CN109415851B

CN109415851B - Weft feeding arrangement with endless running belt and method for controlling the same

Info

Publication number: CN109415851B
Application number: CN201780039919.3A
Authority: CN
Inventors: 帕·约瑟夫松; B·约翰松; B·哈尔瓦松
Original assignee: Van Der Waals Sweden
Current assignee: Van Der Wee China Textile Machinery Co ltd
Priority date: 2016-07-06
Filing date: 2017-06-20
Publication date: 2021-07-09
Anticipated expiration: 2037-06-20
Also published as: EP3481980B1; WO2018009120A1; EP3481980A1; EP3481980A4; CN109415851A

Abstract

The present application describes a method and a device for feeding weft yarns to a weaving machine (10) using a yarn feeding device (16), the yarn feeding device (16) comprising at least one endless running belt (22) driven by a controlled motor (24). The running belts each comprise at least one yarn delivery element (26), the yarn delivery element (26) being adapted to withdraw a yarn (40) from the yarn store (14) and release the yarn in a set position to form one or more yarn loops as a yarn buffer for the weaving machine. There is also at least one yarn restraining element (30) adapted to retain the yarn in a loop.

Description

Weft feeding arrangement with endless running belt and method for controlling the same

Technical Field

The present disclosure relates to a yarn feeding arrangement. In particular, the present disclosure relates to a weft feeding arrangement suitable for weaving looms operating at high speed and potentially also making it possible to use yarns having a relatively high weight per length unit.

Background

Weft pre-winders are used to eliminate yarn tension variations to ensure high textile quality and productivity of textile machines, such as shuttleless looms or knitting machines.

The general trend in weaving is the increasing speed of textile machines. At the same time, the weaver strives to weave coarser yarns and weaker yarns. Coarser yarns and higher speeds result in increased tension in the weft yarns. With conventional weft yarn pre-winders, the increased speed and coarser yarn results in larger pull-out yarn balls in the weft yarn pre-winder, which need to be reduced using high braking forces, but unfortunately results in undesirably high output yarn tensions.

For example, when weaving carpets, coarse jute is often used as the weft yarn. The ball braking element in a conventional weft pre-winder is typically a brush ring or a flexible frustoconical braking element. At today's machine speeds, brush rings typically wear in as little as one day, and flexible frustoconical braking elements can wear in months.

Another example is the weaving of technical fabrics with coarse synthetic yarns; wherein one faces the same problems as carpet weaving machines.

Furthermore, when using shuttleless looms in the form of rapier looms, the insertion device in the rapier loom consists of one or two rigid or flexible rapier which mechanically transport the weft thread from one end of the machine shed to the other. The most common system is two rapier, which meet in the middle of the shed, the weft front end being transferred from the first feeding rapier to the second receiving rapier. The first rapier first accelerates from zero to full speed and then decelerates again to zero at the front end transfer point. This type of movement is similar to that of the second rapier. This results in a weft tension that goes from low to high and back to low. In fact, when the rapier decelerates, the mass in the weft yarn makes it move faster than the rapier itself, resulting in yarn overflow. This effect increases with the yarn count, i.e. the weight of the yarn per length unit, and is a real problem for rovings and fast machines. To solve this problem, passive or controlled yarn brakes are being used.

The mechanical devices of the rapier mechanism must be made as light as possible if the machine speed is to be increased. On the other hand, higher speeds result in higher yarn tensions, which requires a stiffer and stronger rapier system.

Weaker yarns are cheaper and therefore attractive in use. Weaker yarns have less tensile strength and the risk of yarn breakage increases rapidly if too high a braking force is applied to control the ball, or to provide sufficient tension for the rapier function. GB1355687 describes a yarn feeder in which a member directly connected to the loom moves back and forth to remove yarn in line with the motion of the rapier from the yarn package during the forward and return motion of the rapier. Thereby, the speed of the yarn being drawn from the yarn package can be reduced to half. This arrangement will form a yarn buffer. In general, the yarn buffer will provide an arrangement capable of holding a yarn that can be withdrawn with a lower force during at least a part of the weaving cycle than would be required if the yarn were withdrawn directly from the yarn storage. GB2131055 also describes a weft yarn metering device.

