| 摘要 |
The device and method disclosed employ a conduit with a bend and preferably a double bend intermediate its ends through which yarn is moved, as by currents of air from a vacuum pump; adjacent the bend or the upstream bend of the double bend a photoprojector and photoreceiver switch detect the presence of yarn at the short-turn of that yarn being drawn thereacross and interrupting the beam of light therebetween to detect a predetermined length of yarn whereupon the photoreceiver switch deactivates the means used to draw yarn through the conduit and thereby establishes a predetermined length of yarn. The device and method are usefully employed with yarn piecers and knotters to avoid excessive yarn wastage and to insure that sufficient yarn is provided to effect piecing or knotting.
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