WO2007074486A1

WO2007074486A1 - Method for making knitted fabric and related weft knitting machine

Info

Publication number: WO2007074486A1
Application number: PCT/IT2005/000774
Authority: WO
Inventors: Leopoldo Bertagnoli
Original assignee: Leopoldo Bertagnoli
Priority date: 2005-12-29
Filing date: 2005-12-29
Publication date: 2007-07-05
Also published as: BRPI0520820A2; CN101389799A; EP1971711A1; TW200738929A

Abstract

The procedure comprises the following stages: dividing the needles into a first and second group of needles intercalated with one another; raising the needles in the first group along a path (A-Al) until they clear the previously-formed loop, while keeping the needles of the second group on a lower fabric-retaining level (A-B); partially lowering the needles in the first group along a path (Al-A3) on a higher fabric-retaining level (A3); keeping the latches of the needles in the first group open at said higher level (A3) while raising (B-B1) the needles in the second group to prevent the fabric from rising.

Description

"METHOD FOR MAKING KNITTED FABRIC AND RELATED WEFT KNITTING MACHINE"

DESCRIPTION Technical field The present invention relates to a method for making knitted fabric on a weft knitting machine, and to a knitting machine with a single needle bed suitable for implementing said method. State of the art

Known weft knitting machines have a large number of feeding systems (i.e. stations where the needles take up at least one yam and produce a course of stitches), even as many as 120 for a circular machine with cylinder diameters up to 60 inches, the feeding systems being evenly distributed around the cylinder of needles. In such machines, the knitting of the yarns is generally achieved at each feeding system by means of needles and sinkers placed according to an arrangement well known to persons skilled in the art. It is common knowledge that the sinkers cooperate with .the needles in such machines, the former generally moving at right angles to the vertical motion of the latter, to hold down the last course of fabric knitted while the needles rise to take up one or more yams to form the next course of stitches.

Objects and summary of the invention

One object of the invention is to substantially simplify this type of machine, reducing its cost and facilitating its construction and operation, particularly for fine gauges, such as 30 needles per inch or more. According to one embodiment, the invention proposes to avoid the need to use sinkers, thereby obtaining a substantial simplification of the machine and other advantages that will emerge from the following description.

According to a first aspect, the invention provides a knitting method on a weft knitting machine, preferably a single cylinder machine, characterized by dividing the needles selected to form the stitches at the level of a feeding system into at least one first, group and one second group, intercalated with one another; and wherein, at the level of said feeding system, the needles of the first and second groups are controlled so that, while the needles of one group rise, the needles of the other hold down the previously-formed fabric and vice versa. In essence, therefore, according to the method of the present invention, the needles are controlled so that a part of them performs the function (typical of sinkers) of holding down the already formed fabric while the other needles rise to clear the previously formed stitch.

The intercalated groups of needles can be arranged in various ways. For instance, the needles of the first group can be the ones in the even- numbered positions and the needles of the second group can be the ones in the odd-numbered positions. Or, for instance, alternate pairs of needles can be considered, or the even-numbered pairs can form the first group of needles and the odd-numbered pairs can form the second group of needles. But other arrangements can also be adopted.

It should be clear that, in the context of the present description and attached claims, terms such as to raise, lifting and upstroke referring to the movement of the needles are conventionally used to mean a movement that extracts the needles from the grooves in the needle bed and brings them up to where the yarn is delivered, which is not necessarily a vertically upward movement.

According to an improved embodiment of the invention, at the level of the feeding system, the needles of the first and second groups are raised into positions that are staggered in relation to one another, so that when the first group of needles is lifted, the second group of needles holds down the previously-formed fabric, and when the second group of needles is lifted, the first group of needles holds down the previously-formed fabric, while the needles of the first group are partially lowered before the needles of the second group are raised.

In a particular embodiment, the method involves the following steps:

- dividing the needles that take up the yarn into a first and a second group of needles intercalated with one another; - at the level of said at least one feeding system, raising the needles of the first group and opening the latches to clear the previously formed loop on the shank of the needle, while keeping the needles of the second group on a lower fabric-retaining level so as to prevent the fabric from rising;

- partially lowering the needles of the first group to a higher fabric-retaining level where the ends of the open latches come into the vicinity of the already formed fabric; - keeping the latches of the needles of the first group open on said higher fabric-retaining level while the needles of the second group are raised. The lower fabric-retaining level at which the needles of the second group are kept is preferably lower than the loop clearing level defined by the top edge of the needle bed, and when the latches of the needles of the first group have been lowered to said higher fabric-retaining level, they are kept open by a latch retaining member. According to the known state of the art for weft knitting machines, such level of the loop clearing plane can be adjusted by means of mechanisms that move the camboxes, and therefore also the needle lifting cams, with respect to the needle bed. By means of said mechanisms, said level can be set in the most convenient position so that the needles of the first and second group can hold the fabric effectively in the above-mentioned positions.

According to the invention, the fabric can consequently be prevented from rising during the formation of new courses of stitches without the need to use sinkers, thus obtaining a simplification of the machine. The method and the means indicated are valid for any machine gauge and stitch density per unit area of fabric, and for any kind of weft, and they are particularly advantageous for machines with gauges higher than 30 needles per inch for producing extra-fine fabrics. The invention leads to a simplification of the construction of circular knitting machines, eliminating 50% of the knitting elements, the outer crown for supporting the sinkers on the revolving needle bed, the camboxes and related cams for controlling the horizontal movements of the sinkers, and the related mechanical supporting and fixing members.

A further advantage consists in the reduction of friction, wear, overheating and breakages in the knitting area, and the consequent reduction in energy consumption and in the costs of servicing and operating the machinery.

Adopting the method of the present invention consequently enables the construction of more straightforward and more efficient circular and flatbed knitting machines, also hosiery knitting machines, than are currently available, that enable the knitting even of ultra-fine fabrics thanks to the absence of the sinkers, while retaining the feature of being able tϋ^" simultaneously or separately knit on every delivery line the ground yarn, the colored yarn and the elastomer yam, to obtain plain and patterned fabrics (even with jacquard patterns), and even two- or three-fold plated knitting.

The invention consequently also relates to weft knitting machines designed for implementing the above described knitting method.

According to a first aspect, the weft knitting machine includes a needle bed, at least one feeding system for delivering at least one yarn with a guide eye and, in line with said feeding system, a cambox with means for controlling the needles, wherein the cambox defines two different paths for two groups of needles intercalated with one another, said paths being shaped so that when the needles of the first group are raised to clear a stitch previously formed thereon, the fabric is held down by the needles of the second group, and when the needles of the second group are raised to clear a stitch previously formed thereon, the needles of the first group hold down the already formed fabric.

