JPS63140655A - Head-positioning device - Google Patents

Abstract

PURPOSE:To generate a uniform torque by changing a length of permanent magnet radially of a shaft in the manner of corresponding to an oscillation angle of a coil. CONSTITUTION:A rotary carriage 2 with a head 1 placed thereon is rotatably supported by a shaft 3 and a yoke 4 is integrally combined with a strut 5 to constitute a head-positioning device. On the inside of said yoke 4, four flat permanent magnets 6 corresponding to a coil oscillation angle and varying in length radially of said shaft 3 are arranged in opposition to each other. Also, a flat coil 7 is supported by a coil carrier 8 to be fixed to the rotary carriage 2, and arranged between the permanent magnets 6. Thus, a deficiency of magnetic flux uncontributory to torque generation due to its leakage at ends of said permanent magnets 6 is increased only by a radial length of each of said ends of the permanent magnets 6, and said increase in magnetic flux of the permanent magnets 6 compensates torque for deficiency and makes torque uniform over the whole range of the coil oscillation angle.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a head positioning device that is small and lightweight, has a wide coil swing range, and generates approximately uniform torque within the range.

[Conventional technology]

FIG. 2 shows a plan view of an example of a conventional head positioning device.

Conventional positioning devices are as disclosed in Japanese Patent Application Laid-Open No. 58-31562,
A rotary carriage 2 on which a magnetic head 1 is mounted is rotatably supported on a shaft 3. A pair of flat yokes 4 are integrally connected by ``:21.'' On one side of the yaw '4, there is a flat, fan-shaped Doku magnet (yc, also referred to simply as a magnet) 6. There are 4 magnets arranged facing each other, 40 each, and the opposing magnets have opposite polarity, forming a -circuit magnetic circuit.Flat coil 7
is a coil support 8 fixed to the rotary carriage 2
When a current flows through the coil 7, which is supported by the permanent magnets 601 and placed between the permanent magnets 601, a force is applied to the coil 7 due to the action and reaction of the magnetic force generated by the coil 0 and the magnetic force of the permanent magnet.
A torque was generated around the shaft 3, which caused the head 1 to rotate.

[Problems that the invention can solve]

However, with the above-mentioned technology, non-uniformity of generated torque has been a major problem.

FIG. 3 is an explanatory diagram showing the positions of coils and permanent magnets of a conventional head positioning device.

The coil 7 rotates around the center 1o of the shaft 3 in the direction of an arrow 11 in the figure from a point A to a point B. The midpoint between point A and point B is set as 0 point. The range between points A and B is called the coil swing angle. Four sector-shaped permanent magnets 6 are arranged facing each other with a coil 7 in between, and two of them on one side are shown in the figure.

Since the permanent magnet 6 is fan-shaped, the length L in the radial direction 12
is constant. When the coil 7 is at the coil swing angle center 0, the force that moves the coil 7, that is, the torque, is proportional to the length of the coil on the magnet, 2XM. When coil 7 is at point A, which is the maximum value of the coil swing angle, the torque is 2X the length of the coil on the magnet.
It occurs in proportion to N. In the case of a sector-shaped permanent magnet 6, L=
Since M=N, ideally the torque should be constant with respect to the coil swing angle. However, in reality, the magnetic flux density generated by the permanent magnet 60 is not constant in the coil swing angle range, and leakage of magnetic flux is particularly significant at the ends of the permanent magnet 6, and this leakage magnetic flux does not contribute to the generated torque.

FIG. 4 shows a torque distribution diagram of a conventional head positioning device. The vertical axis indicates the torque that drives the rotating body when a constant current is applied to the coil 7, and the horizontal axis indicates the position of the coil 7, that is, the coil swing angle. As mentioned above, in an ideal case where there is no leakage, the torque distribution is a constant value at any point of the coil swing angle, as shown in Fig. 15. However, due to magnetic flux leakage at the ends of the permanent magnet 6, the torque distribution is maximum near the 0 point at the center of the coil swing angle, as shown in actual m14, and as it approaches point A or B at both ends, the torque decreases, and as it approaches the end of the magnet. It was confirmed that the generated torque suddenly decreased near points A and B.

