JP2012176446A - Tool for polishing - Google Patents

Abstract

PROBLEM TO BE SOLVED: To flatten a surface of a polishing object with accuracy.SOLUTION: A tool for polishing has a polishing face which includes: a first region which includes a rotating center position and satisfies L=0; a second region which comes into contact with the first region, between the first region and an outer circumferential line of the polishing face and satisfies 0.6≤L/R≤1; a third region which comes into contact with the second region, between the second region and the outer circumferential line and satisfies 0.4≤L/R<0.6; and a fourth region which comes into contact with the outer circumferential line, between the third region and the outer circumferential line and satisfies 0.8≤L/R≤1.

Description

  The present invention relates to a polishing tool.

  In the manufacturing process of metal products, ceramic products, etc., polishing is performed to flatten and mirror the surface. In such a polishing process, for example, as shown in Patent Document 1, a slurry having polishing abrasive grains and liquid is supplied between a polishing tool such as a grindstone and an object to be polished. Is rotated to polish the surface of the object to be polished (hereinafter also referred to as “surface to be polished”). In Patent Document 1, in order to flatten the polished surface of the object to be polished with higher accuracy, a groove is formed on the surface after polishing, and at least a part of the groove is used as a central axis of the polishing tool. On the other hand, the structure inclined in the depth direction is proposed.

JP-A-2005-118996

  In the polishing that is generally performed in general, as shown in FIG. 10A, the polishing tool 120 is spread over a wide region S2 including the entire target range (S1 in FIG. 10A) of the polishing object 110. This is performed by moving the polishing surface 122 in sliding contact. The above-described Patent Document 1 is also performed by sliding the polishing tool 120 over the entire wide region S2 including the entire target range S1 of the polishing target 110 to be polished. FIG. 11 is a plan view showing a polishing surface 122 of a polishing tool 120 which is an example of a polishing tool disclosed in Patent Document 1. As shown in FIG. The polishing tool 120 includes a plurality of grooves 123 arranged in a grid pattern on the polishing surface 122.

  The polishing tool described in Patent Document 1 can obtain a polished surface with relatively high flatness in the case shown in FIG. However, as shown in FIG. 10B, the polishing process may be performed so as to form a recess 130 on one surface of the object to be polished. In such a polishing process, the polishing target range S <b> 1 becomes the bottom surface 132 of the recess 130. In this case, the polishing tool 120 cannot be moved and brought into sliding contact within a range wider than the polishing target range S2. In this case, the movement range of the polishing tool is limited by the side surface 134 of the recess 130, and the movement range S <b> 2 of the polishing tool 120 is narrow to coincide with the polishing target range S <b> 1, and the bottom surface 132 of the recess 130 and the polishing tool 120. Distribution tends to occur in the contact state with the polishing surface 122. FIG. 10C shows the actual polishing target range S2 when polishing is performed using a polishing tool provided with a grid-like groove described in Patent Document 1 on the polishing surface as shown in FIG. 10B. It is the cross-sectional shape. Thus, even when polishing is performed using the conventional polishing tool 120, in the case shown in FIG. 10B, as shown in FIG. 10C, the polishing target range S1 (the flatness of the bottom surface 122 of the recess 120). The present application has been made for the purpose of solving such a problem.

In order to solve the above-mentioned problem, the present application is a polishing tool including a polishing surface, the polishing surface rotating around a rotation axis passing through a rotation center position positioned at the center of the polishing surface, and the polishing surface Includes a contact portion that contacts the object to be polished and a recess that includes the rotation center position and does not contact the object, and represents a distance from an arbitrary position on the polishing surface to the rotation center position as x ( m), and R _(x) (m) is the circumference of the virtual circle that passes through the arbitrary position with the rotation center position as the center, and the portion of the circumference of the virtual circle that passes through the contact portion When the total circumference of the virtual circle is L _(x) (m), the polishing surface includes the first region that includes the rotation center position and satisfies L _(x) = 0, and the first region wherein between the peripheral line of the polishing surface, and contact with the first region and, 0.6 ≦ L _(x) R _(x) and a second region satisfying 0.6 ≦ 1, between the outer periphery line and the second region, and in contact with the second _{region, 0.4 ≦ L (x) /} R (x) A third region satisfying <0.6, and a fourth region satisfying 0.8 ≦ L _(x) / R _(x) ≦ 1 between the third region and the outer peripheral line and in contact with the outer peripheral line And a polishing tool characterized by comprising a region.

