TWI796448B - Retainer unit with marking wheels and pins - Google Patents

Abstract

The present invention provides a holder unit capable of easily forming a scribed line along a scanning direction of the holder unit, and a scribing wheel and pin thereof. The pin 70 is a pin that supports the scribing wheel 60 , and includes a restricting portion 80 that prevents the scribing wheel 60 from moving relative to the pin 70 in the axial direction of the pin 70 .

Description

Retainer unit with marking wheels and pins

The present invention relates to a holder unit and its marking wheel and pin.

A scribing device is used to form scribe lines on brittle material substrates such as glass substrates. A holder unit and a scanning device for scanning the holder unit are provided on the scribing device. The holder unit includes a holder body, pins and scoring wheels. The holder body is installed on the scanning device. The pins are supported by the holder body. The marking wheel is supported on a pin. Patent Document 1 discloses a scribing unit ( 20 ) as an example of a holder unit. The scribing unit (20) includes a scribing wheel (60), a pin (32) rotatably supporting the scribing wheel (60), and a support frame (33) for supporting the pin (32). A scoring line is formed on the brittle material substrate by scanning the brittle material substrate in a specific scanning direction with the scribing unit (20).

[Prior Art Literature] [Patent Document]

[Patent Document 1] Japanese Patent Laid-Open No. 2012-106479

In the previous scribing device, for example, the case where the holder unit scans in a linear direction In this case, the non-linear scribe line is formed on a brittle material substrate. In one example, the non-linear scribing line includes a linear portion along the scanning direction of the scribing wheel, and a non-linear portion advancing in a direction different from the scanning direction. When the non-linear part is formed at one or several places of the scribed line, there are cases where the linear part and the non-linear part of the substantially entire scribed line are alternately formed, etc. The shape of the non-linear scribed line is various. In terms of improving the quality of the brittle material substrate after fracture, it is preferable to form scribe lines along the scanning direction. This is true not only in the case of forming linear scribed lines, but also in the case of forming scribed lines in shapes other than straight lines.

(1) The pin of the scribing wheel according to the present invention supports the scribing wheel, and has a restricting portion that prevents the scribing wheel from moving relative to the pin in the axial direction of the pin.

When the reaction force acting on the axial direction of the pin during the scanning of the scribing wheel is generated in the case of the scribing wheel, the reaction force is received by the restricting portion of the pin. Therefore, movement of the scribing wheel relative to the pin in the axial direction of the pin is suppressed. Thereby, scribe lines along the scanning direction of the holder unit can be easily formed.

(2) In a preferred example, in the pin of the scribing wheel of (1), the restricting portion includes a recess formed on the outer periphery of the pin.

Therefore, the configuration of the restricting portion is simple.

(3) In a preferred example, in the pin of the scribing wheel of (2), the surface of the above-mentioned concave portion is a curved surface.

Therefore, stress concentration is less likely to occur in the concave portion.

(4) The marking wheel system related to the present invention is supported by any one of the pins in (1) to (3), It includes a regulated portion in contact with the above-mentioned regulated portion.

According to the above-mentioned scribing wheel, the same effect as that of (1) is obtained.

(5) In a preferred example, the scribing wheel of (4) is a scribing wheel supported by the pin of (2), and the restricted portion includes a convex portion inserted into the concave portion.

Therefore, the configuration of the restricted portion is simple.

(6) In a preferred example, the scribing wheel of (5) is a scribing wheel supported by the pin of (3), and the surface of the above-mentioned convex part is a curved surface.

Therefore, stress concentration is less likely to occur on the convex portion.

(7) The cage unit according to the present invention includes the pin of any one of (1) to (3), and the marking wheel of any one of (4) to (6).

According to the above-mentioned retainer unit, the same effect as that of (1) is obtained.

(8) In a preferred example, the retainer unit of (7) includes the pin of (3) and the scribing wheel of (6), and the radius of curvature of the concave portion is larger than the radius of curvature of the restricted portion.

Since the concave part and the convex part are in line contact, the frictional resistance during scribing becomes small.

According to the holder unit and its scribing wheel and pins related to the present invention, it is possible to easily form a scribe line along the scanning direction of the holder unit.

