阅读说明：本技术 火花塞的制造方法 (Method for manufacturing spark plug ) 是由 西村航太 胜川典英 于 2019-07-10 设计创作，主要内容包括：本发明提供一种火花塞的制造方法,能够提高检查精度。包括：火花塞测定工序,测定包含对象部位的对象图像中的对象部位的实测尺寸或对象部位所包含的实测像素数；基准器拍摄工序,对分别具有呈预先确定的已知尺寸的基准部位的多个基准器以包含基准部位的方式分别拍摄而取得多个基准图像；基准器测定工序,分别测定多个基准图像中的基准部位的实测尺寸或实测像素数；回归直线导出工序,根据多个基准器的实测尺寸或实测像素数、已知尺寸,通过最小二乘法求出回归直线；及判定工序,基于使用表示回归直线的关系式对对象部位的实测尺寸进行校正而得到的校正值,判定对象部位是否处于预定的范围内。(The invention provides a method for manufacturing a spark plug, which can improve the inspection precision. The method comprises the following steps: a spark plug measurement step of measuring an actual measurement size of a target portion or an actual measurement pixel number included in the target portion in a target image including the target portion; a reference device imaging step of imaging a plurality of reference devices each having a reference portion of a predetermined known size so as to include the reference portion, thereby acquiring a plurality of reference images; a reference device measurement step of measuring an actually measured size or an actually measured pixel number of a reference portion in each of a plurality of reference images; a regression line derivation step of obtaining a regression line by a least square method from the measured dimensions or the measured pixel numbers and the known dimensions of the plurality of standards; and a determination step of determining whether or not the target site is within a predetermined range based on a correction value obtained by correcting the actual measurement size of the target site using a relational expression indicating a regression line.)

1. A method of manufacturing a spark plug, comprising:

a spark plug imaging step of imaging a target portion of a spark plug to be measured to obtain a target image; and

a spark plug measurement step of measuring a measured size of the target portion in the target image or a measured number of pixels included in the target portion in the target image,

the method of manufacturing the spark plug further includes:

a reference device imaging step of imaging a plurality of reference devices each having a reference portion having a predetermined known size and different known sizes so as to include the reference portion, and acquiring a plurality of reference images;

a reference device measurement step of measuring an actual measurement size of the reference portion in each of the plurality of reference images or an actual measurement pixel number included in the reference portion in each of the plurality of reference images;

a regression line derivation step of obtaining a regression line by a least square method from the measured dimensions of the plurality of standards or the measured pixel numbers included in the plurality of standards and the known dimensions; and

and a determination step of determining whether or not the target portion is within a predetermined range, based on a correction value obtained by correcting the measured size of the target portion or the measured pixel number included in the target portion obtained in the spark plug measurement step using a relational expression indicating the regression line.

2. The method of manufacturing a spark plug according to claim 1,

in the spark plug measurement step, the correction value is displayed on a display device that displays a measurement result of the target portion.

3. The method for manufacturing a spark plug according to claim 1 or 2, wherein,

the target portion is a spark gap formed between two electrodes.

4. The method for manufacturing a spark plug according to any one of claims 1 to 3, wherein,

before the reference measuring step, the number of pixels included in the reference portion in one of the plurality of reference images is measured, the pixel size of each pixel is calculated from the known size and the number of pixels, and the reference measuring step and the spark plug measuring step are performed using the pixel size.

Technical Field

The present invention relates to a method for manufacturing a spark plug, and more particularly, to a method for manufacturing a spark plug including a step of inspecting dimensions of various portions of the spark plug.

Background

There is known a technique for manufacturing a spark plug by checking sizes of various portions such as a spark gap that affects ignition performance by image processing (patent document 1).

[ patent document 1 ] Japanese patent laid-open publication No. 2002-313525

Disclosure of Invention

Problems to be solved by the invention

In this technique, improvement in inspection accuracy is required.

