WARP-GUARD DEVICE FOR WEAVING MACHINES, WARPING MACHINES AND KNITTING MACHINES

Abstract: A warp-guard device for weaving machines, warping machines and knitting machines comprises sensor means (2, 3) for detecting one or more broken yarns (Fr) forming part of a series of yarns (F) lying in the same warp plane (O), monitoring means (10, 12, 13, 14, 15) associated with the sensor means (2, 3) for signalling the broken yarns and stopping the machine. The sensor means (2, 3) are located inside a tubular body (4) located in the vicinity of the yarns (F). The tubular body (4) is connected to suction means (6) and is provided with at least one longitudinal slit (7, 8) for sucking through it at least one of the ends (F1, F2) of one or more broken yarns (Fr) intended to interact with the sensor means (2, 3). The sensor means (2, 3) comprise an array of opto-electronic elements (2) able to emit light beams (B) and facing corresponding opto-electronic elements (3) able to receive the light beams and signal the presence of the end of a broken yarn located between them. The receiving opto-electronic elements (2) are associated with corresponding signalling opto-electronic elements (9) for emitting light signals (W) in the event of broken yarns being detected.

Description: WARP-GUARD DEVICE FOR WEAVING MACHINES, WARPING MACHINES AND KNITTING MACHINES Technical field The present invention is applicable to the sector of weaving and knitting looms and specifically relates to a warp-guard device for detecting one or more broken yarns in a series of warp yarns. Background art It is known that the abovementioned machines are designed to handle a large number yarns which form the warp of the fabric or the knitted article being processed and which are subject to breakage and may be very delicate. Therefore, it is necessary to detect the broken yarns as soon as possible and indicate the position thereof so that the machine can be stopped immediately and the continuity of the yarns restored before resuming processing. In order to solve this problem, monitoring or warp-guard devices have been developed, said devices in the majority of cases being of the drop wire type, described and claimed, for example, in the European patents EP-A-0, 1 1 ,261 , EP-A-0,262,724, EP-A-0,284,591 , EP-A-0,508,51 4, EP-A-0, 1 87,745 and EP- A-0,276,206. In these known devices, each yarn is inserted into a fork-shaped metal drop wire which is combined with a bar formed by a metal core and by a casing, also made of metal, which are electrically isolated from each other and connected to the terminals of an electric circuit. When a yarn breaks, the drop wire falls onto the bar, physically closing the electric circuit which l causes stoppage of the machine. According to a more recent version of these known devices, which is described in European Patent Application EP-A-0,350,776, when each drop wire falls it intercepts a low-power laser beam between an emitter and one or more receivers. Chinese Patent Application CN-A-20761 1 5 describes a device used for the processing of particularly delicate yarns, which may break as a result of the intrinsic weight of the drop wire. In this device a rotating comb is used, said comb collecting the ends of the broken yarns, winding them around their axis of rotation and allowing tensioning of a cable which is parallel to the axis of rotation and which actuates a switch located at one of the ends. Even though the abovementioned drop wire devices have been gradually improved, they have a series of recognised drawbacks including, for example, the need to insert the drop wires of the individual yarns one by one, the stress induced by the drop wires on the delicate yarns, the need for assembly, on the loom, of the device with the drop wires all mounted, the need for assembly of the device in a predetermined position with the limited possibility of displacement and adjustment, excessive sensitivity to dust and moisture, the impossibility of being able to view the breakage zones of the yarns or, in the case where viewing is possible, the low detection resolution, which is in the region of 300-500 mm. Moreover, the drop wire devices cannot be used in the processing of yarns made of conductive materials such as, for example, carbon fibres, since these may create false contacts with the drop wires, or in potentially dangerous environments owing to the risk of producing electric arcs when there is contact between the drop wires and the bars. In order to overcome at least partially these drawbacks, yarn-guard devices of the electro-optical type, i.e. devoid of mechanical elements such as the drop wires and consisting essentially of a coherent light source or a lower-power laser beam between an emitter and one or more receivers, have been developed. United States patents US-A-4, 1 77,838 and US-A-4,248,272 discloses an electro-optical device which comprises a low-power