Device for tensioning warp yarns in a weaving loom

Abstract: The device (9A,7A,10a,10b,11A) for tensioning the warp yarns (T) allows for tension by operation of the tensioning members (11A,11B) to apply tension to opposite lateral ends of warp yarn sheet and can be adjusted as necessary and required in accordance with the time of weft picking and/or the time of shed closing. Thus, timed application of tension to warp yarns at the time of picking provides for smooth separation of warp yarns at the lateral ends, thereby forming a shed opening without a delay. As a result, failure in weft picking due to inadequate and improper shed opening can be prevented successfully. The decrease of diffrence of tension in the open shed and the closed shed points in the weaving cycle reduces vibration of droppers and as a consequence also fluffering and even the number of breaks of warp threads (T).

Description: The present invention relates to a device for applying tension to opposite lateral ends of a sheet of warp yarns in a weaving loom. It is generally known in the art that the tension of warp yarns arranged in a array or a sheet in a weaving loom differs between the center and the opposite lateral ends of the sheet as determined along the sheet width, i.e. the warp yarn tension is lower toward the lateral ends of the sheet. Such loser tension causes poor separation of warp yarns in forming a shed opening by separated upper and lower arrays of warp yarns. If the warp yarn separation is inadequate, particularly, on the side from which the weft yarn is inserted, it may result in failure in weft insertion. A device which is designed to increase the tension of warp yarns at the lateral ends of warp yarn sheet is disclosed e.g. in JP 52-110967, JP 58-169545 and JP 59-43150. In the devices according to JP 52-110967 and JP 59-43150, spring force is utilized to apply tension to the lateral ends of warp yarn sheet. The device according JP 58-169545 uses a pair of tensioning members which are positioned in parallel to each other at the lateral ends of warp yarn sheet so as to hold the warp yarns therebetween and which are disposed extending at such an angle with respect to a line along the widthwise direction of the warp yarn sheet that the outer end of each of the tensioning members is positioned closer to cloth fell than the inner end thereof. In either of the devices according to JP 52-110967 (& FR-A- 2339 014) and JP 59-43150, substantially constant tension can be applied to the lateral ends of warp yarn sheet. If the tension is increased for improvement in separation of warp yarn into upper and lower sheets, however, the warp yarns at the lateral ends will be constantly subjected to a high tension, which may cause the warp yarns to break. In the device according to JP 58-169545, in which the warp yarn tension is increased by an increase in the shed opening, the time at which tension is applied depends solely on a predetermined shedding curve, with the result that there is no freedom of adjusting the time of tension application. Even by easing motion, the warp yarn tension differs between the time of shed opening and shed closing of the warp yarn sheet because each shed opens and closes at a different time, compared to the other. The rate of difference is higher at the lateral ends of the sheet, where the basic tension is lower. As a result of said difference in yarn tension, the droppers at the lateral ends of the warp yarn sheet will vibrate and possibly even jump more, compared to droppers in the more central parts of the warp yarn sheet. Such increased vibration may cause the warp yarns at the lateral part to be fluffered and even to break and/or the selvage to become irregular. Therefore, it is an object of the present invention to provide a device which permits adjustment of tension application time so that the warp yarns are tensioned at the right time for weft picking. According to the present invention this problem is solved by the teaching contained in claim 1. The depending claims are related to particular embodiments of the invention. The tensioning member of the device is operated to press on the opposite lateral ends of warp yarn sheet for each weft picking at a time which is selectably adjusted by the tension application time adjusting means according to the invention. The warp yarns at the lateral ends can be tensioned at the right time for weft picking. Thus, timed application of tension to warp yarns in accordance with lateral end of warp yarns the time of weft picking provides for smooth separation of warp yarns at the lateral ends, thereby to forming a shed opening without a delay. As a result, failure in weft picking due to inadequate shed opening is prevented successfully. It is another object of invention to decrease fluffering by vibrating in the lateral ends of the warp yarn sheet. According to the invention reducing the difference in tension in the warp thread in the open and the closed shed position is achieved by adjusting the time of pressing on the lateral ends of the warp