Patent Publication Number: US-2020277216-A1

Title: Systems and methods for processing thin glass ribbons

Description:
This application claims the benefit of priority under 35 U.S.C. § 119 of U.S. Provisional Application Ser. No. 62/578,816 filed on Oct. 30, 2017 the content of which is relied upon and incorporated herein by reference in its entirety. 
    
    
     BACKGROUND 
     Field 
     The present disclosure generally relates to systems and methods for processing a glass ribbon. More particularly, it relates to systems and methods for handling a glass ribbon as part of the manufacture of thin glass sheets from a moving glass ribbon. 
     Technical Background 
     Production of glass sheets typically involves producing a glass ribbon from a molten glass material, and then cutting or separating individual glass sheets from the glass ribbon. Various techniques are known for producing the glass ribbon. For example, with a down-draw process (e.g., fusion draw process), the ribbon is drawn downward, typically from a forming body. Other glass making processes include, for example, float, up-draw, slot-style and Fourcault&#39;s-style processes. In yet other examples, the glass ribbon can be temporarily stored in roll form, and later unwound for subsequent cutting or separation of individual glass sheets. 
     To meet the demands of many end use applications, continuing efforts have been made to produce thinner glass sheets (e.g., about 1 millimeter (mm) or less). As the thickness of the glass ribbons from which the glass sheets are formed becomes thinner, they are also more susceptible warp (or flatness deviations) and other concerns (such as surface damage that may be imparted during the process steps to provide a thinner glass ribbon). Warp can occur in one or more of the width or length direction of the glass ribbon. The glass production process layout may also contribute to deviations in flatness. For example, with some thin rolled glass formation techniques, the process layout includes a transitioning the glass ribbon from a vertical orientation to a horizontal orientation. During this turn, the glass is still at a viscosity that is low enough to be easily influenced by gravity and some edge effects can induce a noticeable transverse deformation. In the longitudinal direction, a pulling force can be applied to stabilize the glass ribbon by developing a tension. A resulting compressive component then appears on the edges that in turn can generate wrinkles or warp across the width. A flatter glass ribbon reduces the amount of material that may need to be removed, such as by grinding and/or polishing, to achieve a given final thickness. For example, flatness on the order of 100 micrometers (for a sheet size of about 250 mm×600 mm) may be necessary for some applications. 
     As a point of reference, during the glass forming process, a glass ribbon is first formed in a viscous state, and is then cooled to a viscoelastic state and finally to an elastic state. The common practice to minimize warp is to pass the glass ribbon through nip rolls at a location close to the end of the purely viscous regime. Nip rolls are cylindrical and can be set at a fixed gap or at a fixed pinch force. Typically one of the two nip rolls is driven and the other is idle to apply a desired force. Regardless, the mechanical effect applied to the glass ribbon by the nip rolls is essentially unidirectional (a “squeezing” effect) and characterized as a short line or linear mode of contact. For some end use applications, the linear contact applied by the nip rolls alone cannot achieve a desired level of flatness. 
     Accordingly, systems and methods for processing a glass ribbon, for example reducing warp in a glass ribbon, are disclosed herein. 
     SUMMARY 
     Some embodiments of the present disclosure relate to a method for processing a glass ribbon. A glass ribbon is supplied from a supply apparatus to an upstream side of a conveying apparatus. The conveying apparatus comprises a conveyor device and a pulling device. The pulling device is located at a downstream side of the conveying apparatus opposite the upstream side. The conveyor device establishes a primary plane of travel from the upstream side to the downstream side. A pulling force is applied on the glass ribbon and the glass ribbon is continuously conveyed along a travel path. In this regard, the travel path includes first, second and third bends. The first bend is formed at a first location between the upstream side and the pulling device. The first bend defines a curve that is convex to the primary plane of travel. The second bend is formed at a second location between the first location and the pulling device. The second bend defines a curve that is concave to the primary plane of travel. The third bend is formed at a third location between the second location and the pulling device. The third bend defines a curve that is convex to the primary plane of travel. A vertical distance between the third location and the primary plane of travel is greater that a vertical distance between the first location and the primary plane of travel. The travel path further includes in the primary plane of travel from a location downstream of the third location and to the pulling device. At least one of the first, second, and third bends imparts a stress into a surface of the glass ribbon to flatten the glass ribbon. In some embodiments, a viscosity of the glass ribbon at the third bend is greater than a viscosity of the glass ribbon at the first bend. In other embodiments, at least one of the first, second and third bends is cause, at least in part, by an interface between the glass ribbon and a bending tool along with gravity. 
     Yet other embodiments of the present disclosure relate to a system for processing a glass ribbon. The system comprises a conveying apparatus. The conveying apparatus comprises a conveyor device, a pulling device, a first bending tool, a second bending tool, and a third bending tool. The conveyor device establishes a primary plane of travel from an upstream side to a downstream side. The pulling device is located at the downstream side for conveying a glass ribbon along a travel path. The first bending tool is proximate the upstream side. The second bending tool is between the first bending tool and the downstream side. A vertical distance between the second bending tool and the primary plane of travel is greater than a vertical distance between the first bending tool and the primary plane of travel. The third bending tool is between the second bending tool and the downstream side. A vertical distance between the third bending tool and the primary plane of travel is greater than the vertical distance between the second bending tool and the primary plane of travel. The first, second and third bending tools, at least in part, establish the travel path as comprising first, second and third bends. The first bend is formed at a first location between the upstream side and the pulling device. The first bend defines a curve that is convex to the primary plane of travel. The second bend is formed at a second location between the first location and the pulling device. The second bend defines a curve that is concave to the primary plane of travel. The third bend is formed at a third location between the second location and the pulling device. The third bend defines a curve that is convex to the primary plane of travel. The travel path further includes in the primary plane of travel from a location downstream of the third location and to the pulling device. In some embodiments, the first, second and third bending tools are configured to establish line contact with the glass ribbon. 
     Yet other embodiments of the present disclosure relate to a bending tool assembly for processing a glass ribbon. The bending tool assembly comprises an upstream bending tool, a downstream bending tool, an upstream support unit, a downstream support unit, and a base unit. The upstream support unit supports opposing ends of the upstream bending tool. The downstream support unit supports opposing ends of the downstream bending tool. The base unit comprises a plate, a first side leg and a second side leg projecting from opposite ends of the plate, a first cross-beam connected to the first side leg, and a second cross-beam connected to the second side leg. The first and second cross-beams support the upstream and downstream support units relative to the plate. Further, the bending tool assembly is configured such that at least one of the opposing ends of at least one of the upstream and downstream bending tools is selectively movable relative to the plate. 
