WO2011056781A1 - Laser scoring of a moving glass ribbon having a non-constant speed - Google Patents

Abstract

Laser scoring of a glass ribbon (13) which moves at a non-constant speed is performed using a tilted track (15) and a carriage (14) which travels down the track. The carriage can include a flying optical head (51) which receives laser light from a flexible laser beam delivery system (61) coupled to a laser (41). Variations in the speed of the ribbon which are less than or equal to ±3% of the ribbon's nominal speed can be accommodated by varying the speed of the carriage and adjusting the output power of the laser (41). Greater speed variations can additionally involve adjusting the tilt angle α the track. Adjustments of the orientation of a first lens unit (53) within the flying optical head (51) can be made to maintain the major axis of the laser beam along the score line as the tilt angle is changed.

Description

LASER SCORING OF A MOVING GLASS RIBBON

HAVING A NON-CONSTANT SPEED

[0001] This application claims the benefit of priority of US Provisional Application Serial No. 61/257,593 filed on November 3, 2009.

FIELD

[0002] This disclosure relates to methods and apparatus for laser scoring a moving glass ribbon and, in particular, to methods and apparatus for scoring a moving glass ribbon where the speed of the ribbon varies over time.

[0003] The following discussion refers to a glass ribbon which moves in a vertical direction, which is a typical application for the methods and apparatus disclosed herein. However, this orientation has been assumed only to facilitate the presentation and should not be interpreted as limiting the disclosure in any manner.

[0004] Similarly, although one application of the methods and apparatus disclosed herein is to unplanned (unintended) variations in the speed of a ribbon resulting from, for example, variations in the process used to produce the ribbon, it is to be understood that the methods and apparatus of the disclosure are equally applicable to planned (intended) speed changes, such as those associated with a change in glass composition, production rate, sheet dimensions, or the like.

DEFINITIONS

[0005] As used herein and in the claims, the term "vent" means a cut formed in a glass surface whether the cut goes completely or only partially through the thickness of the glass. Thus, the term encompasses complete vents, partial vents, complete median cracks, and partial median cracks, where complete vents and complete median cracks go entirely through the thickness of the glass and partial vents and partial median cracks go partially through the thickness of the glass.

[0006] As used herein and in the claims, the term "light-emitting device" means any device from which light emanates and includes active devices that generate light (e.g., a laser) and passive devices that receive and emit light generated by another device (e.g., a device which receives a beam from a laser and shapes and/or focuses the beam).

BACKGROUND

[0007] Scoring of glass is conventionally accomplished using mechanical tools. However, an alternative exists that uses laser radiation, e.g., CO₂ laser radiation at a wavelength of ΙΟ.όμηι, to heat the glass and create tensile stress via a temperature gradient. The use of a laser for glass scoring is discussed in commonly-assigned U.S. Patent No. 5,776,220 entitled "Method and apparatus for breaking brittle materials" and U.S. Patent No. 6,327,875 entitled "Control of median crack depth in laser scoring."

[0008] As shown in FIG. 1, during laser scoring, a vent is created in a major surface 1 14 of glass 112 along a score line 1 15. In order to create the vent, a small initiation flaw 11 1 is formed on the glass surface near one of its edges, which is then transformed into the vent by propagating a laser light beam 121 having a footprint 1 13 across the surface of the glass followed by a cooling area produced by a cooling nozzle 1 19. Heating of the glass with a laser light beam and quenching it immediately thereafter with a coolant creates a thermal gradient and a corresponding stress field, which is responsible for the propagation of the initiation flaw to form the vent.

[0009] Commonly-assigned U.S. Patent Publication No. 2008/0264994 (the '994 publication) describes a system for laser scoring of a moving glass ribbon in which a traveling carriage moves along a linear track which is inclined at an angle a with respect to a line transverse to the direction of motion of the ribbon.

