Method and apparatus for reducing weft waste in a gripper weaving loom

In a gripper weaving loom which weaves several different types of weft threads into a fabric, it is desirable to keep weft material waste to a minimum. For this purpose a weft thread (7) already inserted into the loom shed is simultaneously held by a weft presenting clamp (13) and by a holding clamp (18). As soon as the weft is held by both clamps the weft is cut by a cutter (20) effective between the two clamps to form a trailing weft end (7B) of the already inserted weft and a leading weft end (7A) of a weft yet to be inserted. The holding clamp (18) keeps holding the trailing end (7B) until beat-up of the weft by the reed (4) is completed. For this purpose, the holding clamp (18) moves with the reed (4) into the beat-up position. When beat-up is completed the holding clamp (18) releases the trailing weft end (7B) and returns into a weft receiving position (22B). The weft presenting clamp (13) still holds the leading end (12A). The holding clamp (18) is arranged to move with the reed, while the cutter (20) is stationary between the two clamps.

PRIORITY CLAIM

This application is based on and claims the priority under 35 U.S.C. §119 of German Patent Application 102 13 639.4, filed on Mar. 27, 2002, the entire disclosure of which is incorporated herein by reference.

FIELD OF THE INVENTION

The invention relates to a method and an apparatus for presenting a clamped weft thread to a weft insertion gripper that moves the weft thread into the loom shed. The presentation of the weft thread to the insertion gripper is performed so as to minimize weft waste.

BACKGROUND INFORMATION

European Patent Publication EP 0,240,075 B discloses a method and apparatus for minimizing weft waste, whereby at least two weft thread supply mechanisms are used for producing the fabric.

According to the known method substantially the following steps are performed.1. At least two weft threads, including one first and one second weft thread, are to be sequentially inserted into the loom shed. Each weft thread is clamped by a respective clamp of a corresponding weft presentation lever of a presentation and clamping mechanism, whereby the presentation levers are in a position A.2. A weft thread selector chooses in response to a control program between the two weft threads for presenting one of the two weft threads to a weft insertion gripper.3. The respective presentation lever is moved into a second or presentation position B thereby bringing the selected weft thread into the moving path of the weft insertion gripper which takes over the weft thread for insertion into the loom shed.4. The presentation lever is then moved into a position C which is located close to the insertion edge of the fabric on a line that is an extension of the beat-up line or an extension of the interlacing points along the beat-up line of a fabric being woven.5. At this point the weft thread taken over by the gripper is still connected to the weft supply. After the insertion into the loom shed and after the beat-up the weft thread is clamped and held in the clamped position C by the respective clamp.6. The beat-up weft thread is then cut between the selvage edge of the fabric and the clamp that is still in position C, thereby severing the trailing end of the inserted weft thread from the leading end of the clamped weft thread held ready for the next insertion.7. The respective presentation lever, following the cutting of the weft thread, is held in the position C or it is moved back into the position A.

The above conventional method and the conventional apparatus for performing the known method have a significant disadvantage, namely that each type of weft thread to be inserted into the loom shed necessarily has a different length of weft waste. This is so because each weft presenting clamp of a plurality of weft presenting clamps has a different spacing from the fabric weft entrance edge. More specifically, the weft clamp positioned closest to the fabric edge yields the smallest length of weft waste. The weft waste for the next weft thread is larger than that of the first weft thread and so on so that the weft waste increases from weft thread to weft thread in a group of a plurality of weft threads. The increasing weft waste lengths are determined by the construction of the loom and present a substantial disadvantage. A further conventional disadvantage is seen in that the weft thread is cut in the area where the reed performs its beat-up. As a result, the weft thread must be pulled out all the way to the interlacing point. In order to reduce the weft waste, the known apparatus employs a pull-back mechanism that pulls back the next weft thread to be inserted after it has been cut near the interlacing point or beat-up line. The weft pull back mechanism is additionally necessary to maintain the required weft tension for the next following weft insertion.

