BACKGROUND

CROSS-REFERENCE TO RELATED APPLICATION

[0001] This application claims the benefit of priority under 35 U.S.C. § 119 of U.S. Provisional Application Serial No. 62/877,025 filed on July 22, 2019, the content of which is relied upon and incorporated herein by reference in its entirety.

FIELD OF THE DISCLOSURE

[0002] The present disclosure relates to the production of glass sheets and, more particularly, to apparatus and methods for controlling an accumulation of devitrified glass during glass sheet production.

BACKGROUND

[0003] Glass sheets are used in a variety of applications. For example, they may be used in glass display panels such as in mobile devices, laptops, tablets, computer monitors, and television displays. Glass sheets may be manufactured by a fusion drawdown process whereby molten glass is drawn over a glass forming apparatus to produce glass sheets. In some examples, the glass forming apparatus includes edge directors that direct molten glass towards edge portions of the glass sheets being formed. Often times, however, devitrification of the molten glass can occur on the edge directors. As used herein, devitrification refers to the crystallization of formerly amorphous glass. The crystallized materials is referred to herein as devit and/or devit material. FIG. 12, for example, illustrates accumulated devit 102 on an edge director 104. Accumulated devit on the edge directors may cause molten glass to fall on unwanted parts of the glass forming apparatus. Additionally, accumulated devit on the edge directors may cause hollow beads to form in the molten glass, which may lead to cracks in the formed glass. Accumulated devit may also cause the draw of narrower glass ribbons during the glass forming process, which in many cases is an undesirable effect. As such, there are opportunities to improve the production of glass sheets.

SUMMARY

[0004] Features disclosed herein allow for the removal or prevention of devit on glass forming apparatus, such as edge directors. Devit may include, for example, cristobalite, mullite, and/or tridymite crystals.

[0005] In some examples, a devit control system can direct a laser (e.g., a laser beam) to heat particular regions of a glass forming apparatus that have either already accumulated a significant amount of devit or are prone so to do. The devit control system may include a mirror system that can be controlled to direct the laser to specific locations for determined amounts of time to deliver determined amounts of energy. The energy provided by the laser allows for crystal heating, for example, above the glass’s liquidus temperature (i.e., the lowest temperature at which glass remains completely liquid).

[0006] In some examples, an optical fiber coupled with a laser generator (also known as a laser source, or a laser) such as a diode laser generator, C02 laser generator, or a fiber laser generator, can be controlled to heat regions of the glass forming apparatus, such as edge directors, with devit formation. The laser proceeds through the optical fiber and reaches an optical collimator to be collimated. In some examples the collimator can provide control information back to a monitoring device for laser beam control.

[0007] In some examples, a beam shaping element, such as diffractive optical element (DOE) or spatial light modulator (SLM), can be employed by the devit control system. The beam shaping element modifies (e.g., shapes) an incident laser beam such that a projected laser beam pattern on accumulated or expected devit has a predetermined energy distribution. The devit control system may tailor the spatial distribution of the energy provided by the laser to meet application needs (e.g., a uniform energy across accumulated devit, an energy gradient across accumulated devit to account for contours and thermal properties of edge directors, etc.).

[0008] In some examples, the devit control system can control one or more tightly focused, high-power laser beams to ablate (e.g., vaporize) accumulated crystals and remove significant crystal growth from portions of the glass forming apparatus, such as edge directors. The energy from the laser beams heats and physically dislodges devit from the glass forming apparatus until it has been entirely (or mostly) removed. [0009] The disclosure describes, in an embodiment, an apparatus comprising a memory device storing instructions; and a controller comprising at least one processor and configured to execute the instructions. When executed, the instructions cause the controller to: preselect a portion of a glass forming apparatus; configure a reflecting apparatus to reflect a laser beam from a laser generator to the preselected portion of the glass forming apparatus; and activate the laser generator to generate the laser beam to heat the preselected portion of the glass forming apparatus for devit control.

[0010] The disclosure describes, in another embodiment, an apparatus comprising a laser generator operable to generate a laser beam; a reflecting apparatus configured to reflect the laser beam from the laser generator to a glass forming apparatus; and a controller communicatively coupled to the laser generator and the reflecting apparatus. The controller may be configured to: preselect a portion of the glass forming apparatus; configure the reflecting apparatus to reflect the laser beam from the laser generator to the preselected portion of the glass forming apparatus; and activate the laser generator to generate the laser beam to heat the preselected portion of the glass forming apparatus for devit control.

[0011] The disclosure describes, in yet another embodiment, a method for removing devit material from a glass forming apparatus, comprising the steps of: preselecting a portion of the glass forming apparatus; configuring a reflecting apparatus to reflect a laser beam from a laser generator to the preselected portion of the glass forming apparatus; and activating the laser generator to generate the laser beam to heat the preselected portion of the glass forming apparatus.

