Magnetic coupling device

A magnetic coupling device includes a driving magnet array having multiple annular sector-shaped, circumferentially arranged first permanent magnets, and a driven magnet array having multiple circular sector-shaped, circumferentially arranged second permanent magnets with pole surfaces facing pole surfaces of the first permanent magnets. The driven magnet array is rotated by the driving magnet array being rotated. A repulsion zone where a repulsive force acts is designed to have an area that is 5% to 15% of that of an attraction zone where an attractive force acts between a specific first permanent magnet and a specific second permanent magnet, with a radial first centerline of the specific first permanent magnet overlapping a radial second centerline of the specific second permanent magnet so that opposite poles face each other, including between first and second permanent magnets respectively adjacent the specific first and second permanent magnets with overlapping the centerlines.

BACKGROUND OF THE INVENTION

Field of the Invention

The present invention relates to a magnetic coupling device having a driving magnet array of a plurality of first permanent magnets arranged circumferentially and having alternating polarities, and a driven magnet array of a plurality of second permanent magnets arranged circumferentially and having alternating polarities, the pole surfaces of the first permanent magnets and the second permanent magnets facing each other, the driven magnet array being rotated by rotating the driving magnet array.

Description of the Related Art

Such magnetic couplings are known as a means of transmitting power in a non-contact manner. A vacuum deposition apparatus such as an ALD (Atomic Layer Deposition) system, for example, is used in a production process of semiconductors, in which a film is deposited on a deposition target such as a semiconductor wafer while rotating the wafer. Such a vacuum deposition apparatus uses a magnetic coupling device that has a plurality of driven magnet arrays arranged around the rotation axis of a driving magnet array to transmit rotation from the drive side to the driven side in a vacuum atmosphere that is physically shut out from the drive side, to allow deposition of various types of films on the rotating deposition target while shutting out particles generated from the power system of the drive side.

A substrate processing apparatus of Patent Document 1, for example, has rectangular strips of permanent magnets circumferentially arranged on the surface of a ring-like drive gear (driving magnet array), and rectangular strips of permanent magnets circumferentially arranged also on the surface of a driven gear (driven magnet array). A partition member is provided between the driven gear and the drive gear to divide the atmosphere from the vacuum atmosphere. A wafer is placed on a table that rotates with the driven gear.

Patent Document 2 discloses a magnetic gear that transmits torque by magnetic attraction and repulsion between magnetic teeth, which are permanent magnets radially arranged and having alternating N and S poles on the outer circumferential part of each rotating disc on the drive side and driven side facing each other with a predetermined gap therebetween. The permanent magnets used in this magnetic gear have a radial shape (e.g., involute curve).

PRIOR ART DOCUMENT

Patent Document

SUMMARY OF THE INVENTION

For uniform film deposition on the deposition target in the vacuum deposition apparatus described above, it is necessary to rotate the driven magnet array at a constant low speed of about 1 rpm in a stable manner. However, the magnetic coupling devices disclosed in Patent Documents 1 and 2 had issues of inability to rotate at constant speed, and of unstable movement when the rotation has started or is about to stop because of poor followability of the driven side.

The present invention was made in view of the circumstances described above, its object being to provide a magnetic coupling device capable of stable rotation at constant speed owing to good followability of the driven magnet array.

To solve the above problem, a magnetic coupling device according to the present invention includes: a driving magnet array having a plurality of first permanent magnets in an annular sector shape arranged to have alternating polarities along a circumferential direction; and a driven magnet array having a plurality of second permanent magnets in an annular or circular sector shape arranged to have alternating polarities along a circumferential direction and to have pole surfaces facing pole surfaces of the first permanent magnets, the driven magnet array being rotated by the driving magnet array being rotated, wherein with a first centerline in a radial direction of a specific one of the plurality of first permanent magnets overlapping a second centerline in a radial direction of a specific one of the plurality of second permanent magnets so that opposite poles face each other, a repulsion zone where a repulsive force acts is designed to have an area that is 5% to 15% of an area of an attraction zone where an attractive force acts, including a first permanent magnet adjacent the specific first permanent magnet and a second permanent magnet adjacent the specific second permanent magnet.

