Inspection device for article being inspected, spark plug inspection method, and method for manufacturing spark plug

A method for inspecting an identification mark formed on a rear end surface of a metal terminal of a spark plug, comprising the steps of:

• holding the spark plug such that a predetermined distance is established along an image capturing direction orthogonal to the rear end surface of the metal terminal between the rear end surface and a camera that captures an image of the rear end surface;
• illuminating the rear end surface with irradiation light by an illuminator having a light source which is disposed between the rear end surface and the camera with respect to the image capturing direction at a position such that reflected light resulting from regular reflection of the irradiation light emitted from the light source and impinging on the rear end surface is not incident on the camera;
• capturing an image of the rear end surface in the image capturing direction by using the camera;
• performing image processing on an image captured by the camera, and acquiring characteristic information of the identification mark from an image of the identification mark in the captured image;
• comparing the characteristic information of the identification mark and characteristic information of a reference mark acquired beforehand from an image of the reference mark;
• and
• judging whether or not the identification mark and the reference mark are the same mark.

A method for manufacturing a spark plug, comprising:

• a manufacturing step of manufacturing the spark plug by attaching to a metallic shell a ceramic insulator which holds a forward end portion of a metal terminal;
• a marking step of forming an identification mark on a rear end surface of the metal terminal;
• and
• an inspection step of inspecting the identification mark, wherein
• the inspection step comprises the steps of:
• holding the spark plug such that a predetermined distance is established along an image capturing direction orthogonal to the rear end surface of the metal terminal between the rear end surface and a camera that captures an image of the rear end surface;
• illuminating the rear end surface with irradiation light by an illuminator having a light source which is disposed between the rear end surface and the camera with respect to the image capturing direction at a position such that reflected light resulting from regular reflection of the irradiation light emitted from the light source and impinging on the rear end surface is not incident on the camera;
• capturing an image of the rear end surface in the image capturing direction by using the camera;
• performing image processing on an image captured by the camera, and acquiring characteristic information of the identification mark from an image of the identification mark in the captured image;
• comparing the characteristic information of the identification mark and characteristic information of a reference mark acquired beforehand from an image of the reference mark;
• and
• judging whether or not the identification mark and the reference mark are the same mark.