Method and apparatus for mitigating edge roller profile differences

Abstract

A glass manufacturing method includes forming a glass ribbon from a molten material. The glass ribbon includes a first surface and a second surface. The method includes contacting the first surface with a first edge roller and the second surface with a second edge roller, rotating the first edge roller at a first rotational speed and rotating the second edge roller at a second rotational speed. The method includes generating a first torque signal representative of a torque applied to the first edge roller and a second torque signal representative of a second torque applied to the second edge roller. The method also includes time-dependently modulating the first rotational speed and the second rotational speed to counter variations in a torque sum signal of the first torque signal and the second torque signal.

Description

[Technical field]

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS This application claims the benefit of priority under 35 U.S.C. Section 119 of U.S. Provisional Patent Application Serial No. 63 / 220,110, filed July 9, 2021, the contents of which are reliably incorporated by reference in their entirety.

[0002] FIELD OF THE DISCLOSURE The present disclosure relates generally to glass ribbon manufacturing apparatus and methods. [Background technology]

[0003] Glass forming equipment is commonly used to form various glass products, such as glass sheets used in LCD displays and the like. These glass sheets can be produced using a downdraw process in which molten glass is flowed downward onto a forming wedge to form a continuous glass ribbon. In the downdraw process, various rollers can be used to provide traction to the continuous glass ribbon, tension the ribbon, or guide the glass ribbon. For example, edge rollers can pinch the edges of the continuous glass ribbon to guide the glass ribbon. Such edge rollers can be arranged in pairs to contact both sides of the glass ribbon. If the edge rollers do not have a corresponding shape, the separation distance between the rollers can change as a function of time (e.g., with rotation of the edge rollers), resulting in thickness variations in the glass sheet. These thickness variations can render the glass sheet unsuitable for certain applications, such as high definition displays. Summary of the Invention [Means for solving the problem]

[0004] A first aspect of the present disclosure includes a glass manufacturing method including forming a glass ribbon from a quantity of molten material, the glass ribbon including a first surface and a second surface; contacting the first surface with a first edge roller and the second surface with a second edge roller; rotating the first edge roller at a first rotational speed and rotating the second edge roller at a second rotational speed; generating a first torque signal representative of a torque imparted to the first edge roller and a second torque signal representative of a second torque imparted to the second edge roller; generating a torque sum signal of the first torque signal and the second torque signal; and time-dependently modulating the first rotational speed and the second rotational speed to counter fluctuations in the torque sum signal.

[0005] A second aspect of the present disclosure relates to a method for modulating the first rotational speed and the second rotational speed in a time-dependent manner, the method comprising: T =A*sin(θ 1,2 +Φ)+ω N , and use the target rotation speed ω T where A is a modulation amplitude and Θ 1、2 is the angular position of the first edge roller or the second edge roller, Φ is the modulation phase, and ω N is a target rotation speed of the first edge roller and the second edge roller.

[0006] A third aspect of the present disclosure includes a method according to the first or second aspect, further comprising determining a modulation phase by determining a time delay between a roll position signal representative of the angular position and the torque sum signal, and converting the time delay into a phase angle.

[0007] A fourth aspect of the present disclosure further includes filtering the torque sum signal using a band pass filter having an upper cutoff frequency and a lower cutoff frequency prior to determining the modulation phase; N is between an upper cutoff frequency and a lower cutoff frequency.

[0008] A fifth aspect of the present disclosure includes a method according to any of the first to fourth aspects, further including sensing a thickness of the glass ribbon downstream of the first edge roller and the second edge roller, and determining a modulation amplitude A based on the thickness of the glass ribbon.

[0009] A sixth aspect of the present disclosure includes a method according to any of the first to fifth aspects, wherein determining the modulation amplitude A includes periodically modulating the first angular velocity and the second angular velocity using a first value of the modulation amplitude A, determining whether the first value results in a decrease in thickness variation of the glass ribbon, and if the first value results in a decrease in thickness variation of the glass ribbon, increasing the modulation amplitude A until a decrease in thickness variation is no longer observed.

[0010] A seventh aspect of the present disclosure includes a method according to any of the first to sixth aspects, wherein the first edge roller and the second edge roller have different cross-sectional shapes such that a separation distance between the first edge roller and the second edge roller changes periodically with rotation of the first edge roller and the second edge roller.

[0011] An eighth aspect of the present disclosure includes a method according to any of the first to seventh aspects, wherein the torque sum signal serves as a proxy for separation distance such that when the torque sum signal is greater than the average torque value, the separation distance is greater than the average distance.

[0012] A ninth aspect of the present disclosure includes a method according to any of the first to eighth aspects, wherein modulating the first rotational speed and the second rotational speed to counteract changes in the torque sum signal includes decreasing at least one of the first rotational speed and the second rotational speed during a period when the separation distance is increasing, and increasing at least one of the first rotational speed and the second rotational speed during a period when the separation distance is decreasing.

[0013] A tenth aspect of the present disclosure includes a method according to any of the first to ninth aspects, wherein modulating the first rotational speed and the second rotational speed to counteract changes in the torque sum signal reduces a moving window thickness range of the glass ribbon achieved when the first rotational speed and the second rotational speed are not modulated.

[0014] An eleventh aspect of the present disclosure includes a method of making glass including: forming a glass ribbon from a quantity of molten material, the glass ribbon including a first surface and a second surface; contacting the first surface with a first edge roller and the second surface with a second edge roller, the first edge roller and the second edge roller having different cross-sectional geometries such that a separation distance between the first edge roller and the second edge roller varies periodically depending on a speed at which the first edge roller and the second edge roller rotate; driving the first edge roller and the second edge roller at a first rotational speed and a second rotational speed, respectively; generating a torque sum signal representative of a total torque imparted to the first edge roller and the second edge roller; determining a time delay between the torque sum signal and an electrical roll position signal representative of one or both of the first rotational position and the second rotational position; and updating the first rotational speed and the second rotational speed based on the time delay, the first rotational position, and the second rotational position.

[0015] A twelfth aspect of the present disclosure includes the method according to the eleventh aspect, wherein the updating step includes modulating the first rotational rate and the second rotational rate in a time-dependent manner.

[0016] A thirteenth aspect of the present disclosure is a method for modulating a frequency band according to the following equation: T =A*sin(θ 1,2 +Φ)+ω N , and use the target rotation speed ω T where A is a modulation amplitude and Θ 1、2 is the angular position of the first edge roller or the second edge roller, Φ is the modulation phase determined from the time delay, and ωN is the target rotation speed of the first edge roller and the second edge roller, includes the method according to any of the eleventh to thirteenth aspects.

[0017] A fourteenth aspect of the present disclosure includes a method according to any of the eleventh to thirteenth aspects, further including sensing a thickness of the glass ribbon downstream of the first edge roller and the second edge roller, and determining a modulation amplitude A based on the thickness of the glass ribbon.

[0018] A fifteenth aspect of the present disclosure includes a method according to any of the eleventh to fourteenth aspects, wherein determining the modulation amplitude A includes periodically modulating the first angular velocity and the second angular velocity using a first value of the modulation amplitude A, determining whether the first value results in a decrease in thickness variation of the glass ribbon, and if the first value results in a decrease in thickness variation of the glass ribbon, increasing the modulation amplitude A until no decrease in thickness variation is observed.

[0019] A sixteenth aspect of the present disclosure includes a method according to any of the eleventh to fifteenth aspects, wherein the torque sum signal serves as a proxy for separation distance such that when the torque sum signal is greater than the average torque value, the separation distance is greater than the average distance.

[0020] A seventeenth aspect of the present disclosure includes the method according to any of the eleventh to sixteenth aspects, wherein the updating step includes increasing the first rotational speed.

