JP2009014414A - Method of manufacturing optical fiber sensor unit, and optical fiber sensor unit - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method of manufacturing an optical fiber sensor unit for fixing surely a fiber holder for storing and holding each tip of a floodlighting optical fiber and a light-receiving optical fiber to the tip inside of a protection tube, and detecting surely existence of liquid in contact with the tip part. <P>SOLUTION: In this method of manufacturing the optical fiber sensor unit equipped with a tube 101 and the optical fiber holder 112 inserted on the tube tip, and having a sealing member 106 for sealing the tube tip, fused on the tube tip in the fluid-tight state, when fusing the sealing member on the tube, a die 104 having a cavity 104b agreeing with a post-fusing outer shape of the sealing member is prepared, and the sealing member before melting having an outer shape agreeing with the cavity is put in the cavity, and the cavity is heated, and the sealing member is fused on the tube before the sealing member is completely melted. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a method of manufacturing an optical fiber sensor unit that optically detects a liquid level using a light projecting optical fiber and a light receiving optical fiber, and an optical fiber sensor unit manufactured by the manufacturing method.

  For example, as an optical fiber sensor unit for optically detecting the liquid level of a chemical solution in a chemical solution tank, a light projecting optical fiber and a light receiving optical fiber are arranged in parallel, and the tip portion is made of a fluororesin member sealed in a conical shape. The thing of the structure which coat | covered these fibers with the protection tube is known (for example, refer patent document 1).

  This optical fiber sensor unit accommodates the optical fiber for light projection and the optical fiber for light reception held in a resin case, and caulking and fixing the resin case with the resin case penetrating inside the distal end of the protective tube. Detection light emitted from the optical fiber is optically coupled to the light receiving optical fiber on the inner surface of the distal end of the protective tube.

  Such an optical fiber sensor unit has a conical prism portion (hereinafter referred to as a “conical prism member”) at the tip, and when the conical prism member is in the air, the light emitted from the optical fiber for projection is conical prism. The light is reflected within the member and enters the optical fiber for receiving light. On the other hand, when the conical prism member is in the liquid, most of the light emitted from the light projecting optical fiber passes through the conical prism member and travels into the liquid, so that the amount of light received by the light receiving optical fiber is significantly reduced. Therefore, by detecting the change in the amount of light from the optical fiber for receiving light, it is possible to determine whether the tip of the optical fiber sensor unit exists in the air or is submerged in the liquid, and the level of the liquid level. Is supposed to be detected.

  As a manufacturing method of the optical fiber sensor unit, for example, a manufacturing method as shown in FIGS. 5A to 5E and FIGS. 6A to 6D has been conventionally performed. In FIGS. 5 and 6, the right side shows the lower side and the left side shows the upper side when viewed in the direction of the action of gravity. Hereinafter, this manufacturing method will be described with reference to the drawings.

  First, the metal rod 202 is inserted from the upper end opening of the protective tube 201 made of, for example, a fluorine resin member having excellent chemical resistance (see FIG. 5A). Next, a detection member is formed at the tip 201 a of the protective tube 201. The detection member forming mold 204 is installed horizontally, and for example, a conical recess 204b is formed on the upper surface 204a, and the distal end 201a of the protective tube 201 can be slightly inserted into the opening 204c (see FIG. (Refer FIG.5 (b)).

  Next, a fluororesin member 205 having excellent chemical resistance is placed in the recess 204b of the mold 204, and a detection member (hereinafter referred to as “conical prism”) having a cone shape formed by heating and melting the mold 204 is formed. 206 ”(refer to FIG. 5C).

  Next, the distal end portion 201a of the protective tube 201 is inserted into the opening 204c of the mold 204 and pressed against the melted conical prism member 206, and the distal end portion 201a of the protective tube 201 is melt bonded to the flat portion 206a of the conical prism member 206. (See FIG. 5 (d)).

  Next, the molten conical prism member 206 is solidified by cooling the mold 204 by air A or the like shown in FIG. 5E (see FIG. 5E).

  After cooling the mold 204 and solidifying the conical prism member 206 in this manner, the protective tube 201 is removed from the mold 204 and the metal rod 202 is pulled out from the protective tube 201. In this way, the protective tube 201 in which the detection member 206 is liquid-tightly joined to the distal end portion 201a is formed (see FIG. 5 (f)).

