Patent Publication Number: US-2013240591-A1

Title: Method and apparatus for separating a pane of brittle material from a moving ribbon of the material

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to separating a pane of a brittle material from a moving ribbon of the material, and in one configuration, to separating panes of glass from a moving ribbon of glass, while reducing the introduction of disturbances into the upstream ribbon. 
     2. Description of Related Art 
     Specialized glasses have found increased applicability, including substrates, in the manufacture of display devices. For example, liquid crystal displays (LCDs) have become increasingly popular for displaying information in calculators, watches, video games, audio and video equipment, portable computers and even car dashboards. The improving quality and size of LCDs has made the LCDs an attractive alternative to cathode ray tubes (CRTs) which are traditionally used in television sets and desktop computer displays. In addition, other flat panel display (FPD) types, such as plasma displays (PDs), field emission displays (FEDs) and organic light-emitting polymer displays (OLEDs) are being developed as alternatives to LCDs. Thin film transistor liquid crystal displays (TFT-LCD) are used in notebook computers, flat panel desktop monitors, LCD televisions, and Internet and communication devices, to name only a few. It is increasingly useful to incorporate electronic components onto a glass sheet (glass substrate) used in the display device. Some display devices such as TFT-LCD panels and OLED panels are made directly on flat glass sheets. For example, the transistors are arranged in a patterned array and are driven by peripheral circuitry to provide (switch on) desired voltages to orient the molecules of the LC material in the desired manner. 
     In-plane stress (and resulting strain) can result in a variation of the alignment of the transistors and the pixels. This can result in distortion in the display panel. As such, in LCD and other glass display applications, it is exceedingly beneficial to provide glass (substrates) that are within acceptable tolerances for distortion. 
     Flat panel display manufacturers are finding that demands for larger display sizes and the economies of scale are driving manufacturing processes to larger size pieces of glass. Industry standards have evolved from Gen III (550 mm×650 mm), Gen III.5 (600 mm×720 mm), and Gen IV (1,000 mm×1,000 mm) sizes and larger. As the desired size of the glass pieces increases, the difficulty of the production and handling increases. 
     The manufacturing of the glass used as the substrate is extremely complex. The drawdown sheet or fusion process, described in U.S. Pat. No. 3,338,696 (Dockerty) and U.S. Pat. No. 3,682,609 (Dockerty), herein incorporated by reference, is one of the few processes capable of delivering the glass without requiring costly post forming finishing operations such as lapping and polishing. 
     However, the fusion process requires the separation and removal of panes from a continuously moving ribbon of glass. Traditionally, the separation of the panes has been performed by forming a separation line in the ribbon of glass. Then a vacuum cup array is attached to the glass below the score line and the portion of the ribbon below the score line is rotated less than 15° to cause the glass to break at the score line and thus form the desired glass pane. This breaking produces a newly formed leading edge on the moving ribbon and a newly formed trailing edge on the glass pane. 
     However, this exertion of such a large bending moment on the ribbon, imparts significant potential energy to the ribbon, particularly upon the snapping of the pane from the ribbon. Introduction of this energy (and mechanical disturbance) into the upstream ribbon can lead to undesirable characteristics in subsequent glass panes. 
     Therefore, there is a need to provide for the separation of a pane from a continuously moving ribbon of brittle material, while reducing imparted disturbances which can propagate upstream along the ribbon. The need also exists for increasing control over the crack propagation used to separate a pane from the ribbon. 
     BRIEF SUMMARY OF THE INVENTION 
     The present system provides for the repeatable and uniform separation of a pane of brittle material from a continuously moving ribbon of the brittle material, while reducing the introduction of disturbances into the upstream ribbon. 
     In selected configurations, the system provides for the separation of a pane of glass from a continuously moving ribbon of glass. For purposes of description, the following discussion is set forth in terms of glass manufacturing. However, it is understood the invention as defined and set forth in the appended claims is not so limited, except for those claims which specify the brittle material is glass. 
