Optical apparatus for monitoring for thread breakage

Optical apparatus for monitoring for thread breakage in tufting machines in which a carrier web is passed upwardly to a spiked roller and is deflected by the spiked roller into a substantially horizontal direction so that it can be passed under a row of needles which, in order to form tufted material, periodically introduces threads into the carrier web by up and down movement, said monitoring apparatus making use of a laser beam scanning device, characterised in that when the needles (13) are open a preferably narrow retroreflecting strip (14) is arranged directly below and behind the needle tips and directly above the tufted material (15), parallel to the row of needles (12) and substantially at right angles to the surface of the tufted material;

• and in that the laser beam scanning device (17) is arranged in front of the spiked roller (11), wherein said laser beam scanning device generates a scanning beam (18) which periodically scans the retroreflecting strip (14) and which extends substantially parallel to the part of the carrier web (16) extending between the spiked roller (11) and the row of needles (12) and at right angles to the retroreflecting strip (18), and wherein said laser beam scanning device contains a light receiver (19) operating in an autocollimating arrangement, said light receiver (19) being connected to an electronic fault evaluating circuit (29) which transmits a fault signal if a scanning beam interruption signal caused by the absence of a thread (20) extending through the needles (13) or between the needles (13) and the carrier web (16) is missing.