Method and apparatus for recognizing foreign substances in and separating them from a pneumatically conveyed fiber stream

A method of processing fiber comprising the following steps:

• (a) removing fiber tufts from a series of fiber bales;
• (b) pneumatically conveying the fiber tufts in a duct;
• (c) forming images of the conveyed material as it passes through a first location of the duct;
• (d) determining at least one of a degree of lightness and a color of the fiber tufts by an image processing device;
• (e) determining a degree of lightness of foreign substances, conveyed with the fiber tufts, by the image processing device;
• (f) comparing the measuring values obtained by the image processing device in steps (d) and (e) with at least one settable limit value;
• (g) initiating a switching operation when said limit value is exceeded for branching off the fiber tufts to a waste receiver from the duct at a second location thereof;
• said second location being situated downstream of said first location as viewed in a conveying direction of the fiber tufts;
• and
• (h) establishing a sensitivity of performing step (g) within defined limit values for all types of fiber material.