WO2011146368A2

WO2011146368A2 - Fusion draw method ribbon position control scheme

Info

Publication number: WO2011146368A2
Application number: PCT/US2011/036604
Authority: WO
Inventors: Jonghak Kim; Hung Cheng Lu; James P. Peris
Original assignee: Corning Incorporated
Priority date: 2010-05-20
Filing date: 2011-05-16
Publication date: 2011-11-24
Also published as: WO2011146368A3; JP2013533191A; CN102906035B; CN102906035A; TWI496749B; TW201144239A; JP5782507B2; KR101811900B1; KR20130090781A

Abstract

A glass manufacturing system for forming a continuously moving ribbon of glass comprising a fixed roll, a floating roll, a first sensor, a second sensor, a controller and a mechanism operably connected to the controller. The fixed and floating rolls include a fixed axis of rotation with an initial fixed location and a floating axis of rotation with an initial floating location, respectively. The fixed and floating rolls are oriented parallel to one another so as to be a predetermined distance apart with the continuously moving ribbon of molten glass disposed therebetween. The first sensor is configured to monitor a location of the fixed axis. The second sensor is configured to monitor a location of the floating axis. The controller is in communication with the first sensor and the second sensor. The mechanism is operably configured to move the fixed roll when a difference between an initial location of the floating axis and a subsequent location of the floating axis exceeds a predetermined value.

Description

FUSION DRAW METHOD RIBBON POSITION CONTROL SCHEME

CLAIMING BENEFIT OF PRIOR FILED U.S. APPLICATION

[0001] This application claims the benefit of priority under 35 U.S.C. § 1 19 of U.S.

Provisional Application Serial No. 61/346,537, filed on May 20, 2010. The content of this document and the entire disclosure of publications, patents, and patent documents mentioned herein are incorporated by reference.

FIELD

[0002] The present disclosure relates to a fusion draw machine and, more specifically, apparatus and methods of controlling a ribbon position in a fusion draw machine.

BACKGROUND

[0003] Fusion draw machines utilize rolls that guide a ribbon of molten glass. Because even slight variations in the location of the rolls can affect the attributes of the manufactured glass sheets, there is a need for a method or an apparatus that can reduce, correct or prevent such variations.

SUMMARY

[0004] The following present a simplified summary of the disclosure in order to provide a basic understanding of some example aspects described in the detailed description.

[0005] In one example aspect, a method of making a glass sheet is provided and includes the steps of forming a ribbon of molten glass with a glass manufacturing system comprising a fixed roll with a fixed axis of rotation and a floating roll with a floating axis of rotation, the fixed roll and the floating roll arranged parallel to one another such that the fixed and floating rolls are a predetermined distance apart, the fixed and floating rolls adapted to draw the ribbon of molten glass between the rolls, the fixed axis of rotation including an initial fixed location and the floating axis of rotation including an initial floating location; detecting a second location of the floating axis; and executing a position control scheme if a difference between the second location of the floating axis and the initial floating location of the floating axis exceeds a predetermined value. The position control scheme includes the steps of determining a final target location of the fixed axis based on a first set of one or more factors including the second location of the floating axis; determining a correction amount by which the fixed axis is to be moved to reach the final target location; and moving the fixed axis by the correction amount to the final target location of the fixed axis.

[0006] A glass manufacturing apparatus for producing a continuously moving ribbon of glass is provided and comprises a fixed roll, a floating roll, a first sensor, a second sensor, a controller and a mechanism. The fixed roll comprises a fixed axis of rotation with an initial fixed location. The floating roll comprises a floating axis of rotation with an initial floating location. The fixed and floating rolls oriented parallel to one another so as to be a predetermined distance apart. The first sensor is configured to monitor a location of the fixed axis. The second sensor is configured to monitor a location of the floating axis. The controller is in communication with the first sensor and the second sensor. The mechanism is operably connected to the controller and is configured to move the fixed roll when a difference between the location of the floating axis and the initial floating location exceeds a predetermined value.

