The present invention relates to a single-cylinder circular weft knitting machine with device for keeping the needle tabs open at a feed or drop of the machine

As is known, single-cylinder circular weft knitting machines have, at each feed or drop, one or more yarn guides, each of which can move on command from an inactive position, in which it is spaced, with its yarn delivery end, from the needles of the machine, so as to prevent the needles of the machine from gripping the yarn dispensed by it, to an active position, in which it is closer, with its yarn dispensing end, to the head or tip of the needles that are moved to knit at said feed or drop, so that said needles can grip the yarn dispensed by the yarn guide in order to form loops of knitting.

At each feed or drop, below the yarn guide or yarn guides, there is a device known as throat plate, which has the triple function of keeping the tabs of the needles open when said needles are moved to knit, i.e., extracted upwardly from the needle cylinder in order to grip the yarn or yarns dispensed at the feed or drop, of providing a support for the yarn guide or yarn guides that are moved to the active position to feed the needles, and of orienting/positioning the dispensed yarns at the needles.

More particularly, single-cylinder circular knitting machines are usually provided with a circular plate or dial, which is arranged in an upward region and coaxially to the needle cylinder on a plane that is substantially perpendicular to the axis of the needle cylinder. The circular plate or dial supports a plurality of hooks or needles, which are oriented radially with respect to the axis of the circular plate or dial and can move radially in order to cooperate with the needles of the needle cylinder in forming knitting.

The circular plate or dial is also provided with a circular cutter, the teeth of which protrude radially from the peripheral region of the circular plate or dial and can engage the yarn or yarns at the end of their dispensing to the needles so as to entrain the yarn or yarns at a complementary blade that cuts it and at a suction inlet which faces the upper face of the circular plate or dial and retains the cut end of the yarn, which extends from said inlet to the yarn guide that dispenses it, when the corresponding yarn guide is moved from the active position to the inactive position. The suction inlet retains the yarn until it is subsequently supplied to the needles. As an alternative and/or in addition to the yarn suction inlet there can be a clamp by which the yarn is clamped before being cut.

In these machines, safety in the grip of the yarn by the needles depends on the trajectory followed by the yarn when the corresponding yarn guide is moved from the inactive position to the active position. This trajectory depends on the position of the dispensing end of the yarn guide in relation to the position of any hooks or needles that are each moved to protrude between two contiguous needles proximate to the feed or drop, and on the position of the suction inlet or of the clamp with respect to the feed or drop and on the height of the circular plate or dial with respect to the yarn guide dispensing end.

When the needles have to grip the yarn at a feed in the so-called

"tuck" position, i.e., when the needles are raised with their head or tip just above the knockover sinkers, problems can arise as regards the correct grip of the yarn by the needles.

The expression "tuck" position is understood to designate a position in which the needles of the needle cylinder are raised to such a level that the loop of knitting formed previously is unable to pass below the tab and therefore is in the head or tip of the needle at the subsequent descent, after said needle has gripped the yarn at the feed or drop being considered and has formed a new loop of knitting, which also will be in the head of needle together with the preceding loop. During the grip of the yarn by the needles in the "tuck" position, the throat plate performs the function of preventing the tabs of the needles from closing onto the head and therefore of ensuring the correct grip of the yarn dispensed at the feed being considered.

Throat plates of the known type are usually provided in one piece and are fixed to the supporting structure of the machine or to a component of the machine that is integral with the supporting structure.

In machines of the known type, for some types of fineness and for some positions of the yarn guides, the throat plate may be unable to prevent assuredly the closure of the tabs of the needles or to allow to arrange the dispensing end of the yarn guides at such levels as to define a trajectory for the yarn that ensures its grip by the needles.

The aim of the present invention is to solve the problem described above, by providing a single-cylinder circular weft knitting machine with device for keeping the needle tabs open at a feed or drop of the machine that ensures a correct grip of the yarn by the needles in any operating condition even when the needles are moved to knit in the "tuck" position at the feed being considered.