There is a constant desire to improve the feeding of weft yarns to textile machines. Therefore, there is a need for an improved weft feeding apparatus.

Disclosure of Invention

It is an object of the present invention to provide an improved weft feeder arrangement.

This and/or other objects are achieved by a weft feeding device as described in the description.

As already recognized, it would be advantageous to reduce the speed at which the yarn is drawn from a yarn storage (e.g. a spool or pre-winder) to the loom. This will reduce the force required to react when increasing the speed of the weaving machine, especially when using coarser yarns (e.g. jute, some synthetic yarns or carbon fibres) with a relatively high weight per length unit. Another need is to provide weft feeding that reduces yarn tension.

Furthermore, although the device described in GB1355687 allows the speed at which the yarn is drawn from the yarn feeder to be reduced, it has limitations and drawbacks. Firstly, the apparatus of GB1355687 has the limitation that the deceleration can only be 50% and not more. Furthermore, the fact that during the forward and backward movement of the rapier, the member is directly connected to the weaving machine and moves back and forth to remove the yarn from the yarn package in line with the movement of the rapier makes it impossible to withdraw the yarn from the yarn storage when the rapier is not moving (e.g. during beating). In other words, in GB1355687, the yarn can only be drawn from the yarn store when the rapier moves. Therefore, most of the time available during the weaving cycle is not used for drawing the yarn from the yarn storage. This is because the rapier is generally not moving during a significant portion of the weaving cycle. Next, the device moves in unison with the rapier. This results in the speed at which the yarn is withdrawn from the weft feeder being proportional to the speed of the rapier and therefore varying significantly during the cycle of the rapier loom. The fact that the device moves in unison with the rapier limits the functionality due to the drive mechanically coupled to the rapier in the weaving machine, since it is not possible to improve the functionality by utilizing other suitable times in the weaving machine cycle to more balance the speed and/or compensate for other movements in the weaving machine. Third, the device requires a traveler that is guided along a track that applies additional friction and moving parts, which may be disadvantageous in certain applications.

According to one embodiment, a yarn feeding device for feeding a weft yarn to a weaving machine is provided. The weaving machine can in particular be a weaving machine comprising at least one rapier. The weaving machine may also be an air-jet weaving machine or a water-jet weaving machine. The yarn feeding device comprises at least one running endless belt driven by a controlled motor. The running belts each comprise at least one yarn transfer element. The yarn delivery element is adapted to withdraw yarn from the yarn storage and release the yarn at set positions to form one or more yarn loops for use as a yarn buffer for a weaving machine. Thus, an efficient yarn feeding device is provided which is capable of supplying yarn to a weaving machine with low tension while significantly reducing the maximum yarn take-off speed at which yarn is taken off from a yarn storage. Furthermore, at least one yarn restraining element is provided to retain the yarn as a loop. Thereby, the yarn may be held in place, which may facilitate the formation of yarn loops. The at least one yarn restraining element may be a clamp, a brush or a surface having an element located above the surface and spaced from the surface by a distance corresponding to at least the thickness of the yarn.

According to one embodiment, the yarn feeding device is adapted to form two loops. Thereby, the formed yarn buffer can be adapted to be fed to a double-faced rapier loom in an efficient manner. According to one embodiment, the yarn feeding device is adapted to be connected to a double rapier weaving machine and wherein one of said two loops is associated with the movement of a first rapier and the other of said two loops is associated with the movement of a second rapier.

According to one embodiment, the yarn feeding device is adapted to be connected to a multiple channel weaving machine. A device is thus obtained which enables a very low maximum withdrawal speed from the yarn store.

According to one embodiment, the yarn transport element is set to move at a maximum speed less than half the maximum speed of the rapier.

According to one embodiment, the yarn transferring element is a pin.

According to one embodiment, the yarn storage comprises a pre-winder and the yarn feeding device is adapted to draw the yarn from the pre-winder.

