The present invention relates to a control device for adjusting the
radial position of the sinkers in a circular knitting machine, and, in particular,
for adjusting their radial position in those machines which are equipped with
devices for varying the density of the formed fabric, by means of an axial shift
of the sinkers ring.
It is known that in circular knitting machines, the stitch loops
are formed by the vertical reciprocating movement of the needles running inside
slots provided along the generatrices of the revolving needle cylinder, and of
radially movable sinkers which are arranged on a ring revolving with the needle
cylinder and located at the end of the cylinder, in such a position that the feed
yarn comes into engagement with a needle, with a sinker, with the subsequent needle,
and so on. It is also known that, in order to obtain a good operation and a good-quality
product, the sinkers must be given a certain radial mobility, in order to always
keep properly tensioned the loops, in order to enable the needle latches to open,
and the formed stitch loops to be discharged, with the needles being prevented
from penetrating, during the production of the subsequent course, the loops formed
in the preceding course. Should such an event occur, a faulty knitted fabric would
The need is known as well, during the production of a tubular knitted
fabric destined, e.g., to form a hosiery article, for the length of the stitch
loops formed at each course, viz., the density of the fabric, to be changed, in
order to obtain lengths of tubular knitted fabric showing different extensibility.
This is generally achieved by axially shifting the sinker ring, driven
by means of lifting cams. An equivalent contrivance to it is, on the contrary,
the axial shift, to the opposite direction, of the stitch forming cams acting
on the needle butts. This, because such a contrivance is equivalent to the shifting,
relatively to the sinker knocking-over plane (the A or B level in Figures 1A and
1B), of the whole path of the needles.
In order to give the yarn loops a proper tension, the radial mobility
of the sinkers is realized, in the most widely used machines, according to Figures
1A and 1B, by placing said sinkers on lower, annulus-shaped revolving support
1, provided with radial slots 2, inside which the sinkers 3 are guided during their
reciprocating movement in the radial direction.
In the upper portion of each sinker 3, two vertical butts 4 and 5
are provided, which alternatively get engagement with two concentrical cam rings
6 and 7 having a substantially circular contour in a plane perpendicular to the
axis of the needle cylinder and with their center being positioned on the axis
of the cylinder. The cam rings 6 and 7 are supported by an upper, annulus-shaped
stationary support 8.
The contour of rings 6 and 7 is shown in Figure 2.
The inner can ring 6 is radially stationary and rigid with, the support
8, by being fastened to it by means of stud bolts 9; the outer cam ring 7 is subdivided
into a plurality of segments ― in exemplifying Figure 2, four segments ―
and is fastened to the support 8 by means of pins 10 inserted inside hollows 11,
having a larger size, so forming a slack link which allows the cam ring 7 to radially
move through a certain stroke into discrete positions. A circumferential spring
12 applies a containment force to the portions of the outer cam ring 7, weakly
pushing it inwards. However, the inwards force radially applied by the spring 12
should never exceed the tensile strength of the yarn 14, and when the needle 13
pulls the yarn 14 outwards, and applies an outwards-directed tensile force to the
recess 15 of the sinker 3, the same spring should yield and allow the sinker to
The recess 15, viz., the sinker, is pushed inwards by the spring
12 through an as long distance as allowed by the yarn 14; the yarn 14 is hence
always under tension, and the loop is never slack.
- Figure 1A corresponds to long loops, with the sinkers high at level A.
- Figure 1B corresponds, on the contrary, to short loops, with the sinkers low
at level B.
One can observe that, with long loops, the "abundance" of yarn enables
the sinkers 3 to move inwards by a longer stroke. The A and B levels are normally
denominated as the "sinker knocking-over levels".
According to Figure 2, both the contours of the innermost cam ring
6 are active: the inner contour 6i engages the butts 4, and pushes inwards the
sinkers 3 when the corresponding needles are lowered under them, and the outer
contour 6e engages the butts 5 and pushes outwards the sinkers 3 when the corresponding
needles start sinking after yarn catching.
Through the portions along which the inner cam ring 6 does not act,
the radial position of the sinkers 3 in then determined by the outermost cam ring
The cam ring 7 operates ― as regards the sinkers ― by
means of its inner contour only, which gets engaged with the butts 5 and pushes
the sinkers 3 inwards, keeping the yarn loops always under tension.
This known technical solution does not show serious drawbacks when
the machine runs at not very high speeds.
In high-productivity machines, which operate at speeds higher than
1,000 revolutions per minute, the effects of the centrifugal forces applied to
the sinkers, and applied by these latter to the cam ring 7, are such that such
a technical solution cannot be any longer adopted without serious drawbacks.
In fact, it should be reminded that a circular knitting machine must
be capable of considerably varying its revolution speed during the production of
an article, e.g., when a change in needle selection is carried out.
If then, when high-speed operation is expected, a stronger spring
12 is adopted, which is also capable of counteracting the effect of the centrifugal
forces developed at high speeds, when the machine operates at slow speeds, the
centrifugal forces applied to the spring are small, and the force of the spring
can hence exceed the tensile strength of the yarn 14, and, consequently, tear
Thus, in order to be able to control the radial position of the sinkers
in high-speed circular knitting machines, it is necessary to resort to a control
system which determines a radial approach and a radial pushing away of the outer
cam ring 7 as a function of the length of the formed loops.
In the prior art, some technical solutions to meet this requirement
have been proposed.
In GB-A-2091301, the approach and pushing away of the cam ring which
controls the radial position of the sinkers is controlled by levers which move
on vertical planes passing through the axis of the cylinder, and are directly driven
by the lifting of the needle cylinder.
