Broken end detection system for warpers utilizing novel optical system

Claim 1

In yarn inspection apparatus for a warper for detecting broken yarns in a yarn sheet extending in a feed plane between a measuring roll and a warper beam by detection of broken yarn ends thrown to one side of the feed plane through a selected inspection axis extending transversely of the yarn sheet immediately downstream from the measuring roll as the yarn sheet turns about the latter; an optical system producing a monitoring light beam along said inspection axis and spanning the yarn sheet comprising a detector head mounted at one end of the measuring roll outwardly adjacent one edge of the yarn sheet; said detector head including a lamp having a filament of selected size for producing light, a semitransparent mirror, and a first lens located along a first optical axis segment, a first reflecting mirror inclined at 45* to said first optical axis segment and to a second optical axis segment paralleling said inspection axis, and a second lens located along said second optical axis segment, said lenses and first reflecting mirror coacting to project light from said lamp passing through said semitransparent mirror and lenses and redirected 90* by said first reflecting mirror in a first direction in a narrow cross section monitoring beam along said inspection axis, said detector head including a photodetector located alOng a branch optical axis intersecting the first optical axis at said semitransparent mirror to receive returning light passing through said lenses toward said semitransparent mirror in a direction opposite said first direction; a retroreflective target assembly mounted at the opposite end of the measuring roll outwardly adjacent the opposite edge of the yarn sheet along said inspection axis, the target assembly including a target lens in the path of incident rays of the beam projected along the inspection axis by said first and second lenses, a second reflecting mirror inclined at 45* to the axis of said target lens to redirect light passing through the latter along a third optical axis segment at right angles to said inspection axis, a substantially flat surface of retroreflective material of selected area perpendicular to said third optical axis segment facing the incident rays projected from said detector head for retroreflecting incident rays of said beam striking said retroreflective material back along their incident ray paths, said detector head lenses providing a spot of light on the target lens having a maximum dimension which is only a fraction of the diameter of the target lens.