The above described functions are performed by a conventional apparatus that has a mechanism for presenting and clamping the weft threads in a gripper loom. The known apparatus comprises essentially a weft presenting lever equipped with a thread clamp for each weft thread to be inserted into the loom shed. The weft presenting levers are positioned next to each other and approximately in parallel to the fabric edge or selvage on the weft insertion side of the loom shed. The clamp of the first weft presenting lever is positioned closest to the fabric edge when the clamp is in the positions A and C. The clamp on the last weft presenting lever is positioned furthest away from the fabric edge. Thus, it is clear that the free length of weft thread becomes longer and longer starting at the first position of the first clamp and increasing with the following clamps. The weft thread cutter is mounted in a fixed position next to the fabric edge and cuts longer and longer weft thread ends. Moreover, as a rule, the longer the weft thread between the clamp and the weft cutter, the smaller is the thread tension. However, it is desirable that a certain assured tension is present in the weft thread as it is cut. As a result, the known apparatus does not ensure that the selvage along the weft entrance side of the loom shed is always meeting the required quality standards.

German Patent Publication DE-OS 25 31 954 discloses a controllable weft thread clamping mechanism comprising a plurality of clamping points. Each clamping point is displaceable or adjustable relative to a reference plane. Further, the clamping points are arranged at equal spacings from one another and one above the other. One clamping position at a time can be shifted into the reference plane. Each clamping position is constructed to cooperate with a controlled weft thread selector. These weft thread selectors are known as such. This combination of a clamping position with a controlled weft thread selector has the advantage that the weft thread to be inserted into the loom shed can be transported into a first reference plane where the weft insertion gripper can seize the weft thread without any problems. Another advantage of the known apparatus is seen in that the respective clamping position can be moved into a second reference plane which corresponds to the position of the interlacing point at the fabric edge. This conventional feature makes it possible that when the weft thread is beat-up to the beat-up line of the fabric, the weft thread is clamped by the respective clamping position of the clamping mechanism and is held in tension at the entrance side of the loom shed between the fabric edge and the clamping position. This tension in the weft thread at this position is advantageous for the cutting by the weft cutter or scissors mounted between the clamping position and the fabric edge. However, the weft waste cannot be minimized with such an arrangement because the weft threads cannot be presented directly to the weft insertion gripper.

German Patent Publication DE 30 42 053 C1 discloses a weaving loom with an apparatus for reducing weft thread waste. However, the known weaving loom employs rather complicated features or mechanisms for the reduction of weft waste. These mechanisms in combination with the cutter for severing the beat-up weft thread is technically quite involved and correspondingly prone to trouble. In the known apparatus the cut-off trailing end of the inserted and beat-up weft thread is stretched by pneumatically effective nozzles, which due to their pneumatic nature require a weft thread end that cannot be relatively short.

German Patent Publication DE 197 39 853 C2 discloses a weft thread presenting and clamping mechanism with a plurality of weft presenters each of which is equipped with a clamp. These presenters and clamps are arranged in the loom for cooperation with at least one weft pull-back mechanism. The cooperation with the pull-back mechanism is such, that all weft threads of a group of weft threads are presented approximately in the same point to the weft insertion gripper in order to realize a minimum of weft waste. All wefts of a group are to be inserted into a loom shed in a predetermined sequence as controlled weft selector.

OBJECTS OF THE INVENTION

In view of the foregoing it is the aim of the invention to achieve the following objects singly or in combination:to provide a method and apparatus for minimizing weft thread waste while simultaneously avoiding the above outlined disadvantages of the prior art;to avoid cutting a weft thread that has already been inserted and beat-up in the loom shed at the point where interlacing occurs, in other words, to cut the weft thread immediately upon completion of the weft insertion, preferably at the beginning of a beat-up motion of the reed of the loom;to avoid the use of a weft pull-back mechanism while still assuring that the weft thread is held at the proper tension at least when the weft is cut; andto make sure that a minimum cut-off length is uniform for all inserted weft threads of a group of weft threads to assure the formation of a quality selvage at the entrance edge of the loom shed.

