Thread shape dimension measuring device and thread shape dimension measuring method
This thread shape dimension measuring device includes an illumination unit, an imaging unit, a focal distance adjustment unit, a calibration value setting unit, and a control unit. The illumination unit selectively emits parallel light in two directions. The imaging unit selectively performs capturing of a first captured image and a second captured image. The focal distance adjustment unit adjusts a focusing position of the imaging unit by receiving an adjustment instruction from the control unit. The calibration value setting unit has a difference value between a focal distance of the second captured image from a focusing position to the imaging unit before the focusing position adjustment and a focal distance of the first captured image from a focusing position to the imaging unit. The control unit calculates the thread shape dimension on the basis of the captured first captured image and the second captured image.
1 . A thread shape dimension measuring method for measuring a thread shape dimension of a threaded portion in a threaded pipe having the threaded portion formed at an end portion and on which a pair of flank surfaces defining each thread ridge of the threaded portion are both formed in an overhanging manner in a view seen in a cross section including a pipe axis, the thread shape dimension measuring method comprising:
a first illumination step of illuminating the end portion by emitting parallel light in a first illumination direction inclined in a direction forming an angle larger than a lead angle of the threaded portion with respect to a direction orthogonal to the cross section including the pipe axis;
a second illumination step of illuminating the end portion by emitting parallel light in a second illumination direction inclined to a side opposite to the lead angle of the threaded portion with respect to a direction orthogonal to the cross section including the pipe axis;
an imaging step of, in an imaging side facing an emitting source of the parallel light with the end portion interposed therebetween, capturing a first captured image of the end portion by receiving light that has passed between thread ridges of the threaded portion from the parallel light emitted in the first illumination direction, and capturing a second captured image of the end portion by receiving light that has passed between thread ridges of the threaded portion from the parallel light emitted in the second illumination direction; and
an arithmetic processing step of calculating the thread shape dimension of the threaded portion on the basis of the first captured image and the second captured image, wherein
when one of the pair of flank surfaces whose portion on a cross section including the pipe axis is able to be directly imaged from the imaging side is defined as a first flank surface, and one thereof whose portion on the cross section including the pipe axis is not able to be directly imaged from the imaging side is defined as a second flank surface,
in the arithmetic processing step,
a shape dimension of the first flank surface is calculated on the basis of the first captured image captured in a first state in which a focusing position is adjusted to match a position of the first flank surface on the cross section, and
a shape dimension of the second flank surface is calculated on the basis of the second captured image captured in a second state in which a focusing position is brought closer to the pipe axis by a predetermined distance than that in the first state so that the focusing position matches a position of the second flank surface on the cross section.
2 . The thread shape dimension measuring method according to claim 1 , wherein the predetermined distance is obtained on the basis of an amount of deviation between a true position of the second flank surface in a pipe axis direction and a position of the second flank surface in the pipe axis direction calculated on the basis of the second captured image captured in the first state.