TECHNICAL FIELD

The present invention relates to a tubular body inner surface inspection apparatus and a tubular body inner surface inspection method.

BACKGROUND ART

An inner surface inspection of a tubular body that inspects the inner surface of a tubular body typified by a metal tube such as a steel tube or a resin pipe is an important inspection item particularly in metal tubes such as steel tubes, and usually a visual inspection is performed by additionally providing a process separately from the production process of the tubular body.

The visual inspection of a tubular body depends greatly on the skill of the inspector, and an adequate visual inspection is difficult to perform particularly in an inner surface inspection that inspects the inner surface of a tubular body. Hence, outflows of shameless flaws and serious complaints may occur particularly in a deep portion in the axial direction of the tubular body. In addition, there is also unevenness of the inner surface of a tubular body that is difficult to detect depending on the inspection technique; hence, it is important to monitor the inner surface of the tubular body directly.

As a method for inspecting such an inner surface of a tubular body, there is a method using an imaging optical system in which light of a light source is caused to be applied in a disc shape by means of a conical mirror or a conical prism, and the reflected light of the inner surface of a tubular body is imaged with an imaging element. As the method for inspecting such an inner surface of a tubular body, there are methods like those disclosed in JP 2007-285891A, JP 2012-159491A, and JP 2015-163844A.

For example, JP 2007-285891A discloses a technology in which an imaging optical system is constructed by illumination light produced by a light source that applies light of the light source in a disc shape by means of a conical mirror or a conical prism and an imaging system based on an imaging sensor; beams of light are applied one after another to the inner surface of an object to be inspected while the imaging optical system is moved concurrently; a trail of light showing the shape of the inner surface is obtained by the applied light; the trail of light is imaged with the imaging sensor; the distances between a standard position of the imaging optical system and portions of the inner surface of the object to be inspected are calculated one after another from light trail image data obtained by the imaging mentioned above; and thereby the shape of the inner surface of the object to be inspected is measured.

Further, JP 2012-159491A discloses an apparatus that applies annular laser light to the inner surface of a tubular body while moving along the axial direction of the tubular body and obtains a light-section image using the resulting annular beam image, and consequently detects unevenness flaws and figure-like flaws of the inner surface simultaneously and individually.

Further, JP 2015-163844A discloses an apparatus in which a light source section that applies laser light expanded in a ring shape to the inner surface of a body to be inspected and an imaging section that images the reflected light at the inner surface of the body to be inspected of the applied laser light are arranged so as to be coaxial by means of an optically transparent tube, and the transparent tube is provided with properties of controlling the state of polarization in order to suppress the occurrence of ghosts derived from the transparent tube at the time of imaging.

CITATION LIST

Patent Literature

Patent Literature 1: JP 2007-285891APatent Literature 2: JP 2012-159491APatent Literature 3: JP 2015-163844A

SUMMARY OF INVENTION

Technical Problem

Here, the frame rate at the time of imaging annular laser light depends on the performance of the camera used, and hence it is difficult to obtain light-section images one after another at high speed. In general, a two-dimensional area camera is used for the imaging of light-section images. In this case, imaging is performed including useless regions other than the laser light irradiation region of the inner surface of the tubular body necessary for inspection, and hence it is difficult to improve the imaging frame rate. Furthermore, also the time of transferring data not necessary for processing is needed; thus, a common two-dimensional area camera is not suitable for cases where it is intended to perform high speed inspection.

Furthermore, for example, in order to inspect a tubular body with an inner diameter of more than or equal to 250 mm, which is occasionally called a medium-diameter tube, it is necessary to increase the size of the captured image in order to perform imaging while ensuring the resolving power of the captured image (in other words, while ensuring the size of the captured image). As a consequence, the frame rate is reduced, and the imaging takes a long time.

In addition, when actually performing an inspection of a tubular body, a support member for supporting the light source is used; but to the area camera, annular laser light is blocked by the support member, and an unimaged region occurs.

In regard to the occurrence of the unimaged region mentioned above, in the technologies disclosed in JP 2007-285891A or JP 2015-163844A above, the shadow of the support member for supporting the light source can be eliminated, but it is impossible to completely exclude a voltage supply cable for the light source etc. Hence, in the technologies disclosed in JP 2007-285891A and JP 2015-163844A mentioned above, although the unimaged region can be made smaller, it is impossible to completely eliminate the unimaged region. Further, as the tubular body that is the object to be inspected becomes larger and longer, the spacing between the light source and the imaging section becomes wider; hence, in the technologies disclosed in JP 2007-285891A and JP 2015-163844A mentioned above, it becomes necessary to provide a support member that supports the light source and the imaging section in order to ensure the strength of the imaging optical system.