[0010] FIGS. 2 and 3 of the present application schematically illustrate the system of the '994 publication. In these figures, the glass ribbon is identified by the reference number 13, the traveling carriage by the number 14, the linear track by the number 15, the support structure (support frame) for the track by the number 11 , and the equipment which produces the ribbon, e.g., a fusion draw machine, by the number 9. As discussed in the '994 application, as seen from a fixed reference frame (e.g., the xyz reference frame in FIG. 2), the glass ribbon moves in the direction of vector 16 at a speed Sribbon and the carriage moves in the direction of vector 17 at a speed S_caiTiage, where Sribbon, S_caiTiage, and the angle a satisfy the relationship :

S ',carnage Sribbon/sin a. Eq. (1)

[0011] In this way, the carriage keeps pace with the ribbon, or, more precisely, the magnitude of the component of the carriage's velocity that is parallel to the direction of motion of the ribbon equals S_ribbon- Consequently, as seen from the ribbon, the carriage simply moves in the direction of vector 18, i.e., across the ribbon along a line 7 perpendicular to the ribbon's direction of motion, at a speed S_scom given by:

'score s ',carnage cos a. Eq. (2) [0012] As described in the '994 publication, a light-emitting device that provides a laser light beam and a nozzle that provides a stream of a cooling fluid (e.g., water) are coupled to the carriage and together form a vent across the width of the ribbon as the carriage moves along the linear track. In some embodiments, a mechanical scoring head (e.g., a scoring wheel) is also coupled to the carriage for forming an initiation flaw in the glass ribbon. Alternatively, the initiation flaw can be formed by equipment separate from the carriage.

[0013] FIG. 4 schematically illustrates these aspects of the '994 publication, where reference numbers 21, 22, and 23 represent the locations at the beginning of the scoring process of (1) the footprint of the cooling fluid, (2) the footprint of the laser light beam, and (3) the initiation flaw, and reference numbers 31 and 32 represent the locations of the footprint of the cooling fluid and the footprint of the laser light beam at a later point in time, after initiation has been completed.

[0014] As discussed in the '994 publication, a control system can be used to control the motion of the carriage so that Eq. (1) is satisfied. As an input, the control system can obtain information as to Sribkm fr°^m rollers which guide the ribbon or a separate sensor which monitors the ribbon's speed. The '994 publication also describes satisfying Eq. (1) by controlling the inclination angle a of linear track 15. However, the publication does not discuss criteria for changing S_caiTiage versus changing a or the issues associated with maintaining effective vent formation when S_caiTiage and/or a are changed. The present disclosure addresses these issues and provides methods and apparatus for maintaining effective laser scoring in the face of changes in Sribbon.

SUMMARY

[0015] In accordance with a first aspect, a method is disclosed for making glass sheets which includes:

(I) forming a moving glass ribbon (13), the ribbon having a time- varying speed

Sribbon,

(II) forming a vent in a surface of the ribbon (13) along a line (7) transverse to the ribbon's direction of motion by a method which includes:

(a) translating a carriage (14), which carries a light-emitting device (51) and a nozzle (1 19), along a linear track (15) at a speed S_carriage, the linear track being inclined at an angle a with respect to the line (7) so that the motion of the carriage has (i) a first component (18) that is parallel to the line (7) and (ii) a second component that is parallel to the direction of motion (16) of the ribbon (13), the light-emitting device (51) emitting a light beam produced by a laser (41) and the nozzle (1 19) emitting a cooling fluid;

(b) dynamically adjusting S_Cama_ge, the angle a, or both S_Cama_ge and the angle a so that the second component of the motion of the carriage (14) keeps pace with the ribbon (13); and

(c) compensating for the dynamic adjustment of step (II)(b) by changing the

power Piaser of the laser (41) that produces the light beam emitted by the light- emitting device (51); and

(III) separating a glass sheet from the ribbon (13) along the vent formed in step (II).

[0016] In accordance with a second aspect, there is provided the method of aspect 1 , wherein:

(i) Sribbon is of the form:

Sribbon = So + ASo,

where So and ASo are, respectively, a nominal constant component and a time varying component of the ribbon's speed; and

(ii) when |ASo| > 0.03 So, step (II)(b) comprises changing a.

[0017] In accordance with a third aspect, there is provided the method of aspect 1 wherein:

(i) step (II)(b) comprises changing a;

(ii) at the ribbon, the light beam emitted by the light-emitting device has a length L and a width W;

(iii) the light-emitting device comprises a first lens unit which determines L and a second lens unit which determines W;

(iv) the first lens unit comprises at least one lens element;

and

(v) step (II) further comprises adjusting the angular orientation of the at least one lens element to compensate for changes in the orientation of the light beam relative to the line as a result of the change in a.

[0018] In accordance with a fourth aspect, there is provided the method of aspect 3 wherein the second lens unit comprises at least one lens element and the angular orientation of that element is held constant relative to the carriage as a is changed. [0019] In accordance with a fifth aspect, there is provided the method of aspect 3 or aspect 4 wherein the first and second lens units each contain only one lens element.