BRIEF DESCRIPTION OF THE DRAWINGS

[0007] These and other features, aspects and advantages of the present disclosure are better understood when the following detailed description is read with reference to the

accompanying drawings, in which:

[0008] FIG. 1 is a schematic representation of a glass manufacturing system with a pull roll assembly;

[0009] FIG. 2 is a schematic representation of the pull roll assembly including a plurality of pairs of rolls to which an apparatus and a method discussed herein can be implemented;

[0010] FIG. 3A schematically shows a first embodiment of the apparatus for sensing and controlling locations of a fixed roll and a floating roll;

[0011] FIG. 3B schematically shows a second embodiment of the apparatus for sensing and controlling locations of the fixed roll and the floating roll;

[0012] FIG. 4A shows locations of the fixed roll and the floating roll prior to operation;

[0013] FIG. 4B shows locations of the fixed roll and the floating roll altered by roll wear;

[0014] FIG. 4C shows locations of the fixed roll and the floating roll realigned using the apparatus and the method discussed herein; [0015] FIG. 5A is a flow chart showing a control logic by which the fixed roll and the floating roll are realigned based on estimated roll wear; and

[0016] FIG. 5B is a flow chart showing a control logic by which the fixed roll and the floating roll are realigned based on estimated roll wear and ribbon position.

DETAILED DESCRIPTION

[0017] High quality thin glass sheets for use in flat panel displays can be produced through a fusion process such as an overflow downdraw process. FIG. 1 shows an example

embodiment of a glass manufacturing system 10, or a fusion draw machine, more

specifically, that implements the fusion process for manufacturing a glass sheet 17. The glass manufacturing system 10 may include a melting vessel 12, a fining vessel 14, a mixing vessel 16 (e.g., the illustrated stir chamber), a delivery vessel 18 (e.g., the illustrated bowl), a forming vessel 20 (e.g., the illustrated isopipe), a pull roll assembly 22 and a traveling anvil machine 24 (TAM).

[0018] The melting vessel 12 is where the glass batch materials are introduced as shown by arrow 26 and melted to form molten glass 13. The fining vessel 14 has a high temperature processing area that receives the molten glass 13 from the melting vessel 12 and in which bubbles are removed from the molten glass 13. The fining vessel 14 is connected to the mixing vessel 16 by a finer to stir chamber connecting tube 28. Thereafter, the mixing vessel 16 is connected to the delivery vessel 18 by a stir chamber to bowl connecting tube 30. The delivery vessel 18 delivers the molten glass 13 through a downcomer 32 to an inlet 34 and into the forming vessel 20. The forming vessel 20 includes an opening 36 that receives the molten glass 13 which flows into a trough 38 and then overflows and runs down two sides of the forming vessel 20 before fusing together at what is known as a root 40. The root 40 is where the two sides come together and where the two overflow walls of molten glass 13 rejoin before being drawn downward by the pull roll assembly 22 to form the glass ribbon 15. Then, the TAM 24 scores the drawn glass ribbon 15 which is then separated into individual glass sheets 17.

[0019] As shown in FIG. 2, the pull roll assembly 22 may include a plurality of sets of rolls that are provided along the edges of ribbon 15 of molten glass for guiding the ribbon 15 in a downward direction and a controller 54 that controls the operation of the rolls. One set of rolls provided at a predetermined location along the ribbon 15 of the molten glass includes a pair of rolls at a first end 56 and a pair of rolls located oppositely at a second end 58. The pull roll assembly 22 may include sets of edge rolls (ER) 42, 44, driven stub rolls (DSR) 46, 48 and/or idle stub rolls (ISR) 50, 52 that are disposed in a downstream direction along the ribbon 15 of molten glass. The sets of rolls generally may be arranged in the following order in a downstream direction: ER, DSR and ISR. The rolls may be embodied in a variety of manners. For example, each of the rolls may include a longitudinal axis that is horizontally oriented, as shown for the rolls 42, 44 and the rolls 50, 52. Additionally, the pair of rolls on first end 56 and the pair of rolls on a second end 58 may be in operative connection with one another so that the rolls on each side of the ribbon 15 rotate as one, as shown for the rolls 50, 52. Alternatively, the longitudinal axis of each of the rolls may be downwardly tilted, for example, as shown for the rolls 46, 48. While the ER, DSR and ISR are shown in FIG. 2 as having a particular configuration, the horizontal, downwardly tilted or operatively connected configuration may be applicable to any set of rolls. Moreover, as discussed more fully below, the horizontal or downwardly tilted rolls can include a fixed roll and a floating roll that are arranged parallel to one another.

