JPH0755041B2 - Linear motor - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION A. Field of Industrial Application The present invention relates to a linear motor that generates thrust in a linear direction.

B. Summary of the Invention In a linear motor that generates thrust in a linear direction, the present invention keeps power consumption low by passing magnetic flux from a coil of a fixed part through a magnetic closed circuit including a gear gap of a movable part. -It is intended to reduce the weight and reduce the cost.

C. Conventional Technology Conventionally, in a video camera, a so-called autofocus mechanism or a power zoom mechanism uses, for example, a motor with a brush, and the driving force (rotational force) of the motor is transmitted through a reduction gear. It is transmitted to the focus ring and zoom ring. However, there are problems with acoustic noise, vibration, response characteristics, reliability of brushes, gears, and the like.

D. Problems to be Solved by the Invention In order to solve the above problems, various motors for directly moving a lens have been proposed. However, if the lens is moved directly, the load will be heavy, and problems will remain regarding weight, size, power consumption, cost, etc.
It has not been put to practical use.

Therefore, the present invention has been proposed in view of the above-mentioned conventional problems, and for example, a linear motor that does not cause a problem in weight, size, power consumption, cost, etc. even when the lens is directly moved. The purpose is to provide.

E. Means for Solving the Problems In order to achieve the above-mentioned object, the linear motor of the present invention has a fixed portion having a magnet, a yoke, and at least one coil, and is held at a constant interval facing the magnet. The magnetic circuit for the magnetic flux generated by the coil is composed of a magnetic closed circuit including the magnetic gap between the yoke and the movable iron piece. It is a thing.

F. Action According to the present invention, most of the energy of the coil is concentrated near the magnetic gap between the movable iron pieces, and an extremely high thrust can be obtained even with a small current.

G. Example Hereinafter, one example of the present invention will be described in detail with reference to the drawings. The present embodiment applies the present invention to a motor for an autofocus of a video camera.

FIG. 1 is a sectional view showing a linear motor 1 of this embodiment. The linear motor 1 has a hollow cylindrical shape, and includes a fixed portion 10 and a movable portion 20 that slides on the fixed portion 10. The fixed portion 10 has a magnet 11, bobbins 12 and 13, coils 14 and 15, and stator yokes 16 and 17. The magnet 11 is, for example, a rubber magnet,
It is provided in a ring shape in a substantially central position across the two stator yokes 16 and 17. The magnet 11 is magnetized in the thickness direction, that is, in the radial direction in the mounted state, and has an S pole on the outer peripheral side and an N pole on the inner peripheral side. Bobbins 12,13
Are provided on both sides of the magnet 11, and the bobbin
Coils 14 and 15 are respectively wound around 12 and 13 along the circumferential surface. The coils 14 and 15 are connected in series, and terminal 1
The voltage is applied from 8,19.

On the other hand, the movable part 20 is composed of two movable iron pieces 21, 2 which are separated.
2 and a movable base 23. The movable iron pieces 21 and 22 correspond to yokes, and a magnetic gap G is formed between them. The magnetic circuit for the magnetic flux B _C generated by the coils 14 and 15 on the fixed portion 10 side is the stator yoke 16 and 17
And the movable iron pieces 21 and 22 and the magnetic gap G between them, thereby forming a magnetic closed circuit. The outer peripheral surfaces of the movable iron pieces 21 and 22 are subjected to so-called Teflon processing, for example, and serve as sliding surfaces that slide on the inner peripheral surface of the fixed portion 10. Movable base 23
Is provided from the movable iron piece 21 to the movable iron piece 22. The movable iron piece 21 and the movable base 23 also serve as a lens housing, and the lens 31 is provided at the end of the movable iron piece 21.
Lenses 32 are provided at the ends of the movable base 23, respectively.