[0020] In accordance with a sixth aspect, there is provided the method of aspect 1 wherein:

(i) Sribbon is of the form:

Sribbon = So + ASo,

where So and ASo are, respectively, a nominal constant component and a time varying component of the ribbon's speed; and

(ii) when |ASo|≤ 0.03 So, a is held constant in step (II)(b).

[0021] In accordance with a seventh aspect, there is provided the method of aspect 6 wherein the change in Pi_aser of step (II)(c) satisfies the relationship:

dPlaser/dSribbon = k-Ctn(⁽X),

where k is a constant.

[0022] In accordance with an eighth aspect, there is provided the method of aspect 7 wherein Pi_aser is expressed in percent of maximum laser power and k <1.0.

[0023] In accordance with a ninth aspect, there is provided the method of aspect 1 wherein step (II) comprises transmitting laser light from the laser to the light-emitting device along a path which includes a flexible laser beam delivery system which encases the laser light in a housing which has a first end which is affixed to the laser or a support structure for the laser and a second end which is affixed to the linear track or a support structure for the linear track, the housing including at least one joint and at least one extension tube which permit rotation and translation of first and second ends relative to one another in three dimensions.

[0024] In accordance with a tenth aspect, there is provided the method of any one of aspects 1-9 wherein the glass ribbon is formed by a downdraw process.

[0025] In accordance with an eleventh aspect, there is provided the method of any one of aspects 1-10 wherein the glass sheet is a substrate for a display device.

[0026] In accordance with a twelfth aspect, a method is disclosed for making glass sheets which includes:

(I) forming a moving glass ribbon (13);

(II) forming a vent in a surface of the ribbon (13) along a line (7) transverse to the ribbon's direction of motion by a method which includes translating a carriage (14), which carries a light-emitting device (51) and a nozzle (119), along a linear track (15), the linear track being inclined at an angle a with respect to the line (7) so that the motion of the carriage has (i) a first component (18) that is parallel to the line (7) and (ii) a second component that is parallel to the direction of motion (16) of the ribbon (13), the light-emitting device (51) emitting a light beam produced by a laser (41) and the nozzle (119) emitting a cooling fluid; and

(III) separating a glass sheet from the ribbon (13) using the vent formed in step (II); wherein:

(i) at the ribbon (13), the light beam emitted by the light-emitting device has a length L and a width W;

(ii) the light-emitting device (51) includes a first lens unit (53) which determines L and a second lens unit (55) which determines W;

(iii) the first lens unit (53) includes at least one lens element (81);

(iv) a is changed so as to change the relative magnitudes of the first and second components (18,16) of the motion of the carriage (14); and

(v) the angular orientation of the at least one lens element (81) is adjusted to compensate for changes in the orientation of the light beam relative to the line (7) as a result of the change in a.

[0027] In accordance with a thirteenth aspect, there is provided the method of aspect 12 wherein the second lens unit comprises at least one lens element and the angular orientation of that element is held constant relative to the carriage as a is changed.

[0028] In accordance with a fourteenth aspect, there is provided the method of aspect 12 wherein the first and second lens units each contain only one lens element.

[0029] In accordance with a fifteenth aspect, there is provided the method of any one of aspects 12-14 wherein the glass ribbon is formed by a downdraw process.

[0030] In accordance with a sixteenth aspect, there is provided the method of any one of aspects 12-15 wherein the glass sheet is a substrate for a display device.

[0031] In accordance with a seventeenth aspect, a method is disclosed for making glass sheets which includes:

(I) forming a moving glass ribbon (13);

(II) forming a vent in a surface of the ribbon (13) along a line (7) transverse to the ribbon's direction of motion by a method which includes: (a) translating a carriage (14), which carries a light-emitting device (51) and a nozzle (1 19), along a linear track (15) which is inclined at an angle a with respect to the line (7) so that the motion of the carriage has (i) a component (18) that is parallel to the line (7) and (ii) a component that is parallel to the direction of motion (16) of the ribbon (13), the light-emitting device (51) emitting a laser light beam and the nozzle (1 19) emitting a cooling fluid; and

(b) transmitting laser light (43) from a laser (41) to the light-emitting device (51) along a path which includes a flexible laser beam delivery system (61) which encases the laser light (43) in a housing which has a first end (65) which is affixed to the laser (41) or a support structure for the laser and a second end (67) which is affixed to the linear track (15) or a support structure (11) for the linear track, the housing including at least one joint (62) and at least one extension tube (64) which permit rotation and translation of first and second ends (65,67) relative to one another in three dimensions; and

(III) separating a glass sheet from the ribbon (13) using the vent formed in step (II).

