WO2006072969A1

WO2006072969A1 - Circular knitting machine and method for taking up the fabric produced by a circular knitting machine

Info

Publication number: WO2006072969A1
Application number: PCT/IT2005/000005
Authority: WO
Inventors: Tiberio Lonati
Original assignee: Santoni S.P.A.
Priority date: 2005-01-05
Filing date: 2005-01-05
Publication date: 2006-07-13
Also published as: EP1838913A1; CN101115875A; CN101115875B; JP2008527188A

Abstract

A method for taking up the fabric (4) produced by the cylinder (3) of a circular knitting machine (1), comprising the steps of taking down the fabric (4) and taking up the fabric (4) by actuating in rotation a take-down and take-up assembly (6) independently from the cylinder (3) at a speed differing from the speed of the cylinder (3). It is further provided for a circular knitting machine comprising a cylinder (3) that can be actuated in rotation at a first angular speed so as to produce at least a tubular fabric (4), and a take-down and take-up assembly (6) that can be actuated in rotation at a second angular speed so as to engage and take up the fabric (4) produced by the cylinder (3), in which said take-down and take-up assembly (6) can be actuated in rotation independently from the motion of the cylinder (3) at a second angular speed differing from the first angular speed of the cylinder (3).

Description

CIRCULAR KNITTING MACHINE AND METHOD FOR TAKING UP THE FABRIC PRODUCED BY A CIRCULAR KNITTING MACHINE

_.DESCRIPTION

The present invention relates to a circular knitting ma- chine and to a method for taking up the fabric produced by a circular knitting machine .

The present invention relates to the textile field, and in particular to the production of fabrics by means of circular knitting machines equipped with a rotary cylinder and a take-down and take-up assembly for taking down and taking up the fabrics produced by the rotary cylinder . In further detail , as disclosed and described in patent ITl .309.184 , issued to the same Applicant , devices for taking down and taking up tubular fabrics are generally mounted turnably onto the machine frame and act onto the tubular fabrics from the corresponding cylinder . As a rule , the movable take-down and take-up assembly comprises a device for flattening tubular fabrics being fed and one or more traction elements for controlled feeding of the fabric being worked.

As is known, the movable take-down and take-up , assembly turns integrally with the machine cylinder . In other words , both the machine cylinder and the take-down and take-up assembly turn around a common central rotation axis with the same angular speed . The simultaneous synchronized movement of the machine cylinder and of the take-down and take-up assembly is achieved by dragging the take-down and take-up assembly, or by a mechanical drive imparting to the take-down and take-up assembly the same angular speed as the cylinder .

The take-down and take-up assembly can take up the tubular fabric as rolls or laps after taking down said fabric , or it can be equipped with cutting means cutting automatically the fabric from the cylinder, which fabric is then open through suitable outspreading devices and taken down in already open rolls . The knitting machines described above have some drawbacks , mainly in case discontinuous or over-plied yarns , i . e . subj ect to an intrinsic structural fabric twisting, which phenomenon is commonly known as "turn" . This behavior, due to the intrinsic stresses of the struc- ture of the aforesaid yarns , which have twists increasing their structural resistance, affects the structure of tubular fabrics produced by knitting machines to a significant extent , which fabrics can be deformed or plied with a cylindrical shape having a "twisting" or a deformed flat shape, if cut directly by the take-down and take-up assembly .

The tubular fabrics produced and taken up by the machine therefore tend to deform because of the stresses referred to above . This results in some cases in serious problems of deformation for the manufactured items produced with the fabric thus taken up in rolls , even after further finishing treatments of said items , with a subsequent quality decrease of the textile manufactured items . In an attempt to overcome these problems , some manufacturing contrivances have been implemented for balancing yarns so as to avoid self-plying structures . Some of these are the use of balanced twisting yarns

(which are however quite expensive) , the use of opposed twisting yarns (which have however an unwanted effect known as "millerays" ) , or the taking-up of the tubular fabric and its subsequent manual cutting following the natural twisting of the fabric .

In the latter solution, the knitted tube is hung and dropped without stresses , so as to let it deform with its natural helical twist . The fabric is then manually cut in a twisted way with respect to the "ribs" or vertical cords of the knitted fabric , i . e . in "twisted warp" , though following the deformation helix of said fabric . The flat fabric thus obtained is cut "twistedly" , though following its deformation line , and it is thus possible to prevent subsequent deformations of the flat fabric , since the fabric has already got twisted and has thus reached its structural stability.

However, it should be pointed out that also when automatically taking up the fabric tube , without cutting the latter directly in the take-up assembly, permanent folds on said fabric are sometimes created, which folds are oblique with respect to the following cutting line and thus worsen the quality of the fabric and of the finished item. Using said fabrics with "twisted cutting" it is thus possible to obtain clothing items that can then be treated in various ways , for instance dyed, washed at .high temperatures , milled for softening them or other, though keeping their structure .

