MACHINE

FIELD OF THE INVENTION This invention relates to an actuator for a shed-forming device for a weaving machine, to a shed-forming device, to a weaving machine comprising the actuator as well as to methods of operating the actuator.

BACKGROUND TO THE INVENTION Weaving machines based on a Jacquard shed-forming mechanism have been used for more than two centuries and allow materials having a complex pattern to be woven. In such weaving machines, warp threads are moved to form a shed through which a weft thread can be inserted. Each warp thread is lifted or lowered according to the pattern which needs to be formed. A Jacquard mechanism comprises an actuation device placed above the loom and a harness connecting this actuation device to each individual warp yarn stretched on the loom. The harness comprises a series of harness cords that are controlled by the actuation device. Each harness cord controls one or more heddles and is guided in a harness board. An eyelet is formed in each heddle for receiving a warp thread. The conventional actuation device uses reciprocating knives that are driven synchronically with the main shaft of the weaving machine. A selection mechanism commands hooks, that are linked to the harness cords, to connect to, or disconnect from, the reciprocating knives in order to raise or lower harness cords according to a desired weaving pattern. A selection mechanism of this type is described in Swiss Patent Application CH 570 486. The actuation device is a complex mechanical device that is not readily accessible, which causes problems with assembly and maintenance.

Several attempts have been made to create an actuation assembly with a simple and modular design. US 515,775 describes an actuation assembly with a modular design based on electromagnets. Each warp thread has an actuator comprising a lever and an electromagnet. One end of the lever is selectively attracted towards the electromagnet while the other end of the lever is attached to a warp thread via an arrangement of cords.

EP 1 069 218 describes an actuation device with a modular design based on rotary electric actuators. Each warp thread is raised or lowered by winding a control cord connected to the thread. The cord is wound by an electric motor and pulley.

EP 0 353 005 describes a loom with electronically controlled linear actuators, such as a stepping motor with a crank arm for back and forth movement.

In these machines each warp thread is individually controlled by an actuating mechanism associated with that thread. As each actuating mechanism is physically large, accommodating the full set of actuating mechanisms for the large number of warp threads on the loom poses a difficult design problem. In EP 1 069 218 the weaving machine has two large panels, mounted in a V-shape above the loom. Actuators are mounted on the panels and a cord extends between each actuator and a heddle. Such machines are physically large, heavy and very expensive. Accommodating a large number of actuators in a confined space can generate significant quantities of heat, and such machines require efficient cooling systems to avoid overheating. A further problem is that dust from the weaving machine can degrade performance of the actuators, causing them to fail.

SUMMARY OF THE INVENTION

Objects of the present invention include provision of an improved actuator for a shed-forming device, e.g. of a weaving machine or loom and/or of an improved shed- forming device and a weaving machine or loom incorporating the actuator as well as of methods of operating the actuator.

A first aspect of the present invention provides an actuator for a shed- forming device for a weaving machine, the actuator being arrangeable for moving at least one warp thread, e.g. by being connectable to the at least one warp thread, the actuator comprising an artificial muscle having an input for receiving an actuation signal, the configuration of the artificial muscle being variable in response to the actuation signal in order to move the at least one warp thread.

The use of an artificial muscle as an actuator has the benefit of a fast response when a change in configuration is required, which allows the weaving machine to weave fastly (and therefore economically) complex weaving patterns. Artificial muscles have reduced power requirements (and heat output) when compared to

conventional actuators based on electric motors. This reduces operating costs of the weaving machine. Further advantages of the actuator according to the present invention include at least one of: compactness, robustness; reduced noise during operation and reduced cost to manufacture. An artificial muscle can be a unitary (i.e. one piece) actuator which does not rely on two or more moving parts to slide against, or within, one another. This has important benefits when used in the dusty environment of a weaving machine by reducing service intervals as well as reduced down time caused by actuators which have failed due to clogging.

Because each thread, or each group of threads, can be operated by a separate artificial muscle, it is possible to add further modules to scale the shed forming device for the weaving machine to any desired size.

The artificial muscle can be integrated within a control cord which is connected to a heddle. This will be called an 'active control cord'. In one embodiment, the artificial muscle incorporated within the active control cord is variable in length to vary the overall length of the active control cord according to the state of an actuation. The actuation can comprise an electrical or pneumatic control signal which is applied to the artificial muscle. As each active control cord now incorporates an artificial muscle in order to operate the heddle, there is no need for a separate actuating mechanism, such as a motor, an electromagnet, a pneumatically-driven piston or a complex mechanical arrangement to operate the cords. This can significantly reduce the size and complexity of the overall shed- forming device.

