Controlling web tension, and accumulating lengths of web, by actively controlling velocity and acceleration of a festoon

In a processing operation wherein a continuous web of material is advanced through a processing step defined by first and second spaced nips, each nip being defined by a pair of nip rolls, a method of controlling web tension, and of accumulating a limited length of the web, in the respective section of web, the method comprising:

• (a) providing a festoon, having upper and lower festoon rolls, operative on the respective section of web;
• (b) applying a first generally static force component to the upper festoon rolls, the first generally static force component having a first value and direction;
• (c) applying a second variable force component to the upper festoon rolls, the second variable force component having a second value and direction, modifying the first generally static force component, and thereby modifying (i) the effect of the first generally static force component on the upper festoon rolls and (ii) corresponding translational acceleration of the upper festoon rolls;
• and
• (d) adjusting the value and direction of the second variable force component repeatedly, each such adjusted value and direction of the second variable force component (i) replacing the previous such value and direction of the second variable force component and (ii) acting in combination with the first static force component to provide a target net translational acceleration to the upper festoon rolls.

In a processing operation wherein a continuous web of material is advanced through a processing step, a method of controlling the tension in the respective section of the web, comprising:

• (a) providing a festoon, having upper and lower festoon rolls, operative for controlling tension on the respective section of web;
• (b) providing an actuator to apply an actuating force to the upper festoon rolls;
• (c) measuring a first velocity of the web after the festoon;
• (d) measuring a second velocity of the web at the festoon;
• (e) measuring motor current of the actuator;
• (f) measuring web tension before the festoon;
• (g) measuring web tension after the festoon;
• (h) measuring translational velocity of the upper festoon rolls;
• (i) sensing the position of the upper festoon rolls;
• (j) measuring acceleration of the upper festoon rolls;
• and
• (k) providing force control commands to the actuator based on the above measured values, including computed acceleration A*p of the upper festoon rolls, to thereby control the actuating force imparted to the upper festoon rolls by the actuator to control the web tension.

Processing apparatus defining a processing line, for advancing a continuous web of material through a processing step along a given section of the processing line, the processing apparatus comprising:

• (a) a first and second rolls defining a first nip;
• (b) third and fourth rolls defining a second nip, the first and second nips collectively defining the given section of the web;
• (c) a web storage buffer operating on the web in the given section of the processing line, thereby to control tension in the web and to accumulate a limited length of the web sufficient to sustain operation of the process on the length of web during routine temporary stoppages of web feed to the given section of the processing line or taking the web away from the given section of the processing line;
• (d) an actuator applying net translational force to the web storage buffer;
• and
• (e) a controller driving the web storage buffer, and computing and controlling net translational acceleration of the web storage buffer such that the web storage buffer is effective to control tension, at a desired level of constancy, and to accumulate a limited length of the we, in the respective section of the processing line.