Abstract:
A method having particular utility for making outer and inner formed windshield glass sheets is performed by glass sheet positioning centrally on a forming face ( 34 ) of a forming mold ( 32 ) to form each glass sheet to a design shape regardless of any size difference between the glass sheets from one cycle to the next.

Description:
BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   This invention relates to a method for positioning glass sheets for forming. 
   2. Background Art 
   Glass sheets are conventionally formed by heating on a conveyor within a furnace and then forming prior to delivery for cooling. Such cooling can be slow cooling to provide annealing or faster cooling that provides heat strengthening or tempering. In connection with heating of the glass sheets, see U.S. Pat. Nos. 3,806,312 McMaster et al.; 3,947,242 McMaster et al.; 3,994,711 McMaster; 4,404,011 McMaster; and 4,512,460 McMaster. In connection with glass sheet forming, see U.S. Pat. Nos. 4,204,854 McMaster et al.; 4,222,763 McMaster; 4,282,026 McMaster et al.; 4,437,871 McMaster et al.; 4,575,390 McMaster; 4,661,141 Nitschke et al.; 4,662,925 Thimons et al.; 5,004,491 McMaster et al.; 5,330,550 Kuster et al.; 5,376,158 Shetterly et al.; 5,472,470 Kormanyos et al.; 5,900,034 Mumford et al.; 5,906,668 Mumford et al.; 5,925,162 Nitschke et al.; 6,032,491 Nitschke et al.; 6,173,587 Mumford et al.; 6,227,008 Shetterly; 6,418,754 Nitschke et al.; 6,543,255 Bennett et al.; 6,578,383 Bennett et al.; 6,718,798 Nitschke et al.; 6,729,160 Nitschke et al. In connection with the cooling, see U.S. Pat. Nos. 3,936,291 McMaster; 4,470,838 McMaster et al.; 4,525,193 McMaster et al.; 4,946,491 Barr; 5,385,786 Shetterly et al.; 5,917,107 Ducat et al.; 6,079,094 Ducat et al.; and 6,513,348 Bennett et al. 
   Vehicle windshields are conventionally manufactured from outer and inner formed glass sheets and an intermediate layer of polyvinyl butyral. The outer and inner glass sheets have different sizes since the outwardly curved shape of the formed windshield necessitates that the outer glass sheet be slightly greater in size than the inner glass sheet. Also, upon manufacturing, there can be slight variations in the size of flat glass prior to the forming. Thus, switches which have previously been utilized to sense the approach of a glass sheet to initiate transfer from a conveyor for forming do not necessarily initiate transfer that positions the glass centrally on a forming mold for the forming. 
   SUMMARY OF THE INVENTION 
   An object of the present invention is to provide an improved method for positioning a heated glass sheet for forming. 
   In carrying out the above object, the method for positioning a heated glass sheet for forming is performed by conveying a heated glass sheet on a horizontal conveyor in a horizontally plane of conveyance along a direction of conveyance toward a forming station having a forming mold including a downwardly facing curved forming face that is positioned above the plane of conveyance and has a forming portion for forming a glass sheet of a predetermined size. The spacing along the direction of conveyance between downstream and upstream extremities of the conveyed glass sheet is detected to determine any difference from the glass sheet of the predetermined size and a control signal is generated to indicate any such difference. The conveyance of the glass sheet is continued below the forming mold and the control signal is used to centrally position the glass sheet along the direction of conveyance below the forming portion of the forming face. The centrally positioned glass sheet is transferred from the conveyor to the forming mold for forming of the glass sheet against the forming face. 
   The downstream extremity of the conveyed glass sheet is preferably initially detected by a detector and the upstream extremity of the conveyed glass sheet is subsequently detected by the detector in coordination with the conveyance to generate the control signal, and the conveyance of the glass sheet is coordinated with the control signal to provide the central positioning of the glass sheet along the direction of conveyance below the forming portion of the forming face. More specifically, the subsequent detection of the upstream extremity of the conveyed glass sheet generates the control signal which is coordinated with the conveyance to provide the central positioning of the glass sheet for the transfer from the conveyor to the mold forming face. Also, the conveyance of the glass sheet is decelerated upon approaching the central position below the mold forming face and is transferred to the forming face at the central position while still moving. 
   The glass sheet positioning method as disclosed is used to alternately convey and position vehicle windshield outer and inner glass sheets for the forming with the outer glass sheets having a slightly greater distance between their downstream and upstream extremities than the inner glass sheets. 