[0012] The disclosure describes, in a further embodiment, an apparatus comprising a laser generator operable to generate a laser beam; a reflecting apparatus configured to reflect the laser beam from the laser generator to a glass forming apparatus; and a controller communicatively coupled to the laser generator and the reflecting apparatus. The controller may be configured to: preselect a portion of the glass forming apparatus; configure the reflecting apparatus to reflect the laser beam from the laser generator to the preselected portion of the glass forming apparatus; and activate the laser generator to generate the laser beam; wherein devit material is disposed on the glass forming apparatus, and wherein molten glass is disposed, along a path of the laser beam, between the preselected portion of the glass forming apparatus and the laser generator, and wherein the laser beam heats the molten glass. [0013] The disclosure describes, in yet a further embodiment, a method for removing devit material from a glass forming apparatus, comprising the steps of: preselecting a portion of the glass forming apparatus; configuring a reflecting apparatus to reflect a laser beam from a laser generator to the preselected portion of the glass forming apparatus; and activating the laser generator to generate the laser beam, wherein devit material is disposed on the glass forming apparatus, and wherein molten glass is disposed, along a path of the laser beam, between the preselected portion of the glass forming apparatus and the laser generator, and wherein the laser beam heats the molten glass.

BRIEF DESCRIPTION OF DRAWINGS

[0014] The above summary and the below detailed description of illustrative embodiments may be read in conjunction with the appended Figures. The Figures show some of the illustrative embodiments discussed herein. As further explained below, the claims are not limited to the illustrative embodiments. For clarity and ease of reading, Figures may omit views of certain features.

[0015] FIG. 1 schematically illustrates an exemplary glass forming apparatus with a devit control system in accordance with some examples.

[0016] FIG. 2 schematically illustrates portions of the exemplary glass forming apparatus of FIG. 1 in accordance with some examples.

[0017] FIGs. 3, 4, 5, and 6 are block diagrams of exemplary devit control systems in accordance with some examples.

[0018] FIG. 7 illustrates a thermal model of a glass layer heated with a laser in accordance with some examples.

[0019] FIG. 8 A illustrates an infrared transmission spectrum of cristobalite that may be used by a devit control system to direct a laser in accordance with some examples.

[0020] FIG. 8B illustrates an infrared transmission spectrum of tridymite that may be used by a devit control system to direct a laser in accordance with some examples.

[0021] FIG. 9 illustrates transmission graphs for various devit materials that may be used by a devit control system to direct a laser in accordance with some examples.

[0022] FIG. 10 illustrates a devit control system that includes sensor feedback in accordance with some examples. [0023] FIG. 11 illustrates an exemplary method that may be carried out by a devit control system in accordance with some examples.

[0024] FIG. 12 illustrates devit as accumulated on prior art glass forming apparatus.

DETAILED DESCRIPTION

[0025] The present application discloses illustrative (i.e., example) embodiments. The disclosure is not limited to the illustrative embodiments. Therefore, many implementations of the claims will be different than the illustrative embodiments. Various modifications can be made to the claims without departing from the spirit and scope of the disclosure. The claims are intended to cover implementations with such modifications.

[0026] At times, the present application uses directional terms (e.g., front, back, top, bottom, left, right, etc.) to give the reader context when viewing the Figures. The claims, however, are not limited to the orientations shown in the Figures. Any absolute term (e.g., high, low, etc.) can be understood as disclosing a corresponding relative term (e.g., higher, lower, etc.).

[0027] The present disclosure presents apparatus and methods to remove devit accumulation on edge directors by heating the regions of the edge directors that accumulate devit with a laser thereby removing (e.g., melting) the accumulated material. In some examples, the apparatus and methods may be used to close hollow beads that can form as a result of molten glass not fusing properly below an edge director. As is known in the art, a“bead” refers to the edge zones of a glass ribbon formed during manufacture, particularly by the fusion draw method.

[0028] In some examples, a laser wavelength is determined for the laser directed at the devit, thereby allowing for an effective removal of the devit. In some examples, a laser wavelength (or several wavelengths) can be chosen such that the laser will penetrate the molten glass flowing over the edge director and be substantially absorbed by the devit material itself, thereby raising the temperature of the devit to its melting point (or, in some examples, at least its softening point). The molten glass flow may then“flush” the devit away from the edge director.

[0029] In some examples the molten glass can be heated directly with a laser which, due to conduction and radiation effects, heats accumulated devit. In some examples the molten glass can be rerouted away from an edge director (e.g., by tilting the forming apparatus, for instance) to expose the devit, and directly heating the devit with a laser until it pools away from the edge director. In yet other examples, a platinum edge director, rather than the devit, can be heated using the laser. The platinum edge director may then conduct heat to the area where the devit is in contact with the edge director. With enough increase in temperature, the devit at the platinum-devit interface melts and is released from its hold on the platinum edge director.