[0020] As shown in FIG. 3A-3B, two embodiments of a mechanism 21 are provided that moves the longitudinal axes of the rolls in the pull roll assembly 22 based on communication with the controller 54. Each pair of rolls includes a fixed roll 60 with a fixed axis 62 of rotation and a floating roll 64 with a floating axis 66 of rotation and the rolls 60, 64 are arranged parallel to one another a predetermined distance apart. The ribbon 15 is drawn between the fixed roll 60 and the floating roll 64, and the rotational directions of the fixed roll 60 and the floating roll 64 are such that the rolls 60, 64 direct the ribbon 15 of glass in a downward direction. As shown in FIG. 4A, prior to the start of rotation, the fixed roll 60 and the floating roll 64 are at an initial fixed location 68 and an initial floating location 70. For example, the initial fixed location 68 and the initial floating location 70 can be points Xi and X₂ respectively on an axis.

[0021] During operation of the glass manufacturing system 10, the floating roll 64 can float in that the floating axis 66 can move in response to forces applied to the floating roll 64. This can be enabled, for example, by a mechanism 23, shown to the right of the ribbon 15 in

FIGS. 3A-3B, where the floating roll 64 applies a constant amount of force against the ribbon 15 of glass while the fixed roll 60 applies an equal amount of reactive force in the opposite direction against the ribbon 15. In this mechanism 23, an L-shaped member 72 is configured to pivot about a fixed point 74 and includes, on a first end 76, a weight 78 and, on a second end 80, a second link 82 that is pivotably coupled thereto and is configured to move in a substantially linear fashion or horizontally in FIGS. 3A-3B. The weight 78 thus biases the L-shaped member 72 to rotate clockwise and the second link 82 to move toward the ribbon 19 so as to apply a constant amount of force against the ribbon 15. The amount of force applied to the ribbon 15 may be altered by changing the weight 78. In comparison, the location of the fixed roll 60 is fixed unless a mechanism 25, such as a motor 84, a gear box and a belt drive (FIG. 3A) or a servo-mechanism such as linear actuator 86 (FIG. 3B), is operated to change the location. In FIG. 3A, the motor 84 can rotate an arm 88 in either clockwise or counterclockwise direction thus moving a first link 90, which is pivotably connected to the arm 88 and is configured to move in a substantially linear fashion, toward and away from the ribbon 19. In FIG. 3B, the movement of the first link 90 is controlled by the linear actuator 86 which can be powered electrically, hydraulically, pneumatically or the like. The substantially linear movement of the fixed roll 60 is partly illustrated in phantom in FIGS. 3A-3B and the floating roll 64 can also move in a similar fashion.

[0022] As further shown in FIGS. 3A-3B, the locations of the fixed axis 62 and the floating axis 66 may be detected by a first sensor 92 and a second sensor 94 respectively. The first and second sensors 92, 94 can detect or monitor the locations of the fixed axis 62 and the floating axis 66 respectively along a line and may be embodied as cable transducers or string potentiometers. Moreover, the locations of the fixed axis 62 and the floating axis 66 may be altered by way of translation such that orientations of the axes 62, 66 are unchanged.

Additionally, the glass manufacturing system 10 may be equipped with a measurement device 96 adjacent the area where the pull roll assembly 22 is located as shown in FIGS. 3A- 3B. The measurement device 96 may be configured to measure the ribbon position at various points across a draw of the ribbon 19 and may utilize ultraviolet rays for the measurements. The measurement device 96 may be located near a setting zone of the ribbon 19 where the product stress and flatness of the glass sheet are determined.

