Printing presses, such as those used for printing newspapers and the like, utilize plates which have the particular impression to be printed etched on them. These plates are attached to a portion of the printing press known as a plate cylinder. When printing newspapers and the like, these plates will need to be changed several times a day in order to reflect the different editions or different newspapers printed on each printing press unit.
Heretofore, in order for a plate to be removed and changed on a plate cylinder, the press unit would have to be disengaged from the press drive system or the entire printing press stopped. With the press unit disengaged, the plate could then be removed from or placed on the plate cylinder by engaging in an activity known as "barring."
Barring is the common way to rotate a plate cylinder and remove or replace a particular plate. Barring consists of manually disengaging a press unit, inserting a metal bar in the gaps found beside the plate cylinder and using the bar as a lever to manually rotate the cylinder at a low speed. Thus, a pressman will "inch" the plate cylinder a fraction of a rotation, engage in the specific activity that required disengagement of the press unit (usually changing the plate), and repeat this process until the plate cylinder is fully rotated. This barring process is obviously very labor intensive, as well as time consuming.
If a press unit is not disengaged from the main drive of the printing press, all of the plates on the press units must be changed simultaneously. Under such circumstances, several pressmen simultaneously must remove and replace plates on each individual press unit in the entire press while the entire press is driven at extremely low inching speeds. Naturally, this activity results in a great disruption of pressroom activities.
The inching drive mechanism of the present invention overcomes the foregoing disadvantages by allowing each individual press unit to be disengaged from the entire press drive system, and simultaneously allowing each disengaged unit to be rotated by a low speed motor.