GB975236A - Improvements in and relating to examining apparatus for textile thread - Google Patents

Abstract

975,236. Photo-electric thread examining devices. GEB. LOEPFE A.G. Dec. 13, 1960 [Dec. 31, 1959], No. 42792/60. Heading G1A. An electro optical thread examining device for textile thread winding machines which comprises a light transmitter and a light receiver, in which light emitted by the transmitter impinges the thread and in which the receiver emits an electrical output signal which changes when the thread is irregular, is characterized in that in order to reliably detect surface irregularities of the thread the light proceeding from the transmitter is so guided as to impinge on the thread at the same point from at least two different directions and that the receiver has an at least approximately logarithmic relationship between intensity of illumination and the output signal so that a thread irregularity having a given magnitude will always give rise to practically the same change in output signal, which change will not be affected by the intensity of light in the area of impingement. In the diagrammatic arrangement, Fig. 1, light from a source 1 passes through an aperture in the wall 4 of an enclosure member 12 to impinge on the thread 8 moved at right angles to the plane of the drawing, and below which is disposed a mirror 7 so that, in effect, the thread is impinged by a direct beam from the source 1 and further by a beam reflected from the mirror 7, both beams being incident on the photo-cell 10. In the circuit arrangement, Fig. 2, the light source 2 is energized by the secondary winding 8 of a transformer 17 which also provides operating voltages for two valves 23, 24. The cell 25, which is such as to produce a logarithmic relation between its current or voltage output and the incident light, is coupled to the valve 23 having its output fed to a cold-cathode thyratron which, when triggered, operates a relay 35 and contacts 36 controlling the operation of the winding machine for the thread. Reference is made to the use of a monocrystalline silicon cell. In other arrangements Figs. 5 and 6 (not shown), a high vacuum, semiconductor diode or photo-resistance cell is used in series with a non-linear resistor. Alternatively a resistance photo-cell with a linear characteristic may be used, and a non-linear member incorporated in the associated valve circuit so as to obtain the desired logarithmic characteristic. In a modification for scanning a number of threads simultaneously, Fig. 8 (not shown), an examining beam is focused on a transverse area embraced by all the threads with the mirror 7 disposed at a small distance below the threads, as indicated in Fig. 1. In a further modification, Fig. 9 (not shown), employing a compensating beam to eliminate or reduce the effects of variation of the frequency or intensity of the examining beam, a subsidiary light beam is directed to a photo-cell having directly or indirectly, by an appropriate valve circuit, a logarithmic output which is combined in opposition to the logarithmic output of the cell 10 responsive to the variations or irregularities of the thread being examined.