GB2078264A

GB2078264A - Circular Knitting Machine

Info

Publication number: GB2078264A
Application number: GB8114270A
Authority: GB
Original assignee: BREMATEX SpA
Current assignee: BREMATEX SpA
Priority date: 1980-05-14
Filing date: 1981-05-11
Publication date: 1982-01-06
Also published as: IT1153811B; JPS575950A; DE3117882A1; GB2078264B; CS251064B2; IT8009432A0

Abstract

A circular knitting machine is equipped to form areas of fabric using only the needles on an arc of the needle cylinder. The or each cam 1 for stitch formation, under which also the inoperative needles travel, is moved cyclically to be lowered for the formation of rows of stitches by the needles of operative needle arc, while it is raised for the passage past it of the inoperative needles, to prevent repeated tensioning of the stitches held by the inoperative needles. The cam may be controlled by a lever 20 actuated by a fluid cylinder. <IMAGE>

Description

SPECIFICATION Circular Knitting Machines The present invention relates to circular knitting machines, and more particularly to machines for knitting stockings and socks, and operative to form areas of fabric by means only of the needles of an arc of the needle cylinder, while the needles excluded from operation are kept lowered and hold the stitches.

During operation of previously proposed machines of the type specified above, only those needles in operation are lifted to take a thread at the or each feed, and are then lowered by a corresponding stitch formation cam,-a so-called triangular can,-under which the excluded needles also travel.

The repeated passage of the excluded needles under the bottom apex of the triangular cam or cams give rise to repeated straining of the thread loops of the stitches held by the excluded needles, which causes damage with defects in the fabric, and even breakages.

According to the invention, there is provided in a circular knitting machine of the type operative to form areas of fabric using only the needles of a needle arc of the needle cylinder, while nonoperative needles are kept lowered and hold the stitch, with the operative needles being lifted to take a thread facing the or each feed, and being lowered by a corresponding stitch forming cam under which the inoperative needles also travel, the improvement comprising means for moving the stitch formation cam cyclically such that the cam is lowered for the formation of rows of stitches on the needles of said needle arc during the passage past it of said needle arc, and that the cam is raised for the passage past it of the inoperative needles whereby to avoid repeated tensioning of the stitches held by the inoperative needles.

In an embodiment of the invention, a stitch formation cam (with the appropriate countercam) is mounted on a slide parallel with the axis of the needle cylinder, for the adjustment of the effective length of the cam. A servo-control- either double-acting or with a counteracting means-is provided for raising and lowering the slide cyclically. The needle cylinder assembly includes an annular track with a cam profile developed correspondingly to the amplitude of the operative needle arc to determine the actuation of the servo-control.The extension of the cam profile may be varied to obtain a continuous adaptation of the instant aneous amplitude of the arc of needles in operation. in addition, provision may be made for a cam profile corresponding to the maximum amplitude of the operative needle arc, particularly when the part rows are used for the formation of a pocket for a heel or other part with a yarn which is relatively heavy and therefore stronger than the yarn with which the continuous rows are formed.

The invention is applicable to machines equipped for operation with continuous rotational movement of the needle cylinder and to machines equipped for operation with alternating motion of the needle cylinder during the formation of a pocket or, for working with only one arc of needles in operation. For machines which can operate with alternating motion, provision is made for two substantially symmetrical stitch formation cams facing the or each feed. In this case, in an embodiment of the invention, independent means are provided for controlling the lowering of the two cams for stitch formation, active alternately during respective reverse motions of the needle cylinder, correspondingly to the stitch formation cam which is active alternately and temporarily.These means may comprise two tracks with cam profiles having an angular offset like that of the lower apices of the two stitch formation cams and feelers aligned and actuated alternately. As an alternative to this, these means may include a track with a cam profile and two feelers having an angular offset like that of the lower apices of the two stitch formation cams and actuated alternately.

Embodiments of the invention will now be described, by way of example only, with reference to the accompanying diagrammatic drawings, in which: Figure 1 is a front eievation showing a stitch formation cam and associated components for use with a needle cylinder which operates with continuous rotational motion; Figures 2 and 3 are sections respectively on lines Il-Il and Ill-Ill of Figure 1; Figure 4 is a section on line IV--IV of Figure 3; Figure 5 shows a portion of fabric with a pocket; Figure 6 shows the distribution of needles to form the pocket; Figures 7 and 8 are two views of a system for controlling the stitch formation cam illustrated in Figures 1 to 4;; Figure 9 is a developed view showing stitch formation cams for use with a needle cylinder which operates with alternating motion; Figure 10 shows a control arrangement for lowering the cams of Figure 9; Figures 11 and 1 2 show an alternative arrangement to that of Figures 9 and 10.

