Patent Description:
In a conventional float glass process, glass batch materials are melted in a furnace to form a glass melt. The glass melt is poured onto the top of a pool of molten metal, typically molten tin, at the entrance end of a float bath. The glass melt spreads out over the top of the molten tin to form a glass ribbon. This glass ribbon is stretched and pulled by mechanical devices in the float bath to provide the glass ribbon with a desired uniform thickness or a desired thickness profile (i.e., contour or thickness variation across the width of the ribbon). The glass ribbon exits the float bath and can be transported to a lehr for controlled cooling to strengthen or temper the glass, if desired.

While in the float bath, one or more coatings can be applied onto the top of the glass ribbon by a conventional chemical vapor deposition (CVD) coating process. In this in-bath CVD coating process, vaporized coating materials are transported to one or more coaters positioned in the float bath above the glass ribbon. The coating materials exit the bottom of the coater(s) and are deposited on top of the glass ribbon to form a coating. The structure and operation of a conventional float glass process as well as that of a conventional CVD coating process will be well understood by one of ordinary skill in the art and, therefore, will not be described in detail.

During the coating process in the float bath, the coater gap, i.e., the distance between the bottom of the CVD coater and the top of the hot float glass ribbon, is important for the coating process. This distance impacts the color uniformity of the resultant coating and also the thickness of the coating. Further, this coater gap is important for the safety of the coater, which could be damaged if the coater accidentally contacts the underlying hot glass ribbon. In a conventional float glass system, the in-bath CVD coater is typically only about <NUM> centimeters (<NUM> inches) above the top of the hot glass ribbon, which can be on the order of about <NUM> (<NUM>,<NUM>°F).

In most conventional float glass systems, the distance of the CVD coater above the glass ribbon is set or adjusted by an operator relying on visual observation and past coating experience. Typically, the operator looks through a window on the side of the float bath and judges whether the coater gap he observes is correct based on his practice and experience. If he determines that the coater gap is incorrect or needs adjustment, the operator uses a movement system connected to the coater to raise or lower the coater and then visually reassesses whether the new coater gap looks correct. Further, the uniformity of the coater gap across the coating area (i.e. the parallelism between the bottom of the coater and the top of the glass ribbon) is important. If the coater is tilted with respect to the top of the glass ribbon, this can adversely impact the coating process and the resultant coating and could lead to coater damage if a portion of the coater accidentally contacts the hot glass ribbon.

Additionally, the thickness of the glass ribbon is important. The desired glass ribbon thickness depends upon the final use of the glass being made and must be within certain tolerances for the glass to be commercially acceptable for its intended purpose. The glass ribbon thickness is dependent upon such factors as the rate of addition of the glass melt into the float bath and the travel speed of the glass ribbon through the float bath. Therefore, the operators of the glass furnace and/or the float bath need to know whether the thickness of the glass ribbon exiting the float bath is within the specified limits for the final product. However, the glass ribbon thickness as it exits the float bath is difficult to measure due to the high temperature of the glass ribbon, the flexibility of the hot glass ribbon, and the fact that the glass ribbon is typically tilted as it exits the float bath. It is particularly difficult to accurately measure the thickness of glass ribbons greater than <NUM> millimeters thick. If the glass ribbon thickness is out of specification, the resultant glass sheets cannot be used for their intended purpose, thus decreasing the productivity of the float glass process. By reducing the time the thickness of the glass ribbon is out of specification, the yield of the float glass process can be increased.

Glass can also be formed using a downdraw process, in which the glass ribbon moves vertically downwardly under the force of gravity as it cools. Examples of downdraw processes include the slot downdraw process, in which molten glass flows out of a slot below the glass furnace to form a glass ribbon; and the fusion (or overflow) downdraw process in which molten glass overflows the opposed sides of a forming trough and the two glass films fuse below the trough to form a glass ribbon. In a downdraw process, as in a float glass process, the thickness of the glass ribbon is an important factor.