     In the fusion glass formation process, a glass ribbon transitions from a liquid state to a downstream solid state. The introduction of disturbances into the glass in the visco-elastic region of the glass can result in undesired nonuniformity or stresses in the resulting solid state glass. Traditionally, the separation of a pane from the ribbon introduced significant energy in the form of a vibration, wave or distortion to the solid portion of the ribbon. Such distortion migrates upstream into the visco-elastic region of the ribbon. The distortion can introduce nonuniformity and nonlinearity in an uncontrolled manner, and can decrease the quality of the resulting panes. 
     In the present system, the ribbon is restrained upstream of a score line prior to separating the pane from the ribbon. The restraint of the ribbon can be accomplished by contacts upstream of the score line on the first side and the second side of the ribbon, wherein the contacts are either opposite, overlapping or offset. The restraint can be prior to, substantially simultaneous with or subsequent to forming the score line in the ribbon. The restraint of the ribbon is selected to facilitate separation of a pane from the ribbon and minimize or reduce the introduction of a disturbance or bending moment into the upstream ribbon. 
     The present system separates the pane from the ribbon and reduces the propagation of disturbances upstream in the ribbon by contacting opposing sides of the ribbon with a pair of opposing bars, wherein the bars move with the ribbon, thereby restraining a portion of the ribbon upstream of a score line. A downstream press bar contacts the ribbon downstream of a score line to separate the pane from the ribbon along the score line, while the ribbon is temporarily restrained upstream of the separation line. 
     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. 
     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 as claimed below. Also, the above listed aspects of the invention, as well as the preferred and other embodiments of the invention discussed and claimed below, can be used separately or in any and all combinations. 
     The accompanying drawings are included to provide a further understanding of the invention, and are incorporated in and constitute a part of this specification. The drawings illustrate various embodiments of the invention, and together with the description serve to explain the principles and operation of the invention. It should be noted that the various features illustrated in the figures are not necessarily drawn to scale. In fact, the dimensions may be arbitrarily increased or decreased for clarity of discussion. 
    
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
         FIG. 1  is a schematic view of a fusion glass fabrication apparatus. 
         FIG. 2  is a front elevational schematic view of the ribbon extending from a fusion glass fabrication apparatus. 
         FIG. 3  is a side elevational schematic view of the ribbon with the upstream press bar and an offset upstream backing bar in a retracted position. 
         FIG. 4  is a side elevational schematic view of the ribbon with the upstream press bar opposite upstream backing bar in a retracted position. 
         FIG. 5  is a side elevational schematic view of the ribbon with an overlapping upstream press bar and the upstream backing bar in a retracted position. 
         FIGS. 6   a - 6   d  are side elevational schematic views of a first configuration for the separation of a pane from the ribbon. 
         FIGS. 7   a - 7   f  are side elevational schematic views of a second configuration for the separation of a pane from the ribbon. 
         FIGS. 8   a - 8   f  are side elevational schematic views of a third configuration for the separation of a pane from the ribbon. 
         FIGS. 9   a - 9   f  are side elevational schematic views of a fourth configuration for the separation of a pane from the ribbon. 
         FIGS. 10   a - 10   d  are side elevational schematic views of the contact surface of the bars. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     In the following detailed description, for purposes of explanation and not limitation, example embodiments disclosing specific details are set forth in order to provide a thorough understanding of the present invention. However, it will be apparent to one having ordinary skill in the art having had the benefit of the present disclosure, that the present invention can be practiced in other embodiments that depart from the specific details disclosed herein. Moreover, descriptions of well-known devices, methods and materials are omitted so as not to obscure the description of the present invention. 
     The present invention relates to the separation of a pane of brittle material from a moving ribbon of the material, wherein selected configurations reduce separation induced upstream disturbances to the ribbon. For purposes of description, the present invention is set forth as separating glass panes from a moving ribbon of glass. 
       FIG. 1  is a schematic diagram of glass fabrication apparatus  10  of the type typically used in the fusion process. Apparatus  10  includes forming isopipe  12 , which receives molten glass (not shown) in cavity  11 . The molten glass flows over the upper edges of cavity  11  and descends along the outer sides of isopipe  12  to root  14  to form ribbon of glass  20 . Ribbon of glass  20 , after leaving root  14 , traverses fixed edge rollers  16 . Ribbon  20  of brittle material is thus formed and has a length extending from root  14  to terminal free end  22 . As glass ribbon  20  travels down from isopipe  12 , the ribbon changes from a supple 50 millimeter thick liquid form at, for example, root  14  to a stiff glass ribbon of approximately 0.03 mm to 2.0 mm thickness at terminal end  22 . 