According to one embodiment, the yarn storage is a spool and the yarn feeding device is adapted to draw yarn directly from the spool.

According to one embodiment, a yarn feeding arrangement comprises a yarn storage, a yarn feeding device according to any of the above embodiments and a weaving machine with at least one rapier.

According to one embodiment, the yarn feeding arrangement further comprises a slide feed device interconnected between the yarn storage and the yarn feed device. Thereby an improved yarn feed can be provided.

According to one embodiment, a yarn feeding arrangement comprises a yarn storage, a yarn feeding device according to any of the above embodiments, and a weaving machine provided with at least one rapier. The loom is a multiple channel loom and the loom is adapted to switch channels after each pick of the loom. Thereby increasing the time to form the loop. According to one embodiment, the yarn feeding device is configured to form one or more loops for a channel at least partly during the time when another channel in the weaving machine is active. In particular, the yarn feeding device may be configured to form a loop during a first time interval, and wherein the loop is consumed by the weaving machine during a second time interval, and wherein the duration of the first time interval is at least twice the duration of the second time interval.

The invention also extends to a method for controlling a weft feeding arrangement according to the above as well as to a controller and a computer program product for controlling a weft feeding arrangement according to the above.

The speed of the air or water jet loom is also limited due to the high take-off tension from the conventional pre-winder. The prewinder of the spraying machine is built on the same basic principle as the prewinder of the rapier loom, with the addition of a system for measuring and giving a predetermined picking length. The picking length is usually achieved by adjusting the diameter of the drum and incorporating yarn release and stop elements (commonly referred to as stop magnets) in the rapier prewinder concept. By setting the diameter of the drum and a fixed number of windings to exit the drum, a predetermined picking length is achieved.

Therefore, the buffer mechanism formed by the weft feeding apparatus described herein can also be used for an air-jet loom or a water-jet loom. The weft feeding device is then placed downstream of the jet pre-winder, which is then adapted to deliver the correct pick length to the jet loom.

Drawings

The invention will now be described in more detail, by way of non-limiting example, with reference to the accompanying drawings, in which:

figure 1 is a view showing a weft feeding arrangement with two channels,

figures 2 a-2 d depict different aspects of the weft feeding device,

figure 3 depicts another layout,

figure 4 depicts a weft feeding arrangement controlled by a controller,

figure 5 is a flow chart showing the different steps performed in forming a weft buffer,

FIG. 6 is a view of the controller,

figure 7 depicts a slide-feed device,

FIG. 8 depicts a weft feeding arrangement with a slide feeding device, an

Figure 9 shows various aspects of the different timings and speeds of the yarn feeding arrangement.

Detailed Description

Hereinafter, a weft feeding arrangement for a rapier loom will be described. In the drawings, like reference characters designate like or corresponding elements throughout the several views. It should be understood that these drawings are for illustration purposes only and are not intended to limit the scope of the present disclosure in any way. Moreover, features from different described embodiments may be combined to meet specific implementation requirements.

When the weaving machine is operating in a weft yarn hybrid mode, yarn is fed from a different yarn store and the weaving machine switches the yarn stores so that there is at least one time interval between each pick to pick the yarn (i.e. the machine is operating in a mode to switch channels between each pick), between the withdrawal of a weft yarn from another weft yarn store plus two beat-up events, plus up to about 11/2 weaving machine cycles available to load a yarn buffer. Weft yarn mixing can run on 2 or more channels, typically from 2 channels up to 4 channels. Other weave patterns that result in two consecutive picks never being inserted from the same channel are also possible. In all these cases, the result is a time gap when another channel is inserted, so at least about 11/2 loom cycles of time are available to load the thread buffer.

In fig. 1, an exemplary setup is depicted. The arrangement in fig. 1 depicts a multiple channel rapier loom 10. The loom 10 is a double-faced rapier loom having two rapier tapes 11 and 12. The loom in fig. 1 uses two channels, but a multi-channel rapier loom 10 having any number of channels is contemplated. Each channel is fed by weft thread in a weft thread store. In fig. 1, each weft storage comprises a pre-winder 14. The pre-winder 14 can in turn draw the yarn from the spool 13. The interconnection between the respective weft thread storage and the weaving machine 10 is a weft thread feeding device 16. The weft feeding device 16 will be described in more detail below.

