JP2005118429A - Very small diameter endoscope - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a very small diameter endoscope for supplying illumination light sufficient for observation by increasing mechanical strength in an axial direction, while keeping flexibility. <P>SOLUTION: The very small diameter endoscope is provided with an insertion part 1 including: an objective lens 11; an image fiber bundle 12 for observation for transmitting an image formed by the objective lens 11; and a fiber cable 13 for illumination for supplying the illumination light. The fiber cable 13 for illumination includes illumination cable groups 33a, 33b, having a plurality of unit illumination cables 30 which are obtained by binding a plurality of optical fibers 31 in parallel and coating them with a coating layer 32, and is formed in a cylindrical shape by which the image fiber bundle 12 for observation is freely put through a center part. The unit illumination cables 30 are arranged in a state it is spirally wound around the outer periphery of the image fiber bundle 12 for observation and are not in parallel with the image fiber bundle 12. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to medical and industrial ultra-fine diameter endoscopes.

  In a medical site or an industrial site, when observing a minute internal state such as a blood vessel of a human body or a piping of an industrial facility, an ultra-fine diameter endoscope having an ultra-fine insertion portion with an outer diameter of about 0.2 to 2 mm Is used. A medical ultrathin endoscope is inserted into a body cavity of a human body via a catheter.

  In the insertion portion of the ultrafine endoscope, an objective lens arranged at the tip, an observation image fiber bundle that transmits an image formed by the objective lens, a plurality of illumination fiber cables that supply illumination light, A protective layer (skin) for protecting the observation image fiber bundle and the illumination fiber cable is provided. The observation image fiber bundle and the illumination fiber cable are branched at the branch portion of the insertion portion base, and the observation image fiber bundle is extended to the image receiving end, and the illumination fiber cable is extended to the light transmission end. Such a conventional ultra-thin diameter endoscope is disclosed in Patent Document 1, for example.

Recently, various new proposals have been made so that a sufficient amount of light can be secured without increasing the outer diameter of the insertion portion. For example, in Patent Document 2, a protective layer, an illumination light transmission layer having a higher refractive index than the protective layer, and a clad having a lower refractive index than the illumination light transmission layer are provided on the outer peripheral surface of the image circle for image transmission. It is disclosed that a lighting layer is sequentially provided, and illumination light is incident on the illumination light transmission part layer obliquely. According to this configuration, since the illumination light is guided from the low refractive index cladding layer into the high refractive index illumination light transmission layer, the illumination light can be transmitted without being attenuated. Patent Document 3 discloses that an outer casing of an endoscope is formed by an optical fiber bundle extending in a spiral shape and an adhesive means (embedding medium) for connecting the optical fiber bundles. According to this configuration, a large number of optical fiber cables are provided to the endoscope without increasing the outer diameter of the insertion portion, and more illumination light can be supplied.
Japanese Patent Laid-Open No. 5-264907 Japanese Patent No. 2914676 JP-A-8-229001

  In the above-mentioned Patent Document 2, as an optimal material for forming the illumination light transmission part layer, resins such as polystyrene (PS), polymethyl methacrylate (PMMA), and silicone rubber having good transmittance are proposed. However, the synthetic resin itself has a problem that it lacks durability because it has low strength (mechanical strength) against pulling, bending, and twisting in the axial direction of the endoscope.

  On the other hand, in the structure according to Patent Document 3, a plurality of optical fiber bundles are woven and further connected by adhesive means (embedding medium). It seems that the strength against tension is increasing. However, since the optical fiber is very thin and easy to break, the amount of light reaching the distal end of the insertion portion may be reduced if it breaks during weaving. Patent Document 3 mentions a cured adhesive such as an epoxy resin as an adhesive means for the optical fiber bundle. However, when the cured adhesive is used, the outer casing cannot obtain sufficient flexibility, and the catheter is bent in a complicated manner. There is also a risk that it cannot be inserted into a pipe or pipe.

  The present invention has been made in view of the above problems, and it is possible to obtain an ultra-thin endoscope capable of supplying sufficient illumination light for observation while increasing mechanical strength in the axial direction while maintaining flexibility. Objective.

