Title of Invention

A CORRELATION SEARCH-BASED HOT SLAB LENGTH MEASUREMENT SYSTEM ADAPTABLE IN A CONTINUOUS CASTING SUB PROCESS

Abstract

This invention relates to a correlation search - based hot slab length measurement system adaptable in a continuous casting sub process of steel manufacturing process, comprising; a high resolution camera (7) disposed in a metal casing (8) having an aperture (3) for allowing light from the hot slab to be directed inside the casing (8); a telephoto lens (6) capturing the finer details of the slab surface and focusing the slab image onto a couple charges device (CCD); at least two laser pointers (1,2) installed on both side of the camera (7) such that the laser pointers (1,2) make equal angles with the principal axis of the camera (7) to achieve accurate depth calibration from the slab side surface, the reflection of the laser pointers (1,2) in the captured frame adapted to determine the distance; between the camera (7) and the object; a metal halite bulb for swamping the infra red radiation emerging from the hot slab; and an embedded hardware (14) hosting an image processing algorithm (14) connected to the high resolution camera (7) via a USB-link (13), the embedded hardware (14) receiving the images captured by the camera (7) and comprising a correlation search- based optical flow between two successive image frames obtained at a fixed time interval selected in accordance with the casting speed of the slab, the optical flow so computed being converted into motion vector data corresponding to the actual motion of the slab which data transmitted to the operator via a communication unit (15) attached to the host (14).

