TECHNICAL FIELD

The present disclosure relates to a yarn brake. In particular the present disclosure relates to a yarn brake used in conjunction with feeding yarn to a textile machine.

BACKGROUND

Yarn feeders are used to eliminate yarn tension variations to ensure high quality and also to supply the correct amount of yarn to a textile machine, e.g. a shuttleless weaving machine or knitting machine. Hereby textile quality and productivity of the textile machine can be increased.

One feature of a yarn feeder is to provide a suitable yarn tension for the yarn fed to a textile machine. The yarn tension applied can be provided in different manners. For example, a frustum-conical braking element can be used that cooperates with the spool body rim to create an essentially constant braking force, see EP 0 534 263.

There are different ways of setting and controlling the yarn tension from a yarn feeder: - A yarn braking element cooperating in a flexible manner with a spool body of a yarn feeder can be used to provide a braking force acting on a yarn drawn from the spool body when forced against the spool body.

- A yarn brake can also be placed after the yarn feeder, at some location along the path from the yarn storage to the textile machine. The yarn brake can be of nip type or yarn deviation type. Typical nip type brakes are leaf brakes and disc brakes. A yarn brake of nip type is described in EP 2354070.

Further the yarn tension can be set in different manners: - Mechanically by help of a nob or similar that sets the yarn brake to a position where a desired brake force is obtained.

- A motor or actuator that sets the yarn brake to a position where a desired brake force is obtained. For example, US 6539982 describes a closed loop system where a motor is controlled to sense the brake element position and to control the brake element to a desired position when the brake position deviates from the desired brake element position.

There are also systems where the yarn tension is modulated or changed during the weft insertion to obtain different yarn tension at different parts, or zones, in the weft insertion cycle. Examples of such systems with varying yarn tension are for example described in EP 1743967 and US 5343899. Such systems are advanced, but also difficult to use. For example, it can be difficult to find the right settings for each zone. Moreover, such systems are typically also complex and expensive. Even more advanced are systems that comprises a combination of a controlled tensioner (yarn brake), in zones, and a yarn tension sensor. Such systems are of course also complex and expensive and can be demanding to use. Example of such a system is described in EP 1646573. There is a constant desire to provide improved feeding of yarn. Hence, there is a need for devices that can improve or facilitate feeding of yarn to a textile machine.

SUMMARY

It is an object of the present invention to provide an improved feeding of yarn and in particular to provide an improved yarn brake that can facilitate feeding of yarn in a correct manner and with low complexity.

This object and/or others are obtained by the yarn brake and related devices as set out in the appended claims. As has been realized, there is a need in weaving mills to repeat settings when an article, e.g. a knitted or woven manufacture is set up again, and also to transfer a setting from one textile machine to another. With the manual systems of today this is not possible, as there is no way to read out the brake force or the mechanical setting / pre-tension / position of the yarn brake used to control the yarn tension.

Today, the only way to perform a setting is to pull yarn by hand and try to feel if the setting is right or to use a spring gauge and pull by hand and measure the static yarn tension, then adjust and try again until the right level is found. Both methods take time and require an element of trial and error.

Further, a yarn tension sensor is good but also expensive and adds to the complexity. In accordance with the invention a much less complicated and much less expensive system is provided that can provide many of the benefits from more advanced and expensive systems, but at low cost and complexity. An object of the invention is therefore to enable repeatable and transferable settings of a set brake force with low complexity.

This can be achieved by a yarn brake configured to have a defined reference position. The reference position can typically be defined as a zero position when the yarn brake just starts to act on the yarn. For example, that is when the two brake surfaces in a nip tension just touch each other, or the brake element just touch the spool body rim without applying any braking force on the yarn. This zero-position can be determined by a manual input or automatically by a sensor, as describe in co-pending patent application No.

