EP3481980B1

EP3481980B1 - Weft yarn feeding arrangement with endless running belt and a method for controlling the arrangement

Info

Publication number: EP3481980B1
Application number: EP17824625.2A
Authority: EP
Inventors: Pär JOSEFSSON; Birger Johansson; Bjrön HALVARSSON
Original assignee: Vandewiele Sweden AB
Current assignee: Vandewiele Sweden AB
Priority date: 2016-07-06
Filing date: 2017-06-20
Publication date: 2021-10-27
Anticipated expiration: 2037-06-20
Also published as: CN109415851B; CN109415851A; WO2018009120A1; EP3481980A4; EP3481980A1

Description

TECHNICAL FIELD

The present disclosure relates to a yarn feeding arrangement. In particular, the present disclosure relates to a weft yarn feeding arrangement suitable for a weaving machine operated at high speed and potentially also with yarns with relative high weight per length unit.

BACKGROUND

Weft yarn pre-winders are used to eliminate yarn tension variations to ensure high textile quality and productivity of a textile machine, e.g. a shuttleless weaving machine or knitting machine.
A general development trend in weaving is that the speed of the weaving machine is constantly being increased. At the same time the weavers strive to weave coarser yarns and also weaker yarns. Coarser yarns and higher speeds lead to increased tension of the weft yarn. Using conventional weft yarn pre-winders, increased speeds as well as coarser yarns result in a bigger take off yarn balloon in the weft yarn pre-winder, which needs to be reduced using a high braking force but thereby unfortunately leading to an undesirably high output yarn tension.
For example, when weaving a carpet, coarse Jute is often used as weft yarn. The balloon braking elements in a conventional weft yarn pre-winder is typically either a brush ring or a flexible truncated-cone formed brake element. With the machine speeds of today a brush ring is often worn out in as little as a day and a flexible truncated-cone brake element can be worn out in a few months.
Another example is weaving technical fabric with coarse synthetic yarns; where one faces the same problem as in a carpet weaving machine.
Further, when using a shuttleless weaving machine in the form of a rapier weaving machine, the insertion means in the rapier weaving machine consists of one or two rigid or flexible rapiers that mechanically transfers the weft yarn from one end of the shed of the machine to the other. The most common system is two rapiers which meet in the middle of the shed where the weft yarn tip is transferred from the first, giving, rapier to the second, receiving, rapier. The first rapier is first accelerating from zero to full speed and then decelerating to zero again at the tip transfer point. This type of motion is analogous for the second rapier. This leads to a weft yarn tension that goes from low to high and then back to low again. In fact, when the rapier decelerates, the mass in the weft yarn causes it to move faster than the rapier itself causing a surplus of yarn. This effect increases with the yarn count, i.e. the yarn weight per length unit, and is a real problem for coarse yarns and fast machines. In order to solve this problem passive or controlled yarn brakes are being used.
If the machine speed is to be increased, the mechanical arrangement for the rapier mechanism must be made as light as possible. On the other hand, higher speeds results in higher yarn tension which requires a more rigid and stronger rapier system.
Weaker yarns are cheaper and are thus attractive to use. Weaker yarns have less tensile strength and if a too high brake force is applied in order to control the balloon, or to give enough tension for the rapier function, the risk for yarn break is increasing rapidly. GB 1355687 describes a yarn feeder where a member directly connected to the weaving machine moves back and forth to remove yarn in unison with the movement of the rapier from a yarn package during both a forward and return movement of the rapier. Hereby, the speed at which the yarn is drawn from the yarn package can be reduced to one half. This arrangement will form a yarn buffer. A yarn buffer will, generally speaking, provide an arrangement that can hold a bit of yarn that can be drawn with a small force during at least a part of the weaving cycle compared to the force required if the yarn would have been drawn directly from the yarn storage. Also, GB 2131055 describes a weft yarn metering device.
Further, DE 10203733 describes a linear measurement and magazine storage arrangement for a thread, which comprises thread feed elements and thread length-measuring elements together with magazines. Reversing elements for thread parts are designed to bring about interaction with thread parts between thread support elements. The magazines are designed with retaining devices which retain thread parts in predetermined positions.
There is a constant desire to improve weft yarn feeding to textile machines. Hence, there is a need for an improved weft yarn feeding device.