[0021] An eighteenth aspect of the present disclosure is a glass manufacturing apparatus including a former configured to form a glass ribbon from a quantity of molten material, the former defining a draw path extending from the former through which the glass ribbon can be formed; an edge roll assembly including an edge roller pair disposed on either side of the draw path, the edge roller pair including a first edge roller having a first cross-sectional shape and a second edge roller having a second cross-sectional shape, the first cross-sectional shape differing from the second cross-sectional shape such that the first edge roller and the second edge roller are separated from each other by a separation distance that varies depending on a speed at which the first edge roller and the second edge roller rotate; and a winding mechanism mechanically coupled to the first edge roller and the second edge roller and configured to wind the first edge roller at the first rotation. the apparatus includes one or more drive units configured to rotate a first edge roller about a rotation axis at a first rotational speed and a second edge roller about a second rotation axis at a second rotational speed, and further configured to generate a first torque signal representative of a first torque imparted to the first edge roller and a second torque signal representative of a second torque imparted to the second edge roller; and a controller communicatively coupled to the one or more drive units and operable to generate a torque sum signal from the first torque signal and the second torque signal and to modulate the first rotational speed and the second rotational speed using the torque sum signal such that the first rotational speed and the second rotational speed are inversely proportional to a variable separation distance.

[0022] A nineteenth aspect of the present disclosure includes the apparatus according to the eighteenth aspect, further comprising a thickness sensor configured to sense a thickness of the glass ribbon downstream of the first edge roller and the second edge roller, and the controller is operable to modulate the first rotational speed and the second rotational speed based on the thickness of the glass ribbon.

[0023] A twentieth aspect of the present disclosure includes the apparatus according to the eighteenth or nineteenth aspects, wherein the controller is operable to periodically modulate the first rotational speed and the second rotational speed using a modulation phase calculated based on a time delay between the torque sum signal and an electric roll position signal generated by the one or more drive units, the electric roll position signal representing a rotational position of at least one of the first edge roller or the second edge roller.

[0024] The following detailed description sets forth additional features and advantages of the glass ribbon manufacturing apparatus and methods, and the replaceable heating cartridges used in such apparatus and methods, some of which will be readily apparent to those skilled in the art from the description, or will be recognized by practicing the embodiments described herein, including the detailed description and accompanying drawings, according to the claims.

[0025] It should be understood that the foregoing general description and the following detailed description describe various embodiments, and are intended to provide an overview or framework for understanding the nature and character of the claimed subject matter. The accompanying drawings are included to provide a further understanding of the various embodiments, and are incorporated in and constitute a part of this specification. The drawings illustrate various embodiments described herein, and together with the description serve to explain the principles and operation of the claimed subject matter. [Brief description of the drawings]

[0026] [Figure 1] 1 is a schematic diagram of a glass manufacturing apparatus according to one or more embodiments shown and described herein. [Diagram 2] 2 is a schematic cross-sectional view of a glass manufacturing apparatus according to one or more embodiments described herein, taken through line 2-2 in FIG. 1. [Figure 3A] 3 is a schematic cross-sectional view of a glass manufacturing apparatus according to one or more embodiments described herein, taken through line 3-3 in FIG. 2. [Figure 3B]FIG. 3B is a schematic diagram of a plot of the separation distance between edge rollers of the edge roller pair of the glass manufacturing apparatus shown in FIGS. 1-3A in accordance with one or more embodiments described herein. [Figure 4A] FIG. 2 illustrates a plot of a torque sum signal of torque supplied to an edge roller of an edge roller pair of a glass manufacturing apparatus according to one or more embodiments described herein. [Figure 4B] FIG. 4B illustrates a period domain transform of the plot of the torque sum signal shown in FIG. 4A in accordance with one or more embodiments described herein. [Figure 5A] FIG. 2 illustrates a frequency domain plot of a low pass filter portion of a band pass filter used to filter the torque sum signal in accordance with one or more embodiments described herein. [Figure 5B] FIG. 2 illustrates a frequency domain plot of a high pass filter portion of a band pass filter used to filter the torque sum signal in accordance with one or more embodiments described herein. [Figure 6A] 1 is a plot of an unfiltered torque sum signal of the torque supplied to an edge roller of an edge roller pair of a glass manufacturing apparatus according to one or more embodiments described herein. [Figure 6B] FIG. 6B illustrates a plot of a filtered torque sum signal produced by filtering the torque sum signal of FIG. 6A using the bandpass filter shown in FIGS. 4A and 4B in accordance with one or more embodiments described herein. [Figure 7] FIG. 1 illustrates a plot including a torque sum signal overlaid on an electric roller position signal in accordance with one or more embodiments described herein. [Figure 8] FIG. 1 is a flow diagram of a method for modulating the rotational speed of an edge roller of a glass manufacturing apparatus according to one or more embodiments described herein. [Figure 9] FIG. 9 is a flow diagram of a method for determining a modulation phase and modulation amplitude that can be used to modulate the rotation rate during the method of FIG. 8 in accordance with one or more embodiments described herein. [Figure 10] FIG. 13 shows a plot of thickness flapping tendencies of a glass ribbon produced using multiple modulation amplitudes to modulate the rotational speed of an edge roller according to one or more embodiments described herein. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0027] Reference will now be made in detail to embodiments of a glass ribbon manufacturing apparatus and method that modulates rotational speeds of edge rollers in a time-dependent manner to counter variations in a torque summation signal associated with an edge roller pair. Wherever possible, the same reference numerals are used throughout the drawings to refer to identical or similar parts. The glass ribbon manufacturing apparatus of the present disclosure may include a glass forming body that forms a glass ribbon from a quantity of molten material, and a plurality of edge rollers disposed downstream from the glass forming body. The plurality of edge rollers may include an edge roller pair including a first edge roller and a second edge roller disposed to contact opposite sides of the glass ribbon. One or more drive units may rotate the first and second edge rollers at first and second rotational speeds and generate a torque signal representative of a torque applied to the first and second edge rollers. The first edge roller may have a different cross-sectional shape than the second edge roller such that a separation distance between the first edge roller and the second edge roller may vary as a function of time, such that the torque signal also varies as a function of time. A controller may receive the torque signal and generate the torque summation signal. The controller can modulate a rotational speed at which the one or more drive units rotate the first and second edge rollers to counteract variations in the torque sum signal. Such time-dependent modulation can reduce variations in the separation distance between the first and second edge rollers to reduce thickness variations in the glass ribbon. As a result, glass sheets produced via the apparatus described herein can have a more uniform wall thickness than glass sheets produced without time-dependent roller speed modulation.

[0028] As used herein, the term "thickness flapping" refers to periodic thickness variations that occur in the draw direction near the edges of a glass ribbon while the glass ribbon is being formed using a downdraw process (e.g., fusion draw process, slot draw process).

[0029] 1 illustrates generally an embodiment of an apparatus 10 for producing glass, such as a glass ribbon 12. The apparatus 10 includes a melting vessel 15 configured to receive batch materials 16 generally from a storage bin 18. The batch materials 16 may be introduced to the melting vessel 15 by a batch delivery device 20 driven by a motor 22. An optional controller 24 may be provided to operate the motor 22, and a molten glass level probe 28 may be used to measure the glass melt level in a standpipe 30 and communicate the measured information to the controller 24.

