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Field of the invention

The present invention relates in general to the machines for manufacturing knit fabrics and relates in particular to an innovative system for leading and controlling the needles, especially during the descending step of the latter, throughout the manufacturing of stitches on circular machines for hosiery and knitwear.

State of the Art

The circular machines for hosiery and knitwear comprise essentially a rotating cylinder having at its periphery a plurality of parallel vertical grooves in which as many needles are housed having a vertical arrangement. The cylinder is rotated at determined speeds and the needles are fed with at least one thread to be knitted in one or more feeding stations, also called feeders, combined with the cylinder.

The needles can perform operative ascending and descending movements along the respective grooves and with respect to a plane defined by a plurality of radial elements, said sinkers, mounted on the upper part of the cylinder and arranged in the gaps among the needles. The needles are driven for taking each time, in the feeding station or stations, at least one thread to be knit when they are in a top position and for forming, during their descent together with the sinkers, a new knit loop with the thread they have just taken and for downloading the previously manufactured stitch. The needles can also be selectively activated through respective needle jacks arranged in the same grooves of the needles and combined with suitably - managed selecting groups.

Each needle usually has a shank having, at an upper ending thereof, a hook with its own opening and closing tongue and, at a lower ending thereof, an angled jut, the more usually called heel and so termed in the following of the description. The tongue is connected to the needle shank by means of a pin so as to rotate of an angle in a vertical plane between the opening and closing positions of the needle hook itself. The heel radially protrudes from the groove of the cylinder in which the needle is housed.

The needle jacks are provided too with at least one heel and can be engaged by respective ascent and descent cam means depending on the needles to be activated.

Furthermore, some kinds of needles among those available nowadays and most used are also provided, along the shank just over their heel, with a protrusion facing towards the same part of the heel and which in the following will be considered and termed as pre-heel. This pre-heel is less jutting than the heel and can be variously realized along the needle shank. It has however a lower sloping side which forms an inclined plane extending towards the upper layer of the heel starting from a front side thereof, substantially vertical. It has to be noted that, when such needles are usually mounted and employed, their pre-heel remains embedded into the groove housing the respective needle without radially projecting from the cylinder. However, the ascending and descending movements of the needles in each feeding station are driven by fixed cam means, also called triangles, but in the following simply termed as cams/cam. Such cams are led by a fixed skirt arranged around and adjacent to the cylinder and are designed for engaging the heel of the needles upon the rotation of the cylinder itself.

In particular, in each feeding station at least one ascent cam with a profile such to engage the heel of the needles so that to displace the latter upwards from bottom along the respective grooves and at least one descent, or knit, cam, with such a profile to engage the heel of the needles so that to displace the latter downwards from top. Then, with the ascent cam as well as with the descent cam, a respectively ascent and descent counter-cam is usually combined, defining with the respective cam a necessary track for the passage of needle heels and leading them.

More in particular, a descent cam, on the side from which the needles come led from the rotating cylinder, can have a sloping profile with a more or less pronounced angle, that is to say more or less steep, according to the force component to be exerted on the needle heel.

In the most conventional circular machines for hosiery and knitwear, the cylinder can reach a determined maximum rotation speed on the order of 250 - 300 rounds/minute. The profile of the ascent and descent cams, especially the profile of the descent cam, is then selected to allow a safe grip of the thread to be knitted by the needle hook and a correct knitting without remarkable problems. This is true also where the sloping profile of the descent cam joins a subsequent substantially horizontal lower length to the cam itself through a sharp, or substantially sharp, corner.

On the contrary, in the most modern circular knitting machines, designated for a higher productivity, the cylinder can rotate at speeds on the order of 450 - 500 rounds/minute or even higher, for example 600 rounds/minute. However, it has been immediately realized that the descent cams used in circular knitting machines having relatively low speeds cause problems if used on knitting machines having higher speeds. And in fact, at these higher working speeds the profile at least of the descent cam had to be changed with respect to the profile of an alike descent cam adopted in more conventional machines under penalty of risk of needle breaking, in particular problems of needle head cropping, a more pronounced wear of cams and needle heels and a higher difficulty in manufacturing stitches.