1: marking device

10:Mobile device

11:Mobile station

12: track

13: Rotary straight conversion device

13A: Motor

13B: Feed screw part

20: Platform device

21: Platform

22: motor

30: Hold body

31: bridge body

31A: guide part

32: Pillar

33: Connecting part

34: Scribing head

35: Retainer connector

40: Retainer unit

50: retainer

51: Groove

51A: surface

51B: face

52: Support hole

60:Scribing wheel

61: Body Department

61A: 1st side

61B: 2nd side

62: Knife tip

63: Insertion hole

70: pin

70A: One end

71: Outer peripheral surface

80: Restricted Department

81: Concave

81A: Noodles

81B: Vertex

90: Restricted Department

91: convex part

91A: surface

91B: Vertex

180: Restricted Department

181: convex part

181A: Surface

190: restricted department

191A: surface

280: Restricted Department

281: Concave

290: restricted department

291: convex part

DT: thickness direction

GB: Brittle material substrate

HA: height

J: Center axis of rotation

LA: straight line

LB: straight line

SA: Clearance

SB: Gap

XA: Depth

XB: width

Fig. 1 is a perspective view of a scribing device according to an embodiment.

FIG. 2 is a cross-sectional view of the retainer unit in FIG. 1 .

Fig. 3 is a cross-sectional view of a cage unit according to a first modification.

Fig. 4 is a cross-sectional view of a cage unit according to a second modification.

(implementation form)

The scribing device 1 shown in FIG. 1 is used to divide a substrate formed of a brittle material such as a glass substrate or a ceramic substrate (hereinafter referred to as "brittle material substrate GB"), and is used to form a scribe on the surface of the brittle material substrate GB. draw the line. An example of the brittle material substrate GB is a glass substrate. An example of the glass substrate is alkali-free glass. Alkali-free glass is used in flat panel displays and the like.

The main elements constituting the scribing device 1 are the moving device 10 , the platform device 20 , the holding mechanism 30 and the holder unit 40 . The mobile device 10 scans the brittle material substrate GB in the scanning direction. The mobile device 10 includes a mobile station 11 on which the platform device 20 is mounted. The mobile station 11 is placed on a pair of rails 12 . The rotary linear conversion device 13 moves the mobile platform 11 along the track 12 . An example of the rotation-to-straight-forward conversion device 13 is a feed screw device, and includes a motor 13A serving as a drive source, and a feed screw portion 13B connected to an output shaft of the motor 13A.

The stage device 20 includes a stage 21 rotatable around a rotation center axis J, and a motor 22 for rotating the stage 21 . The brittle material substrate GB is placed on the platform 21 , is adsorbed to the platform 21 by a vacuum suction mechanism (not shown in the figure), thereby being held on the platform 21 . The motor 22 is accommodated on the platform 21 Inside. The motor 22 regulates the position of the brittle material substrate GB in the rotation direction of the stage 21 by rotating the stage 21 .

The holding mechanism 30 holds the holder unit 40 . The holding mechanism 30 includes a bridge body 31 installed across the platform 21 from above, and a pair of pillars 32 supporting the bridge body 31 . A guide portion 31A is provided on the bridge body 31 . A scribing head 34 is movably attached to the guide portion 31A via a connection portion 33 . The connection part 33 and the scribing head 34 move along the guide part 31A. The connecting portion 33 and the scribing head 34 are connected via a lifting mechanism (not shown). Driven by the lifting mechanism, the scribing head 34 moves in the vertical direction relative to the connecting portion 33 . A holder unit 40 is detachably attached to the scribing head 34 via a holder joint 35 .

The main elements constituting the holder unit 40 shown in FIG. 2 are the holder 50 , the scribing wheel 60 , and the pin 70 (hereinafter referred to as “pin 70 ”) of the scribing wheel 60 . Since the scribing wheel 60 is a consumable item, it is replaced periodically. In one example, the scribing wheel 60 is replaced by replacing only the scribing wheel 60 or the holder unit 40 .

An example of a material constituting the holder 50 is magnetic metal. The holder 50 is generally cylindrical or prism shaped. The holder 50 includes a groove portion 51 for accommodating a part of the scribing wheel 60 , and a support hole 52 penetrating through the holder 50 so as to communicate with the groove portion 51 . The groove portion 51 opens to the brittle material substrate GB in a state where the holder 50 is attached to the scribing head 34 (see FIG. 1 ).

