The present invention relates to a Raschel-type linear
knitting machine, commonly also known as Raschel-type warp machine and used for
manufacturing textile items of any type.
The peculiar feature of known warp machines consists in
that the fabric that has just been formed is pulled downwards by means of suitable
take-down devices, so that because of friction the old loop is not lifted together
with the needle, which is going to take the new yarn, but is left in a lowered position
so as to be discharged in its turn from the needle and leave space on the stem for
the new loop that has just been formed.
Moreover, thanks to the take-down action the loop adhering
to the needle is able to rotate the needle latch when said needle moves downwards
so as to close the jack carrying new yarn, thus enabling it to discharge the old
knitting stitch and to form a new loop (in the case of a latch needle).
As is known, take-down devices comprise at least two rollers,
which by means of pressure keep and take down the knitted fabric on its whole length,
exerting a force opposed to the upward movement of the needle. As a rule, rollers
have a smooth surface, preferably made of rubber, so as not to spoil the fabric
undergoing take-down and ensure a uniform traction on the whole piece length. However,
rollers actually rotate at a constant speed whereas the piece is formed "jerkily",
i.e. when needles get down and discharge stitches. As a consequence, the fabric
is taken down even when no new loops are formed. This imbalance of the force of
traction is partly counterbalanced by fabric elasticity, however the pressure exerted
by rollers cannot be high so as not to result in permanent fabric deformations.
Consequently, when needles get up to take new yarn and force the loop wound on its
stem to get up, they are prevented from doing so by the take-down action, though
part of the fabric wound on the rollers is pulled upwards because of elasticity
and sliding between the rollers.
This phenomenon is very dangerous as far as the fabric-building
process is concerned and results in poor quality and even needle breaks when needles
do not manage to discharge the old stitch and still take new stitches.
In known machines this drawback was solved first by strongly
limiting manufacturing speed, since the faster the needle is lifted, the more the
loop adheres to its stem since it has not time to slide on the latter.
Known machines were then equipped with holding-down elements,
which fit in between the needles and prevent the stitch to get up along the stem
beyond a given extent. This element is commonly known as "stitch-comb" and is applied
under different forms to looms equipped both with latch needles and with compound
needles. It should be pointed out that in latch needles the latch is integral with
the needle by means of a hinge pin enabling rotation on it, whereas in compound
needles needle and latch are separate and are to be moved individually.
As is known, a warp machine comprises as many holding-down
elements as needles. Each element acts upon a needle basically on the knock-over
plane of the needlebed, preferably slightly above it, so as to track down loop welts
and prevent them from getting up with the needle. Each holding-down element is further
shifted forward so as to keep the loop on the needle stem when the needle begins
to be lifted, starting from the lower dead center of its stroke, and stays in this
position until the needle has achieved its upward movement. Said elements now get
backwards so that the needle gets down and forms a new stitch.
Forces acting on each holding-down element when keeping
the stitch in a lowered position are small, about few hectograms and mainly depend
on yarn type and knitting density.
Generally, holding-down elements are mounted onto bars
(one for single-needlebed machines and two for double-needlebed machines), which
are movably connected to the machine frame for instance by means of two arms.
However, known machines have some drawbacks.
Warp machines are equipped with up to more than three thousand
needles pro needlebed, which are arranged on a bar of more than three and a half
meters of length and, moving simultaneously, discharge the force of friction setting
in with the loops just formed onto the bar carrying in its turn more than three
thousand holding-down elements. As a consequence, the total force discharged onto
the bar of holding-down elements (which is the sum of the force pro needle for the
number of needles moving simultaneously) reaches very high values, i.e. some hundreds
of kilos. Consequently, bars carrying holding-down elements should be very strong
in order to bear such an intense stress.
Moreover, so as to prevent the bar of holding-down elements
from bending in its effort to prevent loops from getting up, lever arms are arranged
about every half meter, thus increasing machine cost and complexity. Thus, for instance,
8 arms are applied on a 3.5 meter bar if the machine is single-needlebed, whereas
16 are present if it is double-needlebed.
Such oversize of the bar carrying holding-down elements
requires a machine with strong and heavy structure so as to support and move these
elements at a given speed. However, operating speeds are still small because of
the forces of inertia due to the high masses involved. Therefore, beyond strong
disadvantages as far as manufacturing costs are concerned, there are also strong
disadvantages concerning the final operating speed of the machine.
