JPH0549226A - Linear actuator - Google Patents

Abstract

PURPOSE:To provide a linear actuator, small in size, light in weight and high in thrust, linearity and reliability. CONSTITUTION:A linear actuator is constituted of permanent magnets, formed so as to have a hollow cylindrical shape and secured to the inner peripheral surface of a side yoke 1 formed of a ferromagnetic material so as to have a hollow cylindrical shape with bottom, a magnetic circuit, formed of a column type center yoke 3, projected from the bottom of the side yoke 1 coaxially with the same yoke 1 and consisting of a ferromagnetic material to form a magnetic circuit, and a movable piece, provided in a magnetic gap formed between the permanent magnets and the center yoke 3 movably into axial direction. The permanent magnets are constituted of a first permanent magnet 2a, provided between the bottom of the side yoke 1 and the vicinity of an opening, and a second permanent magnet 2b, magnetized so as to have a reverse polarity to the first permanent magnet 2a and provided near the opening of the side yoke, while the movable piece is provided with a driving coil 6 and a detecting coil 8 which are faced to the first permanent magnet 2a and the second permanent magnet 2b respectively.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a linear actuator used for positioning a robot, a magnetic disk device, an optical disk device, etc., and adjusting a writing pressure of a pen plotter, and more particularly to a small-sized, high-thrust linear actuator.

[0002]

2. Description of the Related Art Conventionally, as this type of linear actuator, for example, a linear actuator having a structure shown in FIG. 4 is known. Figure 4
In the figure, 1 is a side yoke, which is formed of a ferromagnetic material such as soft iron into a hollow cylinder with a bottom. Reference numeral 2 denotes a permanent magnet, which is formed in a hollow cylindrical shape, is magnetized in the radial direction, and is fixed coaxially to the inner peripheral surface of the side yoke 1. Next, 3 is a center yoke, which is formed of a ferromagnetic material similar to that of the side yoke 1 into a columnar shape, and is provided coaxially at the center of the bottom portion of the side yoke 1. A magnetic circuit can be formed with the above configuration. Next, 4 is a mover, which is formed by winding a drive coil 6 around the end of a bobbin 5 formed of a non-magnetic material in the shape of a hollow cylinder. It is arranged in an annular magnetic gap 7 formed therebetween and is movably interposed in the axial direction.

With the above structure, if the drive coil 6 constituting the mover 4 is energized in the forward and reverse directions, the drive coil 6, that is, the mover 4 can be moved in the axial direction according to Fleming's left-hand rule. Therefore, the functional member (not shown) such as the arm mounted on the mover 4 can be positioned and the like.

[0004]

In the linear actuator having the above-mentioned structure, a position sensor is required because it is necessary to recognize the momentary position of the functional member mounted on the mover 4, and at the same time, the mover 4 has a position sensor. A speed sensor is required because it is necessary to control the moving speed to be constant. Therefore, when using a linear actuator, a space for mounting the speed sensor is required. For this reason, there is a problem that the structure of the entire apparatus becomes complicated and the miniaturization is hindered.

In order to solve the above problems, various proposals have been made so far, and means such as integrally providing a detection coil for speed detection in the vicinity of the drive coil 6 are taken (for example, in practice). KAISHO 60-44478, JP-A-61-258661
No. However, in the former case, since it is necessary to separately provide the detection coil with a permanent magnet for generating an electric signal, there is a drawback that the space occupied by the detection means is required. On the other hand, although the latter has the advantage that the permanent magnet is shared, there is a problem that it requires two detection coils, which hinders downsizing of the entire apparatus.

On the other hand, in recent years, the demand for this type of linear actuator has become stricter, and not only the size of the actuator is limited due to restrictions in terms of space and weight, but also higher thrust, longer stroke, and higher Linearity is required. Therefore, in the structure shown in FIG. 4, the size of the magnetic gap 7 must be reduced to the limit. Further, it is almost difficult to provide the detection coils at both ends of the mover 4 because the thrust, the stroke characteristics, and the linearity are affected and there is no space. The detection coil is the drive coil 6
If it is provided close to, the sensitivity is affected by the magnetic field induced in the drive coil 6, there is a lot of opportunity to extract noise at the same time as the detection signal, and there is a problem in that malfunctions occur and reliability decreases. .

The present invention solves the problems existing in the above-mentioned prior art, and provides a linear actuator which is compact and lightweight, and is capable of exerting high speed and high thrust, and further improving linearity and reliability. The purpose is to

[0008]

In order to achieve the above object, in the present invention, a hollow cylindrical permanent magnet is formed on the inner peripheral surface of a side yoke formed of a ferromagnetic material in a hollow cylindrical shape with a bottom. A magnetic gap is formed between the permanent magnet and the center yoke by fixing a columnar center yoke made of a ferromagnetic material on the bottom of the side yoke so as to project coaxially with the side yoke. In a linear actuator in which a mover is provided so as to be movable in the axial direction, a permanent magnet is provided between a bottom permanent magnet of a side yoke and the vicinity of an opening, and a permanent magnet opposite to the first permanent magnet. It is composed of a second permanent magnet that is magnetized to have a polarity and is provided in the vicinity of the opening of the side yoke.
The technical means of providing the drive coil and the detection coil by facing the permanent magnet and the second permanent magnet respectively.

[0009]

With the above structure, the leakage of magnetic flux at the opening of the side yoke is prevented, and as a result, the magnetic flux density in the annular magnetic gap formed between the first permanent magnet and the center yoke is changed in the axial direction. Not only can the effect of homogenization be expected over the entire range, but the magnetic field generated by the second permanent magnet can be positively utilized for speed detection.