Twisted cutting does not give rise to any aesthetical problem on the finished item, since for given thinnesses the finished item is homogenous after the various treatments and vertical cords or "wales" can no longer be dis- tinguished from horizontal courses . The fact that the fabric has been cut twistedly with respect to the vertical cords is thus irrelevant from an aesthetical point of view. Thanks to a cutting of the tubular fabric carried out af- ter its deformation and considering said deformation, it is thus possible to obtain items which are stable and do not deform either during pre-sale or post-sale treatments because of various washing and ironing operations . Figure 10 shows a knitted tube 4 manufactured with plied yarns , which before deforming appears as an ordinary tube manufactured with conventional yarns , and which is cut along a cutting line following the vertical knitted cords or wales 4a and parallel to the central axis "X" . The flat

^■ fabric thus obtained, as shown in Figure 11 , is cut paral- IeI to the vertical knitted cords or wales 4a, and tends afterwards to twist as shown in Figure 11 (in an exaggerated way for reasons of clarity) causing the deformation of the knitted items manufactured with said fabric 4. Figure 10a shows the same knitted tube 4 after deformation taking place when said tube 4 is hung without external tractions , as indicated by angle α built between the ori- entation line of the vertical cords or wales 4a after deformation and the corrected cutting line 5 in "twisted warp" . Said cutting line 5 , "twisted" with respect to the wales 4a, enables to obtain the fabric as in Figure 11a, which is cut twistedly with respect to the wales 4a, but being already deformed will no longer deform, thus being dimensionalIy stable .

However, manufacturing fabrics according to the aforesaid empirical manual process is quite expensive , little reliable and low repeatable , since it depends on the opera- tor' s ability .

Moreover, said technique cannot apply to seamless items , which are not cut and sewn but keep the same structure as the knitted tube produced by the knitting machine . Eventually, it should be pointed out that taking up the fabric in a tube sometimes causes permanent folds on said fabric, which not being produced "correctly" considering subsequent fabric deformation result in a quality decrease of the finished item. Thus , products with different quality are often present , together with a high amount of scraps , with subsequent quite relevant economical losses . • •

Under these circumstances , the technical task underlying the present invention is to provide a circular knitting machine and a method for manufacturing fabrics that can basically obviate the aforesaid drawbacks . In the framework of said technical task, an important aim of the in- vention is to conceive a circular knitting machine whose take-down and take-up assembly, operating on tubular fabrics produced by the machine cylinder, allows to take up the knitted tube considering the subsequent fabric deformation due to its internal stresses . Another technical task of the invention is to provide a machine and a method that enable to take up the knitted tube produced by the machine in a geometrically detected and mathematically controlled way thanks to the control system of said knitting machine, so as to obtain flat fabrics that are dimen- sionally stable and are not subj ect to subsequent structural deformations .

A final technical aim of the invention is to provide a machine and a method that enable to take up the knitted tube produced by the machine by carrying out automatically a fabric cutting which takes into account the internal stresses of the fabric and which is therefore "correct" with respect to subsequent fabric deformation . The technical task and the aims referred to are basically achieved by a circular knitting machine and by a method for manufacturing fabrics characterized in that they comprise one or more of the technical solutions claimed below. The following contains by way of mere indicative and non- limiting example the description of some preferred - though not exclusive - embodiments of a machine according to the invention, shown in the accompanying drawings , in which :

- Figure 1 is an elevation view of a machine according to the invention, partially sectioned and represented according to a first embodiment for taking up the fabric in a tube ; - Figure Ia is a view as in Figure 1 of a second embodiment of the machine , in which the displacement between take-down and take-up assembly and cylinder is carried out by means of a mechanical device;

- Figure Ib shows a stationary frame of the machine as in the preceding figure ;

- Figure 2 is an elevation view of a third embodiment of the device of Figure 1 , in which the take-down and take-up assembly also cuts automatically, outspreads and takes up the outspread fabric , the fabric thus manufactured being schematically represented;

- Figure 3 shows a perspective view of the lower portion of a knitting machine with a device for taking up , in open form automatically by cutting, tubular fabrics produced by a cylinder of the knitting machine of Figure 2 ; - Figure 4 shows a perspective view of the supporting frame of the take-down and take-up assembly of the machine as in Figure 2 ; - Figure 5 is a perspective view of the take-down and take-up assembly of the machine as in Figure 2 ;

- Figure 6 is a magnified perspective view of cutting means of the take-down and take-up assembly of Figure 5 ; - Figure 7 is an elevation view of a machine according to the invention, partially sectioned and according to a first variant of the first embodiment of the present invention;

- Figure 8 is an elevation view of a machine according to the invention, partially sectioned and according to a second variant of the first embodiment of the present invention;

- Figure 9 is an elevation view of a machine according to the invention, partially sectioned and according to a third variant of the first embodiment of the present invention;

- Figure 10 shows schematically a non-deformed tubular fabric with the indication of the traditional cutting line, parallel to the rotation axis and to the axis of the "ribs" of the knitted fabric ;

- Figure 10a is a view as in Figure 10 , with the fabric deformed due to inner stresses and with the indication of the axis of the "ribs" of deformed fabric and the correct cutting line ,- - Figure 11 shows schematically a fabric cut in a traditional way, parallel to fabric ribs , and subj ect to structural deformation; - Figure 11a shows schematically a fabric cut with a correct inclination according to the present invention and without structural deformation;

- Figure 12 shows a tubular fabric with the indication of the helical cutting line corresponding to its structural deformation .