  The present invention protects an objective lens, an observation image fiber bundle for transmitting an image formed by the objective lens, an illumination fiber cable for supplying illumination light, and the observation image fiber bundle and the illumination fiber cable. In the ultra-thin diameter endoscope having an insertion portion provided with an outer skin layer, the illumination fiber cable is composed of an illumination cable group having a plurality of unit illumination cables in which a plurality of optical fibers are bundled in parallel and covered with a coating layer. The illumination cable group constitutes a fiber tube through which the observation image fiber bundle can be inserted in the center, and the unit illumination cable is spirally wound around the outer periphery of the observation image fiber bundle. Arranged and non-parallel to the image fiber bundle for observation .

  It is preferable that all the unit illumination cables constituting the illumination cable group are wound in the same direction. In this case, the unit illumination cables constituting the illumination cable group correspond to a state in which twisting is applied with the axial direction of the observation image fiber as the rotation center when all the unit illumination cables are viewed as a unit.

  The fiber tube can be formed by stacking a plurality of fiber tubes having different diameters. When the fiber tube has a multilayer structure, all the unit illumination cables of the illumination cable group constituting each fiber tube are wound in the same direction, and the unit illumination cable of the illumination cable group constituting the adjacent fiber tube is The winding directions are preferably opposite to each other. If the winding direction of the unit illumination cables of the illumination cable group constituting the adjacent fiber tubes directly or indirectly is reverse, the external forces applied to the endoscope work so as to cancel each other, and the illumination fiber cable Durability is further improved. It is practical to interpose an intermediate protective layer between adjacent lighting cable groups.

  Unit illumination cables constituting the illumination cable group may be wound around the outer periphery of the observation image fiber bundle in different directions. In this case, the unit illumination cables constituting the illumination cable group can be arranged on the outer periphery of the observation image fiber bundle while being knitted. Even in this braided state, the mechanical strength of the illumination fiber cable and the endoscope can be increased without losing flexibility.

  At least one of the covering layer, the outer skin layer, and the intermediate protective layer can be formed by extrusion using a synthetic resin material. Alternatively, it can be formed by a heat shrinkable tube. As the synthetic resin material, it is preferable to use a fluorine-based resin or a thermoplastic resin.

  A coating layer made of a fluorine-based resin can be provided on the surface of the outer skin layer. By providing this coating layer, it is possible to reduce frictional resistance generated when the insertion portion is inserted into or removed from the catheter, for example, and operability is facilitated. The outer skin layer can be provided with a through hole for inserting the observation image fiber bundle into the fiber tube.

  It is practical to form the optical fiber from a non-stretchable multicomponent glass or synthetic resin in the axial direction.

  According to the present invention, since the plurality of unit illumination cables constituting the illumination fiber cable are arranged in the same or different directions around the outer periphery of the observation image fiber bundle, the flexibility is impaired. In addition, the mechanical strength against pulling or twisting in the axial direction can be increased. Thereby, the ultra-thin diameter endoscope excellent in durability is obtained.

Further, according to the present invention, the unit illumination cable is formed by bundling a plurality of optical fibers in parallel and then covering the unit illumination cable with a coating layer, so that an external force such as knitting or twisting is applied to the unit illumination cable. However, it is difficult for the optical fiber to be disconnected, it is possible to prevent a decrease in the amount of light due to the disconnection of the optical fiber, and it becomes easy to secure a necessary amount of light.

  FIG. 1 is an overall configuration diagram schematically showing an ultrafine endoscope according to a first embodiment of the present invention. The ultra-thin endoscope includes a flexible insertion portion 1, a branch portion 2 located at the insertion portion base, an image receiving portion 3 (first insertion portion) branched by the branch portion 2, and a light transmission portion 4. (Second insertion part). Although not shown, an imaging device (endoscope video camera) can be connected to the image receiving unit 3, and a light source device can be connected to the light transmitting unit 4.