[0030] The apparatus 10 may also include a fining vessel 38, such as a fining tube, disposed downstream of the melting vessel 15 and coupled to the melting vessel 15 via a first connecting tube 36. A mixing vessel 42 may also be disposed downstream from the fining vessel 38. A delivery vessel 46 may be disposed downstream from the mixing vessel 42. As shown, a second connecting tube 40 connects the fining vessel 38 to the mixing vessel 42, and a third connecting tube 44 connects the mixing vessel 42 to the delivery vessel 46. Also shown is a downcomer 48 that delivers the glass melt from the delivery vessel 46 to an inlet 50 of a forming vessel 60. In the embodiment shown generally in FIG. 1, the melting vessel 15, the fining vessel 38, the mixing vessel 42, the delivery vessel 46, and the forming vessel 60 are examples of various glass processing stations that may be disposed in series along the apparatus 10.

[0031] The melting vessel 15 is typically formed from a refractory material such as refractory (e.g., ceramic) brick. The apparatus 10 may further include components typically formed from platinum or platinum-containing metals such as platinum-rhodium, platinum-iridium, and combinations thereof, but these components may also include refractory metals such as molybdenum, palladium, rhenium, tantalum, titanium, tungsten, ruthenium, osmium, zirconium, and alloys thereof and / or zirconium dioxide. The platinum-containing components may include one or more of the first connecting tube 36, the fining vessel 38, the second connecting tube 40, the standpipe 30, the mixing vessel 42, the third connecting tube 44, the delivery vessel 46, the downcomer 48, and the inlet 50. The forming vessel 60 may also be formed from a refractory material and is designed to form the glass melt into a glass ribbon 12.

[0032] FIG 2 is a cross-sectional perspective view of the apparatus 10 taken along line 2-2 of FIG 1. As shown, a forming vessel 60 includes a forming wedge 62 including a pair of downwardly sloping forming surface portions 66a, 66b extending between ends 64a, 64b of the forming wedge 62. The downwardly sloping forming surface portions 66a, 66b converge along a draw direction 68 to form a bottom edge, hereinafter referred to as a root 70. Molten glass 17 may fill a trough extending between ends 64a, 64b, extend downwardly over the downwardly sloping forming surface portions 66a, 66b, and converge at the root 70 to form a glass ribbon 12. A draw surface 72 extends through the root 70. The glass ribbon 12 may be drawn in the draw direction 68 along the draw surface 72. The draw surface 72 passes vertically through the base 70 to bisect the forming vessel 60. However, it should be understood that in alternative configurations, the draw surface 72 may not pass vertically through the base 70. Although Figures 1 and 2 generally depict one embodiment of a glass forming apparatus and forming vessel, it should be understood that aspects of the present disclosure may be used with a variety of other forming vessel configurations.

[0033] 1-2, the apparatus 10 also includes at least one edge roller assembly for drawing the glass ribbon from the root 70 of the forming vessel 60. For example, the illustrated apparatus 10 includes first and second edge roller assemblies 130a, 130b (see FIG. 1). The first edge roller assembly 130a includes a first edge roller pair 132 configured to engage a first edge of the glass ribbon 12 as the glass ribbon 12 is drawn from the root 70 of the forming wedge 62. The second edge roller assembly 130b includes a second edge roller pair 134 configured to engage another second edge of the glass ribbon 12 as the glass ribbon 12 is drawn from the root 70 of the forming wedge 62. The first and second edge roller assemblies 130a, 130b assist in drawing the glass ribbon 12 from the root 70 of the forming wedge 62. For example, the first and second edge roller assemblies 130a, 130b can provide desired edge characteristics and proper fusion of the edge portions of the molten glass 17 drawn from either side of the downwardly inclined forming surface portions 66a, 66b. In some embodiments, the first and second edge roller assemblies 130a, 130b can be positioned at various locations within the viscous zone of the glass drawn from the root portion 70. For example, in some embodiments, the first and second edge roller assemblies 130a, 130b can be positioned directly below the root portion 70. In some embodiments, the first and second edge roller assemblies 130a, 130b are positioned below the root portion 70 a distance that can depend on the composition of the glass ribbon 60 and other factors of the manufacturing process (e.g., draw speed, glass ribbon thickness, etc.).

[0034] 2 and 3A show one embodiment of the first edge roller assembly 130a. The second edge roller assembly 130b (see FIG. 1) can be substantially identical in structure to the first edge roller assembly 130a in some embodiments. As shown in FIG. 2, the first edge roller assembly 130a includes a first edge roller pair 132. The first edge roller pair 132 includes a first edge roller 132a and a second edge roller 132b. The first and second edge rollers 132a, 132b are configured to simultaneously engage the first major surface 110a and the second major surface 110b of the glass ribbon 12, respectively, as the glass ribbon 12 is drawn from the root 70 of the forming wedge 62. The first edge roller assembly 130a includes a first shaft 136 mechanically coupled to the first edge roller 132a and a second shaft 138 mechanically coupled to the second edge roller 132b. FIG. 2 shows the first and second shafts 136, 138 as being substantially cylindrical and extending linearly between the first and second edge rollers 132a, 132b in a direction perpendicular to the draw direction 68 (e.g., the x-direction of the coordinate axes shown in FIG. 2). In an embodiment, the first and second shafts 136, 138 can extend through a housing (not shown) that contains the glass ribbon 12. The housing can help shield the components of the apparatus 10 (e.g., one or more drive units 137, the controller 150 shown in FIG. 1) and maintain a controlled environment around the glass ribbon. Alternative configurations of the first and second shafts 136, 138 are contemplated and are within the scope of the present disclosure. For example, in an embodiment, the first and second shafts 136, 138 can extend at least partially in the draw direction 68 (e.g., obliquely relative to the x-axis shown in FIG. 2).

[0035] In an embodiment, the first and second shafts 136, 138 are rotationally driven by one or more drive units 137. The one or more drive units 137 can be mechanically coupled to the first and second edge rollers 132a, 132b to rotate the first edge roller 132a around the first rotation axis 140a at a first rotation speed ω1 and the second edge roller 132b around the second rotation axis 140b at a second rotation speed ω2. In an embodiment, the first and second rotation speeds ω1, ω2 are equal and opposite to each other (e.g., the first edge roller 132a can rotate in a clockwise direction and the second edge roller 132b can rotate in a counterclockwise direction such that the first edge roller assembly 130a guides the glass ribbon 12 in the drawing direction 68). In an embodiment, the first and second rotation speeds ω1, ω2 are selected to correspond to a desired drawing speed of the glass ribbon.

[0036] In an embodiment, the one or more drive units 137 include a suitable drive mechanism (e.g., a suitable motor, such as an electric or hydraulic motor, or other suitable actuator) configured to rotate the first and second edge rollers 132a, 132b about the first and second rotational axes 140a, 140b. It should be understood that the one or more drive units 137 can take a variety of forms. For example, in an embodiment, the first and second shafts 136, 138 are mechanically linked such that a single drive unit rotates both the first and second shafts 136, 138 with a single mechanical output, such as a rotating drive shaft. In an embodiment, the mechanical output of the one or more drive units 137 can be mechanically connected to the first and second shafts 136, 138, such as by a transmission, to rotate the first and second shafts 136, 138 in a desired series of directions. The one or more drive units 137 may include a first drive unit mechanically coupled to the first shaft 136 and a second drive unit mechanically coupled to the second shaft 138. In such an embodiment, each drive unit may independently rotate one of the first and second edge rollers 132a, 132b.