In an alternative embodiment, a heddle which is mountable within a support frame comprises an artificial muscle. This will be called an 'active heddle'. One or more artificial muscles can be incorporated within each heddle. Applying an actuation to the one or more artificial muscles causes the position of an eyelet on the heddle to move, thus moving a warp thread. This provides an even more compact solution since the incorporation of an artificial muscle within the heddle avoids the need for a separate control cord for the heddle. Such a heddle remains also usable in combination with known weaving preparation equipment. The at least one artificial muscle associated with a control cord or a heddle is preferably capable of varying in length. Advantageously, an artificial muscle is used which can contract upon application of an actuation. Various artificial muscles are

already known which are capable of operating in this way. A field of artificial muscles simulate the effect of natural muscles, by contracting or elongating upon application of an actuation (such as a stimulating signal) and relaxing to a normal state when the actuation is removed or reversed. Such elements can be packaged into a form which allows them to be integrated within a control cord or heddle. Artificial muscles have been proposed which are based on polymer gels, carbon nanotubes or a piezo electrical material, such as piezo electrical fibres. The artificial muscles can alternatively comprise a pneumatic muscle, a pneumatic tube, a hydraulic muscle, a hydraulic tube or another fluidic element.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the invention will be described, by way of example only, with reference to the accompanying drawings in which:

Figure 1 schematically shows a shed-forming device with each heddle operated by a respective active cord according to a first embodiment of the present invention;

Figure 2 schematically shows an active cord which uses an electrically stimulated artificial muscle in accordance with an embodiment of the present invention; Figure 3 schematically shows an active cord which uses a fluid-based artificial muscle with an embodiment of the present invention;

Figure 4 schematically shows a shed-forming device with a group of heddles operated by an active cord with an embodiment of the present invention;

Figure 5 shows a modification to the arrangement of Figure 4; Figure 6 schematically shows a shed-forming device with each heddle operated by a pair of active cords with an embodiment of the present invention;

Figure 7 schematically shows a shed-forming device with resilient heddles with an embodiment of the present invention;

Figure 8 schematically shows a control cord which is entirely formed of an artificial muscle with an embodiment of the present invention;

Figure 9 schematically shows a heddle frame in which each heddle is entirely formed of active material with an embodiment of the present invention;

Figure 10 schematically shows a heddle frame in which each heddle includes a cord of active material with an embodiment of the present invention;

Figure 11 schematically shows a heddle frame in which each heddle includes a pair of cords of active material with an embodiment of the present invention; Figure 12 schematically shows a heddle frame in which each heddle includes artificial muscles which bend in response to an actuation with an embodiment of the present invention.

DESCRIPTION OF PREFERRED EMBODIMENTS The present invention will be described with respect to particular embodiments and with reference to certain drawings but the invention is not limited thereto but only by the claims. The drawings described are only schematic and are non-limiting. In the drawings, the size of some of the elements may be exaggerated and not drawn on scale for illustrative purposes. Where the term "comprising" is used in the present description and claims, it does not exclude other elements or steps. Furthermore, the terms first, second, third and the like in the description and in the claims, are used for distinguishing between similar elements and not necessarily for describing a sequential or chronological order. It is to be understood that the terms so used are interchangeable under appropriate circumstances and that the embodiments of the invention described herein are capable of operation in other sequences than described or illustrated herein.

Figure 1 schematically shows a shed-forming device according to a first embodiment of the invention. An array of heddles 50 is mounted across the weaving machine. Generally, a heddle 50 is an element that can guide at least one warp thread in order to move that warp thread in a perpendicular direction with respect to the lengthwise direction of that warp thread. A first end of each heddle 50 is connected to an active cord 10 and a second end of the heddle is connected to a resilient return member 55, such as a spring. The remote end 58 of spring 55 connects to a support frame of the weaving machine or the floor. Each heddle includes an eyelet 51 for receiving, guiding and moving a warp thread 1. Each heddle 50 is of a conventional form whereby a central eyelet 51 is arranged between two lamina. Typically, a heddle is formed in a known manner from a strip of metal that comprises an eyelet 51. For simplicity, only three of the heddles are shown, although it will be appreciated that the

