SORTING SYSTEM AND METHOD FOR GLASS SHEETS

Abstract: A discriminating type defect detector detects the size and position of any defect which exists on ribbon-shape glass sheets withdrawn from a kiln and conveyed on a line conveyor. It sends them as defect data to a control unit. The unit sorts the quality of cut glass sheets based on the fault data. A sheet pick-up machine having a push-up device and suction conveyor, picks up prods. of desired grade under control of the unit.

Description: Technical Field This invention relates generally to a glass-plate sorting system for sorting glass plates on a glass-plate manufacturing line. Background Art The manufacture of glass plates generally involves the of cutting and sorting of glass plates out of a glass strip pulled up from the furnace while the glass strip travels on the line conveyor. In cutting glass plates out of the glass strip, a single-grade sorting system has heretofore been employed where only those glass plates which are above the aimed-at quality are sorted out, with the balance discarded. The conventional single-grade sorting/cutting system, however, has a disadvantage of poor yields in manufacturing products having strict quality requirements. Glass plates for automotive windshields, for example, are required to be free of flaws, and of a high quality from the viewpoint of safety. In the manufacturing process of glass plates for automotive windshields, therefore, they are inspected for the presence/absence of flaws, and any glass plates in which flaws are found are discarded. Disclosure of Invention Glass-plate products have a wide variety of applications ranging from glass plates for photocopying machines, which require high quality, to glass panes for buildings, which may be of lower quality. Consequently, producing glass plates by sorting high-grade products and low-grade ones simultaneously on the glass-plate manufacturing line would lead to glass-plate manufacture at the yield of the low-grade products. The quality of glass plates from which automotive windshields are obtained is such that a glass plate need not be free of flaws over the entire surface thereof, but only the see-through area thereof, which is critical for the vision of an automobile driver, must be free of flaws. The remaining peripheral areas immediately around the see-through area may have a certain degree of flaws, and the outermost fringe area of the plate, which are usually discarded, may have any types of flaws. In the manufacturing process of automotive windshields, therefore, glass-plate production yield can be improved by obtaining glass plates by detecting the sizes and locations of flaws in glass plates and judging what sizes of flaws would exist in the assumed see-through area, periphery area and fringe area of a glass plate . In order to implement the above-mentioned method for obtaining glass plates, a discriminating-type flaw detector is needed, which is capable of detecting at high accuracy the types, sizes and locations of flaws in a glass strip, such as bubbles formed by the air bubbles entrapped inside the glass plate, foreign particles remaining in the glass plate, knots formed by the almost molten foreign matter remaining in the glass plate in a shape having a streaming tail, drips formed by the metallic tin existing in the tin bath deposited on the glass plate surface. The present applicant has already developed a discriminating-type flaw detector meeting such a requirement and filed a patent application under the title of "A Discriminating-Type Flaw Detector For Light-Transmitting Plate Materials" on May 27, 1987 (Japanese Patent Application No. 62-128089). This discriminating-type flaw detector is a flying-spot type flaw detector that scans the entire surface of a glass plate with a light spot, detects transmitted light, transmitted and diffused light, reflected light, and reflected and diffused light by means of a plurality of light receptors, and discriminates the sizes and other parameters of flaws based on a combination of detected results. This invention is designed to improve yield by producing flaw data representing the types, sizes and locations of flaws, sending the data to the control unit of the glass-plate sorting system to determine whether the glass plate can be cut in accordance with the quality requirements of the glass plate, using the discriminating-type flaw detector. Consequently, this invention is concerned with a glass-plate production system for cutting a glass strip travelling on a line conveyor into cut-lengths of glass plates and sorting the cut glass plates in accordance with required quality grades, which comprises a discriminating-type flaw detector that detects flaws on a glass strip and outputs the flaw data representing the sizes and locations of the flaws, a control unit for discriminating the quality grades of the cut glass plates, and a plurality of sorting units for sortlng glass plates of desired quality grades. The use of the glass-plate sorting system of this invention makes it possible to