WO2005066056A1

WO2005066056A1 - Device and method for detecting the presence and/or movement of a thread

Info

Publication number: WO2005066056A1
Application number: PCT/IT2005/000004
Authority: WO
Inventors: Elena Biagi; Leonardo Masotti
Original assignee: Actis Active Sensors S.R.L.
Priority date: 2004-01-09
Filing date: 2005-01-05
Publication date: 2005-07-21
Also published as: ITFI20040004A1; CN1910101A; CN100577545C

Abstract

The device for detecting a thread, comprises at least a first tight emitter (3)and at least a first tight receiver (5), disposed so that the tight beam (F1) emittedy the emitter and received by the receiver intersects the path (P) of the thread (F). The light beam received by the first receiver produces a first signal containing information on the thread. Also provided is at least a processing circuit (9) of said signal produced by the receiver, which extracts information from the signal on the presence and/or movement of the thread on the basis of the fluctuations of said signal caused by the irregular structure of said thread.

Description

"DEVICE AND METHOD FOR DETECTING THE PRESENCE AND/OR MOVEMENT OF A THREAD" DESCRIPTION Technical field The present invention relates to a device for detecting the presence or the movement of a thread. Devices of this type can be useful in all situations wherein it is necessary to feed a thread of various characteristics in a process. The invention also relates to a method to detect the presence and/or the movement and/or the speed of a thread. State of the art Optical devices have been developed for various industrial applications to detect the characteristics of a moving thread. For example, US - patent 5.684.598 describes an opto-electronic device comprising emitter and receiver systems to observe a band of moving threads. The object of this device is to bring to light any defects in the moving thread, but it does not have the function of detecting the presence of the thread, nor of determining the movement and/or the speed thereof. US patent 5.221.960 describes an opto-electronic device to detect the presence of a thread being fed. The device uses an emitter and a receiver disposed in front of a reflecting surface while the thread passes with a transverse movement, with respect to the longitudinal direction thereof, in front of the reflecting surface and intersects the beam of the detector. US patent 7.095.200 describes an opto-electronic system to detect the presence of a moving thread. Also in this case the emitter and the receiver are disposed in front of a reflecting surface on which the yarn runs in a direction transverse to the longitudinal direction thereof. Markings are produced on the reflecting surface to aid detection of the yarn. Objects and summary of the invention The object of the present invention is to produce a new type of opto- electronic device capable of detecting the presence and/or absence of a thread, any movement of the thread and, in a particular improved embodiment of the invention, also to determine the feed speed of the thread along a path. In substance, the invention relates to a device to detect a thread, comprising: at least a first light emitter and at least a first light receiver, disposed so that -the -light beam emitted by the emitter and received by the receiver intersects a path of said thread, the light beam received by the first receiver producing a first signal containing information on said thread; and at least a processing circuit of said signal. Characteristically, according to the invention, the processing circuit extracts information from the signal on the presence and/or on the movement of the thread on the basis of the fluctuations of said signal caused by the irregular structure of said thread. In practice, the invention is based on the effect which the irregular and variable structure of the thread or yarn has on a light beam, in particular a collimated beam, such as a laser beam. The passage of the thread or yarn causes modulation of the beam and therefore, by detecting the modulated beam, a modulated signal by the variable or irregular structure of the yarn is obtained. The signal can be obtained by working in transparency or in reflectance, that is, picking up the beam which intersects the yarn or detecting the beam reflected thereby. The mode in transparency or reflectance is advantageously chosen on the basis of the type of yarn. The information which can be obtained by detecting the light beam modulated by the passage of the thread can be different, combined with or alternate to one another, according to the use for which the device is destined. For example, in a first embodiment the processing circuit detects the movement of the thread by means of the fluctuations of said first signal. In this case the device is used solely to check whether the thread is moving (exceeding a minimum threshold speed) or whether there is no movement. In the second case the thread can either be not moving or absent. To discern between the two conditions, the device can be designed to detect the presence or absence of the yarn. In a practical embodiment, the processing circuit extracts a variable component from the signal produced by the receiver of the modulated beam by means of high-pass or band-pass filtering, for example with a band-pass filter tunable as a function of the speed of the thread and/or of the characteristic structure thereof. In an improved embodiment, the device can comprise: at least a first emitter/receiver pair and a second emitter/receiver pair, which emit two light beams that intersect the path of the thread in two points at a predetermined distance along said path, and by means of which a first and a second signal containing information on the thread are produced; and at least a processing circuit of said signals which determines the feed speed of the thread on the basis of said first and said second signal and of the distance between said emitter/receiver pairs. Also in this case, just as in the solution to detect movement of the thread, the device is based on recognition of the fact that the irregular or variable structure of the yarn or of the thread causes modulation of the light signal picked up in transparency or in reflectance. According to a further aspect, the invention relates to a method to obtain information on a thread along a feed path, comprising the steps of: emitting a light beam towards said thread; detecting a light beam which has intersected the path of the thread; - producing from said detected light beam a first signal containing information on said thread, characterized in that information on the presence and/or movement of said thread is extracted from said signal on the basis of the fluctuations of the signal caused by the irregular structure of the thread. Further advantageous features and embodiments of the device and of the method according to the invention are indicated in the appended claims and shall be described in greater detail with reference to some examples of embodiment. Brief description of the drawings The invention shall be better understood by following the description and accompanying drawing, which shows a practical non-limiting example of the invention. In the drawing: Figure 1 shows a block diagram of the device according to the invention in a first embodiment; Figures 2A to 2D schematically show the signal in various stages of processing by the processing circuit to determine movement of the thread; Figures 3A and 3B schematically show the signal processed by the processing circuit to detect the presence or absence of the thread; Figure 4 shows a block diagram of the second embodiment of the device according to the invention, configured to determine the feed speed of the thread along the path thereof, and Figures 5A- and 5B schematically show the pattern of the signals produced by the two detectors disposed at a predetermined distance along the path of the thread.