  Next, a fiber holder 209 accommodated in a state where the distal ends of the light projecting optical fiber 207 and the light receiving optical fiber 208 are fixed is inserted from the upper end opening side of the protective tube 201 (see FIG. 6A), and the distal end surface thereof. 209a is brought into contact with the flat portion 206a of the conical prism member 206 (see FIG. 6B). In this state, the front end surfaces of the light projecting optical fiber 207 and the light receiving optical fiber 208 are in contact with the flat portion 206 a of the conical prism member 206.

Next, a retaining ring 210 (see FIG. 6C) formed of a fluorine-based resin member is inserted from the front end side of the conical prism member 206, and is stopped at a position immediately after passing through the rear end portion of the fiber holder 209. Then, the retaining ring 210 is heated and thermally contracted, the diameter of the protective tube 201 is reduced and heat crimped, and the fiber holder 209 is fixed at a desired position in the protective tube 201 (see FIG. 6D). In this way, the optical fiber sensor unit 2 is formed.
JP 2002-131115 A (page 3, FIG. 2)

  However, when manufacturing such an optical fiber sensor unit 2, a step of attaching and detaching the metal rod 202 to and from the protective tube 201 when the conical prism member 206 is fused and connected to the distal end portion 201 a of the protective tube 201 (step shown in FIG. 5). ) And a step of inserting the fiber holder 209 accommodated in a state in which the tip ends of the light projecting optical fiber 207 and the light receiving optical fiber 208 are fixed in the protective tube 201 (step shown in FIG. 6), There is a problem that the manufacturing work takes time.

  Furthermore, since Teflon (registered trademark) material that is easily charged is easily adsorbed with dust, there is a concern that dust may accumulate on the fiber detection end due to long distance insertion and insertion direction.

  Depending on the object (device) to which the liquid level detection sensor is to be mounted, the hole diameter for inserting the protective tube 201 should be made as small as possible so that the gap between the protective tube 201 and the insertion hole is made as small as possible. May be required. In such a specification, when the retaining ring 210 is used in the manner shown in FIG. 6D, the hole diameter must be increased by at least the outer diameter of the retaining ring 210, and the liquid level detection is performed. Sensor installation may be difficult.

  Furthermore, since the protective tube 201 is contracted by heat by the retaining ring 210 made of a fluorine resin member and the diameter of the protective tube 201 is reduced, the fiber holder 209 is fixed in the protective tube 201. There is a possibility that the fiber holder 209 is loose in the protective tube 201 or the fiber holder 209 may come out of the protective tube 201 in some cases.

  When the fiber holder 209 is rattled in the protective tube 201, the optical coupling between the leading end surface of the light projecting optical fiber 207 and the light receiving optical fiber 208 and the flat surface portion 206a of the conical prism member 206 changes, and detection errors and It causes performance deterioration such as detection failure. Further, when the fiber holder 209 comes out of the protective tube 201, it cannot be detected.

  Note that FIG. 2 of Patent Document 1 also describes a method in which the vicinity of the rear end portion of the resin case of the protective tube is thermally crimped to shrink the protective tube, and the resin case is fixed in the protective tube. There is also a possibility that the same problem as described above may occur. Various measures have conventionally been taken to fix the fiber holder in the protective tube by heat caulking, but in any case, there is a possibility that the heat caulking portion may be loosened as described above.

  Therefore, a manufacturing method of the optical fiber sensor unit 3 shown in FIG. 7 is proposed as a related invention of the present invention. Hereinafter, the related invention will be described with reference to the drawings. In addition, about the structure similar to FIG.5 and FIG.6, corresponding code | symbol is attached | subjected and detailed description is abbreviate | omitted.

  When the optical fiber sensor unit 3 is manufactured, a protective tube 301 is first prepared which is made of a fluororesin member and accommodates the light projecting optical fiber 307 and the light receiving optical fiber 308 inserted therein (see FIG. 7A). .

  Next, a fiber holder 312 made of a heat-resistant member having a heat-resistant temperature sufficiently higher than the heat-resistant temperature of the protective tube 301 and having a press-fit portion having an outer diameter larger than the inner diameter of the protective tube 301 formed on at least a part of the outer peripheral surface. Is prepared and fixed to the fiber holder 312 in a state in which the respective one end portions of the optical fibers 307 and 308 are accommodated (see FIG. 7A).

