GB943106A - Improvements in methods of and apparatus for guiding fabrics - Google Patents

Abstract

943,106. Feeding webs. TURNER BROS. ASBESTOS CO. Ltd. Aug. 10, 1962 [May 10, 1961], No. 17084/61. Heading B6B. [Also in Division G3] The transverse position of each of several webs of material 1 which are finally united, e.g. to form conveyer belting, is controlled by causing a high frequency electric current to flow sequentially in conducting strips 54 in or on each web, and then detecting their position by electromagnetic means which produces signals to control correcting rolls 30, 31. The correcting rolls are mounted as shown in Fig. 7, one in fixed bearings below the web, the other above the web on a rocker arm 39<SP>4</SP> tiltable by an electromagnet 43<SP>4</SP> energized by the signals. There are two pairs of rolls for each web, each arranged to pull the web outwards from the centre when its electromagnet is energized. Fig. 15 shows an arrangement for one of five webs, which are united at calender rolls 12 in the complete machine, in which the current is induced in the conducting strip by coils 68, 69, the conductor circuit being completed by earthed capacitor plates 70, 82. In a preferred embodiment the current is induced by a capacitive circuit which includes adjustable plates, one for each belt, and a common metal run-out table. In another alternative, current is passed directly through the conductor by brushes. The detecting device comprises two pick-up coils 71, 72 arranged on either side of the conducting strip as shown or alternatively arranged above and below the strip in line with the desired position (Figs. 9 . . . 13, not shown). In either case, the coils are connected in series opposition and their resultant output is amplified and phase compared with a reference to produce a D.C. signal whose magnitude and polarity correspond to the size and direction of the positional error. The pick-up coils are situated close to the rolls 12 and are common to all the webs; a motor driven or a static distributer (Fig. 14, not shown) causes the sequential energization of the conducting strips and correspondingly switches the D.C. error signal to the appropriate electromagnet circuits. Each circuit includes a capacitor to store the signal while the other circuits are switched in turn so that correction is maintained throughout the switching cycle. The capacitors form the input to transistor amplifiers which energize the electromagnets, diodes being interposed to select the appropriate amplifier according to the polarity of the signal. The conducting strip 54 may comprise metal wire, a yarn of glass coated with metal, or graphite impregnated yarn woven or moulded in the fabric, preferably the selvedge, or it may be attached to the fabric by adhesive. Specification 870,734 is referred to.