     Such draw down sheet or fusion processes, are described in U.S. Pat. No. 3,338,696 (Dockerty) and U.S. Pat. No. 3,682,609 (Dockerty), herein incorporated by reference. The details are omitted so as to not obscure the description of the example embodiments. It is noted, however, that other types of glass fabrication apparatus can be used in conjunction with the invention. For those skilled in the art of glass forming, it is known that there are multiple methods to achieve such a structure, such as laminated down draw, slot draw and laminated fusion processes. 
     For purposes of definition and as best shown in  FIG. 3 , as ribbon  20  descends from root  14 , the ribbon travels at a velocity vector V describing movement of the ribbon and forms a generally flat configuration having a generally planar first side  32  and a generally planar second side  34 . In certain configurations, ribbon  20  includes lateral beads or bulbous portions  36  (shown in  FIG. 2 ) which are sized for engagement by fixed rollers  16  or control surfaces during travel of the ribbon from isopipe  12 . With respect to ribbon  20 , the terms “opposed” or “opposing” mean the contact on both first side  32  and second side  34  of the ribbon. 
     Depending upon the stage or operation within the sequence, the term “upstream” means between the intended location of a score line  26  (or the actual location of the score line) and root  14 . The term “downstream” means between the intended location of score line  26  (or the actual location of the score line) and the terminal end  22  of ribbon  20 . Other uses of the terms upstream and downstream shall refer to the specific location of interest, and mean toward root  14  or toward terminal end  22  of ribbon  20 , respectively. 
     The separation of a pane  24  from ribbon  20  occurs within a given distance range from root  14 . That is, under constant operating parameters, the glass ribbon  20  reaches a generally predetermined solid state at a generally constant distance from the root  14 , and is thus amenable to separation. The separation of pane  24  from ribbon  20  occurs along score line  26  formed in at least one side of the ribbon. 
     As discussed above in the Summary of the Invention, the present invention is directed at reducing the levels of undesirable distortion exhibited when panes  24  or substrates are flattened by providing for the repeatable and uniform separation of a pane of brittle material from a continuously moving ribbon  20  of the brittle material, while reducing the introduction of disturbances into the upstream ribbon. 
     The present apparatus includes upstream press bar  60  ( FIG. 3 ) for engaging first side  32  of ribbon  20  and upstream backing bar  80  for engaging second side  34  of the ribbon. Each of the upstream press bar  60  and upstream backing bar  80  contact ribbon  20  upstream of score line  26  to locally restrain the ribbon during and after separation of pane  24 . 
     As seen in  FIGS. 6-9 , in further configurations, downstream press bar  70 , secondary upstream backing bar  90  and downstream backing bar  100  can be employed. 
     Press bars  60 ,  70  and backing bars  80 ,  90 ,  100  are formed of a cross beam  50  and a contact surface  56 , wherein the contact surface is usually a separate material than the cross beam. Cross beam  50  is a generally rigid member sufficient to remain substantially undeformed (undeflected) along the operable length of the bar during operating conditions. For example, deflections of less than approximately 0.005 inches and typically less than 0.003 inches along a 5 foot length of cross beam  50  have been found satisfactory. Aluminum or steel has been found to be a satisfactory material for cross beams  50 . Press bars  60 ,  70  and backing bars  80 ,  90 , and  100  are sized to extend substantially the entire length of score line  26 , and provide a continuous line of contact with ribbon  20  along the score line. 
     The material forming contact surface  56  is a polymeric material such as a thermoplastic, thermoset or thermoplastic elastomer. Silicone having a hardness of approximately 60 Shore A plus or minus 10, has been found a satisfactory material. However, it is understood that depending upon the configuration of the apparatus, and the desired characteristics of the interface between the respective bar and ribbon  20 , the performance characteristics of the material forming contact surface  56  can be changed. For example, upstream backing bar  80 , when also functioning as the scoring bar, may be formed of a harder surface than upstream press bar  60 . 