  Next, the other end of each optical fiber is inserted from the one opening end 301a of the protective tube 301, and the fiber holder 312 is press-fitted into the one opening end 301a of the protective tube 301 (see FIG. 7B). .

  Next, a detection member 306 formed of a fluororesin member and forming an optical path for guiding the light projected from the light projecting optical fiber 307 to the one opening end 301a of the protective tube 301 is joined in a liquid-tight state. (See FIGS. 7C to 7F).

  In performing this joining operation, the following procedure is used. First, a detection member forming die 304 that is horizontally installed and has a conical recess 304b formed at a predetermined position on the upper surface 304a is prepared (see FIG. 7C). Note that the opening 304c of the recess 304b has a small gap between the opening portion 301a on one side of the protective tube 301 whose outer diameter has been slightly expanded by press-fitting the fiber holder 312 to a predetermined length (several millimeters). It is set as the hole diameter inserted so that insertion / extraction is possible.

  Then, a transparent fluorine-based resin member 305 having excellent chemical resistance is placed in the recess 304b of the mold 304, and the mold 304 is heated (see FIG. 7C). As a result, the fluororesin member 305 is melted to form a detection member (hereinafter referred to as “conical prism member”) 306 having a conical shape and having a prism function (see FIG. 7D).

  Next, the one-side open end 301a of the protective tube 301 is vertically inserted into the opening 304c of the mold 304 and pressed against the molten conical prism member 306, and the one-side open end 301a of the protective tube 301 is pressed into the conical prism member. It melt-joins to the peripheral part of the plane part (rear surface) 306a of 306 (refer FIG.7 (e)).

  Next, the conical prism member 306 is solidified by cooling the die 304 by air A or the like shown in FIG. 7F, and then the protective tube 301 is pulled away from the die 304 (see FIG. 7G). . In this way, the protective tube 301 in which the conical prism member 306 is liquid-tightly joined to the one end opening end portion 301a is formed.

  Then, the remaining resin member of the conical prism member 306 adhering to the outer peripheral surface of the protective tube 301 is scraped off as necessary so that the conical prism member 306 forms an appropriate optical path for the optical fibers 307 and 308 for light projection and reception. To do.

  According to such a manufacturing method of the optical fiber sensor unit 3, the fiber holder, which is a drawback of the above-described conventional manufacturing method of the optical fiber sensor unit 2, is reliably prevented from rattling or coming out of the protective tube. can do.

  Further, the one-side opening end portion 301a of the fluororesin-based protection tube 301 and the conical prism member 306 are joined in a liquid-tight manner by fusion joining, and the heat resistance temperature of the fiber holder 312 is higher than the heat resistance temperature of the protection tube 301. When the protective tube 301 and the conical prism member 306 are melt-bonded, the fiber holder 312 can be prevented from melting.

  Further, when the one side opening end portion 301a of the protective tube 301 and the conical prism member 306 are joined, at least the one side opening end portion 301a to be joined of the protective tube 301 and the conical prism member 306 which melts the vicinity thereof. It suffices to press it vertically, and there is no problem even if the remaining portion of the protective tube 301 hangs down or bends.

  Thus, unlike the conventional method for manufacturing the optical fiber sensor unit 2 described above, it is not necessary to improve the workability in the manufacturing process and to increase the space in the height direction, and to save the work environment. It becomes.

  However, when the newly proposed method for manufacturing the optical fiber sensor unit 3 related to the present invention is carried out, if the fluororesin member 305 accommodated in the recess 304b of the mold 304 is heated until it is uniformly melted, the fluororesin Volume expansion occurs when the member 305 is melted to become the conical prism member 306 (see the melted fluorine-based resin member 305a indicated by hatching in FIG. 8A). When the protective tube 301 is fused to the conical prism member 306 and then the mold 304 is cooled to room temperature, the conical prism member itself shrinks in volume by cooling after the protective tube 301 and the conical prism member 306 are fused. Sinking occurs. Due to the volume contraction (resin sink) after the volume expansion once occurs, the protective tube 301 is led out through the gaps formed between the lenses 315 and 316 and the light projecting / receiving fibers 307 and 308 and the fiber holder 312. Air may flow from the side (see the air flow indicated by the arrow in FIG. 8B), and bubbles may be generated between the end surface 312a of the fiber holder 312 and the conical prism member 306 (FIG. 8 ( (See bubble 306c shown in c)). Due to the generation of such bubbles, the optical path of the detection light emitted from the lens 315 of the light projecting optical fiber 307 changes, and it may not be possible to accurately determine the presence or absence of the liquid to be detected.