[0032] In accordance with a eighteenth aspect, there is provided the method of aspect 17 wherein the flexible laser beam delivery system comprises a beam expander.

[0033] In accordance with a nineteenth aspect, there is provided the method of aspect 17 or aspect 18 wherein the glass ribbon is formed by a downdraw process.

[0034] In accordance with a twentieth aspect, there is provided the method of any one of aspects 17-19 wherein the glass sheet is a substrate for a display device.

[0035] Apparatus for practicing the above methods is also disclosed.

[0036] The reference numbers used in the above summaries of the various aspects of the disclosure are only for the convenience of the reader and are not intended to and should not be interpreted as limiting the scope of the invention. More generally, it is to be understood that both the foregoing general description and the following detailed description are merely exemplary of the invention and are intended to provide an overview or framework for understanding the nature and character of the invention.

[0037] Additional features and advantages of the invention are set forth in the detailed description which follows, and in part will be readily apparent to those skilled in the art from that description or recognized by practicing the invention as described herein. The accompanying drawings are included to provide a further understanding of the invention, and are incorporated in and constitute a part of this specification. It is to be understood that the various features of the invention disclosed in this specification and in the drawings can be used in any and all combinations.

BRIEF DESCRIPTION OF THE DRAWINGS

[0038] FIG. 1 is a schematic diagram illustrating the laser scoring process.

[0039] FIG. 2 is a schematic diagram illustrating a laser scoring system according to the

'994 publication.

[0040] FIG. 3 is a schematic diagram illustrating the motions of the carriage of FIG. 2 in more detail.

[0041] FIG. 4 is a schematic diagram illustrating locations of the cooling fluid, laser light beam, and initiation flaw at the beginning of the scoring process and at a later point in time.

[0042] FIG. 5 is a graph which plots: (1) S_SCOre (left hand vertical axis) versus S_ribbon

(horizontal axis) (curve 57); and (2) percent maximum laser power (right hand vertical axis) versus Sribbon (horizontal axis) (curve 59). S_score and S_ribb_on are in millimeters/second; a = 3.8° for these curves.

[0043] FIG. 6 is a schematic diagram illustrating a system for providing laser light to a flying optical head.

[0044] FIG. 7 is a perspective view of an embodiment which employs a flexible laser beam delivery system to provide laser light to a flying optical head.

[0045] FIG. 8 is a side view of the system of FIG. 7.

[0046] FIG. 9 is a top view of the system of FIG. 7.

[0047] FIG. 10 is a perspective view of the flying optical head of FIG. 7 with a portion of its housing removed to illustrate the locations of the first and second lens units and the turning mirror used in this embodiment.

[0048] FIG. 11 is a perspective view of the first lens unit of the flying optical head of FIG. 7.

[0049] FIG. 12 is a schematic drawing illustrating the shape and orientation of a laser beam as it passes through the flying optical head of FIG. 7.

DETAILED DESCRIPTION

[0050] In general terms, the speed of a glass ribbon can be described as composed of a nominal component So and an offset ASo from the nominal value:

Sribbon = So + ASQ. Eq. (3) [0051] Both So and ASo can be functions of time. For example, So can change as a result of an intended change in, for example, production rate, while ASo can change as a result of an unintended change in process conditions. Typically, the changes in Sribbon due to changes in So will be less frequent than the changes in Sribbon due to ASo, although the reverse can be true during, for example, the debugging of a new process where a series of nominal ribbon speeds may need to be tested. For the purposes of the following discussion, it will be assumed that So is constant over the time frame of interest and that ASo represents fluctuations in the ribbon's speed about So and includes both intended and unintended fluctuations.

[0052] In order for the carriage to keep pace with the ribbon as S_ribb_on changes, i.e., in order for the motion of the carriage to be a straight line as seen from the ribbon, one or both of Scamage and a needs to change. Typically, changing S_cama_ge can be simpler than changing a. However, in accordance with the present disclosure, it has been discovered that S_caiTiage can only be changed over a limited range without sacrificing the quality of the edges of the glass sheets separated from the ribbon.

