[0001] This invention relates to a tensioning device for a yarn carrier of a yarn working
machine. The invention finds particular, although not exclusive, use for controlled
supply of yarn from a carrier to a braid point in a braiding machine.
[0002] A braiding machine generally comprises a circular array of an even number of carriers,
each carrier having a substantially perpendicular spindle, on which bobbins wound
with yarn or yarn packages are mounted. During the braiding process, a proportion
of the carriers revolve in one direction around the centre of the machine while the
remainder revolve in the opposite direction. The path of the carriers is diverted
by gears so that they pass either inside or outside others travelling in the opposite
direction. The yarns carried by the moving carriers are wound under and over each
other to produce braid.
[0003] An example of the course followed by the carriers is illustrated diagramatically
in Fig. 1, in which the solid lines represent the paths of the carriers around the
gears, the small dotted lines represent slots in the gears whereby the carriers are
engaged and moved, and the large black and white dots represent the carriers moving
in respective directions.
[0004] In most conventional braiding machines, as in Fig. 1, there are twice as many carriers
as there are gears. Eight gear, sixteen carrier machines are particularly popular.
Generally, to increase the rate at which the braid is produced, the gear size (or
"pitch") is reduced, allowing the carriers to rotate at higher speeds.
However, increase in rotational speed also results in increased likelihood of yarn
breakage.
[0005] In operation, yarn is supplied from each carrier to a "braid point" where the braid
is produced and drawn away. The speed at which the braid is drawn away or "taken up"
may be varied to produce braids of differing structure e.g. "open" and "closed" braids.
[0006] To obtain satisfactory results, it is important for the rate at which the yarn is
supplied to the braid point to be controlled. For example, to achieve a braid of even
formation, it is important to ensure that the yarn is taken up from each bobbin at
the same speed such that the same length of yarn is supplied from each bobbin. The
yarn from each bobbin must also be sufficiently taut. Supply control is facilitated
by the use of yarn take off guides and tensioning devices on each carrier.
[0007] Generally yarn from a bobbin or package mounted on a carrier passes through a first
yarn guide, through a yarn guide of a tensioning device, and then through a second
yarn guide before delivery to the braid point. In each case the guide might be a hook,
roller, loop, aperture or other suitable engagement means.
[0008] An example of a known tensioning device is a spring-loaded lever having its fulcrum
towards the base of the carrier, and provided with a hook to act as a yarn guide.
In operation yarn is drawn from the upper part of the bobbin or package through a
first guide means, then pulled down through the hook on the tension device and up
again to a second yarn guide near the top of the carrier. As yarn is pulled taut through
the second guide means the lever pivots upwards against spring bias.
[0009] Another known tensioning device comprises a slide mounted on an elongate shaft parallel
with the carrier spindle. The slide carries a lateral hook to engage the yarn and
is able to slide upwardly of the shaft only by compressing a spring mounted on the
shaft between itself and an upper stop element. As yarn is drawn through the second
guide means, the slide moves up the shaft, and the force of the spring ensures that
the yarn is kept taut. However, friction is generated as the inner surface of the
ring slides over the shaft, and, again the ring and hook can provide considerable
inertia. For fine, weak yarn, the weight of the hook hanging on the yarn can cause
the yarn to break.
[0010] Both the aforesaid devices are widely used for braiding heavy duty yarn at relatively
modest speeds. However, satisfactory results are not obtained for high speed braiding
using fine yarn. The weight of the spring-loaded lever and the spring force and inertia
of the slide, respectively often cause fine yarn to snap, which means the machine
must be switched off and rethreaded, resulting in loss of valuable manufacturing time.
Even without snapping, the yarn supply is often uneven owing to the excessive tension
thereon. Thus particular problems and difficulties arise with these known devices
when braiding at high speeds, using fine yarns.
[0011] A further tensioning device which was used up until the 1920s for yarn carried on
bobbins of only a few centimeters in diameter consisted of a weighted spring inside
each spindle shaft. The yarn was drawn from the bobbin, into the spindle shaft and
held taut by the weight. This arrangement proved wholly unsatisfactory because, by
having the tension device inside the spindle, it was difficult to rethread the yarn
once each bobbin needed replacing, or in the event of yarn breakage.
[0012] Braiding has many different applications, ranging from, for example, "armouring"
for large diameter electric cables to surgical sutures of only 1/64˝ in diameter.
However, as discussed above it has proved particularly difficult to obtain satisfactory
results using fine yarns when operating at high carrier speeds such as required in
the production of surgical sutures. To increase manufacturing capacity it is desirable
for the machines to operate reliably at high carrier speeds whilst reducing the likelihood
of yarn breakage.
[0013] An object of the present invention is to provide a carrier having a tensioning device
suitable for use with fine, light duty yarn. With this in mind, the invention seeks
to overcome at least some of the aforementioned drawbacks.