Detailed description of the preferred embodiments of the invention With initial reference to Figures 1 to 3, a configuration of the device will initially be described capable of identifying the presence or absence of the thread and/or the movement thereof. The reference P generically indicates the path of a generic thread or yarn F which is fed in the direction of the arrow f. The thread F can be a thread or yarn of any type, providing it has an irregular structure caused by twisting, fibers projecting from the surface thereof or the like. Disposed in a predetermined position along the path P of the thread F is a sensor or opto-electronic detector, indicated generically with 1 and comprising an emitter and a receiver 5. The emitter 3, for example a semiconductor laser or a LED, is powered by a power supply circuit generically indicated with 7. The receiver 5, for example a photodiode or a phototransistor receives the light beam F1 emitted by the emitter 3 after it has intersected the path P of the thread F and, therefore, after it has been intercepted and modulated by the thread F. It would also be possible to place the emitter 3 and receiver 5 in a different position to the one indicated, for example both on the same side with respect to the path P, optionally in front of a reflecting surface. The beam F1 picked up by the receiver 5 produces an electric signal S which is processed by the processing circuit indicated generically with 9. The processing circuit comprises a first high-pass filter 11 which filters the output signal S produced by the receiver 5 (see Figure 2A) to obtain a filtered signal S1 (see Figure 2B). The signal S1 can be sent directly to an envelope detector 13 at the output of which is a signal S2 representing the envelope of the signal S1 (see Figure 2C). The signal S2 is filtered by a low- pass filter 15 to obtain an output signal S3 which is compared in a comparator circuit 17 with a reference signal Ref. Figure 2D shows the shape of the signal S3 in two possible situations with two different curves indicated with (a) and (b). The curve (a) is above the reference signal while the curve (b) is below said signal. These two situations correspond, as shall be more apparent below, to a situation with the thread moving (curve a) and with the thread stopped (curve b). . In fact, thanks to the presence of irregularities in the thread the signal S, produced by the detector 5 when the thread is moving through the sensor 1 , has a highly variable shape. This variation is given by the variation of the structure of the thread in its various sections which intersect the beam F1 of the sensor 1 in succession. In the example shown these variations are detected optically by transparency with the consequent production of a highly variable electric signal S, or with a variable component superposed on a constant component. Subsequent filtering using the high-pass filter 11 eliminates the fixed component of the signal and allows easier and more efficient processing of the signal S1 comprising only the high frequency variation determined by the variable structure of the yam. It is clear that the faster the thread, characterized by the same irregular structure, moves, the higher the frequencies of the variation in the signal S and therefore of the signal S1 will be. Therefore, for a specific type of thread it is possible to define a threshold of reference (the signal Ref) so that when the signal S3 obtained by detecting the envelope (signal S2) and by low-pass filtering using the filter 15 has a value greater than the reference Ref, the thread F can be considered in movement, while when this signal is below the value of reference Ref the thread can be considered to be stopped. The comparator circuit 17 can be interfaced with an actuator or alarm signal generator 19 which can be predisposed to emit an alarm or in general a signal, when the thread is stopped, that is, when the signal S3 has a pattern of the type represented by the curve (b) in Figure 2D. Alternatively, the situation with the thread stopped detected by the comparator 17 can be used to refuse enabling of start up or operation of specific equipment, or the presence of moving thread can supply a signal to enable other operations. The processing circuit 9 can, additionally or alternatively to the high-pass filter 11 , have a band-pass filter 12 with a tunable band, indicated with a dashed line in Figure 1. In fact, in addition to the speed of the thread, the pattern of the signal S depends greatly on the structure thereof. After establishing the speed at which a specific type