Shed sensing stop motion system for high speed looms

Automatic loom stopping apparatus for detecting yarn breakage or improper shedding defects and generating loom stop signals to be associated with a loom wherein warp yarns are displaced during weaving in two shed sheets of yarn periodically to an open shed condition locating the shed sheets at upper and lower limit shed positions, the apparatus comprising at least two vertically spaced monitoring light beam units respectively including a first and second light detector positioned adjacent the warp yarn path between the supply end and the weaving zone of the loom and including means forming first and second horizontal transverse light beams perpendicular to the warp yarns spanning the warp yarn path, one of said light beams forming a center beam located to pass through the open shed to be interrupted by any portion of a warp yarn or broken end occurring when the shed is open and the second light beam being located to be interrupted by one of the shed sheets occupying the upper or lower limit shed positions, said detectors each having means providing detector signals responsive to interruption of the associated light beam by yarns passing therethrough, signal processing means for producing processed signals responsive to said detector signals including means for producing delayed and narrowed pulse signals from the detector signals of said second detector responsive to interruption of the second light beam by a shed sheet at the upper or lower limit shed position to produce a short duration window pulse during only a predetermined midtime portion of the period when the shed is open, a first gate circuit receiving the processed signals from said first detector and the window pulses for producing a gate defect signal when yarn defects causing interruption of said first light beam occur during the open shed periods signified by the window pulses, and stop relay means activated responsive to said gate defect signals to stop the loom.