Patent DE-10012520-A1 (DE)
Title: Preparation of a printing cylinder uses the cylinder layout with a reference mark for the separation of the text data for screen etching and separate image data for engraving in the separations for color runs
Inventor: BREIHOLDT JAN
IPC: B41C1/05
Filed: 2000-03-15
Abstract: To prepare a printing cylinder, a reference mark is generated as text data (TD) in the cylinder layout and applied to the printing cylinder (2) at the periphery against a fixed reference point. The image data (BD) and text data (TD) are separated at the cylinder layout, and an etching mask (12) is prepared for the text data (TD). The indentations are etched in the printing cylinder (2) at the text zone and the reference mark by the etching mask (12). The etched printing cylinder (2) is loaded into an engraving machine (18), where the engraving tool uses the reference mark as a single phase reference point. The indentations for the image zone are engraved from the image data (BD) into the etched printing cylinder (2) in register with the etched text zone. The text zone is prepared directly on to the printing cylinder (2) by a tool (10) at the workstation (11), from the etching mask (12) and the separated text data (TD). The text data (TD) have a higher resolution than the image data (BD), which are both as PostScript (RTM) data. The text data (TD) are converted into a bit map of high resolution at a screen image processor (9). The bits of the bit map are taken as control data (SD) for the tool head (10) at the etching workstation (11). A varnish is applied to the printing cylinder (2), and the etching mask (12) is produced by the working of the tool head (10) on it, using a laser tool head (10) with at least one controlled laser beam. The image data (BD) are converted into a contone map at a screen image processor (15). Its gray values are taken to produce the engraving data (GD) to control the engraving tool (17) at the engraving machine (18). The gray values of the contone map source data (QD) have an independent resolution from the printing screen, and are converted by interpolation in the engraving data (GD) of the printing screen. Identical screen image processors (9,15) are used to give the bit map and the contone map. The text zone and the reference mark are imposed for a color run, and marked text data (TD are arranged for a different color from the run. The image data (BD) and text data (TD) are separated according to their color runs. The cylinder layout for the printing cylinder (2) is developed at a workstation (5), which separates the image data (BD) and the text data (TD). The etching mask (12) is prepared for halftone gravure printing. For the single phasing of the printing cylinder (2), loaded into the engraving machine (18), an engraving start pulse is generated on each rotation of the cylinder which marks the cylinder with a start point. Using the reference mark, the peripheral angle displacement is set between the required engraving start point to engrave the image zone and the engraving tool as the reference point, with compensation at the established angular shift. The peripheral angular shift is compensated before engraving, where the cylinder (2) is rotated in relation to the engraving tool (17) by the established peripheral angular shift so that the required engraving start point is under the engraving tool on each rotation for each engraving start pulse. When the printing cylinder (2) is loaded into the engraving machine (18), any axial shift is registered against a nominal axial position, with compensation for any deviation by shifting the axial setting of the engraving tool. The angular and/or axial shift is computed from the image from a video camera of the printing cylinder (2) surface, which includes at least the reference mark. At the same time, images are taken of indentations from a test engraving. The image data (BD) and text data (TD) are used to give printing screens. The reference mark can be taken from the image data (BD).