Impurity Weight Measurement

Abstract

A method for measuring the weight of impurities in a mixed volume of fibers and impurities by mechanically separating the impurities are from the fibers, whereupon some undesired fibers still remain admixed to the impurities due to imperfections of the mechanical separation. A total weight of the separated impurities and the undesired fibers is gravimetrically measured. An image of the separated impurities and the undesired fibers is created. A weight of the undesired fibers is estimated from the image. The estimated weight of the undesired fibers is subtracted from the total weight to yield a corrected weight of the impurities. The mechanical separation and the subsequent electronic correction yield a more accurate weight of the impurities.

1 . A method for measuring a weight of impurities in a mixed volume of fibers and impurities, comprising the steps of:
 mechanically separating the impurities from the fibers, some undesired fibers still remaining admixed to the impurities due to imperfections of the mechanical separation,   gravimetrically measuring a total weight of the separated impurities and the undesired fibers,   creating an image of the separated impurities and the undesired fibers,   estimating a weight of the undesired fibers from the image, and   subtracting the estimated weight of the undesired fibers from the total weight to yield a corrected weight of the impurities.   
     
     
         2 . The method according to  claim 1 , wherein the mechanical separation comprises the steps of:
 providing an air current,   feeding the mixed volume onto a surface of a rotating primary taker-in cylinder located in the air current,   mechanically stripping off the impurities from the primary taker-in cylinder,   transferring part of the mixed volume from the primary taker-in cylinder to a secondary taker-in cylinder located in the air current,   separating the impurities from the fibers on the secondary taker-in cylinder, and   collecting impurities separated on the primary taker-in cylinder and the secondary taker-in cylinder.   
     
     
         3 . The method according to  claim 2 , wherein the primary taker-in cylinder has a diameter of at least one of 20-30 cm and 25 cm, and the secondary taker-in cylinder has a diameter of at least one of 10-20 cm and 16 cm. 
     
     
         4 . The method according to  claim 2 , wherein the primary taker-in cylinder rotates at a rotational speed of at least one of 1300-1700 rpm and 1500 rpm, and the secondary taker-in cylinder rotates at a rotational speed of at least one of 900-1200 rpm and 1050 rpm. 
     
     
         5 . The method according to  claim 2 , wherein the primary taker-in cylinder has a surface linear velocity of at least one of 15-25 m/s and 19.7 m/s, and the secondary taker-in cylinder has a surface linear velocity of at least one of 5-12 m/s and 8.7 m/s. 
     
     
         6 . The method according to  claim 2 , wherein the centrifugal acceleration on the surface of the primary taker-in cylinder is at least one of 1860-4740 m/s 2  and 3090 m/s 2 , and the centrifugal acceleration on the surface of the secondary taker-in cylinder is at least one of 444-1580 m/s 2  and 967 m/s 2 . 
     
     
         7 . The method according to  claim 2 , wherein the surface of at least one of the primary taker-in cylinder and the secondary taker-in cylinder bears a serrated structure. 
     
     
         8 . The method according to  claim 2 , wherein the primary taker-in cylinder and the secondary taker-in cylinder have the same rotational direction. 
     
     
         9 . The method according to  claim 2 , wherein the air current below the taker-in cylinders has essentially a horizontal direction. 
     
     
         10 . An apparatus for measuring the weight of impurities in a mixed volume of fibers and impurities, comprising:
 a separation device for mechanically separating the impurities from the fibers,   a gravimetric scale for measuring a total weight of the separated impurities and undesired fibers remaining admixed to the impurities,   a sensor for creating an image of the separated impurities and the undesired fibers, and   a processor for:
 detecting the undesired fibers within the image, 
 estimating a weight of the undesired fibers from the image, and 
 subtracting the estimated weight of the undesired fibers from the total weight to yield a corrected weight of the impurities. 
   
     
     
         11 . The apparatus according to  claim 10 , wherein the separation device comprises:
 an air current channel,   a fiber feeding device located at a front end of the air current channel,   a primary taker-in cylinder located in the air current channel behind the fiber feeding device,   at least one stationary stripping device located near the surface of the primary taker-in cylinder,   a secondary taker-in cylinder located in the air current channel behind the primary taker-in cylinder, surfaces of the primary taker-in cylinder and the secondary taker-in cylinder being adjacent to each other, and   an impurity collecting apparatus located below the primary taker-in cylinder and the secondary taker-in cylinder.   
     
     
         12 . The apparatus according to  claim 11 , wherein the primary taker-in cylinder and the secondary taker-in cylinder are mutually arranged such that part of the mixed volume is transferrable from the primary taker-in cylinder to the secondary taker-in cylinder. 
     
     
         13 . The apparatus according to  claim 11 , wherein the minimum distance between the surfaces of the taker-in cylinders is at least one of 0.1-1 mm and 0.25 mm. 
     
     
         14 . The apparatus according to  claim 11 , wherein the primary taker-in cylinder has a diameter of at least one of 20-30 cm and 25 cm, and the secondary taker-in cylinder has a diameter of at least one of 10-20 cm and 16 cm. 
     
     
         15 . The apparatus according to  claim 14 , wherein the separation device comprises a drive mechanism for the primary taker-in cylinder, the drive mechanism for driving the primary taker-in cylinder at a rotational speed of at least one of 1300-1700 rpm and 1500 rpm, and the separation device comprises a drive mechanism for the secondary taker-in cylinder, the drive mechanism for driving the secondary taker-in cylinder at a rotational speed of at least one of 900-1200 rpm and 1050 rpm. 
     
     
         16 . The apparatus according to  claim 11 , wherein at least one of the primary taker-in cylinder and the secondary taker-in cylinder has a width in axial direction of at least one of 30-70 cm and 50 cm. 
     
     
         17 . The apparatus according to  claim 11 , wherein the surface of at least one of the primary taker-in cylinder and the secondary taker-in cylinder bears a serrated structure. 
     
     
         18 . The apparatus according to  claim 17 , wherein the height of the serrated structure is at least one of 1-4 mm and 2.5 mm. 
     
     
         19 . The apparatus according to  claim 11 , wherein at least one additional stationary stripping device is located near the surface of the secondary taker-in cylinder. 
     
     
         20 . The apparatus according  claim 11 , wherein the distance between the at least one stripping device and the surface of the respective taker-in cylinder is at least one of 0.1-1 mm and 0.2-0.6 mm. 
     
     
         21 . The apparatus according to  claim 11 , wherein the fiber feeding device includes a fiber feeding roller and a fiber feeding plate.