JP6708706B2 - Spark plug manufacturing method - Google Patents

Description

The present invention relates to a method for manufacturing a spark plug.

2. Description of the Related Art Conventionally, as a method for manufacturing a spark plug including an insulator obtained by firing a molded body, a method of using a jig for preventing collapse is known in order to suppress bending of the insulator after firing. This is because the molded body is placed vertically in the container, and this container is placed in the firing furnace and fired, but the molded body collapses in the container before firing, and as a result, the insulator bends. There is a risk. For example, in Patent Document 1 below, a support plate having a plurality of support holes formed therein is described as a jig for preventing falling. The molded body is inserted into the support hole of the support plate and held in a vertical posture.

JP2012-84549A

However, in the method using the fall prevention jig as described above, when the size of the insulator is different due to the difference in the product number, a dedicated fall prevention jig is required for each product number. Further, when the fall prevention jig is deteriorated due to heat or the like, the insulator cannot be held in the vertical posture, and therefore the fall prevention jig needs to be replaced as appropriate. Therefore, there is a problem that the manufacturing cost is high.

The present invention has been completed based on the above circumstances, and provides a method for manufacturing a spark plug capable of suppressing the bending of a molded body during firing without using a jig for preventing fall. The purpose is to

A method for manufacturing a spark plug of the present invention is a method for manufacturing a spark plug including an insulator formed by firing a molded body, wherein the molded body has a cylindrical shape with an axial hole formed along an axis. A step portion that protrudes outward in the radial direction is formed at an intermediate portion in the axial direction, and the plurality of molded bodies are placed in a container with an open upper surface so that the axis line is oriented in the vertical direction. And a calcination step of arranging the container on which the plurality of molded bodies are placed in a calcination furnace, and calcination of the plurality of molded bodies. From the step after the step to the firing step, the photographing step of photographing the molded body placed in the container from the upper side in the vertical direction with a camera, and the molded body reflected in the image acquired in the photographing step. Based on the imaging, while calculating the degree of inclination of the axis of the molded body from the vertical direction, among the plurality of molded bodies placed in the container, the degree of tilt is more than a predetermined degree of inclination. And a detection step of detecting a molded body that is greatly inclined.

According to the above-described manufacturing method, the molded body in which the degree of tilt is greater than the predetermined degree of tilt is detected based on the imaging of the molded body in the image captured by the camera. By correcting the posture of (1), it is possible to prevent the molded body from falling in the container before firing. Therefore, it is possible to suppress the bending of the molded body during firing without using a jig for preventing falling.

In the spark plug manufacturing method of the present invention, in the detecting step, a first extracting step of extracting a contour of the shaft hole from an image pickup of the molded body and a first extracting step of extracting an outer edge of the stepped portion from an image pickup of the molded body 2 extraction step may be performed to calculate the inclination degree based on the contour of the shaft hole and the outer edge of the step. According to such a method, it is possible to detect a molded body whose inclination degree is larger than a predetermined inclination degree, based on the imaging of the molded body shown in the image acquired in the imaging step.

In the spark plug manufacturing method of the invention, in the first extracting step, the center position of the shaft hole is calculated based on the contour of the extracted shaft hole, and in the second extracting step, the center position of the shaft hole is extracted. The center position of the step is calculated based on the outer edge of the step, and in the detecting step, the inclination degree is calculated based on the horizontal distance between the center position of the shaft hole and the center position of the step. It may be a method. According to such a method, it is possible to easily detect a molded body in which the degree of tilt is greater than the predetermined degree of tilt, based on the imaging of the molded body shown in the image acquired in the imaging step.

Further, in the method for manufacturing a spark plug of the present invention, the inclination degree is a horizontal distance between a central position of the shaft hole and a central position of the step portion, and the step from the tip of the molded body to the step portion. The tilt angle of the molded body is calculated based on the distance in the direction along the axis, and in the detecting step, a molded body in which the tilt angle is larger than a predetermined tilt angle may be detected. According to such a method, it is possible to detect a molded body in which the degree of inclination is greater than the predetermined degree of inclination, in consideration of the difference in size of the formed body due to the difference in product number.