It would be desirable to provide a more convenient and accurate way of determining the glass ribbon thickness in a glass manufacturing process that reduces or eliminates at least some of the problems associated with known processes. For example, it would be desirable for float bath operators to have a less subjective way of setting the coater gap in a float glass system to prevent accidental contact of the coater with the glass ribbon and/or to improve the coating process. For example, it would be desirable to provide a more convenient and accurate way of determining the glass ribbon thickness either in the float bath and/or after the glass ribbon exits from the float bath. For example, it would be desirable to provide a glass ribbon thickness measurement system for glass ribbons thicker than about <NUM>. For example, it would be desirable to provide a system that could not only simplify the setting of the coater gap but which also allows for determining the glass ribbon thickness and/or the thickness of a coating on the glass ribbon. For example, it would be desirable to provide a more convenient and accurate way of determining the glass ribbon thickness in a downdraw glass manufacturing process.

<CIT> relates to methods and apparatuses for determining a thickness of glass substrates.

The article "<NPL>, concerns an apparatus for online measurement of float glass thickness making use of a diffractive element.

<CIT> relates to a scanning monochromatic spatial low-coherent interferometer that can be used to simultaneously measure geometric thickness and refractive index.

The article "<NPL>, relates to a technique for simultaneous measurement of the phase index, group index and the thickness of transparent plates by use of a low-coherence interferometer.

<CIT> relates to certain optical distance measuring methods and a related apparatus.

<CIT> relates to a float glass manufacturing system in which a chemical vapor deposition coater is located above a pool of molten tin, wherein a sensing unit is used to regulate the gap between the molten glass residing on the molten tin and the coater. The sensing unit is implemented to the CVD coater and uses gas discharged against the glass surface from an outlet at the bottom positioned closely adjacent to the glass surface and measures the back pressure resulting from impingement of the gas against the surface.

The present invention relates to a float glass system, in which molten glass is cooled to form a glass ribbon moving along a glass ribbon path, as defined in appended independent claim <NUM>. Specific variants of the float glass system are the subject of appended dependent claims <NUM> to <NUM>. The float glass system comprises at least one optical low-coherence interferometry probe located adjacent the glass ribbon path. An optical low-coherence interferometry (OLCI) system is operatively connected to the at least one probe.

The float glass system comprises a float bath having a pool of molten metal. At least one chemical vapor deposition coater is located in the float bath above the pool of molten metal. At least one optical low-coherence interferometry probe is connected to the at least one coater, being located in the coater, and is connected to an optical low-coherence interferometry system.

The at least one probe can be located adjacent to at least one transparent window on a bottom of the coater.

Two or more probes can be positioned at a spaced distance from each other on the coater. For example, the probes can be spaced diagonally from each other with respect to the coater. One or more probes can be located at or near a forward corner of the coater (with respect to a direction of travel of the glass ribbon) and one or more other probes can be located at or near the diagonally opposite corner of the coater.

A plurality of coaters can be located in the float bath. Some or all of the coaters can include one or more OLCI probes. The probes can be connected to the same OLCI system or to different OCLI systems.

The float glass system can further, or alternatively, comprise at least one other optical low-coherence interferometry probe located adjacent an exit end of the float bath and connected to an optical low-coherence interferometry system. For example, the at least one other probe can be located outside of the float bath. In a preferred configuration, the at least one other probe is movably mounted on a support such that the at least one other probe can be scanned across the glass ribbon.

Another float glass system comprises a float bath having a pool of molten metal and at least one optical low-coherence interferometry probe located within the float bath and connected to an optical low-coherence interferometry system. The at least one probe can be mounted on a support in the float bath and can be either fixedly or movably mounted.

Another float glass system comprises a float bath having a pool of molten metal and at least one optical low-coherence interferometry probe located at a point past the exit end of the float bath but before the location where the glass ribbon is cut and packed. The at least one optical low-coherence interferometry probe can be connected to an optical low-coherence interferometry system.

The present invention is also directed towards a chemical vapor deposition coater as defined in appended independent claim <NUM>. Specific variants of the float glass system are the subject of appended dependent claims <NUM> and <NUM>. The chemical vapor deposition coater comprises a coater housing having a bottom, with at least one transparent window in the bottom of the housing. At least one optical low-coherence interferometry probe is located in the coater housing adjacent the window. The optical low-coherence interferometry probe is connected to an optical low-coherence interferometry system.