In the case of a double-faced rapier loom, the weft feeding device 16 can be adapted to form a weft buffer divided into two different loops. In fig. 1, it is depicted that the yarn feeding device forms a weft buffer with two loops. In a double rapier loom, one loop of weft yarn is used for each half insertion. Each weft buffer may comprise one or more weft yarn loops. In a configuration where two weft yarn loops are formed, the motor may drive two belts, where each belt is adapted to form one weft yarn loop. In one embodiment, the belt speed and preferably also the motor speed is continuous. The continuous belt speed can be controlled to a low speed to reduce the take-off speed from the yarn store, but high enough to form a weft yarn loop before the loom uses it. The tape has attached to it a yarn conveying element, such as a pin, which forms the weft yarn into loops. When the appropriate length of the stitch is reached, the pin can enter an inclined ramp, such as a plate or a wire, or the like, and the pin continues without yarn, eventually reaching the position where the formation of a new weft yarn stitch begins, for later use, where two weft yarn cycles follow. When the yarn is pushed out of the pin, it is simultaneously pushed into a clamp formed by an inclined ramp, for example a leaf spring. The gripper holds the yarn in a dedicated position until the rapier pulls the yarn out of the gripper at the beginning of insertion, or the second loop after the weft tip transfer.

Different arrangements for forming a yarn buffer made of one or more yarn loops are conceivable. According to one embodiment, a dedicated motor is provided for each running belt. The speed of the motor is controlled to meet the requirement that the weft yarn loop be formed in time before the rapier of the loom pulls the yarn from the buffer. At the same time, it is advantageous if the weft thread is drawn out of the thread store at a low maximum withdrawal speed. It is therefore advantageous to control the motor to work synchronously with the weaving machine, so that the motor will drive the running belt at a substantially constant speed and at a sufficiently high speed to enable the stitches of the thread buffer to be ready just before the time when the stitches of the yarn are formed by the rapier picks of the weaving machine.

The speed of the motor driving the running belt can be adjusted. The reason for adjusting the speed of the motor driving the moving belt may be that the speed of the weaving machine is changing or that some other parameter affecting the time required for forming the loops of yarn is changing.

Since the motor drive for running the belt can be electronically controlled, it can be synchronized with the weaving machine by an electronic arrangement. For example, by electronic setting of the engagement point with respect to the weaving machine circulation angle, the time at which the yarn transport element engages with the weft yarn and starts pulling out the weft yarn from the yarn storage can be optimized. Since the arrangement is electronic, it can be adjusted during operation of the weaving machine and the weaving process is not stopped.

By providing a programmable motor drive, different parameters can be set electronically to suit the actual pattern/design woven on the loom and the actual loom settings. When the weaving machine is stationary but also during operation, this can usually be done when the pattern is changed, if for example the machine speed is changed during operation or other parameters are changed during operation. The motor driving the belt and its control is independent of the loom, i.e. not coupled to the loom, so that it is free to move itself from the loom and to set the speed pattern freely. The yarn feeding device can thus be controlled independently of any motor in the weaving machine, but can still be controlled by receiving signals from the weaving machine, which can be used to control the motor of the yarn feeding device, to take account of different events of the weaving process in the weaving machine.

The length of the loops can be adjusted to suit the width of the cloth, i.e. the length of the weft yarn pulled into the weaving shed by the rapier. The optimum loop length may vary between different settings depending on the nature of the weft yarn used in a particular situation, as well as several loom-related parameters. According to one embodiment, the length of the second loop may be shorter than the length of the yarn drawn in by the rapier. The last part of the insertion is thus drawn out of the weft storage (e.g. the pre-winder), with a high yarn tension, which causes the yarn to be stretched before it reaches and comes to rest. This behavior is advantageous for preventing confusion and other weft insertion problems. In another exemplary embodiment, one or more of the formed weft loops can be made slightly longer than the length of the yarn pulled in by the rapier to ensure as low a weft tension as possible throughout the insertion process.