PCT/SE2017/050045. The yarn brake comprises a position sensor to detect the position of a movable member of the yarn brake such as a braking element or braking element holder in relation to the defined zero position. The detected position is output to give a value indicating the tension of the yarn. The output position as given by the position sensor can be used in different manners. In other words, the output position is output from the device to be used outside the adjustable yarn brake. The position sensor output can for example be presented to the operator on a display on the yarn brake or the yarn feeder, or the position sensor output can be transferred to a textile machine and presented on a textile machine display or used in control systems in the textile machine. The position sensor output can also be transferred to a portable unit, for example a smart phone, and presented there. Further, the position sensor output can be stored in a memory for later use. In particular, the position sensor output together with other information regarding the current setting of the textile machine and / or the yarn feeder can be stored. For example, the yarn type/material, yarn number, machine speed and width and brake characteristics can be stored and used for future use. Brake characteristics can for example be how much braking force the yarn brake applies to a specified yarn at each specified pre-tension setting. Such position sensor output can be stored locally at the yarn brake or the textile machine and can also be sent to a central location such as a central controller or server connected to many yarn brakes.

If the same yarn brake and the same yarn are used in another set-up, it is then possible to transfer settings from one yarn feeder to another yarn feeder or from one textile machine to another textile machine. It is also possible to store settings and repeat them when the same article is used at a later point in time.

Knowing the textile machine width and speed, the brake characteristics and the yarn it is possible to make setting tables where a setting for a new article, not run before, can be found. If there is a display of the setting of the brake it is possible to directly find a good setting for a new article. A look up table or a computer program / application can be used together with specified the weaving machine width and speed, yarn and brake type and a recommended yarn brake setting to find a recommended pre-tension. The yarn brake is then adjusted until the recommended pre-tension is reached. The current yarn tension can be shown on the display. Even if it is not the perfect setting it is a good start that can be fine- tuned and then stored as a default setting next time the article is manufactured.

In accordance with one embodiment an adjustable yarn brake is provided. The adjustable yarn brake is configured to have a set reference position. The adjustable yarn brake comprises a position sensor configured to output a signal indicative of the position of a movable member of the adjustable yarn brake in relation to the reference position, wherein the brake force of the adjustable yarn brake is determined by the position of the movable member. The adjustable yarn brake is configured to output the signal from the position sensor to a display or to store the output signal from the position sensor in a memory. The display can be a local display provided on the adjustable yarn brake or located somewhere else such as on a textile machine or on a controller interface. The display can also be a display on a handheld unit such as a smart phone or similar. Likewise, the memory can be a local memory in the adjustable yarn brake or a memory located somewhere else such as on a textile machine or in a controller or some server configured to receive and store position sensor output data from the adjustable yarn brake and also from other such adjustable yarn brakes. Hereby, the position of the yarn brake can be determined and can be easily re-used at a later point in time or at another set-up to re-create the same yarn tension. In accordance with one embodiment the yarn brake comprises a display connected to the position sensor. Hereby, the brake force can be displayed directly to an operator in a cost- efficient manner without a need for complex computer systems or other complex

components. In the alternative or as a supplement, the output from the position sensor is configured to be operatively connected to a display at another location such as to a display on a textile machine or on a hand-held unit such as a smart phone.

The yarn brake can be of different types. In accordance with some embodiments the adjustable yarn brake is configured to have the reference position set manually. The yarn brake can then comprise an input device for receiving a manual input signal representing the reference position when a brake force of the adjustable yarn brake just starts to act as determined by an operator. In some embodiments, the adjustable yarn brake is configured to have the reference position set automatically. The adjustable yarn brake is then configured to have the reference position of the adjustable yarn brake set in response to the output signal of a movement/position sensor adapted to automatically detect when said reference position is reached.

The position sensor can be an absolute sensor. Hereby the sensor can be disconnected and still provide a correct output when connected again. For example, the sensor can

advantageously comprise a rotatable permanent magnet. The sensor comprising the rotatable permanent magnet can be configured to rotate less than one full revolution for the whole setting range of the sensor.

The invention also extends to methods for controlling a yarn feeder in accordance with the above.