laser aimed transversely with respect to the warp yarns underneath the plane in which they lie, while a receiver is located at the opposite end in a position aligned with the radius. In the event of breakage, a yarn falls from the plane in which it lies, or intersects with others, forming an obstruction between the two warp planes and interrupting the laser beam. Another known electro-optical device, described and illustrated in European Patent EP-A-0, 1 37,064, envisages a light source located underneath the weaving surface and a detector consisting of several elements located above the weaving surface. At the start of processing, the configuration of the warp is acquired and the image obtained is compared with successive other configurations acquired with each beating-up operation of the machine, in synchronism with the movement of the weaving members. From this comparison a signal as to breakages of yarns during processing is obtained. Even though these electro-optical devices have solved some of the problems which are typical of drop wire devices, they still possess certain drawbacks such as the need to be arranged in a well-defined position with the limited possibility of displacement and adjustment. Moreover, they are sensitive to dust, moisture and pollution from the surrounding environment. Disclosure of the invention The main object of the present invention is that of eliminating the abovementioned drawbacks, by providing a warp-guard device which has characteristics of high reliability, flexibility and safety. A particular object is that of providing a warp-guard device which is able to perform detection of the broken yarns with a high degree of precision and with yarns made of any material. Another particular object is that of devising a warp-guard device which is substantially insensitive to dust, moisture and external disturbances. A further object is that of providing a warp-guard device which is intrinsically safe in any environment and operating conditions. Another particular object is that of devising a warp-guard device which may be mounted in different positions and after preparation of the machine onto which it will be applied. Another particular object is that of devising a warp-guard device which allows viewing and easy and immediate location of the breakages. These objects, as well as others which will appear more clearly below are achieved, in accordance with Claim 1 , by a warp-guard device for weaving looms, warping machines and knitting machines, comprising sensor means for detecting one or more broken yarns forming part of a series of yarns lying in a warp plane, monitoring means associated with said sensor means for signalling the broken yarns and stopping the machine, characterized in that said sensor means are located inside a tubular body located in the vicinity of the plane of said series of yarns, said tubular body being connected to suction means and being provided with at least one longitudinal slit for sucking through it at least one of the ends of one or more broken yarns intended to interact with said sensor means. Owing to this configuration, the device does not possess the traditional drop wires and therefore does not require insertion thereof and for this reason is also suitable for very delicate yarns. Moreover, the device may be arranged in different positions between the beam and the frames, does not required synchronization mechanisms, is self- cleaning and is substantially insensitive to dust and moisture. In addition, the device may be used safely also with yarns made of conductive material and in potentially dangerous environments since there are no contacts which may cause sparks. Brief description of the drawings Further features and advantages of the invention will be more clearly understood in the light of the detailed description of a preferred, but not exclusive embodiment of the warp-guard device according to the invention, illustrated by way of a non-limiting example with the aid of the attached drawings in which Fig. 1 shows a schematic perspective view of a weaving machine in which a warp-guard device according to the invention is installed; Fig. 2 shows a laterally sectioned view of the machine and the device according to Fig. 1 ; Fig. 3 shows a perspective view of a partially sectioned detail of the device according to the invention; Fig. 4 shows a view of the detail of Fig. 3 sectioned along a transverse plane; Fig. 5 shows a cross-sectional view, on a larger scale, of a detail according to Fig. 4; Fig. 6 shows a cross-sectional view of the detail of Fig. 4 along a plane indicated by VI-VI; Fig. 7 shows a plan view of the detail according to Fig. 5 in the direction of the arrow VII; Fig. 8 shows an exploded view of the detail according to Fig. 4; Fig. 9 shows a representation of the operating diagram of a detail of the device according to the preceding figures; Fig. 1 0 shows an