NDIR gas sensor and manufacturing method thereof
Patent Information
- Application Number
- JP2023079128
- Authority / Receiving Office
- JP · JP
- Patent Type
- Applications
- Current Assignee / Owner
- Filing Date
- 2023-05-12
- Publication Date
- 2026-01-09
AI Technical Summary
The manufacturing of NDIR gas sensors is hindered by high mold costs when using metal cells and durability issues with resin cells due to thermal expansion differences, leading to alignment and reflective film damage.
The NDIR gas sensor employs a resin pipe with a metal mirror fixed to its outer peripheral end, using engaging members and adhesives for precise alignment, and integrates a bandpass filter to enhance light transmission and durability.
This design allows for easy manufacturing, accurate positioning, and increased light intake while minimizing thermal stress-induced damage, ensuring high positional accuracy and reduced detection errors.
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Abstract
Description
[Technical field]
[0001] The present invention relates to an NDIR gas sensor and a method for manufacturing the same. [Background technology]
[0002] The NDIR gas sensor is equipped with a light source, a light receiving element, and a cell with a mirror that reflects the light from the light source and guides it to the light receiving element. If the mirror is shaped to form a part of a spheroid and the light source and the light receiving element are placed at the two foci of the spheroid, the light from the light source is reflected by the mirror and guided to the light receiving element (Patent Document 1: JP-A-5-503352). [Prior art documents] [Patent documents]
[0003] [Patent Document 1] Special table 5-503352 Summary of the Invention [Problem to be solved by the invention]
[0004] If the cell is made entirely of metal, the cost of the mold will be high. Also, if the cell is made of resin and a reflective film such as aluminum is formed on the inner surface by deposition, the difference in thermal expansion coefficient between resin and metal will cause problems with the durability of the reflective film.
[0005] An object of the present invention is to provide an NDIR gas sensor which is easy to manufacture and in which alignment between a substrate and a mirror is easy, and a method for manufacturing the same. [Means for solving the problem]
[0006] The NDIR gas sensor according to a first aspect of the present invention is an NDIR gas sensor comprising a substrate on which a light source, a light receiving element, and a driving circuit for the light source and the light receiving element are mounted, and a cell with a mirror fixed to the substrate, The mirror has a shape constituting a part of a spheroid and has an elliptical shape in a plan view, a light source and a light receiving element are disposed on the substrate at two focal positions of the spheroid; A bandpass filter is provided for one of the light source and the light receiving element, The cell includes a resin pipe having an elliptical shape in a plan view and the mirror, the mirror is made of metal, and its outer peripheral end is fixed to the pipe with resin; An engaging member is provided on one of the cell and the substrate, and an engaging hole is provided on the other, and the engaging member is engaged with the engaging hole and fixed by an adhesive.
[0007] The NDIR gas sensor according to a second aspect of the present invention is an NDIR gas sensor comprising a substrate on which a light source, a light receiving element, and a driving circuit for the light source and the light receiving element are mounted, a cell with a mirror, and an intermediate substrate, The mirror has a shape constituting a part of a spheroid and has an elliptical shape in a plan view, a light source and a light receiving element are disposed on the substrate at two focal positions of the spheroid; The cell includes a resin pipe having an elliptical shape in a plan view and the mirror, the mirror is made of metal, and its outer peripheral end is fixed to the pipe with resin; the cell and the intermediate substrate are integral or bonded together; the intermediate substrate is fixed to the substrate so as to be parallel to a surface of the substrate on which the light source and the light receiving element are mounted and to accommodate the light source and the light receiving element; the intermediate substrate has openings above the light source and above the light receiving element, and a bandpass filter is provided in the opening above the light source or above the light receiving element; A second engagement member is provided on one of the intermediate substrate and the substrate, and a second engagement hole is provided on the other, and the second engagement member is engaged with the second engagement hole and fixed by an adhesive.
[0008] In this invention, the light source and the light receiving element are arranged at two focal points of the mirror, so that a large amount of light is incident on the light receiving element. In addition, the resin pipe can easily lengthen the optical path length. The light source and the light receiving element can be arranged at the center of the substrate, so that even if the gas sensor is thermally deformed, the amount of light incident on the light receiving element does not change much. The metal mirror has its end embedded in the resin pipe, so that the mirror can be accurately attached to the pipe, and the mirror and the resin pipe can be molded as a single unit. Instead of providing an Al reflective film on the cell, the metal mirror is fixed, so that there is no problem of the reflective film being damaged by thermal stress. The cell is fixed to the substrate or intermediate substrate by an engagement member, so that the positional accuracy of the cell relative to the substrate is high, and this, combined with the high positional accuracy of the mirror relative to the cell, allows the light source and the light receiving element to be accurately positioned at both focal points of the mirror.