     Contact surface  56  can be connected to cross beam  50  by any of a variety of mechanisms including adhesives, bonding or friction fit. As shown in the  FIGS. 6-9  and called out in  FIGS. 10   a - 10   d , cross beam  50  includes a channel  51  having a given cross section, and contact surface  56  includes a corresponding locking tab  57  for engaging the channel. Although contact surface  56  is set forth as a member defining a surface as well as locking tab  57 , it is contemplated the contact surface can be limited to a surface layer or film disposed on a substrate, wherein the substrate performs the function of the locking tab. 
     Referring to  FIGS. 10   a - 10   d , contact surface  56  can define any of a variety of interfaces with ribbon  20 . For example, contact surface  56  can define an inclined plane with respect to the surface of ribbon  20 . In such configuration, as contact surface  56  engages ribbon  20 , increased force is exerted along predetermined positions of the contact surface. Contact surface  56  extends along the length of score line  26  and contact ribbon  20  along an appropriate ½″ length of the ribbon. 
     Each of the upstream press bar  60 , upstream backing bar  80 , downstream press bar  70 , secondary upstream backing bar  90  and downstream backing bar  100  travel at a velocity vector substantially equal to the velocity vector V of ribbon  20 . Press bars  60 ,  70  and backing bars  80 ,  90  and  100  are carried by a carriage  120  for translation with the appropriate velocity vector matching ribbon  20 , as is known in the art. 
     For purposes of description, press bars  60 ,  70  and backing bars  80 ,  90 ,  100  are described in terms of travel on common carriage  120 . Carriage  120  can be movable relative to a rail  124 , wherein the movement of the carriage can be imparted by any of a variety of mechanisms including magnetic, mechanical, or electromechanical, such as motors, gears, and/or rack and pinion. Thus, press bars  60 ,  70  and backing bars  80 ,  90 ,  100  can be moved with the same velocity vector V of ribbon  20 , and upon contact with the ribbon maintain contact at a specific location on the ribbon. 
     In certain configurations, upstream backing bar  80  also functions as a score-nosing bar, without deviating from the present apparatus. That is, as seen in  FIGS. 6-9 , upstream backing bar  80  contacts second side  34  of ribbon  20  upstream of score line  26 , as well as contacting the second side of the ribbon opposite the score line (or the intended position of the score line). 
     As shown schematically in  FIGS. 3-5 , upstream press bar  60  is connected to carriage  120  for engaging first side  32  of ribbon  20  and the upstream backing bar is connected to the carriage for engaging second side  34  of the ribbon to restrain the ribbon. 
     Upstream press bar  60  and upstream backing bar  80  can contact the opposing sides of ribbon  20  in an opposite, an offset, or overlapping relation. In the “opposite” relation seen in  FIG. 4 , upstream press bar  60  and upstream backing bar  80  engage ribbon  20  at a common distance from root  14 . For ribbon  20  having a vertical velocity vector V, the opposite contact occurs at a given height (vertical position along the ribbon). In the “offset” relation seen in  FIG. 3 , upstream press bar  60  and upstream backing bar  80  engage ribbon  20  at different distances from root  14 . That is, there is no common length of the ribbon contacted on first side  32  by upstream press bar  60  and second side  34  by upstream backing bar  80 . In the “overlapping” relation seen in  FIG. 5 , a portion of each of the upstream press bar  60  and upstream backing bar  80  contact the respective side of ribbon  20  along a common length of the ribbon. For example, in the overlapping relation, if each of the upstream press bar  60  and upstream backing bar  80  has a ½″ contact with the ribbon approximately ¼″ of the contact of each of the upstream press bar and the upstream backing bar can overlap along a common ¼″ length of the ribbon to restrain the ribbon. 
     Upstream press bar  60  and upstream backing bar  80  can be controlled to simultaneously or sequentially contact the respective sides of ribbon  20 . However, it is advantageous to have both upstream press bar  60  and upstream backing bar  80  contacting ribbon  20 , during and after separation of pane  24 . 