     Additional features and advantages will be 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 embodiments described herein, including the detailed description which follows, the claims, as well as the appended drawings. 
     It is to be understood that both 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 into 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 operations of the claimed subject matter. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a simplified side view of a system for processing a glass ribbon in accordance with principles of the present disclosure; 
         FIG. 2  schematically illustrates imposition of a bend into a traveling glass ribbon; 
         FIG. 3  is a graph of a typical glass viscosity curve in which areas for flattening are designated; 
         FIG. 4  is a perspective view of a bending tool assembly in accordance with principles of the present disclosure and useful with glass ribbon floor conveying units of the present disclosure; 
         FIG. 5  is an enlarged side perspective view of a portion of the bending tool assembly of  FIG. 4 ; 
         FIG. 6A  is a side view of the bending tool assembly of  FIG. 4 ; 
         FIG. 6B  is another side view of the bending tool assembly and illustrating upstream and downstream bending tools in positions differing from the positions of the  FIG. 6A ; 
         FIG. 7  is a simplified side view of another floor conveying unit in accordance with principles of the present disclosure processing a glass ribbon, and including the bending tool assembly of  FIG. 4 ; 
         FIG. 8  is a graph of measured warp in a comparative sample glass sheet of the Example section; and 
         FIG. 9  is a graph of measured warp in an example glass sheet of the Example section. 
     
    
    
     DETAILED DESCRIPTION 
     Reference will now be made in detail to various embodiments of systems and methods for processing a glass ribbon, and in particular for removing warp from, or improving flatness in, a glass ribbon, for example a continuous glass ribbon. Whenever possible, the same reference numerals will be used throughout the drawings to refer to the same or like parts. 
     Some aspects of the present disclosure provide glass ribbon handling systems and methods in which a continuously conveyed or traveling glass ribbon is subjected to temporary bends at locations along the path of travel in such a way that final flatness is improved. The extent or curvature of the imparted bends and the mechanisms (or bending tools) utilized to achieve the bends can be selected in accordance with an expected viscosity of the glass ribbon as described below so as to generate a stress field that tends to straighten the profile of the glass ribbon across the width. With this in mind, one embodiment of a system  20  in accordance with principles of the present disclosure and useful in forming and processing a glass ribbon  22  is schematically shown in  FIG. 1 . Although the system  20  is described herein as being used to process a glass ribbon, it should be understood that the systems and methods of the present disclosure can also be used to process other types of materials such as polymers (e.g., plexi-glass™), metals, or other substrate materials. 
     The system  20  includes a glass ribbon supply apparatus  30  and a conveying apparatus  32 . As described in greater detail below, the glass ribbon supply apparatus  30  can assume a wide variety of forms appropriate for generating and delivering the glass ribbon  22  to an upstream side  40  of the conveying apparatus  32 . The conveying apparatus  32  causes the glass ribbon  22  to travel from the upstream side  40  to a downstream side  42 . In this regard, the glass ribbon  22  cools and thus experiences an increasing viscosity from the upstream side  40  to the downstream side  42 . Further, the conveying apparatus  32  is configured to lessen or remove warp (deviations in flatness) from the glass ribbon  22  as it progresses to the downstream side  42 . 
     In some non-limiting embodiments, the glass ribbon supply apparatus  30  incorporates fusion processes in which molten glass  50  is routed to a forming body  52 . The forming body  52  comprises an open channel  54  positioned on an upper surface thereof, and a pair of converging forming surfaces  56  that converge at a bottom or root  58  of the forming body  52 . The molten glass  50  flows into the open channel  54  and overflows the walls thereof, thereby separating into two individual flow of molten glass that flow over the converging forming surfaces  56 . When the separate flow of molten glass reach the root  58 , the recombine, or fuse, to form a single ribbon of viscous molten glass (i.e., the glass ribbon  22 ) that descends from the root  58 . Various rollers  60  contact the viscous glass ribbon  22  along the edges of the ribbon and aid in drawing the ribbon  22  in a first, downward direction  62  (such as a vertical direction). The present disclosure is equally applicable to other variations of down draw glass making processes such as a single sided overflow process or a slot draw process, which basic processes are well known to those skilled in the art. 
     In some embodiments, the glass ribbon supply apparatus  30  can further include a redirecting device  64  that redirects the glass ribbon  22  from the first direction  62  into a second direction  66  for delivery to the conveying apparatus  32 . The redirecting device  64  is represented in  FIG. 1  by rollers  68 . In some embodiments, the glass ribbon  22  is turned by the redirecting device  64  through an angle of 90 degrees and the second direction  66  is horizontal. In some embodiments, the redirecting device  64  does not physically contact the glass ribbon  22  (e.g., air bearings), or, in the event that contact is necessary, such as when rollers are used, contact can be limited to the edge portions of the glass ribbon  22 . 
     Other glass ribbon formation techniques are also acceptable that may or may not include the 90 degree turn described above, may or may not incorporate fusion processes, etc. Regardless, the molten, viscous glass ribbon  22  is continuously supplied to the upstream side  40  of the conveying apparatus  32 . 
     The conveying apparatus  32  includes a conveyor device  70  (referenced generally), a pulling device  72  and one or more bending tools, such as bending tools  74 ,  76 ,  78 . In general terms, the conveyor device  70  establishes a primary plane of travel P from the upstream side  40  to the downstream side  42 . The pulling device  72  is located at or immediately proximate the downstream side  42 , and exerts a pulling force onto the glass ribbon  22  and continuously conveys the glass ribbon  22  along a travel path defined, at least in part, by the bending tools  74 ,  76 ,  78  as described below. 
     The conveyor device  70  can assume various forms appropriate for supporting the glass ribbon  22  and can include transport devices, such as rollers  80 . The rollers  80  can have any format appropriate for interfacing with (e.g., contacting) the glass ribbon. For example, the rollers  80  can each comprise or exhibit a material, stiffness, surface coating, etc., appropriate for directly contacting the glass ribbon  22  in a manner that does not overtly negatively affect selected properties of the glass ribbon  22 . Some or all of the rollers  80  can be driven rollers of a type known to one of ordinary skill. Other conveying formats are also acceptable, such as a belt conveyor, non-contact conveyor (e.g., air bearing), etc. While  FIG. 1  reflects only a few of the rollers  80  immediately adjacent the downstream side  42 , in other embodiments, one or more transport devices (e.g., rollers) may be included adjacent the upstream side  40  or between the upstream and downstream sides  40 ,  42 . Regardless, the rollers  80  (or other conveying device arrangement) collectively establish the primary plane of travel P as the vertically lowermost extent at which the conveyor device  70  contacts or otherwise directly interfaces with the glass ribbon  22 . In some non-limiting embodiments, the conveyor device  70  is configured for installation to the floor of a glass production facility, and thus can include framework (not shown) supporting the rollers  80  (or other transport devices) as is known in the art. 
