Method for detecting shape of butt joint of welded steel pipe, and quality control method and apparatus for welded steel pipes using the shape detecting method

A method for detecting a shape of a butt joint of a welded steel pipe, the method comprising:

• irradiating, by a light projecting unit, a specific detection range including a butt joint of a welded steel pipe, using one of a fan-shaped light beam and a spot light beam;
• receiving, by a data output unit comprising a lens and an image sensor, light reflected from the specific detection range;
• generating, based on the reflected light, geometric coordinate data representing changes in position and shape of the butt joint;
• selecting, by a processor, from the geometric coordinate data, coordinates of a start point and an end point of the specific detection range, a first selected point located between the start point and the butt joint, and a second selected point located between the butt joint and the end point;
• calculating, by the processor, a first approximate circle that includes the start point, the end point, and the first selected point, by performing the following steps:
• determining a first line between the start point and the first selected point and a second line between the first selected point and the end point;
• determining a first perpendicular line that is perpendicular to and bisects the first line and a second perpendicular line that is perpendicular to and bisects the second line;
• determining a first intersection point where the first perpendicular line and the second perpendicular line intersect;
• and
• defining the first approximate circle having a first center at the first intersection point and passing through the start point, the end point and the first selected point;
• and
• calculating, by the processor, a second approximate circle that includes the start point, the end point, and the second selected point, by performing the following steps:
• determining a third line between the start point and the second selected point and a fourth line between the second selected point and the end point;
• determining a third perpendicular line that is perpendicular to and bisects the third line and a fourth perpendicular line that is perpendicular to and bisects the fourth line;
• determining a second intersection point where the third perpendicular line and the fourth perpendicular line intersect;
• and
• defining the second approximate circle having a second center at the second intersection point and passing through the start point, the end point and the second selected point;
• and
• calculating, by the processor, a distance between the first center of the first approximate circle and the second center of the second approximate circle, and using the distance as an index representing the shape of the butt joint.

A method for detecting a shape of a butt joint of a welded steel pipe, the method comprising:

• irradiating, by a light projecting unit, a specific detection range including a butt joint of a welded steel pipe, using one of a fan-shaped light beam and a spot light beam;
• receiving, by a data output unit comprising a lens and an image sensor, light reflected from the specific detection range;
• generating, based on the reflected light, geometric coordinate data representing changes in position and shape of the butt joint;
• selecting, by a processor, from the geometric coordinate data, coordinates of a start point and an end point of the specific detection range, a first selected point located between the start point and the butt joint, and a second selected point located between the butt joint and the end point;
• calculating, by the processor, a first approximate circle that includes the start point, the end point, and the first selected point, by performing the following steps:
• determining a first line between the start point and the first selected point and a second line between the first selected point and the end point;
• determining a first perpendicular line that is perpendicular to and bisects the first line and a second perpendicular line that is perpendicular to and bisects the second line;
• determining a first intersection point where the first perpendicular line and the second perpendicular line intersect;
• and
• defining the first approximate circle having a first center at the first intersection point and passing through the start point, the end point and the first selected point;
• and
• calculating, by the processor, a second approximate circle that includes the start point, the end point, and the second selected point, by performing the following steps:
• determining a third line between the start point and the second selected point and a fourth line between the second selected point and the end point;
• determining a third perpendicular line that is perpendicular to and bisects the third line and a fourth perpendicular line that is perpendicular to and bisects the fourth line;
• determining a second intersection point where the third perpendicular line and the fourth perpendicular line intersect;
• and
• defining the second approximate circle having a second center at the second intersection point and passing through the start point, the end point and the second selected point;
• and
• calculating, by the processor, a first differential distance in an X-axis direction between the first center of the first approximate circle and the second center of the second approximate circle and a second differential distance in a Z-axis direction between the first center and the second center and using the first and second differential distances as indices representing the shape of the butt joint.

A quality control apparatus for welded steel pipes, the apparatus comprising:

• a non-contact displacement meter comprising:
• a light projecting unit configured to irradiate a specific detection range including a butt joint of a welded steel pipe with a fan-shaped light beam or to scan the specific detection range with a spot light beam;
• and
• a data output unit comprising a lens and an image sensor, the data output unit configured to receive light reflected from the specific detection range irradiated or scanned with the light beam from the light projecting unit and to output, based on the reflected light, geometric coordinate data representing changes in position and shape of the butt joint;
• and
• an arithmetic processor comprising:
• an approximate circle calculating/processing unit configured to:
• select, from the geometric coordinate data obtained by the non-contact means, coordinates of a start point and an end point of the specific detection range, a first selected point located between the start point and the butt joint, and a second selected point located between the butt joint and the end point;
• determine a first line between the start point and the first selected point and a second line between the first selected point and the end point;
• determine a first perpendicular line that is perpendicular to and bisects the first line and a second perpendicular line that is perpendicular to and bisects the second line;
• determine a first intersection point where the first perpendicular line and the second perpendicular line intersect;
• calculate a first approximate circle having a first center at the first intersection point and passing through the start point, the end point, and the first selected point;
• determine a third line between the start point and the second selected point and a fourth line between the second selected point and the end point;
• determine a third perpendicular line that is perpendicular to and bisects the third line and a fourth perpendicular line that is perpendicular to and bisects the fourth line;
• determine a second intersection point where the third perpendicular line and the fourth perpendicular line intersect;
• calculate a second approximate circle having a second center at the second intersection point and passing through the start point, the end point, and the second selected point;
• and
• average the first approximate circle and the second approximate circle so as to calculate an imaginary circle and calculate, as a difference value, a maximum deviation of the first approximate circle or the second approximate circle from the imaginary circle in a thickness direction of the welded steel pipe;
• and
• a judgment processing unit configured to compare the difference value calculated by the approximate circle calculating/processing unit, with a predetermined threshold value, so as to judge whether the shape of the butt joint of the welded steel pipe is acceptable or not.