[0023] As shown in FIGS. 4A-4B, the method and apparatus discussed herein are provided to allow realignment of the fixed roll 60 and the floating roll 64 in circumstances where the floating roll 64 has diverted from a properly aligned location due to changes in operating conditions, arising from, for example, roll wear, which may lead to inconsistencies in the shape of the ribbon 15. FIG. 4A shows the ribbon 15 drawn downward through the upstream edge rolls 42, 44 and the driven stub rolls 46, 48 (or the idle stub rolls 50, 52) in a vertically straight configuration. FIG. 4A thus shows properly aligned locations for the fixed roll 60 and the floating roll 64 (i.e., the initial fixed location 68 and the initial floating location 70). The fixed roll 60 and the floating roll 64 may be part of either the driven stub rolls 46, 48 or the idle stub rolls 50, 52. In FIG. 4B, the fixed roll 60 and the floating roll 64 are in misaligned locations because the diameters of the rolls 60, 64 have decreased through usage or wear. As described above, while the location of the fixed axis 62 is unchanged by roll wear, the location of the floating axis 66 has shifted toward the left in FIG. 4B because the floating roll 64 is configured to maintain a constant force against the ribbon 15. This causes the ribbon 15 to deviate from the vertical and straight configuration, indicated by a dotted line in FIG. 4B, and it becomes necessary to realign the rolls 60, 64 such that ribbon 19 will be drawn in the desired vertical and straight manner, as shown in FIG. 4C.

[0024] FIG. 5A shows a first embodiment of a position control scheme 100 (i.e., "a feedforward control scheme") for adjusting the locations of the rolls 60, 64 such that a vertical and straight ribbon draw is achieved. The position control scheme 100 represents a looped method or control logic by which the controller 54 adjusts the locations of the axes 62, 66 of the rolls 60, 64. It must also be noted that the controller 54 can be a single processing apparatus or multiple discrete apparatuses operating in conjunction with the pull roll assembly 22. The controller 54 is in electrical communication with the sensors 92, 94 and the measurement device 96. The position control scheme 100 may be configured to be executed whenever the location of the floating axis 66 is offset from the initial floating location 70 by an amount exceeding a predetermined value thereby controlling the frequency of adjustment. In the first embodiment of the position control scheme 100, the location of the floating axis 66 is measured by the second sensor 94 at step 114 and is relayed to adder- subtractor 106 and estimator 102. The estimator 102 may include an algorithm for estimating roll wear rw_e based on the detected location >_r of the floating axis 66 that was measured by the second sensor 94. The estimated roll wear rw_e is likely to be great if the deviation of the detected location >_r of the floating axis 66 from the initial floating location 70 is great. The location of the fixed axis 62 is unchanged by the use of the rolls 60, 64 and only the location of the floating axis 66 is altered as the rolls 60, 64 wear out and the diameters of the rolls 60, 64 thus become smaller. For example, the fixed axis 62 and the floating axis 66 can be shifted to points Xi and X₂-d respectively from the initial fixed location 68 and the initial floating location 70, and the second sensor 94 would detect that the floating axis 66 has moved toward the left by a distance d. Based on such detection, assuming each of the rolls 60, 64 undergo the same amount of roll wear over time, the estimator 102 may determine that a roll wear of d/2 is attributable to each of the fixed roll 60 and the floating roll 64, and the controller 54 may determine that the fixed axis 62 and the floating axis 66 need to be moved by d/2 to the right in FIG. 4B or i.e., points Xi+d/2 and X₂-d/2 to accomplish a vertical and straight orientation of the ribbon 19. Then, based on the location of the floating axis 66, the estimated roll wear rw_e from the estimator 102 is relayed to an outer-loop feed forward controller 104 which generates a first auxiliary target location u/_d of the fixed axis 62. Next, at the adder- subtractor 106, a final target location w of the fixed axis 62 is determined based on the first auxiliary target location u/d of the fixed axis 62 from the outer-loop feed forward controller 104 and the detected location >_r of the floating axis 66 from step 114. For example, a value of the final target location u/ may be equal to the first auxiliary target location u/d minus the detected location >_r of the floating axis 66, as shown in FIG. 5A. Next, an inner- loop feedback controller 108 generates, based on the final target location u/θΐ the fixed axis 62 from the adder- subtractor 106, a correction amount u_r by which the fixed axis 62 must be moved from its present location. At step 110, a second set of factors d which may be disturbance factors representing effects arising from waves propagating upward from the TAM, a flow rate of molten glass, a process drift arising from temperature, etc. can be input for consideration in the position control scheme 100. Thereafter, at step 112, the second set of factors can be taken into account to further adjust the correction amount u_r, and the location of the fixed axis 62 can be moved by the correction amount u_r to realign the rolls 60, 64. Step 112 can also accumulate as data the correction amount u_r, disturbance factors d and detected location >_r of the floating axis 66 so that a physical, mathematical or other relationship between these parameters can be determined. Then, the entire position control scheme 100 can be repeated starting from step 114.

