EP4116476A1

EP4116476A1 - Motorized positive yarn feeder with selectable operating mode, and yarn feeding apparatus using the same

Info

Publication number: EP4116476A1
Application number: EP22183487.2A
Authority: EP
Inventors: Mirko Ruggeri; Giovanni Pedrini; Pietro Zenoni
Original assignee: LGL Electronics SpA
Current assignee: LGL Electronics SpA
Priority date: 2021-07-08
Filing date: 2022-07-07
Publication date: 2023-01-11
Also published as: IT202100017966A1; CN115595717A

Abstract

A motorized positive yarn feeder with selectable operating mode is provided with a motorized reel (12) having a yarn (Y) wound thereon, which picks up the yarn from a spool (S) and feeds it to a textile machine (TM); a control unit (CU) can operate selectively in a position control mode, in which it receives a position signal (θTM) from the textile machine (TM), and, on the basis of a position signal of the reel (12), it controls the position of the reel (12) in a closed loop according to a transmission ratio that can be set electronically with respect to the position of the textile machine (TM), or in a tension control mode, in which it controls the speed of the reel (12) in a closed loop on the basis of a tension signal of the yarn, so as to stabilize the tension of the yarn (Y) at a reference tension value or at a tension profile that can be set by a user.

Description

The present invention relates to a motorized positive yarn feeder with selectable operating mode, and a yarn feeding apparatus that uses it.
As is known, in a generic yarn feeding process, numerous yarns can be fed to a textile machine by respective motorized yarn feeders of the "positive" type.
This type of feeder is provided with a motorized reel, on which the yarn is wound repeatedly (e.g., 3 or 4 windings) so as to adhere to it by friction. When the reel is rotated, the yarn is unwound from a spool upstream and is fed to a textile machine downstream.
Feeders are known which operate according to an operating mode known as "under controlled tension". A feeder of this type is described, e.g., in EP1710334B1 .
In this case, the yarn tension is monitored continuously by a tension sensor, which can be integrated in the feeder itself. A control unit, which is also optionally integrated in the feeder, modulates the speed of the reel on the basis of the signal received from the tension sensor, so as to stabilize the tension of the yarn fed to the textile machine at a fixed value or at a profile set by the user, to the advantage of the quality of the garment.
The controlled tension operating mode is usually preferred for knits that contain designs or patterns (Jacquard knits) because, owing to the design, the amount of yarn picked up by the textile machine varies in a manner that is difficult to predict during the production of the garment.
As is known, feeders that operate under controlled tension are not capable of ensuring that the textile machine is fed the correct amount of yarn. In fact the tension, although controlled proximately to the point where the yarn leaves the feeder, can vary before the yarn reaches the textile machine, owing to the friction between the yarn and the various yarn guide rings that are located along the path, the effects of friction naturally not being subject to control.
It follows from this that the different influences of frictions between one yarn and another lead to differences in the lengths of yarns supplied by the different feeders, with possible defects in the garment.
In order to control the amount of yarn supplied, feeders are also known which operate according to a mode known as "under controlled speed". A feeder of this type is described, e.g., in EP1491673A1 .
In this case, the feeder is set to control the feeding speed of the yarn so as to stabilize it at a fixed value or at a profile set by the user.
The controlled speed operating mode is usually preferred for smooth knits, meaning, without designs or patterns (Jersey knits), since the adjustment of the rotation speed of the reels as a function of the rotation speed of the textile machine makes it possible to obtain garments that are uniform and free from "banding".
As is known, devices that operate under controlled speed are less influenced by friction, but are prone to other drawbacks.
In particular, it has been found that even a minimal error in the adjustment of the speed causes a progressive compounding of the error in the adjustment of the position of the reel, since mathematically speaking the position, as is well-known, is given by the integral of the speed.
Therefore, over the long term, an error in the position of the reel translates into a major error in the amount - understood as "length" - of yarn fed compared with the actual requirement of the textile machine.
For this reason, Jersey knits are often executed using positive feeders with mechanical actuation, in which the rotation of the reel is imparted directly by the textile machine through a belt transmission system which is designed for a preset transmission ratio. This system ensures that the length of yarn provided by the feeder always corresponds exactly to the length required by the textile machine, so as to improve the quality of the garment in terms of uniformity. This is normally called operation "in mechanical axial alignment".
However, belt feeders are not capable of operating in controlled tension mode, and operation in mechanical axial alignment, although satisfactory in terms of quality of production, still has major limitations in terms of versatility and adjustment possibilities (e.g., in order to vary the transmission ratio it is necessary to replace the pulleys of the belt transmission system with others of different diameter) and also of flexibility and simplicity of setting up the line.
Feeders are likewise known, e.g., from US3858416 , EP2067886B1 , EP2572023B1 and EP2809838B1 , that are capable of operating both in controlled tension mode and in controlled speed mode, which can use different logics to switch from one mode to the other.
However, all these feeders are affected by the inaccuracy problems of feeders that operate under controlled speed, in terms of compounding the error in the amount of yarn provided.
In light of the above, the aim of the present invention is to provide a motorized positive yarn feeder in which the most suitable operating mode is selected as a function of the type of knitting, with a more precise and reliable response than the known solutions in terms of length of yarn provided with respect to the length of yarn required by the textile machine.
Within this aim, an object of the invention is to provide a yarn feeding apparatus that uses yarn feeders according to the invention.
The above aim and object and others which will become clearer from the description that follows, are achieved by a yarn feeder having the characteristics recited in the appended claim 1, while the appended dependent claims define other characteristics of the invention which are advantageous, although secondary.
Now the invention will be described in more detail, with reference to some preferred, but not exclusive, embodiments thereof, which are illustrated for the purposes of non-limiting example in the accompanying drawings, wherein:

