What is the function of the oscillating ink roller?
Why the press vendor need to provide the adjustment of this roller in width and position of the return match the plate cylinder position?
In the old days, press operator would change the sweep width and position quite often.
The function of the oscillator is to make the ink applied from the ink fountain to ink roller become more even.
Each ink zone width (in Heidelberg press) is 32.5mm, the max. sweep width of the oscillator is 35mm. So we always find that the ink key position of an individual ink key would be affected by the ink key value next to it (having two ink key - left and right).
Normally, if the job is having large ink coverage, then the sweep width would be set to max. width. For less ink coverage job, the sweep width would set to as small as possible. In some rare case, even turn off the oscillation.
I did not know, nowadays, not many press operator would try to analyze the total ink coverage and adjust it accordingly.
Normally the position of the return would be set at the nip area. However, why the design allow the adjustment there? The oscillator would travel in horizontal direction. One return trip is the same as the plate cylinder having two turns (printed two sheets). At the end of the each direction, the speed of the oscillator is ZERO. At this moment the effect on the ink evenness is the worst. The speed of the oscillator is keep on changing during the traveling. At the end of the journey, the speed is zero, then the speed would be increased when towards center, from the center to the other end, the speed would be decrease and reach zero at the other end. The effect of the ink evenness would be the best in certain part of the movement.
Sometimes, press operator will change the position, the change would be according the content of the print job. For example, if a job having a important area at the certain area. The operator would change the position of the oscillator and place the most evenness ink area to that place to make the important part having the most evenness ink.