[0025] FIG. 5B shows a second embodiment of the position control scheme 101 for adjusting the locations of the rolls 60, 64. The second embodiment (i.e., "a feed-forward and feedback control scheme") includes the first embodiment of the position control scheme 101, which is enclosed within a dotted line, and incorporates a measurement of a ribbon position j¾ into the position control scheme 101. At step 118, the ribbon position j¾ is detected by the measurement device 96 as described above and is relayed to adder- subtractor 122. The adder-subtractor 122 is also input with a reference ribbon position r which is provided by a reference block 120. The adder-subtractor 122 thus determines an error amount r-j¾ by which the ribbon 15 is offset from the reference ribbon position r by subtracting the detected ribbon position j¾ from the reference ribbon position r. The error amount r-j¾ is then relayed to an outer-loop feedback controller 124 which determines a second auxiliary target location up. The second auxiliary target location up is then relayed to adder-subtractor 106 which subtracts the detected location >_r of the floating axis 66 from the sum of the first auxiliary target location u/_d and the second auxiliary target location up to obtain the final target location w of the fixed axis 62. Thus, the second embodiment of the position control scheme 101 differs from the first embodiment in that the final target location w of the fixed axis 62 is determined by further taking into account the ribbon position j¾. Moreover, in the second embodiment, step 116 can also accumulate as data the ribbon position j¾ and the detected location >_r of the floating axis 66 so that a physical, mathematical or other relationship between these parameters can be determined. Furthermore, a relationship between the ribbon position j¾, the DSR roll position and the ISR roll position can also be determined from the obtained data. Then, the entire position control scheme 101 can be repeated at step 118

[0026] Exemplary, non-limiting embodiments include:

[0027] CI . A method of making a glass sheet comprising: forming a ribbon of molten glass with a glass manufacturing apparatus comprising a fixed roll with a fixed axis of rotation and a floating roll with a floating axis of rotation, the fixed roll and the floating roll arranged parallel to one another such that the fixed and floating rolls are a predetermined distance apart, the fixed and floating rolls adapted to draw the ribbon of molten glass between the rolls, the fixed axis of rotation including an initial fixed location and the floating axis of rotation including an initial floating location; detecting a second location of the floating axis; and executing a position control scheme if a difference between the second location of the floating axis and the initial floating location of the floating axis exceeds a predetermined value, the position control scheme comprising the steps of: determining a final target location of the fixed axis based on a first set of one or more factors including the second location of the floating axis; determining a correction amount by which the fixed axis is to be moved to reach the final target location; and moving the fixed axis by the correction amount to the final target location of the fixed axis.

[0028] C2. The method of CI, wherein the position control scheme comprises the step of estimating roll wear based on the second location of the floating axis, the first set of factors further including roll wear.

[0029] C3. The method of CI or C2, wherein the glass manufacturing apparatus further comprises a measurement device configured to detect a second ribbon position relative to an initial ribbon position, the first set of factors further including the second ribbon position.

