Sliding member and sliding mechanism

Abstract

Provided is a sliding member, which is reduced in friction under sliding conditions of high load and high speed under an oilless condition, and is excellent in wear resistance. The sliding member includes: a shaft; and at least one intervening member, in which: the at least one intervening member is located between the shaft and a bearing, and is operable independently of the shaft; and at least one surface of the at least one intervening member on a shaft side includes a sliding surface under one of a radial load and an axial load.

Claims

1. A sliding part comprising: a shaft; and two or more intervening members, each located between the shaft and a bearing, and each being operable independently of the shaft and the bearing, the two or more intervening members having a first intervening member facing the shaft and a second intervening member having a surface facing the bearing, wherein at least one surface of the two or more intervening members on a shaft side comprises a sliding surface under one of a radial load and an axial load, and wherein a material for forming the first intervening member is different from a material for forming the second intervening member.

2. The sliding part according to claim 1, wherein: the shaft comprises a rotary shaft; at least one intervening member of the two or more intervening members is rotatable independently of the shaft and the bearing; and at least one surface of the at least one intervening member on the shaft side comprises a sliding surface under a radial load.

3. The sliding part according to claim 2, wherein the at least one intervening member is configured to rotate in a same direction as the shaft under a radial load.

4. The sliding part according to claim 1, wherein at least one intervening member of the two or more intervening members comprises a self-lubricating material.

5. The sliding part according to claim 4, wherein the self-lubricating material is selected from the group consisting of polyacetal, polytetrafluoroethylene, polyethylene, polyamide, polyimide, and polyphenylene sulfide.

6. The sliding part according to claim 1, wherein at least one intervening member of the two or more intervening members comprises a member in which a metal material has, on one surface or both surfaces thereof, a film formed of one of diamond-like carbon, WS.sub.2, MoS.sub.2, and graphite.

7. The sliding part according to claim 1, wherein a material for forming the sliding surface is different from a material for forming a surface facing the sliding surface.

8. The sliding part according to claim 1, wherein a friction coefficient on the sliding surface is different from a friction coefficient on a surface facing the sliding surface.

9. The sliding part according to claim 1, wherein a friction coefficient of the second intervening member on the surface facing the bearing is different from a friction coefficient of the bearing on a surface facing the second intervening member.

10. An apparatus comprising: the sliding part of claim 1; and a conveying mechanism configured to convey a sheet through utilization of rotation of the shaft in the sliding mechanism.

Description

BRIEF DESCRIPTION OF DRAWINGS

(1) FIG. 1A, FIG. 1B, FIG. 1C, and FIG. 1D are views for illustrating an example of a sliding mechanism of the present invention.

(2) FIG. 2A and FIG. 2B are views for illustrating another example of the sliding mechanism of the present invention.

(3) FIG. 3 is a graph for showing a change in friction coefficient in Example 1 and Comparative Example 1.

(4) FIG. 4 is a view for illustrating an example of a conveying apparatus of the present invention.

DESCRIPTION OF EMBODIMENTS

(5) The present invention is described in detail below by describing embodiments of the present invention.

(6) FIG. 1A to FIG. 1D are views for illustrating an example of a sliding mechanism of the present invention. FIG. 1A is a schematic perspective view, and FIG. 1B to FIG. 1D are each a sectional view of a portion enclosed by the dotted line in FIG. 1A in a plane parallel to the drawing sheet.

(7) The sliding mechanism illustrated in FIG. 1A includes: a sliding member 4; and a bearing 3 for supporting the sliding member 4, and the sliding member 4 is configured to slide with respect to the bearing 3. The sliding member 4 includes: a shaft 1; and at least one intervening member 2, in the example illustrated in FIG. 1A to FIG. 1D, one intervening member 2. The shaft 1 is a rotary shaft configured to rotate about its shaft center. The intervening member 2 is located between the shaft 1 and the bearing 3, and is operable, in the example illustrated in FIG. 1A to FIG. 1D, is rotatable, independently of the shaft 1. In addition, a surface of the intervening member 2 on a shaft 1 side is a sliding surface under a radial load acting in a direction vertical to the shaft 1. Therefore, the intervening member 2 is configured to rotate in the same direction as the shaft 1 and slide with respect to the shaft 1 and the bearing 3 under a radial load.