SUMMARY OF THE INVENTION

The above objects have been achieved according to the invention by the combination of the following weft handling steps and structural features of the present loom. Immediately following the insertion of a weft thread into the loom shed and prior to the beat-up of the inserted weft thread the latter is gripped by a first weft presentation clamp and by a second weft holding clamp, referred to herein as first and second clamps or as presenting clamp and holding clamp. Immediately following the clamping by the first and second clamps, the weft is cut by a weft cutter positioned between a weft presentation position of the first clamp that presents the weft thread to a weft insertion gripper and a weft take-up position of the second clamp that holds the weft thread. The cutting occurs during the beat-up motion of the loom reed, preferably immediately at the beginning of the beat-up motion. The cutting of the weft thread produces a trailing weft end of the inserted weft thread and a leading weft end of the weft thread waiting for a following insertion. The sequence of insertion of different weft threads depends on the weaving pattern. An immediately following insertion may use the same weft thread or it may use another weft thread in a sequence of other weft threads. The invention is equally suitable for all types of weft insertions. The trailing weft end is held by the second clamp until weft beat-up is completed. For this purpose the second clamp travels along with the reed in the beat-up direction. Once beat-up is completed, the second clamp releases the trailing weft end and travels back into its weft take-up position. For this purpose the motion of the second clamp is coordinated or even synchronized in part with the motion of the reed. The weft presenting or first clamp keeps holding the leading end of the weft while the first clamp is returned into the weft presentation position, but not necessarily in coordination with the reed motion because another weft presenting clamp may be effective for the next weft insertion while the second clamp cooperates with all weft insertion first clamps forming a group of, for example, six weft presenting clamps.

The motion of the second clamp according to the invention is, as mentioned above, coordinated or synchronized with the reed motion. As a result, the second clamp can advantageously cooperate with any one of a plurality of weft thread presenting first clamps. A further advantage is seen in that the weft cutter can be positioned away from the beat-up line. Thus, the invention achieves advantageously that the weft thread can be cut during the motion of the reed in its beat-up motion direction toward the beat-up line of the fabric. Further, according to the invention the motion sequence of the plurality of weft presenters with their first clamps and their position are so selected that in both positions of the presenting clamps, namely in the rest position and in the presenting position, the weft thread is equally tensioned. As a result, the invention achieves a very small waste of weft threads compared to conventional weft waste, without the need for a weft pull-back mechanism.

The foregoing advantages are achieved even if a plurality of weft presenters with their first clamps cooperate with the single second clamp in sequence for presenting, for example weft threads of different colors substantially at the same presentation point (16) for the insertion gripper to efficiently seize the respective weft thread, whereby for each weft thread a uniformly minimal weft waste is achieved.

The above described sequence and the conventional operations of a gripper weaving loom is controlled by the electronic loom control unit which controls the individual components of the loom such as the weft thread presenters, the insertion gripper, the withdrawal gripper, the reed, the holding or second clamp, and the weft cutter. The drive of the loom components can take place either by a central loom control drive, whereby the drive power is derived from the main loom drive shaft or the individual components can be operated by electromotor drives which are individually controlled by the main loom control.

A loom according to the invention is characterized in that the above mentioned holding or second clamp is mounted next to the weft insertion edge of the loom shed and that this second clamp is coordinated or synchronized in its motion with the motion of the loom reed for holding the cut-off or trailing end of an inserted weft thread and that the weft cutter is positioned close to the weft presentation point (16) of a weft presenting or first clamp and between the weft presenting first clamp and the weft holding second clamp.

