Device for counting turns unwinding from weft feeders of weaving looms

Abstract: The device comprises a piezoelectric transducer (30) rigidly associated to the side of the solid of revolution (A-B) generated by the unwinding thread (F) and adapted to emit an electric pulse upon every passage of the thread at the generatrix of the solid of revolution which is arranged in the meridian plane which contains or intersects the axis of a feeler associated with the transducer.

Description: The present invention relates to a device for counting the turns unwinding from weft feeders of weaving looms, allowing an automatic adjustment of the speed of said feeders. Typically weft feeders are devices provided with a fixed drum on which a rotating arm, moved by an asynchronous motor, winds a plurality of thread turns which are progressively unwound by the loom or by another textile machine; the tension of the thread at the output of the feeder is controlled by a braking means which can be constituted by a ring of bristles or by a set of metallic laminae. The reserve of turns wound on the fixed drum varies between a maximum and a minimum value indicated by corresponding mechanical and/or optical feelers. In order to avoid disadvantages deriving from continuous stops and starts of the motor, which can produce tangling and/or undesirable variations in the tension of the thread, it is important that the reserve of turns be always comprised between said maximum and minimum values, and this implies that the feed speed of the turns of the reserve must coincide, or substantially coincide, with the removal rate. The latter, however, is generally unknown and in any case is significantly variable during the operation of the textile machine, especially in the case of shuttle-less looms, such as jet looms and the like. A known weaving machine with fixed drums is disclosed by EP-A-0 286 590. In the known machine, the thread is unwound from the drum through a control ring which is provided with optical detectors for monitoring the unwound thread. However, the latter monitoring arrangement including the optical detectors is rather complicated and rather non-reliable in operation. A device for the automatic control of the weft yarn feed in air looms is known from EP-A-0 189 919. As shown in figure 1, EP-A-0 189 919 provides for a sensor for monitoring yarn, whereat the sensor is placed at a certain distance and out of the path of the unwound yarn. Again, Such arrangement is rather complicated and does not achieve a reliable monitoring of the yarn. GB-A-2 069 184 discloses a loom feeding system with a pivotable ferrous member sensing the thickness of the yarn wound onto the loom feeding drum. Moreover, a pivotable sensor is provided to sense the storage level of yarn. However, said system is also non reliable, as far as thread turn monitoring is concerned. In view of the foregoing, it is an aim of the invention to provide a device for counting the turns which unwind from the drum of the pre-feeder and provide a consequent indication of the unwinding rate of the thread which, numerically processed by a microprocessor, allows to vary the rotation rate of the turn-depositing arm so as to adapt the deposition rate of the turns to the removal rate. An object of the present invention is to provide a counting device which is extremely simple, reliable and capable of transducing the speed datum in terms of electric pulses which can be applied directly to the processing microprocessor. A further object of the present invention is to provide a device the installation whereof does not compromise at all the correct unwinding of the thread from the drum of the feeder. This aim, these important objects and others which will become apparent from the following detailed description are achieved by a device for counting turns unwinding from weft feeders, as defined in the appended claims. The characteristics and advantages of the present invention will become apparent from the following detailed description and with reference to the accompanying drawings, given by way of non-limitative example, wherein: figure 1 is a schematic partial sectional view of a weft feeder with the counting device according to the present invention, figure 2 is a partial enlarged-scale front view taken along the line II-II of figure 1, figure 3 is a partial sectional view, similar to figure 1, illustrating a different embodiment of the invention, figure 4 is a partial enlarged-scale front view of the embodiment of figure 3. Initially with reference to figures 1 and 2, 10 generally indicates the known weft feeder which comprises a fixed base 11, a motor shaft 12 and a fixed drum 13 which is freely rotatably mounted on said shaft 12 and is prevented from rotating by the action of permanent magnets 14 which co-operate with corresponding magnets 15 rigidly associated with the base 11. In a per se known manner, the shaft 12 has an axial cavity 12a and a cantilevered arm 16 which is also hollow; the thread F passes in the cavity of the shaft and of the arm and unwinds from a spool (not illustrated) to be wound