SUMMARY

It is an object of the present invention to provide an improved weft yarn feeder arrangement. This object and/or others are obtained by the weft yarn feeding device as set out in the appended claims.
As has been realized, it would be advantageous to reduce the speed at which yarn is drawn from a yarn storage, such as a bobbin or a pre-winder, to a weaving machine. This would reduce the forces required to cope with when increasing the speed of the weaving machine, in particular when a coarser yarn having a relatively high weight per length unit is used such as Jute, some synthetic yarns or carbon fiber. Another desired is to provide weft yarn feeding that reduces the yarn tension.
Also, while the device described in GB 1355687 allows for a reduced speed at which the yarn is drawn from the yarn feeder, it has limitations and drawbacks. First the device of GB 1355687 has a limitation in that the speed reduction can only be 50% and not more. Also, the fact that the member is directly connected to the weaving machine and moves back and forth to remove yarn in unison with the movement of the rapier from a yarn package during both a forward and return movement of the rapier makes it impossible to draw yarn from the yarn storage when the rapier is not moving such as during beat up. In other words, in GB 1355687 it is only possible to draw yarn from a yarn storage when the rapier is moving. As a result, a significant fraction of the time available during a weaving cycle is not used to draw yarn from the yarn storage. This is because during a significant fraction of the weaving cycle the rapier(s) is/are typically not moving. Second, the device moves in unison with the rapier. This results in that the speed at which the yarn is drawn from the weft yarn feeder is directly proportional to the speed of the rapier and hence varies significantly during a cycle of a rapier machine. The fact that the device moves in unison with the rapiers as it is mechanically coupled to the drive of the rapiers in the weaving machine limits the functionality as it is not possible to improve the function by utilizing other suitable moments in the weaving machine cycle to even out the speed even more and/or compensate for other movements in the weaving machine. Third, the device requires a traveler guided along a rail, which imposes additional friction forces and a moving part, which could be a disadvantage in some applications.
In accordance with one embodiment a yarn feeding device for feeding 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 can 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 motor is configured to drive the running belt at essentially constant speed. The running belt comprises at least one yarn transport element each. The yarn transport element(s) are adapted to draw yarn from a yarn storage and release the yarn at a set location to form a loop or loops of yarn acting as a yarn buffer for the weaving machine. Hereby an efficient yarn feeding device is provided that can provide yarn to the weaving machine with low tension and at the same time significantly reduce the maximum yarn take-off speed from the yarn storage. Further, at least one yarn restraining element is provided to hold the yarn in a loop. Hereby the yarn can be kept in place, which can facilitate the yarn loop formation. The at least one yarn restraining element can be a clamp, a brush or a surface having an element located above said surface and distanced from said surface by a distance corresponding to at least the thickness of the yarn.
In accordance with one embodiment the yarn feeding device is adapted to form two loops. Hereby the formed yarn buffer can be adapted to feed a double-sided rapier weaving machine in an efficient manner. In accordance with one embodiment the yarn feeding device is adapted to be connected to a two-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.
In accordance with one embodiment the yarn feeding device is adapted to be connected to a multi-channel weaving machine. Hereby a set-up which can achieve a very low maximum take-off speed from the yarn storage can be obtained.
In accordance with one embodiment the yarn transport element is set to move at a maximum speed less than half the maximum speed of a rapier.
In accordance with one embodiment the yarn transport element is a pin.
In accordance with one embodiment the yarn storage comprises a pre-winder and the yarn feeding device is adapted to draw yarn from the pre-winder.
In accordance with one embodiment the yarn storage is a bobbin and the yarn feeding device is adapted to draw yarn directly from the bobbin.
In accordance with one embodiment a yarn feeding arrangement comprising a yarn storage, a yarn feeding device according to any of the embodiments above, and a weaving machine having at least one rapier.
In accordance with one embodiment the yarn feeding arrangement further comprising a slip feed device interconnected between the yarn storage and the yarn feeding device. Hereby an improved yarn feeding can be provided.
In accordance with one embodiment a yarn feeding arrangement comprising a yarn storage, a yarn feeding device according to any of the embodiments above, and a weaving machine having at least one rapier is provided. The weaving machine is a multi-channel weaving machine and the weaving machine is adapted to switch channel after each pick of the weaving machine. Hereby the time for forming loops can be increased. In accordance with one embodiment the yarn feeding device is configured to form a loop or loops for a channel at least partly during a time when another channel is active in the weaving machine. In particular, the yarn feeding device can 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 first time interval has a duration being at least twice the duration of the second time interval.
The invention also extends to methods for controlling a weft yarn feeding arrangement in accordance with the above and to a controller and computer program product for controlling the weft yarn feeding device in accordance with the above.
An air jet or waterjet machine is also limited in speed due to the high take off tension coming from a conventional pre-winder. The pre-winder for a jet machine is built on the same principle as a pre-winder for a rapier machine, with the addition of a system to measure and give a predetermined pick length. The pick-length is commonly achieved by adjustment of the diameter of the drum and a yarn release and stopping element, normally called a stopper magnet, added to the rapier pre-winder concept. By setting the diameter of the drum and a fixed number of windings to leave the drum, a predetermined pick length is achieved.
The buffer mechanism formed by the weft yarn feeding device as described herein can therefore also be used for an air jet weaving machine or a waterjet weaving machine. The weft yarn feeding device is then placed downstream the jet pre-winder, and the jet pre-winder is then adapted to output the right pick length to the jet weaving machine.

