Oscillating form roller and apparatus and method for controlling the

Abstract

An apparatus and method for oscillating the dampening form roller in a lithographic printing press to provide a substantially uniform application of dampening fluid on the printing plate. The form roller is comprised of a rotatable shaft and a cylindrical roller concentrically disposed on the shaft. A double-ribbed barrel cam is coupled to the roller so as to be rotatable therewith and first and second cylindrical cam followers are disposed a predetermined distance apart on the shaft for receiving the cam therebetween so that a first major surface of the cam is in contact with the first cam follower and a second major surface of the cam is in contact with the second cam follower. The 'rise and fall' of the cam as the cam rotates relative to the cam followers imparts an oscillating motion to the roller. The rate of oscillation is substantially the same as the rate of rotation of the cam relative to the cam followers. The rate of oscillation is controlled by means of first and second roller bearings which are proximately disposed on the shaft. By adjusting the frictional engagement between the respective inner and outer races of the bearings, the speed of the shaft is controlled. The greater the relative difference between the rotational speed of the roller and the rotational speed of the shaft, the greater will be the rate of oscillation because the cam will rotate at a greater speed relative to the cam followers. Conversely, a lesser relative rotational speed differential between the shaft and roller will result in a lesser rate of oscillation of the roller.