Winding – tensioning – or guiding – Unidirectional winding and unwinding – Variable number of windings on support
Reexamination Certificate
1999-07-26
2001-07-10
Mansen, Michael R. (Department: 3653)
Winding, tensioning, or guiding
Unidirectional winding and unwinding
Variable number of windings on support
C242S15000R, C242S419100, C139S452000
Reexamination Certificate
active
06257516
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to an axial disc brake as well as to a yarn feeding device having an axial disc brake.
BACKGROUND OF THE INVENTION
In an axial disc brake as known from WO91/14032, intended for the weft yarn rotatingly withdrawn from a storage drum of a yarn feeding device by a textile machine, in one embodiment the mutually contacting braking surfaces are provided exactly perpendicular to the axis of the storage drum. In a further embodiment, the braking surface provided on the front side of the storage drum is oriented precisely perpendicular to the storage drum axis, while the other braking surface is formed by a convexly rounded outer edge of a funnel-shaped braking element having a funnel angle of almost 180°. The braking surface which is perpendicular to the storage drum axis in a further embodiment is unitarily formed with the storage drum. In case of an overhead-withdrawal of the yarn from the storage drum the yarn is rotating like the pointer of a clock and then is entering essentially axially and from the outer side in between the braking surfaces. The yarn is braked by the braking surfaces and then is withdrawn approximately centrally via an opening provided in one of the braking surfaces. In the embodiment having braking surfaces oriented exactly perpendicular to the storage drum axis the yarn is deflected twice by 90°. Such strong deflection may mean under undesirable conditions high load for the yarn and might lead to undefined friction conditions. Centering one of the braking elements on the axis of the storage drum is without problems because of the orientation of the braking surface exactly perpendicular to the storage drum axis. However, a lateral displacement of the braking element, e.g. caused by an axial component of the yarn tension exerted onto said brake element, may cause a disturbance of the mutual contact between both braking surfaces. With the strong deflection of the yarn when entering in between the braking surfaces the friction force depends on the deflection angle and increases by an exponential function depending on said deflection angle and might be superimposed onto the actual braking effect between the braking surfaces. This might lead to a high yarn breakage quota in case of vulnerable yarn qualities like cheap woolen- or cotton-yarns of low quality.
In a yarn brake of a yarn feeding device as known from EP-A-652312, a braking surface having a circumferentially continuous extension and the shape of a frusto-cone coat directly contacts the rounded withdrawal rim of the storage drum of said yarn feeding device. The axis of said frusto-cone coat of said braking surface approximately coincides with the axis of said storage drum. The other barking surface is defined by said rounded withdrawal rim of said storage drum and is designed—in an axial section of said storage drum with a curvature following a circle arc section. The center of said circle arc section is situated inside said storage drum, but is positioned a significant radial distance from the storage drum axis. The frusto-conical braking surface is formed by a deformable band. In case of precise centering of the band in relation to the storage drum axis, the contact zone between the braking surfaces is a full circle. In case that the yarn is forced through the contact zone and/or a small lateral displacement or tilt of the axis of the frusto-cone coat occurs in relation to the storage drum axis, the form of the contact zone changes into a geometrical form other than a full circle.
It is an object of the invention to create an axial disc brake of the kind as disclosed above as well as a yarn feeding device with which a yarn geometry can be achieved which is advantageous for the yarn, avoids strong deflections, and which is accompanied by a correct mutual centering of the braking surfaces with proper mutual contact relationship in their contact area between the braking surfaces.
Said task can be achieved according to the invention by providing an axial disc brake having a pair of form stable braking surfaces axially yieldably pressed against one another with predetermined contact pressure. The braking surfaces define an inlet gap in the area of an outer circumference of the disc brake, with the downstream braking surface having a central withdrawal opening. A braking element is provided which is movably supported at least in the axial direction. One of the braking surfaces is spherically convex with the sphere center thereof located approximately along the axis of the disc brake, and the other braking surface is conical with a cone axis approximately coinciding with the axis of the disc brake. The generatrix of the cone of the other braking surface in the contact zone of the respective braking surfaces is a tangent to the generating circle of the spherical other braking surface. The above disc brake can advantageously be provided on a yarn feeding device for a textile machine, particularly a projectile or gripper weaving machine, the yarn feeding device having a yarn storage drum for overhead yarn withdrawal, which storage drum is provided frontally with a withdrawal region defining a circular yarn guiding surface, wherein the disc brake is arranged coaxially with the storage drum adjacent a front end thereof.
Due to the cooperation between the spherical braking surface and the conical braking surface in contact therewith, the mutual contact zone is inclined, in which contact zone the withdrawn yarn is braked. The withdrawn yarn is drawn from the exterior towards the central withdrawal opening and is simultaneously rotating like the pointer of a clock about the axis of the disc brake. As a result, a very advantageous yarn geometry with weak deflection is achieved. The incoming yarn enters into the contact zone in a straight manner and is then deflected only gently behind the contact zone and into the withdrawal opening. In addition, constant contact relationships and a proper mutual centering of the braking surfaces result from the cooperation of the braking surfaces, since the contact zone remains a full circle even with deviations of the cone axis in relation to the axis of the disc brake or the storage drum, and even when the spherical braking surface becomes displaced. The diameter of said full circle remains unchangeable due to the geometrical conditions. Due to the advantageous yarn geometry the danger of yarn breakages is small since the yarn coming from the yarn guiding surface without deflection enters the disc brake while rotating like the pointer of a clock and is only gently deflected behind the contact zone of the braking surfaces. The reduction of the respective deflection angle and the avoidance of any deflection in the entrance area of the disc brake has a particularly positive effect on the yarn, because of the strong exponential influence of the deflection angle. The yarn is braked practically only in the contact zone such that the constant braking effect of the braking surfaces leads to a very advantageous, almost constant yarn tension in the outgoing yarn. Occasionally occurring relative displacements between the breakage surfaces do not change the contact- and braking relationships between the braking surfaces, since the full circle of the contact zone is maintained constantly as the braking surfaces are apt to automatically mutually align each other in a correct way. Also manufacturing- or assembling-tolerances are without significant influence on the braking effect due to the perfect cooperation between the conical braking surface and the spherical convex braking surface. The spherical convex braking surface is provided at the entrance side of the yarn. The center of the sphere is positioned in or along the axis of the disc brake or the storage drum, respectively.
In one embodiment, the tangent corresponding to the conical braking surface defines an angle of less than 90° with respect to the brake axis, and the orientation of the tangent essentially determines the entrance-direction of the yarn such that the yarn follows an optim
Fritzson Joachim
Jacobsson Kurt Arne Gunnar
Tholander Lars Helge Gottfrid
Flynn ,Thiel, Boutell & Tanis, P.C.
Iro AB
Mansen Michael R.
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