The present invention also concerns a method of determining a coater gap in a float glass system as set forth in appended claim <NUM>. The method comprises measuring the distance from the bottom of the CVD coater to a top of a glass ribbon in a float bath using at least one OLCI probe. The method can alternatively or additionally comprise using the OLCI probe to determine the thickness of a coating and/or coating layers on the glass ribbon.

The present invention also concerns a method of determining the thickness of a glass ribbon in a float bath of a float glass system as set forth in appended claim <NUM>. The method comprises measuring a thickness of a glass ribbon at one or more locations within the float bath using at least one OLCI probe located within the float bath. The method can alternatively or additionally comprise using the OLCI probe to determine the thickness of a coating and/or coating layers on the glass ribbon.

The present invention is also directed towards use of at least one OLCI probe to determine a coater gap of a chemical vapor deposition coater in a float bath of a float glass system, as set forth in appended claim <NUM>.

The present invention also relates to use of at least one OLCI probe to determine a glass ribbon thickness for a glass ribbon in a float bath of a float glass system, , as set forth in appended claim <NUM>. The probe can additionally or alternatively be used to measure the thickness of a coating on the glass ribbon.

The invention will be described with reference to the following drawing figures wherein like reference numbers identify like parts throughout.

As used herein, spatial or directional terms, such as "left", "right", "inner", "outer", "above", "below", "top", "bottom", and the like, relate to the invention as it is shown in the drawing figure. It is to be understood that the invention can assume various alternative orientations and, accordingly, such terms are not to be considered as limiting. As used herein, all numbers expressing dimensions, physical characteristics, processing parameters, quantities of ingredients, reaction conditions, and the like, used in the specification and claims are to be understood as being modified in all instances by the term "about". All ranges disclosed herein are to be understood to encompass the beginning and ending range values. The term "film" refers to a region of a coating having a desired or selected composition. A "layer" comprises one or more "films". A "coating" or "coating stack" is comprised of one or more "layers". The term "over" means "on or above". For example, a coating layer "formed over" a substrate does not preclude the presence of one or more other coating layers located between the formed coating layer and the substrate. By "glass ribbon path" is meant the path the glass ribbon follows during the glass manufacturing process.

Optical low-coherence interferometry (OLCI) is an optical technique that relies on the coherency of the source to provide precise determination of the optical distance between the interfaces of two materials that are optically discontinuous at those interfaces. In a typical OLCI system, the power of a low-coherence light source (such as a superluminescent diode) is divided into a sample arm and a reference arm through a coupler. The light reflected by a sample (through the sample arm) and the light reflected by a reference reflector, such as a moving mirror (reference arm), are coupled back through the coupler to a detector. Optical interference is observed when the optical pathlengths of the beams reflected by the sample and the reference reflector are the same (i.e., differ by less than the coherence length). The refractive indices of the material or materials the light passes through can be used to convert these optical distances into physical distances. OLCI systems can be double path systems in which the emitted and reflected light travel along separate paths or single path systems in which the emitted and reflected light are collinear.

An exemplary float glass system <NUM> incorporating aspects of the invention is shown in <FIG>. The float glass system <NUM> has a furnace <NUM> where glass batch materials are melted to form a glass melt. The furnace <NUM> can be an air fuel furnace or an oxyfuel furnace. A float bath <NUM> is located downstream of the furnace <NUM>. The float bath <NUM> contains a pool of molten metal <NUM>, such as molten tin. The glass melt is introduced into the entry end <NUM> of the float bath <NUM> and onto the top of the molten tin <NUM>. The glass melt spreads across the surface of the molten tin <NUM> to form a glass ribbon <NUM>. The glass ribbon <NUM> exits the float bath <NUM> at the exit end <NUM>. A lehr <NUM> can be located downstream of the float bath <NUM>. The glass ribbon <NUM> can be transported via a conventional conveyor system <NUM> to the lehr <NUM>, where the glass ribbon <NUM> can be controllably cooled to provide glass with a controlled distribution of mechanical stress across and through the thickness of the glass ribbon (tempered), if desired. The surface of the molten metal <NUM> in the float bath <NUM> and the conveyors <NUM> that transport the glass ribbon out of the float bath <NUM> define the glass ribbon path <NUM> (i.e., the path the glass ribbon <NUM> follows during the process).

