JP2002369492A - Permanent magnet, magnetic circuit for generating magentic field and linear actuator using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a permanent magnet that can increase the quantity of magnetic fluxes in the magnetic gap section of a linear motor, can reduce cogging of the motor, and can improve the positioning accuracy of the motor, without significantly increasing the size or the cost of the motor, when the magnet is used in the motor and can increase the output of an undulator when the magnet is used in the undulator. SOLUTION: This permanent magnet having a rectangular cross section is constituted to have an N or S pole on its surface and the opposite polarity of its paired facing left and right side faces.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a permanent magnet for generating a sinusoidal magnetic field such as a wiggler or an undulator used for an accelerator or an insertion light source.
The present invention also relates to a permanent magnet for an actuator used for causing a movable coil to reciprocate in a linear direction, and more particularly to a permanent magnet for a linear actuator having a small size, a large thrust, and a low leakage magnetic field.

[0002]

2. Description of the Related Art In a linear actuator for reciprocating a movable coil so as to swing or vibrate in a linear direction, a torque ripple is formed by forming a magnetic flux density distribution in a magnetic gap portion of a magnetic circuit into a sine wave shape. Many patents have been filed for inventions that can be eliminated and improve linearity. For example, Patent Publication No. 2
No. 642240 discloses that a permanent magnet has a substantially trapezoidal cross section in a cross section direction perpendicular to the magnet arrangement direction, or that both ends of a magnet are perpendicular to the magnet arrangement direction in a cross section direction. A shape in which the shape is cut out in a substantially sinusoidal shape is described. Hereinafter, the above-mentioned Patent Publication No. 264224
The permanent magnet described in No. 0 will be described.

This permanent magnet has a certain magnetization direction in the thickness direction, and a magnet having an N pole or an S pole on one side is arranged in parallel with the longitudinal direction, and the polarity of the adjacent magnet always has the opposite polarity. As shown in the figure, a plurality of magnets having different polarities are arranged, and further, the magnets are arranged so as to be opposed to each other in a thickness direction of the magnet at a predetermined interval. At this time, the magnets facing each other are arranged so as to always have opposite polarities. Usually, in order to reduce the magnetic resistance, a yoke is arranged on the surface opposite to the magnetic gap with respect to the magnet, and is arranged continuously so that the magnetic flux of the adjacent magnet flows effectively. The drive coils are arranged in the magnetic gap portions spaced at a fixed interval. The drive coil is arranged so that a current flows in a direction perpendicular to a direction of a magnetic flux flow generated in the magnetic gap portion,
This current and the magnetic flux in the magnetic gap generate a thrust according to the Fleming left-hand rule, and this thrust drives the drive coil in the magnet parallel arrangement direction. Further, by changing the direction of the current flowing through the drive coil, the drive coil can be reciprocated. In a configuration in which a general rectangular permanent magnet is arranged, the magnetic flux density distribution in the magnetic gap becomes a rectangular wave shape. Can be approximated to a sine wave, and in a linear motor or the like having a polyphase coil, the linearity is not impaired, the torque ripple is small, and the coil mover can be positioned with high accuracy.

[0004]

However, in this magnetic circuit, it is necessary to machine the magnet into a special shape, and there is a problem that the manufacturing cost of the magnet is increased. In order to further apply high thrust to the drive coil,
The yoke must be thicker in order to use a magnet material having high-performance magnetic properties or to increase the thickness of the magnet and to allow the magnetic flux of adjacent magnets to flow effectively. However, this method increases the weight of the apparatus and increases the cost, which is not economical. By increasing the magnet thickness to obtain higher thrust or using a magnet material with high magnetic properties, the leakage magnetic field generated from the magnetic circuit increases, so these devices are installed in the semiconductor manufacturing equipment. In this case, the leakage magnetic field adversely affects a magnet or a control device disposed around the magnetic circuit. Therefore, a magnetic shield material such as permalloy having a high initial permeability must be used in a large amount in such a place where the leakage magnetic field is large, so that the size of the apparatus becomes large, which causes a significant cost increase. There was a problem that it would.

[0005]

Therefore, in the present invention, conventionally, an N pole or an S pole is formed on the surface facing the magnetic gap, and magnetized in a certain direction with respect to the thickness direction of the magnet (for example, The magnetic pole configuration of the magnet was N pole on the magnetic gap surface side of the magnet, and the S pole of the opposite magnetic pole was formed on the surface opposite to the magnetic gap surface and in contact with the yoke. Without changing, we have devised to configure opposite polarity on the left and right magnet side faces where adjacent magnets touch.