obtain glass plates of two quality grades by sorting high-grade and low-grade plates. In doing so, the control unit of the glass-plate sorting system automatically discriminates glass plates being cut into high-grade, low-grade and defective ones, based on the flaw data transmitted from the discriminating-type flaw detector, to sort the high grade and low-grade ones in the sorting unit and discard the defective ones by the eliminating/discarding unit. Thus, product yield can be improved by sorting, together with the high-grade products, the low-grade products that have heretofore been discarded in the conventional single-grade sorting system. When the glass-plate sorting system is used in the automotive windshield manufacturing line, product yield can be improved by tracking the flaws in a glass strip detected by the discriminating-type flaw detector, assuming see-through, peripheral and fringe areas of an automotive windshield on the glass plate cut out from the glass-strip, and judging the acceptability of the glass plate based on the flaw existing in these areas. Brief Description of Drawings Fig. 1 is a diagram illustrating the construction of a glass-plate sorting system of this invention. Fig. 2 is a diagram illustrating a discarding roll. Fig. 3 is a diagram illustrating an example of the construction of a sorter. Fig. 4 is a diagram of assistance in explaining the operation required for sorting two grades of glass plates. Fig. 5 is a diagram illustrating the see-through, peripheral and fringe areas of an automotive windshield assumed on a glass plate from which an automotive windshield is obtained. Figs. 6A and 6B are diagrams of assistance in explaining the operation required for sorting automotive wind-shields. Best Mode for Carrying out the Invention Fig. 1 is a diagram illustrating a glass-plate sorting system of this invention in which a glass-plate manufacturing line ranging from a discriminating-type flaw detector to a glass-plate sorting unit is shown. The manufacturing line has a line conveyor 100 extending in the Y-axis direction, on which a glass strip pulled up from a furnace is transported. A discriminating-type flaw detector 101 is a flying-spot discriminating-type flaw detector, as noted earlier, that scans the glass strip in the X-axis direction, normal to the Y-axis direction, with a light spot to detect flaws present in the glass strip and output flaw data representing the types, sizes (large-, medium- or small-size) and locations (X, Y) of the detected flaws. The flaw data thus produced are sent to a control unit 102 comprising a computer, for example. Upon receipt of the flaw data from the discriminating-type flaw detector 101, the control unit 102 identifies the sizes and locations of the flaws present in the glass strip, and initiates the tracking of the flaws. A trimming-line marker 103 marks a plurality of trimming lines in the Y-axis direction at predetermined intervals on the glass strip clearing the discriminating-type flaw detector 101. The trimming- line marker 103 is controlled by the control unit 102 to determine the x-axis locations of the trimming lines. A diagonal cutter 104 marks a plurality of cutting lines in the X-axis direction at predetermined intervals on the glass strip clearing the trimming-line marker 103. The diagonal cutter 104 has a cutter that travels in the diagonal direction in synchronism with the Y-axis speed of the glass strip. The travelling of the cutter and cutting-line settings are controlled by the control unit 102. A breaker 105 breaks, or cuts, the glass strip clearing the diagonal cutter 104 along the cutting lines into glass-plate rows. The breaker 105 is of a type that breaks the glass strip while moving up and down on the breaker roll under the control by the control unit 102. A trimming cutter 106 cuts and removes the trimmings along the trimming lines of the glass-plate rows broken by the breaker 105. The operation of the trimming cutter 106 too is controlled by the control unit 102. A slitter 107 slits the glass-plate rows along the trimming lines into a plurality of glass plates which are then slightly separated apart by small gaps in the X-axis direction. The slitter 107 too is controlled by the control unit 102. A separator 108 further separates the slit glass plates in the X-axis direction by the revolution of separating rolls to classify the plates by courses. The operation of the separator 108 too is controlled by the control unit 102. An eliminating/discarding unit 109 has such a construction that defective glass plates can be discarded by each course, based on the control by the control unit 102. Fig. 2 shows the construction of the eliminating/discarding unit for one course, in which as a defective glass plate 80 being discarded comes on a discarding roll 90, the defective plate 80 goes down on the discarding roll 90 for disposal in accordance with the control by the control unit 102. As indicated by numerals 110-1, 110-2, ---, and 110-6, six units of sorters are provided to sort glass plates based