Photocopying – Contact printing – Machine
Patent
1993-01-04
1994-10-25
Wintercorn, Richard A.
Photocopying
Contact printing
Machine
G03B 2704
Patent
active
053593901
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to the transmissive exposure of copy pairs, and specifically, in particular, systems in which light-sensitive materials with copy originals laid on them are exposed during a through movement below or, in the case of upward exposure, above a light source. In the case of offset printing, the copy original is usually a photographic film and the light-sensitive material is an aluminum printing plate. In the case of the blueprint process, the copy original is, for example, a transparent drawing and the light-sensitive material is a blueprint paper or a blueprint foil. In the latter case, namely the use of transparent or light-transmitting blueprint foils, a plurality of the same can also be laid one on top of the other and exposed simultaneously. If, for example, three blueprint foils are to be exposed simultaneously, then, including the copy original, four material layers must be moved through the path of the light beam.
The invention proceeds from an apparatus for the transmissive exposure of copy pairs, having a light source directed onto a glass plate and a pressure device disposed on the other side of the glass plate, as well as a respective pair of transport rollers in front of and behind the transmission gap formed between the glass plate and the pressure device. Such an apparatus is known from EP-PS 0,117,294 B1.
The pressure device acts on the copy pairs in the course of transmission to the glass plate and is intended to cause these to be held in intimate contact during the exposure. If spacings remain as a result of included air pockets, then unsharpnesses designated as "hollow copies" are created.
In the known construction, the pressure device is a foam layer which rests on a rigid plate. At its lower surface, the upper end of a compression spring is supported, the lower end of which compression spring acts on a tie rod with settable force, which tie rod acts on the light source housing with the glass plate, so that the latter experiences, going beyond its weight, an additional surface pressure on the foam layer. A complete elimination of hollow copies is not achieved with this construction. This also applies to the further mentioned possibilities of the pressing-on by means of a multiplicity of closely disposed springs or of a cushion standing at excess pressure, with which in each instance a full-area pressing-on is to be achieved.
Similar considerations are also applicable to a construction which is known from EP-PS 0,110,940 B1 and in which the glass plate is pressed by means of a pressure-settable springing towards a bearing plate, over which the copy pairs are drawn in the course of the transmissive exposure.
DE-OS 1,522,850 further discloses a construction with upward exposure, in which a flat plate is pressed by resilient spring force downwards against the glass plate; in this case, the flat pressure plate carries a foam layer, which is provided with a brush covering, e.g. a velour layer. This construction also does not reliably prevent the occurrence of hollow copies.
The object of the present invention is the provision of an apparatus for transmissive exposure, with which an improved quality of the copying result is achieved and the occurrence of hollow copies is reliably prevented.
Proceeding from the initially considered construction, the achievement of the set object takes place, according to the invention, in that the pressure device comprises a plurality of pressure shoes which are disposed side by side in the transverse direction and which are pressed in the height direction by resilient spring force towards the glass plate, with a flat base surface, which are tiltable about the longitudinal axis and transverse axis.
As a result of the division, according to the invention, of the pressure zone into a multiplicity of pressure surfaces, which are displaceable in the direction of pressing-on and thus exhibit two tilting degrees of freedom, i.e. virtually a cardan joint, which pressure surfaces are in this case rigid in themselves, in spite of dispensing with
REFERENCES:
patent: 4551016 (1985-11-01), Maher et al.
patent: 4566787 (1986-01-01), Lullau
Siegfried Theimer Grafische Geraete GmbH
Wintercorn Richard A.
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