Abstract: A light detector is supported in a mask box which extends into the cavity accommodating the looptaker with an edge of the surface adjacent the looptaker and upstream to the air currents generated by the looptaker closer to the looptaker than an edge downstream in order to discourage lint build up on the adjacent surface. A light source is fashioned with a lens projecting into the cavity accommodating the looptaker similarly to discourage lint build up.

Abstract: A low bobbin thread detection system for sewing machines. A light source transmits a beam of light through a pair of passageways contained in the bobbin case and toward a photodetector enclosed in a shield to shelter it from stray light. The light shield contains a pair of spaced apertures whose axes are in optical alignment with the light source and the bobbin case passageways. The thread carrying bobbin lies intermediate the passageways and does not permit the transmission of light from the first to the second passageway while thread remains thereon. When sufficient thread has been consumed from the bobbin, light may pass from the light source to the photodetector. Light which is directed at the shield surrounding the photodetector from any angle other than that coincident with the optical axis formed by the two apertures is blocked from impinging on the photodetector and will not falsely trigger a low bobbin thread alarm.