Referring to the accompanying figures , number 1 globally refers to a circular knitting machine according to the present invention . The circular knitting machine 1 (not shown completely in the figures) comprises a movable cylinder 3 and a stationary supporting frame 2 (Figure Ib) , including a lower stationary frame having a base 2a, three lateral propping legs 2b and an upper propping ring 2c . The movable cylin- der 3 is mounted onto the upper ring 2c , on which cylinder at least a tubular fabric (represented in Figure 2 and referred to with number 4 ) is progressively manufactured. The knitting machine 1 further comprises a take-down and take-up assembly 6 operatively engaged with the supporting frame 2 on the cylinder 3 for taking up the tubular fabric produced by the cylinder 3. The movable cylinder 3 can be actuated so as to turn around a central rotation axis "X" and with a predefined angular speed suiting the tubular fabric currently manufactured . The take-down and take-up assembly 6 comprises a supporting frame 7 turning around the central rotation axis "X" , the top of said frame being preferably provided with flattening means 8 for flattening the tubular fabrics from the cylinder 3. The flattening means 8 include a spreading frame (which can have any suitable shape) for progressively changing the cylindrical shape of the tubular fabric by flattening the latter basi- cally in a diametrical direction, and a pair of parallel rollers 9 suitable spaced one from the other and delimiting the fabric under feeding .

A fabric return roller 13 lies in a central portion of the supporting frame 7 of the take-down and take-up assembly 6 , and a set of traction rollers 14 for feeding the fabric through the components of the take-down and take-up assembly 6 is engaged basically on the same lying plane as the return roller 13. A take-up assembly 15 for the outspread fabric is arranged downstream from the set of traction rollers 14. As an alternative it can be provided for a device , known per se , for taking up the tubular fabric in overlapping layers .

In a third embodiment as shown in Figure 2 , referring to a machine usually known as "OPEN" in which the fabric is cut automatically in the machine, under the parallel rollers 9 , cutting means 10 can be operatively arranged, which shall be described in further detail below and which progressively cut the fabric under feeding along a predefined cutting traj ectory, and opening and outspreading means 11 for spreading the cut fabric in a single layer .

With reference to Figure 2 , the opening and outspreading means 11 further comprise two divaricating rollers 12 for - li¬

the fabric and the lateral edges thereof obtained by cutting, from which the fabric reaches the aforesaid return roller 13 for the outspread fabric . Each divaricating roller 12 is preferably and advantageously provided with an independent motor 12a, which further helps to outspread the fabric under feeding . The divaricating rollers 12 are preferably inclined following lines diverging downwards , which results in a more uniform distribution of tractions exerted onto the fabric on the circumference of the cylin- der . Figure 4 shows a support 43 for said divaricating rollers 12. -

According to the invention, the machine further comprise means 16 , 23 , 44 for varying the relative angular position between the take-down and take-up assembly 6 and the cyl- inder 3 during fabric take-up .

Said means 16, 23 , 44 will be disclosed in detail in the following description of specific embodiments and can basically comprise , depending on the various cases : - control means 16 actuating in rotation the take-down and take-up assembly 6 independently from the cylinder 3 ; interconnecting means 23 , which can be selectively shifted from a first operating condition in which the take-down and take-up assembly 6 is integral with the cylinder 3 (and turns integrally with the latter) , and a sec- ond operating condition in which the take-down and take-up assembly 6 moves at a given relative instantaneous angular speed with respect to the cylinder 3 ; - an intermittent offset device 44 , 45 , 46 of mechanical type, which offsets the relative angular position between the take-down and take-up assembly 6 and the cylinder 3 in at least one angular position of the turn of said cylinder 3.

It should be pointed out that in the present text the term "angular speed" includes both instantaneous relative angular speed (i . e . at each instant) and the global or "average" angular speed obtained after a plurality of turns . Therefore, even if the take-down and take-up assembly 6 turns integrally with the cylinder 3 for a whole turn and is then "offset" of some degrees in an intermittent way, there will be anyhow a different angular speed between the take-down and take-up assembly 6 and the cyl- inder 3.

Advantageously, the machine 1 further comprises control means 16 operatively associated with the take-down and take-up assembly 6 for actuating it in rotation at an angular speed varying from a minimum value below the angular speed of the movable cylinder 3 , to a maximum value, above the angular speed of the movable cylinder 3. Preferably, said control means 16 are operatively associated with at least an electronic control unit 17 (schematically shown in Figure 3 ) arranged for instance inside a housing com- partment within the supporting frame 2 , and designed to adjust the angular speed of the take-down and take-up assembly 6 depending on the twisting rate of the tubular fabric produced on the cylinder 3. In other words , the electronic control unit 17 manages through the control means 16 the angular speed of the take-down and take-up assembly 6 so that the latter turns faster or slower than the cylinder 3 of the machine 1 so as to fulfill the aims of the invention, defining the traj ectory for taking up the fabric . Preferably, the electronic control unit 17 is integrated into the conventional global electronic control system of the knitting machine, so as to be controlled by the conventional control means of the machine . In the embodiment of Figure 2 , the electronic control unit 17 preferably acts upon the independent motors 12a of the divari cating rollers 12 for controlling an optimal fabric takedown proportionally to the fabric cutting angle , which de- pends on the relative rotation between the take-down and take-up assembly 6 and the cylinder 3.

