Patent Application
20090139271
The present invention relates to a method for feeding a plurality of yarns of constant yarn length to a textile machine, in accordance with the introduction to the main claim. The invention also relates to an arrangement for implementing said method.
As it is known, devices which enable yarn to be fed in constant quantity to a textile machine have been commercially available for some time. These devices, used for example on circular knitting machines, comprise a plurality of wheels about which a number of yarn turns are wound. These wheels are rotated by a transmission member (belt) connected to a variable expansion pulley and rigid with the drive shaft of the machine which rotates the usual machine cylinder thereof on which the article (for example knitted fabric) is formed.
By virtue of this direct connection with the machine shaft, the wheels provide a constant yarn quantity to the machine, this quantity being adjustable because of the facility for expanding the pulley keyed onto this shaft.
Although the aforesaid known device enables a constant predetermined yarn quantity to be fed with absolute certainty to the textile machine, it presents various drawbacks. For example, if different yarn quantities are to be fed for different feed units, different transmission belts have to be used together with corresponding variable expansion pulleys adjusted to each ensure a constant yarn feed, but with said yarn quantities being different for different pulley groups. This known solution therefore requires a large number of pulleys, the number of which must however be limited for obvious reasons of bulk and of space limits about the textile machine.
The known system also presents a considerable drawback related to the fact that the yarn quantity absorbed by the textile machine always depends on the adjustment of the machine members which withdraw the yarn and which process it. For example, in a knitting machine these members are stitch cams which determine the stroke of a usual needle forming the fabric or stitch.
The problems in the aforesaid known devices derive precisely from the fact that the needle stroke determined by the cams should be constant with time to ensure correct stitch formation. However in reality this is not the case, in that mechanical wear and temperature variations detract from this constancy. For example, expansion undergone by the materials defining the various machine parts in passing from a cold machine to a hot machine causes the needle stroke to vary, with constant variation in the quantity of yarn fed. As the ratio of yarn absorbed to yarn fed determines the yarn tension, modifying the stroke of the needles acting on the yarns results in modification of their tension, with consequent formation of defects (streaks) in the finished product.
Consequently, even if the constant quantity yarn feed devices operate correctly, the wear undergone by the mechanical parts forming the stitch (needles, sinkers and cams) and the dimensional variations of such parts (thermal expansion) during normal machine operation lead to a lack of constant quantity yarn feed, with consequent production of defective or poor quality products.
To this there is also added the fact that to ensure a constant yarn quantity fed to a textile machine by a wheel connected to its drive shaft, said yarn must be free of elasticity. In reality this is not the case. Each yarn possesses its own elasticity resulting in yarn elongation depending on the tension to which it is subjected, this tension also varying as the yarn quantity present on the spool from which the yarn is unwound varies (spool full or empty). These tension variations at the entry to the yarn feed wheel cause variations in the yarn quantity at the entry to the machine stitch formation members, with consequences for the article production.
All this is more evident the greater the fineness (number of needles per inch) of the knitting machine. Current machines have more than 44 needles per inch, and it is clear that as the stitch loop is very small, a small variation in the stroke of the needle forming the stitch makes it highly possible that defective articles will be produced, even if only one of the yarns being worked undergoes variation in the absorbed yarn length (LFA).
Devices are also known for feeding yarns at constant tension to a textile machine. These devices operate such as to achieve, by closed-loop regulation, continuous control (measurement/regulation) of the feed yarn tension, which is maintained constant at a set value. However even the use of these devices does not ensure that a constant yarn quantity always reaches the machine.