It has been therefore attempted to essentially operate on the profile of the descent cam, by realizing in the lower part of said descent cam sloping a rounded area so as to remove the presence of every sharp, or substantially sharp corner, and by modifying, on the other side, the counter-cam by providing it with a radial hollow on its upper side in front of the rounded area of the descent cam. However, this other arrangement of the descent cam and the respective counter-cam led to other drawbacks the field technicians know well and which occur in particular at the level of the needles that take the thread to be knitted, when their heads reach the sinker plane. In this regard note that the thrust of the descent cam on the needle heel generates drawbacks resulting more pronounced at high working speeds. In fact, the thrust from top the descent cam exerts on needles when they are lowered is substantially applied on part of the heel far away from the shank of each needle. An overturning moment thus occurs tending to displace the upper part of the needle at the level of its top hook in the cylinder outside direction, with the result of affecting the correct grip of the thread by the needle hook part and/or of uselessly stressing the thread.

Also, as usually occurs, where the needles are firmly held in a radial direction in respective grooves by means of annular springs surrounding the cylinder, the overturning moment on the needles, deriving from the thrust of the descent cam on needle heels, can occur with undesired effects.

In addition, when the needles reach the totally lowered position, their heel rests on the counter-cam with some tendency to rebound upwards against the overlying profile of the descent cam, with the result that the needles are subjected to waggles and vibrations which can, not unusually, led to the cropping thereof, that is to say to the breaking of their top part. And this occurs as more markedly as faster the cylinder rotation is and, therefore, the passage of the needle heel along the track defined by descent cam and respective counter cam.

It has to be noted also that the number of needles in the descending step that take the thread depends on the inclination of the sloping profile of the descent cam. If such an inclination is relatively gradual, the number of needles which are lowered simultaneously is greater, meaning a more relevant tension on the thread and therefore higher stress on the latter due to the summation of forces exerted by each needle on the thread and that can lead to the defibering of the latter, thus weakening if not breaking thereof. It would be therefore desirable having descent cams with a steeper sloping profile such to reduce as much as possible the number of simultaneously descending needles with their hook under the sinker plane and mainly call back the respective thread lengths to form the knit loop with the needles that are at the end of the descent run and before they have to start the subsequent substantially horizontal run defined by the cam itself.

From what above it is thus of great importance realizing the conditions for controlling and leading the needles in the descending step, that is to say while forming the stitches, on circular machines for hosiery and knitwear.

Object and summary of the invention

The present invention has been conceived just with the aim of reaching such conditions, thus to solve the above stated issues and effectively compensate for drawbacks and disadvantages of the known art, as well as with the aim of providing innovative modalities for controlling and leading, in the descending step, the needles on the cylinder in order to allow a correct knitting also at highest rotation speeds of the cylinder with lower thread stresses, a more correct carrying out of stitches, a better quality of the resulting knit fabric and also with the advantage of removing a functional member such as the descent counter-cam on the contrary present in conventional machines.

Such an aim and said object are reached with a circular machine improved according to claim 1. In particular, the circular machine comprises supporting means adapted to lead the needles in the descending step and designed for contacting the needles, called descending needles, moving towards the lowered position and for preventing them from instantaneously rotating on the heel and for moving the hook away in a radial direction from the corresponding groove.

The Applicant proposes three embodiments of such supporting means, one independent from another and therefore reserves the right to file as many divisional patent applications.

According to a first embodiment of the invention, the descending step of the needles due to the descent cam can be assisted and led by supporting means comprising a rotating element or roll combined with said descent cam.

In particular, such a roll can be connected and rotated by a driving motor, at variable speed too. More in particular, then, it is located in front of the sloping profile of the descent cam in the lower part of such a profile for engaging the heel of at least two or three descending needles that, in their turn and at the end of the descent run, are on the opposite side with respect to the descent cam.

The roll will have a peripheral surface contacting the heels that can be smooth, knurled, stepped, or grooved and that, besides assisting the needle descent, will have the task of countering the thrust of the descent cam on the needle heel tending to laterally flex the heels as well as to cause the overturning of the needles outwards and sometimes also the breaking of needle heels. Further, the action of the roll becomes particularly advantageous in presence of a descent cam with a rather steep sloping profile and high rotation speeds of the cylinder and further allows removing a conventional counter-cam jointly with the descent cam.

According to another embodiment of the invention, on the cylinder of a circular machine needles are mounted and used provided with both a heel and a pre-heel as defined above, and the descent cam is prearranged so that to engage, at the same time, both the heel and the pre-heel so that to more correctly hold and lead each needle in the respective groove during its descent displacements; this in presence of a roll or not, as described above.