The knitting machine can further include automatic detecting means (not shown in the figures ) , for instance optical means or of other type , which enable to detect automati- cally the inclination of the fabric deformation helix, and which are operatively connected to the electronic control unit 17.

Said means can be activated for instance when starting production, manufacturing a portion of tubular fabric without tractions , letting it deform freely and detecting its deformation . The value thus detected can be compared with the one manu- ally set or with the one predicted depending on the type of yarn and on the remaining manufacturing parameters , as a further check on the correctness of machine settings . In particular and by way of example, the relative rotation of the take-down and take-up assembly 6 with respect to the cylinder 3 is subj ect to the following mathematical equations :

P = π - 2r - tan ( 90-α) P = πD - tan ( 90-α) in which (see Figures 11a and 12 ) "P" is the torsion rate of the tubular fabric , i . e . the number of millimeters of tubular fabric required so that the cylinder 3 is offset of one turn with respect at least to the take-down and take-up assembly 6 ; "D" and "r" are respectively the di- ameter and radius of the tubular fabric; and "α" refers to the helix inclination degrees set (or automatically detected by the detecting means) in the electronic control unit 17 before activating the machine 1. If the machine 1 is for instance a 30" circular knitting machine and helix inclination is of 5° , the rate according to one of the above equations is of :

P = π - 762 mm - 11 , 43

P = 27 , 348 mm = 27.348 m

In this case the take-down and take-up assembly is delayed with respect to the cylinder 3 of one turn every 27 , 348 mm of tubular fabric produced . Considering that the tubular fabric produced at every turn, which depends on various parameters of the manufacturing process and can be obtained from the rotation speed of the expander roller ( said value can be detected directly by the control unit 17 or be set manually) , can be for instance of :

Prg = 60 mm/turn the rate in mm divided by the tubular fabric produced (Prg) gives the number of turns required for an offset of 360⁰C (one turn) between the cylinder 3 and the take-down and take-up assembly 6.

27 , 348 mm : 60 mm/turn = 455.8 turns

Moreover, the 360 ° offset between the cylinder 3 and the take-down and take-up assembly 6 divided by the corresponding numbers of turns required for the take-down and take-up assembly 6 to be offset of 360⁰C, gives the angular offset pro turn between the take-down and take-up assembly 6 and the cylinder 3.

360° : 455.8 turns = 0.789 ° for every cylinder turn According to said parameters the take-down and take-up as- sembly 6 is thus delayed with respect to the cylinder 3 of 0.789 ° at every turn of the latter, the speed of the expander being proportionally lower than the speed of the cylinder . Conversely, if the machine 1 is a 30" circular knitting machine and helix inclination is of -5 ° , the rate according to the above equation is of : P = π - 762 mm- (-11.43) = -27 , 348 mm In this case the take-down and take-up assembly 6 in rotation is in advance with respect to the cylinder 3 of one turn every 27 , 348 mm of tubular fabric produced. According to a first embodiment of the present invention as shown in Figure 1 , the take-down and take-up assembly 6 can be actuated in rotation around the central rotation axis ^UX" and is associated with the cylinder 3 through interconnecting means 23 , which can be selectively shifted from a first operating condition in which the take-down and take-up assembly 6 is integral with the cylinder 3 , and a second operating condition in which the take-down and take-up assembly 6 moves at a given relative instantaneous angular speed with respect to the cylinder 3. In particular, said interconnecting means 23 comprise at least a first driving element 24 transmitting the integral motion to the cylinder 3 , and at least a second driving element 25 transmitting the associated motion to the takedown and take-up assembly 6 and an auxiliary motor acting upon the second motion driving element 25. The first motion driving element 24 is for instance a crown wheel turning integrally with the cylinder 3 and mounted onto the frame of the take-down and take-up assembly 6 by means of a convention bearing system 24a, and the second motion driving element 25 is a toothed wheel mounted onto the take-down and take-up assembly 6 and operatively associated with the crown wheel . The association between first 25 and second 25 driving element , cyl- inder 3 and take-down and take-up assembly - 6 could be inverted obtaining basically the same results . Basically, the take-down and take-up assembly 6 turns integrally with the cylinder 3 if the auxiliary motor 25 is inactive, whereas when said auxiliary motor 25 is actuated by the machine control system, the take-down and take-up assembly 6 undergoes a relative rotation with respect to the cylinder, thus globally turning at a absolute rotation speed differing, being higher or lower depending on the various cases , from cylinder 3 speed . This technical solution enables to obtain a very high driving ratio between the first 24 and the second 25 driving element ( for instance 1/4 , 200 ) , and therefore to ob-' tain a very high accuracy in the difference between the rotation speeds of the cylinder 3 and of the take-down and take-up assembly 6.