A quality control apparatus for welded steel pipes, the apparatus comprising:

• a non-contact displacement meter comprising:
• a light projecting unit configured to irradiate a specific detection range including a butt joint of a welded steel pipe with a fan-shaped light beam or to scan the specific detection range with a spot light beam;
• and
• a data output unit comprising a lens and an image sensor, the data output unit configured to receive light reflected from the specific detection range irradiated or scanned with the light beam from the light projecting unit and to output, based on the reflected light, geometric coordinate data representing changes in position and shape of the butt joint;
• and
• an arithmetic processor comprising:
• an approximate circle calculating/processing unit configured to:
• select, from the geometric coordinate data obtained by the non-contact means, coordinates of a start point and an end point of the specific detection range, a first selected point located between the start point and the butt joint, and a second selected point located between the butt joint and the end point;
• determine a first line between the start point and the first selected point and a second line between the first selected point and the end point;
• determine a first perpendicular line that is perpendicular to and bisects the first line and a second perpendicular line that is perpendicular to and bisects the second line;
• determine a first intersection point where the first perpendicular line and the second perpendicular line intersect;
• calculate a first approximate circle having a first center at the first intersection point and passing through the start point, the end point, and the first selected point;
• and
• determine a third line between the start point and the second selected point and a fourth line between the second selected point and the end point;
• determine a third perpendicular line that is perpendicular to and bisects the third line and a fourth perpendicular line that is perpendicular to and bisects the fourth line;
• determine a second intersection point where the third perpendicular line and the fourth perpendicular line intersect;
• calculate a second approximate circle having a second center at the second intersection point and passing through the start point, the end point, and the second selected point;
• and
• calculate a distance between the first center of the first approximate circle and the second center of the second approximate circle;
• and
• a judgment processing unit configured to compare the distance calculated by the approximate circle calculating/processing unit, with a predetermined threshold value, so as to judge whether the shape of the butt joint of the welded steel pipe is acceptable or not.

A quality control apparatus for welded steel pipes, the apparatus comprising:

• a non-contact displacement meter comprising:
• a light projecting unit configured to irradiate a specific detection range including a butt joint of a welded steel pipe with a fan-shaped light beam or to scan the specific detection range with a spot light beam;
• and
• a data output unit comprising a lens and an image sensor, the data output unit configured to receive light reflected from the specific detection range irradiated or scanned with the light beam from the light projecting unit and to output, based on the reflected light, geometric coordinate data representing changes in position and shape of the butt joint;
• and
• an arithmetic processor comprising:
• an approximate circle calculating/processing unit configured to:
• select, from the geometric coordinate data obtained by the non-contact means, coordinates of a start point and an end point of the specific detection range, a first selected point located between the start point and the butt joint, and a second selected point located between the butt joint and the end point;
• determine a first line between the start point and the first selected point and a second line between the first selected point and the end point;
• determine a first perpendicular line that is perpendicular to and bisects the first line and a second perpendicular line that is perpendicular to and bisects the second line;
• determine a first intersection point where the first perpendicular line and the second perpendicular line intersect;
• calculate a first approximate circle having a first center at the first intersection point and passing through the start point, the end point, and the first selected point;
• determine a third line between the start point and the second selected point and a fourth line between the second selected point and the end point;
• determine a third perpendicular line that is perpendicular to and bisects the third line and a fourth perpendicular line that is perpendicular to and bisects the fourth line;
• determine a second intersection point where the third perpendicular line and the fourth perpendicular line intersect;
• calculate a second approximate circle having a second center at the second intersection point and passing through the start point, the end point, and the second selected point;
• and
• calculate a first differential distance in an X-axis direction between the first center of the first approximate circle and the second center of the second approximate circle and a second differential distance in a Z-axis direction between the first center and the second center;
• and
• a judgment processing unit configured to:
• compare the first differential distance in the X-axis direction between the first center of the first approximate circle and the second center of the second approximate circle and the second differential distance in the Z-axis direction between the first center and the second center, with respective predetermined threshold values, so as to judge whether the shape of the butt joint of the welded steel pipe is acceptable or not.