The length of the buffer thread loop can be controlled by a mechanical arrangement for setting the position at which the thread transport element picks up the thread and starts forming the loop and the position at which the thread transport element releases the thread, i.e. the position at which no more thread is drawn out of the thread store. The release position is set by a release mechanism, such as an inclined surface of the running belt end. The inclined surface will force the yarn to be released from the yarn conveying element, e.g. a pin. The position at which the yarn is picked and/or released can be set manually or controlled by an actuator controlling the position. Whereby the shape and length of the yarn loops can be adjusted. The yarn release mechanism may also be made electronically by means of an actuator adapted to push the weft yarn from the yarn transferring element. According to some exemplary embodiments, when an actuator or motor is used, the loop length may be changed during operation of the loom without the need to stop the loom.

Since the yarn conveying element needs to be returned to the yarn picking position before starting the formation of a new stitch, the length of the running belt will control, at least to some extent, the speed at which a stitch is formed.

As mentioned above, the running belt can be driven synchronously with the weaving machine. Synchronization can be obtained by providing control parameters related to the settings of the weaving machine before or during operation of the weaving machine. Synchronization may be achieved using a controller having a control input signal and providing a control output signal for driving the belt motor. For example, the setting parameters used as control parameters may include one or more of a pick length, a loom speed, a current loom angle, a weave pattern. It is also advantageous to use a signal which indicates when the rapier of the weaving machine starts to stop moving respectively in the control of the motor for driving the running tape.

Furthermore, a controlled yarn brake can be placed between the first stitch, i.e. the first stitch used during insertion in a loom cycle, and the loom. The controlled yarn brake can be activated before the yarn front delivery in order to brake the yarn in order to achieve the yarn tension required for a safe yarn front delivery.

Exemplary configurations illustrating some of the above teachings are shown in fig. 2 a-2 d. In fig. 2a, one channel of a multi-channel weaving machine comprising a yarn feeding arrangement is shown. This arrangement corresponds to the arrangement shown in fig. 1. In fig. 2a, a controlled yarn brake 20 is provided after the yarn feeding device 16. In the case of two yarn loops being formed, a second controlled yarn brake 18 can be placed between the two yarn loop buffers. The second controlled yarn brake 18 can be activated when the first loop is filled with yarn 40 and before the second loop is filled with yarn 40. The yarn feeding device 16 can thus be controlled so that the second loop takes the yarn 40 from the pre-winder 14 instead of the first loop already filled. It also ensures that when the first rapier inserts the yarn, the yarn is taken out from the first coil buffer instead of the second coil buffer. The yarn brake 18 can be deactivated at the front end transport, so that the yarn during the second rapier movement can also be taken out of the buffer at low tension.

In fig. 2b, the yarn feeding device 16 is seen from the side. The yarn feeding device comprises a running belt 22 driven by a motor 24.

In fig. 2c, a detail of fig. 2b is depicted, showing an exemplary embodiment of a release mechanism. In fig. 2c, the yarn 40 has been picked up by the yarn conveying element 26 (e.g. a pin). An inclined surface 28 is provided at the end of the running belt 22. When the yarn conveying element 26 reaches the inclined surface 28, the yarn conveyed by the yarn picking member is forced to be released from the yarn conveying element 26. The yarn is held in place by a yarn restraining element 30. The yarn limiting element 30 is here a clamp 30.

In fig. 2d, detail a of fig. 2a is shown. Detail a is the release portion of the running belt 22 of the yarn feeding device 16. In fig. 2d, the yarn conveying element 26, here formed by two pins 26, releases the yarn 40 in a set yarn release position. The yarn is held in place by a yarn restraining element 30. The yarn limiting element 30 is here a clamp 30.