     The pulling device  72  can assume a variety of forms appropriate for driving or pulling the glass ribbon  22 , and in some embodiments can be or can include a conventional nip roll device comprising first and second rollers  90 ,  92 . One or both of the rollers  90 ,  92  can be a driven roller as is known in the art. With these and similar configurations, the pulling device  72  can further include a controller (not shown), for example a computer-like device, programmable logic controller, etc., programmed to control a speed or travel rate of the glass ribbon  22  along the conveying apparatus  32 . Other pulling device configurations are also acceptable. 
     With the above general parameters of the conveyor device  70  and the pulling device  72  in mind, the bending tool(s)  74 ,  76 ,  78  can assume various forms and can be located at various positions relative to the primary plane of travel P, the upstream side  40  and the downstream side  42  for interfacing with the glass ribbon  22  in the manners described below. In more general terms, an arrangement and configuration of the bending tool(s)  74 ,  76 ,  78  included in the conveying apparatus  32  are selected to subject the glass ribbon  22  to a succession of temporary bends that serve to reduce the warp components in the glass ribbon  22 , while minimizing direct contact with the glass ribbon  22 . Forces engaged in the bending steps are provided by the pulling force generated at the pulling device  72 . As a point of reference, bending of the traveling glass ribbon  22  can be seen as a combination of upward force(s) U and downward force(s) D, as generally reflected by  FIG. 2 . The upward force U component can be provided by a physical means that drives the glass ribbon  22  to a position higher than the primary plane of travel P. This physical means can be a solid surface (static or in rotation) with or without an air bearing, leading to an interaction that can be friction, rolling or non-contact. The downward force D component can be provided by gravity when a viscosity of the glass ribbon  22  is sufficiently low, or by the use of a mechanical means that forces the glass ribbon  22  to a lower position. Regardless, the bending generates a surface stress field that tends to straighten or flatten the profile of the glass ribbon  22  across the width (as opposed to a linear force as otherwise effectuated by a nip roll). 
     Returning to  FIG. 1 , and as mentioned above, the conveying apparatus  32  is configured to produce each of the series of flatness-improving bends at locations along the travel path as a function of expected viscosity of the glass ribbon  22 . In this regard, the glass ribbon  22  cools while traveling from the upstream side  40  to the downstream side  42 ; thus, a viscosity of the glass ribbon  22  progressively increases from the upstream side  40  to the downstream side  42 . The addition of curvature changes, when done at an appropriate viscosity, can provide significant improvement of the initial shape. If curvature changes are done at a viscosity that is too low, local shearing can occur that may undesirably modify a thickness of the glass ribbon  22 . If curvature changes are done at too high a viscosity, the local stresses generated within the glass ribbon  22  during the successive bending may not be sufficient to fully flatten or remove warp. A configuration of the conveying apparatus  32  is based upon these constraints, as well to utilize gravity as a bending force component where viable. As a point of reference,  FIG. 3  illustrates an example viscosity curve (as a function of temperature). A region  94  along the viscosity curve where gravity-induced bending in accordance with principles of the present disclosure is beneficial is identified, as is a region  95  where forced bending (e.g., bending caused or imparted at least in part by a force applied to the glass ribbon by an interface with a structure) in accordance with principles of the present disclosure. At region  96 , nip roller flattening can be appropriate. It has surprisingly been found that at regions where the glass ribbon  22  has a viscosity in the range of about 10 6 -10 8  Poise, gravity-driven bending is viable; and at regions where the glass ribbon  22  has a viscosity in the range of about 10 8 -10 9  Poise, forced bending is appropriate (for a glass ribbon thickness on the order of 1 mm and velocity of 10-12 m/min). In some embodiments, other viscosity/bending technique relationships are also acceptable. 
     Returning to  FIG. 1 , and with the above general background in mind, the conveying apparatus  32  is configured to produce one or more bends (e.g., change in direction relative to the primary plane of travel P) along the travel path of the glass ribbon  22 , such as a first bend  100 , a second bend  102 , and a third bend  104 . One or more (including all) of the bends  100 - 104  can induce surface stresses in the glass ribbon  22  that remove warp in the glass ribbon  22 . The bends  100 - 104  are created by an interface of the glass ribbon  22  with one or more of the bending tools  74 ,  76 ,  78 , along with gravity and the pulling force applied by the pulling device  72 . 
     To provide a better understanding of the locations of bending tools  74 ,  76 ,  78  and of the bends  100 - 104  relative to one another, orthogonal vertical V and horizontal H directions are designated in  FIG. 1 . The vertical direction V can be perpendicular to the primary plane of travel P, and the horizontal direction H can be parallel with the primary plane of travel P. In the descriptions below, “vertical” and “vertically” are in reference to the vertical direction V; “horizontal”, “horizontally”, “upstream” and “downstream” are in reference to the horizontal direction H. Further, opposing, first and second major faces  110 ,  112  of the glass ribbon  22  are identified in  FIG. 1 . 
     The travel path of the glass ribbon  22  relative to the conveying apparatus  32  initiates at the upstream side  40  at an upstream location  120  that is in or closely proximate the primary plane of travel P. The first bending tool  74  is located proximate, but downstream of, the upstream location  120 , and provides a bearing surface  122  (referenced generally, such as a physical surface, an air bearing, etc.) positioned vertically above the primary plane of travel P (and vertically above the upstream location  120 ). A location of the first bending tool  74  relative to the upstream side  40  is further correlated with an expected viscosity of the glass ribbon  22 ; the first bending tool  74  is positioned to interface with first major face  110  of the glass ribbon  22  at a point where a viscosity of the glass ribbon  22  is conducive to gravity-induced bending. With this arrangement, the first bending tool  74  and gravity force the first bend  100  into the glass ribbon  22  as the glass ribbon  22  progresses from the upstream location  120  to the bearing surface  122 , and then beyond (downstream of) the bearing surface  122 . The glass ribbon  22  can be viewed has having a first segment  124  and a second segment  126  at opposite sides of the first bend  100 . Because the interface region  122  is positioned vertically above the upstream location  120 , the first segment  124  progresses vertically away from the primary plane of travel P from the upstream location  120  to the bearing surface  122 . As the glass ribbon  22  travels beyond the bearing surface  122 , gravity causes the second segment  124  to progress vertically toward the primary plane of travel P from the first bend  100 . The first bend  100  is a curvature in the glass ribbon  22  between the first and second segments  124 ,  126 , and has an apex  127  (i.e., the apex is where a slope of the curve of the first bend  100  is zero). The curve provided by the first bend  100  is convex relative to the primary plane of travel P. 