JP 2012-159491A above proposes, in regard to an unimaged region like that mentioned above, a technology in which an unimaged region is compensated for such that the imaging object region is changed between the forward way and the backward way of a test probe. However, to control the movement position of the test probe, the size of the apparatus may be increased, and simplicity may be reduced.

Thus, the present invention has been made in view of the problem mentioned above, and an object of the present invention is to provide a tubular body inner surface inspection apparatus and a tubular body inner surface inspection method capable of inspecting the inner surface of a tubular body at higher speed, with higher resolving power, and in a simpler way regardless of the size of the tubular body.

Solution to Problem

According to an aspect of the present invention in order to achieve the above-mentioned object, there is provided a tubular body inner surface inspection apparatus that detects a defect existing on an inner surface of a tubular body, the apparatus including: a tubular body imaging apparatus including N (N≥2) imaging units each including a laser light source that applies laser light, an optical element that reflects laser light applied from the laser light source in a circumferential direction of the inner surface of the tubular body, as annular laser light, an area camera that images a region of the inner surface of the tubular body where the annular laser light is applied, and thereby generates an annular beam image, and a linking member that links together and fixes the laser light source and the area camera, in which the imaging units are linked in series along a tube axial direction of the tubular body in such a manner that positions of the linking members in a plane orthogonal to a tube axis are different from each other; a movement apparatus that moves the tubular body imaging apparatus along the tube axial direction of the tubular body; and an arithmetic processing apparatus that, while moving the tubular body imaging apparatus by means of the movement apparatus, performs image processing on a plurality of annular beam images generated in each of the imaging units and assesses whether a defect exists on the inner surface of the tubular body or not.

The area camera in each of the imaging units preferably generates a plurality of annular beam images by imaging portions corresponding to regions of an entire visual field of the area camera where the annular laser light is not blocked by the linking member and furthermore corresponding to end regions of the entire visual field of the area camera, which end regions are set individually in end portions in a direction orthogonal to a pixel information transfer direction that is a direction in which pixel information that is information regarding a charge or a voltage of each pixel of an imaging element included in the area camera is transferred in the imaging element.

The arithmetic processing apparatus preferably uses an annular beam image obtained from each of the imaging units to calculate a centroid position and a radius of an irradiation portion of the annular laser light, performs a polar coordinate transformation on a coordinate system of annular beam images obtained from each of the imaging units, on the basis of the calculated centroid position and an amount of separation between the centroid position and the irradiation portion of the annular laser light, and generates, for each of the imaging units, light-section images each including a light-section line that is a line segment obtained by the polar coordinate transformation and corresponding to the irradiation portion of the annular laser light, generates partial stripe image frames in each of which obtained light-section images of each of the imaging units are sequentially arranged along the tube axial direction, adjusts the partial stripe image frames on the basis of a positional relationship between the N imaging units, connects the partial stripe image frames in planes orthogonal to the tube axis, and generates a stripe image frame, calculates a depth image showing unevenness condition of the inner surface of the tubular body and a luminance image showing luminance distribution of the annular laser light on the inner surface of the tubular body, on the basis of the stripe image frame, and detects a defect existing on the inner surface of the tubular body on the basis of the depth image and the luminance image.

The arithmetic processing apparatus preferably uses an annular beam image obtained from each of the imaging units to calculate a centroid position and a radius of an irradiation portion of the annular laser light, performs a polar coordinate transformation on a coordinate system of annular beam images obtained from each of the imaging units, on the basis of the calculated centroid position and an amount of separation between the centroid position and the irradiation portion of the annular laser light, and generates, for each of the imaging units, light-section images each including a light-section line that is a line segment obtained by the polar coordinate transformation and corresponding to the irradiation portion of the annular laser light, adjusts the obtained light-section images of the imaging units on the basis of a positional relationship between the N imaging units, connects the light-section images in planes orthogonal to the tube axis, and thereby generates a stripe image frame in which the connected light-section images are sequentially arranged along the tube axial direction, calculates a depth image showing unevenness condition of the inner surface of the tubular body and a luminance image showing luminance distribution of the annular laser light on the inner surface of the tubular body, on the basis of the stripe image frame, and detects a defect existing on the inner surface of the tubular body on the basis of the depth image and the luminance image.

A region mutually overlapping in a partial way preferably exists between annular beam images of imaging units.

Wavelengths of beams of laser light applied from the laser light sources in imaging units may be different from each other, and in a prior stage of the area camera in each of the imaging units, a wavelength selection filter that transmits light of the same wavelength as the wavelength of the beam of laser light of the laser light source included in the same imaging unit as the area camera may be provided.