In a practical embodiment, the two paths of the needles of the first and second group each have an upstroke of the needles of each needle group, said upstrokes being staggered along the path of the relative movement between the cams and the needle bed; the upstroke of each of said paths overlaps with a portion of the other path set on a lower level than the maximum height reached by the needles on said upstroke.

In a particularly advantageous embodiment, the first path of the needles comprises an initial stretch of upstroke of the needles of the first group that coincides with an initial, preferably substantially horizontal stretch on a lower fabric-retaining level of the needles of the second group. Thereafter, the first path comprises a preferably horizontal stretch on a higher fabric-retaining level, coinciding with the upstroke of the needles of the second group, where the latches of the needles of the first group are kept open by a latch retainer member.

It is preferable, especially for fine-gauge machines used in the. production of top-quality fine fabrics, to have the needles of. the, even- numbered positions that constitute the lower fabric-retaining level on the feeding systems in the odd-numbered positions while the other needles constitute the upper fabric-retaining level, and vice versa on the feeding systems in the even-numbered positions. This avoids the constant, identical repetition of the paths of the needles on all the feeding systems, which can give rise to vertical or horizontal ribbing effects in the fabric.

According to one embodiment of the invention, in a circular single-knit machine for making plain knitted fabrics (jersey) or knitting with tuck stitch and/or float stitch effects, e.g. 1/1, the needle control means comprise a respective butt for guiding a first and a second group of needles intercalated with one another, placed respectively on different levels, said butts engaging in respective cambox channels designed to obtain said paths. In practical terms, observing the form of said channels in each feeding system and in the direction of rotation of the needle cylinder, the first channel comprises an initial stretch of upstroke to bring the needles up to the level where they take up the yarn with or without releasing the last stitch formed. Said stretch of upstroke comes to coincide with a horizontal stretch of the second channel wherein the needles of the second group come to be with their hooks on a level with the fabric. The first channel continues with a horizontal stretch where the needles of the first group are kept on a higher fabric-retaining level, where the ends of their open latches come to be on a level with the fabric, said needles being kept with their latches open by means of a latch retainer member. Coinciding with said horizontal stretch of path of the first channel, the second channel comprises a greater or lesser stretch of upstroke of the needles, suitable to bring the needles up to the level where they can take up the yarn with or without releasing, i.e. clearing the last stitch formed.

Thus, while the needles of the first group are raised to the level where they take up the yarn, the needles of the second group are kept on a level with the fabric and thus hold it down, preventing it from being lifted together with the rising needles due to friction. Moreover, while the needles of the second group are raised, the ends of the open latches of the needles of the first group form an upper support for the fabric, preventing it from being lifted due to friction by the needles that rise to take up the yarn.

Another embodiment of the invention concerns a circular single-bed machine that also enables the creation of jacquard fabrics, and that comprises needles with only one butt on the same level and selecting jacks that cooperate with selection devices of known type, e.g. piezoelectrically- controlled devices. Said jacks can, for instance, be of oscillating type and have a number of selecting butts on which, in line with the various feeding systems, the selecting levers of respective selection devices or actuators take act.

In this machine, according to the invention and as further explained below, for each feeding system there are two cams for lifting the jacks situated on different levels one after the other in the direction of rotation of the cylinder, said cams being capable of lifting respective jack raising/lowering butts to a yarn take-up level. For each feeding system there are two selecting devices for selecting the jacks (and thus also the needles) situated one after the other in the direction of rotation of the cylinder in order to lift them respectively onto said first or second raising cam. With the cooperation of specific cams for lowering the needles and jacks, this gives rise to the above-described knitted fabric production method according to the invention.

According to the invention, the latch retainer members, which are preferably integral with the guide eye for the respective feeding system have a smooth, continuous surface extending adjacent to the needle raising and lowering path, said surface being defined by: a first stretch of sloping edge at the level of the ascending stretch of said first group of needles, immediately downstream from where their latches open; a second, similar stretch of sloping edge in line with the ascending stretch of said second group of needles, immediately downstream from where their latches open; and a stretch with a horizontal edge, extending in the vicinity of the fabric, for keeping the latches of the needles of the first group open while the needles of the second group rise. The latch retainer member integral with the guide eye preferably has a hole radial to the cylinder for delivering the ground yarn and two passages, e.g. holes or grooves, tangential to the cylinder for delivering two plating yarns. The lack of sinkers and related members, and the corresponding space saving, enables a more favorable arrangement of said holes for the proper positioning of the yarns in relation to the path of the needles.

In order to form the stitch loops in a machine without sinkers, the needles cooperate with the top edge of the walls of the respective grooves in the needle bed. In a preferred embodiment of the invention, said top edge preferably has a curved profile with a descending slope that becomes steeper in the direction in which the fabric slides. In practical terms, the walls of the needle bed on either side of the grooves where the needles slide have a top edge (in a substantially radial plane, i.e. containing the axis of the needle bed) with a curved profile that slopes downwards increasingly steeply in the direction in which the fabric slides. Such profile has a first stretch, towards the outside of the needle bed, with a gentle gradient and a second stretch, towards the inside of the needle bed, with a steeper gradient. Thus, during stitch formation, the different yarns (e.g. three) delivered to each feeding system to form a plated fabric, because they are staggered angularly, with the ground yarn closer to the needles, said ground yarn comes into contact with the second, steeper stretch of the profile and is easier (than the other yarns) for the needles and the weight of the fabric to pull towards the internal end of said profile. This facilitates clearing of the previous loop and the separation of the yarns, with the ground yarn towards the front of the fabric and the others towards the back of the fabric.

