Optical thread breakage monitoring apparatus for tufting machines

Claim 1

Optical thread breakage monitoring apparatus for tufting machines, in which a carrier web is passed from below to a feed roller and is deflected by the latter into a substantially horizontal direction to be passed beneath a row of needles which periodically introduce threads into the carrier web by upward and downward movement for the formation of tufted material, using a laser beam scanning device which has a narrow retroreflecting strip arranged immediately beneath and behind the needle tips when the needles are opened, immediately above and substantially perpendicular to the surface of the tufted material, and also parallel to the row of needles, wherein the scanning device generates, by means of a mirror wheel and a strip-like concave mirror, a scanning beam in the form of a laser beam which periodically scans the retroreflecting strip and extends substantially parallel to the part of the carrier web which extends between the feed roller and the row of needles and perpendicular to the retroreflecting strip, and contains a light receiver operating in autocollimation which is connected to an electronic fault evaluating circuit which, on the absence of a scanning beam interruption signal brought about by the needles and/or the threads extending between the needles and the carrier web, transmits a fault signal, wherein the laser beam scanning device is vertically arranged in front of the feed roller and substantially below the level of the row of needles, and wherein a strip-like deflecting mirror arranged substantially at the level of and parallel to the row of needles deflects the scanning beam which emerges substantially vertically out of the scanning device in the direction of the retroreflecting strip, characterised in that the deflecting mirror (11) deflects the incident laser beam somewhat obliquely upwardly to a strip-like plane mirror (12) extending parallel to it which deflects the laser beam upwardly to the concave mirror (13) arranged on the opposite side of the deflecting mirror (11) from the needle row (14), with the concave mirror (13) being arranged parallel to and horizontally opposite to the needle row (14); and in that the mirror wheel (17) is arranged directly below the deflecting mirror (11) with its axis of rotation disposed somewhat tilted relative to the horizontal and receives the laser beam (20) vertically from below and also directs the laser beam essentially downwardly, however somewhat obliquely in the direction of the row of needles (14) to a strip-like deflecting mirror (23) arranged at the base (21) of the housing (22) near the wall (25) facing the tensioning roller (10), with the strip-like deflecting mirror (23) extending parallel to the deflecting mirror (11) and reflecting the laser beam upwardly past the mirror wheel (17) to the deflecting mirror (11).