operating diagram of the circuit logic of the device according to the invention; Fig. 1 1 shows a block diagram of the software installed in the device according to the invention. Detailed description of the preferred embodiment(s) With reference to the said figures, a warp-guard device according to the invention, denoted in its entirety by the reference number 1 , may be installed on a weaving or knitting loom, on a warping machine or on similar machines in which at least one series of warp yarns F arranged in a plane O are present. Figs. 1 and 2 schematically shows a weaving loom which is indicated T and in which two separate warp-guard devices 1 are shown, mounted in two different positions between the beam S and the heald-carrying frames L. In a per se known manner, the device 1 comprises sensor means for detecting one or more broken yarns FR forming part of the yarn O and associated with control means for signalling the abovementioned broken yarns and stopping the machine T. In particular, the sensor means are of the opto-electronic type and any consist of a first series of emitting elements 2 able to emit light beams B and a second series of receiving elements 3 able to receive the light beams B and interact with a broken yarn. Under normal conditions, the light beams sent by the emitting elements 2 will be captured by the receiving elements 3, generating an electric signal with a constant value which will indicate the continuity of the yarns. Advantageously, the emitting opto-electronic elements 2 may consist of infrared LEDs, while the receiving opto-electronic elements 3 may consist of phototransistors sensitive to the same light frequency band as the emitting elements. Both these types of electronic components are widely available commercially and have an extremely low cost. According to the invention, the sensor or opto-electronic means 2,3 are housed inside a tubular body 4 located in the vicinity of the yarns F of the warp O and the tubular body 4 is connected, by means of a duct 5, at one or both its ends, to external suction means 6. Moreover, the tubular body 4 is provided with one, or preferably two longitudinal slits 7, 8 for sucking inside it one or both the ends Fi , F 2 of a broken yarn F. Once sucked inside the tubular body 4, the ends Fi, F 2 of the broken yarn will interfere with the light beams B emitted by the emitting elements 2 and will interrupt the electric signal produced by the receiving elements 3, thus allowing the system to detect the breakage and stop the machine. The external suction means 6 may consist of a volumetric pump or blower which is low-cost and is widely available on the market and which has a delivery and head sufficient to ensure suction of several yarns inside the tubular body 4. Suitably, these characteristics may be modified by varying the speed of the motor driving the pump or blower by means of an inverter. In order to ensure in any case detection of the ends Fi, F2 sucked in through the slits 7, 8, the latter are situated at a predetermined minimum distance D, greater than the height H of the cross-section of the pipe, so as to ensure in any case interruption of the light beams in the event of breakage. Advantageously, the tubular body 4 may consist of a profiled section or extruded pipe made of metallic or plastic material, having a constant cross- section and substantially rectangular with rounded edges, with slits 7, 8 arranged along one of its larger sides. In order to visually detect the presence of broken yarns, each receiving element 3 is connected to a corresponding signalling opto-electronic element 9 which emits a light signal W in the event of broken yarns FR being detected. In order to increase the degree of resolution of detection, the emitting opto- electronic elements 2 and receiving opto-electronic elements 3 which are distributed uniformly over the whole length of said tubular body may be moved towards each other, with a small interval P as required, in keeping with the dimensions of the said elements. The emitting opto-electronic elements 2 and receiving opto-electronic elements 3 as well as the signalling elements 9 are mounted on modular printed boards 1 0 which comprise circuit components which are designed to scan the breakages. Preferably, each modular printed circuit comprises about 25 emitting elements 2 and a corresponding number of receiving elements 3 and signalling elements 9. The various modular circuits 1 0 are mounted on the tubular element so as to cover its whole longitudinal extension. Fig. 10 shows a possible diagram of the circuit logic of each modular board 1 0 which comprises, for each group of emitting and receiving elements 2, 3, an analog circuit 1 1 with amplification, comparison and filter functions, which converts the electric signals from analog into digital, and a digital circuit 1 2 which is managed by a microprocessor and which performs scanning