In Figures 1 to 4 of the drawing, a stitch formation cam or triangular cam for use during continuous rotational motion of a needle cylinder is denoted by 1, while 3 denotes the counter-cam spaced from cam 1 to define a channel through which move needle butts lowered by the cam 1. 5 denotes a cam for subsequently raising the needles. Cam 1 and counter-cam 3 are conventionally mounted on a slide in the form of a rail 7 which is adjustable vertically to control the extent of lowering imposed by the cam 1, in such a manner as to ensure the desired length of stitch and equalize the length of the various rows of stitches formed facing several different feeds provided along the periphery of the needle cylinder.Adjustment is maintained by means of adjustment and holding screws 9A, 9b which define abutments. 10 denotes a reaction spring for holding the rail 7 lifted in case the latter has a degree of play.

The embodiment of the invention differs from conventional arrangements in that there is provided on a block 12 forming a guide for the rail 7, a control arrangement for the cyclic displacement of the rail 7. For this purpose, there is formed on the block 12 a smaller block 14 which defines a fluid cylinder 1 6 having a piston 18. The latter acts on a lever 20 hinged about an intermediate pivot 22 and able to act on the assembly of the rail 7 and of the cams 1 and 3 by its end 20A. In the example shown, the end 20A of the lever 20 acts on the upper edge of the cam 1, against the action of the spring 10. In this case the spring 21 biases the rail against the abutment 9A, and the rail pushed by the lever 20 against the bias of the spring 10 can move within a range controllable by the adjustment of the abutment 9B.Alternatively, the fluid cylinder 16 may be a double-acting cylinder.

During the formation of the fabric M (Figure 5) it is necessary at times to provide for the temporary operation of only the needles comprised within an arc T (Figures 5 and 6) excluding from operation the needles of the complementary arc (3600--T). This is required, for instance, to form a pocket S for a heel, which may be effected with an alternating motion of the needle cylinder or also with a continuous motion of the needle cylinder with devices known per se and conventionally used in, for example, the knitting of hosiery. In any case provision must be made for the operation of only the needles of arc T, or-according to a preset programme-the needles of arcs To smaller than arc T, in such a way as to obtain a shaped pocket.During the formation of the pocket portion S of the fabric M, the needles of arc 3600T must be left out of operation. This may be effected either by keeping lifted out of operation the needles which engage in the stitch, so as to make them pass the cam 1, or keeping these inoperative needles lowered with the stitch engaged, and causing them therefore to travel in the channel between the cams 1 and 3 (or the like) without having taken a new thread and without forming a stitch. In the latter case the inoperative needles kept lowered, tend to strain the thread of their stitch every time they pass under the bottom end of the cam or of each cam 1 (or equivalent), which is repeated for the number of rows with which the pockets is formed, the stitch of each inoperative needle being always the same.This strains the thread of these stitches and may cause breakages or, at least defects in the finished fabric. The embodiments of the invention prevents this by means of the cyclic control for lowering the cam 1 (or equivalent) in the stitch forming position only during the travel of the needle arc T in front of the, or each, cam 1, and then raising the or each cam outside of the needle arc T, so that the inoperative needles are not lowered to the stitch formation level but remain raised by a few tenths of a millimetre in relation to the needles of the arc T which are operative and that, consequently, after taking the thread they are lowered from the cam 1 (or equivalent).

To effect such a control, provision is made for example on the needle cylinder 25, or on an extension 25A of same (Figures 7 and 8), for a cam 26 which may be developed for example correspondingly to the needle arc T, to act upon a microswitch 27 adapted to control an electricallyactuated fluid valve 28 which controls the cylinder/piston 1 6, 1 8 or to act directly on a valve.

A simple solution of this type may be provided for the control of a cam 1 suited for machines which operate with continuous rotational motion of the needle cylinder.

For reasons given above, the cam 1 is lowered during the travel of the needles of the arc T. When only the needles of an arc To within the arc T are made to operate, some of the needles of the arc T are held down and lowered by the cam 1 as needles which are operative. But this is in practice not harmful for two reasons: in the first place generally the thread for forming a pocket S is coarser and stronger than the thread used for the fabric M; secondly, the number of times that the needle of the are T will travel inoperatively under the cam 1 is lower than the number of times during which the needles of the complementary arc 3600--T travel during the formation of the actual pocket S.

