SHED-FORMING DEVICE

Abstract

The disclosure concerns a shed-forming device including a jacquard device in which the heddles, are connected to a pull-back element, for exerting a downward force on the heddle, wherein for each heddle, a yarn tensioning element is provided to change the yarn tension in at least one associated warp thread, and where a control or steering unit is provided for steering or controlling the yarn tension in at least one associated warp thread, separately for each heddle, in order to bring the total downward force on the heddle to a specific value or vary this according to a specific profile.

Description

FIELD OF THE DISCLOSURE

The disclosure concerns a shed-forming device comprising a jacquard device with a number of heddles for positioning at least one associated warp thread, wherein each heddle is connected to a pull-back element for exerting a downward force on the heddle.

BACKGROUND

During successive weft insertion cycles on a weaving machine, one or more weft threads are inserted into a shed formed between the warp threads. In order to weave according to a predefined weaving pattern, the various warp threads must be correctly positioned in each shed relative to one or more levels at which weft threads are inserted. A jacquard machine is used for positioning several warp threads differently in each shed.

Positioning takes place by means of heddles which are connected to respective hooks via cords, wherein each heddle has a heddle eye. The hooks can be moved up and down by means of upwardly and downwardly moving knives, and selected by selection means so as to be held or not held in one of a number of possible positions. Each warp thread extends through a heddle eye of a heddle, so that each different position of the heddle corresponds to a different position of the warp thread.

To allow the shed formation to take place correctly and to facilitate the downward movement of the hooks, each heddle is connected to a pull-back spring which is provided for exerting a downward force on the heddle. In the lowest position of a heddle, the extension of the spring is at its smallest, so that the downward force exerted by this pull-back spring on the heddle is then at a minimum. The pull-back spring is selected such that this minimum force is still just sufficient to allow the hook connected to the heddle to engage correctly on a selection edge of a knife.

In the lowest position of the heddle, the warp threads which extend through the heddle eye also exert an upward force on the heddle. This is the result of the yarn tension in these warp threads. In this lowest position, the pull-back spring must therefore exert a downward force on the heddle which is greater than said upward force, and the resulting downward force must also be just sufficient to allow the selection hook to engage on a selection edge of a knife. Consequently, this minimum downward tensile force may not be too small.

When the heddle is moved to a higher position by the knife, the downward spring force increases proportionally with the upward movement of the heddle, so as to finally reach a value which is much greater than necessary. As a result, the mean tension on the warp threads is much higher than necessary. A higher tension means more wear on machine components, more extensive and more frequent damage to the warp threads themselves, and more energy consumption of the machine.

SUMMARY

The object of this disclosure is to remedy these disadvantages.

This object is achieved by providing a shed-forming device with the features specified in the first paragraph of this description, wherein according to this disclosure, the shed-forming device comprises, per heddle, a yarn tensioning element which is provided to change the yarn tension in at least one associated warp thread, and the shed-forming device comprises a control or steering unit which is provided, in cooperation with the respective yarn tensioning elements, for steering or controlling the yarn tension in at least one associated warp thread separately for each heddle, such that the total downward force on the heddle is brought to a specific value or varies according to a specific profile.

The tension profile in the warp yarn can be steered or controlled by means of a shed-forming device according to this disclosure such that at all times, the combined effect of the yarn tension and the spring exerts a downward force on the heddles which is sufficiently large to achieve a good shed formation but reaches lower top values than with existing shed-forming devices. This means less wear, less yarn damage and a lower energy consumption.

In addition, pull-back elements may be selected which are not as powerful. In the lowest heddle position, the yarn tension can still be steered or controlled to a lower value than with the existing shed-forming device. The pull-back element must then provide a lower force in order to achieve the minimum required downward force.

The steering or control system may also be designed to allow the total downward force during the weaving process to take a number of successive values which are predefined. In some cases also certain machine parameters, such as machine position or machine speed, or data connected with the weaving pattern or weave structure, may be made available to the steering or control system in order to be taken into account in determining the target value for the total downward force.

Said profile may be selected for example from a collection of two or more reference profiles or two or more reference series, such as e.g. tables or files, with at least one reference value for the yarn tension. During weaving then, for example on the basis of machine parameters and/or weaving pattern data, a suitable reference profile or reference series may be selected.

