OPERATION THEREOF

BACKGROUND OF THE INVENTION

The present invention relates to a loom with assigned yarn sensor and a method for the operation thereof, according to the preambles of the independent claims.

DESCRIPTION OF THE PRIOR ART

Yarn sensors for measuring at least one yarn parameter are used in looms in order to monitor or measure the weft thread to be inserted. Examples are provided by the following specifications: EP-0'573'656 Al, EP-2'050'847 Al , EP-2'157'218 Al, ΕΡ-2Ί 75Ό58 Al, US-2008/0185066 Al , WO-89/12122 Al, WO-2006/133833 Al .

So-called yarn clearers are used in spinning or winding machines for securing the yarn quality. A yarn clearer system comprises a measuring head with at least one sensor which scans the moved yarn. WO-2010/063128 A 1 provides an example for a yarn clearer measuring head. It is the object of yarn clearing to detect defects such as thick places, thin places or foreign matter in the yarn, to evaluate them according to specific quality criteria and to optionally remove them from the yarn. The yarn clearer requires timeouts in between for null balancing and/or for adjustment, in which no yarn is disposed in the sensor of the measuring head. Such timeouts arise in normal operation repeatedly in the removal of a defect or during a cop change in a winding machine. Such timeouts never occur or only rarely occur in looms, so that null balancing or an adjustment of a yarn clearer assigned to a loom is hardly possible. CN-101706337 A discloses an apparatus for measuring the mechanical tension of a yarn. The yarn runs over a sensing device and exerts a force on the same directed

perpendicularly to the longitudinal axis of the yarn. For the purpose of automatically adjusting the apparatus, the yarn is stopped and lifted off from the sensing device by means of a support device. The support device is actuated electromagnetically and is brought back to its idle position by means of a tension spring. The possibility for changing the position of the yarn by such a support device is limited with respect to location and time. The support device can deflect the yarn only at one point. It may be difficult to maintain the yarn deflection over a prolonged period of time.

SUMMARY OF THE INVENTION

It is an object of the present invention to enable null balancing or an adjustment in a yarn sensor assigned to a loom.

These and other objects are achieved by the loom in accordance with the invention and the method in accordance with the invention as defined in the independent claims.

Advantageous embodiments are stated in the dependent claims.

The invention is based on the idea of providing on the loom an apparatus for removing the weft thread from the measuring region of the yarn sensor and for inserting the weft thread into the measuring region. It is especially advantageous to provide a pneumatic drive for the apparatus. It allows moving large masses, therefore also that of a more complex system of yarn guide elements. Moreover, the pneumatic drive ensures the stable maintenance of different layers as long as necessary. It is a further advantage that the change of position can occur with a selectable speed in the pneumatic drive. The terms such as "position" or "change in position" always relate in the present specification to a position of an at least locally defined longitudinal axis of the tensioned weft thread. A change of position in this sense always contains a motion component perpendicularly to the longitudinal axis of the weft thread; a movement component parallel to the longitudinal axis is possible but not relevant. The present invention does not deal with a pure movement of the weft thread along the longitudinal axis, even if the present invention allows or even facilitates such a movement. The loom in accordance with the invention is assigned a yarn sensor which comprises a measuring region for measuring values of at least one parameter of a weft threads to be inserted. The loom contains an apparatus for removing the weft thread from the measuring region and for inserting the weft thread into the measuring region.

The apparatus for removing the weft thread from the measuring region and for inserting the weft thread into the measuring region is preferably driven pneumatically.

In a preferred embodiment, the apparatus preferably comprises guide means for fixing a position of the weft thread and moving means for changing the position of the guide means. The guide means and the moving means can be arranged and set up in such a way that the change in the position is a parallel displacement of a longitudinal axis of the weft thread. The moving means can be arranged as a single-acting or double-acting pneumatic cylinder. The guide means are preferably arranged for guiding the weft thread moved along its longitudinal axis. They comprise at least two guide elements for guiding the weft thread, which guide elements are spaced from one another along the longitudinal axis. Two of the guide elements can be arranged as guide eyelets fixed to a common support.

It is especially advantageous if the yarn sensor is built into a yarn clearer measuring head and the measuring region is disposed in a measuring slot of the yarn clearer measuring head. The loom is for example a jet loom and preferably an air-jet loom. The yarn sensor and the apparatus can be arranged upstream with respect to a weft storage unit of the loom.