weaving machine will comprise many hundreds or thousands of such heddles. The top end of each heddle 50 is connected in a known manner with a connection 14 to an active cord 10. The bottom end of each active cord 10 is guided in a harness board 40. The top end of each active cord 10 is connected to a mounting point 13 of a support frame 15 of the machine, e.g. a crossbeam of the weaving machine. Each active cord 10 includes an artificial muscle 11 that is arranged between two harness cords 18 and 19. The harness cord 18 connects the artificial muscle 11 to the support frame 15, while the harness cord 19 connects the artificial muscle 11 to the heddle 50. This combination of harness cords 18, 19 with an artificial muscle 11 will be called an 'active cord.' The artificial muscle 11 can be fixed or connected to any one of the cords 18 or 19 by a mechanical fixation, e.g. a soldered or welded connection or a glued connection. The connection 14 between the cord 19 and the heddle 50 can also be made in a similar way, e.g. a soldered or welded connection or a glued connection. When using thread-like cords, this connection can also be made by knotting, by splicing or suchlike.

In this embodiment, the artificial muscle 11 has a predetermined length in a resting state. On application of a control signal 12 the artificial muscle 11 can be caused to reduce in length (i.e. contract). Upon subsequent application of another control signal, or the ceasing of the application of the control signal, the artificial muscle 11 returns to it's steady (relaxed) state. In Figure 1, active cord 10 is shown in a contracted state while active cords 20, 30 are shown in a steady (relaxed) state. As artificial muscle 11 contracts, heddle 50 is pulled upwards, against the downwardly- directed return force exerted by spring 55. As heddle 50 carrying its eyelet 51 moves upwards, a warp thread also moves upwards. Harness board 40 permits movement of the heddle 50 in a vertical direction (as viewed in Figure 1) as the artificial muscle 11 varies in length. When a control signal is applied to artificial muscle 11 to cause the active cord 10 to relax, artificial muscle 11 increases to its normal length and the downwardly-directed return force exerted by spring 55 causes heddle 50 to move downwards to it's original position, returning the eyelet 50 and warp thread to their original position. Each artificial muscle 11, 21, 31 is independently controllable by a respective control signal 12, 22, 32. This allows each heddle 50, and hence the corresponding warp thread, to be independently moved into an 'up' or 'down' position.

The space created between warp threads which are moved in this manner is known as a shed. In a known manner, a weft thread can be inserted through the shed. The position of each heddle 50 can be varied between each picking operation to create a desired pattern. A controller 60 generates control signals 12, 22, 32 for operating the artificial muscles 11, 21, 31. Controller 60 can also generate control signals 61, 62 for operating other functions of the weaving machine such as picking (inserting a weft thread), beating-up and operating drive motors which will advance the warp threads or woven cloth. Control signals are generated in a co-ordinated manner. All of these functions are well-known and do not need to be described in any further detail. The controller 60 can also receive input signals 63 which provide information about the state of the machine and of the type of textile material that is to be woven. The control functionality described here can be implemented in software, with a general-purpose microprocessor or microcontroller executing instructions retrieved from a storage device. The software may be stored on an electronic memory device, hard disk, optical disk or other machine-readable storage medium. The software may be delivered as a computer program product on a machine-readable carrier or it may be downloaded directly to the controller via a network. Alternatively, the controller can be implemented in hardware or in an application specific integrated circuit (ASIC). In Figure 1 an artificial muscle is incorporated within each control cord for a heddle. Artificial muscles are actuators which have similar properties to natural muscles. A particular characteristic of artificial muscles is force generation taking place in the volume as a result of atomic or molecular interactions. Often, in a similar way to natural muscles, artificial muscles consist of elastic material of variable form. Force generation in known artificial muscles may be based, for example, on electrostatic forces of attraction, on the piezo-electric effect, on ultrasound generation, on a form memory of materials, on ion exchange, on an extension of carbon nanotubes and/or on the incorporation of hydrogen into metal hydrides. The force generation of artificial muscles may also be based on another chemical or physical reaction. Depending on the active principle, artificial muscles may be produced from polymers, in particular polymer gels, from ferroelectric substances, from silicon, from alloys with a form memory or the like. A detailed description of various types of artificial muscles,

