| 摘要 |
A feeler for monitoring a thread reserve in weft feeders, comprising a light-emitting device constituted by a light source which directs light rays onto a thread wound in spaced turns on the drum of the feeder, and a receiver which collects the light rays and converts them into electrical signals that indicate the presence or absence of turns of thread. A first focused optical transmission system forms a first pointlike luminous image of the light source on the turn being monitored and, in the absence of the turn, a second pointlike luminous image of the light source located on a screen surface which is arranged below the turns. A second focused optical projection system selectively projects the first or second luminous image, along respective differentiated optical paths, onto at least one optical sensor which emits discriminated signals that correspond to the length of the corresponding optical paths.
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