Method of detecting a broken line up yarn and a detector for use in the method

Abstract: A broken line up yarn detecting method characterized in that a light emitter 21 is adapted to travel transversely with respect to a row of yarns W comprising many warps W1, W2... Wn supplied in a line up condition, said light emitter 21 radiat­ ing a fine beam to the yarns sequentially from one end W1 to the other Wn, and flickerings caused by presence/absence of yarns while the beam travels widthwise are transmitted to a photoelectric conversion means 3 and thereafter to a count means 4 where the number of flickerings is electrically counted to obtain the current value for the number of existing yarns, which current value is compared with a threshold by a compa­ rator which emits a signal (ab) for indicating an abnormal condi­ tion if the current value differs from the threshold.

Description: The present invention relates to a method of detecting a broken line up yarn and a detector used in this method. The present invention can be used as a technique for detecting broken yarn for devices dealing with many line up yarns such as warp knitting machines, looms, warping machines etc. Background of the Invention. Previously proposed devices such as warp knitting machines, looms and warping machines, utilize a plurality of line up yarns for knitting, weaving, winding, sizing, etc., while the yarns are being supplied to the device. When even one of the line up yarns breaks, these devices must immediately detect it and stop the operation; otherwise defective articles are produced. Such warp knitting machines and looms have previously adopted a dropper-type detector, each warp being provided with a dropper and, when a warp breaks, the respective dropper falls under its own weight whereupon the machine is stopped mechanically or electrically. Recent warp knitting machines and looning machines run at remarkably high speed and the above-described dropper type detector is time-wasting and inefficient because it requires the preparatory process of inserting each warp through a respective dropper, and furthermore this type of detector malfunctions easily owing to improper dropper fall or bad electrical contact, thereby failing to fully work as a monitoring/controlling means for these high-speed machines. Under these circumstances, a photoelectric detector has been adopted which is more responsive and capable of monitoring and controlling the machine without contact with the warps. This photoelectric detector adopts a broken yarn detection system in which a light emitter and a light receiver are axially aligned on opposite sides of a row of warps so that the axis of emitted light coincides with that of received light, and an alarm is sent out when a broken warp crosses the emitted light and hence interrupts the received light. However, this photoelectric detector can malfunction under the influence of ravellings and other floating objects, and consequently fails to be a reliable monitoring means for line up yarns consisting of many warps. FR-A-1274801 discloses a broken yarn detection system in which a reduced size image of a row of yarns being detected is produced optically using a lens. This image is traversed by a photoelectric sensor and counter device which is reciprocated transversely of the image. The photoelectric sensor and counter device has a slit therein so that, in theory, a separate obscuring of light falling on the sensor occurs each time a yarn image is aligned with the slit. The counter counts the number of yarn images detected during each traverse, compares this with the number of yarns which should have been detected, and produces an alarm signal when there is a disparity between the actual number of yarns detected and the number which should have been detected. With such a system, it is difficult, if not impossible, to detect broken yarns in rows where the yarns are very fine and/or very closely spaced apart. This is also a problem with the yarn detection system of DE-A-2822080 where a light emitter/receiver is moved a relatively small fixed distance using a cam. The presence/absence of a yarn between each emitter/receiver pair is detected and an alarm signal is produced if one or more of the emitter/receiver pairs fails to detect a broken yarn. Such a system uses light-emitting diodes as the emitters and photo-transistors as the receivers. CH-A-520061 discloses a system for detecting and reporting the ends down condition of textile yarn or thread forming machines, such as spinning and twisting machines. In such a sensor, traversing photoelectric detectors are used for the detection of yarn ends and so such an arrangement also suffers from potentially the same problem as that noted above for DE-A-2822080 and FR-A-1274801. It is an object of the present invention to provide a broken yarn detecting method and apparatus which is capable of detecting broken yarns efficiently even in a machine where the yarns are very fine and/or very closely spaced apart. According to the present invention, there is provided a method of detecting a broken line up yarn comprising the steps of: causing a light emitter for radiating a fine beam of light and a light receiver to travel transversely with respect to a row of yarns supplied in a line up condition so that the light emitter directs the beam of light towards the yarns sequentially from one end of the row to the other end thereof; photoelectrically converting flickerings caused by presence/absence of yarns received by the light receiver; using the resultant electrical signals to check for a missing yarn; and generating a signal upon detection of a missing yarn; characterised in that: a laser beam is transmitted via an optical fibre to the light emitter from a laser emitter as a light source; the photoelectric converting step is effected in a photoelectric converter, and optical transmission to the latter from the light receiver is performed via an optical fibre; the electrical signals are used to check for a missing yarn by electrically counting said signals to obtain the current value for the number of existing yarns and comparing such current value with a threshold; and