Glass manufacturing – With mechanical cutter – scorer – or scriber for article or... – With annealing means
Reexamination Certificate
1997-11-26
2001-04-24
Vincent, Sean (Department: 1731)
Glass manufacturing
With mechanical cutter, scorer, or scriber for article or...
With annealing means
C065S174000, C065S182200, C083S086000, C406S088000, C406S089000, C414S676000, C414S677000
Reexamination Certificate
active
06220056
ABSTRACT:
This invention claims priority to German patent application Serial No. 196 49 488.5-22 DE, filed Nov. 29, 1996.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention concerns a device for handling thin panes of glass or similar work pieces and products in conveyor systems, machining installations, and the like by pneumatic forces.
2. Summary of the Related Art
Thin plate glass is used on a large scale to produce displays, where scratches, inclusions, deposits, etc. larger than approximately 10 &mgr;m are seen as defects because they cause intolerable local distortion of the image in the finished display. Therefore, extensive control measures must be provided to detect and reject products that cannot be used.
Since there are also high demands regarding the flatness and parallelism of the plate glass used for window displays, the manufacturing process usually includes a surface polishing step. This makes it possible to eliminate many defects but it makes production considerably more expensive. There have therefore been great attempts to eliminate the polishing operation.
In recent plate glass manufacturing processes, the demands for flatness and parallelism of the glass surfaces can be maintained to a better extent on drawn or floated raw glass, so that polishing can be eliminated because of the cost advantages. However, this also eliminates the possibility of eliminating defects. On the other hand, plate glass in the thickness range of 30 to 300 &mgr;m for small display formats cannot currently be polished or it can be polished only at a high cost. Current projections indicate that formats up to 650×1000 mm with a plate glass thickness of 50 &mgr;m can be expected. In addition, the specifications with regard to the size of defects and the number of defects per unit of area have become increasingly more strict with the newer display grades of glass, e.g., field emission display (FED), plasma display panel (PDP), plasma addressed liquid crystal (PALC), thin film transistor (TFT) or super twisted nemetic (STN), so that glass manufacturers are forced to comply with stricter requirements to be able to offer a technically and economically acceptable product.
An indispensable manufacturing step is formatting the raw glass, which is manufactured in large plates or as a wide strip for economic reasons. Formatting therefore includes cutting to the desired display size, including processing of edges and comers, which may optionally be followed by a final cleaning.
A device for conveying glass in the form of a plate or a strip is already known from German Patent DE 1,756,070 B2, where the glass rests on a cushion of gas at a distance from a lower structure and can be conveyed horizontally relative to the lower structure without coming in contact with it. The lower structure is provided with slots side by side for the passage of the gas, although the slots are designed alternately as gas discharge and exhaust slots and are connected to appropriate pressure and vacuum sources. This generates an alternating field of mutually opposed forces which a thin pane of glass cannot withstand. Furthermore, only one of the two glass surfaces, at best, can be protected from soiling.
Furthermore, European Patent EP 336,332 B1 discloses a device for gripping, stacking and unstacking plate glass as well as conveying it, where vacuum grippers, which are known from another technology, are used. However, suction grippers cannot be used with glass below a certain minimum thickness because thin plate glass would sag in the area of the vacuum grippers or could even break in the worst case. Furthermore, vacuum grippers are not suitable for holding very thin plate glass for machining such as cutting, grinding and/or polishing because they result in uneven gripping, which cannot be maintained uniformly in the machining area. Moreover, the vacuum grippers do not prevent soiling of the glass surfaces in conveyance and machining.
SUMMARY OF THE INVENTION
The invention provides a device for handling thin plate glass in machining facilities, especially in cutting installations, that will make it possible to secure and convey both the existing raw glass formats as well as the finished formats in such a way that the surfaces are not damaged, deposits of dirt particles, cutting splinters, etc. are prevented and the possibility of fracture of the glass is ruled out. It must be pointed out that extremely gentle handling of the glass is demanded by the omission of polishing for technical or economic reasons, the trend toward larger and larger display formats and the fact that specifications regarding the size and frequency of defects.
To achieve this goal, a device of the type defined initially is proposed; it is characterized by at least two plates with flat surfaces on at least one side arranged parallel to each other at a distance sufficient for accommodating the pane of glass without contact, where the plates have numerous gas passages and all the gas passages in a plate can each be connected through one or more channels, etc, to a gas delivery device for generating an excess pressure or a reduced pressure. Preferably at least some of the gas passages are arranged opposite each other in pairs.
With this device, excess pressure can act on both plates in a first mode of operation, so that the pane of glass is held between the plates without coming in contact with them, or excess pressure may act on one plate while a reduced pressure acts on the other plate in a second mode of operation, so the pane of glass is pressed against one plate and held there. In the first mode of operation, a stream of gas emitted at both sides of the pane of glass held between the plates, preferably equally strong on both sides, is maintained to ensure that any dust, etc. that might be present is removed toward the outside and nothing can penetrate from the outside. At the same time, the pane of glass is not allowed to come in contact with either the top or bottom plate and therefore can be conveyed horizontally between the plates without any risk of scratching the glass surface. The gas stream produced is preferably emitted from pairs of opposite orifices.
The known self-regulating effect can be utilized; this comes about due to the fact that a vertical displacement of the pane of glass, i.e., an approach to one of the plates, leads to an increase in the cross section of flow between the pane of glass and the other plate, a decrease in pneumatic pressure with no change in gas throughput on this side and the development of forces that counteract the vertical displacement. The gravity acting perpendicularly on the pane of glass in one direction can easily be compensated through the control technology by having a marginally higher excess pressure act on the bottom plate if the pane of glass must be positioned accurately exactly in the middle between the plates.
The second mode of operation, where the pane of glass is held against one of the plates, serves either to work on the glass while the plate is stationary or to displace the pane of glass together with the plate into another position, e.g., to convey it from the working position to a storage position or stacking position.
As long as the pane of glass is between the two plates, measures are taken on the excess pressure side to ensure, as before, that this glass surface cannot become soiled. On the vacuum side, the pane of glass is in contact with the plate, so that no contaminants can enter there if the surface of the plate is flat and smooth enough or if a suitable seal is provided at the edge between the plate and the pane of glass.
The arrangement of paired opposing gas passages ensures that in the first mode of operation, approximately the same pneumatic forces act everywhere on both sides of the glass surface, thus preventing the thin pane of glass from bulging out of the plane. In addition, a certain smoothing effect on the thin pane of glass can be achieved in this way.
In the second mode of operation, a smoothing effect that corresponds to the smoothing of paper by m
McDonnell & Boehnen Hulbert & Berghoff
Schott Glaswerke
Vincent Sean
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