[0030] C4. The method of C3, wherein executing the position control scheme comprises the steps of estimating the roll wear based on the second location of the floating axis, and determining a first auxiliary target location of the fixed axis based on the roll wear, the first set of factors further including the second location of the floating axis, the second ribbon position and the roll wear, the position control scheme further comprising the step of determining a second auxiliary target location of the fixed axis based on the second ribbon position, the final target location defined as the second location of the floating axis subtracted from the sum of the first auxiliary target location and the second auxiliary target location.

[0031] C5. The method of any of CI to C4, wherein the position control scheme further comprises the step of adjusting the correction amount based on a second set of one or more factors.

[0032] C6. The method of C5, wherein the second set of factors comprises at least one disturbance factor.

[0033] C7. The method of any of CI to C6, wherein the glass manufacturing apparatus comprises driven stub rolls and idle stub rolls, and the fixed roll and the floating roll controlled by the method are part of at least one of the driven stub rolls and the idle stub rolls.

[0034] C8. The method of any of CI to C7, wherein the predetermined value is adjustable to control a frequency at which the position control scheme is executed.

[0035] C9. The method of any of CI to C8, wherein, if a difference between the second location of the floating axis and the initial location of the floating axis is represented as a vector having a given value in a given direction with an initial point located at the initial floating location, and wherein the correction amount is one half of the given value in a direction substantially opposite the given direction.

[0036] CIO. The method of any of CI to C9, wherein the step of moving the fixed axis is by way of translation.

[0037] CI 1. A glass manufacturing apparatus for producing a continuously moving ribbon of glass comprising: a fixed roll comprising a fixed axis of rotation with an initial fixed location; a floating roll comprising a floating axis of rotation with an initial floating location, the fixed and floating rolls oriented parallel to one another so as to be a predetermined distance apart; a first sensor configured to monitor a location of the fixed axis; a second sensor configured to monitor a location of the floating axis; a controller in communication with the first sensor and the second sensor; and a mechanism operably connected to the controller and configured to move the fixed roll when a difference between the location of the floating axis and the initial floating location exceeds a predetermined value.

[0038] C12. The apparatus of CI 1, wherein, during operation of the apparatus in which the fixed roll and the floating roll draw the ribbon of molten glass between the rolls, the location of the fixed axis is fixed and the location of the floating roll is floating such that a constant amount of force is applied by the floating roll on the ribbon.

[0039] C13. The apparatus of CI 1 or C12, wherein the controller moves the fixed roll by a correction amount.

[0040] C14. The apparatus of any of CI 1 to C13, wherein the mechanism includes a servo- mechanism.

[0041] C15. The apparatus of any of CI 1 to C14, wherein the first sensor and the second sensor include a string potentiometer.

[0042] CI 6. The apparatus of any of Cl l to C15, furthering comprising a measurement device configured to measure a second ribbon position relative to an initial ribbon position.

[0043] CI 7. The apparatus of CI 6, wherein the measurement device emits ultraviolet radiation.

[0044] C18. The apparatus of any of CI 1 to C17, further comprising driven stub rolls and idle stub rolls, the fixed roll and the floating roll controlled by the method being part of at least one of the driven stub rolls and the idle stub rolls. [0045] It will be apparent to those skilled in the art that various modification and variations can be made to the present disclosure without departing from spirit and scope of the invention. Thus, it is intended that the present invention cover the modifications and variations of this disclosure provided they come within the scope of the appended claims and their equivalents.