In particular, the take-down and take-up assembly 6 is connected to the cylinder 3 by means of at least a dragging frame 42 (Figures 1 and 4) extending under the cylin- der 3. When the cylinder 3 is actuated in rotation around the central rotation axis "X" , it turns together with the dragging frame 42 , comprising in further detail for instance two dragging arms 42a thus dragging in rotation also the take-down and take-up assembly 6. The movement of the cylinder 3 is obtained thanks to conventional driving means 30 , which are not described in further detail because they are known per se . In a second embodiment as shown in Figure Ia, the means 16 , 23 , 44 for varying the relative angular position comprise an intermittent offset device 44 , 45 , 46 of mechanical type, which offsets the relative angular position be- tween the take-down and take-up assembly 6 and the cylinder 3 in at least an angular position of the turn of said cylinder 3.

In practice , in such a case there are still for instance a first motion driving element 24 (for instance a crown wheel) turning integrally with the cylinder, and a second motion driving element 25 (for instance a toothed wheel) mounted onto the take-down and take-up assembly 6 and operatively associated with the first motion driving element 24. In such a case, however, there is no auxiliary motor 26 , but the mechanical offset device comprises a stationary element 45 (for instance a rack or a cam) integral with the stationary supporting frame 2 o the machine and cooperating with the second motion driving element 25 when the latter during the rotation of the take-down and take-up assembly 6 gets in contact with it on its traj ectory, so as to cause a given rotation of the second element 25 and thus a given offset for each turn between the take-down and take-up assembly 6 and the cylinder 3. In such a case the second motion driving element 25 should be mounted onto the take-down and take-up assembly 6 by means of an appropriate mounting device 46 (comprising for instance bearings and a known "free wheel" device) and can be equipped with an actuating lever cooperating with a cam 45 and getting back in position by means of a spring after turning the second element 25. Basically, known mechanisms that are not disclosed in further detail in the present description can be used for the intermittent offset device 44 , 45 , 46.

In a further execution variant , it can be provided for a rotary frame 7 integral with the cylinder 3 or anyhow turning in a synchronized way together with the cylinder 3 , onto which the take-down and take-up assembly 6 can be mounted, which in this case can be shifted on said rotary frame so as to obtain the desired difference of angular speed between the take-down and take-up assembly 6 and the cylinder 3.

In the third embodiment as shown in Figures 2 to 6 , referring to a machine conventionally designed as "open" -type machine, the take-down and take-up assembly 6 is further equipped with cutting means 10 cutting automatically the fabric before it is taken up .

As can be seen in Figures 5 and 6 , said cutting means 10 comprise at least a cutting element 10a shifting between a first position, in which it is basically parallel with respect to said central rotation axis "X" , and a second po- sition, in which it is inclined with respect to said central rotation axis "X" , so as to cut the tubular fabric from the cylinder 3 on a basically helical cutting traj ec- tory whose rate preferably corresponds to the twisting rate of said tubular fabric .

The position of the cutting element 10a is chosen proportionally to the difference of angular speed between the cylinder 3 and the take-down and take-up assembly 6 , so as to define the desired inclination of the cutting helix in order to follow the twisting helix of the tubular fabric produced by the machine . As can be seen in Figures 5 and 6 , the cutting means 10 preferably further comprise at least an electric motor 40 , advantageously controlled by the electronic control unit 17 for actuating the cutting element 10.

The cutting element 10a is further advantageously associated with actuating means 39 for shifting the cutting ele- ment 10a between the first and second position so as to place it in a suitable position for cutting the tubular fabric under feeding .

The actuating means 39 can be manual . In this case , the suitable position of the cutting element 10a for cutting the tubular fabric under feeding is achieved directly by an operator acting upon the actuating means 39 by shifting the latter with respect to a graduated scale 39a, before every activation of the machine 1 or when, due to manufacturing needs , a tubular fabric with different parameters with respect to the previous one has to be manufactured on said machine 1. As an alternative, the actuating means 39 can be automatic and therefore be controlled directly by the electronic control unit 17 so as to define in an automatic and programmed way the cutting element 10 according to the desired inclination . It should be pointed out that the cutting traj ectory, inclined with respect to the central axis "X" and preferably basically helical , is established depending on the twisting rate of the tubular fabric due to yarn stresses and is obtained though a difference of angular speed between the cylinder and the take-down and take-up assembly .

According to a first variant of the first embodiment of the present invention as shown in Figure 7 , the control means 16 comprise at least an electric motor 18 , preferably a brushless motor or of any other convenient type , and driving means 19 operatively placed between the electric motor 18 and the take-down and take-up assembly 6 for actuating in rotation the latter at a predefined angular speed. As can be seen in Figure 7 , the electric motor 18 is inte- grally engaged with a lateral edge 7a of the supporting frame 7 of the take-down and take-up assembly 6 so as to rotate together with the latter around the central rotation axis "X" , and the driving means 19 , connected to a drive shaft 18a developing below the electric motor 18 , extend mainly below the take-down and take-up assembly 6. In further detail , the driving means 19 comprise a first drive pulley 20 fitted onto the drive shaft 18a of the electric motor 18. The first drive pulley 20 turns integrally with the drive shaft 18a around a first rotation axis "Y" basically parallel to the central rotation axis "X" of the cylinder 3 and of the take-down and take-up as- sembly 6. The driving means 19 further comprise a second drive pulley 21 lying basically on the same plane as the first drive pulley 20. The second drive pulley 21 opera- tively cooperates with the first drive pulley 20 and is stationary and integrally engaged with the stationary sup- porting frame 2 on the central rotation axis "X" . A drive belt 22 is further operatively placed between the first and second drive pulley 20 , 21. Said drive belt 22 partially envelopes the first and second drive pulley 20 , 21 so as to draw into rotation the take-down and take-up as- sembly 6 as a result of a rotation of the first drive pulley 20 around the first rotation axis "Y" .

