Yarn supply system

The take up means (5) is inhibited in response to a predetermined operating conditions of the flat knitting machine.

FIELD OF THE INVENTION 
The present invention relates to a yarn supply system for a flat knitting 
machine. 
BACKGROUND OF THE INVENTION 
A prior art yarn supply system for a flat knitting machine comprises a yarn 
spool, a yarn tensioning unit comprising a yarn storing and feeding device 
to which a yarn can be supplied from the yarn spool for an intermediate 
store of the yarn on a storage drum of the feeding device. The yarn can be 
actually withdrawn from said storage drum through a yarn tensioning device 
arranged at the withdrawal end of the storage drum. The yarn withdrawn 
from the storage drum of the yarn feeding device is fed to a yarn take-up 
arm which is pivotally journalled under a spring-load and which is adapted 
for intermittently taking up an excess of yarn in case the yarn tension 
drops below a predetermined yarn tension value. 
A flat knitting machine comprises a stationary needle bed and a carriage 
which can be reciprocated with respect to said needle bed for operating 
the needles and for moving a thread feeder arranged at the carriage along 
the needle bed so as to supply the yarn to the respective operated 
needles. The movement of the carriage of a flat knitting machine does not 
terminate at the respective ends of the needle bed of the knitting 
machine, but there is a so-called over-movement of the carriage with 
respect to the needle bed of the flat knitting machine. This over-movement 
of the carriage at both end positions of its horizontal movement over the 
needle bed is carried out when changing the thread feeder arranged at the 
carriage during the colour change as well when only changing the direction 
of the movement of the carriage when further working by means of the same 
thread feeder without changing the colour. The yarn consumption of the 
knitting machine during the normal operation when the carriage is within 
the normal working area, i.e., between the respective ends of the needle 
bed, is essentially constant. The yarn consumption drops at the respective 
remote ends, i.e., during the over-movement of the carriage. Hence, a 
surplus of yarn is to be taken back in a controlled manner at the 
respective remote ends of the fabric so as to make the edges of the 
knitted fabric look satisfactory. 
In the prior art yarn supply system, the spring-loaded arm intermittently 
takes up the surplus or excess of yarn by a pivot movement. 
The spring-loaded arm has the tendency to cause vibrations and oscillations 
in the yarn tension which in turn negatively affects the continuity in 
building up the respective stitches and thus results in an unsufficient 
knitting quality. 
In view of this state of art, the present invention s based on the 
technical task of how to further develop a yarn supply system for a flat 
knitting machine adapted for manufacturing a high quality knitted fabric 
having an essentially constant stitch size. 
This technical task is solved by a yarn supply system in accordance with 
the prior art portion of claim 1 having the features indicated in the 
characterising portion thereof. 
In accordance with the present invention, the operation of the yarn take-up 
means is inhibited in response to predetermined operating conditions of 
the flat knitting machine. These operating conditions may be the relative 
position of the carriage with respect to the needle bed and/or the actual 
movement of the yarn withdrawn from the yarn tensioning unit. 
Preferably, the operation of the yarn take-up means is inhibited during the 
so-called "normal" operation of the flat knitting machine, i.e., during 
the movement of the carriage between the respective ends of the needle 
bed. Hence, the occurrence of any oscillations of the yarn take-up means 
during the normal knitting operation is prevented. In other words, slight 
oscillations may only occur at the very short operating time during the 
over-movement of the carriage. As a result therefrom, the knitted fabric 
manufactured by a flat knitting machine having a yarn supply system in 
accordance with the present invention has a very constant stitch size and 
thus a high quality. 
Advantageous embodiments in accordance with the present invention are 
defined in the subclaims.