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 yarn feeder,

- Fig. 2, is a view of a detail of a yarn feeder,

- Fig. 3 is a view illustrating a system for controlling the yarn tension for a number of yarn feeders,

- Fig. 4 is a flow chart illustrating steps performed when controlling yarn tension,

- Fig. 5 is a view of an alternative braking means,

- Fig. 6 is illustrating a yarn feeder with an electronic yarn tension actuator,

- Fig. 7 is illustrating an alternative execution of a yarn feeder with an electronic yarn tension actuator, - Fig. 8 is a view of a first yarn feeder comprising a position sensor,

- Fig. 9 is a view of a second yarn feeder comprising a position sensor,

- Figs. 10a - 10c depicts a yarn feeder arrangement with a separate adjustable yarn brake,

- Figs 11a and 1 lb illustrate implementation of a position sensor, and

- Fig. 12 is a flow chart illustrating steps performed when determining the position of an adjustable yarn brake.

Figs 13a- 13c illustrate an adjustable yarn brake in accordance with another embodiment. DETAILED DESCRIPTION

In the following yarn brakes and yarn feeding arrangements for a textile 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 or to achieve a desired yarn feeding arrangement. For example, a separate yarn brake can be provided without a yarn feeder up-streams the yarn brake.

The invention aims at enable repeatable and transferable settings of a yarn brake force for a yarn brake. The yarn brake is configured to have a defined reference position used as a zero position. The zero position can be set manually and also automatically as is for example described in co-pending patent application No. PCT/SE2017/050045. The description below with reference to Figs. 1 - 7 describes examples of such automatic setting of the zero- position described in PCT/SE2017/050045.

In Fig 1, a yarn feeder 10 is depicted. In the yarn feeder 10 of Fig. 1 an extension arm 12, usually called top cover in the field of yarn feeders, is arranged extending from a housing 14 for example as described in US 5,947,403. The yarn feeder 10 comprises an adjustable brake comprising a yarn braking element 16, which is shown in Fig. 1 in its braking position. The yarn braking element 16 can for example be a frustum conical element 16 but can be also be of another type or shape. The braking element can be made of a plastic material such as PEEK or PET. The braking element 16 can be arranged in a flexible manner. The flexible manner in which the braking element cooperates with the spool body can be achieved in different ways. The flexibility can be achieved by having the braking element 16 suspended by springs and/or the braking element can be made, at least in part, of a flexible/elastic material that is deformed when the braking element is forced against the spool body or the flexibility can be provided in some other manner. The flexible action of the braking element cooperating with the spool body can hence be of any conventional type and is not discussed in more detail herein. The yarn braking element 16 cooperates in a customary manner with the withdrawal rim of the spool body 18. The yarn braking element 16 can thus be moved back and forth along an axis A to control the braking force applied to a yarn withdrawn from the yarn feeder 10. In one embodiment, the yarn braking element 16 can be attached to the extension arm 12 via, an along the axis A slidable brake element holder 27 provided at the extension arm 12.

In Fig. 1, the yarn braking element 16 is in the braking position in which it is axially pressed with a predetermined, settable axial force against the spool body 18. This position can be changed by running a motor of a brake motor assembly 20 to vary the contact pressure of the yarn braking element 16, by making the brake element holder 27 move along the axis A in a manner known per se.

In order to enable an electrically controlled setting of the brake force without the use of a downstream yarn tension sensor, a reference position in which the position of the braking element corresponds to a known braking force needs to be established. In accordance with one embodiment a position where the braking force just starts to act is established. In such a position, there will be a braking force, but the braking force will have a very small magnitude that will not impact the yarn tension in any significant way. Such a position can be called a 0-position (zero-position) of the braking element or initial braking position. In other words, this is the position where the braking element just comes into contact with the spool body. This position can be saved in a memory to establish a reference position that can be used when electrically controlling the braking force. The memory can be located in the yarn feeder or it can be located at another position such as in a control system arranged separately or integrated in the textile machine.

A number of methods can be used to determine such an initial braking position. In accordance with one first embodiment, the initial braking position can be determined manually. For example, a thin instrument (not shown in the drawings), e.g. an ordinary gauge in the form of a thin sheet of metal or plastic, typically about 0.1 mm thick or less can be placed in the gap between the braking element 16 and the spool body 18. The braking element 16 is then driven towards the spool body 18 by for example actuating a pushbutton 5 and when the braking element squeezes the instrument between the braking element and the spool body so that it no longer can be removed without use of an additional force, a manual command is given into the memory by actuating a 0-setting pushbutton 6 to set the initial braking position. The initial braking position can also be set by simply visually looking at the braking element 16 when it precisely reaches the spool body 18 and set the initial braking position into the memory accordingly. There can also be a pushbutton 7 to move the brake holder 27 in direction from the spool body. In an alternative execution, the pushbuttons 5, 6 and 7 can be located at the Human Machine Interface (HMI) on a central control unit, for example in the machine terminal of a textile machine.