  An object of the present invention is to securely fix a fiber holder to be accommodated in a state where the optical fiber for light projection and the optical fiber for light reception are held inside the distal end of the protective tube, and to ensure that there is no liquid in contact with the distal end portion of the protective tube. An object of the present invention is to provide a method of manufacturing an optical fiber sensor unit to be detected and an optical fiber sensor unit manufactured by the manufacturing method.

The manufacturing method of the optical fiber sensor unit according to claim 1 of the present invention includes:
A method of manufacturing an optical fiber sensor unit comprising a tube and an optical fiber holder inserted at the distal end of the tube, and a sealing member for sealing the distal end of the tube fused to the distal end of the tube so as to be in a liquid-tight state In
In fusing the sealing member to the tube,
Prepare a mold having a cavity that matches the outer shape of the sealing member after fusion,
A sealing member before melting having an outer shape matching the cavity is accommodated in the cavity,
The cavity is heated and the sealing member is fused to the tube before the sealing member is completely melted.

  By manufacturing the optical fiber sensor unit by such a manufacturing method, the sealing member accommodated in the cavity is not melted when the cavity is heated, and only the region in contact with the cavity and the vicinity thereof are melted. As a result, the melted region of the sealing member is fused to the end portion of the tube, and the remaining unmelted region does not cause thermal contraction even when the mold is cooled, and comes into contact with the fiber holder of the sealing member. It remains in close contact with the end face of the fiber holder without creating bubbles in the region. Thereby, a highly reliable optical fiber sensor unit can be manufactured.

Moreover, the manufacturing method of the optical fiber sensor unit of Claim 2 of this invention is the manufacturing method of the optical fiber sensor unit of Claim 1,
The tube and the sealing member are made of a fluororesin.

  Because the tube and the sealing member are made of fluororesin, the optical fiber sensor unit of the present invention can be used to produce an optical fiber that has no chemical bubbles and that is covered with fluororesin and has excellent chemical resistance. A sensor unit can be manufactured.

Moreover, the manufacturing method of the optical fiber sensor unit of Claim 3 of this invention is the manufacturing method of the optical fiber sensor unit of Claim 2,
The fiber holder is made of a liquid crystal polymer.

  By carrying out the manufacturing method of the optical fiber sensor unit according to the present invention, even if a liquid crystal polymer that is not extremely high in melting temperature but excellent in injection moldability is used for the fiber holder, the fiber holder is not thermally deformed. The sealing member made of resin and the tube can be fused, and the optical fiber sensor unit can be manufactured at low cost.

An optical fiber sensor unit according to claim 4 of the present invention is
It is manufactured by the manufacturing method according to any one of claims 1 to 3.

An optical fiber sensor unit according to claim 5 of the present invention is
A synthetic resin tube having a hollow cylindrical shape, a synthetic resin optical fiber holder held inside the distal end of the tube to hold an optical fiber disposed in the tube, and a fusion welded to the distal end of the tube In the optical fiber sensor unit having a sealing member made of a synthetic resin that functions as an optical reflecting surface while sealing the tip of the tube,
The optical fiber holder is formed in an outer dimension that can be press-fitted into the tube and is press-fitted from the distal end side of the tube,
The sealing member has a surface that directly or indirectly contacts the end surface of the optical fiber holder, and the sealing member and the tube are in a state where the peripheral portion of the surface is melted and the central portion is not melted. It is characterized in that the tip is joined.

  According to the present invention, a method of manufacturing an optical fiber sensor unit that securely fixes an optical fiber holder that is accommodated while holding the tip of an optical fiber inside the tip of the protective tube, and that reliably detects the presence or absence of liquid in contact with the tip of the protective tube. And the optical fiber sensor unit manufactured by this manufacturing method can be provided.