[0053] In particular, it has been discovered that laser power needs to be controlled as Scamage changes in order to keep the laser scoring process within an acceptable process window. Specifically, laser power needs to be increased as Scamage increases and decreased as it decreases. However, the level of changes that can be made to the laser power while maintaining the system in its process window turns out to be quite limited. This effect is illustrated in FIG. 5, which plots Sribbon in mm/sec along the horizontal axis, scoring speed in mm/sec along the left hand vertical axis, and laser power in percent of maximum power along the right hand vertical axis. The curves shown in this figure are based on measured data obtained for an a value of 3.8°.

[0054] The experiments which produced the data of FIG. 5 revealed that the edge properties of the glass sheets separated from the ribbon were repeatedly acceptable in the narrow range of ±3% about the ribbon's nominal speed (50 mm/sec in this case). That is, in terms of Eq. (3) above, a combination of carriage speed and adjustment in laser power can be used to accommodate changes in ribbon speed when |ASo|≤ 0.03-So, but when |ASo| > 0.03-So, a also needs to be changed to provide reliable edge quality.

[0055] FIG. 5 also reveals that the changes in laser power needed to compensate for changes in Sribbon can be a linear function of Sribbon- Such a linear dependence can facilitate control of the laser scoring process. For such an embodiment, dPi_aser dSribbon can be written as dPiaser/dSribbon⁼ k'Ctn(a), where k is a constant. That is, while the rate at which scoring speed increases when S_caiTiage is increased to match an increase in S_ribbon is ctn(a) (i.e.,

dSscoring/dSribbon⁼ ctn(a); see Eqs. (1) and (2) above), the rate at which the laser power needs to be increased to maintain reliable edge formation can be less than, greater than, or equal to ctn(a) depending on the value of k. In the case of the data of FIG. 5, where laser power is expressed as a percentage of maximum power, k is less than 1.0. As will be evident, the specific value of k for any particular application and for any particular units for laser power (e.g., percent of maximum power, watts, or the like) can be readily determined by skilled persons from the present disclosure.

[0056] FIGS. 6-9 illustrate apparatus that can be used to change the angle a to

accommodate changes in Sribbon, e.g., changes > 0.03-So. In particular, FIG. 6 schematically illustrates an overall exemplary arrangement of apparatus which can be used for this purpose, while FIGS. 7-9 show a specific exemplary embodiment. In FIG. 6, the glass ribbon from which individual glass sheets are separated is represented by reference number 13, the linear track for the moveable carriage by the number 15, and the equipment which produces the ribbon, e.g., a fusion draw machine, by the number 9. To simplify the presentation, the carriage is represented by flying optical head 51 in FIGS. 6-9, it being understood that the carriage can include other equipment, including a nozzle for a cooling fluid. Flying optical head 51 receives laser beam 43 produced by laser 41 and directs the beam towards ribbon 13. As discussed above in connection with FIGS. 1-4, the laser beam in combination with a cooling fluid extends an initial flaw formed in the glass to produce a vent across the width of the ribbon at which an individual glass sheet is separated from the ribbon.

[0057] In FIG. 6, the laser beam is shown being guided to the flying optical head by mirrors 45 and 47, which are located within a housing 49 having suitable apertures or couplings (not shown) for receiving light from the laser and transmitting light to the flying optical head. The locations and angular orientations of mirrors 45 and 47 can be under active control so as to keep the laser beam aimed at the flying head as the angle a is changed.

Although only two mirrors are shown, additional mirrors can be used if desired.

[0058] In addition to being used to accommodate changes in a, the locations and angular orientations of the mirrors can also be used to compensate for relative movement between laser 41 and track 15 caused by changes in temperature (e.g., from room temperature to the elevated operating temperatures associated with manufacture of the glass ribbon), mechanical vibrations, and the like. Because of the power levels required, laser 41 is generally quite massive and thus in a manufacturing setting will often be mounted on a support structure separate from that used for track 15. As a consequence, laser 41 and track 15 can undergo relative movement with respect to one another, thus necessitating continual aiming of the laser beam at the flying optical head. Such continual aiming can be achieved by actively changing the orientations and/or locations of mirrors 45 and 47 using a computer control system which obtains input data from suitable transducers as to the locations of the laser (and/or its support system) and the linear track (and/or its support system).