by said arm onto the drum 13 in spaced turns which constitute a reserve of thread which is variable between a maximum value and a minimum value indicated by a mechanical feeler 17 associated for example with an optical device DO capable of emitting, in a known manner, electric signals of reserve minimum and maximum. Spacing of the turns is ensured by an also known advancement system which uses a plurality of rods 18 which cyclically rise from slots of the drum 13. The shaft 12 is rotated, with an angular speed Np, by an asynchronous electric motor M which is powered by a variable-frequency system 22 of the known PWM type described in chapter 16 of the "Hexfet Designer's Manual" of Int. Rectifier, California, USA. The system 22 is driven by a microprocessor µP which sends frequency increase or decrease signals in the manner described hereinafter by means of a port "Pu". The outputs of the optical device DO associated with the feeler 17 are fed to respective input ports "Pi" of the microprocessor µP. The thread is fed from the drum to the loom or to another textile machine and unwinds with a linear speed Vt which is generally unknown, passing through a thread guiding ring 19. The tension of the thread during unwinding of the turns is controlled by a braking means which is typically constituted by a ring of bristles or metallic laminae 20 which elastically engage the thread and are carried by an annular support 20a co-operating, in the case of laminae, with a conical ring 20b which is axially movable by means of a knob 21 for adjusting the braking action. In the unwinding motion, the thread F defines a solid of revolution which is substantially constituted by a first frustum-shaped portion A which extends between the drum 13 and the thread-guiding ring 19 and by a second conical portion B which extends beyond the thread-guiding ring. According to the present invention, the linear unwinding speed Vt of the thread is measured, sensing the passage of said thread in a generic meridian plane of said solid of revolution by employing at least one transducer 30 which is arranged at said meridian plane, is located substantially tangent to said solid and is responsive to the tangential component of the motion of the thread. The transducer is constituted by a piezoelectric crystal, for example of the type PXE.5 manufactured by the Philips company. A feeler 31, in the shape of an oscillable bar or plate, is mechanically connected with said crystal (in particular is in contact therewith) and is adapted to be moved by the thread which cyclically passes on said plate or bar upon every unwinding of turns. The crystal and the associated feeler form a sort of piezoelectric pickup which can provide a pulsed electric signal SE upon the passage of every turn. In the embodiment of figures 1 and 2, the transducer 30 is rigidly connected to the annular support 20a and has its feeler 31 in contact with one of the laminae of the braking means 20 or with a set of bristles thereof, so that when the thread passes below said lamina or set of bristles it transmits a corresponding vibration to the feeler 31 causing the transducer 30 to generate an electric signal SE which, after being amplified and squared, is sent to an input port "Pi" of the microprocessor µP. Said microprocessor is programmed to count the pulses emitted in the time unit, to calculate the consequent speed Vt of the unwinding thread (with Vt = 2πnr , where r is the radius of the solid of revolution in the point being considered and n is the number of turns, which is equal to the number of counted pulses in the time unit) and to compare the speed Vt thus calculated to the winding speed Va, which is equal to the peripheral speed V = 2πNpR of the arm 16 (R being the radius of the circle traced by the end of said arm), which is in turn proportional to the power supply frequency of the motor M. From the comparison between the two speeds Vt and Va, the microprocessor obtains a differential datum and, according to the sign of the latter, increases or decreases the power supply frequency of the motor M depending respectively on whether Va < Vt or Va > Vt In the embodiment of figures 3 and 4, the transducer 30 is rigidly associated with the support 19a of the thread-guiding ring 19, preferably on the internal side of said support, as illustrated in the figure, and is provided with a feeler constituted by an oscillable bar 31 which intersects the conical portion B of the solid of revolution defined by the unwinding turns. In this case, too, the thread, by rotating along the periphery of the ring 19, cyclically makes contact with the bar 31, which transmits to the transducer 30 the vibration imparted thereto by the thread, with the consequent emission of pulsed signals SE. Where technical features mentioned in any claim are followed by reference signs, those reference signs have been included for the sole purpose of increasing the intelligibility of the claims and accordingly such reference signs do not have any limiting effect on the scope of each element identified by way of example by such reference signs.