In DE-A-3246653, the contour segments constituting the outer cam
ring 7 are articulated and hinged to the support 8, and they are made radially
approachable and movable away with a pivoting movement by means of telescopic
In DE-A-2020524, the length of the stitch loops is controlled by
subdividing the sinkers into two half-sinkers, arranged side-by-side and capable
of relative radial movement, which makes it possible to change the overall configuration
of the sinkers.
The radial movement of the two half-sinkers is controlled by acting
on the butts located at their ends, one upwards, and the other downwards, which
are engaged inside two cam/countercam ring are assemblies, analogous to those
as hereinabove described, positioned on different planes perpendicular to the axis
of the cylinder.
The cam ring and coutercam ring are moved by radially moving sliders,
inwards urged by radial springs, and driven by means of further periferally positioned
approaching and pushing-away cams.
Such radial springs cause the position of the sinkers to be influenced
by the revolution speed of the machine.
But such technical solutions result complex, and do not secure the
accuracy and gradualness of the radial movement.
The control device according to the present invention makes it possible
to adjust the radial position of the outer cam ring 7 as a function of the level
of the sinkers 3 with gradualness and accuracy.
It will first be disclosed with reference to the practical embodiment
of Figure 3, wherein the elements 6, 7, 8, 9, 10, correspond to the same elements
as of Figure 2.
According to the invention, the outer cam ring 7, and, more precisely,
its component segments, have, along their outer contour or periphery, a plurality
of shaped portions in form of peripheral protrusions 16, preferably having a curved
Externally around the cam ring 7, a substantially circular countercam
ring 17 is concentrically located, whose inner contour is provided with shaped
inner portions in form of recesses 18 with gradual radial approach and pushing-away
profile i.e. with zones which are closer to the center and further zones spaced
relatively further away from the center in a complementary formation to the protrusions
16. The countercam ring 17 is supported and held in position by the annular-shaped
In the Figures, the protrusions 16 are provided on the outer circular
cam ring 7 and the recesses 18 are provided on the circular countercam ring 17.
It is evident that such an arrangement can be inverted, with the recesses 18 being
provided on the cam ring 7, and the protrusions 16 being provided on the circular
countercam ring 17, without changing the spirit and the scope of the invention,
the two arrangements being perfectly equivalent.
It results evident that, when the machine is operating, and the needle
cylinder is revolving, and with it also the sinker bearing group revolves, the
cam ring 7 ― or, better, its component segments ― by the effect of
the centrifugal force acting on the sinkers 3 adhere to the counter cam ring 17,
so that the protrusions 16 of the cam ring 7 are in contact with the recesses 18
of the countercam ring 17 and vice versa.
The adjustement of the radial position of the cam ring 7 is determined
by making the countercam ring 17 ― i.e. its segments ― rotate through
a discrete angle around the centre C, which lays on the axis of the needle cylinder,
according to arrows R. With such a rotation into discrete angular positions, the
protrusions 16 engage a portion of the recesses 18, which is more or less near
to the centre C, and through such a contact the component segments of the cam ring
7 are respectively moved inwards or retracted.
In Figures 3A and 3B there is respectively shown the A position ―
long loops ― which corresponds to a longer inwards advancement of the sinkers,
and the B position ― short loops ― corresponding to a longer outwards
retraction of the sinkers.
The rotation R from a position of minimum radial inwards advancement,
to a position of maximum radial inwards advancement of the cam ring 7, and, consequently,
of the sinkers, is enslaved by known means ― e.g., by means of a kinematic
transmission containing conical gearings ― to the respectively minimum and
maximum axial level of the sinker knocking-over plane, i.e., the recess 15.
Such kinematic transmission is shown, for exemplifying purposes,
in Figures 4 and 5A and 5B.
Figure 4 is a diagram showing the circular knitting machine and the
kinematic transmission in an elevational view. Figure 5A shows a top plan view
of the transmission and the contercam ring 17, and Figure 5B shows a side view
of the upper part of the kinematic transmission.
The lifting of the splined needle cylinder of the machine, and, with
it, of the circular support 1 which supports and guides the sinkers 3, is achieved
by means of a cylinder-holder plate 19 which is pivotally mounted around a pivot
20, according to a kinematic arrangement known in the art.
The lifting of the circular support 1 causes the stitch loops formed
in cooperation by the needler 13 and the sinkers 3 to be made longer. Simultaneously
to the lifting and the sinking of the needle cylinder caused by the pivoting movement
of the plat 19, its movement in the axial direction is transmitted to a vertical
rod 21, which moves as shown by arrow A&min;.
The rod 21 is rigid with an arm 22, which translates coherently,
remaining parallel to itself, relatively to a stationary frame 23, according to
the movement allowed by a through pin 24 which moves rigid with the arm 22 inside
a through slot 25 provided in the support 23.
The vertical motion of the arm 22 is transmitted, by means of an
adjustable push-rod 26, to an arm 27, which is constrained with a pivot pin 28
to move according to a pivotal motion B&min; about a horizontal axis; a conical
gear wheel 29 rotates with the pin 28, and makes a second conical gear 30 rotate
according to revolving motion C&min; about a vertical axis.
A pivot pin 31 is rigid, with its lower end, with the conical gear
wheel 30 and, with its upper end, with an arm 32 which, by means of a fork-shaped
end 33, engages with a vertical stud 34 rigid with the countercam ring 17, and
causes the above mentioned rotation R. A through bore 35 provided at the other
end of the arm 32, and a clamp 36 make it possible to lock the arm 32 on the revolving
pivot pin 31.
The contact of the arm 22 with the push-rod 26 is always secured
by a spring 37.
The device according to the invention makes it possible to gradually
and accurately position all the component segments of the cam ring 7 by means of
the rotation of one single actuator element, and does not resort to a plurality
of complex components, whose action must be coordinated and controlled.