Web tension control

Abstract

A method for controlling a tension of a continuous web comprises: moving said web along a web path; controlling a first actuator of a first dancer mechanism to generate a first force to move first rollers of said first dancer mechanism along a respective first path on a respective first surface, said first rollers contacting said web at a first portion of said web path; and controlling a second actuator of a second dancer mechanism to generate a second force to move second rollers of said second dancer mechanism along a respective second path on a respective second surface, said second rollers contacting said web at a second portion of said web path, said second portion being separate from said first portion. Said first force and second force are determined so that the tension of said web is substantially equal near said first portion and near said second portion.

1 . A method for controlling a tension of a continuous web, the method comprising:
 moving said web along a web path;   controlling a first actuator of a first dancer mechanism to generate a first force to move each of one or more first rollers of said first dancer mechanism along a respective first path, wherein each first path is on a respective first surface that intersects with said web path, wherein said one or more first rollers contact said web at a first portion of said web path; and   controlling a second actuator of a second dancer mechanism to generate a second force to move each of one or more second rollers of said second dancer mechanism along a respective second path, wherein each of said second path is on a respective second surface that intersects with said web path, wherein said one or more second rollers contact said web at a second portion of said web path, wherein said second portion is separate from said first portion,   wherein said first force and said second force are determined so that the tension of said web is equal at a first location in or near said first portion and at a second location in or near said second portion, so that the tension of said web is controlled over a portion of said web path between said first portion and said second portion.   
     
     
         2 . The method according to  claim 1 , further comprising forming an image on said web on a portion of said web path between said first portion and said second portion. 
     
     
         3 . The method according to  claim 1 , wherein one or more third rollers contact said web at a third portion of said web path and move said web along said web path, wherein said third portion is between said first portion and said second portion;
 wherein said first actuator and said second actuator are controlled so that the tension of said web between said first portion and said third portion, and the tension of said web between said second portion and said third portion, are equal to each other.   
     
     
         4 . The method according to  claim 1 , further comprising
 sensing, at said first portion, a measure of a third force that acts on said one or more first rollers as said web moves along said web path.   
     
     
         5 . The method according to  claim 1 , further comprising
 sensing, at said second portion, a measure of a fourth force that acts on said one or more second rollers as said web moves along said web path.   
     
     
         6 . The method according to  claim 1 , wherein at least one of said first force and said second force is a torque. 
     
     
         7 . The method according to  claim 1 , wherein at least one of said first actuator and said second actuator is an electric actuator. 
     
     
         8 . The method according to  claim 1 , wherein said one or more first rollers differ in number from said one or more second rollers. 
     
     
         9 . The method according to of  claim 8 , wherein
 said first force is determined based on a number of said one or more first rollers.   
     
     
         10 . The method according to  claim 1 , wherein at least one of said first actuator and said second actuator is controlled to generate a constant force. 
     
     
         11 . The method according to  claim 1 , wherein said first dancer mechanism further comprises one or more fourth rollers that contact said web at said first portion, wherein each of said one or more first rollers moves along said respective one or more first paths relative to said one or more fourth rollers. 
     
     
         12 . The methods according to  claim 1 , wherein said second dancer mechanism further comprises one or more fifth rollers that contact said web at said second portion, wherein each of said one or more second rollers moves along said respective one or more second paths relative to said one or more fifth rollers. 
     
     
         13 . A computer program comprising instructions which, when executed by one or more processor, causes the one or more processors to execute the method according to  claim 1 . 
     
     
         14 . A control unit for an apparatus for controlling a tension of a continuous web to be moved along a web path, wherein said control unit is arranged to:
 control a first actuator of a first dancer mechanism to generate a first force to move one or more first rollers of said first dancer mechanism along a respective first path, wherein each first path is on a respective first surface that intersects with the web path, wherein said one or more first rollers are arranged to contact said web at a first portion of said web path; and   control a second actuator of a second dancer mechanism to generate a second force to move each of one or more second rollers of said second dancer mechanism along a respective second path, wherein each second path is on a respective second surface that intersects with said web path, wherein said one or more second rollers are arranged to contact said web at a second portion of said web path, wherein said second portion is separate from said first portion,   wherein said first force and said second force are determined so that the tension of said web is equal at a first location in or near said first portion and at a second location in or near said second portion, so that the tension of said web is controlled over a portion of said web path between said first portion and said second portion.   
     
     
         15 . An apparatus comprising:
 a first dancer mechanism;   a second dancer mechanism; and   a control unit for controlling a tension of a continuous web to be moved along a web path, wherein said control unit is arranged to:   control a first actuator of said first dancer mechanism to generate a first force to move one or more first rollers of said first dancer mechanism along a respective first path, wherein each first path is on a respective first surface that intersects with the web path, wherein said one or more first rollers are arranged to contact said web at a first portion of said web path; and   control a second actuator of said second dancer mechanism to generate a second force to move each of one or more second rollers of said second dancer mechanism along a respective second path, wherein each second path is on a respective second surface that intersects with said web path, wherein said one or more second rollers are arranged to contact said web at a second portion of said web path, wherein said second portion is separate from said first portion,   wherein said first force and said second force are determined so that the tension of said web is equal at a first location in or near said first portion and at a second location in or near said second portion, so that the tension of said web is controlled over a portion of said web path between said first portion and said second portion.   
     
     
         16 . The method of  claim 8 , wherein said second force is determined based on a number of said one or more second rollers. 
     
     
         17 . The method according to  claim 4 , further comprising controlling said first actuator based on said measure of said third force. 
     
     
         18 . The method according to  claim 5 , further comprising controlling said second actuator based on said measure of said fourth force.