METHOD, SYSTEM AND SENSOR FOR DETECTING A CHARACTERISTIC OF A TEXTILE OR METAL THREAD FED TO AN OPERATING MACHINE

Abstract

A method for detecting a characteristic of a textile or metal thread fed to an operating machine, by the generation of a light signal impacting the thread to create a shadow on an optical sensor device connected to means for monitoring a characteristic of the thread on the basis of an electrical signal emitted by such sensor device as a function of the shadow generated on said sensor device by the thread itself, the characteristic being a physical characteristic of the thread such as its diameter or a characteristic of the feed of the thread when in movement, such as its speed. The signal may be detected in analog mode or a digital mode, the signal detected in the digital mode providing real time calibration of the signal detected in analog mode to generate an electrical signal used by the monitoring means to monitor the characteristics of the thread.

Claims

1. Method for detecting and monitoring a characteristic of a thread (F) fed to an operating machine (M), said method comprising optical-type detection of such monitored characteristic, said optical-type detection being performed with an illumination of the thread, the method providing for a first detection of said characteristic using means (3) of analog type and a second detection of said characteristic using means (4) of digital type, the second detection of the digital type allowing a digital value of the monitored characteristic to be determined, said digital value being used to calibrate an analog value of the monitored characteristic obtained in the first detection of the analog type to precisely identify the definitive value of said monitored characteristic, said first detection of the characteristic of analog type and said second detection of such characteristic of digital type being performed independently, separately and generating corresponding data which are sent to a monitoring unit (8), characterised in that in a first stage said monitoring unit (8) determines the digital value of the above characteristic on the basis of the data detected using the digital-type means (4) and calculates a calibration variable (C(t)) on the basis of said determined digital value, said calibration variable (C(t)) varying over time, in a second stage said monitoring unit (8) modifying the data detected by the analog-type means (3) on the basis of the calibration variable which is a function of such value of the characteristic of digital type determined in the second detection, said modification taking place in real time and allowing the detection of the characteristic of analog-type to be calibrated so to determine the definitive value of the monitored characteristic.

2. Method according to claim 1, characterised in that the monitoring unit (8) compares such definitive value of the monitored characteristic with predefined values or monitoring parameters of the monitored characteristic so as to check whether or not it corresponds to said predetermined set values; where such correspondence does not occur, said monitoring unit (8) generates a warning signal and/or acts on a feed of the thread to the operating machine to prevent a thread having a characteristic differing from the predefined set characteristic from being processed.

3. Method according to claim 1, characterised in that the calibration variable is sampled by the monitoring unit (8) at a frequency above 100-150 Hz, advantageously above 200 Hz and preferably above 300 Hz.

4. (canceled)

5. Method according to claim 1, characterised in that it is provided that said first and second detections are performed by illuminating the digital-type means (4) and the analog-type means with light rays laying on each of two spatial axes (X, Y) at right angles to each other, said detections with light rays on said two spatial axes being capable of being compared or crossed with each other to determine a physical characteristic of the thread (F).

6. Method according to claim 1, characterised in that the characteristic of the thread which is detected and monitored is alternatively a physical characteristic of the thread (F) or a characteristic associated with the feed of such thread (F) to a textile machine.

7. Method according to claim 6, characterised in that the physical characteristic is at least one of thread diameter (d), the fineness, the presence of local surface variations in the thread (F) itself, the presence of knots along the thread, its hairiness, its geometrical shape or the number of twists to which the thread has been subjected.

8. Method according to claim 6, characterised in that the characteristic associated with feeding of the thread (F) to the operating machine (M) is its rate of feed.

9. Method according to claim 1, characterised in that provision is made for a sequence of at least two stages of illumination of the thread (F), one of such stages comprising zero illumination or dark.

10. Method according to claim 7, characterised in that provision is made for a sequence of three stages of illumination of the thread (F) in order to have a said first and second detection alternately on one of said axes (X, Y), one of such stages comprising the dark.