and particularly of Electroactive Polymer (EAP) actuators, is given in "Electroactive Polymer (EAP) Actuators as Artificial Muscles: Reality, Potential and Challenges", Joseph Bar-Cohen, Second Edition, ISBN 0-8914-5297-1 and, for example, in US 2004/0118366, US 2002/0026794, EP 0 924 033 A2 and US 6,109,852. It is particularly advantageous to use electroactive polymers as they can have actuation strain >300%, a fast reaction time (which can be in the Thee range), modest actuation requirements (generally 1-7V for ionic EAP and 10-150V/Iϊn for electronic EAP) and a low consumed power of the order of milliwatts. It is preferred that the artificial muscles are made of a material that deforms under electrical signals, such that such artificial muscles can be arranged within a cord 10, 20 and can be controlled by means of an electrical signal. In particular, the mechanical energy generated by the artificial muscle can originate from the electrical energy of the signal. Electrically-controlled artificial muscles of artificial muscle elements have the advantage that they can be readily controlled with the conventional control units of the weaving machine with minimal additional apparatus.

Figure 2 schematically shows an artificial muscle of the EAP type which is integrated with a harness control cord. The EAP artificial muscle varies in length in response to the application of an electric field across, or passage of current through, an element of EAP material. In this embodiment the upper control cord 18 provides mechanical connection between the artificial muscle 11 and the support frame 15 and also carries wires 18 A, 18B which carry the required electric field or current for operating the artificial muscle 11. The artificial muscle comprises first and second electrodes HB, HC which sandwich an element HA of EAP material. The first and second electrodes HB, HC of the artificial muscle form an input for receiving an actuation input signal or driving force, e.g. an electric field or a current. The muscle may be in the form of a roll of the material. The wires 18A, 18B within harness cord 18 can be separate metallic portions of the cord 18 which are insulated from one another or they can be electrically conductive fibres which are integrated with structural fibres of the cord 18. Control signals 12, 22, 32 are supplied to the support frame 15, and each control signal is electrically coupled to a respective cord 18. The control cord 18 and the artificial muscle 11 are also electrically connected, e.g. by means of a mechanical connector that carries electrical signals between the cord 18 and

artificial muscle 11. The left hand part of the drawing in Figure 2 shows the artificial muscle in a relaxed state with a length Ll and the right-hand part of the drawing shows the artificial muscle in a contracted state with a reduced length L2. In this way the length of the artificial muscles is changed by changing the configuration of the artificial muscle upon actuating the artificial muscle.

It is also possible to provide artificial muscles which are based on fluidic, e.g. hydraulic or pneumatic techniques. It is, of course, necessary to convert the electrical signal output by controller 60 into a fluid (e.g. air) supply which forms the actuation input to the artificial muscle, e.g. by actuating a valve arranged in the fluid supply to the artificial muscle. Such an artificial muscle 11, 21 can comprise a tubular element which receives a supply of compressed fluid in order to vary the length of the artificial muscle. The tubular element has an outer tubular shape like a cord. One known type of pneumatic artificial muscle is the artificial muscle as shown in Figure 3. The actuator comprises an inflatable elastic bladder HD which is generally cylindrical in shape, having an interior cavity HE. The bladder is surrounded by a braided shell HF. The left-hand drawing of Figure 3 shows the artificial muscle at rest with length Ll. The upper control cord 18 is in the form of a tube with a supply channel 18C which connects to the cavity HE. To operate the muscle, a supply of pressurised fluid (e.g. air) is applied to the bladder via channel 18C. Since the artificial muscle is weak for deformation in the radial direction this causes the bladder 1 ID to inflate and to shorten to a reduced length L2, pulling cord 19 and heddle 50 upwards. The interior cavity 1 IE has an input HG for receiving the supply of pressurised fluid. In this way the configuration of the artificial muscles can be changed, and thus also its length.

It will be appreciated that the terms upwards and downwards relate to the way that the apparatus is shown in Figure 1 and that the apparatus may, of course, be oriented in any direction. For clarity, the active element 11 is shown placed near the middle along the active cord 10 although it can be positioned according to an alternative (not shown) at one end of the active cord 10. The spacing between heddles 50, and thus the connections 14 of respective cords 10, 20, is mainly dictated by the density of the textile material that is being woven.

