Patent GB-1532704-A (GB)
Title: Method of and apparatus for producing printing surfaces
IPC: G03F5/20
Filed: 1976-02-27
Abstract: 1532704 Facsimile DR-ING RUDOLF HELL GmbH 27 Feb 1976 [28 Feb 1975] 07918/76 Heading H4F Printing cylinders 2, Fig. 1, of various diameters are engraved for subsequent production of half tone facsimiles, by apparatus comprising a permanent scanning drum I having a diameter greater than that of the largest printing cylinder to be employed, and on which originals 12 of varying sizes are mounted for "opto electronic" scanning. The drum 1 and cylinder 2 are rigidly coupled and driven by a synchronous motor 4 under the control of a master clock To, 9. Scanning and engraving are performed respectively along open and closed circumferential lines with intermittent advancement of scanning head 15 and engraving tool 56 between lines. Scanning and engraving are performed under the control of clocks T 3  and T 4  respectively derived from the master clock by dividers 40 and 57 and incorporates inter line phase reversal 46 and 61 to generate a standard gravure screen pattern. Successive line scans of original 12 are initiated at reference line 70; in response to a delayed signal derived from optoelectric monitoring of a reference mark 73. A user operable control 88 defines the circumferential extent of the line scan which is always less than the total drum circumference. During axial advancement of the engraving tool 56, cylinder 2 continues to rotate so that engraving of each line does not generally commence at any refence circumferential position. This results in the need for picture line storage means 28 incorporating specialized data handling control. The data handling requirements are further complicated by the fact that the line engraving period is slightly in excess of the period of rotation of the cylinder. Storage means 28 incorporates two line stores operated alternately and oppositely in loading and unloading modes. An indexing signal, indicative of the cylinder's instantaneous angular disposition, is received by store 28 and converted into an address relating to the stored data location of the requisite commencing element to be engraved. After several revolutions the compounded delay between engraving and scanning exceeds one revolution period. In this case it is necessary (in order to avoid attempting to operate one of the line stores simultaneously in the load and unload mode) to defer subsequent line scanning for one revolution period. This delay occurs since advancement of the scanning head 15 takes place while that part of the drum 1 not carrying the original 12 passes thereby, whereas engraving of cylinder 2 is interrupted after each complete closed line had been engraved. In another embodiment, Fig. 5 (not shown) provision is made for engraving a plurality of "repeats" in the circumferential direction (i.e. along a line). In this case each line of the original is still scanned in one revolution of drum 1 and in the related engraving revolution of cylinder 2 the stored data is read out for engraving as often as required. Axial pattern repetition is achieved by rescanning of the original. In another embodiment, Fig. 6 (not shown) a plurality of picture originals are mounted axially on the scanning drum from which simultaneous engraving of a common printing cylinder with the various images is derived. The engraving tool may comprise an electron beam or a laser.