According to a second variant of the first embodiment of the present invention as shown in Figure 8 , the motor 18 constituting together with the driving means 19 the con- trol means 16 for actuating in rotation the take-down and take-up assembly 6 , is integrally engaged with the stationary supporting structure 2. In other words , under these circumstances the take-down and take-up assembly 6 turns independently from the motor 18 , which is station-¹ ary. s can be seen in Figure 8 , the driving means 19 , designed to actuate in rotation the take-down and take-up assembly 6 , comprise a first toothed wheel 27 fitted onto the drive shaft 18a of the motor 18 so as to turn around a first rotation axis "Z" basically parallel to the central rotation axis "X" of the cylinder 3 and of the take-down and take- up assembly 6. The driving means 19 further comprise a second toothed wheel 28 lying basically on the same plane as the first toothed wheel 27 and cooperating with the latter . The fourth toothed wheel 28 is integrally engaged with the take-down assembly 6 so as to turn together with the latter around the central rotation axis "X" . As an alternative and in a fully equivalent manner, instead of the toothed wheels 27 , 28 , it could be provided for a pair of pulleys connected by means of a suitable drive belt . In further detail , the fourth toothed wheel 28 wholly sup- ports the take-down and take-up assembly 6 through suitable rolling means 28a operatively placed between the fourth toothed wheel 28 and the stationary supporting frame 2. Advantageously, the control means 16 further comprise a motor 29 of known type engaged with the stationary supporting frame 2 and second driving means 30 (of known type) operatively placed between the motor 29 and the cylinder 3 of the machine 1 so as to actuate in rotation the latter around the central rotation axis "X" at a predefined angular speed. In particular, the second driving means 30 comprise a first and a second drive pulley 31 , 32 lying on the same plane and operatively connected one to the other by a drive belt 33. The first drive pulley 31 is fitted onto a drive shaft 29a of the motor 29 and can freely rotate around a first rotation axis "B" basically parallel to the central rotation axis "X" of the cylinder 3 and of the take-down and take-up assembly 6. Conversely, the second drive pulley 32 is fitted onto a corresponding drive shaft 34 so as to turn together with the latter around a second rotation axis "C" basically parallel to the first rotation axis "B" . The second driving means 30 further comprise a third and a fourth toothed wheel 35 , 36 lying on the same plane basically parallel to the lying plane of the first and second drive pulley 31 , 32 and cooperating so as to actuate in rotation the cylinder 3. The third toothed wheel 35 is in- tegral with the drive shaft 34 so as to turn together with the latter and with the second drive pulley 32 around the second rotation axis "C" . The fourth toothed wheel 36 is integrally engaged with the cylinder 3 of the machine 1 and engages the third toothed wheel 35 so as to actuate in rotation said cylinder at a desired angular speed . The fourth drive pulley 36 supports at least partially the cylinder 3 of the machine 1 through suitable rolling means 36a operatively placed between the fourth toothed wheel 36 and the stationary supporting frame 2. According to a third variant of the first embodiment of the present ^' invention as shown in Figure 9 , the control means 16 control and manage the movement of the cylinder 3 of the machine 1 and of the take-down and take-up assembly

6 by means of one motor 18 ' integrally engaged with the stationary supporting frame 2. In this case, the control means 16 are equipped with first and second driving means 37 , 38 , which can be basically the same as the driving means 19 of the second variant of the first embodiment

(Figure 8 ) , for the rotation of the take-down and take-up assembly 6 , and as the second driving means 30 , for the rotation of the cylinder 3. Under these circumstances , both the first and the second driving means 37 , 38 exploit the movement of the drive shaft 18a ' of the motor 18 ' with which they are engaged on opposite sides .

Obviously in this case, in order to vary the rotation speed of the take-up assembly with respect to the speed of the cylinder, the first driving means 37 (or alternatively the second driving means 38) comprise a speed variator 41 , which can be actuated manually or preferably automatically by the electronic control unit 17. In order to reduce the reference numbers used to identify the components of the machine 1, the elements constituting the first driving means 37 have been basically provided with the same reference numbers used in the description of the driving means 19 of the second variant of the first embodiment , and the elements constituting the second driving means 38 have been basically provided with the same numbers used in the description of the second driving means 30. Obviously, the examples described above with reference to the various driving means used to actuate in rotation the cylinder 3 and the take-down and take-up assembly 6 , do not limit in any way the present invention, which can also envisage any other type of known drive for turning the take-down and take-up assembly 6 independently from the cylinder 3 of the machine 1. The invention has important advantages .

First of all , the machine and the method according to the present invention enable to obtain fabrics with a high level of quality and finish, which are not subj ect to significant structural deformations in the following manufacturing steps . This can be achieved thanks to a fabric take-up anticipating the subsequent natural twisting helix of the fabric^' due to inner tensions , thus preventing the following deformation of the fabric taken up "correctly" . Eventually, it should be pointed out that a machine and a method according to the present invention are not highly complex and are quite cheap .