of the signals, counting of the events and actuation of the output commands. All the modular circuits 10 are connected to the same timing signal generator 1 3 and reset signal generator 1 4. The microprocessors have, installed them, a program for detecting, filtering and managing the incoming signals as well as for actuating the output commands. An example of a program, schematically shown in Fig. 1 1 , envisages an auto- test upon start-up, followed by repetitive and asynchronous cycles for monitoring the infrared LEDs of each modular board 1 0, with a predetermined scanning frequency which is determined on the basis of the following considerations. Assuming that the minimum duration of the signal generated by detection of a broken yarn is equal to about 1 ms, according to the Nyquist theory, in order to obtain certainty as to detection at least 2 samples per signal are required, namely a sampling frequency of at least 2 kHz for each LED/phototransistor pair is required. Since the pairs installed on each circuit board are equal to about 25, a minimum scanning frequency equal to about 50 kHz is required. Therefore, for safety reasons, a scanning frequency of about 70 kHz was prechosen. When a breakage is detected, the counter associated with the corresponding sensor 3 is incremented by one unit. If this counter reaches a predetermined number N of events, it produces stoppage of the machine and the corresponding breakage signal. The counters mounted on each board 1 0 are reset cyclically every interval of TRC seconds in order to prevent the accumulation of false events due to disturbances or impurities of the air inside the tubular body 4. Thus, in order for stoppage of the machine to occur, at least N signals for events during the period TRC must occur. In order to prevent multiple sampling of the same event, a further software filter is introduced during reading of the sensors, said filter consisting of an integration time TF. This results in a maximum delay, during stoppage of the machine, equal to TF multiplied by the number of events to be detected, i.e. TF* N (ms). If N = 3, TRC = 2 s and TF = 50 ms, there will be an operating delay equal to 1 50 ms. Suitably, the electronic circuit may also comprise an interface of the CAN-bus or serial type 1 5, for connection to a central control unit CPU or to a personal computer PC as well as to other external communication devices for the collection, transmission and analysis of the breakage detection data and their statistical frequency, in order to establish a correlation with the possible causes. In order to ensure easier external viewing of the signal indicating breakage of the yarns Fr, the signalling elements 9 face an element for deviating the optical path, which is located outside the tubular body in order to allow a clear view, on the outside, of the breakage signal. In particular, this deviating element may consist of a prismatic bar 1 6 with a triangular or trapezoidal cross-section, resting on an open profiled member 1 7 opposite a longitudinal opening 1 8 facing the signalling elements 9. Thus, the light beams W emitted by the signalling elements 9 may be viewed from the outside on the inclined lateral surfaces of the prismatic bar 1 6. From the description given above, it is obvious that the warp-guard device according to the invention achieves the predefined objects and in particular attention is drawn to the high degree of reliability and safety in any surrounding environment, the flexibility of use and positioning on any weaving machine or warping machine, the possibility of use with any type of yarn, the absence of stress for the yarns being monitored, the possibility of connection to PCs or other intelligent devices. In addition, it can be easily understood that the device according to the invention has the advantages of an extremely simple and compact structure, a limited weight, a low cost compared to the technological advantages, a notable insensitivity to disturbances of both an electromagnetic and an environmental nature and an extremely low emission of electromagnetic disturbances. The warp-guard device according to the invention may be subject to numerous modifications and variations all falling within the inventive idea expressed in the accompanying claims. All the details may be replaced by other equivalents without departing from the scope of the invention. Although the warp-guard device has been described with particular reference to the accompanying figures, the reference numbers used in the description and in the claims are used in order improve understanding of the invention and do not constitute any limitation as to the scope of protection claimed. The instant application is based upon and claims priority of patent application No. VI2000A00001 9, filed on 24.01 .2000 in Italy, the disclosure of which is hereby expressly incorporated herein by reference thereto.

