Printing unit drive system

A printing press comprising,

• first and second blanket cylinders defining a printing nip and having a first position in which said blanket cylinders are cooperable to print on opposite sides of sheet material advanced through the nip and a second position in which said blanket cylinders are ineffective to print on the sheet material,
• a first bearer fixedly connected with said first blanket cylinder and having a circular outer surface,
• a second bearer fixedly connected with said second blanket cylinder and having a circular outer surface of the same diameter as the diameter of the circular outer surface of said first bearer, said outer surfaces of said first and second bearers being disposed in rolling engagement when said blanket cylinders are in said first position, said first and second bearers forming a set of blanket cylinder bearers,
• first and second plate cylinders which engage said blanket cylinders when the blanket cylinders are in the first position, each of said plate cylinders being spaced apart from and ineffective to transfer an image to the associated blanket cylinder when the blanket cylinders are in the second position,
• a third bearer fixedly connected with said first plate cylinder and having a circular outer surface disposed in rolling engagement with the circular outer surface of said first bearer when said blanket cylinders are in said first position,
• a fourth bearer fixedly connected with said second plate cylinder and having a circular outer surface disposed in rolling engagement with the circular outer surface of said second bearer when said blanket cylinders are in said first position, said third and fourth bearers having circular outer surfaces of the same diameter and forming a set of plate cylinder bearers,
• throw-off means for effecting relative movement between said first and second blanket cylinders from the first position to the second position in which said blanket cylinders are ineffective to print on sheet material and are spaced apart from said plate cylinders, said throw-off means being effective to relatively move said blanket cylinders from the second position to the first position in which said blanket cylinders are effective to print on sheet material and are in engagement with said plate cylinders,
• means for drivingly interconnecting said first and second blanket cylinders when in their first and second positions, said means for drivingly interconnecting said first and second blanket cylinders comprising,
• first and second gears having equal numbers of teeth and having design pitch circles of the same diameters as said first and second bearers,
• said first and second gears being different from standard gears in that said first and second gears each have a design pitch diameter which is greater than the number of teeth on the gear divided by the diametral pitch of the gear,
• means for connecting said first gear to said first blanket cylinder in a coaxial relationship with said first bearer, and
• means for connecting said second gear to said second blanket cylinder in a coaxial relationship with said second bearer,
• said first and second gears having gear teeth which are disposed in meshing engagement when said blanket cylinders are in their first and second positions,
• said design pitch circles of said first and second gears having a single point of intersection when said blanket cylinders are in said first position,
• said first and second gears forming a set of blanket cylinder gears which is associated with said set of blanket cylinder bearers,
• a third gear having gear teeth disposed in meshing engagement with gear teeth of said first gear when said first and second blanket cylinders are in their first and second positions,
• a fourth gear having gear teeth disposed in meshing engagement with gear teeth of said second gear when said first and second blanket cylinders are in their first and second positions,
• means drivingly connecting said third gear with said first plate cylinder in a coaxial relationship with said third bearer,
• said third gear having a design pitch circle of a diameter which is greater than the diameter of said third bearer, said design pitch circle of said third gear overlapping and having two points of intersection with the design pitch circle of said first gear when said blanket cylinders are in said first position,
• said third gear having a working pitch circle which is of a smaller diameter than its design pitch circle, the working pitch circle of said third gear being tangent to the working pitch circle of said first gear when said blanket cylinders are in said first position,
• the number of gear teeth on said first gear meshing with the gear teeth of said third gear being less than that required to rotate the surface of said first plate cylinder at the surface speed of said first blanket cylinder,
• said means drivingly connecting said third gear with said first plate cylinder including means for effecting rotation of said first plate cylinder relative to said third gear to effect rotation of the surface of said first plate cylinder at the surface speed of said first blanket cylinder,
• means drivingly connecting said fourth gear with said second plate cylinder in a coaxial relationship with said fourth bearer,
• said fourth gear having a design pitch circle of a diameter which is greater than the diameter of said fourth bearer, said design pitch circle of said fourth gear overlapping and having two points of intersection with the design pitch circle of said second gear when said blanket cylinders are in said first position,
• said fourth gear having a working pitch circle which is of a smaller diameter than its design pitch circle, the working pitch circle of said fourth gear being tangent to the working pitch circle of said second gear when said blanket cylinders are in said first position,
• the number of gear teeth on said second gear meshing with gear teeth of said fourth gear being less than required to rotate the surface of said second plate cylinder at the surface speed of said second blanket cylinder,
• said third and fourth gears each being different from standard gears in that said third and fourth gears each have a design pitch diameter which is greater than the number of teeth on the gear divided by the diametrical pitch of the gear,
• said third and fourth gears forming a set of plate cylindrical gears which is associated with said set of plate cylinder bearers,
• said means for drivingly connecting said fourth gear with said second plate cylinder including means for effecting rotation of said second plate cylinder relative to said fourth gear to effect rotation of the surface of said second plate cylinder at the surface speed of said second blanket cylinder.