BRIEF DESCRIPTION OF THE DRAWINGS

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

Fig. 1 is a view illustrating a weft yarn feeding arrangement with two channels,
Figs. 2a - 2d depict different aspects of a weft yarn feeding device,
Fig. 3 depicts an alternative layout,
Fig. 4 depicts a weft yarn feeding arrangement controlled by a controller,
Fig. 5 is a flow chart illustrating different steps performed when forming a weft yarn buffer,
Fig. 6 is a view of a controller,
Fig. 7 depicts a slip feed device,
Fig. 8 depicts a weft yarn feeding arrangement with a slip feed device, and
Fig. 9 illustrates different timing and speed aspects of a yarn feeding arrangement.

DETAILED DESCRIPTION

In the following a weft yarn feeding arrangement for a rapier weaving machine will be described. In the figures, the same reference numerals designate identical or corresponding elements throughout the several figures. It will be appreciated that these figures are for illustration only and are not in any way restricting the scope of the invention. Also, it is possible to combine features from different described embodiments to meet specific implementation needs.
When a weaving machine is running in weft mix mode where yarn is fed from different yarn storages and the weaving machine switches yarn storage from which it picks yarn between each pick (i.e. the machine is run in a mode where it switches channel between each pick), there is at least a time gap when weft yarn is drawn from another weft yarn storage plus the time of two beat up events adding up to a time of approximately 1½ weaving machine cycle available for loading a yarn buffer. Weft mix can be run on 2 or more channels, typically from 2 and up to 4 channels. Other weaving patterns which result in that two successive picks are never inserted from the same channel are also possible. In all such scenarios, the result is a time gap when another channel is inserting and hence a time of at least approximately 1½ weaving machine cycle available for loading the yarn buffer.
In Fig. 1 an exemplary set-up is depicted. The set-up in Fig. 1 depicts a multi-channel rapier weaving machine 10. The weaving machine 10 is a double-sided rapier machine having two rapiers 11 and 12. The weaving machine in Fig. 1 is working with two channels, but any number of channels of a multi-channel rapier weaving machine 10 are envisaged. Each channel is fed with weft yarn from a weft yarn storage. In Fig. 1 each weft yarn storage comprises a pre-winder 14. The pre-winders 14 can in turn draw yarn from a bobbin 13. Interconnected between the respective weft yarn storages and the weaving machine 10 are weft yarn feeding devices 16. The weft yarn feeding devices 16 will be described in more detail below.
In case a double-sided rapier machine is used, a weft yarn feeding device 16 can be adapted to form a weft yarn buffer divided into two different loops. In Fig. 1, the yarn feeding devices are depicted forming weft yarn buffers with two loops. One loop of weft yarn is used for each half of the insertion in the double-sided rapier machine. Each weft yarn buffer can comprise one or more weft yarn loops. In a configuration with two weft yarn loops being formed a motor can 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 speed of the belt can be controlled to a speed that is low to reduce take off speed from the yarn storage, but high enough to form the weft yarn loop before it is used by the weaving machine. The belts have a yarn transport element, such as a pin, attached thereto that brings the weft yarn to form a loop. When a proper length of the loop is reached, the pin can go into an inclined ramp, for example a plate or wire, or similar and the pin continues without the yarn, ending up at a position starting to form a new weft yarn loop to be used later, here two weft cycles later. When the yarn is pushed from the pin it is at the same time pushed in to a clamp formed by the inclined ramp and for example a leaf spring. This clamp holds the yarn in place at a dedicated location until the rapier pulls the yarn out of the clamp at start of insertion, or for the second loop, after weft yarn tip transfer.
Different set-ups for forming the yarn buffer made of one or more yarn loops can be envisaged. In accordance with 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(s) is formed in time before the rapier of the weaving machine draws yarn from the buffer. At the same time, it is advantageous that weft yarn is drawn from the yarn storage at a low maximum take-off speed. It can therefore be advantageous to control the motor to work in synchronization with the weaving machine such that the motor will drive the running belt at essentially constant speed and at a speed high enough to enable a loop of the yarn buffer to be ready at the time just before the time when yarn of the formed loop is picked by a rapier of the weaving machine.
The speed of the motor driving a running belt can be adjusted. A reason for adjusting the speed of the motor driving a running belt can be that the speed of the weaving machine varies or that some other parameter is varying that impacts the time required for forming a yarn loop.