Claims: A device for counting turns of a thread (F) unwinding from a weft feeder (10) for weaving looms and the like, said device comprising means (30,31) for detecting the passage of the thread (F) which unwinds from a drum (13) of the weft feeder (10), said means (30,31) being arranged laterally to the solid of revolution (A,B) generated by the unwinding thread (F), being responsive to the tangential component of the thread movement and generating an electric pulse (SE) upon each passage of the thread (F), characterized in that said means (30,31) for detecting includes a transducer (30) and a feeler (31) associated with the transducer (30), said feeler (31) extending from said transducer (30) substantially tangent to said solid of revolution (A,B), such that, at each passage, the thread (F) imparts a vibrating movement to the feeler (31) causing said transducer (30) to generate said electric pulse (SE). A device for automatically adjusting the reserve of turns on a drum (13) of a weft feeder (10), said device comprising means (30,31) for detecting the circumferential speed component (V t ) of a thread (F) unwinding with respect to the drum (13), means (µP) for comparing said circumferential speed component (V t ) with the rotating speed (Va) of a rotatable arm (16) winding the thread (F) on the drum (13) and for generating a differential speed, and means (22) for controlling the motor (M) actuating the rotatable arm (16) depending on the sign of said differential speed to selectively increase or decrease the thread winding speed, characterized in that said means (30,31) for detecting the circumferential speed component (V t ) includes a transducer (30) and a feeler (31) associated with the transducer (30), said feeler (31) extending from said transducer (30) substantially tangent to a solid of revolution (A,B) generated by the unwinding thread (F), such that, at each passage, the thread (F) imparts a vibrating movement to the feeler (31) causing said transducer (30) to generate an electric pulse (SE) representative of the circumferential speed component (Vt) of the thread (F). A device according to claim 1 or 2, characterized in that said transducer (30) generates said electric pulse (SE) upon each passage of the thread (F) at the generatrix of said solid of revolution (A,B) arranged in the meridian plane containing or intersecting the axis of said feeler (31). A device according to claim 3, characterized in that said transducer (30) comprises a piezoelectric pickup and said feeler (31) comprises a bar or plate, said pickup generating said electric signal (SE) every time an unwinding turn moves said bar or plate or produces a vibration thereof. A device according to claims 1 or 2 and 3-4,characterized in that said transducer (30) is rigid with a support (20a) of a braking means (20) of the weft feeder (10), and in that the feeler (31) is in contact with the braking means (20) which transmit thereto the vibration generated by the passage of the thread (F). A device according to claims 1 or 2 and 3-4,characterized in that said transducer (30) is rigid with a thread-guiding ring (19) of the weft feeder (10), and in that the feeler bar (31) intersects the conical portion (B) of said solid of revolution (A,B) which extends beyond said thread-guiding ring (19), said bar (31) being cyclically engaged by the thread (F) which rotates along the periphery of the thread-guiding ring (19) during the unwinding of the turns. A device according to any of claims 1 to 6, characterized in that the output signal of the transducer (30) is applied, after amplification and squaring, to the input port (Pi) of a microprocessor (µP) which furthermore controls the power supply frequency of the motor (M) for the actuation of the rotatable arm (16) for winding the reserve turns on the drum (13). A device according to claim 7, characterized in that said microprocessor (µP) is programmed to count the turns which unwind from the feeder (10) and calculate the corresponding thread unwinding speed (V t ), to compare said unwinding speed (V t ) with the rotation rate (V a ) of said rotatable arm (16), which is proportional to the power supply frequency of said actuation motor (M), to increase or decrease the speed of said rotatable arm (16), by means of corresponding variations of the power supply frequency, every time the differential of the compared unwinding and winding speeds is positive or respectively negative. A device according to any of claims 1 to 8, characterized in that said piezoelectric transducer (30) is located on the outside of said solid of revolution (A,B) generated by the unwinding thread (F).

Inventors: ZENONI PIETRO, ZENONI, PIETRO
Applicants: LGL ELECTRONICS SPA, L.G.L. ELECTRONICS S.P.A.
Application year: 1990
Main classification: D03D47
IPC codes: B65H51, B65H61, D03D47