In a machine according to the invention, there may also be a pair of latch opening devices to start the knitting process, or to restart it after the yarn has broken, each latch-opening device being positioned respectively to coincide with said upstrokes of the first and second groups of needles. Moreover, in a particular embodiment suitable for fine-gauge machines, e.g. more than 36 needles per inch, needles are used wherein the part that comes into contact with the stitch is narrower. This avoids the need, as explained in detail later on, to widen the grooves in the needle bed (as is conventionally done) to make space between said part of the needle and its groove, thus making the construction of the needle bed easier and less expensive. Brief description of the drawings

The invention is better explained with reference to the attached drawings, which show a non-limiting example of the invention. In the drawings:

Fig. 1 shows a partial cross section in a vertical radial plane of a circular weft knitting machine according to the invention, of the type for producing plain knitted fabrics G^ersey) or with 1/1 tuck stitch and float stitch effects;

Fig. 2 shows a plan view of a partial cross section along H-Il of the camboxes and the path of the needles in the machine of Fig.1 , wherein (for the sake of clarity) the needles are shown rotated 90° around their axis with respect to their actual position; Fig. 2A shows front and side views of the needles used in the machine in Fig.1 ;

Figs. 2B and 2C each show an enlarged partial front view of the upper part of the needle bed and of the needles in the machine in Fig.1 , respectively in the classic embodiment and in an innovative embodiment suitable for fine-gauge machines;

Fig. 3 shows an enlargement of detail III in Fig. 2;

Fig. 4 shows a cross section along IV-IV of Fig. 3;

Fig. 5 shows an enlargement of detail V in Fig.1 ;

Fig. 6 shows an enlargement of detail Vl in Fig.1 , in this case the radial cross section coincides with a needle-opener;

Fig. 7 shows a view along VII-VII of Fig.6;

Fig. 7A shows needles and camboxes in a circular knitting machine according to another embodiment of the invention, in a view similar to that of Fig.1 ; Fig. 8 shows a view similar to that of Fig.1 of a circular weft knitting machine for making fabrics with jacquard patterns according to the invention;

Figs. 9A and 9B show front and side views, respectively, of a needle and corresponding jack in the machine of Fig. 8;

Fig. 9C shows the arrangement of the butts for the needles and jacks in a stretch of the cylinder in the machine of Fig. 8;

Figs. 10 and 10A respectively show plan views along X-X of the camboxes and the path of the needles in the machine of Fig. 8, and a top view along XA-XA;

Figs. 10B and 10C show enlargements of portions of Fig.10; Fig. 1OD shows an enlargement of a portion of Fig. 10A; and Fig. 11 shows a similar view to that of Fig. 2 of a circular weft knitting machine according to the invention, in a simplified version.

Detailed description of preferred embodiments of the invention The circular knitting machine shown in Figs. 1 and 2 comprises a frame 10 and drive means 11 that support and drive a revolving cylinder 1 , or needle bed, with a plurality of needles N obliged to turn together with the cylinder, but free to be moved vertically (parallel to the axis of rotation of the needle bed) within suitable grooves by means of a system of cams. The machine comprises a plurality of feeding systems with fixed cam systems AL; AL1 , AL.2, AL3, AL4, ... (Fig. 2) - also called camboxes - for moving the needles, said systems being associated with respective devices for delivering the yarn, distributed evenly around the circumference of the cylinder.

Each yarn delivery device is provided with a guide eye 7, arranged above each cam system. In a preferred embodiment, each guide eye is designed and arranged so as to provide the needles simultaneously with at least three yarns G1 , E1 , V1 (see also Figs. 3 and 4) and is capable of being translated vertically or rotated from the working position L to the resting position F (Fig. 2) to facilitate the threading of and/or maintenance on the feeding system.

The structure of the guide eye is illustrated in detail in Figs. 3 and 4, and each guide eye is designed to be associated with the upstroke and dόwnstroke profiles of the cams controlling the needles of the corresponding camboxes AL1 - AL4.... The cylinder, or needle bed, is provided with a number of vertical grooves 2 (see Figs. 4 and 5) corresponding to the number of needles N that can be selected to take up the yarn or remain at rest by mechanical, electromechanical or electronic means at each feeding system.

According to the present invention, a mechanical needle selection is adopted for the machine shown in Figs.1 and 2, using two guide channels CS1 and CS2 to control the upstroke of the needles and one guide channel CFM to control stitch formation, with the lowering of the needles inside their respective grooves 2.

Each guide channel CS1 and CS2 is defined between respective upper and lower cam profiles.

All the needles (Figs.2, 2A) have a first butt TM in an upper position, hereinafter also called the stitch forming butt, and engaged in the guide channel CFM to form the stitch. An upper cam CFM1 delimits the stitch forming channel CFM and, by acting on the stitch forming butt TM, it gradually lowers the corresponding needle to form the stitch with the yarn engaged by the needle at the level of the corresponding feeding system.

Moreover, the needles are divided into two groups that are intercalated with one another. According to the embodiment illustrated, the needles are preferably divided into a first group comprising (in the embodiment illustrated) the needles of the even-numbered positions and a second group comprising the needles of the odd-numbered positions, or vice versa. In Fig. 3, the needles of the even-numbered positions are indicated as NP, and those in the odd-numbered positions as ND. The needles of the two groups differ from one another in that they have a selecting butt alternately in an intermediate TS1 or low TS2 position, engaged respectively in the guide channel CS1 and CS2. Each cambox AL, AL1 , AL2, AL3, AL4... has an arrangement of cams, and a consequent arrangement of channels CMF, CS1 and CS2, that can vary according to the type of movement to induce in the needles of the two groups at the level of said cambox.

To be more precise, in the configuration illustrated in Fig. 2, the camboxes AL1 and AL2 are set so as to raise and lower all the needles so that they each form a stitch, although said movement is staggered (as explained later on) for the two groups of needles (ND, NP) intercalated with one another.

In the preferred embodiment illustrated herein, the two camboxes AL1 , AL2 have substantially identical channels CS1 , CS2, except that the shapes of the respectively upper and lower selecting channels CS1 and CS2 of the cambox AL1 are inverted in the cambox AL2. In other words, the upper channel CS1 of the cambox AL1 , where the intermediate selecting butts TS1 slide, is the same shape as the lower channel CS2 of the cambox AL2, where the low selecting butts TS2 slide. Similarly, the channel CS2 of the cambox AL1 has the same shape as the channel CS1 of the next cambox AL2. Vice versa, the stitch forming channels CFM are substantially the same in the two camboxes AL1 , AL2.

As will become clear later on, the aim of this inversion in the shape of the guide channels CS1 , CS2 for the intermediate and low selecting butts TS 1 , TS2 respectively is to reverse the sequence whereby the needles of the two groups (even needles and odd needles) are raised and lowered in line with the two subsequent feeding systems associated with the subsequent camboxes AL1 , AL2: this enables a smoother fabric to be obtained.

By way of example, the camboxes AL3 and AL4 in Fig. 2 are shown with different channel configurations from the camboxes AL1 and AL2. The cambox AL3 has a stitch forming guide channel CFM substantially the same as the channel CFM of the previous camboxes, in terms of the profile of upper cam at least. Vice versa, the two channels CS1 and CS2 for the intermediate and low selecting butts TS1 and TS2 respectively have different shapes from the channels CS1 , CS2 of the camboxes AL1 , AL2.

