Apparatus And Method For Automatically Analyzing Extruded Films

Abstract

The invention relates to an apparatus ( 20 ) for automatically analyzing extruded films, in particular stretched films ( 7 ), wherein a neck-in portion is formed at each of both edges of the film at a specific distance from an extrusion lip of a film extruder along the longitudinal transport direction of the film, and a respective method. The apparatus comprises two edge detectors ( 31 a, 31 b ) being arranged along a first line substantially transversal to the longitudinal direction and being spaced from each other by a specific distance, wherein each one edge detector ( 31 a, 31 b ) is configured to detect, preferably to continuously detect the lateral position of one respective edge of the neck-in portion of the film, a calculation means for determining the spatial relation between at least one lateral position at the extrusion lip and a respective lateral position at the neck-in portion on the basis of the two lateral positions of the edges of the neck-in portion of the film.

1 . Apparatus for automatically analyzing extruded films, in particular stretched films, wherein a neck-in portion is formed at each of both edges of the film at a specific distance from an extrusion lip of a film extruder along the longitudinal transport direction of the film, the apparatus comprising:
 two edge detectors being arranged along a first line substantially transversal to the longitudinal direction and being spaced from each other by a specific distance, wherein each one edge detector is configured to detect, preferably to continuously detect the lateral position of one respective edge of the neck-in portion of the film,   a calculation means for determining the spatial relation between at least one lateral position at the extrusion lip and a respective lateral position at the neck-in portion on the basis of the two lateral positions of the edges of the neck-in portion of the film.   
     
     
         2 . Apparatus according to  claim 1 , further comprising:
 wherein the calculation means determines the width of the film along the first line on the basis of the two lateral positions of the edges of the neck-in portion of the film, and wherein   the calculation means determines the spatial relation between the at least one lateral position at the extrusion lip and the respective lateral position at the neck-in portion on the basis of the width of the film along the first line preferably taking into account a width of an opening of the extrusion lip.   
     
     
         3 . Apparatus according to any one of preceding claims, further comprising:
 storage means for storing at least one functional relationship, preferably an equation defining a relationship between at least one lateral position at the extrusion lip and a respective lateral position at the neck-in portion for a reference film having a specific width and thickness at the extrusion lip, wherein preferably the functional relationship is defined for a specific material of the extruded film, and wherein   the calculation means corrects the functional relationship on the basis of the two lateral positions of the edges of the neck-in portion of the film or on the basis of the width of the film and wherein   the calculation means is further configured to determine the spatial relation between at least one lateral position at the extrusion lip and a respective lateral position at the neck-in portion using the corrected functional relationship.   
     
     
         4 . Apparatus according to any one of preceding claims,
 wherein the edge detectors comprise optical, capacitive, inductive or acoustical sensors, and wherein preferably the sensors are arranged in an array form, preferably along a linear array of specific length being parallel to the first line, wherein the specific length is in the range of 5 to 100 cm, preferably 10 to 50 cm, and/or   wherein the edge detectors perform a one-side measurement by using reflection or a two-side measurement by using transmission.   
     
     
         5 . Apparatus according to any one of preceding claims, further comprising:
 at least one component for creating at least one mark on the extruded film at at least one lateral position at the extrusion lip in the border region of the first and/or second lateral side of the film and   at least one component for detecting the lateral position of the mark at the neck-in portion.   
     
     
         6 . Apparatus according to  claim 5 , wherein the component for creating at least one mark comprises:
 at least one nozzle means for directing a gas stream, preferably an air stream to a surface of the film exiting the extrusion lip of the film extruder, wherein the nozzle means are configured and arranged in such a manner that the gas stream locally causes a cooling of the extruded film to create a local mark   and preferably further comprising:   a frame which is adapted to support at least one nozzle means, wherein the nozzle means is configured to be movable in a scanning manner in parallel to the extrusion lip of the film extruder along the width of the extruded film or web and/or to support a linear array of nozzle means at one or both ends of the extrusion lip of a film extruder such that a plurality of gas streams can be directed to one or both border regions of the film, wherein one or both linear arrays of nozzles are arranged substantially along a line parallel to the extrusion lip of the film extruder.   
     
     
         7 . Apparatus according to  claim 5 , wherein the component for creating at least one mark comprises:
 at least one nozzle means for directing a substance, preferably a liquid or paste-like material, more preferably an ink or resin and more preferably fluorescent ink to a surface of the film exiting the extrusion lip of the film extruder, wherein the nozzle means are configured and arranged in such a manner that the substance creates a local mark on the extruded film   and preferably further comprising:   a frame which is adapted to support at least one nozzle means, wherein the nozzle means is configured to be movable in a scanning manner in parallel to the extrusion lip of the film extruder along the width of the extruded film or web and/or to support a linear array of nozzle means at one or both ends of the extrusion lip of a film extruder such that a plurality of gas streams and/or substances can be directed one or both border regions of the film, wherein one or both linear arrays of nozzles are arranged substantially along a line parallel to the extrusion lip of the film extruder.   
     
