GB944200A - Improvements in processes and apparatus for regulating the draft in textile drafting machines - Google Patents

Abstract

944,200. Automatic control of textile drafting. SPECIAL INSTRUMENTS LABORATORY Inc. March. 22, 1961, No. 10511/61. Heading G3R. [Also in Divisions D1 and G1] In a process for automatically regulating the thickness of a sliver or yarn from a textile drafting mechanism, the short and long term variations in mass per unit length of the sliver are independently detected and the draft ratio is adjusted in response to these variations. As shown in Fig. 4 a sliver 84 is drafted by pairs of rollers 80 and 82 and the short term and long term variations in sliver mass per unit length are detected by detectors 86 and 88 respectively. A servo-mechanism 90 which is operated by the long term detector 88, adjusts the standard against which the short term detector 86 compares the mass per unit length of the sliver; this detector operates a further servo-mechanism 92 which adjusts a control mechanism 94 to regulate the draft ratio and so compensate for the measured variations. In Figs. 1 and 3 a suitable detector and control circuit are shown. A source 12 of beta rays (e.g. radio strontium or thallium) is placed close to a sliver 2 emerging from drafting rollers 4 and 6. Ionisation chambers are positioned at 14, 16 so as to measure the absorption of the beta rays passing through the sliver and an adjustable absorber 18 respectively. The absorber 18 gives a standard rate of absorption against which the rate of absorption in the sliver is measured. The ionisation chambers are connected to a circuit 59 (shown in detail in Fig. 3) which control, via a servomotor 52 and variable transmission unit 62, the relative speed of rotation of the drafting roller pairs to regulate the thickness of the sliver. As shown in Fig. 3 the difference in degree of ionisation in chambers 30 and 31 (i.e. those shown at 14 and 16 in Fig. 1) is measured by triodes 38, 40, the outputs from which are fed to a push-pull D.C. amplifier 42 and then to a phase converter 44, for converting D.C. to A.C. signals. The signals from converter 44 are then amplified by an A.C. amplifier 46 and a power amplifier 48. The plate circuit of amplifier 48 includes a coil 50 of the two phase servomotor 52 having a field coil 54. This circuit causes motor 52 to rotate in one direction when the mass of the sliver is below the standard value and in the opposite direction when the mass of the sliver is above the standard value. Alternatively the collecting potential in one chamber could be held positive while the collecting potential in the other chamber is held negative and the collecting electrodes could be connected together and linked to a single electrometer tube. In the arrangement of Fig. 4 the detector 88 may take the form of that in Fig. 1 and the drive from the motor 52 may be used to alter the standard against which the short term detector makes its comparisons.