Further, in the spark plug manufacturing method of the present invention, the second extraction step sets a region larger than the contour of the shaft hole based on the contour of the shaft hole extracted in the first extraction step, A method of extracting the outer edge of the step portion included in the area by binarizing the image of the area may be used. According to such a method, the outer edge of the step can be easily extracted in the second extraction step.

According to the present invention, it is possible to suppress the bending of the molded body during firing without using a jig for preventing the falling.

Partial cross-sectional schematic view showing a spark plug manufactured by the method for manufacturing a spark plug in the present embodiment. Schematic diagram showing a plurality of molded bodies placed in a container Schematic diagram showing how a plurality of molded bodies placed in a container are photographed by a camera The figure which shows the imaging of the molded object reflected in the image acquired in the imaging process. The figure which shows the image which performed the binarization process to the imaging of the molded object. The figure which shows the image which performed the binarization process to the area|region set based on the outline of the shaft hole. Diagram explaining how to calculate the tilt angle

Preferred forms of the present invention are shown below.
<Example>
Hereinafter, one embodiment of the present invention will be described in detail with reference to FIGS.
As shown in FIG. 1, the spark plug P manufactured by the manufacturing method according to this embodiment includes an insulator 50, a center electrode 51, a metal shell 52, and a ground electrode 53. Spark discharge is performed in the gap between the electrodes 53 (spark discharge gap). Hereinafter, each component of the spark plug P will be described with the lower side (firing part side) in FIG. 1 as the front end side and the upper side (opposite to the firing part) in FIG. 1 as the rear end side.

The insulator 50 has a cylindrical shape in which the shaft hole 11 is formed along the axis Z. The shaft hole 11 penetrates the insulator 50 in the axial direction. The center electrode 51 is arranged at the tip of the shaft hole 11 and is electrically connected to a terminal fitting 58 arranged at the rear end of the shaft hole 11. An electrical connection portion 59 that electrically connects the center electrode 51 and the terminal fitting 58 is arranged in the middle of the shaft hole 11. The electrical connection portion 59 is a resistor, conductive glass, or the like.

The tip end side portion of the insulator 50 is assembled inside the metal shell 52, and the rear end side portion of the insulator 50 projects outside the metal shell 52. The ground electrode 53 is provided at the tip of the metal shell 52.

The insulator 50 is provided with the step portion 12 that engages with the engaging portion 54 formed inside the metal shell 52. The step portion 12 is provided at an intermediate portion of the insulator 50 in the axial direction and projects outward in the radial direction. The step portion 12 has a constant protruding dimension over the entire circumference of the insulator 50.

The step portion 12 is formed in a predetermined range in the axial direction of the insulator 50. The step portion 12 includes a surface on the front end side in the axial direction of the insulator 50 (hereinafter referred to as a step portion front end surface 12S) and a surface on the rear end side in the axial direction of the insulator 50 (hereinafter, referred to as a step portion rear end surface 12U). And the step outer peripheral surface 12G located between the step front end surface 12S and the step rear end surface 12U. Both the step portion front end surface 12S and the step portion rear end surface 12U are inclined with respect to the axis Z. The step end surface 12S is inclined so as to face the inclined surface 55 formed on the locking portion 54 of the metal shell 52. The step portion outer peripheral surface 12G is a circumferential surface parallel to the axis Z.

The insulator 50 has a portion extending from the step portion 12 to the tip side along the axis Z (hereinafter, referred to as a first shaft portion 13) and a portion extending from the step portion 12 to the rear end side along the axis Z (hereinafter, referred to as “first shaft portion 13”). The second shaft portion 14) is provided. The outer diameter dimension of the first shaft portion 13 is smaller than that of the second shaft portion 14. As a result, the projecting dimension of the step portion tip surface 12S from the outer peripheral surface of the first shaft portion 13 (hereinafter referred to as the step portion tip dimension BS) is smaller than that of the step portion rear end surface 12U from the outer peripheral surface of the second shaft portion 14. It is larger than the projecting dimension (hereinafter referred to as the stepped portion rear end dimension BU).

Both the front end surface of the insulator 50 (hereinafter referred to as the shaft end surface 13S) and the rear end surface of the insulator 50 (hereinafter referred to as the shaft rear end surface 14U) are surfaces orthogonal to the axis Z. The tip portion of the center electrode 51 projects forward from the shaft tip surface 13S, and the end surface 58T of the terminal fitting 58 is in contact with the shaft rear end surface 14U.