Figure 1 schematically illustrates a plurality of yarn feeders according to the invention while they feed yarn to a textile machine;
Figure 2 schematically illustrates in more detail one of the yarn feeders of Fig. 1 while it feeds yarn to the textile machine, according to an embodiment of the invention;
Figure 3 is a view similar to Figure 2, showing an alternative embodiment of the invention;
Figure 4 is a graph showing the progression of tension over time in a first step, with the yarn feeder operating in a first operating mode;
Figure 5 is a graph showing the progression of tension over time in a second step, with the yarn feeder still operating in the first operating mode;
Figure 6 is a graph showing the progression of tension over time in the second step, with the yarn feeder operating in a second operating mode;
Figure 7 is a graph showing the progression of tension over time in a third step, with the yarn feeder still operating in the second operating mode;
Figure 8 is a flowchart describing a first criterion for automatic switching between two different operating modes;
Figure 9 is a flowchart describing a second criterion for automatic switching between two different operating modes.

As illustrated in Figure 1, a yarn feeding apparatus according to the present invention comprises a series of motorized positive yarn feeders 10 that feed respective yarns Y to a generic textile machine TM.
Each one of the feeders 10 comprises a motorized reel 12 on which the yarn Y is wound repeatedly (e.g., 3 or 4 windings) so as to adhere to the reel by friction. When the reel 12 is rotated, the yarn Y is unwound from a spool S upstream and is fed to the textile machine TM downstream.
The feeder 10 is provided with a control unit CU which is connected in order to receive a position signal of the reel 12 from position measurement means 16 and a tension signal of the yarn exiting from the feeder 10 from a tension sensor 20, which can be advantageously incorporated in the feeder 10.
According to the invention, the control unit CU is programmed to operate selectively in a position control operating mode, in which it receives a position signal θTM from the textile machine TM, and, on the basis of the signal received from the position measurement means 16, it controls the position of the reel 12 in a closed loop according to a transmission ratio that can be set electronically with respect to the position of the textile machine TM, or in a tension control operating mode, in which it controls the speed of the reel 12 in a closed loop on the basis of the signal received from the tension sensor 20, so as to stabilize the tension of the yarn Y at a reference tension value or at a tension profile that can be set by the user.
With reference now also to Figure 2, the textile machine TM is provided with an encoder E for generating the position signal of the textile machine θTM via a communication controller TMC. This last item converts the signal generated by the encoder E into a signal suitable for transmission on a communication line, in this embodiment a serial communication line L, to which all the feeders 10 are connected.
The signals generated by the position measurement means 16 and by the tension sensors 20 of the various feeders 10 can be advantageously monitored by the operator using a central control system (not shown) which is connected to the serial communication line L.
The position signal θTM is multiplied in a multiplier block RB according to a transmission ratio (typically less than 1, e.g., 1/100 according to the geometric characteristics of the machine and of the feeder) which is configurable by the user U, so as to generate a multiplied position signal of the textile machine θTMR.
The position measurement means 16 can comprise an additional encoder EF, or a set of Hall sensors or other systems capable of generating signals as a consequence of the rotation of the reel.
The control unit CU comprises a position conversion block POS which converts the signal of the second encoder EF into a reel position signal θR, and a speed conversion block VEL which converts the signal of the second encoder EF into a reel speed signal ωR.
The multiplied position signal of the textile machine θTMP and the reel position signal θR are compared in a first subtracter node NP of a position control loop PL in order to generate a position error θE.
The position error θE is converted into a speed reference ω by means of a first proportional-integrative controller PI1.
The speed reference ω and the reel speed signal ωR are compared in a second subtracter node NV of a speed control loop VL in order to generate a speed error ωE.
The speed error ωE is converted into a current reference I by means of a second proportional-integrative controller PI2.
In this embodiment, the reel 12 is actuated by an electric three-phase motor M. The three current signals that power the motor M are converted into an equivalent current signal IR by quadrature by means of a current conversion block CUR.
The current reference I and the equivalent current signal IR are compared in a third subtracter block NI of a current control loop IL, so as to generate a current error IE.
The current error IE is converted into a voltage reference V by means of a third proportional-integrative block PI3.
The voltage reference V is sent to adjustment and actuation means which, in this embodiment, comprise a pulse width modulator PWM which controls the electric voltage supplied to the motor M by means of a MOSFET bridge.
The transmission ratio can be entered directly by the user or calculated by the control unit CU, on the basis of geometric considerations, in a calculation block CR as a function of the length of yarn that the user U wishes to be inserted at each machine turn.
By virtue of the position control of the reel carried out according to the embodiments described above, the feeder always provides exactly the amount of yarn that is taken in by the textile machine, as if the feeder and the textile machine were connected by a mechanical transmission (controlled in mechanical axial alignment). This makes it possible to prevent the compounding of error that is found in traditional systems in which, in order to control the amount of yarn fed, the speed of the reel is controlled.
