Abstract:
A method of handling molded plastic glazing panels during processing is disclosed, using one or more stabilizing handling tabs projecting outwardly from the perimeter of each panel, and which is molded at the same time as with the glazing panel itself is molded. Each tab has spaced apart bosses, each having through opening adapted to mate with pins projecting from a holder structure. Gussets may be molded into the bosses to control drip when the panel is coated with a liquid and to stiffen the bosses. The tabs enable stable positioning of the panel to avoid formation of optical flaws in the panels, and to facilitate compact vertical stacking of the panels during handling.

Description:
BACKGROUND OF THE INVENTION 
     This invention concerns manufacturing of molded plastic glazing panels, particularly curved glazing panels used in automotive vehicles. 
     The use of molded plastic glazing panels for the windows of automotive vehicles offers many advantages, such as reduced weight, superior resistance to fracture and/or dislodgment in the case of accidents, and greater freedom in vehicle styling due to the ease of forming glazing panels in any desired shape. 
     These advantages have not heretofore been realized on a large scale due to the difficulty in matching the optical clarity and scratch resistance of conventional glass panels. Such plastic panels must be resistant to obscuration due to UV radiation exposure, and must also block UV transmission to prevent deterioration of interior trim surfaces and fabric materials by UV radiation. 
     Polycarbonate has been widely proposed for this application, and the technology for hard coating this plastic has been developed which allows for the manufacture of UV and scratch resistant plastic glazing panels. This technology involves coating the panels, as by dipping the panels in tanks of liquid coating material and subsequent curing of the coating in an oven. Other coating processing steps have been developed as well for this application, such as a plasma coating. 
     In the automotive industry, any defect in a glazing panel which creates a visible optical flaw during the handling and processing would result in rejection of the part. Accordingly, handling and processing must be carried out in such a way as to minimize creating optical flaws. 
     The manufacture of automotive components is done on a vast scale in a very competitive environment, and thus, the processing of glazing panels must be carried out highly efficiently while still producing quality parts. There is a high probability of producing defective parts while handling the panels during dipping into a tank of liquid coating, as drips or the running of the liquid coating material onto the glazing may result in a visible flaw. 
     At the same time, the distinct curved shape of the glazing panels makes compact racking of the panels difficult. Any bumping of the panels as they are racked may also create scratches or other surface defects necessitating rejection of the part. 
     Accordingly, it is an object of the present invention to provide a method for handling of molded plastic glazing panels during processing steps which minimizes the incidence of optical flaws, yet allows large numbers of the panels to be efficiently handled during processing, and compactly stacked together in a vertical array. 
     SUMMARY OF THE INVENTION 
     The above object as well as others which will be understood upon a reading of the following specification and claims are achieved by a handling process in which one or more handling tabs are molded integrally with the transparent plastic glazing panel, projecting in an outward direction from the perimeter of the panel. 
     The tab or tabs each have a pair of side-by-side spaced apart engagement features engaged by mating features on a support structure so as to resist side-to-side and rotational movement of the panel. These engagement features may be comprised of a pair of bosses, each formed with a hole adapted to receive one of a pair of holder pins fixed to the support structure. The bosses may be stiffened with gussets extending towards the glazing panel, but blending into the tab short of the panel perimeter. The gussets promote controlled liquid run off to prevent puddling and dripping, and stiffen the bosses to resist front to rear movement of the panel. 
     As noted, the spaced apart bosses eliminate side to side rotation of the panel while the bosses and gussets provide stiffening structure able to resist front to rear movement of the panel. The tab enables holding the panel so as to resist any buoyancy induced tendency for movement of the panel during tank dipping, and allows the panel to be held in a tilted position for compact horizontal stacking of curved panels on racks, conveyors, hanger brackets, or supporting structure on other transfer devices used to handle the panels. 
     A raised ridge extending about each hole on the rear face of the tab minimizes the tendency of coating liquid to be retained between the rear tab face and an adjacent support surface against which the tab is abutted in hanging the panel. 
