Tension Control System for Deformable Nip Rollers

Abstract

A method and apparatus for controlling web tension in a web printing press having a plurality of sets of deformable nip rollers, each set driven by a separate driver, the web passing sequentially through each set of deformable nip rollers and forming a web segment therebetween. The driver of a downstream set of deformable nip rollers is adjusted to set the tension of a first web segment and a controller adjusts a first characteristic of the driver of the upstream set of deformable nip rollers to maintain the tension of a second web segment constant. Alternatively, a sensor measures a second characteristic of the second web segment and the controller adjusts the first characteristic of the driver of the upstream set of deformable nip rollers based on the measurement from the sensor.

1 . A method for controlling web tension in a web printing press having a plurality of sets of deformable nip rollers, each set of deformable nip rollers driven by a separate driver, the web passing sequentially through each set of deformable nip rollers, each adjacent set of deformable nip rollers forming a web segment therebetween, comprising the steps of:
 adjusting a first characteristic of the driver of a downstream set of deformable nip rollers to set the tension of a first web segment which is between the downstream set of deformable nip rollers and an upstream set of deformable nip rollers; and   adjusting a first characteristic of the driver of the upstream set of deformable nip rollers to maintain a constant tension on a second web segment which is immediately preceding the upstream set of deformable nip rollers.   
     
     
         2 . The method of  claim 1 , further comprising the step of:
 measuring a second characteristic of the second web segment; and   wherein the step of adjusting a first characteristic of the driver of the upstream set of deformable nip rollers is based on the measurement of the second characteristic.   
     
     
         3 . The method of  claim 2 , wherein the first characteristic is the rotational speed of the driver. 
     
     
         4 . The method of  claim 2 , wherein the second characteristic is the tension of the second web segment. 
     
     
         5 . The method of  claim 2 , wherein the second characteristic is the speed of the second web segment. 
     
     
         6 . The method of  claim 2 , wherein the second characteristic is the amount of torque in the driver of a set of deformable nip rollers immediately preceding the upstream set of deformable nip rollers. 
     
     
         7 . An apparatus for controlling web tension in a web printing press having a plurality of sets of deformable nip rollers, each set of deformable nip rollers driven by a separate driver, the web passing sequentially through each set of deformable nip rollers, each adjacent set of deformable nip rollers forming a web segment therebetween, comprising:
 means for adjusting a first characteristic of the driver of a downstream set of deformable nip rollers to set the tension of a first web segment which is between the downstream set of deformable nip rollers and an upstream set of deformable nip rollers; and   a controller for adjusting a first characteristic of the driver of the upstream set of deformable nip rollers to maintain a constant tension on a second web segment which is immediately preceding the upstream set of deformable nip rollers.   
     
     
         8 . The apparatus of  claim 7 , further comprising:
 a sensor for measuring a second characteristic of the second web segment; and   wherein the controller adjusts the first characteristic of the driver of the upstream set of deformable nip rollers based on the measurement from the sensor.   
     
     
         9 . The apparatus of  claim 7 , wherein the first characteristic is the rotational speed of the driver. 
     
     
         10 . The apparatus of  claim 8 , wherein the sensor measures the tension of the second web segment. 
     
     
         11 . The apparatus of  claim 8 , wherein the sensor measures the speed of the second web segment. 
     
     
         12 . The apparatus of  claim 8 , wherein the sensor measures the torque in the driver of a set of deformable nip rollers immediately preceding the upstream set of deformable nip rollers.