Patent GB-1242692-A (GB)
Title: Yarn speed or yarn length measurement apparatus
IPC: B65H61/00
Filed: 1968-09-20
Abstract: 1,242,692. Monitoring yarn electrically. PHILIPS ELECTRONIC & ASSOCIATED INDUSTRIES Ltd. Sept.20, 1968 [Sept.25, 1967], No. 44840/68. Headings G1A and G1N. A device for measuring yarn speed or length includes a pulsed light source 9 and two photoelectric detectors 10, 10a comprising pick-up means A through which is passed a yarn 1 so that two electrical signals are produced, a first having a low frequency component Sd representative of yarn diameter and a high frequency noise component Sr, produced by the passage of yarn irregularities past the photo-cell, of which noise component the amplitude and frequency are proportional to yarn speed, and a second, from the reference detector 10a, being proportional to light intensity. The two signals are summed vectorially in means, 19, a difference signal S being amplified at 11 and fed to conductors 12 and 13. The latter leads via a differentiating circuit, 2, to an amplitude detector 3 which produces a yarn speed signal Vg, which may be recorded. Conductor 12 leads to a D.C. restorer lla which inserts a zero reference level, thus yielding the signal Sd, which may be recorded, and is led to an integrator 14 which generates a signal, representative of length, to an error counting and/or cutting device, 18. The time-constant of the integrator is controlled, at 15 from a multi-vibrator 27 of which the markspace ratio is proportional to yarn speed, and at 16 from a threshold current signal so that for yarn irregularities exceeding a predetermined limit the integrator capacitor charges and for irregularities below the limit the capacitor discharges. The light source is a gallium arsenide diode energized from a multi-vibrator of which the offtime t 2  is short so as not to permit unilluminated the complete passage of a standard length of yarn through the pick-up means. The multi-vibrator output is controlled by a circuit loop 25 which includes a comparator 22 in which the light intensity reference signal, after amplification at 20 and rectification at 21, is compared with a voltage signal Vre#, being dependent upon the nominal average, yarn thickness. The multi-vibrator output is used also to synchronize the detector 3 being fed through a comparator 26, to which the other input signal is a voltage Vo which is a reference speed signal characteristic of the yarn type, so as to give an output signal Vs of which the duration is proportional to the reference speed and which gates the amplitude detector 3. This gating signal is of sufficiently short duration to exclude from the detector the pulse switching transients present on the noise signal Sr. Circuit details are given in Fig. 9 (not shown). The pick-up means may be capacitive and the noise detector 3 may be a frequency detector when the network 2 will be a differentiating circuit, high-pass filter or a high band-pass filter. In the embodiment of Fig. 4 (not shown), a yarn length M is measured only, an integrator (5) being switched on and off by a multivibrator (6) of which the period is set by a calibrating length Mo being passed through the apparatus. Where frequency detection is employed the integration may be performed digitally using a pulse counter.