In order not to load the structure of the bar carrying
holding-down elements too much, the take-down system is modified by bringing its
pressure between rollers and its rotation speed to the limit which the fabric can
bear, which results, as is well known, in risks involving breaks or permanent deformations.
The aim of the present invention is to solve the problems
of prior art by proposing a linear knitting machine without the drawbacks mentioned
above. In particular, an aim of the present invention is to show a linear knitting
machine which has a slim structure and is therefore easier to manufacture, transport
and install in the plant. As a consequence, an aim of the present invention is to
provide a linear knitting machine in which the forces acting upon the various components
are small, which is advantageous as far as component size and lifetime are concerned.
A further aim is to propose a linear knitting machine which is easy to manufacture
and has low costs. Another aim of the invention is to propose a linear knitting
machine with holding-down elements that are able to cooperate with take-down devices,
which should not be operated at their limit with possible fabric damage. A further
aim of the invention is to propose a linear knitting machine enabling to obtain
a high-quality fabric, i.e. uniform, compact and without abnormal elongations. A
final aim of the present invention is to provide a linear knitting machine ensuring
high speeds of use and therefore a high production in time unit.
These and other aims, as will be more evident from the
following description, are achieved according to the present invention thanks to
a linear knitting machine in accordance with the appended claims.
Further characteristics and advantages of the invention
will be more evident with the description of a preferred though not exclusive embodiment
of the invention, disclosed to a merely indicative purpose in the following figures:
- Figure 1 shows an isometric view of holding-down means and of force-discharging
means associated with a needlebed of a linear knitting machine according to the
invention in accordance with a preferred embodiment;
- Figure 2 shows an isometric view of the holding-down elements and of the engagement
elements in a preferred embodiment of the linear knitting machine of Figure 1;
- Figure 3 shows a front view of the holding-down means of the discharging means
associated with the corresponding needlebed of the linear knitting machine of Figure
- Figure 4 shows a section of the linear knitting machine of Figure 3 according
to lines IV-IV, in which holding-down elements and discharging means are in two
different operating positions;
- Figure 5 shows an isometric view of bars carrying holding-down elements associated
with the corresponding needlebeds of the double-needlebed linear knitting machine
of Figure 1;
- Figure 5a shows a magnified detail of Figure 5;
- Figure 6 shows a lateral view of the bars carrying holding-down elements associated
with the corresponding needlebeds of the double-needlebed linear knitting machine
of Figure 1;
- Figure 6a shows a magnified detail of Figure 6;
- Figure 7 shows an isometric view of a body housing the holding-down elements
associated with the force-discharging means of a linear knitting machine according
to the invention;
- Figure 8 shows an isometric view of the holding-down elements, of the discharging
means and of the anti-deviation means in a first execution variant of the linear
knitting machine according to the invention;
- Figures 9a and 9b show an isometric view of a holding-down element, of the discharging
means and of the anti-deviation means in a second execution variant of a linear
knitting machine according to the invention.
With reference to the figures mentioned above, a linear
knitting machine 1 according to the invention comprises a machine frame, at least
one needlebed 3 associated with said machine frame, a plurality of needles 4 sliding
in the needlebed 3 and holding-down means 8 cooperating with the needles 4 on the
needlebed 3. Said means 8 can shift between a forward position, which occurs when
the needle 4 is lifted in the needlebed 3, in which they act upon the stitch so
as to keep it on the stem 5 of said needle 4, and a rear position, when the needle
4 gets down, in which they do not act upon the stitch, as can be seen in Figure
4 (said figure does not show the stitch which, in the embodiment of said machine,
lies between the holding-down means 8 and the needlebed 3). A linear knitting machine
1 according to the invention is characterized in that it further comprises holding
means 15 fastened to the machine frame and discharging means 19 associated and integral
with the holding-down means 8. Said discharging means 19 can be engaged in forward
position with the holding means 15 so as to discharge onto the machine frame the
force generated by the holding-down means 8 while keeping the stitch of the stem
5 of the needle 4, and can be disengaged from said holding means 15 when they are
brought to the rear position.