In an aspect of the invention, the system switches between the two operating modes (position control and tension control) on command by the user. In this case, the control unit CU can be provided with a user interface (not shown) for making the selection.
As an alternative, or in addition, the control unit CU can be programmed to switch automatically between position control and tension control, and vice versa, when predetermined conditions correlated to the measurement of the tension occur.
In particular, Figure 4 shows the progression of tension over time during a Jersey knit operation, in which the feeder 10 operates in position control mode. In this step, the control unit CU continues to monitor the instantaneous voltage with a relatively high band, e.g., comprised between 500Hz and 1000Hz.
A first criterion, shown schematically in the flowchart of Figure 8, can cause the system to start in position control mode (block 110) and continue to monitor the tension (block 112). If, in block 114, the system begins detecting a series of periodic tension peaks, as illustrated in Figure 5, highlighting an irregular pickup of yarn by the textile machine (e.g., during the knitting of a pattern), the control unit CU automatically switches to tension control mode (block 116), which will act to reduce the positive and negative tension peaks, as illustrated in Figure 6.
The yarn tension continues to be monitored in the block 118.
If during operation under controlled tension the system, in block 120, detects that the peaks have stopped, as illustrated in Figure 7, highlighting once again a regular pickup of yarn by the textile machine, the control unit CU switches to the position control mode again.
According to a different criterion for automatically switching from position control mode to tension control mode, which is shown schematically in the flowchart of Figure 9, a minimum threshold and a maximum threshold of the average tension measured are set.
The system starts in position control mode (block 210) and continues to monitor the tension (block 212). If the system, in block 214, detects that the average tension has gone outside the threshold interval, the control unit CU automatically switches to tension control mode (block 216) in order to return the average tension to within the preset threshold interval.
The yarn tension continues to be monitored in the block 218.
If during operation under controlled tension, in block 220, the system detects that the tension has returned to within the threshold interval, the control unit CU switches to the position control mode again.
Otherwise, in block 222 the control unit CU checks to see if a preset limit (e.g., a time limit or a preset number of attempts) has expired.
If the limit has not expired, the control unit continues to operate in tension control mode.
If the limit is reached, the control unit CU can generate an alarm (block 224) and, optionally, stop the textile machine.
According to another different criterion, the control unit CU can be programmed to operate in tension control mode when the position signal θTM of the textile machine TM indicates that it is stopped, and to operate in position control mode when the textile machine TM is in motion. This criterion is particularly advantageous in that it allows the operator to knot the yarns when the textile machine is stopped.
In an advantageous embodiment of the invention, the feeder 10 is also enabled to perform take-up steps in which it rotates in the opposite direction with respect to the feeding direction in order to keep the yarn Y under tension when the textile machine TM temporarily stops picking up or returns part of the yarn previously picked up.
In this case, the control unit CU could be programmed to operate in position control mode during feeding and in tension control mode during take-up, returning the tension of the yarn to a preset value during this last step. When, after the take-up step, the textile machine TM resumes picking up yarn Y, the control unit CU automatically switches to position control mode.
The fact that the textile machine is in motion can be deduced from the movement of the encoder E onboard the textile machine TM.
The condition in which the textile machine TM is picking up yarn can be deduced from the instantaneous tension measured by the tension sensor 20. In particular, while the device is operating in position control mode, during which it follows the movement of the encoder E of the textile machine TM, the control unit CU can be programmed to interpret a sudden collapse in the instantaneous tension as a break in picking up the yarn, even if the textile machine TM is still in motion. In this situation, as mentioned previously, the control unit CU automatically switches to tension control mode, taking up yarn in order to restore the desired tension.
In this step, the control unit CU can also control the position of the reel 12 and, if it detects a positive movement greater than a preset amount (for example, the amount of take-up plus 2 or 3 turns), then it knows that the feeder has resumed providing yarn to the machine, and therefore it switches to position control mode again.
An additional criterion for switching between the two operating modes consists in checking the change of position made by the reel 12 while the feeder operates in tension control mode and, when this change of position is positive and close (according to preset thresholds) to the change of position required by the reference position ϑTMR, returning to operate in position control mode.
The yarn take-up function is particularly advantageous for textile machines fitted with devices known as "stripers".
