JPH0540704Y2 - - Google Patents

Description

[Detailed description of the invention] [Field of industrial application] The present invention relates to an actuator for magnetic disks, and particularly to a rotary (swing type) actuator in which a magnetic head swings in a circular arc trajectory. .

[Conventional technology]

Conventionally, to position a magnetic head on a recording track such as a magnetic disk, a swinging or rotating actuator as shown in FIGS. 3 and 4 has been used. In both figures, permanent magnets 2 are fixed to a yoke 1, and are arranged facing each other with different polarities, and are assembled by supports 3 to form a magnetic circuit via a gap 4. Reference numeral 5 designates an arm, to which a flat moving coil 6 is fixed at one end and a magnetic head (not shown) at the other end. It is arranged so that it can rotate and swing freely. When a signal current is applied to the moving coil 6, a driving force around the shaft 7 acts on the moving coil 6 according to Fleming's left-hand rule, causing the arm 5 to rotate and swing, thereby releasing the magnetic field fixed to the arm 5. The head is positioned on a predetermined recording track on the magnetic disk. Note that the rotation direction is switched by reversing the direction of the current flowing to the coil. In the actuator having the above structure, when position control is performed by detecting the swing speed of the arm 5, if the magnetic disk serving as the recording medium is large, such as 5 inches, 8 inches, or 14 inches, the magnetic head may also be multi-staged. Therefore, the detection means can be independently installed. However, in the case of a small magnetic disk with a diameter of 3.5 inches, for example, there is a problem in that space for separately installing a detection means cannot be secured. In order to solve this problem, attempts have been made to manufacture a compact actuator at low cost by using the movable coil 6 that drives the arm 5 also as a coil for detecting the swing speed.

[Problem that the invention attempts to solve]

Although the above-mentioned improved actuator for magnetic disks has the characteristics of being compact and inexpensive, it has many problems such as noise being extracted at the same time as the detection signal, malfunctions occurring, and reliability being slightly low. Additionally, it is relatively difficult to control, and there is still room for improvement in terms of accuracy.

It is an object of the present invention to solve the above-mentioned problems and to provide an actuator for a magnetic disk that is compact and capable of high-precision control.

[Means for solving problems]

In order to solve the above problems, in this invention,
Permanent magnets made of rare earth magnets are fixed to the inside of the yokes arranged above and below, and a magnetic circuit is formed by making the different poles of the permanent magnets face each other, and a movable coil formed in a flat shape at one end and a magnetic head at the other end. It consists of arms that are each fixed to each other and can swing freely.
In the magnetic disk actuator configured by disposing a moving coil in the gap of the magnetic circuit, a permanent magnet made of a ferrite magnet is fixed to the back surface of the lower yoke, and other magnets are connected to the permanent magnet through the gap. yokes are disposed facing each other, and a detection coil and a cancel coil formed in a flat shape so as to cross the magnetic flux of the permanent magnet made of the ferrite magnet are respectively wound in opposite directions and placed adjacent to each other in the gap; A technical measure has been adopted in which the detection coil and the cancel coil are provided so as to be able to freely swing together with the arm.

[Effect]

With the above configuration, a highly accurate and highly reliable control action can be achieved by providing the detection coil separately from the movable coil, while the cancel coil prevents the effect of noise on the detection coil, and furthermore, the overall This makes it possible to achieve smaller size. In other words, since the permanent magnets for detection and noise cancellation do not require a very large magnetic flux density, the yoke is used in common with the magnetic circuit for driving, and a thin magnetic circuit is formed using ferrite magnets. , which aims to reduce the dimension in the thickness direction.