Different yarn restriction elements can be envisaged. For example, the yarn in the loop buffer may stay between two plates having a distance of at least one yarn thickness. The yarn is then free and no additional force is required to pull the yarn out of the clamp. The two plates prevent the yarn from twisting or tangling.

By providing different settings of the yarn feeding device, the yarn path can be adjusted to the specific situation. In fig. 3, an alternative arrangement is depicted. In fig. 3, the running tape is configured to run in a direction substantially parallel to the direction in which a weft yarn is inserted into the weaving machine, in contrast to the configuration in fig. 2, in which the running tape runs in a direction substantially perpendicular to the direction in which a weft yarn is inserted into the weaving machine.

In fig. 4, an arrangement comprising a controller 32 is shown. The controller 32 may be connected to the yarn feeding device 16 and adapted to control the yarn feeding device 16. As mentioned above, synchronization may be obtained using a controller having control input signals and providing control output signals for driving the motor of the yarn feeding device 16. Other drive settings of the yarn feeding device 16, such as the stitch length, can also be performed by the controller 32.

In fig. 5 a flow chart is shown illustrating some steps that may be performed when controlling a motor for driving a yarn feeding arrangement as described herein. The yarn feed arrangement will form a yarn loop buffer. First, in step 501, control parameters for driving the running belt are determined. The control parameter may be any parameter described herein, and the parameter may be updated even in a driving mode of running the belt. The parameters that may be determined may include one or more of the pick length, loom speed, current loom angle, weave pattern, belt length, position of the yarn transport element on the belt relative to the loom position, release mechanism position and timing. It is also advantageous to use the signal when the rapier of the weaving machine starts to stop moving respectively. The values of these parameters can then be used. Next, in step 503, the driving speed of the motor and the synchronization with the loom are set based on the parameter values. The motor may be operated at a substantially constant speed. Then, in optional step 505, the length of the loop formed by the yarn feeding device is set by the controller 32. Then, in step 507, the motor 24 is controlled to a set speed and synchronization with the loom is performed. The set speed and/or synchronization may be varied during driving of the motor 24 if one or more control parameters are changed.

In fig. 6, a controller 32 for controlling the yarn feeding device is depicted. The controller 32 may comprise an input/output 81 for receiving input signals indicative of the angular weaving cycle position of the weaving loom and for controlling other parameters of the yarn feeding device as described above. The input/output 81 outputs a motor control signal to the motor 24 to control the speed of the motor 24. The input/output 81 is also capable of outputting control signals to adjust other settings of the yarn feeding device, such as the length of the running belt and other settings described herein. The controller 32 also includes a microprocessor, which may also be referred to as a processing unit 82. The processing unit 82 is connected to the memory 83 and may execute computer program instructions stored in the memory 83. The memory 83 is also capable of storing data that can be accessed by the processing unit 82. The data in the memory may include pre-stored data relating to the loom 10. The computer program instructions may be adapted to cause a controller to control a yarn feeding apparatus comprising a motor according to the teachings herein. The controller may be located at any suitable location. For example, the controller may be integrated into the motor 24. The controller may use any suitable means for inputting and outputting data, and may use both wireless and wired communication devices.

In another exemplary embodiment, a slide feed apparatus is added. The slide feed device is a driven roller which rotates at a (continuous) peripheral speed which is higher than the required yarn speed. Such a device is described in US 5660213. When the yarn feeding device pulls the yarn when building the loop buffer, the yarn will be pulled against the roller and the friction between the yarn and the rotating roller will contribute to pulling the yarn further, thereby reducing the yarn tension. Once the speed imparted to the yarn by the roller exceeds the speed consumed by the yarn feeding device, the force of the yarn on the roller is reduced and therefore the tension is reduced until equilibrium is reached and the roller does not give any further force to the yarn. Fig. 7 depicts an exemplary slide feed apparatus 38 in two different views.

In fig. 8, an arrangement with a slide feed device 38 interconnected between the yarn storage 14 and the yarn feed device 16 is depicted.