Advantageously, the tension reference value to be used during operation in tension control mode (both during feeding and, optionally, during take-up), can be recalculated during operation in position control mode on the basis of an average tension measured in this step. In particular, during operation in position control mode, there can be a deviation in the average tension that is measured from the average tension that is desired, owing to friction. Therefore, in tension control mode, in order to compensate for the effects of friction it is recommended that the value of the average tension to be used as a reference for the tension is the updated value.
The embodiment of Figure 3 differs from the previous embodiment solely in that the loop for adjusting the speed is absent. Therefore, for this embodiment the description will not be repeated, and the elements equivalent to the embodiment of Figure 2 are indicated by the same references with the addition of an apostrophe.
In the embodiment of Figure 3, the position error θE' is converted directly, by means of a proportional-integrative-derivative block PID', into a current reference I' which, similarly to the previous embodiment, is compared with the equivalent current signal IR' in the subtractor node NI' in order to generate the current error IE'.
In practice it has been found that the yarn feeder according to the invention makes it possible to select the operating mode both manually and automatically according to the most suitable switching criterion for the type of knitting.
In particular, the position control mode makes it possible to control the consumption of yarn, in terms of length of yarn supplied with respect to the length of yarn required by the textile machine, in a much more precise and reliable manner than in the traditional solutions in which the speed of the reel is controlled.
The feeder according to the invention, in tension control mode, has a precision and reliability in the supply of yarn (in terms of length of yarn supplied per machine turn) that is comparable to that of mechanical feeders actuated by mechanical transmissions, with the advantages deriving from electric drive relating to greater flexibility of adjustment (e.g., of the transmission ratio) and greater simplicity in setting up the line.
In addition to this, the possibility to alternate, under manual and/or automatic control, between position control mode (for knitting without designs and/or patterns) and tension control mode (for knitting with designs and/or patterns) makes the feeder according to the invention much more versatile for the various kinds of knitting for which it can be used.
Another advantage of the feeder according to the invention is that it facilitates the step of calibrating the travel of the needles of the textile machine.
As is known, in fact, calibrating this travel requires the production of a sample garment, during which a constant amount of yarn per machine turn must be supplied. In this step, the operator adjusts the travel of the needles by attempts, seeking to equalize the tensions of all the yarns downstream of the feeders.
Since this procedure requires a high level of precision in the supply of yarn in constant amounts, to date it has given satisfactory results only when mechanical positive feeders are used.
However, such feeders are obviously not fitted with tension sensors, which means the operator has to use a portable reference instrument.
The device according to the invention, being provided with its own tension sensor, makes it possible to perform the adjustment in a more practical and rapid manner. In fact the operator, by way of the central control system, can monitor in real time the tensions of all the yarns and optionally act only on the yarns that deviate most from the desired tension. This desired tension can be advantageously an average tension calculated by the central control system, and the yarns in which the tension is too high or low can be graphically highlighted so as to facilitate their identification by the operator.
This system is evidently more advantageous the higher the number of yarns fed to the textile machine.
Furthermore, the tension sensor can detect when the machine stops or resumes picking up the yarn, synchronizing with the knitting of the machine. This makes it possible to use the feeder to dispense the yarn to textile machines provided with stripers which are capable of stopping and resuming the consumption of some of the yarns while the textile machine is in motion.
Also, the tension sensor makes it possible to detect yarn breakage if the take-up system is present. In fact, in the event of yarn breakage, the tension will abruptly collapse and the feeder will start to rotate in the opposite direction in an attempt to return the tension to the desired level.
When this does not happen within a preset time, the control unit can be programmed to interpret these circumstances as a consequence of yarn breakage and generate a corresponding alarm.
Some preferred embodiments of the invention have been described, but obviously the person skilled in the art may make various modifications and variations within the scope of protection of the claims.
In particular, it is evident in and of itself that the different embodiments and the different criteria of operation described above, pertaining to aspects of programming, can be implemented simultaneously and selected by the user according to the specific needs.
Furthermore, the person skilled in the art will be able to devise criteria other than, or modified with respect to, those described for the automatic switching between operating modes. For example, the control unit could start in tension control mode and switch to position control mode when it detects a substantially constant tension with no peaks right from the start.
Also, the feeder could make use of motors of a different type from those described herein, e.g., brushless DC motors, permanent-magnet synchronous motors, single-phase brushed DC motors, asynchronous motors, stepper motors, and others, which can still be driven with MOSFET bridges and the PWM technique, or other technologies such as transistors or MOSFETs operating as linear amplifiers.
The disclosures in Italian Patent Application No. 102021000017966 from which this application claims priority are incorporated herein by reference.
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