     The bosses have a generous draft taper to facilitate removal from the mold, and the holes are also similarly tapered. A series of inversely tapered ribs arranged about each hole interior may also be used to allow engagement with a constant diameter hanger pins. 
     The pins may also be tapered and formed with a larger diameter end, creating a step which serves to capture the tab once emplaced on the pins, preventing unintended movement off the pins as may result from vibrations or bumping of the support structure. 
     The tab engagement features may be configured identically for each glazing panel configuration such as to allow standardized fixturing and efficient use of automated handling equipment such as robots. That is, variations of the support structure can be used with a “universal” tab, or different tab configurations could be used on the same or different parts. A J-hook or bracket extension can be utilized to lower the position of the panel on the support structure. 
     At the conclusion of the panel processing, the tabs are trimmed off, with a slight step at the intersection of the tab and panel facilitating cut off. 
    
    
     DESCRIPTION OF THE DRAWING FIGURES 
     FIG. 1 is a block diagram of the handling process according to the present invention. 
     FIG. 2 is a front view of a glazing panel molded to have a stabilizing handling tab integral therewith. 
     FIG. 3 is an enlarged fragmentary perspective view of a portion of the glazing panel shown in FIG. 2, showing details of the stabilizing handling tab. 
     FIG. 4 is a fragmentary perspective view of a glazing panel and adjacent support structure on which the glazing panel is emplaced. 
     FIG. 5 is an enlarged fragmentary section view of the glazing panel of FIG. 2, showing further details of the handling tab. 
     FIG. 6 is a side elevational view of a curved contour glazing panel emplaced on a holder structure in a tilted position. 
     FIG. 7 is a perspective fragmentary view of a portion of the glazing panel relocated on a rack by a J-hook. 
     FIG. 8 is a perspective fragmentary view of a glazing panel with an alternate form of handling tab. 
     FIG. 9 is a front view of a glazing panel having two handling tabs formed integrally with the runner plugs. 
     FIG. 10 is a perspective view of a holder rack loaded with glazing panels supported thereon by handling tabs. 
     FIG. 11 is a front view of a rack span depicting loading of glazing panels thereon with a robot arm. 
     FIG. 12 is a diagram showing movement of a rack loaded with glazing panels through typical processing stations. 
     FIG. 13 is a perspective view of a glazing panel loaded onto a conveyor using the stabilizing handling tabs for continuous processing. 
     FIG. 14 is a diagram depicting continuous processing of glazing panels supported on a conveyor with an integral handling tab. 
     FIG. 15 is a perspective view of an alternate form of a bracket and support pins for engaging the handling tab according to the invention. 
     FIG. 16 is a fragmentary perspective view of a handling tab supported on the bracket shown in FIG.  15 . 
     FIG. 17 is a sectional view of the handling tab and bracket shown in FIG.  16 . 
     FIG. 18 is a perspective view of another form of bracket shown installed on a support bar shown in phantom lines. 
     FIG. 19 is a sectional view of another construction of the bracket shown in FIG.  18 . 
     FIG. 20 is a sectional view of a handling tab installed on a bracket of a type shown in FIG.  19 . 
    
    
     DETAILED DESCRIPTION 
     In the following detailed description, certain specific terminology will be employed for the sake of clarity and a particular embodiment described in accordance with the requirements of 35 USC 112, but it is to be understood that the same is not intended to be limiting and should not be so construed inasmuch as the invention is capable of taking many forms and variations within the scope of the appended claims. 
     The present invention relates to handling of molded plastic glazing panels as manufacturing process steps are carried out on the panel. As examples of such steps, various coating and treating processes have been devised for improving the scratch resistance, UV transmission characteristics, weathering qualities, chemical solvent resistance, etc. of glazing panels molded from polycarbonate so as to realize the advantages of injection molded plastic automotive glazing. Other typical steps include inspection (automatic or manual), application of a black out border, oven curing of coatings, removal of runners, primer and adhesive seal application, etc. Whatever coating or treatment processes are practiced, efficient handling must be realized to enable such panels to be manufactured at reasonable cost. 
