Improved weft-thread transport unit for a needle-weaving loom

Abstract: A weft-thread transport unit for needle-weaving looms comprising an endless belt (1), trapezoidal in cross-section, fitted between a driver roller whose effective diameter is varied by two conical disks (2, 2') and an idler roller (4), the weft thread A being made to adhere to the belt (1) by means of a pressure element (9, 90, 90'). The two disks (2, 2') which comprise the driver roller are both axially mobile against the action of substantially equal elastic elements (12, 12') and the belt presents on the parts in contact with the rollers one or more blocking elements smaller than the width of the belt which are engaged by corresponding flanges on the external surfaces of the driver and idler rollers.

Description: The invention relates to a device for weft-thread transport on a textile loom and, in particular for a needle-weaving loom. More particularly, the present invention relates to an improved weft-thread transport unit on a needle-weaving loom, in which the weft thread is transported by a trapezoidal belt onto which the weft thread is pressed. A variable driver-roller whose effective diameter is determined by two conical disks, one of which is axially mobile, and at least one idler roller define the path of the endless belt. Because the effective diameter of the driving roller varies, bringing together or separating the driver-roller conical disks changes the forward speed of the belt. Weft-thread transport units using trapezoidal cross-section endless belts which run between a variable effective-diameter driver-roller and an idler roller have been known from Swiss Patent 565 879. According to an embodiment of that patent, the weft thread is made to adhere to the belt by means of a pressure roller which acts on a stretch of the belt between the driver-roller and the idler. The use of a trapezoidal belt subject to stresses, both of traction between the two rollers and of pressure from the weft-thread retaining roller, requires the cross-section area to be relatively large, thus preventing its use in cases where the belt must turn through a small radius of curvature. To overcome this drawback, the European Patent 0160 659 claims a device for thread-transport by means of an endless belt running between a variable effective-diameter driver-roller and an idler roller, onto which the weft thread is pressed by a roller which causes the endless belt to assume an S-shaped curve of small radius of curvature. The endless belt claimed in the cited Patent is fitted with a transverse web on at least one of its sides to permit the use of comparatively thin-section belts capable of accepting the pronounced curvature. The above-mentioned thread transport units present a further drawback in that the variation of the effective diameter of the driver-roller (caused by changing the axial separation of the conical disks) to increase or reduce the belt speed and, thus, the quantity of weft thread delivered, causes the belt to be subjected to a force perpendicular to the direction of advancement. Such a force renders the belt non-planar, since the planes of rotation of the center-sections of the driver-roller and the idler-roller no longer coincide. This can lead to greater wear on the belt and less reliability in obtaining the transmission ratios required and, consequently, the desired quantity of weft-thread transport. The device which is the object of the present invention is a weft-thread transport unit for needle-weaving looms which does not present the drawbacks complained of in devices known to the present art. The weft-thread transport unit for needle-weaving looms according to the present invention comprises an endless belt, trapezoidal in cross-section, fitted between a driver roller whose effective diameter is varied by two conical disks and an idler roller, the weft thread being made to adhere to the belt by means of a pressure element, characterized by the two disks which comprise the driver roller being both axially mobile against the action of substantially equal elastic elements and by the belt presenting on the parts in contact with the rollers one or more blocking elements smaller than the width of the belt which are engaged by corresponding flanges on the external surfaces of the driver and idler rollers. According to a first embodiment of the device according to the invention, the elastic elements which oppose the axial movement of the disks which comprise the driver roller comprise helical springs. According to a second embodiment of the device according to the invention, the blocking elements present on the belt comprise a groove running the entire length of the belt. According to a third embodiment of the device according to the invention, the blocking elements present on the belt comprise multiple parallel grooves running the entire length of the belt. According to a fourth embodiment of the device according to the invention, the belt presents, in addition to grooves along the entire length of the belt, other cutouts which reduce its rigidity. According to a fifth embodiment of the device according to the invention, the cutouts present on the belt are rectangular, elliptical, circular or herring-bone in shape. According to a sixth embodiment of the device according to the invention, the pressure element which acts on the weft thread to make it adhere to the belt and be transported by it comprises a roller which forces the belt against the idler roller. According to a seventh embodiment of the device according to the invention, the pressure element comprises a pair of rollers both acting on the stretch of belt around the idler roller at points which form an angle of between 60° and 180° with the idler roller center. The groove on the belt of the device according to the present invention may present various shapes in cross-section. It is important that at least one of these grooves have substantially the same cross-section as the corresponding flanges on the idler roller so that their engagement in the said groove will prevent any axial movement of the belt. The embodiment of the driver roller according to the invention with both conical disks mobile will maintain the position of the center-point between the two disks substantially unaltered on the roller axis. The combination of the substantially symmetrical displacement of the conical disks which constitute the driver roller with the groove on the belt into which the corresponding flanges on the idler roller fit, ensure no axial stress acts on the belt and so prevent any deformation of the same. The attached diagrams show some embodiments of the device according to the invention and its components, but they are by way of example and do not limit the scope of the invention. Figure 1 is a schematic side-view of the weft-thread transport device according to the invention with the driver roller set at its minimum diameter. Figure 2 is a side-view of the device of Fig. 1 with the driver roller set at its maximum diameter. Figure 3 is a side-view of the driver roller of the device of Fig. 1. Figure 4 is a side-view of the driver roller of the device of Fig. 2. Figure 5 is a schematic side-view of another embodiment of the weft-thread transport device in which the pressure element comprises a pair of rollers. Figures 6 to 9 show some forms of grooves in the belt used by the device according to the invention and of the corresponding teeth or flanges on the idler roller. The equivalent elements in the diagrams are identified by identical number references. Figs. 1 to 4 show the endless trapezoidal belt 1 which runs between the driver roller comprising the two conical disks 2 and 2' which move along the shaft 3 and the idler roller 4 provided with a flange 14' which engages with the corresponding groove in the belt (see figs. 6 to 9). The weft thread A is pressed against the belt 2 and the idler roller 4 by the pressure roller 9. The roller 6 rotates the screw rod 5, which actuates the rocker lever 7 on the pivot 8. The conical disks 2 and 2' which comprise the variable effective diameter driver roller are fitted to the shaft 3 and can move either separating or closing together along the said shaft 3 for substantially equal distances. Two springs 12 and 12' oppose the reciprocal separation of the two disks. In fig. 5 the system for pressing the weft thread against the belt and the idler roller is shown with a pair of pressure rollers 90 and 90' which give better consistency of transport of the weft thread. Figs. 6 to 9 show schematically, in plan and cross-section, some sections of belt 1 provided with one or more grooves 14 according to the invention and the corresponding idler roller profiles with their flanges 14' which engage the same grooves. Fig. 6 shows grooved belts where rectangular cutouts have also been removed to reduce the rigidity of the same belt; the cutouts are in three rows of which the center is the largest in area. In the belts shown in Fig. 7 the cutouts are elliptical or rectangular with the shorter side rounded. Fig. 8 shows circular cutouts in the belts. Fig. 9 shows elongated rectangular cutouts arranged in two rows forming a herring bone pattern. The weft-thread transport device operates in the following manner: The weft thread A is made to pass through a guiding eye 10 made from low-friction material, which is upstream of the transport unit and leads the thread across the traction section of the belt 1 which turns round the idler roller 4 fitted with the flange 14' which engages the groove 14 in the same belt. One or more pressure rollers 9, 90 or 90' are provided and kept in contact with the belt by one or more tension springs to keep the weft thread constantly adhering to the belt. The endless belt 1 runs between the two conical disks 2 and 2', which are kept under pressure and driven towards each other by the two helical springs, 12 and 12' fixed at their extremities by the locking elements 13 and 13'. The conical disks 2, 2', the springs 12,12' and the locking elements 13,13' are keyed onto the shaft 3 which is rotated by the loom motor (not shown) via a suitable gear ratio. Since the length of the belt 1 is fixed and the diameter of the idler roller is also fixed and invariable, the belt 1 will arrange itself around the roller comprising the two conical disks with an effective diameter which varies as a function of the separation of the roller formed by the two disks 2, 2' and the idler roller 4. Varying the effective diameter of the belt 1 turning round the driver roller 2, 2' will give different belt speeds and thus different quantities of weft thread transported. The quantity of thread transported is controlled by the roller 6 on the screw rod 5 turning in the lever 7 which pivots on the shaft 8. Each position of the lever has a corresponding distance between the driver roller 2, 2' and the idler roller 4, and a different effective diameter of the same driver roller 2, 2', which determines the quantity of thread delivered. Because the variation of the effective diameter of the driver roller comprising the two conical disks 2, 2' is achieved by a symmetrical separation or coming together of the two disks about a point equidistant from both, the axial displacement of the belt along the roller is substantially nil. The groove 14 on the belt 1 and the corresponding flange 14' on the idler roller contribute to the avoidance of any axial displacement and thus prevent any wear on the belt, so guaranteeing constant and efficient delivery of weft thread.