As the motor drive used for running the belt can be electronically controlled, it can be synchronized with the weaving machine by electronic settings. For example, the time when a yarn transport element engages with the weft yarn and starts to pull weft yarn from the yarn storage can be optimized by electronical setting of the engagement point in relation to the weaving machine cycle angle. As the setting is electronical it can be adjusted during the running of the weaving machine and without stopping the weaving process.
By providing a programmable motor drive it is possible to electronically set different parameters to adapt to the actual style/pattern woven on the weaving machine and to the actual weaving machine set up. This can typically be done at a style change, when the weaving machine is standing still, but also during running, if for example the machine speed is changed during running or if other parameters are changed during running. The motor that drives the belt(s) and its control(s) is autonomous from the weaving machine, i.e. not coupled to the weaving machine and thereby free to make its own movements and speed patterns freely from the weaving machine. Hereby the yarn feeding device can be controlled independently of any motor in the weaving machine, but still be controlled to take into account different events of the weaving process in the weaving machine by receiving signals from the weaving machine that can be used for control of the motor of the yarn feeding device.
The length of the loops can be adjusted to fit the cloth width, i.e. the length of weft yarn drawn in to the weaving shed by the rapier(s). Depending on the properties of the weft yarn that is used in the specific case, as well as several weaving machine related parameters, the optimal loop length may differ between different setups. In accordance with one embodiment the length of the second loop can be shorter than the length of yarn drawn in by the rapiers. By this the last part of the insertion is drawn from the weft yarn storage, for example a pre-winder, with a higher yarn tension which results in that the yarn is stretched before arrival and standstill. Such a behavior can be advantageous to prevent snarls and other weft insertion problems. In another exemplary embodiment, one or more of the formed weft yarn loop(s) can be made slightly longer than the length of yarn drawn in by the rapiers to ensure lowest possible weft yarn tension during the whole insertion.
The length of the buffer loop can be controlled by a mechanical setting used to set the position at which the yarn transport element picks the yarn and starts to form the loop and the position at which the yarn transport element releases the yarn, i.e. where no more yarn is drawn from the yarn storage. The release position is set by the release mechanism such as an inclined surface at the end of the running belt. The inclined surface will force the yarn to be released from the yarn transport element such as a pin. The positions at which the yarn is picked and/or released can be set either manually or controlled by an actuator that controls the position(s). Hereby it is possible to adjust the shape and length of a yarn loop. The yarn release mechanism can also be made electronically by help of an actuator that is adapted to push the weft yarn from the yarn transport element. In accordance with some exemplary embodiments when an actuator or motor is used, a change of the loop length can be made during running of the weaving machine, without stopping the weaving machine.
The length of the running belt will at least to some extent control the speed at which loops are formed, since a yarn transport element needs to return to the yarn pick position before a new loop can start to be formed.
As set out above, the running belt can be driven in synchronization with the weaving machine. Synchronization can be obtained by providing control parameters relating to the settings of the weaving machine before or during running of the weaving machine. The synchronization can be obtained using a controller provided with control input signals and providing control output signals used for driving the belt motor(s). For example, setting parameters used as control parameters can comprise one or more of pick length, speed of the weaving machine, current weaving machine angle, weaving style/pattern. It can also be advantageous to use a signal indicative of when the rapier(s) of the weaving machine starts respectively stops moving in the control of a motor used for driving a running belt.
Further, a controlled yarn brake can be placed between the first loop, i.e. the first loop used during insertion in a weaving machine cycle, and the weaving machine. The controlled yarn brake can be activated before yarn tip transfer in order to brake the yarn so the yarn tension that is needed for a safe yarn tip transfer is reached.