The present invention has been made to meet the above-described demand, and an object thereof is to provide a method for manufacturing a spark plug capable of improving inspection accuracy.

Means for solving the problems

To achieve the object, the present invention comprises: a spark plug imaging step of imaging a target portion of a spark plug to be measured to obtain a target image; and a spark plug measurement step of measuring an actual measurement size of the target portion in the target image or an actual measurement pixel number included in the target portion in the target image. Further comprising: a reference device imaging step of imaging a plurality of reference devices each having a reference portion having a predetermined known size and different known sizes so as to include the reference portion, and acquiring a plurality of reference images; a reference device measurement step of measuring the actual measurement size of a reference portion in each of the plurality of reference images or the actual measurement pixel number included in the reference portion in each of the plurality of reference images; a regression line derivation step of obtaining a regression line by a least square method from the measured dimensions of the plurality of standards or the measured pixel number and the known dimensions included in the plurality of standards; and a determination step of determining whether or not the target portion is within a predetermined range, based on a correction value obtained by correcting the actual measurement size of the target portion or the actual measurement pixel number included in the target portion obtained in the spark plug measurement step using a relational expression indicating a regression line.

Effects of the invention

According to the method of manufacturing a spark plug of the first aspect, the actual measurement size or the actual measurement pixel count of the target portion measured on the image is corrected based on the correction values derived based on the plurality of references having different known sizes. Thus, the accuracy of correction of the actual measurement size or the actual measurement pixel number of the target region can be improved as compared with the case of using the correction formula derived based on 1 reference. As a result, the inspection accuracy can be improved.

According to the method of manufacturing a spark plug of the second aspect, in the spark plug measuring step, the correction value is displayed on the display device that displays the measurement result of the target site. Thus, in addition to the effects of the first aspect, the operator can confirm the adequacy or not from the value displayed by the display device.

According to the method of manufacturing a spark plug of the third aspect, the target portion is a spark gap formed between the two electrodes. Therefore, in addition to the effects of the first or second aspect, the inspection accuracy of the spark gap formed between the two electrodes can be improved.

According to the method of manufacturing a spark plug described in the fourth aspect, before the reference device measuring step, the number of pixels included in the reference portion in one of the plurality of reference images is measured, and the pixel size of each pixel is calculated from the known size and the number of pixels. A reference device measuring step and a spark plug measuring step are performed using the pixel size. This can improve the correlation of the regression analysis, and therefore can further improve the inspection accuracy in addition to the effect of any one of the first to third aspects.

Drawings

Fig. 1 is a cross-sectional side view of a spark plug according to an embodiment.

Fig. 2 is a schematic view of an inspection apparatus.

Fig. 3(a) is a front view of the reference device, and fig. 3(b) is a schematic diagram of an imaging element that images the reference device.

Fig. 4 is a correlation diagram showing a relationship between a known dimension and a measured dimension of a reference device.

Description of the reference numerals

10 spark plug

13 center electrode

16 ground electrode

17 spark gap (target part)

23a pixel

24 object image

27 display device

30 reference device

31 reference site

40 reference image

51 regression line

Known dimension of K reference site

Actual measurement size of L-reference site

Actual measurement size of M target part

Detailed Description

Preferred embodiments of the present invention will be described below with reference to the accompanying drawings. Fig. 1 is a cross-sectional side view of a spark plug 10 according to an embodiment. In fig. 1, the lower side of the paper surface is referred to as the front end side of the spark plug 10, and the upper side of the paper surface is referred to as the rear end side of the spark plug 10. The spark plug 10 includes a center electrode 13 held by an insulator 11 and a ground electrode 16 connected to a main metal fitting 15.

The insulator 11 is a cylindrical member formed of alumina or the like having excellent mechanical properties and high-temperature insulation properties, and has a shaft hole 12 penetrating along the axis O. A center electrode 13 is disposed on the tip end side of the axial hole 12.