     
         8 . Apparatus according to  claim 7 , wherein the component for detecting the lateral position of the mark at the neck-in portion comprises a sensor, preferably an optical camera, configured to detect the substance at the neck-in portion. 
     
     
         9 . Apparatus according to any one of preceding claims, wherein the extruder comprises a plurality of adjusting means for adjusting the width of respective portions of the extrusion lip of the extruder, further comprising:
 means for receiving thickness information of the film along a second line substantially parallel to the first line, wherein preferably the second line is at the same position as the first line or at a position spaced apart from the first line preferably downstream in the longitudinal transport direction, and wherein   the calculating means are configured to generate control signals for controlling respective adjusting means of the extruder on the basis of the thickness information and   a) the two lateral positions of the edges of the neck-in portion of the film and/or   b) the width of the neck-in portion of the film and/or   c) the information of the lateral position of the mark.   
     
     
         10 . Apparatus according to any one of preceding claims, further comprising:
 a frame being arranged substantially along the first line, wherein the frame is configured to support the two edge detectors and preferably to support a gauging instrument for measuring the thickness of the film, wherein more preferably the frame comprises guiding means along which the gauging instrument is movable in both directions such that the gauging instrument is capable to measure the thickness of the film across the whole width of the film.   
     
     
         11 . A system for automatically controlling a film extruder in particular for automatically controlling the thickness of extruded films, in particular of stretched films, comprising an apparatus for automatically analyzing extruded films according to any one of the preceding claims comprising:
 further control means for controlling individual adjusting means for adjusting the local width of respective portions of the extrusion lip of the film extruder on the basis of the analysis of the extruded film.   
     
     
         12 . Method for automatically analyzing extruded films, in particular stretched films, wherein a neck-in portion is formed at each of both edges of the film at a specific distance from an extrusion lip of a film extruder along the longitudinal transport direction of the film, comprising the following steps:
 detecting, preferably continuously detecting the lateral position of one respective edge of the neck-in portion of the film, using two edge detectors being arranged along a first line substantially transversal to the longitudinal direction and being spaced from each other by a specific distance,   determining the spatial relation between at least one lateral position at the extrusion lip and a respective lateral position at the neck-in portion on the basis of the two lateral positions of the edges of the neck-in portion of the film using a calculation means.   
     
     
         13 . Method according to  claim 12 , further comprising:
 determining the width of the film along the first line on the basis of the two lateral positions of the edges of the neck-in portion of the film, and   determining the spatial relation between the at least one lateral position at the extrusion lip and the respective lateral position at the neck-in portion on the basis of the width of the film along the first line preferably taking into account a width of an opening of the extrusion lip.   
     
     
         14 . Method according to  claim 12  or  13 , further comprising the steps of:
 storing at least one functional relationship, preferably an equation defining a relationship between at least one lateral position at the extrusion lip and a respective lateral position at the neck-in portion for a reference film having a specific width and thickness at the extrusion lip, wherein preferably the functional relationship is defined for a specific material of the extruded film, and 
 correcting the functional relationship on the basis of the two lateral positions of the edges of the neck-in portion of the film or on the basis of the width of the film and determining the spatial relation between at least one lateral position at the extrusion lip and a respective lateral position at the neck-in portion using the corrected functional relationship. 
 
     
     
         15 . Method according to any one of  claims 12  to  14 , further comprising the steps of:
 creating at least one mark on the extruded film at at least one lateral position at the extrusion lip in the border region of the first and/or second lateral side of the film and detecting the lateral position of the mark at the neck-in portion. 
 
     
     
         16 . Method according to any one of  claims 12  to  15 , further comprising the steps of:
 adjusting the width of respective portions of the extrusion lip of the extruder, receiving thickness information of the film along a second line substantially parallel to the first line, wherein preferably the second line is at the same position as the first line or at a position spaced apart from the first line preferably downstream in the longitudinal transport direction, and 
 generating control signals for controlling respective adjusting means of the extruder on the basis of the thickness information and the two lateral positions of the edges of the neck-in portion of the film or the width of the neck-in portion of the film. 
 
     
     
         17 . A method for automatically controlling a film extruder in particular for automatically controlling the thickness of extruded films, in particular of stretched films, comprising the steps of:
 automatically analyzing extruded films according to any one of  claims 12  to  16 , and controlling individual adjusting means for adjusting the local width of respective portions of the extrusion lip of the film extruder on the basis of the analysis of the extruded film.