The functions and effects of the magnetic coupling device due to such a structure will be described. According to this structure, the first permanent magnets arranged in the driving magnet array have an annular sector shape. Here, an annular sector refers to a shape left after cutting off a circular sector with a smaller radius from a circular sector with a larger radius. Namely, it is a shape surrounded by two circular arcs and two radii. On the other hand, the second permanent magnets arranged in the driven magnet array have an annular, or circular, sector shape.

The plurality of first permanent magnets and second permanent magnets are arranged along the circumferential direction such as to have alternating magnetic poles. Namely, the magnets are arranged to have S pole and N pole alternately. Normally, the driven magnet array has a smaller radius than the driving magnet array and one or a plurality of driven magnet arrays are arranged relative to one driving magnet array. The driven magnet arrays can be rotated by rotating the driving magnet array.

In the above structure, the first permanent magnets and second permanent magnets are arranged so that the magnets have a predetermined positional relationship. Namely, with a first centerline in a radial direction of a specific first permanent magnet overlapping a second centerline in a radial direction of a specific second permanent magnet, and with opposite poles (N pole and S pole) facing each other, the area of repulsion zones is designed to be 5% to 15% of the area of attraction zones between the specific first permanent magnet and the specific second permanent magnet, including first and second permanent magnets adjacent the specific first permanent magnet and the specific second permanent magnet. It was confirmed that, with the zones designed to be in this range, the driven magnet array had better followability and was able to rotate stably at constant speed.

In the present invention, the first permanent magnets and the second permanent magnets should preferably be arranged tightly along a circumferential direction. Such a tight arrangement allows transmission of torque as desired.

In the present invention, it is preferable to provide a mechanism of moving the driven magnet array along the radial direction. With such a mechanism, it is possible to adjust the ratio of areas of the repulsion zone and the attraction zone suitably.

In the present invention, a pole piece made of a ferromagnet should preferably be provided on pole surfaces of the first permanent magnets and the second permanent magnets. This can make the magnetic fields more uniform.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

First, a preferred embodiment of a magnetic coupling device according to the present invention is described.FIG.1Ais a plan view illustrating a schematic diagram of a magnetic coupling device100according to the present invention.FIG.1Bis a side view (cross-sectional view) of the magnetic coupling device shown inFIG.1A.FIG.1Cis a view showing pole pieces and a mechanism of moving the driven magnet array as compared withFIG.1B.FIG.2Ais a plan view showing magnet arrangements of a driving magnet array and a driven magnet array, and their positional relationship.FIG.2Bis a cross-sectional view showing poles of the magnets.FIG.2Cis a partially enlarged view ofFIG.2Awith the shading omitted so that the boundary between a repulsion zone and an attraction zone can be more easily seen.

<Configuration of Magnetic Coupling Device>

A driving magnet array10has multiple first permanent magnets14arranged along a circumferential direction on a surface (upper surface) of a disc12. FIG.2A shows part of the disc12, in which the first permanent magnets14are arranged to have alternating polarities, i.e., to have S pole and N pole alternately. The first permanent magnets14are fixed to the disc12by mechanical means such as screws. Alternatively, the magnets may be secured using an adhesive.

The driving magnet array10is driven by a motor or the like to rotate around a rotation axis16. Any known drive system configuration may be used and illustration thereof is omitted here.

Five driven magnet arrays20are provided on a lower surface of a support plate30. The number of the driven magnet arrays20is not limited to a particular value. The driven magnet arrays20can rotate around the rotation axes26and, as will be described later, follow and rotate when the driving magnet array10rotates.