In fig. 9, the weft yarn speed is depicted at different positions in the arrangement of a weaving machine 10 comprising a yarn storage 14, a yarn feeding device 16 and two rapier grippers. In fig. 9, two alternating channels, a first channel and a second channel, are used. The figure depicts two loom cycles, which is twice 360 degrees. The movement of the two rapiers for the first channel, described in more detail here, is illustrated by the curve 51. When the first (give) rapier picks a weft yarn for the first channel, the start of insertion is at position 57 and the end of insertion is at position 58. Curve 50 refers to the second of the two alternating channels. The time available for forming the yarn buffer (two loops in this example) is the time between 58 (when the insertion ends) and 57 (when the next insertion for the first channel begins). The first buffer, i.e. the one closest to the loom (meaning the first-giving rapier), starts to fill after the end of insertion 58 and can generally continue until approximately half of the available time is used. This is illustrated by curve 52. The second buffer (for the second receiving rapier) can start filling after the first buffer is ready and continue until the end of the first rapier cycle, i.e. before the weft front end is delivered. The filling of the second buffer is shown by curve 53 and the yarn front transfer takes place at transfer position 59.

Depending on the type of loom, different timing sequences will be used. For example, in air-jet or water-jet looms, the weft is inserted into the shed of the loom through nozzles that blow into the yarn using compressed air or pressurized water. Then, when the insertion is ready and the stop magnet stops delivering the yarn to the loom, the formation of the yarn buffer can be started. The first action is to activate the yarn brake 20, then the stop magnet of the jet prewinder opens and the formation of the weft buffer can be started by the thread forming element 26 drawing the yarn from the prewinder. The formation of the weft buffer continues while the other channel is inserting yarn and must be ready before insertion into the channel begins. At the start of the insertion, the release brake 20 is released and the weft yarn is blown into the jet loom. In one embodiment, the full pick length can be stored in a weft buffer formed by the yarn feeding device. In another embodiment, the last part of the pick is taken from the pre-winder.

The speed of the weft thread taken out of the thread storage is represented by curve 54. It can be seen that the speed is constant most of the time during filling of both buffers and drops to zero during insertion of the weft yarn by the second acceptor gripper when no buffer is filled. The weft speed from the yarn store is much lower than the maximum speed 60 of the rapier in curve 51. Typically, it may be only 25% to 35% of the highest speed.

The force of the controlled yarn brake 20 is shown by curve 55. In addition, the force from the controlled yarn brake 18 is shown by curve 56. The controlled yarn brake 20 is activated to provide a high yarn braking force during the first buffer filling, here represented by curve 52, to ensure that the weft yarn 40 is taken out of the yarn storage and not from the weaving machine. The controlled yarn brake 20 can also be used to control the weft yarn tension so that the weft insertion works as desired. The controlled yarn brake 18 is activated before the filling of the second buffer starts, here identified by curve 53. This is done in order to ensure that the weft thread 40 is taken out of the thread storage instead of the first buffer.

The yarn feeding apparatus as described herein has a number of benefits. For example:

the yarn tension in the loom is very low.

The yarn speed from the pre-winder is very low and therefore there is no bulking problem.

Reduction of the speed of the yarn from the spool

The motor forming the damper can run continuously, so the motor can be small and consume little energy.

It is possible to operate using only one buffer. However, when the speed is slowed down during the front end transfer, the yarn moving from the buffer will also slow down, but the inertial mass will cause an irregular behavior of the yarn, which may cause problems, and if not properly handled by the controlled yarn brake, this phenomenon may cause a sudden drop and rise in yarn tension, which may cause loom stops or other weaving problems.

The length of the running tape forming the loop, in combination with its distance to pull the yarn and the starting point of the pull (in synchronism with the loom) plus the speed (in synchronism with the loom), determines the loop length and when the loop is formed. By setting these parameters, the result is that the yarn speed profile from the yarn storage and the controlled yarn speed loop buffer can be optimized.

