Yarn tension device for a flat knitting machine

A disc type tensioning, or braking device for a float heel knitting machine.

This invention relates to a yarn tension device for a flat knitting 
machine. 
Typically, such a device comprises a yarn brake having a pair of juxtaposed 
brake plates between which the yarn is passed in use, at least one of the 
brake plates being urged against the other by spring pressure. However, in 
yarn tension devices of this type, problems can arise in the region of the 
yarn brake itself and/or upstream of the brake with respect to the 
direction of yarn movement, insofar as yarns which are difficult to work 
(such as knopyarns) can jump out of the brake: such jumping-out can also 
be caused by an unsteady run of the yarn or by accumulations of or loops 
in the yarn, for example. In order to prevent this, it has been the 
conventional practice to use yarn guide loops. However, in order to 
function efficiently, these loops must be disposed at a relatively short 
distance from the brake so that considerable skill is required and 
considerable time taken up to thread the yarn in. 
A changeover has however recently been made, not only in the area of the 
yarn brake but also in other areas of the yarn tension device, to the use 
of elements in place of the yarn guide loops which enable so-called open 
threading of the yarn. German OS No. 29 36 581 discloses an example of 
this where the yarn is introduced into the individual yarn tension 
elements not by being threaded in at the end side into a loop, but rather 
by being put in on the longitudinal side thereof. In order to stop the 
yarn from jumping out of the brake, at least as far as possible, instead 
of placing the brake at a point in the course of a mainly straight run of 
yarn, it has been put lower and thus a deflection of the course of the 
yarn is achieved which should effect a tension on the yarn which is 
directed inside the brake. However, it has been found necessary to make a 
compromise here because the advantage of placing the brake far down for 
the purpose of better holding the yarn inside the brake, is out-weighed to 
a certain extent by the disadvantage arising from the considerable braking 
effect imposed due to the increased looping angle of the yarn on the axis 
of the brake. It has therefore not been possible to place the thread brake 
as far down as it should have been to ensure that the yarn could not jump 
out, for otherwise there would have been a risk of tearing the yarn and/or 
of a reduced brake adjustment. Accordingly, it has not been possible with 
yarn tension devices designed for completely open threading completely to 
prevent the yarn from coming out of the brake. 
An object of the present invention is therefore to create a yarn tension 
device of the type described above which completely prevents the yarn from 
becoming inadvertently unthreaded over all of the component parts 
(including the yarn brake) without other disadvantages having to be 
incurred, and which thus ensures reliable functioning of the flat knitting 
machine to which the yarn tension device is fitted. 
Accordingly, the present invention provides a yarn tension device for a 
flat knitting machine, comprising a yarn brake having a pair of juxtaposed 
brake plates between which the yarn is passed in use, at least one of the 
brake plates being urged against the other by spring pressure, and a 
securing device which defines a yarn path between the brake plates, the 
securing device permitting open threading of the yarn into the yarn path 
but automatically closing the access to the yarn path after the yarn has 
been inserted therein. 
The yarn tension device of the invention thus makes it possible for the 
yarn to be threaded in openly into the yarn brake and also into all of the 
other components as before from the peripheral side and by means of the 
longitudinal course of the yarn. At the same time it is safely ensured 
that the yarn cannot inadvertently leave the thread brake again because 
the securing device has automatically reclosed the yarn path, into which 
the yarn has been laid, in a radial direction towards the outer 
circumference. The position of the yarn brake can thus be shifted upwards 
as compared with the above-described conventional arrangement, so that it 
can be placed in the course of a yarn path running in an essentially 
straight line, with the result that the looping angle (which increases the 
braking effect) can be made negligibly small. It has been found that even 
a loop or such like in the yarn, formed for instance when the machine has 
been shut down, cannot lead to the yarn becoming unthreaded from the yarn 
brake. 