an alarm signal is generated when the current value is different from the threshold. Also according to the present invention, there is provided a detector capable of performing the method as defined in the last preceding paragraph, said detector comprising: a carrier adapted to travel to and fro transversely with respect to a row of yarns supplied in a line up condition; a light emitting/receiving means movable with the carrier and provided with a light emitter for radiating a fine beam of light and a light receiver for receiving flickerings caused by the presence/absence of yarns whilst the carrier travels, with the light emitter radiating the beam to the row of yarns; a photoelectric conversion means for emitting pulse signals corresponding to the number of flickerings in response to an intermittent change in quantity of flickering light entering the light receiver; and means for using pulse signals to check for a missing yarn and for generating a signal upon detection of a missing yarn; characterised in that: a laser emitter is used as a source of light for providing optical energy to the light emitter; an optical fibre is arranged to tranmit a laser beam from the laser emitter to the light emitter; the carrier is adapted to move to and fro on a rail disposed transversely of the row of yarns; an optical fibre is arranged to perform optical transmission from the light receiver to the photoelectric conversion means; and the pulse signal using means comprises (a) a count means for counting the pulse signals from the photoelectric conversion means for every pass of the carrier along the row of yarns and for emitting a signal of the current value for the number of existing yarns, (b) a threshold setting means for emitting a threshold signal by inputting a value corresponding to the number of yarns constituting the row of yarns, and (c) a comparator for comparing the current value signal from the count means with the threshold signal from the threshold setting means and for outputting an alarm signal when these signals do not coincide with each other. The photoelectric conversion means is preferably a semi-conductor photoelectric conversion element such as a photodiode. The count means, the threshold setting means and the comparator may be provided by a microcomputer. In one embodiment, the light receiver is arranged to receive a beam of light from the light emitter which has reflected from the row of yarns, and the photoelectric conversion means outputs peak-form pulse signals in response to a periodical increase in the quantity of light coming from the light receiver. In another embodiment, the light emitter and light receiver are disposed symmetrically with the row of yarns therebetween, and the photoelectric conversion means outputs through-form pulse signals in response to a periodical decrease in the quantity of light caused by the interruption of laser light by the light emitter over the yarns. Preferably, the rail has rows of comb teeth for maintaining a regular spacing between the yarns so that the light emitting/receiving means can operate on the row of yarns kept at a regular spacing in the line up condition. The attached drawings illustrate embodiments and applications of the present invention. Fig. 1 is a block diagram of one embodiment of the present invention using a microcomputer as a component thereof; Fig. 2 is a block diagram of another embodiment of the present invention; Fig. 3(a) is a pulse graph in the case where a photoelectric conversion means is adapted to receive reflected light; Fig. 3(b) is a pulse graph in the case where a photoelectric conversion means is adapted to receive direct light; Fig. 4 is a view showing one embodiment of the present detector; Fig. 5 is an enlarged View showing a carrier and a rail of Fig. 4; Fig. 6 is a sectional view showing the present detector applied to a warp knitting machine; Fig. 7 is an explanatory view showing one portion of Fig. 6 in an enlarged scale; Figs. 8 to 11 illustrate travel mechanisms of the carrier; Fig. 12 is a view showing where to apply the present invention to a warp knitting machine; Fig. 13 is the same view but in case of a loom; and Fig. 14 is the same view but in case of a warping machine. Referring to Figs. 1 and 2, a light emitting/receiving means 2 comprises a light emitter 21 and a light receiver 22. This means 2 is disposed in a carrier 1 and adapted to travel transversely with respect to a row of yarns W. (See Figs. 4 to 10.) A laser emitter 24, for example a laser diode, is used as a source of light for providing optical energy to the light emitter 21, to which a laser beam is transmitted via an optical fiber 23. Laser is not always necessary but a beam as emitted by a light emission diode can be used, in which case the light emitter 21 preferably uses a per se known spatial filter to prevent scattering and to radiate a fine beam. The light receiver 22 preferably uses a converging lens so that it can catch any flickering of the beam radiated to the row of yarns W. In Figs. 1 and 2, the light receiver 22 receives a reflected light, and in response to a periodic increase in quantity of reflected light from the receiver 22, a photoelectric conversion means 3 outputs peak-form ( -form) pulse signals (p). (See Fig. 3(a).) The present invention is not limited to this reflection type, but applicable to a direct light type wherein the light emitter and receiver 21 and 22 are disposed symmetrically with the row of yarns W therebetween, said receiver 22 perceiving a periodical decrease in quantity of light aused by the warps W1, W2...Wn interrupting the beam from the emitter 21, and the photoelectric conversion means outputs trough-form ( -form) pulse signals (p). (See Fig. 3(b).) Optical transmission from the light receiver 21 to the photoelectric conversion means 3 is performed via an optical fiber 25. The means 3 can use a photoelectric conversion element such as a PIN photodiode, an avalanche diode, a photo cell or a phototransistor. A known counter can be used as a count means for counting the pulse signals (p) from the photoelectric conversion means 3 for every pass of the light emitting/ receiving means 