KR-20260064226-A - Laser welding control method for LNG cargo holds and laser welding control system for LNG cargo holds implementing the same

KR20260064226AKR 20260064226 AKR20260064226 AKR 20260064226AKR-20260064226-A

Abstract

A laser welding control method for an LNG cargo tank and a laser welding control system for an LNG cargo tank implementing the same are disclosed. The laser welding control method for an LNG cargo tank according to the present invention comprises the steps of: applying a filter to a captured image to exclude the wavelength of a laser light source; applying a High Dynamic Range (HDR) method to the image from which the laser light source wavelength has been excluded to obtain an HDR image; preprocessing the obtained HDR image by removing the remaining parts while leaving only the Region of Interest (ROI) and then setting a reference line; extracting coordinates through calibration from the image in which the preprocessing and reference line have been set; and controlling a laser welding device to track a welding line using the extracted coordinates.

Inventors

박정원
조영호
박신구

Assignees

에이치디한국조선해양 주식회사
에이치디현대중공업 주식회사
에이치디현대삼호 주식회사

Dates

Publication Date: 20260507
Application Date: 20241031

Claims (10)

A step of excluding the laser light source wavelength by applying a filter to the captured image; A step of obtaining an HDR image by applying an HDR (High Dynamic Range) method to an image from which the above laser light source wavelength has been excluded; A step of preprocessing the acquired HDR image by removing the remaining parts while leaving only the ROI (Region of Interest), and then setting a baseline; A step of extracting coordinates through calibration from an image in which the above-mentioned preprocessing and baseline are set; and, A laser welding control method for an LNG cargo tank comprising the step of controlling a laser welding device to follow a welding line through the extracted coordinates.
In paragraph 1, A laser welding control method for an LNG cargo tank, characterized in that the above-mentioned image is captured on the same axis as the laser beam.
In paragraph 1, The step of extracting the above coordinates is, A laser welding control method for an LNG cargo tank comprising a step of converting a video image into grayscale.
In paragraph 3, The step of extracting the above coordinates is, A laser welding control method for an LNG cargo tank, further comprising the step of distinguishing the boundary lines of the weld line in the above grayscale converted image.
In paragraph 4, The step of extracting the above coordinates is, A laser welding control method for an LNG cargo tank, further comprising the step of extracting pixels from the above baseline to the above boundary line and coordinateing the pixels.
An image filter unit that excludes the laser light source wavelength from the captured image; HDR image acquisition unit that acquires an image using the HDR (High Dynamic Range) method from an image in which the above laser light source wavelength is excluded; An image preprocessing unit that removes the remaining parts while leaving only the ROI (Region of Interest) in the above-mentioned HDR image, and then sets a baseline; A coordinate extraction unit that extracts coordinates through calibration from an image in which the above-mentioned preprocessing and baseline are set; and, A laser welding control system for an LNG cargo tank comprising: a laser welding device control unit that controls the laser welding device to follow the welding line through the extracted coordinates.
In paragraph 6, A laser welding control system for an LNG cargo tank characterized by the above-mentioned image being captured on the same axis as the laser beam.
In paragraph 6, The above coordinate extraction unit is, A laser welding control system for an LNG cargo tank characterized by converting video images into grayscale.
In paragraph 8, The above coordinate extraction unit is, A laser welding control system for an LNG cargo tank characterized by distinguishing the boundary lines of the weld line in the above grayscale converted image.
In Paragraph 9, The above coordinate extraction unit is, A laser welding control system for an LNG cargo tank characterized by extracting pixels from the above baseline to the above boundary line and converting the pixels into coordinates.

Description

Laser welding control method for LNG cargo holds and laser welding control system for LNG cargo holds implementing the same The present invention relates to a laser welding control method for an LNG cargo tank and a laser welding control system for an LNG cargo tank implementing the same. More specifically, the invention relates to a laser welding control method for an LNG cargo tank and a laser welding control system for an LNG cargo tank implementing the same, wherein image processing technology is applied to minimize the influence of the laser beam during welding line tracking and accurately track the welding line. Due to its characteristics, liquefied natural gas (LNG) must be stored and transported at cryogenic temperatures; to this end, ships or storage tanks used for storing or transporting LNG require highly reliable cargo tanks. The cargo tanks of LNG carriers are critical structures for safely storing and transporting cryogenic LNG. LNG carrier cargo tanks are classified into MOSS and membrane types. Inside membrane-type cargo tanks, membrane-shaped components are manufactured from metal materials such as Invar or stainless steel, and multiple panels are connected by welding. Conventional membrane welding methods have mainly applied traditional arc welding technologies such as TIG (Tungsten Inert Gas) or plasma welding. However, while TIG and plasma welding have the advantages of good weld quality and aesthetics, the welding speed is slow, resulting in low welding work efficiency. To address these issues, the introduction of laser welding technology has been considered. Laser welding offers advantages such as high precision and consistency, fast welding speeds, a small heat-affected zone, and low deformation. Automated laser systems can ensure uniform welding quality, and the use of high-energy-density laser beams can significantly improve welding speeds. However, there are still several technical challenges in laser welding of LNG cargo tank membranes. Major challenges remain, such as the difficulty of laser welding on metal surfaces with high reflectivity, precise laser beam control and positioning for large structures, ensuring welding quality for curved and corner sections, and real-time monitoring and quality control during the welding process. Specifically, LNG cargo tank membranes consist of very thin metal panels, so the welding depth and energy control must be very precise during laser welding. Otherwise, excessive welding may damage the membrane or reduce airtightness. In addition, optimization of the size and shape of the laser welding device is required, and due to the structural characteristics of the vessel, welding operations must be possible at various positions and angles. Therefore, developing a laser welding device specialized for welding the membranes of LNG cargo tanks and achieving high-quality welding through this is an important task in this technology field to increase the efficiency of the manufacturing process and ensure the stability of the cargo tanks. Meanwhile, since the laser beam of a conventional fiber laser welding device has a diameter of several hundred micrometers, welding must be performed through 'beam wobbling' when the gap size increases during membrane welding. Here, 'beam wobbling' refers to a method of rapidly moving the laser beam in a circular or straight line perpendicular to the weld seam. However, applying a wobble head to a laser welding device to implement 'beam wobbling' has disadvantages. The addition of motors and other components for wobbling increases the system's weight, making installation and relocation difficult and reducing productivity. Furthermore, the increased complexity of the system can affect maintenance and durability. Additionally, 'beam wobbling' increases welding time and can cause sagging during side and overhead welding of cargo tanks, potentially leading to quality issues. Therefore, there is a need to develop a laser welding system capable of responding to gap increases by increasing the effective cross-sectional area of the laser beam without configuring additional devices for 'beam wobbling' such as wobble heads and motors. FIG. 1 is a perspective view of a laser welding system for an LNG cargo tank according to one embodiment of the present invention. FIG. 2 is a front view of a laser welding device for an LNG cargo tank according to an embodiment of the present invention. FIG. 3 is a perspective view of a laser welding device for an LNG cargo tank according to an embodiment of the present invention. FIG. 4 is a perspective view of a laser welding device for an LNG cargo tank according to one embodiment of the present invention, viewed from another side. FIG. 5 is a configuration diagram illustrating a light homogenization section of a laser welding device for an LNG cargo tank according to an embodiment of the present invention. Figure 6 is an image comparing the cross-sectional profile of a typical laser beam with a