The first shaft portion 13 includes a tip shaft portion 15 located on the tip end side and an intermediate shaft portion 16 located on the step portion 12 side. The tip shaft portion 15 has an outer diameter dimension smaller than that of the intermediate shaft portion 16. The tip shaft portion 15 has a tapered shape in which the outer diameter dimension is slightly reduced toward the shaft portion tip surface 13S. The intermediate shaft portion 16 has a tubular shape having a constant outer diameter along the axis Z of the insulator 50.

On the outer peripheral surface of the first shaft portion 13, a step surface 17 that is inclined with respect to the axis Z is formed between the tip shaft portion 15 and the intermediate shaft portion 16. The step surface 17 faces the inclined surface 57 of the step portion 56 formed inside the metal shell 52. The projecting dimension BD of the step surface 17 from the outer peripheral surface of the tip shaft portion 15 is smaller than the step portion tip dimension BS.

Next, an example of a method of manufacturing the spark plug P in this embodiment will be described. In the method of manufacturing the spark plug P, as a manufacturing process of the insulator 50, an arrangement step of placing a plurality of molded bodies 10 in the container 20 and a molded body 10 placed in the container 20 are photographed by the camera C. Of the molding step, the detection step of detecting the molded body 10 in which the tilt angle θ is tilted more than a predetermined tilt angle based on the imaging of the molded body 10 in the image acquired in the shooting step, and the detection step. Based on the result, an alignment step of aligning the molded bodies 10 and a firing step of placing the container 20 on which the molded bodies 10 are placed in a firing furnace and firing the molded body 10 are sequentially performed. The tilt angle θ corresponds to an example of the degree of tilt.

The molded body 10 has the outer shape of the insulator 50 by press-molding a raw material powder obtained by mixing a binder (for example, PVA) with alumina powder and a predetermined sintering aid powder, and then cutting the powder as required. It is a molded unfired insulator. The molded body 10 contracts by firing to become the insulator 50. For this reason, although the size of the molded body 10 is larger than the size of the insulator 50, the molded body 10 has the same configuration as the insulator 50 described above. Therefore, the configuration of the molded body 10 is given the same reference numeral as that of the configuration of the insulator 50 described above, and duplicate description is omitted.

First, as shown in FIGS. 2 and 3, an arrangement step of placing a plurality of molded bodies 10 in the container 20 is performed. In the arranging step, the container 20 is packed so that the axis Z of each molded body 10 is oriented in the vertical direction (so that the axis Z is in the direction along the vertical direction). The container 20 is an existing container that houses the molded body 10 and is used for firing. The container 20 includes a bottom wall 21 on which the plurality of molded bodies 10 are mounted, and a peripheral wall 22 that collectively surrounds the four molded bodies 10 mounted on the bottom wall 21 on all sides, and the entire top surface is open. Has been done. When viewed from above, the container 20 has a rectangular shape.

As shown in FIG. 3, the molded body 10 is placed on the bottom wall 21 in a vertical posture in which the shaft rear end surface 14U is in contact with the bottom wall 21 and the shaft front end surface 13S faces upward. The plurality of molded bodies 10 are in a state where their step portion outer peripheral surfaces 12G are in contact with each other. The molded body 10 located at the end of the container 20 comes into contact with the other adjacent molded body 10 and the peripheral wall 22 of the container 20. Each molded body 10 abuts on the peripheral wall 22 of another adjacent molded body 10 or container 20 to be self-supporting. At this time, the axis Z of each molded body 10 placed in the container 20 is not always completely parallel to the vertical direction, but may be slightly inclined with respect to the vertical direction. Further, the degree of inclination of the axis Z of each molded body 10 from the vertical direction is not always uniform, and the degree of inclination in one container 20 may cause a bending failure or a bending failure of the insulator 50. The molded body 10 that is inclined more than the inclination degree (predetermined inclination degree) and the molded body 10 whose inclination degree is not so large as to cause such a defect, that is, the molded body 10 that is smaller than the predetermined inclination degree are included. There is.