A yarn feeder, comprising a reel (12) on which a yarn (Y) is adapted to be wound repeatedly, said reel (12) being entrained in rotation by a motor (M) in order to pick up said yarn (Y) from a spool (S) and feed it to a textile machine (TM), a control unit (CU) being connected in order to receive a position signal of the reel (12) from position measurement means (16) and a tension signal of the yarn fed by the feeder (10) from a tension sensor (20), characterized in that said control unit (CU) is programmed to operate selectively in a position control mode, in which it receives a position signal (θTM) from the textile machine (TM), and, on the basis of the signal received from said position measurement means (16), it controls in a closed loop the position of the reel (12) with respect to the position of said textile machine (TM) according to a transmission ratio that can be set electronically, or in a tension control mode, in which it controls the speed of said reel (12) in a closed loop on the basis of the signal received from the tension sensor (20), so as to stabilize the tension of the yarn (Y) at a reference tension value or at a tension profile that can be set by a user.
The yarn feeder according to claim 1, characterized in that said control unit (CU) comprises:
- a multiplier block (RB), in which said position signal (θTM) is multiplied according to said transmission ratio in order to generate a multiplied position signal (θTMR) of the textile machine,

- a position control loop (PL), in which said multiplied position signal (θTMR) of the textile machine is compared with a reel position signal (θR) in order to generate a position error (θE), which is converted into a speed reference (ω) by means of a first proportional-integrative controller (PI1),

- a speed control loop (VL), in which the speed reference (ω) is compared with a reel speed signal (ωR) in order to generate a speed error (ωE) which is converted into a current reference (I) by means of a second proportional-integrative controller (PI2),