     Upstream press bar  60  and upstream backing bar  80  can be movably connected to carriage  120  for movement between a retracted non-ribbon contacting position and an extended ribbon contacting position. Any of a variety of mechanisms can be used for moving upstream press bar  60  and upstream backing bar  80  relative to carriage  120 . For example, cams can couple bars  60 ,  80  to carriage  120 . Alternatively, mechanical actuators such as rack and pinion or threaded engagements, hydraulic or pneumatic pistons or cylinders can be used. 
     Thus, upstream press bar  60  and upstream backing bar  80  can move relative to carriage  120  between a retracted non-contacting position and an extended ribbon contacting position. Alternatively, upstream press bar  60  and upstream backing bar  80  can be fixed with respect to carriage  120 , and the carriage can be moved relative to rail  124  to selectively engage the bars with ribbon  20 . 
     In selected configurations, as seen in  FIGS. 6   a - 6   d , upstream press bar  60  and downstream press bar  70  can be incorporated into a single cross beam  50 , and thus move in concert. Alternatively, upstream press bar  60  and downstream press bar  80  can be tied to a common carrier or yoke. Conversely, upstream press bar  60  and downstream press bar  70  can be independently controlled (operated) to provide sequential or independent contact with ribbon  20  as seen in  FIGS. 7-9 . 
     Similarly, upstream backing bar  80 , secondary upstream backing bar  90  and downstream backing bar  100  can be carried by single cross beam  50  to move in concert between the retracted position and the extended position. Alternatively, each of the upstream backing bar  80 , secondary upstream backing bar  90 , and downstream backing bar  100  can be carried by an independent and independently actuated cross beam  50 , as desired. 
     In one configuration, press bars  60 ,  70  and scoring assembly  130  contact first side  32  of ribbon  20  within an approximate 3 inch length of the ribbon. Thus, for those configurations in which score line  26  is equally spaced from the upstream press bar and downstream press bar, the bars are within approximately 1.5 inches from the score line. 
     Similarly, upstream backing bar  80 , secondary upstream backing bar  90  and downstream backing bar  100  span approximately 3 inches or less along the length of the ribbon  20 . In certain configurations, upstream press bar  60  can be within 2 inches or less than 1 inch from score line  26 . Downstream press bar  70  can be less than 3 inches to less than approximately 1 inch from score line  26 . In one configuration bars  60 ,  70  are located within a 37 mm length of ribbon  20 . 
     Load sensors or force sensors, such as piezoelectric or spring biased sensors, can be connected between respective bar  60 ,  70 ,  80 ,  90 ,  100  and carriage  120  to measure the load on the respective bar. The sensors are connected to a central controller so that the desired loads can be determined, monitored and controlled. 
     A scoring assembly  130  is used to selectively form score line  26  in first side  32  of ribbon  20 . Scoring assembly  130  can travel with one or both upstream press bar  60  and upstream backing bar  80 . For purposes of description, scoring assembly  130  is set forth as carried by carriage  120 . Thus, scoring assembly  130  will travel along the direction of travel of ribbon  20 , at a velocity vector matching the ribbon. As scoring assembly  130  translates along the same direction of travel as ribbon  20 , score line  26  can be formed to extend transverse to the direction of travel of the ribbon. 
     Scoring assembly  130  can be any of a variety of configurations well known in the glass scribing art, including but not limited to lasers, wheels, or points. 
     For those configurations of scoring assembly  130  that require contact with ribbon  20  to form score line  26 , the scoring assembly is also movable between a retracted non-contacting position and an extended ribbon contacting position. 
     Typically, scoring assembly  130  cooperates with upstream backing bar  80  to form the score line  26  along first surface  32  of ribbon  20 , such that the upstream backing bar also functions as a scoring bar opposite the contact of scoring assembly  130  and ribbon  20 . 
     Score line  26  extends across a substantial width of ribbon  20 . For the configuration of ribbon  20  having beads  36 , score line  26  extends substantially the entire distance between the beads. Thus, the score line can extend from approximately 70% of the width of ribbon  20  to 100% of the width. Typically, score line  26  has a depth of approximately 10% of the thickness of ribbon  20 . The actual depth of score line  26  depends in part upon scoring parameters such as scoring pressure, the geometry of the scoring assembly, the thickness of the ribbon, the material of the ribbon, and the characteristics of glass fabrication apparatus  10 . For representative ribbon thickness, score line  26  can have a depth ranging from approximately 70 microns to approximately 130 microns. 
