Title of Invention

A NON CONTACT DEVICE BASED ON MACHINE VISION FOR THE MEASUREMENT OF ROOT GAP IN WELDED JOINTS

Abstract

This invention relates to a device for measuring the weld root gap and the gap between the two top edges in a weld consisting of a camera (2), two light sources (3) placed at two different locations, a shroud (4) covering the weld zone and a computer operated through a image processing software when the shroud shielding the image from external light by covering on all the four sides of the camera, wherein the computer collects the image through the camera, the collected image being processes by the image processing software on standard edge detection operations by cropping up first image to include only root portion (zone 2) excluding the top edge, using the cropped zone 2 for edge detection to detect the root (zone 3), cropping a second image (zone 1) to detect the top edges and converting the resultant image to binary image thus detecting the root gap and the distance between top edges.

Full Text

FIELD OF INVENTION The present invention relates to a device for measuring weld root gap and distance between edges of an weld using an electronic camera, software and a lighting source. More particularly, the invention relates to a device for detecting the root gap and the gap at the top of the joint in a weld fit-up by machine vision. BACKGROUND OF THE INVENTION Welding is a well-established manufacturing method for joining components. In welding, the most widely used method is the arc welding processes where the two parts are set in close contact with each other such that there exists a specific gap at the abutting surface and is called the root gap. The root gap is an important parameter in welding operation and has to be controlled to get good quality in weld. Generally the parts are set with the required root gap and the two parts are restrained from moving and they are mechanically joined together using clamps or similar appliances. The gap, thus set, may still be different from the required gap since the welding heat may lead to the variation of the gap in spite of the clamps. Thus the measurement of the gap and maintaining it are important for the welding operation. The root gap is measured by different gages such as vernier calipers, screw gages or weld gages utilizing mechanical arrangements and employing profile projectors and shadowgraphs using optical and electronic gadgets. Imaging technology for measurements in medical and mechanical fields are well- established technologies. Patent JP11047932 discloses about the measurement of root gap of a weld especially for two tubes. The two tubes are aligned and by means of two hydraulic cylinders the two surface positions are located and this is used for the correction of the misalignment. The invention utilizes mechanical devices whereas the proposed invention discusses about a machine-vision based system for the root gap in a weld. JP8101001 utilizes the mechanical measurement by using rulers for the measurement, whereas the present invention is totally a non-contact machine vision based system. US5026967 describes the welding parameters for the laser welding of dissimilar materials and does not refer to the weld root gap detection. JP2000263274 describes the aligning the edges mechanically using a rotating device and standard reference for a particular job. The present invention uses the machine vision method to identify the root gap. JP60257976 refers to the use of magnetic field generated by the welding current for detecting the root gap. The present invention uses the machine vision for the root gap measurement using an optical system JP60257976 is working on a principal of using the magnetic field created in the groove by the welding current. The present invention does not use magnetic field at all. The proposed invention also is not involved with any technical character related to any welding step. Presence of welding current flow is important for the invention as per Patent JP60257976 but the proposed invention does not require any welding. Patent GB1449044 discusses about a machine vision based system for detecting the weld shape. A shadow of an edge is used as a method of finding the root gap. The protection of a light on varying contoured surface produces a projected image of the shadow, which is affected by the surface contour. By taking a video of the shadow of the edge formed on the weld contour, the exact shape of the weld root and the edges are found. This enables the contour of the surface to be detected at one particular location. For the next location, the light source is moved along with the shadow forming edge and again the analysis is conducted. The root gap or the weld contour of the entire weld is not measured simultaneously as in proposed invention in contrast, root gap or the weld contour is measured at various points as number of stages. A wedge [2A] is placed in front of the light source. A shadow is formed on the job [4]. This image of the shadow is picked up by the camera [3] at an angle (Fig-2). This method of employing the light is called "structured lightning" in industrial parlance. The image captured by the camera is shown in the patent GB1449044 figure (3). The shape of the groove or that of a completed weld can be checked as shown in the Figures 4, 6 and 7. However this requires that the image is acquired at every section of the job for finding the root gap and the gap between the edges at the top. Whenever a shadow is formed by an edge, there will be spreading of shadow because of diffraction due to the edge effect on one side and the measurement may not be at the place intended. The present invention is based on acquisition of the image of a larger area and using image processing to detect edges in the larger area at a time for increased productivity. The present invention uses a light source [1] for illuminating an area of the job. Since the proposed invention uses larger illuminated area, diffraction resulted from edge effect due to structured light using edge or slit is eliminated. OBJECTS OF THE INVENTION It is therefore an object of the invention to propose, a device for measuring the gap between the two edges of the root and top of a weld fit up