Abstract:
Apparatus and methods are provided for separating a pane ( 11 ) of a brittle material from a moving ribbon ( 13 ) of the material without contact between the newly-formed leading edge of the ribbon and the newly-formed trailing edge of the pane. The apparatus includes a pane engaging assembly ( 15 ), a transporter ( 29 ), and a connector assembly ( 31 ) which together ensure that the pane ( 11 ) and the sheet ( 13 ) do not contact each other once separation occurs. In this way, edge chipping and the resulting occurrence of surface defects on the separated pane are decreased.

Description:
FIELD OF THE INVENTION 
     This invention relates to glass manufacturing and, in particular, to the problem of separating panes of glass from a moving ribbon of glass without excessive generation of glass chips through edge contact and resulting damage. 
     More generally, the invention relates to separating panes of any brittle material from a moving ribbon of the material. For ease of presentation, however, the following discussion is in terms of glass manufacturing, it being understood that the invention as defined in the appended claims is not so limited except for those claims which specify that the brittle material is glass. 
     BACKGROUND OF THE INVENTION 
     Specialized glasses such as those used as substrates in the manufacture of liquid crystal displays and similar devices have demanding standards regarding surface defects. One source of such defects is glass chips generated during the separation of panes of glass from a moving ribbon of glass. 
     In the past, such separation has been performed manually using the following steps. First, a separation line (score line) was formed in the ribbon of glass using an automated moving scribe/moving anvil assembly. Then, the operator attached a vacuum cup array to the glass below the score line and applied a bending moment to the glass to cause it to break at the score line and thus form the desired glass pane. This breaking produced a newly-formed leading edge on the moving ribbon and a newly-formed trailing edge on the glass pane. 
     To avoid damage to these newly-formed edges, the operator would endeavor to immediately move the pane away from the oncoming leading edge of the ribbon. As will be evident, this was not easy to do because, among other things, it was difficult to apply the same bending moment to the pane each time it was to be separated form the moving ribbon. Different bending moments resulted in different orientations for the pane at the time of separation, making it even more difficult to avoid edge contact. Different bending moments also affect the break signature or quality of the break independent of edge contact. Moreover, even with identical bending moments, individual panes of glass can separate at different angles making the avoidance of edge contact even more difficult to achieve. 
     As a result, only highly skilled and trained operators could perform the pane separation procedure, and even with such operators, edge contact and break signature variation occurred leading to rejected panes. 
     SUMMARY OF THE INVENTION 
     In view of the foregoing, it is an object of the present invention to provide methods and apparatus for overcoming the problem of edge contact during the separation of a pane of a brittle material from a moving ribbon of the material. It is also an object of the invention to provide methods and apparatus for applying a repeatable, uniform bending moment to a pane of a brittle material to separate the pane from a moving ribbon of the material. 
     To achieve these and other objects, the invention in accordance with one of its aspects provides apparatus for separating a pane ( 11 ) of a brittle material from a moving sheet ( 13 ) of the material along a separation line ( 47 ), said pane and said sheet having a width W, said pane when separated having a length L, said movement of the sheet being described by a vector {overscore (V)} sheet , said apparatus comprising: 
     (a) a pane engaging assembly ( 15 ) adapted to releasably engage the moving sheet within an area defined by the length L and width W of the to-be-separated pane; 
     (b) a transporter ( 29 ) adapted to bring the pane engaging assembly into engagement with the moving sheet and to rotate that assembly about an axis which substantially coincides with the separation line, said rotation causing the pane to separate from the sheet; and 
     (c) a connector assembly ( 31 ) for connecting the pane engaging assembly and the transporter so that the pane engaging assembly moves relative to the transporter upon separation of the pane from the moving sheet so that the pane and the sheet do not contact each other once separation occurs. 
     In accordance with other aspects, the invention provides a method for separating a pane ( 11 ) of a brittle material from a moving sheet ( 13 ) of the material along a separation line ( 47 ), said pane and said sheet having a width W, said pane when separated having a length L, said movement of the sheet being described by a vector {overscore (V)} sheet , said method comprising: 
     (a) releasably engaging the moving sheet ( 13 ) within an area defined by the length L and width W of the to-be-separated pane; 
     (b) rotating the to-be-separated pane about an axis which substantially coincides with the separation line, said rotation causing the pane to separate from the sheet; and 
     (c) moving the separated pane relative to the moving sheet either passively using gravity as the motive force (i.e., the sole motive force) or actively using at least one of a hydraulic force, a mechanical spring force, a pneumatic force, and a vacuum, either alone or in combination with gravity, as the motive force, so that the pane and the sheet do not contact each other once separation occurs. 