(8) <Shaft 1>

(9) The shaft 1 is a rotary shaft in FIG. 1A to FIG. 1D, but is not limited thereto. The shaft 1 may be a rocking shaft configured to pivot with respect to a bearing, or a slide shaft configured to reciprocate with respect to the bearing.

(10) The shape of the shaft 1 is a cylindrical shape in FIG. 1A to FIG. 1D, but is not particularly limited. For example, the shaft 1 may have a hollow tubular shape. In addition, the surface of the shaft 1 may be subjected to surface processing for forming, for example, fine irregularities having a striped pattern, a dotted pattern, or the like.

(11) A material for forming the shaft 1 is not particularly limited, and examples thereof include a metal, a resin, and ceramics. However, in consideration of the use conditions of high load, a hard material is preferred, and a SUS material, a SUM material, and the like are preferred.

(12) In order to prevent corrosion and oxidation, the surface of the shaft 1 may be subjected to surface treatment, for example, plating such as Ni plating, Cr plating, gold plating, silver plating, copper plating, and zinc plating, or thermal spraying of an alloy or ceramics. A material to be used for the surface treatment is not necessarily a single substance. Different kinds of substances may be present in a scattered manner, or different kinds of materials may be formed on the pattern.

(13) <Intervening Member 2>

(14) The intervening member 2 is a member which is located between the shaft 1 and the bearing 3, and prevents the shaft 1 from being brought into contact with the bearing 3. The intervening member 2 is not fixed to the shaft 1, and is rotatable independently of the shaft 1. In addition, the intervening member 2 is not fixed to the bearing 3, and is rotatable independently of the bearing 3. Further, the surface of the intervening member 2 on the shaft 1 side is a sliding surface under a radial load, and the intervening member 2 is configured to rotate in the same direction as the shaft 1 and slide with respect to the shaft 1 and the bearing 3 under a radial load. Therefore, when a relative speed between the shaft 1 and the bearing 3 is defined as V.sub.0, a relative speed between the shaft 1 and the intervening member 2 is defined as V.sub.1, and a relative speed between the intervening member 2 and the bearing 3 is defined as V.sub.2, the relationship V.sub.0=V.sub.1+V.sub.2 (where V.sub.1, V.sub.2>0) is established.

(15) When the intervening member 2 is not provided and the shaft 1 is configured to slide while being brought into contact with the bearing 3, the allowable PV value of the bearing 3 needs to be considered with V.sub.0, and hence a load P is limited. When a used load is higher than the limited load P, the allowable PV value of the bearing 3 is exceeded, and hence it is necessary to change the bearing 3 and select a material withstanding higher load and higher speed. However, as described above, few materials usable at high speed under high load exhibit low friction at present.

(16) In the present invention, the intervening member 2 is provided, and hence V.sub.0 can be considered by being divided into V.sub.1 and V.sub.2, which enables a local reduction in speed V in the PV value. Therefore, the bearing 3 can be used even under the conditions in which the allowable PV value of the bearing 3 is exceeded as the entirety of the sliding member. That is, a material exhibiting low friction can be selected even when the allowable PV value has a narrow range.

(17) Further, when the intervening member 2 is provided, the sliding member 4 has formed therein a sliding surface other than a sliding surface with respect to the bearing 3 (a surface of the intervening member 2 on a bearing 3 side), and thus includes a plurality of sliding surfaces. Therefore, even when some of the sliding surfaces are increased in friction coefficient owing to some cause, other sliding surfaces slide, and hence an abrupt increase in friction is suppressed as the entirety of the sliding member 4, and a stable friction coefficient is obtained.

(18) A material for forming the intervening member 2 is not particularly limited, and examples thereof include a metal, a resin, and ceramics. Examples of the resin include engineering plastics such as polyether ether ketone (PEEK), polyacetal (POM), polytetrafluoroethylene (PTFE), polyethylene (PE), polyamide (PA), polyimide (PI), and polyphenylene sulfide (PPS). Examples of the metal include SUS, SUM, Cu, Al, and Ag. The material for forming the intervening member 2 is preferably a self-lubricating material, which exhibits a self-lubricating property. Examples of such self-lubricating material include: resins such as POM, PTFE, PE, PA, PI, and PPS; and metals such as soft metals, e.g., Cu, Al, and Ag. In addition, the following resin may also be used: the resin mixed with a glass filler, graphite, or a fluororesin, the resin mixed with oil or grease, or the resin mixed with both of the materials. One kind of those materials may be used alone, or two or more kinds thereof may be used as a mixture.