[0059] FIGS. 7-9 illustrate an embodiment which can passively accommodate changes in a as well as changes in the relative locations of laser 41 and track 15 due to temperature changes, mechanical vibrations, and the like. This embodiment includes a flexible laser beam delivery system 61 which encases the laser light in a housing which has a first end 65 which is affixed to laser 41 or to a support structure for the laser and a second end 67 which is affixed to linear track 15 or to a support structure for the linear track, e.g., support structure 1 1 in FIGS. 7-9. Affixing second end 67 to linear track 15 has the advantage that as the angle a is varied, the laser beam remains aimed at the flying optical head 51 since the track, the second end, and the optical head move as a unit as a is changed.

[0060] As shown in FIGS. 7-9, the delivery system's housing includes at least one joint 62 and at least one extension tube 64 which permit rotation and translation of first and second ends 65 and 67 relative to one another in three dimensions. In this way, the first and second ends of the delivery system can move relative to one another without substantially degrading either the input of light to the system from the laser or the output of light to the flying optical head. This is an important advantage since it provides a robust system which can be installed and then allowed to function for extended periods of time without operator intervention. The combination of at least one joint and at least one extension tube also facilitates installation, alignment, and servicing of the scoring system. In this regard, it should be noted that beam pointing accuracy requirements are quite strict; for example, a suitable specification for the deviation of the center of the beam from the center line of the flying optical head can be ± ΙΟΟμιη or less at a distance of 3 meters or more from the last mirror of the delivery system.

[0061] As also shown in FIGS. 7-9, flexible laser beam delivery system 61 can include beam expander 63 to facilitate transfer of the laser light to the flying optical head and then onto the glass ribbon. See co-pending, commonly-assigned U.S. Patent Application No. 12/220,948 entitled "Scoring of Non-Flat Materials" (hereinafter the '948 application). The delivery system can also include a circular polarizer (not shown in FIGS. 7-9). The system can be constructed using commercially-available equipment such as that produced by

American Laser Enterprises of Wixom, Michigan.

[0062] Turning to flying optical head 51, as shown in FIG. 10, the flying head can include a first lens unit 53 which controls the length of the laser beam on ribbon 13, a second lens unit 55 which controls the width of the laser beam, and a turning mirror 69 which directs the beam towards the ribbon. The first lens unit can, for example, include a single negative cylindrical lens element which expands the beam in a direction along the z-axis of FIG. 2 (i.e., in a direction perpendicular to the plane of the paper in FIG. 2), while the second lens unit can, for example, include a single positive cylindrical lens element which contracts the beam in a direction orthogonal to track 15 in a plane through the centerline of the track and parallel to the x-y plane in FIG. 2. More lens elements can, of course, be used in either or both of the first and second lens units.

[0063] FIG. 12 illustrates the effects of the first and second lens units on the propagating beam. As shown in this figure, the beam enters the flying optical head having a circular cross section 83 and propagating in the direction of arrow 91. It enters the first lens unit 53 which expands the beam so that upon leaving that unit it has the configuration shown by reference number 85. Thereafter, the beam passes through the second lens unit and is reflected onto the ribbon by mirror 69. In FIG. 12, the combined effect of the second lens unit and the mirror is represented by the reference number 93. If track 15 were horizontal, the resulting beam at the ribbon would have the configuration and orientation identified by the reference number 89 in FIG. 12. However, when track 15 is tilted below horizontal by the angle a, at the ribbon, the beam takes on the orientation identified by the reference number 87 in FIG. 12. That is, the beam is rotated upward by the angle a.

[0064] It should be noted that if S_caiTi_age and a are chosen so that Eq. (1) is satisfied, the angled beam still translates across the ribbon in a straight line, e.g., line 7, but the major axis of the beam no longer lies along that line. In practice, it has been found that such a mismatch between the path of the beam and the beam's major axis can result in unreliable scoring and/or poor edge quality since the major axis of the beam is no longer fully aligned with the path traversed by the cooling liquid and the initiation flaw. [0065] To address this problem, the first lens unit can be constructed as shown in FIG. 11 so as to allow the cylinder axis of lens element 81 (or the cylinder axis of multiple lens elements, if used) to be rotated so as to bring the orientation of the beam's major axis in alignment with the beam's direction of motion across the surface of the ribbon. As shown in FIG. 1 1, lens unit 53 can include a housing 73 to which are mounted a stepper motor 75 which drives a gear 77 which, in turn, drives a larger gear 79 to which lens element 81 is affixed. The stepper motor is activated by a controller (not shown) which coordinates the orientation of lens element 81 with the angle of track 15. In particular, as illustrated in FIG. 12, the controller causes the cylinder axis of the lens element (or lens elements) to rotate about an axis parallel to track 15 by a, the direction of rotation causing beam 87 to rotate into alignment with beam-orientation 89.