Full Text

FIELD OF INVENTION The invention relates to a system for hot slab length measurement passed torch cutting machine. More particularly, the invention relates to a correlation search- based hot slab length measurement system in a continuous casting sub-process of steel manufacturing process. BACKGROUND OF INVENTION In a continuous casting process of steel manufacturing, molten steel is poured into a vertically aligned water-cooled mold of rectangular cross-section, from where it emerges as a continuous strand which is a solidified shell encapsulating the liquid material. The continuous strand is further cooled by water sprays and bent using rollers till its complete solidification including attainment of horizontal alignment. Due to thermal and bending stress including oxidation and oscillation in the process, several prominent and rich textures are often engraved, in the form of oscillation marks and scales, which are visible on the strand surface. The existing method of determining a slab length which has passed a reference point, essentially depends upon the turn count of the rollers. However, such a method of the slab computing length, always suffers from the drawback that the mass of the continuous strand slips on the roller bed leading to inaccurate turn count of the rollers. OBJECTS OF THE INVENTION It is therefore an object of the invention is to propose a slab length measurement system in a continuous casting sub-process of steel manufacturing process. Another object of the invention is to propose a slab length measurement system in a continuous casting sub-process of steel manufacturing process, which is enabled to automatically determine the cut length of the hot slab. A still another object of the invention is to propose a slab length measurement system in a continuous casting sub-process of steel manufacturing process, which is capable to measure the length of the hot slab accurately. SUMMARY OF THE INVENTION Accordingly, there is provided a slab length measurement system in a continuous casting sub-process of steel manufacturing process, in which a high-resolution camera is provided to continuously monitor the slab movement to determine the length of hot slab thus passed a reference point. This is a machine vision system thus, the images when fed into an embedded hardware unit hosting an algorithm, the captured frames can be analyzed to determine the optical flow between two subsequent frames separated in a time space. BEIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS The invention can now be described in detail with the help of the figures of the accompanying drawings in which, Fig. 1 - is a schematic view of a known continuous caster. Fig. 2 - is a schematic diagram of the slab length measurement system, according to the invention. Fig. 3 - is a side view of a slab surface. An exemplary embodiment of the invention as depicted in the accompanying drawings will now be explained in details. However there can be several other embodiments all of which are deemed covered by this specification. As shown in Figure 2, the slab length measurement system is positioned adjacent to one side of the roller table of the continuous caster. The system is positioned at about 8 meters distance from the roller bed of the continuous caster of Figure 1 and positioned at about 4 meters from the start of the secondary cooling zone as shown in figure 1. The slab caster is generally full of vibrations due to oscillation of the vertical mold. Accordingly, no camera can be kept close to the hot slab and a telephoto lens is used to obtain good optical resolution making it more sensitive to vibration. To overcome the vibration, the inventive system is equipped with vibration absorbers at two different levels. As shown in Figure 2, the system is provided with a shock-absorption device comprising a base 23 mounted on the concrete platform at the shop floor, a rubber padding 22 is disposed between the base 23 and a vertical member to absorb the vibrations induced because of the heavy mechanical oscillations of the mold. A shock absorber 20 provided at the bottom portion (19) of the system to cancel out any faintest vibrations left so far. The main system is configured within a metal housing 8 mounted on the bottom portion (19). Light form the slab goes inside the housing 8 through a circular aperture 3 of diameter for example, 50 mm, which has a glass wall to prevent the dust entering the housing (8). An air-purging outlet 4 is provided to prevent dust accumulation onto the outer glass surface. The IR radiation can be harmful for the couple charged device (CD) cells. In order to protect the photo sensor from the infra red radiation, an IR filter 5 with suitable cut-off frequency is provided just after the aperture 3. The lights from the opening 3 is gathered and focused on the image plane of a camera 7, and a lens 6. The camera 7 and the lens 6 is mounted on a vertical slider 9. Since the slab is red hot, the fine surface details get masked due to excessive infra red radiation from the surface. Though the infra red part of the accumulated light from the couple charged device (CCD) does not contain visible information, it has sufficient energy to excite the CCD cells to add up charge. This phenomena produces blur image of the object emitting infra red radiation. To overcome this problem the infra-red component is swamped by putting