In a preferred embodiment of the present invention, the securing device is 
formed by at least one securing projection standing away from one of the 
brake plates, said projection being provided towards the outer periphery 
of the brake plate with an oblique surface which projects into a receiver 
in the opposing brake plate, and the brake plates are movable relative to 
one another to open and close the yarn path. This is a very simple design 
arrangement in which it is ensured that the yarn can be brought in over 
the oblique surface from the outside to the inside, whereby when the yarn 
slides away over the oblique face of the securing projection, the latter 
is freed out of the receiver. 
In a variant of this, at least one of the brake plates is provided with an 
inner recess to form an outer annular brake edge, and it is expedient if 
the oblique face of the securing projection extends to below this brake 
edge. This ensures with certainty that with open threading the relevant 
yarn comes up against the oblique face of the securing projection and can 
slide along the same. 
Advantageously, the securing projection is fixed relative to said one of 
the brake plates, and the brake plate which has the receiver is movable in 
opposition to the action of a pressure spring. The securing projection 
itself can be designed in various ways. Thus, in one embodiment the 
securing projection is fixed as a (for example) wedge-shaped element on 
said one of the brake plates or on a brake plate holder lying behind said 
one of the brake plates, and engages in an opening in the outer brake 
plate. In another embodiment, the securing projection is formed as a 
stamped-out shape on the relevant brake plate, which is itself formed from 
sheet metal, and engages either in an opening or an impression on the 
opposing brake plate. In a further embodiment, the securing projection is 
in the form of an upwardly bent blade element which has been stamped out 
of the base of the relevant brake plate (again shaped from sheet metal) 
and which also engages either in an impression or a stamped-out orifice on 
the opposing brake plate. The securing projection can also be a curved 
wire strap. 
In a still further embodiment, the securing projection extends over a 
certain acute angle area along a circular arc on the respective brake 
plate. This can be realised by designing the securing projection as an 
elongated, circular nose or by forming the securing projection from two 
(for example) round noses disposed at a distance on the arc of a circle. 
In this way, the yarn can be threaded in and held safely inside the yarn 
path, the formation of fairly large loops in the yarn is prevented, and a 
small yarn looping angle which always remains constant is ensured. 
In a preferred example of the present invention, twist prevention means is 
provided between the two brake plates, the twist prevention means facing 
towards the securing projection. This too helps the yarn to be threaded in 
safely and held in a locked manner in the yarn path because the two brake 
plates are prevented from twisting relative to one another and thus it is 
always guaranteed that the securing projection can fall back into its 
receiver on the opposing brake plate without further ado after the yarn 
has been threaded in.

In all of the various embodiments described herein, there is provided a 
yarn tension device 11 which carries a yarn 10 in such a manner that open 
threading of the yarn is possible, i.e. the yarn can be inserted from its 
longitudinal side into the device 11. The device includes a yarn brake 12 
provided with a securing device 13 which prevents with certainty the yarn 
10 from becoming unthreaded out of the brake 12 during operation. Although 
not shown as such in the drawings, the yarn tension device 11 is designed 
to be fitted to a flat knitting machine. 
In the yarn tension device shown in FIGS. 1 to 3, a housing 16 has disposed 
on its underside a holder 17 for the brake 12. A yarn guide 18 is 
positioned before the brake 12 in the direction of movement of the yarn, 
indicated by arrow A, the yarn guide 18 also being disposed on the 
underside of the housing 16. The guide 18 allows the yarn 10 to run in an 
approximately horizontal direction to the brake 12. From the brake, the 
yarn 10 passes via a deflection unit 19 to a spring gripping arm 21 into 
which the yarn 10 can also be openly threaded. At the arm 21, the yarn is 
deflected into almost the opposite direction and is passed to a further 
thread guide (not shown). The arm 21 is pretensioned by means of the 
thread running there-through, and is connected to mechanical and/or 
electrical control elements inside the housing 16 which effect a switching 
off of the flat knitting machine in the event of the yarn breaking and 
subsequent spring-back of the arm 21. 