In this respect, said devices effectively ensure that the yarn leaving them has a constant tension. However, this tension can change close to the textile machine, for example a knitting machine, because of passage of the yarn through thread guides located along the path between each device and those members (needles in the latter case) which withdraw it and work it within the stitch formation cylinder. These thread guides exert friction on the moving yarn, modify its tension and consequently cause a variation in the yarn length or quantity absorbed by the machine. This can also happen by erroneous regulation of the reference tension (or zero tension, this being the tension measured by the device in the absence of load on the measurement member or load cell). As a result of the aforegoing there is hence a real possibility of forming a defective product. This possibility can only be avoided by specific (and continuous) regulation of the machine members forming the stitch. However as these are subjected to the aforesaid wear and dimensional modifications, the already described problem also exists in relation to these members, i.e. maintaining the yarn length absorbed by the textile machine constant with time (with a consequent production problem).
EP050742 describes the use of a constant tension yarn feed device which simultaneously precisely measures the fed yarn quantity or length (LFA) and uses this measured value to regulate by feedback those machine members forming the stitch. Although effective, this known solution requires the textile machine to include, for these members, actuators (such as electric stepping motors) or regulating devices to be operated to maintain the desired LFA value controlled with precision.
Although such actuators are present on machines of recent production, they are not present on textile machines produced some time ago and neither is it possible to insert them in these latter, given the complexity of including such actuators.
Finally, such actuators for regulating the stitch formation members are currently present on all new machines with a small number of feeders such as stocking, stocking tights and seamless machines, but are absent on large-diameter knitting machines, given the large number of feeders (84, 96, . . . ).
Finally, yarn feed devices for looms are also known, known as accumulation feeders, which are able to withdraw the yarn from a spool, and deposit it on its own rotating member from which it is withdrawn by the textile machine. The rotating member is opposed by a tensioning element able to define the final tension at which the yarn is withdrawn from the machine.
Although ensuring yarn withdrawal at controlled tension (defined by the tensioning element), this known solution does not ensure that this tension is maintained with time because of the inevitable wear of the tensioning element, normally composed of a plastic ring or annular brush. This means that said member or element has to be replaced or adjusted in good time to avoid production of defective articles.
Hence from the aforegoing it will be apparent that currently available devices, although appreciated in use, present limits and drawbacks related mainly to wear of mechanical parts (of the devices themselves or of the textile machine members with which they cooperate) which inevitably lead to the inability to maintain an LFA which is constant with time for each article produced, or which is equal for all yarns fed to a textile machine.
An object of the present invention is therefore to provide a method and an arrangement for feeding, in a controlled manner by known yarn feed control devices, a plurality of yarns to a textile machine such that the length of each yarn absorbed (or LFA) is always constant with time for the entire production of articles of the same type, or is equal for all yarns fed to the machine.
A particular object of the invention is to provide a device and method of the aforesaid type which enable this constant LFA to be achieved without any need to intervene on the textile machine to which each yarn is fed or on the devices which feed them, hence enabling said device to be applied to, and said method to be implemented on, any type of machine, of new production or already installed and operating, provided or not provided with actuators for regulating the stitch formation members for article production.
Another object is to provide an arrangement and a method of the stated type able to ensure a constant absorbed yarn length independently of the inevitable friction to which the yarn is subjected due to its cooperation with thread guides or equivalent elements prior to its absorption by the textile machine.
Another object is to provide a method and an arrangement of the stated type able to intercept any formation of a residual yarn deposit or of loose elements which could limit free yarn travel in proximity to each thread guide before this is able to cause a quality defect in fabric production (for example related to streaking), and also to prevent yarn breakage.
Another object is to provide a method and an arrangement of the stated type able to ensure the maintenance of a constant absorbed yarn length which is equal or different for each yarn feed to the textile machine and applicable in combination with all known yarn feed devices.
A further object is to provide a method and an arrangement of the stated type which can be used on textile machines producing continuous fabric, such as looms, on knitting machines, and on machines producing separate articles, such as stocking, tights and similar machines.
These and other objects which will be apparent to the expert of the art are attained by a method and an arrangement in accordance with the accompanying claims.