The N imaging units may be linked such that the area camera, the laser light source, and the optical element are aligned in an alignment order of (an area camera, a laser light source, an optical element), (an optical element, a laser light source, an area camera), etc. between the plurality of imaging units.

The N imaging units may be linked such that the optical element, the laser light source, and the area camera are aligned in an alignment order of (an optical element, a laser light source, an area camera), (an area camera, a laser light source, an optical element), etc. between the plurality of imaging units.

The N imaging units may be linked such that the area camera, the laser light source, and the optical element repeat an alignment order of (an area camera, a laser light source, an optical element) between the plurality of imaging units.

According to another aspect of the present invention in order to achieve the above-mentioned object, there is provided a tubular body inner surface inspection method for detecting a defect existing on an inner surface of a tubular body, the method using a tubular body inner surface inspection apparatus including a tubular body imaging apparatus including N (N≥2) imaging units each including a laser light source that applies laser light, an optical element that reflects laser light applied from the laser light source in a circumferential direction of the inner surface of the tubular body, as annular laser light, an area camera that images a region of the inner surface of the tubular body where the annular laser light is applied, and thereby generates an annular beam image, and a linking member that links together and fixes the laser light source and the area camera, in which the imaging units are linked in series along a tube axial direction of the tubular body in such a manner that positions of the linking members in a plane orthogonal to a tube axis are different from each other, a movement apparatus that moves the tubular body imaging apparatus along the tube axial direction of the tubular body, and an arithmetic processing apparatus that, while moving the tubular body imaging apparatus by means of the movement apparatus, performs image processing on a plurality of annular beam images generated in each of the imaging units and assesses whether a defect exists on the inner surface of the tubular body or not, the method including: a step of using an annular beam image obtained from each of the imaging units to calculate a centroid position and a radius of an irradiation portion of the annular laser light; a step of performing a polar coordinate transformation on a coordinate system of annular beam images obtained from each of the imaging units, on the basis of the calculated centroid position and an amount of separation between the centroid position and the irradiation portion of the annular laser light, and generating, for each of the imaging units, light-section images each including a light-section line that is a line segment obtained by the polar coordinate transformation and corresponding to the irradiation portion of the annular laser light; a step of generating partial stripe image frames in each of which obtained light-section images of each of the imaging units are sequentially arranged along the tube axial direction, then adjusting the generated partial stripe image frames on the basis of a positional relationship between the N imaging units, connecting the partial stripe image frames in planes orthogonal to the tube axis, and generating a stripe image frame, or adjusting the obtained light-section images of the imaging units on the basis of the positional relationship between the N imaging units, connecting the light-section images in planes orthogonal to the tube axis, and thereby generating a stripe image frame in which the connected light-section images are sequentially arranged along the tube axial direction; a step of calculating a depth image showing unevenness condition of the inner surface of the tubular body and a luminance image showing luminance distribution of the annular laser light on the inner surface of the tubular body, on the basis of the stripe image frame; and a step pf detecting a defect existing on the inner surface of the tubular body on the basis of the depth image and the luminance image.

The area camera in each of the imaging units may generate a plurality of annular beam images by imaging portions corresponding to regions of an entire visual field of the area camera where the annular laser light is not blocked by the linking member and furthermore corresponding to end regions of the entire visual field of the area camera, which end regions are set individually in end portions in a direction orthogonal to a pixel information transfer direction that is a direction in which pixel information that is information regarding a charge or a voltage of each pixel of an imaging element included in the area camera is transferred in the imaging element.

A region mutually overlapping in a partial way preferably exists between annular beam images of imaging units.

Wavelengths of beams of laser light applied from the laser light sources in imaging units may be different from each other, and in a prior stage of the area camera in each of the imaging units, a wavelength selection filter that transmits light of the same wavelength as the wavelength of the beam of laser light of the laser light source included in the same imaging unit as the area camera may be provided.

The N imaging units may be linked such that the area camera, the laser light source, and the optical element are aligned in an alignment order of (an area camera, a laser light source, an optical element), (an optical element, a laser light source, an area camera), etc. between the plurality of imaging units.

The N imaging units may be linked such that the optical element, the laser light source, and the area camera are aligned in an alignment order of (an optical element, a laser light source, an area camera), (an area camera, a laser light source, an optical element), etc. between the plurality of imaging units.

The N imaging units may be linked such that the area camera, the laser light source, and the optical element repeat an alignment order of (an area camera, a laser light source, an optical element) between the plurality of imaging units.

Advantageous Effects of Invention

As described above, according to the present invention, it becomes possible to inspect the inner surface of a tubular body at higher speed, with higher resolving power, and in a simpler way regardless of the size of the tubular body.