Within this aim, an object of the invention is to provide a machine which, by achieving higher reliability in the grip of the yarn by the needles, effectively avoids knitting errors and therefore allows to provide qualitatively superior products.

Another object of the invention is to provide a single-cylinder circular weft knitting machine with a device for keeping the needle tabs open at a feed or drop of the machine that is simple to install.

A further object of the invention is to provide a machine that allows to obtain a correct grip of the yarn or yarns by the needles, moved to knit in the "tuck" position, regardless of the working height of the dial.

Another object of the invention is to provide a machine which, by ensuring the correct grip of the yarn by the needles, even when they are moved to knit in the "tuck" position, increases the textile possibilities and productivity with respect to machines of the known type.

This aim, as well as these and other objects that will become better apparent hereinafter, are achieved by a single-cylinder circular weft knitting machine with device for keeping the needle tabs open at a feed or drop of the machine, comprising:

- a needle cylinder having a vertical axis which has, on its lateral surface, a plurality of axial slots, each of which accommodates a needle that can move parallel to the axis of the needle cylinder;

- a sinker ring, which is arranged coaxially to the needle cylinder, proximate to its upper end, and accommodates a plurality of knockover sinkers, each arranged on a radial plane with respect to the needle cylinder, each one of said knockover sinkers being arranged between two adjacent needles and being movable radially with respect to said needle cylinder;

- at least one yarn guide, which is arranged at a feed or drop of the machine;

- a device for keeping the tabs of the needles open at a feed or drop of the machine;

characterized in that said device comprises:

- a supporting element associated with the supporting structure of the machine proximate to a feed or drop of the machine;

- a plate associated detachably with said supporting element below said at least one yarn guide; said plate having an arc-shaped side that faces the lateral surface of the needle cylinder above the knockover sinkers.

Further characteristics and advantages of the machine according to the invention will become better apparent from the description of a preferred but not exclusive embodiment of the machine according to the invention, illustrated by way of nonlimiting example in the accompanying drawings, wherein:

Figure 1 is a schematic perspective view of a portion of the machine according to the invention at a feed or drop with a group of yarn guides in the inactive position;

Figure 2 is an enlarged- scale view of a detail of Figure 1 ;

Figure 3 is a schematic perspective view of the same detail as Figure 2 enlarged further, with a yarn guide in the active position, with a group of needles in the step for lifting in the "dropped" position and with some hooks of the dial extracted so as to protrude between the needles;

Figure 4 is a view of the same detail as Figure 3, in the same operating conditions, but seen from a different angle with respect to Figure 3;

Figure 5 is a view of the same detail as Figures 3 and 4, seen from yet another angle;

Figure 6 is a view of the same detail of the preceding figures, seen in a manner similar to Figure 5, with the hooks of the dial omitted, with the yarn guide lowered with respect to the position shown in the preceding figures, and with the needles in the "tuck" position;

Figure 7 is a schematic sectional view of the device for keeping open the tabs of the needles, taken along a vertical plane that passes through the axis of the needle cylinder of the machine.

With reference to the figures, the machine according to the invention, of which only a portion has been illustrated for the sake of simplicity, comprises, in a per se known manner, a needle cylinder 2 (shown only partially in Figure 7 and omitted in the other figures for the sake of simplicity and greater clarity) that has a vertical axis and has, on its lateral surface, a plurality of axial slots 3, inside each of which a needle 4 is accommodated which can be actuated with an alternating motion along the corresponding axial slot 3 in order to grip one or more yarns dispensed at a feed or drop of the machine and form knitting. The motion of the needles 4 along the corresponding axial slots 3 is obtained, in a per se known manner, as a consequence of the actuation with a rotary motion of the needle cylinder 2 about its own axis with respect to needle actuation cams, not shown, which face the lateral surface of the needle cylinder 2 and define paths for the heels 4a of the needles 4 that protrude from the lateral surface of the needle cylinder 2.