[0066] As shown in FIG. 10, the second lens unit 55 can also be equipped with a stepper motor and a gear train for changing the orientation of the cylinder axis of this unit. However, in practice, it has been found that misalignment between the cylinder axis of the second lens unit and a normal to the score line on the ribbon is much less troublesome than misalignment between the cylinder axis of the first lens unit and the score line. Accordingly, for many applications, the second lens unit can have a fixed orientation relative to the carriage, thus reducing the complexity and cost of the optical system.

[0067] As will be understood, the apparatus shown in FIGS. 10 and 1 1 is merely illustrative and a variety of other mechanisms can be used to change the orientation of the cylindrical axes of the lens element(s) of the first and second lens units. Moreover, the designations "first lens unit" and "second lens unit" should not be read as implying an order in which the units operate on the laser beam. Although shown in the figures with the first lens unit preceding the second lens unit, the units can have the opposite arrangement if desired. The first and second lens units can have a variety of prescriptions depending on the specifics of the scoring system. The '948 application contains representative examples of powers, spacings, etc. for the first and second lens units that can be used in connection with the present disclosure. The prescriptions of that application were obtained using the commercially-available ZEMAX optical design software (ZEMAX Development

Corporation, Bellevue, Washington). Similarly, prescriptions for the optical systems of the present disclosure can be obtained using ZEMAX or other commercially-available or custom optical design programs. [0068] In practice, the various aspects of the disclosure discussed above can be used in combination to produce a system which automatically compensates for changes in ribbon speed. For example, using input data regarding Sribbon, a controller can simultaneously adjust (1) Scaniage, (2) Piaser, (3) the angle a of track 15, and (4) the orientation of the major axis (or both the major and minor axes) of the laser beam so as to achieve laser scoring and edge quality within desired process windows. Through the use of a flexible laser beam delivery system, such adjustments can be made in real time without the need for manual intervention.

[0069] As can be seen from the foregoing, the present disclosure provides methods and associated apparatus that facilitate laser scoring which, in turn, provides the benefits of clean and strong edges, insensitivity to glass composition and thickness, and minimal disturbance of ribbon motion. In addition, by increasing the track angle a, laser scoring can be performed at a reduced scoring speed which permits deep scoring or full body cutting.

[0070] A variety of modifications that do not depart from the scope and spirit of the disclosure will be evident to persons of ordinary skill in the art. For example, instead of performing scoring in only one direction and then resetting for the next score, the system can be constructed so that scoring can be performed for both directions of travel, e.g., from left to right in FIG. 2, then from right to left, and so on. The following claims are intended to cover modifications, variations, and equivalents to the embodiments set forth herein of these and other types.

Claims

What is claimed is:

1. A method of making glass sheets comprising:

(I) forming a moving glass ribbon, the ribbon having a time-varying speed Sribbon;

(II) forming a vent in a surface of the ribbon along a line transverse to the ribbon's direction of motion by a method which comprises:

(a) translating a carriage, which carries a light-emitting device and a nozzle, along a linear track at a speed S_caiTiage, the linear track being inclined at an angle a with respect to the line so that the motion of the carriage comprises (i) a first component that is parallel to the line and (ii) a second component that is parallel to the direction of motion of the ribbon, the light-emitting device emitting a light beam produced by a laser and the nozzle emitting a cooling fluid;

(b) dynamically adjusting S_camage, the angle a, or both S_caiTiage and the angle a so that the second component of the motion of the carriage keeps pace with the ribbon; and

(c) compensating for the dynamic adjustment of step (II)(b) by changing the power Piaser of the laser that produces the light beam emitted by the light- emitting device; and

(III) separating a glass sheet from the ribbon along the vent formed in step (II).

2. The method of Claim 1 wherein:

(i) Sribbon is of the form:

Sribbon = So + ASo,

where So and ASo are, respectively, a nominal constant component and a time varying component of the ribbon's speed; and

(ii) when |ASo| > 0.03 So, step (II)(b) comprises changing a.

