Stock-controlling method for a storage yarn feeder with rotary drum

Abstract

A yarn feeder is provided with a drum which is driven to rotate by a motor controlled by a control unit for drawing yarn from a reel and winding it upon itself in the shape of loops forming a stock. The control unit estimates the stock on the drum on the basis of an information indicative of the amount of yarn which is unwound from the drum upon request from a downstream machine, and of an information indicative of the amount of yarn which is wound on the drum, and retroactively controls the motor to substantially stabilize the stock on a reference value. The control unit also performs a parallel correction routine in which compares the stock with the reference value to estimate a stock status RES<REF_RES or RESREF_RES, wherein RES is the estimated stock and REF_RES is the reference value.

Claims

1. A stock-controlling method for a storage yarn feeder, said yarn feeder being provided with a drum which is driven to rotate by a motor controlled by a control unit for drawing yarn from a reel and winding it upon itself in the shape of a plurality of loops forming a stock, in which said control unit: estimates the stock on the drum on the basis of an information indicative of the amount of yarn which is unwound from the drum upon request from a downstream machine, and of an information indicative of the amount of yarn which is wound on the drum, and retroactively controls said motor to substantially stabilize said stock on a reference value, wherein said control unit also performs a parallel correction routine in which: compares said stock with said reference value to estimate a stock status
RES <REF_RES or RES >REF_RES, wherein RES is said estimated stock and REF RES is said reference value, compares said estimated stock status with a presence signal generated by sensor means adapted to generate an absolute binary information indicative of the presence/absence of yarn in a monitored area of the drum, and in case of an inconsistency between said estimated stock status and said presence signal, said control unit corrects said stock so that it converges toward said monitored area of the drum.

2. The method of claim 1, wherein, when correcting the stock, said control unit either adds or subtracts a correction value from said reference value, depending on whether said sensor means respectively indicate a presence of yarn or an absence of yarn in the monitored area.

3. The method of claim 1, wherein, when correcting the stock, said control unit either adds or subtracts a correction value to the estimated stock, depending on whether said sensor means respectively indicate a presence of yarn or an absence of yarn in the monitored area.

4. The method of claim 1, wherein said correction value corresponds to a minimum length of yarn which can be wound on or unwound from the drum in a controlled and a measurable manner.

5. The method of claim 1, wherein the processing frequency of said parallel correction routine corresponds to the processing frequency at which said control unit retroactively controls said motor.

6. The method of claim 1, wherein the amount of yarn wound on the drum is calculated based on a speed of rotation or a position of the motor.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The disclosure will be now described in more detail with reference to a few preferred, non-exclusive embodiments shown by way of non-limiting example in the attached drawings, wherein:

(2) FIG. 1 is a diagrammatical view in side elevation of a storage yarn feeder of the type to which in the present disclosure refers; and

(3) FIG. 2 is a flowchart describing the stock-controlling method according to the disclosure applied to a yarn feeder as shown in FIG. 1.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

(4) With initial reference to FIG. 1, a storage yarn feeder 10 comprises a drum 12 having a plurality of loops of yarn Y wound thereon, which are adapted to be unwound upon request from general textile machine M arranged downstream. While the yarn is unwound from drum 12, the latter is driven to rotate by a motor 14 to draw fresh yarn from a reel R and wind it upon itself in the form of new loops.

(5) A control unit CU is programmed to control motor 14 in such a way as to stabilize the stock on the drum on a predetermined, optimum level, on the basis of the method described hereinafter.

(6) In a way known per se, the method provides estimating the stock RES stored on drum 12 on the basis of both the amount of yarn delivered, which is measured by sensor means 15 which are adapted to count the number of loops or portion of loops which are unwound from the drum, and the amount of yarn loaded, which is calculated, e.g., on the basis of the speed of rotation and/or the position of motor 14; and then, controlling by feedback the rotation of motor 14 in such a way as to maintain stock RES substantially constant and equal to a reference value REF_RES. Such control by feedback may be conventionally carried out, e.g., by a PID controller or the like, which is adapted to minimize the error RES_PID resulting from the difference between the reference value and the estimated amount, i.e.:
RES_PID=REF_RESRES

(7) In addition, the method according to the disclosure provides performing a correction routine, parallel to the control by feedback, which is shown in FIG. 2 and comprises the steps of: comparing the estimated amount of stock RES with the reference amount of stock REF_RES in order to obtain a stock status, i.e.,
RES<REF_RES or RESREF_RES, comparing said stock status with a signal generated by presence sensor 16 associated to drum 12, which is adapted to generate an absolute binary information RES_PRES indicative of the presence/absence of yarn in a predetermined area of drum 12 delimiting an optimum stock (e.g., presence of yarn, RES_PRES=1; absence of yarn, RES_PRES=0), and in case of inconsistency of the two items of information (e.g., RES<REF_RES and RES_PRES=1 (block 100) or RESREF_RES and RES_PRES=0 (block 300)) correcting the estimated stock RES in such a way that the stock converges towards the area of drum 12 monitored by presence sensor 16.

(8) The inconsistency between the calculated stock status, which results from the comparison between the estimated amount of stock RES and the reference amount of stock REF_RES, and the measured stock status, which is measured by presence sensor 16, is indicative of the fact that the feeder tends to an overloading/emptying condition which is not compensated by the control loop.

(9) Therefore, with the method according to the disclosure, as this situation of inconsistency occurs, error RES_PID input to PID controller 500 is corrected in such a way as to compensate for such effect and avoid drift phenomena.

(10) In particular, as shown in FIG. 2, with the correction of the amount of stock RES, a correction factor DRES is added to (block 200), or subtracted from (block 400), reference value REF_RES, depending on whether presence sensor 16 indicates presence (block 100) or absence (block 300) of yarn in the monitored area respectively.

(11) Preferably, correction factor DRES corresponds to a single winding pulse. A winding pulse is regarded to as the minimum length of yarn which may be wound/unwound on/from the drum in a controlled and measurable way, in terms of loop or portion of a loop. For instance, with a winding sensor provided with three photoelectric cells equally-spaced about the axis of the drum, such minimum length is of a loop.

(12) The above situation that the amount of stock converges towards the area of the drum monitored by presence sensor 16, occurs regardless of the initial condition of the stock. Therefore, an initial loading procedure is not required.

(13) Preferably, the correction routine operates at a frequency corresponding to the frequency of processing of the PID control loop, e.g., 100 Hz.

(14) With an alternative embodiment of the disclosure, the estimated amount of stock RES (blocks 200 and 400) is corrected incrementally by a predetermined correction factor DRES, according to the following formulas:
RES=RES+DRES (block 200) or RES=RESDRES (block 400).

(15) A few preferred embodiments of the disclosure have been described herein, but of course many changes may be made by a person skilled in the art. For instance, in estimating the amount of stock, the condition RES=REF_RES is arbitrarily associated to the condition RES>REF_RES but, of course, it could be associated to the condition RES<REF_RES in a completely equivalent manner. Moreover, although the amount of yarn loaded is calculated on the basis of the speed of rotation and/or the position of the motor in the above-described embodiments, in a way known per se it could also be measured by sensor means, similarly to the measurement of the amount of yarn unwound.