JPH0528941Y2 - - Google Patents

Description

[Detailed description of the invention] <Industrial application field> The present invention is a moving coil used for transporting and accessing recording/reproducing heads such as magnetic disks, optical disks, magneto-optical disks, and moving head type card reader/writer devices. Regarding type linear DC motors.

<Prior Art> As shown in Fig. 3, a conventionally commonly used linear DC motor has a center yoke 3 on the outer periphery of a short side of a rectangular center yoke 3 made of a soft magnetic material.
The drive coil 1 is wound so that it can move along the long side of the. Permanent magnets 2, 2' in the form of rectangular flat plates magnetized in the thickness direction along the center yoke 3 are disposed on both outer sides of the drive coil 1 so that the same magnetic poles face each other. Further, a magnetic circuit is formed in which outer yokes 4, 4' are connected to both outer sides of the permanent magnets 2, 2' and magnetically short-circuited at both ends of the center yoke 3, thereby obtaining a linear DC motor.

When a direct current is applied to the drive coil 1, according to the left-hand rule of framing, the drive coil 1 generates thrust by the permanent magnets 2 and 2' in accordance with the direction of the current, and moves along the center yoke 3. be done.

<Problems to be solved by the invention> However, in the conventional linear DC motor, as the stroke of movement of the drive coil 1 becomes longer, the inner yoke 3, outer yokes 4, 4' become closer to both ends of the stroke. The magnetic flux density passing through becomes large, and a situation of magnetic saturation occurs. Here, when a direct current is passed through the drive coil 1, the magnetic flux generated from the drive coil 1 and the magnetic flux generated by the permanent magnets 2, 2' are added, resulting in a significant state of magnetic saturation.
This phenomenon appears as a phenomenon determined by the polarity of the permanent magnets 2, 2' and the direction of the current flowing, and is shown by the broken line in Figure 4, which is a characteristic curve diagram showing the relationship between the coil position L and thrust N in Figure 2. As shown in B, there is a drawback that the thrust force N varies greatly depending on the position L of the coil.

<Means for Solving the Problems> The present invention eliminates such drawbacks of the conventional method, and eliminates the drawbacks of the conventional method. It is in contact with the outside of two flat permanent magnets 2 and 2' which are magnetized in the thickness direction with a constant gap on both sides of the drive coil 1 and have the same magnetic pole facing each other, and are in contact with the outside of the center yoke 3. In a magnetic circuit in which two outer yokes 4, 4' are magnetically shorted at both ends, the central portions of the outer yokes 4, 4' or both the center yoke 3 and the outer yokes 4, 4' are shorted. This is a linear DC motor that has a constriction in the side direction to minimize the vertical cross-sectional area and maximize it at both ends of the long side, and the width of the permanent magnet is less than the width of the constriction.

<Function> The magnetic field due to the sum of the magnetic flux generated by the permanent magnets 2 and 2' and the magnetic flux generated by the drive coil 1 becomes almost uniform, and the moving thrust generated by the current of the drive coil 1 in the magnetic field is shifted to a position in the long side direction. It can be made almost uniform regardless.

<Example> As shown in FIGS. 1 and 2, an example of the linear DC motor of the present invention is a rectangular flat center yoke 3 that is wound around the outer periphery of the short side so as to be movable along the long side direction. Permanent magnets 2, 2' in the shape of a rectangular plate are placed at a constant interval on both sides of the drive coil 1.
are arranged with their longitudinal directions aligned. The permanent magnets 2 and 2' are magnetized in the direction of their thickness, and are arranged in parallel so that the same magnetic poles are in the direction of the center yoke 3. Further, on both outer sides of the permanent magnets 2 and 2', constricted portions 5 are provided so that the magnetic cross-sectional area is maximum at the ends and minimum at the center in the longitudinal direction so as to be magnetically short-circuited at both ends of the center yoke 3. York 4,
A linear direct current motor having a magnetic circuit with 4' installed therein is obtained. The outer yokes 4, 4' having such constricted portions 5 can be easily obtained by punching. Further, the outer yokes 4, 4' are formed so that the width of the constricted portion is the same as the width of the permanent magnets 2, 2'. As a result, the outer yoke 4,
Both ends in the long side direction of 4' are larger than the width of the permanent magnets 2, 2', making it possible to reduce leakage magnetic flux more than in the past.

When current is applied to the drive coil 1, the magnetic flux generated by the drive coil 1 and the permanent magnets 2, 2'
Even if the magnetic flux generated in the center yoke 3 or the outer yokes 4, 4' is locally saturated, the thrust does not become non-uniform.

In other words, in the relationship between the coil position L and the thrust force N in FIG.
The change is small and is significantly improved compared to the conventional broken line B.

<Effects of the invention> As described above, according to the invention, the outer yokes 4, 4' constituting the magnetic circuit and the vertical cross-sectional area of the magnetic path of the center yoke 3 can be moved by the drive coil 1 as necessary. By changing the thrust force depending on the position, the generated thrust becomes nearly uniform regardless of the position of the drive coil 1, thereby improving controllability. Moreover,
By making the width of the permanent magnets 2, 2' less than or equal to the width of the constricted portion 5 of the outer yokes 4, 4', leakage magnetic flux can be reduced and efficiency can be improved.

[Brief explanation of drawings]

Fig. 1 is an external perspective view of one embodiment of the linear DC motor of the present invention, Fig. 2 is an exploded perspective view of Fig. 1, Fig. 3 is an external perspective view of an example of a conventional linear DC motor, and Fig. 4 1 is a characteristic curve diagram showing the relationship between the position of a drive coil and thrust in a linear DC motor. Note that 1... drive coil, 2, 2'... permanent magnet, 3... center yoke, 4, 4'... outer yoke, 5... constricted portion.

Claims (1)

[Scope of utility model registration request] A rectangular flat center yoke 3 has a rectangular flat center yoke 3 around which a moving coil 1 that is slid along the long side is wound around the outer periphery of the short side. The center yoke 3 is in contact with the outside of the two permanent magnets 2 and 2'.
2 which are constructed by magnetically shorting each end of the
the outer yokes 4, 4' and the center yoke 3
At least two of the outer yokes 4, 4' are provided with a constricted portion 5 in the short side direction where the magnetic cross-sectional area is the smallest, and the width of the permanent magnet is set at the center of at least two of the outer yokes 4, 4'. A linear DC motor whose width is less than the width of the constricted portion 5 provided at .