  According to the polishing tool according to one aspect of the present invention, the surface of the object to be polished can be flattened with high accuracy.

BRIEF DESCRIPTION OF THE DRAWINGS It is a figure explaining one Embodiment of the polishing tool of this invention, (a) is a schematic perspective view of a polishing tool, (b) is a schematic perspective view which shows the state which is performing the grinding | polishing process using the polishing tool. FIG. 4C is a schematic cross-sectional view corresponding to FIG. It is a schematic sectional drawing explaining an example of the grinding | polishing process performed by mounting | wearing the grinding | polishing apparatus with the grinding | polishing tool shown in FIG. (a) And (b) is a schematic top view which shows the locus | trajectory of the grinding | polishing tool in a to-be-polished surface. (A) is a schematic plan view which shows the grinding | polishing surface of the grinding | polishing tool shown in FIG. 1, (b) is sectional drawing which expands and shows the grinding | polishing surface vicinity of the grinding | polishing tool. (A) is a graph which shows the value calculated | required by calculation about the cross-sectional shape of the to-be-polished surface of a target object after grind | polishing using the polishing tool shown in FIG. (B) has shown the measured value of the cross-sectional shape of the grinding | polishing surface vicinity of a target object at the time of grinding | polishing using the tool for grinding | polishing shown in FIG. (A) And (b) is a figure for demonstrating calculation of the calculated value shown to Fig.5 (a). (A)-(d) is a graph which shows the result of having calculated | required the shape of the to-be-polished surface after grinding | polishing about the polishing tool of a shape different from the polishing tool of Fig.6 (a). (A)-(d) is a graph which shows the result of having calculated | required the shape of the to-be-polished surface after grinding | polishing about the polishing tool of a shape different from the polishing tool of Fig.6 (a). (A)-(c) is a graph which shows the result of having calculated | required the shape of the to-be-polished surface after grinding | polishing about the polishing tool of a shape different from the polishing tool of Fig.6 (a). It is a figure explaining the grinding | polishing process using the tool for grinding | polishing. It is a schematic plan view explaining the grinding | polishing surface of the grinding | polishing tool which is an example of the conventional grinding | polishing tool.

  Embodiments of the present invention will be described below with reference to the drawings.

  A polishing tool according to an embodiment of the present invention will be described. FIG. 1 is a diagram for explaining a polishing tool 1 according to the present invention, where (a) is a schematic perspective view of the polishing tool 1, and (b) is a state in which a polishing step is performed using the polishing tool 1. The schematic perspective view shown, (c) is a schematic sectional drawing corresponding to (b).

The polishing tool 1 of the present embodiment has a main body 2 that polishes the surface of the object T. The main body 2 has a circular polishing surface 4 facing the surface to be polished of the object T to be polished. The main body 2 is transmitted with the rotational driving force by the rotating shaft 3 and rotates together with the rotating shaft 3. In the present embodiment, the polishing tool 1 is rotated along a virtual surface I including the polishing surface 4 while the polishing surface 4 rotates around the rotation axis C passing through the rotation center position O positioned at the center of the polishing surface 4. Move and polish the object T. FIGS. 1B and 1C show a state in which the hole portion 20 having the bottom surface 12 is formed on the surface of the object T.

  FIG. 2 is a schematic cross-sectional view illustrating a polishing process performed by attaching the polishing tool 1 to the polishing apparatus 50. The polishing apparatus 50 transmits a rotational driving force to the rotating shaft 3, a support base 6 that supports the polishing tool 1 and the object T, a supply unit Sp that supplies a polishing fluid onto the surface to be polished of the object T, and the rotating shaft 3. And a driving force transmission portion Rt.

  The polishing method using the polishing tool 1 described above includes a step of installing the main body 2 on the surface to be polished of the object T, a step of supplying the polishing fluid F onto the surface to be polished of the object T, and polishing. And polishing the main body 2 while supplying the working fluid F. Abrasive grains are dispersed in the polishing fluid F. The polishing surface 4 of the polishing jig 1 and the surface to be polished of the object T slide through the polishing fluid F, and the surface to be polished is polished. The main body 2 rotates with the rotation shaft 3 and the center of rotation located at the center of the polishing surface 4 moves on the surface to be polished as a locus 32 as shown in FIG. 3A or FIG. 3B, for example. To do. In FIG. 3A, the rotation center of the main body 2 of the polishing tool 1 moves from the start point 22a to the end point 32b while drawing a spiral trajectory 32. In FIG. 3B, the rotation center of the main body 2 moves while bending from the start point 32a to the end point 32b.