In a second embodiment, a sensor is provided to detect a movement of the braking element 16 when the motor 20 is run to move the braking element towards the spool body. When the braking element 16 does not move anymore but the motor 20 still runs, this indicates that the braking element has hit the spool body and the initial braking position can be set as the position when the sensor first detects no movement with the motor still running. The sensor can be any type of sensor that detects a movement. The sensor can for example be of optical type, sensing the distance between the movable braking element holder and the cone. The sensor can also be of the magnet - Hall sensor type, or an inductive sensor. A sensor insensitive for dust is typically advantageous.

In Fig. 2, showing a detail of the yarn feeder 10 of Fig. 1, a possible setup with such a movement sensor is depicted. In Fig. 2 a Hall sensor 25 is used together with a permanent magnet 24. The Hall 25 sensor is located at the moving brake element holder 19 and the magnet 24 is attached to the braking element 16. As alternative the Hall sensor can be located at a fixed location on the yarn feeder 10 and the permanent magnet 24 is attached to the moveable braking element 16.

In a third embodiment, the motor torque of the motor 20 used to move the braking element 16 is monitored. When the motor torque increases this signals that the braking element 16 has precisely reached the spool body 18 and started to stretch some elastic element of the braking element such as the springs 26 shown in Fig. 2. The position where the motor torque starts to increase is set in the memory as the initial braking position.

In a fourth embodiment, a sensor that detects deformation of an elastic part of the braking element 16 can be used when determining the initial braking position. In such an embodiment, a sensor is provided to sense when some part of the braking element starts to be deformed and use that moment as having precisely reached the initial braking position. For example, if the braking element 16 is provided with springs 26 that are stretched when the braking element hits the spool body a sensor sensing that the spring 26 is stretched can be used to set the initial braking position. In Fig. 5 a further embodiment of the Hall sensor - permanent magnet type of solution is depicted. In the embodiment according to Fig. 5, another type of braking element is used. The braking element 30 is of a type known for example in EP 0963335 and is made of an elastomer, for example polyurethane. The Hall sensor 32 is located at a fixed location of the yarn feeder 10, and the permanent magnet 31 is attached to the brake element 30. In Fig. 6 a further embodiment is shown. In accordance with the embodiment shown in Fig. 6 an actuator 35, for example an electromagnet or electrical motor, is used to apply the braking force to a brake holder 38 which in turn transfers the force via the springs 26 to the braking element 16. The actuator 35 can be position-controlled and has a

movement/position sensor, for example a Hall sensor 36 co-acting with a permanent magnet 37. When the actuator starts to move to apply force, both the Hall sensor 36 and the Hall sensor 25 detect movement. When the braking element 16 comes in contact with the spool body 18 the Hall sensor 25 detects that the permanent magnet 24 is not moving anymore, while the Hall sensor 36 of the actuator 35 still detects movement, and this is then used as the indication that the 0-position of the braking element is reached.

Fig. 7 shows a further embodiment. In the embodiment of Fig 7 an actuator 35, for example an electromagnet or electrical motor, is used to apply the braking force to the brake holder 38 which in turn transfers the force via springs to the braking element 16. The actuator can be position-controlled and has a movement/position sensor, for example a Hall sensor 36 and a permanent magnet 37. When the actuator starts to move to apply force the Hall sensor 36 detects movement. When the braking element 16 comes in contact with the spool body 18, the current used to drive the actuator 35 will increase. A sensor, for example in the drive circuit, is used to monitor the drive current and is correlating the actual current with the actual position of the actuator, detected by the Hall sensor 36 and the permanent magnet 37. When the drive current starts to increase this is then used as the indication that the 0- position of the braking element is reached. When a reference position such as the initial braking position (0-position of the braking element) has been determined, the desired braking force is then set based on this reference position. In accordance with one embodiment the desired braking force is set as a percentage of the maximum force applicable. The desired braking force can in accordance with another embodiment be set in relation to the range of movement when the motor or actuator drives the braking element towards (and from) the spool body.

