JPH0540903A - Device for generating magnetic field - Google Patents

Abstract

(57) [Abstract] [Purpose] To provide a magnetic field generator that can structurally prevent mutual influence of coils, consumes less current in a steady state, and has improved rising characteristics of a magnetic field. In a magnetic field generator including a coil (1), magnetic yokes (2, 3) equipped in association therewith, and a drive circuit (30) for energizing the coil (1). , The coil (1) is connected to the magnetic yoke (2,
3) is composed of a plurality of coils having the same structure, and the drive circuit (30) switches the energization to the coils in parallel or in series, and a constant current drive in series. It comprises means (31) for

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention mainly relates to a magnetic field generator used in a magneto-optical recording / reproducing apparatus.

[0002]

2. Description of the Related Art Conventionally, a magneto-optical recording / reproducing apparatus is equipped with an optical head for recording / reproducing on / from a recording medium and a magnetic field generator for generating a magnetic field during recording. And, usually, the magneto-optical recording / reproducing apparatus is
During reproduction, only the optical head is driven and the magnetic field generator is not driven. However, at the time of recording, the magnetic field generator also operates to generate a magnetic field in which the direction of magnetization is reversed in the magnetic pole of the recording medium, thereby enabling recording with the optical head. When erasing recorded information, the magnetic field generator operates to generate a magnetic field so that the magnetic poles of the recording medium have the same direction of magnetization, thereby enabling information erasing by the optical head. There is.

As shown in FIGS. 8 and 9, the magnetic field generator used here is a magnetic yoke comprising an outer yoke 2 surrounding the coil and an inner yoke 3 passing through the center of the coil 11. The polarity of the magnetic field can be changed by switching the direction of energization to the coil 11 by providing a coil.

[0004]

However, in the above-mentioned conventional example, when this is used for data information of a computer or the like, several mm to A rising speed of several tens of milliseconds is required. For this reason, in the magnetic field generator using one coil as described above, it takes too much time to reach the required magnetic field level, which is unsatisfactory.

Therefore, as shown in FIG. 10, the inner coil 1
A magnetic field generator employing a coil structure composed of a combination of 2a and an outer coil 12b has also been proposed. Here, first, the inner coil 12a having small resistance and inductance is used.
Since the outer coil 12b is energized when the required magnetic field level is reached, the rising speed can be kept within the required range.

However, in such a structure, since the number of windings of the inner coil is small and the peak current for generating the required magnetic field must be increased, the capacity of the drive power source of the device must be increased. I won't. Further, since the coils of different shapes are combined, it is necessary to protect the drive circuit from the high-voltage counter electromotive voltage generated at the time of switching the energization, and a separate protection circuit must be provided.

[0007]

SUMMARY OF THE INVENTION The present invention has been made based on the above circumstances and is structurally capable of preventing the mutual influence of coils.
An object of the present invention is to provide a magnetic field generator that consumes a small amount of constant current and has improved rising characteristics of a magnetic field.

[0008]

Therefore, according to the present invention,
In a magnetic field generator including a coil, a magnetic yoke associated with the coil, and a drive circuit for energizing the coil, the coil has a plurality of identical configurations common to the magnetic yoke. The above-mentioned drive circuit is provided with a switching means for switching the energization to the coil in parallel or in series, and means for constant current driving in the series state.

[0009]

Embodiments of the present invention will be specifically described below with reference to the drawings. FIG. 1 is an exploded view of a main part of a magnetic field generator according to the present invention, in which reference numeral 1 is two coils having the same structure, 2 is an outer yoke, and 3 is an inner yoke. Is. The inner yoke 3 is attached to the outer yoke 2 by caulking or screwing, and has an integral yoke structure which is magnetically coupled. Further, each lead wire of the coils 1 and 1 is provided with an appropriate relay board (not shown).
Is connected to the drive circuit 30 side via. As shown in FIG. 2, they are arranged in tandem with respect to the inner yoke 3.

FIG. 3 shows a magneto-optical recording / reproducing apparatus incorporating such a magnetic field generator. here,
The above-mentioned magnetic field generator is mounted on the support plate 4, and the support plate 4 is supported by the support shaft 6 at its pivot point 5a via the support shaft 6.
It is rotatably held by the ridge holder-5. More specifically, one end of the support plate 4 supports a boss provided on the outer yoke 2 of the magnetic field generating device, and the other end thereof constitutes a frame of the magneto-optical recording / reproducing device. Side plate 9
It is positioned so as to be engaged from below with a fixed shaft 7 that is installed between them. Then, the supporting plate 4 is elastically contacted with the plate spring 8 provided thereon on the fixed shaft 7 so that A in FIG.
It is biased in the direction of the arrow.

In such a structure, before the cartridge is mounted on the recording medium, the cartridge holder 5 is in the upper position, the support plate 4 engages with the fixed shaft 7, and the direction opposite to the arrow A direction. The magnetic field generator is retracted from the cartridge insertion passage. When the cartridge is loaded, the cartridge driving device (not shown) moves the cartridge holder 5 downward. At this time, the support plate 4 interlocks and rotates in the direction of the arrow A,
The magnetic field generator is lowered to a predetermined height by the positioning portion of the trig holder-5. Then, the biasing force of the spring 8 is increased. After the loading is completed, the recording medium is rotated by the spindle motor and recording / reproducing is performed by the optical head (not shown).