At least one chemical vapor deposition (CVD) coater <NUM> is located in the float bath <NUM>. A positioning system <NUM> is connected to the coater <NUM> to raise and lower the coater <NUM> and/or to tilt the coater <NUM> (i.e., left, right, forward, backward, with respect to a direction of travel of the glass ribbon <NUM>). The positioning system <NUM> can include one or more motors or positioning arms connected to the housing of the coater <NUM>. For ease of discussion, only one CVD coater <NUM> is shown in <FIG>. However, it is to be understood that more than one CVD coater <NUM> could be located in the float bath <NUM> and the invention could be practiced with each coater or with less than all of the coaters. The CVD coater <NUM> is configured to apply coating materials onto the top of the glass ribbon <NUM> as the ribbon <NUM> moves through the float bath <NUM> on top of the molten tin <NUM>. A conventional CVD coater <NUM> includes a plenum block where the coating material vapors are mixed and a discharge block located on the bottom of the coater <NUM> where the mixed coating materials are discharged from the coater <NUM>, such as through a coating slot, onto the top of the float glass ribbon <NUM>. The coating materials react or combine to form a coating on top of the ribbon <NUM>. One of ordinary skill in the float glass coating art will be familiar with the general concepts of the float glass system described so far and, therefore, a detailed explanation of the above components will not be provided.

However, in accordance with the invention, at least one OLCI assembly <NUM> is operatively connected to the coater <NUM>. In the illustrated embodiment, the OLCI assembly <NUM> has at least one probe <NUM> positioned inside the float bath <NUM>. The probe <NUM> can be connected to or carried on the coater <NUM>. The probe <NUM> is located in the coater <NUM>, e.g., within the coater housing <NUM>. The probe <NUM> is connected to a directional coupler <NUM> via an optical cable <NUM>. The optical cable <NUM> runs through a conduit <NUM> formed in the coater <NUM> and then out of the float bath <NUM>. The probe <NUM> includes a lens assembly <NUM> connected to the outer end of the optical cable <NUM>. As used herein, by "inner end of the optical cable <NUM>" is meant the end of the optical cable <NUM> outside of the float bath <NUM> (e.g., connected to the directional coupler <NUM>) and by "outer end of the optical cable <NUM>" is meant the opposite end of the optical cable <NUM>. The probe <NUM> can include an optional housing <NUM>, such as a stainless steel housing, to protect the lens assembly <NUM>. The housing <NUM> can have an open bottom (as in the embodiment shown in <FIG>) or the bottom of the optional housing <NUM> can include a transparent window or cover plate <NUM> (as discussed below with respect to <FIG>) that is transparent to the light used in the OLCI system <NUM>. The conduit <NUM> is connected to a cooling source <NUM>, such as a source of cooling fluid, such as air, nitrogen, or similar fluid, to cool the interior of the conduit <NUM> and help prevent damage to the optical cable <NUM>. A collimator <NUM> is operatively connected with the optical cable <NUM>. In the preferred embodiment shown in <FIG>, the collimator <NUM> is located outside of the float bath <NUM> between the probe <NUM> and the directional coupler <NUM>. Alternatively, the collimator <NUM> can be located inside the optional housing <NUM>. The probe <NUM> and optical cable <NUM> define the sample arm <NUM> of the OLCI assembly <NUM>.

A removable, transparent window <NUM> is located on the bottom of the coater <NUM>. Due to the harsh environment in the float bath <NUM>, this window <NUM> should be able to withstand the high temperatures associated with the float glass process. The material for the window <NUM> can be any material that is optically transparent at the wavelength of the OLCI source and is sufficiently durable in the conditions to which it is exposed. Specific examples of materials useful for the window <NUM> include quartz and fused silica.

The window <NUM> can have any desired thickness. For example, the window <NUM> can have a thickness of at least <NUM>, such as at least <NUM>, such as at least <NUM>, such as at least <NUM>, such as at least <NUM>, such as at least <NUM>, such as at least <NUM>.