This non-uniformity of torque within the coil swing angle has been a serious defect in controlling the motion of the coil. In other words, the constants of the control circuit system are generally fixed, so if the torque varies greatly depending on the head position (same as the coil position), the servo's transmission characteristics will change, making head position tracking control and head movement control impossible. This is because it becomes

In order to overcome this problem, conventional head positioning devices use a coil swing angle that is reduced in order to ensure torque uniformity. However, at the same time, this has resulted in a reduction in the data area used in magnetic disk devices, etc., a decrease in the recording capacity of the drive, and an increase in the cost per unit. Furthermore, in order to maintain the same coil swing angle, it was necessary to widen the permanent magnets to such an extent that the effect of leakage magnetic flux could be ignored. The magnets use expensive rare earth metals, which increases the cost of the entire device. It also required a large amount of space.

The pillars that connect the yokes are also called side yokes, and in the case of magnetic disks, in order to improve data reliability, they must be made of a magnetic material such as iron to prevent leakage of magnetic flux to the data surface.

Therefore, if the column is close to the permanent magnetic flux, the non-uniformity of the torque will be further exacerbated, so the column must be placed as far away from the permanent magnet as possible, which has led to an even larger device.

As described above, in the conventional head positioning device, 1) torque non-uniformity within the coil swing angle range, particularly at both ends, was significant;

2) 1) makes position tracking control and movement control of the coil, that is, the head difficult.

3) In order to avoid problems 1) and 2), it is necessary to reduce the coil swing angle of magnetic disks, etc., which causes a decrease in capacity and an increase in cost per bit.

4) In order to widen the swing angle, the magnet is made larger and the clearance between the side yoke and the magnet is increased, which requires a large space, which hinders the reduction in size and weight of the device and causes an increase in cost.

5) In order to compensate for non-uniformity in torque, it is necessary to use expensive elements with small variations on the control circuit side, which increases the cost of the device.

It has the following problems.

The present invention is intended to solve these problems, and aims to be small, space-saving, have good torque uniformity over the entire swing angle of one coil, and have excellent servo control characteristics, while reducing the amount of magnets used. The purpose of the present invention is to provide an inexpensive head positioning device with less.

[Means for solving problems]

The head positioning device of the present invention includes a rotary carriage that is rotatably supported on a shaft and has a head mounted thereon, a flat coil that is fixed to the four-tally carriage, a coil support that supports the flat coil, and a gap that is axially spaced from the coil. In a swing-type head positioning device consisting of a pair of yokes and a pair of yokes arranged in the axial direction, the length of the permanent magnets in the radial direction relative to the shaft changes in accordance with the swing angle of the coil. characterized by things.

[Effect]

According to the above configuration of the present invention, only the radial length of the permanent magnet end is increased to compensate for the lack of magnetic flux that does not contribute to torque generation due to leakage at the end of the permanent magnet, and this increase in magnetic flux of the permanent magnet This replenishes torque deficiency and generates uniform torque over the entire coil swing angle.

〔Example〕

FIG. 1 is a plan view showing an example of the head positioning device of the present invention.

A rotary carriage 2 carrying a magnetic head 1 is rotatably supported on a shaft 3, and a pair of flat yokes 4 are integrally connected by a support 5. Note that one side of the yoke 40 is not shown, and four flat permanent magnets 6, whose lengths in the radial direction with respect to the shaft 3 change in accordance with the coil swing angle, are arranged facing each other inside the yoke 4. ing. still,
The drawing shows only two permanent magnets 6 on one side. These permanent magnets 6 are adjacent or facing each other and have opposite polarities. The flat coil 7 is supported by a coil support 8 fixed to the rotary carriage 2 and arranged between permanent magnets 60. The functions of these elements are as described above.

FIG. 5 is a sectional view showing an example of the head positioning device of the present invention. The action of element 2 number 1 shown in the figure is the same as described above. Although the pair of beams 4 are divided into two parts and connected by a support (side yoke) 5, they may be integrated. Alternatively, the upper gJ two permanent magnets may be removed, and the lower yoke, permanent magnet, coil, and upper yoke may be stacked in this order. Furthermore, the two adjacent magnets described above may be used as one magnet, and the magnet may be magnetized in the opposite direction with respect to the center line.

In the following embodiments, a case will be described in which four magnets (permanent magnets) are used as a representative example.