     A pane engaging assembly  140  is employed to capture ribbon  20  downstream of score line  26  and control removal of pane  24  upon separation from ribbon  20 . A representative pane engaging assembly and associated transporter are described in U.S. Pat. No. 6,616,025, herein expressly incorporated by reference. 
     The pane engaging assembly  140  includes pane engaging members  142 , such as soft vacuum suction cups. It is understood other devices for engaging pane  24 , such as clamps or fingers that engage the lateral edge of the ribbon (pane) can be used. The number of pane engaging members  142  can be varied in response to the size, thickness and weight of pane  24 . 
     Pane engaging assembly  140  can engage ribbon  20  either before or after score line  26  has been formed. In addition, pane engaging assembly  140  can include a drop cylinder for imparting a vertical movement of pane  24  from newly formed terminal end  22  of ribbon  20 . 
     With respect to separation of pane  24  from ribbon  20  along score line  26 , a combination of the bars contacting the ribbon is employed to propagate a crack along the score line. Any of a variety of combination of contacts between the bars and ribbon  20  can be employed to separate pane  24 . For example, it is contemplated downstream press bar  70  can be employed to provide a breaking function (function as a breaking bar). Alternatively, both upstream press bar  60  and downstream press bar  70  can act cooperatively against ribbon  20  to induce separation along score line  26 . 
     Generally, upper press bar  60  and upper backing bar  80  restrain a portion of ribbon  20  therebetween. By restraining the portion of ribbon  20 , deviation of the ribbon from the gravity induced velocity vector is reduced. In addition, restraining a portion of ribbon  20  upstream of score line  26  allows the dampening characteristics of contact surfaces  56  to reduce the transmission of disturbances (energy) into the ribbon. 
     In contrast to prior systems, a localized bending is applied about score line  26 , wherein the localized bending is sufficient to propagate a crack along the score line. 
     The contact of upstream press bar  60 , upstream backing bar  80  (and secondary upstream backing bar  100 ) during and immediately after separation of pane  24  from ribbon  20 , function to dampen the transmission of mechanical vibrations upstream in the ribbon. Thus, movement of ribbon  20  above score line  26  is thus reduced during the separation process. The continued contact between upstream backing bar  80  and upstream press bar  60  with ribbon  20  after separation absorbs a portion of the energy imparted by the separation process, and thus reduces the amount of disturbance that can migrate upstream in the ribbon. 
     In addition, by locating continuous lines of contact from the respective bars proximal to score line  26 , such as within 3 inches (7.6 cm), a more uniform energy distribution is applied across ribbon  20  in the location of the score line, thereby improving separation characteristics of pane  24 . It is believed accuracy of the separation line with respect to score line  26  is increased as bars  60 ,  80  (and  70 ) provide a more uniform stress along the length of the score line. This allows the position of score line  26  to vary by as much as 1 mm without sacrificing efficiency of the separation process. 
     Press bars  60 ,  70  and backing bars  80 ,  90 ,  100  can also be employed to substantially maintain (or create) a substantially planar configuration of the ribbon in the area of score line  26  before or after formation of the score line. 
     For purposes of illustration, four different specific arrangements of upper press bar  60  and upper backing bar  80  contacting ribbon  20  are set forth in detail. 
     Referring to  FIGS. 6   a - 6   d , a first configuration of the assembly is employed to separate pane  24  from terminal end  22  of ribbon  20 . As seen in  FIG. 6   a , upstream backing bar  80  is brought to contact second side  34  of ribbon  20  and scoring assembly  130  is drawn across at least a portion of the width of the ribbon to form score line  26 . Pane engaging assembly  140  is shown engaged with ribbon  20 , prior to formation of score line  26 . However, it is understood that the pane engaging assembly can engage ribbon  20  after formation of score line  26 . Referring to  FIG. 6   b , upstream backing bar  80  functions as the score-nosing bar or anvil. Although scoring assembly  130  is shown as returning to an upstream position relative to upstream press bar  60 , it is understood the scoring assembly can move laterally (horizontally in  FIG. 6   b ) between a scoring position and a non scoring position. Subsequently to the formation of score line  26 , upstream press bar  60  and downstream press bar  70  are brought into contact with first side  32  of ribbon  20  to locate score line  26  intermediate the upstream press bar and the downstream press bar and restrain a portion of the ribbon upstream of score line  26  by the contact of upstream backing bar  80  and the upstream press bar with the ribbon. Upstream press bar  60  and upstream backing bar  80  can be sized and located to contact ribbon  20  and either an offset, overlapping or opposite relation. Further, although upstream press bar  60  and downstream press bar  70  are shown as incorporated into single crossbeam  50 , each press bar is called out as an individual structure. That is, each of the upstream press bar  60  and downstream press bar  70  can encompass respective contact surface  56  and a portion of the common crossbeam  50 . 