In particular, the descent cam has its own profile sloping downwards from top designed for engaging the needle heel in the descending step, and a supporting means is combined therewith, in the shape of additional cam, designed for engaging the radially outermost surface, that is to say the front side of the pre-heel of the descending needles, while the sloping profile of the descent cam acts on the heel of these needles themselves.

In particular, the additional cam is placed between the descent cam and the cylinder to be faced towards the pre-heel of the needles in descending step and can be constituted of a standalone element or integrated and integral with said cam, however such with an angular extension to engage the pre-heel of at least some of the needles that are from time to time at the end of the descent run.

More particularly, then, at the periphery of the cylinder, at the level of the descent cam, the vertical grooves have a radial hollow with such a depth to let at least part of the needle pre-heel (otherwise embedded in the leading grooves of the needles) protrude radially from the cylinder and to allow the contact among the additional cam and the pre-heels when they reach the level thereof.

Therefore and advantageously, the needles in descending step become engaged at two levels, respectively at the heel level and at the pre-heel level of each needle, on the other hand with counteracting forces that allow holding the needles in the respective grooves without overturning outwards being possible. Due to this solution, springs that usually hold the needles become less critical.

According to yet another embodiment of the invention, when needle jacks with respective heels are combined with the needles on the cylinder, the descending step of the needles, due to the sloping profile of the descent cam, can also be assisted and led by means of needle jacks, both in presence and in absence of an additional cam such as that afore described acting on the front side of the needle pre- heel.

Then, an abutting element designed for contacting the heel of the needle jacks of the descending needles, is combined with the needle jacks at the opposite part with respect to the needles themselves, to lead them in the respective descent run. The abutting element can have the shape of cam having a profile substantially similar to the profile of the descent cam.

Preferably such a cam is mounted for swinging on an oscillation pin and it is held in contact with the heel of needle jacks from time to time involved through elastic means by adjustable force. This in order to gently assist the descent of needle jacks and, through these, of needles, thereby compensating for gaps that can arise in the long term from wear of moving elements and, also in this case, with the possibility of eliminating a counter-cam jointly with the descent cam. Alternatively, the abutting element in the shape of cam has an adjustable distance from the descent cam for balancing gaps due to wear of needles and needles jacks. The cam is therefore movable in height for getting closer to the heels of needle jacks so that to lead the last ones for a run as equal as possible to the profile of sloping and horizontal sides of the descent cam.

According to a further aspect of the invention the descent cam can have, from the side of its sloping side, a variable profile for changing the angle as necessary, in particular to make an ending, i.e. lower, length of said sloping side and therefore of the descent run of the needles, steeper than the initial, i.e. upper, length.

For this purpose with the descent cam an auxiliary cam element is associated having one side thereof facing towards the needle heel and provided with a profile differing from the profile of the initial length of the sloping side of said cam, in particular less tilted with respect to the horizontal line. The auxiliary cam element is movable between a distant position and a position wherein it is close to the descent cam so that, in this second position, it is alongside and arranged coplanar with the afore said initial length of the sloping side of said cam just for changing the profile and angle thereof. All of the foregoing such that the ending length of the sloping side of the descent cam affects the ending part of the descent of a limited number of needles, preferably two, three or just four, thereby allowing a better call back without thread stress nor defibering during the formation of the knit loops and a higher safety of needle integrity, especially at the level of their hook and their tongue.

The field technician will understand that the auxiliary cam element can be used irrespectively of the presence of the supporting means. The Applicant therefore reserves the right to file a divisional patent application related to a circular machine, although conventional, comprising the above described auxiliary cam element.

Brief Description of the Drawings

Moreover, the invention will be further illustrated in the description course made with reference, by way of example only and without limitation, to the attached drawings, in which:

figure 1 shows a needle of the type with a heel and a pre-heel along its shank;

figure 2 schematically shows a descent cam (represented by dashed lines) jointly with an additional cam for controlling the descending step of the needles;

figure 3 shows a partial vertical section of the cylinder with needles at the level of the cams in figure 2; figure 4 shows a perspective view of some needles at the cams of figure 2;

figure 5 shows a part of the cylinder with a controlling mode for the descent of needles by means of a roll combined with the descent cam;

figure 6 shows a front view of the system in figure 5;

figure 7 shows a controlling mode for the descent of needles by means of the needle jacks;

figure 8 shows a descent cam and separately an auxiliary cam element for changing the profile thereof;

figure 9 shows the descent cam complete with auxiliary cam element referring to the needles to be driven; and

figure 10 shows a view according to the arrows A-A in figure 9. Detailed description of the invention

In said drawings, a rotating cylinder is globally denoted with numeral 21 , arranged with vertical rotation axis, for circular machines for hosiery and knitwear, having at its periphery a plurality of vertical, parallel grooves 22 opening outwards and housing as many knitting needles 31.