Claims

1. A method for taking up a fabric (4 ) produced by a cylinder (3 ) of a circular knitting machine ( 1) , turning around a central axis ( "X" ) , comprising the following steps : taking down said fabric (4 ) produced by the cylinder (3 ) taking up said fabric (4) by actuating in rotation a take-down and take-up assembly ( 6) placed on said cylinder (3 ) for taking down and taking up said fabric (4 ) ; characterized in that it further comprises a step in which the angular position of said take-down and take up assembly ( 6 ) is varied with respect to said cylinder (3 ) during said step in which said fabric (4 ) is taken up .

2. The method according to claim 1 , characterized in that during said step of taking up said fabric (4 ) said takedown and take-up assembly ( 6) is actuated in rotation at an angular speed differing from the speed of said cylinder (3 ) .

3. The method according to claims 1 or 2 , characterized in that during the step of taking up said fabric (4 ) said take-down and take-up assembly (6) is actuated in rotation independently from said cylinder (3 ) .

4. The method according to claim 1 , characterized in that it comprises a step in which the angular position of said take-down and take-up assembly ( 6) is offset with respect to said cylinder (3 ) in at least an angular position at every turn of said cylinder (3 ) during said step of taking up said fabric (4) .

5. The method according to any of the preceding claims , characterized in that said fabric (4) is taken up directly as a tube .

6. The method according to any of the preceding claims , characterized in that it further comprises a step in which the tubular fabric (4) from the cylinder (3 ) is clenched before said step of taking up the fabric (4 ) .

7. The method according to any of the preceding claims , characterized in that the difference in angular speed between said cylinder (3 ) and said take-down and take-up assembly (6) is given as a function of the twisting rate of said tubular fabric (4) . i

8. The method according to any of the preceding claims , characterized in that it further comprises a step in which said fabric (4 ) is progressively cut along a predefined cutting traj ectory, before said step of taking up said fabric (4 ) .

9. The method according to claim 8 , characterized in that said cutting traj ectory is inclined with respect to said central rotation axis ( "X" ) .

10. The method according to claims 8 or 9 , characterized in that said steps of taking down said fabric (4 ) produced by the cylinder, of cutting said fabric (4) and of taking up said fabric (4) are carried out by actuating in rotation a take-down and take-up assembly (6) , equipped with cutting means (10 ) designed to cut said tubular fabric (4) from said cylinder (3 ) , and arranged on said cylinder (3 ) for taking down and taking up said fabric (4 ) , in which said cutting means ( 10) are actuated in rotation at a speed differing from said cylinder (3 ) .

11. The method according to claim 10 , characterized in that said cutting means (10 ) are integrally associated with said take-down and take-up assembly ( 6) , which can be actuated independently from said cylinder (3 ) at a speed that can differ from the speed of the cylinder (3 ) .

12. The method according to any of the claims 8 to 11 , characterized in that it further comprises the following steps : clenching said tubular fabric (4) from the cylinder (3 ) before said step of cutting the fabric (4 ) ; divaricating said cut fabric (4 ) on lateral edges thereof defined by the cutting operation; and outspreading said divaricated fabric (4) before taking up said fabric (4 ) .

13. The method according to any of the claims 8 to 12 , characterized in that said step of cutting said tubular fabric (4) takes place along a basically helical cutting traj ectory.

14. The method according to any of the claims 8 to 13 , characterized in that said cutting traj ectory is determined depending on the twisting rate of said tubular fabric (4 ) and on the difference of angular speed between said cylinder (3 ) , said take-down and take-up assembly ( 6 ) and said cutting means (10) .

15. A method for producing a fabric (4 ) on a circular knitting machine (1) , comprising the steps of actuating in rotation a rotary cylinder (3) so as to produce said fabric (4) and of taking up said fabric (4 ) through a method according to any of the preceding claims .

16. A circular knitting machine comprising : a supporting frame (2) ; a cylinder (3) associated with the supporting frame (2 ) and actuated in rotation around a central rotation axis ( "X" ) at a first angular speed so as to produce at least a tubular fabric (4) ; a take-down and take-up assembly (6) operatively as- sociated with said supporting frame (2 ) and actuated in rotation around said central rotation axis ( "X" ) at a second angular speed so as to engage and take up said tubular fabric (4 ) produced by said cylinder (3 ) , characterized in that it further comprises means (16 , 44) for varying the relative angular position between said take-down and take-up assembly (6) and said cylinder (3 ) during fabric take-up .

17. The machine according to claim 17 , characterized in that said take-down and take-up assembly ( 6) can be actu- ated in rotation around the central rotation axis ( "X" ) at a second angular speed differing from the first angular speed of said cylinder (3 ) .

18. The machine according to claims 17 or 18 , characterized in that said take-down and take-up assembly ( 6 ) can be actuated in rotation around the central rotation axis ( "X" ) independently from the motion of said cylinder (3 ) .

19. The machine according to claim 16 , characterized in that said means (16 , 44) for varying the- relative angular position comprise an intermittent offset device (45 , 46) of mechanical type , which offsets the relative angular position between said take-down and take-up assembly (6) and said cylinder ( 3 ) in at least an angular position of the turn of said cylinder (3 ) .