11. System for detecting and monitoring a characteristic of a thread (F) fed to an operating machine (M), said system being capable of implementing the method mentioned in claim 1, the system comprising detection means of an optical type (2) for the monitored characteristic and acting together with illumination means (12), said optical detection means (2) comprising a detection part operating in analog mode (3) and a detection part operating in digital mode (4), each of said parts (3, 4) generating its own electrical signal corresponding to data for the monitored characteristic, the data for the characteristic detected by the detector part operating in analog mode (3) being calibrated by the data for the characteristic detected by the detecting part operating in digital mode (4), a monitoring unit (8) being functionally connected to said detection part operating in analog mode (3) and to said detection part operating in digital mode (4), said monitoring unit (8) being capable of receiving and processing data for the monitored characteristic independently detected by said detecting parts operating in analog mode (3) and in digital mode (4), said monitoring unit (8) determining the value of the monitored characteristic as a function of the data received from said detection parts (3, 4), characterised in that the data for the detected characteristic from the detection part operating in analog mode (3) is calibrated by a calibration variable which varies over time, said calibration variable being defined by a value of the monitored characteristic detected by the detection part operating in digital mode and determined by the monitoring unit (8), the determination of such calibration variable making it possible to said monitoring unit (8) to calibrate the data for the characteristic detected by the detection part operating in analog mode (3) and to define the definitive value of the monitored characteristic.

12. System according to claim 10, characterised in that alternatively said detection parts operating in analog mode (3) and the detection parts operating in digital mode (4) belong to a single sensor (2) or separate sensors (2).

13. System according to claim 11, characterised in that said monitoring unit (8) is connected to a memory unit (9) containing predetermined values of the monitored characteristic, said monitoring unit (8) comparing the definitive value of the monitored characteristic with such predetermined values in order to generate a warning and/or to stop feed of the thread to the machine if there is a discrepancy between the definitive value of the monitored characteristic and the predetermined values.

14. Monitoring system according to claim 11, characterised in that said illumination means are a single light source.

15. System according to claim 11, characterised in that said detection part operating in analog mode (3) and said detection part operating in digital mode (4), the monitoring unit (8), the memory unit (9), and the illumination means (12) for said detection parts (3, 4) are parts of a single body (5), said detection parts being struck simultaneously by a shadow projected by the thread (F) when such thread is illuminated by said illumination means (12).

16. System according to claim 11, characterised in that it provides for a pair of detection parts operating in analog mode (3) and a pair of detection parts operating in digital mode (4) located on each of two axes spatially at right angles to each other (X, Y), each of such pairs acting together with a corresponding lighting device (12), the thread (F) fed to the operating machine moving between said detection parts operating in analog mode (3) and detection parts operating in digital mode (4).

17. System according to claim 16, characterised in that there are two detection parts operating in analog mode (3A, 3B) and one detection part operating in digital mode (4) on one (X) of such spatial axes (X, Y), said detection parts being at a short distance from each other.

18. System according to claim 11, characterised in that the monitored characteristic is alternately a physical characteristic of the thread (F) such as its diameter, fineness, surface deformation, geometry, number of twists, interlacing, hairiness, or a knot, or a characteristic associated with the feed of the thread (F), that is the feed rate.

Description

[0049] For a better understanding of the present invention the following drawings are attached hereto purely by way of non-limiting example; in these:

[0050] FIG. 1 shows a diagrammatical view of a known analog sensor while it is detecting a dimensional characteristic of a thread F;

[0051] FIG. 2 shows a diagrammatical view of a system according to the invention;

[0052] FIG. 3 shows a diagrammatical view of a first variant of the system in FIG. 2; and

[0053] FIG. 4 shows a diagrammatical view of a second variant of the system in FIG. 2.

[0054] With reference to the figures mentioned and FIG. 2 in particular, this shows a system 1 for detecting a characteristic of a thread F fed to an operating machine M. This thread acts together with an optical sensor 2 which in the example in the figure has an analog detection part 3 and a digital detection part 4 associated with a single container body 5 and located at a short distance between them in such body 5. This makes it possible to have a detection system 1 (or detection unit or detection device) of very small dimensions such that it can be used with other identical systems for each thread monitored in textile machines operating on hundreds of threads, such as knitting machines or the like.