Claims

1. A yarn feeding device (16) for feeding a weft yarn to a weaving machine (10), comprising at least one running endless belt (22) driven by a controlled motor (24) configured to drive said running endless belt at a substantially constant speed, each of said running endless belts comprising at least one yarn transfer element (26) adapted to draw a yarn (40) from a yarn store (13, 14) and to release said yarn in a set position to form one or more yarn loops as a yarn buffer for said weaving machine, said yarn feeding device further comprising at least one yarn limiting element (30) adapted to retain a yarn (40) in a loop.

2. Yarn feeding device according to claim 1, characterised in that the at least one yarn limiting element is a clamp (30).

3. Yarn feeding device according to claim 1, characterised in that the at least one yarn limiting element is a brush.

4. Yarn feeding device according to claim 1, characterised in that the at least one yarn limiting element comprises a surface and an element located above the surface and spaced from the surface by a distance corresponding at least to the thickness of the yarn.

5. Yarn feeding device according to any one of claims 1 to 4, characterised in that the weaving machine comprises at least one rapier (11, 12).

6. Yarn feeding device according to claim 5, characterised in that the yarn feeding device is adapted to form two loops.

7. Yarn feeding device according to claim 6, characterised in that it is adapted to be connected to a double rapier weaving machine and wherein one of said two loops is associated with the movement of a first rapier (11) and the other of said two loops is associated with the movement of a second rapier (12).

8. Yarn feeding device according to claim 5, characterised in that the yarn feeding device is adapted to be connected to a multi-channel weaving machine.

9. The yarn feeding apparatus of claim 5, wherein the yarn transport member moves at a maximum speed less than half the maximum speed of the rapier.

10. Yarn feeding device according to claim 5, characterised in that the yarn conveying element is a pin (26).

11. Yarn feeding device according to claim 5, characterised in that the yarn storage comprises a pre-winder (14) and in that the yarn feeding device is adapted to draw yarn from the pre-winder.

12. Yarn feeding device according to claim 5, characterised in that the yarn storage is a spool (13) and that the yarn feeding device is adapted to draw yarn directly from the spool.

13. Yarn feeding arrangement comprising a yarn storage (13, 14), a yarn feeding device (16) according to any one of claims 1-12 and a weaving machine (10).

14. Yarn feeding arrangement according to claim 13, further comprising a slide feeding device (38) interconnected between the yarn storage (13, 14) and the yarn feeding device (16).

15. Yarn feeding arrangement, comprising a yarn storage (13, 14), a yarn feeding device (16) according to any one of claims 1 to 12 and a weaving machine (10), characterized in that the weaving machine is a multi-channel weaving machine and that the weaving machine is adapted to switch channels after each pick of the weaving machine.

16. Yarn feeding arrangement according to claim 15, characterized in that the yarn feeding device is configured to at least partly form a stitch or stitches for one channel during the activity of another channel in the weaving machine.

17. Yarn feeding arrangement according to claim 15 or 16, wherein the yarn feeding apparatus is configured to form a loop during a first time interval, and wherein the loop is consumed by the weaving machine during a second time interval, and wherein the duration of the first time interval is at least twice the duration of the second time interval.

18. A method of controlling a drive for a yarn feeding device (16) for feeding a weft yarn to a weaving machine (10), the yarn feeding device comprising at least one running endless belt (22) driven by a controlled motor (24), the running endless belts each comprising at least one yarn conveying element (26), one or more of the yarn conveying elements being adapted to draw a yarn (40) from a yarn store (14) and release the yarn in a set position to form a yarn loop or yarn loops to serve as a yarn buffer of the weaving machine, characterized in that at least one yarn restraining element (30) is provided to hold the yarn (40) in a loop, the method comprising:

-determining a control parameter value (501) for driving the running endless belt;

-setting the driving speed of the motor to work synchronously with the weaving machine, such that the motor will drive the running endless belt (503) at a substantially constant speed, and

-controlling the motor (24) to a set speed (507).

19. The method of claim 18, wherein the set speed is reset when the control parameter is changed.

20. A computer-readable storage medium storing instructions which, when executed on a computer, cause the computer to control a driver of a yarn feeding apparatus in a method according to claim 18 or 19.