     The second bend  102  is formed downstream of the first bend  100 , and is produced by gravity and a location of at least the second bending tool  76 . In particular, the second bending tool  76  is positioned vertically above, and horizontally downstream of, the interface region  122  of the first bending tool  74 . A location of the second bending tool  76  is further correlated with an expected viscosity of the glass ribbon  22 ; the second bending tool  76  is positioned to interface with the first major face  110  of the glass ribbon  22  at a point where the viscosity of the glass ribbon  22  has increased (relative the viscosity at the point of interface with the first bending tool  74 ) to a level at which the glass ribbon  22  is unlikely to experience a substantive bend due solely to the force of gravity. In other words, at the point of interface with the second bending tool  76 , a viscosity of the glass ribbon  22  is sufficiently high enough such that the glass ribbon  22  will not simply curve around the second bending tool  76  in a manner similar to interaction of the glass ribbon  22  with the first bending tool  74  described above. However, a distance between the first and second bending tools  74 ,  76  (both vertically and horizontally) in combination with an expected viscosity of the glass ribbon  22  is such that the second bend  102  will be formed in the glass ribbon  22  (upstream of the second bending tool  76 ) due to gravity. In other words, a position of the second bending tool  76  and expected viscosity of the glass ribbon  22  is such that the glass ribbon  22  defines the second segment  126  as described above (i.e., vertically toward the primary plane of travel P) and a third segment  128  at opposite sides of the second bend  102 . The second bending tool  76  causes third segment  128  to progress vertically away from the primary plane of travel P in traveling from the second bend  102  to the second bending tool  76 . The second bend  102  represents a curvature in the glass ribbon  22  between the second and third segments  126 ,  128 , and has an apex  129 . The curve established by the second bend  102  is concave relative to the primary plane of travel P. If the viscosity of the glass ribbon  22  too high and/or the second bending tool  76  more closely positioned to the first bending tool  74 , the force of gravity alone may not be sufficient to cause the second bend  102  to form. With these explanations in mind, then, the second bending tool  76  is configured and located to support the glass ribbon  22  along the travel path as the glass ribbon  22  progresses toward the third bending tool  78 . 
     The third bend  104  is formed downstream of the second bend  102 , and is produced by the third bending tool  78  and gravity. In particular, the third bending tool  78  is positioned vertically above, and horizontally downstream of, the second bending tool  76 . A location of the third bending tool  78  is further correlated with an expected viscosity of the glass ribbon  22 ; the third bending tool  78  is positioned to interface with the second major face  112  of the glass ribbon  22  at a point where the viscosity of the glass ribbon  22  has increased (relative to the viscosity of the glass ribbon  22  at the point of interface with the first bending tool  74 ) to a level appropriate for forced bending and is unlikely to experience a substantive bend due solely to the force of gravity. In other words, a viscosity of the glass ribbon  22  is sufficiently high that the glass ribbon  22  will not experience local shearing upon contacting a surface (such as the third bending tool  78 ), but sufficiently low as to readily deform in response to the contact. A position of the third bending tool  78  is correlated with an expected viscosity of the glass ribbon  22  at the point of interface with the third bending tool  78  such that the glass ribbon  22  includes the third segment  128  as described above (i.e., progressing vertically away the primary plane of travel P) and a fourth segment  130  at opposite sides of the third bend  104 . The fourth segment  130  progresses vertically toward the primary plane of travel P from the third bend  104 . The third bend  104  represents a curvature in the glass ribbon  22  between the third and fourth segments  128 ,  130 , and has an apex  131 . The curve establishing the third bend  104  is convex relative to the primary plane of travel P. As a point of reference, absent the third bending tool  78 , gravity would likely cause the glass ribbon  22  to eventually deflect from the direction of the third segment  128 , gradually curving back toward the primary plane of travel P as the glass ribbon  22  progressed away from the second bending tool  76 . The third bending tool  78  is imposed into this natural, gravity-induced path, forcing the glass ribbon  22  to experience a more distinct curve, appropriate for producing the surface stresses described above (e.g., sufficient for removing warp components in the glass ribbon  22 ). Thus, and as reflected by  FIG. 1 , the third bend  104  is formed in the glass ribbon  22  such that the apex  131  of the third bend  104  is slightly upstream of the third bending tool  78 . That is to say, the glass ribbon  22  does not form a distinct curve at or around the third bending tool  78 ; rather, the third bending tool  78  is formatted and positioned (relative to the second bending tool  76 ) so as to impart a deflection into the travel path that, in combination with gravity and viscosity of the glass ribbon  22  at the point of interface with the third bending tool  78 , generates the third bend  104  appropriate for removing warp. Regardless, a vertical distance between the primary plane of travel P and the third bend  104  is greater than the vertical distance between the primary plane of travel P and the first bend  100 . 
     The travel path of the glass ribbon  22  continues from the apex  131  of the third bend  104  toward the primary plane of travel P. Adjacent the downstream end  42 , the first major face  110  is supported by (e.g., in contact with) the rollers  80 . The glass ribbon  22  can lie in the primary plane of travel P along the rollers  80  and at the pulling device  72 . In some embodiments, a location of the rollers  80  is correlated with an expected viscosity of the glass ribbon  22  at the point of interface with rollers  80 ; for example, where a viscosity of the glass ribbon  22  has increased to level appropriate for direct, non-damaging contact with a roller surface. 
