Optical paper sorting method device and apparatus

Abstract

An optical paper sorting system uses diffuse reflectance to identify a sheet of paper, conveyed on a conveyor, as either white or groundwood grade. A light source illuminates a sheet of paper and an optical collection system collects and filters the light diffusely reflected from the sheet of paper. The reflected light strikes a detector which produces a photoelectric current proportional to the intensity of the filtered light in a specific region in the electromagnetic spectrum, preferably ultraviolet. The signal from the detector may be digitized and processed by a computer which classifies the sheet as either white or groundwood, and activates an ejection device to produce an air blast for diverting whichever grade is selected for ejection.

1 . An apparatus for separating a material containing less than a selected amount of lignin from a material containing more than the selected amount of lignin, the materials being of the same color or of a different color, comprising 
 a conveyor for conveying the material to a collection bin,    a detection device disposed adjacent to the conveyor, comprising a light source positioned to emit light comprising an ultraviolet component to strike the material, a detector for detecting ultraviolet light and generating an electrical signal proportional to an intensity of detected ultraviolet light, the detector being positioned to detect ultraviolet light diffusely reflected off of the material, an optical filter disposed between the material and the detector to eliminate components of diffusely reflected light outside of the ultraviolet range, and an instrument for measuring a level of the electrical signal,    a comparing device for comparing the level of the electrical signal to a reference level to determine whether the material contains less than or more than the selected amount of lignin, and    an ejection device disposed downstream of the detection device, for receiving an ejection signal from the comparing device when the material contains more than or less than the selected amount of lignin and ejecting the material in response.    
   
   
       2 . The apparatus as defined in  claim 1  in which the material is a paper product.  
   
   
       3 . The apparatus as defined in  claim 2  in which the comparing device comprises a computer.  
   
   
       4 . The apparatus as defined in  claim 2  in which the light source also emits light components outside of the ultraviolet range.  
   
   
       5 . The apparatus as defined in  claim 2  in which the ejection device comprises an air nozzle receiving air from a compressor.  
   
   
       6 . The apparatus as defined in  claim 5  in which the air nozzle is controlled by a solenoid valve activated by the ejection signal.  
   
   
       7 . The apparatus as defined in  claim 3  in which an air nozzle is disposed adjacent to a terminal end of the conveyor and diverts the material into a rejection bin.  
   
   
       8 . The apparatus as defined in  claim 2  in which the selected amount of lignin is determined by a threshold relative reflectance defined by the equation  
       [%  R]   TS =[%  R]   high  groundwood+([%  R]   low  white−[%  R]   high  groundwood)/2  
     where [% R] TS  is the threshold relative reflectance, [% R] high  groundwood is an upper limit of groundwood relative reflectance range, and [% R] low  white is a lower limit of white relative reflectance range.