3. The method of Claim 1 wherein:

(i) step (II)(b) comprises changing a;

(ii) at the ribbon, the light beam emitted by the light-emitting device has a length L and a width W;

(iii) the light-emitting device comprises a first lens unit which determines L and a second lens unit which determines W;

(iv) the first lens unit comprises at least one lens element; and

(v) step (II) further comprises adjusting the angular orientation of the at least one lens element to compensate for changes in the orientation of the light beam relative to the line as a result of the change in a.

4. The method of Claim 3 wherein the second lens unit comprises at least one lens element and the angular orientation of that element is held constant relative to the carriage as a is changed.

5. The method of Claim 3 or Claim 4 wherein the first and second lens units each contain only one lens element.

6. The method of Claim 1 wherein:

(i) Sribbon is of the form:

Sribbon = So + ASo,

where So and ASo are, respectively, a nominal constant component and a time varying component of the ribbon's speed; and

(ii) when |ASo|≤ 0.03 So, a is held constant in step (II)(b).

7. The method of Claim 6 wherein the change in Pi_aser of step (II)(c) satisfies the relationship :

dPiaser/dSribbon = k-ctn(a),

where k is a constant.

8. The method of Claim 7 wherein Pi_aser is expressed in percent of maximum laser power and k <1.0.

9. The method of Claim 1 wherein step (II) comprises transmitting laser light from the laser to the light-emitting device along a path which includes a flexible laser beam delivery system which encases the laser light in a housing which has a first end which is affixed to the laser or a support structure for the laser and a second end which is affixed to the linear track or a support structure for the linear track, the housing including at least one joint and at least one extension tube which permit rotation and translation of first and second ends relative to one another in three dimensions.

10. The method of any one of Claims 1 -9 wherein the glass ribbon is formed by a downdraw process.

1 1. The method of any one of Claims 1 -10 wherein the glass sheet is a substrate for a display device.

12. A method of making glass sheets comprising:

(I) forming a moving glass ribbon;

(II) forming a vent in a surface of the ribbon along a line transverse to the ribbon's direction of motion by a method which comprises translating a carriage, which carries a light- emitting device and a nozzle, along a linear track, the linear track being inclined at an angle a with respect to the line so that the motion of the carriage comprises (i) a first component that is parallel to the line and (ii) a second component that is parallel to the direction of motion of the ribbon, the light-emitting device emitting a light beam produced by a laser and the nozzle emitting a cooling fluid; and

(III) separating a glass sheet from the ribbon using the vent formed in step (II); wherein:

(i) at the ribbon, the light beam emitted by the light-emitting device has a length L and a width W;

(ii) the light-emitting device comprises a first lens unit which determines L and a second lens unit which determines W;

(iii) the first lens unit comprises at least one lens element;

(iv) a is changed so as to change the relative magnitudes of the first and second components of the motion of the carriage; and

(v) the angular orientation of the at least one lens element is adjusted to compensate for changes in the orientation of the light beam relative to the line as a result of the change in a.

13. The method of Claim 12 wherein the second lens unit comprises at least one lens element and the angular orientation of that element is held constant relative to the carriage as a is changed.

14. The method of Claim 12 wherein the first and second lens units each contain only one lens element.

15. The method of any one of Claims 12-14 wherein the glass ribbon is formed by a downdraw process.

16. The method of any one of Claim 12-15 wherein the glass sheet is a substrate for a display device.

17. A method of making glass sheets comprising:

(I) forming a moving glass ribbon; (II) forming a vent in a surface of the ribbon along a line transverse to the ribbon's direction of motion by a method which comprises:

(a) translating a carriage, which carries a light-emitting device and a nozzle, along a linear track which is inclined at an angle a with respect to the line so that the motion of the carriage comprises (i) a component that is parallel to the line and (ii) a component that is parallel to the direction of motion of the ribbon, the light-emitting device emitting a laser light beam and the nozzle emitting a cooling fluid; and

(b) transmitting laser light from a laser to the light-emitting device along a path which includes a flexible laser beam delivery system which encases the laser light in a housing which has a first end which is affixed to the laser or a support structure for the laser and a second end which is affixed to the linear track or a support structure for the linear track, the housing including at least one joint and at least one extension tube which permit rotation and translation of first and second ends relative to one another in three dimensions; and

(III) separating a glass sheet from the ribbon using the vent formed in step (II).

18. The method of Claim 17 wherein the flexible laser beam delivery system comprises a beam expander.

19. The method of Claim 17 of Claim 18 wherein the glass ribbon is formed by a downdraw process.

20. The method of any one of Claims 17-19 wherein the glass sheet is a substrate for a display device.