     While the conveying apparatus  32  has been described as including three of the bending tools  74 ,  76 ,  78 , and as defining the travel path as including three of the bends  100 ,  102 ,  104 , any other number of bending tools, either lessor or greater, can be acceptable. For example, additional bending tools can be provided to support the glass ribbon  22  along the desired travel path (e g , akin to the second bending tool  76  as described above). Regardless, the conveying apparatuses of the present disclosure are formatted to form at least one curve or bend in the travel path of the glass ribbon  22  at a location corresponding with an expected viscosity of the glass ribbon  22  at the point of the bend appropriate to generate a surface stress sufficient to remove warp components from the glass ribbon  22 . In the case of a viscous membrane (e.g., a viscous glass ribbon), the stress generated by bending is in part used to macroscopically deform the glass ribbon  22  and also to flatten it locally. These stresses are relaxed in a short time, making the local deformation permanent. The glass ribbon  22  experiences this flattening along at least one or more of the bends  100 ,  102 ,  104 . While the travel path of the glass ribbon  22  from the upstream side  40  to the downstream side  42  has been described as initiating with the convex (relative to the primary plane of travel P) first bend  100 , in other embodiments, the travel path from the upstream side can comprise one or more other bends upstream of the first bend  100  (e.g., one or more concave (relative to the primary plane of travel P) bends upstream of the convex first bend  100 ). 
     The bending tools utilized with the conveying apparatuses of the present disclosure, such as the bending tools  74 ,  76 ,  78 , can assume various forms appropriate for interfacing with the glass ribbon  22  as the glass ribbon  22  is conveyed along the travel path in a manner that mechanically produces the warp-reducing bends as described above. In more general terms, the bending tools are configured to establish a line type contact or interface with the glass ribbon  22  with minimal or no thermal effect (i.e., the bending tool does not create a “thermal scar” on the glass ribbon  22 ). In some embodiments, one or more or all of the bending tools provided with the floor conveying units of the present disclosure, such as one or more of the bending tools  74 ,  76 ,  78  can be a static body (e.g., a stationary or non-rotating rod). The static bending tools useful with the floor conveying units and methods of the present disclosure can comprise a high thermal conductivity material to avoid thermal gradient-driven deformations in the glass ribbon  22 . In some embodiments, the static-type bending tools incorporate a low coefficient of friction material (or other material configured to have a low friction interface with a glass ribbon) at least at the face intended to interface with the traveling glass ribbon  22  to minimize drag and sticking concerns. For example, the static-type bending tools can comprise or include silicon carbide, graphite, etc., at least at the face intended to interface with the glass ribbon  22 . In yet other embodiments, the static-type bending tools can include an air bearing that interfaces with the traveling glass ribbon  22  (e.g., the first bending tool  74  can have an air bearing construction). The air bearing constructions may be used as a bending tool at locations at which moderate forces are appropriate for producing the desired bend or curve in the glass ribbon  22 . 
     In some embodiments, one or more or all of the bending tools provided with the conveying apparatuses of the present disclosure, such as one or more of the bending tools  74 ,  76 ,  78 , can have a rolling-type construction, such as a roller rotatably supported by a shaft. In some embodiments, the rolling-type bending tools can incorporate a lower thermal conductivity design to promote the low thermal gradient-driven deformation mentioned above. For example, the rolling-type bending tools can comprise or include an alumina material at least at the surface intended to interface with the traveling glass ribbon  22 ; appropriate alumina bodies (tube, rods, etc.) are readily available, and can handle high temperatures. Other non-limiting examples of materials useful with the rolling-type bending tools include high strength ceramics (e.g., silicon carbide). 
     In some embodiments, one or more or all of the bending tools provided with the conveying apparatuses of the present disclosure are configured to address possible heat transfer concerns by providing forced circulation around a high thermal conductivity material. These optional constructions may be helpful to smooth thermal gradients and reduce the level of residual stress (in-plane component). For example, the bending tool can be configured such that the glass ribbon  22  travels over a high effusivity body that in turn generates curvature inversions. In related embodiments, one or more or all of the bending tools can be configured to provide heat transfer from both major faces  110 ,  112  of the glass ribbon  22  to enhance the overall effect. 
     In some embodiments, one or more or all of the bending tools provided with the conveying apparatuses of the present disclosure, such as one or more or all of the bending tools  74 ,  76 ,  78 , can incorporate a self-alignment mechanism. As a point of reference, it may be beneficial to produce proper alignment of the bending tool in-line with the principal traveling direction of the glass ribbon  22  to avoid occurrences of compressive/tensile forces onto the glass ribbon  22  that can, in turn, drive out-of-plane deformations. The self-alignment mechanism can assume various forms appropriate for maintaining alignment with the principal traveling direction. For example, a device providing an upstream rotation axis normal to the plane of the glass ribbon  22  can be linked to the bending tool; with this construction, the downstream pulling force (applied by the pulling device  72 ) generates a moment that aligns the assembly (e g , akin to a weather vane). 
     In some embodiments, one or more or all of the bending tools provided with the conveying apparatuses of the present disclosure, such as one or more or all of the bending tools  74 ,  76 ,  78 , can be configured to provide position adjustability relative to the conveyor system  70 , and in particular relative to the primary plane of travel P (vertically and/or horizontally adjustable). As a point of reference, in the case of bending the glass ribbon  22  at high viscosity, the relative position of two successive bending tools along the travel path may need to be controlled within tight tolerances (e.g., within 100 micrometers over distances of 100 mm). The spacing between the two successive bending tools can be greater than about 50 mm (along the glass ribbon travel path) in some embodiments; at shorter distances, a minor misalignment between successive bending tools may generate significant out-of-plane stresses and/or instabilities. Further, parallelism in the glass ribbon between successive bending tools can be beneficial in order to generate a consistent bending radius across the width of the glass ribbon  22 . With this in mind, the bending tool(s) can be supported relative to the conveyor device  70  by framework (not shown) or other structures that permit vertical and/or horizontal adjustment. In related embodiments, an appropriate actuator (e.g., pneumatic, mechanical, electronic, etc.) can be linked or connected to the bending tool, with operation of the actuator controlled by a controller (e.g., PLC). With these and other embodiments, a position of one or more of the bending tools can be automatically adjusted prior to or during a glass ribbon production operation. For example, conditions during initial start-up of the system  20  (e.g., heat-up and glass ribbon initiation or threading) may not be compatible with the bending tool locations otherwise desired during normal production; under these and other circumstances, automated repositioning of one or more of the bending tools can be provided. Similarly, different glass ribbon properties and/or production requirements may implicate different bending tool locations; automated repositioning (e.g., for example in response to operator entered production constraints) of one or more of the bending tools can be provided. 
