Apparatus for sensing yarn movement and for signaling breakage of the yarn

Apparatus for sensing lengthwise movement of a strand of yarn of non-uniform surface texture and for producing an electrical signal when the yarn stops, said apparatus comprising a guide for causing the yarn to travel along a predetermined and substantially linear path, a light source located on one side of said path for casting a beam of light across said path, a photoelectric detector located on the opposite side of said path in opposing relation with said light source to receive said beam, said guide comprising a nose made of wear-resistant material and having a throat for guiding said yarn along said path, said throat having entrance surfaces engageable with said yarn before the yarn reaches said beam and having exit surfaces spaced along said path from said entrance surfaces and engageable with said yarn after the yarn passes through said beam, a holder of light-transmitting material having a tongue projecting into said throat between said entrance and exit surfaces, pockets in said tongue and receiving said light source and said photoelectric detector, said tongue having a yarn-receiving throat located between said pockets, said entrance and exit surfaces of the throat of said nose holding said yarn out of engagement with the throat of said holder, said detector producing an output signal whose frequency varies as a function of changes in the intensity of said beam, the intensity of the beam received by said detector changing during movement of said yarn due to non-uniformity of the surface texture of the yarn, and means responsive to the output signal of said detector for producing said electrical signal when the frequency of said output signal remains substantially constant for a predetermined period of time.