     FIG. 1 illustrates the operating principles of the invention. As shown therein, pane engaging assembly  15  has been brought into engagement with a moving ribbon  13  of a brittle material. As indicated by arrows  51 , both the pane engaging assembly and the ribbon of brittle material are moving with substantially the same speed in substantially the same direction at the instant shown, i.e., they each have substantially the same vector velocity. As also shown in the figure, a score line  47  has been formed in the brittle material and a stop  49  is in position so that a bending moment can be applied about the score line. The score or separation line is substantially perpendicular to the vector {overscore (V)} sheet  and defines the length L of the to-be-separated pane. It can be formed by a scoring assembly  21  of the type discussed below or other scoring assemblies known in the art. 
     Arrows  53  and  55  represent the forces that, in accordance with the invention, are brought to bear so that ( 1 ) the pane becomes separated from the ribbon and ( 2 ) the pane immediately moves away from the ribbon once separation has been achieved. 
     In particular, arrow  53  represents a bending moment that is applied to the pane through the pane engaging assembly and causes the pane to separate from the ribbon at the score line. As can be seen in FIG. 1, this bending moment is applied by rotating the pane engaging assembly about score line  47 . In this way, a pure bending moment is applied to the score line which causes it to open up and drive through the sheet. As discussed in detail below, transporter  29  acting through connector  31  produces this rotation (see FIGS.  4 - 5 ). 
     Arrow  55  represents a force which moves the separated pane away from the still advancing ribbon. The force can be an active force, a passive force, or a combination of an active and passive force. FIG. 1 shows the system in a horizontal orientation in which case the force needs to be an active force, e.g., a hydraulic force, a mechanical spring force, a pneumatic force, a vacuum, or the like. For a vertical orientation, the pane can move passively away from the ribbon under the force of gravity. 
     Force  55  acts on the separated pane through the cooperation of pane engaging assembly  15 , transporter  29 , and connector assembly  31  (see, for example, FIGS.  5  and  12 ). For active systems, the connector assembly allows the active force to produce relative motion between the pane engaging assembly/separated pane combination and the transporter. Such an active force can originate from, for example, a force generator, e.g., a pneumatic cylinder, mounted on the connector assembly, the transporter, and/or some other part of the apparatus or its housing. In the case of a passive system which uses gravity as a motive force, the connector assembly allows the pane engaging assembly/separated pane combination to undergo a controlled “fall” relative to the transporter so that the pane falls away from the moving ribbon. 
     It should be noted that through the application of bending moment  53 , some rotation of the pane about score line  47  will take place and thus force  55  will no longer be parallel to velocity vector  51  when it performs its function of moving the pane away from the leading edge of the moving ribbon. For example, for a typical liquid crystal display glass having a thickness of about 0.7 millimeters with a score line which penetrates 10% or less of the thickness of the sheet, separation will normally take place at an angle greater than zero and less than about 10°. All that is required, however, is that force  55  has a component in the direction of vector  51  that is sufficient to move the pane away from the leading edge of the ribbon once separation has occurred, not that the force is parallel to vector  51 . 
     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 it is claimed. 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. The drawings are not intended to indicate scale or relative proportions of the elements shown therein. 
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a schematic drawing illustrating the operating principles of the invention. 
     FIGS. 2-11 are a set of schematic drawings illustrating the separation of a pane from a moving ribbon in accordance with the invention. 
     FIG. 12 is a schematic drawing illustrating components of the connector assembly of the invention. 
     FIG. 13 is a schematic drawing illustrating components of the pane engaging assembly of the invention. 
     FIG. 14 shows an embodiment of the apparatus of FIG. 12 in which the transporter employs an industrial robot. 