  FIG. 4 is a diagram showing the polishing tool 1 in more detail. 4A is a view showing the polishing surface 4 of the polishing tool 1, and FIG. 4B is an enlarged sectional view showing the vicinity of the polishing surface 4 of the polishing tool 1. As shown in FIG.

The polishing tool 1 includes, on the polishing surface 4, a contact portion 30 that comes into contact with the object T and a recess portion 34 that does not come into contact. In the polishing tool 1, in addition to one recess 34 arranged at the center position including the rotation center position, each recess 34 having substantially the same shape is spaced apart at equal intervals along the outer peripheral direction of the polishing surface 4. One is arranged. In the polishing tool 1, the recess 34 is separated into a plurality of parts, but the number, arrangement, shape, and the like of the recesses 34 are not particularly limited as long as the following conditions described below are satisfied. In the polishing tool 1, the distance from the rotation center position O at an arbitrary position on the polishing surface 4 is x (m), and the circumferential length of a virtual circle passing through the arbitrary position centered on the rotation center position O is R _{(x )} (M), there are four portions P1 to P4 of the circumference of the virtual circle D passing through the contact portion 30. In this embodiment, when the total length over the entire circumference of the virtual circle is L _(x) (m), the total length L _(x) (m) is along the circumferential direction of each of P1 to P4. Total length.

In the polishing tool 1, the polishing surface 4 includes the rotation center position O, the first region A1 that satisfies L _(x) = 0, and the side closer to the outer peripheral line E of the polishing surface 4 than the first region A1. The second region A2 that is in contact with the first region A1 and satisfies 0.6 ≦ L _(x) / R _(x), and the second region A2 that is disposed closer to the outer peripheral line E than the second region A2. The third region A3 satisfying 0.4 ≦ L _(x) / R _(x) <0.6, and the outer peripheral line E in contact with the outer peripheral line E from the third region A3. And a fourth region A4 that satisfies 0.8 ≦ L _(x) / R _(x) ≦ 1. The polishing tool 1 having such characteristics can make the bottom surface 12 of the hole portion 20 after polishing have a relatively high flatness. In FIG. 4, a virtual circle E1 that satisfies the distance x = 0.5r is illustrated as an example, where r is the radius of the inscribed circle of the polishing surface 4 with the rotation center position O as the center.

In the example shown in FIG. 4, more specifically, (L _(x) / R _(x) ) = 1 in the second region A2 and the fourth region A4. By providing the second region A2 so as to be in contact with the first region A1 where no contact portion exists, the edge portion 36 of the contact portion of the second region A2 is formed at the boundary portion between the second region A2 and the first region A1. Is placed. The edge portion 36 relatively increases the polishing rate of the bottom surface 22 of the hole portion 20 to be polished, and suppresses the slurry from being partially retained on the bottom surface 22 of the hole portion 20. The distribution of the polishing state is suppressed. Thus, it is preferable that 2nd area | region A2 satisfy | fills 0.9 <= L _(x) / R _(x) at the point which makes the residence restraint effect of a slurry high. In addition, it has the same effect also about 4th area | region A4, and the residence of the slurry in the part corresponding to 4th area | region A4 is suppressed by providing the edge part 38 of the contact part of 4th area | region A4, and bottom face The flatness of 22 can be increased.

Further, in the polishing tool 1 of the present embodiment, the value of L _(x) / R _(x) disposed between the third region A3 and the fourth region A4 increases as x increases. 5 area | region A5 is further provided. In the fifth region A5, since the value of L _(x) / R _(x) increases as x increases, the value satisfying 0.4 ≦ L _(x) / R _(x) <0.6 The slurry collected in the third region A3 is relatively easy to move to the fourth region A4 side. In the polishing tool 1, uneven polishing due to excess slurry is suppressed.