The needles 31 on the cylinder 21 can perform vertical ascent and descent displacements or runs, between a raised position, at which at least part of the shank protrudes above the cylinder, and a lowered position, at which the shank is entirely housed in the corresponding groove, respectively driven by at least one ascent cam and by at least one descent cam, the cams being arranged on a support surrounding the rotating cylinder. Of these cams only one descent cam is represented and considered herein, generally denoted with numeral 41 , since the ascent cam is not involved and is irrelevant for the invention purposes. The ascent and descent cams, also called driving cams, have a curvature radius compatible with the cylinder radius and are at such a periphery level of said cylinder that, by the rotation of the latter, the needles move towards, and their heels encounter, said cams in the direction denoted with the arrow F.

In particular, each needle 31 comprises a shank 32 having, at its top, a hook 33 with a respective opening and closing tongue 34 rotatable on a pin 34' and, in a lower part thereof, a heel 35 that, when the needle is housed in the respective groove 22 of the cylinder, radially protrudes from the latter. In addition, each needle 31 - figure 1- can be provided, along its shank 32, with a pre-heel 36 just above the heel 35. This pre-heel has its substantially vertical front side 37 joining to the back of the heel 35 through an inclined plane 38.

Respective needle jacks 131 can be combined with the needles; in its turn each needle jack 131 has at least one respective heel 132.

As represented, the descent cam 41 is composed of a body having a substantially horizontal portion 42, designed for being fastened on a fixed support - not represented - placed around the cylinder 21 , and a vertical portion 43 extending downwards from the horizontal portion and having an inner face 44 facing towards the cylinder periphery. Along the lower edge of its vertical portion 43, the descent cam 41 has a sloping profile or side 45 with a top-down way in the direction F of cylinder rotation. The sloping side is followed by a horizontal, or substantially horizontal length 46, from which a length 47 with ascending profile then extends. The sloping side 45 joins the horizontal profile length 46 through a corner area 48 that can preferably have a sharp corner. The sloping side 45 and the horizontal side 46 of the descent cam 41 are designed for engaging the heel 35 of the needles 31 in their descending step throughout the knitting consequent upon the cylinder rotation.

In particular in figure 3, which refers to an embodiment of the invention, part of the cylinder 21 is represented in vertical section, with a needle 31 and a needle jack 131 both inserted in a respective groove 22, with the heel 35 of the needle engaged by the descent cam 41 and the pre-heel 36 also protruding radially from said groove 22 due to a recess or radial hollow 23 obtained around the cylinder 21 at the level of the descent cam. Additionally, the descent cam 41 is also prearranged for operating on the radially outermost surface, that is on the front side 37 of the pre-heel 36 of those needles themselves, called descending needles, whose heel is engaged by the descent cam profile or at least of some of said needles close to the end of the descent run due to the sloping side 45 of said cam, as shown in figures 2-4 of the drawings.

The action on the front side 37 of the needle pre-heel 36 is then realized by an abutting element, preferably in form of an additional cam 141 , combined with the descent cam 41 , on the inner face of the latter facing towards the cylinder - figure 3. Such an additional cam 141 has a descending portion 145 and a substantially horizontal portion 146 that follow almost in parallel the profile of the sloping and horizontal sides 45 and 46 of the descent cam. The additional cam can be realized as a standalone component suitably combined with the inner face 44 of the descent cam or else integrated with, and fastened to, said cam. To prevent the needle heel from being worn, the additional cam can be realized in a suitable material, such as Teflon.

However, the action of the additional cam 141 on the front side of the pre-heels 26 of the from time-to-time involved needles 31 , is designed to counteract the descent cam thrust on the needle heel, otherwise tending to cause an overturning movement of the needles outwards of their grooves - figure 3.

According to another embodiment, the descending step of the needles due to the descent cam 41 can also be assisted and led by an auxiliary rotating element or roll 51 combined with said descent cam. Such a roll can be realized alternatively or in association with the additional cam operating on the front side of the needle pre-heel.