  As shown in FIG. 2 in an enlarged manner, the insertion unit 1 includes an objective lens 11 disposed at the tip, an observation image fiber bundle 12 disposed behind the objective lens 11, and an illumination light exposed at the tip. An illumination fiber cable 13 to be supplied and an outer skin layer 14 that protects the observation image fiber bundle 12 and the illumination fiber cable 13 are provided. As the objective lens 11, a fixed focus lens, for example, a SELFOC lens (registered trademark) is used. The observation image fiber bundle 12 is a fiber bundle formed by bundling a large number of image fibers in parallel, and is covered with a protective layer made of resin, for example. Although not shown, a coating layer made of a fluororesin material or the like is provided on the surface of the outer skin layer 14. The coating layer has a function of reducing frictional resistance when the insertion portion 1 is inserted or removed from, for example, a catheter. When the insertion portion 1 is introduced into the observation target, an image of a portion illuminated by the illumination fiber cable 13 is formed on one end surface of the observation image fiber bundle 12 by the objective lens 11, and the inside of the observation image fiber bundle 12 is formed. And is injected from the other end surface. The other end surface of the observation image fiber bundle 12 is located on the end surface of the image receiving unit 3, and an image emitted from the other end surface is observed on a TV monitor via an imaging device connected to the image receiving unit 3.

  As shown in FIG. 3, the branch portion 2 includes an insertion portion side opening 20 a through which the observation image fiber bundle 12 and the plurality of illumination fiber cables 13 are led out to the insertion portion 1, and the observation image fiber bundle 12. Two symmetrical branching members 20 having an image receiving portion side opening 20b leading to 3 and a light transmitting portion side opening 20c leading a plurality of illumination fiber cables 13 to the light transmitting portion 4 are fixed. The insertion part side opening 20a, the image receiving part side opening 20b, and the light transmission part side opening 20c communicate with each other. The outer skin layer 14 of the base of the insertion portion inserted through the insertion portion side opening 20a communicates the inside and outside of the outer skin layer 14 (more specifically, the outer skin layer and the inside of a fiber tube to be described later). A through-hole 14a is formed through which is inserted. The insertion portion of the observation image fiber bundle 12 including the through hole 14 a is fixed in a watertight manner by the branch member 20. An anti-bending tube 23 covering the insertion portion base is bonded or welded to the insertion portion side opening 20a. A first protective tube 21 through which the observation image fiber bundle 12 is inserted is bonded or welded to the image receiving unit side opening 20b, and a second protection through which the illumination fiber cable 13 is inserted into the light transmitting unit side opening 20c. The tube 22 is bonded or welded.

  The ultra-thin endoscope having the overall configuration described above has main characteristics in the illumination fiber cable 13 and its arrangement. Below, with reference to FIGS. 4-6, the fiber cable 13 for illumination which is the characterizing part of this invention is demonstrated.

  The illumination fiber cable 13 includes a plurality of unit illumination cables 30 as shown in FIG. The unit illumination cable 30 includes a plurality of (several to several tens) optical fibers 31 formed of non-stretchable multi-component glass or synthetic resin in the axial direction and bundled in parallel. It is formed to cover. Although the optical fiber 31 alone is very thin and easily broken, the mechanical strength can be increased by coating a plurality of optical fibers 31 bundled in parallel. That is, according to the unit illumination cable 30, the optical fiber 31 is not easily disconnected even if it is deformed, such as knitted or twisted, and a decrease in light amount due to the disconnection of the optical fiber 31 can be prevented. 4, (a) is a unit illumination cable provided with three optical fibers 31, (b) is a unit illumination cable provided with seven optical fibers 31, and (c) is a unit illumination provided with 19 optical fibers 31. Each cable is shown.

  As shown in FIGS. 5 and 6, the illumination fiber cable 13 includes a first illumination cable group 33a and a second illumination cable group 33b each having a plurality of the unit illumination cables 30 described above. The first illumination cable group 33a and the second illumination cable group 33b are stacked via an intermediate protective layer 34 made of synthetic resin, and constitute a fiber tube through which the observation image fiber bundle 12 can be inserted in the center.

