WO1994024356A1

WO1994024356A1 - A fabric stretching frame

Info

Publication number: WO1994024356A1
Application number: PCT/AU1994/000191
Authority: WO
Inventors: Peter Leonard Aubourg; Robert Gabor Pongrass; William Brian Wilson
Original assignee: Wilcom Tufting Pty. Ltd.
Priority date: 1993-04-16
Filing date: 1994-04-15
Publication date: 1994-10-27

Abstract

A tufting frame, comprising: four beams of fixed lengths arranged to form the periphery of the frame to define a rectangular working area within the frame, and onto which backing material is, in use, attached to be tensioned for tufting; and four expansion mechanisms interconnecting the adjacent ends of respective pairs of beams, and each operable to drive both the associated beam ends in opposed directions away from each other to tension the backing material for tufting; the arrangement being such that equal operation of all four expansion mechanisms will enlarge the area bounded by the beams and result in each beam being positioned parallel to its starting position.

Description

"A Fabric Stretching Frame"

TECHNICAL FIELD

Tufting is the process of inserting fibre tufts into a backing material to make carpets, rugs, wall hangings and similar articles. This invention concerns a tufting frame on which the backing material is tensioned to enable tufting to be carried out.

BACKGROUND OF THE INVENTION

Currently in tufting the backing material, made up of orthogonal warp and weft yarns, will typically be laid across a fixed frame and attached to a line of sharp pins around the edges. Small sections of the backing material are then pulled out, either by hand or using a hand held claw and lever, in order to tension the material to a degree suitable for tufting. The backing material can then react against the tufting needle with sufficient force for the needle carrying the tufts to penetrate it. The tension on the backing material is maintained by the pins which hold individual yarns. It follows that in order to increase the tension on the backing, it must be pulled so that the pins engage another yarn in the backing. The minimum increase in tension that is obtainable is that produced by stretching the backing material so that the pins engage the next yarn. This stepwise increase in the tension limits the accuracy with which the tension can be set.

In order to increase the tension by even one increment the backing must be stretched much further than the distance between two yarns. Typically, the backing must be pulled out about ten yarn spacings to hook onto the next yarn. As a result the tension in the backing is far higher while it is being pulled than is the final tension.

Manually stretching the backing material is time consuming and requires hard physical labour because of the high tension required. The resulting stretched backing material will often not be stretched to a consistent even tension, but will often vary in tension and have localised soft spots particularly around the edges and near the corners. Furthermore the warp and weft of the backing material will often not be maintained straight and orthogonal over its entire area. In particular scallops will form along the edges, emanating from the pins where the yarns have been unevenly stretched. When backing material is manually tufted the skill and strength of the operator is employed to compensate for any irregularities in the tensioning of the backing material. In an automated tufting system, for instance as described in co-pending application PCT/AU92/00401, it has been found that irregularities in the stretched backing material can create tufting errors, or can exacerbate the effects of existing sources of error.

DESCRIPTION OF THE PRESENT INVENTION

The present invention provides a tufting frame, comprising: four beams of fixed lengths arranged to form the periphery of the frame to define a rectangular working area within the frame, and onto which backing material is, in use, attached to be tensioned for tufting; and four expansion mechanisms interconnecting the adjacent ends of respective pairs of beams, and each operable to drive both the associated beam ends in opposed directions away from each other to tension the backing material for tufting; the arrangement being such that equal operation of all four expansion mechanisms will enlarge the area bounded by the beams and result in each beam being positioned parallel to its starting position.

Outward movement of the beams increases the load on the attached backing material. This load is increased in a continuous fashion commensurate with the extent of the outward movement of the beams to create consistent even tension in the yarns of the backing material.

A further advantage is that, using the invention, it is possible to maintain the yarns in the backing material 'square' or orthogonal to each other as the backing is tensioned. 'Squareness' facilitates automation of the tufting process since it ensures that any offset in the tufts caused by local distortion in the backing material remains consistent and predictable. Since the stretching mechanism is intrinsic to the frame the frame is easily portable. A portable frame permits easy automation of the handling systems through all the processes involved in the production of tufted products since it is a rigid structure which is independent of the automatic tufting machine and of the size of the design contained within it.

A fully automated process using such a frame would require the unstructured backing material to be handled only once, when it is stretched on to the removable frame. After this task has been completed the removable frame is placed within the tufting system where it is automatically tufted. After tufting has taken place the frame may be removed from the tufting machine, freeing it for further tufting. Latex could be applied to the back of the tufts to fix them in place at a different location. The finishing, shearing and sculpting, processes could then be carried out away from the tufting machine while the tufted product is maintained under dimensional stability on the frame. If the tension in the backing relaxes during downstream processing it is able to be adjusted at any required time by operating the frame.