[0037] In an embodiment, the apparatus 10 includes one or more pull roller assemblies (not shown) in addition to the first and second edge roller assemblies 130a, 130b. The one or more pull roller assemblies can contact the first and second major surfaces 110a, 110b of the glass ribbon 12 to apply tension to the glass to determine the thickness 166 of the glass ribbon 12. The first and second edge roller assemblies 130a, 130b can counteract variations in the width of the glass ribbon 12 (e.g., in the ±X direction shown on the coordinate axes in FIG. 1 ) due to tension applied by the pull roller assemblies. The first and second edge roller assemblies 130a, 130b can be cooled to a temperature below the temperature of the glass ribbon 12 to cool the edges of the glass ribbon 12 to help reduce lateral shrinkage of the glass ribbon 12 below the root 70. The first and second edge roller assemblies 130a, 130b may also help to merge the different streams of molten glass 17 traveling over the angled forming surface portions 66a, 66b. In an embodiment, one or more edge rollers of the first and second edge roller assemblies 130a, 130b include a knurled surface, which may prevent slippage of the glass ribbon 12 and may also provide additional cooling.

[0038] 1 and 2, in an embodiment, the apparatus 10 can include a thickness sensor 160 oriented to sense a thickness 166 of the glass ribbon 12. Although the thickness sensor 160 is shown aligned with a central portion of the glass ribbon 12 (e.g., between the first and second edge roller assemblies 130a, 130b), the thickness sensor 160 can be positioned to measure the thickness 166 at any location within the glass ribbon 12. For example, the thickness sensor 160 can be positioned to measure the thickness 166 at a location below the first edge roller assembly 130a in the downward draw direction (e.g., the -Z direction of the coordinate axes shown in the figures). The thickness sensor 160 can be movable to measure the thickness 166 at various locations of the glass ribbon 12.

[0039] The thickness sensor 160 can take a variety of forms depending on the implementation. For example, the thickness sensor 160 can include solid probes that contact the first and second major surfaces 110a, 110b to measure the thickness 166. In other examples, the thickness sensor can employ a fluid (e.g., gas) to sense the thickness 166 of the glass ribbon 12 based on feedback (e.g., pressure feedback) from the fluid flow impinging on the first and second major surfaces 110a, 110b. In yet other examples, the thickness sensor 160 can include an acoustic sensor. In the illustrated embodiment, the thickness sensor 160 is a laser sensor that emits a laser beam that is incident on the glass ribbon 12 at a measurement location 170. A first portion of the laser beam is reflected from the first major surface 110a and a second portion of the laser beam is transmitted through the glass ribbon and reflected from the second major surface 110b. The reflected light is detected by a thickness sensor, and the difference between the signals reflected from the first and second major surfaces 110a, 110b can be used to measure the thickness 166. Although a single thickness sensor 160 is shown in Figures 1-2, some embodiments of the device 10 can include multiple thickness sensors such that the thickness 166 can be measured simultaneously at various locations.

[0040] In an embodiment, the thickness sensor 160 is communicatively coupled to the controller 150 of the apparatus 10. As described herein, the thickness measurements can be used to determine a modulation amplitude A that the controller 150 uses to modulate the first and second rotational speeds ω1, ω2 of the first and second edge rollers 132a, 132b. For example, the measurements by the thickness sensor 160 can be used to determine whether a particular modulation amplitude A reduces the variation in thickness 166 over a given measurement period (e.g., 10 minutes, 30 minutes, 60 minutes) and determine whether the modulation amplitude A should be adjusted.

[0041] 1, 3A, and 3B, the first and second edge rollers 132a, 132b may differ from one another in cross-sectional shape. In the example shown in FIG. 3A, for illustrative purposes, the first edge roller 132a is shown to include a first cross-sectional shape 142a that is substantially elliptical, while the second edge roller 132b is shown to include a second cross-sectional shape 142b that is substantially circular. Such different cross-sections may be due to wear and / or machining errors of the first and second edge rollers 132a, 132b. As a result, the first and second edge rollers 132a, 132b may be separated from one another (perpendicular to the stretch direction 68) by a variable separation distance 144 as the first and second edge rollers 132a, 132b rotate. The variable separation distance 144 may vary depending on the rotational position of each of the first and second edge rollers 132a, 132b. For example, as the first and second edge rollers 132a, 132b rotate about the first and second rotational axes 140a, 140b (see FIG. 2), the rotational positions of each of the first and second edge rollers 132a, 132b change as a function of time depending on the first and second rotational speeds ω1, ω2. As the first and second edge rollers 132a, 132b rotate, the portions of the first and second edge rollers 132a, 132b that are closest to each other in a direction perpendicular to the stretch direction 68 (e.g., the ±y direction shown in FIG. 3) may change. For example, if the first and second rotational speeds ω1, ω2 are of the same magnitude, the variable separation distance 144 may change periodically as a function of the first and second rotational speeds ω1, ω2. The cross-sectional shapes shown for the first and second edge rollers 132a, 132b are merely exemplary. As a result of mechanical wear of the first and second edge rollers 132a, 132b, the surface profile of the rollers may become complex such that the variable separation distance 144 changes as a function of rotational position in a manner different than that shown in FIG. 3B.

[0042] 3B illustrates a plot 300 of the variable separation distance 144 for an example in which the first and second edge rollers 132a, 132b rotate at the same rotational speed. The x-axis of FIG. 3B is normalized time (e.g., as a percentage of the rotational period) and the y-axis illustrates normalized magnitude of the variable separation distance. As shown, the variable separation distance 144 varies according to a sine wave having a period corresponding to the rotational speed of the first and second edge rollers 132a, 132b (e.g., as determined by one or more drive units 137). In one example, the variable separation distance 144 can change as the first and second edge rollers 132a, 132b rotate at the same speed according to a function having multiple frequency components, which vary according to the difference in radial dimensions between the first and second edge rollers 132a, 132b at corresponding angular positions on the first and second edge rollers 132a, 132b (e.g., related to how the first and second edge rollers 132a, 132b are initially aligned prior to actuation by one or more drive units 137).

[0043] Due to the variable separation distance 144, the volume of molten glass in the glass ribbon 12 per unit time across the first edge roller pair 132 can vary as a function of the magnitude of the variable separation distance 144. For example, during a time interval when the first and second edge rollers 132a, 132b are relatively close to each other (e.g., during time interval 304 shown in FIG. 3B), the flow of molten glass 17 between the first and second edge rollers 132a, 132b can be impeded more than when the first and second edge rollers 132a, 132b are relatively far apart (e.g., during time interval 302 shown in FIG. 3B). This non-constant flow of molten glass 17 through the first edge roller pair 132 can result in a variation in thickness of the glass ribbon 12. In the example described herein with respect to FIGS. 3A-3B, the thickness of the glass ribbon 12 near the edge engaged by the first edge roller pair 132 can vary periodically according to a sinusoidal wave as shown in FIG. 3B. These thickness variations (thickness flapping) can render glass sheets cut from the glass ribbon 12 unsuitable for some applications, such as for use in high definition displays. Out-of-roundness of the edge rollers in the apparatus 10 can ultimately lead to thickness flapping of the glass ribbon.

[0044] In light of the above, the apparatus 10 includes a controller 150 communicatively coupled to one or more drive units 137 that controls the rotation of the first and second edge rollers 132a, 132b. The controller 150 can include computer readable instructions stored in a memory 152 and executed by a processor 154. The processor 154 can access these instructions according to an addressing scheme that controls the operation of the first and second edge roller assemblies 130a, 130b according to the methods described herein. The memory 152 can include one or more control modules configured to operate the first and second edge roller assemblies 130a, 130b using a feedback control scheme that utilizes torque signals generated by the one or more drive units 137. For example, in an embodiment in which the one or more drive units 137 include a single drive unit configured to rotate both the first and second shafts 136, 138, the single drive unit can generate a torque signal representative of the total torque generated and transmitted to the first and second edge rollers 132a, 132b. In embodiments where the one or more drive units 137 include a pair of drive units, with each drive unit configured to individually rotate one of the first and second shafts 136, 138, each drive unit may individually generate a torque signal representative of the torque generated and transmitted to each of the first and second edge rollers 132a, 132b. A control module stored in memory 152 may cause the processor 154 to analyze the torque signals generated via the one or more drive units 137 and use the torque signals to control the first and second angular velocities ω1, ω2.