  In the polishing tool 1 of the present embodiment, in the virtual circle at an arbitrary position on the polishing surface, the intersection line of the virtual circle and the polishing surface is divided into a plurality of partial arcs, and each partial arc is substantially the same. It is said that the length. Thereby, the distribution of the pressure applied to the polished surface can be made uniform with high precision along the rotation direction, and the flatness of the polished surface after polishing can be further increased. In the polishing tool 1, the distance between the partial arcs is substantially the same over the entire circumference of the virtual circle. This also makes it possible to make the pressure distribution on the polished surface uniform with high precision along the rotational direction.

Moreover, in the polishing tool 1 of the present embodiment, the value of L _(x) / R _(x) is a constant value of 0.5 in the entire third region A3. In addition, each of the partial arcs described above has substantially the same length, and the distance between the partial arcs is substantially the same over the entire circumference of the virtual circle. The contact portion 30 includes a radial edge portion 35 along the radial direction of the polishing surface 4 at a boundary portion with the concave portion 34. A relatively high pressure is applied to the surface to be polished at the portion where the radial edge portion 35 is in contact with the surface to be polished, and the radial edge portion 35 is formed along a direction perpendicular to the radial edge portion 35. By sliding, the surface to be polished is polished at a relatively high polishing rate, and the flatness of the surface to be polished is relatively high. That is, as shown in FIG. 4, in the polishing tool 1, the third region A3 includes a plurality of recesses 34 dispersed along the circumference of the virtual circle, and the shape and arrangement of the recesses 34 rotate with respect to the rotation center position. Symmetrical relationship. For this reason, in polishing performed by rotating the polishing surface about the rotation center axis, the stress distribution on the surface to be polished is equalized in the circumferential direction, and a stable polishing state can be maintained.

  In the polishing tool 1 of the present embodiment, when the radius of the inscribed circle of the polishing surface centered on the rotation center position is r, the distance x is 0 <x ≦ 0.2r in the first region A1. In the second region A2, the distance x satisfies 0.2r <x ≦ 0.3r, and in the third region A3, the distance x satisfies 0.85r <x ≦ 1.0r. The inventors of the present application have confirmed through simulation that the surface of the polished surface is flattened with high accuracy by setting the range of the distance x to such a range.

  Fig.5 (a) has shown the value calculated | required by calculation about the cross-sectional shape of the to-be-polished surface of the target object T after grind | polishing using the tool 1 for grinding | polishing shown in FIG. FIG. 5B shows an actual measurement value of the cross-sectional shape in the vicinity of the polishing surface of the object T when polishing is performed using the polishing tool 1 shown in FIG. The numerical values on the vertical axis shown in FIG. 5A are the numerical values used in the numerical simulation, and the scale of the vertical axis shown in FIG. 5A and the scale of the vertical axis in the coordinate axes shown in FIG. , Almost matched.

The cross-sectional shape shown in FIG. 5B is a cross-sectional shape when polished under the following polishing conditions. As the main body 2 of the polishing tool 1, a urethane main body 2 having a density of about 0.78 g / cm ³ and a Shore hardness A defined by ISO 7619 of about 93 degrees is used. The diameter was about 40 mm. Further, alumina having an average particle diameter of about 3 μm was used as the abrasive grains mixed with the polishing fluid F. While rotating the polishing surface 4 of the main body 2 at about 213 rpm, the polishing tool 1 was reciprocated linearly while a load of about 2 kg was applied. The moving speed of the polishing tool 1 in this linear motion was 500 mm / min, and the machining time, that is, the moving time was 28 minutes in total.

The calculated value of the cross-sectional shape shown in FIG. 5A is calculated using a so-called Preston equation. 6 (a) and 6 (b) are diagrams for explaining calculation of the calculated values shown in FIG. 5 (a). FIG. 6A shows the distribution of the values of L _(x) / R _{(x) on} the polishing surface 4 of the polishing tool 1. FIG. 6B shows a calculation method of the polishing amount of the surface to be polished Ts in a state in which the polishing tool 1 is only rotated around the rotation axis C without moving the rotation axis C of the polishing tool 1. It is a figure for demonstrating. As shown in FIG. 6B, the polished surface Ts corresponding to the rotation center O of the polishing surface 4 is the origin, and the polishing amount G (x, y) at the coordinate position (x, y) of the polished surface Ts is It can be obtained by the Preston equation represented by the following equation (1).