    
    
     The reference numbers used in the drawings correspond to the following: 
       11  separated pane 
       13  moving sheet or ribbon 
       15  pane engaging assembly 
       17  frame 
       19  sheet engaging members 
       21  scoring assembly 
       23  anvil 
       25  scribe 
       27  transporter for scribe 
       29  transporter 
       31  connector assembly 
       33  connecting member 
       35  connecting member 
       37  linear bearing assembly 
       37   a  linear bearing 
       37   b  linear support rail 
       39  reset assembly 
       41  manufacturing line which produces ribbon  13   
       43  pane transport system 
       45  pane grippers 
       47  separation line 
       49  stop 
       51  arrows representing the vector {overscore (V)} sheet    
       53  arrow representing the bending moment used to separate a scored pane from the moving sheet 
       55  arrow representing a motive force for moving a separated pane away from the moving sheet 
       57  arrows representing linear motions of transporter 
       59  arrow representing rotational motion of transporter 
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     As discussed above, the present invention relates to the separation of glass panes from a moving ribbon of glass without allowing contact of the newly-formed leading edge of the ribbon with the newly-formed trailing edge of the pane. The invention also relates to applying a repeatable uniform bending moment to a pane of a brittle material so as to minimize variations in the break signature of panes formed from the ribbon. 
     FIGS. 2-11 show a representative sequence of steps for forming such a pane in accordance with the invention. In each of these figures, the reference number  41  represents a glass manufacturing line, e.g., an overflow downdraw glass manufacturing line for producing LCD glass, and the reference number  43  represents a pane transport system which includes pane grippers  45  for moving a separated pane to further stages of the manufacturing process, e.g., to an edging station, an inspection station, etc. 
     FIG. 2 shows the overall system at start-up with glass ribbon  13  having just entered scoring assembly  21 , which comprises anvil  23 , scribe  25 , and scribe transporter  27 . As is conventional, the scoring assembly is preferably of the moving scribe/moving anvil type, although other types of scoring systems can be used if desired, e.g., laser based systems. 
     FIG. 3 shows the further progression of ribbon  13  beyond the scoring assembly and into the region of the pane engaging assembly  15 . The pane engaging assembly includes frame  17  which carries sheet engaging members  19 . FIG. 13 shows a preferred form for frame  17 . As shown in this figure, four pane engaging members  19  are deployed at the four corners of the frame, with the width W′ and length L′ of the frame being less than the width W and length L of pane  11 . The pane engaging members  19  are preferably soft vacuum suction cups, although other apparatus for engaging a sheet of glass, e.g., clamps, can be used if desired. More or less than four pane engaging members can be used as desired. 
     Pane engaging assembly  15  is carried by transporter  29  through connector assembly  31 . Transporter  29  can be an industrial robot (see FIG. 14) and/or fixed automation for providing linear and rotational motion to the pane engaging assembly and the connector assembly (see arrows  57  and  59  in FIGS.  12  and  14 ). As discussed above, for the passive, gravity-based embodiment of FIGS. 2-11, connector assembly  31  performs the important function of allowing the pane engaging assembly/separated pane combination to undergo a controlled “fall” relative to the transporter and thus the leading edge of ribbon  13  once separation has occurred. 
     FIG. 12 schematically illustrates a preferred construction for connector assembly  31 . As shown therein, the assembly includes connecting member  33  attached to frame  17  and connecting member  35  attached to transporter  29 . The connecting members are joined through a linear bearing assembly or block  37  which includes a pair of linear bearings  37   a  and a corresponding pair of linear support rails or guides  37   b , one of each of which is schematically illustrated in FIG.  12 . 
     The linear bearing assembly confines the motion of frame  17  to the axis defined by linear rails  37   b , said axis being substantially perpendicular to score line  47 . Since the linear bearing assembly rotates with transporter  29 , the assembly is automatically ready to move along the angle of the pane at the moment of separation irrespective of variations in that angle from pane to pane. Other structures for producing the desired motion of frame  17  can of course be used in the practice of the invention, including the active systems discussed above in connection with FIG.  1 . Generally, such structures will be of the linear guide or linear shaft type, although mechanical linkages producing other types of motion, e.g., motion along an arc, can be used if desired. 