As can be seen from FIGS. 2 and 3, the yarn brake 12 comprises two mutually 
opposed brake plates 26 and 27 which are lined up on a shaft 28 fixed so 
that it stands at right-angles to the holder 17. The two brake plates 26 
and 27 are each designed as a dome-shaped sheet metal part, with the brake 
plate 26 (which is adjacent to the holder 17) possessing an annular hollow 
29 surrounded concentrically by an annular brake edge 31 defined or formed 
on both the outside and the inside by a diagonally running wall. The brake 
plate 27, which is opposite the hollow 29 and the annular brake edge 31 of 
the brake plate 26, has a level annular wall 32 which at the edge merges 
with a conically returning shoulder 33. The outside diameter of the 
annular wall 32 is a little smaller than the diameter of the annular brake 
edge 31, so that the edge 31 lies opposite to the starting area of the 
shoulder 33 adjacent to the annular wall 32. A pressure spring 34 acts at 
one end thereof on the inside of the annular wall 32 of the brake plate 
27, the other end of the spring 34 lying against an internally threaded 
bolt 36 which is screwed onto external threading on a free end 24 of the 
shaft 28. By suitably twisting the bolt 36 relative to the shaft 28, the 
pretension imposed by the spring 34 on the brake plate 27 can be adjusted. 
The pressure spring 34 is of conical design. In the illustrated 
construction, the brake plate 26 is held against rotation relative to the 
shaft 28 by means of a sleeve 23, while the brake plate 27 is mounted on 
the sleeve 23 so that it is both rotatable and movable axially relative to 
the shaft 28. 
In the embodiment of FIGS. 1, 2 and 3, the aforementioned securing device 
13 is formed by two securing noses 37 and 38 of identical design which are 
spaced apart from one another along the arc of a circle. Each nose 37, 38 
is of approximately wedge-shaped design and possesses therefore a lead-in 
or oblique face 41 which faces the outer periphery of the yarn brake 12. A 
boundary face 42 is provided, facing away from the oblique face 41 and 
towards the shaft 28, which stands away from the base of the hollow 29 of 
the brake plate 26 in either perpendicular or slightly inclined fashion. 
The securing noses 37 and 38 are of circular section (although they may be 
of oval design) and are secured for instance by means of a rivet on the 
base of the hollow 29 at a distance from the shaft 28 or the sleeve 23, 
whereby a sufficient gap 43 is left for the yarn or yarns which are to be 
used. The oblique face 41 is disposed on each securing nose 37, 38 such 
that is starts in an area below the plane of the annular brake edge 31. In 
the other brake plate 27 and at positions opposite to the securing noses 
37 and 38, a pair of receivers in the form of respective bores 46 and 47 
are provided, into which the securing noses 37 and 38 respectively 
penetrate. The length of the securing noses 37 and 38 is determined such 
that they will still penetrate through the bores 46 and 47 even when the 
yarn 10 is running between the brake plates 26 and 27. This means that the 
brake plate 27 can be moved away from the brake plate 26 by approximately 
the thickness of the yarn 10, as shown in FIG. 3. Both of the securing 
noses 37 and 38 have a gap which gives an acute looping angle of the yarn 
10 on the shaft 28 or the sleeve 23, which is still to be presented. An 
anti-rotation device 51 is disposed approximately diametrically opposite 
to the securing noses 37 and 38. The device 51 comprises a pin 52 which is 
fixed to and which projects out of the bottom of the hollow 29, and a bore 
53 in the opposing brake plate 27 into which the pin 52 extends. The pin 
52 is longer than the securing noses 37 and 38, so that in the event of 
the securing noses 37 and 38 becoming disengaged from the bores 46 and 47 
in the opposing brake plate 27 while the yarn is being threaded in, the 
pin 52 prevents the brake plate 27 from being turned. 
The embodiment shown in FIGS. 4 and 5 uses brake plates 26' and 27' which 
are designed essentially like the brake plates 26 and 27 of FIGS. 2 and 3. 