Claims: CLAIMS 1 . Warp-guard device for weaving machines, warping machines and knitting machines, comprising sensor means (2, 3) for detecting one or more broken yarns (Fr) forming part of a series of warp yarns (F), monitoring means (1 0, 1 2, 1 3, 14, 1 5) associated with said sensor means (2, 3) for signalling the broken yarns (Fr) and stopping the machine, characterized in that said sensor means (2, 3) are located inside a tubular body (4) located in the vicinity of said yarns (F), said tubular body (4) being connected to suction means (6) and being provided with at least one longitudinal slit (7, 8) for sucking through it at least one of the ends (Fi, F 2 ) of one or more broken yarns (Fr) intended to interact with said sensor means (2, 3). 2. Warp-guard device according to Claim 1 , characterized in that said sensor means (2, 3) comprise a plurality of opto-electronic elements (2) able to emit light beams (B) and facing corresponding opto-electronic elements (3) able to receive said light beams (B) and signal the presence of an end (Fi , F 2 ) of broken yarn located therebetween. 3. Warp-guard device according to Claim 2, characterized in that said receiving opto-electronic elements (2) are associated with corresponding signalling opto-electronic elements (9) for emitting light signals (W) in the event of broken yarns being detected. 4. Warp-guard device according to Claim 2, characterized in that said emitting opto-electronic elements (2) consist of infrared LEDs and said receiving opto-electronic elements (3) consist of phototransistors which are sensitive to the same light frequency band as said emitting elements. 5. Warp-guard device according to Claim 3, characterized in that said emitting opto-electronic elements (2) and receiving opto-electronic elements (3) and said signalling elements (9) are mounted on one or more modular printed circuits (1 0) associated with said tubular body (4). 6. Warp-guard device according to Claim 5, characterized in that each of said modular printed circuits (1 0) comprises a microprocessor which has, installed in it, a program for detecting, filtering and managing the inputs signals, as well as for actuating the output commands. 7. Warp-guard device according to Claim 6, characterized in that said printed circuit (1 0) comprises an interface of the CAN-bus or serial type (1 5) for connection to a processing unit (PC) and/or to other external communication devices (CPU) for collecting and analysing the data relating to detection of the breakages and their statistical frequency. 8. Warp-guard device according to Claim 3, characterized in that said signalling elements (9) face an element (1 6) for deviating the optical path, located outside said tubular body (4) so as to allow viewing, from the outside, of the signal indicating a broken yarn. 9. Warp-guard device according to Claim 8, characterized in that said element ( 1 6) for deviating the optical path consists of a prismatic bar with a triangular or trapezoidal cross-section, facing said signalling elements (9). 1 0. Warp-guard device according to Claim 2, characterized in that said emitting electronic elements (2), said receiving electronic elements (3) and signalling devices (9) are uniformly distributed along the whole longitudinal extension of said tubular body (4) at a constant interval (P). 1 1 . Warp-guard device according to Claim 1 , characterized in that said tubular body (4) has a pair of longitudinal slits (7, 8) located a predetermined minimum distance (D) from each other. 1 2. Warp-guard device according to Claim 1 , characterized in that said predetermined minimum distance (D) is greater than the height (H) of the cross-section of the pipe, so as to ensure interruption of the light beams in the event of breakage. 1 3. Warp-guard device according to Claim 1 2, characterized in that said tubular body (4) consists of a profiled section or pipe with a constant cross-section, which is substantially rectangular with rounded edges, with one or two slits (7, 8) arranged along one of its greater sides. 14. Warp-guard device according to Claim 1 , characterized in that said profiled section is connected to said suction means (6) at at least one of its ends. 1 5. Warp-guard device according to Claim 14, characterized in that said suction means (6) consist of a volumetric pump or blower with a delivery and head sufficient to ensure suction of several yarns inside said tubular body (4).

Inventors: SPEROTTO RINALDO, SPEROTTO, RINALDO
Applicants: SPEROTTO RINALDO, SPEROTTO, RINALDO
Application year: 2001
Main classification: D03D51
IPC codes: D02H13, D03D51, D04B35