Development of hot-engraved letter reading device using a two-dimensional laser distance meter KYOSUKE SATO *

Transcription

1 Development of hot-engraved letter reading device using a two-dimensional laser distance meter BY KYOSUKE SATO * SYNOPSIS: We have developed a technique which can read engraved letters for controlling physical distribution on a bloom of temperature of 800 and installed it in producing line of our works. In order to recognize and read, we have developed the measuring system in which a two- dimensional laser range finder with an optical and athermanous filter moves and measures the surface of the bloom and the depth of letters. Additionally, we have improved reading rate of letters to 95 % and prevented different materials from flowing out by reciprocating laser range finder over the surface of the bloom. Keywords: Identification, QA, Reader, Automatic reading, Bloom, Distance meter * Steel Bar & Wire Rod Technology Sec. Kurashiki Steel Bar & Wire Rod Dept. JFE Steel Corporation, Steel Bar & Wire Rod Division, Japan 1

2 1. Introduction In Billet Mill of JFE Steel Corporation West Japan Works (Kurashiki), we have been improving the level of quality assurance in the process from receipt of materials to shipment of products to date. Automation has been completed by utilizing a barcode reader or the like when managing information at the time of shipment of products or during product movements between manufacturing processes. Meanwhile, the discrimination of the material on the entry side of the reheating furnace had been carried out by the operator visually checking the tracking information and the engraved letter of the product, and manually entering the judgment result. Because there was a risk of human error, the identification abnormality at charging to reheating furnace was a large possibility of delivering different materials to customers, and it was necessary to improve. We established an automatic reading technology for hot-engraved letter in research and development, and we realized an improvement in the level of quality assurance by making this technology real. In this paper, the outline of automatic reading device of hot engraved letters and the start-up situation are reported. 2. Layout of Billet Mill Layout of Billet Mill is shown as Figure 1. Materials are heated by reheating furnace or soaking pits. Especially, materials of large ingots and for diffusion annealing are applied to soaking pits. Heated materials are roughly rolled by 2Hi reversible roll, Break Down mill (hereinafter referred to as BD mill). After this, it is hot-scarfed and sheared as needed. Relationship of round bar size and rolling process is shown as Table 1. φ270mm and up round bars are cut by BD hot saw, and are carried away from rolling line. On the other hand, for rolling φ260mm and under round bars, intermediate cross-section blooms are carried to the continuous finishing Vertical-Horizontal mill (hereinafter referred to as VH mill), has two vertical rolling stands and two horizontal rolling stands. After rolled in VH mill, rolled bars are measured by profile meter, and cut by VH hot saw. Cut bars (billets) are cooled in cooling bed, and carried to conditioning lines. First rolling process Second rolling process Reheating furnace 2Soaking pits 3Breakdown mill 7 4Hot scarfer 5Shearing machine 6Breakdown hot saw 7Bloom Grinder 8Trun table 9VH mill 10Profile meter 11VH hot saw 12Hot stamper 13Cooling bed Fig.1 Layout of Billet Mill line 2 2

3 Table 1 Relationship of round bar size and rolling process Round bar size BD Mill VH Mill Φ90 to 260 mm Intermediate cross-section bloom rolling Finishing rolling Φ270 to 450mm Finishing rolling - 3. Outline of the engraved letter reading device 3.1 Engraved letters The material of Billet Mill uses a semi-finished product called bloom which is a source of steel products manufactured by continuous casting machine. Because the chemical composition and size of product are determined according to the production order, it is important to manage each bloom. Cast blooms are stamped engraved letters on the cross section of hot blooms which are nearly max 1,000. The engraved letters consist of 7 digits, and as shown in the Table 2, use numbers 0 through 9 and alphabet A through D. Moreover, these have a special shape so as not to be misrecognized by the operator. For example, 1 is tilted slightly obliquely, 8 and B have a difference so that they can be easily distinguished. The size of letter is 10 mm in width, 20 mm in height, engraved depth is 3 mm. The space between letters is 20mm. The photograph of engraved letters on the cross section of the bloom is shown in the Figure 2. In this case, 1306C02 are engraved. The stamping machine receives the engraved letters information instructed by the database server, and selects letter shaped punch and stamps it with an impact cylinder. Identification management of each bloom is realized with engraved letters. Table 2 The engraved letters 3