[0009] In the manufacturing method of the NDIR gas sensor of this invention, a metal mirror is set so as to be positioned in the fixed mold, the movable mold is brought close to the fixed mold, and resin is injected into the gap between the fixed mold and the movable mold to insert-mold a cell with the mirror. In addition to this, in the manufacturing of the NDIR gas sensor, a light source, a light receiving element, and a driving circuit are attached to the substrate, and the substrate and the cell are fixed to each other with an engagement member, an engagement hole, and an adhesive. Instead of fixing the substrate and the cell, the substrate and intermediate substrate may be fixed to each other with an engagement member, an engagement hole, and an adhesive. The intermediate substrate and the cell may be molded as one unit, and they may be fixed to each other with an engagement member, an engagement hole, and an adhesive.
[0010] In a second manufacturing method of the NDIR gas sensor of the present invention, a flange surface having an elliptical shape in a plan view and a side wall surrounding the outer periphery of the flange surface are provided at the upper end of the cell, and after molding of the cell, a metal mirror is placed on the flange surface, and the surface of the mirror opposite to the flange surface is fixed to the cell with resin.
[0011] In this manufacturing method, although not limited to any particular one, since there is no restriction due to mirrors, the intermediate substrate can be molded integrally with the cells. The resin used is a thermosetting resin, an ultraviolet curing resin, or the like.
[0012] In this invention, a cell in which a metal mirror is positioned on a resin pipe can be easily manufactured. [Brief description of the drawings]
[0013] [Figure 1] Cross-sectional view of the NDIR gas sensor of the embodiment [Diagram 2] Plan view of the NDIR gas sensor of the embodiment [Diagram 3] Cross-sectional view of a modified NDIR gas sensor [Figure 4] FIG. 1 is a schematic diagram showing insert molding of a cell in an embodiment; [Diagram 5] FIG. 1 is a cross-sectional view of the NDIR gas sensor of the second embodiment, showing the state before the mirror is attached. [Figure 6] 1 is a cross-sectional view of an NDIR gas sensor according to a second embodiment of the present invention; DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0014] The best mode for carrying out the present invention will be described below. EXAMPLES
[0015] An embodiment and its modifications are shown in Fig. 1 to Fig. 6. Fig. 1 and Fig. 2 show an NDIR gas sensor 2 of the embodiment, which includes a substrate 4 and a cell 6. The cell 6 includes a resin pipe 6 that is elliptical in plan view, and a metal mirror 8 that is fixed to the top of the pipe 6 by insert molding, and the metal mirror 8 has the shape of a part of a spheroid and is elliptical in plan view. An outer peripheral end 9 of the metal mirror 8 is embedded in the resin pipe, and the metal mirror 8 is fixed to the pipe 6.
[0016] A light source 10 and a light receiving element 12 are provided on a substrate 4, and are arranged at two focal points of a metal mirror 8 that constitutes part of a spheroid, and when light from the light source 10 is reflected by the mirror 8, it is incident on the light receiving element 12. The light source 10 is a MEMS heater, an infrared LED, an infrared lamp, etc., and the light receiving element 12 is a thermopile, a thermoelectric element, a photodiode, etc.
[0017] In the embodiment, a resin intermediate substrate 14 is provided, and a bandpass filter 16 for the light from the light source 10 is fixed to the intermediate substrate 14, and transmits light of detection wavelengths of, for example, CO2, methane, refrigerant, etc. The bandpass filter 16 may be provided on the light receiving element 12 side, rather than on the light source 10 side. Also, two pairs of a bandpass filter and a light receiving element may be provided, and the transmission wavelength of one of the bandpass filters may be excluded from the detection wavelengths, to monitor the light intensity of the light source 10.
[0018] As shown in FIG. 3, instead of providing the intermediate substrate 14, for example, the bandpass filter 16 may be attached to a pipe-shaped holder 24, and the light source 10 or the light receiving element 12 may be disposed within the holder 24.
[0019] 1 and 2, the driving circuit 17 is composed of a driving circuit for the light source 10, a signal processing circuit for the light receiving element 12, a processor for determining the concentration of gases such as CO2, and a memory. The driving circuit 17 is connected to an external circuit (not shown) via a terminal (not shown) at the end of the substrate 4 or a terminal provided on the bottom surface of the substrate 4. In this embodiment, the NDIR gas sensor 2 outputs a gas concentration such as the CO2 concentration, and a power supply, a gas concentration display circuit, a communication interface with related devices, and the like are provided on the external circuit side. The power supply, display circuit, communication interface, and the like may be provided within the NDIR gas sensor 2.