In a preferred embodiment, each yarn tensioning element comprises a roller which is driven by a motor and is in contact with at least one warp thread, and is intended to rotate in the one or the other direction of rotation in order to move said warp thread in a direction opposite the feed direction of the warp threads, or to move the warp thread or to facilitate the movement thereof, so as to move with the movement thereof (i.e. a moving warp thread) in a direction which is the same as the feed direction of the warp threads, in order to increase or decrease respectively the yarn tension in said warp thread.

The pull-back elements may be any type of element which is designed to exert a force, such as amongst other elements in which the force is supplied at least partially by a pneumatically driven element and/or by force of gravity. Preferably, these are elements in which the downward force is supplied at least partially, and preferably exclusively or mainly, by an elastically deformable element. In a most preferred embodiment, the pull-back elements are springs.

The yarn tensioning device preferably comprises measuring means in order, in at least one warp thread or in several (at least two) warp threads which form a part group, to measure the yarn tension or a variable which is a measure of the yarn tension. Preferably, a steering unit is also provided with means for repeatedly or continuously comparing the measured yarn tension, or the variable which is a measure of the yarn tension, with a reference value, and when a difference is established between the measured yarn tension or variable on the one hand and the reference value on the other, generating a control signal for driving a yarn tensioning element (e.g. by adapting the current with which the motor is controlled or by adapting the motor torque) such that the difference between the measured value and the reference value is reduced.

A control unit preferably comprises a regulator which is provided, on setting a specific target value for the yarn tension, to generate a control signal for driving a yarn tensioning element (e.g. by adapting the current with which the motor is controlled or by adapting the motor torque) such that the target value is approached or reached. The regulator is preferably a regulator of the type with “feed-forward control”.

In a particular embodiment of a steering or control unit, machine parameters may also be made available, such as the machine position or machine speed, or data connected with the weaving pattern or weave structure, and one or more of these parameters may be used for control or steering.

If one or more yarn tension influencing circumstances differ for different part groups of warp threads, then in this weaving machine different reference yarn tension profiles may be determined for these part groups, and these reference yarn tension profiles may be adapted separately and if necessary differently in the different part groups during the weaving process, according to circumstances which have changed during the weaving process. The yarn tension may thereby on average be kept slightly lower while the maximum values of the yarn tension are not as high.

The yarn tensioning device comprises for example detection means for detecting the status of one or more yarn tension influencing circumstances during weaving, and/or comprises storage means and/or data-processing means in order to predefine the time or phase of the weaving process at which the yarn tension influencing circumstance occurs, for example on the basis of the weaving pattern and/or on the basis of the proposed path of warp threads between the yarn store and the fabric.

Preferably, in this weaving machine and according to the method of this disclosure, a control system is applied using a “bidirectional forced feed-forward function”. This means that, on a change of movement of the yarn, the yarn tensioning unit intervenes to facilitate this change so as to react more quickly.

Further particular features of this shed-forming device are described in the claims.

The disclosure is now explained further with reference to the description which follows of a possible embodiment of a jacquard machine according to this disclosure. It is emphasised that the device and method described are merely examples of the general principle of the disclosure, and thus may in no way be regarded as a limitation of the scope of protection specified in the claims or of the area of application of the disclosure.

BRIEF DESCRIPTION OF THE DRAWINGS

In this description, reference signs are used to refer to the attached figures, in which:

FIG. 1 is a diagrammatic side view of a structure of a weaving machine and a bobbin creel with associated yarn tensioning device;

FIG. 2 is a graph showing the following for a pile-forming pile warp thread in a number of successive weft insertion cycles during weaving, according to the prior art:

• • the development of the position of the heddle eye (in mm),
  • the development of the upward or downward component of the force (in N) which is exerted on the heddle as a result of the yarn tension in the pile-forming pile warp thread,
  • the development of the downward spring force exerted by the pull-back spring on the heddle of the pile warp thread (in N), and
  • the development of the sum of the downward spring force (in N) on the heddle and the upward or downward component of the force (in N) which is exerted on the heddle as a result of the yarn tension in the pile-forming pile warp thread.