  Hereinafter, a manufacturing method of an optical fiber sensor unit concerning one embodiment of the present invention and an optical fiber sensor unit manufactured by this manufacturing method are explained based on a drawing. FIG. 1 is a manufacturing process diagram showing a manufacturing method of an optical fiber sensor unit 1 according to the present invention. In FIG. 1, the right side shows the lower side and the left side shows the upper side when viewed in the direction of the action of gravity. In addition, the same code | symbol is attached | subjected to the same member as the member shown in FIG. 7, and detailed description is abbreviate | omitted.

  In manufacturing the optical fiber sensor unit 1 according to an embodiment of the present invention, first, a fiber holder 112 is prepared which is accommodated in a state in which the leading ends of the light projecting optical fiber 107 and the light receiving optical fiber 108 are fixed (see FIG. 1 (a)). In the case of this embodiment, the fiber holder 112 is made of a liquid crystal polymer (hereinafter referred to as “LCP”), which is a thermoplastic resin having excellent moldability, high heat resistance and high chemical resistance. Yes. Further, the outer diameter of the fiber holder 112 is formed to be slightly larger than the inner diameter of the protective tube 101 and can be press-fitted into the distal end portion 101 a of the protective tube 101. That is, the fiber holder 112 has a shape that has the same effect as when the press-fitting portion is formed on the outer peripheral portion by making the outer diameter larger than the inner diameter of the protective tube 101.

  As shown in FIG. 2, the fiber holder 112 has the light projecting optical fiber 107 and the light receiving optical fiber 108 inserted side by side at a predetermined depth along the axial direction, for example, approximately 2/3 of the total length, in the rear end surface 112b. An oval hole 112c is formed as viewed from the possible side, and two holes 112d and 112e are formed in the tip surface 112a along the axial direction with a predetermined distance along the long axis direction of the oval hole 112c. And communicated with the hole 112c with a slight step.

  Cylindrical refractive index distribution type optical fiber lenses (GRIN lenses) 113 and 114 are inserted into and fixed to the holes 112d and 112e on the distal end surface 112a side of the fiber holder 112, respectively. The front end surfaces 113a and 114a of the lenses 113 and 114 are flush with the front end surface 112a of the fiber holder 112, and the rear end surfaces 113b and 114b are located at step portions (communication portions) with the holes 112c. . When the optical fibers 107 and 108 are made of plastic having a low heat-resistant temperature, the fiber holder 112 and the GRIN lenses (made of glass) 113 and 114 are used as heat insulating materials in the process of fusing the conical prism member 106 to the protective tube 101 (described later). This produces a secondary effect of keeping the temperature of the optical fibers 107 and 108 below the heat-resistant temperature. However, if the heat-resistant temperature condition of the optical fiber is satisfied through all the steps described later, the structure in which the front end surfaces 107a and 108a of the optical fibers 107 and 108 are aligned with the front end surface 112a of the fiber holder 112 without using the GRIN lenses 113 and 114. It is also possible to adopt.

  Further, the front end portions (one end portions) of the light projecting optical fiber 107 and the light receiving optical fiber 108 are inserted side by side into an oval hole 112c on the rear end surface 112b side of the fiber holder 112, and the front end surfaces 107a, 108a of the cores 107A, 108A are inserted. The lenses 113 and 114 are in contact with the rear end surfaces 113b and 114b, respectively. Then, the coverings 107B and 108B of the light projecting optical fiber 107 and the light receiving optical fiber 108 are respectively adhered to the inner surface of the hole 112c of the fiber holder 112 with an adhesive and fixed so as not to deviate.

  These light emitting / receiving optical fibers 107 and 108 are inserted into the rear end (other end) of each end of the protective tube 101 from the opening end of the front end 101a of the protective tube 101, and the rear end ( The fiber holder 112 is pressed into the distal end portion 101a of the protective tube 101 (see FIG. 1A). This press-fitting operation is performed until the distal end surface 112a of the fiber holder 112 is flush with the distal end portion 101a of the protective tube 101 (see FIG. 1B). Thus, by inserting the projecting / receiving optical fibers 107 and 108 into the protective tube 101 and press-fitting the fiber holder 112 into the distal end portion 101a of the protective tube 101, the workability is good and the work can be easily performed even in a narrow place. It becomes possible. As another example that can be adopted in this step, it is also possible to insert a spacer (not shown) formed as a separate member together with the fiber holder 112 into the distal end portion 101 a of the protective tube 101. This spacer is made of a heat-resistant material having a disk shape having a uniform thickness, for example, and a through hole for passing light in the thickness direction is provided so as to match the position of the lenses 113 and 114. One surface of the spacer is in contact with the front end surface 112a of the fiber holder 112, and the other surface is in contact with the upper surface of the conical prism material 105 described later. That is, as a completed form of the optical fiber sensor unit, in the embodiment using no spacer, the conical prism member (sealing member) 106 is in direct contact with the end face of the fiber holder 112, whereas the spacer is used. In this embodiment, the conical prism member (sealing member) 106 is in indirect contact with the end surface of the fiber holder 112 via a spacer. When such a spacer is used, a space is generated between the conical prism member (sealing member) 106 and the fiber holder 112, so that there is a disadvantage in that the optical performance is lowered. The advantage that an effect is acquired arises. Therefore, what form should be adopted may be determined according to the specifications required for the optical fiber sensor unit.