   Furthermore, the centrally positioned glass sheet is transferred from the conveyor to the forming mold by any step including: lifting the glass sheet upwardly from the conveyor by a continuous ring; lifting the glass sheet upwardly from the conveyor by a segmented ring; drawing a vacuum at the curved forming face of the forming mold; moving the forming mold downwardly toward the conveyor; blowing gas upwardly from below the glass sheet to lift the glass sheet upwardly from the conveyor; and any combination of two or more of these steps. 
   Also, the glass sheet is laterally located prior to heating and subsequent conveyance to the forming station. 
   The objects, features and advantages of the present invention are readily apparent from the following detailed description of the preferred embodiments when taken in connection with the accompanying drawings. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a side elevational view of a glass sheet forming system that performs a method for positioning glass sheets in accordance with the invention. 
       FIGS. 2   a  and  2   b  illustrate a detector of a detection system for respectively detecting downstream and upstream extremities of a conveyed glass sheet in preparation for forming. 
       FIGS. 3   a  and  3   b  respectively illustrate the manner in which larger and smaller glass sheets are centrally positioned on a forming face of a curved forming mold to provide forming to a design shape. 
       FIG. 4  is a top plan view taken along the direction of line  4 - 4  in  FIG. 1  to illustrate transfer apparatus embodied as a lifter including a continuous ring. 
       FIG. 5  is a view taken in the same direction as  FIG. 4  illustrating another embodiment of the transfer apparatus lifter which is a segmented ring. 
       FIG. 6  is a partial side elevational view similar to  FIG. 1  illustrating the system forming station wherein the transfer apparatus includes lift jets for blowing air upwardly from below the conveyor. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   With reference to  FIG. 1 , a glass sheet forming system is generally indicated by  10  and includes a loading station  12  for loading glass sheets G, a furnace  14  for heating the glass sheets, a forming station  16  for forming the glass sheets, and a quench station  18  for cooling the glass sheets for slow cooling to provide annealing although it is also possible to provide faster cooling for tempering or heat strengthening when required by the application of the particular type of glass sheet being processed. 
   With continuing reference to  FIG. 1 , a conveyor  20  of the forming system is illustrated as being of the roll type including rolls  22  that convey the glass sheets for heating in the furnace  24  and for movement into the forming station  26  for the forming. The conveyor rolls  22  support each glass sheet G in a horizontal plane of conveyance for movement along a direction of conveyance as shown by arrow C. It is also possible to convey the glass sheets on other types of conveyors, such as on air hearth conveyors in which case the horizontal plane of conveyance normally will be slightly tilted in a lateral direction transverse to the direction of conveyance. 
   At the loading station  12  each glass sheet is loaded either manually or by automated apparatus such as one or more robots for conveyance on the rolls  22  of conveyor  20 . A lateral positioner  24  of the loading station laterally positions each loaded glass sheet G with respect to the direction of conveyance so as to be in the proper location upon ultimately reaching the forming station  16  after passage through a heating chamber  26  of the furnace  14  for heating to a forming temperature in any conventional manner. 
   The forming station  16  as shown in  FIG. 1  includes a housing  28  that defines a heating chamber  30  in which a forming mold  32  is located. This heated chamber  30  as disclosed is not as hot as the heating chamber  26  of furnace  14 , more specifically, the furnace heating chamber will normally be on the order of 600-680° C. in different locations, while the heating chamber  30  where the forming mold  32  is located will be about 500° C. The forming mold  32  is located above the rolls  22  of the conveyor  20  and has a downwardly oriented forming face  34  of a curved shape. This forming face has a forming portion for forming a glass sheet of a predetermined size. More specifically, as shown in  FIGS. 3   a  and  3   b , the forming portion of forming face  34  has a central location CL along the direction of conveyance C. A glass sheet of the predetermined size when centrally positioned on the conveyor, or on the forming face  34  as is hereinafter described, will have the midpoint between its downstream and upstream extremities along the direction of conveyance located at the forming face central location CL. 
   A controller  36  of the forming system through a connection  38  operates a schematically indicated drive  40  of the conveyor  20 . Furthermore, a detection system  42  of the system includes a detector  44  located upstream from the forming mold  32  and having a connection  46  to the controller  36 . 
