Plate cylinder with plate lockup mechanism and related printing press and method

1. A plate cylinder comprising:

a plate cylinder body having a longitudinally-extending first hole and a longitudinally extending plate-receiving gap connected to the first hole, the plate cylinder body having a longitudinally-extending second hole parallel to the first hole; and

a lock-up mechanism including:

a torsion bar extending in the longitudinally extending first hole and having a surface for contacting an end of a plate located in the gap;

a swing bar extending longitudinally in the second hole and being movable perpendicular to the longitudinal direction due to the second hole being oversized compared to dimensions of the swing bar within the second hole;

an arm connecting the swing bar and the torsion bar, the torsion bar being rotatable as the swing bar moves within the second hole;

an activator; and

a lever connecting the activator to the swing bar, the activator rotating the lever to move the swing bar thereby rotating the torsion bar.

2. The plate cylinder as recited in claim 1 wherein the activator is an air cylinder.

3. The plate cylinder as recited in claim 1 wherein the lock-up mechanism has a spring forcing the torsion bar toward a lock-up position, the swing bar being in contact with an upper surface of the second hole in the lock-up position.

4. The plate cylinder as recited in claim 3 wherein, when the activator is activated, the lever rotates until a stop hits the plate cylinder body, the torsion bar being rotated against action of the spring to a release position, the swing bar being out of contact with the upper surface in the release position.

5. An offset printing press comprising the plate cylinder as recited in claim 1 and a blanket cylinder.