Method and apparatus for dynamically controlling a web printing press

A method for dynamically controlling a web printing press having a nip roller and a driver of the nip roller, the method comprising:

• controlling a speed of the driver in a tension-control mode during a start-up phase of operation of the printing press, the controlling of the speed of the driver in the tension-control mode being based on the upstream web tension so as to maintain the tension at a first desired tension value, the web moving continuously through the printing press in the tension-control mode;
• then
• achieving a steady-state speed of the driver;
• then
• determining a driver velocity ratio during a transition phase of the printing press operation, the driver being at the steady-state speed during the transition phase, the velocity ratio being a ratio of the speed of the driver needed to produce a given desired tension value to a value of a velocity command of the web printing press;
• then
• controlling the speed of the driver in a velocity-control mode during a printing phase of the printing press operation, the controlling of the speed of the driver in the velocity-control mode being based on the driver velocity ratio for maintaining the tension at a second desired tension value;
• then
• switching to the tension-control mode when the tension is sensed during the velocity-control mode and the tension moves outside of a desired web tension limit band, a time when the tension during the velocity control mode is likely to move outside of the desired web tension limit band, in response to an operator input, or periodically;
• then
• determining a revised driver velocity ratio during a time when the driver is at another steady-state speed in the tension-control mode;
• and then
• switching to the velocity-control mode using the revised driver velocity ratio.

An apparatus for dynamically controlling a web printing press having a nip roller contacting a web, the apparatus comprising:

• a driver for the nip roller;
• a tension control device for modifying a speed of the driver based on a tension in the web upstream of the nip roller in a tension-control mode during a first phase of printing press operation so as to maintain the tension at a first desired tension value, the web moving continuously through the printing press in the tension-control mode;
• and
• a speed control device for controlling the speed of the driver in a velocity-control mode during a second phase of printing press operation, the controlling of the speed of the driver in the velocity-control mode being based on a driver velocity ratio, the driver velocity ratio being a ratio of the speed of the driver for producing a second desired tension value with respect to a command speed of the printing press.