The operating principle of the linear motor 1 of this embodiment is similar to that of the iron core type motor. That is, as shown in the enlarged view of FIG. 2, the magnet 11 always has a constant magnetic flux.
B _M1 and B _M2 are generated, and this magnetic flux exists so as to surround the coil 14 and the coil 15, respectively. Then, when a DC voltage is applied to the terminals 18 and 19, a current flows through the coils 14 and 15, and a magnetic flux B _C is generated by the coils 14 and 15. The direction of this magnetic flux B _C differs depending on the direction of current flow. Then, the magnetic fluxes B _M1 and B _M2 and the magnetic flux B _C cancel each other out or strengthen each other to generate a thrust in one direction, so that the movable portion 20 moves in the arrow X direction or the arrow Y direction. There is. For example, when current is applied to the coils 14 and 15 in the directions shown in FIG.
The left portion of the gear G has an S pole and the right portion has an N pole, and a thrust force is generated in the arrow Y direction, and the movable portion 20 moves in that direction. The moving range of the movable part 20 is set by the width W of the magnet 11. According to such a linear motor 1,
An extremely high thrust can be obtained with a small current. This is equivalent to the coil being concentratedly wound around the ends of the movable iron pieces 21 and 22, and most of the energy of the coils 14 and 15 is concentrated near the magnetic gap G. Therefore, the amount of magnet 11 is small. In addition, power consumption can be suppressed low. Furthermore, the structure is simple, and the size and weight can be reduced, and the lens can be housed in the lens barrel.
The cost can be reduced.

By the way, in the above-described linear motor 1, by simply applying a DC voltage to the terminals 18 and 19, the movable portion 20 will stick to the end position within the movement range set by the width W of the magnet 11. I will end up. Therefore, in practice, for example, the third
It is necessary to dynamically control the position of the movable part 20, that is, the lenses 31 and 32 by using a closed loop control system as shown in the figure. In FIG. 3, the imaging light enters a CCD (charge coupled device) 41 which is a solid-state imaging device through a lens system 30 corresponding to the lenses 31 and 32. The signal from the CCD 41 is sent to the focus detection circuit 42 to detect the focus state. The detection signal from the focus detection circuit 42 is sent to the focus control circuit 43, and a control signal based on the detection signal is sent from the focus control circuit 43 to the linear motor 1. The position of the lens system 30 is controlled by the linear motor 1 according to the control signal. Here, the lens system 30, the CCD 41, the focus detection circuit 42, the focus control circuit 43, and the linear motor 1 constitute a closed loop control system of the focus, and dynamic control can be performed. In the example of FIG. 3, the signal from the CCD 41 is the signal processing circuit 5.
The CCD 41 is also used for focus detection and imaging, but it is also possible to use an imaging tube, and various configurations are conceivable.

Further, in this embodiment, the fixed portion 10 includes two coils 1
It has 4,15, but one of the coils has a movable part.
It is possible to move 20. Further, a non-magnetic material may be inserted in the magnetic gap G. Furthermore, the coil and magnet do not have to be provided all around.

Further, the present invention can be applied not only to a video camera but also to a still camera. Furthermore, the present invention can of course be used in devices other than cameras.

H. Effect of the Invention As is apparent from the above description of the embodiments, according to the linear motor of the present invention, the magnetic circuit for the magnetic flux by the coil of the fixed part is a magnetic closed circuit including the magnetic gap between the movable iron pieces of the movable part. It is possible to obtain an extremely high thrust even with a small current. Therefore, for example, even when the lens is moved directly, the power consumption can be suppressed low. In addition, the structure is simple, the size and weight can be reduced, and the cost can be reduced.

[Brief description of drawings]

FIG. 1 is a sectional view showing a linear motor according to an embodiment of the present invention, FIG. 2 is an enlarged sectional view of an essential part of FIG. 1, and FIG. 3 is a block diagram showing an example of a closed loop control system. 1 …… Linear motor, 10 …… Fixed part 11 …… Magnet, 14,15 …… Coil 20 …… Movable part, 21,22 …… Movable iron piece G …… Magnetic gap

Claims (1)

[Claims] 1. A movable part, which has a fixed part having a magnet, a yoke and at least one coil, and two movable iron pieces facing the magnet and held at a constant interval so as to be movable with respect to the fixed part. And a magnetic circuit for a magnetic flux generated by the coil, which is a magnetic closed circuit including a magnetic gap between the yoke and the movable iron piece.