Additionally or alternatively, the window <NUM> can have a thickness less than or equal to <NUM>, such as less than or equal to <NUM>, such as less than or equal to <NUM>, such as less than or equal to <NUM>, such as less than or equal to <NUM>, such as less than or equal to <NUM>, such as less than or equal to <NUM>.

Fused silica is particularly useful for a light source with a wavelength of about <NUM> nanometers (nm), such as in the range of <NUM> to <NUM>, such as <NUM>, and/or in which the ambient temperature is less than <NUM>, such as less than <NUM>. In a preferred embodiment, the window <NUM> is made of quartz and has a thickness of <NUM> (<NUM> inch).

The window <NUM> can be of any shape, such as square, rectangular, circular, oval, etc. In a preferred embodiment, the window <NUM> is square and has sides of <NUM> by <NUM> (<NUM> inch by <NUM> inch). Preferably, the window <NUM> is removable from the coater <NUM> for cleaning or replacement. The window <NUM> can be connected to the coater housing in any conventional manner, such as by being carried in a frame that is attached to the coater housing by threaded connections or fasteners, such as bolts.

A light source <NUM> is connected to the directional coupler <NUM> via an optical cable <NUM>. The reference arm <NUM> of the OLCI assembly <NUM> is defined by a reference reflector <NUM>, such as a moving mirror, connected through another collimator <NUM> by an optical cable <NUM> to the directional coupler <NUM>. A detector <NUM>, such as a photodiode, is connected to the directional coupler <NUM> via an optical cable <NUM>. A measurement output system <NUM> is connected to the detector <NUM>, such as by an optical cable <NUM>.

While for ease of discussion the components of the OLCI assembly <NUM> described above are shown separated from each other in the drawings, it will be appreciated that some or all of these components can be located in a common housing, such as with the commercially available systems noted below. For example, the collimator <NUM> can be located within the optional housing <NUM>, as discussed above.

In the above discussion, the OLCI assembly <NUM> was described as a double path OLCI system (having separate reference and sample arms). While the double path system is preferred, the invention could also be practiced using a conventional common path OLCI assembly (in which the reference beam and the sample beam travel along the same path).

Examples of OLCI devices that can be used to practice the invention include the Fogale Nanotech Unit (LISE System), commercially available from Fogale Nanotech Inc. of San Francisco, California, and OptiGauge™ devices, commercially available from Lumetrics Inc. of Rochester, New York.

In the above exemplary embodiment, only one probe <NUM> is shown in the coater <NUM> simply for ease of discussion. However, as shown in <FIG>, the coater <NUM> can incorporate multiple probes <NUM> connected to a multiplex coupler <NUM> via optical cables <NUM>. The probes <NUM> can be positioned along the sides and/or across the front and/or across the rear and/or at diagonally opposed corners of the coater <NUM>, to provide multiple measurements locations, as will be described in more detail below. These multiple measurements can be used to determine the tilt of the coater <NUM> with respect to the glass ribbon <NUM> (i.e., the uniformity of the coater gap across the coating area) and also to provide information regarding the thickness of the glass ribbon <NUM> and/or variations in thickness across the width of the ribbon <NUM>. The probe <NUM> can additionally or alternatively also provide information regarding the thickness of a coating or coating layers on the glass ribbon <NUM>. This information can be used to adjust or position the coater <NUM> to a desired configuration or to adjust the operating conditions of the glass pulling equipment to control the thickness of the glass ribbon <NUM>.

The coater <NUM> can have two or more probes <NUM> positioned at a spaced distance from each other. For example, the probes <NUM> can be located at or near diagonally opposed corners of the coater <NUM>. In the example illustrated in <FIG>, one or more probes <NUM> is located at or near a forward corner of the coater (upper right corner of the coater <NUM> shown in <FIG>) and one or more other probes <NUM> is located at or near the diagonally opposite corner of the coater <NUM> (lower left corner of the coater <NUM> in <FIG>).