2 across the row of yarns. A known register can be used as a threshold setting means 5 for setting the number of yarns W. A known comparator 6 can be used to compare the current value signal from the count means 4 with the threshold signal from the threshold setting means 5 and emit an alarm signal (ab) if there is a difference therebetween. These means 4, 5 and 6 may be integrally constructed as a microcomputer MC as shown in Fig. 1 if more reliability and miniaturization is desired. The current value for the number of yarns is counted for comparison with the threshold and if there is a difference, an alarm signal (ab) is sent out to a carrier controller 7 and a machine controller 8 in order to stop the machine. The machine may also be stopped by turning off a main switch (not shown) of the machine via said alarm signal (ab). In Fig. 4, the carrier 1 with the light emitting/ receiving means 2 is adapted to travel back and forth in a pipe-like rail R having rows of comb teeth C1 and C2 thereon. A slit S is formed in the rail R between said rows of teeth C1 and C2, through which slit the means 2 emits and receives light. The carrier 1 of Fig. 4 is adapted to travel by the interaction of a traction cord 11 fitted with weights (wt) and a pull-back feed roller 12. Numerals 23 and 25 are optical fibers, 24 is a laser emitter, and 3 is a photoelectric conversion means (OE converter). A microcomputer MC includes the count means 4, the threshold setting means 5 and the comparator 6. Fig. 5 shows the carrier 1 and the rail R on an enlarged scale. The row of yarns W is supplied in she direction indicated by the arrow, the yarns being maintained in a side-by-side mutually parallel relationship by the rows of teeth C1 and C2 on the rail R during their travel across the slit S. This detector is most suitable for the warp knitting machine where the row of yarns W is supplied in a superposed condition as schematically shown in Figs. 6 and 7. When applying this detector to the warp knitting machine, the light emitting/receiving means 2 may be disposed at any of positions P1, P2, P3, P4, P5 and P6 of the machine N as shown in Fig. 12. Alternative travel mechanisms for the carrier 1 and the means 2 will be described hereinbelow. The carrier 1 is adapted to travel by a reversible conveyor 13 in Figs. 8 and 9. In Fig. 10, cords 14 and 15 are reciprocated by reels 16 and 17, thereby moving the carrier 1. In Fig. 11, a flexible band 18 restricted by guides G1 and G2 is reciprocated by a motor 19 whereby the carrier 1 travels. The method of the present invention adopts a system that the light emitter 21 radiates a fine beam to the yarns W sequentially from the yarn W1 at one end of the row to the yarn Wn at the other end of the row, said yarns W being supplied in a line up condition in the direction of the arrow. If one of the yarns W breaks, the reflection type light receiver 22 receives no reflected light from the broken yarn, thereby decreasing the number of flickerings and consequently the number of peak-form pulse signals output by the photoelectric conversion means 3. Therefore the current value counted by the count means 4 becomes smaller than the value set by the threshold setting means 5 and the comparator 6 emits an alarm signal (ab) If the light receiver 22 is of the type which is adapted to receive direct light from the emitter and one of the yarns W breaks, the broken yarn does not interrupt the beam and the beam enters the photoelectic conversion means 3, thereby decreasing the output of trough-form pulse signals. Therefore the current value becomes smaller than the threshold and the comparator 6 emits an alarm signal (ab) in the same manner as the above case. It is very rarely that the current value for the number of yarns becomes larger than the threshold, but on infrequent occasions, some of the yarns W split and therefore the comparator 6 is also adapted to send out an alarm signal (ab) in this case. The detector of the present invention adopts a system in which the carrier 1 with the light emitting/ receiving means 2 is adapted to shuttle along the rail R disposed transversely with respect to the row of yarns W and a fine beam is radiated to the line up yarns to cause flickerings in the light received by the receiver. By adapting the travel speed of the carrier 1 to the rotational speed of the machine, any desired mechanical follow-up is easily attainable. Furthermore, this detector ensures highly accurate performance because it monitors normal yarns whose optical properties are quite different from those of ravelling and other floating objects and which have a stable altitude and position. This detector does not malfunction in the manner described above for the prior photoelectric detector for monitoring an abnormal broken yarn. As described above, the present invention can solve the problems of inefficient preparatory process and mechanical follow-up as seen in the previously described dropper type detector and it can keep up with the technical progress of the recent high-speed textile machinery. Furthermore, the malfunction problem of the previously described photoelectric detector can be solved by monitoring normal yarns. Thus the present invention provides a highly effective broken yarn detection technique. In this point, the present invention basically guarantees the progress of textile machinery to high-speed and highly accurate operation. While certain preferred embodiments of the present invention have been shown and described it is to be understood that the invention is not limited thereto but may be modified in various ways. Furthermore, the present method and detector are intended for use in not only the warp knitting machine N but also the textile machines for weaving and processing line up yarns such as a loom L or a warping machine Y. (See Figs 13 and 14.) In case of the loom L, the present invention is preferably applied to a position L1 which is between a breast beam B and a heald H and which is near the breast beam B where the warps make the least vertical movement. In case of the warping machine Y, a position Y1, Y2 or Y3 is preferable where the warps Y line up at the same level.