     In  FIG. 6   c , upstream press bar  60  and downstream press bar  70  are urged towards upstream backing bar  80 , while pane engaging assembly  140  draws the ribbon from the vertical path and ribbon  20  is separated along score line  26 . It is understood, upstream press bar  60  can contact ribbon  20  simultaneous with contact of downstream press bar  70 , or prior to contact of the downstream press bar with the ribbon. In either scenario, a portion of ribbon  20  is restrained between upstream press bar  60  and a portion of upstream backing bar  80 , such that the ribbon remains restrained upstream of the separation line, after separation of the ribbon. 
     In  FIG. 6   d , upstream press bar  60 , downstream press bar  70 , upstream backing bar  80 , and scoring assembly  130  are realigned with ribbon  20  for forming subsequent pane  24 . 
     It is also noted that upon upstream press bar  60  and upstream backing bar  80  having at least a slight overlapping relation along the length of ribbon  20 , the application of a bending moment to upstream ribbon  20  is reduced. The amount of overlap of upstream press bar  60  and upstream backing bar  80  is at least partially determined by the type and thickness of material forming ribbon  20 . 
     Referring to  FIG. 7   a , upstream backing bar  80  and at least upstream press bar  60  are brought into contact with ribbon  20 , prior to forming score line  26  (and thus restrain the ribbon). Again, pane engaging assembly  140  is engaged with ribbon  20  prior to formation of the score line. However, it is understood that pane engaging assembly  140  can engage ribbon  20  after formation of score line  26 . In  FIG. 7   b , scoring assembly  130  is brought into contact with first side  32  of ribbon  20  and bears against a portion of backing bar  80  to form score line  26 . In  FIG. 7   c , scoring assembly  130  is retracted. In  FIG. 7   d , the downstream press bar  70  is urged against first side  32  of ribbon  20  to separate pane  24  from the ribbon. In  FIG. 7   e , downstream press bar  70  and scoring assembly  130  are in the retracted position, while upstream backing bar  80  and upstream press bar  60  remain in contact with ribbon  20 , thereby dampening the transmission of any disturbance resulting from the separation of pane  24  from the ribbon. In  FIG. 7   f , the bars are returned to an initial position for separating a subsequent pane  24  from ribbon  20 . 
     Again, the relation of upstream backing bar  80  and upstream press bar  60  (and downstream press bar  70 ) can be offset, opposite or overlapping. Although upstream press bar  60  and downstream press bar  70  can be simultaneously moved into contact with first side  32  of ribbon  20 , and simultaneously moved after formation of score line  26  to separate pane  24 , it is anticipated that independently moving the downstream press bar to initiate crack propagation along the score line is advantageous. 
     Referring to  FIG. 8   a , secondary upstream backing bar  90  and upstream press bar  80  are initially brought into contact with second side  34  and first side  32  of ribbon  20  respectively. In addition, downstream press bar  70  can optionally contact the first side of ribbon  20  to further stabilize and control the ribbon. In  FIG. 8   b , upstream backing bar  80  and scoring assembly  130  are brought into contact with ribbon  20  to form score line  26  intermediate upstream press bar  60  and downstream press bar  70 . A portion of upstream backing bar  80  contacts second side  34  of ribbon  20  upstream of score line  26 . Thus, ribbon  20  is restrained upstream of score line  26  by a portion of upstream backing bar  80  and secondary upstream backing bar  90  on second side  34  of the ribbon and upstream press bar  60  on first side  32  of the ribbon. Pane engaging assembly  140  engages ribbon  20 . In  FIG. 8   c , scoring assembly  130  is retracted after score line  26  is formed. In  FIG. 8   d , downstream press bar  70  is urged further against first side  32  of ribbon  20  causing pane  24  to separate from the ribbon. In  FIG. 8   e , separated pane  24  is removed by pane engaging assembly  140 , and newly formed terminal end  22  of the ribbon is restrained by a portion of upstream backing bar  80 , secondary upstream backing bar  100  and upstream press bar  60 . In  FIG. 8   f , the bars are returned to a ready position to begin the sequence for separating a subsequent pane  24  from ribbon  20 . 