[0045] 4A-4B show plots of the torque sum signal received by the controller 150 of the apparatus 10 described herein with respect to FIGS. 1-3B. FIG. 4A shows a time domain plot 400 of the torque sum signal (e.g., representing the sum of torques applied to the first and second shafts 136, 138 via one or more drive units 137). FIG. 4B shows a period domain (in seconds) transform plot 402 of the torque sum signal shown in FIG. 4A. As shown in FIG. 4B, the torque sum signal includes a dominant periodic component 404 having a period of 12.5 seconds (s). In this example, the dominant periodic component 404 of the torque sum signal coincides with the rotational period of the first and second edge rollers 132a, 132b. Without wishing to be bound by theory, it is believed that the periodicity of the torque sum signal is caused by the variable separation distance 144 (see FIG. 3A). When the variable separation distance 144 is decreasing (or less than the average or median value), it is believed that a relatively higher torque is applied by the one or more drive units 137 to the first and second edge rollers 132a, 132b (e.g., compared to when the variable separation distance 144 is at a minimum value) to maintain rotation of the first and second edge rollers 132a, 132b at the programmed speed due to friction with the glass ribbon 12. When the variable separation distance 144 is increasing (or greater than the median or average value), it is believed that a lower torque is applied to the first and second edge rollers 132a, 132b than when the variable separation distance 144 is decreasing (e.g., compared to when the variable separation distance 144 is at a maximum value). The greater the separation distance, the less friction with the molten glass 17 and the less torque required to maintain the nominal rotation speed.

[0046] In this manner, the torque signal generated by the one or more drive units 137 provides a feedback signal that is a proxy for the magnitude of the variable separation distance 144. With this in mind, and referring back to FIG. 1 , the controller 150 can receive the torque signals, generate a torque sum signal from the torque signals (e.g., in the case where individual torque signals associated with each edge roller are generated by the one or more drive units 137), and time-dependently modulate the first and second rotational speeds ω1, ω2 to counter variations in the torque sum signal. For example, the controller 150 can reduce thickness flapping of the glass ribbon 12 by controlling the operation of the one or more drive units 137 to rotate the first and second shafts 136, 138 at variable speeds to reduce variability in the overall glass pulled between the first and second edge rollers 132a, 132b.

[0047] In an embodiment, the controller 150 periodically modulates the first and second rotational speeds ω1, ω2 of the first and second edge rollers 132a, 132b. In an embodiment, the controller 150 periodically modulates the first and second rotational speeds ω1, ω2 according to: ω T =A*sin(θ 1,2 +Φ)+ω N (1) Here, ω T is a target speed associated with the first rotation speed ω1 and the second rotation speed ω2, A is a modulation amplitude, and θ 1、2 is the angular position of the first edge roller 132a or the second edge roller 132b, Φ is the modulation phase, and ω N is the nominal rotational speed of the first edge roller 132a and the second edge roller 132b (e.g., related to the drawing speed of the glass ribbon 12).

[0048] In an embodiment, the controller 150 adjusts the value θ 1,2ω1, ω2。 For example, in an embodiment, the one or more drive units 137 include an encoder that outputs an electric roll position signal (e.g., voltage, current) that varies proportionally to the rotational position (e.g., in a range of 0° to slightly less than 360°) of the first and second shafts 136, 138 relative to a reference position. The electric roll position signal generated by the encoder of the one or more drive units 137 may vary periodically as a function of the first and second rotational speeds ω1, ω2. In an embodiment, the first and second rotational speeds ω1, ω2 may vary periodically relative to a nominal rotational speed ω1, ω2 (e.g., before modulation). N Corresponding to the nominal rotation speed ω N may be input to the controller 150 as a predetermined input related to the desired draw rate of the glass ribbon 12.

[0049] The angular positions θ of the first edge roller 132a and the second edge roller 132b 1,2 can determine the magnitude of the variable separation distance 144. That is, the angular position θ 1,2 can determine the magnitude of the variable separation distance 144 depending on the cross-sectional shape of the first and second edge rollers 132a, 132b. However, precise geometric information regarding the cross-sectional shape of the first and second edge rollers 132a, 132b may not be available (e.g., the first and second edge rollers 132a, 132b may change shape over long-term operation of the apparatus 10). Thus, an electrical roll position signal generated via one or more drive units 137 may be generated to counteract variations in the variable separation distance 144, ω N In some cases, it may not be sufficient to determine the degree to which the variable separation distance 144 is changing over time to determine the degree of modulation of the signal.

[0050] As described herein with reference to Figures 1, 3A, 3B, 4A and 4B, the periodic variation of the torque sum signal generated via one or more drive units 137 can serve as a proxy for variable separation distance 144. The magnitude of variable separation distance 144 can be estimated by the variation of the torque sum signal about a mean or median value of the torque sum signal. Thus, the torque sum signal can be used to estimate ω in Equation 1. N The modulation degree of the signal can be determined.

[0051] The modulation phase Φ in Equation 1 can determine when the controller 150 modulates the first and second angular velocities ω1, ω2 to a particular degree. The magnitude of the variable separation distance 144 determines the rotational position θ of the first and second edge rollers 132a, 132b, which is related to the magnitude of the torque sum signal as described above. 1,2 Considering that the modulation phase Φ depends on the reference electronic roll position signal, the modulation phase Φ can be determined based on a time delay between the reference electronic roll position signal and the torque sum signal. For example, the time delay between the start of corresponding periods of the torque sum signal and the electronic roll position signal can be used to determine the modulation phase Φ in Equation 1. An example of determining such a time delay is described herein with respect to FIG.

[0052] 4A and 4B, the torque sum signal, which is representative of the torque applied to the first and second edge rollers 132a, 132b via the one or more drive units 137, includes multiple frequency (or periodic) components in addition to a dominant periodic component 404 with a period related to the first and second rotational speeds ω1, ω2. As shown, the torque sum signal also includes multiple low periodic (or high frequency) components 406 and multiple high periodic (or low frequency) components 408.

[0053] In an embodiment, the low-frequency component 406 and the high-frequency component 408 of the torque sum signal may be absent from the electric roll position signal generated by the encoder of the one or more drive units 137 because the electric roll position signal may be independent of the exact geometry of the first and second edge rollers 132a, 132b (and may not include components resulting from mechanical interactions between the rollers). The low-frequency component 406 and the high-frequency component 408 may not be due to radial variations in the edge roller geometry. In an embodiment, the low-frequency component 406 and the high-frequency component 408 are due to mechanical and / or electrical noise. Thus, the phase difference measured between the torque sum signal and the electric roll position signal may vary between successive rotation periods, and therefore the low-frequency component 406 and the high-frequency component 408 may cause inaccuracies in the estimation of the modulation phase Φ described herein. Thus, the controller 150 (see FIG. 1 ) of the apparatus 10 may include filtering logic to filter the torque sum signal generated by the one or more drive units 137. The filtering logic is (for example, the nominal rotation speed ω N A bandpass filter may be implemented to pass a spectral band of interest around component 404 that includes the target at first and second rotational speeds ω1, ω2 (corresponding to

[0054] 5A and 5B show frequency domain plots of a low pass filter portion 500 and a high pass filter portion 504 of a band pass filter used to filter the torque sum signal, according to an example embodiment. The low pass filter portion 500 and the high pass filter portion 504 can be used to filter out a number of low periodic components 406 and high periodic components 408 of the torque sum signal shown in FIGS. 4A-4B. In this example, the dominant periodic component 404 (see FIG. 4B) has a period of 12.5 s, which corresponds to a frequency of 0.08 Hz. As shown in FIG. 5A, the low pass filter portion 500 filters out signal components having frequencies above a cutoff frequency 502 of approximately 0.09 Hz. As shown in FIG. 5B, the high pass filter portion 504 filters out signal components having frequencies below a cutoff frequency 506 of approximately 0.02 Hz. Thus, the frequencies associated with the dominant periodic component 404 (see FIG. 4B) lie between the cutoff frequencies 502 and 506 of the bandpass filters shown in FIGS. 5A-5B.

