Apparatus and method for determining shape of end of welding bead

1. An apparatus for determining the shape of an end of a welding bead formed by irradiating a weld material with a welding laser, comprising:

a laser emitting unit for emitting the welding laser onto the weld material;

a monitor unit for continuously capturing images of a portion on the weld material irradiated with the welding laser;

a storage unit for storing the images captured by the monitor unit;

an image extracting unit for extracting one of the images from the storage unit when the average luminance within the image is equal to or less than a predetermined image extracting threshold;

a bead recognition unit for recognizing a bead region in the image extracted by the image extraction unit; and

a bead shape determination unit for calculating the position of an end of the bead region based on the bead region recognized by the bead recognition unit, and for determining whether the shape of the end of the bead region is convex or concave in the extending direction of the bead region;

wherein the bead shape determination unit includes

a representative point calculation module for calculating a representative point of the bead region;

a center position calculation module for calculating a center position of the end of the bead region;

an intermediate point calculation module for calculating an intermediate point between the representative point of the bead region and the center position of the end of the bead region;

a straight line calculation module for calculating two straight lines which extend parallel to each other on both sides of the line connecting the center position and the intermediate point, and intersect with the periphery of the end of the bead region; and

a curvature calculation module for calculating intersection points between the two straight lines and the periphery of the end, calculating a degree of curvature based on the intersection points and the center position, and then determining whether the shape of the end of the bead region is convex or concave by use of the degree of curvature.

2. The apparatus according to claim 1 , wherein the monitor unit includes:

a first monitor device for capturing an image during a welding process;

a second monitor device for capturing an image after the completion of the welding process; and

a light splitting device for splitting light from the portion irradiated with the welding laser into light beams in two directions toward the first monitor device and toward the second monitor device, and

wherein the amount of light beam guided to the first monitor device is less than the amount of light beam guided to the second monitor device.

3. The apparatus according to claim 1 , wherein the bead recognition unit includes:

a region recognition module for determining, as bead region candidates, regions within the image each having luminance equal to or greater than a predetermined region recognition threshold; and

a determination module for determining whether each of the bead region candidates is the bead region based on an aspect ratio of the bead region candidates.

4. The apparatus according to claim 1 , wherein the degree of curvature is a distance to the center position from a line connecting the intersection points with each other.

5. The apparatus according to claim 1 , wherein

when the image extraction unit extracts plural images, the curvature calculation module determines whether the shape of the end of the bead region is convex or concave by use of the average of degrees of curvature obtained from the plural images.

6. A method for determining the shape of an end of a welding bead formed by irradiating a weld material with a welding laser, comprising:

emitting the welding laser onto the weld material;

capturing images of a portion irradiated with the welding laser on the weld material along the time course;

storing the images in a storage unit;

extracting one of the images from the storage unit when the average luminance within the image is equal to or less than a predetermined image extracting threshold;

recognizing a bead region in the image extracted from the storage unit; and

calculating the position of the end of the bead region based on the recognized bead region, and determining whether the shape of the end of the bead region is convex or concave in the extending direction of the bead region,

wherein the process for determining whether the shape of the end of the bead region is convex or concave includes

calculating a representative point of the bead region;

calculating a center position of the end of the bead region;

calculating an intermediate point between the representative point of the bead region and the center position of the end of the bead region;

calculating two straight lines which extend parallel on both sides of the line connecting the center position and the intermediate point, and intersect with the periphery of the end of the bead region; and

calculating intersection points between the two straight lines and the periphery of the end, calculating a degree of curvature based on the intersection points and the center position, and then determining whether the shape of the end of the bead region is convex or concave by use of the degree of curvature.

7. The method according to claim 6 , wherein the process for capturing the images includes:

splitting light from the portion irradiated with the welding laser into light beams in two directions toward a first monitor device and toward a second monitor device;

capturing an image during a welding process by the first monitor device; and

capturing an image after the completion of the welding process by the second monitor device, and

wherein the amount of light beam guided to the first monitor device is less than the amount of light beam guided to the second monitor device.

8. The method according to claim 6 , wherein the process for recognizing the bead region includes:

determining, as bead region candidates, regions having luminance equal to or greater than a predetermined region recognition threshold within the image; and

determining whether each of the bead region candidates is the bead region based on an aspect ratio of the bead region candidates.

9. The method according to claim 6 , wherein the degree of curvature is a distance to the center position from a line connecting the intersection points with each other.

10. The method according to claim 6 , wherein when plural images are extracted from the storage unit, whether the shape of the end of the bead region is convex or concave is determined by use of the average of degrees of curvature obtained from the plural images in the process for determining whether the shape of the end is convex or concave.