Yarn tensioner for weaving machines

This invention relates to a yarn tensioner for weaving machines in which a filling is intermittently removed from a supply spool by means of a filling insertion mechanism, comprising annular brush means loosely surrounding a rotatable drum means with a smooth surface, means whereby said brush means is mounted on said drum means so as to be freely displaceable within an axially limited range, a first, fixed yarn guiding eyelet means mounted between the supply spool and the drum means, said first eyelet means being adapted to feed a yarn along an approximately axial direction to said drum means, and a second and also fixed yarn guiding eyelet means mounted at the other end of said drum means and adapted to forward said yarn in an approximately axial direction, said yarn when being between said two yarn guiding eyelet means passing on the surface of said drum means and underneath said brush means.

The invention relates to a yarn tensioner for weaving machines. 
The filling to be inserted into weaving machines is taken off, filling by 
filling, from large yarn supply spools mounted outside the machines on a 
special structure or creel. The nature of filling insertion entails that 
the filling is alternatingly taken off at high speed within short time 
intervals and then supposedly remains at rest. However, because of 
inertia, the filling taken off of the spool cannot be immediately stopped. 
While yarn-braking systems are conventionally installed between the supply 
spool and the filling insertion mechanism for instance a gripper, which do 
becalm the yarn and always cause some yarn tension for the purpose of 
insertion feeding, and which ensure satisfactory seizure of the yarn by 
the filling insertion mechanism, these yarn-brakes cannot seize the yarn 
earlier than, if then, behind the guide eyelet of the spool or bobbin 
creel, --when seen in the direction of motion of the yarn --, so that the 
yarn from bobbin to the guide eyelet remains undecelerated and slack. 
This slack hanging yarn depending on material and torque tends to twist, 
which may interfere with the subsequent filling insertion. 
The invention therefore addresses the problem of avoiding these drawbacks 
and to ensure there will be no twisting. This problem is solved by the 
invention by mounting an annular brush freely displaceable within an 
axially limited range in such a manner on a rotating drum with a smooth 
surface that the brush surrounds the drum, and by mounting a first fixed 
guide eyelet between the supply spool and the drum, which feeds the yarn 
to the drum along an approximately axial direction, and a second 
yarn-guiding eyelet, also fixed, at the other end of the drum, which 
forwards the yarn in the approximately axial direction, the yarn within 
the region between the two guiding eyelets passing on the drum surface but 
under the brush. Because of the light pressure from the brush, the slack 
yarn is formed into a loop wound on the drum and tensioned in the process. 
Advantageously, the bristles of the annular brush are so arranged that 
they are at an angle or are slanted with respect to the direction of 
rotation of the drum. In a further embodiment of the invention, the second 
yarn guiding eyelet is mounted at a distance from the axis of rotation of 
the drum which is less than the drum radius.