of thread is fed along the path P thereof, it is possible to determine the maximum signal frequency depending on the structure of the thread. In this configuration the device has increased sensitivity. The band-pass filter 12 is advantageously tunable to allow the device to be set according to the type of yarn or thread F to be detected (and/or as a function of the speed which the thread must have). The use of a band-pass filter centered on the maximum signal frequency also allows enhanced discernment between a situation with the thread moving at a correct operating speed and with the thread moving at a greater or lower speed with respect to the nominal speed at which it should be fed. The processing circuit 9 shown in Figure 1 also presents a section dedicated to detecting the presence or absence of thread, irrespective of whether it is moving or stopped. This section comprises a low-pass filter 21 which receives the input signal S and the output of which is applied to an envelope detector 23. The output signal S4 from the envelope detector 23 has a pattern similar to the signal S3 in Figure 2D. Figures 3A and 3B schematically show a possible pattern of the signal S1 and a possible corresponding pattern of the signal S4. Figure 3B also shows the signal of reference Ref. In general the signal S4 will not have the same intensity as the signal S3 and, therefore, cannot be compared directly with the same reference signal Ref. The circuit (in this embodiment) has a programmable distribution frame 25 which returns the value of the signal S4 to a value compatible with the signal Ref used by another comparator 18 which can therefore be used to determine the presence or absence of yarn. The components 18, 21 , 23 and 25 of the processing circuit 9 allow the presence or absence of the thread to be detected thanks to the fact that the presence of the thread considerably reduces the value of the signal S with respect to the situation in which thread is absent. Therefore, when the signal S4 has the pattern of the curve (c) in Figure 3B, the circuit will interpret the situation as a situation in which thread is present, while when the signal S4 has the pattern of the curve (d) in Figure 3B, the circuit will interpret the situation as a situation in which thread is absent. It must be understood that the signal S4 could also be compared with a reference signal Ref1 differing from the signal Ref. In the above the emitter and the receiver 5 are disposed so that the beam F1 intersects the thread F in movement along the path P. Therefore, detection is performed by transparency. It would also be possible to perform detection by reflection, when the characteristics of the yarn are suitable. Figure 4 shows an alternative embodiment of the device according to the invention. It must be understood that in actual fact the same device can have all the components in both the diagram in Figure 1 and the diagram in Figure 4, to supply complex information on the movement and on the presence of the thread F along the path P. In a combined solution, at least some parts of the system in Figure 1 can be shared by the system in Figure 4. The diagram in Figure 4 shows, at a reciprocal distance D along the path P of the yarn F, two sensors indicated with 51 A and 51 B. Each sensor comprises an emitter/receiver pair indicated with 53A, 55A for the sensor 51A and with 53B, 55B for the sensor 51 B. The emitters 53A and 53B can be constituted by semiconductor lasers or by LEDs supplied by a power supply circuit 57. The signals SA and SB produced by the receivers 55A and 55B (for example, phototransistors or photodiodes) are analog signals which are sampled and converted into digital signals by two corresponding analog-digital converters 58A and 58B. The sampled and digitalized signals are sent to a processing unit 61 , for example a DSP (Digital Signal Processing) device. The unit 61 and the analog-digital converters 58A and 58B form components of a processing circuit generically indicated as a whole with 63. The signals SA and SB supplied by the detectors 55A and 55B are modulated by the movement of the thread F which, as observed previously, has an irregular structure. As each portion of yarn passes through the. sensors 51 A and 51 B in succession with a delay determined by the distance D between the two sensors and by the speed v of the thread, by comparing the two signals detected by the receivers 51 A and 51 B and detecting the delay therebetween it is possible to determine the speed of the thread. For this purpose, at predetermined intervals of time the processing unit