4 Fig.2 The photograph actually engraved 3.2 Reading method As a technique for reading letters, a method of photographing with a camera and recognizing it from the letter image is known. However, when the reading object itself emits light, it is difficult to distinguish letters because there is no light and darkness, so letters can not be correctly recognized. Since the max temperature of bloom is about 800, the steel material itself emits light, and recognition by camera shooting is difficult. Therefore, we focused on the difference in distance between bloom's surface and the bottom of the engraved letter. The depth of the letters is measure with a two-dimensional laser rangefinder and acquire distance data. We developed a device that recognizes letters by creating images from the obtained distance data. The specifications of the selected two-dimensional laser rangefinder are shown in the Table 3 (1). The working distance from the bloom is 350 mm, and the measurement range is 350 plus or minus 145 mm. The line direction measurement range is 210 mm. It is wider sufficiently than the size of the engraved letters. Also, in order to measure hot blooms of max 800,the laser is class 2 and blue semiconductor laser with a wavelength of 405nm. Table 3 The specifications of two-dimensional laser rangefinder Item Reference installation distance Measurement range(z) Measurement range(x) Laser type Wavelength Details 350mm ±145mm 210mm Blue semiconductor laser 405nm Laser class Class 2(IEC ) 4

5 3.3 Device outline The measuring method of the engraved letter reading device is shown in the Figure 3. Laser distance meter is installed to match the height direction of the engraved letters with laser line direction. Then, while the bloom is stopped, by scanning bloom s cross sections with a laser distance meter in the width direction of the letters, this device scans the entire range of 7 digit letters. Although the temperature of the bloom decreases slightly due to transportation, the max temperature is about 800. A laser distance meter was installed at a distance of 350 mm from the flower shape, and heat countermeasures are applied. If the scanning speed is too fast, since the letter width is only 10 mm, letters can not be scanned well. Therefore, the scanning velocity is 300 mm / sec. The measurement range of the laser range finder in the letter height direction is 210 mm. The place where the letters are engraved is not always the same position for punching the machine, so it has a sufficient wide field of view for the letter height 20 mm. Fig.3 The measuring method of the engraved letter reading device 5

6 3.4 Counter measures against radiation heat The temperature of Bloom is max 800, and the distance between the laser range finder and bloom is only 350 mm. It is designed not to break the laser rangefinder by taking measures against radiation heat. As shown in Figure 4, the laser rangefinder was covered with a sensor box made of a heat-resistant SUS plate, and an IR cut filter that allows only visible light to pass was installed. The sensor box is cooled by air and the temperature is kept constant. As shown in the Figure 5, the temperature distribution around the sensor box was photographed by thermography. Although there is a hot bloom near the sensor box, it can be confirmed that the temperature of the sensor box is at normal level, and that radiant heat countermeasures are effectiveness. Fig.4 Measures against radiation heat Sensor box (30 ) Bloom (700 ) Fig.5 The temperature distribution around the sensor box 6

7 4. Letter recognition process (2) The letter recognition process consists of 3 steps. Step 1 is making letter image from measurement result of laser distance meter. The basic idea is to binarize whether it is a letter part or not, according to whether the measured value of the laser distance meter is above or below the threshold value. However, the actual bloom s cross section is bumpy, in the case of judging based on the absolute value of the laser distance meter and threshold value, there was a possibility that the parts without letters may be misrecognized as letters. As shown in the Figure 6, binarization of only the letter portion was realized by using the following method. Since the change in the shape of the bloom is more gradual than the engraved letter, the local change of the distance value is calculated, and the region where the change is small is set as the "reference surface". By subtracting the reference surface from the measured distance and comparing the obtained value with the threshold value to binarize it, only the letter portion was detected without being influenced by bending or gradient. Fig.6 Making letter image 7

8 Step 2 is cutting out letters area. As shown in the Figure 7, for the obtained image, the black intensity in each of the row and column direction is detected and the position of the letters is identified. Columns Black intensity Rows Black intensity Cut image Fig.7 Image processing unit Step 3 is pattern recognition. As shown in the Figure 8, the letter part learned in advance is compared with the correct letter training data. By calculating its possibility, the highest letter is recognized. With the above three steps, letter recognition is automatically performed from the measurement value of the laser rangefinder. Possibility 25% 12% Result 30% 20% 15% 92% 65% Fig.8 Training data (example) 8

9 Recognition rate % 5. Result of device operation The recognition rate after introducing this reading device to JFE Steel is shown in the Figure 9. The target before introduction was 95%, but the reading precision immediately after introduction was 77%. After that, by strengthening the training data from online measurement results, it exceeded the initial target and achieved 96%. About 350 blooms are processed per day, and it is the result obtained throughout the year. The remaining 4% is derived from a defect of engraving as shown in the Figure 10. As described above, we have confirmed the usefulness of the engraved letter automatic reading device by the twodimensional laser rangefinder, and achieved the development of automated equipment that does not depend on human judgment Launch Current Taregt Fig.9 The recognition rate Fig.10 Bloom which has the defect of engraving 9

10 6. Conclusion JFE Steel West Japan Works (Kurashiki) billet mill introduced a device that reads engraved letters on a hot bloom cross section using a blue laser two-dimensional laser rangefinder. In addition, its reading accuracy exceeded the initial target, achieving 96%. We are continuously modifying our equipment and operation to satisfy customer. <Reference> (1) KEYENCE, 2014, LJ-V7000 Series (2) JFE Steel, engraved letter reading device, JP A 10