For example, in case the motor is a stepper motor, the number of steps relative to the reference position can be used to control the braking force. In accordance with another example, when the motor is a DC motor, an encoder or another sensor can be used to detect the rotation of the motor respectively the axial movement of the brake element holder 27, thus determining the braking force and thereby the yarn tension. Either the sensor is of absolute type, or a relative type of sensor. In case of relative type of sensor, a homing position can be needed and provided.

An alternative to an encoder is to have a rotating magnet and two Hall sensors with a relative position between each other, e.g. 90 degrees inter-distance can be used. This will form two sinusoidal signals 90 degrees separated, thus providing a good angle sensor. One can typically extract up to 10-15 positions per revolution with good resolution for this system. Another type of sensor that can be used in a similar manner to generate the corresponding functionality is a so called rotary magnetic sensor chip.

Knowing the case- specific parameters it is possible to set the desired yarn tension based on the found and stored initial position value (0-position of the braking element) without the use of a downstream yarn tension sensor. This can for example be done using a look-up table that has desirable values (set-values) for various combinations of yarn

tension/yarn/weaving machine type, width and speed/braking element/ type of yarn feeder (or any desired sub-set of such parameters). By locating the look-up table in a central control system, it is possible to remotely control a number of yarn feeders from one single location.

In Fig. 3, a control system 1 for controlling the yarn tension of a number of yarn feeders 10 is depicted. The control system comprises a central controller 2 connected to each of the yarn feeders 10 of the system. The controller 2 can comprise a memory 3 storing a look-up table as set out above and a control unit 4 adapted to control the braking force of the yarn feeders 10 to which it is connected either by wire or wirelessly. Hereby it is obtained that the yarn tension for a number of yarn feeders can be set remotely from a single central location. For example, if one particular setting of the yarn tension yields a good

performance of the textile machine, this setting can be saved in the look-up table and reused for other yarn feeders running the same "textile application". Thus, in some embodiments the system is adapted to apply a self-learning algorithm that saves useful settings for one machine and enables re-use of that setting for the same machine or for a machine having the same configuration. The controller and/or the memory can in one embodiment be located in the weaving machine or knitting machine, and the weaving machine terminal (HMI) can be used to monitor and enter settings.

The set-up in accordance with Fig. 3 can be used to enable transferable and repeatable settings. In accordance with an exemplary mode of operation the operator sets the yarn tension by manually turning a set knob or some other device used to set the braking force. The position is sensed by the position sensor and the position sensor value is output to reflect the set yarn tension. The position is shown on a build in display and is also possible to read out to the weaving machine or a remote unit, e.g. smart phone. A well working setting can hereby be transferred to other weaving machines and also be stored, manually or automatically, in a set-sheet and used as start value next time the same or similar article is woven. If several channels or machines have the same yarn, the setting can be repeated and transferred to the other feeders. In order to further facilitate fast and accurate setting of the adjustable yarn brake, a centralized control centre system can be used collect and compare information from different adjustable yarn brakes. This will enable a central system to identify problems and to promote well working settings. For example, the control centre such as the controller 2 above can be configured to identify Weaving machine stop - type, location, time until running again, intervention to mend the problem, weaving pattern, when the stop occurred, channel, bobbin etc. When doing this, the sensor position data from the adjustable yarn brake can be used to identify recent setting changes of the braking force or other brake force settings that result in reduced productivity for a particular textile machine.

For example, data from the position sensor of the adjustable yarn brake can be analysed to determine when, how frequent and how much is the yarn tension knob adjusted. Also, the data can be analysed to determine how the setting of the brake force is linked to the machine stops (frequency and type of stop) and to which bobbins or full/empty bobbins.