  The first illumination cable group 33a forms a cylindrical small-diameter fiber tube by spirally winding a plurality (10 in the illustrated embodiment) of unit illumination cables 30 along the outer periphery of the observation image fiber bundle 12. doing. The unit illumination cables 30 constituting the first illumination cable group 33a are all wound in the same direction (for example, the right-handed screw direction), and are not parallel to the observation image fiber bundle 12. In the second illumination cable group 33b, a plurality (17 in the illustrated embodiment) of unit illumination cables 30 are arranged on a concentric circle with the observation image fiber bundle 12 as the center, and then all the unit illumination cables 30 are placed in an intermediate protective layer. A cylindrical large-diameter fiber tube is formed by spirally winding the outer periphery of 34. The outer periphery of the second illumination cable group 33 b is covered with the outer skin layer 14. The unit illumination cables 30 constituting the second illumination cable group 33b are all wound in the direction opposite to the winding direction of the unit illumination cables 30 constituting the first illumination cable group 33a, and the observation image fiber bundle 12 and It is non-parallel. As described above, when the winding directions of the unit illumination cables 30 are opposite to each other in the first illumination cable group 33a and the second illumination cable group 33b that are adjacent to each other via the intermediate protective layer 34, pulling or twisting in the axial direction is performed. Even if an external force such as an external force is applied to the insertion portion 1, the external forces act so as to cancel each other, so that the mechanical strength of the illumination fiber cable 13 can be further increased.

  Next, a manufacturing procedure of the ultra-thin endoscope shown in FIGS. 1 to 6 will be described.

  First, in a state where several to several tens of optical fibers 31 are bundled in parallel, the outer periphery of the optical fibers 31 is covered with a coating layer 32 to produce a unit illumination cable 30 as shown in FIG. The covering layer 32 can be formed by extrusion molding using a synthetic resin material, or can be formed using a heat shrinkable tube. As the synthetic resin material for forming the coating layer 32, it is preferable to use a fluororesin material, or a thermoplastic resin material such as polyethylene or polyurethane.

  Next, as shown in FIG. 7, a core material (core wire) 35 having a diameter substantially equal to or larger than the outer diameter of the observation fiber bundle 12 is prepared, and a plurality of outer circumferences of the core material 35 are provided around the outer periphery. The unit illumination cables 30 are arranged, and one end of each unit illumination cable 30 is bonded to the core member 35. Subsequently, the unit illumination cables 30 are all wound around the core member 35 in the same direction (for example, right-handed screw direction) from one end side bonded to the core member 35. Thereby, the 1st illumination cable group 33a (small diameter fiber tube) is obtained. When all the unit illumination cables 30 are wound, an intermediate protective layer 34 that covers the outer periphery of the unit illumination cable 30 is formed. The intermediate protective layer 34 is formed by extrusion molding using a synthetic resin material, similarly to the covering layer 32 of the unit lighting cable 30, or by using a heat shrinkable tube.

  Subsequently, a plurality of unit illumination cables 30 are arranged on the entire outer periphery of the intermediate protective layer 34, and one end of each unit illumination cable 30 is bonded to the intermediate protective layer 34, and unit illumination is performed from the bonded one end side. The cable 30 is wound around the outer periphery of the intermediate protective layer 34. At this time, the winding direction of the unit illumination cable 30 is set to be opposite to the winding direction of the unit illumination cable 30 wound around the core member 35 in the previous process (see FIG. 7). Thereby, the 2nd illumination cable group 33b (large diameter fiber tube) is obtained. When all the unit illumination cables 30 are wound around the intermediate protective layer 34, the outer skin layer 14 that covers the outer periphery of the unit illumination cable 30 is formed. Similar to the intermediate protective layer 34 and the covering layer 32 of the unit lighting cable 30, the outer skin layer 14 is formed by extrusion using a synthetic resin material or by using a heat shrinkable tube. When the outer skin layer 14 is formed, the surface of the outer skin layer 14 in the range to be the insertion portion 1 is covered with a coating layer made of a fluororesin material.

  After the coating, the second illumination cable group 33b, the intermediate protection layer 34, the first illumination cable group 33a, and the core member 35 covered with the outer skin layer 14 are cut to a predetermined length, and a compressive force is applied from both ends in the axial direction. Add. Then, the inner diameter of the core member 35 is slightly expanded by the compressive force, and a gap is generated between the core member 35 and the first illumination cable group 33a. Using this gap, the core material 35 is removed. As a result, a cylindrical illumination fiber cable 13 in which the observation image fiber bundle 12 can be inserted in the center is obtained. Both end surfaces of the illumination fiber cable 13 (the front end surface of the insertion portion and the end surface of the light transmission portion) are polished so that illumination light can enter and exit.