FIG. 3 is a graph showing the following for a pile-forming pile warp thread in a number of successive weft insertion cycles during weaving with a controlled or steered yarn tension according to the disclosure:

• • the development of the position of the heddle eye (in mm),
  • the development of the upward or downward component of the force (in

N) which is exerted on the heddle as a result of the yarn tension in the pile-forming pile warp thread,

• • the development of the downward spring force exerted by the pull-back spring on the heddle of the pile warp thread (in N),
  • the development of the sum of the downward spring force (in N) on the heddle and the upward or downward component of the force (in N) which is exerted on the heddle as a result of the yarn tension in the pile-forming pile warp thread, and
  • the mean of said sum of forces.

DETAILED DESCRIPTION

In a particular installation, a weaving machine (1) in cooperation with a jacquard device (2) is installed next to a bobbin creel (3), and a beam stand (4) with four rollers (40)-(43) each containing a yarn store is arranged in the space between the weaving machine (1) and the bobbin creel (3).

A yarn tensioning device (6) is installed in the space between the bobbin creel (3) and the weaving machine (1), and consists of a yarn tensioning module (20) which extends in the horizontal direction parallel to a vertical plane containing the front sides (30a) of the plurality of mutually adjacent creel units (30). The yarn tensioning module (20) consists of two panel-like carriers (21), (22) with a flat outer surface, which run symmetrically relative to a horizontal plane towards each other in the direction of the weaving machine (1), wherein they converge and join together at an angle. The yarn tensioning module (20) has a V-shaped profile viewed in a vertical cross-section. Each carrier (21), (22) carries a large number of rows of yarn tensioning elements (8) placed closely adjacent to each other. For reasons of clarity, only three yarn tensioning elements (8) are shown for each carrier (21), (22). For each warp thread which is guided from a respective bobbin in the bobbin creel (3) to the weaving machine (1), a guide tube (10) is provided for guiding the warp thread without tension to a respective yarn tensioning element (8).

The warp threads are moved further from the yarn tensioning elements (8) to a grid (100) with the same width as the yarn tensioning module (20) but with a smaller height. From the grid (100), the warp threads (11), (12) run to the weaving machine (1) where they pass through the heddle eye of a respective heddle (16), (17), shown symbolically by a vertical line with a circular widening which depicts the heddle eye. A respective pull-back spring (18), (19) exerts a downward force on each heddle (16), (17).

According to the prior art, the warp threads are supplied in stretched state from the bobbin creel (3) to a first grid (X). FIG. 1 shows the situation of the prior art with the straight line (S1) which runs from the top row of bobbins in the bobbin creel (3) firstly through the grid (X) of an existing installation and then on to the grid (100), and the straight line (S2) which runs from the bottom row of bobbins in the bobbin creel (3) via the grid (X) of an existing installation and then on to the grid (100). For the sake of clarity, the grid (X) does not form part of the installation according to this disclosure and is merely added to the figure in order, by comparison with the prior art, to be able to present an effect of the disclosure.

The lines (S1), (S2) show the size of the angles (relative to a horizontal plane) at which the warp yarns are brought to the grid (X) and then on to the grid (100) according to the prior art, and consequently the angle which the supplied warp threads then take.

During weaving, the heddles (16), (17) are moved up and down in order to position the warp threads (11), (12) correctly according to the predefined weaving pattern. The pull-back springs (18), (19) in their lowest position provide the necessary downward force for allowing the shed formation to proceed correctly, but must also overcome the upwardly directed force which is a consequence of the yarn tension.

If the heddle is moved to a higher position for shed formation, the downward spring force increases proportionally with the upward movement of the heddle in order finally to reach a value which is much greater than necessary.

On FIG. 2, for a number of successive weft insertion cycles (the state of the main shaft of the weaving machine is shown on the horizontal axis in degrees), graph line G1 shows the development of the downward force which the springs (18), (19) exert on the heddle (16), (17) (on the left vertical axis, in N) of a pile-forming pile warp thread; and graph line G2 shows the development of the alternating upward and downward component of the force (in N) which is exerted on the heddle (16), (17) as a result of the yarn tension in the pile-forming pile warp thread. The latter force is referred to in brief below as the “yarn tensioning force”.

For the sake of clarity, where a force (spring force or yarn tensioning force) is marked as negative in FIGS. 2 and 3, this means that the force is pulling the heddle upward. This is clear for example because the yarn tensioning force is negative in the graph regions where the heddle is in its lowest position. It is evident that the force exerted by the yarn tension on the heddle then has an upwardly directed component which pulls the heddle upward.

