METHOD FOR CONTROLLING THE CONSUMPTION RATE OF A YARN BEING UNWOUND FROM AN ACCUMULATION FEEDER TOWARD A TEXTILE MACHINE, AND APPARATUS FOR CARRYING OUT SUCH METHOD

Abstract

 The yarn tension is stabilized on a reference tension (T_ref) by a weft braking device (20) driven by a control unit (CU) that receives a measured tension signal (T_meas) from a tension sensor (22). The yarn consumption rate (YS_meas) is continuously measured and is continuously compared with a reference rate (YS_ref). If the difference between the yarn consumption rate (YS_meas) and the reference rate (YS_ref) falls within a predefined error range that indicates that the machine is operating with constant consumption, then adjust the reference tension (T_ref) so as to minimize the difference between the yarn consumption rate (YS_meas) and the reference rate (YS_ref), otherwise disable the adjustment of the reference tension (T_ref).

Description

[0001] The present invention relates to a method for controlling the consumption rate (m/sec) of a yarn being unwound from an accumulation feeder toward a textile machine, particularly a circular knitting machine, and an apparatus for carrying out such method.

[0002] As is known, a generic circular knitting machine can be fed by a plurality of yarns that are unwound from respective yarn feeders known as "accumulator feeders".

[0003] A generic accumulator yarn feeder comprises a drum on which winding means wind a plurality of yarn loops which form a reserve. Such winding means can consist of a motorized flywheel that winds the yarn on the drum, or the drum proper can be rotated in order to wind the yarn onto it. The yarn is taken from a distaff upstream and passed on to the textile machine downstream on request therefrom.

[0004] EP2031106B1 discloses how to control the yarn tension being unwound from the drum so as to keep it substantially constant. To this end, a tension sensor arranged downstream of the feeder detects the yarn tension and sends it to a control unit. The control unit drives, in feedback, means for braking the yarn so as to stabilize the tension on a preset value.

[0005] As is known, some applications also require that the machine always receives the same quantity of yarn over time. However, such requirement conflicts with the adjustment of the yarn tension, since modulating the braking varies the speed of the yarn passed to the machine and, as a consequence, the consumption of yarn.

[0006] To solve such drawback, where possible, it is known to measure the quantity of yarn unwound by the feeder and correspondingly adjust the "knit triangles" of the textile machine (i.e., the strokes of the needles), so as to compensate the yarn rate variations.

[0007] However, such solution can not be applied on large-diameter knitting machines for reasons of cost and encumbrance, given the high number of knit triangle controllers that would be needed. In these machines, therefore, only the yarn tension is controlled, e.g., by way of the method disclosed in the above mentioned EP2031106B1.

[0008] In Jacquard large-diameter knitting machines, where the yarn consumption is continuously modulated (as much as 30-50%) in order to provide complex patterns, the lack of control of the yarn consumption rate does not lead to problems, because the pattern hides any defects generated by uncontrolled consumption.

[0009] However, some types of knitting alternate variable consumption steps with constant consumption steps. In knitting steps with constant consumption, the lack of control of the yarn consumption rate produces defects on the finished garment, in the form of "stripes".

[0010] Furthermore, the above solution is not applicable to older or less expensive knitting machines (e.g., the machines for stockings) which do not allow adjustment of the knit triangles.

[0011] However, as is known, the adjustment of the yarn consumption rate would be desirable on these machines also, especially in knitting steps with constant consumption, both to eliminate defects in the garment, and especially to ensure the repeatability of the size between one garment and the next.

[0012] Therefore, the aim of the present invention is to provide a method for controlling the consumption rate of a yarn being unwound from an accumulation feeder toward a textile machine, which can be adopted practically and economically, including on existing knitting machines without adjustment of the knit triangles, in particular, large-diameter knitting machines and machines for stockings, as well as to provide an apparatus for carrying out such method.