- a current control loop (IL), in which the current reference (I) is compared with an equivalent current signal (IR) of the motor (M) in order to generate a current error (IE), which is converted into a voltage reference (V) by means of a third proportional-integrative block (PI3), and

- adjustment and actuation means (PWM, MOS) adapted to control the rotation of the motor (M) on the basis of said voltage reference (V).
The yarn feeder according to claim 1, characterized in that said control unit (CU') comprises:
- a multiplier block (RB'), in which said position signal (θTM') is multiplied according to said transmission ratio in order to generate a multiplied position signal (θTMR) of the textile machine,

- a position control loop (PL'), in which said multiplied position signal (θTMR) of the textile machine is compared with a reel position signal (θR') in order to generate a position error (θE'), which is converted into a current reference (I') by means of a proportional-integrative-derivative controller (PID'),

- a current control loop (IL'), in which said current reference (I') is compared with an equivalent current signal (IR') of the motor (M') in order to generate a current error (IE'), which is converted into a voltage reference (V') by means of a proportional-integrative block (PI3'), and

- adjustment and actuation means (PWM', MOS') adapted to control the rotation of the motor (M') on the basis of said voltage reference (V').
The yarn feeder according to claim 2 or 3, characterized in that said motor (M, M') is of the three-phase type and said control unit (CU, CU') comprises a current conversion block (CUR, CUR') which is adapted to calculate said equivalent current signal (IR, IR') by quadrature from the three current signals that feed said motor (M, M').
The yarn feeder according to any one of claims 1-4, characterized in that said control unit (CU, CU') comprises a calculation block (CR, CR') which is adapted to calculate said transmission ratio as a function of the length of yarn that the user (U, U') wishes to be inserted at each machine turn.
The yarn feeder according to claim 1, characterized in that said control unit (CU) is provided with a user interface for manually selecting the position control mode or the tension control mode.
The yarn feeder according to claim 1, characterized in that said control unit (CU) is programmed to continuously monitor the tension of the yarn and to automatically switch between said position control and tension control modes when predetermined conditions correlated to the measurement of the tension occur.
The yarn feeder according to claim 7, characterized in that said control unit (CU) is programmed to:
- start in said position control mode (110),

- switch to the tension control mode (116) when a series of periodic tension peaks (114) is detected,

- switch again to said position control mode (110) when said periodic tension peaks (120) cease.
The yarn feeder according to claim 7, characterized in that said control unit (CU) is programmed to:
- start in position control mode (210),

- switch to tension control mode (216) when the average tension falls outside a preset threshold interval (214), in order to return the average tension to within said threshold interval,

- if the tension falls inside the threshold interval (220), switch to said position control mode (210) again,

- if the tension does not fall inside the threshold interval by a preset limit (220, 222), generate an alarm (224).
The yarn feeder according to claim 7, characterized in that said control unit (CU) is programmed to operate in tension control mode when said position signal (θTM) indicates that said textile machine (TM) is stopped, and to operate in position control mode when said textile machine (TM) is in motion.
The yarn feeder according to any one of claims 1-10, characterized in that it is enabled to perform take-up steps in which it rotates in the opposite direction with respect to the feeding direction in order to keep the yarn (Y) under tension when said textile machine (TM) temporarily stops picking up or returns part of the yarn picked up.
The yarn feeder according to claim 11, characterized in that said control unit (CU) is programmed to operate in position control mode during feeding and in tension control mode during take-up, returning the tension of the yarn to a preset value during this last step.
The yarn feeder according to claim 12, characterized in that said control unit (CU) is programmed to generate a yarn breakage alarm when, during take-up, it is unable to return the tension to a desired level within a preset time.
The yarn feeder according to any one of claims 1-13, characterized in that said reference tension value is recalculated during operation in position control mode on the basis of an average tension measured in this step.
A yarn feeding apparatus, characterized in that it comprises:
- at least one yarn feeder according to any one of claims 1-14, and

- a textile machine (TM) adapted to transmit said position signal of the textile machine (θTM) to said control unit (CU) via a communication controller (TMC) and a communication line (L).
The yarn feeding apparatus according to claim 15, characterized in that it comprises a central control system connected to said communication line (L) for the monitoring, by an operator, of the signals generated by said position measurement means (16).