That is, according to the present invention, in a permanent magnet having a rectangular cross-sectional shape, one surface of the permanent magnet has an N pole or an S pole having a single magnetic pole, and the surface of the permanent magnet is opposed to the magnetic pole surface.
It is a permanent magnet whose magnetization direction is continuously changed so as to form another magnetic pole (S pole or N pole) on the left and right side surfaces of the pair.
Here, the cross-sectional shape of the permanent magnet may be a trapezoid or a polygon, or may be a substantially rectangular shape, one side of which is formed in an arc shape.

First, the flow of magnetic flux in a conventional magnetic circuit using a magnet having a fixed magnetization direction with respect to the thickness direction of the magnet is described as follows. Through the yoke arranged on the back side of the magnet with respect to the gap, the magnetic flux passed through the magnetic gap, passed through the adjacent magnet arranged in the opposite polarity, and flowed to the side of the opposing magnet. Therefore, magnetic saturation easily occurs in the yoke, and it has been difficult to reduce the leakage magnetic flux.

In this respect, according to the present invention, for example, the magnet is formed in a substantially rectangular shape, the magnetic pole of the permanent magnet is formed as the N pole surface, and the other magnetic S poles are formed on the right and left side surfaces where the adjacent magnets are in contact. By doing so, the flow of the magnetic flux, which has been flowing through the yoke on the back surface of the magnet until now, is passed from the magnet directly to the adjacent magnet without passing through the yoke. This makes it possible to reduce the magnetic resistance of the magnet and raise the operating point of the magnet, and make the apparent magnetization direction length longer than the magnetization direction length of a magnet having a constant magnetization direction in the thickness direction. Accordingly, the magnetic flux density in the magnetic gap can be increased, and a higher thrust can be generated by the drive coil. Also, since the thickness of the yoke can be made thinner than before, the leakage magnetic flux at the back of the yoke can be reduced very slightly, without further increasing the size, weight, and cost. An actuator magnet with an increased magnetic flux density in the magnetic gap can be provided, and the manufacturing cost of the permanent magnet is also substantially rectangular, so that an inexpensive permanent magnet can be provided.

Further, when a rectangular permanent magnet as shown in FIGS. 1 and 4 is used, the magnetic gap through which the mover coil passes becomes a uniform gap, so that foreign matter is less likely to enter the concave portion of the magnet. Since it is easy to maintain a clean environment, it is particularly suitable for use in semiconductor manufacturing equipment that requires a high degree of cleanliness.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention shown in FIGS. 1 to 11 will be described below. FIG. 1 is a cross-sectional view of the permanent magnet according to the first embodiment. As shown in the figure, the polarity of the permanent magnet is such that the upper surface of the magnet indicates an N pole and the side surface which is in contact with the surface indicating the N pole on the left and right forms an S pole. The magnetization direction of the permanent magnet is configured to change continuously inside the magnet. Although the form of magnetization is exactly the same in shape and characteristics, the first means is to use a permanent magnet that has been previously made magnetically anisotropic in the orientation shown in this figure in the permanent magnet manufacturing process. The second invention uses an isotropic magnet that is not magnetized and whose magnetic easy axis is not determined in the manufacturing process. It is to give. The magnetizing method is performed by using a magnetizing yoke having the same configuration as the orientation mold used for molding in a magnetic field shown in FIG.

FIGS. 2A and 2B are cross-sectional views of a permanent magnet showing second and third embodiments. As shown in this figure, the magnetization direction inside the permanent magnet changes continuously as in FIG. 1, but the cross-sectional shape is a trapezoidal or polygonal shape of a substantially rectangular magnet main body. The cross-sectional shape includes a part that forms a straight line or an arc. FIG. 3 is a sectional view of a permanent magnet according to a fourth embodiment. In this example, one side of the cross section is formed in an arc shape as shown in the figure, and the magnetization direction inside the permanent magnet changes continuously as in FIG.

