Machine vision control on printing cylinders

The Paloma project was conducted in the paper industry. The main goal of the project was to react to pattern printing errors on large paper rolls. An error occurs when paper wedges in the printing cylinders and starts to wind up unexpectedly.

A camera monitors the cylinders during the production process. If the slightest error is detected, the process is stopped before the paper winds up onto the cylinder and halts the production. The camera is set at a distance to cover all five printing cylinders. Digital image processing techniques are used for detecting printing errors. The specific feature of the project is the need for ensuring immediate system reaction due to the speed of the cylinder rotation, i.e. the system has to respond in one tenth of a second. Within this timeframe, the error has to be detected and a command to stop the printing process has to be issued.

An Imaging Source camera was used in this project. The processing runs on the Compact Vision System. Its real-time operating system guarantees fast image processing and instantaneous reaction to errors in production. Since the errors are detected by monitoring the relative change in the printed colour on the paper roll, the system is not limited to a specific colour pattern. However, the error detection threshold is set accordingly, for the system not to react to the insignificant printing differences, and unnecessarily stop the production process.