[0014] According to the invention a carrier for a yarn working machine, particularly but
not exclusively a braiding machine as aforesaid, has a spindle to support a bobbin
or yarn package, and at least one fixed yarn take off guide and associated tensioning
device for guiding yarn from the bobbin or package to a yarn working station, characterised
in that the tensioning device is mounted on the carrier remote from the spindle and
comprises a yarn guide element connected to an elastically resilient element, the
latter being capable of being elongated or stretched and thereby placed under increased
tension as yarn passing through the guide element is drawn off the bobbin or package.
[0015] Preferably the yarn guide element of the tensioning device is in the form of an eyelet.
Most advantageously such an eyelet or other element is made of ceramics which is surface
finished so that it has an extremely smooth surface. In this respect, reducing surface
roughness to an absolute minimum reduces the likelihood of snagging and yarn breakage,
and generally promotes free flow of yarn therethrough.
[0016] A suitable resilient element is a tension spring, conveniently a helical spring,
which can be produced at high tolerance to have the requisite tension.
[0017] Preferably the spring or other resilient element is arranged to cause actuation of
a fault indicator when in a low tension or rest position.
[0018] In a preferred embodiment of carrier such a spring is arranged substantially upright,
with an eyelet directly connected to its upper end. Furthermore, the lower end of
the spring (or other resilient element) is conveniently connected to a dropper, the
arrangement being such that when the spring is held under tension by active take off
of yarn through the eyelet the dropper is raised, but when that tension is released
(e.g. upon yarn breakage) the dropper falls to activate a fault indicator.
[0019] Preferably, the spring or other resilient element is also capable of actuating a
means for inhibiting free rotation of the spindle when tension in the element is at
a predetermined minimum. This is so that the spindle may only rotate and allow supply
yarn of adequate tensions.
[0020] With this in mind, in particularly preferred embodiments, the spindle for the bobbin
or package is conveniently mounted on a ratchet, and a pawl which cooperates with
the ratchet is provided, said pawl being displaced from engagement with the ratchet
(typically by lifting the pawl out from between ratchet teeth), once the tension in
the spring reaches a predetermined maxiumum. Thus, free revolution of the ratchet
and thereby the bobbin or package mounted on the spindle, and consequent unwinding
of yarn therefrom is permitted only when the yarn being taken off is adequately tensioned.
In this respect, an actuator for lifting the pawl is conveniently operated by the
yarn guide element of the tensioning device, most simply by displacement along with
said yarn guide element.
[0021] The invention will be described further with reference to the accompanying drawings
in which:
Fig. 1 is a schematic diagram illustrating operation of a braiding machine, as previously
referred to;
Fig. 2 is a schematic view of an exemplary practical embodiment of a carrier for a
braiding machine, in accordance with the invention, with a yarn bobbin mounted thereon;
and
Fig. 3 is a side view of the carrier shown in Fig. 2.
[0022] Referring to Figs. 2 and 3, the carrier (1) comprises a spindle (6) mounted axially
of a basal disc (4). Also mounted on the disc (4), adjacent and parallel to the spindle
(6) is an elongate shaft (8). A first yarn take off guide (10), in the form of a winding
terminating in a hook (10a), is positioned on an upper part of the shaft (8). The
hook (10a) carries a surface finished ceramic piece (10b), which has a through-hole
to allow smooth passage of yarn therethrough. This take off guide (10) is mounted
above an actuation arm (12) which is slidably located on the shaft (6) and a helical
spring (11), encircling the shaft (8) acts therebetween.
[0023] The actuation arm (12) is connected to a pawl member (20) which is also slidably
located on the shaft (8) by way of a shank (19). The pawl member (20) engages the
teeth of a ratchet (23) which is mounted on the spindle (6) just above the disc (4).
[0024] A tensioning device (14) is also mounted on the carrier (1) quite separately from
the spindle (6). This comprises a ceramic eyelet (15) attached to the top of a helical
tension spring (17) which is arranged generally vertically, parallel to the spindle
(6) and the shaft (8). In this respect, the terminal winding at the top of the spring
(17) engages the eyelet (15). The eyelet is surface finished by a special coating
to enable exeptionally smooth throughflow of yarn therethrough. The spring (17) is
supported on a short auxiliary shaft (18) and its lower end is connected to a dropper
(27) a portion of which is located around the lower end of the shaft (8), and lies
substantially perpendicular to, or otherwise projecting outwardly from, the axis of
the shaft (8). One or more switches (not shown) are arranged outside the revolving
path of the carriers, to be actuable by the dropper (27) in its rest position to switch
off the power supply. These switches act as fault indicators in that they ensure the
machine stops in the event of yarn breakage or other mishap.
[0025] At the upper end of the shaft (8) a second yarn take off guide (30) is provided in
the form of an apertured arm. The aperture in the take off guide (30) is also provided
with a smooth inner surface coating (30a) for reducing likelihood of yarn snagging
as it passes therethrough.
[0026] The illustrated carrier (1) is specifically intended for use as part of a braiding
machine, and its function will be described in that context, even though, as will
be appreciated, the invention is not limited to this particular application.
