Process and apparatus for fault detection in a liquid sheet and curtain coating process

Abstract

The present invention relates to a process and an apparatus for detecting a fault in a flowing liquid sheet and in particular in a coating curtain. The process comprises the following steps: transmitting an electromagnetic beam to the sheet so as to irradiate approximately the entire width of the sheet in a direction approximately transverse to the sheet; recovering a beam reflected by the sheet by way of a collector; defining a reference position of the reflected beam on the collector; and noting the deviations of the reflected beam in relation to the previously defined reference position.

What is claimed is:  
     
         1 . A process for detecting a fault in a flowing liquid sheet, the process comprising the steps of: 
 transmitting an electromagnetic beam to the sheet so as to irradiate approximately an entire width of the sheet in a direction approximately transverse to the sheet;    recovering a beam reflected by the sheet by means of a collector;    defining a reference position of the reflected beam on the collector; and    noting deviations of the reflected beam in relation to the previously defined reference position.    
     
     
         2 . A detection process according to  claim 1 , wherein the electromagnetic beam is emitted by an electromagnetic source which is moved in the transverse direction by means of a rail, the collector being moved in a synchronized way with the electromagnetic source.  
     
     
         3 . A detection process according to  claim 1 , wherein the electromagnetic beam is emitted by an electromagnetic source which is moved by means of a rotating mirror.  
     
     
         4 . A detection process according to  claim 1 , wherein the electromagnetic beam irradiates approximately the entire width of the sheet through a slot.  
     
     
         5 . A detection process according to  claim 2 , wherein the beam reflected by the sheet is recovered by the collector which is arranged approximately perpendicular to a plane defined by the sheet when the sheet is in a stable position.  
     
     
         6 . A detection process according to  claim 3 , wherein the beam reflected by the sheet is recovered by the collector which is arranged approximately perpendicular to a plane defined by the sheet when the sheet is in a stable position.  
     
     
         7 . A detection process according to  claim 5 , wherein the collector is a position detector.  
     
     
         8 . A detection process according to  claim 6 , wherein the collector is a position detector.  
     
     
         9 . A detection process according to  claim 5 , wherein the collector is a screen on which the deviations of the reflected beam are observed by means of a camera.  
     
     
         10 . A detection process according to  claim 6 , wherein the collector is a screen on which the deviations of the reflected beam are observed by means of a camera.  
     
     
         11 . A process according to  claim 4 , wherein the reflected beam is recovered on a suitable paper.  
     
     
         12 . A process according to  claim 1 , wherein the emitted beam is a light beam.  
     
     
         13 . A process according to  claim 1 , wherein the emitted beam is a laser beam using visible or infrared light.  
     
     
         14 . A coating process using a curtain of a photographic composition, wherein the composition runs on a surface to a lip from which the composition flows so as to form the curtain, the process comprising the steps of: 
 transmitting an electromagnetic beam to the curtain so as to irradiate approximately an entire width of the curtain in a direction approximately transverse to the curtain;    recovering a beam reflected by the curtain by means of a collector;    defining a reference position of the reflected beam on the collector;    noting deviations of the reflected beam in relation to the previously defined reference position; and    stopping the flow of the curtain when a position of the reflected beam on the collector is offset from the position set in relation to the reference position.    
     
     
         15 . A coating process according to  claim 14 , wherein the emitted beam irradiates the curtain in a direction approximately transverse to the curtain at a distance from the lip of between 0 and 10 cm.  
     
     
         16 . A process according to  claim 15 , wherein the emitted beam irradiates the curtain in a direction approximately transverse to the curtain at a distance from the lip of about 2 cm.  
     
     
         17 . A detection apparatus for detecting a fault in a flowing liquid sheet comprising: 
 a radiating source for emitting an electromagnetic beam;    a shifting device adapted to move the radiating source so that the beam emitted by the radiating source irradiates approximately an entire width of the sheet in a direction approximately transverse to the sheet; and    a collector to recover a beam reflected by the sheet.    
     
     
         18 . An apparatus according to  claim 17 , wherein the collector is a position detector.  
     
     
         19 . An apparatus according to  claim 17 , wherein the collector is a screen on which deviations of the reflected beam are observed by means of a camera.  
     
     
         20 . An apparatus according to  claim 17 , wherein the shifting device is a rail which moves the radiating source and the collector in a synchronized way.  
     
     
         21 . An apparatus according to  claim 17 , wherein the shifting device is a rotating mirror.  
     
     
         22 . A detection apparatus for detecting a fault in a flowing liquid sheet comprising: 
 a radiating source for emitting an electromagnetic beam;    a slot through which the radiating source irradiates approximately an entire width of the sheet in a direction approximately transverse to the sheet; and    a collector to recover a beam reflected by the sheet.