on the control by the control unit 102. Fig. 3 shows the construction of one of the sorters viewed in the Y-axis direction. Above a line conveyor 100 is provided a suction conveyor 111 extending in the X-axis direction, while a lifter 112 is provided below the line conveyor 100. The lifter 112 pushes up the glass plate 113 travelling in the Y-axis direction on the line conveyor 100 based on the control by the control unit 102. The lifting operation by the lifter 112 is controlled in various modes, such as the selective lifting mode in which glass plates are lifted by selecting plates from courses; the collective lifting mode in which glass plates are lifted only when all the courses for one glass plate row can be lifted; and the course-wise lifting mode in which only those glass plates for a specified course are lifted. The glass plates 113 lifted are sucked by the suction conveyor 111 and transported in the X-axis direction to a transfer car 115 via a brush conveyor 114. Now, the two-grade sorting process to sort high-grade and low-grade plates using the glass-plate sorting system having the above-mentioned construction will be described in the sequence of the process, referring to Fig. 4. Fig. 4 illustrates the sequence of the cutting and sorting operations of a glass strip travelling on the line conveyor 100. PROCESS (a) When the glass strip 120 pulled up from the furnace travels on the line conveyor 100 to the discriminating-type flaw detector 101, the detector 101 detects flaws existing in the glass strip 120, and transmits the flaw data representing the types, sizes and locations of the flaws to the control unit 102. Now, assume that there exist a large-size flaw L and a medium-size flaw M in the glass strip 120, as shown in the figure. PROCESS (b) As the glass strip 120 arrives at the trimming-line marker 103, four trimming lines T₁, T₂, T₃ and T₄ are marked on the glass strip 120 in th Y-axis direction by the trimming-line marker 103. PROCESS (c) Then, cutting lines C₁, C₂, C₃, --- are successively marked in the X-axis direction by the diagonal cutter 104. PROCESS (d) As the glass strip 120 marked with trimming and cutting lines arrives at the breaker 105, the breaker 105 breaks the glass strip 120 into glass-plate rows along the cutting lines. Fig. 4 shows a broken glass-plate row 121 between the cutting lines C₁ and C₂. It is assumed that the glass-plate row 121 has the large-size flaw L and the medium-size flaw M, mentioned above. PROCESS (e) The trimming cutter 106 cuts and removes trimmings E₁ and E₂, which are the edge parts of the glass-plate row 121, along the trimming lines T₁ and T₄. PROCESS (f) The trimmed glass-plate row 121 is slit into three glass plates G₁, G₂ and G₃ by the slitter 107, and the glass plates G₁, G₂ and G₃ are slightly separated apart in the X-axis direction. PROCESS (g) The three glass plates thus slit G₁, G₂ and G₃ are further separated apart in the X-axis direction by the separator 108 to direct to the first, second and third courses. Since the control unit 102 keeps track of the locations of the flaws detected by the discriminating-type flaw detector 101 and controls the locations of the trimming lines marked by the trimming-line marker 103 and the cutting lines marked by diagonal cutter 104, the control unit 102 knows what sizes of the flaws exist at what locations in the glass plates separated apart by the separator 108. Thus, the control unit 102 identifies the glass plate having the medium-size flaw M as a high-grade-out, that is, a low-grade product, the glass plate having the large-size flaw L as a low-grade-out, that is, a defective plate being discarded, and the remaining as a high-grade product. In this way, the glass plates are sorted into high-grade, low-grade and defective products. In doing so, the control unit 102 knows that the glass plate G₁ has the large-size flaw L, the glass plate G₂ has the medium-size flaw M, and the glass plate G₃ has no flaws, and therefore determines the glass plate G₃ as a high-grade product, the glass plate G₂ as a low-grade product, and the glass plate G₁ as a defective product. Based on the judgement, the control unit 102 controls the eliminating/discarding unit and the sorter. PROCESS(h) As the glass plates G₁, G₂ and G₃ arrive at the eliminating/discarding unit 109, the control unit 102 lowers the discarding roll 90 for the first course, on which the defective plate G₁ travels, for removal from the line and disposal. PROCESSES (i) and (j) When the remaining low-grade product G₂ and the high-grade product G₃ on the second and third courses arrive at the sorting section having a plurality of sorters, the control unit 102 controls the sorters to sort the high-grade and the low-grade products. Now, assume that each sorter sorts high-grade or low-grade products for each course. That is, the sorter 110-1 sorts high-grade products for the first course, the sorter 110-2 sorts high-grade products for the second course, the sorter 110-3 sorts high-grade products for the third course, the sorter 110-4 sorts