[0055] In the example shown in FIGS. 5A-5B, the cutoff frequency 502 associated with the low pass filter portion 500 is closer to the dominant periodic component 404 (e.g., in this example, the difference between the cutoff frequency 502 and the frequency of the dominant periodic component 404 is 0.01 Hz) than the cutoff frequency 506 of the high pass filter portion 504 (e.g., in this example, the difference between the cutoff frequency 506 and the frequency of the dominant periodic component 404 is 0.06 Hz). That is, the band pass filter is configured to filter out high frequency components having frequencies greater than 0.01 Hz than the frequency associated with the dominant periodic component 404. Such a configuration may be beneficial because higher frequency components are closer to the dominant frequency component 404 and tend to reduce the accuracy of the modulation phase Φ described herein more than lower frequency components. The cutoff frequencies 502, 506 are configurable parameters and may be selected based on the desired speed of the first and second edge rollers 132a, 132b. In an embodiment, the cutoff frequencies 502, 506 are determined by analyzing the filtered torque sum signal to determine values ​​of the cutoff frequencies 502, 506 that produce consistent results for determining the modulation phase Φ described herein. The particular cutoff frequencies 502, 506 used may vary and may have a different relationship to the dominant periodic component 404 than that shown in Figures 5A-5B.

[0056] With reference to FIG. 1, in an embodiment, filtering the torque signal generated by one or more drive units 137 using a bandpass filter, such as the bandpass filter described herein with respect to FIGS. 5A-5B, can introduce a phase shift into the torque sum signal. Such a filter-induced phase shift can reduce the accuracy of the modulation phase Φ generated using the methods described herein. Thus, in an embodiment, memory 152 can include filter compensation logic configured to phase shift the filtered torque sum signal by an amount necessary to compensate for the filter-induced phase shift associated with the bandpass filter. In an embodiment, the bandpass filter is used to filter multiple torque sum signals that include multiple different dominant frequency components (e.g., different frequencies) and established filtering theory algebraic expressions are used to determine the phase shift of each of the torque sum signals. Using such relationships based on the frequencies associated with the dominant periodic components 404 (see FIG. 4B), the phase shift used to process the filtered torque signal can be calculated.

[0057] FIG. 6A illustrates a time series plot 602 of a raw torque sum signal generated by one or more drive units 137 (see FIG. 1A). FIG. 6B illustrates a time series plot 604 of a filtered torque sum signal, which represents the raw torque sum signal shown in FIG. 6A after being filtered by a bandpass filter as described herein with respect to FIGS. 5A and 5B, and then phase shifted to compensate for the filter-induced phase shift. As shown, the filtered torque sum signal is a generally smooth periodic signal having a period related to the dominant periodic component 404 (see FIG. 4B). As shown in FIG. 6B, the amplitude of the filtered signal varies periodically at a frequency lower than that related to the dominant periodic component 404. Without wishing to be bound by theory, it is believed that such periodic variations in amplitude are the result of mechanical interactions between the first and second edge rollers 132a, 132b. The filtered torque sum signal shown in FIG. 6B provides a baseline for establishing a time delay between the electrical roll position signal generated via the one or more drive units 137.

[0058] 7 illustrates a time series plot 680 including an overlay of a raw torque sum signal 700 generated by the one or more drive units 137, a filtered torque sum signal 702, an electric roll position signal 704 generated via the one or more drive units 137, and a time delay 706 associated with corresponding portions of the filtered torque sum signal 702 and the electric roll position signal 704. As shown in FIG. 7, the electric roll position signal 704 includes a saw tooth function in which the amplitude of the signal varies from a minimum when the rotational position of the one or more drive units 137 is 0° to a maximum when the rotational position of the one or more drive units 137 is just under 360°. The transition between the maximum and minimum values ​​(shown as a vertical line in the electric roll position signal 704) represents the point in time when one of the first and second edge rollers 132a, 132b (see FIG. 1) has completed a rotation.

[0059] 1 and 7, the raw torque sum signal 700 may represent a sum of torque signals generated by one or more drive units 137 during rotation of the first and second edge rollers 132a, 132b. For example, the raw torque sum signal 700 may represent a sum of a first torque signal generated by a first drive unit rotating the first edge roller 132a about the first axis of rotation 140a and a second torque signal generated by a second drive unit rotating the second edge roller 132b about the second axis of rotation 140b. The filtered torque sum signal 702 may be generated by processing the raw torque sum signal 700 with a bandpass filter, such as the bandpass filter described herein with respect to FIGS. 5A and 5B. The raw torque sum signal 700 and the filtered torque sum signal 702 are normalized to a reference value.

[0060] 7, a time delay 706 between the filtered torque sum signal 702 and the electrical roll position signal 704 may be determined by calculating the difference between a first time when one of the first and second edge rollers 132a, 132b completes a rotation (or rotation period) and a second time when the filtered torque sum signal 702 begins a period of fluctuation. In an embodiment, the period of fluctuation begins when the filtered torque sum signal 702 includes an average value of the periodic oscillation of the amplitude of the filtered torque sum signal 702. In an embodiment, the value of the time delay 706 may be converted to a modulation phase Φ as described herein by multiplying the value of the time delay 706 by a dominant frequency of interest as shown by component 404 in FIG. 4B.

[0061] In an embodiment, a value of time delay 706 is calculated for multiple consecutive time periods of each of electric roll position signal 704 and filtered torque sum signal 702, and an average of these values ​​is used to calculate the modulation phase Φ as described herein. Averaging multiple values ​​of time delay 706 over multiple cycles has the benefit of providing a more accurate estimate of the time delay and therefore a calculation of modulation phase Φ that reduces thickness flapping more than embodiments that rely on a single time delay 706 calculation to calculate modulation phase Φ. In an embodiment, controller 150 automatically calculates the value of time delay 706 based on measurement times associated with filtered torque sum signal 702 and electrical roll position signal 704 having particular values ​​(e.g., when filtered torque sum signal 702 includes an average or median value and when electrical roll position signal 704 includes a maximum or minimum value).

[0062] FIG. 8 is a flow diagram of a method 800 for modulating the rotational speed of edge rollers of a glass forming apparatus using a torque sum signal. Method 800 may be performed by controller 150 of apparatus 10 as described herein with respect to FIGS. 1-3. Accordingly, reference is made to various components illustrated in FIGS. 1-3 to aid in describing method 800. As a result of performing method 800, glass ribbon 12 may have a more uniform thickness 166 than would be achieved by operating first and second edge roller assemblies 130a, 130b at a constant rotational speed. Although reference is made here to first edge roller assembly 130a, method 800 may also be performed to control the rotation of edge rollers of second edge roller assembly 130b or other edge roller assemblies in apparatus 10.