[0030] In some examples, directed laser energy can be used to ablate (e.g., melt or vaporize) devit crystal growth on edge directors. The pulse energy, beam width, power level, and/or wavelength of the laser can be tuned to match material absorption and vaporization properties of the devit crystals. These examples may be useful for applications that require significant crystal removal (e.g., chip away at the devit growth until only a fine layer remains, at which time one of the aforementioned examples can be used to remove the residual material from the edge director via heating).

[0031] In some examples, a control system can be employed to position a mirror to reflect a laser beam to a location of interest, such as an edge director with accumulated devit. The control system may include a 1 -dimensional or 2-dimensional galvanometer- driven mirror set, a rotating polygon, an acousto-optic modulator, a voice-coil driven mirror set, a servo or stepper motor set, or a combination of these to position the mirror. In some examples, a 2-dimensional galvanometer-driven mirror set can be used to raster a laser beam over the devit while a thermal imaging camera can be used as feedback to precisely control laser energy delivery. Position and energy can be controlled such that neither the forming apparatus nor the edge director are inadvertently overheated, resulting in thermo-mechanical stresses that can either crack or deform components. In some examples, an imaging camera may also be used to provide mirror position feedback during the operation.

[0032] In some examples, the laser can be raster-scanned (e.g., at a rate of between 0.001 Hz and 10,000 Hz) over the edge director in a“maintenance” mode to periodically clean the edge director in a preset pattern. In some examples, the formation of devit can be preempted by heating an edge director periodically, such as once a month, once week, or at any other interval. The control system may configure the mirrors to deflect the laser beam over one or more edge directors using a fixed pattern, for example. In some examples, the devit can be uniformly heated based on thermal images of the devit provided by thermal image cameras. The control system may also program the laser to deliver a predetermined energy to the edge directors to remove or prevent accumulated devit. [0033] Referring to Figure 1, glass forming apparatus 20 includes a forming wedge 22 with an open channel 24 that is bounded on its longitudinal sides by walls 25 and 26. The walls 25 and 26 terminate at their upper extent in opposed longitudinally extending overflow weirs 27 and 28, respectively. The overflow weirs 27 and 28 are integral with a pair of opposed and substantially vertical forming surfaces 30 that, in turn, are integral with a pair of opposed downwardly inclined converging forming surfaces 32. The pair of downwardly inclined converging surfaces 32 terminate at a substantially horizontal lower apex that comprises a root 34 of the forming wedge 22. Each of the downwardly inclined converging surfaces 32 may include a pair of edge directors 50. Only one downwardly inclined converging surface 32 and corresponding pair of edge directors are shown in FIG. 1.

[0034] Molten glass is delivered into open channel 24 by means of a delivery passage 38 that is in fluid communication with the open channel 24. A pair of dams 40 are provided above overflow weirs 27 and 28 adjacent each end of open channel 24 to direct the overflow of the free surface 42 of molten glass over overflow weirs 27 and 28 as separate flows of molten glass. Only the pair of dams 40 that are located at the end of the open channel 24 that is adjacent the delivery passage 38 are shown in FIG. 1. The separate flows of molten glass flow down over the pair of opposed substantially vertical forming surfaces 30 and the pair of opposed downwardly inclined converging forming surfaces 32 to the root 34 where the separate flows of molten glass, shown in broken lines in FIG. 1, converge to form the glass ribbon 44. Each pair of edge directors 50 keeps molten glass along a respective downwardly inclined converging forming surface 32, until the molten glass reaches the root 34.

[0035] Pulling rolls 46 are located downstream of the root 34 of the forming wedge 22 and engage side edges 48 at both sides of the glass ribbon 44 to apply tension to the glass ribbon 44. The pulling rolls 46 may be positioned sufficiently below the root 34 that the thickness of the glass ribbon 44 is essentially fixed at that location. The pulling rolls 46 may draw the glass ribbon 44 downwardly at a prescribed rate that establishes the thickness of the glass ribbon as it is formed at the root 34.

[0036] FIG. 1 also illustrates an exemplary devit control system 10 that can include a laser generator 12 that is configured to generate and emit a laser beam 13. In an embodiment, the laser beam 13 increases the temperature of the molten glass flowing over a site where the devit is present so that the increased temperature of the molten glass raises the temperature of the devit to at, near, or above the melting temperature of the devit so that the viscous flow of the molten glass can shear off the devit from the forming apparatus 20 and/or edge director 50. As illustrated in the aspect of FIG. 1, the laser beam

13 can be directed by laser generator 12 to any of the pair of edge directors 50 via, for example, reflecting apparatus 14.

[0037] In an embodiment, reflecting apparatus 14 can include a reflecting surface 15 that is configured to receive the laser beam 13 generated and emitted by the laser generator 12 and reflected onto at least a predetermined area of an edge director 50. Reflecting apparatus 14 may be, for example, a mirror configured to deflect a laser beam from laser generator 12. Reflecting apparatus 14 may therefore function as a beam steering and/or scanning device. In FIG. 1, the laser beam 13 is illustrated as being advanced by reflecting apparatus 14 as reflected laser beams 17 to a plurality of preselected portions of edge directors 50.