To be more precise, the channel CS1 in the cambox AL3 is delimited by a cam 13A that raises the needles less than the raising cam 12A defining the channel CS1 in the cambox ALl Likewise, the channel CS2 of the cambox AL3 is delimited by a cam 13B that raises the needles less than the raising cam 12B of the cambox ALL So, in line with the feeding system where the cambox AL3 is positioned, all the needles (both the even- numbered NP and the odd-numbered ND) hold down the previously-formed loop without clearing it, and engage the yarn again to form a new stitch.

In the next cambox AL4, yet another needle raising cam arrangement is illustrated, where the intermediate guide channel CS1 for selecting the needles with the intermediate selecting butt TS1 has much the same shape as that of the channel CS1 of the cambox AL1, while the lower channel CS2 is delimited by a cam 14B that holds the needles inside the needle bed, in a resting position, with the low selecting butts TS2. , In the area above the camboxes AL1 , AL2, AL3, AL4, in line with the guide eye 7, there are curves representing the trajectory of the heads of the needles of the two groups of needles intercalated with one another. One type of dotted line with the reference TrD indicates the trajectory of the odd- numbered needles ND, while a different dotted line with the reference TrP shows the trajectory of the even-numbered needles NP. In practical terms, the curves TrP and TrD represent the envelope of the positions occupied by the hooks of the even-numbered NP and odd-numbered ND needles, respectively. Note that, in line with the camboxes AL1 , AL2, the trajectories TrD, TrS are the same and inverted (i.e. the trajectory TrD has the same shape in line with the cambox AL2 as the trajectory TrP in line with the cambox AL1 , and vice versa).

In line with the cambox AL3, the trajectories TrP and TrD are lower because the stitches are not cleared, while in line with the cambox AL3 the trajectory TrP of the even-numbered needles is repeated in the same way as in line with the cambox AL2, and the odd-numbered needles (low selecting butt TS2) remain at rest.

Clearly, the configuration of the four camboxes AL1 , AL2, AL3, AL4 is illustrated purely as an example to show possible variable cambox configurations.

Basically, and with particular reference to the feeding system corresponding to the cambox AL1 (see also the enlargement of Fig. 3), the innovation that does away with the need for sinkers consists in making the needles of the odd-numbered positions ND, with the stitching butt TM and the selecting butt TS1 in the intermediate position, and the needles of the even-numbered positions NP, with the stitching butt TM and the selecting butt TS2 in the low position, take turns in holding down the fabric, i.e. the even-numbered needles NP remain momentarily at rest in the stretch coming between the positions indicated by A and B (Fig. 3) until the odd-numbered needles ND have cleared the stitch in position A1 and then dropped back into position A3 so that their latches 3 hold the fabric down during the upstroke of the even-numbered needles NP from position B to position B1. When the odd-numbered needles ND rise from position A to position A1 along the channel CS 1 of the cam system or cambox AL1 of Fig. 2, the even-numbered needles NP stay low in their channel CS2, from position A to position B.. In this phase, the even-numbered needles NP hold down the previously^formed fabric, preventing it from being drawn upwards by the displacement of the odd-numbered needles ND. The latter are raised up to position Al In this vertical rising movement, the latches 3 on the odd- numbered needles ND open and the loops or stitches formed on each needle are cleared, i.e. they slide along the shank of the needle and underneath the open latch 3.

Basically, in this phase, the hooks of the even-numbered needles NP perform the same function in relation to the odd-numbered needles ND as the hooks of sinkers, i.e. they hold the fabric down.

Then, after the odd-numbered needles ND have reached position A1 and unloaded the old stitch M, they are brought back down to position A3, on an intermediate level between A1 and A, to hold the fabric down and prevent it from rising by means of their open latches 3 resting on a lower profile PF of a surface 19 of the guide eye 7, as the even-numbered needles NP rise from position B to position B1 to clear their stitch M. The surface 19 with the lower profile PF of the guide eye thus acts as a latch retainer member.

In this phase, the latches 3 of the odd-numbered needles ND perform the same function in relation to the even-numbered needles NP as the hooks of sinkers, holding the fabric down.

After the even-numbered needles NP have cleared their loops in position B1 , the odd-numbered needles ND are brought back up to position A4. The stitching butts TM (Fig. 2) of both the even-numbered needles NP and the odd-numbered needles ND then encounter the upper cam profile of the stitching channel CFM and follow a common path from position B3 along which they descend to take up the yarn and form the new loop in position A5.

The same sequence of operations takes place in the next feeding system (cambox AL2), except that the needles NP and ND are inverted, i.e. the needles NP follow the trajectory followed by the needles ND in the previous cambox, and vice versa.

This inversion is not indispensable, i.e. the process functions even if the needles ND and NP always perform the same movement in line with successive camboxes, but their inversion gives the fabric a smoother finish.

If fabrics with a knitting structure containing tuck stitches and/or float stitches are required, the needles can be brought into tuck stitch or float stitch positions by adjusting the position of the cams, as shown and described for the camboxes AL3 and AL4. The geometrical shape of the guide eye 7 (Figs. 3 and 4) is strictly correlated with the above-described stitch forming cycle and is designed to ensure stitch formation and to protect the latches on the needles, and enable their opening and closing. In fact, the guide eye has a first sloping edge 16 coming up against the needles, that coincides with the first ascending profile from A to A1 for the needles of a first group (e.g. the odd-numbered needles ND) so as to ensure the opening of their respective latches 3. This first sloping edge 16 is followed by a dip 17, then by a similar sloping edge 18 coming up against the needles, that coincides with the second ascending profile of the needles of the second group, (e.g. the even-numbered needles NP) from B to B1 to enable the opening and subsequent protection of their latches 3. The sloping edge 18 is followed by the previously-mentioned straight lower profile PF.

In the preferred embodiment illustrated in the drawings, the right end (looking at Figs. 3 and 4) of the guide eye is suitable for delivering the three yarns that can be served to each feeding system in the correct position. A ground yarn G1 is delivered through a first hole G, oriented radially to the cylindrical needle bed; the elastomer E1 is delivered through a second hole or groove E, situated in a higher position and almost at right angles to the first; and the colored yarn or plating yarn V1 is delivered through a third hole or groove V situated below the others and almost parallel to the second.