In Figs. 2a - 2d an exemplary configuration illustrating some of the above teachings is shown. In Fig 2a one channel of a multi-channel weaving machine including a yarn feeding arrangement is shown. The set-up corresponds to the set-up shown in Fig. 1. In Fig. 2a, a controlled yarn brake 20 is provided after the yarn feeding device 16. In case two yarn loops are formed, a second controlled yarn brake 18 can be placed in between the two yarn loop buffers. The second controlled yarn brake 18 can be activated when the first loop is filled up with yarn 40 and before the second loop is filled up with yarn 40. Hereby the yarn feeding device 16 can be controlled such that the second loop takes yarn 40 from the pre-winder 14 and not from the first, already filled up loop. It also ensures that when the first rapier inserts yarn, the yarn is taken from the first loop buffer and not from the second loop buffer. The yarn brake 18 can be deactivated at the tip transfer so the yarn during the second rapier movement can be taken with low tension also from this buffer.
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 illustrating an exemplary embodiment of a release mechanism is depicted. In Fig. 2c yarn 40 has been picked by a yarn transport element 26, such as a pin. An inclined surface 28 is provided at the end of the running belt 22. When the yarn transport element 26 reaches the inclined surface 28, the yarn transported by the yarn picking member is forced to be released from yarn transport element 26. The yarn is held in position by a yarn restraining element 30. The yarn restraining element 30 is here a clamp 30.
In Fig. 2d a detail A from Fig. 2a is shown. The detail A is the release section of the running belt 22 of the yarn feeding device 16. In Fig. 2d, the yarn transport element 26, here formed by two pins 26 has released the yarn 40 at a set yarn release position. The yarn is held in position by a yarn restraining element 30. The yarn restraining element 30 is here a clamp 30.
Different yarn restraining elements can be envisaged. For example, yarn in the loop buffer can rest between two plates that have a distance of at least one yarn thickness. The yarn is then free and no extra force is needed to pull the yarn out from a clamp. The two plates prevent the yarn from twisting or snarling.
The yarn path can be adapted from case to case by providing a different set-up of the yarn feeding devices. In Fig. 3 an alternative set-up is depicted. In Fig. 3 the running belts are configured to run in a direction essentially parallel to the direction in which weft yarn is inserted into the weaving machine, as opposed to the configuration in Fig. 2, where the running belts run in a direction essentially perpendicular to the direction in which weft yarn is inserted into the weaving machine.
In Fig. 4 a set-up including a controller 32 is shown. The controller 32 can be connected to the yarn feeding device 16 and adapted to control the yarn feeding device 16. As set out above, synchronization can be obtained using a controller provided with control input signals and providing control output signals used for driving the motor(s) of the yarn feeding devices 16. Other drive settings of the yarn feeding device 16 such as loop length can also be made by the controller 32.
In Fig. 5 a flow chart is shown, illustrating some steps that can be performed when controlling a motor used to drive a yarn feeding arrangement as described herein. The yarn feeding arrangement will form a yarn loop buffer. First, in a step 501, control parameters used for driving the running belt are determined. The control parameters can be any of the parameters described herein and the parameters can be updated, even in the drive mode of the running belt. The parameters that can be determined can comprise one or more of pick length, speed of the weaving machine, current weaving machine angle, weaving style / pattern, length of the belt, position of the yarn transport element on the belt in relation to weaving machine position, release mechanism position and timing. It can also be advantageous to use signal(s) when the rapier(s) of the weaving machine starts respectively stops moving. Values for these parameters can then be used. Next, in a step 503, a drive speed of the motor and the synchronization with the weaving machine is set based on the parameter values. The motor can be run at an essentially constant speed. Then, in an optional step 505, the length of the loop formed by the yarn feeding device is set by the controller 32. Then, in a step 507, the motor 24 is controlled to the set speed and synchronization with the weaving machine is performed. The set speed and or synchronization can vary during the drive of the motor 24 if one or more of the control parameter changes.