61 calculates the mutual correlation between the two signals SA and SB. It must be understood that the processing circuit 63 can also be provided with additional components to those represented schematically. In particular, the signals SA and SB can be subjected to filtering before being converted from analog signals to digital signals, for example to eliminate the fixed component, using respective high-pass filters and/or band-pass filters such as those described with reference to Figure 1. Figures 5A and 5B schematically show a portion of signal SA produced by the receiver 51A and determined by modulation of the optical beam FA emitted, by_ the emitter 53A implemented by passage of the thread F. The portion of thread that determined the pattern of the signal SA will pass with a temporal delay τ through the sensor 51 B, so that it will cause analogous modulation of the optical beam FB emitted by the emitter 53B and this will give rise to a signal SB with analogous temporal pattern by the receiver 55B. The temporal delay τ between the two signals is indicated in Figures 5A and 5B. The function of mutual correlation between the two signals SA and SB is calculated by the processing unit 61 according to the following formula

where τ_maχ is the maximum value of the delay between the two signals SA and SB. The value of τ_max is fixed so that the interval of integration has a significant duration. In fact, the criterion for calculation of the speed of the thread F is based on the possibility of recognizing passage of the same portion of thread in front of the two receivers 55A and 55B determining the delay of these passages. To guarantee that the signal received and processed refers effectively to the same portion of thread, the interval of integration must be sufficiently long. From calculation of the mutual correlation function c(τ) the processing unit 61 obtains the value of the delay τ which corresponds to its maximum and, therefore, on the basis of the predetermined distance D between the two sensors 51 A and 51 B, it calculates the feed speed of the yarn. As observed above, the device in Figure 4, which is able to calculate the speed of the yarn, can be used on its own, or also as an integral part of a more complex and complete device which comprises one, the other, or both of the sections described above of the processing circuit in Figure 1. In particular, it would, for example, be possible for one of the two sensors 51 A or 51 B to be used to produce the signal S which, according to the procedure described with reference to Figure 1 , allows the presence or absence of yam to be determined (by means of filtering in 21 and envelope detection in 23). The devices in Figures 1 and 4 can also simply be put together in a single more complex device, which in this case has three sensors, each forming an emitter/receiver pair. It is understood that the drawing only shows an embodiment, provided purely as a practical example of the invention, and- that said inveniton may vary in forms and arrangements without however departing from the scope of the concept on which it is based. Any reference numerals in the appended claims are provided purely for the purpose of facilitating reading of the claims with reference to the description and to the drawing, and do not limit the scope of protection represented by the claims.