metal halite bulbs which in effect, increases the reflected component of light in the visible range. The external infrared cut-off filter 5 mounted in front of the camera 7 and lens unit 6 prevents infra red light to reach the coupled charged device (CCD). A calibration unit consisting of 12 dots distributed over a steel sheet determines the extrinsic and intrinsic parameters of the camera 7. In order to determine the lateral distance between the image plane of the camera 7 and the slab surface, two laser pointers 1 and 2 are installed in the housing 8 such that they make equal angles with the principal axis of the camera 7. The wavelengths of the laser pointers 1 and 2 are chosen such that they are easily distinguishable on the red-hot slab surface in the image captured by the camera 7. Projection of the laser pointers 1 and 2, in the captured image can lead to distance computation through simple mathematics. The assembly of the camera 7 and the laser pointers 1 and 2, are driven by 12V DC power unit 11 which is installed inside the housing 8. The system exploits the extensive texture information present on the side surface of the cast hot slab due to scale formation and oscillation masks engraved while casting. The high resolution camera 7 equipped with high focal length lens 1 and 2, captures the finer details of the surface which is further analyzed to produce accurate movement of the slab. The images captured by the camera 7 is sent to an embedded hardware 14, hereinafter known as 'the host' through a physical USB 2.0 link 13 between the camera 7 and the host 14. The embedded hardware 14 hosts an image processing algorithms to compute the correlation search based optical flow between two successive image frames, as shown in Figure 3, obtained at a fixed time interval. The fixed time interval is chosen in accordance with the casting speed that is to say, the speed by which the hot slab moves on the roller bed as shown in Figure 1. The casting speed normally varies from 0 meter / min to 1.2 meter / min. Once the optical flow between the two successive image frames is computed by the host unit 14, it is converted into the motion vectors pertaining to the actual motion of the slab. This data is sent to the operator through RS - 232 communication unit 15 attached to the host 14. A clean air purging unit 18 is provided which delivers purified air in downward direction so that the stream of the clean air circulates inside the metal housing 8 and surface out from the outlets 4 and 24. To protect the electronics of the units, for example, the camera (7), D.C. power unit (11), hardware unit (14), the metal housing (8) is equipped with water cooling arrangement in which, water flowing through a plurality of copper tubes inside the hollow walls of the housing 8, with an inlet 17 and an outlet 16. The images, adjacent to each other in time domain, captured by the camera 7 are fed into the host 14. EXAMPLE Five 100 x 100 pixels wide, overlapping blocks in the first 30% width of the image are selected according to the standard deviation of the pixel values inside the bounding rectangles. Where, Xi : Denotes the gray value of the vectorized ith pixel in the block -X : Denotes the average gray value of the block and n : Donates the number of pixels in the block Given the brightness constancy and temporal coherence assumption, one can safely assume the later image is space shifted 2-D version of the former image. Thus the motion vector between two images can be determined by the peak of the correlation surface obtained using normalized cross correlation as defined below. If image A has dimensions (Ma, Na) and image B has dimensions (Mb, Nb), the equation for the two-dimensional discrete cross-correlation is :- REFERENCES A. PATENT SPECIFICATION 1. US 3159749 dated January 1964 2. US 3633010 dated January 1972 3. US 3428817 dated February 1969 B. LITERATURE 1. WORLD STEEL UNIVERSITY WEBSITE, Continuous casting Link: 2. BERTHOLD K.P. HORN and BRIAN G. SCHUNCK, Determining Optical Flow, 3. ADELSON, E H. AND BERGEN, J R. 1986. The early detection of motion boundaries. In iEEE Proceedings of Workshop on Vtsual Motzon (Charleston, S.C., May). 151 156. 4. ADR5 G. 1985. Determining three-dimensmnal motion and structure from optical flow generated by several moving objects. IEEE PAMI 7,4, 384 401. 5. ANANDAN P. 1989. A computational framework and an algorithm for the measurement of visual motion. Int. J. Comput. 6. BLACK, MJ. AND ANANDAN, P. 1993 A framework for robust estimation of optical flow In Proceedings of ICCV (Berlin, May), 7. FERMIN, I. IMIYA, A. 1994. Two-dimensional motion computation by randomized method. Tech. Rep. TR ICS-4-6-1994, Dept of Information and Computer Sciences, Chiba University, Japan. 8. E. De Micheli, V. Torre, S. Uras, the Accuracy of the Computation of Optical Flow and of the Recovery of Motion parameters, IEEE Transactions on Pattern Analysis and Machine Intelligence. 9. REICHARDT, W., SCHLOGL, R.W., AND EGELHOAF, M. 1988. Movement detectors of the correlation type provide sufficient information for local computation of 2d velocity fields. 