JPS6256751B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a linear motor, and particularly to the arrangement of a yoke in a stator thereof.

Conventionally, in order to reduce the weight of linear motors, particularly the stator, attempts have been made to create linear motors as shown in FIGS. 1 and 2.

In this figure, reference numeral 1 denotes a stator, which consists of a yoke 3A and a yoke 3B each having a permanent magnet 2 attached to its inner surface. Both yokes 3A and 3B extend in parallel with a predetermined gap 4, and both ends are mutually It is joined. A field magnetic flux 5 in the same direction is formed in the air gap 4 by the permanent magnet 2 .

A movable element 6 is movably fitted loosely into the yoke 3B, and the movable element 2 is composed of a bobbin 7 and an excitation coil 8 wound around the bobbin 7. Note that the movable element 6 is supported by a guide bar (not shown) extending parallel to the yoke 3B. Then, the movable element 6
moves along the longitudinal direction of the yoke 3B.

In this linear motor, the flow state of the field magnetic flux 5 is as shown by the broken line in FIG.
The magnetic flux increases near both ends of A and 3B, but the magnetic flux gradually decreases toward the center. Therefore, even if the central part of the yokes 3A and 3B is made thinner than the two end parts, the magnetic flux density will only approach the value near both ends, and this will not cause much of a problem in the flow of magnetic flux.In other words, the thrust of the motor will decrease. Instead, it is possible to reduce the weight of the stator and the amount of yoke material used.
By the way, it is not preferable to cut the surface of the yokes 3A, 3B on the side facing the gap 4 to provide a concave surface because the gap size changes.
On the surface of 3B opposite to the side facing the gap 4, a concave surface 9 protruding toward the gap 4 is provided at the intermediate portion in the longitudinal direction, and a thin part 10 is formed in the center. Note that the thickness of this thin portion 10 is
The yokes 3A and 3B are designed to have such bending strength that the amount of deflection of the yokes 3A and 3B in response to the magnetic attraction force generated between the yokes 3A and 3B does not exceed a certain limit value.

However, this conventional linear motor has yoke 3.
Since A and 3B are arranged in the vertical direction, that is, in the vertical direction where gravity acts (direction of arrow V), the center thin part 10 of the upper yoke 3B is deflected due to the magnetic attraction force and the own weight of the yoke 3B. It's getting easier. Therefore, the thickness of the thin portion 10 cannot be made very thin, and there is a limit to the weight ratio of the motor.

An object of the present invention is to provide a linear motor that can be made lighter than conventional ones.

To achieve this objective, the present invention provides a stator comprising a plurality of yokes extending in parallel and having both ends magnetically connected to each other, and a permanent magnet for generating field magnetic flux in the gap between the yokes. and a movable element including a bobbin movably fitted loosely into one of the yokes and an excitation coil wound around the bobbin, and a field magnetic flux formed in the gap between the yokes; Due to interaction with the current of the excitation coil flowing in a direction interlinking with the field magnetic flux, the movable element can move along the longitudinal direction of the yoke, and is opposite to the surface of the yoke that faces the air gap. On the side surface, a concave surface is formed in the middle part of the movable element movement area of the yoke where the magnetic flux density is low to make it thin, and both end parts of the yoke where the magnetic flux density is high are thicker than the thin part. Depending on the magnetic flux density in each cross section of the yoke, the surface opposite to the surface facing the air gap has a tapered surface that gradually becomes thicker from the thin middle part to the thicker end parts. Ori,
The yokes are arranged so that the direction of the field magnetic flux is horizontal.

Next, embodiments of the present invention will be described with reference to the drawings. FIG. 3 is a diagram showing the first embodiment.

The difference between the linear motor shown in FIG. 3 and the linear motor shown in FIG. (in the direction of arrow H). The other configurations and functions of the linear motor are the same as those of the conventional linear motor described above, so their explanation will be omitted.