FIG. 6 is an explanatory diagram showing the positions of coils and permanent magnets in an example of the head positioning device of the present invention.

The coil 7 rotates around the center 10 of the shaft 3 in the direction of an arrow 11 in the figure from point A to point B.

The coil swings between points A and B, and this angle is called the coil swing angle. The midpoint between point A and point B is defined as 0 point. The shape of the permanent magnet 6 is such that the length L in the radial direction of 12 degrees increases toward the end.

The torque that moves the coil 7 is applied to the coil 7 on the permanent magnet 6.
is proportional to the length of This is called the effective length Q of the coil. When coil 7 is at the fill swing angle center O, the effective length Q of the coil is
is Q=M+M'. Further, when the coil 7 is at the maximum value of the coil swing angle, Q=N+N'. Now, from the shape of the permanent magnet, M+M'>N+N'. 7 is a diagram showing the change in the effective length of the coil with respect to the coil swing angle of the head positioning device of the present invention. The vertical axis is the effective length Q of the coil, and the horizontal axis is the coil swing angle. As mentioned above, at point 0, Q, = M-)-M'A point or B
At the point, Q,=N+N''1:' exists. Q increases as shown by the solid line 15 in the figure between the 0 point and the A point, and between the 0 point and the B point.

Q is shown as a function f(α) of the coil swing angle α.

FIG. 8 is an explanatory diagram showing changes in the magnetic flux density in the gear in the effective length portion of the coil with respect to the coil swing angle of the head positioning device of the present invention.

The vertical axis represents the magnetic flux density R in the gap (space in which the coil moves) between the lower magnet and the upper magnet in the effective length of the coil. The horizontal axis represents the coil swing angle α. The magnetic flux density R decreases at the end points A and B due to magnetic flux leakage, as in the case of 1iA16. Therefore, R is described as a function g(α) of the coil swing angle α.

FIG. 9 is a distribution diagram of the generated torque with respect to the coil swing angle of the head positioning device of the present invention.

The horizontal axis represents the swing angle α of the coil, and the vertical axis represents the torque T generated when the coil is energized.

The generated torque T is proportional to the magnetic flux density R and the effective length Q of the coil. T=RXQ=/(α)×1(α). Here, f(α) is a function that increases between OAs, and g(α) is a function that decreases between OAs, and the product of these shows a nearly constant value C, T=f
(α)X! ! (α)+Q, making it possible to obtain a torque of approximately constant value as shown by the solid line 17 within the range of the coil swing angle. In other words, by determining the permanent magnet shape (length L) so that the increasing tendency of the effective length of the coil and the decreasing tendency of magnetic flux density cancel each other out, it is possible to maintain uniformity of torque within the coil swing angle. In particular, it has become possible to prevent a sudden decrease in torque even when the coil approaches the end of the permanent magnet.

FIG. 10 is an explanatory diagram showing another example of the permanent magnet shape of the head positioning device of the present invention.

The permanent magnet 6 may change its shape discontinuously as shown in the figure, and a substantially uniform torque can be obtained. Based on this isosceles trapezoid, II! The shape in which a protrusion is provided at the corner (or two corners) is easy to achieve precision in manufacturing, and therefore the permanent magnet 6 can be positioned with high precision with respect to the center 10. Therefore, the shift in the shape of the torque distribution with respect to the coil swing angle (lateral shift of the torque distribution in FIG. 9) was small, and the torque uniformity could be improved.

By obtaining sufficient torque uniformity within the range of the coil swing angle, there is little change in the servo transmission characteristics, and the reliability of head position tracking control and head movement control is ensured, making it possible to improve magnetic disk drives. etc. reliability has been significantly improved. Furthermore, since there is no need to use highly accurate and expensive elements in the control circuit, the cost of the device can be reduced.

FIG. 11 is a plan view showing the application of the head positioning device of the present invention to a magnetic disk device.