The design and arrangement of the yarn tensioner will be first explained 
with reference to FIG. 1. The filling 21 from a supply spool or bobbin V 
passes through a yarn guiding eyelet 15 to the yarn tensioner S. 
Thereupon, the yarn is made to pass through a second yarn guiding eyelet 
17 to a yarn brake B and then to a filling insertion mechanism indicated 
here as a gripper rod G. The yarn supply to the yarn tensioner S, and 
further guidance, essentially takes place in the axial direction. The yarn 
brake B is always set for the same value. If there were no yarn tensioner 
S, the resulting slack filling between the supply spool V and the yarn 
brake B might twist. A drum 7 on which is mounted on annular brush 11 is 
an essential component of the yarn tensioner S, both the drum and the 
brush being indicated schematically. These components will be discussed 
more specifically with reference to the following FIGS. 
FIG. 2 also shows in much simplified form the design of the yarn tensioner 
S. The shaft 5 of a drum 7 rests in the supports 3, themselves resting on 
a base plate or supporting arm 1. The drive for the drum 7 in this 
instance is illustrated as a belt drive in the form of a pulley 9. The 
drum 7 with a smooth surface rests on the shaft 5. An annular brush 11 
surrounds the drum 7. The brush 11 lies loosely on the surface of the drum 
7; furthermore the brush may be freely moved in the axial direction within 
given limits. These limits are determined by the rings 13 shown in FIG. 2, 
which are mounted to the base plate 1 through the intermediary of the 
braces 14; other embodiments than rings are possible. In lieu of closed 
rings, other limit-members such as bails or the like may be provided. 
A first yarn guiding eyelet 15 is mounted to the left of the drum 7, in the 
direction of the supply spool (not shown). The guiding eyelet may be 
mounted to one of the supports 3 or to the base plate 1. A second guiding 
eyelet is also rigidly mounted at the right end of the drum 7; it is 
denoted by 17. The radial spacing b between the first guiding eyelet 17 
and the rotational axis 8 is at least as large as the radius r of the drum 
7, or somewhat larger. This is to ensure that the yarn will not be pulled 
over the edge of the drum 7. To that end, the exit aperture of the yarn 
guiding eyelet 15, if necessary, may be displaced sufficiently in the 
axial direction that the aperture is still located above the surface of 
the drum 7, as indicated in FIGS. 2 and 4. The yarn 21 further is made to 
pass on the drum surface underneath the bristles of the annular brush 11 
and into the second yarn guiding eyelet 17 at the other end of the drum 7. 
The spatial arrangement of this second yarn guiding eyelet 17 is so chosen 
that the yarn 21 is guided along the direction indicated by the arrow over 
the edge 7' of the drum 7. To that end the spacing a between the yarn 
guiding eyelet 17 and the axis of rotation 8 of the drum 7 is selected 
smaller than radius r of the drum 7. The edge 7' of the drum 7 is rounded 
to prevent damaging the thread. 
FIG. 3 shows the yarn tensioner S of FIG. 1 in axial elevation, viewed from 
the right. The drum 7 is surrounded by a ring 13 which is solidly mounted 
through brace 14 to the base plate 1. The ring is interrupted at one place 
in the drawing to better show the arrangement of the annular brush 11. The 
bristles 12 are shown on part of the circumference of the brush 11 and 
loosely touch the surface of the drum 7. As already mentioned, it is 
advantageous to direct the bristles somewhat at a slant with respect to 
the direction of rotation of the drum 7 as indicated by an arrow. The 
position of the second yarn guiding eyelet 17 is shown in phantom. 
The functioning of the yarn tensioner will now be described with reference 
to FIGS. 2 and 4, FIG. 4 being a top view of the representation of FIG. 2. 
When the yarn tensioner is in the rest position, the filling 21 is made to 
pass in the direction of the arrow through the first yarn guiding eyelet 
15 to the surface of the drum 7 and passes on the drum surface, underneath 
the annular brush 11, on to the second yarn guiding eyelet 17. Because of 
its tensioning, the yarn 21 follows the shortest path between the two yarn 
guiding eyelets 15 and 17. The filling will be tensioned as long as it is 
taken off of the supply spool and inserted by the appropriate mechanism 
into the shed. This remains essentially the case also when the drum 7 is 
rotating. This is so because of the very smooth drum surface and the very 
slight brush pressure arising from the bristles being at a slant with 
respect to the direction of rotation of the drum. The moment the filling 
insertion is interrupted, and the associated yarn tension drops --whether 
during a filling transfer or at the end of the filling insertion at the 
outside of the weaving machine --the undecelerated section of filling 
between the supply spool and the brake will continue to unwind because of 
the masses in motion, and because of the slight pressure exerted by the 
brush, the yarn section being carried along by the rotating drum 
continuing to unwind because of the masses in motion and thereby forming 
into a flat loop corresponding to the solid line shown drawn into the 
FIGS. The slack yarn between the spool and the brake thereby is tensioned 
to such an extent that on one hand twisting is prevented and on the other 
hand no further yarn is removed from the spool in spite of the tension. 
The moment the length of the loop is wound on the drum 7, the annular 
brush 11 maintains the yarn 21 in its present position despite the 
continued rotation of drum 7, the yarn being deflected at the brush 11 and 
from there arriving at the second yarn guiding eyelet 17. The moment the 
filling 21 is removed at the right from the second yarn guiding eyelet 
17--upon the subsequent filling insertion--the yarn segment lying on the 
drum will be stretched, regardless of any further rotation of this drum 7, 
and be returned to the position 22 shown in dashed lines. The particular 
magnitude of yarn deflection on the drum always corresponds to the 
instantaneous length of the loop formed by inertia. The yarn deflection on 
the drum 7 takes place by itself. Therefore the tension in the yarn 
remains the same after each removal. 
The size or length of the loop wound on the drum is of subordinate 
significance with respect to the essence of the invention; care merely 
must be paid that the coilings of the fillings on the drum can be smoothly 
removed therefrom upon the subsequent filling insertion. This assuredly 
will be the case when the drum dimensions, i.e., the drum radius, is so 
chosen that even the longest possible yarn loop that may occur in 
operation can be reliably wound on less than half a drum circumference. 
But even several yarn windings on the drum are permissible, provided care 
is taken that the take-off speed of the yarn through the filling insertion 
mechanism, upon filling insertion, exceeds the peripheral speed of the 
drum. 
It will be obvious to those skilled in the art that many modifications may 
be made within the scope of the present invention without departing from 
the spirit thereof, and the invention includes all such modifications.