     A typical approach heretofore proposed is to first mold the glazing panels and then perform the coating and other treatments of the panels at a completely separate processing facility, perhaps at another plant. 
     This separate processing greatly increases manufacturing costs due to the extensive handling of the panels thereby entailed. 
     Other approaches might require very sophisticated and costly handling equipment to avoid creating optical flaws during processing. 
     Accordingly, the present invention provides a generally applicable method of handling such glazing panels during whatever particular process is being conducted on those glazing panels, which allows processing after molding of the panels at the same site as a part of an integrated manufacturing facility. 
     The transfer of the panels incidental to each processing step is contemplated as carried out by any of various transfer devices, such as conveyors allowing continuous or indexing movement of a series of panels, or by accumulating conveyors, etc. Transfer of individual panels by robot devices, or of groups of panels, as on racks may also be utilized, be used in conjunction with continuous or indexing conveyors, in which batch processing is used for certain process steps, and continuous transfer is used for other steps. 
     FIG. 1 is a block diagram representation of typical processing using the handling steps according to the present invention. This includes Step I, in which a glazing panel is injection molded from a transparent plastic, such as a polycarbonate or acrylic, so as to have one or more outwardly projecting handling tabs formed integrally therewith, the tab described in detail below. 
     In step II, the glazing panel is removed from the mold, inspected, and any preliminary processing is carried out such as cleaning and eliminating static charges. 
     In step III, the glazing panel is then emplaced on the holder structure of a transfer device, such as on a carrier rack, a conveyor hanger, robot gripper, etc. using the handling tabs as a connection to the holder structure. 
     In step IV, the glazing panel is transferred repeatedly, incidental to undergoing various subsequent processing steps, such as being dipped in a tank or disposed in a flow coating apparatus, and moved into and out of a curing oven. Such transfers are carried out using the engagement of a holder structure with the handling tabs. 
     Many other processes might be included, as for example plasma coating, application of black-out paint, etc.; and these all could involve handling of the panel using an engagement with one or more handling tabs. It will be understood by those skilled in the art that some of such processes typically will be carried out in clean room environments. 
     In step V, the panel is removed from the last transfer device holder structure, in step VI, the handling tab or tabs are trimmed from the panel, and in step VII, final inspection and packing are carried out. 
     Trim method utilized to remove the tab from the panel may be routing, laser cutting, water jet cutting, etc. 
     Referring to FIG. 2, the stabilizing handling tab  10  is integrally formed with the glazing panel  12 , extending generally outwardly from the perimeter thereof. 
     Runner plugs R are also shown, which would typically be trimmed after removal from the mold. 
     The handling tab  10  includes a generally planar portion  14  (FIG. 3) which is preferably slightly thinner than the glazing panel  12  to create a step on one or both sides to facilitate later trimming of the tab  10  from the panel  12 . A pair of laterally spaced apart features comprising tapered bosses  16  project from the planar portion  14 . Each of the bosses  16  is formed with a through hole  18 . The taper of the bosses  16  is to provide a draft angle for easier removal from the mold. 
     In order to allow snug engagement with a straight sided pin, a series of tapered ribs  20  may optionally be arranged about the interior of each hole  18 . 
     A stiffener gusset  22  may extend from one side of each boss  16  towards the glazing panel  12  and blends into the planar portion  14  at a point short of the intersection between the tab  10  and the glazing panel  12 . The gussets  22  stiffen the bosses  16 , and create a controlled path for draining liquids to avoid drips onto the glazing panel  12 . 
     Since the gussets  22  blend into the planar portion  14  short of the steps  24  they do not interfere with or otherwise make more difficult, the trimming operation described. 
     A holder structure  26  associated with a transfer device has pairs of pins  28 , spaced apart and sized to be received in the holes  18 , to thus allow the glazing panel  12  to be hung thereon. 