Claims: A weft-thread transport unit for needle-weaving looms comprising an endless belt (1), trapezoidal in cross-section, fitted between a driver roller whose effective diameter is varied by two conical disks (2, 2') and an idler roller (4), the weft thread A being made to adhere to the belt (1) by means of a pressure element (9, 90, 90'), characterized in that the two disks (2, 2') which comprise the driver roller are both axially mobile against the action of substantially equal elastic elements (12, 12') and that the belt presents on the parts in contact with the rollers one or more blocking elements smaller than the width of the belt which are engaged by corresponding flanges on the external surfaces of the driver and idler rollers. A weft-thread transport unit for needle-weaving looms according to Claim 1, characterized in that the equal elastic elements (12, 12') which oppose the axial movement of the disks (2, 2') which comprise the driver roller are helical springs. A weft-thread transport unit for needle-weaving looms according to Claim 1 or 2, characterized in that the blocking elements on the belt comprise a groove running the entire length of the belt. A weft-thread transport unit for needle-weaving looms according to Claim 1 or 2, characterized in that the blocking elements on the belt comprise a plurality of parallel grooves. A weft-thread transport unit for needle-weaving looms according to Claim 1 or 4, characterized in that the belt comprises other cutouts which reduce its rigidity in addition to the plurality of grooves running its full length. A weft-thread transport unit for needle-weaving looms according to Claim 5, characterized in that the cutouts on the belt are square, rectangular, elliptical, circular or herring bone in shape. A weft-thread transport unit for needle-weaving looms according to Claims 1 to 6, characterized in that the pressure element (9) which acts on the weft thread to make it adhere to the belt (1) and be transported by it comprises a roller which forces the belt against the idler roller. A weft-thread transport unit for needle-weaving looms according to Claims 1 to 6, characterized in that the pressure element comprise a pair of rollers which act on the stretch of belt that turns around the idler roller at points which form an angle of between 60° and 180° with the idler roller center.

Inventors: PRODI PAOLO, VILLA MARCO, PRODI, PAOLO, VILLA, MARCO
Applicants: COMAT S R L, COMAT S.R.L.
Application year: 1998
Main classification: D03D47
IPC codes: B65H51, D03D47