The first permanent magnet14has a shape of an annular sector. Here, an annular sector refers to a shape left after cutting off a circular sector with a smaller radius from a circular sector with a larger radius. Namely, it is a shape surrounded by two circular arcs and two radii. The center of the circular arcs referred to here coincides with the center of the disc12. The two radii are lines passing through the center of the disc12.

The annular sector has four corners, which need not be sharp and may be rounded for reasons in terms of production or the like. Alternatively, a chamfer of a suitable size may be provided.

As illustrated inFIG.2A, the first permanent magnets14are tightly arranged along the circumferential direction in a ring shape. The first permanent magnets14are formed in the shape of an annular sector so that the magnets are tightly arranged. “Tightly” refers to an arrangement with as little space as possible. The term does not necessarily mean complete absence of a space. There may exist a slight inevitable space depending on the surface roughness or the like of the first permanent magnets14. Such cases are included in the definition of “tightly” as used herein. The same applies to cases where inevitable spaces are formed due to errors involved in assembly or production.

The number of the first permanent magnets14in the array (number of poles) is about 20 to 320, depending on the size of the magnetic coupling device100.

The driven magnet array20has multiple second permanent magnets24arranged along the circumferential direction on the surface (lower surface) of a disc22. As illustrated inFIG.1B, the poles of the first permanent magnets14and the poles of the second permanent magnets24are disposed such as to face each other in parallel. The first permanent magnets14and the second permanent magnets24are arranged with a predetermined distance between their poles (seeFIG.2B, too).FIG.1Cis similar toFIG.1Bbut further includes pole pieces18,28and a mechanism of moving the driven magnet array. Also, the support plate30is shown in a cross-sectional view, and the slit32is shown.

The rotation axis26is integrally attached to the center of the disc22so that the disc22and the rotation axis26are integrally supported on the support plate30such as to be rotatable. The rotation axes26are equally spaced along the circumferential direction around the rotation axis16of the disc12.

When the magnetic coupling device100according to the present invention is used for a vacuum deposition apparatus, the driving magnet array10is placed in the atmosphere and the driven magnet arrays20are placed in a vacuum atmosphere. Therefore, the system on the driven side including the driven magnet arrays20is divided by a partition member (not shown). The basic configuration of the vacuum deposition apparatus is well known and illustration and description thereof will be omitted.

While the second permanent magnets24arranged on the lower surface of the discs22are in a circular sector shape as shown inFIG.2A, the magnets may be in an annular sector shape similarly to the first permanent magnets14. The second permanent magnets24have an array of six poles, but the number of poles is not limited to this. A preferable number of poles (number of magnets) is from 4 to about 48, depending on the size of the magnetic coupling device100.

The second permanent magnets24in a circular sector shape would have three corners, which need not be sharp, and may be rounded similarly to the first permanent magnets14for reasons in terms of production or the like. Alternatively, a chamfer of a suitable size may be provided.

The fewer the number of poles of the second permanent magnets24, the poorer the followability of the driven magnet array20. Too large a number of poles will increase the effect of the areas of inevitable spaces between adjacent second permanent magnets24, which raises the issue of lowered torque. This applies also to the first permanent magnets14.

Rare earth magnets are a preferable material for the first permanent magnets14and second permanent magnets24, and specifically, samarium-cobalt magnets or neodymium magnets are selected. This does not mean that the magnets should be limited to specific materials.

<Relative Positional Relationship Between Permanent Magnets>

Next, the relative positional relationship between the first permanent magnets14and the second permanent magnets24will be described.FIG.2Ashows part of the driving magnet array10and only one of the plurality of driven magnet arrays20.

An arbitrarily given one of the multiple first permanent magnets14will be referred to as a specific first permanent magnet140, and reference numeral141is assigned to the two first permanent magnets adjacent thereto.