(19) In addition, the material may be subjected to surface coating. A specific example thereof is the metal material of the SUS base material, Al base material, or the like having a film formed on one surface or both surfaces thereof and formed of a solid lubricant, such as diamond-like carbon (DLC), WS.sub.2, MoS.sub.2, graphite, POM, PTFE, or PE. The surface coating may be film formation with a pattern having a periodic structure, and a film may be formed by mixing a plurality of kinds of solid lubricants.

(20) In order to prevent a situation in which the intervening member 2 rotates integrally with the shaft 1 without sliding with respect to the shaft 1, it is preferred that a material for forming the sliding surface (the surface of the intervening member 2 on the shaft 1 side) be different from a material for forming a surface facing the sliding surface (the surface of the shaft 1), or that a friction coefficient on the sliding surface be different from a friction coefficient on the surface facing the sliding surface. In addition, in order not to suppress the rotation of the intervening member 2 by the bearing 3, it is preferred that a material for forming the sliding member 4 on a surface facing the bearing 3 (the surface of the intervening member 2 on the bearing 3 side) be different from a material for forming the bearing 3 on a surface facing the sliding member 4, or that the friction coefficient of the sliding member 4 on the surface facing the bearing 3 be different from the friction coefficient of the bearing 3 on the surface facing the sliding member 4.

(21) The shape of the intervening member 2 is a tubular shape covering the shaft 1 in a circumferential direction in FIG. 1A to FIG. 1D, but is not particularly limited. The intervening member 2 may have a flat surface as illustrated in FIG. 1B, but it is also appropriate that the intervening member 2 be subjected to surface processing for forming, for example, fine irregularities having a striped pattern, a dotted pattern, or the like, or have a plurality of holes on its side surface. In addition, as illustrated in FIG. 1C, the intervening member 2 may include a convex portion 5 on the surface on the shaft 1 side. In this case, in order to prevent a load from concentrating only on the convex portion 5, the shaft 1 preferably includes a concave portion 5 in which the convex portion 5 is fitted. In addition, in a state in which the convex portion 5 is fitted in the concave portion 5 with no gap, there is a risk in that the intervening member 2 rotates integrally with the shaft 1 without sliding with respect to the shaft 1, and V.sub.1 becomes 0. Therefore, it is preferred that play exist, and the width of the convex portion 5 be larger than that of the concave portion 5. In addition, as illustrated in FIG. 1D, the intervening member 2 may include, on both ends, flange portions 6 projecting on the bearing 3 side. It is also appropriate to form the flange portion 6 on one end or in the whole or part of the end in a circumferential direction, or form a plurality of flange portions 6 so as to be apart from each other in the circumferential direction. In the case of forming the flange portions 6 on both the ends, it is preferred to form a gap between the flange portions 6 and the bearing 3. In the case of forming the flange portion 6 without a gap, there is a risk in that the bearing 3 and the intervening member 2 are fixed to each other, rotation of the intervening member 2 is suppressed, V.sub.2 becomes 0, and the effects of the present invention are not obtained.

(22) The inner diameter of the intervening member 2 is preferably from 100.5% to 110% with respect to the outer diameter of the shaft 1. When the diameters fall within such range, a gap is formed between the intervening member 2 and the shaft 1, and a situation in which the intervening member 2 rotates integrally with the shaft 1 without sliding with respect to the shaft 1 is prevented. In addition, the outer diameter of the intervening member 2 is preferably from 80% to 99.95% with respect to the inner diameter of the bearing 3. When the diameters fall within such range, a situation in which rotation of the intervening member 2 is suppressed by the bearing 3 can be prevented. The inner diameter of the intervening member 2 is preferably 50 mm or less. The use of an intervening member having an inner diameter of more than 50 mm increases a gap, and thus reduces the ratio of a contact portion, with the result that the effects of the present invention are difficult to obtain. In addition, the thickness of the intervening member 2 is preferably 10 mm or less, and a smaller thickness is more preferred.