Claims

CLAIMS What is claimed is:

1. A method of making a glass sheet (17) comprising:

forming a ribbon of molten glass (15) with a glass manufacturing apparatus comprising a fixed roll (60) with a fixed axis of rotation (62) and a floating roll (64) with a floating axis of rotation (66), the fixed roll and the floating roll arranged parallel to one another such that the fixed and floating rolls are a predetermined distance apart, the fixed and floating rolls adapted to draw the ribbon of molten glass between the rolls, the fixed axis of rotation including an initial fixed location and the floating axis of rotation including an initial floating location;

detecting a second location of the floating axis; and

executing a position control scheme if a difference between the second location of the floating axis and the initial floating location of the floating axis exceeds a predetermined value, the position control scheme comprising the steps of:

determining a final target location of the fixed axis based on a first set of one or more factors including the second location of the floating axis;

determining a correction amount by which the fixed axis is to be moved to reach the final target location; and

moving the fixed axis by the correction amount to the final target location of the fixed axis.

2. The method of claim 1, wherein the position control scheme comprises the step of estimating roll wear based on the second location of the floating axis, the first set of factors further including roll wear.

3. The method of claim 1 or claim 2, wherein the glass manufacturing apparatus further comprises a measurement device (96) configured to detect a second ribbon position relative to an initial ribbon position, the first set of factors further including the second ribbon position.

The method of claim 3, wherein executing the position control scheme comprises the steps of estimating the roll wear based on the second location of the floating axis, and determining a first auxiliary target location of the fixed axis based on the roll wear, the first set of factors further including the second location of the floating axis, the second ribbon position and the roll wear, the position control scheme further comprising the step of determining a second auxiliary target location of the fixed axis based on the second ribbon position, the final target location defined as the second location of the floating axis subtracted from the sum of the first auxiliary target location and the second auxiliary target location.

The method of any of claims 1 to 4, wherein the position control scheme further comprises the step of adjusting the correction amount based on a second set of one or more factors.

The method of claim 5, wherein the second set of factors comprises at least one disturbance factor.

The method of any of claims 1 to 6, wherein the glass manufacturing apparatus comprises driven stub rolls (46, 48) and idle stub rolls (50, 52), and the fixed roll and the floating roll controlled by the method are part of at least one of the driven stub rolls and the idle stub rolls.

The method of any of claims 1 to 7, wherein the predetermined value is adjustable to control a frequency at which the position control scheme is executed.

The method of any of claims 1 to 8, wherein, if a difference between the second location of the floating axis and the initial location of the floating axis is represented as a vector having a given value in a given direction with an initial point located at the initial floating location, and wherein the correction amount is one half of the given value in a direction substantially opposite the given direction.

10. The method of any of claims 1 to 9, wherein the step of moving the fixed axis is by way of translation.

11. A glass manufacturing apparatus for producing a continuously moving ribbon of glass (15) comprising:

a fixed roll (60) comprising a fixed axis of rotation (62) with an initial fixed location;

a floating roll (64) comprising a floating axis of rotation (66) with an initial floating location, the fixed and floating rolls oriented parallel to one another so as to be a predetermined distance apart;

a first sensor configured to monitor a location of the fixed axis; a second sensor configured to monitor a location of the floating axis;

a controller (54) in communication with the first sensor and the second sensor; and

a mechanism operably connected to the controller and configured to move the fixed roll when a difference between the location of the floating axis and the initial floating location exceeds a predetermined value.

12. The apparatus of claim 11, wherein, during operation of the apparatus in which the fixed roll and the floating roll draw the ribbon of molten glass between the rolls, the location of the fixed axis is fixed and the location of the floating roll is floating such that a constant amount of force is applied by the floating roll on the ribbon.

13. The apparatus of claim 11 or claim 12, wherein the controller moves the fixed roll by a correction amount.

14. The apparatus of any of claims 11 to 13, wherein the mechanism includes a servo- mechanism.

15. The apparatus of any of claims 11 to 14, wherein the first sensor and the second sensor include a string potentiometer.

The apparatus of any of claims 11 to 15, furthering comprising a measurement device (96) configured to measure a second ribbon position relative to an initial ribbon position.

The apparatus of claim 16, wherein the measurement device (96) emits ultraviolet radiation.

18. The apparatus of any of claims 11 to 17, further comprising driven stub rolls (46, 48) and idle stub rolls (50, 52), the fixed roll and the floating roll controlled by the method being part of at least one of the driven stub rolls and the idle stub rolls.