[0010]

1 is a longitudinal sectional view of an essential part showing an embodiment of the present invention, in which the same parts are designated by the same reference numerals as in FIG. In FIG. 1, reference numerals 2a and 2b respectively denote a first permanent magnet and a second permanent magnet, which are formed in a ring shape by a Nd-Fe-B system rare earth permanent magnet material (HS25CR manufactured by Hitachi Metals) and in a radial direction. And is fixed coaxially to the inner peripheral surface of the side yoke 1. The first permanent magnet 2a is provided between the bottom of the side yoke 1 and the vicinity of the opening, and the second permanent magnet 2b is magnetized to have a polarity opposite to that of the first permanent magnet 2a and the opening of the side yoke 1. Provide in the vicinity.

Each of the first and second permanent magnets 2a and 2b may be formed by axially stacking a plurality of ring pieces each having a short axial length and formed into a fan shape. You may form and form the several segment formed in the circumferential direction. Next, 8 is a detection coil, which is provided on the outer peripheral surface of the mover 4 with a slight distance from the drive coil 6 and facing the second permanent magnet 2b. The drive coil 6 and the detection coil 8 are provided so as to cross the magnetic flux generated from the first permanent magnet 2a and the second permanent magnet 2b, respectively.

FIG. 2 is a view showing the air gap magnetic flux density distribution of the magnetic air gap 7 in FIG. 1, in which the position from the bottom surface of the side yoke 1 and the stroke position of the detection coil 8 are shown along the horizontal axis. In this case, the side yoke 1 in FIG.
By S41, outer diameter 28mm, inner diameter 20mm, length 28mm
The center yoke 3 was formed of SS41 to have a diameter of 12 mm and a length of 28 mm. Further, the first permanent magnet 2a and the second permanent magnet 2b are measured for those formed to have an outer diameter of 20 mm, an inner diameter of 18 mm, and axial lengths of 18 mm and 6 mm. As is clear from FIG. 2, the first permanent magnet 2
The air gap magnet density distribution a due to a shows a relatively flat distribution with a peak value of less than 5000 G, and the air gap magnetic flux density distribution b due to the second permanent magnet 2b has a peak value 50 at approximately the middle of the stroke.
It shows a distribution with less than 00G.

The drive coil 6 shown in FIG. 1 has the above structure.
When the electric current is applied in the forward and reverse directions, the mover 4 can be moved in the axial direction similarly to that shown in FIG. Then, due to the movement of the mover 4, the detection coil 8 crosses the magnetic flux generated by the second permanent magnet 2b, so that a signal current corresponding to the magnitude of the moving speed flows through the detection coil 8. Therefore, the mover 4
Control system (not shown)
Positioning of the mover 4 and other controls can be performed via the. In this case, speed detection is especially necessary near the middle part of the stroke, but as shown in FIG. 2, the peak value of the air gap magnetic flux density distribution by the second permanent magnet 2b (see FIG. 1) is near the middle part of the stroke. Since it exists, the detection accuracy can be improved.

FIG. 3 is a diagram showing the relationship between stroke and thrust. In this case, the drive coil 6 (see Fig. 1) has a wire diameter
A 0.2 mm copper wire was formed by 344 turns (8 layers × 43 rows). As is clear from FIG. 3, the thrust is 550 gf and the linearity is kept within 10% even when the stroke is 9 mm. As shown in FIG. 1, since the second permanent magnet 2b magnetized with the opposite polarity to the first permanent magnet 2a is provided near the opening end of the side yoke 1, leakage flux from the opening is prevented. However, as a result of ensuring the effective magnetic flux density in the magnetic gap 7, it can be recognized that the difference in thrust at the axial position has been significantly reduced.

In this embodiment, the permanent magnet is Nd-F.
Although the example of forming the e-B rare earth permanent magnet material has been described, it may be formed of another permanent magnet material or another rare earth permanent magnet material. In addition, in this type of linear actuator, a short ring made of a conductive material such as Cu can be provided on the surface of the center yoke in order to speed up the rise and reversal of the current of the coil that constitutes the mover.

[0016]

Since the present invention has the structure and operation as described above, the thrust is uniform at the axial position of the magnetic air gap formed by the second permanent magnet to prevent the leakage of the magnetic flux at the opening. In addition to the effect of making the magnetic flux more positive, this magnetic flux is also positively used for speed detection, so that the overall size and weight of the device can be reduced. The detection coil is not affected by the magnetic field induced in the drive coil,
This has the effect of significantly improving detection accuracy and reliability.

[Brief description of drawings]

FIG. 1 is a longitudinal sectional view of an essential part showing an embodiment of the present invention.

FIG. 2 is a diagram showing a void magnetic flux density distribution of the magnetic void in FIG.

FIG. 3 is a diagram showing a relationship between stroke and thrust.

FIG. 4 is a longitudinal sectional view of an essential part showing an example of a conventional linear actuator.

[Explanation of symbols]

 1 Side yoke 2a 1st permanent magnet 2b 2nd permanent magnet 6 Drive coil 8 Detection coil

Claims (1)

[Claims] 1. A hollow-cylindrical permanent magnet fixed to the inner peripheral surface of a side yoke formed of a ferromagnetic material in the shape of a hollow cylinder with a bottom, and a columnar shape made of a ferromagnetic material at the bottom of the side yoke. In a linear actuator in which a center yoke is provided so as to project coaxially with a side yoke to form a magnetic circuit, and a mover is provided in a magnetic gap formed between a permanent magnet and a center yoke so as to be axially movable, The first permanent magnet is provided between the bottom of the side yoke and the vicinity of the opening, and the second permanent magnet is provided in the vicinity of the opening of the side yoke and is magnetized to have a polarity opposite to that of the first permanent magnet. A linear actuator comprising a permanent magnet and a drive coil and a detection coil provided on the mover so as to face the first permanent magnet and the second permanent magnet, respectively.