The center electrode 13 is a rod-shaped member extending along the axis O, and a core material mainly composed of copper or copper is covered with nickel or a nickel-based alloy. The core material may be omitted. The center electrode 13 is held by the insulator 11, and the tip end side of the center electrode 13 protrudes from the tip end of the insulator 11.

The terminal fitting 14 is a rod-shaped member for connecting high-voltage cables (not shown), and is formed of a conductive metal material (for example, mild steel). The terminal fitting 14 is disposed on the rear end side of the insulator 11 with the tip end side inserted into the shaft hole 12. The terminal fitting 14 is electrically connected to the center electrode 13 inside the axial hole 12.

A metal body 15 is fixed to the front end side of the outer periphery of the insulator 11. The metal shell 15 is a substantially cylindrical member formed of a conductive metal material (for example, mild steel). A ground electrode 16 is connected to the tip of the metal shell 15. The ground electrode 16 is a rod-shaped metal (for example, made of a nickel-based alloy) member whose tip end side is bent. A spark gap 17 is formed between the front end portion of the ground electrode 16 and the center electrode 13.

The body metal fitting 15 includes a trunk portion 60 having a male screw 61 formed on an outer peripheral surface thereof, a seat portion 62 adjacent to a rear end side of the trunk portion 60, a connecting portion 63 adjacent to a rear end side of the seat portion 62, a tool engagement portion 64 adjacent to a rear end side of the connecting portion 63, and a fastening portion 65 adjacent to a rear end side of the tool engagement portion 64. The male screw 61 formed in the trunk portion 60 is screwed into a screw hole of an internal combustion engine (not shown). The seat portion 62 is a portion for closing a gap between a screw hole of an internal combustion engine (not shown) and the male screw 61.

The connecting portion 63 is a portion that is plastically deformed in a curved shape when the metal body 15 is assembled to the insulator 11 using the fastening portion 65. The tool engagement portion 64 is a portion for engaging a tool such as a wrench when the male screw 61 is screwed into a threaded hole of an internal combustion engine. The fastening portion 65 is a portion that is plastically deformed and bent inward in the radial direction when the body metal fitting 15 is assembled to the insulator 11. A packing 66 is disposed between the seat 62 and the male screw 61. In a state where the spark plug 10 is mounted on the internal combustion engine, the packing 66 is sandwiched between the seat 62 and the internal combustion engine, and airtightness is ensured.

The spark plug 10 is manufactured by, for example, the following method. First, the center electrode 13 is inserted into the axial hole 12 of the insulator 11, and the tip of the center electrode 13 is disposed so as to protrude from the tip of the insulator 11. Next, while ensuring the electrical conduction between the terminal fitting 14 and the center electrode 13, the terminal fitting 14 is inserted into the axial hole 12, and then the metal shell 15 to which the ground electrode 16 is connected in advance is fastened and assembled to the outer periphery of the insulator 11. The ground electrode 16 is bent so as to form a spark gap 17 of a predetermined size between the ground electrode 16 and the center electrode 13, and the spark plug 10 is obtained.

Fig. 2 is a schematic view of the inspection apparatus 20. The inspection device 20 performs dimensional inspection of various portions including the spark gap 17 of the spark plug 10. Hereinafter, the spark gap 17 will be described as an example of a measurement target portion of the spark plug 10.

The inspection device 20 is a device that images the center electrode 13 and the ground electrode 16 including the spark gap 17 (target portion) of the spark plug 10 and inspects whether the spark gap 17 is within a predetermined range. The inspection device 20 includes: a camera 21 provided with an imaging element 23 such as a CCD; and a lens 22 for setting the size of the field of view captured by the camera 21. The imaging element 23 images a field of view (range) in which the lens 22 is set, including the center electrode 13 and the ground electrode 16 of the spark gap 17, as a target image 24.