〔Example〕

1 and 2 are an enlarged sectional view and a partially omitted bottom view of essential parts showing an embodiment of the present invention, respectively, and the same parts are designated by the same reference numerals as in FIGS. 3 and 4. . In both figures, 8 is a housing, which is made of a non-magnetic material such as aluminum alloy and has a fan-shaped planar shape. Reference numeral 9 denotes a bearing, which rotatably holds the shaft 7 fixed to the arm 5. Next, in the housing 8, permanent magnets 2, 2 made of, for example, rare earth magnets each having a fan-shaped or trapezoidal planar shape are arranged with different poles facing each other, via yokes 1a, 1b made of soft magnetic material. ,
Form a magnetic circuit. Next, on one side of the housing 8 is a yoke 10 made of a soft magnetic material such as an iron plate.
and a permanent magnet 11 made of, for example, a ferrite magnet.
are arranged to face each other, and a detection coil 12 and a cancel coil 12a are interposed therebetween. That is, a permanent magnet 11 formed into a substantially trapezoidal shape is fixed to the lower surface of the yoke 1b, and a yoke 10 fixed to the housing 8 is disposed opposite to form a magnetic circuit.
Then, an arm 13 made of a non-magnetic material such as resin is fixed to the lower end of the shaft 7, and a detection coil 12 and a cancel coil 12a buried in the free end are interposed so as to cross the magnetic flux of the permanent magnet 11. It is. Note that the detection coil 12 and the cancel coil 12a are formed by winding in opposite directions, are arranged adjacent to each other on the same plane, and are movable at least on the same trajectory.

With the above configuration, when the arm 5 rotates or swings around the shaft 7 by energizing the movable coil 6, the arm 13 also rotates in cooperation with it, and a signal current is generated in the detection coil 12. This allows the speed and position of the arm 5 to be detected, and the positioning and other controls of the arm 5 to be performed via the control system. In this case, since the movable coil 6 and the detection coil 12 are arranged adjacent to each other, the detection coil 12 is
However, the induced magnetic flux can be canceled by the adjacent cancel coil 12a, and the detection coil 12 can function as a sensor without being affected by noise or other factors. It can be demonstrated.

In this embodiment, an example is shown in which the housing is made of an aluminum alloy, but it may be made of other materials as long as they are non-magnetic. Note that molding by die casting means is advantageous for mass production. Although the detection coil and other detection means may be provided on either one of the housings, the thickness of the entire actuator can be reduced by providing a recessed portion in a part of the housing. Furthermore, since the magnetic flux density that should act on the detection coil and the cancel coil does not need to be very large, for example, permanent magnets made of ferrite magnets are surface magnetized, and even if the magnetic circuit is formed with yokes facing each other, That's enough.

[Effect of idea]

Because the actuator for magnetic disks of the present invention has the configuration and function described above, it is small, thin, and inexpensive, yet it is equipped with an independent detection means, allowing for high-precision control. can be done. In addition, the cancel coil installed adjacent to the detection coil has the effect of canceling out the magnetic flux that acts on the detection coil due to the current of the moving coil and other noises, so there is no malfunction and reliability can be greatly improved. There is.

[Brief explanation of the drawing]

1 and 2 are an enlarged cross-sectional view and a partially omitted bottom view of the main parts showing an embodiment of the present invention, respectively, FIG. 3 is a partially fragmented cross-sectional plan view showing the conventional one, and FIG. It is a view taken along arrow A in FIG. 3. 1, 1a, 1b... Yoke, 2, 11... Permanent magnet, 5, 13... Arm, 6... Moving coil,
12...Detection coil, 12a...Cancel coil.

Claims (1)

[Scope of Claim for Utility Model Registration] A magnetic circuit formed by fixing permanent magnets made of rare earth magnets to the insides of yokes disposed above and below, and having different poles of the permanent magnets facing each other, and a magnetic circuit formed in a flat shape at one end. An actuator for a magnetic disk comprises a movable coil and a swingable arm with a magnetic head fixed to the other end thereof, and the movable coil is disposed in the gap of the magnetic circuit. A permanent magnet made of a ferrite magnet was fixed to the back surface of the yoke, and another yoke was arranged opposite to this permanent magnet with an air gap interposed therebetween, and was formed into a flat shape so as to cross the magnetic flux of the permanent magnet made of the ferrite magnet. An actuator for a magnetic disk, characterized in that a detection coil and a cancel coil are each wound in opposite directions and provided adjacent to each other in the gap, and the detection coil and the cancel coil are provided so as to be able to freely swing together with the arm. .