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Summary:
This is the second of a series of papers in computer simulation of web offset printing process. The effect of vibrator oscillation on press performance was studied extensively in this paper. The oscillation of vibrators causes a lateral flow of ink across the inking zones of the roller train. The extent of lateral flow of ink increases with the magnitude of vibrator oscillation, and the stroke length is more effective than the oscillation rate. Ink also tends to migrate further away from the input zone as the image coverage of the plate decreases. A bar graph test form was used to study the dynamic behavior of inkers. Both press time constant and incubation period are independent of any change in ink feedrate, if the ink film thickness is used as the control variable. Dynamic properties vary with the magnitude and direction of ink feedrate change, if the optical density is used as the control variable. The 60-20-20 inker tends to respond to a step change in the ink feedrate slightly faster than the 100-0-0 inker. The oscillation of vibrators does not affect these behaviors, but causes the press time constant to depart from the linear relationship with the reciprocal of image coverage. The larger the stroke length and/or the faster the oscillation rate, the greater the departure. However, the linear relationship of mean ink residence time with the reciprocal of image coverage is not affected by the oscillation of vibrators. A T-bar test form was specifically designed for appraising print quality attributes such as ghosting and starvation. The oscillation of vibrators significantly reduces starvation, but has a negligible effect on ghosting. The larger the stroke length and/or the faster the oscillation rate, the less the starvation. Ghost is slightly more severe if the heavy coverage is placed closer to the leading than the trailing edge. The 100-0-0 inker produces slightly less ghost and less starvation than the 60-20-20 inker. These results of computer simulation are presented in this paper. Implications to closed-loop control of the printing process are also discussed.