  Next, a conical prism member (sealing member) 106 is fused to the tip 101a of the protective tube 101 (see FIGS. 1C to 1F). A mold 104 for partially melting the conical prism material 105 that is the base of the conical prism member 106 is installed horizontally, and a conical recess 104b is formed at a predetermined position on the upper surface 104a (FIG. 1C). reference). In the case of the present embodiment, the concave portion 104b has a concave shape that matches the outer shape of the conical prism member 106 (conical prism material 105) of the optical fiber sensor unit 1. The opening 104c of the recess 104b has a distal end 101a of the protective tube 101 whose outer diameter is slightly expanded by press-fitting the fiber holder 112 to a predetermined length (several millimeters) through a slight gap. It is set as the hole diameter inserted so that insertion / extraction is possible.

  Then, a conical prism material (sealing member) 105 made of a fluororesin member having a conical shape matching the recess 104b and having excellent chemical resistance and translucency is fitted into the recess 104b of the mold 104. (See FIG. 1C), the mold 104 is heated (see FIG. 1D). It should be noted that the upper surface of the conical prism material 105 (the surface in contact with the fiber holder 112) is sufficiently flat enough to match the end surface of the fiber holder 112.

  The heating (temperature, time) of the mold 104 is controlled so that only the area of the conical prism material 105 that contacts the mold 104 is melted and the other areas that are in contact with the fiber holder 112 are not melted. For example, in the present embodiment, the region of the conical prism material 105 in contact with the mold 104 rises to about 350 ° C. and melts, but the region in close contact with the fiber holder 112 rises only to about 200 ° C. and melts. There is nothing. As a result, the conical prism material 105 melts only in the region in contact with the mold 104, but the other regions do not melt, and is fused to the protective tube 101 after curing and serves as a detection member having a prism function. Member 106 is formed.

  Next, the distal end portion 101a of the protective tube 101 is vertically inserted into the opening 104c of the mold 104 and pressed against the fused conical prism member 106 (see FIG. 1E). As a result, only the region of the conical prism member 106 that contacts the protective tube 101 is melted and melt-bonded to the protective tube 101, and the regions that are in contact with the fiber holder 112 other than the region that is bonded to the conical prism member 106 are not melted. The fiber holder 112 is in close contact with the end surface 112a.

  Next, after the mold 104 is cooled by air A or the like shown in FIG. 1 (f) to solidify the melted region of the conical prism member 106, the protective tube 101 and the conical prism member 106 are removed from the mold 104. Pull out (see FIG. 1 (g)). In this way, the protective tube 101 in which the conical prism member 106 is liquid-tightly joined to the distal end portion 101a is formed.

  Then, the remaining resin member of the conical prism member 106 adhering to the outer peripheral surface of the protective tube 101 is scraped off as necessary so that the conical prism member 106 forms an appropriate optical path for the optical fibers 107 and 108 for projecting and receiving. To do.

  By implementing such a manufacturing method of the optical fiber sensor unit 1, a new function can be exhibited in addition to the functions of the above-described manufacturing method of the optical fiber sensor unit 3 related to the present invention.

