JP2606903Y2 - Field yoke of linear motor - Google Patents

Description

[Detailed description of the invention]

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a field yoke of a linear motor having a plurality of permanent magnets attached to a surface and a traveling direction.

[0002]

2. Description of the Related Art Conventionally, a field yoke made of a ferromagnetic material and having a uniform thickness is provided with a magnetic field pole of a permanent magnet attached to the surface thereof (for example, Japanese Utility Model Publication No. 4-24786, No. 5).
Figure).

[0003]

However, in the prior art, since the thickness of the field yoke is uniform, the magnetic flux density of the magnetic field produced by the permanent magnet varies as shown in FIG. The thickness of the field yoke was such that magnetic saturation did not occur in areas where the magnetic flux density was dense. For this reason, the thickness of the field yoke is the same as that of the portion where the magnetic flux density is high even though it is not effective as a magnetic path even in the portion where the magnetic flux density is coarse. There was a problem of getting heavy. Therefore, an object of the present invention is to make the magnetic flux density of the yoke uniform and reduce the weight of the field yoke.

[0004]

In order to solve the above-mentioned problems, the present invention is directed to a method of forming a surface of a ferromagnetic material.
In the direction such that the center of the convex portion and the center of the concave portion are
Part and the concave part are formed alternately, and an even number
Permanent magnets are alternately attached at equal intervals in the direction of travel
In the field yoke of the linear motor thus obtained,
The recesses are located at both ends in the traveling direction of the
Between the center of the concave portion and the center of the concave portion and between the adjacent permanent magnets
A field yoke for a linear motor, wherein the distances between the centers of the magnetic fields are equal . The present invention also provides a cross-sectional shape of the concave and convex portions.
Is characterized by being square or trapezoidal.
The concave and convex portions are connected by a curve represented by a predetermined function.
It is characterized by that.

[0005]

The cross section of the field yoke 1 changes so that the magnetic path length across the adjacent permanent magnets becomes equal, and the magnetic flux distribution becomes uniform. If the field yoke is used as the mover, the weight of the mover can be reduced by the amount corresponding to the concave portion.

[0006]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a perspective view showing an embodiment of the present invention. A plurality of permanent magnets 2 having a predetermined pole pitch P and a width W (near 4/5 of the pole pitch P) are alternately replaced with adjacent poles on the surface and the traveling direction of the field yoke 1 made of a ferromagnetic material. Even number
Individual, affixed. On the back surface of the field yoke 1, the width of the permanent magnet 2 is 3/2 of the width W, and the height of the field yoke 1 is 1 / H.
The recesses 3 having a depth D of 2 are permanently located at both ends of the yoke.
It is an intermediate point between the magnet 2 and the inner permanent magnet 2 adjacent thereto.
So that the center of the convex portion 4 is formed at a position
It is provided orthogonal to. After that, on the back of the field yoke 1
Is that the concave portions 3 are formed at every pole pair pitch 2P.
The concave and convex portions 4 are formed as a pair within the pole pair pitch 2P.
You. As a result of the magnetic field analysis by the finite element method, as shown in FIG. 2, in the case of the above-mentioned specifications, the magnetic flux density Φ is rough at the corners of the convex portion 4 but almost satisfactory at the other portions. There was found. FIG. 3 is a partial cross-sectional view showing the second embodiment, in which a rectangular corner portion of the embodiment is taken, and the concave portion 3 and the convex portion 4 are trapezoidal. The vertex of the convex part 4 is set to the side B1
, The bottom of the projection 4 is the bottom of the side B2, and the top and bottom are connected by a straight line. As compared with the embodiment, the number of steps increases in manufacturing, but the magnetic flux density becomes more uniform. In this case, it has been found that the analysis result indicates that B1 should be approximately P / 2 and B2 should be approximately (P + W) / 2. FIG. 4 is a partial sectional view showing the third embodiment, in which the concave portion 3 and the convex portion 4 are connected by a continuous curve. The pole pitch of the permanent magnet 2 and P, and the thickness of the field yoke H, the depth of the recess D, and, also, the convex portion 4
Permanent magnet 2 was affixed with the back surface of the heart as the origin
Let X be the direction of travel along the rear surface, and
When the position in the contraction direction is Y, the concave portion 3 and the convex portion 4 are approximated by a curve represented by the following equation that makes the magnetic flux density theoretically uniform. Y = HD (1-tanh (4π / 3-4π (X− (W / 2−P / 3)) / P))
/ 2 where 0 ≦ X ≦ P In this case, although it is difficult to manufacture, the magnetic flux density can be made almost completely uniform. The field yoke of the present invention is preferably applied to a mover, but can also be applied to a stator.

[0007]

As described above, according to the present invention, when the present invention is applied to a mover, a portion that does not function as a magnetic path on the back surface of the field yoke can be cut off to reduce the weight. Therefore, the payload can be increased by the reduced weight,
It has the effects of reducing the rated current and suppressing the temperature rise, and is most suitable for use in ultra-precision, high-thrust drive applications such as an exposure apparatus (stepper) used in semiconductor manufacturing. In addition, when applied to the stator, less material is required.

[Brief description of the drawings]

FIG. 1 is a perspective view showing a field yoke showing an embodiment of the present invention.

FIG. 2 is a partial cross-sectional view showing a magnetic flux distribution in the field yoke of the present invention.

FIG. 3 is a partial sectional view showing a field yoke according to a second embodiment of the present invention.

FIG. 4 is a partial sectional view showing a field yoke according to a third embodiment of the present invention.

FIG. 5 is a partial sectional view showing a magnetic flux distribution of a conventional field yoke.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Field yoke 2 Permanent magnet 3 Concave part 4 Convex part

──────────────────────────────────────────────────の Continuation of the front page Examiner Kiyoji Yamashita (56) References JP-A-3-222666 (JP, A) JP-A-63-171155 (JP, A) JP-A 5-88192 (JP, U) Kaihei 5-9182 (JP, U) JP-A 61-25085 (JP, U) (58) Fields investigated (Int. Cl. ⁷ , DB name) H02K 41/03

Claims (4)

(57) [Scope of request for utility model registration] 1. A ferromagnetic material and a surface advancing direction
The protrusions are arranged such that the center of the protrusions and the center of the recesses are equally spaced.
And the recess are formed alternately, and an even number of
Permanent magnets are attached at equal intervals in the direction of travel with alternating polarity
In the field yoke of the linear motor, the recesses are located at both ends in the traveling direction of the field yoke.
The distance between the centers of the adjacent permanent magnets is
A field yoke for a linear motor, wherein the distance is equal to the distance between the center and the center of the recess . 2. A field yoke for a linear motor according to claim 1, wherein said concave and convex portions have a rectangular cross section. 3. A field yoke for a linear motor according to claim 1, wherein said concave and convex portions have trapezoidal cross-sectional shapes. 4. A method according to claim 1, wherein the back surface at the center of the convex portion is defined as an origin.
The traveling direction along the back surface on which the permanent magnet is attached
Let X be the position, and let Y be the position in the direction toward the protrusion.
At this time, the convex portion and the concave portion become a curve represented by the following equation.
The linear motor according to claim 1, wherein
Field yoke. Y = HD (1-tanh (4π / 3-4π (X− (W / 2−P / 3)) / P))
/ 2 where the distance between the centers of adjacent permanent magnets is P,
The thickness of the convex portion is H, the depth of the concave portion is D, and the permanent magnet is
Is W, and 0 ≦ X ≦ P.