Measurement of non uniformity of tension and diagnostics of defects of a sheet of flock printing material

Non uniformity of tension of flock printing material in the printing device decreases the quality of printed images. In order to reduce this non uniformity of tension a method based on the analysis of the shape of the first eigenmode of vibrations is proposed. Also when defect in the flock printing material takes place, it is important to perform its diagnostics as soon as possible. This is also performed from the distorted shape of the first eigenmode of vibrations obtained by using time averaged projection moiré. For this purpose not only the first eigenmode is to be used, but for some types of defects located in specific places of the sheet of flock printing material the analysis of several first eigenmodes is required. It is assumed that a sheet of flock material is an elastic layer with the elastic modulus and the density linearly varying in the thickness direction and having zero values on the lower plane. The square sheet of flock material is analyzed. On the upper plane of the lower and upper boundaries all the displacements are assumed equal to zero, except on the upper plane of the upper boundary linear variation of the displacement in the direction of the y axis is assumed. The first eigenmodes are determined and investigated. Investigation of vibrations of flock material by taking the layer of glue and separate flocks into account by using a two dimensional model is performed. This model is used for the determination of parameters of the previous model. It is assumed that flock material consists from a number of narrow two dimensional elastic strips and their upper parts are connected by an elastic layer. The first eigenmodes are determined and investigated. Experimental investigations of the eigenmodes of vibrations have been performed. The obtained experimental results show satisfactory agreement with the numerical ones. The obtained results are used in the process of design of packages made from flock material