[0063] In block 802, the controller 150 receives torque signals associated with edge rollers disposed on either side of the glass ribbon 12. For example, the controller 150 may receive torque signals generated by one or more drive units 137 used to rotate the first and second edge rollers 132a, 132b of the first edge roller assembly 130a described herein. In an embodiment, the controller 150 may receive a single torque signal associated with a particular edge roller pair. For example, in an embodiment, a single drive unit may be used to rotate both the first edge roller 132a and the second edge roller 132b such that a single torque signal (representing a torque sum signal) is received by the controller 150. In such an embodiment, the controller may generate the torque sum signal by receiving a torque signal from a single drive unit.

[0064] In block 804, the controller 150 combines the torque signals received in block 802 into a torque sum signal. For example, in embodiments using separate drive units (e.g., separate motors) to rotate the first and second edge rollers 132a, 132b, each drive unit may generate a torque signal. The controller 150 may receive and combine each separate torque signal into a torque sum signal. The torque sum signal may be filtered using a bandpass filter as described herein with respect to FIGS. 5A-5B to remove frequency components outside a predetermined frequency range associated with a target rotational speed of the first and second edge rollers 132a, 132b (e.g., the target rotational speed may be based on a desired drawing speed of the glass ribbon 12). After filtering, the filtered torque sum signal may be phase shifted based on a predetermined filter-induced phase shift associated with the bandpass filter. This filtered and phase-shifted torque sum signal may then be used to determine the modulation phase Φ, as described herein.

[0065] In block 806, the controller 150 modulates the first and second rotational speeds ω1, ω2 of the first and second edge rollers 132a, 132b in a time-dependent manner to counteract the changes in the torque sum signal. As described herein, time intervals in which the torque sum signal increases over time can indicate that the variable separation distance 144 (see FIG. 3A) is decreasing. During such time intervals, the controller 150 can increase the rotational speeds of the first and second edge rollers 132a, 132b (e.g., increase the first and second rotational speeds ω1, ω2) to maintain the speed at which the glass passes through the first edge roller assembly 130a. Time intervals in which the torque sum signal decreases over time can indicate that the variable separation distance (see FIG. 3B) is increasing. During such time intervals, the controller 150 can decrease the rotational speeds of the first and second edge rollers 132a, 132b (e.g., decrease the first and second rotational speeds ω1, ω2). In an embodiment, the controller 150 can provide control signals to increase or decrease the first and second rotational speeds ω1, ω2 by a predetermined amount (e.g., stored in a look-up table) based on the trend of the torque sum signal. For example, if the torque sum signal increases by a threshold amplitude for a predetermined period (e.g., about ¼ of the rotation period of the first and second edge rollers 132a, 132b), the controller 150 can increase the first and second rotational speeds ω1, ω2 until a decrease in the amplitude of the torque sum signal is detected. The degree of modulation of the first and second rotational speeds ω1, ω2 can be changed in proportion to the degree of increase or decrease of the torque sum signal. Modulating the first and second rotational speeds ω1, ω2 can reduce the effect of the variable separation distance 144 (see FIG. 3A) on the thickness of the glass ribbon over the rotation period of the first and second edge rollers 132a, 132b. This modulation reduces the effect of the first and second edge rollers 132a, 132b not being perfectly round.

[0066] In an embodiment, the controller 150 periodically modulates the first and second rotational velocities ω1, ω2. In such an embodiment, when the controller 150 first receives the torque signal in block 802, the first and second edge rollers 132a, 132b rotate at a nominal target angular velocity ω N The first and second rotational speeds ω1, ω2 may be periodically modulated to allow the first and second edge rollers 132a, 132b to rotate at a speed that depends on their angular position (e.g., as measured by an electrical roll position signal generated by one or more drive units 137 described herein). For example, in an embodiment, the controller 150 rotates the one or more drive units 137 at an angular velocity that varies as a function of the angular position of the first and second edge rollers 132a, 132b. The controller 150 identifies angular positions of the first and second edge rollers 132a, 132b at which the torque sum signal increases and decreases from an average value, and modulates the first and second rotational speeds ω1, ω2 relative to a nominal target angular speed ω depending on the degree to which the torque sum signal differs from the average value at a particular angular position. N It can be raised or lowered above or below.

[0067] In an embodiment, the controller 150 periodically modulates the first and second rotational rates ω1, ω2 according to Equation 1 herein. In such an embodiment, the controller 150 may execute a method 900 shown in FIG. 9 to generate the modulation amplitude A and modulation phase Φ parameter values ​​described herein. In block 902, the controller 150 may determine the modulation phase Φ of Equation 1 based on a time delay between the electric roll position signal and the torque sum signal. For example, the controller 150 may calculate the time delay using a filtered and phase-shifted torque sum signal and an electric roll position signal generated via an encoder associated with one or more drive units 137 using a procedure similar to that described above with respect to FIG. 7 (e.g., by determining the time difference between when the electric roll position signal indicates the start of a rotation period and when the torque sum signal is at an average or median value). In an embodiment, the controller 150 may include validation logic to validate the calculated modulation phase Φ as described herein. For example, the controller may use the estimated modulation phase Φ to phase shift a previously measured torque sum signal using the estimated modulation phase Φ. Controller 150 can compare the phase-shifted torque sum signal to the electrical roll position signal to determine whether the estimated modulation phase Φ meets a tolerance, and if not, can re-estimate the modulation phase Φ by measuring additional cycles of the torque sum signal and the electrical roll position signal.

[0068] At block 904, the controller 150 may determine the modulation amplitude A of Equation 1. The modulation amplitude A may be determined using a trial and error method of incrementally increasing the modulation amplitude A. During the period in which the modulation amplitude A is held constant, the controller 150 may monitor the thickness 166 (e.g., using measurements from the thickness sensor 160). For example, the controller 150 may continuously monitor the thickness 166 and determine the thickness range of the glass ribbon 12 over a predetermined measurement period (e.g., 5 seconds, 10 seconds, 30 seconds, 1 minute, 3 minutes, 5 minutes, 10 minutes, 30 minutes, 1 hour, 2 hours). This measured thickness range may be compared to a previously measured value associated with a previous modulation amplitude A. If a decrease in the thickness range is measured, the controller 150 may increase the modulation amplitude A by a predetermined increment (e.g., 0.1, 0.2, 0.3, 0.4) and determine whether the increase in modulation amplitude A results in a further decrease in the thickness range. If an increase in thickness range is observed with a particular value of modulation amplitude A, controller 150 may decrease modulation amplitude A to a previous value (e.g., the last value of modulation amplitude A at which a decrease in thickness range was observed). Controller 150 may gradually increase modulation amplitude A using fixed or variable increments until a decrease in thickness variation (or range) is no longer observed. The increments used by controller 150 to update modulation amplitude A may vary depending on the degree of decrease in the observed thickness variation. EXAMPLES

[0069] The embodiments described herein are further clarified by the following examples. Figure 10 shows a plot 1000 of experimental results of modulating the rotational speed of an edge roller using Equation 1 herein. The experimental results were achieved during the manufacture of Corning Lotus® NXT glass. The modulation phase Φ was determined using the method described herein with respect to Figure 7. Line 1002 in plot 1000 represents a moving window range of measured glass ribbon thickness. Vertical lines 1006, 1008, 1010, 1012, 1014, 1016, 1018, and 1020 represent the time points at which the modulation amplitude A was increased according to the method 900 described herein with respect to Figure 9.