Artificial muscle 11, 21, 31 can vary in length by an amount which is sufficient to raise a warp thread in order to allow the insertion of a weft thread. Typically an

eyelet 50 is required to move through a distance of around 60 mm up to 100 mm. In Figure 1 the artificial muscle 11 forms part of an active cord 10 and a variation in the length of artificial muscle 11 is directly translated into a similar respective movement of heddle 50. In Figures 2 and 3 the actuation to the artificial muscle 11 is carried by cables

(in the case of electrical signals) or tubes (in the case of air or other fluid) which are integrated with cord 18. As an alternative, the cables or tubes can be mounted in parallel with cord 18 between the support frame 15 and artificial muscle 11.

Figure 4 shows a variant of Figure 1 in which each active cord 10, 20 controls a group of heddles. Cord 10 connects, via supplementary cords 15, 16, 17 to heddles 50, 71, 72. As previously described, cord 10 includes an artificial muscle 11, the state of which is controlled by a control signal 12. Each heddle 50, 71, 72 has the same form as previously described in Figure 1. Cord 20 connects to a set of heddles in a similar manner to cord 10. The artificial muscle 21 of cord 20 is shown in a contracted state, which has pulled that group of heddles upwards with respect to the group of heddles 50, 71, 72.

Figure 5 shows a variant of Figure 4 in which the artificial muscles 11, 21 for the cords 10, 20 are arranged and housed within a housing 80 which provides protection to the artificial muscles. Figure 6 shows that alternative embodiment of the invention in which each heddle 150 is moved by a pair of active cords 10, 110. A first active control cord 10 connects to a first end 152 of heddle 150 and a second active control cord 110 connects to a second end 153 of heddle 150. The other ends 13, 113 of cords 10, 110 are connected to the frame of the machine. Each end 152, 153 of heddle 150 is mounted within a slot of harness board 40, 140. These boards 40, 140 guide the heddle 150 in a vertical direction. Each control cord 10, 110 includes an artificial muscle 11, 111. The state of the artificial muscles 11, 111 is controllable by a control signal 12, 112. It can be seen that a second control cord 110 replaces the spring 55 used in Figure 1. Artificial muscles 11, 111 are operated at the same time, but they change state in the opposite direction to each other, i.e. one contracts as the other returns to a relaxed state. Heddle 150 is shown in a 'down' position. To achieve this, artificial muscle 11 is relaxed while artificial muscle 111 is contracted. This can be contrasted with heddle

160 which is shown in an 'up' state. To achieve this, artificial muscle 21 is contracted while artificial muscle 121 is relaxed.

Figure 7 shows a further embodiment of the invention. This embodiment has a similar arrangement to Figure 1. Whereas Figure 1 uses a return spring 55 to bias the position of heddle 50, this embodiment achieves a similar effect by forming heddle

250, comprising a thread eye 251, from a resilient material. The heddle 250 extends from the artificial muscle 11 to the remote end 258.

In the embodiments shown in Figures 1-7 an active cord comprises an artificial muscle which is connected in series with harness cord (e.g. artificial muscle 11 connected to harness cords 18, 19 in Figure 1). Figure 8 shows an alternative embodiment where this combination of elements is replaced with a single length of cord 450 which acts as an artificial muscle. This can take the form of a length of cord- like material which is a combination of structural fibres and active fibres which contracts/extends or otherwise deforms when an electrical control signal is applied to the active fibres. European Patent Application EP 1 420 094 describes a material which is suitable for use as an active cord 450 in this manner. The active cord 450 is arranged between a mounting point 13 and a heddle 451. The heddle 451 consists of an eyelet for guiding a warp thread. The heddle 451 is further connected to a resilient cord 452 that tensions the active cord 450. Figures 1-8 show arrangements where an array of heddles are each movable by an active cord which incorporates an artificial muscle. Figures 9-12 show arrangements where the heddle itself incorporates an artificial muscle. In each of these Figures, an array of heddles is held within a heald frame 300. A heald frame 300 is known from WO 01/48284. The heald frame has crossbars 301, 302 and sidebars 303, 304.