(23) FIG. 2A and FIG. 2B are views for illustrating another example of the sliding mechanism of the present invention. FIG. 2A is a sectional view in a plane vertical to the shaft 1, and FIG. 2B is a partial enlarged view of FIG. 2A. The sliding mechanism illustrated in FIG. 2A and FIG. 2B includes an intervening member A 21 and an intervening member B in the stated order from the shaft 1 side. The intervening member A 21 and the intervening member B 22 are rotatable independently of each other, and are each configured to rotate in the same direction as the shaft 1 under a radial load. In addition, at least one of a surface of the intervening member A 21 on the shaft 1 side or a surface of the intervening member B 22 on the shaft 1 side is a sliding surface under a radial load. For example, in the case where the surface of the intervening member A 21 on the shaft 1 side is a sliding surface, the intervening member A 21 is configured to slide with respect to the shaft 1 and the intervening member B 22 is configured to slide with respect to the bearing 3 under a radial load. The surface of the intervening member B 22 on the shaft 1 side may be a sliding surface or may not be the sliding surface under a radial load. That is, the intervening member B 22 may be configured to slide with respect to the intervening member A 21, or may be configured to rotate integrally with the intervening member A 21 without sliding with respect to the intervening member A 21. That is, when a relative speed between the intervening member A 21 and the intervening member B 22 is defined as V.sub.3, the relationship V.sub.30 is established. It should be noted that, under the conditions of such high load that the allowable PV value is exceeded even when V.sub.0 is divided into V.sub.1 and V.sub.2, it is preferred that the surface of the intervening member B 22 on the shaft 1 side be a sliding surface under a radial load, that is, the intervening member B 22 be configured to slide with respect to the intervening member A 21 and the relationship V.sub.3>0 be established. In order to allow the intervening member B 22 to slide with respect to the intervening member A 21, it is preferred that a material for forming the intervening member A 21 on a surface facing the intervening member B 22 be different from a material for forming the intervening member B 22 on a surface facing the intervening member A 21, or that the friction coefficient of the intervening member A 21 on the surface facing the intervening member B 22 be different from the friction coefficient of the intervening member B 22 on the surface facing the intervening member A 21.

(24) It is also appropriate to form three or more layers or four or more layers of intervening members 2. In the case of forming three layers, a layer of an intervening member C may be added between the intervening member A 21 and the intervening member B 22 of the sliding mechanism illustrated in FIG. 2A and FIG. 2B. In this case, when relative speeds between: the intervening member C added; and the intervening member A 21 and the intervening member B 22 are defined as V.sub.2C and V.sub.3C, respectively, the relationship V.sub.2C, V.sub.3C>0 is preferably established. In this case, it is preferred that, in the intervening member C, a material for forming a sliding surface with respect to the intervening member A be different from a material for forming a sliding surface with respect to the intervening member B. In addition, in the case of adding the intervening member C, it is acceptable that the intervening member A and the intervening member B be formed of the same material when the materials of the sliding surfaces of the intervening member C are different from each other.

(25) <Bearing 3>

(26) The bearing 3 is a member for supporting the shaft 1 through the intervening member 2, and is a member to be used by being fixed to a framework, a housing, or the like.

(27) The shape of the bearing 3 is a tubular shape covering the intervening member 2 in a circumferential direction in FIG. 1A to FIG. 1D and a flat plate shape in FIG. 2A and FIG. 2B, but is not particularly limited. For example, a semi-cylindrical shape, a shape having a curvature, or the like may be adopted. The shape of the bearing 3 is appropriately determined in accordance with the shape of the intervening member 2, and is selected in view of the degree of freedom of the shaft 1 in consideration of a load because the load changes a contact area. In addition, in order to support the shaft 1, a plurality of bearings 3 may be provided to be dispersedly arranged at several positions. In addition, the surface of the bearing 3 brought into contact with the intervening member 2 may be subjected to surface processing for forming, for example, fine irregularities having a striped pattern, a dotted pattern, or the like.

(28) A material for forming the bearing 3 is generally selected and determined depending on the use conditions of the load (P) and the speed (V), and the material of the intervening member 2. The material for forming the bearing 3 is not particularly limited, and examples thereof include a metal, a resin, and ceramics. A hard material having less strain under high load is preferred. In addition, a material having good moldability is preferably used for fixation to a framework, a housing, or the like. Examples of the resin include engineering plastics such as PEEK, POM, PTFE, PE, PA, PI, and PPS. Examples of the metal include SUS, SUM, Cu, Al, and Ag. In addition, the material may be the metal material having a resin layer formed on its surface.