For a better understanding of the present invention the following drawings are provided by way of non-limiting example in which:
With reference to
Each device 4 is connected, for example via a serial line, to a microprocessor unit 6 able to check that the feed of each yarn 2 takes place with constant yarn length (LFA) absorbed by the machine 5; in other words, the unit 6 checks that the LFA value remains constant during the entire production stage of the machine 5. This is achieved by acquiring data on the absorbed yarn length (LFA) measured for each yarn 2 by the corresponding device 4, then modifying if necessary the feed tension of said yarn 2 by acting on the corresponding device 4, to obtain the necessary correction to the LFA value in order to maintain the measured LFA value equal to the desired setpoint value.
In
The arrangement of
With particular reference to
To implement the method for maintaining constant the length of each yarn absorbed (LFA) by the machine in producing the article, a reference value for said LFA is defined. This value or setpoint can derive from a self-learning cycle (known per se) by the devices 4 during which each device measures the value of the length or quantity yarn fed to the textile machine (5) for producing the article, said value then being memorized in the unit 6 as the reference value for each device 4 after an analysis by an operator responsible for producing the product obtained, this analysis being targeted on obtaining a defect-free article.
Alternatively, this setpoint can be memorized directly in each device 4 (if the control unit 6 is present in each device) on the basis of previously obtained production data. In both cases, each device 4 (controlled by the internal or external unit 6) can operate on the basis of an LFA value equal to or different from the data on which the other devices of the inventive arrangement operate.
The setpoint value can also be an average LFA value calculated among all the devices 4 after producing a first verified and accepted product.
While producing the single article, it can happen that the fed yarn quantity (LFA) for each revolution or rotation of the usual knitting machine cylinder is not constant and moreover is different for each individual feeder during the entire “production cycle”, and hence varies during the various sages of the process due, for example, to discontinuous absorptions due to stitch patterns, selections or contractions; hence the control method of the invention can be implemented by carrying out a check at each cycle end. The object of this control is therefore to minimize during all the “production cycles” the calculated error between the yarn quantity (LFA) fed by each device and the relative setpoint (possibly self-learnt value), in order to make them constant and equal for each article produced.
According to the method implemented by the diagram of
In state 2 (block 21), while the machine is in the “production cycle”, the unit does not execute any operation; however, as soon as it detects (by the aforedescribed manner) passage to “zero cycle”, the unit 6 passes to the next state. In this next state 3 (block 22), the control unit 6 interrogates, for example via the serial line, the individual devices 4 to collect information on the yarn quantity fed (LFA) during the “production cycle”.
Having carried out the interrogation, in state 4 (block 23) the control unit compares the consumptions or length of absorbed yarn (LFA) of each device 4 with the set or self-learnt setpoint and makes the necessary corrections to the working tension of each device 4 in order to eliminate the extent of the possible error. In practice, if the unit detects that the yarn feed is greater than that set, it increases the working tension of the device 4 whereas if it detects that it is less it reduces its working tension. The extent of the tension correction to be transferred to the individual feed device can be of a constant value (possibly programmable) or a function of the calculated error.
In the next state 5 (block 24) the unit 6, before passing the correction of block 23 to the individual device 4, verifies that the difference between the new working tension and the starting tension is not greater than a fixed or programmable value, before passing to the next state. If the state 6A (block 25) and the unit 6 verify that the extent of the difference between the new working tension and the starting setpoint is greater than a fixed or programmable value, it proceeds by halting the machine or indicating to the operator that it is entering a limiting region, beyond which it could be impossible to maintain the consumption or fed yarn length constant. For example, the tension could be very close to the minimum or maximum tension settable on the device 4 or to the maximum tension withstandable by the yarn.
Having verified that the value of the new tension to be set is acceptable, the unit 6 (state 6B, block 26) sets for each device the new tension value to be used in the next production cycle. This unit enters a waiting state and in state 7 (block 27) it limits itself to monitoring machine passage from the “zero cycle” state to the “production cycle” state.