In Fig. 6 a controller 32 for controlling a yarn feeding device is depicted. The controller 32 can comprise an input/output 81 for receiving input signals indicative of the angular weaving cycle position of the weaving machine and other parameters used for controlling the yarn feeding device as set out above. The input/output 81 outputs a motor control signal to the motor 24 for controlling the speed of the motor 24. The input/output 81 can further output a control signal 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 further comprises a micro-processor that also can be referred to as a processing unit 82. The processing unit 82 is connected to and can execute computer program instructions stored in a memory 83. The memory 83 can also store data that can be accessed by the processing unit 82. The data in the memory can comprise pre-stored data relating to the weaving machine 10. The computer program instructions can be adapted to cause the controller to control the yarn feeding device comprising a motor in accordance with the teachings herein. The controller can be located at any suitable location. For example, the controller can be integrated in the motor 24. The controller can input output data using any suitable means, both wireless and wireline communication devices can be used.
In another exemplary embodiment, a slip feed device is added. The slip feed device is a driven roller that rotates with a (continuous) peripheral speed that is higher than the necessary 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 pull the yarn further thus decreasing the yarn tension. As soon as the roller gives more speed to the yarn than what is consumed by the yarn feeding device the force from the yarn against the roller will decrease and hence the pulling force will also decrease until a balance is reached and the roller will not give any further force to the yarn. Fig. 7 depicts an exemplary slip feed device 38 in two different views.
In Fig. 8 a set up with slip feed device 38 interconnected between the yarn storage 14 and the yarn feeding device 16 is depicted.
In Fig. 9 the weft yarn speed at different positions in an arrangement comprising a yarn storage 14, yarn feeding device 16 and a weaving machine 10 having two rapiers is depicted. In Fig. 9 two alternating channels, a first and a second channel, are used. The diagram depicts two weaving machine cycles, which is two times 360 degrees. The movement of the two rapiers for the first channel that is described in more detail here is illustrated by the curve 51. Start of insertion, when the first (giving) rapier picks the weft yarn for the first channel is at the position 57 and the end of the insertion is at the position 58. Curve 50 refers to the second one of the two alternating channels. The time available for forming the yarn buffer, in this example two loops, is the time between 58, when the insertion ends, and 57, when next insertion for the first channel starts. The first buffer, the one closest to the weaving machine (intended for the first, giving rapier) starts to be filled up just after end of insertion 58, and can typically go on until approximately half of the available time is used. This is illustrated by a curve 52. The second buffer (intended for the second, receiving rapier) can start to be filled just after the first buffer is ready and continue until just before the first rapier cycle is ended, i.e. just before weft yarn tip transfer. The filling of the second buffer is illustrated by a curve 53 and the yarn tip transfer takes place at a transfer position 59.
Depending on the type of weaving machine different timing sequences will be employed. For example, in an air-jet or waterjet machine the weft yarn is inserted by a nozzle which blows the yarn into the shed of the weaving machine using compressed air or pressurized water. The forming of the yarn buffer can then start when the insertion is ready and the stopper magnet has stopped the delivery of yarn to the weaving machine. The first action is to activate the yarn brake 20, then the stopper magnet of the jet pre-winder opens and the forming of the weft yarn buffer can start by the loop forming element 26 drawing yarn from the pre-winder. The forming of the weft yarn buffer continues while another channel is inserting yarn and must be ready before the start of the insertion for the channel in question. At start of insertion, the brake 20 is released and the weft yarn is blown into the jet weaving machine. In one embodiment, the full pick length can be stored in the weft yarn 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 yarn taken from the yarn storage is illustrated by a curve 54. As can be seen the speed is for most of the time constant during the filling of the two buffers, and drops to zero during the weft yarn insertion by the second, receiving, rapier, when no buffer is filled. The weft yarn speed from the yarn storage is much lower than the top speed 60 of the rapiers in curve 51. Typically, it can be only 25% to 35% of the top speed.
The force of the controlled yarn brake 20 is illustrated by a curve 55. Also, the force from the controlled yarn brake 18 is illustrated by a curve 56. The controlled yarn brake 20 is activated to provide a high yarn braking force during the filling up of the first buffer, here illustrated by curve 52, to ensure that the weft yarn 40 is taken from 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 the weft insertion works as desired. The controlled yarn brake 18 is activated before start of filling the second buffer, here illustrated by a curve 53. This is done to ensure that the weft yarn 40 is taken from the yarn storage and not from the first buffer.
There are numerous benefits with a yarn feeding device as described herein. For example:

