Technical field

The invention relates to a method for the continuous measurement of the cohesive forces of roving or a similar fiber bundle, during which running roving in a drafting zone is acted upon by constant draft, whereby axial resistive force is induced in the roving in the area of drafting acting against the drafting, whereby in the area of the action of the axial resistive force the roving trajectory is deflected from a straight-line path by a contact member of a force sensor upon which the roving acts by a transverse force, which is measured.

The invention also relates to a device for the continuous measurement of the cohesive forces of roving or a similar fiber bundle, which comprises at least one drafting zone formed between a feeding device of roving and a draw-off mechanism of roving, whose driving rollers are coupled to individual drives for setting and inducing constant draft of roving in the drafting zone, and a contact member of a force sensor which extends to the path of roving between the feeding device and the draw-off mechanism and which deflects the roving trajectory from a straight-line path, whereby the force sensor serves to measure the transverse force, by which the roving acts upon the contact member of the force sensor.

Background art

During ring spinning, the roving being fed is first mechanically attenuated and then twisted. In order to produce high quality yarn, it is necessary to provide high quality roving characterized by a high level of fiber separation and fiber parailization, as well as a low value of linear mass unevenness.

As during conventional ring spinning, roving is first mechanically drawn through high draft, for example as many as sixty times, and the required largest possible uniformity of mutual displacement of the roving fibers depends on the uniformity of the forces acting between the fibers or between fiber bundles, naturally the smallest possible fluctuation in the cohesive forces of the roving is required as well. One of the control techniques for finding out the quality of roving is a technique that has been used for centuries - namely the measurement of the cohesive forces of roving on a testing tearing machine. The result of the measurement is a diagram of the dependence of the cohesive forces on a relative elongation of the roving, which has a characteristic climax, corresponding to the maximum cohesion of the roving sample being measured.

The disadvantage of this method for measurement is the discontinuity of measurement, consisting in the repeated clamping of samples of a defined length in a testing machine, as well as the fact that it is especially the properties of the least cohesive spot of the sample being tested that are found by measuring. If there is only one such spot and, moreover, if it is considerably different from the rest of the roving sample, we are not able to find virtually any information about the remaining part of the sample. Moreover, discontinuous measurement is labor-intensive and therefore not very effective.

That is why there is a tendency to measure the cohesive forces between the fibers of roving continuously.

DE 19538142 A1 describes an embodiment of a measuring device in which roving is guided between two pairs of rollers, whereby the draw-off speed of the second pair is larger than the feeding speed of the first pair. In the middle of the path between the pairs of rollers the roving is supported by a measuring device with a supporting tensioning roller, and thus the path of the roving forms legs of a triangle. The disadvantage is the drafting and measuring a long section of the roving - 0.5 m long and longer, which also leads to detecting the least cohesive spot of the measured section of the roving, as it is during the discontinuous measurement on a tearing machine. Due to the great weight of the device and low stiffness of its mechanical part, the measuring system has its own very low frequency, which does not enable to measure the fluctuation in the size of the cohesive forces on short sections of the roving, nor does it enable to conduct high-speed measurement.

The measuring system according to FR 2651888 B1, due to a higher stiffness of the sensing means, has a slightly higher frequency. However, the disadvantage is a large moving mass of the roller pair with a mechanism for deriving their pressure. The result is a low frequency of the individual measurements of the force (sampling), which leads to a great length of the roving between the two measurements, since it holds true that this length is inversely proportional to the frequency of measurement. Furthermore, elongation and measurement is also conducted on a long section of the roving, but with the disadvantages that have been described above.

According to CZ187253B1 the measurement of the cohesive forces in roving is conducted by combing the end of the roving fed continuously through a rotating shaped metallic roller, whereby it is the resistance to the combing of thefibers in the roving that is measured. What is measured is the mutual interaction of the metallic teeth of the combing roller and the fibers at a high relative speed of the roller circumference, which amounts to approximately 20 m/s. The primary purpose of the device is to find the force necessary for slackening a fiber bundle during spindleless spinning. The total resistive force is the sum of several force components, whereby the cohesive force between the fibers constitutes only one less significant part. Nevertheless, this measurement cannot characterize roving as a linear formation in terms of fluctuation in the cohesive forces between the fibers of roving along its length.

The aim of the invention is to eliminate or reduce the drawbacks of the background art, especially to achieve more accurate localization of the less cohesive regions of roving.