[0038] The reflecting surface 15 in one example can comprise a gold-coated mirror although other types of mirrors may be used in other examples. Gold-coated mirrors may be desirable under certain applications to provide superior and consistent reflectivity with respect to infrared lasers, for example. In addition, the reflectivity of gold-coated mirrors is virtually independent of the angle of incidence of laser beam 13 and, therefore, the gold-coated mirrors are particularly useful as scanning or laser beam-steering mirrors.

[0039] The reflecting apparatus 14 in the embodiment illustrated in FIG. 1 may also include a regulating mechanism 16 configured to adjust an attitude of the reflecting surface 15 of the reflecting apparatus 14 with respect to the receipt of the laser beam 13 and a location of a preselected portion of an edge director 50. For example, reflecting apparatus 14 can rotate or tilt reflecting surface 15 to direct laser beam 13 to a predetermined portion of an edge director 50 as reflected laser beams 17, for example.

[0040] According to one example, the regulating mechanism 16 can comprise a galvanometer that is operatively associated with the reflecting surface 15 so that the reflecting surface 15 can be rotated by the galvanometer along an axis in relation to the glass ribbon 44. For example, the reflecting surface 15 can be mounted on a rotating shaft 18 that is driven by a galvanometer motor and rotated about axis 18a as shown by double arrow 19.

[0041] FIG. 2 illustrates another view of reflecting apparatus 14 directing a laser beam 13 from laser generator 12 to an edge director 50. Although reflecting apparatus

14 is illustrated directing laser beam 13 to just one edge director 50, reflecting apparatus 14 can move reflecting surface 15 such as to direct laser beam 13 to the other edge director 50. In some examples, reflecting apparatus 14 may alternately direct the laser beam 13 to portions of one edge director 50, then to portions of the other edge director 50.

[0042] In some examples, devit control system 10 can direct laser beam 13 to edge directors 50 to apply an energy to devit formed on the edge directors 50, thereby heating up the devit on the edge directors 50 to at least the liquidus temperature of the devit. As a result, devit formed on the edge directors 50 may melt or fall off of the edge directors 50. In some examples, devit control system 10 routinely (e.g., periodically, or from time- to-time) directs laser beam 13 to edge directors 50 regardless of whether devit is formed on edge directors 50. In this manner, the energy from laser beam 13 may cause edge directors 50 to maintain a minimum temperature such that devit does not, or is unlikely to, form on edge directors 50.

[0043] In some examples, devit control system 10 can be activated continuously. In some examples, devit control system 10 can be activated during scheduled maintenance periods.

[0044] In some examples, a pulse energy, beam width, power level, and/or wavelength for laser beam 13 can be selected such that energy from laser beam 13 heats accumulated devit sufficiently without inadvertently overheating other components of devit control system 10. For example, laser generator 12 may employ a diode laser (such as, for example, a diode laser emitting a laser beam having a wavelength of 0.976 micrometers, pm). In some examples, laser generator 12 employs a CO2 laser.

[0045] In some examples, a power level for laser beam 13 can be selected such that energy from laser beam 13 heats at least one of forming apparatus 20, edge director 50, molten glass disposed on and/or adjacent to forming apparatus 20 and/or edge director 50, and devit disposed on and/or adjacent to forming apparatus 20 and/or edge director 50 or contained within or around the molten glass.

[0046] FIG. 3 illustrates portions of exemplary devit control system 10 wherein solid lines with an arrow represent laser beams (e.g., laser beam 13, reflected laser beams 17) and dashed lines represent electrical control signals. In this example, devit control system 10 can include laser power control 55 and control computer 52. Each of laser power control 55 and control computer 52 can include one or more processors, one or more field-programmable gate arrays (FPGAs), one or more application-specific integrated circuits (ASICs), one or more state machines, digital circuitry, or any other suitable circuitry. In some embodiments, one or more of laser power control 55 and control computer 52 may be implemented in any suitable hardware or hardware and software (e.g., one or more processors executing instructions stored in memory). For example, a non-transitory computer readable medium such as, for example, a read-only memory (ROM), an electrically erasable programmable read-only memory (EEPROM), flash memory, a removable disk, CD-ROM, any non-volatile memory, or any other suitable memory, may store instructions that may be obtained and executed by any one or more processors of laser power control 55 and control computer 52 to execute one or more of the functions described herein.

[0047] Laser power control unit 55 can control the operation of the laser generator

12 so that the pulse energy, beam width, power level, and/or wavelength of the laser beam

13 generated at laser generator 12 comprises preselected values. In addition, laser power control unit 55 can control the time intervals during which the laser generator 12 generates the laser beam 13. In turn, a control computer 52 can be provided to control the operation of the laser power control unit 55 whereby the laser power control unit 55 may cause laser generator 12 to generate, during preselected time intervals, a laser beam 13 having preselected wavelength and power characteristics. At the same time, the control computer 52 may be operatively associated with the reflecting apparatus 14 to control the functioning of the regulating mechanism 16, and in a particular example where a galvanometer is employed, the motor of the galvanometer. Accordingly, the control computer 52 can be capable of adjusting the attitude and positioning of the reflecting surface 15 with respect to the receipt of the laser beam 13 by the reflecting surface 15 and the locations of preselected portions of the edge directors 50 for the removal, or prevention, of devit.

