Air-jet weaving is a widely used process for producing fabrics. A weft thread is accelerated by compressed air andpositioned in the reed channel. An improperly controlled yarn brake system causes backward movements of the weftthread and fabric defects. With the aid of an actively controlled braking system, these defects have to be avoided. Theweft insertion system is physically modeled as a one-dimensional mass-spring-damper-system. The model is extendedby the forces exerting on the weft threads, namely from the main nozzle and relay nozzles as well as the yarn brake.Subsequently, the physical model is validated in order to determine the model parameters. The weft insertion is monitoredby means of a high speed camera and the position of the thread tip is determined by real-time image processing algorithms.A Model Predictive Control (MPC) determines the optimal braking force with explicit consideration of the model, so thata highly dynamic yarn braking system brakes the weft appropriately. This ensures that the weft thread reaches the endposition. Moreover, incorrectly inserted wefts and thus fabric defects are avoided.