Principle of the invention

The goal of the invention is achieved by a method for continuous measurement of the cohesive forces of roving, whose principle consists in that deflection of the roving trajectory from a straight-line path by a contact member of a force sensor is performed inside a drafting zone at the shortest possible distance from rollers of a feeding device and the length of the drafting zone is selected to be a little greater than the length of the longest fiber in the roving, whereby the axial resistive force during constant drafting is determined from the size of the transverse force measured by the force sensor by means of a suitable calibration and changes in this axial resistive force are determined from the changes in the size of the transverse force during constant drafting, whereby the axial resistive force is equal to the sum of the cohesive force of the roving, which is to be determined, and the force needed to straighten not completely straightened or mutually interwoven fibers, whereby the first force is substantially greater than the other, because also the number of fibers that are parallel to each other in the roving cross-section is considerably higher than the number of fibers that are not parallel to each other. Therefore, hereinafter, the force being measured will be considered as equal to the cohesive tensile force of the roving.

Shortening the drafting zone and placing the point of deflection of the roving trajectory from a straight-line path by a contact member of the force sensor to the vicinity of the rollers of the feeding device enables to detect a region with smaller cohesion significantly more accurately than when applying the hitherto known and used method with a long drafting zone of a typical length in tens of centimeters.

The calibration of the force sensor is performed by the passage of yarn, which is formed from the same material as is or will be the material of the measured roving, through the drafting zone, which is arranged vertically, whereby the yarn is loaded by calibration weight which is lowered at a constant speed, the speed being equal to the size of the input speed of the roving into the drafting zone, by which the roving will be measured, whereby the transverse force measured by the force sensor, which acts upon the contact member of the force sensor is directly proportional to the force exerted by the calibration weight.

Preferably, calibration can be performed for different speeds of yarn corresponding to the expected input speeds of the roving into the drafting zone and for different materials of the roving.

To perform specifically the method according to the invention, it is advantageous if the length of the drafting zone is by 5 - 15 mm greater than the length of the longest fiber in the roving.

More accurate results are obtained by measuring the cohesive forces in two or more drafting zones arranged in series. The principle of the device according to the invention consists in that the contact means of the force sensor is located at the beginning of the drafting zone as close as possible to the rollers of the feeding device of the roving out of a possible contact with them and out of the straight-line path between the feeding device and the draw-off mechanism, is embraced by the roving and serves to deflect it from a straight-line path.

The individual drive of the feeding device is then preferably coupled to its own control unit, whose output and that of the force sensor are connected to an analyzer, whereby the drive of the feeding device, the drive of the draw-off mechanism and the analyzer are coupled to a computer, comprising a program for collecting the measured data for the evaluation of the results of the measurement of the cohesive forces of a fiber bundle, as well as for controlling the motors of the drives of the drive rollers of the feeding device and the draw- off mechanism of the roving. Further advantages and features result from the other dependent claims for the device.

Description of drawings

An exemplary embodiment of the device according to the invention is schematically represented in the enclosed drawings, where Fig. 1 represents a diagram of the drafting zone with a pair of input and output rollers, a contact member of the force sensor and the measured fiber bundle, which is being drafted through the zone, Fig. 2 represents a cross-section C-C through the drafting zone according to Fig. 1 , Fig. 3 shows a diagram of an exemplary embodiment of mutual interconnection of drive motors blocks, their power supply and control, a force sensor, an analyzer for data collection and analysis and an external computer for controlling the motors, displaying the measured data and the results of the computational analyses in an arrangement of a device with one drafting zone, Fig. 4. shows an arrangement of two or more drafting zones following one another, whereby the second illustrated drafting zone has the same sense of curvature of the path of a fiber bundle as the first zone, Fig. 5. shows an arrangement of two or more drafting zones following one another, whereby the second illustrated drafting zone has a reverse sense of curvature of the path of a fiber bundle than the first zone and Fig. 6 illustrates the calibration of the device with one drafting zone.

Examples of embodiment

In an exemplary embodiment of a device for continuous measurement of the cohesive forces of a fiber bundle according to Figs. 1 to 3, a drafting force is formed in a manner similar to a ring spinning machine. Roving 3 is carried from an unillustrated supply package in the direction x to the drafting zone 4 by a feeding device 1 comprising a pair of feeding rollers 11, 12, whereby the driving feeding roller 1 is coupled to an individual drive 13, composed of a stepper motor or other suitable type of motor.