[0027] Thus, when this carrier is used on a braiding machine, a bobbin (3) wound with yarn
is mounted on the spindle (6). Yarn is drawn from the bobbin (3) and threaded through
the hook (10a), down through the eyelet (15) and up through the aperture of arm (30)
and thence to the braid point. Once the machine is operating, as yarn is drawn through
the arm (30), the spring (17) is stretched and the eyelet (15) rises from the lower
position depicted in solid lines in Fig. 2, to the upper position depicted in broken
lines. The dropper (27) connected to the lower end of the spring (17) is also raised
from its rest position.
[0028] Indeed, when adequate tension is applied to draw off the yarn, the eyelet (15) contacts
the actuation arm (12) and raises it from its rest position shown in solid lines to
the position shown in broken lines against the bias of the spring (11). This consequentially
lifts the pawl member (20) out of engagement with the ratchet (23) to allow free revolution
of the spindle and ongoing supply of yarn to the braid point.
[0029] In the event of yarn breakage the eyelet (15) falls and the spring (17) immediately
returns to its lower position. This allows the actuation arm (12) to fall back to
its rest position, which in turn causes the pawl (20) to fall into engagement between
the teeth of the ratchet (23), preventing revolution of the spindle. Thus, yarn no
longer continues to be drawn off the bobbin (3).
[0030] Also, when the spring (17) drops down to its lower, unstressed position, the dropper
(27) falls back to its rest position where it may actuate the above mentioned switches
(not shown) to cut off the power supply to the braiding machine.
[0031] As previously mentioned, the present device is particularly appropriate for use in
braiding fine yarns at high speeds. Since the eyelet and spring are much lighter in
weight than any other presently available yarn, and frictional forces are also minimised
so that likelihood of breakage is reduced and smooth, even, yarn take off can be achieved
at relatively high speeds.
[0032] In this respect the present tensioning device allows conventional braiding machines
of, for example, 70mm gear pitch to be adapted to operate more reliably at higher
speeds than at present (e.g. up to 400 or 500rpm) than at present. Also fine yarns
of less then 175 decitex can be used without problem on machines provided with this
type of tensioning device. Such yarns are used to produce braids of less than 2mm
in diameter, which may be used as surgical sutures.
[0033] In the foregoing detailed description the yarn is referred to as wound on a bobbin.
Alternatively, particularly in the case of fine yarns, the yarn may be stored on a
"cross-wound package" which is of generally cylindrical shape, tapering at its upper
and lower ends. Unlike a bobbin it does not have end flanges. Obviously, in the foregoing
description such a package could be used in place of a bobbin.
[0034] Although previously mentioned, to avoid any doubt it is stated again, that the foregoing
description of the illustrated embodiment is only exemplary and any construction details
may be varied within the scope of the invention. In particular the yarn guide element
of the tensioning device need not be an eyelet, although that is very suitable in
practice, and the spring could be replaced by other suitable elastically resilient
means.
1. A carrier (1) for a yarn working machine, the carrier having a spindle (6) to support
a bobbin or yarn package (3) and at least one fixed yarn take-off guide (10) and associated
tensioning device for guiding yarn from the bobbin or package (3) to a yarn working
station, characterised in that a tensioning device (14) is mounted on the carrier
(1) remote from the spindle (6) and comprises a yarn guide element (15) associated
with an elastically resilient element (17), the latter being capable of being elongated
or stretched and thereby placed under increasing tension as yarn passing through guide
element (15) is drawn off the bobbin or package (3).
2. A carrier (1) according to Claim 1 wherein the resilient element (17) is arranged
to cause actuation of a fault indicator when tension in the element (17) reaches a
predetermined minimum.
3. A carrier (1) according to claim 1 or 2 wherein the resilient element (17) is arranged
to actuate a means for inhibiting free rotation of the spindle (6) when tension in
the element (17) reaches a predetermined minimum.
4. A carrier (1) according to Claim 3, comprising a ratchet (23) for rotation with the
spindle (6) and a pawl (20) for engagement with the ratchet (23) thereby to inhibit
free rotation of the spindle (6), the pawl (20) being displaceable from engagement
with the ratchet (23) once tension in the resilient element (17) reaches a predetermined
minimum.
5. A carrier (1) according to Claim 4 wherein an actuator (12) for displacing the pawl
(20) is operated by the yarn guide element (15) of the tensioning device (14).
6. A carrier (1) according to any preceding claim wherein the resilient element (17)
comprises a tension spring.
7. A carrier (1) according to Claim 6 wherein the tension spring is supported on a shaft
(18).
8. A carrier according to any preceding claim wherein the yarn guide element (15) of
the tensioning device (14) is in the form of an annular eyelet.
9. A carrier according to any preceding claim wherein the yarn guide element (15) of
the tensioning device (14) is made of ceramics.
10. A yarn working machine provided with a carrier according to any preceding claim.