The pin 70 supports the scoring wheel 60 . The pin 70 is inserted into the support hole 52 . One end portion 70A of the pin 70 has a tapered shape. The relationship between the support hole 52 and the pin 70 can be selected arbitrarily. In the 1st example, pin 70 with no The method is fixed to the support hole 52 in such a way that it can rotate relative to the support hole 52. The fixing method is pressing or following. In the case of the first example, it is preferable that the maximum inner diameter of the support hole 52 is substantially equal to the maximum outer diameter of the pin 70 . In the second example, the pin 70 is inserted into the support hole 52 in such a manner that it cannot rotate relative to the support hole 52 . In the case of the second example, the maximum inner diameter of the support hole 52 is slightly larger than the maximum outer diameter of the pin 70 . Hereinafter, the direction in which the central axis of the pin 70 extends is referred to as the pin axial direction.

Examples of materials constituting the scribing wheel 60 are sintered diamond (Poly Crystalline Diamond), cemented carbide, single crystal diamond and polycrystalline diamond. In another example, a hard material may be applied to the scribing wheel 60 . The hard material is, for example, diamond.

1mm~

7mm之範圍內。於一例中，劃線輪60之外徑為

2mm。劃線輪60之厚度之一例為0.64mm。再者，槽部51之厚度方向DT上之長度，即，槽部51之內表面中於厚度方向DT相向之2個面51A、51B之厚度方向DT之間之距離之一例為0.66mm。 The scribing wheel 60 is mainly divided into a main body 61 and a blade tip 62 . The main body portion 61 is in the shape of a disc, and is the radially inner portion of the scribing wheel 60 than the blade tip portion 62 . The blade tip portion 62 is V-shaped in cross section, and is formed over the entire circumference of the outer peripheral portion of the scribing wheel 60 . The so-called V-shaped cross section refers to a shape that is tapered toward the front end of the outer periphery of the scribing wheel 60 in the section of the scribing wheel 60 cut by a plane along the thickness direction of the scribing wheel 60 (hereinafter referred to as "thickness direction DT"). In the following description, a cross section perpendicular to a plane parallel to the radial direction of the scribing wheel 60 is referred to as an orthogonal cross section. In a preferred example, an example of the outer diameter of the marking wheel 60 is included in

1mm~

Within the range of 7mm. In one example, the outer diameter of the marking wheel 60 is

2mm. An example of the thickness of the scribing wheel 60 is 0.64 mm. The length in the thickness direction DT of the groove portion 51, that is, an example of the distance in the thickness direction DT between the two surfaces 51A and 51B facing each other in the thickness direction DT on the inner surface of the groove portion 51 is 0.66 mm.

An insertion hole 63 penetrating through the body portion 61 in the thickness direction DT is formed at the center portion of the body portion 61 . A pin 70 is inserted into the insertion hole 63 . The body portion 61 has a first side forming one end of the insertion hole 63 surface 61A, and the second side surface 61B forming the other end of the insertion hole 63 . The portion of the first side surface 61A accommodated in the groove portion 51 faces the surface 51A of the groove portion 51 with a predetermined gap SA interposed therebetween. The portion of the second side surface 61B accommodated in the groove portion 51 faces the surface 51B of the groove portion 51 with a predetermined gap SB therebetween. The relationship between the size of the gap SA and the size of the gap SB in the thickness direction DT can be arbitrarily selected according to the position and size of the regulating portion 80 described below. In the first example shown in FIG. 2, the size of the gap SA in the thickness direction DT is equal to the size of the gap SB. In the second example, the size of the gap SA in the thickness direction DT is different from the size of the gap SB.

The size of the gaps SA and SB in the thickness direction DT can be set arbitrarily. In a preferred example, the size of the gaps SA, SB in the thickness direction DT is based on the ease of restraining the inclination of the scribing wheel 60 in the groove portion 51 of the holder 50 in the thickness direction DT, and the foreign matter on the gaps SA, SB. It depends on the difficulty of SB blockage. An example of the foreign matter is chips of the brittle material substrate GB generated by the formation of the scribe line. An example of the maximum size of the gaps SA and SB in the thickness direction DT is 10 μm, respectively. When the size of the gaps SA and SB is 10 μm or less, it is easy to suppress the inclination of the scribing wheel 60 in the groove portion 51 of the holder 50 in the thickness direction DT. An example of the minimum value of the size of the gaps SA and SB in the thickness direction DT is 2 μm, respectively. When the size of the gaps SA and SB is 2 μm or more, it is difficult for foreign matter to clog the gaps SA and SB. Furthermore, the scribing wheel 60 and the holder 50 are less likely to interfere. An example of a desirable range of the total size of the gaps SA and SB in the thickness direction DT is 4 μm to 20 μm.