Moreover, a particular advantage derives, for the purpose of the present invention, from the curved profile of the top edge 2B of the grooves 2 in the cylinder (Fig. 5) - called the knock over profile. Given its rounded shape, it serves to keep the ground yarn G1 , the plating or elastomer yarn E1 , and the plating or colored yam V1 separate in the so-called yarn take-up stretch from P to R. The ground yarn G1 rests on a surface sloping more steeply towards the inside of the needle bed than the plating yarns, e.g. an elastomer yam (E1) or colored yarn (V1). The dotted line in Fig. 5 indicates the loops of the three yarns. G1 , E1 , V1 in an initial stage of stitch formation, and the continuous line shows the same loops in the final stage, i.e. with their required final length. Note that, during their formation, these loops slide along the knock over profile from stretch P-R to stretch R-S each in their respective initial positions, i.e. with the ground yarn G1 on the front of the fabric and the plating yarns E1 , V1 on the back of the fabric.

The difference in the gradient of the supporting elements for the two or three yarns means that, as the hook U on the needle takes up the yarn and the needle drops back inside the needle bed, the ground yarn G1 slides towards the inside of the needle bed more rapidly than the plating yarns E1 and V1.

This ensures that the relative positions of the two or three yarns are constantly maintained, preventing the yarn from overlapping or overriding one another during loop formation, eliminating the risk of the yarns becoming inverted, and thus assuring that one yarn is always visible on the front of the fabric and the second and third are only visible on the back.

Sporadic or even only momentary inversions can cause considerable damage in the production of fabrics because the resulting defects can only be detected on inspection after completing the piece of fabric, i.e. when there is no alternative but to scrap the production or reduce its price.

Another equally advantageous function performed by the curved profile on the top edge 2B of the groove 2 of the needle bed, is that - in the so-called knock over stretch from R to S (Fig. 5), after the yarns have been taken up and the needle N has consequently dropped back inside the needle bed - it facilitates the sliding of the yarns being delivered towards the inside of the needle bed 1 (point S).

Thanks to the effect of the sloping plane, designed to distribute the load and the friction due to the tension of the yarn over the whole surface from P to S, there is less localized wear on the edge of the needle bed and the old loop 4V is brought towards the inside of the needle bed in a withdrawn position Z, aligned with the bottom of the grooves 2, where the needles N slide, and consequently does not interfere with the subsequent upstroke of the needles.

In this way, the loop knock over effect obtained with conventional sinkers is also achieved in the position of greatest pressure on the fabric.

With reference to Figs 6 and 7, the machine comprises latch-opening devices 15A and 15B that can be permanently or removably associated with each feeding system (e.g. AL1 and AL2 in Fig. 2), suitable for installing on the fixed structure (e.g. the cambox 5) by mechanical or magnetic means so as to guarantee the opening of the latches 3 even if there is no old loop at the start of the two upstrokes A-Al, B-B1 of the needles N. The angular and radial position of the latch-opening devices is assured by positioning elements EP1 and EP2 fixed on each feeding system and/or on the device itself. These latch-opening devices may also be of pneumatic type, i.e. using air flows with a controlled pressure, suitably oriented and designed to be actuated continuously or according to the operator's needs, e.g. when returning to work.

Fig. 2B shows the upper part of the needle bed and the needles of a circular machine, as described above, in a classic embodiment, wherein the upper end of the grooves 2 in the needle bed has a wider opening 2A in line with the upper part of the respective needle N when this is in its lowest position for stitch formation. Fine-gauge machines (e.g. more than 36 needles per inch) according to the present invention can be used with needles that are narrower in the part with the hook, as shown by the dimension (t) of Fig. 2C, leaving a distance (z) equating to at least the maximum diameter of yarn being used between the needle hook and the walls of the respective groove 2.

This avoids the need for machining to create said wider opening 2A in the grooves 2, with an economic advantage in the construction of the machine.

In the figures described so far, each cambox AL has a stitch forming channel CFM in addition to the two needle raising channels CS1 and CS2 and each needle has a stitch forming butt TM and a needle raising butt TS 1 or TS2. An even further simplified machine can be made, however, wherein each needle N has a single butt TS1 or TS2, the needles of the two intercalated groups (e.g. even-numbered and odd-numbered ND, NP) respectively having butts TS1 and TS2 at two different heights. In this case, the camboxes AL will only have the channels CS1 and CS2, which will control both the raising of the needles and their lowering to form the stitch. A cambox configuration of this type is shown in Fig. 7A, wherein an even- numbered needle and an odd-numbered needle are also shown, respectively, with the butts TS1 and TS2. The same numbers indicate the. same or ■. equivalent parts as in Fig. 2. The camboxes AL1 .... AL 8 shown in Fig. 7A have cams variously arranged according to the previous description referring to Fig. 2. In particular, camboxes with cams at rest 14B (cambox AL8) and camboxes with tuck stitch cams 13A, 13B (cambox AL5) are also illustrated.

According to the known technique used in weft knitting machines, the height of the loop clearing plane is adjustable by means of mechanisms that reciprocally translate the cambox, and thus the needle raising cams, in relation to the needle bed. In the machine of Fig. 1 said regulating mechanism comprises the fact that the cam-holders 5 are fixed to a ring- shaped plate 6 resting on the base 10 with a ring 12 inserted between them. The ring-shaped plate 6 and the ring 12 are coupled to one another by means of a thread 6A cut on a respectively external and internal cylindrical surface of said parts and coaxial to the needle bed. Moreover, a toothed wheel 6B is mounted on the ring-shaped plate and engages with an internally toothed crown 12A on the ring 12. Thus, turning the wheel 6B manually with the aid of an Allen wrench inserted in a corresponding axial cavity 6C induces a micrometric raising or lowering of the ring-shaped plate 6 and, with it, of all the camboxes in the machine: this enables a very fine adjustment of the height of the lower and upper fabric-retaining needles, positioning them so that the needles of the first or second group always hold the fabric effectively.

The above description illustrates a first, particularly straightforward embodiment of a circular knitting machine according to the invention, but the basic concepts of the present invention can also be applied to more complex machines, e.g. for the production of knitted fabrics with jacquard patterns. A machine of this type is illustrated in Figs. 8 to 10B. The same numbers are used to indicate parts that are the same as, or equivalent to those of Figs.1-7A.

The machine of Figs. 8-10 again has a frame 10 with drive means 11 for supporting and turning a cylinder or needle bed 1 with a plurality of needles N obliged to turn together with the cylinder 1 and free to be moved parallel to the axis of rotation of the cylinder inside grooves 2, under the control of suitable cams as described below.