Graph line G4 shows the position of the heddle eye (in mm on the vertical axis on the right-hand side).

Graph line G3 shows the development of the sum of the spring force and the yarn tensioning force. Here we see two high peaks (P1), (P2) of this total force. The graph line G3 shows the forces to which the different machine components are subjected. It should be noted that the graphs in FIGS. 2 and 3 show the forces which are the result of movements of a single pile warp thread, whereas on a typical face-to-face weaving machine for example, 32,000 pile warp threads or more may be present.

FIG. 3 shows the development of the spring force and the yarn tensioning force on the heddle of a pile-forming pile warp thread when the yarn tension is controlled or steered so as to achieve lower peak values and a lower mean of the sum of the spring force and yarn tensioning force.

Because of this steering or control, also a spring may be used with a lower spring constant and a lower spring pretension force (0.15 N lower)—this is the downwardly directed spring force when the heddle is in its lowest position. The pretension force may be lower because, thanks to the steering or control of the yarn tension, less upward yarn tensioning force is exerted by the pile warp thread.

In FIG. 3, the same indications (G1), (G2), (G3) and (G4) are used for the graph lines as on FIG. 2, with the same meanings: namely the development of the downward spring force (G1), the development of the yarn tensioning force (G2), the development of the sum of the spring force and the yarn tensioning force (G3), and the position of the heddle (G4). The left vertical axis gives the values of the forces (in N), and the right vertical axis gives the values of the positions of the heddle (in mm). The horizontal axis gives the state of the main shaft of the weaving machine in degrees.

Graph line (G5)—the dotted line—gives the value of the mean of said sum of the spring force and yarn tensioning force.

It is clear from graph line (G3) that for the total force on the heddle, the high peaks have disappeared (compare with FIG. 2, peaks P1 and P2). In addition, the mean value of this total force is lower. In the design without a steering or control system (FIG. 2), the calculated mean of this total force is 2.91 N, while in the design with control system, this total force is 2.72 N (graph line G5 on FIG. 3).

These effects mean a lower load on the machine, wherein again it must not be forgotten that the values from the graphs show the forces which are the result of the movements of a single pile warp thread, whereas on a typical face-to-face weaving machine for example, 32,000 pile warp threads or more may be present.

The advantageous aspects of this disclosure are not restricted to pile warp threads but also apply to warp threads of another type which are positioned by the jacquard device, or to single-face weaving machines.

Claims

1. Shed-forming device comprising a jacquard device with a number of heddles, for positioning at least one associated warp thread, wherein each heddle is connected to a pull-back element, for exerting a downward force on the heddle, wherein the shed-forming device comprises, per heddle, a yarn tensioning element which is provided to change the yarn tension in at least one associated warp thread, and that the shed-forming device comprises a control or steering unit which is provided, in cooperation with the respective yarn tensioning elements, for steering or controlling the yarn tension in at least one associated warp thread, separately for each heddle, such that the total downward force on the heddle, is brought to a specific value or varies according to a specific profile.

2. Shed-forming device according to claim 1, wherein each yarn tensioning element comprises a roller which is driven by a motor and which is in contact with at least one warp thread, and which is intended to rotate in the one or the other direction of rotation in order to move said warp thread in a direction opposite the feed direction of the warp threads, or to move the warp thread or to move with the movement thereof or to facilitate the movement thereof in a direction which is the same as the feed direction of the warp threads, in order to increase or decrease respectively the yarn tension in said warp thread.

3. Shed-forming device according to claim 1, wherein that parameters of the jacquard device or of a weaving machine cooperating with the jacquard device, or data or parameters connected with the weaving pattern, are made available to the control or steering unit in order to be taken into account in determining the target value for the total downward force.

4. Shed-forming device according to claim 1, wherein it comprises a storage unit in which two or more reference yarn tension profiles and/or two or more reference series of at least one reference value for the yarn tension are stored, and that the control or steering unit is provided to select a reference profile or reference series from this collection in order to use these as target value(s) or a succession of target values for steering or control.

5. Shed-forming device according to claim 1, wherein the pull-back elements are springs.