Method of and apparatus for controlling lateral deviations of a travelling fabric web
First Claim
1. A method of controlling lateral deviations of a traveling web from a setpoint position thereof, said web having a pattern defining a guidance criterium along said web in a direction of travel thereof, said method comprising the steps of:
- (a) storing a sequence of reference signals corresponding image point by image point across said web to values representing a reference scan along a line perpendicular to said direction of travel and distinguishing the guidance criterium at a location corresponding to a setpoint location of the guidance criterium of the web during the travel thereof;
(b) with an image/signal converter acquiring an image of said pattern across said web as said web is traveling past said converter, converting a single row of image points of said image across said web into a sequence of image signals each representing an average image value along an imaginary column parallel to said direction but arrayed across a width of the web, digitalizing said image values, image point by image point across said width, into a digital signal having the guidance criterium of said image distinguished by a distinct actual value representing an instantaneous location of the guidance criterium during the travel of the web, and storing the digitalized signal;
(c) shifting the digital signal formed in step (b) relative to the stored reference sequence of step (a) image point by image point in a series of shifting cycles and for each shifting cycle, calculating a similarity function whose value is a measure of a degree of correspondence of said reference sequence and the digital signal;
(d) for each image acquisition in step (b) determining the best correspondence of said reference signal and said digital signal from said similarity function, thereby deriving from the shift a correction value by which the actual position of the guidance criterium of said web deviates from the setpoint location thereof;
(e) actuating an effector to adjust the lateral position of said web in accordance with said correction value; and
(f) repeating steps (b) through (e) with successive acquisitions of images from strips across said web transverse to said direction of travel at a predetermined cadence.
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Accused Products
Abstract
The travel of a fabric web is corrected by an image acquisition from a region thereof including a guidance criterium which can be interrupted to produce a single row of image points, the signals of which are digitalized and compared with a reference signal by relative shifting of the stored signals in two shift registers. The number of shifts required to bring about correlation is determined as a measure of the actual position of the web and compared to a setpoint position for operation of an effector restoring the web to its set point position.
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Citations
13 Claims
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1. A method of controlling lateral deviations of a traveling web from a setpoint position thereof, said web having a pattern defining a guidance criterium along said web in a direction of travel thereof, said method comprising the steps of:
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(a) storing a sequence of reference signals corresponding image point by image point across said web to values representing a reference scan along a line perpendicular to said direction of travel and distinguishing the guidance criterium at a location corresponding to a setpoint location of the guidance criterium of the web during the travel thereof; (b) with an image/signal converter acquiring an image of said pattern across said web as said web is traveling past said converter, converting a single row of image points of said image across said web into a sequence of image signals each representing an average image value along an imaginary column parallel to said direction but arrayed across a width of the web, digitalizing said image values, image point by image point across said width, into a digital signal having the guidance criterium of said image distinguished by a distinct actual value representing an instantaneous location of the guidance criterium during the travel of the web, and storing the digitalized signal; (c) shifting the digital signal formed in step (b) relative to the stored reference sequence of step (a) image point by image point in a series of shifting cycles and for each shifting cycle, calculating a similarity function whose value is a measure of a degree of correspondence of said reference sequence and the digital signal; (d) for each image acquisition in step (b) determining the best correspondence of said reference signal and said digital signal from said similarity function, thereby deriving from the shift a correction value by which the actual position of the guidance criterium of said web deviates from the setpoint location thereof; (e) actuating an effector to adjust the lateral position of said web in accordance with said correction value; and (f) repeating steps (b) through (e) with successive acquisitions of images from strips across said web transverse to said direction of travel at a predetermined cadence. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8)
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9. An apparatus for controlling lateral deviations of a traveling web from a setpoint position thereof, said web having a pattern defining a guidance criterium along said web in a direction of travel thereof, said apparatus comprising:
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means for storing a sequence of reference signals corresponding image point by image point across said web to values representing a reference scan along a line perpendicular to said direction of travel and distinguishing the guidance criterium at a location corresponding to a setpoint location of the guidance criterium of the web during the travel thereof; an image/signal converter including means for acquiring an image of said pattern across said web as said web is traveling past said converter, converting a single row of image points of said image across said web into a sequence of image signals each representing an average image value along an imaginary column parallel to said direction but arrayed across a width of the web, digitalizing said image values, image point by image point across said width, into a digital signal having the guidance criterium of said image distinguished by a distinct actual value representing an instantaneous location of the guidance criterium during the travel of the web, and storing the digitalized signal; means for shifting the digital signal relative to the stored reference sequence image point by image point in a series of shifting cycles and for each shifting cycle, calculating a similarity function whose value is a measure of a degree of correspondence of said reference sequence and the digital signal; means, connected with said means for shifting and in each image acquisition, for determining the best correspondence of said reference signal and said digital signal from said similarity function, thereby deriving from the shift a correction value by which the actual position of the guidance criterium of said web deviates from the setpoint location thereof; and an effector connected to said means for determining the best correspondence and adjusting the lateral position of said web in accordance with said correction value. - View Dependent Claims (10, 11, 12)
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13. A method of controlling lateral deviations of a traveling web from a setpoint position thereof, said web having a pattern defining a guidance criterium along said web in a direction of travel thereof, said method comprising the steps of:
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(a) storing a sequence of reference signals corresponding image point by image point across said web to values representing a reference scan along a line perpendicular to said direction of travel and distinguishing the guidance criterium at a location corresponding to a setpoint location of the guidance criterium of the web during the travel thereof; (b) averaging image values along a multiplicity of imaginary columns parallel to said direction but arrayed across a width of the web, digitalizing said image values image point by image point across said width in a single row, into a digital signal having the guidance criterium of said image distinguished by a distinct actual value representing an instantaneous location of the guidance criterium during the travel of the web, and storing the digitalized signal; (c) shifting the digital signal formed in step (b) relative to the stored reference sequence of step (a) image point by image point in a series of shifting cycles and for each shifting cycle, calculating a similarity function whose value is a measure of a degree of correspondence of said reference sequence and the digital signal; (d) for each average of image values in step (b) determining the best correspondence of said reference signal and said digital signal from said similarity function, thereby deriving from the shift a correction value by which the actual position of the guidance criterium of said web deviates from the setpoint location thereof; and (e) actuating an effector to adjust the lateral position of said web in accordance with said correction value.
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Specification