 . In the present invention, the support bar 300 can be integrally formed with the cantilever tongue 328, or connected with it by laser welding. In one embodiment, the thickness of the support bar 300 is greater than or equal to 30 μm, and the support bar 300 is made of polymer or metal (such as stainless steel).

Referring to FIGS. 4-6, in one embodiment of the present invention, the two piezoelectric sheets 321, 322 and the support frame 320 are connected together to form a micro-driver 32; then, the magnetic head 31 and the micro-driver 32 are bonded; Next, the magnetic head 31 and the micro-driver 32 are installed on the suspension member 8 to form the HGA 3 .

In the present invention, the magnetic head 31 is partially installed on the support frame 32 through epoxy glue or ACF 40. Preferably, the magnetic head 31 is partially mounted on the top arm 390 . The micro-actuator 32 is installed on the cantilever 8 by connecting the two piezoelectric plates 321, 322 on it with the cantilever tongue 328 by ACF. Correspondingly, the electrode contacts 321a and 322a on the two piezoelectric sheets 321, 322 are electrically connected to the electrode contacts 328a on the cantilever tongue 328, thereby electrically connecting the micro-driver 32 and the two cables 311 on the cantilever 8. connect. At this time, the support bar 300 is pressed under the support frame 320 for abutting against the bottom arm 392 of the support frame 320 . In one embodiment, one end of the support bar 300 is close to the pivot portion 394 . In the present invention, the plurality of metal balls 405 are used to electrically connect the electrode contacts 204 and the electrode contacts 113 on the magnetic head 31 , so as to electrically connect the magnetic head 31 to the cable 309 . Through the cables 309 , 311 , the electrode contacts 308 electrically connect the magnetic head 31 and the micro-driver 32 with a control system (not shown). Apparently, the HGA 3 can also be assembled in this way: firstly, the micro-drive 32 is connected to the suspension member 8 , and then the magnetic head 31 is installed on the micro-drive 32 .

7-9, 10a, 10c show the first working mode of the micro-driver 32 to realize the head position adjustment function. In this embodiment, the two piezoelectric sheets 321, 322 have the same polarization direction, as shown in Figure 10a, one end 404 of the two piezoelectric sheets 321, 322 is commonly grounded, and the other Two voltages with two different waveforms 406, 408 are respectively applied to one terminal 401a and 401b (as shown in Fig. 10c). FIG. 7 shows the initial state of the micro-driver 32 , that is, the state when no voltage is applied to the piezoelectric sheets 321 , 322 on the micro-driver 32 . When the voltage with waveforms 406, 408 is applied to the two piezoelectric strips 321, 322, in the first half cycle, as the driving voltage changes, the piezoelectric strip 321 gradually shrinks to a shortest position, while at the same time The piezoelectric sheet 322 gradually expands to a longest position (corresponding to the maximum displacement position); and then gradually returns to its original position. In the present invention, since the piezoelectric sheet 321 is connected to the free ends 392 b and 390 b of the support frame 320 , the piezoelectric sheet 322 is connected to the free ends 392 a and 390 a of the support frame 320 . In the aforementioned half period, with the change of the driving voltage 406 , 408 , the top arm 390 will be rotated to the left by the piezoelectric strips 321 , 322 around the pivot portion 394 , and then return to its original position. Because the pivot portion 394 is formed on the lead post 393 . When the driving voltage 406, 408 enters the second half cycle (opposite to the phase of the first half cycle), the piezoelectric sheet 322 gradually shrinks to a shortest position, while the piezoelectric sheet 321 gradually expands to a shortest position. long position; then gradually returns to its original position. In the present invention, because the width of the pivot portion 394 is smaller than that of the lead post 393, the pivot portion 394 can assist the horizontal rotation of the magnetic head 31, that is, the lead post 393 is easily moved by the small width pivot portion 394. bending, so that the magnetic head 31 can obtain greater rotation. In addition, because the support bar 300 is against the bottom arm 392 of the support frame 320, a parallel gap is formed between the top arm 390 and the cantilever tongue 328, so that the top arm 390 can be more easily driven by the piezoelectric plates 321, 322. Spin freely.

7-9, 10b, 10d show another working mode in which two piezoelectric sheets 321, 322 realize the function of adjusting the position of the magnetic head. In this embodiment, the two piezoelectric sheets 321, 322 have opposite polarization directions, as shown in FIG. 10b. One end 404 of the two piezoelectric sheets 321, 322 is commonly grounded, and the other ends 401a and 401b are respectively applied with a voltage having the same sinusoidal waveform 407 (refer to FIG. 10d ). Driven by the above-mentioned voltage, within the same half period, the piezoelectric sheet 321 will gradually shrink while the piezoelectric sheet 322 will gradually expand, thereby rotating the top arm 390 of the support frame 320 to the left; when the voltage enters the lower half In one cycle, the piezoelectric sheet 321 will expand while the piezoelectric sheet 322 will contract, thereby rotating the top arm 390 to the right.

In the present invention, since the magnetic head 31 is partially installed on the top arm 390 of the support frame 320, the magnetic head 31 will rotate along with the top arm 390 with its central part (corresponding to the pivot portion 394) as the center of rotation. rotate. Thus, a good head position adjustment can be obtained.