FIG. 4 shows a fifth embodiment, in which two permanent magnets 1a having three different magnetization directions are magnetized in a fixed direction so as to have the same magnetization direction as the first embodiment.
FIG. 1 shows a total of five permanent magnets, two for b and one for 1c.
The cross section has the same shape as the magnet of FIG. 1a has a magnetization direction in the horizontal direction indicated by an arrow, and 1b
Has a magnetization direction inclined by 38 ° with respect to the vertical direction. The inclination angle of the magnetization direction is 38 ° ± 10 ° from the processing accuracy in manufacturing the permanent magnet. 1c has a certain magnetization direction in the vertical direction. In addition, a portion having a vertical component is 1/3 of L with respect to the entire width L of the magnet, and the combined width of a portion having a horizontal magnetization direction and a portion having a magnetization direction inclined by 38 ° is L. 1/3 is appropriate for each of the left and right sides, and the portion having a horizontal magnetization direction is suitably 1/10 to 20 with respect to the entire L, and particularly preferably 1/20.
In the case where the division ratio in the width direction is set, and particularly in the range where the inclination angle from the perpendicular direction of the magnetization direction is 38 ° ± 5 °,
When the magnetic circuit is configured, a magnetic field close to a sine wave can be obtained. In the embodiment, L = 20 mm, L1 = 7 mm,
L2 = 5 mm, L3 = 2 mm, height h = 8 mm, permanent magnet made of Hitachi Metals NdFeB rare earth permanent magnet HS-4
4CH was used.

Next, FIG. 5 shows a mold configuration in a conventional magnetic field molding process for producing a permanent magnet having uniform magnetic anisotropy in one direction. 2a and 2b are arranged so that the dice 3 is sandwiched between the magnetic field orienting coils, and pulse currents in the same direction are simultaneously applied to the coils of 2a and 2b,
The magnetic field orienting coil generates a magnetic flux in a direction according to the current direction and the right-handed screw rule. The generated magnetic flux passes through the pole pieces 6a and 6b made of carbon steel S45C or the like, and efficiently generates a uniform strong orientation magnetic field 5 in the cavity 4. Such a mold configuration and a magnetic field This is an optimal configuration for providing uniform unidirectional magnetic anisotropy to the magnetic powder filled in the cavity.

FIG. 6 shows a configuration of a molding die in a magnetic field which is a means for manufacturing the permanent magnet of the first, second, third, and fourth embodiments of the present invention. In the conventional molding die in a magnetic field, the magnetic field orientation coils are arranged so as to surround the pole pieces 6a and 6b arranged on both sides of the die 3 as described above. As a result, a uniform magnetic field in a single direction is generated in the inner peripheral region of the magnetic field orientation coil, but a magnetic field whose magnetization direction changes continuously cannot be generated. Therefore, as shown in FIG. 6, the magnetic field alignment conductors 12a and 12b are arranged immediately before the cavity filled with the magnetic powder. By applying pulse currents in opposite directions to the magnetic field alignment conductors 12a and 12b, an alignment magnetic field 15 is generated around the magnetic field alignment conductors 12a and 12b. Further, by forming a portion 13a of the die opposite to the position in the die where the magnetic field aligning conductor is disposed with the cavity 14 as a center from the nonmagnetic material, the portion 13a faces the cavity surface on the magnetic field aligning conductor side in the cavity. The magnetic resistance toward the opposite surface can be increased, and the magnetic flux generated from the inner surface of the cavity on the magnetic field alignment conductor side can be made to flow toward the side surface of the cavity. Thereby, the magnetic powder filled in the cavity can be oriented in the magnetization direction that continuously changes from the center of the cavity inner surface to the cavity side surface, or can be made anisotropic.

FIG. 7 is a top view showing one cycle of an example in which the permanent magnet shown in the first embodiment of the present invention is used and a magnetic circuit for generating a sine wave magnetic field for a linear motor is constructed. It is the side view. Incidentally, it goes without saying that the permanent magnets shown in the second to fifth embodiments can also be used as the permanent magnets of this example. Now, 31 and 32 are permanent magnets of the first embodiment, 33 is a yoke, and permanent magnets 31 and 3 are provided.
2 on the back. These materials are composed of magnetic materials such as carbon steel for general structural use (SS400). Numeral 35 indicates a magnetic gap, and numeral 34 indicates a flow of a main magnetic flux in the magnetic circuit. The numerical values shown in parentheses are approximate dimensions.