     FIG. 12 also shows reset assembly  39  which is used to move linear bearings  37   a  from a lower position (second position) to an upper position (first position) along linear rails  37   b . The reset assembly can, for example, be a pneumatic cylinder. Other means for moving linear bearings  37   a  along linear rails  37   b  can, of course, be used if desired, e.g., a hydraulic powered system, an electrical motor driving a mechanical linkage, and the like. In addition to resetting the location of the pane engaging assembly, the reset assembly can also limit the downward travel of the combination of that assembly and a separated pane of glass. In practice, it has been found that a controlled “fall” of approximately a half an inch to an inch (15-25 millimeters) is sufficient to avoid edge contact problems. 
     If active separation is desired, the reset assembly can pull on connecting member  33 , rather than simply allowing that member to fall under the force of gravity. For example, if only passive separation is desired and a pneumatic cylinder is used as the reset assembly, then one needs only to release the pressure in the cylinder once the pane engaging assembly has engaged the sheet. On the other hand, if full or partial active separation is desired, rather than merely releasing the pressure in the cylinder, a vacuum can be applied to the cylinder so that it actively pulls the pane away from the ribbon once separation has occurred. 
     The reset assembly will typically include proximity switches or similar devices for providing information to an overall control system (not shown) regarding the location of the pane engaging assembly. In particular, information that pane engaging assembly  15  has moved downward relative to transporter  29  can be used as a signal to cease the rotation of the transporter since such downward movement means that the pane has separated from the ribbon. 
     Returning to the sequence of FIGS. 2-11, FIG. 4 shows the formation of separation line  47  in glass ribbon  13  by scribe  25 . As also shown in this figure, pane engaging members  19  have engaged the sheet. This engagement can take place either before or after the sheet has been scored. The engagement can be achieved by using a hard placement of the pane engaging members with respect to the sheet in combination with the use of sufficiently soft engaging members, e.g., soft vacuum suction cups, that will not cause undue motion of the sheet. 
     If the engagement is done after scoring, the engagement should not create a bending moment about the score line which will cause the pane to prematurely separate from the sheet. That is, the engagement needs to be accomplished while maintaining the plane of the glass. A reduced bending moment during engagement can be achieved by controlling the distance between the uppermost pane engaging member and the score line. In practice, a distance of 150 millimeters has been found to work successfully for 0.7 and 1.1 millimeter LCD glass. Other distances can of course be used if desired. 
     Whether pane engaging assembly  15  is engaged with the pane before or after scoring, for a fully passive system, the assembly needs to be attached to the pane before the bending moment which separates the pane from the ribbon is applied. As long as the plane of the glass is maintained, ribbon  13  can support substantial weight even when scored. The sheet only loses its strength when the score line opens up and is driven through the sheet by the application of a bending moment which creates a tension/compression gradient in the glass. 
     FIG. 5 illustrates the application of the bending moment. As shown in this figure, the bending moment is applied about the back side (unscored side) of the sheet using anvil  23  as a stop about which rotation takes place. Immediately upon separation, linear bearings  37   a  slide downward along linear rails  37   b  (see FIG.  12 ), thus automatically moving the trailing edge of the now separated pane away from the leading edge of the continually moving ribbon  13 . In this way, the desired reduction in edge damage is achieved by the invention. 
     FIGS. 6-9 illustrate movement of the separated pane from the point of separation in FIG. 5 to the point at which pane grippers  45  of pane transport system  43  engage the pane. As discussed above, pane transport system  43  serves to move the separated pane to other processing stations in the glass manufacturing facility. The continued forward movement of ribbon  13  and the resetting of scoring assembly  21  is also shown in FIGS. 6-9. 
     FIGS. 10 and 11 show the final steps in one cycle of the process, namely, the return of transporter  29  and its associated pane engaging assembly  15  and connector assembly  31  to a position adjacent to ribbon  13 . Thereafter, the process repeats with each pane being reliably separated from ribbon  13  and delivered to pane transport system  43  without detrimental contact between the edge of the ribbon and the edge of the pane. 
     Although specific embodiments of the invention have been described and illustrated, it will be apparent to those skilled in the art that modifications and variations can be made without departing from the invention&#39;s spirit and scope. The following claims are thus intended to cover the specific embodiments set forth herein as well as such modifications, variations, and equivalents.