FIG. 4 is a diagram showing two embodiments of the present invention. The difference from the first embodiment is that three yokes 3A, 3B, 3
C, a gap 4 is formed between the yokes 3A and 3B and between the yokes 3B and 3C, and a diamond-shaped hole 11 is formed in the longitudinal center of the central yoke 3B.
The movable element 6 is loosely fitted into the yoke 3B. In this linear motor as well, the yoke 3
A, 3B, and 3C are arranged at the center and on the left and right sides thereof, and the direction of the field magnetic flux formed between them is horizontal. Note that the screw holes 12 bored in the end face of the central yoke 3B are for mounting the stator 1.

FIG. 5 shows an example in which the linear motor according to the second embodiment is used in a lens driving device of an electrophotographic copying machine.

The stator 1 is attached to the machine frame 13 of the lens driving device using the screw hole 12, and the yoke 3A,
3B and 3C are arranged horizontally. The mover 6 is attached to a carriage 15 via a connecting member 14, and bearings 16 provided at both ends of the carriage 15 are movably fitted into guide bars 17, respectively. Further, a lens 18 is attached to a predetermined position of the carriage 15, and travels at a predetermined speed as the movable element 6 moves.

In the above embodiment, a linear motor in which a permanent magnet is mounted on the inner surface of a yoke has been described, but the present invention can also be applied to a linear motor in which a permanent magnet is interposed between the joints at both ends of a yoke.

The present invention has the above-described configuration, and the only force that acts in the horizontal direction between the yokes is the magnetic attraction force, and the weight of the yokes acts in the vertical direction. Therefore, the thickness of the yoke, particularly the thickness of the thin portion, can be reduced to a thickness that has a bending strength close to the limit value of the amount of deflection due to the yoke resisting the magnetic attraction force. Therefore, the yoke can be made thinner than the conventional one, and a lightweight and inexpensive linear motor can be provided. Note that, as in the present invention, depending on the magnetic flux density in each cross section of the yoke, the surface of the yoke on the opposite side to the surface facing the air gap becomes thicker sequentially from the thinner middle portion to the thicker end portions. Because it has a tapered surface, the magnetic resistance inside the yoke does not increase locally by making the wall thinner, and the magnetic properties of the yoke are maintained as they are. There is no possibility that the motor output will decrease.

[Brief explanation of the drawing]

1 and 2 are a front view and a perspective view of a conventional linear motor, FIGS. 3 and 4 are perspective views of a linear motor according to each embodiment of the present invention, and FIG. 5 is a front view and a perspective view of a conventional linear motor. FIG. 2 is a partially cross-sectional front view of a lens driving device using a linear motor according to an embodiment. 1...Stator, 2...Permanent magnet, 3A, 3B,
3C... Yoke, 4... Air gap, 5... Field magnetic flux,
6...Mover, 7...Bobbin, 8...Exciting coil, 9...Concave surface, 10...Thin wall portion, H...Horizontal direction.

Claims (1)

[Claims] 1. A stator consisting of multiple yokes extending in parallel and magnetically connected to each other at both ends, and a permanent magnet for generating field magnetic flux in the gap between the yokes, which can be moved to either one of the yokes. The movable element includes a bobbin that is loosely fitted into the bobbin, and an excitation coil that is wound around the bobbin. Due to the interaction with the flowing current of the excitation coil, the movable element can move along the longitudinal direction of the yoke, and the movable element can move in the moving area of the yoke on the surface opposite to the surface of the yoke that faces the air gap. A concave surface is formed in the middle part of the yoke where the magnetic flux density is low to make it thin, and both ends of the yoke where the magnetic flux density is high are thicker than the thin part, and the surface opposite to the surface facing the gap of the yoke. The yokes are arranged so that the yoke has a tapered surface so that it becomes thicker from the thin middle part to the thicker end parts, and the direction of the field magnetic flux is horizontal. linear motor.