Automatic web height control in a packaging machine

Abstract

A packaging machine that uses cylinders to automatically adjust the pressure gradient on a web feed roller system is presented. The cylinders are controlled by an air operated or an electrical sensing device that senses the edge of the web. When the sensor detects the web rising it will increase the pressure on bottom of the feed rollers and lower the pressure at the top. This action drives the web down. When the web falls below the proper height the reverse happens and the web is driven back up. This system creates a seeking process that is always driving the web to the correct height. The system can also be used on a pivoting feed roller system. The sensor feedback turns an eccentric that changes the pressure gradient, moving the web to the proper height.

What is claimed is:  
     
         1 . A method to control web height of a web in a packaging machine having feed rollers comprising the steps of: 
 sensing the web height of the web;    comparing the web height to at least one threshold; and    increasing the pressure in a first cylinder located near a bottom of the feed rollers to increase a first magnitude of pressure at the bottom of the feed rollers and decreasing the pressure in a second cylinder located near a top of the feed rollers to decrease a second magnitude of pressure at the top of the feed rollers if the web height is above the threshold.    
     
     
         2 . The method of  claim 1  further comprising the step of: 
 decreasing the pressure in the first cylinder to decrease the first magnitude of pressure and increasing the pressure in the second cylinder to increase the second magnitude of pressure if the web height is below the threshold.  
 
     
     
         3 . The method of  claim 2  wherein the threshold comprises an upper threshold and a lower threshold and wherein the step of increasing the pressure in a first cylinder and decreasing the pressure in the second cylinder if the web height is above the threshold comprises the step of increasing the pressure in a first cylinder and decreasing the pressure in the second cylinder if the web height is above the upper threshold.  
     
     
         4 . The method of  claim 3  wherein the step of decreasing the pressure in the first cylinder and increasing the pressure in the second cylinder if the web height is below the threshold comprises the step of decreasing the pressure in the first cylinder and increasing the pressure in the second cylinder if the web height is below the lower threshold.  
     
     
         5 . The method of  claim 2  wherein the threshold comprises an upper threshold and a lower threshold and wherein the step of decreasing the pressure in the first cylinder and increasing the pressure in the second cylinder if the web height is below the threshold comprises the step of decreasing the pressure in the first cylinder and increasing the pressure in the second cylinder if the web height is below the lower threshold.  
     
     
         6 . The method of  claim 1  wherein the step of sensing the web height includes the steps of sensing an edge of the web by forcing air through both sides of an air operated sensor and detecting a change in air back pressure.  
     
     
         7 . The method of  claim 1  wherein the first cylinder and second cylinder are hydraulic cylinders and wherein the step of increasing the pressure in the first cylinder and decreasing the pressure in the second cylinder comprises the steps of increasing a first amount of hydraulic fluid in the first cylinder and decreasing a second amount of fluid in the second cylinder.  
     
     
         8 . The method of  claim 1  wherein the first cylinder and second cylinder are pneumatic cylinders and wherein the step of increasing the pressure in the first cylinder and decreasing the pressure in the second cylinder comprises the steps of increasing a first amount of air in the first cylinder and decreasing a second amount of air in the second cylinder.  
     
     
         9 . A device for maintaining a height of a web to a desired position in a packaging machine having feed rollers comprising: 
 a first cylinder in moveable contact with a top of one of the feed rollers;    a second cylinder in moveable contact with a bottom of one of the feed rollers;    a controller in communication with the first cylinder and the second cylinder; and    a sensor in communication with the controller, the sensor detecting the height of the web, the controller commanding at least one of the first cylinder and the second cylinder to contact one of the top and the bottom to move the web to the desired position.    
     
     
         10 . The device of  claim 9  wherein the first cylinder and the second cylinder are hydraulic cylinders.  
     
     
         11 . The device of  claim 9  wherein the first cylinder and the second cylinder are pneumatic cylinders.  
     
     
         12 . The device of  claim 9  wherein the sensor is an air sensor and wherein the air sensor detects the height of the web by sensing back air pressure.  
     
     
         13 . The device of  claim 9  wherein the controller commands the first cylinder to contact the top of the one of the feed rollers if the height of the web is above the desired position.  
     
     
         14 . The device of  claim 9  wherein the controller commands the second cylinder to contact the bottom of the one of the feed rollers if the height of the web is below the desired position.  
     
     
         15 . A packaging machine having a web height control module to automatically control the height of a web, the packaging machine for converting a web into a plurality of pouches comprising: 
 an infeed section to supply the web to a sealing section;    the sealing section sealing and cutting the web, the sealing section receiving the web from the infeed section and comprising: 
 a first seal station for forming a bottom seal;  
 a second seal station for forming vertical seals;  
 a pair of feed rollers frictionally engaging the web to pull the web through the first seal station and the second seal station;  
 a cutter receiving the web from the pair of feed rollers and adapted to cut the web proximate to the vertical seals; and  
   the web height control comprising: 
 a first cylinder in moveable contact with a top of at least one of the pair of feed rollers;  
 a second cylinder in moveable contact with a bottom of at least one of the pair of feed rollers;  
 a controller in communication with the first cylinder and the second cylinder; and  
 a web position sensor to detect the height of the web.  
   
     
     
         16 . The packaging machine of  claim 15  wherein the first cylinder and the second cylinder are pneumatic cylinders.  
     
     
         17 . The packaging machine of  claim 15  wherein the first cylinder and the second cylinder are hydraulic cylinders.  
     
     
         18 . The packaging machine of  claim 15  wherein the controller commands the first cylinder to contact the top of the at least one of the feed rollers to increase the pressure at the top of the at least one of the feed rollers if the height of the web is above a desired position.  
     
     
         19 . The packaging machine of  claim 15  wherein the controller commands the second cylinder to contact the bottom of the at least one of the feed rollers to increase the pressure at the bottom of the at least one of the feed rollers if the height of the web is below a predetermined position.  
     
     
         20 . The packaging machine of  claim 19  wherein the controller commands the first cylinder to contact the top of the at least one of the feed rollers to increase the pressure at the top of the at least one of the feed rollers if the height of the web is above the predetermined position.