DETAILED DESCRIPTION OF PREFERRED EXAMPLE EMBODIMENTS AND OF THE BEST MODE OF THE INVENTION

FIGS. 1 and 2illustrate schematically the weft insertion side of a weaving loom.FIG. 2shows the upper warp threads1and the lower warp threads2forming a loom shed6. The warp threads1and2pass through the loom heald frame or shafts3and through the lamellae of the loom reed4toward the interlacing point5which is positioned in a weft beat-up line8. The shed6is formed upstream of the beat-up line8and a fabric9is formed along the beat-up line8. The fabric9travels in the direction of an arrow A1away from the beat-up line8.FIG. 1shows, for example, six different weft threads7which are inserted into the loom shed6by a weft insertion gripper10. Once a weft thread7C is inserted into the loom shed6it is beat-up by the reed4that moves back and forth between the full line back position and the dashed line beat-up or forward position as shown inFIG. 2by an arrow A2. Once the weft insertion gripper10has moved a weft thread into the loom shed6, a weft withdrawal gripper not shown, moves the weft thread entirely through the loom shed prior to beat-up. The finished fabric9is continuously withdrawn in the direction of the arrow A1.

FIG. 1illustrates only one weft presenter12to simplify the illustration. However, since there are, for example six weft threads7supplied by respective spools not shown, there will be used six weft presenters12. A thread guide11having, for example six thread guide eyes15, guides the weft threads7so that the respective weft presenter12carrying a first clamp13shown in its rest position12A and schematically in its weft presenting position12B, can pick-up its weft thread leading end7A. As shown inFIG. 1each weft presenter12shown in its rest position12A has a bail configuration which forms a tiltable or swivelable lever that carries at its free end the weft presenting or first clamp13and is journaled at its opposite end on a journal axis14. Thus, the weft presenter12is movable back and forth along a sector of a circular motion as indicated by the double arrow14A that has its center in the journal axis14. Preferably, the journal axis14passes through the respective thread guide eye, for example guide eye15. The clamp13clamps that part of the weft thread7, which will become the leading end7A of a respective weft thread7after cutting. More specifically, the weft presenter12is movable about the journal axis14from its rest position12A to its weft presenting position12B and back again. By passing the respective journal axis14through the corresponding thread guide eye15it is assured that the spacing between the thread guide eye15and the weft presenting or first clamp13remains constant which has the advantage that the thread tension in the leading end7A of the weft is also constant in any position of the thread presenter12. Each thread presenter12in its thread presenting position12B presents the weft thread to the insertion gripper10in substantially the same presenting point16. The term “substantially” as used in the present context means that the presenting point16may vary slightly from one presenter to the other as long as the leading weft end7A is properly presented to the gripper10as shown in FIG.1.

If a weft thread7is selected by a weft selector controlled by the main loom control not shown, the weft presenter12moves from its rest position12A to its presenting position12B which is located next or close to the weft insertion edge17of the fabric9. InFIG. 1only the weft presenting clamp13is shown in the presentation position12B to hold the weft thread leading end7A in the presenting point16for seizing by the gripper10which moves the weft thread into the open loom shed6. Approximately in the center of the shed the weft thread is taken over by a second gripper, not shown, which pulls the thread entirely through the shed to the exit side of the shed. Once the weft thread has been taken over by the second gripper, the insertion gripper10returns to its position outside of the loom shed ready for the next weft insertion.

When the weft insertion is complete, the reed4is moved out of its back position4A into the dashed line beat-up position4B as shown inFIG. 2by the arrow A2. As the reed4moves clockwise or forward inFIG. 2, the inserted weft thread7C is pushed toward the interlacing point5and beat-up along the beat-up line8. At this time the weft presenter12with its presenting or first clamp13is still in the presenting position12B. As the weft thread7C is pushed toward the beat-up line8prior to cutting the part of the weft thread that after cutting will become the leading end7A of the weft thread, is clamped by the weft presenting or first clamp13for holding the leading weft end7A in the presenting point16. Thus, a portion of the weft thread not yet cut is held between the weft presenting first clamp13and a weft holding second clamp18in a position for cutting by a weft cutter20.

The insertion of the weft thread into the first clamp13and into the second clamp18can be facilitated by a presenting hook19arranged laterally of and operatively connected to the reed4as best seen in FIG.2. The presenting hook19moves with the reed4and aids in the reliable insertion of the weft thread7into both clamps13and18. Using the presenting hook19is not necessarily required, but its use may rather depend on the type of weft threads to be woven.