  Here, A: proportionality constant, F: pressure applied per unit area, S: rotational speed. The proportional constant of A is a constant determined by the material of the main body 2 of the polishing tool 1, the material of the surface to be polished, and the like. In order to obtain the polishing amount G (x) when the rotary shaft C is moved along the Y-axis direction and reciprocated linearly while rotating around the rotary shaft C, the following equation (2) ) And integrating in the Y direction by the amount corresponding to the amount of movement along the Y-axis direction.

  Here, G (x) is a polishing amount when the rotary shaft C is moved around the rotary axis C and moved along the Y-axis direction to reciprocate linearly.

  As can be seen by comparing FIG. 5 (a) and FIG. 5 (b), the calculated value of the polished shape based on the Preston equation corresponds well to the shape data after actual polishing, and the conventional polishing is performed. The shape of the bottom surface of the hole portion 22 is flat compared to the shape after polishing (see FIG. 10) in the case where the tool for use is used. By using the polishing tool 1, the shape of the polishing surface can be flattened with high accuracy.

  The polishing tool described in the present application was made by the inventor of the present invention who found a new condition for flattening the shape after polishing by trial and error of the present inventor based on the above calculation.

FIGS. 7A to 7D are results obtained by calculating the shape of the polished surface after polishing for a polishing tool having a shape different from the polishing tool of the above embodiment. In addition, the numerical value of the vertical axis | shaft in each graph shown to FIGS. 7-9 is the value of the parameter used for calculation, and the scale of the vertical axis | shaft in each figure respond | corresponds to the reduced scale of the actual value shown in FIG.3 (b). is doing. In the calculation results shown in FIGS. 7A to 7D, the values of L _(x) / R _(x) in the third region A3 are different among the shapes of the polishing tool. In FIG. 7A, the value of L _(x) / R _(x) in the third region A3 is 0.3, and in FIG. 7B, L _(x) / R _(x) in the third region A3. value is 0.4, the value of _{L (x) / R (x} ) in the third region A4 in FIG. 7 (c) is 0.6, _L in the third region A3 in FIG. 7 (d) _{( x)} The value of / R _(x) is 0.7. As shown in FIG. 7, the value of L _(x) / R _(x) in the third region A3 affects the shape after polishing. When the value of L _(x) / R _(x) in the third region A3 is in the range of 0.4 to 0.6, the flatness of the polished surface is sufficiently high.

FIGS. 8A to 8D are results obtained by calculating the shape of the polished surface after polishing for a polishing tool having a shape different from the polishing tool of the above embodiment. First, the calculation results shown in FIGS. 8A to 8D are different from the polishing tool 1 of the above embodiment in that the fifth area A5 is not provided. 8A to 8D, in the range corresponding to the fifth region A5, the value of L _(x) / R _(x) is the same value as the fourth region A4. The calculation result shown in FIG. 8D is different from the shape of the polishing tool 1 only in that it does not have the fifth region A5. Further, in the calculation results shown in FIGS. 8A to 8C, among the shapes of the polishing tool, the value of L _(x) / R _(x) in the fourth region A4 is also the same as that of the polishing tool 1. Is different. In FIG. 8A, the value of L _(x) / R _(x) in the fourth region A4 is 0.7, and in FIG. 8B, the value of L _(x) / R _(x) in the fourth region A4. The value is 0.8. In FIG. 8C, the value of L _(x) / R _(x) in the fourth region A4 is 0.9.

As shown in FIG. 8, the value of L _(x) / R _(x) in the fourth region A4 does not greatly affect the shape after polishing in the calculation. However, in a portion where the value of L _(x) / R _(x) in the fourth region is close to 1.0, it is difficult for excess slurry to enter the gap between the polished surface and the polished surface. The present inventors have confirmed that the flatness of the film is high. In the fourth region, it is preferable that the value of L (x) / R (x) is 0.9 or more. In addition, as is clear when comparing FIG. 8D and FIG. 5A in particular, the value of L _(x) / R _(x) is x between the third region A3 and the fourth region A4. In order to increase the flatness of the surface to be polished, it is preferable to further include a fifth region A5 that increases with an increase in the thickness.