     An exemplary bending tool assembly  150  in accordance with principles of the present disclosure and useful with the floor conveying units of the present disclosure, such as the floor conveying unit  32  ( FIG. 1 ), is shown in  FIG. 4 . The bending tool assembly  150  includes an upstream bending tool  160 , a downstream bending tool  162 , an upstream support unit  164  (referenced generally), a downstream support unit  166  (referenced generally), and a base unit  168 . Details on the various components are provided below. In general terms, the bending tool assembly  150  can be mounted relative to a conveyor device, such as the conveyor device  70  ( FIG. 1 ) described above, locating the bending tools  160 ,  162  upstream of a pulling device, such as the pulling device  72  ( FIG. 1 ). The bending tools  160 ,  162  are configured and located to interface with a continuously conveyed glass ribbon (not shown) in a manner that decreases warp or improves flatness. The upstream support unit  164  retains the upstream bending tool  160  relative to the base unit  168 , and in some embodiments permits selective positioning of the upstream bending tool  160  relative to the conveyor device, and in particular relative a primary plane of travel (such as the primary plane of travel P ( FIG. 1 ) described above) of the conveyor device. The downstream support unit  164  similarly retains the downstream bending tool  162  in some embodiments. 
     The bending tools  160 ,  162  can each assume any of the forms described throughout this disclosure, and in some embodiments are or include a cylindrical rod  180  (identified for the upstream bending tool  160 ). One or both of the bending tools  160 ,  162  can comprise a roller, incorporating rolling features (e.g., bearings  182 , one of which is identified in  FIG. 4 ) that provide rotation of the rod  180  about a central axis thereof (upon mounting to the corresponding upstream support unit  164  and downstream support unit  166  as described below). Optionally, one or both of the bending tools  160 ,  162  can further include heat shield(s)  184  (one of which is identified in  FIG. 4 ) mounted to the rod  180  and configured to protect a corresponding one of the rolling features (e.g., one of the bearings  182 ) from heat radiating from a glass ribbon (not shown). One or both of the bending tools  160 ,  162  can have other constructions that may or may not be illustrated by  FIG. 4 , and may or may not have a roller-type format. 
     The upstream support unit  164  includes opposing, first and second upstream support bodies  190 ,  192 . The upstream support bodies  190 ,  192  can be identical in some embodiments, and are each generally configured to support an end region of the upstream bending tool  160  (e.g., the cylindrical rod  180  of the upstream bending tool  160 ), and to establish a spatial position of the upstream bending tool  160  relative to the base unit  168 .  FIG. 5  illustrates a portion of the first upstream support body  190  in greater detail. The upstream support body  190  forms or defines a tool receiving slot  194  and a guide slot  196 . A size and shape of the tool receiving slot  194  corresponds with features of the upstream bending tool  160  to permit selective assembly or mounting of the upstream bending tool  160  to the upstream support body  190 . For example, a size and shape of the tool receiving slot  194  can correspond with a size and shape of the bearing  182  carried by the rod  180 , such that the bearing  182  nests within the slot  194  in the mounted state of  FIG. 5 . Further, the upstream bending tool  160  can include one or more additional components that selectively hold or lock the bearing  182  relative to the support body  190  in the mounted state, such as a collar  200  and a spring  202  or similar component that biases the collar  200  into engagement with the support body  190 . With this construction, the upstream bending tool  160  can be selectively secured to, and removed from, the first upstream support body  190  (as well as the second upstream support body  192  ( FIG. 4 )). Other mounting constructions are also acceptable, and may or may not provide for removable assembly of the upstream bending tool  160  to the upstream support unit  164  ( FIG. 4 ). 
     The guide slot  196  is included in some optional embodiments, and is generally configured to facilitate a moveable connection between the first upstream support body  190  and the base unit  168 . For example, in some embodiments, the guide slot  196  is sized and shaped to slidably receive a fastener  210  included with the base unit  168 . With this optional construction, the fastener  210  can be loosened to permit raising or lower of the support body  190  (and thus of the upstream bending tool  160  carried there by) relative to the base unit  168 ; once the support body  190  is at a desired vertical position, the fastener  210  can then be tightened to secure the support body  190  relative to the base unit  168 . In this regard, the support body  190  can form or carry an indicator  212  (e.g., a groove) that serves to correlate or identify a vertical position of the support body  190  relative to a scale or other indicia included with the base unit  168  as described in greater detail below. The first upstream support body  190  (and the base unit  168 ) can incorporate other mounting configurations that may or may not include the guide slot  196 . 
     Returning to  FIG. 4 , the downstream support unit  166  can be constructed similar to, such as identical to, the upstream support unit  164  as described above including, for example, opposing first and second downstream support bodies  220 ,  222 . In some embodiments, the downstream support bodies  220 ,  222  are configured to establish a more permanent connection or assembly of the downstream bending tool  162 . For example, in some embodiments, the downstream bending tool  162  may not be readily removable from the downstream support unit  166 . 
     The base unit  168  can include a plate  230 , opposing first and second side legs  232 ,  234 , and framework  236  (referenced generally). The side legs  232 ,  234  can be identical in size and shape, and are attached to and project from opposite ends of the plate  230 . The framework  236  includes opposing first and second cross-beams  240 ,  242 , and optional opposing first and second arms  244 ,  246 . The cross-beams  240 ,  242  are movably connected to a corresponding one of the side legs  232 ,  234 , and to a corresponding one of the support bodies  190 ,  192  or  220 ,  222  included with the upstream and downstream support units  164 ,  166 . The arms  244 ,  246  extend between and interconnect the cross-beams  240 ,  242 . With this construction, the plate  230  provides a robust structure for installing the bending tool assembly  150  relative to a floor conveying unit such that the plate  230  and the legs  232 ,  234  are held stationary. Each of the cross-beams  240 ,  242  can be selectively moved relative to the corresponding leg  232 ,  234  to collectively raise or lower a corresponding end of the upstream and downstream support units  164 ,  166  (and thus an end of the corresponding upstream and downstream bending tool  160 ,  162  carried thereby) relative to the plate  230 . Further, an end of each of the upstream and downstream bending tools  160 ,  162  can be individually raised or lowered relative to plate  230  via movement of the corresponding support body  190 ,  192 ,  220 ,  222  relative to the corresponding cross-beam  240 ,  242 . 
