GB816491A - Improvements in apparatus for detecting weft abnormalities in woven materials - Google Patents

Abstract

816,491. Testing fabrics. ROBERTSON, J. D. May 13, 1957, No. 15140/57. Classes 42 (1) and 42 (2). An abnormal condition of the weft elements relative to the warp elements of a travelling woven web is detected by stretching the web by means of rollers 16 and inducing distortions of the warp elements, pivoted rollers 18, 20 being provided at longitudinally spaced locations and arranged to be engaged and actuated by different portions of the same warp elements and means responsive to the differential actuations of the pivoted rollers for signalling the presence of an abnormal condition. As shown, the rollers 16 are transversely adjustable on a frame and the upper roller 16 is urged into contact with the web by means of a solenoid 68. The web passes over four rollers on the frame and to relieve the web of tension while it is gripped by the rollers 16 one of the rollers is arranged to rotate at a higher speed than the others. The solenoids 68 may be operated intermittently and a magnetic clutch may be provided on the roller drive so that the roller is rotated faster only for the period that the rollers 16 engage the web. The rollers 18, 20 are provided with pivot shafts 19, 21 respectively which carry arms provided with steel armatures which project into the air core of each of two coils 116, 124 respectively. When the rollers are in alignment each armature will extend equal distances within the air core of each of the coils 116 or 124. When the rollers swing out of alignment in opposite directions the impedances of the coils become unequal. The coils are connected as part of an inductive bridge which is thrown out of balance when the impedance of the coils varies. Any unbalanced condition of the bridge results in a signal being transmitted to an amplifying unit whose signal may be used to control the operation of a weft straightening mechanism.