Claims

CLAIMS 1. Device for detecting a thread, comprising: at least a first light emitter and at least a first light receiver, disposed so that the light beam emitted by the emitter and received by the receiver intersects a path of said thread, the light beam received by the first receiver producing a first signal containing information on said thread; and at least a processing circuit of said signal; characterized in that said processing circuit extracts information from the signal on the presence and/or movement of the thread on the basis of the fluctuations of said signal caused by the irregular structure of said thread.

2. Device as claimed in claim 1 , characterized in that said processing circuit detects the movement of the thread by means of the fluctuations of said first signal.

3. Device as claimed in claim 2, characterized in that said processing circuit extracts a variable component from said signal by means of high-pass or band-pass filtering.

4. Device as claimed in claim 3, characterized in that said processing circuit performs band-pass filtering with a band tunable as a function of the characteristics of the thread.

5. Device as claimed in claim 3 or 4, characterized in that said processing circuit comprises an envelope detector which detects the envelope of the filtered signal.

6. Device as claimed in claim 5, characterized in that said processing circuit comprises a low-pass filter which filters the output signal of the envelope detector.

7. Device as claimed in claim 6, characterized in that said processing circuit comprises a comparator to compare the output signal of said low-pass filter with a reference signal.

8. Device as claimed in one or more of the previous claims, characterized in that said circuit performs low-pass filtering of said first signal produced by said first receiver to detect the presence or absence of said thread.

9. Device as claimed in claim 8, characterized in that the circuit detects the envelope of the filtered signal by means of a second envelope detector.

10. Device as claimed in claim 9, characterized in that the circuit compares the output signal of said second envelope detector and the reference signal.

11. Device as claimed in one or more of the previous claims, characterized in that it comprises: at least a first emitter/receiver pair and a second emitter/receiver pair, which emit two light beams that intersect the path of the thread in two points at a predetermined distance along said path, and which produce a first and a second signal containing information on said thread; and at least a processing circuit for said signal which determines the feed speed of the thread on the basis of said first and said second signal and of the distance between said emitter/receiver pairs.

12. Device as claimed in claim 11 , characterized in that said processing circuit comprises analog/digital conversion means of said two signals and digital processing means of the signal.

13. Device as claimed in claim 11 or 12, characterized in that said processing circuit periodically calculates the mutual correlation between said two signals and extracts the maximum value of said mutual correlation to determine the delay between the two signals and from said delay, on the basis of the distance between the two emitter/receiver pairs, the speed of the thread.

14. A method to obtain information on a thread along a feed path, comprising the steps of: emitting a light beam towards said thread; - detecting a light beam which has intersected the path of the thread; producing from said detected light beam a first signal containing information on said thread, characterized in that information on the presence and/or movement of said thread is extracted from said signal on the basis of the fluctuations of the signal caused by the irregular structure of the thread.

15. Method as claimed in claim 14, characterized in that the movement of the thread is detected by means of the fluctuations of said first signal.

16. Method as claimed in claim 15, characterized in that band-pass or low-pass filtering of said signal is performed.

17. Method as claimed in claim 16, characterized in that the envelope of the filtered signal is detected.

18. Method as claimed in claim 17, characterized in that low-pass filtering of the envelope is performed and the filtered signal is compared with a reference.

19. Method as claimed in one or more of the previous claims, characterized in that the presence or absence of the thread in said path is detected by performing low-pass filtering of said first signal.

20. Method as claimed in claim 19, characterized in that low-pass filtering of said first signal is performed.

21. Method as claimed in claim 20, characterized in that the envelope of the filtered signal is detected.

22. Method as claimed in claim 21 , characterized in that the envelope signal is compared with a reference signal.

23. Method as claimed in one or more of claims 14 to 22, characterized in that the feed speed of said thread is determined by comparing two signals produced detecting two light beams which intersect, in points disposed at a predetermined distance, the path of the thread.

24. Method as claimed in claim 23, characterized in that the mutual correlation between said two signals and the time delay between the two signals are determined and, from said delay, the feed speed of the thread is determined on the basis of said predetermined distance.