As shown in <FIG>, one or more optional other OLCI probes <NUM> can be positioned above the glass ribbon <NUM> (i.e. above the glass ribbon path) at one or more locations downstream of the float bath <NUM>, such as between the float bath <NUM> and the <NUM> lehr, to measure the thickness of the float glass ribbon <NUM> after the ribbon <NUM> exits the float bath <NUM>. The probe(s) <NUM> can be connected to the OLCI assembly <NUM> described above or to a separate OLCI assembly <NUM>, as shown in <FIG>. The probe(s) <NUM> can be mounted on a support <NUM>. In a preferred embodiment, the support <NUM> includes a traversing system such that the OLCI probe <NUM> is movable across at least a portion of the width of the glass ribbon <NUM> to determine the thickness of the ribbon <NUM> at various points across its width. Alternatively, multiple probes <NUM> could be positioned at fixed locations across the width of the support <NUM> above the glass ribbon <NUM> such that multiple thickness readings can be obtained. The probe(s) <NUM> can additionally or alternatively also provide information regarding the thickness of a coating or coating layers on the glass ribbon <NUM>.

As also shown in <FIG>, one or more optional further OLCI probes <NUM> can be installed on one or more supports <NUM> located within the float bath <NUM> (i.e. not connected directly to the coater <NUM>). These further probe(s) <NUM> can be connected to the OLCI assembly <NUM> described above or to a separate OLCI assembly <NUM>, as shown in <FIG>. For example, the probe(s) <NUM> can be positioned at fixed locations on one or more supports <NUM> and connected to a multiplex coupler <NUM>, as described above. Thus, the glass ribbon thickness can be measured at multiple locations across the width of the ribbon <NUM> and at multiple locations along the direction of glass ribbon <NUM> travel using the probe(s) <NUM>. This information can be used to adjust the operating conditions of the glass pulling equipment to control the thickness of the glass ribbon <NUM>. In <FIG>, the further probes <NUM> in the float bath <NUM> are shown connected to one OLCI assembly <NUM> and the other probes <NUM> located outside of the float bath <NUM> are connected to another OLCI assembly <NUM>. However, it is to be understood that the probes <NUM> in the float bath <NUM> and the probes <NUM> outside of the float bath <NUM> can be connected to the same OLCI assembly, such as the OLCI assembly <NUM> discussed above. The probe(s) <NUM> can additionally or alternatively also provide information regarding the thickness of a coating or coating layers on the glass ribbon <NUM>.

Although various aspects of the invention described above (such as the coater <NUM> with OLCI probe(s) <NUM> shown in <FIG>, the exterior bath other probe(s) <NUM> in <FIG>, and the interior bath further probe(s) <NUM> shown in <FIG>) are illustrated in separate drawings, it will be appreciated that this is simply for ease of discussion and the float glass system <NUM> of the invention could incorporate any one or more of these aspects in a single process. For example, the float glass system <NUM> could incorporate one or more coaters <NUM> having one or more probes <NUM> as shown in <FIG> and <FIG>; and/or one or more other probes <NUM> located at the exit end of the float bath <NUM>, such as at one or more locations between the float bath <NUM> and the lehr <NUM>, as shown in <FIG>; and/or one or more in bath further probes <NUM> positioned in the float bath <NUM> outside of the coater(s) <NUM>, as shown in <FIG>.

Operation of the float glass system <NUM> of the invention will now be described with particular reference to <FIG> and <FIG>. Light from the light source <NUM> is directed through the directional coupler <NUM> into both the sample arm <NUM> and the reference arm <NUM>. In the sample arm <NUM>, the light is directed from the probe <NUM>, through the quartz window <NUM>, and then through the float glass ribbon <NUM> on top of the molten tin <NUM>. As shown in <FIG>, light <NUM> is reflected back from the various interface surfaces. This reflected light travels to the detector <NUM>, which calculates the distances between the interfaces. The bottom surface of the window <NUM> (which is preferably aligned with the bottom of the coater <NUM>) can be used as a reference to measure the distance from the bottom of the coater <NUM> to the top of the glass ribbon <NUM>.