10.SOBEY, P AND SmNIVASAN, M.V. 1991. Measurement of optical flow by a generalized gradient scheme. ll.SPETSAKIS, M.E. 1994. An optical flow estimation algorithm that uses Gabor filters and affine model for flow. 12.Tsai, R.Y. HUANG, T.S. 1984. Uniqueness and estimation of three- dimensional motion parameters of rigid objects with curved surfaces. IEEE PAMI 13.ZOLTOWSKt, m.d. 1987 Signal processing applications of the method of total least squares. In IEEE 21st Annual Aszlomar Conference. WE CLAIM 1. A correlation search - based hot slab length measurement system adaptable in a continuous casting sub process of steel manufacturing process, comprising : - a high resolution camera (7) disposed in a metal casing (8) having an aperture (3) for allowing light from the hot slab to be directed inside the casing (8); - a telephoto lens (6) capturing the finer details of the slab surface and focusing the slab image onto a couple charges device (CCD); - at least two laser pointers (1,2) installed on both side of the camera (7) such that the laser pointers (1,2) make equal angles with the principal axis of the camera (7) to achieve accurate depth calibration from the slab side surface, the reflection of the laser pointers (1,2) in the captured frame adapted to determine the distance; between the camera (7) and the object; - a metal halite bulb for swamping the infra red radiation emerging from the hot slab; and - an embedded hardware (14) hosting an image processing algorithm (14) connected to the high resolution camera (7) via a USB-link (13), the embedded hardware (14) receiving the images captured by the camera (7) and comprising a correlation search- based optical flow between two successive image frames obtained at a fixed time interval selected in accordance with the casting speed of the slab, the optical flow so computed being converted into motion vector data corresponding to the actual motion of the slab which data transmitted to the operator via a communication unit (15) attached to the host (14). 2. The system as claimed in claim 1, comprising a shock - absorption device (20,21,22,23) to absorb the vibrations induced due to the high mechanical oscillation of the mold. 3. The system as claimed in claim 1, wherein the camera (7) and the lens (6) in an assembly is mounted on a vertical slider (9). 4. The system as claimed in claim 1 or 2, wherein the camera (7) and the lens (6) assembly is driven by a power- drive unit (11) disposed in the housing (8). 5. The system as claimed in claim 1, comprising a clean air purging unit (18) which delivers purified air inside the metal casing (8) and surface out from outlets (4,24). 6. The system as claimed in any of the preceding claims, wherein the metal housing (8) is provided with water-cooling arrangement having one each inlet and outlet (17,16). 7. The system as claimed in claim 1, comprising an infra-red filter (5) provided before the aperture (3) to cut-off infra-red radiation from reaching the CCD. 8. The system as claimed in any of the preceding claims, wherein the metal housing (8) is mounted on a second level base (19) of the shock absorption device. 9. A correlation search - based hot slab length measurement system adaptable in a continuous casting sub process of steel manufacturing process, as substantially described herein and illustrated with reference to the accompanying drawing. This invention relates to a correlation search - based hot slab length measurement system adaptable in a continuous casting sub process of steel manufacturing process, comprising; a high resolution camera (7) disposed in a metal casing (8) having an aperture (3) for allowing light from the hot slab to be directed inside the casing (8); a telephoto lens (6) capturing the finer details of the slab surface and focusing the slab image onto a couple charges device (CCD); at least two laser pointers (1,2) installed on both side of the camera (7) such that the laser pointers (1,2) make equal angles with the principal axis of the camera (7) to achieve accurate depth calibration from the slab side surface, the reflection of the laser pointers (1,2) in the captured frame adapted to determine the distance; between the camera (7) and the object; a metal halite bulb for swamping the infra red radiation emerging from the hot slab; and an embedded hardware (14) hosting an image processing algorithm (14) connected to the high resolution camera (7) via a USB-link (13), the embedded hardware (14) receiving the images captured by the camera (7) and comprising a correlation search- based optical flow between two successive image frames obtained at a fixed time interval selected in accordance with the casting speed of the slab, the optical flow so computed being converted into motion vector data corresponding to the actual motion of the slab which data transmitted to the operator via a communication unit (15) attached to the host (14).

Documents:

01175-kol-2008-abstract.pdf

01175-kol-2008-claims.pdf

01175-kol-2008-correspondence others.pdf

01175-kol-2008-description complete.pdf

01175-kol-2008-drawings.pdf

01175-kol-2008-form 1.pdf

01175-kol-2008-form 2.pdf

01175-kol-2008-form 3.pdf

01175-kol-2008-gpa.pdf

1175-KOL-2008-(30-07-2014)-ABSTRACT.pdf

1175-KOL-2008-(30-07-2014)-CLAIMS.pdf

1175-KOL-2008-(30-07-2014)-CORRESPONDENCE.pdf

1175-KOL-2008-(30-07-2014)-DESCRIPTION (COMPLETE).pdf

1175-KOL-2008-(30-07-2014)-DRAWINGS.pdf

1175-KOL-2008-(30-07-2014)-FORM-1.pdf

1175-KOL-2008-(30-07-2014)-FORM-2.pdf

1175-KOL-2008-(30-07-2014)-OTHERS.pdf

1175-KOL-2008-CORRESPONDENCE 1.1.pdf

1175-KOL-2008-FORM 1.1.pdf

1175-kol-2008-form 18.pdf

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