Next, a photographing step of photographing the molded body 10 placed in the container 20 with the camera C is performed. The photographing process is performed after the arrangement process and before the firing process. In the photographing step, as shown in FIG. 3, the molded body 10 placed in the container 20 is photographed by the camera C from the upper surface side in the vertical direction. The camera C is set so that the optical axis A is parallel to the vertical direction. The optical axis A of the camera C may be a direction along the vertical direction, and need not be strictly parallel to the vertical direction.

The camera C includes a telecentric lens, and the size of the image of the molded body 10 in the captured image changes even if the distance between the lens and the molded body 10 to be photographed changes in the direction of the optical axis A of the camera C. Has the effect of not doing it. Therefore, the image of the molded body 10 can be captured without distortion, and accurate dimension measurement can be performed.

The camera C photographs all the molded bodies 10 arranged in one container 20 in a plurality of times. That is, a plurality of shot images are shot for one container 20. It should be noted that the image may be taken once for one container 20 (that is, an image of one shot may be taken) without taking the image in plural times. Each image is a gray scale image in which the upper surface of the peripheral wall 22 of the container 20, the upper surfaces of the plurality of molded bodies 10 arranged in parallel, and the gaps between the molded bodies 10 are displayed. As shown in FIG. 4, the upper surface of each molded body 10 shown in each image is composed of a shaft hole 11, a shaft end surface 13S, a step surface 17, and a step front surface 12S. Further, on the upper surface of each molded body 10 shown in each image, the shadow of the first shaft portion 13 and the like are darkly projected on the step surface 17 and the stepped end surface 12S.

Next, the detection step of detecting the molded body 10 in which the tilt angle θ is tilted more than the predetermined tilt angle is performed based on the imaging of the molded body 10 shown in the image acquired in the photographing step. As shown in FIG. 7, the inclination angle θ is a value indicating the degree of inclination of the axis Z with respect to the reference line B parallel to the vertical direction (gravitational direction). In this embodiment, the reference line B is parallel to the optical axis A of the camera C. Note that, in FIG. 7, below the molded body 10, the center position 32 of the shaft hole 11, the outer edge 33 of the step portion 12, and the center position 34 of the step portion 12 are projected on a plane perpendicular to the reference line B. showed that.
In the detection step, the tilt angle θ of each molded body 10 is calculated. The inclination angle θ of each molded body 10 is calculated as follows.

First, the first extraction step of extracting the contour 31 of the shaft hole 11 from the image of the molded body 10 and calculating the center position 32 of the shaft hole 11 based on the extracted contour 31 of the shaft hole 11, A second extraction step of extracting the outer edge 33 of the step portion 12 from the image and calculating the center position 34 of the step portion 12 based on the extracted outer edge 33 of the step portion 12 is performed.

In the first extraction step, the image of the molded body 10 as shown in FIG. 4 is binarized as shown in FIG. 5 to extract the contour 31 of the shaft hole 11. The threshold value for binarization is set such that the shaft end surface 13S is converted to white and the shaft hole 11 is converted to black. Thereby, the shaft hole 11 can be made clear and the contour 31 of the shaft hole 11 can be specified. The XY coordinates of the center position 32 of the shaft hole 11 on the image are calculated based on the identified contour 31 of the shaft hole 11.

In the second extraction step, based on the contour 31 of the shaft hole 11 extracted in the first extraction step, as shown in FIG. 6, a region R which is slightly larger than the contour 31 of the shaft hole 11 is set, and the region R is set. The image of is binarized. The region R includes at least the entire upper surface of the molded body 10A from which the outer edge 33 of the step portion 12 is extracted, a part of the upper surface of another molded body 10B in contact with this molded body 10A, and the upper surface of the peripheral wall 22 of the container 20. The size includes a part. The region R is, for example, a circular shape with the contour 31 of the shaft hole 11 as the center and a diameter dimension larger than the outer diameter dimension of the stepped portion 12 obtained from the size of the molded body 10A based on the product number of the molded body 10A. be able to.