In the step of forming scribe lines on the brittle material substrate GB, the holder unit 40 scans in a specific scanning direction in a state where the scribing wheel 60 is pressed against the surface of the brittle material substrate GB. As the scanning method, a method of moving the holder unit 40 relative to the brittle material substrate GB, using A method of moving the brittle material substrate GB relative to the holder unit 40, and a method of combining these methods. When scribing the brittle material substrate GB, not only the first reaction force including the component acting in the opposite direction to the scanning direction acts on the scribing wheel 60, but also the second reaction force including the pin axial component acts. This is mainly caused by the inhomogeneity of the surface of the brittle material substrate GB. Inhomogeneity of the surface texture is caused by, for example, a plurality of microscopic irregularities distributed unevenly on the surface, curvature of the surface, and the like. The second reaction force includes a reaction force acting on one side of the pin axis, that is, the first pin axis, and a reaction force acting on the other side of the pin axis, that is, the second axis. Since the concave-convex shape of the surface of the brittle material substrate GB is different for each site, the direction and intensity of the second reaction force acting on the scribing wheel 60 change as the scribing wheel 60 moves forward. Since the scribing wheel 60 is not fixed to the pin 70, the scribing wheel 60 is displaced relative to the pin 70 in the pin axial direction as the second reaction force acts on the scribing wheel 60. In the following description, the movement of the scribing wheel 60 relative to the pin 70 in the pin axial direction is referred to as "wheel axial displacement".

The direction and amount of displacement of the wheel shaft mainly depend on the relationship between the strength of the second reaction force acting on the first pin shaft and the strength of the second reaction force acting on the second pin shaft. A non-linear scoring line is formed due to axial displacement of the wheel. By suppressing this displacement, it becomes difficult to form a non-linear scribed line. The cage unit 40 has a displacement suppression structure that suppresses axial displacement of the wheel. The displacement suppressing structure includes a restricting portion 80 provided on the pin 70 and a restricted portion 90 provided on the scribing wheel 60 .

The configuration of the restricting portion 80 can be selected arbitrarily. In the example shown in FIG. 2 , the restricting portion 80 includes a concave portion 81 formed on the outer periphery of the pin 70 . Therefore, the structure of the restricting part 80 is simple. The concave portion 81 is a portion formed by, for example, grinding the outer peripheral portion of the pin 70 so as to be in contact with the restricted portion 90 , and does not include minute unevenness formed during the manufacture of the pin 70 . The concave portion 81 goes around the outer circumference of the pin 70 once. The position of the recess 81 in the axial direction of the pin 70 can be selected arbitrarily. In one example, the concave portion 81 is provided at the center of the pin 70 in the axial direction. The surface 81A of the concave portion 81 is a curved surface that is recessed toward the central axis side of the pin 70 with respect to the outer peripheral surface 71 of the pin 70 . Therefore, stress concentration is less likely to occur in the concave portion 81 . The surface 81A on the orthogonal section has a specific radius of curvature RA.

The diameter of the pin 70 is included in the range of 0.4mm~1.1mm. The depth XA of the concave portion 81 is included in the range of 0.5 μm˜3.0 μm. The depth XA of the concave portion 81 is represented by, for example, the distance between the straight line LA passing through the outer peripheral surface 71 of the pin 70 and the apex 81B of the concave portion 81 on an orthogonal cross section.

The width XB of the concave portion 81 on the pin axis is equal to the thickness of the scribing wheel 60 . The width XB of the concave portion 81 is represented by the distance between one edge and the other edge of the concave portion 81 on the straight line LA passing through the outer peripheral surface 71 on the orthogonal section. The width of the concave portion 81 is equal to or greater than the thickness of the scribing wheel 60 . The width of the concave portion 81 is within the range of 0.4 mm to 1.2 mm.