[0013] The above aim and other advantages, which will become more apparent from the description that follows, are achieved by the method having the characteristics recited in claim 1, and by the apparatus having the characteristics recited in claim 10, while the dependent claims define other characteristics of the invention which are advantageous, although secondary.

[0014] Now the invention will be described in more detail, with reference to a preferred but not exclusive embodiment thereof, which is illustrated for the purposes of non-limiting example in Fig. 1, which is a schematic diagram of a textile machine that receives yarn from an accumulation feeder by way of the method according to the invention.

[0015] With reference to Fig. 1, a weft feeder 10 for textile machines comprises a fixed drum 12 and a flywheel 14, which is driven by a motor 15 in order to take yarn F from a distaff 16 and wind it on the drum 12 in the form of loops which form a reserve. The yarn F is unwound from the drum 12 on request from a generic textile machine downstream, advantageously a circular knitting machine 17.

[0016] The quantity of reserve on the drum 12 is controlled by a triplet of sensors. A first sensor S1, preferably a Hall probe, detects the passage of magnets like M which are integral with the flywheel 14 in order to determine the quantity of yarn wound on the drum and the winding speed. A second sensor S2, preferably a mechanical sensor, provides a binary information item on the presence or otherwise of a minimum reserve quantity at an intermediate region of the drum 12. A third sensor S3, preferably an optical sensor, generates a pulse UWP for each yarn loop unwound from the drum.

[0017] Arranged downstream of the weft feeder 10 is a weft braking device 20 driven by a control unit CU which is programmed to stabilize the yarn tension being unwound from the drum 12 on a preset value by way of a feedback control loop.

[0018] To this end, arranged downstream of the weft braking device 20 is a tension sensor 22 which is adapted to measure the tension of the yarn F being unwound from the drum and to generate a corresponding measured tension signal T meas.

[0019] The control unit CU comprises a tension control block CT which is programmed to compare the measured tension signal T_meas with a reference tension T_ref which represents the desired tension, and consequently generate a braking signal BI for the weft braking device 20 which is such as to minimize the difference between the measured tension and the reference tension.

[0020] In a manner that is conventional per se, the control unit CU of the feeder is connected to the knitting machine 17 by way of a bus 30 for the mutual exchange of information such as the speed of the machine, alarms, statuses, and setting of parameters.

[0021] There is further a system for detecting accidental stoppages of the yarn.

[0022] In particular, under normal operating conditions, the feeder 10 receives a pulse UWP from the sensor S3 for each turn unwound from the drum 12. Since the yarn drawing rate at a given rotation speed of the downstream machine is almost constant, under normal conditions the intervals between successive pulses will vary only to a negligible extent. But if the time elapsed since the most recent pulse appreciably exceeds the average interval, then the machine will shut down as this points to the possibility that the weft has undergone an accidental stoppage, either owing to the breakage of the yarn or owing to the loss of the yarn by the needles of the machine 17. For more details on such system for detecting accidental stoppages of the yarn, which lies outside the aims and objects of the present invention, reference is made to EP2031106B1.

[0023] In order to exactly stabilize the yarn consumption rate in the steps in which the machine operates with constant consumption, a method is applied which, according to the invention, comprises the following steps:

• continuously measuring the consumption rate YS meas of the yarn drawn by the machine 17,
• continuously comparing the consumption rate YS_meas with a reference rate YS_ref,
• if the difference between the consumption rate YS_meas and the reference rate YS_ref falls within a predefined error range that indicates that the machine is operating with constant consumption, then adjust the reference tension T_ref so as to minimize the difference between the consumption rate YS_meas and the reference rate YS_ref, otherwise disable the adjustment of the reference tension T_ref.

[0024] Therefore, automatically, control of the consumption rate is disabled in the steps in which the machine operates with variable consumption, in order to make complex patterns (when control of the consumption rate is substantially irrelevant), and it is re-enabled when the machine operates with constant consumption in order to produce smooth knits (when control of the consumption rate is essential in order to prevent "stripes" in the finished garment, or size discrepancies).