To make such a diagnosis more efficient, the adjustable yarn brake can be configured to send the signal from the position sensor to another location at a pre-determined time interval or when some pre-determined event has occurred. Examples of such events can be when the setting is changed or how much the setting is changed. The time for detecting and reporting such events can also be logged by the adjustable yarn brake and sent to the control center. In Fig. 4 a flow chart illustrating some procedural steps that can be performed when controlling the yarn tension in accordance with the teachings hereinabove is shown. First, in a step 401, the braking element is driven towards the spool body in a state where there is no braking force. Next, in a step 403, a position is determined when the braking element just reaches the spool body and thus makes contact with the spool body. The position

determined in step 403 is saved as a reference position, in a step 405. Then, the braking force, and thereby the yarn tension is controlled by measuring how an electrically driven motor or actuator drives the braking element in relation to said reference position in a step 407.

To enable a repeatable setting of the yarn tension used in a particular set-up in a cost- efficient manner, a position sensor can be used and configured to output an output signal indicative of the position of a movable member of an adjustable yarn brake. The position can then be displayed and/ or stored and re-used later to achieve a similar or identical set-up at a later point in time or at a different textile machine. In accordance with some

embodiments a display is provided on the yarn brake or in some embodiments on a yarn feeder in which the yarn brake is located. By providing a display close to the position sensor the sensor can in some embodiments be in wireline connection with the display and there is no need for a wireless interface connected to the position sensor. Hereby, the design can be made even less complex and also compact. In addition, the cost can be kept low. However, it is also envisaged that the display can be located at another location such as at the textile machine or at a portable device such as a smart phone or similar. A number of embodiments including a position sensor will now be described in conjunction with Figs. 8 - 13.

In Fig. 8, a view of a yarn feeder 10 similar to Fig. 1 and comprising a position sensor 50 to detect the position of a movable member of an adjustable yarn brake such as a braking element or braking element holder in relation to the defined zero position is shown. The position sensor 50 is typically located inside the yarn feeder 10 and is described in more detail below. The detected position is output to give the tension of the yarn. The output signal from the position sensor can be displayed on a display 52 provided on the yarn feeder 10. The setting buttons 5 and 7 are described above in conjunction with Fig. 1. Also, a reset button 6 is provided as described above in conjunction with Fig. 1.

In Fig. 9, a view of another yarn feeder 10 with a manual setting of the yarn brake and comprising a position sensor 50 to detect the position of a movable member of an adjustable yarn brake such as a braking element or braking element holder in relation to the defined zero position is shown. Again, the position sensor 50 is typically located inside the yarn feeder 10 and is described in more detail below. As a difference to the yarn feeder in Fig. 8, the yarn feeder 10 in Fig 9 comprises a manual knob 58 to set yarn tension / position of braking element holder. The output signal from the position sensor can be displayed on a display 52 provided on the yarn feeder 10. The zero or reference position can be reset using the button 56.

In Figs. 10a - 10c yet another yarn feeder arrangement is shown. In Fig. 10a, the yarn feeder 10 is similar to the type shown in Fig 9 and is supplemented with a separate adjustable yarn brake 60 placed down-streams the yarn feeder 10. While Fig. 10a shows a manually adjustable yarn feeder, it is also envisaged that the yarn feeder could be an electrically adjustable yarn feeder as is shown in Fig. 1. In Fig. 10b, a manually adjustable separate yarn brake 60 is shown. The yarn brake 60 of Fig. 10b comprises a position sensor 50 to detect the position of a movable member 68 of the adjustable yarn brake 60, such as a braking element or braking element holder or as here a brake leaf in relation to the defined zero position. The position sensor 50 is typically located inside the yarn brake 60 and is described in more detail below. The yarn brake 60 in Fig 10b comprises a manual knob 66 to set yarn tension / position of the yarn brake element 68. The output signal from the position sensor 50 can be displayed on a display 62 provided on the yarn brake 60. The zero or reference position can be reset using the button 64.

In Fig. 10c, an electrically adjustable separate yarn brake 60 is shown. The yarn brake 60 of Fig. 10c comprises a position sensor 50 to detect the position of a movable member 78 of the yarn brake 60, such as a braking element or braking element holder or as here a brake leaf in relation to the defined zero position. The position sensor 50 is typically located inside the yarn brake 60 and is described in more detail below. The yarn brake 60 in Fig 10c comprises adjustment buttons 75, 77 to set yarn tension / position of the yarn brake. The output signal from the position sensor 50 can be displayed on a display 72 provided on the yarn brake 60. The zero or reference position can be reset using the button 76.