yarn sheet according to the time of the shed is closing of the warp yarn sheet. This measure reduces vibration of droppers and fluffering and consequently warp yarn breaks considerably. Tensioning the warp yarn sheet according to the time, the shed is closing provides for increasing the tension of the lateral part of the warp yarn sheet. At the same time the difference in tension of the lateral part of the warp yarn sheet is limited between the open shed and the closed shed position of the warp sheet in the weaving cycle. It is apparent from the foregoing, that according to the invention, the time at which the tensioning member is operated to apply tension to opposite lateral ends of warp yarn sheet can be adjusted as desired in accordance with the time of weft picking or the time of closing and opening the warp yarn shed. Thus, timed application of tension to warp yarns in accordance with the time of picking can make possible smooth separation of warp yarns at the lateral ends thereby to form a shed opening without a delay. As a result, failure in weft picking due to inadequate shed opening can be prevented successfully. Timed application of tension to warp yarns in accordance with the closing of the shed basically reduces the differences of yarn tension in the weaving cycle. This difference makes possible a smooth separation of warp yarns at the lateral ends thereby to form a shed opening without a delay. As a result, failure in weft picking due to inadequate shed opening can be prevented successfully. The device for tensioning the warp yarns allows for tension by operation of the tensioning member to apply tension to opposite lateral ends of warp yarn sheet and can be adjusted as necessary and required in accordance with the time of weft picking. Thus, timed application of tension to warp yarns provide for smooth separation of warp yarns at the lateral ends, thereby forming a shed opening without a delay. As a result, failure in weft picking due to inadequate shed opening can be prevented successfully. Examples of the invention are described with reference to the schematic drawings. Fig. 1 to 9 show a first embodiment and Fig. 1A to 4A show another embodiment of the invention and details thereof; Fig. 1 and 1A is a schematic side view showing the warp yarn tensioning device in a weaving loom; Fig. 2 and 2A is perspective view showing the tensioning device of Fig. 1; Fig. 3 and 3A is a back view showing the tensioning device; Fig. 4 (a),(b) and (c) provide for sectional side views, showing the tensioning device in different operating positions; Fig. 4A (a),(b) and (c) provide for sectional side views, showing the tensioning device in different operating positions; Fig. 5 provides for diagrams showing shedding curves and a swing curve of the tensioning roller; Fig. 6 provides for a diagram, showing curves representing distributions of warp yarn tension; and Fig. 7 to 9 are sectional side views showing other embodiments of the present invention, respectively. Referring to Fig. 1 which is a schematic side view showing an embodiment of the device according to the present invention as applied to a jet loom, warp yarns T unwound from a warp beam 19 are moved over a back roller 1 and a easing roller 2 and further through respective warp break detectors 3 and healds 4, and then woven by a reed 5 into a fabric W which is wound by a take-up roll 6. References W₁ designates a cloth fell and N depicts a main picking nozzle which is swingable together with the reed 5. Referring to Fig. 2, the easing roller 2 is supported by and between a pair of easing levers 7A and 7B which are swingable about pivot shafts 8a and 8b, respectively. The easing levers 7A, 7B have connected thereto at the distal ends thereof a pair of rods 9A, 9B, which are in turn connected to crank mechanism (not shown). The crank mechanism operates in synchronism with the rotation of the loom so that the rods 9A, 9B make one stroke of reciprocating motion for one complete rotation of the loom. Support brackets 10A, 10B are fixed to the proximal ends of the respective easing levers 7A, 7B, and tensioning rollers 11A, 11B are cantilevered at one ends thereof to the support brackets 10A, 10B via connectors 12A, 12B. As shown in Figs. 1 and 3, the tensioning rollers 11A, 11B extend inward of the warp yarn sheet T and positioned at an angle with respect to a plane formed by warp yarn sheet T₁ between the back roller 1 and easing roller 2. The support brackets 10A, 10B have formed therein elongated holes 10a through which bolts 13A, 13B extend to be screwed into the connectors 12A, 12B. In the above arrangement, the connectors 12A, 12B are detachably fixed to the support brackets 10A, 10B by means of the bolts 13A, 13B. As shown in the sketches (a), (b) and (c) of Fig. 4, the elongated hole 10a extends in a direction across the warp yarn sheet T₁ between the back roller 1 and easing roller 2, thus permitting the tensioning rollers 11A, 11B to be positioned adjustably along the hole 10a, hence in a direction across the warp yarn sheet