low-grade products for the first course, the sorter 110-5 sorts low-grade products for the second course, and the sorter 110-6 sorts low-grade products for the third course. As a high-grade product G₃ on the third course arrives at the sorter 110-3, the control unit 102 controls the lifter 112 of the sorter 110-3 to selectively lift the high-grade product G₃. Similarly, as a low-grade product G₂ on the second course arrives at the sorter 110-5, the control unit 102 controls the lifter 112 of the sorter to lift the low-grade product G₂. As described above, the two-grade sorting process using the sorting system of this invention is capable of sorting high-grade and low-grade products simultaneously. Sorting the low-grade products that have heretofore been discarded in this way lead to increased yield in the manufacture of glass plates. Next, the sorting process of automotive windshields using the sorting system shown in Fig. 1 will be described in the following. As noted earlier, the quality of glass plates from which automotive windshields are obtained is such that the glass plates need not be free of flaws over the entire surface thereof. Although the see-through area 2, which is critical in terms of driver's visibility, of a glass plate 1 shown in Fig. 5 must be free of flaws, the peripheral area 3 around the see-through area 2 may have a certain degree of flaws. Moreover, the fringe area 4, which is eventually discarded, may have any types of flaws. In the manufacture of automotive windshields, therefore, yield can be improved by sorting glass plates for windshields by detecting the sizes and locations of flaws in glass plates, and judging what size of flaws exist in the see-through area 2, peripheral area 3 and fringe area 4 assumed on the glass plate 1. Now, the sorting process, using the sorting system shown in Fig. 1, of glass plates for automotive windshields whose see-through area is of a high grade having no flaws, and whose peripheral area is of a low grade where small flaws are permitted will be described in the order of production sequence, referring to Figs. 6A and 6B. Figs. 6A and 6B shows the cutting and sorting sequence of a glass strip on the line conveyor 100. PROCESS (a) As a glass strip 130 pulled up from the furnace travels on the line conveyor 100 to the discriminating-type flaw detector 101, the detector 101 detects a flaw existing in the glass strip 130, and transmits flaw data representing the types, sizes and locations of the flaws to the control unit 102. Now assume that there exist two small flaws S₁ and S₂ in the glass strip 130, as shown in the figure. PROCESS (b) As the glass strip 130 arrives at the trimming-line marker 103, three trimming lines T₁, T₂ and T₃ are marked in the Y-axis direction by the trimming-line marker 103. PROCESS (c) Then, cutting lines C₁, C₂, --- are successively marked by the diagonal cutter 104. Since the control unit 102 keeps track of the locations of the flaws detected by the discriminating-type flaw detector 101 and controls the locations of the trimming lines marked by the trimming-line marker 103 and the cutting lines marked by the diagonal cutter 104, the control unit 102 knows what sizes of flaws exist at what locations in the glass plates separated apart by the separator 108. Furthermore, the control unit 102 assumes see-through, peripheral and fringe areas on the glass plate, sets quality grades for the see-through and peripheral areas to judge the acceptability of the glass plate in accordance with the quality grade settings. In the process (c) shown in the figure, the control unit 102 assumes the see-through areas O₁ and O₂ and the peripheral areas P₁ and P₂ on the glass plate being cut, and knows that one small flaw S₁ is present in the peripheral area P₁ and the other small flaw S₂ is present in the see-through area O₂. Thus, the control unit 102 determines the glass plate being cut having the small flaw S₁ as a good product, and the glass plate being cut having the small flaw S₂ as a no-good product. The control unit also controls the eliminating/discarding unit and the sorter, based on the judgement. PROCESS (d) As the glass strip 130 marked with trimming and cutting lines arrives at the breaker 105, the breaker 105 breaks the glass strip 130 into glass-plate rows along the cutting lines. Fig. 6A shows a broken glass-plate row 131 between the cutting lines C₁ and C₂. PROCESS (e) The trimming cutter 106 cuts and removes trimmings E₁ and E₂, which are the edge parts of the glass-plate row 131 along the trimming lines T₁ and T₃. PROCESS (f) The trimmed glass-plate row 131 is slit into two glass plates G₁ and G₂ by the slitter 107, and the glass plates G₁ and G₂ are slightly separated apart in the X-axis direction. As is evident from the above description, the glass plate G₁ is a good product, and the glass plate G₂ a no-good product. PROCESS (g) The two glass plates thus slit G₁ and G₂ are further separated apart in the X-axis direction by the separator 108 to direct to the first and second courses. PROCESS(h) As the