As shown in FIG. 6, the threshold for binarizing the image of the region R is such that the gap around the molded body 10A is black, the molded body 10A, the other molded body 10B in contact with the molded body 10A, and the peripheral wall 22 are white. The value converted to. As a result, the outer edge of the maximum inscribed circle that contacts the inside of the white region showing the other molded body 10B and the peripheral wall 22 and the black region showing the gap around the molded body 10A is the outer edge of the stepped portion 12 of the molded body 10A. It can be specified as 33. Then, the XY coordinates of the center position 34 of the step portion 12 on the image are calculated based on the specified outer edge 33 of the step portion 12. The inscribed circle may be a perfect circle or an ellipse. When the outer edge 33 of the specified step portion 12 apparently forms an ellipse due to the inclination of the molded body 10A, the XY coordinates of the center position of the ellipse are calculated.

Next, as shown in FIG. 7, a horizontal distance between the center position 32 of the shaft hole 11 calculated in the first extraction step and the center position 34 of the step portion 12 calculated in the second extraction step (hereinafter, The horizontal distance δ) is calculated, and the horizontal distance δ and the distance in the direction along the axis Z from the tip of the molded body 10 to the step portion 12 (hereinafter, referred to as the axial distance L) are calculated. The tilt angle θ of is calculated. The tilt angle θ is calculated by the tilt angle θ=arcsin (horizontal distance δ/axis line distance L). The axial distance L is the distance along the axis Z of the molded body 10 from the shaft end surface 13S of the molded body 10 to the outer edge on the rear end side of the step front surface 12S (the outer edge on the front end side of the step outer peripheral surface 12G). Is a fixed value defined for each product number.

In the detection step, the tilt angle θ of all the molded bodies 10 in the container 20 is calculated, and the molded body 10 having the tilt angle θ larger than a predetermined tilt angle is detected. The predetermined tilt angle is an angle that causes a bending failure or a bending failure of the insulator 50.

The detection result of the detection step may be displayed on the image captured by the camera C. In this display, for example, the tilt direction of the axis Z of each molded body 10 may be indicated by an arrow, or the numerical values of the horizontal distance δ and the tilt angle θ may be displayed. Further, the color of the arrow or numerical value displayed on the molded body 10 having the tilt angle θ larger than the predetermined tilt angle is different from the color of the arrow or numerical value displayed on the molded body 10 having the tilt angle θ smaller than the predetermined tilt angle. May be indicated by. In addition, a fixed number may be added to each molded body 10 in advance, and a fixed number of the molded body 10 having a tilt angle θ larger than a predetermined tilt angle may be displayed on the screen. This makes it possible to easily identify the molded body 10 having a large inclination angle θ in the container 20 and easily perform the alignment work after the detection step.

Next, an alignment step of aligning the molded bodies 10 is performed based on the result of the detection step. In this alignment step, the molded bodies 10 detected in the detection step are rearranged so that the tilt angle θ becomes smaller than a predetermined tilt angle. The aligning process can be performed by a machine such as a picking robot or manually by an operator. The upper end of the target molded body 10 is picked up and moved diagonally upward in a direction opposite to the tilt direction, and then the bottom wall of the container 20. 21 to reduce the tilt angle θ. Further, the molded body 10 detected in the detection step may be extracted, and in that case, a cushioning material may be arranged in the gap formed by extracting the molded body 10.

After that, the container 20 on which the molded body 10 is placed is placed in a firing furnace, and a firing step of firing the molded body 10 is performed.
With the above, the manufacturing process of the insulator 50 is completed.

After the manufacturing process of the insulator 50, an electrode arranging process of assembling the center electrode 51, the electrical connection portion 59, the terminal metal fitting 58 and the like to the insulator 50 to form an integrated structure, and a metal shell 52 and the like to the structure. And an assembling step of assembling. Known steps can be adopted for the electrode disposing step and the assembling step.
With the above, the method for manufacturing the spark plug P is completed.

Next, the operation and effect of the embodiment configured as described above will be described.
The method of manufacturing the spark plug P of this embodiment is a method of manufacturing the spark plug P including the insulator 50 formed by firing the molded body 10. The molded body 10 has a cylindrical shape in which a shaft hole 11 is formed along the axis Z, and has a step portion 12 protruding outward in the radial direction at an intermediate portion in the axial direction.