[0055] Compactness of system 1 is also achieved thanks to the fact that only 1 light source or LED (not shown in FIG. 2) capable of generating light which “impacts” on thread F and allows a shadow to be generated on both of said detection parts 3 and 4 such as to allow said parts to emit electrical signals corresponding to the dimensions of such shadow upon them is also present in body 5. In particular, analog detection part 3 may be a photodiode, while part 4 may be a CMOS or CCD sensor, or a similar semiconductor sensor. Part 4 spatially digitises the shadow of the thread created thereupon, using a vectorial sensor.

[0056] The semiconductor sensors in part 4 define a matrix of photodetectors, through which the spatial digitalisation mentioned above is achieved.

[0057] Thanks to the use of these semiconductor sensors it is possible to obtain an “instantaneous photo” of the thread in a few microseconds, regardless of the speed at which the thread is being fed, as will be described below.

[0058] There is also the possibility of making an accurate determination of the diameter of such thread when moving towards a textile machine (or a winding machine for a metal thread or similar operating machine).

[0059] This accurate measurement cannot, for example, be made using the description described in WO 00/62013 in that, according to that prior document, the characteristics of the thread are measured by interferometry, as already described; as the thread is in movement and therefore vibrating, determination of the interference fringes in a way that is useful for measuring its diameter is, to say the least, imprecise.

[0060] From the shadow generated by the thread on part 4 it is possible to determine the diameter of the thread immediately without processing the signal, as takes place in WO 00/62013.

[0061] Detection parts 3 and 4 (or, for simplicity, analog sensor 3 and digital sensor 4 respectively) are connected to a monitoring or evaluation unit 8 of the microprocessor type (also present in body 5) which calculates the value of a monitored characteristic of thread F (for example, the diameter) on the basis of the electrical signals or data emitted by those parts 3 and 4. Unit 8 receives and analyses the signals originating from both sensor 3 and sensor 4.

[0062] This unit 8 is connected to a memory unit 9 into which predetermined accepted values (or monitoring parameters) for the monitored characteristics are inserted, and using these unit 8 compares the data found or actual data with them in order to evaluate how they correspond to the predetermined values; if there is no uniformity between the actual value and the value in memory, unit 8 acts in a known way, for example, by producing a visible and/or audible warning, generating a signal to a device feeding thread F to machine M or other known device, to prevent a thread F having characteristics differing from those desired from continuing to be used by machine M.

[0063] System 1 provides that the measurement made by digital part 4 of sensor 2 (which takes the form of an electrical signal) provides a real-time calibration of the measurement made in analog part 3 (which also takes the form of an electrical signal). It should be noted that the term “calibration” indicates a periodical determination of the measurement from analog part 3 of sensor 2 and comparing this measurement with the value of the diameter measured by digital part 4 of such sensor.

[0064] The “calibrated” electrical signal originating from such parts 3 and 4 is used by unit 8 to perform the evaluation indicated above.

[0065] Also considering possible errors in the analog sensor, in the short term the measurement of diameter made by such sensor or analog part 3 may also be expressed by a linear equation with the power measured by analog part 3.

d=H(1−C(t).Math.P.sub.MIS)

Where P.sub.MIS è is the value of the power measured by analog part 3 (photodiode), a value which varies over time, H is the known dimension of analog part 3, while C is a variable (which we will define as the “calibration variable”) that is a function of time and depends on various factors: the illuminating optical power, any dirt present, any transparency of the thread and any variability in the gain of the electronics (thinking of background values which vary with temperature). The value of the variable C(t) over time is evaluated at a predetermined frequency, higher than 100-150 Hz, advantageously higher than 200 Hz, preferably at 300 Hz. Through this periodical evaluation of C(t) at the sampling frequencies indicated above, factors which might have an adverse effect on the value of C(t), as indicated above, factors which vary with very much lower frequencies, can be overcome. Vice versa, the above-mentioned frequencies used to evaluate the value of C(t) at precise instances in time can be used to identify the dimensional value of the thread, in that at these frequencies the only component which can vary quickly is the transverse position of the thread itself. It has in fact been found that in practical situations the thread can move linearly or even transversely, with vibration. Because however it has been found that the vibration frequencies are at most equal to a few tens of hertz, these movements do not affect measurement if sampling is carried out at frequencies higher than 100-50 Hz; as indicated above, such vibrations therefore have no effect on the value of C(t) at the time when it is being measured.