The inspection device 20 includes: an arithmetic device 25 for performing arithmetic processing based on the actual measurement dimension M of the spark gap 17 in the target image 24 captured by the imaging element 23; an input device 26 for inputting the size of each pixel of the imaging element 23 (pixel size described later) and the like to the arithmetic device 25; and a display device 27 for displaying the measurement result of the spark gap 17 by the arithmetic device 25. The inspection device 20 causes the imaging element 23 to image the center electrode 13 and the ground electrode 16 including the spark gap 17 to obtain an object image 24 (spark plug imaging step), and the arithmetic device 25 measures the actual measurement dimension M of the spark gap 17 in the object image 24 (spark plug measurement step). As described below, the inspection apparatus 20 corrects the actual measurement dimension M of the spark gap 17 (target site) to improve the inspection accuracy.

Referring to fig. 3 and 4, a method of correcting the actual measurement dimension M by the inspection apparatus 20 using the reference device 30 will be described. Fig. 3(a) is a front view of the reference device 30.

As shown in fig. 3a, the reference device 30 is a plate-shaped (for example, made of metal or ceramic) member formed by a member that prevents light from passing therethrough, and includes a reference portion 31 having a predetermined known dimension K. The reference device 30 includes a first portion 32, a second portion 34 disposed at a predetermined distance from the first portion 32, and a connecting portion 36 connecting the first portion 32 and the second portion 34. Edges 33, 35 of first portion 32 and second portion 34 are both straight, and edges 33, 35 are parallel. The reference portion 31 is a portion between the edges 33, 35. The known dimension K of the reference location 31 is the distance between the edges 33, 35 (the length of a line perpendicular to the edges 33, 35). The known dimension K is a dimension inherent to the reference gauge 30 measured by using a gauge such as a calibrated feeler gauge. The reference device 30 is prepared by preparing a plurality of reference devices having different known dimensions K (for example, reference devices having different known dimensions K by 0.1 mm).

Fig. 3(b) is a schematic diagram of the imaging element 23 that images the reference device 30. In the figure, arrows X and Y indicate directions in the plane of the imaging element 23. The imaging element 23 is a set of pixels 23a that convert the intensity of luminance into an electric signal. The reference device 30 is captured by the imaging element 23 as a reference image 40 (dark portion) including a reference portion 41. The reference image 40 includes a first portion 42, a second portion 44 disposed at a predetermined distance from the first portion 42 in the Y direction, and a connecting portion 46 connecting the first portion 42 and the second portion 44.

The imaging element 23 detects an edge 43 of the first portion 42 where the contrast of light and dark changes and an edge 45 of the second portion 44 where the contrast of light and dark changes. The actual measurement dimension L of the reference portion 41 (bright portion) in the reference image 40 measured by the inspection apparatus 20 is the distance between the edges 43 and 45 (the length of a straight line extending in the Y direction perpendicular to the edges 43 and 45). Here, when the known dimension K is compared with the actual measurement dimension L, a difference (error) occurs between the actual measurement dimension L and the known dimension K due to the influence of the field of view of the inspection apparatus 20, halation, the accuracy of the lens 22, calculation error, and the like.

In order to reduce this error, the inspection apparatus 20 first causes the imaging device 23 to image 1 of the plurality of fiducials 30 having different known dimensions K, and acquires 1 reference image 40. The known dimension k (mm) of the reference device 30 is divided by the number of pixels 23a in the Y direction included in the reference portion 41 in the reference image 40, and the dimension per pixel (hereinafter referred to as "pixel dimension") is calculated. The calculated pixel size (mm) is input from the input device 26 (see fig. 2) to the arithmetic device 25. In this way, the arithmetic device 25 can calculate the actual measurement size L by multiplying the calculated pixel size by the number of pixels of the reference portion 41 detected by the imaging element 23. As a result, the calculation error of the calculation device 25 can be suppressed.

Next, the inspection apparatus 20 causes the imaging element 23 to image a plurality of fiducials 30 having different known dimensions K so as to include the reference portion 31, and acquires a plurality of reference images 40 including the reference portion 41 (a fiducial imaging step). Next, the actual measurement dimensions L of the reference portions 41 in the reference image 40 are measured (reference instrument measurement step). Next, regression analysis is performed based on the known dimension K of the fiducial marker 30 and the measured dimension L of the fiducial image 40.