In a preferred embodiment, the driving feeding roller 1! has a grooved or knurled surface and the pressure feeding roller 12^ which is pressed against it by the driving feeding roller in a known unillustrated manner, is provided with a rubber coating. The roving 3 is withdrawn from the drafting zone 4 by a draw- off mechanism 2 comprising a pair of draw-off rollers 21, 22, whereby the driving draw-off roller 21 is coupled to an individual drive 23, composed of a stepper motor or other suitable type of motor. The driving draw-off roller 2J. and the pressure draw-off roller 22 are made similarly to the rollers H, 12 of the feeding device . In the illustrated embodiment, the individual drive 13 of the driving feeding roller is coupled to its own control unit 131 ^ar| d power unit 132. The individual drive 23 of the driving draw-off roller 21 is also coupled to its own control unit 23J. and power unit 232. The control unit 13_1 of the individual drive 13 of the driving draw-off roller H is connected to an analyzer 6, to which is connected also the output of the force sensor 42, whose contact member 41 is arranged between the feeding device 1 and the draw-off mechanism 2 in the path of the roving 3, which is deflected from a straight-line path between the feeding device 1 and the draw-off mechanism 2 by the contact member 4J_. The contact member 4J_ is located as near as possible to the gripping point of the pair of feeding rollers H, 12, that is in the wedge formed by the surfaces of the feeding rollers H, 12, facing the drafting zone, so that by the contact with the roving 3 it would reduce to the smallest possible extent the influence on the mutual displacement of the fibers, which occurs in the drafting zone 4 in front of the draw-off mechanism 2. In an illustrated embodiment, the force sensor 42 is composed of a tensiometer sensor and the contact member 41 is formed by a pin mounted in the tensiometer sensor. The force sensor 42 may also consist of, for example, a capacitive or inductive force sensor, whereby the sensor is always provided with a mechanical part, which changes the trajectory of the roving 3.

The control unit 131 of the individual drive 13 of the driving feeding roll V\ , the control unit 231 of the individual drive 23 of the driving of the draw-off roller 21 and the analyzer 6 are connected to an external computer 7.

The longitudinal axis of the contact member 41 of the force sensor 42 is parallel to the axes of rotation of the rollers 11, 2, 21, 22. The path along which the roving 3 moves within the drafting zone 4 is curved on the circumference of the contact member 41 , the part of the path in front of the contact member 41 corresponds in the illustrated embodiment to the direction of the feed of the roving 3 in front of the feeding rollers 11 , 12 and forms with a part of the path behind the contact member 41 the angle , which is at the same time the angle of the embracement of the contact member 41. With respect to the location of the contact member 41 it is advantageous if its diameter is as small as possible, since a thinner contact member 41 can be placed nearer the gripping point of the input pair of the feeding rollers 11_, 12 and, at the same time, a thinner contact member 41_ has a smaller weight, which leads to an increase in the frequency of the force sensor 42. However, it is necessary to take into account the fact that a thin contact member 4J. bends more, which brings a danger of its contact with the lower metallic driving feeding roller 1JL Therefore the diameter of the contact member 4J. is optimized on the basis of its gir and bending stiffness (Young's model of flexibility).

The outer diameter of the contact member 41 of the force sensor 42 therefore ranges from 4 to10 mm, in an exemplary embodiment it is preferably 5 mm. The angle a is selected as small as possible, so that the roving 3 measured would be affected by the contact member 41 as little as possible, but, at the same time, would be proportional to the sensitivity of the force sensor 42 and would range from 1° to 40°, preferably from 10° to 20°. When using the tensiometer sensor, the force sensor 42 is adjustable by turning about the longitudinal axis of the contact member 41 in such a manner that the measurement would correspond to the direction of the resultant of the forces, by which the roving 3 acts upon the contact member 41. In this arrangement, the tensiometers provide the largest signal.

The tensiometer force sensor 42 has its own frequency - at least 1000 Hz, preferably higher, such as in the range from 1300 to 2000 Hz.

Behind the pair of feeding rollers 21 , 22 is arranged a suction nozzle 5 of the roving 3, which ensures sucking off the whole voiume of the roving 3 after its passing through the drafting zone 4 , thus preventing the fibers from embracement around the draw-off rollers 21 and 22 or from accumulating in the vicinity of the device.

The length L of the drafting zone 4 of the roving 3 is defined by the gripping points of the roving 3 between the pair of feeding rollers 11 and 12 and the pair of draw-off rollers 21 and 22 and in Fig. 1 is emphasized with a thick line.

