Optimizing a spinning process with respect to foreign materials

A method for optimizing a spinning process, through which a fiber material fed in the form of raw fibers and output in the form of yarn passes, with respect to foreign materials in the fiber material, wherein:

• at a first position in the spinning process, a stream of fiber flocks pneumatically conveyed in an air stream is monitored for foreign materials,
• foreign materials are eliminated from the stream of fiber flocks according to a removal criterion,
• and, based on the monitoring, first foreign material information relating to the foreign materials is determined, wherein the first foreign material information is a removal rate (B) that substantially indicates a number of removals per unit mass of fiber flocks or per unit time,
• at a second position in the spinning process,
• yarn which has been spun from the fiber flocks and is conveyed along its longitudinal direction is monitored for foreign materials,
• foreign materials detected in the yarn are cleared out of the yarn according to a clearing criterion,
• and based on the monitoring, a second foreign material information relating to the foreign materials is determined, wherein the second foreign material information is a clearing rate (C) that substantially indicates a number of clearing operations per unit mass of yarn, per unit length of yarn, or per unit time,
• a passage time (Δt) is determined as that time interval during which a fiber passes from the first position to the second position in the spinning process,
• the first foreign material information is determined at a first time (t1) and the second foreign material information is determined at a second time (t2) which is after the first time (t1) by the passage time (Δt),
• the first foreign material information thus determined and the second foreign material information thus determined are assigned to each other such that they relate to substantially the same sample of the fiber material,
• a change is made to the spinning process on the basis of the first foreign material information and the second foreign material information assigned thereto, wherein the change to the spinning process includes a change to the removal criterion and/or a change to the clearing criterion, and
• a product of costs (KE) for a removal determined in advance and of the removal rate (E) is taken into account in the change to the spinning process, and/or
• a product of the costs (KC) for a clearing operation determined in advance and of the clearing rate (C) is taken into account in the change to the spinning process.