In <FIG>, the optical distance from the bottom of the probe <NUM> to the bottom of the quartz window <NUM> is designated X<NUM>. The optical distance from the bottom of the probe <NUM> to the top surface of the glass ribbon <NUM> is designated X<NUM>. The optical distance from the bottom of the probe <NUM> to the bottom surface of the glass ribbon <NUM> is designated as X<NUM>. Having determined these optical distances, the coater gap can easily be determined by subtracting X<NUM> from X<NUM>. Further, the optical thickness of the glass ribbon <NUM> can be obtained by subtracting X<NUM> from X<NUM>. The physical thicknesses can be calculated from the optical thicknesses by dividing the optical thickness by the optical index (n) of the medium (e.g., glass) at the wavelength of the light source and the temperature of the medium. For example, the optical index of the ambient medium between the window <NUM> and the surface of the glass ribbon can be defined as n=<NUM>, while the optical index of a glass ribbon <NUM> at <NUM> is typically about n=<NUM>. With the invention, the coater gap can be easily verified and precisely changed on a real time basis to accommodate various coating materials or deposition parameters.

As will be appreciated from the above discussion and with particular reference to <FIG>, using multiple OLCI probes <NUM> in the coater <NUM> not only helps to determine the coater distance above the glass ribbon <NUM> but also can be used to determine whether the coater <NUM> is properly aligned with respect to the top of the glass surface, i.e. whether the coater bottom is parallel to the top of the glass ribbon <NUM> or is tilted with respect to the top of the glass ribbon <NUM>. For example, in some instances, it may be desirable to tilt the coater <NUM> left or right or upstream or downstream with respect to the direction of travel of the glass ribbon <NUM>. In the practice of the invention, the distance of the bottom of the coater <NUM> from the top of the glass ribbon <NUM> can be more precisely defined and the positioning system <NUM> can be used to raise and lower the coater <NUM> more precisely or to tilt the coater <NUM>, if desired. This more precise distance measurement provides better control of the coating process and also positive safety to prevent contact of the bottom of the coater <NUM> with the top of the glass ribbon <NUM>. Since there is no physical contact with the glass ribbon <NUM> in determining the glass ribbon thickness, the top of the glass ribbon <NUM> is not disturbed or marred. Additionally, with the use of a multiplex coupler <NUM> and multiple probes <NUM>, multiple OLCI distance measurements can be taken across the width of the ribbon <NUM> to determine if there are thickness variations across the ribbon <NUM>, which can then be corrected. Further, the probe <NUM> and the quartz window <NUM> are easily removed or installed in the coater <NUM>, for example for replacement of the probe <NUM> or for cleaning or replacing the quartz window <NUM> if it becomes damaged by the heat in the float bath <NUM> or if damaged by molten metal in the float bath <NUM>.

With respect to <FIG> and <FIG>, the OLCI device(s) located outside of the float bath <NUM> can be used to determine the thickness of the glass ribbon <NUM> as it exits the float bath <NUM>. In <FIG>, the housing <NUM> is illustrated as including the optional cover plate <NUM>. As will be appreciated from the above discussion, the OLCI probe(s) <NUM> on the support <NUM> can be used to measure the thickness of the glass ribbon <NUM> as it exits the float bath <NUM>. These measurements provide information not only about the thickness of the glass ribbon <NUM> but also about the thickness variation (contour), if any, across the width of the glass ribbon <NUM>. This information allows the operator to make adjustments to the float bath <NUM> to change the average thickness of the ribbon <NUM> or to adjust the thickness variation across the width of the ribbon <NUM> (such as to provide a more uniform thickness across the width of the ribbon <NUM>). The OLCI probes used in the invention allow for the more accurate measurement of the glass ribbon at thicknesses above those possible with conventional systems. Also, the invention does not physically contact the top of the ribbon <NUM> and, therefore, will not mar the glass surface. Additionally, the thickness measurements obtained by the OLCI devices and processes of the invention do not depend on the orientation or the flatness of the glass ribbon <NUM>. For example, if the glass ribbon <NUM> has minor crests and troths, such as due to movement on the conveyor system <NUM>, the thickness measurement obtained from the OLCI probes is still a true thickness since the OLCI process measures the distance of the glass ribbon <NUM> from the top surface to the bottom surface (i.e. the distance between the top and bottom interface surfaces) regardless of whether those surfaces are parallel or curved.