The rollers 11. and 12 of the feeding device 1 , the rollers 21. and 22 of the draw-off mechanism 2, as well as the contact member 41 of the force sensor 42 are adjustably arranged on an unillustrated frame of the device. It is possible to change the length L of the drafting zone 4 and the angle a of the embracement of the contact member 41 of the force sensor 42 by a mutual change of their position. Changing the angle of the embracement of the contact member 41 results in a change in the size of the radial force by which the roving 3 acts upon the contact member 4J of the force sensor 42. By the mutual displacement of the axes of the rollers 11, 12 of the feeding device 1 it is possible to achieve the off-setting of the axes SI of the rollers 11, 12 and, in case of need, change them. Similarly, it is possible to achieve the off-setting of the axes S2 in the case of the rollers 21, 22 of the draw-off mechanism 2 by their mutual displacement and, in case of need, change it.

An important feature of the device is a very short drafting zone 4, the high sensitivity of the force sensor 42, as well as the fact that its own frequency is high. The length L of the drafting zone 4 is only slightly greater than the length of the longest fibers contained in the roving 3 which is being monitored. Generally, the length L is selected to be greater by 5 - 15 mm than the maximum length of the fiber in the monitored roving 3. Also, a small distance of the contact member 41 on which the running roving 3 is bent from the place of the mutual contact of the feeding rollers 11, 12 is of great importance. Therefore, it is possible to localize the less cohesive spot of the roving with the aid of the device according to the invention with significantly greater accuracy.

During the measurement, the draft of the roving 3 is set by the independent setting of its input speed VI by the feeding device Λ and of the output speed V2 by the draw-off mechanism 2 by means of the individual drives 13 and 23 _j whereby the running roving 3 is in the drafting zone acted upon by constant draft, as a result of which in the roving 3 in the area of the draft a resistive force against this draft is induced. In the area of the action of the axial resistive force, the roving 3 is deflected from a straight-line path by the contact member 41_ of the force sensor 42, which is acted upon by the roving 3 with a transverse force, which is measured. The ratio V2/V1 characterizes the draft size B of the roving 3 and the difference V2-V1 characterizes the drafting speed r of the roving 3. The angle g is selected as small as possible, by which means it is possible to achieve a small extent of influencing the mutual displacement of the fibers, which occurs in the drafting zone 4 in front of the draw-off mechanism 2.

The speeds V and V2 are measured by the control impulses of the stepper motors, which usually constitute the individual drives 13, 23, as has been stated above, the draft being determined from the ratio of the control impulses of the drive 23 of the draw-off mechanism 2 and the control impulses of the drive 13 of the feeding device 1- Nevertheless, the speeds VI and V2 can be measured also in a different manner, for example by means of incremental sensors - either external or built-in in the motors. Deflection of the roving occurs at the shortest possible distance from the rollers 1 , 12 of the feeding device and the length L of the drafting zone 4 is selected slightly longer than the length of the longest fiber in the roving 3. The cohesive force between the fibers of the roving 3 is determined by computation from the size of the transverse force on the basis of the calibration of the force sensor 42, the changes in this cohesive force being determined from the changes in the size of the transverse force during constant draft.

The method according to the invention will become more accurate if measurement is conducted in two drafting zones 4 connected in series. The measurement conditions in this method are very close to the conditions of drafting the roving during actual ring spinning.

The device can be supplemented with another sensor or other sensors (not shown), detecting a previously identified specific spot on the roving 3 or more spots on the roving 3 and enabling repeated measurement and analysis of the cohesive forces of the roving 3 during repeated passages of the same sample of the roving 3 connected, for example, into a closed loop. That allows obtaining further information about the cohesive forces of a fiber bundle being tested and indirectly also about its structure.

The calibration of the force sensor 42 is carried out very accurately by means of weight 8 hung on yarn 30 which is inserted in the device and made from the same material as the roving 3 measured, as is shown in Fig. 6. The drafting zone 4 is for the calibration arranged in a vertical position of the yarn 30 which is withdrawn. The yarn is held between the feeding rollers 11., 12, which rotate at a speed equal to the speed of feeding the roving during the measurement. The yarn 30 is bent over the contact member 41 by weight 8 and is drawn between the opened draw-off rollers 21_, 22, whereby in the illustrated embodiment it touches the driving draw-off roller 21., which either stands or rotates, whereby in a preferred embodiment it rotates at the same speed as the feeding rollers 1_1 , 12. In an alternative embodiment, the driving draw-off roller 21 rotates at the same speed as during the measurement of the roving 3. The sensor 42 measures the transverse force, which acts upon its contact member 41. This transverse force measured during the calibration is proportional to a force exerted by the calibration weight. The ratio of these forces is regarded as a calibration constant. During the subsequent measurement of the cohesive forces of the roving 3 _j the radial force measured by the force sensor 42 is converted by this calibration constant into the cohesive force of the roving.