As soon as the weft thread7has been reliably clamped by the first clamp13and the second clamp18the weft will now be cut by the weft cutter20such as scissors which are positioned close to the weft presenting position12B of the weft first clamp13. This cutting according to the invention takes place while the reed4is still moving toward the beat-up position4B. Preferably, the cutting takes place as soon as possible following the s beginning of the clockwise beat-up movement of the reed4.

The cutting of the weft thread results in a trailing weft end7B of the inserted weft thread7C and in a leading weft end7A of the weft thread to be inserted in its following sequence.

The cut-off trailing end7B is held by the holding second clamp18while the leading end7A of a weft end7coming from a supply spool not shown is held by the presentation first clamp13for presenting the leading end7A to the insertion gripper10. Depending on the controlled selection of the weft thread sequence, the next leading weft end to be inserted is not necessarily the leading end of the weft thread that has just been cut. Rather, a leading end next to be inserted may be part of any of the other five weft threads that have been previously cut and were held by its own weft presenting first clamp13.

FIG. 2shows one embodiment of a drive mechanism for imparting the required motion to the second clamp18. For this purpose the second clamp18is mounted to the free end of a journal lever22that is journaled to a journal axis21for moving back and forth as indicated by the arrow A3, between a back position22B through a central position22A to a forward position22C. This motion of the journal lever22and thus of the holding clamp18is controlled by the main loom control and follows the motion of the loom reed4to the beat-up position4B, but does not need to go all the way to the rear position4A of the reed4. Thus, the lever22follows the reed motion only substantially.

As shown inFIG. 2following a weft insertion into the loom shed6the journal lever22is in the central position22A. As the reed4moves clockwise in the direction of the arrow A2toward the beat-up line8the reed passes into the area of the central position22A of the journal lever22carrying the holding clamp18. At the same time, the lever22moves backward to its back position22B, toward the back position4A of the reed4. Thus, the weft thread that will be beat-up comes with its trailing end into the range of the holding second clamp18which seizes and clamps the weft thread. From the position22B where the weft thread has been clamped, the journal lever22moves into its forward position22C toward the beat-up line8substantially in synchronism with the motion of the reed4. The dashed line of the reed4inFIG. 2indicates the reed beat-up position4B. When the reed4is in the position4B the second clamp18is opened to release the trailing end7B of the now beat-up weft thread7C. The journal lever22can now return into its central position22A.

While the journal lever22with its second clamp18moves back into the central or starting position22A, the weft presenter12with its first clamp13also tilts back into its rest position12A in order to make room for another weft presenter12. However, if the same weft thread is to be again inserted then the weft presenter12can remain in its weft presenting position12B.

FIG. 3shows a modified embodiment of the invention in which the weft presenter12with its first clamp13moves along a linear path25between its rest position12A and its weft presenting position12B next to the cutter20. A linear drive25A drives the respective weft presenter12along the linear path25. Each weft presenter12or rather its weft presenting first clamp13can thus be moved into the weft presenting point16which is substantially the same for all presenters12. The linear movement path25of the weft presenter12from its rest position12A to the presenting position12B and back again is so selected that the leading weft end7A clamped by the first clamp13is held in tension at least in the rest position and in the weft presenting position. It is not critical if the tension is not constant between the rest position12A and the weft presenting position12B when the presenter moves between these two positions as long as the tension is the same in both end positions. Following the positioning of the weft thread leading end7A in the presentation point16, the insertion gripper10seizes the weft thread and moves it into the loom shed6. The following steps in the sequence of operation is the same as that described above with reference toFIGS. 1 and 2.

The linear motion of the weft presenter12and its clamp13can, for example, be derived from a piston cylinder drive or from a cam drive or from a linear electric motor. Similarly, rather than carrying the holding or second clamp18on a swiveling or journal lever22it is possible to move the holding clamp along a linear path between its end positions. However, a motion of the holding or second clamp18along its circular path is preferred for facilitating the coordination or at least partial synchronization with the motion of the reed4.