JP2560466B2 - Speed detector - Google Patents

Description

The present invention relates to a speed detecting device used for access control of a voice coil motor, and a speed detecting device which is downsized and is not affected by mutual inductance of a voice coil. For the purpose of providing, a bar magnet is provided side by side in the longitudinal direction of one core of a closed magnetic circuit having two parallel cores, and the bar magnet has a magnetic flux density sufficient to saturate the magnetic flux flowing in the core. , A core including the bar magnet and a core not including the bar magnet, the speed detection coil is wound in a movable loop shape, and the other is wound with a voice coil for constituting a voice coil motor, The speed detection coil and the voice coil are provided with a connecting mechanism capable of integrally moving in parallel with the iron core, and the speed corresponding to the speed driven by the voice coil is increased. Configured to detect the speed by the voltage generated in the detection coil.

[Industrial applications]

The present invention relates to a speed detection device used for access control of a voice coil motor (Voice Coil Moter, hereinafter abbreviated as VCM).

In recent years, along with the demand for high-speed access of optical disk devices and the like, VCM requirements have become important. Further, in the case of the optical disk device, the VCM has a speed sensor, and by utilizing this output for feedback control of the VCM, high speed and high performance control can be realized.

Further, with the demand for miniaturization of the optical disk device, miniaturization of the speed detection device and the VCM device is also required. Until now, a speed circuit was created separately from the VCM device to detect the speed. However, it is necessary to effectively use the space with the miniaturization, and for that purpose, a device for using one magnetic circuit for VCM and speed detection is desired.

[Conventional technology]

FIG. 3 shows a sectional view of the main part of a conventional speed detecting device. In the figure, reference numeral 1 is a closed magnetic circuit having an iron core 1a and an iron core 1b which are parallel to each other. Reference numeral 2 denotes a bar magnet that gives the closed magnetic circuit 1 a required magnetic flux density. A VCM 3 has a voice coil 4 wound around the iron core 1b in a movable loop shape. Reference numeral 5 denotes a closed magnetic circuit, which is arranged in a place where it is not affected by the magnetic flux generated by the voice coil 4. 5a and 5b are iron cores parallel to each other,
Reference numeral 6 is a bar magnet that gives the closed magnetic circuit 5 a required magnetic flux density. Reference numeral 7 denotes a speed detecting coil, which is wound around the iron core 5b in a movable loop shape. Reference numeral 8 denotes a connecting mechanism for connecting the voice coil 4 and the speed detecting coil 7 to the iron cores 1b and 5b so that they can move in parallel with each other. The connecting mechanism 8 is formed of a non-magnetic member and is flexible to support the same. The description of the mechanism is omitted.

It is well known that the function of VCM3 is that a desired speed can be obtained by controlling the current flowing through the voice coil 4. At this time, since the speed detection coil 7 is integrally linked with the voice coil 4, the speed detection coil 7 corresponds to the speed.
A voltage is generated at and the speed can be detected. However, this speed detection device has a drawback that it cannot be miniaturized because it uses two closed magnetic circuits.

FIG. 4 is a cross-sectional view of a main part of a conventional speed detecting device with one closed magnetic circuit. This example is a mechanism devised in order to eliminate the drawback of FIG. 3, and the same parts are designated by the same reference numerals. A voice coil 4'and a speed detecting coil 7 ', which are adjacent to each other, are wound around the iron core 1b in a movable loop shape. This method can be miniaturized, but since there are two coils adjacent to the same iron core 1b, mutual inductance causes a voltage to be induced in the speed detection coil 7'by the current flowing in the voice coil 4 '. It will detect the induced voltage added to the electromotive force due to the speed,
There is a drawback that the speed cannot be detected accurately.

[Problems to be Solved by the Invention]

Therefore, the speed detection device cannot be sufficiently miniaturized due to the miniaturization of the VCM device, and if it is attempted to miniaturize the VCM device, the distance between the VCM and the speed detection device becomes small, and the mutual inductance from the voice coil greatly influences it. A problem has arisen.

The present invention has been made in view of the above conventional problems, and an object of the present invention is to provide a speed detection device that is miniaturized and is not affected by mutual inductance due to a voice coil.

[Means for solving the problem]

FIG. 1 is a cross-sectional view of an essential part showing the structure of the present invention. One core 1 of a closed magnetic circuit 1 having two parallel cores 1a and 1b
A bar magnet 2 is provided side by side in a in the longitudinal direction thereof, and the bar magnet 2 has a magnetic flux density sufficient to saturate the magnetic flux flowing in the iron cores 1a and 1b. The speed detection coil 7 is wound around the one of the iron core 1b not including the magnet 2 in a movable loop shape, and the voice coil 4 for constituting the voice coil motor 3 is wound around the other, and the speed detection coil 7 and the The voice coil 4 is the iron core 1a, 1
A connecting mechanism 9 that can move in parallel with b is provided,
The speed is detected by the voltage generated in the speed detecting coil 7 corresponding to the speed driven by the voice coil 4.