9A to 9C show the results of calculating the shape of the polished surface after polishing for a polishing tool having a shape different from the polishing tool of the above embodiment. In the calculation results shown in FIGS. 9A to 9C, the values of L _(x) / R _(x) in the second region A2 are different among the shapes of the polishing tool. In FIG. 9A, the value of L _(x) / R _(x) in the second region A2 is 0.7, and in FIG. 9B, the value of L _(x) / R _(x) in the second region A2 The value is 0.8, and in FIG. 9C, the value of L _(x) / R _(x) in the second region A2 is 0.9. As shown in FIG. 9, in the calculation, the value of L _(x) / R _(x) in the second region A2 does not greatly affect the shape after polishing. However, the second region A2 has the effect of removing the slurry described above. When the value of L _(x) / R _(x) in the second region A2 is 0.9 or more, the actual polishing is performed. The inventor of the present application has confirmed that the effect of suppressing the slurry retention is great and the flatness can be increased.

By using a polishing tool having a value of L _(x) / R _(x) of 0.9 or more in the second region A2, when polishing, the polishing surface 4 of the polishing tool 1 and the object T It is possible to prevent the polishing fluid F from staying between the surface to be polished Ts. Therefore, it is possible to suppress the abrasive grains G in the polishing fluid F from being settled and depositing unevenly on the surface to be polished. Accordingly, the abrasive grains G are not depleted and the abrasive grains G are also prevented from staying, and the abrasive grains G spread more uniformly on the surface to be polished Ts, so that the entire surface to be polished Ts is flattened with higher accuracy. be able to.

In the present embodiment, a so-called pothole is described as an example in which a polishing tool is partially slidably brought into contact with the surface to be polished, and polishing is performed using the polishing tool of the present invention. It is not limited only to so-called pothole polishing. In the above embodiment, urethane is used. However, the material of the main body of the polishing tool 1 is not particularly limited, and the shape and size of the polishing tool, the material of the object, and the like are not particularly limited. Of course, the present invention is not limited to the above-described embodiments, and various improvements and modifications may be made without departing from the scope of the present invention.

DESCRIPTION OF SYMBOLS 1,120 Polishing tool 2 Main body 3 Rotating shaft 4 Polishing surface 12 Bottom surface 20 Hole portion 30 Contact portion 32 Trajectory 32a Start point 32b End point 34 Recess 35, 36 Edge portion 110 Object to be polished 122 Polishing surface 130 Recess 132 Bottom surface

Claims (7)

A polishing tool comprising a polishing surface, wherein the polishing surface rotates about a rotation axis passing through a rotation center position located at the center of the polishing surface,
The polishing surface includes a contact portion that contacts a target object to be polished, and a concave portion that includes the rotation center position and does not contact the target object.
X (m) is a distance from an arbitrary position on the polishing surface to the rotation center position;
R _(x) (m) is the circumferential length of the virtual circle that passes through the arbitrary position with the rotation center position as the center,
When the total circumference of the imaginary circle of the circumference of the imaginary circle passing through the contact portion is L _(x) (m),
The polished surface is
A first region including the rotation center position and satisfying L _(x) = 0;
A second region satisfying 0.6 ≦ L _(x) / R _(x) 0.6 ≦ 1 between the first region and the outer peripheral line of the polishing surface and in contact with the first region;
A third region satisfying 0.4 ≦ L _(x) / R _(x) <0.6 between the second region and the outer peripheral line and in contact with the second region;
A fourth region satisfying 0.8 ≦ L _(x) / R _(x) ≦ 1 between the third region and the outer peripheral line and in contact with the outer peripheral line. tool. The fifth region is further provided between the third region and the fourth region, and a value of L _(x) / R _(x) increases as x increases. Polishing tool. The polishing tool according to claim 1, wherein the second region satisfies 0.9 ≦ L _(x) / R _(x) ≦ 1.   The polishing tool according to any one of claims 1 to 3, wherein the third region includes a plurality of concave portions dispersed along the circumference of the virtual circle. The second region satisfies L _(x) / R _(x) ≦ 1, and the concave portion of the first region and the concave portion of the third region are separated via the second region. The polishing tool according to claim 4.   The polishing tool according to claim 1, wherein the shape and arrangement of the recesses are rotationally symmetric with respect to the rotation center position. When the radius of the polishing surface centered on the rotation center position is r,
The distance x in the first region is 0 <x ≦ 0.2r,
The distance x in the second region is 0.2r <x ≦ 0.3r,
The polishing tool according to claim 1, wherein the distance x in the third region is 0.85r <x ≦ r.

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