At the upper end of the needle cylinder 2 there is a sinker ring (not shown in order to allow to view the knockover sinkers 5), which is arranged coaxially to the needle cylinder 2 and is integral with it in its rotary motion with respect to the needle actuation cams. The sinker ring has a plurality of radial slots, inside each of which there is a knockover sinker 5 which lies on a vertical plane that passes through the axis of the needle cylinder 2, i.e., on a radial plane. Each knockover sinker 5 is arranged between two contiguous needles 4 and can move on command toward and away from the axis of the needle cylinder 2, i.e., radially, so as to cooperate with the needles 4 in forming the loops of knitting by defining a resting surface for the yarn or yarns while the needle 4, after gripping the yarn or yarns, is descending inside the needle cylinder 2 and in order to tension the loop of knitting against the stem of the needle 4 while it is rising in order to again grip the yarn or yarns dispensed at a feed or drop of the machine. The motion of the knockover sinkers 5 also is obtained by means of corresponding actuation cams, which face in an upward region the sinker ring and define paths for the heels 5a of the knockover sinkers 5 that protrude upwardly from the sinker ring.

At each feed or drop of the machine there is at least one yarn guide 6, which has the function of providing the needles 4 of the machine with a yarn in such a position as to obtain the grip of the yarn by the needles 4 that are moved to knit at said feed or drop.

The machine according to the invention is provided with a device 7 for keeping open the tabs 4b of the needles 4 at a feed or drop of the machine.

According to the invention, the device 7 comprises a supporting element 8, which is associated with the supporting structure of the machine proximate to a feed or drop of the machine and a plate 9 that is associated detachably with the supporting element 8. The plate 9 has a side 9a that is arc-shaped and faces the lateral surface of the needle cylinder 2 above the knockover sinkers 5. The arc-shaped side 9a is intended to engage the tabs 4b of the needles 4 when they are raised so as to exit from the upper end of the needle cylinder 2 and from the knockover sinkers 5 so as to keep the tabs 4b of the needles 4 open and allow the head or tip 4c of such needles to grip the yarn dispensed by the yarn guide or yarn guides 6 arranged at the feed or drop of the machine.

The supporting element 8 can be associated directly with the supporting structure of the machine or with an element 15 that is fixed to the supporting structure of the machine below the group of yarn guides 6 that is located at each feed or drop of the machine. The fixing of the supporting element 8 to the supporting structure of the machine or to an element 15 that is integral therewith can be performed in a per se known manner by means of screws 11.

Conveniently, the plate 9 has a thickness that is lower than the thickness of the region of the supporting element 8 with which it is associated. More particularly, the thickness of the plate 9, at least in the region of such plate 9 that lies below the yarn guide 6 during the dispensing of one or more yarns to the needles 4 of the machine, is substantially comprised between 0.05 mm and 5 mm.

The reduced thickness of the plate 9 allows to move the yarn guides 6 to a lower position than attainable with throat plates of the traditional type. Thanks to this fact it is possible to obtain a trajectory of the dispensed yarn or yarns that ensures safely the grip of the yarn by the needles 4 both when they are moved to knit in the "dropped" position, i.e., at such a level that the previously formed loop of knitting passes below the tab 4b of the needle 4, and when they are moved to knit in the "tuck" position. Each yarn guide 6 can move on command, in a per se known manner, from an inactive position, in which its dispensing end 6a is spaced from the position that can be reached by the head or tip 4c of the needles 4 when they are moved to knit at the feed being considered, so as to exclude the grip of the yarn by the needles 4, to an active position, in which its dispensing end 6a is closer to the head or tip 4c of the needles 4 in the position that can be reached by them when they are moved to knit at the feed being considered, so as to allow the grip of the yarn by the needles 4. Figures 3 to 6 show a group of yarn guides 6, only one of which is in the active position, i.e., lowered so as to move its dispensing end 6a so that it faces the heads or tips 4c of the needles 4 that are moved to knit at the feed being considered. In Figures 3 to 5, the needles 4 are moved to knit in the "dropped" position, while in Figure 6 the needles 4 are moved to knit in the "tuck" position.