[0048] For example, control computer 52 may configure regulating mechanism 16 to adjust (e.g., tilt or rotate), for preselected time periods, the reflecting surface 15 of the reflecting apparatus 14 in a plurality of varying attitudes with respect to the receipt of the laser beam 13 and the reflection of the laser beam at the reflecting surface 15 of the reflecting apparatus 14. Consequently, the laser beam 13 can be directed onto a plurality of preselected portions of the edge directors 50 during respective preselected time periods, as illustrated by the reflected laser beams 17 in FIG. 1, for example, thereby controlling the accumulation of devit on the edge directors 50.

[0049] FIG. 4 illustrates a block diagram of an example devit control system 400 that may be used, for example, in place of or in conjunction with the devit control system 10 of FIG. 1. Those of skill in the art will readily understand that FIG. 4, and the description below, represent one possible embodiment of a devit control system, and further that other configurations of a devit control system consistent with the teachings presented herein are possible and contemplated by this disclosure. In this example, devit control system 400 can include a devit removal apparatus 401 with a moving mirror 402 that is configured to reflect laser beams, such as laser beam 13, from a laser generator 12 (not shown) to edge directors 50 of a forming apparatus. In some examples, devit removal apparatus 401 includes a laser generator for generation of the laser beams.

[0050] Devit removal apparatus 401 may further include thermal imagers 420, which may capture thermal images as reflected by thermal imager mirrors 422. For example, each thermal imager mirror 422 may be configured (e.g., positioned) to reflect an image of a corresponding edge director 50 (and, for example, adjacent areas) to a corresponding thermal imager 420. In some examples, each of thermal imagers 420 can be cooled thermal image cameras, such as water cooled thermal imaging cameras, which may also include an air purging system. For example, devit removal apparatus 401 may include air purge inlet 411, which may allow for the introduction of air to devit removal apparatus 401 for performing an air purge through, for example, optics 404, which may allow the generated laser beam to reach moving mirror 402. The purging air entering devit removal apparatus 401 via air purge inlet 411 may also lower/control the temperature of the components within devit removal apparatus 401, maintain a positive pressure inside devit removal apparatus 401 to prevent/minimize contamination from the external environment (e.g., from airborne particulates, gases (such as from the glass melting furnace), etc.), and/or prevent/minimize condensation on optic components, e.g., on components 402, 404, etc.

[0051] Devit removal apparatus 401 may also include a transparent window 408 positioned between adjacent window casings 410. Window casings 410 may be water cooled window casings and may supply air purge to other portions (e.g., front portions) of devit removal apparatus 401, such as mirror surface 402. This purge air prevents/minimizes gases, such as gases emitted during the glass manufacturing process, from condensing on window and/or mirror surfaces and may also serve to cool the windows and/or mirrors so that, for example, materials with lower heat resistance may be used for these components. Moving mirror 402 may direct reflected laser beams, such as reflected laser beams 17, through transparent window 408 towards the forming apparatus 20 and/or towards one or more of the edge directors 50. Devit removal apparatus 401 may further include spacers 414, which may comprise fiber board, stainless steel, a combination of fiber board and stainless steel, or other suitable materials. Each spacer 414 is coupled to a respective furnace wall 412. Furnace walls 412 may reduce or eliminate heat from the outside environment of devit removal apparatus 401, such as heat generated by the glass furnace.

[0052] In some examples, a controller 406 can configure mirrors 422 to reflect images of a respective edge director 50 to a corresponding thermal imager 420. The controller 406 may also configure each of the thermal imagers 420 to capture thermal images of the respective edge directors 50 (and, e.g., adjacent areas), and to provide the images to the controller. Based on the thermal images, the controller 406 may determine that devit is present on an edge director. For example, the controller 406 may determine that a thermal gradient of edge director 50 indicates that the edge director has accumulated devit. In an embodiment, the edge director is at a lower temperature than the devit and the devit, which is crystallized and below the liquidus temperature, is at a lower temperature than the glass ribbon. The controller 406 is configured to detect these differences in temperature between the forming apparatus/edge director, devit, and glass ribbon. As a non-limiting example, the controller 406 may detect a temperature discontinuity and determine that the discontinuity indicates the presence of devit. Additionally, the thermal imaging functionality may also be used to aim and/or control the position of the impingement of the laser beam on the forming apparatus, edge director, glass ribbon, and/or devit associated with each. As a further non-limiting example, the controller 406 may detect a temperature discontinuity between the desired target area for the laser beam and the actual position of impingement of the laser beam (that may be spaced apart from the desired target area) on, but not limited to, the forming apparatus, edge director, glass ribbon, and/or devit associated with each. In this way, a safety feature for the laser beam is realized.