In addition to the needle N, each groove 2 in the cylinder 1 contains an jack or needle lifter S. The shape of the needles N and needle lifters S is illustrated in detail in Figs. 9A, 9B, 9C. Each needle N has a stitching butt TM and each jack or needle lifter S has two raising butts TKA, TKB, respectively upper and lower butts, driven by respective raising cams CSA and CSB of the single camboxes or cam-holders arranged around the cylinder 1 and generically indicated by AL in Fig. 8. As in the example shown in Figs.1 to 7, here again, there is a plurality of feeding systems around the circumference of the cylinder, coinciding with a series of respective camboxes AL. TSV is used to indicate the selecting butts of the jacks S.

Each feeding system is associated with a guide eye 7, similar to the guide eye 7 of the machine of Figs.1 to 7, that is also capable of a rising or oscillating movement so as to be brought into a resting position to enable access to the needle bed.

According to a preferred embodiment, each feeding system is associated with at least two actuators 6B and 6T that have selection levers, indicated by 6B1 for the actuator 6B and 6T1 for the actuator 6T. In the embodiment illustrated, the levers 6B1 are of the double-thrust type (known for instance from US patent N. 6,886,380) and have (Fig.10A) two profiles X and Y that come to bear in the manner described below on the selecting butts TSV of the jacks or needle lifters S. Conversely, the levers 6T1 of the actuators 6T are single-thrust levers and have a single profile W. As shown in Fig. 10, the levers 6B1 are staggered vertically by two positions with respect to the levers 6T1.

As explained in more detail later on, the actuators 6B select the needles one by one to select the needles N that must be enabled in line with each feeding system, and they also make the needles of a first group (e.g. the even-numbered needles) follow a different rising path that is staggered with respect to the needles of a second group (e.g. the odd-numbered needles), intercalated with the needles of the first group.

Each cambox AL (AL1 , AL2, AL3, AL4....) has a stitch forming cam CFM acting on the butts TM of the needles N and, in a lower position, the two needle raising cams CSA and CSB. These cams take effect on the butts TKA and TKB of the needle lifters or jacks S, making them rise, while a further cam profile CD (associated with the cams CSA, CSB) and a further cam profile CA, associated with the stitch forming cam CFM, control the lowering movements of the needle lifters S and needles N, respectively, to make said knitting elements complete the working cycle, which is described in greater detail below with specific reference to Figs. 10, 1OA, 10B, 10C, 10D. The actuators 6B, with their levers 6B1 having a dual-profile X, Y, can be used first to keep the required needles completely at rest in line with their respective feeding systems. In Figs. 10, 10A the first actuator 6B on the left (in the drawing) associated with the guide eye 7A is used to take action with both its profiles X and Y on all the selecting butts TSV of all the needle lifters S As a consequence, each needle lifter is pushed right down into its vertical sliding groove 2 and passes in front of the cambox cams without its butts TKA, TKB being engaged on the respective cams CSA, CSB. Thus, in line with the feeding system with which the guide eye 7A is associated, all the needles N remain low, i.e. at rest. This is a first possible selection afforded by the actuator 6B. Fig.10A shows how the butts TKA₁ TKB pass in front of the needle raising cams CSA, CSB without being raised because they do not enter the channel defined by the cams.

Conversely, in line with the feeding system associated with the next guide eye, indicated by 7B (Fig.10), the actuator 6B brings all the needles N into the working position, making them clear the stitch previously formed on each needle and take up the yarn from the guide eye 7B to create another stitch. Because the machine has no sinkers, the needles N are raised in a staggered sequence so that, for instance, the even-numbered needles NP hold down the knitted fabric while the odd-numbered needles ND clear the loop or previously-formed stitch or loop, and the odd-numbered needles ND hold down the fabric while the even-numbered needles NP clear the previously formed stitch or loop.

For said purpose, supposing that the needles of the odd-numbered positions ND are the first to rise, the levers 6B1 of the actuator 6B are brought act upon the selecting butts TSV of the various needles N with the profiles X and Y so that: no profile of the corresponding lever 6B1 act on the selecting butts TSV of the needles of the odd-numbered positions ND. So, as the cylinder 1 turns, the needle raising butts TKA on the odd-numbered needles ND encounter the upper raising cam CSA and consequently rise; only the profile X of the levers 6B1 act on the selecting butts TSV of the needles in the even-numbered positions NP, so the respective needle lifters S do not engage their upper needle raising butt TKA with the upper raising cam CSA, but they do engage their lower needle raising butt TKB with the lower raising cam CSB. Since the profile of this cam CSB is angularly staggered around the circular trajectory of the needle bed, the even-numbered needles NP rise after a delay with respect to the odd-numbered needles ND. The upper raising cam CSA has an ascending profile that extends from point A to point A1. When the butt TKA of an jack S follows this stretch of cam profile, the hook on the corresponding needle ND follows a portion of the trajectory TrD that extends between two points, again indicated as A and Al Along this path for raising the needles in the odd-numbered positions ND, the previously-formed fabric is held down by the needles in the even- numbered positions NP, that perform the function normally served by sinkers. As a result, as in the example previously illustrated, the needles in the odd-numbered positions ND can clear the stitch during the rising movement from A to A1 , along which their latches 3 open. The jacks or needle lifters of the needles in the even-numbered positions NP engage their lower raising butts TKB with the lower raising cam CSB, which has an ascending profile extending from point B to point B1 , with a flat intermediate stretch between points B2 and B6. The trajectory of the needles in the even-numbered positions NP, indicated by TrP (Fig.10), has a corresponding shape and, using the same references B, B1 , B2, B6, it shows the points coinciding with the points B, B1 , B2 and B6 on the lower raising cam CSB. The point B1 on the trajectory TrP of the even-numbered needles NP is at the same height as the point A1 on the trajectory TrD of the odd- numbered needles ND. Along the ascending path from point B to point B1 , the even-numbered needles NP clear their previously-formed loop or stitch in much the same way as the odd-numbered needles do between point A and point A1. During said movement the already formed fabric needs to be held down to avoid it being drawn upwards by the movement of the even- numbered needles. For said purpose, in much the same way as in the solution described previously with reference to Figs. 1-7, the needles in the odd-numbered positions ND and the corresponding jacks S drop down to an intermediate level between points A and A1 , corresponding to the height of the point indicated by A3 on the trajectory TrD, and remain in said position until both the even-numbered needles and the odd-numbered needles have been lowered to form a stitch. The needle lowering movement is governed by a descending stretch of the cam profile CA associated with the stitch forming cam CM. A3 indicates the points where the descending stretches terminate not only on the trajectory TrD of the needles, but also on the cam profiles CA and CD. Thus, the odd-numbered needles ND are partially lowered by coming to act on the stitch forming butts TM with the stretch of cam CA from point A1 to point A3 of the cam profile, while the jacks are partially lowered by the portion of cam CD coming between points A1 and A3 of said cam. The movement to raise the even-numbered needles NP begins when the odd-numbered needles ND, with their latches 3 open and their stitch cleared, come to be on a level with point A3 on their trajectory TrD. They are held in this position, preventing them from being lifted by the portion of profile between points B6 and B3 of the cam CSB, by the levers 6T1 of the actuator 6T. The levers corresponding to the selecting butts TSV of the jacks S of the odd-numbered needles ND are brought into the active position to work with the profiles W on the butts TSV, so as to prevent the jacks S of the odd- numbered needles ND from engaging the cam CSB.