Claims: A method of detecting a broken line up yarn comprising the steps of: causing a light emitter (21) for radiating a fine beam of light and a light receiver (22) to travel transversely with respect to a row of yarns (W) supplied in a line up condition so that the light emitter (21) directs the beam of light towards the yarns (W) sequentially from one end of the row to the other end thereof; photoelectrically converting flickerings caused by presence/absence of yarns (W) received by the light receiver (22); using the resultant electrical signals to check for a missing yarn; and generating a signal upon detection of a missing yarn; characterised in that: a laser beam is transmitted via an optical fibre (23) to the light emitter (21) from a laser emitter (24) as a light source; the photoelectric converting step is effected in a photoelectric converter (3), and optical transmission to the latter from the light receiver (22) is performed via an optical fibre (25); the electrical signals are used to check for a missing yarn by electrically counting said signals to obtain the current value for the number of existing yarns and comparing such current value with a threshold; and an alarm signal is generated when the current value is different from the threshold. A detector capable of performing the method as defined in claim 1, said detector comprising: a carrier (1) adapted to travel to and fro transversely with respect to a row of yarns (W) supplied in a line up condition; a light emitting/receiving means movable with the carrier (1) and provided with a light emitter (21) for radiating a fine beam of light and a light receiver (22) for receiving flickerings caused by the presence/absence of yarns (W) whilst the carrier (1) travels, with the light emitter radiating the beam to the row of yarns (W); a photoelectric conversion means (3) for emitting pulse signals (p) corresponding to the number of flickerings in response to an intermittent change in quantity of flickering light entering the light receiver (22); and means for using pulse signals (p) to check for a missing yarn and for generating a signal upon detection of a missing yarn; characterised in that: a laser emitter (24) is used as a source of light for providing optical energy to the light emitter (21); an optical fibre (23) is arranged to transmit a laser beam from the laser emitter (24) to the light emitter (21); the carrier (1) is adapted to move to and fro on a rail (R) disposed transversely of the row of yarns (W); an optical fibre (25) is arranged to perform optical transmission from the light receiver (22) to the photoelectric conversion means (3); and the pulse signal using means comprises (a) a count means (4) for counting the pulse signals (p) from the photoelectric conversion means (3) for every pass of the carrier (1) along the row of yarns (W) and for emitting a signal of the current value for the number of existing yarns, (b) a threshold setting means (5) for emitting a threshold signal by inputting a value corresponding to the number of yarns constituting the row of yarns (W), and (c) a comparator (6) for comparing the current value signal from the count means (4) with the threshold signal from the threshold setting means (5) and for outputting an alarm signal (ab) when these signals do not coincide with each other. A detector according to claim 2, wherein the photoelectric conversion means (3) is a semi-conductor photoelectric conversion element. A detector according to claim 3, wherein the photoelectric conversion element (3) is a photodiode. A detector according to claim 2, 3 or 4, wherein the count means (4), the threshold setting means (5) and the comparator (6) are provided by a microcomputer (MC). A detector according to claim 2, 3, 4 or 5, wherein the light receiver (22) is arranged to receive a beam of light from the light emitter (21) which has reflected from the row of yarns (W), and the photoelectric conversion means (3) outputs peak-form pulse signals in response to a periodical increase in the quantity of reflected light coming from the light receiver (22). A detector according to claim, 2, 3, 4 or 5, wherein the light emitter (21) and the light receiver (22) are disposed symmetrically with the row of yarns (W) therebetween, and the photoelectric conversion means (3) outputs through-form pulse signals in response to a periodical decrease in the quantity of light caused by the interruption of laser light by the light emitter (21) over the yarns (W). A detector according to any one of the claims 2 to 7, wherein the rail (R) has rows of comb teeth (C₁,C₂) for maintaining a regular spacing between the yarns (W) so that the light emitting/receiving means can operate on the row of yarns (W) kept at regular spacing in the line up condition.

Inventors: HOOKABE KEISUKE, KANAI KENZO, YAMADA KENJI, HOOKABE, KEISUKE, KANAI, KENZO, YAMADA, KENJI
Applicants: KANAI SCHOOL INC, KANAI SCHOOL INCORPORATION
Application year: 1986
Main classification: B65H63
IPC codes: D04B35, B65H63, D03D51, D02H13