[0053] In some examples, if the controller 406 determines that an edge director has accumulated devit, the controller 406 may cause a laser generator to generate a laser beam, such as laser beam 13. In an embodiment, the laser generator is located within the controller 406 block. The controller 406 may also cause moving mirror 402 to be positioned to reflect the generated laser beam to one or more portions of the edge directors 50, such as reflected laser beams 17. For example, the controller 406 may direct energy from the generated laser to be reflected via a mirror 402 horizontally, and vertically, over an edge director 50. In some examples, the laser beam may be directed over a vertical range that includes a height of an edge director 50. In some examples, the laser beam may be directed over a vertical range that includes a lower portion of each edge director 50 (e.g., a portion most likely to accumulate devit). In some examples, the laser beam may be directed over a horizontal range that includes a width of each edge director 50. In some examples, the laser beam may be directed over a horizontal range that includes a portion of a width of each edge director 50.

[0054] In other embodiments, other configurations of the components shown within the devit removal apparatus 401 are possible, as would be understood by one of skill in the art. As one non-limiting example, optics 404 and moving mirror 402 may be combined. As another non-limiting example, optics 404, moving mirror 402, and controller 406 may be combined into a laser scanning/patterning module.

[0055] FIG. 5 illustrates a block diagram of an example devit control system 500 that includes a laser source 502, which may be a laser generator, such as laser generator 12 of FIG. 1, that generates a laser through a fiber optic cable 503 through an adaptor 506 to a collimator 508. The collimator 508 directs the laser through tube 510, which may be a ceramic tube, to devit 102 accumulated on an edge director 50. Tube 510 may be mounted to (or through) a ball joint 520 that is attached to a mount base 512 of a base 511. FIG. 5 shows components 506, 508, and 510 in various positions caused by movement of ball joint 520. Mount base 512 may be a gimbal mount, for example. Base 511 may be configured to direct the laser beam generated by laser source 502 to devit 102 accumulated on edge director 50. For example, mount base 512 may be positioned to direct the laser beam emitting from tube 510 to a predetermined portion of edge director 50. In some examples, devit control system 500 can include an air purge system to clean tube 510. In some examples, the base 511 can be mechanically positioned to direct the laser beam. In some examples, the base 511 can be positioned by, for example, control computer 52 to direct the laser beam.

[0056] Devit control system 500 may also include a target laser source 504, which may be used to visually confirm the portions of edge director 50 that will receive the laser generated by laser source 502. For example, target laser source 504 (which may also be known in the art as a“tracer laser”) may generate a green laser beam (which may also be known in the art as a“tracer beam), which proceeds through and out of tube 510. The green laser beam may be used to visually determine the positioning of mount base 512 to have the green laser beam and, subsequently, the laser beam generated by laser source 502, aligned to edge director 50 or a portion thereof. For example, a controller may activate target laser source 504, and a user may adjust mount base 512 until the green laser beam is seen on at least a portion of devit accumulated on edge director 50. The controller may then (e.g., upon receiving user input) activate laser source 502, such as a diode laser or CO2 laser, to direct laser energy to devit 102 accumulated on edge director 50.

[0057] FIG. 6 illustrates a block diagram of an example devit control system 600 that is similar to devit control system 500 of FIG. 5 but does not include collimator 508. Instead, devit control system 600 can include an optical coupler 602 that directs the laser beam generated by laser source 502 through an optical fiber 605, such as a sapphire optical fiber, through tube 604. In addition, because the laser is guided through an optical fiber 605 within tube 604, devit control system 600 may not require an air purge system. As illustrated in the figure, devit control system 600 may also include a target laser source 504 to visually align the target of an emitted laser, in this example, devit 102 accumulated on edge director 50.

[0058] In some examples of FIG. 5 and 6, diode lasers operating at or around 1 micrometer wavelength can be employed. In some examples, a fiber-coupled laser may be employed. As is known in the art, a fiber-coupled laser includes a laser source where the output of the laser source is coupled to a fiber (which may be used as the gain medium). A fiber-coupled laser is convenient for routing and/or aligning a laser beam. Fiber-coupled lasers may have better mode quality than other laser configurations, and the laser beam may be delivered with a single mode fiber, for example.

[0059] Alternately, although in the examples of FIG. 5 and 6 lasers for heating the devit are employed, in other examples resistive heating (e.g., heat lamps or flash lamps), infrared light emitting diodes (LEDs), a magnetron, or a laser-induced gas discharge lamp may be employed to generate energy that is directed to the edge directors 50. In some examples, an atmospheric plasma jet can be employed to heat the devit. This approach can result in comparatively extremely high temperature gas jets, and may be employed in cases where laser power may be insufficient to induce devit melting.

