Two-dimensional code reading device, two-dimensional code reading method, method of controlling manufacturing history information of member having substantially circular section orthogonal to the central axis thereof, and method of manufacturing the member using the control method

A two-dimensional code reading method for reading a two-dimensional code composed of a plurality of concave portions carved in a member having a substantially circular section orthogonal to a central axis thereof, comprising the steps of:

• irradiating the two-dimensional code with light from a direction along the central axis of the member;
• and
• picking up an image of the two-dimensional code from a direction along the direction of the central axis,
• wherein the concave portion has a pair of a first inclined portion and a second inclined portion of which a mutual space in the direction of the central axis becomes narrow toward a radial inner side of the member in a section including the central axis and the center of the concave portion,
• wherein the first inclined portion is inclined so as to form an angle β in a clockwise direction with respect to a normal-line direction of a surface of the member in the section,
• wherein the second inclined portion is inclined so as to form an angle β in a counterclockwise direction with respect to the normal-line direction,
• wherein in the step of picking up the image of the two-dimensional code, light reflected in a direction forming an angle θ satisfying expression (3) below with respect to the normal-line direction in the section is received in either of the first inclined portion and the second inclined portion, and
• wherein in the step of irradiating the two-dimensional code with light, either of the inclined portions is irradiated from a direction forming an angle α satisfying expression (4) below with respect to the normal-line direction in the section:
• 30°≦θ≦35° (3)
• Δθ=θ−180°+α+2β (4)
• where β is less than 90°,
• Δθ is not less than −10° but not more than 10°, and
• θ and α are angles in a turn direction reverse to a turn direction at which either of the inclined portions forms the angle β with respect to the normal-line direction.