During the calibration yarn moves at a constant speed, which is identical to the speed of feeding of the roving 3 during the measurement. This is important with respect to the compensation of the frictional effects of the fibers of the roving 3 in contact with the surface of the contact member 41 of the force sensor 42 on which the running roving 3 is bent.

If more measurements of the cohesive forces of the roving are expected to be conducted at more speeds of feeding, it is advantageous to perform the calibration for each expected speed of measurement and the calibration values measured can be connected into a curve in a graph, which defines the parameters of the calibration relationship.

The calibration is carried out similarly also in the case of a change of the material measured in the roving. Calibration curves for different materials can be prepared in advance.

The solution according to the invention also includes software for controlling the individual drives 13 and 23 of the feeding device 1 and of the draw-off mechanism 2, the device for collecting and displaying the measured data, for computer analyses and displaying their results. For this purpose, a system consisting of an analyzer 6 with a computer 7 is used.

In an exemplary embodiment, the setting and controlling of the drives 13 and 23 is performed from the external computer 7, for example via a USB connection or serial line. The measurement of the force by which the roving 3 acts upon the contact member 41 of the tensiometer force sensor 42 is performed in such a manner that a rectangular signal from the control unit 131 of the individual drive 13 of the feeding device 1 and an analog signal from the force sensor 42 are introduced into a specially designed analyzer 6, in which the signal of the force sensor 42 is discretized by the rectangular signal and digitized and processed by an analog-to-digital converter. The digital file thus obtained is brought, for example, via a USB connection, to the external computer 7 for storage on a suitable storage medium, for continuous displaying the data being loaded and for the subsequent analytical processing and displaying of the results.

The device according to the invention can be modified by series connection of two or more drafting zones 4, which is indicated in Figs. 4 and 5. The information about the analyzed roving 3 is in this case more plentiful and provide more details. The draw-off mechanism 2 of the preceding drafting zone 4 is at the same time the feeding device Y_ of the following drafting zone etc., whereby the angles , 2, ...of the embracement of the contact member 41, the off-setting Si, S2, S3, ...of the rollers, the drafts gl, p_2, ... may vary. In the device according to Fig. 4, the paths of the roving 3 of the drafting zones 4, < have mutually the same sense of curvature. In the device according to Fig. 5 the paths of the roving 3 of the drafting zones 4, 4^ have a mutually reverse sense of curvature.

Such devices enable to obtain more detailed information about the cohesive force of the measured roving, and, what is more, the measuring apparatus with two drafting zones is more similar to the actual drafting device of a ring spinning machine, in which it is known that preliminary draft, represented in the measuring apparatus by the first drafting zone, has a positive influence on the quality of the resultant draft of the roving.

Industrial applicability

Both the method and the device according to the invention can be used for the continuous measurement of the cohesive forces of fibers in rovings which are to be further processed, especially on ring spinning machines or for the continuous measurement of the cohesion of fibers of textile strands.

List of references

1 ,1 ', 1 " feeding device

11 driving feeding roller

12 pressure feeding roller

3 the individual drive of the driving feeding roller

131 control unit of the individual drive of the driving feeding roller

132 power supply unit of the individual drive of the driving feeding roller 2, 2',2" draw-off mechanism

21 driving draw-off roller

22 pressure draw-off roller

23 the individual drive of the driving draw-off roller

231 control unit of the individual drive of the driving draw-off roller

232 power supply unit of the individual drive of the driving draw-off roller

3 roving

30 yarn for hanging calibration weight

4, 4 ^' drafting zone

41 contact member of the force sensor

42, 42 ^' force sensor

5 suction nozzle

6 analyzer

7 computer

8 calibration weight

L length of the drafting zone

p1 ,p2 draft size

r drafting speed

51 off-setting of the axes of the rollers of the feeding device

52 off-setting of the axes of the rollers of the draw-off mechanism/of the feeding device of the next drafting zone

53 off-setting of the axes of the rollers of the draw-off mechanism of the next drafting zone

V1 input speed of a fiber bundle

V2 output speed of a fiber bundle

a, a1 ,a2 angle of the embracement of the contact member of the force sensor