An arbitrarily given one of the multiple second permanent magnets24will be referred to as a specific second permanent magnet240. Reference numeral241is assigned to the two second permanent magnets adjacent thereto. Let us now consider a condition where, given the specific first permanent magnet140has S pole, the opposite specific second permanent magnet240has N pole. Given the specific first permanent magnet140has N pole, the opposite specific second permanent magnet240has S pole. In this condition, the opposite poles face each other as shown inFIG.2Bso that the driving magnet array10and the driven magnet array20are stopped in a stable manner because a large attractive force acts between them.

A first centerline X1along the radial direction of the first permanent magnet14is a straight line that divides the annular sector equally on left and right and that passes through the center of the rotation axis16. A second centerline X2along the radial direction of the second permanent magnet24is a straight line that divides the circular sector equally on left and right and that passes through the center of the rotation axis26. As shown inFIG.2A, the first centerline X1of the specific first permanent magnet140and the second centerline X2of the specific second permanent magnet240coincide and overlap with each other.FIG.2Bis a cross-sectional view cut along the centerlines X1and X2.

As shown inFIG.2A, the attraction zone Y includes three attraction zones Y1, Y2, and Y3. The repulsion zone Z includes four repulsion zones Z1, Z2, Z3, and Z4. In the attraction zone Y1, an attractive force acts between the specific first permanent magnet140and the specific second permanent magnet240. In the attraction zone Y2and Y3, an attractive force acts between the first permanent magnets141and the second permanent magnets241adjoining the specific first permanent magnet140and the specific second permanent magnet240.FIG.2Cis a partially enlarged view ofFIG.2Awith the shading omitted so that the boundary between a repulsion zone and an attraction zone can be more easily seen.

In the repulsion zones Z1and Z2, a repulsive force acts between the specific first permanent magnet140and the adjacent second permanent magnets241. In the repulsion zones Z3and Z4, a repulsive force acts between the adjacent first permanent magnets141and the specific second permanent magnet240.

InFIG.2A, the first repulsion zones Z1and Z3and the second repulsion zones Z2and Z4on both sides of the centerlines X1and X2have same areas. Therefore, in this state, the magnet arrays rest stably as no torque is generated.

In the state ofFIG.2A, the outer circumferential end of the driving magnet array10and the outer circumferential end of the driven magnet array20coincide with each other.

Next, the principle of how the driven magnet array20is rotated by rotating the driving magnet array10will be described with reference toFIG.3.FIG.3(a)illustrates the same state as that ofFIG.2A.FIG.3(b)illustrates the positional relationship of the driven magnet array20relative to the driving magnet array10when the driving magnet array10is rotated clockwise a predetermined angle from the state on the left side. As shown, rotating the driving magnet array10clockwise a predetermined angle brings the driven magnet array20to a state where the array is rotated θ° counterclockwise relative to the driving magnet array10.

While the state ofFIG.3(a)is a stable rest condition, when the driving magnet array10rotates clockwise, the driven magnet array20comes to a state where the array is rotated counterclockwise relative to the driving magnet array10, so that the areas of the first repulsion zones Z1and Z3become larger than the areas of the second repulsion zones Z2and Z4, which is an unstable condition. Therefore a torque is generated in a direction in which the magnet arrays return to the position ofFIG.3(a), i.e., in which the driven magnet array20rotates clockwise. Accordingly, as the driving magnet array10keeps rotating clockwise, the driven magnet array20continues to rotate clockwise, following the former.

The areas of the first repulsion zones Z1and Z3are expressed as α+Δα and the areas of the second repulsion zones Z2and Z4are expressed as α−Δα, where α denotes the areas of the first repulsion zones Z1and Z3inFIG.2A, and Δα denotes an increment in area of the first repulsion zones Z1and Z3when the driving magnet array10is rotated θ°. The driven magnet array20rotates in a direction in which the areas of the first repulsion zones Z1and Z3equal to the areas of the second repulsion zones Z2and Z4, i.e., Δα=0. Here, the smaller the areas α of the first repulsion zones Z1and Z3, the more Δα affects α, meaning the torque is generated more promptly in the driven magnet array20so that the array follows the driving magnet array10better.