(29) In order to prevent corrosion and oxidation, the surface of the bearing 3 brought into contact with the intervening member 2 may be subjected to surface treatment, for example, plating such as Ni plating, Cr plating, gold plating, silver plating, copper plating, and zinc plating, or thermal spraying of an alloy or ceramics. In addition, the metal material and the resin material may be mixed and dispersed to form a film in which different kinds of materials are present in a scattered manner.

(30) The present invention has been described above by taking as examples the sliding member and sliding mechanism in which the surface of the intervening member 2 on the shaft 1 side is a sliding surface under a radial load. However, the present invention can be applied to a sliding member and sliding mechanism in which the surface of the intervening member 2 on the shaft 1 side is a sliding surface under an axial load.

(31) The sliding mechanism of the present invention can be used in an oilless state. Therefore, the sliding mechanism does not require an oil tank for retaining an oil or an external mechanism for adding the oil in drops. In addition, the sliding mechanism does not require a shielding mechanism for preventing scattering or leaking of the oil.

(32) The sliding mechanism according to the embodiments of the present invention can be applied to an apparatus including a conveying mechanism, such as a 2D or 3D printer. As an example of such apparatus, a configuration of a 3D printer 7 utilizing an electrophotographic system is schematically illustrated in FIG. 4. The 3D printer 7 according to an embodiment of the present invention is configured to form a three-dimensional article through the following process. First, a laser 8 is radiated to an intermediate transfer drum 10, to form a latent image of a slice image of the article on the intermediate transfer drum 10. An article forming material is supplied from a container 9 for accommodating the article forming material to the transfer drum 10, and thereby a slice image of the article forming material is formed on the transfer drum 10. The formed slice image is transferred from the transfer drum 10 to a convey belt 11, and conveyed to a work holding portion 15 by rotation of convey rollers 12 and 13.

(33) The slice image of the article forming material is thermally fused onto an intermediate laminate 16 with a thermal pressure bonding unit 14 through the convey belt 11, and the intermediate laminates 16 are laminated sequentially to form the three-dimensional article.

(34) The 3D printer 7 includes the convey rollers (12, 13) and the convey belt 11 as a conveying mechanism for the slice image, and may use the sliding mechanism of the present invention for bearing portions of the convey rollers (12, 13).

(35) In addition, the sliding mechanism of the embodiments of the present invention can be applied to one configured to convey an article through utilization of rotation of the shaft of the sliding mechanism: a bearing portion of the intermediate transfer drum 10 or bearing portions of other roller members. The sliding mechanism of the embodiments of the present invention can also be applied to a conveying apparatus configured to convey an article including a paper medium etc., such as a 2D printer.

Example 1

(36) A sliding mechanism illustrated in FIG. 1A and FIG. 1B was produced. It should be noted that a sliding member including two intervening members illustrated in FIG. 2A and FIG. 2B was used as the sliding member. The details of the members are shown in Table 1.

(37) TABLE-US-00001 TABLE 1 Material Shape Size Shaft SUS303 Cylindrical Diameter: 10 mm shape Intervening PTFE Tubular Inner diameter: member A shape 10.1 mm Thickness: 1 mm Outer diameter: 12.1 mm Length: 10 mm Intervening PEEK Tubular Inner diameter: member B shape 12.2 mm Thickness: 1 mm Outer diameter: 14.2 mm Length: 10 mm Bearing SUS304 Tubular Inner diameter: shape 14.3 mm Length: 10 mm

(38) It should be noted that the inner diameter of the intervening member A 21 is 101% with respect to the diameter of the shaft 1, and the outer diameter of the intervening member B 22 is 99.3% with respect to the inner diameter of the bearing 3.

(39) The resultant sliding mechanism was measured for a friction coefficient. Specifically, the shaft 1 was allowed to rotate with a motor under the following conditions, and torque was measured. A load to be applied was measured concurrently with a load cell. The friction coefficient was calculated from the measured torque, the diameter of the shaft, and the load. In addition, the case where the amount of wear was small was evaluated as , and the case where the amount of wear was large was evaluated as x. The results are shown in Table 2.