Once the needles in the even-numbered positions NP have cleared their stitch, they begin to drop from the level corresponding to point B1 towards point B. The jacks S do likewise.

As the cylinder continues to turn, the needles NP and ND encounter the stitch forming cam CFM that lowers them after the yam has been taken up, while the jacks S are lowered by the corresponding descending portion of the cam CD.

In Figs. 1OC and 10D, TKA(P) and TKA(D) indicate the needle raising butts TKA on. the jacks in even-numbered and odd-numbered positions, and TKB(P) and TKB(D) indicate the needle raising butts TKB on the jacks in even-numbered and odd-numbered positions, respectively. Thus, with the sequence of movements described, on each feeding system the needles alternately hold down the fabric, the even-numbered needles NP remaining at rest in the stretch coming between A and B while the odd-numbered needles ND clear the stitch in position A1 , then drop back to position A3 and remain there due to the selecting action of the levers 6T1 of the actuator 6T, holding the fabric down with their latches 3 during the upstroke from B to B1 of the even-numbered needles NP, thereby enabling the clearing of the old stitch in positions A1 (for the odd-numbered needles) and B1 (for the even-numbered needles). Clearly, in the series of feeding systems around the cylinder, the above-described selection between even-numbered needles and odd- numbered needles can be inverted. In other words, in the feeding system next to the one described, the even-numbered needles NP can be raised before the odd-numbered needles ND. The single-thrust levers 6T1 of the actuator 6T₁ of electronically- controlled piezoceramic, electromechanical type for instance, are situated at various heights and can also select the needles one by one, so as to place the required needles in the stitch loaded or tucked position by acting with the profile W on the selecting butts TSV of the needle lifters or jacks S, previously selected by the actuator 6B to rise into position B, in the stretch coming between B2 and B3 of the cam CSB.

In a further simplified embodiment of a knitting machine without sinkers, shown in Fig. 11, the procedure for holding down the fabric while the needles rise can be limited to the stage when the first group of needles rises. In this simplified embodiment, the procedure consequently consists of the following steps:

- at each feeding system, divide the needles to raise to take up the yarn to form a new course of stitches into a first and second group of needles intercalated with one another; - by means of a respective guide channel CS3, raise the needles in the first group on the cam (a) from A to A1 , so that their latches open and they clear the loop previously formed on the shank of the needle;

- by means of respective guide channels CS4, while the needles in the first group rise from A to A1 , keep the needles in the second group on a lower, fabric retaining level A-B defined by a horizontal stretch (b) of the channel CS4 so as to prevent the fabric from rising.

With said arrangement, once the needles in the first group have been raised, they do not drop partially back to a fabric retaining level, but remain raised to their maximum height (A1-B1) while the needles in the second group are also raised. Thus, as the needles in the second group rise, there is no guarantee that the fabric will not be lifted by the friction of the needles in the second group as they rise, with the risk of unwanted tuck stitches forming. This embodiment, which is simpler in the shape of the cams and guide eye, is limited to the production of low-quality fabrics.

It is understood that the drawings merely show an example, simply as a practical demonstration of the invention, which may vary in its embodiments and layouts without departing from the context of the invention. Any reference numbers mentioned in the attached claims are provided merely to facilitate the reading of the claims with reference to the description, and shall not restrict the scope of the protection represented by said claims.

Claims

CLAlMS

1. A knitting method on a weft knitting machine, comprising a bed of needle with latches, cams for controlling said needles and at least one feeding system for at least one yarn delivered to the needle bed, characterized bv dividing the needles selected to form the stitch into at least a first group (ND) and a second group (NP), intercalated with one another; and wherein, coinciding with said at least one feeding system, the needles of the first and second groups are controlled so that while the needles of one group rise, the needles of the other hold down the previously-formed fabric, and vice versa.

2. Method as in claim 1 , characterized in that, coinciding with said at least one feeding system, the needles of the first group and second group are raised into staggered positions with respect to one another, so that when the first group of needles rises, the second group of needles holds down the previously-formed fabric, and when the second group of needles rises, the first group of needles holds down the previously-formed fabric, the needles in the first group being partially lowered before the needles in the second group rise.

3. Method as in claims 1 or 2, characterized by the following steps; - in line with said at least one feeding system, the needles of the first group rise, their latches open and the loop previously formed is cleared on the shank of the needle, while the needles of the second group remain on a lower level (A-B) to hold down the fabric so as to prevent it from rising;

- the needles of the first group are partially lowered again, at a higher fabric-retaining level (A3), where the ends of the open latches (3) of said needles first the first group come to be in the vicinity of the already formed fabric;

- the latches (3) of the needles in the first group are kept open on said higher fabric-retaining level (A3) while the needles of the second group are raised.

4. Method as in one or more of the previous claims, characterized in that said lower fabric-retaining level (A-B) where the needles of the second group are kept is lower than the loop clearing level defined by the top edge of the needle bed, and preferably adjustable in height according to the length of the stitch.

5. Method as in one or more of the previous claims, characterized in that the latches on the needles of the first group, when said needles have been lowered to said higher fabric-retaining level (A3), are kept open by a retaining edge (PF) of a latch retainer member (19, PF).

6. Method as in one or more of the previous claims, characterized in that in line with a first feeding system the needles of the first group are needles in the even-numbered positions and the needles of the second group are needles in the odd-numbered positions, and that in line with a second feeding system the needles of the first group are the needles in the odd-numbered positions and the needles of the second group are the needles in the even-numbered positions.