[0025] The consumption rate YS_meas can be advantageously calculated as the average of the unwinding speeds of the yarns by the respective feeders. For each one of the feeders, such unwinding speed can be calculated by a speed evaluation block SE as a function of the UWP pulses originating from the third sensor S3.

[0026] Preferably, the maximum allowable error YS_err which delimits, in modulus, the ends of the interval of error is established in percentage terms, e.g., 5-10%, but it could also be established in terms of difference.

[0027] The comparison between the consumption rate YS_meas and the reference rate YS_ref is carried out in a speed regulator block YSR, which consequently generates an output signal YSR_out. Such output signal YSR_out is sent to the input of the reference tension T_ref of the tension control block CT by way of a switch YSRS. The latter is closed only when the difference between the measured consumption rate YS meas and the reference rate YSref falls within the predefined error range, by way of a reactivation signal YSRS_en which is generated by the speed regulator block YSR.

[0028] Preferably, the adjustment range of the reference tension is delimited between two preset maximum values, YS_T_ref_min and YS_T_ref_max.

[0029] Furthermore, advantageously the method comprises an alarm procedure that stops the machine if the feed under limit tension conditions (YS_T_ref_min or YS_T_ref_max) lasts more than a preset maximum time.

[0030] Moreover, preferably the method comprises a further alarm procedure that stops the machine if the consumption rate YS_meas does not converge to a value close to the reference rate YS_ref within a preset maximum time.

[0031] The above alarm procedures make it possible to verify whether an anomaly has occurred in the yarn feeding process or whether an operating parameter has changed radically.

[0032] The reference tension T_ref, in steps in which the machine operates with variable consumption, preferably corresponds to the most recent output signal YSR_out set by the speed regulator block YSR.

[0033] Alternatively, the reference tension T_ref could be set to a fixed value chosen by the user.

[0034] As a further alternative, the weft braking device 20 could be locked on the most recent adjusted position of the tension controller CT.

[0035] If the machine is served by a plurality of yarn feeders, the reference rate YS_ref is advantageously calculated by way of a calibration procedure that comprises the following steps:

• disabling the consumption control loop (i.e., the switch YSRS is locked in the open position),
• setting the same reference tension T_ref on all the feeders,
• starting the machine in the portion in which it operates with constant consumption,
• asking each one of the yarn feeders for the respective yarn unwinding rate YS_meas_i, where the index i identifies the i-th feeder, which is calculated by the speed evaluation block SE as a function of the UWP pulses originating from the third sensor S3,
• calculating the reference rate YS_ref as the arithmetic mean of the yarn unwinding rates of all the feeders,
• setting each one of the feeders to the reference rate YS_ref thus calculated,
• re-enabling the consumption control loop.

[0036] Furthermore, the reference rate YS_ref can be updated continuously as a function of the speed of the machine, by way of the formula:

where YS_ref_upd is the updated reference rate, Y_ref_nom is the rated reference rate (e.g., the reference rate calculated by way of the calibration procedure shown above), V_mach is the speed of the machine and V_mach_nom is the rated speed of the machine, i.e., the measured speed of the machine under rated conditions (e.g., the measured speed of the machine during the calibration procedure shown above).

[0037] The speed of the machine, as shown above, is provided to the control unit CU by way of the bus 30.

[0038] A preferred embodiment of the invention has been described, but obviously the person skilled in the art may make various modifications and variations within the scope of protection of the appended claims.

[0039] For example, the yarn consumption rate of the i-th feeder Y_meas_i can be calculated on the basis of the pulses generated by the first sensor S1 instead of by the third sensor S3, assuming that, during operation at constant speed, the quantity of yarn unwound from the drum is equal to the quantity of yarn wound on the drum.

[0040] The disclosures in Italian Patent Application No. 102015000023117 (UB2015A001048) from which this application claims priority are incorporated herein by reference.