     Interconnection between the support units  164 ,  166  and the base unit  168  is further illustrated in  FIG. 6A . The first upstream support body  190  is selectively coupled to the first cross-beam  240  by the fastener  210  (that otherwise is slidably received within the guide slot  196 ) such that the first upstream support body  190  (and thus the end of the upstream bending tool  160  carried thereby) can be raised and lowered relative to the first cross-beam  240 . An upstream scale or measurement tool  250  can be affixed to the first cross-beam  240  proximate the first upstream support body  190  and can include incremented designations (e.g., numbers, hash marks, etc.). A relationship between the indicator  212  of the first upstream support body  190  and the designations included on the scale  250  can indicate a vertical position of the end of the upstream bending tool  160  carried by the first upstream support body  190  relative to the first cross-beam  240  and/or relative to the plate  230 . For example, in the arrangement of  FIG. 6B , the first upstream support body  190  has been vertically raised (as compared to the position of  FIG. 6A ) relative to the first cross-beam  240 . This change in position can be visually indicated to a user by the indicator  212  and the scale  250 ; in the position of  FIG. 6A , the indicator  212  aligns with a first designation along the scale  250  (i.e., “30”), whereas in the position of  FIG. 6B , the indicator  212  aligns with a different designation along the scale  250  (i.e., at a designation between “30” and “40”; approximately “38”). Other scalar-type identification schemes can alternatively be used. 
     With reference between  FIGS. 5 and 6A , the first downstream support body  220  can similarly define a guide slot  252 , and can be selectively coupled to the first cross-beam  240  by a fastener  254  slidably received within the guide slot  252 . Thus, the first downstream support body  220  (and the end of the downstream bending tool  162  carried thereby) can be raised or lowered relative to the first cross-beam  240 . A downstream scale or measurement tool  256  can be affixed to the first cross-beam  240  proximate the first downstream support body  220 ; a relationship between an indicator  258  formed on or carried by the first downstream support body  220  relative to measurement-related information included on the downstream scale  256  can indicate a vertical position of the end of the downstream bending tool  162  carried by the first downstream support body  220  relative to the first cross-beam  240  and/or relative to the plate  230 . For example, a comparison of  FIGS. 6A and 6B  reveals that in the arrangement of  FIG. 6B , the first downstream support body  220  has been vertically lowered (as compared to the position of  FIG. 6A ) relative to the first cross-beam  240 . This change in position can be indicated to a user by the indicator  258  and the downstream scale  256 ; in the position of  FIG. 6A , the indicator  258  aligns with a first designation along the downstream scale  256  (i.e., between “10” and “20”; approximately “13”), whereas in the position of  FIG. 6B , the indicator  258  aligns with a different designation along the downstream scale  256  (i.e., at a designation below “10”; approximately “8”). 
     In some embodiments, the upstream scale  250  and the downstream scale  256  can carry or display identical measurement-related designators, and may be horizontally aligned relative to one another along the first cross-beam  240 . For example, as shown in  FIG. 6A , the designator “30” on the upstream scale  250  can be horizontally aligned with the designator “30” on the downstream scale  256 . With this optional configuration, a user can more readily understand and select a desired vertical spacing between the upstream and downstream bending tools  160 ,  162 . For example, where the scales  250 ,  256  have designators incremented in millimeters and a user desires to 20 mm vertical spacing between the upstream and downstream bending tools  160 ,  162 , the indicator  212  of the first upstream support  190  can be aligned with the “30” on the upstream scale  250 , and the indicator  258  can be aligned with the “10” on the downstream scale  256 . 
     In some embodiments, the first cross-beam  240  can be selectively coupled to the first side leg  232 . For example, the first side leg  232  can form one or more guide slots  260  each sized to slidably receive a fastener  262  that in turn is attached to the first cross-beam  240 . With this exemplary construction, the first cross-beam  240 , and thus the upstream and downstream bending tools  160 ,  162  via the support bodies  190 ,  220 , can be raised and lowered relative to the first side leg  232 , and thus relative to the plate  230 . A midstream scale or measurement tool  264  can be affixed to the first side leg  232  proximate one of the guide slots  260 ; a relationship between an indicator  266  formed on or carried by the first cross-beam  240  relative to measurement-related information included on the scale  264  can indicate a vertical position of the first cross-beam  240  (and thus of the bending tools  160 ,  162 ) relative to the plate  230 . 
     Returning to  FIG. 4 , the second upstream support body  192  and the second downstream support body  222  can be selectively coupled to the second cross-beam  242  commensurate with the descriptions above. With these optional assembly configurations, the first bending tool  160  can be vertically raised and lowered relative to the plate  230  via selected movement of the first and second upstream support bodies  190 ,  192  relative to the corresponding cross-beam  240 ,  242 . In some embodiments, the second upstream support body  192  includes or carries an indicator (hidden) similar to or identical to the indicator  212  ( FIG. 5 ) of the first upstream support body  190 , and the second cross-beam  242  includes or carries an upstream scale  270  similar to or identical to the upstream scale  250  as described above. A vertical location of the second upstream support body indicator along the second upstream support body  192  can be similar to or identical to that of the indicator  212  along the first upstream support body  190 ; incremented designators along the upstream scale  270  included with the second cross-beam  242  can be similar to or identical to those of the upstream scale  250  included with the first cross-beam  240 , and a vertical location of the upstream scale  270  on the second cross-beam  242  can be similar to or identical to that of the upstream scale  250  on the first cross-beam  240 . With these optional construction, a user is provided with a visual indication as to a vertical position of the opposing ends of the upstream bending tool  160  as dictated by the upstream support bodies  190 ,  192 . For example, if a user desires to arrange the upstream bending tool  160  such that the central axis of the rod  180  is substantially horizontal and assuming the plate  230  is horizontally mounted, the first and second upstream support bodies  190 ,  192  are arranged relative to the corresponding cross-beam  240 ,  242  such that the indicator  212  of the first upstream support body  190  and the indicator of the second support body  192  can be aligned with the same incremented designator included with the corresponding upstream scale  250 ,  270 . Additionally, a user can establish a known deviation from horizontal by arranging the first and second upstream support bodies  190 ,  192  at selected, differing vertical locations relative to the corresponding upstream scale  250 ,  270 . Similar or identical alignment features can optionally be included in the downstream support unit  166 . 
     In some embodiments, the second cross-beam  242  can be selectively coupled to the second side leg  234  commensurate with the descriptions above with respect to selective coupling between the first cross-beam  240  and the first side leg  232 . Further, the second cross-beam  242  can include or carry an indicator (hidden) similar to or identical to the indicator  266  ( FIG. 7A ) of the first cross-beam  240 , and the second side leg  234  can include or carry a midstream scale (hidden) identical to the midstream scale  264  associated with the first side leg  232 . With these optional constructions, the upstream and downstream bending tools  160 ,  162  can be collectively vertically raised and lowered relative to the plate  230  by raising or lowering the framework  236  relative to the side legs  232 ,  234 . The arms  244 ,  246 , where included, can serve as handles for manipulate the framework  236  as a whole. Regardless, a user can be provided with a visual indication of vertical alignment of the cross-beams  240 ,  242  relative to the corresponding side leg  232 ,  234  via the indicator of each cross-beam  240 ,  242  (e.g., the indicator  266  of the first cross-beam  240 ) relative to the corresponding midstream scale associated with the corresponding side leg  232 ,  234  (e.g., the midstream scale  264  of the first side leg  232 ). Other mounting configurations that may or may not facilitate collective vertical movement of the upstream and downstream bending tools  160 ,  162  are also acceptable. 