The movement of the yarn guides 6 in order to pass from the active position to the inactive position and vice versa can be a partial rotation or a simple translation. In any case, the movement of each yarn guide 6 in order to pass from the inactive position to the active position has a vertical component that produces a lowering of the yarn guide 6.

Conveniently, the plate 9 and the supporting element 8 have, in a region that is spaced from the arc-shaped side 9a on the opposite side with respect to the axis of the needle center 2, a recess 9b that is arranged below the yarn guide 6.

The presence of the recess 9b allows the yarn guides 6, after the grip of the yarn by the needles 4, to be moved to a preset position despite starting from a position in which they rest against the plate 9. For example, it is possible to perform an oscillating movement of a yarn guide 6 in order to move it away from the needle cylinder 2.

Advantageously, the plate 9 is interchangeable, without the need to also replace the supporting element 8, with other plates of different sizes, as a function of the fineness of the machine and of the thickness of the head or tip 4c of the needles 4 mounted on the machine.

For this purpose, as shown in Figure 7, the plate 9 can be fixed detachably to the supporting element 8 by means of screws 12.

As an alternative, the plate 9 can be associated with the supporting element 8 so that it can slide along a radial direction with respect to the needle cylinder 2, and can be locked, for example by means of screws, to the supporting element 8 in a preset position, so as to allow to adjust its position with respect to the needle cylinder 2 as a function of the fineness of the machine and of the thickness of the head or tip 4c of the needles 4 mounted on the machine.

This possibility to replace the plate 9 or to move the plate 9 with respect to the supporting element 8 allows to arrange the arc-shaped side 9a of the plate 9 closer to the needles 4 so as to perform more effectively the function of keeping open the tabs 4b of the needles 4.

The reduced thickness of the plate 9 also allows to move the hooks 13 or the needles of the dial 14 or of the circular plate, when they are actuated and moved to knit, so that they protrude radially from the dial 14 or circular plate below the supporting element 8 and above the plate 9. This condition is shown in Figures 3, 4, 5.

Substantially, the plane of arrangement of the lower face of the plate

9 lies below the retention plane of the yarn that is present on the head of the hook 13 or of the needle 4.

It should be noted that the reduced thickness of the plate 9, together with its shape, allows to obtain the correct grip of the yarn by the needles 4 even when they are moved to knit in the "tuck" position, as shown in Figure 6, regardless of the working height of the dial 14 or of the circular plate which, together with the yarn guide 6, defines the trajectory of the yarn which, at the beginning of the feed, extends from the dispensing end 6a of the yarn guide 6 to the inlet or to the clamp arranged above the dial 14 or circular plate. This higher reliability and safety in the grip of the yarn by the needles 4 also in the "tuck" position arises from the fact that since the plate 9 has a very low thickness, the yarn guide 6 that is dispensing the yarn can be moved with its dispensing end 6a to a lower level than can be attained with devices of the known type.

In practice it has been found that the machine with the device for keeping the needle tabs open at a feed or drop of the machine according to the invention achieves fully the intended aim, since it allows to obtain a higher reliability and safety in the grip of the yarn by the needles even when they are moved to knit in the "tuck" position, reducing knitting errors and therefore achieving higher productivity and higher quality for the finished product.

The machine with the device for keeping the needle tabs open at a feed or drop of the machine thus conceived is susceptible of numerous modifications and variations, all of which are within the scope of the appended claims; all the details may further be replaced with other technically equivalent elements.

In practice, the materials used, as well as the dimensions, except for what is specified otherwise above, may be any according to requirements and to the state of the art.

The disclosures in Italian Patent Application No. MI2015A000509 (102015902343506) from which this application claims priority are incorporated herein by reference.

Where technical features mentioned in any claim are followed by reference signs, those reference signs have been included for the sole purpose of increasing the intelligibility of the claims and accordingly such reference signs do not have any limiting effect on the interpretation of each element identified by way of example by such reference signs.