     With respect to the series of  FIG. 9 , the configuration is selected to reduce premature unintended crack propagation along score line  26 . Generally, the configuration of  FIG. 9  induces a local compression in first side  32  of ribbon  20  adjacent the score line  26 . This local compressive force reduces the tendency of crack propagation along score line  26 . The bar configuration shown in  FIG. 9 , provides for the initial compression and a subsequent tension across score line  26 , and hence controlled crack propagation. 
     In the series of  FIG. 9 , pane engaging assembly  140  is employed to capture pane  24  and remove the pane from descending ribbon  20 . As seen in  FIG. 9   a , upstream backing bar  80 , secondary upstream backing bar  90  and downstream backing bar  100  are mounted in a common crossbeam  50 , wherein the secondary upstream backing bar and the downstream backing bar project a greater distance than the upstream backing bar. That is, upstream backing bar  80  is recessed relative to secondary upstream backing bar  90  and downstream backing bar  100 , so that second side  34  of ribbon  20  initially contacts the secondary upstream backing bar and the downstream backing bar. Although secondary upstream backing bar  90  and downstream backing bar  100  can be of a softer, more easily compressible material than upstream backing bar  80 , as upstream press bar  60  contacts first side  32  of ribbon  20 , a slight bow is imposed in the ribbon such that a local compressive force is created in the intended area of score line  26 . 
     Although upstream backing bar  80  can be separately controlled from secondary upstream backing bar  90  and downstream backing bar  100 , the apparatus is simplified by mounting upstream backing bar  80 , secondary upstream backing bar  90  and downstream backing bar  100  to a common crossbeam  50 , and employing different size contact surfaces  56 . 
     Referring to  FIG. 9   b , scoring assembly  130  then forms score line  26  in the locally compressed first side  32  of ribbon  20 . Subsequently, as seen in  FIG. 9   c , scoring assembly  130  is retracted, and downstream press bar  70  is urged against the first side of ribbon  20  with sufficient force to generate a localized tension in the first side of the ribbon in the area of score line  26 . Pane  24  then separates from ribbon  20  as seen in  FIG. 9   d  while ribbon  20  remains restrained between secondary upstream backing bar  90  and upstream backing bar  80  on second side  34 , and upstream press bar  60  on the first side. Pane engaging assembly  140  removes pane  24  in  FIG. 9   d . Referring to  FIG. 9   f , the bars and scoring assembly  130  are returned to the ready position for separating a subsequent pane  24 . 
     The present configurations thus provide for an opposed contact of ribbon  20  upstream of score line  26  (or score line location), wherein the upstream opposed contact can be in an offset, opposite or overlapping relation of upstream press bar  60  and upstream backing bar  80 . 
     Subsequently, crack propagation is induced along score line  26  and pane  24  is separated from ribbon  20 . 
     The upstream contact with ribbon  20  is maintained during and after the separation of pane  24 , thereby reducing the introduction of disturbances that can migrate up the ribbon. 
     In certain configurations, the upstream restraining of ribbon  20  can be subsequent to formation of score line  26  and substantially simultaneous with the separating of the ribbon along the score line. In further configurations, the upstream restraining of ribbon  20  precedes the formation of score line  26 . 
     While the invention has been described in conjunction with specific exemplary embodiments thereof, it is evident that many alternatives, modifications, and variations will be apparent to those skilled in the art in light of the foregoing description. Accordingly, the present invention is intended to embrace all such alternatives, modifications, and variations as fall within the spirit and broad scope of the appended claims.