The method in accordance with the invention is used for operating a loom with assigned yarn sensor. The yarn sensor comprises a measuring region for measuring values of at least one parameter of a weft thread to be inserted. The weft thread is removed automatically from the measuring region if required and automatically reinserted into the measuring region again. The automatic removal and reinsertion of the weft thread preferably occur pneumatically. The removal and reinsertion occur by parallel displacement of a longitudinal axis of the weft thread for example. The yarn sensor can be balanced to null or adjusted as a result of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be explained below in closer detail by reference to the schematic drawings, wherein:

Figure 1 schematically shows a loom in accordance with the invention;

Figure 2 schematically shows parts of the loom in accordance with the invention in two different states;

Figure 3 shows a preferred embodiment of parts of the loom in accordance with the invention in two different perspective views.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Figure 1 schematically shows a loom 1 in accordance with the invention, which is arranged in this case as an air-jet loom for example. Yarn 91 envisaged as a weft thread is provided on a bobbin 21. The yarn 91 is transferred from the bobbin 21 to a weft storage unit 22 which can be arranged as a drum storage unit for example. A weft thread 92 which is drawn off from the weft storage unit 22 is accelerated by means of one or several acceleration nozzles 31 , 32 and is supplied to an air feed conduit 8 which is disposed in a weaving shed (not shown) produced by means of a shedding mechanism. The weft thread 92 is conveyed by means of a plurality of relay nozzles 33 through the air feed conduit 8. The relay nozzles 33 are preferably combined into groups of nozzles 34.1 , ..., 34.n of four relay nozzles 33 each. Six groups of nozzles 34.1, 34.n with four relay nozzles 33 each are shown in the embodiment of Figure 1. The acceleration nozzles 31, 32 and the groups of nozzles 34.1, 34.n are respectively supplied via a control valve 1, 42, 44.1, 44.n with compressed air. The supply of compressed air to the control valves 41 , 42, 44.1 , 44.n is not shown in Figure 1 for the sake of simplicity, as also further elements of the jet loom 1. A yarn sensor 5 with a measuring region 51 for the continuous detection of at least one yarn parameter of the weft thread 91 is arranged before the air feed conduit 8, and preferably between the bobbin 21 and the weft storage unit 22. The yarn sensor 5 can be arranged as a yarn clearer, as was used until now for online monitoring of the yarn quality in spinning or winding machines and is known from the state of the art. It can operate according to the capacitive, optical and/or any other principle. The detected at least one yarn parameter can be the yarn mass, the yarn diameter, the yarn hairiness and/or the yarn material for example, which may also contain potential foreign substances. A first weft break stop motion 61 for detecting the drawing off of the weft thread 92 is disposed downstream of the weft storage unit 22. Furthermore, a second weft break stop motion 62 for detecting the arrival of the inserted weft thread 92 is arranged at the output of the air feed conduit 8.

The control valves 41 , 42, 44.1 , 44.n are controlled by a closed-loop control unit 7. The closed-loop control unit 7 can be a separate module or a part of a loom control unit. It receives signals and/or data from the yarn sensor 5, from the first and/or second weft break stop motion 61 , 62 and possibly from further sensors and/or from the jet loom 1 itself. The closed-loop control unit 7 calculates the optimal nozzle opening times for every single weft insertion on the basis of the yarn parameters detected by the yarn sensor 5. The air effectiveness of the specific weft thread section to be currently inserted can be included in the calculation. The air effectiveness of a yarn is defined in WO-89/12122 Al as the ratio of the area of support of the yarn in air in comparison to the yarn mass.

An apparatus 10 for removing the weft thread 91 from the measuring region 51 and for inserting the weft thread 91 into the measuring region 51 is provided in the region of the yarn sensor 5. The apparatus 10 can be controlled by the closed-loop control unit 7 or by another control unit. The apparatus 10 removes the weft thread 91 from the measuring region 51 when required, e.g. when the yarn sensor 5 needs to be balanced to null or adjusted; when the yarn sensor 5 is ready for measuring again, the apparatus 10 inserts the weft thread 91 back into the measuring region 51.

