Method and apparatus for determining slipping in a nip roller

A method for determining a presence of a slipping of a driven nip roller of a nip relative to a web passing through the nip in a web printing press, the method comprising:

• causing a plurality of changes in a speed of a driver driving the nip roller;
• monitoring a respective change in a tension in the web upstream of the nip upon each respective change of the speed of the driver so as to determine a linearity and a slope of a relationship between the tension and the speed of the driver;
• and
• determining the presence of the slipping when the tension is non-linear with respect to the speed of the driver or the slope is substantially less than an expected slope.

A method for determining a presence of a slipping of a driven nip roller of a nip relative to a web passing through the nip in a web printing press, the method comprising:

• causing a plurality of changes in a speed of a driver driving the nip roller;
• monitoring a respective change in a torque of the driver upon each respective change of the speed of the driver so as to determine a linearity and a slope of a relationship between the torque and the speed of the driver;
• and
• determining the presence of the slipping when the torque is non-linear with respect to the speed of the driver or the slope is substantially less than an expected slope.

An apparatus for determining a presence of a slipping of a driven nip roller apparatus for determining the presence of slipping of a driven nip roller of a nip relative to a web passing through the nip in a web printing press, the apparatus comprising:

• a first tension sensor disposed upstream of the nip and having a first tension output being a function of a tension in the web upstream of the nip;
• a second tension sensor disposed downstream of the nip and having a second tension output being a function of a tension in the web downstream of the nip;
• a driver for driving the driven nip roller;
• and
• a processor causing a plurality of changes in a speed of the driver, the processor receiving the first and second tension outputs and determining for each of the changes in speed a respective difference in tension in the web upstream and downstream of the nip based on the first and second tension outputs so as to determine a linearity and a slope of a relationship between the difference in tension and the speed of the driver, the processor determining the presence of the slipping when the difference in tension is non-linear with respect to the speed of the driver or the slope is substantially less than an expected slope.