The yarn tension in to the weaving machine is very low.
The yarn speed from a pre-winder is very low, thus no ballooning problems
The yarn speed from the bobbin is reduced
The motor that forms the buffer can be run continuously, thus the motor can be small and only consume little energy.

It is possible to run with only one buffer. However, at the speed slow down during tip transfer the yarn moving from the buffer will also slow down but the mass of inertial will cause an irregular behavior of the yarn that might cause problems, and that phenomena, if not handled properly by the controlled yarn brakes, will probably cause yarn tension drops and peaks that may result in stops of the weaving machine or other weaving problems.
The length of the running belt(s) that form the loop(s) in combination with the distance it pulls the yarn and the starting point of the pulling (synchronized with the weaving machine) plus the speed (synchronized with the weaving machine) determines the loop length as well as when it is formed. By setting these parameters the result is a yarn speed profile from the yarn storage and a controlled yarn speed loop buffer that can be optimized.

Claims

A yarn feeding device (16) for feeding 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 belt (22) comprising at least one yarn transport element (26), the yarn transport element(s) being adapted to draw yarn (40) from a yarn storage (13, 14) and release the yarn at a set location to form a loop or loops of yarn acting as a yarn buffer for the weaving machine, the yarn feeding device further comprising at least one yarn restraining element (30) adapted to hold the yarn (40) in a loop, characterized in that the motor is configured to drive the running belt at essentially constant speed.
The yarn feeding device according to claim 1, wherein the at least one yarn restraining element is a clamp (30).
The yarn feeding device according to claim 1, wherein the at least one yarn restraining element is a brush.
The yarn feeding device according to claim 1, wherein the at least one yarn restraining element is a surface having an element located above said surface and distanced from said surface by a distance corresponding to at least the thickness of the yarn.
The yarn feeding device according to any of claims 1 - 4, wherein an inclined surface (28) is provided to form a release mechanism.
A yarn feeding arrangement comprising a yarn storage (13, 14), a yarn feeding device (16) according to any of claims 1 - 5, and a weaving machine (10).
The yarn feeding arrangement according to claim 6, further comprising a slip feed device (38) interconnected between the yarn storage (13, 14) and the yarn feeding device (16).
A yarn feeding arrangement comprising a yarn storage (13, 14), a yarn feeding device (16) according to any of claims 1 - 5, and a weaving machine (10), wherein the weaving machine is a multi-channel weaving machine and the weaving machine is adapted to switch channel after each pick of the weaving machine.
The yarn feeding arrangement according to claim 8, wherein the yarn feeding device is configured to form a loop or loops for a channel at least partly during a time when another channel is active in the weaving machine.
The yarn feeding arrangement according to claim 8 or 9, wherein the yarn feeding device 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 first time interval has a duration being at least twice the duration of the second time interval.
The yarn feeding arrangement according to any of claims 6 - 10, wherein the weaving machine comprises at least one rapier (11, 12).
The yarn feeding arrangement according to claim 11, wherein the yarn feeding device is adapted to form two loops.
The yarn feeding arrangement according to claim 12, wherein the weaving machine is a two-rapier weaving machine, the yarn feeding device is connected to the two-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).
The yarn feeding arrangement according to any of claims 6 - 13, wherein the weaving machine is a multi-channel weaving machine and the yarn feeding device is connected to the multi-channel weaving machine.
A method of controlling a drive of a yarn feeding device (16) for feeding 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 belt comprising at least one yarn transport element (26), the yarn transport element(s) being adapted to draw yarn (40) from a yarn storage (14) and release the yarn at a set location to form a loop or loops of yarn acting as a yarn buffer for the weaving machine, wherein at least one yarn restraining element (30) is provided to hold the yarn (40) in a loop, the method comprising:
- determining (501) control parameter values used for driving the running belt are determined.

- setting (503) a drive speed of the motor to work in synchronization with the weaving machine such that the motor will drive the running belt at essentially constant speed, and

- controlling (507) the motor (24) to the set speed.
A computer program product comprising computer program code adapted to, when executed on a computer causes the computer to control a drive of a yarn feeding device in accordance with claim 15.