     The bending tool assembly  150  can optionally include one or more additional components or features. For example, in some embodiments the bending tool assembly  150  can be automated or mechanized, with one or more of the adjustments or measurements described above being made remotely through a controller (e.g. programmable logic controller) or computer interface. 
       FIG. 7  illustrates, in simplified form, one example of a conveying apparatus  32 ′ processing the glass ribbon  22  in accordance with principles of the present disclosure. The conveying apparatus  32 ′ includes the conveyor device  70  and the pulling device  72  as described above, along with the bending tool assembly  150 . Commensurate with previous explanations, the conveyor device  70  establishes the primary plane of travel P from the upstream side  40  to the downstream side  42 . The bending tool assembly  150  is arranged between the upstream side  40  and the downstream side  42 , with the upstream bending tool  160  being upstream of the downstream bending tool  162 . The bending tool assembly  150  establishes a travel path that deviates from the primary plane of travel P, including the glass ribbon  22  traveling over (and in contact with) the upstream bending tool  160  and under (and in contact with) the downstream bending tool  162 . As the glass ribbon  22  is caused to bend at the upstream bending tool  160 , the corresponding bending stress effectuates warp removal as described above. In some embodiments, the upstream and downstream bending tools  160 ,  162  are located to interface with the glass ribbon  22  at a point where the glass ribbon  22  is expected to have a higher viscosity (e.g., an expected viscosity of the glass ribbon  22  at the point of interface with the upstream bending tool  160  is greater than would otherwise be necessary for the glass ribbon  22  to bend about the upstream bending tool  160  solely due to gravity). As a point of reference, threading of the glass ribbon  22  to the conveying apparatus  30 ′ can include removing the upstream bending tool  160  from the upstream support unit  164 , threading the glass ribbon  22  through the conveying apparatus  30 ′, and then installing the upstream bending tool  160  to the upstream support unit  164  (arriving at the travel path of  FIG. 7 ). In other embodiments, the upstream bending tool  160  can be more permanently installed to the upstream support unit  164 . 
     Returning to  FIG. 1 , the systems, conveying apparatuses and methods of the present disclosure can incorporate one or more additional features that aid in the reduction of warp. For example, the conveyor device  70  can include a table or plate having a flat surface projecting from the upstream side  40  in the primary plane of travel P and intended to provide desired heat transfer with the glass ribbon  22 . In some embodiments, the conveying apparatus  32  can include one or more suspension rods or similar structures (e.g., graphite rods) located to prevent the glass ribbon  22  from contacting the flat surface of the table. It has surprisingly been found that by avoiding contact between the traveling glass ribbon  22  and an elongated flat surface reduces occurrences of macro longitudinal waves (e.g., deviations in flatness of greater than 3 mm extending lengthwise in the glass ribbon  22 ) that likely result from lengthy contact with a cold surface. In related embodiments, the support or air table can be formed of a Zircar ceramic (instead of graphite) to provide low emissivity and low thermal conductivity properties. Alternatively or in addition, warp at edges of the glass ribbon  22  can be reduced by reverse bending the glass ribbon  22  over rods arranged perpendicular to the glass ribbon travel path, providing suspension rods adjacent the upstream side  40  with a catenary that drives bending and flattening of the glass ribbon  22 , and/or providing one or more additional nip/flattening rolls that provide roll-on-roll line contact to generate a high local bending pressure. 
     Embodiments and advantages of features of the present disclosure are further illustrated by the following non-limiting examples, but the particular materials and amounts thereof recited in these examples, as well as other conditions and details, should not be construed to unduly limit the scope of the present disclosure. 
     EXAMPLE 
     A comparative sample glass sheet was prepared using a conventional fusion draw method production system including a conveying apparatus receiving a continuous glass ribbon from a down draw fusion supply apparatus. The conveying apparatus included a nip roller at a downstream end thereof, and conveyed the glass ribbon in a primary plane of travel from an upstream end to a downstream end. The glass ribbon was subjected to a 90 degree turn (vertical to horizontal) from the fusion supply apparatus to the conveying apparatus, and was allowed to cool while traversing the conveying apparatus. Following cooling, the comparative sample glass sheet was cut from the glass ribbon; the comparative sample glass sheet had a width of 250 mm and a length of 650 mm. Warp in the comparative sample glass sheet was then measured, and is presented in  FIG. 8 . The range of deviation in flatness exhibited by the comparative sample glass sheet was found to be greater than 300 micrometers. 
     An example glass sheet was prepared using the same glass formulations employed for the comparative sample glass sheet as above. The fusion supply apparatus utilized in preparing the comparative sample glass sheet was also employed as was the conveying apparatus, except that bending tools were incorporated into the conveying apparatus similar to the arrangement of  FIG. 1 , subjecting the glass ribbon to a series of bends. Following cooling, the example glass sheet was cut from the glass ribbon; the sample glass sheet had a width of 250 mm and a length of 650 mm. Warp in the example glass sheet was then measured, and is presented in  FIG. 9 . The range of deviation in flatness exhibited by the example glass sheet was found to be less than 100 micrometers. A comparison of  FIGS. 8 and 9  reveals that with all other parameters being equal, flatness is improved with the conveying apparatuses, systems and methods of the present disclosure. 
     The glass ribbon processing systems, conveying apparatuses, and methods of the present disclosure provide a marked improvement over previous designs and techniques. Some systems, apparatuses and methods of the present disclosure provide for warp reduction in a continuously conveyed glass ribbon through a succession of one or more bends at different viscosities. The upward force component(s) for forming the bend(s) can be provided by a physical means that drives the glass ribbon to a higher position as compare to the normal plane of travel. This physical means can be a solid surface, static or in rotation, with or without air bearing, leading to an interaction that can be friction, rolling or non-contact. The downward force component(s) for forming the bends can be provided by gravity when viscosity is sufficiently low, or by the use of a mechanical means that forces the glass ribbon to a lower position. The glass ribbon bending generates a stress field that tends to flatten the profile of the glass ribbon across the width. 
     Various modifications and variations can be made the embodiments described herein without departing from the scope of the claimed subject matter. Thus it is intended that the specification cover the 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.