[0041] Where technical features mentioned in any claim are followed by reference signs, those reference signs have been included for the sole purpose of increasing the intelligibility of the claims and accordingly, such reference signs do not have any limiting effect on the interpretation of each element identified by way of example by such reference signs.

Claims

1. A method for controlling the consumption rate of a yarn being unwound from an accumulation feeder toward a textile machine, wherein the yarn tension is stabilized on a reference tension (T_ref) by a weft braking device (20) driven by a control unit (CU) that receives a measured tension signal (T_meas) from a tension sensor (22),
characterized in that it comprises the steps of:

- continuously measuring the yarn consumption rate (YS_meas),

- continuously comparing said yarn consumption rate (YS_meas) with a reference rate (YS_ref),

- if the difference between said yarn consumption rate (YS_meas) and said reference rate (YS_ref) falls within a predefined error range that indicates that the machine is operating with constant consumption, then adjust said reference tension (T_ref) so as to minimize the difference between said yarn consumption rate (YS_meas) and said reference rate (YS_ref), otherwise disable said adjustment of the reference tension (T_ref).

2. The method according to claim 1, characterized in that the adjustment of said reference tension (T_ref) is delimited between two preset maximum values (YS_T_ref_min, YS_T_ref_max).

3. The method according to claim 2, characterized in that the machine is stopped if the feeding with tension conditions equal to one of said preset maximum values lasts more than a preset maximum time.

4. The method according to one of claims 1 to 3, characterized in that said machine is stopped if the yarn consumption rate (YS_meas) does not converge to a value close to the reference rate (YS_ref) within a preset maximum time.

5. The method according to one of claims 1 to 4, characterized in that when the adjustment of the reference tension (T_ref) is disabled, the reference tension (T_ref) is set to a fixed value that corresponds to the most recent adjusted tension value.

6. The method according to one of claims 1 to 4, characterized in that when the adjustment of the reference tension (T_ref) is disabled, the reference tension (T_ref) is set to a fixed value chosen by the user.

7. The method according to one of claims 1 to 4, characterized in that when the adjustment of the reference tension (T_ref) is disabled, the weft braking device (20) is locked on the most recent adjusted position.

8. The method according to one of claims 1 to 7, characterized in that said reference rate (YS_ref) is calculated by way of a calibration procedure that comprises the following steps:

- disabling said adjustment of the reference tension (T_ref),

- setting the same reference tension (T_ref) on each one of the feeders that feed said textile machine (17),

- starting the textile machine (17) in a portion in which it operates with constant consumption,

- requesting from each one of the yarn feeders the respective yarn unwinding rate (YS_meas_i),

- calculating said reference rate (YS_ref) as the arithmetic mean of the yarn unwinding rates of all the feeders.

9. The method according to one of claims 1 to 8, characterized in that said reference rate (YS_ref) is updated continuously as a function of the speed of the machine, by way of the formula:

where YS_ref_upd is the updated reference rate, Y_ref_nom is a rated reference rate, V_mach is a measured speed of the machine and V_mach_nom is a rated speed of the machine.

10. An apparatus for controlling the consumption rate of a yarn being unwound from an accumulation feeder (10) toward a textile machine (17), comprising a weft braking device (20) which is driven by a tension control block (TC) which is programmed to stabilize the yarn tension (T_meas), which is measured by a tension sensor (22), on a reference tension (T_ref), characterized in that it comprises:

- means for continuous measurement of the yarn unwinding rate (SE),

- a speed regulator block (YSR) which is adapted to continuously compare said yarn consumption rate (YS_meas) with a reference rate (YS_ref) and to consequently generate an output signal (YSR_out), for the input of the reference tension (T_ref) of said tension control block (TC), which is adapted to minimize the difference between the rates,

- a switch (YSRS) interposed between said output signal (YSR_out) and said input of the reference tension (T_ref),which is driven to close only when the difference between the yarn consumption rate (YS_meas) and the reference rate (YS_ref) falls within a predefined error range, which indicates the fact that the machine is operating with constant consumption.

Drawing