   As shown in  FIG. 2   a , the detector  44  propagates a detection beam  48  that initially detects a downstream extremity  50  of the conveyed glass sheet. Thereafter as shown in  FIG. 2   b , the detector  44  detects an upstream extremity of the conveyed glass sheet such that the controller  36  can measure the spacing or distance between these upstream and downstream extremities and any difference either larger or smaller than the glass sheet of the predetermined size. Furthermore, the subsequent detection of the upstream extremity through the coordination of the controller  36  in driving the conveyor  20  provides an indiction of the location of the conveyed glass sheet so a control signal can be generated such that the glass sheet is moved to the central position below the forming face  34  of the forming mold  32  as shown by phantom line representation in  FIGS. 3   a  and  3   b . More specifically, each centrally positioned glass sheet G regardless of its spacing between its downstream and upstream extremities  50  and  52  will have the same distance downstream and upstream from the central location CL so that the forming of the glass sheet will be to the design shape despite any difference in the glass sheet sizes. It should be appreciated that other types of detectors can be used in addition to the beam propagating detector shown. 
   As illustrated in  FIG. 1 , the forming station  16  includes transfer apparatus collectively indicated by  54  for performing upward transfer of the glass sheet from the central position on the conveyor  20  upwardly to the central position on the forming mold  32  as shown in  FIGS. 3   a  and  3   b  and described above. Just prior to the conveyed glass sheet G reaching the central position on the conveyor  20 , the controller  36  shown in  FIG. 1  slows the conveyor to decelerate the glass sheet. Upon reaching the central position shown in  FIGS. 3   a  and  3   b  but before termination of the conveyance, the transfer apparatus  54  begins the upward transfer of the glass sheet to the forming face  34  of the forming mold  32  at the central position for the forming. 
   Transfer apparatus  54  as shown in  FIG. 1  includes a lifter  56  that is moved vertically by an actuator  58  having a connection  60  to the controller  36 . This lifter  56  as illustrated in  FIG. 4  may be a continuous ring  60  that moves upwardly from below disc shaped wheel rolls  22  in a manner more fully disclosed by U.S. Pat. No. 6,543,255, the entire disclosure of which is hereby incorporated by reference. In addition as shown in  FIG. 5 , the lifter  56  may be embodied by a segmented ring  62  whose portion  64  move upwardly between elongated conveyor rolls  22  to provide the lifting. 
   With reference back to  FIG. 1 , the transfer apparatus  54  as disclosed also includes a vacuum supply  66  that draws a vacuum through a conduit  68  at openings in the forming face  34  of the forming mold  32  under the operation through a connection  70  to the controller  36 . It should be noted that this vacuum supply  66  may have an initial greater vacuum that is provided by a vacuum impulse and subsequently is reduced to prevent deformation of the heated glass sheet at the forming face openings through which the vacuum is drawn. It is also possible to subsequently supply positive pressure air to the forming face openings to provide release of the glass sheet for delivery and subsequent cooling as is hereinafter more fully described. 
   The transfer apparatus  54  shown in  FIG. 1  also includes a vertical control or actuator  72  having a connection  74  to the forming mold  32  to provide vertical movement thereof between the solid indicated upper position and the phantom line indicated lower position under the control of a connection  76  to the controller  36 . 
   As shown in  FIG. 6 , the transfer apparatus  54  can also be constructed to include a gas supply  78  that feeds gas from a pressurized source  80  through a valve  82  operated by a connection  84  to the controller  36  to blow gas upwardly through an array  86  of lift jet nozzles  88 . More specifically, the upwardly blown air passes between the conveyor rolls  22  to actuate the lifting. 
   The forming system  10  has particular utility when utilized to manufacture vehicle windshields which include outer and inner glass sheets that are of a slightly different size than each other. More specifically, the curved shape of the formed windshield results in the outer glass sheets being slightly larger than the inner glass sheets. However, since the glass sheets are centrally positioned along the direction of conveyance shown by arrow C with respect to the center location CL, both the inner and outer glass sheets are formed at the same forming portion of the forming face  34  of the forming mold  32  so as not to have different curvatures than each other. During the manufacturing, the larger outer glass sheets and the smaller inner glass sheets are alternately loaded on the conveyor  20  at the locating station  12  and ultimately heated in the furnace and processed for forming at the forming station  16  as described above. 
   After each glass sheet is formed as illustrated in  FIG. 1 , the cooling station  18  receives the formed glass sheet by a cooling mold  90  operated by delivery apparatus  92  having an actuator  94  from which a connection  96  extends to the mold and with a control connection  98  extending from the actuator to the controller  36  to provide the operation in coordination with the rest of the forming station. 
   It should be appreciated that the cooling station  18  can also be of the quenching station type for providing rapid cooling that tempers or heat strengthens the formed glass sheet in other applications. 
   While different modes of the invention have been illustrated and described, it is not intended that these modes illustrate and describe all possible forms of the invention. Rather, the words used in the specification are words of description rather than limitation, and it is understood that various changes may be made without departing from the spirit and scope of the invention.