using a non- contact optical method. Another object of the invention is to identify the gap for larger areas at a time for purpose of increased productivity. Another object of the invention is to propose a device, which will enable measurement from a far off distance. A still another object of the invention is to measure the root gap even in the environment of intense arc light produced by welding. A yet another object of the invention is to propose a device, which can be used in a zone just ahead of the weld when the welding is in progress. A still another object of the invention is to propose a device that ensures that the measurement is done such that the feedback about the root gap and the gap at the top of the weld joint can be given electronically. A still further object of the invention is to propose a device, which will enable the measurement when the weld root has very little access especially in thick joints. SUMMARY OF THE INVENTION Accordingly, in the present invention there is provided a device for measuring the root gap in a weld comprising; an electronic camera for acquiring the image of the weld groove, suitable light source to illuminate the groove, and a computer with image analysis software to undertake the analysis; Collect the image of the weld groove with the wedge [2A] is placed in front of the light source. A shadow is formed on the job [4]. This image of the shadow is picked up by the camera [3] at an angle (Fig-2). This method of employing the light is called ' structured lighting ' in industrial parlance. The image captured by the camera is shown in the patent GB1449044 figure (3). The shape of the groove or that of a completed weld can be checked as shown in the Figures 4, 6 & 7. However this requires that the image is acquired at every section of the job for finding the root gap and the gap between the edges at the top. Whenever a shadow is formed by an edge, there will be spreading of shadow because of diffraction due to the edge effect on one side and the measurement may not be at the place intended. The present invention is based on acquisition of the image of a larger area and using image processing to detect edges in the larger area at a time for increased productivity. The present invention uses a light source [1] for illuminating an area of the job. Since the proposed invention uses larger illuminated area, diffraction resulted from edge effect due to structured light using edge or slit is eliminated. SUMMARY OF THE INVENTION Accordingly, in the present invention there is provided a device for measuring the root gap in a weld comprising; an electronic camera for acquiring the image of the weld groove, suitable light source to illuminate the groove, and a computer with image analysis software to undertake the analysis; Collect the image of the weld groove with the camera vertically above the weld groove and two light sources located at an angle above the weld; locating the edge of the root, edge of weld top by mathematical operations on the acquired image; measuring the locations of the edge lines at the top and the root and finding the difference between them to identify the root gap and the weld seam position using set up variant I(Fig 2 ) through reflected light ;Measuring the locations of edge lines at the root and finding the difference between them to find the root gap only, using transmitted light ,using the measurement set up variant II(Fig 5). BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS Figure 1- Shows the terminology in a weld joint according to the present intention. Figure 2- Shows an embodiment of the device according to variant I of the invention. Figure 3 - Shows the processed image of the top edge of the weld joint. Figure 4 - shows the processed image of the root edge of weld joint. Figure 5 - Shows an embodiment of the device according to variant II of the invention. Figure 6 - represents definition of zones in the weld image. Figure 7 - represents Cropping zones. DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT OF THE INVENTION The Invention includes a system consisting of an electronic camera for acquiring the image of the weld groove, suitable light source to illuminate the groove, and a computer with image analysis software to undertake the analysis. The image of the weld groove is collected with the camera placed vertically above the weld groove and two light sources located at an angle above the weld. The locating of the edge of the root, edge of weld top is carried out by mathematical operations on the acquired image. Measuring the locations of the edge lines at the top and the root and finding the difference between them to identify the root gap and the weld seam position through set up variant I (Fig 2) using reflected light is performed through the device setup. Measuring the locations of edge lines at the root and finding the difference between them to find the root gap only, using transmitted light, through the measurement set up variant II (Fig 5) is performed in another set of device. The illumination is such that the image of the top surface is brighter compared to the image of the weld groove and the root gap. The image of the root gap (zone 3) is darker than that of the sidewall which is mentioned as zone 1 and zone 3 in the image formation (Fig 6). The image collected from the camera covers a larger area effectively finding the root gap and the top edge for a specified length in an area decided by the camera resolution and the distance between the camera and the job. In the present invention, image collected from the camera is processed by doing the standard edge detection operations using image processing software. The choice of the saturation levels used decides the separation of the edges. A copy of the first image is cropped to include only root portion (excluding the top edge). When this cropped image is used for edge detection only the root is detected. However, when the second image which is cropped so that the cropped image includes the top edge i.e. zone 1 and zone 2 and a portion zone 3, is used for the edge detection, then only the top edges are detected. Hence by using one image and two software operations, the root gap and the distance between the top edges are detected. The