The sensor used to detect the actual position of some moving member of the yarn brake, such as the brake element or brake holder, can be any type of known position sensor. However, the position sensor is preferably of an absolute type. In other words, the sensor should preferably detect the correct position in relation to the zero or reference position even if the position is changed during power off. Relative sensors, for example a simple encoder, do not fulfill this requirement. Further, the setting range of a yarn brake is often relatively long, typical 15 mm. The setting is often made with a knob connected to a screw. If a rotational encoder is placed on the screw it will not work as an absolute sensor, as it cannot alone determine with turn of the encoder wheel it currently is, if settings are done at power off. A sensor that detects the absolute position is therefore typically required.

To provide an absolute sensor it is possible to, for example, connect or build in a rack on for example a brake support or a brake element. The rack drives a cog wheel which has a rotating magnet in its end. An absolute encoder, or a contact less magnet angle sensor of for example magneto-resistive type is then used to create a position signal. The gearing can advantageously be made so the absolute encoder or magnet rotates less than one turn for the whole setting range, enabling an absolute position read out, even if the position is changed during power off.

In Figs 11a and 1 lb, an exemplary implementation of the position sensor 50 is illustrated implemented in a yarn feeder 10. The sensor 50 can of course equally well be provided in a separate yarn brake in a similar manner. Fig. 1 la is a cross sectional view from the side of a yarn feeder 10 comprising a yarn braking element 86. The yarn braking element 86 is here a cone as shown in Fig. 1. Fig. 1 lb is a perspective view of the view in Fig. 11a. In Figs 11a and 1 lb, a rack 85 is connected to a brake support 81. The rack 85 drives a cog wheel 84 which has a rotating magnet 83 in its end. An absolute encoder, or a contactless magnet angle sensor of for example magneto-resistive type, is then used to create a position signal. Here a magnetic angular sensor 82 is used. When the brake support is adjusted to adjust the braking force, the arrangement in Figs. 11a and 1 lb will cause the magnet to rotate and the sensor will output a new position corresponding to the brake force now set. The gearing can be set so that the magnet 83 rotates less than one turn for the whole setting range of the sensor, enabling an absolute position read out, even if the position is changed during power off. In response to the adjustment of the brake the magnet will rotate and the output from the sensor 50 will result in a new angle position that can be transferred to a new position of the brake holder and then be used in any desired manner, for example being displayed or stored.

In Figs. 13a - 13c yet another exemplary embodiment of an adjustable yarn brake 10 is depicted. The embodiment in accordance with Figs. 13a - 13c is similar to the embodiment depicted in Fig. 9. In the embodiment of Fig. 13a - 13c, the position sensor 50 is located off the main body of the adjustable brake 10 as opposed to the embodiment of Fig. 9. As is seen in Fig. 13b the position sensor can be a magnetic sensor 82. Further, a worm screw 85a used to rotate a cog wheel 84 that holds a magnet 83 giving a rotating magnetic field detected by the magnetic sensor 82 is provided. The worm screw 85a corresponds to the rack 85 used in the embodiment described in Fig. 9 and performs the same function. In Fig. 12, a flow chart illustrating steps performed when determining the position of an adjustable brake is shown. First, in a step 901, a reference position for the adjustable yarn brake is determined. The reference position can typically be when a braking force just starts to act on the yarn as described above. Next, in a step 903, a signal from a position sensor is output. The output signal from the position sensor is indicative of the position of a movable member of the adjustable yarn brake in relation to the reference position. In other words, the output signal from the position sensor will give a value indicating how much the movable member of the adjustable brake has moved from the reference position. Then, in a step 905, the output signal from the position sensor is displayed or stored in a memory. The value of the output signal can then be re-used at another time or at another set-up to re-create the same settings in a step 907. Thus, the use of a position sensor that can give the position of a movable member of an adjustable yarn brake, where the position of the movable member gives the braking force of the adjustable yarn brake, it is possible to remember the settings and to re-use the settings. Hereby, a system with low complexity can be formed which is cost-efficient.