  Subsequently, a through hole 14a is formed in the outer skin layer 14 near the base of the insertion portion, and the observation image fiber bundle 12 having the objective lens 11 fixed to the distal end side is connected through the through hole 14a to the illumination fiber cable 13 (first illumination). The observation image fiber bundle 12 is inserted into the hollow of the cable group 33a), and fixed to the inner peripheral surface of the first illumination cable group 33a with an adhesive, for example, at the tip of the insertion portion 1. The rear end of the observation image fiber bundle 12 is linearly led out of the outer skin layer 14 from the through hole 14a and is inserted into the first protective tube 21 through the image receiving portion side opening 20b of the branch portion 2. It is fixed to the end face of the image receiving unit 3. The through hole 14a is formed by pushing the second illumination cable group 33b, the intermediate protection layer 34, and the first illumination cable group 33a by inserting a needle-shaped bar from the outside of the outer skin layer 14. When the outer skin layer 14 and the intermediate protective layer 34 are formed by extrusion, if the release agent is applied in advance to the through hole forming position, the outer skin layer 14 and the intermediate protective layer 34 are easily peeled off, and the through holes 14a can be easily formed. Become. The insertion part of the observation image fiber bundle 12 including the through hole 14 a is fixed to the branch member 20.

  When the observation image fiber bundle 12 is fixed, the illumination fiber cable 13 is slightly bent and guided to the light transmission part side opening 20c of the branching part 2, and is inserted into the second protective tube 22 from the light transmission part side opening 20c. Then, the other end of the illumination fiber cable 13 is fixed to the end face of the light transmitting unit 4. In the case where a gap is generated on the end face of the light transmitting unit 4, the gap is filled with, for example, a resin adhesive to ensure water tightness. Note that the illumination fiber cable 13 may be directly fixed to the end face of the light transmitter 4 without providing the second protective tube 22.

  Subsequently, the anti-bending tube 23, the first protective tube 21, and the second protective tube 22 are respectively bonded or welded to the insertion portion side opening 20a, the image receiving portion side opening 20b, and the light transmission portion side opening 20c of the branch member 20. The insertion portion 1 (the observation image fiber bundle 12 and the illumination fiber cable 13 integrally covered with the outer skin layer 14) is led out from the insertion portion side opening 20 a of the branch member 20 and the folding tube 23. Then, the two branch members 20 are fixed in a state where the base portion of the insertion portion 1, the observation image fiber bundle 12 and the illumination fiber cable 13 are sandwiched.

  As described above, this ultrafine endoscope is obtained.

  In the above, the embodiment including the two-layered illumination fiber cable 13 in which the small-diameter fiber tubes (first illumination cable group 33a) and the large-diameter fiber tubes (second illumination cable group 33b) having different diameters are stacked has been described. However, the illumination fiber cable 13 may have a single-layer structure (illumination cable group 33) as shown in FIGS. 8 and 9, or a multilayer structure of three or more layers. It is desirable to select appropriately according to the outer diameter of the insertion portion of the endoscope.

  10 and 11 show an ultra-thin endoscope according to a second embodiment of the present invention. In the second embodiment, a plurality of unit illumination cables 130 are knitted so as to cover the outer periphery of the observation image fiber bundle 12 to form a cylindrical shape, and the illumination fiber cable 113 is formed. In other words, the plurality of unit illumination cables 130 constituting the illumination fiber cable 113 are randomly wound around the outer periphery of the observation image fiber bundle 12 in different directions. Each unit illumination cable 130 is not parallel to the observation image fiber bundle 12. The mode in which the unit illumination cable 130 is wound by this braiding can also increase the mechanical strength against pulling or twisting of the illumination fiber cable 113 and the endoscope without impairing flexibility. Except for the point that the braided illumination fiber cable 113 is provided, the configuration is the same as that of the first embodiment. In FIG.10 and FIG.11, the code | symbol same as FIGS. 1-6 is attached | subjected with respect to the component which has the same function as 1st Embodiment.

  The ultra-thin endoscope can be formed by the same procedure as in the first embodiment described above. That is, in the manufacturing procedure of the ultra-thin endoscope according to the first embodiment, one end of the unit illumination cable 30 is bonded to the core member 35 and then the unit illumination cable 30 is wound around the core member 35 in the same direction. Instead of the process, the unit illumination cable 130 may be wound around the core member 35 from different directions and knitted into a cylindrical shape.

  The ultrafine endoscopes according to the above embodiments can be applied not only to medical ultrafine endoscopes but also to industrial ultrafine endoscopes.