On the other hand, if the areas α of the first repulsion zones Z1and Z3are too small, the braking effect is lost and there is a risk that the driven magnet array20may overrun. The inventors of the present invention found out through investigation that the driven magnet array20can follow the driving magnet array10well, rotate at constant speed, and smoothly start and stop rotation if the total area of the repulsion zones Z1to Z4(with opposite surfaces having the same polarity (S pole facing S pole, or N pole facing N pole)) is 5% to 15% of the attraction zones Y1to Y3(with opposite surfaces having opposite polarities (S pole facing N pole, or N pole facing S pole)).

To satisfy the above condition, the second permanent magnets24of the driven magnet array20should preferably have a circumferential width W2that is 50% to 150% of the circumferential width W1of the first permanent magnets14of the driving magnet array10, as shown inFIG.4. The radial height H1of the first permanent magnets14should preferably be 50% to 150%, specifically, of the radial height H2of the second permanent magnets24, considering that the driven magnet array20could be shifted closer to the rotation axis16as will be described later, so as to ensure that, when the driving magnet array10and driven magnet array20are positioned as illustrated inFIG.2A, there is a certain overlapping area between the magnet14and the magnets24of the outer half (three in the example ofFIG.2A) and that the magnet14does not overlap the magnets24of the inner half (three in the example ofFIG.2A).

The driven magnet array20may be supported such that the outer circumferential end of the second permanent magnet24is shifted from the outer circumferential end of the first permanent magnet14toward the rotation center of the driving magnet array10(radial direction of the first permanent magnet14) by 0% to 50% of the radial height H2of the second permanent magnet24, as shown inFIG.5. This allows for adjustment of the ratio of areas between the repulsion zones and the attraction zones without changing the number of magnetic poles of the driving magnet array10and the number of magnetic poles of the driven magnet array20. There is also a possibility that the followability of the driven magnet array20could be improved by a shift in position.

The mechanism of moving the driven magnet array20along a radial direction is not limited to a particular one, and various mechanisms are possible. For example, the support plate30may be formed with slits, and a mechanism that guides the rotation axes26may be adopted, to cause the driven magnet arrays20and rotation axes26to move along the radial direction. After adjusting the position, the magnet arrays are fixed in position with a mechanism such as bolts and nuts.

Table 1 shows calculation examples of the ratio of areas between the repulsion zones and the attraction zones when the numbers of poles, widths W1and W2, and heights H1and H2of the first permanent magnets14and second permanent magnets24are varied. While the driving magnet array10has a radius of 86 mm and the driven magnet array20has a radius of 32 mm in the examples shown in Table 1, the present invention is not limited by these values and is applicable to a magnetic coupling device100of any size. In Table 1, the driven magnet array20is at a “standard” position when there is no “shift” in the second permanent magnets24as has been described above, and at a “shifted” position when the driven magnet array20is shifted radially inward by 2 mm as shown inFIG.5.

TABLE 1No. of magnetic poles of drive gear60 poles50 poles40 polesNo. of magnetic poles of driven gear10 poles8 poles6 poles4 polesPosition of driven gearStandardShiftedStandardShiftedStandardShiftedStandardShiftedMagnet width of driven gear (mm)10.0512.5716.7525.13Magnet height of driven gear (mm)16161616Magnet width of drive gear (mm)8.7910.5513.1913.19Magnet height of drive gear (mm)12121212Area of repulsion zone (mm2)59.428.744.720.629.417.747.645.2Area of attraction zone (mm2)233.8202.0247.7211.3263.8212.9246.6185.4Repulsion zone/Attraction zone (%)25%14%18%10%11%8%19%24%

Pole pieces may be disposed on the surfaces of the first permanent magnets14and the second permanent magnets24(on the surfaces facing each other). The pole pieces, which are preferably made of a ferromagnet, can make the magnetic fields generated by the magnets more uniform. The pole pieces may have a size and shape such as to cover each of the magnets.