(40) Shaft rotation speed: 100 rpm

(41) Load: 20 N

(42) Atmosphere: air atmosphere

(43) Temperature: room temperature

Example 2

(44) A sliding mechanism was produced and evaluated in the same manner as in Example 1 except that the materials of the intervening member A 21, the intervening member B 22, and the bearing 3 were changed to POM, SUS304, and PTFE, respectively. The results are shown in Table 2.

Example 3

(45) A sliding mechanism was produced and evaluated in the same manner as in Example 1 except that its sectional shape was changed as illustrated in FIG. 1D by using, as the intervening member A 21, a member having a length of 12 mm and including, on both ends, the flange portions 6 each having a thickness of 0.5 mm and projecting on the bearing 3 side. The results are shown in Table 2.

Example 4

(46) A sliding mechanism was produced and evaluated in the same manner as in Example 1 except that the inner diameter of the bearing 3 was changed to 12.2 mm without forming the intervening member B 22. The results are shown in Table 2.

Example 5

(47) A sliding mechanism was produced and evaluated in the same manner as in Example 4 except that the material of the intervening member A 21 was changed to SUS304, and a DLC film having a thickness of 2 m was formed on the surfaces of the intervening member A 21 on the shaft 1 side and on the bearing 3 side. The results are shown in Table 2.

Comparative Example 1

(48) A sliding mechanism was produced and evaluated in the same manner as in Example 1 except that the intervening member A 21 and the intervening member B 22 were not formed, and the material and inner diameter of the bearing 3 were changed to PTFE and 10.1 mm, respectively. The results are shown in Table 2.

Comparative Example 2

(49) A sliding mechanism was produced and evaluated in the same manner as in Example 4 except that the materials of the intervening member A 21 and the bearing 3 were changed to SUS303 and POM, respectively. The results are shown in Table 2.

Comparative Example 3

(50) A sliding mechanism was produced and evaluated in the same manner as in Example 4 except that the inner diameter of the bearing 3 was changed to 12.1 mm. The results are shown in Table 2.

(51) TABLE-US-00002 TABLE 2 Material of sliding surface Evaluation Intervening Intervening Sectional Friction Shaft member A member B Bearing shape coefficient Wear Example 1 SUS303 PTFE PEEK SUS304 FIG. 1B 0.06 Example 2 SUS303 POM SUS304 PTFE FIG. 1B 0.08 Example 3 SUS303 PTFE PEEK SUS304 FIG. 1D 0.06 Example 4 SUS303 PTFE SUS304 FIG. 1B 0.08 Example 5 SUS303 DLC SUS304 FIG. 1B 0.10 Comparative Example 1 SUS303 PTFE FIG. 1B 0.16 x Comparative Example 2 SUS303 SUS303 POM FIG. 1B 0.13 x Comparative Example 3 SUS303 PTFE SUS304 FIG. 1B 0.16 x

(52) As shown in Table 2, stable friction coefficients were obtained in Examples 1 to 5. In addition, also the amount of wear was observed to be small. The comparison between Example 1 and Example 4 reveals that a lower friction coefficient is obtained in Example 1, and the effects of the present invention are strongly exhibited when a plurality of intervening members are provided.

(53) In addition, a change in friction coefficient with time in Example 1 and Comparative Example 1 is shown in FIG. 3. In Comparative Example 1, the intervening member was not formed, and hence the friction coefficient was not stable and showed a gradually increasing tendency in the test at high speed under high load. On the other hand, in Example 1, the friction coefficient was lower than that in Comparative Example 1 and almost constant.

(54) In Comparative Example 2, the shaft 1 and the intervening member A 21 were formed of the same material, and hence the intervening member A 21 rotated integrally with the shaft 1 without sliding with respect to the shaft 1. Therefore, the friction coefficient was high, and the amount of wear was observed to be large.

(55) In Comparative Example 3, a gap between the intervening member A 21 and the bearing 3 was eliminated, and hence the intervening member A 21 was nearly fixed to the bearing 3 to allow a configuration substantially the same as that in Comparative Example 1. Therefore, the friction coefficient was high, and the amount of wear was observed to be large.

(56) While the present invention has been described with reference to exemplary embodiments, it is to be understood that the invention is not limited to the disclosed exemplary embodiments. The scope of the following claims is to be accorded the broadest interpretation so as to encompass all such modifications and equivalent structures and functions.

(57) This application claims the benefit of Japanese Patent Application No. 2015-050477, filed Mar. 13, 2015, which is hereby incorporated by reference herein in its entirety.