DETAILED DESCRIPTION 
FIG. 1 shows a sketch for explaining the respective working areas of a flat 
knitting machine known per se in the art. 
As described above, a flat knitting machine (not shown) includes a carriage 
(not shown) which is adapted for a reciprocating movement with respect to 
a needle bed of the knitting machine. A thread feeder 1 mounted to the 
carriage is moved along the needle bed. The area between the respective 
ends of the needle bed is the so-called "normal" working area which is 
indicated by the reference number 2 in FIG. 1. For reasons described 
above, the thread feeder 1 must carry out an over-movement beyond the 
normal working area 2 at the respective ends of the fabric to be knitted. 
The area of over-movement at both ends is designated with the reference 
number 3 in FIG. 1. 
A yarn supply system for the flat knitting machine in accordance with the 
preferred embodiment shown in FIG. 2 comprises a yarn spool (not shown), a 
yarn tensioning unit 4, a yarn inhibiting means 6 for inhibiting the 
operation of the yarn take-up means 5. 
The yarn tensioning unit 4 comprises a yarn storing and feeding device 7. 
For the purposes of the disclosure of said device, reference is made to 
the applicant's pre-published European Patent Application No. 84 108 
138.3. 
The yarn storing and feeding device has a storage drum 8, onto which an 
intermediate yarn store 9 can be wound. To be more specific, the storing 
and feeding device 7 includes a hollow shaft 10 extending to a rotating 
winding-on tube 11 for winding the yarn 12 on the storage drum 8 so as to 
form an intermediate yarn store 9. With regard to details of the design 
and mode of operation of yarn feeding devices, reference is made to the 
above-indicated European Patent Application. 
The yarn can be withdrawn from the storage drum 8 in its axial direction 
through a yarn tensioning and clamping device 13 arranged at the 
withdrawal end of the storage drum. The yarn tensioning and clamping 
device 13 establishes a predetermined first yarn tension in the yarn when 
withdrawing the yarn from the storage drum. Instead of the yarn tensioning 
and clamping device, any yarn brake adapted for creating a predetermined 
tension in the yarn when drawing the yarn through it can be used. 
The yarn withdrawn from the storage drum 8 is fed through a yarn movement 
sensor 14 arranged in the path of the yarn between the storage drum 8 and 
the yarn tensioning and clamping device 13. The yarn having passed the 
yarn tensioning and clamping device 13 is fed via a guiding eyelet 15 of 
the yarn take-up means 5 to the thread feeder 1 (FIG. 1) arranged at the 
carriage of the flat knitting machine. 
The yarn take-up means 5 is formed by a pivotable yarn take-up arm known 
per se in the art, which is pre-biased under a spring load such that its 
guiding eyelet 15 tends to draw the yarn away from the yarn tensioning and 
clamping device 13. The pivotable yarn take-up arm 16 is journalled at a 
bearing at the housing of the storing and feeding device 7. 
The inhibiting means for inhibiting the operation of the yarn take-up means 
5 in response to predetermined operating conditions of the flat knitting 
machine comprises an electric holding magnet 17 which is electrically 
connected to a control unit 18 and which holds the pivotable yarn take-up 
arm 16 in the position shown at FIG. 2 when the holding magnet 17 is 
supplied with an inhibiting signal generated by the control unit 18. 
The control unit 18 may comprise a micro-computer or micro-processor which 
is adaptively programmed for generating the inhibiting signal to be fed to 
the holding magnet 17 under predetermined operating conditions of the flat 
knitting machine, which are derived from sensor signals generated by said 
movement sensor 14 and by a position sensor 19. The signal generated by 
the position sensor 19 indicates whether or not the carriage of the flat 
knitting machine is in the normal working area 2 or in the area 3 of 
over-movement. The control unit 18 is also connected to a so-called 
stop-motion relay 20 for actuating same in case of erroneous operating 
conditions indicating that some fault has occurred in the feeding of yarn 
to the flat knitting machine, like a yarn breakage, a clogged thread 
feeder 1 and so on. 
With reference to FIG. 3 an explanation of the flow diagram of the 
programme stored in the micro-processor 18 will be given. 
Box number 21 indicates the start of the programme routine. 
At the programme step number 22, the control unit 18 checks whether the 
sensor signal received from the yarn movement sensor 14 indicates whether 
or not the yarn moves at a predetermined speed. As long as the yarn is 
withdrawn from the storage drum 8 at a certain speed, the control unit 
will go to programme step number 24 for maintaining the holding magnet 17 
in its actuated condition, i.e., for continuously feeding the inhibiting 
signal to the holding magnet 17. Thereinafter, the control unit goes back 
to programme step number 22. 
In case the control unit 18 determines at programme step number 22 that the 
yarn is not moving or not moving at the predetermined minimum speed, it 
goes to programme step number 23. At programme step number 23, the control 
unit 18 checks the output signal generated by the position sensor 19. In 
case the output signal of the position sensor 19 indicates that the 
carriage is not in the normal working area 2, but in one of the areas 3 of 
over-movement, the inhibiting signal is turned off for deactuating the 
holding magnet 17 and thus enabling the operation of the yarn take-up 
means 5. After having de-actuated the holding magnet 17, the control unit 
18 goes back to programme step number 22. In case the control unit 
determines at programme step number 23 that the carriage is within the 
normal working area, the control unit goes to programme step number 25. 
Programme step number 25 is an optional measure for a multi-colour flat 
knitting machine having a plurality of thread feeders 1 and a plurality of 
yarn movement sensors 14, each sensor being associated to one yarn colour. 
At programme step number 25, the control unit detects whether at least one 
movement sensor detects the movement of a yarn. If so, the control unit 
goes back to programme step number 22. Otherwise, it goes to programme 
step number 26, since the detection of no yarn movement in the normal 
working area of the knitting machine indicates that some kind of fault has 
occurred in the feeding of yarn, for example a yarn breakage. Hence, the 
control unit actuates the stop-motion-relay so as to immediately stop the 
flat knitting machine. 
The present invention is not limited to the above-described preferred 
embodiment. 
For example, the yarn tensioning unit located between the yarn spool and 
the yarn take-up means does not necessarily comprise a yarn feeding and 
storing device, although a yarn feeding and storing device with a 
subsequent yarn tensioning device located at the withdrawal end thereof is 
advantageous for obtaining a continuous yarn tension. For example, the 
yarn tensioning unit 4 can be replaced by a simple yarn brake, like a yarn 
disc brake located between the yarn spool and the yarn take-up means. 
Furthermore, the yarn take-up means does not necessarily comprise a 
pivotable yarn take-up arm, since the yarn take-up means can be 
implemented by any unit adapted for taking yarn in case the yarn tension 
drops below a minimum value. 
Moreover, the inhibiting means does not necessarily have to comprise a 
holding magnet but could be carried out, for example by means for 
releasing the spring-load of the yarn take-up means so as to inhibit the 
operation thereof. In addition, the inhibiting means may have the form of 
an electric pre-biasing device for replacing the mechanical spring used 
for pre-biasing the pivotable arm of the preferred embodiment. 
Although the tensioning unit of the preferred embodiment is a storing and 
feeding device having a tensioning and clamping device it can be any kind 
of a yarn braking unit like a brush ring or a combination of a clamping 
device and a braking unit in the form of a brush ring. The clamping device 
can also be a so-called "trapper unit" having a re-shaped clamping opening 
for trapping the yarn when the take-up means is in its actuated position. 
Alternatively, the braking device can have the form of the ball-brake 
disclosed in DE-OS No. 33 16 078.