[0020] The intermediate substrate 14 is fixed to the substrate 4 by, for example, a pin 18, and the pin 18 is set in an engagement hole for positioning in the substrate 4 together with an adhesive. Similarly, a claw 20 is fixed in an engagement hole provided in the cell 6 with an adhesive to fix the substrate 4 and the cell 6. Instead of the claw 20, a pin (not shown) standing on the top surface of the substrate 4 or the bottom surface of the pipe 7 may be fixed in an engagement hole of the opposite member with an adhesive to fix the substrate 4 and the cell 6. Also, the pin 18 may be erected from the substrate 4, engaged with an engagement hole in the intermediate substrate 14, and fixed with an adhesive. Furthermore, instead of the pin 18, a claw (not shown) may be provided on one of the substrate 4 and the intermediate substrate 14, engaged with an engagement hole provided on the other, and fixed with an adhesive.
[0021] 4 shows a schematic diagram of insert molding of a cell 6, where 30 is a fixed mold, which is set so as to position a metal mirror 8 by an appropriate means, and a movable mold 32 is lowered and resin is injected through a resin injection hole 34. Injection molding of the cell 6 so that the metal mirror 8, which has been positioned in advance in the fixed mold 30, is fixed to the resin is called insert molding of the cell 6 equipped with the mirror 8.
[0022] The following shows an example of the size of the NDIR gas sensor 2. The substrate 4 is rectangular or square with each side measuring 20 to 30 mm, and the total height of the cell 6 (height from the substrate 4 to the outer top surface of the mirror 8) is, for example, 15 to 25 mm. The length of the cell 6 in the major axis direction of the spheroid is preferably long enough so as not to interfere with the arrangement of the drive circuit 17.
[0023] The embodiment has the following features. 1) The light source 10 and the light receiving element 12 are disposed at both focal points of the mirror 8. When the light from the light source 10 is reflected by the mirror 8, it is incident on the light receiving element 12, and therefore the amount of light incident on the light receiving element 12 is large. 2) By lengthening the pipe 6 (increasing its height from the substrate 4), the optical path length from the light source 10 to the light receiving element 12 can be increased. In the embodiment, this can be set to 30 mm or more and 50 mm or less. 3) The distance between the light source 10 and the light receiving element 12 is smaller than when they are placed at both ends of the cell. In addition, the light source 10 and the light receiving element 12 are located at the center of the substrate 4. For these reasons, even if the substrate 4 is warped due to the difference in the thermal expansion coefficient between the pipe 7 and the substrate 4, the change in the amount of light incident on the light receiving element 12 from the light source 10 via the mirror 8 is relatively small. In other words, the detection error due to deformation of the NDIR gas sensor 2 is small. 4) The metal mirror 8 is insert-molded into the resin pipe 7. Therefore, the positional accuracy of the mirror 8 in the cell 6 is high, and the cell 6 is easy to manufacture. Furthermore, unlike the case where an Al evaporated film is provided on the top of a resin cell, the mirror is not damaged by thermal stress or the like. 5) Since the cells 6 are fixed to the substrate 4 or the intermediate substrate 14 by the claws 20, the positional accuracy of the cells 6 with respect to the substrate 4 is high, and assembly is easy. When the intermediate substrate 14 is used, the cells 6 may be fixed to the intermediate substrate 14 and then the intermediate substrate 14 may be fixed to the substrate 4, or conversely, the cells 6 may be fixed to the intermediate substrate 14 and then the intermediate substrate 14 may be fixed to the substrate 4.
[0024] Second Example A second embodiment is shown in Figs. 5 and 6. The same reference numerals as in Figs. 1 to 4 denote the same parts, and the embodiment is the same as that in Figs. 1 and 2, except where otherwise noted. 42 is a new NDIR gas sensor, and the cell 46 is made up of a pipe 47 and an intermediate substrate 54. The pipe 47 and the intermediate substrate 54 are molded as an integral body, but they may be molded separately and fixed to each other by pins and adhesives. At the upper end of the cell 46, there is a flange surface 48 that is elliptical in plan view, and a side wall 49 that surrounds the flange surface 48. The flange surface 48 is shaped to fit a flange surface 71 that forms the bottom surface of the outer peripheral end 70 of a metal mirror 68.
