Stop motion system for high speed looms and the like

Automatic loom stopping apparatus to be associated with a loom wherein warp yarns are shedded periodically to open shed condition during weaving for detecting yarn defects arising from warp yarn breakage or improper shedding and actuate loom stop motion means of the loom upon occurrence of such yarn defects, comprising monitor light beam forming means including light beam emitter and detector means positioned adjacent the warp yarn path from the supply end to the weaving zone of the loom to direct the monitor light beam through the open shed along a substantially horizontal transverse light path generally perpendicular to the warp yarns, the detector means providing a detector defect signal when any portion of a warp yarn or broken end interrupts the monitor light beam, signal processing means including amplifier means for producing a processed defect signal responsive to said detector defect signal, timing pulse forming means including rotation sensing means monitoring rotation of a drive shaft of the loom for producing timing pulses indicating a predetermined phase time in the cycle of operation of the loom, a gate control pulse generator for producing short duration window pulses responsive to said timing pulses to indicate times when the shed is in predetermined open condition, a first gate circuit receiving said processed defect signals and said window pulses for producing a first gated defect signal when said yarn defects occur during the open shed periods signified by the window pulses, start-up delay signal means responsive to said timing pulses for producing a gate enable signal commencing at a delay time following loom start-up when the timing pulses occur at a predetermined frequency, a second gate circuit responsive to concurrence of said gate enable signals and said first gated defect signals to produce output stop signals, and stop relay means activated by said output stop signals to stop the loom.