For this reason, only the difference therebetween will be described. In 
FIGS. 4 and 5, the securing device 13' is constructed as a securing comb 
57 of circular shape, the comb enclosing approximately the same acute 
angle as the two securing noses 37 and 38. The securing comb 57 is formed 
as a stamped-out part which projects out of the bottom of the hollow 29' 
in the direction of the other brake plate 27', and which engages in a 
corresponding circular recess 58 in the brake plate 27'. The recess 58 can 
be provided in the form of an impression in the wall 32' of the brake 
plate 27'. Alternatively, the securing comb 57 could be constructed as a 
separate part like the securing noses 37 and 38, and could be secured to 
the base of the hollow 29'. Similarly, the securing noses 37 and 38 in 
FIGS. 2 and 3 could also be stamped out of the bottom of the hollow 29 so 
as to project therefrom. 
The same applies for the embodiment shown in FIGS. 6 and 7, i.e. the thread 
brake 12" with its brake plates 26" and 27" is in principle the same as 
the thread brake 12 with the brake plates 26 or 26' and 27 or 27' 
respectively. The only difference is that the securing device 13" is 
formed by two securing lugs 61 which are disposed at a distance from one 
another and which are stamped out of the base of the hollow 29". These 
lugs 61 are upwardly bend and penetrate into recesses 62 in the opposing 
brake plate 27". The operation for threading the yarn into the tension 
device of FIGS. 6 and 7 will now be described, it being understood that a 
similar operation is employed mutatis mutandis for the other embodiments 
described above. In this operation, the yarn 10 is introduced by means of 
its longitudinal side in the direction of arrow B from the outer 
peripheral area of the yarn brake 12" between the two brake plates 26" and 
27". Since the brake plates have lead-in slopes 67 and 68 pointing towards 
their dividing plane, the yarn 10 is able to prise the two brake plates 
apart and come up against the oblique face 41" of one of the securing lugs 
61. The yarn 10 can slide along this oblique face 41", whereby the brake 
plate 27" is moved away from the brake plate 26" against the action of the 
pressure spring 34, and indeed until the securing lugs 61 are released 
from the recesses 62. Following this the yarn 10 is able to slip behind 
the oblique face 41" and thus behind the securing lugs 61 towards the base 
of the hollow 29", so that the brake plate 27" follows under the action of 
the pressure spring 34. Because the anti-rotation device 51 prevents the 
brake plate 27" from rotating at this time, the securing lugs 61 can 
penetrate into the recesses 62 again. The yarn path is now locked and 
cannot be opened again through any of the possible movements of the yarn, 
because there is no oblique face available from this side. 
FIGS. 8 and 9 show a fourth embodiment of the invention: as before, only 
the differences compared with the previous embodiments will be described. 
In the yarn brake 12'" of FIGS. 8 and 9 the securing device 13'" has a 
wire loop or strap 64 fixed on the brake plate 26'". The strap 64 is 
shaped like a bridge and slopes toward the shaft 28 so that the two end 
portions thereof form a lead-in slope 41'" for the yarn 10. The strap 64 
engages in an approximately banana-shaped recess 65 in the other brake 
plate 27'". 
FIG. 10 shows a variant of the embodiment of FIG. 3, wherein the yarn brake 
12 has securing noses 37 and 38, which are not fixed on the brake plate 
26, but which rather are secured to an extension 71 of the holder 17 by 
means of a pin 72. The pin 72 penetrates through a recess in the brake 
plate 26. A similar method of fixing on the holder 17 is also possible 
with the wire strap 64 shown in FIGS. 8 and 9. 
If desired, the securing noses 37 and 38 in the embodiment of FIGS. 1 to 3, 
the securing comb 57 in the embodiment of FIGS. 4 and 5, the securing lugs 
61 in the embodiment of FIGS. 6 and 7, and the wire strap 64 in the 
embodiment of FIGS. 8 and 9 can be either made of or coated with 
abrasion-proof material. The same applies to the two brake plates in the 
various embodiments described.