[0025] FIG. 5 shows the resin cell 46, which is made up of the pipe 47 and the intermediate substrate 54, molded as one piece. The pins 18 of the intermediate substrate 54 are inserted into the pin holes 19 and fixed with adhesive. In this embodiment, the light source 10 is placed below the opening 55, and the light receiving element 12 is placed below the opening 56. Although not particularly limited, the bandpass filter 16 is fixed so as to cover the opening 56. Before or after fixing the cell 46 to the substrate 4, a metal mirror 68 is placed on the flange surface 48, and the position of the outer peripheral end 70 of the mirror 68 is regulated by the side wall 49. Then, a thermosetting or ultraviolet-curing resin 72 is dripped onto the upper part of the outer peripheral end 70, and the resin 72 is cured by heat or ultraviolet light, and the mirror 68 is fixed to the cell 46.
[0026] In this embodiment, since no insert is formed and there is no restriction due to the mirror 68, the pipe 47 and the intermediate substrate 54 can be molded as a single unit. The mirror 68 is positioned in the height direction and horizontal direction by the flange surface 48 and the side wall 49, and is fixed with resin 72. [Explanation of symbols]
[0027] 2,22 NDIR gas sensor 4. Board 6 Cells 7. Pipes 8 Metal mirror 9 Outer edge 10 light source 12 Photodetector 14 Intermediate board 16 Bandpass Filters 17 Drive circuit 18-pin 19 Pin hole 20 Claws 24 Holder 30 Fixed type 32 Movable type 34 Resin injection hole 42 NDIR gas sensor 46 Cells 47 Pipe 48,71 Flange surface 49 Side wall 54 Intermediate board 55,56 aperture 68 Mirror 70 Outer edge 72 Resin
Claims
1. An NDIR gas sensor comprising: a substrate on which a light source, a light receiving element, and a drive circuit for the light source and the light receiving element are mounted; and a cell with a mirror fixed to the substrate, The mirror has a shape that constitutes a part of a spheroid and is elliptical in plan view, a light source and a light receiving element are disposed on the substrate at two focal positions of the spheroid; a bandpass filter is provided for one of the light source and the light receiving element; the cell includes a resin pipe having an elliptical shape in a plan view and the mirror; The mirror is made of metal, and its outer peripheral edge is fixed to the pipe with resin. The NDIR gas sensor further comprises an engaging member provided on one of the cell and the substrate and an engaging hole provided on the other, the engaging member engaging with the engaging hole and fixed with an adhesive.
2. An NDIR gas sensor comprising a first substrate on which a light source, a light receiving element, and a drive circuit for the light source and the light receiving element are mounted, a cell with a mirror, and an intermediate substrate, The mirror has a shape that constitutes a part of a spheroid and is elliptical in plan view, a light source and a light receiving element are disposed on the first substrate at two focal positions of the spheroid; the cell includes a resin pipe having an elliptical shape in a plan view and the mirror; The mirror is made of metal, and its outer peripheral end is fixed to the pipe with resin. the cell and the intermediate substrate are integral or bonded to each other; the intermediate substrate is parallel to a surface of the first substrate on which the light source and the light receiving element are mounted, and is fixed to the first substrate, and the light source and the light receiving element are accommodated between the intermediate substrate and the first substrate, and further, the space between the first substrate and the cell is divided into a space between the intermediate substrate and the cell and a space between the intermediate substrate and the first substrate, the intermediate substrate has openings above the light source and above the light receiving element, and a band pass filter is provided in the opening above the light source or above the light receiving element; An NDIR gas sensor, wherein a second engaging member is provided on one of the intermediate substrate and the first substrate, and a second engaging hole is provided on the other, and the second engaging member engages with the second engaging hole and is fixed with an adhesive.
3. 3. A method for manufacturing the NDIR gas sensor of claim 1 or 2, comprising the steps of: A method for manufacturing an NDIR gas sensor, comprising the steps of: setting a metal mirror in position on a fixed mold; bringing a movable mold close to the fixed mold; and injecting resin into the gap between the fixed mold and the movable mold, thereby insert-molding a cell with the mirror.
4. 3. A method for manufacturing the NDIR gas sensor of claim 1 or 2, comprising the steps of: A flange surface having an elliptical shape in a plan view and a side wall surrounding the outer periphery of the flange surface are provided at the upper end of the cell, A method for manufacturing an NDIR gas sensor, comprising the steps of: placing a metal mirror on a flange surface after molding a cell; and fixing the surface of said mirror opposite to the flange surface to the cell with resin.