Fig. 4 is a correlation diagram showing a relationship between the known dimension K of the reference portion 31 of the plurality of fiducials 30 and the measured dimension L of the reference portion 41 of the reference image 40. The operator of the inspection apparatus 20 plots a plurality of points 50 indicating the known dimension K and the measured dimension L of the plurality of standards 30 on a graph in which the measured dimension L is taken on the vertical axis and the known dimension K is taken on the horizontal axis, and obtains a regression line 51 by the least square method from the relationship between the known dimension K and the measured dimension L (regression line derivation step).

The arithmetic device 25 corrects the actual measurement dimension M of the spark gap 17 in the target image 24 using the relational expression indicating the regression line 51, and obtains a correction value of the actual measurement dimension M. The inspection device 20 determines whether the spark gap 17 of each manufactured spark plug 10 is within a predetermined range based on the correction value (determination step). In the determination step, the spark plug 10 determined that the spark gap 17 is within the predetermined range proceeds to the next step. The spark plug 10 that determines that the spark gap 17 is not within the predetermined range resets the spark gap 17 by adjusting the curvature of the ground electrode 16.

Since the inspection device 20 performs the dimensional inspection of the spark gap 17 based on the correction value of the actual measurement dimension M, the inspection accuracy can be improved as compared with the case where the actual measurement dimension M is not corrected. Since the correction value of the actual measurement dimension M is obtained based on regression analysis of the plurality of known dimensions K and the actual measurement dimension L, the accuracy of correction can be improved for various actual measurement dimensions M having different values, compared to the case where, for example, the correction formula derived based on 1 reference device 30 is used. This contributes to improvement in inspection accuracy.

The inspection device 20 displays the correction value of the actual measurement dimension M on the display device 27 without displaying the actual measurement dimension M of the spark gap 17 before correction. Thus, the operator of the inspection device 20 can confirm the quality of the spark gap 17 by the value displayed on the display device 27.

The inspection apparatus 20 calculates the size of each pixel (pixel size) based on 1 reference image 40 before measuring the actual measurement size L of the plurality of reference images 40 for the purpose of performing regression analysis based on the known size K and the actual measurement size L. The calculated pixel size is input from the input device 26 to the arithmetic device 25, and the arithmetic device 25 multiplies the pixel size by the number of pixels of the reference portion 41 to calculate the actual measurement size L for performing the regression analysis. This can improve the correlation of the regression analysis, and thus can further improve the accuracy of the correction. This can further improve the inspection accuracy. Note that this operation may be omitted.

The reference device 30 includes a first portion 32 and a second portion 34 arranged with a gap (reference portion 31) therebetween. The spark plug 10 to be measured also includes a center electrode 13 and a ground electrode 16 disposed so as to leave a spark gap 17. The reference portion 31 of the fiducial device 30 is detected as a bright portion in the reference image 40. Similarly, the spark gap 17 is also detected as a bright portion in the object image 24. Since the reference portion 31 of the reference device 30 has a structure similar to the structure of the center electrode 13 and the ground electrode 16 disposed so as to leave the spark gap 17 to be measured, it is possible to suppress the occurrence of an error due to the structure of the reference device 30.

The present invention has been described above based on the embodiments, but the present invention is not limited to the above embodiments at all, and it can be easily estimated that various modifications and variations can be made within the scope not departing from the gist of the present invention.