[Work]

When a current flows through the voice coil 4, a magnetic flux B is generated corresponding to this current. The cores 1a and 1b of the closed magnetic circuit 1 are bar magnets 2.
As a result, the magnetic flux density is saturated, so that the magnetic flux B cannot pass through the iron core but flows outside the iron core as indicated by the broken line. Since the magnetic flux B has a distance between both coils set so as not to interlink with the speed detection coil, the mutual inductance becomes small, and the induced voltage Es due to the mutual inductance M generated in the speed detection coil 8 as shown in FIG. Becomes smaller. Therefore, it is possible to detect a voltage with a small error corresponding to the speed.

〔Example〕

Embodiments of the present invention will be described in detail below with reference to the drawings. In addition,
In order to make the description of the configuration and operation easier to understand, the same parts are denoted by the same reference numerals throughout the drawings, and the duplicated description thereof will be omitted.

FIG. 1 is a cross-sectional view of an essential part showing the structure of the present invention. In the figure, the voice coil 4 constituting the VCM 3 is wound around the iron core 1b, and the speed detection coil 7 is wound around the iron core 1a including the bar magnet 2 in a movable loop shape. Even if the positions of both coils are opposite to each other, the effect is the same. As the bar magnet 2, one having a magnetic flux density sufficient to saturate the magnetic flux flowing through the iron cores 1a and 1b is used.

In 9, the voice coil 4 and the speed detection coil 7 are closed magnetic circuit 1
A connecting mechanism that connects the parallel iron cores 1a and 1b that make up the structure so that they can move in parallel, and is formed of a non-magnetic member, and the description of the flexible mechanism that supports this is omitted. ing.

B indicated by a broken line is when a current flows in the voice coil 4,
This shows the path of the magnetic flux generated corresponding to this current. Since the magnetic flux density is saturated by the bar magnets 2 in the iron cores 1a, 1b of the closed magnetic circuit 1, the magnetic flux B can pass through the iron core. Instead, it flows outside the iron core as shown by the broken line. The spacing between both coils is set in advance so that this magnetic flux B does not interlink with the speed detection coil 7. As a specific example of the outer dimension of the closed magnetic circuit 1, it could be formed to have a size of 50 mm × 15 mm.

VC is controlled by controlling the current flowing through the voice coil 4.
The action as M3 is performed and the desired control speed is obtained.
Since the speed detection coil 7 moves in parallel with the voice coil 4, a voltage corresponding to the speed is obtained.

FIG. 2 shows a characteristic diagram of the mutual inductance and the output voltage of the speed detection coil. If the mutual inductance between the voice coil 4 and the speed detection coil 7 is M, the output voltage corresponding to the mutual inductance M of the speed detection coil 7 is Es, the current flowing through the voice coil 4 is Iv, and the time is t, then M × dIv / There is a relationship of dt = Es, and as shown in the characteristic diagram, the smaller the mutual inductance M, the smaller the output voltage Es corresponding to the mutual inductance M of the speed detection coil 7. That is, the error component becomes small, the output of the speed detection coil 7 becomes a voltage corresponding to only the speed, and the speed can be accurately detected.

〔The invention's effect〕

As is clear from the above description, according to the present invention, the speed detecting device can be downsized and only the speed of the VCM can be effectively detected, so that there is an effect that it greatly contributes to high-performance VCM feedback control.

[Brief description of drawings]

1 is a sectional view showing the structure of the present invention, FIG. 2 is a characteristic diagram of mutual inductance and output voltage of a speed detection coil, FIG. 3 is a sectional view of a main part of a conventional speed detection device, and FIG. Shows a cross-sectional view of a main part of a conventional speed detecting device with one closed magnetic circuit. In FIG. 1, 1 is a closed magnetic circuit, 1a and 1b are iron cores, 2 is a bar magnet, 3 is a VCM, 4 is a voice coil, 7 is a speed detecting coil, and 9 is a connecting mechanism.

Claims (1)

(57) [Claims] 1. A bar magnet (2) is attached to one of the iron cores (1a) of a closed magnetic circuit (1) having two parallel iron cores (1a, 1b) in the longitudinal direction thereof, and the bar magnets (2) are also provided. ) Has a magnetic flux density sufficient to saturate the magnetic flux flowing in the iron cores (1a, 1b), and the iron core (1a) including the bar magnet (2) and the iron core (1b) not including the bar magnet (2). A voice coil (4) for winding the speed detecting coil (7) in a movable loop shape on one of the two and a voice coil motor (3) on the other.
The voice coil (4) is provided with a connecting mechanism (9) that winds the speed detecting coil (7) and the voice coil (4) in parallel with the iron core (1a, 1b). A speed detecting device characterized in that the speed is detected by a voltage generated in the speed detecting coil (7) corresponding to the speed driven by.