The restricted portion 90 includes a convex portion 91 inserted into the concave portion 81 . Therefore, the configuration of the restricted portion 90 is simple. The surface 91A of the convex portion 91 is a curved surface formed between the first side surface 61A and the second side surface 61B in the thickness direction DT and defined by a specific radius of curvature RB. Therefore, stress concentration is less likely to occur on the convex portion 91 . The relationship between the curvature radius RA of the concave portion 81 and the curvature radius RB of the convex portion 91 can be selected arbitrarily. In the first example shown in FIG. 2 , the curvature radius RA of the concave portion 81 is larger than the curvature radius RB of the convex portion 91 . In the case of the first example, since the surface 81A of the concave portion 81 is in line contact with the surface 91A of the convex portion 91, the frictional resistance at the time of scribing becomes small. In the second example, the curvature radius RA of the concave portion 81 is equal to or smaller than the curvature radius RB of the convex portion 91 . The height HA of the convex portion 91 is included in the range of 0.1 μm to 1.0 μm, and the height HA of the convex portion 91 is included in the range of 0.1 μm to 0.5 μm inside. The height HA of the convex portion 91 is represented by the distance between the straight line LB passing through the boundary between the side surfaces 61A, 61B and the surface 91A of the main body portion 61 and the apex 91B of the convex portion 91 . The minimum inner diameter of the protrusion 91 of the insertion hole 63 of the marking wheel 60 is slightly larger than the maximum outer diameter of the pin 70 .

The function and effect of the holder unit 40 will be described. In the state where the scribing wheel 60 is pressed against the brittle material substrate GB and is not scanned, the apex 91B of the restricted portion 90 of the scribing wheel 60 is in contact with the restricting portion 80 of the pin 70 in the orthogonal section. Actually, a certain range of the restricted portion 90 is in line contact with the restricting portion 80 . The restricted portion 90 receives the reaction force acting in the pressing direction from the restricting portion 80 . When the second reaction force acts on the scribing wheel 60 as the scribing wheel 60 scans, the restricting portion 80 of the pin 70 receives the second reaction force intended to move the restricted portion 90 in the pin axial direction. Therefore, the axial displacement of the scribing wheel 60 is hindered, and the scribing wheel 60 advances along the scanning direction to form a linear scribing line on the brittle material substrate GB. Therefore, scribe lines along the scanning direction of the holder unit 40 can be easily formed.

(variation example)

The above-mentioned embodiment is an illustration of the form which the holder unit related to this invention and its scribing wheel and pin can take, and is not intended to limit the form. The retainer unit, its scribing wheel, and the pins according to the present invention may take different forms from those illustrated in the embodiments. One example is a form in which a part of the configuration of the embodiment is replaced, changed, or omitted, or a new configuration is added to the embodiment. An example of a modification example of the embodiment is shown below.

‧The structure of the restricting part 80 and the restricted part 90 can be changed arbitrarily. FIG. 3 shows the structure of the cage unit 40 including the restricting portion 180 and the restricted portion 190 of the first modification. The restricting part 180 contains the shape A protrusion 181 is formed on the outer periphery of the pin 70 . The convex portion 181 is a portion protruding from the outer peripheral surface 71 of the pin 70 so as to be able to contact the restricted portion 190 . The convex part 181 is integrally provided over the position facing the insertion hole 63 of the scribing wheel 60 in the outer peripheral surface 71 of the pin 70 . The position where the protrusion 181 is provided in the axial direction of the pin 70 can be selected arbitrarily. In one example, the concave portion 181 is disposed at the center of the groove portion 51 in the axial direction. The surface 181A of the convex portion 181 is a curved surface defined by a specific radius of curvature RA. The restricted portion 190 includes a concave portion 191 into which the convex portion 181 is inserted. The concave portion 191 is a portion formed by, for example, grinding the insertion hole 63 , and does not include minute irregularities formed during the manufacture of the scribing wheel 60 . The surface 191A of the concave portion 191 is a curved surface formed between the first side surface 61A and the second side surface 61B in the thickness direction DT and defined by a specific radius of curvature RB. Furthermore, in the first modification example, the retainer 50 is not formed as an integral member, but is formed as a member that is divided into a portion including the surface 51A of the groove portion 51 and a portion including the surface 51B, so that the retainer can be easily assembled. Unit 40.