FIG. 8 shows a configuration example of a magnetic circuit for a linear motor when a conventional permanent magnet having a single magnetization orientation is used as a comparative example. Reference numerals 21 and 22 denote permanent magnets having one magnetization direction, 23 denotes a yoke, and 24 denotes a flow of a main magnetic flux in a magnetic circuit. Thus, the flow 24 of the main magnetic flux passes from the permanent magnet 22 through the yoke 23 provided on the back surface thereof, and the adjacent permanent magnets 2 having opposite polarities.
1, through the magnetic gap 25, toward the opposing permanent magnet 22, further through the adjacent permanent magnet 21 having the opposite magnetism, again through the magnetic gap 25, and return to the first permanent magnet. Becomes At this time, the flow 24 of the main magnetic flux always passes through the yoke 23 because of the configuration of the magnetic circuit because the magnetization direction of the permanent magnet is a single and uniform direction. Therefore, in order to effectively configure the magnetic circuit, it is necessary to efficiently pass the magnetic flux generated by the permanent magnet to the adjacent permanent magnet. For this purpose, a material having a high magnetic property, particularly a high saturation magnetization, of the yoke 23 is preferable, and the general structural carbon steel (SS400) is generally used,
It is economical. However, the yoke 23 is often used in the vicinity of the limit of magnetic saturation from the viewpoint of economy and shape restrictions. For this reason, it is necessary to secure the minimum necessary thickness of the yoke 23 so as not to impair the characteristics of the magnetic circuit.

Therefore, in order to improve this, by using the permanent magnet of the present invention shown in FIG. 7 in a magnetic circuit, the flow of the main magnetic flux in the magnetic circuit does not flow through the yoke, and the magnetic flux is generated only by the permanent magnet. The permanent anisotropy generated in the permanent magnet can be configured by changing the magnetization direction inside the permanent magnet to a single and uniform magnetization direction, and by changing the magnetization direction inside the permanent magnet continuously or discontinuously. Thus, a magnetic circuit can be configured without using a yoke.

In FIG. 7, the flow of the main magnetic flux does not pass through the yoke 33, but the positioning of the magnets when the permanent magnets 31, 32 are installed and the minimum mechanical strength required for maintaining the magnetic circuit. The thickness of the yoke is not more than half the thickness of the conventional magnetic circuit. Therefore, it is possible to reduce the weight of the magnetic circuit, and since a large amount of magnetic flux does not flow through the yoke 33, an AC magnetic field generated by the moving coil itself generated during control is applied to a motor having a moving coil such as a linear motor. It is also effective for shielding. If the yoke 33 is made of a general magnetic material such as an electromagnetic soft iron or a permalloy having a small AC loss in order to efficiently shield the AC magnetic field, the magnetic shielding effect is further increased.

FIG. 9 shows a magnetic flux density distribution at the center of the gap in the magnetic circuit for a linear motor having the magnetic circuit configuration shown in FIG. Similarly, the magnetic flux density distribution at the center of the gap in a magnetic circuit using a permanent magnet having a single magnetization direction conventionally used as shown in FIG. 8 is shown. For comparison, a sine wave distribution is shown in FIG. As a result, it can be seen that the gap magnetic flux density distribution largely deviates from the sine wave distribution in the magnetic circuit using the conventional magnet, and the difference is very small in the magnetic circuit using the magnet of the present invention. Therefore, when driving the coil of the mover with a sine wave current, cogging is reduced, and the stopping accuracy of the stator is improved.

FIG. 10 shows an example in which a magnetic circuit for generating a sine-wave magnetic field for a linear motor is constructed using the permanent magnet of the fifth embodiment shown in FIG. That is, in the figure, 41
a and 42a have magnetization directions in the horizontal direction, and 41b and 42a
b has a magnetization direction inclined by 38 ° with respect to the vertical direction,
1c and 42c have magnetization directions in the vertical direction. 41a and 42a are horizontal but have different magnetization directions, and 41a, 41b, 41c, 41b, 42a
And 42a, 42b, 42c, 42b, 41
The set of a constitutes a closed-loop magnetic flux flow. Also in the case of this example, the flow of the main magnetic flux loops in the permanent magnet without passing through the yoke 43, similarly to the flow shown in FIG. Therefore, it is effective to reduce the weight by configuring the yoke thickness and the like to be thin.

FIG. 11 shows an example in which a magnetic circuit for generating a sine wave magnetic field for an undulator is constructed using the permanent magnet of the first embodiment of the present invention. Since a sinusoidal magnetic field distribution is formed at the center of the magnetic gap as shown in this figure, a high output can be obtained stably.