[0070] During the period to the left of vertical line 1006, the edge roller rotational speed was not modulated. As shown, the thickness moving window range was greater than or equal to 4 micrometers (μm) throughout substantially the entire period. Between vertical lines 1006 and 1008, the modulation amplitude A was set to 0.3. This resulted in a thickness moving window range of less than 4 μm during this time window. Thus, at vertical line 1008, the modulation amplitude A was increased to 0.5, which further reduced the thickness moving window range. This reduction in the thickness moving window range continued to be observed until the modulation amplitude was set to 0.9 after vertical line 1012. Between vertical lines 0.9 and 1.1, the thickness moving window range was measured to be less than 3.0 μm, a significant improvement over the unmodulated case. At vertical line 1014, the modulation amplitude A was increased to 1.1, which increased the thickness moving window range from the thickness moving window range when the modulation amplitude A was 0.9. Further increasing the modulation amplitude A to 1.3 at vertical line 1016 further increased the thickness moving window range. Thus, decreasing the modulation amplitude A to 1.1 at vertical line 1018 again observed a decrease in the thickness moving window range compared to when the modulation amplitude A was 1.3. Thus, further decreasing the modulation amplitude A to 0.9 observed an initial minimum thickness moving window range. This example illustrates how the modulation amplitude A can be determined to significantly reduce thickness variation in a glass ribbon.

[0071] Thus, a method of operating a drive unit for edge rollers of a glass manufacturing apparatus has been shown and described. Time-dependent modulation of the rotational speed of the edge rollers to counter the observed variations in the torque sum signal has been shown to substantially reduce thickness flapping caused by edge rollers having different cross-sectional shapes. The torque sum signal usefully serves as a proxy for the variable separation distance between the edge rollers due to the different cross-sectional shapes of the edge rollers, and indicates periods during which the thickness variations in the glass ribbon can be reduced by increasing or decreasing the rotational speed of the edge rollers from a nominal target speed to maintain glass flow through the edge rollers, resulting in a glass sheet of more uniform thickness.

[0072] It will be apparent to those skilled in the art that various modifications and variations can be made to the embodiments described herein without departing from the spirit and scope of the claimed subject matter. Accordingly, this specification is intended to cover modifications and variations of the various embodiments described herein, provided such modifications and variations come within the scope of the appended claims and their equivalents. [Explanation of symbols]

[0073] 12 Glass Ribbon 17 Molten Glass 60 Molded containers 62 Molded Wedge 64a End of forming wedge 66a, 66b forming surface portion of forming wedge 70 Base 72 Stretched surface 110b a second major surface of the glass ribbon 130a First edge roller assembly 132 1st edge roller pair 132a first edge roller 132b second edge roller 136 First Shaft 137 Drive Unit 138 Second Shaft 140a first rotation axis 140b Second rotation axis 160 Thickness Sensor 166 Glass ribbon thickness 170 Measurement position

Claims

1. 1. A method for making glass, comprising the steps of: forming a glass ribbon from a quantity of molten material, the glass ribbon including a first surface and a second surface; contacting the first surface with a first edge roller and the second surface with a second edge roller; rotating the first edge roller at a first rotational speed and rotating the second edge roller at a second rotational speed; generating a first torque signal representative of a torque applied to the first edge roller and a second torque signal representative of a second torque applied to the second edge roller; generating a torque sum signal of the first torque signal and the second torque signal; modulating the first rotational speed and the second rotational speed in a time dependent manner to counter fluctuations in the torque sum signal; The method according to claim 1, further comprising:

2. The time dependent modulating of the first rotational speed and the second rotational speed is performed according to the following equation: oh T =A*sin(θ 1,2 +Φ)+ω N 、 Using the target rotation speed ω T and periodically modulating the first rotational speed and the second rotational speed by calculating where A is the modulation amplitude and Θ 1、2 is the angular position of the first edge roller or the second edge roller, Φ is the modulation phase, and ω N is the target rotation speed of the first edge roller and the second edge roller; The method of claim 1.

3. determining a time delay between a roll position signal representative of said angular position and said torque sum signal; converting the time delay into a phase angle; determining the modulation phase by The method of claim 2.

4. and filtering the torque sum signal using a bandpass filter having an upper cutoff frequency and a lower cutoff frequency prior to determining the modulation phase; N is between the upper cutoff frequency and the lower cutoff frequency, The method according to claim 3.

5. sensing a thickness of the glass ribbon downstream of the first edge roller and the second edge roller; determining the modulation amplitude A based on a thickness of the glass ribbon; The method of claim 2 , further comprising:

6. Determining the modulation amplitude A comprises: periodically modulating the first rotation rate and the second rotation rate using a first value of the modulation amplitude A; determining whether the first value results in a decrease in thickness variation of the glass ribbon; and if the first value results in a decrease in thickness variation of the glass ribbon, increasing the modulation amplitude A until the decrease in thickness variation is no longer observed; The method of claim 5 , comprising:

7. Modulating the first rotational speed and the second rotational speed to counteract variations in the torque sum signal includes: decreasing at least one of the first rotational speed and the second rotational speed during a period when the separation distance is increasing; increasing at least one of the first rotational speed and the second rotational speed during a period when the separation distance is decreasing; Including, The method of claim 1 , wherein the separation distance is the distance between the first edge roller and the second edge roller.

8. modulating the first rotational speed and the second rotational speed to counteract variations in the torque sum signal reduces a moving window thickness range of the glass ribbon achieved when the first rotational speed and the second rotational speed are not modulated. The method of claim 1.

9. 1. A method for making glass, comprising the steps of: forming a glass ribbon from a quantity of molten material, the glass ribbon including a first surface and a second surface; contacting the first surface with a first edge roller and the second surface with a second edge roller, the first edge roller and the second edge roller having different cross-sectional shapes such that a separation distance between the first edge roller and the second edge roller varies periodically depending on the speed at which the first edge roller and the second edge roller rotate; driving the first edge roller and the second edge roller at a first rotational speed and a second rotational speed, respectively; generating a torque sum signal representative of a total torque applied to the first edge roller and the second edge roller; determining a time delay between the torque sum signal and an electrical roll position signal representative of one or both of a first rotational position and a second rotational position; updating the first rotational velocity and the second rotational velocity based on the time delay, the first rotational position, and the second rotational position; The method according to claim 1, further comprising:

10. 1. A glass manufacturing apparatus comprising: a former configured to form a glass ribbon from a quantity of molten material, the former defining a draw path extending from the former along which the glass ribbon can be formed; an edge roll assembly including an edge roller pair including a first edge roller having a first cross-sectional shape and a second edge roller having a second cross-sectional shape, the first cross-sectional shape being different from the second cross-sectional shape such that the first edge roller and the second edge roller are separated from each other by a separation distance that varies depending on the speed at which the first edge roller and the second edge roller rotate; one or more drive units mechanically coupled to the first edge roller and the second edge roller, configured to rotate the first edge roller at a first rotational speed about a first axis of rotation and the second edge roller at a second rotational speed about a second axis of rotation, and further configured to generate a first torque signal representative of a first torque applied to the first edge roller and a second torque signal representative of a second torque applied to the second edge roller; communicatively coupled to the one or more drive units; generating a torque sum signal from the first torque signal and the second torque signal; using the torque sum signal to modulate the first rotational speed and the second rotational speed such that the first rotational speed and the second rotational speed are inversely proportional to the variable separation distance; a controller operable to A glass manufacturing apparatus comprising:

11. a thickness sensor configured to sense a thickness of the glass ribbon downstream of the first edge roller and the second edge roller, the controller being operable to modulate the first rotational speed and the second rotational speed based on a thickness of the glass ribbon. The glass manufacturing apparatus of claim 10.

12. the controller is operable to periodically modulate the first rotational speed and the second rotational speed using a modulation phase calculated based on a time delay between the torque sum signal and an electric roll position signal generated by the one or more drive units, the electric roll position signal representing a rotational position of at least one of the first edge roller or the second edge roller. The glass manufacturing apparatus of claim 11.

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