A magnetic head 1 is fixed to one end of a rotary carriage 2 which is rotatably attached to a shaft 3 fixed to a housing 20 via a bearing 21, and performs recording and reproduction on a rotating recording medium 22. A pair of yokes 4 fixed to the housing 20 are integrally connected by three supports (side yokes). Permanent magnets 6 having the shape of the present invention are arranged opposite to each other inside the yoke. A coil support 8 holding a flat coil 7 fixed to the rotary carriage 2 is arranged in the gap between the permanent magnets 6. When the coil center line moves from point A to point B by an angle EC coil swing angle), the head 1 moves over the recording medium 22. The head rotation angle P is equal to the coil swing angle, and in the case of the magnet shape of the present invention, the coil swing angle E can be secured to be sufficiently wide because, as described above, a decrease in torque due to leakage magnetic flux at the end of the magnet can be prevented. Further, even if the clearances G and H between the side yokes 5 and the permanent magnets 6 are made small, torque uniformity can be ensured by adopting a magnet shape that corrects the leakage of magnetic flux caused by this.

Moreover, the increase in the number of magnets required for this is very small. Therefore, it has become possible to increase the size of the permanent magnet 6 and further increase the coil rotation angle E.

Furthermore, since the side yoke 5 can be made sufficiently large, leakage of magnetic flux to the recording medium can be prevented, improving data reliability of the magnetic disk device. Furthermore, as mentioned above, small magnets can be used efficiently, making it possible to reduce the size, weight, and cost of the device.

〔Effect of the invention〕

As described above, according to the present invention: 1) Good torque uniformity within the coil swing angle range was ensured. In particular, we were able to prevent a decrease in torque at both ends.

2) 1) facilitates head position tracking control and movement control, greatly improving control reliability. 3) A large coil swing angle with good torque uniformity can be achieved with a small magnetic circuit. The usable area of the recording medium can be widely utilized, increasing the capacity and reducing the cost per bit4.
) Since the clearance between the magnet and the magnet and side yoke can be reduced, a compact magnetic circuit can be created, making the device smaller, lighter, and cheaper.

5) Since there is no need to use highly accurate and expensive elements on the control circuit side, the cost of the device has been reduced.

6) Since the side yoke can be made sufficiently large, leakage of magnetic flux to the recording medium can be prevented, and data reliability can be greatly improved.

It has the features and effects shown above.

[Brief explanation of the drawing]

FIG. 1 is a plan view showing an example of the head positioning device of the present invention. FIG. 2 is a plan view of an example of a conventional head positioning device. FIG. 3 is an explanatory diagram showing the positions of coils and permanent magnets of a conventional head positioning device. FIG. 4 is a torque distribution diagram of a conventional head positioning device. FIG. 5 is a sectional view showing an example of the head positioning device of the present invention. FIG. 6 is an explanatory diagram showing the positions of coils and permanent magnets in an example of the head positioning device of the present invention. . FIG. 7 is a diagram showing changes in the effective length of the heavy coil with respect to the coil swing angle of the head positioning device of the present invention. FIG. 8 is an explanatory diagram showing changes in the magnetic flux density within the gear in the effective length portion of the coil with respect to the coil swing angle of the head positioning device of the present invention. FIG. 9 is a distribution diagram of the generated torque with respect to the coil swing angle of the head positioning device of the present invention. FIG. 10 is an explanatory diagram showing another example of the permanent magnet shape of the head positioning device of the present invention. FIG. 11 is a plan view showing the application of the head positioning device of the present invention to a magnetic disk device. 1...Magnetic head, head 2...
...Rotary carriage 3 ..... Axis 4 ..... Meter 5 ..... Pillar (side yoke) 6 ....
...Permanent magnet 7 ...Flat coil (coil) 8 ...
... Coil support 10 ... Center (of shaft) 20 ... Housing 21 ... Bearing 22 ... Recording medium and above Applicant Seiko Epson Co., Ltd. Agent Patent Attorney Mogamisuji (1 other person) 1st Ward 2nd Ward S3 Figure 4 Figure 517 O Figure 6 Filter Tower - Support a Figure 7 Figure 8L Figure 9 Figure 10 figure

Claims (2)

[Claims] (1) A rotary carriage rotatably supported on a shaft and equipped with a head; a flat coil fixed to the rotary carriage; a coil support supporting the flat coil; In a swing type head positioning device consisting of a permanent magnet and a pair of yokes arranged in the axial direction, the length of the permanent magnet in the radial direction with respect to the axis changes in accordance with the swing angle of the coil. Characteristic head positioning device. (2) The head positioning device according to claim 1, wherein the radial length of both ends of the permanent magnet is greater than the radial length of the central portion.