nomenclature used in this specification is shown in fig 1. The distance between point A and point B is the distance between the edges at the top. The root gap is the distance between C and D. There are two variants to the invention and are described below: In variant I, (Fig 2) the device comprises of an electronic camera [2], two light sources [3] a shroud [4] covering the weld zone [1] and computer [5] with a required software. The camera is an electronic type with required resolution and ability to record and transmit the images to the computer. Two light sources are placed at two different locations at an angle such that the two sources, and the camera are aligned along the length of the weld and such that the camera is in between the two light sources. A shroud [4] covers on all the four sides of the camera such that the area covered for the image is shielded from external light. The computer [5] collects the image through the camera and the image is further processed. The image collected from the camera is processed by doing the standard edge detection operations using image processing software. The choice of the saturation levels used decides the separation of the edges. A copy of the first image is cropped to include only root portion (excluding the top edge) referred as cropping zone 2 as per fig 7. When this cropped image is used for edge detection only the root is detected. However, when the second image which is cropped as per cropping zone 1 mentioned in fig 6 so that the cropped image includes the top edge i.e. weld image zone 1 and zone 2 and a portion of zone 3, is used for the edge detection, then only the top edges are detected. The resultant edge image is converted to the binary image and is shown as seen in fig 3 and fig 4. Hence by using one image and two software operations, the root gap and the distance between the top edges are detected. Variant II of the invention is as shown in figure 5 wherein the device comprises of an electronic camera [2], two light sources [3] kept at the bottom and computer [5] with the required software. The camera is an electronic type with required resolution and ability to record and transmit the images to the computer. Two light sources are placed at two different locations at the bottom such that the two sources, and the camera are aligned along the length of the weld ( Fig 5 ). A shroud[4] covers on all the four sides of the camera such that the area covered for the image is shielded from external light. The computer [5] collects the image from the camera and the image is further processed. The image is cropped as per cropping zone 2 as mentioned in Fig 7, so that the cropped image includes the root. The image is processed by the standard edge detection operations by the image processing software. The choice of the saturation levels used decides this separation of the edges. The resultant edge image is converted to the binary image and is shown in fig 4. By calibrating computer monitor pixel values with distance, it is possible to calculate the gap accurately. The invention as herein defined should not be read and construed in a restrictive manner, as several modifications, alterations and adaptations are possible within the scope and ambit of the invention as defined in the appended claims. WE CLAIM 1. A non contact device for measuring the weld root gap and the gap between the two top edges in a weld consisting of a camera (2), two light sources (3) placed at two different locations, a shroud (4) covering the weld zone and PC based image processing system, with the light sources providing adequate light for the area to be analysed, the shroud shielding the location to be analysed from external light and the computer processing the image acquired through the camera and converting the resultant image to binary image thus detecting the root gap and the distance between top edges without any contact with the weld joint thus enabling the measurement just prior to the welding operation. 2. A device as claimed in claim 1, wherein the two light sources (3) are placed at an angle such that the two sources and the camera are aligned along the length of the weld and such that the camera is in between the two light sources. 3. A device as claimed in claim 2, wherein the two light sources (3) are kept at the bottom such that the two sources and the camera are aligned along the length of the weld. 4. A device as claimed in claim 1, wherein when the second image is cropped so that the image includes the top edge i.e. zone 1, zone 2 and a portion of zone 3 is used for the edge detection, when only the top edges are detected. 5. A device as claimed in claims 1 and 4, wherein by using one image only through the device and two software operations the root gap and the distance between the top edges are detected. 6. A device as claimed in the preceding claims wherein measurement of root gap and top edges of a weld are possible by a non-contact optical method, enabling measurement from a far off distance from the weldment or even in the environment of intense arc light produced by the welding or in a zone just ahead of the weld when is in progress or enabling measurement when the weld root has very little access especially in thick joints. ABSTRACT A NON CONTACT DEVICE BASED ON MACHINE VISION FOR THE MEASUREMENT OF ROOT GAP IN WELDED JOINTS This invention relates to a device for measuring the weld root gap and the gap between the two top edges in a weld consisting of a camera (2), two light sources (3) placed at two different locations, a shroud (4) covering the weld zone and a computer operated through a image processing software when the shroud shielding the image from external light by covering on all the four sides of the camera, wherein the computer collects the image through the camera, the collected image being processes by the image processing software on standard edge detection operations by cropping up first image to include only root portion (zone 2) excluding the top edge, using the cropped zone 2 for edge detection to detect the root (zone 3), cropping a second image (zone 1) to detect the top edges and converting the resultant image to binary image thus detecting the root gap and the distance between top edges.