The method for manufacturing the spark plug P includes an arrangement step of placing a plurality of molded bodies 10 in a container 20 having an open upper surface so that the axis Z is oriented in the vertical direction, and a plurality of molded bodies 10 are mounted. And a firing step of firing the plurality of molded bodies 10 in a firing furnace. The molded body 10 placed in the container 20 after the placement step and before the firing step. A tilt angle θ of the axis Z of the molded body 10 from the vertical direction is calculated based on a photographing process of photographing the camera from the upper side in the vertical direction by the camera C and an image of the molded body 10 captured in the image acquired in the photographing process. At the same time, the process further includes a detection step of detecting, among the plurality of molded bodies 10 placed in the container 20, a molded body 10 having a tilt angle θ that is tilted more than a predetermined tilt angle.

According to this method, by correcting the detected posture of the molded body 10, the bending of the molded body 10 at the time of firing can be suppressed without using a jig for preventing fall. Therefore, it is possible to use not the special container provided with the jig for preventing the collapse but the ordinary container 20 not provided with the jig for preventing the collapse. Further, when the molded bodies 10 are aligned by the fall prevention jig, the molded body 10 may be damaged by contact with the fall prevention jig. However, according to the present embodiment, the fall prevention jig is used. Since no jig is used, the occurrence of such scratches can be prevented. Further, in general, the rate at which the molded bodies 10 tilted more than a predetermined tilt angle are generated in one container 20 is low, but it is not efficient to use a jig for preventing collapse of all the molded bodies 10. However, according to the present embodiment, it is efficient because only the molded bodies 10 having the tilt angle θ larger than the predetermined tilt angle need to be aligned.

In the detection step, a first extraction step of extracting the contour 31 of the shaft hole 11 from the image of the molded body 10 and a second extraction step of extracting the outer edge 33 of the stepped portion 12 from the image of the molded body 10 are performed. In the first extraction step, the center position 32 of the shaft hole 11 is calculated based on the extracted contour 31 of the shaft hole 11, and in the second extraction step, the step portion is calculated based on the outer edge 33 of the step portion 12 extracted. The center position 34 of 12 is calculated, and the tilt angle θ is calculated based on the horizontal distance δ between the center position 32 of the shaft hole 11 and the center position 34 of the step portion 12. The inclination angle θ is the horizontal distance δ between the central position 32 of the shaft hole 11 and the central position 34 of the step portion 12, the axial distance L in the direction along the axis Z from the tip of the molded body 10 to the step portion 12, It is calculated based on In the detection step, the molded body 10 whose tilt angle θ is larger than a predetermined tilt angle is detected.

According to this method, it is possible to detect the molded body 10 in which the inclination degree is greater than the predetermined inclination degree, in consideration of the difference in size of the molded body 10 due to the difference in product number. That is, comparing the molded body 10 having a large total length and the molded body 10 having a small total length, the inclination degrees are different even when the horizontal distances δ are equal. Therefore, it is difficult to uniformly determine whether the inclination degree is larger or smaller than the predetermined inclination degree only by the horizontal distance δ. However, according to the method of the present embodiment, it is possible to uniformly determine whether it is larger or smaller than the predetermined inclination degree, taking into consideration the difference in size of the molded body 10 due to the difference in product number.

In the second extraction step, a region R larger than the contour 31 of the shaft hole 11 is set based on the contour 31 of the shaft hole 11 extracted in the first extraction process, and the image of the region R is binarized. Thus, the outer edge 33 of the stepped portion 12 included in the region R is extracted. According to this method, the outer edge 33 of the stepped portion 12 can be easily extracted in the second extraction step.