The holding-down means 8 comprise a plurality of holding-down
elements 9, each of them being designed to cooperate with one of the needles 4 of
the machine 1 on the needlebed 3, and therefore on the knock-over plane, so as to
perform their function of keeping the stitch on the stem 5 of the needle 4 when
the latter is lifted, as shown in Figure 1. In particular, each holding-down element
fits in the space 10 between two adjacent needles 4 when it is in a forward position.
As a consequence, the machine 1, as besides known machines, has the same number
of holding-down elements 9 as the number of needles 4.
In a preferred embodiment of the invention, the holding-down
means 8 further comprise a plurality of housing bodies 13, each of them being designed
to contain a pre-established number of holding-down elements (Figures 5a and 7).
Each housing body 13 contains as many holding-down elements 9 as are prescribed
by the corresponding fineness: for instance, a holding body 13 having fineness 16
will contain in an inch 16 holding-down elements 9. Furthermore, the holding-down
elements 9 are integral with the corresponding holding body 13 since they are melted
with the latter during manufacturing.
Still according to a preferred embodiment, the holding-down
means 8 comprise also a bar 11 movably associated with the machine frame by means
of at least one arm 12 so as to shift between the forward and the rear position
by means of handling means (not shown), which can include at least one electric
motor and means for transmitting motion from the motor to the arms 12. Preferably,
each bar 11 is associated with two arms 12, each of them being fastened onto the
end portions 14 of said bar 11, as can be seen in Figures 5 and 5a.
In this case, the various housing bodies 13 are connected
integrally to the bar 11 and associated one with the other or one beside the other,
so that the holding-down elements 9 are basically parallel to one another. As a
consequence, also the holding-down elements 9 are integral with the bar 11.
In an alternative embodiment, the holding-down elements
9 can also be fastened directly to the bar 11 without the help of housing bodies
According to the invention, the discharging means 19 comprise
at least one engagement element 20 associated and integral with the holding-down
means 8 so as to engage with the holding means 15 in forward position.
The holding means 15 comprise in their turn a stiff element
16 equipped with seats 17 into which the engagement elements 20 fit during their
movement from the rear to the forward position, stay therein until the needles 4
do not stop getting up, and disengage during the movement from the forward to the
A preferred embodiment of the machine 1 comprises a plurality
of engagement elements 20, each being associated with one of the holding-down elements
9 so as to engage with the holding means 15 in forward position. In further detail,
each of these engagement elements 20 is made as one piece with each of the holding-down
elements 9, as can be seen in the accompanying figures. Therefore, on each needle
4, when the bar 11 is brought to the forward position, there is an element having
a first elongated portion acting as holding-down element 9 and keeping the stitch
basically on the knock-over plane, and a second elongated portion, advantageously
placed below the first one, acting as engagement element 20 and discharging the
force generated by the corresponding holding-down element 9 while keeping the stitch
on the stiff element 16 associated with the machine frame. Thus, the portion of
the seat 17 obtained on the stiff element 16 getting in contact with the engagement
element 20 represents a reaction surface 18 absorbing the upward thrust exerted
by the engagement element 20 due to the force imparted by the stitch which would
naturally tend to get up together with the needle 4, and enabling to discharge said
force onto the machine frame locally, i.e. for every single needle 4.
The invention further comprises execution variants differing
from the preferred one disclosed above.
As a matter of fact, the machine 1 can comprise at least
one engagement element 20 associated with at least one of the arms 12, preferably
with both arms.
Conversely, in a second execution variant, the engagement
element 20 can be associated with the bar 11. For instance, it can consist of a
rod connected to at least one portion of the transversal extension of said bar 11
and developing along said transversal extension so as to engage with the stiff element
16, or the bar 11 can comprise a plurality of engagement elements 20 located along
its transversal extension at a pre-established distance designed to engage with
the stiff element 16. Moreover, the engagement element 20 can be associated with
at least one of the housing bodies 13, preferably to each of them. Here again, there
can be a rod connected to the housing body 13 and extending transversally with respect
to the latter, as shown in Figure 7, or a series of engagement elements 20 placed
along its transversal extension at a pre-established distance.
These execution variants of the engagement elements 20
are however less efficient than the preferred one since they do not enable to discharge
force uniformly onto the stiff element 16 on each needle 4.