In FIG. 4, a magnetic field generator, an optical head (denoted by numeral 20 here) and a recording medium (denoted by numeral 10 here) are shown.
(Indicated by) is shown schematically,
The magnetic field generating device generates a magnetic field on the recording medium so as to be magnetized in a direction during recording, and a magnetic field so as to be magnetized in a direction during erasing. Therefore, the energization direction is switched for the coil. This energization switching pattern includes reproduction to erasure, erasure to recording, and reproduction to recording. The rising of the current will be specifically described below by taking the case of reproduction to recording as an example.

Generally, the strength of the magnetic field of the coil when energized is proportional to the number of coil turns and the current. FIG. 5 shows the rise of the current during energization. As is clear from the figure, the coil has an inductance, so that a curve like (b) is obtained, which can be expressed by the equation (1). I = V / R · (1−e ^{−R / L · t} ) (1) where I is current, V is applied voltage, R is coil resistance, L is coil inductance, t is time. That is, it can be understood that the rise of the current is improved as shown in FIG. 5A by reducing the resistance and the inductance.

Therefore, in the embodiment of the present invention, two coils having substantially the same number of turns and the same resistance value are used. The structure of the drive circuit is shown in FIG. 6, and is provided with three-pole changeover switches a, b, c and d provided at both ends of each coil, and a changeover switch e for connecting to the constant current circuit 31. ing. Note that FIG. 7 shows a general circuit structure of the constant current circuit 31. Next, the control situation of the drive circuit will be described with reference to Table 1 below.

[0015]

[Table 1] As shown in A and C in Table 1 above, when the switches are controlled to be switched, the coils are connected in parallel.
Therefore, the resistance value of the entire coil is reduced, and good current rising characteristics can be obtained. Furthermore, after a predetermined time has passed or when a predetermined current value is reached, B and C
When the switches are switched and controlled, the coils are connected in series with each other as shown in FIG. At this time, in the series circuit,
The constant current circuit works to reduce the fluctuation of the current due to disturbance such as temperature change. As a result, the resistance value of the entire coil is increased, and the current consumption for generating the required magnetic field can be reduced. Further, a stable magnetic field can be obtained by the stable current supply.

In the above embodiment, the two coils are
Although it shows the configuration to switch to series or parallel connection,
By switching three or more coils to the required connection relationship,
You may make it achieve the initial purpose. For example, when three coils are used, two of them are switched in series / parallel as described above, and the remaining one is connected in parallel only.
Alternatively, it is conceivable to obtain a desired strength of the generated magnetic field by obtaining a necessary rising characteristic by energizing only in series. That is, the above-mentioned drive circuit can be connected to at least one set of the plurality of coils to obtain the same effect. Further, the constant current circuit included in the drive circuit described above can also perform the same function as a constant voltage circuit or a constant voltage chopper circuit.

[0017]

As described above, the present invention relates to a magnetic field generator including a coil, a magnetic yoke equipped with the coil, and a drive circuit for energizing the coil. The coil is composed of a plurality of coils having the same structure common to the magnetic yokes, and the drive circuit includes switching means for switching energization to the coils in parallel or in series, and constant current drive in series. Since the means are provided, it is possible to structurally prevent the mutual influence of the coils, and further, the current consumption in the steady state is small, the rising characteristics of the magnetic field are improved, and a stable magnetic field is realized. ..

[Brief description of drawings]

FIG. 1 is an exploded perspective view showing an embodiment of a magnetic field generator according to the present invention.

FIG. 2 is a side view of the above-described embodiment in an assembled state.

FIG. 3 is a perspective view showing a state in which the magnetic field generation device is incorporated in a magneto-optical recording / reproducing device.

FIG. 4 is a side view showing how the magnetic field generator is used.

FIG. 5 is a graph showing current characteristics according to the present invention.

FIG. 6 is a circuit diagram showing an embodiment of a coil drive circuit of the magnetic field generator.

FIG. 7 is a circuit diagram showing a specific example of a constant current circuit included in the drive circuit.

FIG. 8 is a perspective view of a conventional coil.

FIG. 9 is a side view of the above conventional example.

FIG. 10 is a perspective view of another conventional coil.

FIG. 11 is a side view of the conventional example.

[Explanation of symbols]

 1 coil 2 outer yoke 3 inner yoke 4 support plate 5 cartridge holder 6 support shaft 7 fixed shaft 8 leaf spring 9 side plate 30 drive circuit 31 constant current circuit a, b, c, d, e switch

Claims (1)

[Claims] 1. A magnetic field generator comprising a coil, a magnetic yoke associated with the coil, and a drive circuit for energizing the coil, wherein the coil is common to the magnetic yoke. A plurality of coils having the same configuration, and the drive circuit includes a switching unit that switches energization to the coils in parallel or in series, and a unit for driving a constant current in a serial state. Magnetic field generator.