In the embodiment, the case where the arithmetic device 25 obtains the correction value of the measured dimension M based on the regression analysis of the known dimensions K and the measured dimensions L of the plurality of standards 30 has been described, but the present invention is not necessarily limited to this. It is needless to say that instead of the actual measurement dimension L of the reference portion 31 of the reference device 30, the number of pixels 23a in the Y direction (hereinafter referred to as "actual measurement pixel number") included in the reference portion 41 in the reference image 40 of the plurality of reference devices 30 may be obtained, and the correction value of the actual measurement pixel number may be obtained based on the actual measurement pixel number and the regression analysis of the known dimension K of the reference device 30. The inspection device 20 compares the correction value of the number of actual measured pixels with a range of the number of actual measured pixels of the spark gap 17 set in advance, and determines whether or not the spark gap 17 is within a predetermined range. In this case as well, the inspection accuracy can be improved as in the embodiment.

In addition, when the correction value of the number of actual measured pixels obtained based on the regression analysis of the number of actual measured pixels and the known dimension K of the reference device 30 is multiplied by the dimension (pixel dimension) of each pixel, the correction value of the actual measured dimension M can be calculated. In this case, the inspection device 20 compares the correction value of the calculated measured dimension M with a range of the spark gap 17 set in advance, and determines whether the spark gap 17 is within a predetermined range. In this case as well, the inspection accuracy can be improved as in the embodiment.

In this case, the display device 27 may display the correction value of the measured size M or the correction value of the number of measured pixels. In any case, the operator of the inspection device 20 can confirm the adequacy of the spark gap 17 by the correction value displayed on the display device 27.

In the embodiment, the case where the tips for suppressing the flame-out action and the like are not disposed on the center electrode 13 and the ground electrode 16 has been described, but the present invention is not necessarily limited thereto. Of course, a tip may be disposed on at least one of the center electrode 13 and the ground electrode 16 of the spark plug 10. In this case, the inspection device 20 can also inspect the size of the spark gap 17 between the center electrode 13 and the ground electrode 16.

In the embodiment, the case of using the reference device 30 having the gap as the reference portion 31 is described, but the present invention is not necessarily limited thereto. It is needless to say that various shapes such as a rectangular plate shape, a needle shape, and a columnar shape can be used. In this case, any portion of the reference instrument whose known size can be measured may be used as the reference portion.

In the embodiment, the ground electrode 16 connected to the metal shell 15 is bent, but the present invention is not necessarily limited thereto. Of course, a straight ground electrode may be used instead of the bent ground electrode 16. In this case, the tip end side of the metal shell 15 is extended in the axial direction, and a linear ground electrode is connected to the metal shell 15 so as to face the center electrode 13.

In the embodiment, the case where the ground electrode 16 is disposed such that the front end portion of the ground electrode 16 and the center electrode 13 face each other in the axial direction is described. However, the positional relationship between the ground electrode 16 and the center electrode 13 may be appropriately set. As another positional relationship between the ground electrode 16 and the center electrode 13, for example, a case where the ground electrode is disposed so as to form a spark gap between a side surface of the center electrode 13 and a front end surface of the ground electrode 16 is cited.

In the embodiment, the spark gap 17 is exemplified as the target site to be inspected for the size of the spark plug 10, but the invention is not necessarily limited thereto. It is needless to say that the size of other target portions of the spark plug 10 can be checked by image processing. The size of the other target portion may be, for example, the outer diameter of the connecting portion 63 of the metal shell 15.

In the embodiment, the description has been given of the case where the dimensions of various portions of the spark plug 10 that ignites the air-fuel mixture by spark discharge are checked, but the present invention is not necessarily limited to this. For example, it is needless to say that the sizes of various portions of the spark plug for igniting the air-fuel mixture by corona discharge, dielectric barrier discharge, or pulse arc discharge can be checked.

In the embodiment, the spark plug 10 in which the gasket 66 is disposed between the seat portion 62 and the male screw 61 is exemplified, but the invention is not necessarily limited thereto. It is needless to say that the present invention can be applied to a so-called tapered-piece type spark plug in which the packing 66 is omitted, the surface of the seat portion 62 facing the front end side is formed into a tapered surface, and the tapered surface of the seat portion 62 is pressed against the internal combustion engine to ensure airtightness.