glass plates G₁ and G₂ arrive at the eliminating/discarding unit 109, the control unit 102 lowers the discarding roll for the second course, on which the defective plate G₂ travels, for removal from the line and disposal. PROCESS (i) When the remaining low-grade product G₁ on the first course arrives at the sorting section, the control unit 102 controls the lifter of the sorter 110-1 to lift the good product G₁ and transport by the suction conveyor to the transfer car. As described above, the sorting process of automotive windshields using the sorting system of this invention makes it possible to sort as a good product the glass plate G₁ that has heretofore been discarded, leading to increased yield in the manufacture of automotive windshields. Although the above description is concerned with the sorting of glass plates for automotive windshields into those of a high grade having no flaws in the see-through area and those of a low grade that allows small flaws in the peripheral area, establishing the criteria for high- and low-grades depends on the quality requirements for specific automotive windshields. Industrial Applicability The glass-plate sorting system of this invention mates it possible to improve yield in the manufacture of glass plates by detecting the sizes and locations of flaws existing in a glass strip by means of a discriminating-type flaw detector of high precision, tracking the flaws by a control unit, and sorting quality grades of the glass plates being cut so as to simultaneously obtain a desired number of products of specified quality grades. When used in the manufacturing line of automotive windshields, the glass-plate sorting system of this invention makes it possible to improve yield in the manufacture of automotive windshields by detecting the sizes and locations of flaws existing on a glass strip by a discriminating-type flaw detector of high precision, tracking the flaws by a control unit, and judging the acceptability of glass plates being cut by establishing criteria for quality grades in the see-through and peripheral areas of windshields on the glass plates being cut.

Claims: 1. A glass-plate sorting system for cutting a glass strip (120;130) travelling on a line conveyor (100) and sorting the quality grades of glass plates (G₁,G₂, G₃) being cut, characterized in that said glass-plate sorting system has a discriminating-type flaw detector (101) for detecting flaws L, M; S₁, S₂) existing in a glass strip and outputting flaw data representing the sizes and locations of said flaws; a control unit (102) for sorting the quality grades of said glass plates being cut based on said flaw data from said discriminating-type flaw detector; and a plurality of sorters (110-1 to 110-6) for sorting glass plates of desired quality grades based on the control of said control unit. 2. A glass-plate sorting system as set forth in Claim 1 wherein said control unit (102) discriminates said glass plates (G₁, G₂, G₃) being cut into three types; high-grade plates (G3), low-grade plates (G₂) and defective plates (G₁); and said sorters (110-1 to 110-6) perform a two-grade sorting by sorting high-grade and low-grade products. 3. A glass-plate sorting system as set forth in Claim 2 wherein said sorters (110-1 to 110-6) have lifters (112) installed below said line conveyor (100) for pushing up glass plates (113), and suction conveyors (111) installed above said line conveyor for sucking and carrying said pushed-up glass plates. 4. A glass-plate sorting system as set forth in Claim 1 for use in automotive windshield manufacturing processes wherein said control unit (102) establishes quality grades that can be accepted as good products on an area of said glass plates (G₁, G₂) corresponding to a see-through area (2) of an automotive windshield and an area of said glass plates corresponding to a peripheral area (3) outside said see-through area, and discriminates glass plates (G₁) of acceptable quality by comparing the sizes and locations of said detected flaws (S₁, S₂) with said established quality grades for these areas. 5. A flaw detecting and glass-plate sorting method for an automotive windshield manufacturing processes, characterized in that the sizes and locations of flaws (S₁, S₂) existing in glass plates (G₁, G₂) from which automotive windshields are cut are detected; quality grades that can be accepted as good products are established on an area of said glass plates corresponding to a see-through area (2) of an automotive windshield and an area of said glass plates corresponding to a peripheral area (3) outside said see-through area; and glass plates (G₁) of acceptable quality are sorted by comparing the sizes and locations of said detected flaws with said established quality grades for these areas.

Inventors: KAWAMURA, HIDETOSHI NIPPON SHEET GLASS CO., LTD., KURASHINA, ISAO NIPPON SHEET GLASS CO., LTD., OKAFUJI, MASAHARU NIPPON SHEET GLASS CO., LTD.
Applicants: NIPPON SHEET GLASS CO., LTD.
Application year: 1988
Main classification: C03B33
IPC codes: B65G49, C03B33, G01N21