Method and apparatus for web tracking with predictive control

A method for controlling operations upon a web moving along a path the web being subject to lateral movement in a direction transverse to the direction of movement of said web along said path, said method comprising the steps of:

• sensing the edge pattern of said web, said edge pattern comprising the cross-track position and the in-track position of said web;
• generating signals representing sensed edge pattern data;
• storing a baseline of said sensed edge pattern data;
• compensating successively-sensed cross-track position data according to the baseline cross-track position data;
• storing said compensated successively-sensed edge pattern data;
• calculating web drift information from said compensated successively-sensed edge pattern data;
• extrapolating said drift information to a predicted web cross-track position at a future web in-track position;
• correcting the cross-track alignment of said web in the event that said predicted web cross-track position exceeds a predetermined allowed limit value, said correction of the cross-track alignment of said web being implemented in advance of said future in-track position, said correction further including the steps of:
• deriving a new steering control value substantially equal to and having a reversed direction from the control value used in a most recent correction in the event said most recent correction was unidirectional;
• deriving a new steering control value substantially equal to said most recently used control value increased by an optimal amount in the event said most recent steering event was not unidirectional;
• calculating elapsed web in-track travel from the most recent correction;
• decreasing said new control value in the event said elapsed travel is less than a predetermined amount;
• and
• implementing said new control value.

A method for controlling operations upon a web moving along a path, the web being subject to lateral movement in a direction transverse to the direction of movement of said web along said path, said method comprising the steps of:

• (a) monitoring the lateral position of the web and generating signals in response thereto;
• (b) determining, in response to said signals, if an operation can be performed upon said web without imposing a correction to lateral web movement;
• and
• (c) in response to a determination that the operation cannot be performed, inhibiting the operation until a determination is made that the operation can be performed.

Apparatus for controlling operations upon a web comprising:

• means for moving the web along a path, the web being subject to lateral movement in a direction transverse to the direction of movement of said web along said path;
• means for monitoring the lateral position of the web and generating first signals in response thereto;
• means responsive to said first signals for generating second signals relative to a prediction that the transition of the web's lateral alignment beyond a predetermined allowable limit will occur during a time period or web length required for an operation;
• means for determining, in response to said signals, if an operation can be performed upon said web without imposing a correction to lateral web movement;
• and
• means for imposing said correction in response to a determination that the operation cannot be performed.

Apparatus for controlling operations upon a web comprising:

• means for sensing an edge pattern of said web, said edge pattern comprising the cross-track position and the in-track position of said web;
• means for generating signals representing sensed edge pattern data;
• means for storing a baseline of said sensed edge pattern data;
• means for compensating said successively-sensed cross-track position data according to said baseline edge pattern;
• means for storing said compensated successively-sensed edge pattern data;
• means for calculating web cross-track drift information;
• means for extrapolating said cross-track information to a predicted web cross-track position at a future web in-track position;
• and
• means for correcting the cross-track alignment of said web in the event that said predicted web cross-track position exceeds a predetermined allowed limit value, said correction of the cross-track alignment of said web being implemented in advance of said future in-track position.

Apparatus for controlling operations upon a web comprising:

• means for moving the web along a path, the web being subject to lateral movement in a direction transverse to the direction of movement of said web along said path;
• means for monitoring the lateral position of the web and generating signals in response thereto;
• means for determining, in response to said signals, if an operation can be performed upon said web without imposing a correction to lateral web movement;
• means for imposing a lateral correction in response to said determination that the operation cannot be performed;
• and
• means for inhibiting said operations until a determination is made that the operation can be performed.

A method for controlling operations upon a web moving along a path, the web being subject to lateral movement in a direction transverse to the direction of movement of said web along said path, said method comprising the steps of:

• calculating a predicted lateral position of the web;
• comparing the predicted lateral position with a predetermined limit to determine if the limit will be exceeded during the course of one of said operations;
• and
• in response to a determination that the limit will be exceeded, imposing a correction to lateral web movement prior to commencing one or more of the operations.

An apparatus for controlling operations upon a web moving along a path, the web being subject to lateral movement in a direction transverse to the direction of movement of said web along said path, comprising

• means for calculating a predicted lateral position of the web;
• means for comparing the predicted lateral position with a predetermined limit to determine if the limit will be exceeded during the course of one of said operations;
• and
• means, responsive to a determination that the limit will be exceeded, for imposing a correction to lateral web movement prior to commencing one or more of the operations.