As described above, the present invention has been described with reference to the illustrated embodiment. However, the ultrafine endoscope device of the present invention is not limited to the illustrated embodiment.

1 is an overall configuration diagram of an ultrafine endoscope according to a first embodiment of the present invention. It is sectional drawing which expands and shows an insertion part front-end | tip part. It is sectional drawing which shows the structure of a branch part vicinity. It is sectional drawing which shows the various Example of the fiber cable for illumination. It is sectional drawing of an insertion part. It is a partial block diagram explaining the covering structure of an insertion part. It is a partial block diagram explaining 1 process of the manufacturing procedure of an ultra-thin diameter endoscope. It is a partial block diagram explaining the covering structure of the insertion part formed in the aspect different from FIG.5 and FIG.6. It is sectional drawing of the insertion part shown in FIG. It is sectional drawing of the insertion part of the ultra-thin diameter endoscope by 2nd Embodiment of this invention. It is a partial block diagram explaining the covering structure of the insertion part shown in FIG.

Explanation of symbols

100 Ultrathin Endoscope 1 Insertion Section 2 Divergence Section 3 Image Receiving Section (First Insertion Section)
4 Light transmitter (second plug)
DESCRIPTION OF SYMBOLS 11 Objective lens 12 Observation image fiber bundle 13 Illumination fiber cable 14 Outer layer 14a Through-hole 20 Branch member 20a Insertion part side opening 20b Image receiving part side opening 20c Light transmission part side opening 21 First protective tube 22 Second protective tube 23 Folding tube 31 Optical fiber 32 Coating layer 33a First illumination cable group (small diameter fiber tube)
33b Second illumination cable group (large diameter fiber tube)
34 Intermediate protective layer 35 Core material

Claims (11)

An objective lens, an observation image fiber bundle that transmits an image formed by the objective lens, an illumination fiber cable that supplies illumination light, and an outer skin layer that protects the observation image fiber bundle and the illumination fiber cable; In an ultrafine endoscope having an insertion portion with
The illumination fiber cable comprises an illumination cable group having a plurality of unit illumination cables in which a plurality of optical fibers are bundled in parallel and covered with a coating layer,
This illumination cable group constitutes a fiber tube that can be inserted through the observation image fiber bundle in the center,
The ultra-small diameter endoscope, wherein the unit illumination cable is arranged in a spirally wound state on the outer periphery of the observation image fiber bundle, and is not parallel to the observation image fiber bundle. 2. The ultra-thin endoscope according to claim 1, wherein all unit illumination cables constituting the illumination cable group are wound in the same direction. The ultra-thin diameter endoscope according to claim 1, wherein the fiber tube is formed by stacking a plurality of fiber tubes having different diameters, and all unit illumination cables of the illumination cable group constituting each fiber tube are wound in the same direction. In addition, the unit illumination cables of the illumination cable group constituting the adjacent fiber tubes are ultra-thin diameter endoscopes whose winding directions are opposite to each other. 4. The ultra-thin endoscope according to claim 3, wherein an intermediate protective layer is interposed between the adjacent illumination cable groups. 2. The ultra-thin endoscope according to claim 1, wherein unit illumination cables constituting the illumination cable group are wound around an outer periphery of the observation image fiber bundle in different directions. The ultrafine endoscope according to any one of claims 1 to 5, wherein at least one of the covering layer, the outer skin layer, and the intermediate protective layer is formed by extrusion using a synthetic resin material. Endoscope. 7. The ultra-thin endoscope according to claim 6, wherein the synthetic resin material is a fluororesin or a thermoplastic resin. The ultra-thin diameter endoscope according to any one of claims 1 to 5, wherein at least one of the covering layer, the outer skin layer, and the intermediate protective layer is formed by a heat-shrinkable tube. mirror. 9. The ultra-thin endoscope according to claim 1, wherein a coating layer made of a fluororesin is provided on the surface of the outer skin layer. The ultra-thin diameter endoscope according to any one of claims 1 to 9, wherein a through-hole for inserting the observation image fiber bundle into the fiber tube is provided in the outer skin layer. . The ultra-thin endoscope according to any one of claims 1 to 10, wherein the optical fiber is formed of non-stretchable multicomponent glass or synthetic resin in the axial direction.

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