As shown in figures 5 and 6, the roll 51 has preferably the shape of wheel and is located in front of a lower part of the sloping side 45 of the descent cam 41 for engaging the lower part of the heel 35 of at least two or three descending needles which, from time to time, come to the end of the descent run just due to said descent cam and before they follow the horizontal length 46 of the latter. Therefore, the roll operates on the needle heel from the part opposite with respect to the descent cam.

The roll 51 will then be carried by a respective shaft 52 placed on a support, not represented, and connected for its rotation to a driving motor, not represented ne!ither.

Further, said roll 5il will have a peripheral surface 53 contacting the needle heel 36, which surface can be smooth, grooved, stepped or knurled. The respective support could be movable and engaged for example by springs for adjusting the position and/or the thrust of the roll 51 towards and on the needle heel, and for balancing the wears that can arise.

In any case the roll 51 , besides assisting the descent of needles, then counteracts the thrust of the descent cam on the needle heel tending to cause the overturning of needles. This being particularly advantageous, as said above, when the descent cam has a sloping side 45 steeper than usual in its ending part (up to more than 45°) and needle descent becomes more difficult and, therefore, its mechanical support is helpful.

Note that, in general, a higher steepness of an ending part of the sloping side 45 of the descent cam 41 is to be pursued and is advantageous for having as few needles as possible - two, three or four - that collect the thread and pull it downwards under the sinker plane during the knit loop manufacturing and for minimizing excessive tensions and subsequent thread defibering.

Always according to the invention, the descent run of the needles due to the descent cam 41 operating on their heel can also be assisted by means of the needle jacks 131 , in this case too both in presence and in absence of the additional cam 141 operating on the front side of the needle pre-heel.

For this purpose and as shown in figure 7 an abutting element 61 , designed for contacting the heel 132 of the needle jacks 131 of the descending needles, can be combined with the heel 132 of the needle jacks 131. Such an abutting element can be in shape of a cam 61 that, in its part facing towards the heel 132 of the needle jacks 131 , has a profile 62 at first sloping and then horizontal 63 similarly to the profile of the descent cam 41 and designed for engaging the heel 132 of the needle jacks 131 that follow, from time to time, the descending movement of needles or of some of the latter.

The cam 61 can be mounted for swinging on a horizontal oscillation pin 64 and is held contacting the heel of the needle jacks that are from time to time involved by elastic thrust means, such as for example a spring 65 with adjustable force, connected with it. The cam 61 then allows gently assisting the descent of needle jacks and, through the last ones, of needles and allows compensating for gaps that can result from the long-term wear of the moving elements.

In a constructive variation, but with similar practical result, an abutting element having a cam shape can be combined with the heels of the needle jacks and having a configuration similar to the above described one, but movable in height for engaging the heels of the needle jacks from below so that to lead the last ones along a run as equal as possible to the profile of the sloping and horizontal sides of the descent cam.

Referring specifically to the descent cam 41 , this can also be prearranged for varying the profile thereof from the side of its sloping side 45, whether it has a front spur 41a or not, as shown in figures 8-10, designed for engaging the pre-heel of the needles in the descending step, as however described in other patent application by the same applicant.

The variation of the profile of the sloping side of the descent cam is desired and has the purpose of changing the angle, in particular for rendering a lower ending length of said sloping side (therefore the ending length of the descent run of the needles) steeper than to the initial, that is to say upper, length.

For this purpose with the descent cam 41 an auxiliary cam element 241 is combined having a side thereof facing towards the heel 35 of the needles 31 and provided with a profile 242 differing from the profile of the initial length 45a of the sloping side 45 of said cam, specifically less inclined with respect to the horizontal line (figures 8 and 9). The auxiliary cam element 141 will be suitably displaceable between an inactive position, far from the cam - figure 8 - and an active position in which it is inserted and alongside the descent cam - figure 9 -, in an arrangement coplanar to the afore said initial length 45a of the sloping side of said cam, aligned with the spur 41a, if provided and present - figure 10.

This possibility of varying the profile of the sloping side of the descent cam is remarkably advantageous in knitting at the highest rotation speeds of the cylinder when the needles are particularly stressed. At high speeds, in fact, the integrity of each needle has to be secured at least at the level of its tongue 34, which bumping more frequently against the top hook 33 can cause a rapid wear of the respective rotation pin 34' whereby the tongue can laterally swing and, accordingly, not be able to correctly couple any more with the hook when in a closed position.