As soon as the control unit 6 realizes that the “zero cycle” stage has passed to the “production cycle” stage (state 8, block 28), it passes to state 1.
The preceding description is evidently only one of the methods of implementing the invention; in this respect, many variants can be made to the method without modifying the invention. Some possible modifications and/or variants to that described in relation to
The object of the inventive method is therefore to minimize during the “machine in production” stage the calculated error between the yarn quantity (LFA) fed from each device and the relative setpoint, which can be obtained as in the previously described case in relation to
The implementation of the method commences with the state 1 (block 30 of
While the machine 5 is in the “machine not in production” state, the unit 6 does not carry out any operation, however when in state 2 (block 31) it checks the state of the machine. As soon as it detects the “machine in production” state, the unit passes to the next state.
In state 3 (block 32) the unit 6 remains awaiting a PRX signal of synchronism or of recognition of the “machine not in production” state. The determination of the arrival of this signal can be achieved by monitoring a signal (hardware) originating directly from the machine, from a suitably positioned sensor, or via a serial command in the case of integration with the machine.
While the machine is in the “machine in production” state, the unit 6 (state 4, block 33) does not carry out any operation, but continues to monitor its state. If the “machine not in production” state occurs, this unit passes from state 1 (block 30); if instead a PRX signal is detected, the unit passes to the next state or state 5 (block 34). In this latter the control unit 6 interrogates via the serial line the individual devices, to collect information on the yarn quantity fed (LFA) during the interval between two synchronism signals (PRX). In the next state 6 (block 35), the control unit 6 compares the length of the fed yarn (LFA) from each device with the set setpoint and makes the necessary corrections to the working tension in order to reduce and eliminate the extent of the error. In practice, if the algorithm finds that the yarn consumption is greater than that set, it increases the working tension of the device whereas if it finds that it is less it reduces its working tension. The extent of the tension correction to be passed to the individual feed device 4 can be a constant value (possibly programmable) or a function of the calculated error.
In the next state 7 (block 36) the unit 6, before transferring this correction to the individual device 4, verifies that the difference between the new working tension and the setpoint tension is not greater than a fixed or programmable maximum allowable correction value, before passing to the next state. If the unit 6 detects (state 8A, block 37) that the extent of the difference in the new working tension is greater than the maximum allowable correction value, it halts the machine and/or indicates to the operator that it is entering a limiting region, beyond which it could be impossible to maintain constant consumption. For example, the tension could be very close to the minimum or maximum tension settable on the feeder or to the maximum tension withstandable by the yarn. This indication takes place in known manner by light-emitting or acoustic devices.
If the corrected tension is acceptable, then (state 8B, block 38) the control unit sets for each device 4 the new tension value to be used for maintaining the desired LFA value constant.
As in the case of
In the light of the aforegoing, the method of the invention can be summarized and generalized in the following manner. A control unit 6 (external to the devices 4 or a part of them or of only one of them), on the basis of a setpoint value (obtained after a sample production and/or self-learning cycle during which an article without defects is obtained), verifies the yarn length (or LFA) fed by each device 4 to the textile machine 5. This check takes place on termination of a reference period which can be the period for producing a finished article or a time period defined by successive reference signals.
The unit 6 compares the real LFA value corresponding to the actual yarn quantity fed by each device 4 to the textile machine during the reference period with the setpoint value; if there is a discrepancy between them, it proceeds to vary the tension value for each individual device 4 for which the discrepancy was detected in order to return the LFA value to the prefixed setpoint value.
The invention results in attainment of the objects of the invention indicated in the introduction to the present document.
Various embodiments of the invention have been described and mentioned. Others are however attainable on the basis of the aforegoing description and are to be considered as falling within the scope of the following claims.
| Number | Date | Country | Kind |
|---|---|---|---|
| MI2007A 002269 | Dec 2007 | IT | national |