Advantageously, the stiff element 16 can be associated
with the machine frame by means of the needlebed 3. In particular, in the preferred
embodiment of the invention, the stiff element 16 is made up of the needlebed 3
itself. Preferably, said needlebed 3 has on its front surface 3a a single transversal
seat 17 or as many seats 17 arranged transversally as the number of needles 4 and,
therefore, of engagement elements 20, so as to enable the insertion of said elements
20, as shown in Figures 1 to 3.
The needlebed 3 is not weakened by the addition of said
seats 17 since it is suitably oversized with respect to the stress it should bear.
The engagement element 20 and its seat 17 made on the stiff
element 16 can have any shape provided that the latter enables a suitable coupling
between the two elements 17, 20 so as to discharge onto the stiff element 16 the
force acting upon the holding-down means 8.
In order to prevent the engagement element 20 in forward
position from deviating laterally and disengage unintentionally from the seat 17
made on the stiff element 16 due to the stress it undergoes, although the anchoring
of the engagement element 20 to the housing body 13 is sufficiently stiff, the discharging
means 19 can advantageously comprise anti-deviation means 21. Said means 21 can
include for instance a transversal rod 22 associated with the engagement elements
20, as can be seen in Figure 8, or engagement elements 20 having a folded extension
23 associated to an end portion 24 thereof, as shown in Figures 9a and 9b.
The linear knitting machine 1 according to the present
invention can further be single-needlebed or double-needlebed: in the latter case
the holding-down means 8, the discharging means 19 and the holding means 15 described
above are associated to each one of the two needlebeds 3. As a matter of fact, as
can be seen schematically in Figures 5 and 5a, the machine 1 is equipped with two
bars 11 designed to carry the holding-down elements 9 with their engagement elements
20, each being associated with one of the two needlebeds 3.
As for known machines, the knitting machine 1 according
to the present invention comprises means for feeding the needles 4 with the yarn
for forming new fabric, comprising a plurality of yarn-carrying elements, commonly
known as "yarn guide", which make enveloping movements around the needle 4 so that
the yarn is taken and kept in the jack 6 of the needle 4 itself and then woven in
the loop previously formed (feature not shown).
Furthermore, the machine 1 comprises means for taking down
the fabric already formed (not shown), cooperating with the holding-down means 8
so as to prevent the stitches of said fabric from getting up along the stem 5 of
the needle 4 when said needle 4 is lifted. Said means comprise at least two rollers,
preferably three, designed to exert a basically constant pressure on the fabric
Eventually, the machine 1 can advantageously comprise stopping
means (not shown) acting upon the various needles 4 so as to avoid the unintentional
closing of the corresponding latch when they are getting up, which would prevent
the jack 6 from being fed with the new yarn.
The invention thus conceived can undergo several changes
and variants, all of which fall within the inventive framework.
In practice, any material or size can be used depending
on the various needs.
Moreover, all details can be replaced by other technically
The invention achieves important advantages.
The linear knitting machine according to the invention
enables to discharge onto the needlebed, or more generally onto a stiff element
associated with the machine frame, the force of friction building up when keeping
the stitch basically at the same height as the needlebed when the needle gets up.
In the preferred embodiment of the invention, said force is discharged even for
every single needle, and therefore in a uniform way basically on the whole length
of the needlebed. Thus, the bar carrying the holding-down elements and the engagement
elements should bear the weight only of the elements it carries but not the stress
upward which would inevitably tend to bend it.
This results in huge advantages concerning the mechanical
construction of the machine, the textile yield, the stability of the system, the
increase of the overall speed of the machine (in number of shots per minutes) and
the optimization of take-down operations. As a matter of fact, for instance, the
bar carrying the holding-down elements and the engagement elements becomes less
strong with a decrease in strength and overall size of the machine and benefits
concerning costs, especially manufacturing costs, manufacturing speeds, since the
inertia of the masses involved is lower, and easy transport and installation in
a manufacturing plant. Furthermore, the fact the bar carrying the holding-down elements
and the engagement elements undergoes a lower stress implies a longer life of the
components forming the holding-down means 8 and the discharging means.
Moreover, the machine disclosed above ensures an efficient
system for preventing the stitch just formed from getting up together with the needle,
which significantly reduces the risk of breaking the needles and enables the take-down
means not to work above their limits. This allows to preserve the quality of the
manufactured fabric, and in particular not to create on the latter stress areas,
abnormal extensions or torsions.