<Other Examples>
The present invention is not limited to the embodiments described by the above description and the drawings, and the following embodiments are also included in the technical scope of the present invention.
(1) In the above embodiment, the configuration of the molded body 10 (insulator 50) was specifically illustrated, but the molded body is not limited to this, and the molded body has a cylindrical shape with an axial hole formed along the axis. It is only necessary that a step portion protruding outward in the radial direction is formed in the intermediate portion in the axial direction, and other configurations may be different from the configurations described in the above embodiments.
(2) In the above-described embodiment, a method of calculating the tilt angle θ and detecting the molded body 10 having a large degree of tilt based on the imaging of the molded body 10 shown in the image acquired in the photographing process has been described. Not limited to, if the tilt degree of the molded body is calculated based on the imaging of the molded body shown in the image acquired in the imaging step, any method may be used to detect the molded body having a large tilt degree, For example, the distance between the shaft holes of the molded bodies arranged in parallel from the image acquired in the imaging step may be calculated, and the degree of inclination of the molded body may be calculated based on the nonuniformity of the distance between the shaft holes. The inclination degree of the molded body may be calculated based on the fact that the contour of the inner shaft hole and the outer edge of the stepped portion become more elliptical as the inclination degree increases.
(3) In the above-described embodiment, the molded body 10 whose tilt angle θ is larger than the predetermined tilt angle is detected. However, the present invention is not limited to this, and for example, in imaging of a molded body shown in an image acquired in a photographing process. A horizontal distance between the center position of the axial hole and the center position of the step portion of each molded body calculated based on the above may be detected to be larger than a predetermined horizontal distance determined for each product number.
(4) In the above embodiment, the case where the inclination angle θ of the molded body 10 is calculated based on the horizontal distance δ between the center position 32 of the shaft hole 11 and the center position 34 of the stepped portion 12 has been described as an example. Alternatively, for example, instead of the center position of the stepped portion, the center position calculated from the outer edge of the step surface 17 may be used, and the position for calculating the horizontal distance may be appropriately determined depending on the step shape of the outer peripheral surface of the molded body or the like. Can be changed.

C... Camera L... Axial distance (distance in the direction along the axis from the tip of the molded product to the step)
P... Spark plug R... Region Z... Axis δ... Horizontal distance (horizontal distance between center position of shaft hole and center position of step)
θ: Inclination angle (degree of inclination)
DESCRIPTION OF SYMBOLS 10... Molded body 11... Shaft hole 12... Step part 20... Container 31... Shaft hole outline 32... Shaft hole center position 33... Step outer edge 34... Step center position 50... Insulator

Claims (5)

A method for manufacturing a spark plug having an insulator formed by firing a molded body,
The molded body has a cylindrical shape in which a shaft hole is formed along the axis and has a step portion that projects outward in the radial direction at an intermediate portion in the axial direction,
An arrangement step of placing a plurality of the molded bodies in a container having an open upper surface so that the axis is oriented in the vertical direction,
Placing the container on which the plurality of molded bodies are placed in a firing furnace, and firing the plurality of molded bodies,
A method of manufacturing a spark plug comprising:
From the arrangement step to before the firing step, a photographing step of photographing the molded body placed in the container from the upper side in the vertical direction with a camera,
Based on the imaging of the molded body shown in the image acquired in the photographing step, the degree of inclination of the axis of the molded body from the vertical direction is calculated, and the plurality of molded bodies placed in the container. Of the bodies, a detection step of detecting a molded body in which the degree of inclination is greater than a predetermined degree of inclination,
Manufacturing method of spark plug. In the detection step, a first extraction step of extracting the contour of the axial hole from the image of the molded body, and a second extraction step of extracting the outer edge of the stepped portion from the image of the molded body are performed,
The method for manufacturing a spark plug according to claim 1, wherein the inclination degree is calculated based on the contour of the shaft hole and the outer edge of the step portion. In the first extracting step, a center position of the shaft hole is calculated based on the extracted contour of the shaft hole,
In the second extracting step, the center position of the step portion is calculated based on the extracted outer edge of the step portion,
The method of manufacturing a spark plug according to claim 2, wherein in the detecting step, the degree of inclination is calculated based on a horizontal distance between a center position of the shaft hole and a center position of the step portion. The degree of inclination is based on the horizontal distance between the center position of the shaft hole and the center position of the step portion, and the distance in the direction along the axis from the tip of the molded body to the step portion. Is a tilt angle of the molded body calculated,
The method for manufacturing a spark plug according to claim 3, wherein in the detecting step, a molded body in which the tilt angle is larger than a predetermined tilt angle is detected. In the second extracting step, based on the contour of the shaft hole extracted in the first extracting step, a region larger than the contour of the shaft hole is set, and the image of the region is binarized, The method of manufacturing a spark plug according to claim 2, wherein an outer edge of the step portion included in the region is extracted.