Documents:

01016-kol-2007-abstract.pdf

01016-kol-2007-claims.pdf

01016-kol-2007-correspondence others 1.1.pdf

01016-kol-2007-correspondence others.pdf

01016-kol-2007-description complete.pdf

01016-kol-2007-drawings.pdf

01016-kol-2007-form 1.pdf

01016-kol-2007-form 18.pdf

01016-kol-2007-form 2.pdf

01016-kol-2007-form 3.pdf

01016-kol-2007-gpa.pdf

1016-KOL-2007-(20-03-2013)-ABSTRACT.pdf

1016-KOL-2007-(20-03-2013)-CLAIMS.pdf

1016-KOL-2007-(20-03-2013)-CORRESPONDENCE.pdf

1016-KOL-2007-(20-03-2013)-DESCRIPTION (COMPLETE).pdf

1016-KOL-2007-(20-03-2013)-DRAWINGS.pdf

1016-KOL-2007-(20-03-2013)-FORM 1.pdf

1016-KOL-2007-(20-03-2013)-FORM 2.pdf

1016-KOL-2007-(20-03-2013)-FORM 3.pdf

1016-KOL-2007-(20-03-2013)-OTHERS.pdf

1016-KOL-2007-(20-03-2013)-PA.pdf

1016-KOL-2007-(20-11-2013)-FORM-13.pdf

1016-KOL-2007-CANCELLED PAGES.pdf

1016-KOL-2007-CORRESPONDENCE-1.1.pdf

1016-KOL-2007-CORRESPONDENCE.pdf

1016-KOL-2007-EXAMINATION REPORT.pdf

1016-KOL-2007-FORM 13.pdf

1016-KOL-2007-FORM 18.pdf

1016-KOL-2007-GPA.pdf

1016-KOL-2007-GRANTED-ABSTRACT.pdf

1016-KOL-2007-GRANTED-CLAIMS.pdf

1016-KOL-2007-GRANTED-DESCRIPTION (COMPLETE).pdf

1016-KOL-2007-GRANTED-DRAWINGS.pdf

1016-KOL-2007-GRANTED-FORM 1.pdf

1016-KOL-2007-GRANTED-FORM 2.pdf

1016-KOL-2007-GRANTED-FORM 3.pdf

1016-KOL-2007-GRANTED-SPECIFICATION-COMPLETE.pdf

1016-KOL-2007-REPLY TO EXAMINATION REPORT.pdf

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