[0060] FIG. 7 illustrates a thermal model 700 that indicates raising surface temperatures of flowing glass, such as molten glass along downwardly inclined converging forming surface 32 to root 34, when heated with a laser, such as a CO2 laser (e.g., 10.6 pm CO2 laser) employed by a devit control system as described herein, based on a distance from the forming apparatus surface (e.g., surface of downwardly inclined converging forming surface 32). As illustrated in the figure, location 702 is the target of each of two lasers. Specifically, the chart shows, in a first instance, raising glass surface temperatures for a CO2 laser transmitting at 20 watts power and having a beam diameter of approximately 8 millimeters. The chart also shows, in a second instance, raising glass surface temperatures for a CO2 laser transmitting at 50 watts power and having a beam diameter of approximately 10 millimeters.

[0061] For each laser, the forming apparatus surface itself, as well as molten glass near the forming apparatus surface, does not experience a large temperature rise (e.g., near 0 degrees Celsius temperature raise) when the laser is applied compared to the temperature rise of the surface of the molten glass farther away from the forming apparatus surface (e.g., at a distance at and above approximately 0.8 inches (2.03 mm) for each laser). The thermal model also indicates that the CO2 laser, transmitting at 20 watts, raises the temperature of the molten glass more so than the CO2 laser transmitting at 50 watts when measured at the same distances from the forming apparatus surface. In some examples, a devit control system as described herein may employ one of these lasers if components underneath a devit layer should be kept from high temperatures or temperature fluctuations.

[0062] FIGS. 8A and 8B illustrate infrared transmission spectrum graphs of different devit crystals, namely cristobalite and tridymite, respectively. Each graph identifies wave numbers (cm ¹ ) on its X-axis, and transmission percentages of laser energy along its Y-axis. As illustrated in FIG. 8A, cristobalite may absorb a maximum amount of laser energy (i.e., as provided by a laser as described herein) around wave number 1100 cm ¹ , where about more than 90% of the laser energy is absorbed (and around less than 10% of the laser energy passes through the cristobalite). FIG. 8B indicates that tridymite may absorb a maximum amount of laser energy at a wave number slightly less than 1100 cm ¹ , where about more than 60% of the laser energy is absorbed (and around less than 40% of the laser energy passes through the tridymite).

[0063] In some examples, a devit control system as described herein, such as devit control system 10, devit control system 400, devit control system 500, or devit control system 600, may include a table identifying transmission absorption rates for one or more devit crystals. The tables may be stored in a memory device, for example. The devit control system may determine a wavelength for a laser based on the tables. For example, the devit control system may configure a laser generator, such as laser generator 12, to generate a laser with a wavelength corresponding to the wavelength that will cause the devit to absorb the maximum, or nearly the maximum, amount of laser energy.

[0064] In some examples, the devit control system can receive data identifying a type of devit (e.g., the type of crystals comprising the devit), and determine a laser wavelength based on the type of devit. In some examples, more than one type of devit may be identified. The devit control system may program the laser generator to generate a laser beam with a wavelength determined for each type of devit, where the laser generator may periodically, and/or from time to time, and/or based on an input signal, change the wavelength of the laser beam output from the laser generator from one determined wavelength to another (e.g., the laser generator may include more than one laser source and the devit control system may switch from one laser source to another). In other embodiments, the devit control system may employ more than one laser and/or more than one wavelength. The multiple lasers and/or multiple wavelengths may be used simultaneously to remove and/or control multiple types of devit that may be present.

[0065] FIG. 9 illustrates a graph identifying further transmission percentages of different devit crystals, namely yttria, spinel, sapphire, alon, and mullite. The graph identifies wave numbers and corresponding wavelengths on its bottom and top X-axis, respectively, and transmission percentages of laser energy along its Y-axis. As noted above with respect to FIG. 8, a devit control system as described herein may determine a wavelength for a laser based on the transmission percentages identified in the graph for the various devit crystals.

[0066] FIG. 10 illustrates a simplified block diagram of a devit control system 1000 that includes a controller 1004 that receives inputs 1002 and an error/sensor signal 1011 from sensors 1010. The inputs 1002 and error/sensor signal 1011 are combined in combiner 1012 to form a controller input signal 1013. Controller 1004 may include one or more processors, such as a GPU (graphics processing unit), CPU (central processing unit), or any other suitable processing device. Inputs 1002 may include, for example, the current wavelength and/or power of a laser and a current devit location (e.g., location of devit on an edge director 50). Sensors 1010 may include, for example, one or more of a thermal camera, a visual camera, a laser power sensor, and a position sensor (e.g., galvanometer position sensor). Controller 1004 may generate adjustment data 1005 based on the controller input signal 1013. Adjustment data 1005 may identify and characterize an adjustment to, for example, the current pulse energy, beam width, power level and/or wavelength of a laser, the direction/target position of the laser, whether the laser is to be turned on or off, a location of devit (e.g., a different location on an edge director), or a sensor 1010 (e.g., the direction of a thermal camera or a change to a position sensor). Scan recipe 1006 receives the adjustment data 1005 and generates outputs 1008 to effect the changes identified by adjustment data 1005 (e.g., by controlling the corresponding equipment such as a galvanometer for laser mirror positioning, a laser generator for laser power, or a sensor 1010). Outputs 1008 may include, for example, a change to any of sensors 1010, a change to laser wavelength, power, or direction, a change to enable or disable a laser, or any other suitable change.