[0066] In other words it has been found that the vibrations affecting the thread in its movement from a bobbin (from which it is unwound) to the operating machine (textile machine or machine operating on a metal thread) are of the order of at most 10 Hz. Using a sampling frequency for the signal detected of at least 100 Hz and preferably higher than 300 Hz, the image of the thread detected by analog part 3 of sensor 2 certainly shows the thread as if it were completely still and such as to allow its characteristics and in particular its diameter to be determined.

[0067] It should be noted that, as will be indicated, the signal detected by part 4 is also sampled at the same frequencies, and this also makes it possible to detect the characteristics of the thread as if it were still in the case of that digital part or sensor 4.

[0068] Unit 8 determines the value of the diameter d1 of the thread on the basis of the data detected by digital part 4 of sensor 2 (associated with the shadow generated on such part 4) at particular moments in time (and at successive and discrete timed frequencies as indicated above). Once this measurement has been made, a formula similar to that indicated above is applied and as both the dimension H of analog sensor 3 and its measured power P.sub.MIS are known it is possible to calculate the variability in calibration C as

C(t)=(1−d1/H)/P.sub.MIS

[0069] When a value of C(t) for each instant of measurement time has been obtained this can be inserted into the formula for calculating “d” using the analog sensor, bringing about calibration of the signal detected by the latter.

[0070] To conclude, if calibration parameter or variable C is calculated by means of a measurement of diameter d1 made by digital part 4 of sensor 2, at for example at least 100 Hz (or higher) the problematical effects mentioned can be compensated for (for the reasons mentioned above). This rate of measurement can be easily achieved with a CMOS sensor and low-cost electronics.

[0071] The method according to the invention therefore provides that analog part 3 of sensor 2 independently detects the characteristic (for example the diameter) of the monitored thread in a manner which is in itself known and produces its own detection signal, sending it to unit 8. The measurement by part 3 of sensor 2 is fast but, as is known, inaccurate.

[0072] In parallel, digital part 4 of sensor 2 independently and in a manner which is in itself known also detects the above-mentioned characteristic (d1) and generates its own signal sending it to unit 8. The latter, using the means described above, calibrates the signal from part 3 with the signal generated by digital part 4, a signal which is more accurate than that from the analog part, and is generated at a low sampling speed, as a result of which a microprocessor unit 8 (or “microcontroller”) of very small (and commercially acceptable) dimensions and costs can be used.

[0073] On the basis of the “calibrated” signal, unit 8 acts to compare this signal with data placed in memory and if there is any difference from the latter, it generates a warning or acts in the manners indicated above.

[0074] FIG. 3, in which parts corresponding to those in the figures already described are indicated using the same reference numbers, shows a system for measuring the fineness of a thread F, which requires two measurement axes (X and Y in FIG. 3). In this case provision is made for the use of two sensors 2, the light rays of which, generated by LED 10, are at right angles to each other. Semi-cylindrical lenses 12 which collimate the light to sensors 2 and unit 8 which is considered to include circuit 20 described above are also present in the figure. The LED are also connected to this unit 8.

[0075] These sensors 2, the LED and unit 8 are all associated with a single body 5.

[0076] A system for measuring fineness needs two measurement axes, and this can be brought about by duplicating the approach described in two dimensions. In order to avoid disturbances in ambient light the system may be pulsed, carrying out selective detection through both the photodiodes and the CMOS sensors. In order to minimise measurement times a sequence of three lighting states may be provided: light on the first axis, light on the second axis, dark. In this way, the measurement difference with respect to dark makes it possible to eliminate disturbances in ambient light without it being necessary to resort to optical filters, and it is therefore also possible to work with visible light.