7. A weft knitting machine comprising: a bed of needles (NP, ND) with latches (3); at least one feeding system for delivering at least one yarn with a guide eye (7); and, in line with said feeding system, a cambox with means (CS1 , CS2; CSA, CSB, 6B, 6T) for controlling the needles; characterized in that said cambox defines two different paths for two groups of needles (NP, ND) intercalated with one another, said two paths being shaped so that while the needles of the first group rise to clear a stitch previously formed thereon, the fabric is held down by the needles of the second group; and while the needles of the second group rise to clear a stitch previously formed thereon, the needles of the first group hold down the previously-formed fabric.

8. Machine as in claim 7, characterized in that: said two paths each has an upstroke of the needles in the respective group, said upstrokes being staggered; and that, coinciding with the upstroke of each of said paths, there is a stretch on the other path lying on a lower level with respect to the maximum height of the needles on said upstroke.

9. Machine as in claim 7 or 8, characterized in that: said cambox and said control means define at least a first path (A-A1- A3-B3-A5) and a second path (A-B-B 1-B3-A5) that differ from one another, for the take-up of the yarn respectively by needles in a first group (ND) and needles in a second group (NP) that are intercalated with one another; the first path includes an initial stretch (A-A1) for raising the needles in the first group (ND) that coincides with an initial stretch (A-B) on the second path of the needles of the second group (NP), that lies on a lower fabric-retaining level; the second path includes a second intermediate stretch (B-B 1) for raising the needles of the second group (NP) in line with a second intermediate stretch (A3-B3) on the first path, that lies on a higher fabric-retaining level, in line with said second intermediate stretch on the first path, wherein a latch retainer member (19, PF) is provided to keep the latches (3) on the needles of the first group open; - the first and second paths include a third and final stitch forming stretch (B3-A5), along which the needles of the first and second group are lowered to form stitches.

10. Machine as in claim 7, 8 or 9, characterized in that said needle bed is cylindrical.

11. Machine as in one or more of the claims from 7 to 10, characterized in that the needles of the first and second groups comprise respective raising butts (TS1 , TS2) situated on respectively different levels, said butts engaging respective cambox channels (CS1 , CS2) shaped to obtain said two paths.

12. Machine as in claim 11 , characterized in that said needles of the first and second groups each comprise a respective stitch forming butt (TM), cooperating with a stitch forming channel (CFM) of said cambox that is common to the needles of the first and second groups.

13. Machine as in one or more of the claims 7 to 12, characterized in that, in line with a first feeding system, the needles of the first group are the needles in the even-numbered positions and the needles of the second group are the needles in the odd-numbered positions, and that in line with a second feeding system the needles of the first group are the needles in the odd-numbered positions and the needles of the second group are the needles in the even-numbered positions.

14. Machine as in one or more of the claims 7 to 13, characterized in that each of said needles is associated with a selecting jack (S) and that, for each feeding system, there are a first selection actuator (6B) and a second selection actuator (6T), side by side, acting on selecting butts (TSA) of said jacks (S), and controlled to raise the selected jacks of a first and second group, intercalated with one another and corresponding to the needles of said first and second groups of needles, respectively on a first raising cam (CSA) and/or on a second raising cam (CSB).

15. Machine as in claim 14, characterized in that said needles are provided with a stitching butt (TM) and that the selecting jacks (S) of the first and second groups are provided with respective raising butts (TKA, TKB) arranged in two distinct positions that are staggered with respect to one another along the length of the jacks, to cooperate respectively with said first and second raising cams.

.

16. Machine as in claim 14 or 15, characterized in that the first selection actuator (6B) is used to select the needles at work or at rest in line with the respective feeding system, and to make the jacks (S) corresponding to the needles of the first group engage with the first raising cam (CSA) so as to raise the working needles of the first group before the working needles of the second group; and that the second selection actuator (6T) is controlled to act on the jacks (S) of the needles of the first group to prevent them from engaging with the second raising cam (CSB), which raises the jacks (S) for the needles of the second group.

17. Machine as in one or more of the claims 14 to 16, characterized in that said first selection actuator (6B) comprises double-thrust levers (6B1) and said second selection actuator (6T) comprises single-thrust levers (6T1).

18. Machine as in one or more of the claims 7 to 17, characterized in that, for each feeding system, said latch retainer member (19, PF) is integral with the guide eye (7).

19. Machine as in one or more of the claims 7 to 18, characterized in that said latch retainer member has a smooth, continuous surface (19) extending adjacent to the path where the needles are raised and lowered, said surface being delimited by: a first stretch of sloping edge (16) in line with the ascending stretch (A-A1) of said first path of the needles, immediately downstream from where their latches open; a second, similar stretch (18) of sloping edge in line with the ascending stretch (B-B1) of said second path of - the needles, immediately downstream from where their latches open; and a horizontal stretch (PF) for keeping the latches of the needles of the first group (ND) open while the needles of the second group (NP) rise.

20. Machine as in one or more of the claims 7 to 19, characterized in that said guide eye (7) has a first hole (G) for delivering the ground yarn, and a second and a third passage (E, V) for delivering two plating yarns, said passages being either holes or grooves for guiding the yam.

21. Machine as in claim 20, characterized in that said needle bed is cylindrical and that said first hole (G) is oriented radially with respect to the needle bed, while said second and said third holes or grooves are oriented tangentially with respect to said needle bed.

22. Machine-as-in-one or more of the claims 7 to 21 , characterized in that the walls of the needle bed delimiting the grooves (2) where the needles (N) slide have a top edge (2B) with a curved profile (R) sloping increasingly downwards in the direction in which the fabric slides.

23. Machine as in claim 22, characterized in that said curved profile has a first stretch (P-R) with a gentle gradient and a second stretch (R-S) with a steeper gradient.

24. Machine as in one or more of the claims 7 to 23, characterized in that it includes latch-opening devices (15A, 15B) for each feeding system.

25. Machine as in claim 24, characterized in that it includes a pair of latch-opening devices for each feeding system, each latch-opening device being positioned so as to coincide with said upstroke of the first (A-A1) and second (B-B1) path of the needles, respectively.

26. Machine as in one or more of the claims 7 to 25, characterized in that it includes needles that are narrowed down in the part containing the hook, so as to leave between the hook (U) of the needle and the walls of the respective groove (2) a distance (z) at least equating to the maximum diameter of yarn being worked, without the need to widen the upper part of the groove (2).