<FIG> is similar to <FIG> but shows the presence of a coating <NUM> over the glass ribbon <NUM>. Thus, in the practice of the invention, not only can the thickness of the glass ribbon <NUM> be calculated but also the thickness of a coating <NUM> (including the thicknesses of the layers forming the coating <NUM>) on the glass ribbon <NUM> can be calculated. In <FIG>, the distance from the bottom of the probe <NUM> to the top surface of the coating <NUM> is designated as X<NUM>. Thus, the thickness of the coating <NUM> is defined as X<NUM> minus X<NUM>.

<FIG> illustrate the concept utilized with a downdraw glass manufacturing process, disclosed herein for reference. The downdraw process is depicted as a conventional fusion downdraw process in which molten glass <NUM> is delivered into a channel <NUM> of a forming trough <NUM> having opposed sides <NUM>, <NUM>. The molten glass <NUM> overflows the channel <NUM> and forms two glass films <NUM>, <NUM> that flow downwardly along the outer surfaces of the sides <NUM>, <NUM>, respectively, and join together under the trough <NUM> to form a glass ribbon <NUM>. The glass ribbon <NUM> moves downwardly under the force of gravity. The vertical plane along which the glass ribbon <NUM> moves defines the glass ribbon path <NUM> for the downdraw process. One or more probes <NUM> are positioned adjacent the glass ribbon <NUM> (i.e. adjacent the glass ribbon path). In the illustrated embodiment, the probes <NUM> are similar to the probes <NUM>, <NUM>, and <NUM> described above but include a bottom cover plate <NUM>, transparent to the light used for the OLCI system, to protect the lens assembly <NUM> from environmental damage. As shown in <FIG>, a plurality of probes <NUM> can be positioned at selected heights with respect to the glass ribbon <NUM> to determine the thickness of the glass ribbon <NUM> at the selected positions. The probes <NUM> are connected to one or more OLCI assemblies <NUM>. The probes <NUM> can be fixedly mounted or, as shown in <FIG>, the probes <NUM> can be mounted on a support <NUM> having a traversing system <NUM> such that the probes <NUM> can be moved across at least a portion of the width of the glass ribbon <NUM> to determine a thickness profile of the glass ribbon <NUM>.

<FIG> shows an example of the signal from a float glass system as shown in <FIG> for a configuration where the coater window is mounted <NUM> (<NUM> inch) from an arbitrary location and the bottom of the window is at the same height as the coater bottom, the glass ribbon surface is at a distance <NUM> (<NUM> inch) below the coater bottom, and the glass is <NUM> thick. <FIG> shows an example of the signal from the system where the cover window is mounted <NUM> (<NUM> inch) from an arbitrary location and is at the same height as the coater bottom, the glass ribbon surface is at a distance <NUM> (<NUM> inch) below the coater bottom, and the glass is <NUM> thick. <FIG> shows an example of the signal from the system for a configuration where the cover window is mounted <NUM> (<NUM> inch) from an arbitrary location and is at the same height as the coater bottom, the glass ribbon surface is at a distance <NUM> (<NUM> inch) below the coater bottom, and the glass is <NUM> thick. <FIG>, <FIG>, respectively, show the signals of <FIG>, and <FIG> in which the optical distances are converted to physical distances by adjusting for the refractive indices of the materials.

Claim 1:
A float glass system (<NUM>) in which molten glass is cooled to form a glass ribbon (<NUM>, <NUM>) moving along a glass ribbon path (<NUM>, <NUM>), comprising:
a float bath (<NUM>) having a pool of molten metal (<NUM>);
at least one chemical vapor deposition coater (<NUM>) located in the float bath (<NUM>);
at least one optical low-coherence interferometry probe (<NUM>, <NUM>) located adjacent the glass ribbon path (<NUM>, <NUM>) in the float bath (<NUM>) above the pool of molten metal (<NUM>);
an optical low-coherence interferometry (OLCI) system (<NUM>, <NUM>) operatively connected to the at least one probe (<NUM>, <NUM>), and
at least one window (<NUM>) located in the bottom of the at least one coater (<NUM>)
wherein the at least one probe (<NUM>, <NUM>) is connected to the at least one coater (<NUM>), with the at least one probe (<NUM>) located in the at least one coater (<NUM>) and aligned with the at least one window (<NUM>).