The apparatus 10 will be explained in closer detail in Figure 2, in which parts of the apparatus 10 are shown schematically in two states. In the first state according to Figure 2(a), the tensioned weft thread 91 extends through the measuring region 51 of the yarn sensor 5. The weft thread 91 can be moved along the longitudinal axis, which is indicated by an arrow 90. The weft thread 91 is guided by two guide elements 121, 122 outside of the yarn sensor 5, which guide elements are spaced from one another in the direction of the longitudinal axis of the weft thread 91 and are disposed on either side of the yarn sensor 5. The guide elements 121 , 122 determine at least locally the position of the weft thread 91 with respect to the yarn sensor 5. They are connected with the yarn sensor 5 via a bearing 13 and moving means 14. The moving means 14 are configured for performing a relative motion perpendicularly to the longitudinal axis between the yarn sensor 5 and the guide elements 121 , 122, and therefore also between the yarn sensor 5 and the weft thread 91. This possibility of movement is indicated with a double arrow 140. The moving means 14 are preferably driven pneumatically. In a second state according to Figure 2(b), the moving means 14 are displaced in relation to the first state in such a way that the weft thread 91 is disposed outside of the measuring region 51 of the yarn sensor 5. In this state, the yarn sensor 5 can be balanced to null or adjusted for example. In the region of the yarn sensor 5, the longitudinal axis of the weft thread 91 extends parallel to the original longitudinal axis, so that the second state is produced by local parallel displacement of the weft thread 91 from the first state and vice versa. The new position is possibly co- determined by further guide means which are not shown here. The moving means 14 can be actuated in such a way that the apparatus 10 can assume the two indicated states in a stable manner, and possibly also further states.

Figure 2 indicates that the yarn sensor 5 is arranged in a stationary manner and the guide elements 121, 122 are moved by the moving means 14. This is a possible embodiment of the invention, but not the only one. Alternatively, the guide elements and therefore the longitudinal axis of the weft thread can be arranged in a stationary manner, whereas the yarn sensor is moved by the moving means. In the end it is only relevant that the moving means 14 produce a relative movement between the yarn sensor 5 and the guide elements 121, 122.

Instead of one or two guide elements 121, 122 the apparatus 10 can have any other arbitrary natural number of guide elements for the weft thread 91. They need not be arranged as eyelets which are enclosed on all sides, as is shown in Figures 1 and 2. Many different guide elements for a thread-like material are known from the state of the art.

Figure 3 shows a preferred embodiment of the yarn sensor 5 and the apparatus 10. A yarn clearer measuring head 5 is fixed in a stationary manner to a first holding element 181. It comprises a measuring slot 51 , through which the weft thread 91 is movable along its longitudinal axis. The longitudinal axis of the weft thread 91 extends in this embodiment horizontally. A pneumatic cylinder 14 with a compressed-air connection 141 is fixed to a second holding element 182 which is also stationary. The inlet of compressed air can occur via a valve (not shown) and by a closed-loop control unit 7 (see Figure 1). A piston engaging in the pneumatic cylinder 14 and which is not shown in Figure 3 can be moved upwardly and downwardly by changing a pressure which can be built up in a pneumatic cylinder 14. The stroke can be approximately 10 to 30 mm. Limit switches are

advantageously used, which recognise when the pneumatic cylinder 14 has reached one of the two end states and transfer a respective signal. A fork-like bearing 13 is attached to the piston, with one respective yarn guide element 121, 122 being provided on its two prongs 131 , 132. The yarn guide elements 121 , 122 can be arranged as upwardly open ceramic eyelets. As a result of a pressure build-up in the pneumatic cylinder 14, the weft thread 91 is lifted upwardly out of the measuring slot 51 ; by reducing the pressure the weft thread 91 is lowered back into the measuring slot 51 by co-operation of its tension and gravity. These changes in the position can occur while the weft thread 91 is running.

The moving means 14 can be driven in another manner, e.g., electrically, instead of pneumatically. The pneumatic drive however offers advantages over other types of drives. The bearing 13 and the guide elements 121, 122 which are attached thereto jointly have a large mass which is respectively inert. The relatively large forces which are required for accelerating this large mass can easily be produced by a pneumatic drive. Moreover, at least two states (weft thread 91 in the measuring slot 51 and outside of the measuring slot 51) can be maintained in a stable manner and over prolonged periods of time.

It is understood that the present invention is not limited to the embodiments as discussed above. The person skilled in the art with the knowledge of the invention will be capable of deriving further variants which are also belong to the subject matter of the present invention.

LIST OF REFERENCE NUMERALS

1 Loom 21 Bobbin

22 Weft storage unit

31 , 32 Acceleration nozzles

33 Relay nozzles

34.1 , ..., 34.n Groups of nozzles

41, 42 Control valves

44.1 , ... , 44.n Control valves 5 Yarn sensor

51 Measuring region

61, 62 Weft break stop motion 7 Closed-loop ontrol unit

8 Air feed conduit

90 Direction of movement of the weft thread

91, 92 Weft thread

10 Apparatus

121, 122 Guide elements for the weft thread

13 Bearing for the guide elements

131, 132 Prongs

14 Moving means

140 Movement perpendicular to the longitudinal axis of the weft thread

141 Connection for compressed air

181, 182 Stationary holding elements