T₁. The sketches (a) (b) and (c) of Fig. 4 show the tensioning roller 11A which is positioned on the side adjacent to the main weft picking nozzle N. The tensioning roller 11A is swingable integrally together with the easing roller 2 about the pivotal shaft 8A. The same is true of the other tensioning roller 11B provided on the opposite side of the loom. Referring to Fig. 5, the curved lines C₁, C₂ show shedding curves of two alternating upper and lower arrays of warp yarns. The curved line C₃ shows a swing curve of the easing roller 2, and the curved line C₄ a swing curve of the tensioning roller 11A, respectively. Abscissa X for the swing curve C₄ represents the position where the tensioning roller 11A is placed just in contact with the warp yarn sheet T₁, and the swing curve C₄ represents the angle to which the tensioning roller 11A has swung from the above position X. In the lower diagram of Fig. 5, the area which is above the abscissa X shows the area in which the tensioning roller 11A is kept in contact with the warp yarn sheet T₁, while the area below the abscissa X shows the area in which the roller is clear of the warp yarn sheet. The sketch (a) of Fig. 4 shows the position of the easing roller 2 and the tensioning roller 11A, where the warp yarn shed is closed, and the sketsch (c) of the same figure shows the position of the easing roller 2 and the tensioning roller 11A, where the warp yarn shed is wide open. The sketch (b) of Fig. 4 shows the position where the tensioning roller 11A has been just moved into, or it is just about to move away from, contact engagement with the warp yarn sheet T₁. Thus, position of the tensioning roller 11A between the condition (a) and (b) of Fig. 4 correspond to the curved line C₄ in the area below the abscissa X in Fig. 5, and position of the tensioning roller 11A between the conditions (b) and (c) correspond to the curved line C₄ in the area above the abscissa X. As the warp yarn sheet T commences to form a shed opening by warp yarns, the tensioning rollers 11A commence to contact with the warp yarn sheet at the lateral end T L of the warp yarn sheet T which is adjacent to the weft picking main nozzle N and at the opposite lateral end T R thereof, respectively. A basic difference of the embodiments of the invention displayed in Fig. 1A, 2A, 3A and 4A (a), (b) and (c) is that the tensioning rollers 11A is moving the warp yarn sheet T away from the back roller 1 and the easing roller 2 and not against back roller 1 and easing roller 2 when the warp yarn sheet must be tensioned Referring to the diagram of Fig. 6, the curved line C₅ indicates the distrubution of warp yarn tension without use of the tensioning rollers 11A, 11B, as measured in the widthwise direction of the warp yarn sheet when the shed is open. The curved line C₆ shows the distribution of warp yarn tension when tension is applied by the tensioning rollers 11A, 11B. It is apparent from the diagram that smoothness in separation of warp yarns into upper and lower sheets at the lateral ends T L and T R can be improved by increasing the tension at such ends of the warp yarn sheet. In addition to such smooth separation of warp yarns, the time at which the tension is applied to the ends T L and T R by the tensioning rollers 11A, 11B can be adjusted so as to form the shed opening at the right time for weft picking. This is accomplished by adjusting the mounting position of the tensioning rollers 11A, 11B along the elongated holes 10a in the support brackets 10A, 10B with respect to the easing levers 7A, 7B in accordance with the weft picking time. In the above embodiment, since the warp yarn sheet at its lateral ends T L and T R will not be subjected constantly to high tension, there is no fear of warp yarn break due to constant application of high tension, as was observed in pior art device. The adjustment of the mounting position of the tensioning rollers 11A, 11B can be performed easily merely by moving the connectors 12A, 12B along the holes 10a in the support brackets 10A, 10B with the bolts 13A, 13B loosened. This adjustment will displace the curved line C₄ in Fig. 5 in upward or downward direction with reference to the abscissa X. According to this embodiment wherein the tensioning rollers 11A, 11B are caused to swing by the swinging motion of the existing easing levers 7A, 7B, no additional drive, hence no additional cost, is required. It is to be noted that the present invention is not limited to the above-described embodiment, but it may be practiced in other various ways, as exemplified by embodiments which are illustrated in Figs. 7 - 9. Referring to Fig. 7, there is provided an air cylinder 14 having a movable rod at the distal end of which is mounted a tensioning member 14a. The tensioning member 14a is moved by the air cylinder 14 to press on a lateral end of warp yarn sheet T₁ between the back roller 1 and easing roller 2. Operation of the air cylinder 14 is controlled by an electromagnetically operated valve (not shown) which is operable to be energized or deenergized at