| 摘要 |
<p>The device comprises an emitter diode (17) and a receiver phototransistor (18) which are arranged at the same face of a transparent plate (19) associated with the drum (11) of the weft feeder (10) and suitable to receive the turns of the weft reserve (RF). The emitter (17) directs onto the transparent plate (19) a beam of rays (R1) which is tilted at a preset angle of incidence ( alpha ), and the receiver (18) receives a beam of rays (R2) that emerge from the transparent plate (19) and form an angle of reflection ( beta ), with respect to the plate, which is different from the angle of incidence ( alpha ) produced by multiple-reflection means (20) located at the other face of the transparent plate (19). The incident rays (R1) and/or the emerging rays (R2) are interrupted by a turn (SP) of the reserve of thread (RF) when the turn reaches the plate (19), so as to screen the receiver (18) from the light; the receiver emits a corresponding turn presence signal (s). <IMAGE></p> |