When it is required to operate with alternating movement of the needle cylinder, provision is made for stitch forming cams in the form of symmetrical triangular cams as denoted by 31A and 31 B in Figure 9, the lower apices of which cams are angularly separated by an arc a.

In this case, during rotation in the direction of the arros FA cam 31 A operates for stitch formation, while during rotation in the opposite direction according to arrow FB cam 31 B operates. In this case, it is necessary to lower cam 31 A only during the travel of the needles of arc T under this cam, in the direction of arrow FA, while cam 318 is held raised. It is required, instead, to lower cam 31 B only during the travel of the needles of hhe arc T in the direction of the arrow FB. For this purpose, provision may be made for two feelers for micro-switches which are offset angularly by the angle a equivalent to that of the cams 31A and 318, and intended to act one in one direction only and the other in the other direction only, the feelers co-acting with a cam the angular extension of which corresponds to that of arc T. In particular, in Figure 10 the extension 33 (similar to that 25A of Figure 7) of the needle cylinder has a cam 35 (similar to the cam 26) the angular development of which corresponds to the arc T. The cam 35 is able to cooperate with feelers 37A and 37B angularly offset by an amount corresponding to the angular offst a between the lower apices of the two cams 31A and 318, the feelers 37A, 378 acting upon microswitches 39A and 39B, the feeler 37A during the movement in the direction of arrow FA, and the feeler 378 during the movement in the direction of the arrow FB; in fact, the feelers can be inclined only in one direction, one opposite the other.It follows from this that the lowering of the two cams 31A and 318 takes place at the proper time, in the above-mentioned manner, the cams being controlled by cylinder/piston systems similar to the systems 1 6-1 8 and subject to the control of the two microswitches 39A and 39B respectively.

In an alternative arrangement as shown in Figures 11 and 12, provision is made for a pair of cams 1 35A and 135B angularly offset by an angle a equivalent to that of cams 31 A and 31 B, and each with an angular development corresponding to the arc T. The two cams 1 35A and 1358 are adapted to act on feelers 137 aligned and able to bend in opposite directions, combined with two microswitches 1 39A and 139B intended to control the two cams 31A and 31B.

When it is intended to operate with continuous rotational motion of the needle cylinder provision may be made for a system of cams 1, 3 for the, or each feed, and the control system of the relevant rail is then determined by a single cam such as cam 26 of a fluid-aperated servo-mechanism associated with the, or with each, stitch forming cam associated with a feed.

Claims

1. A circular knitting machine of the type operative to form areas of fabric using only the needles of a needle arc of the needle cylinder, while non-operative needles are kept lowered and hold the stitch, with the operative needles being lifted to take a thread facing the or each feed, and being lowered by a corresponding stitch forming cam under which the inoperative needles also travel, said machine including means for moving the stitch formation cam cyclically such that the cam is lowered for the formation of rows of stitches on the needles of said needle arc during the passage past it of said needle arc, and that the cam is raised for the passage past it of the inoperative needles whereby to avoid repeated tensioning of the stitches held by the inoperative needles.

2. A machine according to claim 1, wherein the machine further comprises a slide movable parallel with the axis of the needle cylinder, and a counter-cam cooperating with the stitch formation cam, said stitch formation cam and said counter-cam being mounted on the slide, and said means for cyclically moving the stitch formation cam comprises servo-control means for cyclically lifting and lowering the slide, and means defining an annular track rotatable with the needle cylinder and having a cam profile developed correspondingly to the amplitude of the needle arc of operative needles to determine the actuation of said servo-control means.

3. A machine according to claim 1, wherein the machine is operative to knit with an alternating motion of the needle cylinder, said machine comprising two substantially symmetrical, anularly offset, stitch formation cams facing the or each feed, and independent means for controlling the lowering of the respective stitch formation cams and operative alternately during the respective reverse motions of the needle cylinder.

4. A machine according to claim 3, wherein the control means comprise two tracks including cam profiies having an angular offset equivalent to that of the two stitch formation cams, and respective feelers cooperating with the two tracks, said feelers being aligned and operative alternately.

5. A machine according to claim 3, wherein in said control means comprise a track including a cam profile and two feelers having an angular offset equivalent to that of the two stitch formation cams and being alternately operative.

6. A circular knitting machine substantially as hereinbefore described with reference to the accompanying drawings.