| Ink preset is a process to set the output ink by the digital information of the imagecoverage on plate and the quantitative requirements of the ink film thickness. Compared withthe traditional method which relies on expeirence,this technology is of significant value for itsmore precise preset to spare the time of pirnting and reduce the waste of material. This paperstudies ink distirbution characteristic in the ink transfer process and gives a new method torealize the ink preset which can further improve the preset accuracy. The main contirbutionsand innovation points of this paper are summarized as follows:1.Based on the inking system computer simulation method,this paper have acomprehensively study on the laws of the ink transfer process. It's veirifed that when one inkzone output ink, a kind of direct proportion exists between the ink output value and ink layerthickness of each ink zone on the substrate; when a number of ink zones output ink respectively,the ink quantity distirbution on the substrate equals to the sum total of the ink quantity of eachink zone output separately; Etc.2.When one zone output a unit quantity ink, this paper use BP neural network to create themapping relationship between the image coverage rate of ink zones within a certain range andthe ink distirbution on the substrate. Then atfer reading the image coverage rate distirbution ofdigital prepress ifle, using the trained BP neural network, we can get the ink quantitydistirbution vector on the substrate, which is to be a column of the matirx and construct a matirxto express the ink distirbution characteirstics quantitatively under the conditions of the currentimage coverage rate distirbution. It is the first time to solve the quantitative description methodof ink distirbution feature in the pirnting process.3.By the ink distribution characteristics of the matirx, this paper theoretically proves thatfor the inherent limitation of the inking system,the ink quantity on the substrate can not achievethe desired uniform requirements under the condition of a given image coverage rate. Based onthis, this paper uses the matrix singular value decomposition method innovatively, by themethod of truncated singular value, obtain ink preset value which can meet the requirement thatthe root mean square errors of the ink quantity on the substrate and the standard is less than theprescirbed requirement.4.On the basis of the above research, this paper gives a new and integral method to realizethe ink preset. Firstly, calculate the image coverage rates of each ink zone rfom digital prepressfile, and compensate for the geometric expansion of the dot area; then use the trained BP neuralnetwork to produce a matrix which can reflect the distirbution characteristics of the ink; byusing the matirx singular value decomposition method, get the output ink value require of thefountain roller under the condition of the ink quantity distirbution on the substrate is approximate to the standard; after that use the value to calculate the ink preset value of each inkzone. The innovation of this method is that the output ink preset value is obtained based on theink distirbution characteirstics under the specific conditions, including the important inlfuenceof ink transfer characteirstics because of the ink backflow and axial movement. The developedoffset press ink preset system has been equipped by several pirnting companies and producedgood benefits. |