[0077] One example of the use of the system in FIG. 3 is as follows. Wishing to make a measurement at 33 kHz, it is possible to produce individual light pulses having a duration of 10 μs, for an overall time of 30 μs, provided by two pulses (one per axis) and 10 μs of dark to measure the background luminosity. Two CMOS sensors of 512 pixels are sampled at 1 MHz, obtaining a sampling time of approximately 0.5 ms for an individual CMOS, and this becomes 1 ms for both of the sensors if acquired in sequence. 0.5 ms is sufficient for acquisition in parallel. The time for digital processing of the data to calculate measurement of the diameter has to be added to this time, and this is limited to approximately 2 ms for a low cost microcontroller.

[0078] In conclusion the measurement made by the two photodiodes at approximately 300 Hz can be calibrated, and this comprises a data flow at 33 kHz, quite sufficient to detect knots or defects.

[0079] In conclusion, in both the cases described (FIG. 2 and FIG. 3), rate of measurement is guaranteed by the analog sensor, while accuracy derives from the digital sensor.

[0080] FIG. 4, in which parts corresponding to those in the figures already described are indicated by the same reference numbers, shows a system 1 which can also be used to determine the rate of feed of thread F along the X axis (or at right angles to the Y axis).

[0081] With regard to an embodiment of this kind, it is known that anomalies relating to a physical characteristic of a thread (for example, its diameter or fineness) are usually monitored on the basis of predetermined monitoring parameters or values such as a percentage and a length.

[0082] For example, the presence of a knot will be detected through a 50% increase in fineness over a 1 mm length of thread.

[0083] This means that a monitoring unit (such as unit 8) which checks the characteristics of the thread must operate on the basis of a suitable algorithm that is also based on knowledge of the rate at which the thread is fed so that it is possible to calculate in real time how long a detected anomaly in the thread needs to last so as to have a monitored thread length of 1 mm.

[0084] Again, in the system to which the present invention relates, it is therefore of maximum importance to be able to determine the speed of the thread as it is fed to the textile machine reliably, in real time, and as accurately as possible.

[0085] One of the advantages of being able to calculate the speed of the thread in real time is that in this way speed is no longer included in the group of parameters that have to be programmed to monitor feed of the thread to the textile machine. Also the system succeeds in keeping the monitoring threshold independent of the speed of the machine, ensuring measurement of the length needed to evaluate the anomaly in fineness and/or the diameter of the thread even during acceleration or deceleration stages or in cases where the operator changes the process speed.

[0086] The speed signal may also be used as a synchronisation signal to enable or disable monitoring, for example monitoring enabled at above 300 metres/minute.

[0087] In this way, knowledge of the speed makes the system completely independent, but it is does not require any synchronisation signal with the machine and from the machine.

[0088] According to the variant of the invention in question speed is determined by comparing the signals generated by a pair of analog parts 3A and 3B present in sensor 2 located on and operating along the X axis. Knowing the distance between said analog parts, and determining the delay in detection time for a particular characteristic of the thread (for example, a hair, a change in diameter or other characteristic) it is possible to determine the rate at which the thread is fed, using the known mathematical formula linking time, distance and speed. The most robust known technique for such determination comprises calculating the correlation function between the two analog signals, which will show a peak corresponding to the delay in detection time in the situation in which the thread has minimal surface defects.

[0089] In any event, only the data from an analog part out of the two parts 3A and 3B of sensor 2 are used to detect the characteristic of the monitored thread (according to what has been said in relation to FIGS. 2 and 3).

[0090] Various embodiments of the invention have been described. Others are however possible, such as that which provides for the use of two different sensors (always associated with a single supporting body), each having its own LED and its own detector part, a first sensor operating in analog mode (photodiode) and the other sensor in digital mode (CMOS or CCD). Again in this case, however, the signal from the “digital sensor” is used to calibrate the signal emitted by the “analog sensor” (with reference to the nature of the detector part) before the time when monitoring unit 8 determines whether the value of the monitored characteristic is acceptable (that is within predetermined parameters) or not.

[0091] These variants, which are capable of providing a sensor that can be used in a system operating in accordance with the method described to solve the technical problems mentioned above, also have the characteristics mentioned in the following claims.