[0067] For example, based on inputs 1002 and sensors 1010, controller 1004 may generate adjustment data 1005 to disable a laser, tilt and/or rotate a mirror to direct a reflected beam of the laser, and/or enable the laser. In some examples, controller 1004 can receive thermal image data from sensor 1010 identifying and characterizing a thermal image of accumulated devit on an edge director. Based on the thermal image data, controller 1004 can then generate adjustment data 1005 to tilt and/or rotate a mirror to direct a reflected laser beam from a laser generator to the accumulated devit. The controller 1004 may then generate adjustment data 1005 to turn the laser on. Controller 1004 may leave the laser enabled until controller 1004 determines that the devit temperature has reached at least a liquidus temperature based on thermal image data received from sensor 1010. Controller 1004 may then generate adjustment data 1005 to turn off the laser and reposition the mirror to direct a reflected laser beam from the laser generator to another edge director 50.

[0068] FIG. 11 illustrates an exemplary method that may be performed by one or more computing devices, such as control computer 52. Beginning at step 1102, a position of an edge director 50 of a glass forming apparatus 20 can be determined. For example, the position of the edge director 50 may be determined based on image data from a camera directed at the glass forming apparatus 20. At step 1104, a first thermal image of the edge director 50 at the determined position is obtained from a thermal camera, such as a thermal camera 420. For example control computer 52 may direct the thermal camera to obtain a thermal image from a location that includes the determined position and may receive thermal image data identifying and characterizing the thermal image.

[0069] Proceeding to step 1106, the presence of devit on the edge director 50 can be determined based on the first thermal image. For example, control computer 52 may determine that devit has accumulated on the edge director 50 based on thermal inconsistencies across the edge director 50 as identified by the thermal image data. At step 1108, a mirror can be positioned to direct a laser beam to the determined devit. For example, control computer 52 may control reflecting apparatus 14 to change a position of reflecting surface 15 to direct a laser beam 13 to the determined devit on edge director 50. At step 1110, a laser source can be controlled to direct a laser beam to the mirror. For example, control computer 52 may enable laser generator 12 to generate a laser beam towards the reflecting surface 15 of reflecting surface apparatus 14. The laser beam can then be directed toward the devit, as discussed above.

[0070] Proceeding to step 1112, a second thermal image of the edge director 50 at the determined position can be obtained from the thermal camera. At step 1114, a determination can be made as to whether the determined devit has melted and/or been removed. For example, control computer 52 may determine, based on the second thermal image, whether the accumulated devit has reached at least a liquidus temperature. If a determination is made that the devit has not melted, the method may proceed back to step 1108, where the mirror can be controlled to direct the laser beam to the same or different portions of the determined devit. Otherwise, if a determination is made that the devit has melted, the method may proceed to step 1116. At step 1116, the mirror and laser source can be controlled to direct the laser beam across the edge director (e.g., vertically and/or horizontally) to maintain a minimum temperature at the edge director. Alternatively, the laser may be deactivated. The minimum temperature may be one that has been identified to prevent the accumulation of devit on the edge director 50, for example. Control computer 52 may determine whether the temperature at the edge director is at least the minimum temperature based on thermal image data from the thermal camera, for example.

[0071] Although the methods described above are with reference to the illustrated flowcharts, it will be appreciated that many other ways of performing the acts associated with the methods can be used. For example, the order of some operations may be changed, and some of the operations described may be optional.

[0072] In addition, the methods and system described herein can be at least partially embodied in the form of computer-implemented processes and apparatus for practicing those processes. The disclosed methods may also be at least partially embodied in the form of tangible, non-transitory machine-readable storage media encoded with computer program code. For example, the steps of the methods can be embodied in hardware, in executable instructions executed by a processor (e.g., software), or a combination of the two. The media may include, for example, RAMs, ROMs, CD-ROMs, DVD-ROMs, BD- ROMs, hard disk drives, flash memories, or any other non-transitory machine-readable storage medium. When the computer program code is loaded into and executed by a computer, the computer becomes an apparatus for practicing the method. The methods may also be at least partially embodied in the form of a computer into which computer program code is loaded or executed, such that, the computer becomes a special purpose computer for practicing the methods. When implemented on a general-purpose processor, the computer program code segments configure the processor to create specific logic circuits. The methods may alternatively be at least partially embodied in application specific integrated circuits for performing the methods.

[0073] The foregoing is provided for purposes of illustrating, explaining, and describing embodiments of this disclosure. Modifications and adaptations to these embodiments will be apparent to those skilled in the art and may be made without departing from the scope or spirit of this disclosure.