  Specifically, the heat resistance temperature of the fiber holder 112 made of LCP is not as high as that of the fluorine resin as compared with the polyimide (PI) resin, but when the conical prism member 106 is fused to the protective tube 101, the conical prism is used. Since the region in contact with the fiber holder 112 of the member 106 is not melted, a material whose melting point is not as high as that of polyimide (PI) such as LCP or wholly aromatic polyester can be used for the fiber holder 112. In addition, since LCP is excellent in injection moldability, unlike the case where the fiber holder 112 is formed of polyimide or wholly aromatic polyester, no cutting process is required, so that the optical fiber sensor unit can be manufactured at low cost. .

  Further, when the conical prism member 106 is fused to the protective tube 101 as in the proposed method for manufacturing the optical fiber sensor unit 3 related to the present invention described above, the region in contact with the fiber holder 112 of the conical prism member 106 is heated. Bubbles are not generated due to contraction (sinking of the tree fingers). FIG. 3 is an explanatory diagram showing the reason why such bubbles do not occur. As shown in FIG. 3A, in this embodiment, only the region 105a of the conical prism material 105 that contacts the mold 104 is melted by heating the die 104, and the other region, that is, the region 105b that contacts the fiber holder 112 is melted. Does not melt.

  Accordingly, as shown in FIG. 3B, when the protective tube 101 and the fiber holder 112 are attached to the partially melted conical prism material 105, the unmelted region 105b of the conical prism material 105 becomes the fiber holder 112. Even if the mold 104 is cooled after that, the sink of the finger does not occur in this region. As a result, as in the related invention described above, the air passes through the light projecting / receiving optical fibers 107 and 108 and the lens. It is never supplied. As a result, the melted region 105a of the conical prism material 105 is cured and adhered to the fiber holder 112 of the conical prism material 105 even after the melted region 105a is fused and bonded to the protective tube 101 as shown in FIG. The conical prism member 106 can be firmly fused to the tip of the protective tube 101 without generating bubbles in the region.

  FIG. 4 is a cross-sectional view of the optical fiber sensor unit 1 manufactured in the above-described process, cut along the axial direction. In FIG. 4, the lenses 113 and 114 and the conical prism member 106 are drawn with hatching omitted so that the optical path can be easily understood. When the conical prism member 106 at the tip of the optical fiber sensor unit 1 is in the air, the light emitted from the light projecting optical fiber 107 is converged by the lens 113 and is incident on the conical prism member 106, and its optical path is the conical prism member 106. The light is reflected and incident on the lens 114 as shown by the one-dot chain line, converged by the lens 114 and incident on the light receiving optical fiber 108.

  On the other hand, when the conical prism member 106 is in the liquid, most of the light emitted from the light projecting optical fiber 107 through the lens 113 passes through the conical prism member 106 and is emitted into the liquid as indicated by a solid line. The amount of light received by the light receiving optical fiber 108 is greatly reduced. Accordingly, by electrically detecting the change in the amount of light from the optical fiber 108 for receiving light, it is determined whether the tip of the optical fiber sensor unit 1, that is, the conical prism member 6, is present in the air or submerged in the liquid. Thus, the level of the liquid level can be detected.

  As described above, the method for manufacturing an optical fiber sensor unit according to the present invention uses a mold that matches the outer shape of the sealing member, and heats the sealing member by placing the sealing member in the mold. The region in contact with the mold is melted, and only the melted region in contact with the mold is fused to the tube, and the unmelted region of the sealing member is brought into close contact with the fiber holder to complete the manufacture of the optical fiber sensor unit 1. .

  This prevents bubbles from being generated due to thermal contraction of the sealing member (sinking of the finger) in the region of the sealing member in contact with the fiber holder 112. In addition, since the temperature of the sealing member in contact with the fiber holder has reached the temperature at which the sealing member is melted, the material of the fiber holder itself is as high as polyimide or wholly aromatic polyester as LCP. No material can be used. Since LCP is excellent in injection moldability, the manufacturing cost can be reduced correspondingly, and an inexpensive optical fiber sensor unit can be provided.

  Of course, a highly reliable optical fiber sensor unit is produced without generating bubbles in the sealing member even if polyimide, wholly aromatic polyester, or the like, which has excellent heat resistance but can only be manufactured by cutting, is used as the material of the fiber holder 112. can do. However, since LCP is used for the fiber holder as in the present embodiment, an optical fiber sensor unit with reduced costs can be manufactured, which can be said to be the most preferable mode.