20. The machine according to any of the claims 16 to 19 , characterized in that said second angular speed of said take-down and take-up assembly ( 6 ) can be varied between a minimum value below the first angular speed of said cylinder (3 ) , and a maximum value above said first angular speed of said cylinder (3 ) .

21. The machine according to any of the claims 16 to 20 , characterized in that said means (16 , 44) for varying the relative angular position comprise control means (16 ) operatively associated at least with said take-down and take-up assembly ( 6) so as to actuate it in rotation, said control means (16) defining the motion of the take-down and take-up assembly (6 ) according to a predefined rela- tion between the first and the second angular speed .

22. The machine according to claim 21 , characterized in that it further comprises at least an electronic control unit (17) operatively associated with said control means

(16) so as to adjust the angular speed of said take-down and take-up assembly (6) depending on the twisting rate of said tubular fabric (4) produced on said cylinder (3 ) of said machine ( 1) .

23. The machine according to claim 22 , characterized in that it further comprises means for automatically detecting the twisting rate of said tubular fabric (4 ) produced on said cylinder (3 ) , said means for automatic detection being operatively connected to said electronic control unit ( 17) .

24. The machine according to any of the claims 16 to 23 , characterized in that said take-down and take-up assembly (6 ) is associated with said cylinder (3 ) through intercon- necting means (23 ) , which can be selectively shifted from a first operating condition in which said take-down and take-up assembly (6) is integral with said cylinder (3 ) , and a second operating condition in which said take-down and take-up assembly (6) moves at a given relative angular speed with respect to said cylinder (3 ) .

25. The machine according to claim 24 , characterized in that said interconnecting means comprise at least a first motion driving element (24 ) turning integrally with said cylinder (3 ) , and at least a second motion driving element (25 ) associated with said take-down and take-up assembly (6) , and an auxiliary motor (26) acting upon said second motion driving element (25 ) .

26. The machine according to claim 25 , characterized in that said first motion driving element (24) is a crown wheel turning integrally with said cylinder (3 ) , and in that said second motion driving element (25) is a toothed wheel mounted turnably onto said take-down and take-up assembly ( 6) and operatively associated with said crown wheel .

27. The machine according to any of the claims 16 to 23 , characterized in that said control means ( 16) comprise : at least a motor (18) ; and driving means (19) operatively placed between said motor (18 ) and said take-down and take-up assembly ( 6) so as to actuate in rotation the latter at said second angular speed .

28. The machine according to claim 27 , characterized in that said at least one motor ( 18) is integrally engaged with said take-down and take-up assembly (6) so as to turn together with the latter around said central rotation axis ( "X" ) .

29. The machine according to claim 27 , characterized in that said motor (18) is stationary and integrally engaged with said supporting frame (2) .

30. The machine according to any of the claims 16 to 23 , characterized in that said control means ( 16) comprise : a motor ( 18 ' ) integrally engaged with said supporting frame (2 ) ;

. first driving means (37) operatively placed between said motor (18 ' ) and said take-down and take-up assembly ( 6) so as to actuate in rotation the latter around said central rotation axis ( ^λλX" ) at said second angular speed; second driving means (38 ) operatively placed between said motor (18 ' ) and said cylinder (3 ) of said machine ( 1) so as to actuate in rotation the latter around said central rotation axis ( "X" ) at said first predefined angular speed; and means for varying the transmission ratio (41) for varying the rotation speed of said take-down and take-up assembly ( 6) and/or of said cylinder (3 ) , associated with said first driving means (37 ) or with said second driving means (38 ) .

31. The machine according to any of the claims 16 to 30 , characterized in that it further comprises cutting means

(10 ) operatively associated with said take-down and take- up assembly (6) so as to cut progressively said tubular fabric (4 ) along a predefined cutting trajectory.

32. The machine according to claim 31 , characterized in that said cutting means (10 ) are designed to cut said fabric (4 ) according to an inclined traj ectory with respect to the central rotation axis ( "X" ) .

33. The machine according to claims 31 or 32 , characterized in that said cutting means (10 ) are integrally asso- ciated with said take-down and take-up assembly ( 6) .

34. The machine according to any of the claims 31 to 33 , characterized in that said cutting means (10 ) comprise at least a cutting element (10a) shifting at least between a first position, in which it is inclined with respect to said central rotation axis ( "X" ) , and a second position, in which it is inclined in the opposite direction and sym- metrically with respect to said central rotation axis

( "X" ) , ■ said cutting element (10a) shifting between the first and the second graduated angular position depending on the difference of angular speed between the cutting means (10 ) and said cylinder (3 ) .

35. The machine according to claim 34 , characterized in that said cutting means (10 ) can be shifted between a plurality of said graduated operating positions .

36. The machine according to claims 34 or 35 , characterized in that said cutting means (10 ) can be shifted manu- ally between said operating positions .

37. The machine according to claims 34 or 35 , characterized in that said cutting means (10 ) can be shifted automatically between said first and second position and are controlled and actuated by said electronic control unit (17 ) .

38. The machine according to one or more claims 31 to 37 , characterized in that the cutting traj ectory of said cutting means (10 ) is basically helical .