[0022]

According to the present invention, since the flow of magnetic flux is constituted only by permanent magnets without flowing the main flow of magnetic flux in the magnetic circuit into the yoke, the size and weight of the magnetic circuit are increased. Without increasing the cost and increasing the cost, the magnetic flux density in the magnetic gap is increased, and in the linear motor, high thrust and high positioning accuracy are possible, and a magnetic circuit with less leakage magnetic flux can be provided. Linear motor,
The weight can be reduced as a magnetic field generator such as a linear actuator or an undulator.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view of a permanent magnet according to a first embodiment of the present invention.

FIGS. 2A and 2B are cross-sectional views of permanent magnets showing second and third embodiments of the present invention, wherein FIG. 2A is an example in which a trapezoidal shape is formed by a straight line, and FIG.

FIG. 3 is a sectional view of a permanent magnet according to a fourth embodiment of the present invention.

FIG. 4 is a sectional view of a permanent magnet according to a fifth embodiment of the present invention.

FIG. 5 is a view showing a configuration of a conventional permanent magnet in a magnetic field forming mold.

FIG. 6 is a view showing a configuration of a molding die in a magnetic field of the permanent magnet of the present invention.

FIG. 7 is a diagram illustrating a magnetic circuit for generating a sine wave magnetic field when the permanent magnet according to the first embodiment of the present invention is used in a magnetic circuit for a linear motor.

FIG. 8 is a diagram illustrating a configuration example of a magnetic circuit for a linear motor when a conventional permanent magnet is used.

9 is a diagram showing a comparison of the gap magnetic flux density between the magnetic circuit for a linear motor of the embodiment of FIG. 7 of the present invention and the comparative example of FIG. 8;

FIG. 10 is a diagram illustrating a magnetic circuit for generating a sine wave magnetic field when the permanent magnet according to the fifth embodiment of the present invention is used in a magnetic circuit for a linear motor.

FIG. 11 is a diagram illustrating a magnetic circuit for generating a sine wave magnetic field when the permanent magnet according to the first embodiment of the present invention is used in a magnetic circuit for an undulator.

[Explanation of symbols]

1a: Permanent magnet having a horizontal magnetization direction 1b: Permanent magnet having an oblique magnetization direction 1c: Permanent magnet having a vertical magnetization direction 2a, 2b: Oriented coil 3, 3: Dice, 4: Cavity,
5: Orientation magnetic field 6a, 6b: Pole piece (SS400) 12a, b: Conductor for magnetic field orientation, 13: Magnetic die, 13
a: Nonmagnetic dice 14: Cavity, 15: Orientation magnetic field 21, 22: Permanent magnet having a single magnetization direction, 23: Yoke, 24: Main magnetic flux flow 25: Magnetic gap 31, 32: Continuously changed magnetization Permanent magnet having direction, 33: Yoke 34: Flow of main magnetic flux 35: Magnetic gap 41a, 42a: Permanent magnet 41b, 42b: Permanent magnet having oblique magnetization direction 41c, 42c: Perpendicular magnetization Permanent magnet with direction, 4
3: Yoke 51, 52: permanent magnet, 53, 54: yoke, 55: magnetic gap

Claims (7)

[Claims] In a permanent magnet having a rectangular cross section, one surface of the permanent magnet has an N pole or an S pole having a single magnetic pole, and a pair of left and right side surfaces opposed to the magnetic pole surface. A permanent magnet characterized in that the magnetization direction changes continuously so as to constitute another magnetic pole (S pole or N pole). 2. A permanent magnet having a trapezoidal or polygonal cross section, wherein one of the surfaces has an N pole or an S pole of a magnetic pole, and a pair of left and right side surfaces opposed to the magnetic pole surface. Wherein the magnetization direction is continuously changed so as to form another magnetic pole (S pole or N pole). 3. A permanent magnet having a substantially rectangular cross-sectional shape, one side of which has an arc shape, wherein one surface of the permanent magnet forms an N pole or an S pole of a magnetic pole. A permanent magnet, wherein the magnetization direction is continuously changed so as to form another magnetic pole (S-pole or N-pole) on a pair of left and right side surfaces facing each other. 4. A permanent magnet, wherein the magnetization direction according to claim 1 is given to an isotropic permanent magnet having an arbitrary direction of easy magnetization by an external magnetic field. 5. The permanent magnet according to claim 1, wherein one magnetic pole is combined with three or more permanent magnets exhibiting different magnetic anisotropic directions to form the magnetization direction according to claim 1. magnet. 6. A magnetic circuit for generating a magnetic field, comprising the permanent magnet according to claim 1. 7. A linear actuator using the magnetic circuit for generating a magnetic field according to claim 6.