Method of recognizing and evaluating foreign substances in a pneumatically conveyed fiber stream

A method of processing fiber comprising the following steps:

• (a) removing fiber tufts from a series of fiber bales by a tuft removing device of a bale opener traveling along the bale series;
• (b) pneumatically conveying the removed fiber tufts in a duct in a direction of conveyance;
• (c) detecting foreign substances by forming images of the conveyed material by an optical sensor device as the material passes through a location of the duct downstream of the bale opener as viewed in the direction of conveyance;
• (d) determining the location of each fiber bale in the bale series;
• (e) determining at least one of a degree of lightness, a degree of contamination and a color of the fiber tufts by an image processing device analyzing the images generated in step (c);
• (f) associating at least one of a degree of lightness, a degree of contamination and a color of the fiber tufts determined in step (e) with the fiber bale from which the material passing through said location originates;
• and
• (g) automatically controlling the motions of the bale series in a continuously operating bale opener as a function of lightness fluctuations determined from signals generated in step (e).