EXAMPLES

Actual magnetic coupling devices were made for Examples 1 and 2 and Comparative Examples 1 and 2 of Table 2, and tests were conducted in which the driven magnet arrays20were rotated at a constant speed of 1 rpm. In this case, we investigated whether or not there were points where the driven magnet arrays20stopped for 0.2 sec. or more, the angle of displacement of the driven magnet array20when the rotation was stopped (degree of overrun), and the followability (match between an ideal constant-speed rotation and the rotation angle of the driven magnet array). The results are shown in Table 2, andFIG.6toFIG.8.FIG.6toFIG.8show the movement until the magnet array makes one turn. If plotted, the graph would be similarly linear afterwards.

The test result of the followability of Example 1 are as shown inFIG.6. The result of the followability of Example 2 is similar to Example 1 and as shown inFIG.6.FIG.7shows the test result of Comparative Example 1, andFIG.8shows the test result of Comparative Example 2. The rpm can be monitored by attaching a known encoder.

TABLE 2ComparativeComparativeExample 1Example 2Example 1Example 2No. of magnetic poles of drive gear40 polesNo. of magnetic poles of driven gear6 poles4 polesNumber of driven gears5Distance between driving magnet and7.5driven magnet (mm)Position of driven gearStandardShiftedStandardShiftedMagnet width of driven gear (mm)16.7525.13Magnet height of driven gear (mm)16Magnet thickness of driven gear (mm)2.5Magnet width of drive gear (mm)13.19Magnet height of drive gear (mm)12Magnet thickness of drive gear (mm)4Area of repulsion zone (mm2)29.417.747.645.2Area of attraction zone (mm2)263.8212.9246.6185.4Repulsion zone/Attraction zone11%8%19%24%Points of stop for 0.2 sec. or moreNoneNoneNone2 pointsAngle of displacement when stopped (deg.)0.4 to 0.60.4 to 0.60.2 to 0.50.5 to 0.9Followability⊙ FIG. 6⊙Δ FIG. 7◯ FIG. 8

As can be seen from Table 2, the magnet arrays of Example 1 and Example 2, with the ratio of areas between the repulsion zones and the attraction zones being in the range of 5% to 15%, did not come to a stop, and the degrees of overrun when stopping fell within a small range of 0.4° to 0.6°. AsFIG.6shows, the rotation angle of the driven magnet array relative to the time axis stayed substantially on the line of an ideal constant-speed rotation, which means that the magnet array rotated at the constant speed of 1 rpm.

In contrast, the driven magnet array of Comparative Example 1 with the ratio of areas between the repulsion zones and the attraction zones being out of the range of 5% to 15% had a degree of overrun when stopping as low as Examples 1 and 2, but the rotation angle of the driven magnet array relative to time did not stay on the ideal line as shown inFIG.7, which indicated that the driven magnet array had poor followability and failed to rotate at constant speed. The driven magnet array of Comparative Example 2, which was shifted radially inward by 2 mm showed somewhat improved followability as shown inFIG.8. However, the magnet array stopped twice for 0.2 sec. or more per one rotation, and the degree of overrun when stopping was larger than those of Examples 1 and 2. Such stops cause scars, particle generation, and adverse effects on uniform deposition, and therefore must be reduced to less than 0.2 sec.

OTHER EMBODIMENTS

The magnetic coupling device according to the present invention is primarily used for a vacuum deposition apparatus, but may also be used in other devices for other purposes.

While two permanent magnets141adjoin the specific first permanent magnet140, one on each side as shown inFIG.2, there may be a case where the repulsion zone or attraction zone extends over to permanent magnets further adjoining the adjacent magnets, depending on the size of the driving magnet array10or driven magnet array20, or the size of the first or second permanent magnets14or24. These permanent magnets further adjoining the adjacent magnets can also be included in the definition of the term “adjacent”.