     The lateral spacing of the holes  18  establishes an antirotational structural resistance in the general plane of the glazing panel  12 , while the bosses  16  and gussets  22  create stiffness to resist front to rear movement. 
     The tab structure resists any tendency to float due to the buoyancy of the panel when the glazing panel  12  is dipped in a liquid, and also allows tilting of the panels  10  to accommodate their curved shape when stacked horizontally for compactness as indicated in FIG.  6 . The panels  12  can also be tilted when being loaded onto the rack due to the structural support provided by the holder tab  10 . 
     A universal engagement feature configuration is contemplated as preferable for variously configured glazing panels  12 , i.e., the same hole size and spacing will be used, so that an identical holder structure can be used for a variety of glazing panels being handled. For example, a pin diameter of 0.5 inches and spacing of 1.5 inches could be used for typical auto window panels. 
     A J-hook extension  28  (FIG. 7) can be utilized to position the panel lower with respect to the support structure, if required. 
     The remaining tab structure can be varied, as shown in FIG. 8, where the tab  10 A is shortened and has smaller gussets  22 A. The gussets  22  or  22 A could be entirely eliminated in many applications. 
     A raised ridge  32  (FIG. 5) is preferably formed about the holes  18  at the rear face  34  of the tab  10 . This will minimize the tendency to trap liquid between the tab  10  and the adjacent surface of the holder structure  26  due to surface tension and capillary action. 
     More than one tab can be provided, and a pair of tabs  10 B can be formed aligned with the runners R (FIG.  9 ). This arrangement simplifies the trimming operations, as the tabs  10  can be trimmed at the same time as the runners R. 
     FIG. 10 shows a rack  36  used as the transfer device, having a series of cross members  38  with a series of pairs of projecting pins  18  located to allow emplacement of the tabs  10  thereon. 
     A robot arm  40  (FIG. 11) can be used to emplace each panel  12  on the cross members  38 . The rack  36  may have rollers as shown to allow movement along a track  42  as to a dip station  44  (FIG.  12 ), oven  46 , and other processing station  48 . 
     Continuous production is preferred for automotive applications, although batch processing could be combined with continuous movement, using accumulator conveyors. The panels  12  may thus be emplaced on a conveyor used as a transfer device, the conveyor having hangers  50  (FIG.  13 ). The conveyor  52  would move a continuous series of glazing panels  12  through the processing stations  54 ,  56  as indicated in FIG.  14 . 
     An alternate form of a hanger bracket  60  is shown in FIGS. 15-17. This includes a pair of laterally spaced tapered pins  62  projecting from a base plate  64  which can include an upwardly extending portion  66  having attachment holes  68  for attachment to a holder structure  76 . The pins  62  each have an enlarged cylindrical end  70  which creates a step  72  on the upper surface thereof. The tab  74  has a pair of bosses  76  formed with tapered openings  78  sized to receive the pins  62 . The height of the bosses  76  is slightly less than the distance from boss of the pins  62  to the step  72  so that upon placing the tab  74  on the pins  62 , the tab is captured by the step  72  to prevent the panels from shifting off the pins  62  due to shocks or vibrations as the transfer of the panel is being carried out. 
     FIGS. 18-20 show other variations in the bracket. FIG. 18 shows a bracket  80  having a split clamping ring  82  welded to the rear of the base plate  84 , used to clamp the bracket to a pipe support. 
     A pair of pins  86  having angled tips  88  create a hooking action with bosses  92  to retain a tab  90  (FIG.  20 ). The tips  88  may be coated with vinyl of other plastic if compatible with the coating or other processing. 
     The pins  86 A may be constructed of separate attached parts  94 ,  96  as shown in FIG.  19 . 
     Accordingly, it will be appreciated that the handling process utilizing an integrally formed tab allows efficient manufacture of molded plastic glazing panels having optically clear regions with minimal incidence of flaws, to be suited to efficient large scale manufacturing of such panels.