Photocopying – Projection printing and copying cameras – Image transferred to or from curved surface
Patent
1984-06-13
1985-12-03
Hix, L. T.
Photocopying
Projection printing and copying cameras
Image transferred to or from curved surface
355 49, 355 52, 350442, G03B 2768
Patent
active
045563128
DESCRIPTION:
BRIEF SUMMARY
The invention concerns an improvement to be applied to optical printing devices for printing on blanks which are intended for the manufacture of cans by swaging.
Cans are decorated either by means of a strip of paper which is preprinted and wound around and glued onto the can, or by direct printing on the can, or else by printing of the blank which is then to produce the can by swaging.
In this case, the blank generally must be printed with a predeformed image in such a manner that the original image will be reconstituted following the swaging.
Optical apparatuses to obtain a predeformed image have been described in prior documents, particularly in U.S. Pat. Nos. 3,238,909, 3,314,329, 3,964,910, 4,119,484 and in FR Pat. No. A-1 590 126 (corresponding to U.S. Pat. No. 3 627 412) in the name of the applicant, as well as in FR Pat. No. A-2 453 432, in the name of FEREMBAL, which uses a flexible reflecting strip as optical element, turning on the axis of the optical system around the can which is being formed.
Presently, the requirements of users regarding the quality of printing (accuracy, contrast, restoration of colors, etc.) are no longer entirely satisfied by known optical devices; the legibility of texts in small characters, for example, is not always assured. In four-color printing, a lack of clarity has been noted, which requires stopping down of diaphragm aperature so as to increase the depth of the field, thus increasing the exposure time; it was then noted that the diffused light attenuates the shadows in the vicinity of the light zones, which gives a "milky" appearance to the print.
The object of the present invention is an improvement of the anamorphic optical system, which is the object of our French Pat. No. FR-A-1 590 126. In this patent, a printing apparatus is described for printing a predeformed image on swaging blanks, characterized in that it comprises essentially: a toric prism and an aspherical and revolving lens, associated with an achromatic photographic objective of very great focal length.
The toric prism is realized with a very transparent material such as methyl polymethacrylate.
The improvement consists of associating the toric prism and the correction lens in one monolithic element, the prism solely assuring the function of reflection of the light rays, and the lens effecting the optical corrections assuring the linearity of the swaged image. Also, the angle of the prism has been determined in such a manner as to obtain total reflection of the light rays emitted by the source.
FIGS. 1 to 8 illustrate the application of the invention, mainly illustrating the general principle of the invention.
When a can is swaged from a flat, circular blank, it is noted that each point marked on the flat surface of the blank then corresponds to one point on the surface of the swaged can. A relation thus exists between the prior position, on the blank, of any one point of the surface of the metal, and the final position on the swaged can. Then by knowing this relation, it is possible to print the blank before deformation in such a manner that during the swaging the drawing is subject to a deformation such that the desired picture is obtained. In a practical manner, a label which can be wound around the can is generally used; the blank should then be printed in such a manner that, following swaging, a can is decorated with the same picture as if the label had been wound around it.
If the conversion which makes the points of the blank correspond to those of the can is T, then: T.sup.-1 so as to obtain a deformed image from a label, to be used for the printing of the blanks: obtained which is truly of the same appearance as the label: lines forming a system of coordinates to mark the position of a point both before and after swaging.
In the case of round cans, a system of polar coordinates (r, .theta.) is used for the blank, and the position of the points on the can after the swaging is then marked by a system (p, .theta.) wherein p is the position of a point measured on a generatrice of the can from
REFERENCES:
patent: 1669027 (1928-05-01), Seymour
patent: 3073210 (1959-01-01), Packard
patent: 3238909 (1966-03-01), Kendall
patent: 3314329 (1967-04-01), Wolbert
patent: 3627412 (1971-12-01), Jean
patent: 3964910 (1976-06-01), Geist et al.
patent: 4119484 (1978-10-01), Schiffman
Brown Brian W.
Cebal
Hix L. T,.
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