Figure 9 shows an embodiment where an artificial muscle forms the entire heddle 350. The active heddle 350 has an eyelet 351 for receiving a warp thread. A control signal 312 is applied to the artificial muscle forming the heddle 350. Each active heddle 350 is independently controllable. The artificial muscle forming the heddle 350 can be formed of piezo-electrical fibres and elastic fibres, where for example in the part above the eyelet 351 mainly piezo-electrical fibres are provided and in the part under the eyelet 351 mainly elastic fibres are provided. In this way,

when an electrical signal is provided, the upper part of the heddle 351 will for example contract more than the under part, such that the eyelet 351 for moving a warp thread will move upwards. In an alternative embodiment the upper part of the heddle 350 can comprise piezo-electrical fibres that are mainly directed in one direction, while in the lower part of the heddle 350 piezo-electrical fibres are provided that are mainly directed in the opposite direction, such that an application of a control signal the one part shall contract while the other part shall elongate.

Figure 10 shows an alternative embodiment of the invention in which one half of heddle 450 includes an artificial muscle 420 which is controllable by a control signal 412. The other half 430 of heddle 450 can either be formed of a resilient material or can include a return spring similar to that shown as part 55 in Figure 1. According to an alternative (not shown) the artificial muscles 420 of two adjacent heddles can be arranged one above the eyelet 451 and the next one under the eyelet 451. This can reduce the necessary spacing between the heddles 450 within the heddle frame.

Figure 11 shows another alternative embodiment which is similar in operation to Figure 4. Here, each half of heddle 550 includes an artificial muscle 511, 611 which receives a control signal 512, 612. The muscles operate in an opposite manner to one another, so that one contracts while the other extends. In Figure 11 the central portion of the heddle 550 which includes the eyelet 551 for moving a warp thread and which does not incorporate the artificial muscle can be formed of metal in a conventional manner.

In Figures 9-12 an electrical control signal can be carried to an artificial muscle via an electrical guide element which is mounted in the crossbars 301 and 302 and via an electrically conductive path through the structure of the artificial muscle.

In the previously described embodiments artificial muscles have been shown which vary in length so as to move a warp thread. Artificial muscles which vary in length do not necessarily have elements that vary in length, for example elements as shown in Fig. 2 and 3. It is possible to use artificial muscles which have elements that bend (deform) upon application of a control signal. Figure 12 shows a heald frame with an array of active heddles 650, 650A of this kind. Such a heddle 650, 650A can have a shape as known from US 1,847,579. These heddles 650, 650A comprise

artificial muscles 660, 661, 662, 663 which are based on piezo-electric materials that can bend upon application of a control signal. The heddle 650 is shown in a state where no control signal is fed to the artificial muscles 660, 661. The heddle 650A is shown in a state where a control signal is fed to the artificial muscles 662 and 663, such that these muscles 662 and 663 take a shape a shown in Fig. 12, e.g. by bending of the muscles 662 and 663. In this way the length of the artificial muscles 662 and 663 is changed and a warp thread guided through a thread eye 670 will move in order to form a shed. In the example shown, the heddle 650A is moved into an upper position, while the heddle 650 is in a lower position. It is preferred that all of the heddles within the heald frame are controlled to deform in the same direction as this allows heddles to be positioned closely to one another. The artificial muscles 660, 661, 662, 663 have an input for receiving an actuation signal, e.g. a control signal 512, 612 similar to the one as shown in Fig. 11. The length of the artificial muscles can be changed by changing the configuration of the artificial muscle upon actuating the artificial muscle.

The artificial muscle can be formed of a bi-stable material. This is a material which contracts when actuated with an electrical signal (control pulse), and which returns to an extended state when a further signal (control pulse) is applied to the contracted state. Here, it is not necessary to apply a continuous signal to the artificial muscle to maintain the muscle in a contracted state. This can be achieved using a material where a polarisation is achieved magnetically during application of a control signal. The polarisation remains after the control signal is removed.

It should be noted that a weaving machine equipped with a shed forming device using artificial muscles can still be provided with conventional weaving machine equipment such a warp breakage detector, a control unit for the shed forming device and any other known weaving equipment. Such a shed-forming device further remains compatible with a conventional weaving machine or conventional weaving preparation equipment.

According to a variant not shown, it is also possible to provide a position sensor or any other sensor to control the movement of the thread eye or of the artificial muscle, such that the signal of said sensor can be used as a feedback signal to control the artificial muscle. In this way the actuation of the artificial muscle can be controlled

using a feed back control system. This allows to control the position, the velocity and/or the acceleration of a thread eye moving a warp thread according to a set or target course, or using a feedback control system.

The invention is not restricted to the embodiment shown, variant and combination of these embodiments are also possible.