It is explanatory drawing of the manufacturing method of the optical fiber sensor unit which concerns on one Embodiment of this invention. It is sectional drawing of the fiber holder of the optical fiber sensor unit shown in FIG. 1, the optical fiber for light projection, and the optical fiber for light reception. It is sectional drawing explaining the fusion | melting connection of the fiber holder and a conical prism member in the manufacturing process shown to FIG.1 (d)-(e). It is sectional drawing explaining the liquid detection principle of the optical fiber sensor unit concerning this embodiment manufactured with the manufacturing method shown in FIG. It is explanatory drawing of the manufacturing method which melt-joins a conical prism member to the front-end | tip part of the protection tube used for the conventional liquid level detection sensor (optical fiber sensor unit). A fiber holder in which one end of a light projecting optical fiber and a light receiving optical fiber is housed and fixed in a protective tube having a conical prism member at the tip manufactured by the manufacturing method shown in FIG. 5, and a light projecting optical fiber and a light receiving optical fiber are fixed. It is explanatory drawing of the manufacturing method which manufactures the liquid level detection sensor accommodated in the state which carried out. It is explanatory drawing explaining the manufacturing method of the optical fiber sensor unit proposed in relation to this invention in order to solve the fault of a prior art example. It is explanatory drawing explaining the inconvenient point which arises with the manufacturing method in FIG.

Explanation of symbols

1, 2, 3 Optical fiber sensor unit 101 Protection tube 101a Tip 104 Die 104a Upper surface 104b Recess 104c Opening 105 Conical prism material 105a, 105b Region 106 Detection member (conical prism member)
DESCRIPTION OF SYMBOLS 107 Optical fiber for light emission 107a Front end surface 107A Core 107B Cover 108 Optical fiber for light reception 108a Front end surface 108A Core 108B Cover 112 Fiber holder 112a Front end surface 112b Rear end surface 112c, 112d, 112e Hole 113 (Self focus) Lens 113a Front end surface 113b Rear end surface 114 (Self-Focus) Lens 114a Front end surface 114b Rear end surface 201 Protective tube 201a Front end portion 202 Metal rod 204 Die 204a Top surface 204b Recessed portion 204c Opening portion 205 Fluorine resin member 206 Detection member (conical prism member)
206a Plane portion 207 Light emitting optical fiber 208 Light receiving optical fiber 209 Fiber holder 209a Tip surface 210 Retaining ring 301 Protective tube 301a One side opening end 304 Mold 304a Upper surface 304b Recessed portion 304c Opening portion 305 (305a, 305b) Fluororesin Member 306 Conical prism member (detection member)
306a Flat surface (rear surface)
306c Bubble 307 Optical fiber for light projection 308 Optical fiber for light reception 312 Fiber holder 312a End face 315,316 Lens A Air

Claims (5)

A method of manufacturing an optical fiber sensor unit comprising a tube and an optical fiber holder inserted at the distal end of the tube, and a sealing member for sealing the distal end of the tube fused to the distal end of the tube so as to be in a liquid-tight state In
In fusing the sealing member to the tube,
Prepare a mold having a cavity that matches the outer shape of the sealing member after fusion,
A sealing member before melting having an outer shape matching the cavity is accommodated in the cavity,
A method of manufacturing an optical fiber sensor unit, wherein the cavity is heated and the sealing member is fused to the tube before the sealing member is completely melted.   The method for manufacturing an optical fiber sensor unit according to claim 1, wherein the tube and the sealing member are made of a fluororesin.   3. The method of manufacturing an optical fiber sensor unit according to claim 2, wherein the optical fiber holder is made of a liquid crystal polymer.   An optical fiber sensor unit manufactured by the manufacturing method according to any one of claims 1 to 3. A synthetic resin tube having a hollow cylindrical shape, a synthetic resin optical fiber holder held inside the distal end of the tube to hold an optical fiber disposed in the tube, and a fusion welded to the distal end of the tube In the optical fiber sensor unit having a sealing member made of a synthetic resin that functions as an optical reflecting surface while sealing the tip of the tube,
The optical fiber holder is formed in an outer dimension that can be press-fitted into the tube and is press-fitted from the distal end side of the tube,
The sealing member has a surface that directly or indirectly contacts the end face of the optical fiber holder, and the sealing member and the tube are in a state where the peripheral portion of the surface is melted and the central portion is not melted. An optical fiber sensor unit characterized in that the tip is joined.

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