The relationship between the curvature radius RA of the surface 181A and the curvature radius RB of the surface 191A can be selected arbitrarily. In the first example shown in FIG. 3 , the curvature radius RA of the surface 181A is smaller than the curvature radius RB of the surface 191A. In the case of the first example, since the surface 181A is in line contact with the surface 191A, the frictional resistance at the time of scribing becomes small. In the second example, the radius of curvature RA of the surface 181A is equal to the radius of curvature RB of the surface 191A, or smaller than the radius of curvature RB of the surface 191A.

FIG. 4 shows the configuration of a cage unit 40 including a restricting portion 280 and a restricted portion 290 according to a second modification. The limiting portion 280 includes a concave portion 281 formed on the outer peripheral surface 71 of the pin 70 . The concave portion 281 is a portion formed by grinding the outer peripheral surface 71 of the pin 70 so as to be in contact with the restricted portion 290 , and does not include minute unevenness formed during the manufacture of the pin 70 . The concave portion 281 is integrally provided over the position facing the insertion hole 63 of the scribing wheel 60 in the outer peripheral surface 71 of the pin 70 . Shaft of pin 70 The upward position of the concave portion 281 can be selected arbitrarily. In one example, the concave portion 281 is disposed at the center of the pin 70 in the axial direction. The recess 281 is a groove including corners. In the example shown in FIG. 4, the concave portion 281 is a V-shaped groove. The restricted portion 290 includes a convex portion 291 inserted into the concave portion 281 . The convex portion 291 is formed between the first side surface 61A and the second side surface 61B in the thickness direction DT. The convex portion 291 is a protrusion including corners. In the example shown in FIG. 4, the convex portion 291 is a V-shaped protrusion. The minimum inner diameter of the protrusion 291 of the insertion hole 63 of the marking wheel 60 is slightly larger than the maximum outer diameter of the pin 70 .

‧The configuration of the holder unit 40 can be changed arbitrarily. In one example, the restricted portion 90 is omitted from the holder unit 40 . In this case, it is preferable that the width of the restricting portion 80 is larger than the width of the scribing wheel 60 and smaller than the width of the groove portion 51 . Also, the shapes of the restricting portion 80 and the portion to be regulated 90 are not limited to the configurations disclosed in the above-mentioned embodiments, and for example, may have a shape in which a part has a flat portion. Also, the shape of the convex portion 91 and the shape of the concave portion 81 may not match. In this case, it is preferable that the width of the concave portion 81 is larger than the width of the convex portion 91 .

40‧‧‧Retainer unit

50‧‧‧Retainer

51‧‧‧groove

51A, 51B‧‧‧face

52‧‧‧Support hole

60‧‧‧Scribing wheel

61‧‧‧Body Department

61A‧‧‧1st side

61B‧‧‧2nd side

62‧‧‧Tool tip

63‧‧‧Insertion hole

70‧‧‧Pin

70A‧‧‧one end

71‧‧‧outer peripheral surface

80‧‧‧Restricted Department

81‧‧‧Concave

81A‧‧‧face

81B‧‧‧Apex

90‧‧‧restricted part

91‧‧‧convex part

91A‧‧‧face

91B‧‧‧Apex

DT‧‧‧thickness direction

GB‧‧‧brittle material substrate

HA‧‧‧Height

LA‧‧‧straight line

LB‧‧‧straight line

SA‧‧‧Gap

SB‧‧‧Gap

XA‧‧‧depth

XB‧‧‧width

Claims (6)

A pin for a scribing wheel, which supports the scribing wheel, and has a restricting portion that prevents the movement of the scribing wheel relative to the pin in the axial direction of the pin; the restricting portion includes a recess formed on the outer periphery of the pin . The pin of the scribing wheel according to claim 1, wherein the surface of the above-mentioned concave part is a curved surface. A scribing wheel supported by a pin of the scribing wheel according to claim 1, and having a regulated portion in contact with the regulated portion; the regulated portion includes a convex portion inserted into the concave portion. For example, the scribing wheel of claim 3 is a scribing wheel supported by the pins of the scribing wheel of claim 2, and the surface of the above-mentioned convex part is a curved surface. A holder unit comprising the pin of the scribing wheel of claim 1 or 2, and the scribing wheel of claim 3 or 4. The retainer unit according to claim 5 is provided with the pin of the scribing wheel of claim 2 and the scribing wheel of claim 4, and the radius of curvature of the concave portion is greater than the radius of curvature of the restricted portion.

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