Can printing apparatus

A can printing apparatus comprising:

• a main printer having plural plate cylinders for printing different colors and performing printing onto side surfaces of cans;
• a can inspection machine inspecting a printing state;
• and
• a secondary printer performing additional printing to the side surfaces of the cans after the printing by the main printer,
• wherein the can inspection machine includes
• a can rotation device which rotates cans,
• a can imaging device which takes images of the side surfaces of the cans, and
• an image processing device which processes the taken images,
• wherein the secondary printer includes
• a printing head which faces a side surface of a can held by the can rotation device of the can inspection machine and
• a processing unit which gives an instruction of printing to the printing head based on a predetermined printing pattern and processing data of the image processing device of the can inspection machine,
• wherein the can imaging device includes a first camera for taking an image of the entire can, and
• wherein the image processing device includes
• an image inspection means for inspecting whether the image is correctly printed as compared with a master image by using the image taken by the first camera, and
• a density measurement means for measuring densities in positions designated by respective colors by using the image taken by the first camera.