controlled times in response to the time of each weft picking. Thus, the time at which the tension is applied to the lateral ends of warp yarn sheet T₁ can be adusted as required, thereby permitting tension application at the right time for weft picking. In the embodiment shown in Fig. 8 which is applied to a weaving loom having no back roller, there is porvided an air cylinder 14 carrying a tensioning menber 14a which is movable to press on a lateral end of warp yarn sheet T between the easing roller 2 and warp stop bar 15. In the above embodiments shown in Figs. 7 and 8, the air cylinder 14 may be substituted with any suitable means such as electromagnetic solenoid. Referring then to Fig. 9 showing further embodiment of the invention, there is provided a lever 16 swingably supported by a pivotal shaft 20 and having at one end thereof a tensioning member 16a which is engageable with a lateral end of warp yarn sheet. The lever 16 is connected at the other end thereof via a rod 18 to a crank disk 17 which is in turn coupled to a drive of the loom. The end of the rod 18 remote from its connection with the lever 16 is adjustably connected to the crank disk 17 through an elongated hole 17 formed in the disk. Adjustment of the connecting position of the rod 18 to the crank disk 17 can permit timed application of tension by the tensioning member 16a to the lateral end of warp yarn sheet T. As it is apparent from the foregoing, that according to the invention, the time at which the tensioning member is operated to apply tension to opposite lateral ends of warp yarn sheet, can be adjusted as desired in accordance with the time of weft picking. Thus, timed application of tension to warp yarns can make possible smooth separation of warp yarns at the lateral ends thereby to form a shed opening without a delay. As a result, failure in weft picking due to inadequate shed opening can be prevented successfully. Tensioning rollers 11A, 11B; Tensioning time adjusting means including elongated holes 10a, connectors 12A, 12B and bolts 13A, 13B; warp yarn sheet T; Lateral ends of warp yarn sheet T L , T R . The device (9A,7A,10a,10b,11A) for tensioning the warp yarns (T) allows for tension by operation of the tensioning members (11A,11B) to apply tension to opposite lateral ends of warp yarn sheet and can be adjusted as necessary and required in accordance with the time of weft picking and/or the time of shed closing. Thus, timed application of tension to warp yarns at the time of picking provides for smooth separation of warp yarns at the lateral ends, thereby forming a shed opening without a delay. As a result, failure in weft picking due to inadequate and improper shed opening can be prevented successfully. The decrease of difference of tension in the open shed and the closed shed points in the weaving cycle reduces vibration of droppers and as a consequence also fluffering and even the number of breaks of warp threads (T).

Claims: Device for tensioning warp yarns in a weaving loom, comprising a warp yarn tensioning mechanism (9A,7A,8A) including a tensioning member (11A) for applying tension to opposite lateral ends (T L , T R ) of a sheet of warp yarns (T) by pressing on said lateral end portions, characterised in having time adjusting means for adjusting the time of pressing by said tensioning member (11A) on said lateral ends (T L , T R ) of the warp yarn sheet (T) according to a desired period of time, to reduce the difference in tension in the warp threads over the width of the warp yarn sheet (T) in a weaving cycle. Device for tensioning warp yarns according to claim 1, wherein the desired time of tensioning in the weaving cycle is correlated with and falls within the weft picking time. Device for tensioning warp yarns according to claim 1, wherein the desired time of tensioning in the weaving cycle is correlated with and falls within the time of shed closing of the warp yarn sheet (T). Device for tensioning warp yarns according to any of the claims 1 to 3 including a tensioning member (11A 11B) extending inward the warp and positioned at an angle with respect to the plane defined by the warp yarn sheet (T₁) in a way, that the increase of tension is highest at the most lateral part of the lateral end portion of the warp yarn sheet (T₁). Device for tensioning warp yarns according to any of claims 1 to 4, including actuating means driven with reference to the angle of rotation of the main shaft of the weaving loom. Device for tensioning warp yarns according to any of claims 1 to 5, including a pneumatic or hydraulic drive (14) for actuating the tensioning member (14a). Device for tensioning warp yarns according to any of claims 1 to 5, including a lever (16) swingably supported by a pivotal shaft (20) with the tensioning member (16a) fixed on one side of said lever (16).

Inventors: SHINBARA MASAMI C O K K TOYODA, SHINBARA, MASAMI, C/O K.K. TOYODA
Applicants: TOYODA AUTOMATIC LOOM WORKS, KABUSHIKI KAISHA TOYODA JIDOSHOKKI SEISAKUSHO
Application year: 1991
Main classification: D03D49
IPC codes: D03D49