Compared with the prior art, the micro-driver 32 of the present invention can use the central part of the magnetic head 31 as the rotation center to rotate the magnetic head 31, so that the leading edge (leading side) and the trailing edge (trailing side) of the magnetic head 31 can be moved in different directions. , but the existing micro-driver can only swing the trailing edge of the head (because its leading edge is fixed). Like this, because the leading edge and the trailing edge of the magnetic head can move, the present invention can make the magnetic head get larger amplitude swing. Correspondingly, the head position adjustment capacity can be improved.

FIG. 11 shows the test results of the resonance performance of the magnetic head gimbal assembly of the present invention, wherein, 701 represents the excitation resonance curve of the substrate of the cantilever, and 702 represents the excitation resonance curve of the micro-drive. As can be seen from this figure, when the micro-driver 32 is excited, the cantilever resonance does not occur in the low-frequency band, but only the pure micro-driver resonance occurs in the high-frequency band, which will increase the servo system bandwidth of the disk drive and improve its capacity, At the same time reduce the head search and positioning time (seeking and settling time).

In the present invention, referring to FIG. 12 , a disk drive can be formed by assembling the HGA 3 of the present invention with the disk drive housing 108 , disk 101 , spindle motor 102 , and voice coil motor 107 . Since the assembly process and structure of the disk drive of the present invention are well known to those skilled in the art, they will not be described in detail here.

Claims (20)

1. A head gimbal assembly (head gimbal assembly) comprising:

a magnetic head (slider);

a micro-actuator (micro-actuator) for horizontally rotating the magnetic head with the center portion of the magnetic head as a rotation center; and

a suspension (suspension) for supporting the head and the micro-actuator; wherein the micro-actuator comprises a support frame, the support frame comprises a base part, a movable sheet and a guide column connecting the base part and the movable sheet; and

at least one piezoelectric sheet connecting the base and the movable sheet;

wherein the guide post comprises a pivot part for assisting the horizontal rotation of the magnetic head.

2. The hga of claim 1 wherein: the pivot portion is less wide than the guide post.

3. The hga of claim 1 wherein: the cantilever part comprises a supporting device which is formed on a tongue part of the cantilever and used for abutting against the base part of the supporting frame.

4. The hga of claim 3 wherein: the at least one piezoelectric plate is clamped between the cantilever tongue and a support frame of the micro-actuator, and an Anisotropic Conductive Film (ACF) is used for physically and electrically connecting the at least one piezoelectric plate and the cantilever.

5. The hga of claim 1 wherein: the magnetic head part is arranged on the movable sheet of the supporting frame.

6. The hga of claim 3 wherein: the supporting device is integrally formed with or connected with the cantilever part.

7. The hga of claim 3 wherein: the support means is made of a polymer or a metal.

8. The hga of claim 3 wherein: the cantilever member includes a load bar provided with a small projection for supporting the cantilever tongue, and the pivot portion is formed at a corresponding position of the small projection.

9. The hga of claim 3 wherein: a parallel gap is formed between the support frame and the cantilever tongue.

10. The hga of claim 1 wherein: the at least one piezoelectric sheet is a thin film piezoelectric sheet or a ceramic piezoelectric sheet.

11. The hga of claim 1 wherein: the at least one piezoelectric sheet is a single-layer structure or a multi-layer structure including a base layer and a piezoelectric layer.

12. The hga of claim 11 wherein: the piezoelectric layer is a single-layer piezoelectric structure or a multi-layer piezoelectric structure, and the base layer is made of metal, ceramic or polymer (polymer).

13. A micro-actuator, comprising:

the supporting frame comprises a base part, a movable sheet and a guide column for connecting the base part and the movable sheet; and

at least one piezoelectric sheet connecting the base and the movable sheet; wherein,

the guide post includes a pivot portion for assisting the horizontal rotation of the movable piece. .

14. The microactuator of claim 13 wherein: the pivot portion is less wide than the guide post.

15. The microactuator of claim 13 wherein: the base part and the movable sheet are connected in parallel at a preset position through a guide column, wherein each base part is a cuboid.

16. The microactuator of claim 13 wherein: two ends of each piezoelectric piece are respectively connected with the base part and the movable piece, and each piezoelectric piece is provided with a plurality of electrode contacts.

17. The microactuator of claim 13 wherein: the at least one piezoelectric sheet is a thin film piezoelectric sheet or a ceramic piezoelectric sheet.

18. The hga of claim 13 wherein: the at least one piezoelectric sheet is a single-layer structure or a multi-layer structure including a base layer and a piezoelectric layer.

19. The hga of claim 18 wherein: the piezoelectric layer is a single-layer piezoelectric structure or a multi-layer piezoelectric structure, and the base layer is made of metal, ceramic or polymer (polymer).

20. A hard disk drive comprising:

combining magnetic head tabs;

a driving arm connected with the magnetic head folding piece combination;

a magnetic disk; and

a spindle motor to rotate the magnetic disk; the method is characterized in that: the magnetic head gimbal assembly comprises a magnetic head (slider), a micro-actuator (micro-actuator) which horizontally rotates the magnetic head by taking the central part of the magnetic head as a rotation center, and a cantilever part (suspension) which is used for supporting the magnetic head and the micro-actuator; wherein the micro-driver includes:

the supporting frame comprises a base part, a movable sheet and a guide column for connecting the base part and the movable sheet; and

at least one piezoelectric sheet connecting the base and the movable sheet;

wherein the guide post comprises a pivot part for assisting the horizontal rotation of the magnetic head.

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