A further advantage that follows from incorporating the expansion mechanisms into the corners of the frame is that full access from both sides of the frame is maintained. This can be very useful in an automated system where double sided access may relieve the necessity to turn the frame around. The expansion mechanisms may drive the associated beam ends away from each other in opposed directions which ensure even tensioning in both orthogonal directions of the rectangular working area. For a square frame expansion mechanisms angled at 45° with respect to beam axes ensure even tensioning in both orthogonal directions. For rectangular frames it may be necessary to angle the expansion mechanisms to drive the beam ends in slightly different directions if the same tension in both orthogonal directions is an important requirement. The expansion mechanisms may include a sliding mechanism interconnecting each adjacent pair of beams, and screwjacks to regulate beam movement. The expansion mechanism may alternatively comprise a captured wedge, a pivoted jack, pneumatic cylinders or hydraulic cylinders to regulate beam movement.

The use of the invention also facilitates creation of an accurate tension in the backing material. The tension must be high enough for the tufting process to be efficiently effected, but must not be too high. If the yarns are tensioned to too great an extent the yarns may close too quickly as the tufting needle is withdrawn and grip the tufting yarn too soon in the operational cycle. An overstrung backing material may also exacerbate the offset errors.

The tufting frame may also comprise a mechanism to measure the tension in the backing material. The tension measuring mechanism may comprise a bridge which spans the frame, a device to apply a load to the backing material, and a device to measure the deflection of the backing material.

The beams of the frame and the expansion mechanisms are required to be very strong in order to be stiff under torsion and bending. The load on the beams is high, in tufting typically greater than one tonne, and the frame must not deflect significantly under this load and yet must still be portable for use in mass production. Should it be necessary, for example, where the backing material has been incorrectly set, the beams may be moved individually or in combination in order to achieve correct tension.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will now be described by way of example only with reference to the accompanying drawings, in which: figure la is a schematic plan view of a tufting frame embodying the present invention, figure lb is a section of a beam of the frame of figure la taken along the line IB-IB, figure lc is a revealed detail of the sliding inter-relationship between two beams of the frame of figure la, figure Id is a revealed detail of the stretch mechanism at one corner of the frame shown in figure la; figure 2 is a detail of an alternative embodiment of the present invention; figure 3 is a detail of another alternative embodiment of the present invention; figure 4a is a schematic illustration of a load measuring mechanism applied to an embodiment of the present invention when the backing material is loose; and figure 4b is a detail of the mechanism of figure 4a when the backing material has been tightened or stretched.

BEST MODES FOR CARRYING OUT THE INVENTION

Referring now to figures la and lb tufting frame 1 comprises four beams 2, 3, 4 and 5 arranged in a rectangle. The beams have a box-section for lightness and strength, and include a row of pins 6 mounted on their upper surface. The pins may conveniently be provided by a carpet edging strip 7, in which case a double row of pins 8 and 9 are provided as shown in figure lb. The beams are interconnected at their ends by expansion mechanisms 10. The expansion mechanisms are housed in heavy metal cases 11 to provide torsional rigidity to the corners of the frame, and each have an adjustment handle 12, the operation of which will be described in more detail below.

The expansion mechanisms 10 are operated to drive the beam ends together and apart, and to drive them in predetermined opposed directions. In the embodiment shown in figures lc and Id the opposed directions in which the beam ends are able to move are determined by a slider 12 which extends from one of the beams at each corner, and which is slidably received in a socket 13 in the other of the beams of each corner; see figure lc. Slider 12 and socket 13 are angled at 45° to the axes of their respective beams in this embodiment. Other angles are of course possible to ensure even stretching. The ends of beams 2 and 3 also include respective lugs 14 and 15 at right angles to slider 12 and socket 13 so that a screwjack can be mounted to drive the beam ends.

The screwjack will now be described with greater detail with reference to figure Id. Housing 11 is fixed to beam 3, and is slidably attached to beam 2 by means of nuts and bolts 16 and 17 which ride in slots within the housing 11. A threaded shank 18 is bolted to lug 14 of beam 2 by means of lock bolts 19 and 20. Threaded shank 18 is able to travel through threaded holes in lugs 15 and 21 as it is rotated by means of nut 22. In this way rotation of nut 22 drives beams 2 and 3 apart and together.

In use, a backing material (not shown) is laid across frame 1 and attached to the rows of pins 6 with minimal tension. The centres of each side of the backing is usually aligned with centre marks along the sides of the beams. The yarns of the backing material are then manually adjusted to make it square with the frame. This is done by adjusting the yarns on each beam to line up with a string line, or some other convenient datum such as the edge of the frame. The screwjacks are then operated to drive the beams outwards and stretch the backing material to the correct tension. The jacks are usually adjusted in turn by a small amount at a time in order to keep the beams square to each other as the load is applied.

The invention may be embodied in many other forms. For instance, as shown in figure 2, a wedge 23 may be captured between beams 2 and 3 and driven inwards and outwards by turning a nut 24 which draws a threaded shank 25 through a corner plate 26. The cooperating faces 27 of beams 2 and 3 and wedge 23 and include formations 27 to facilitate the wedging action, and caps 28 to ensure correct motion. In figure 3 a further embodiment is shown to comprise a pivot jack 29 which is driven in a similar way to the captured wedge of figure 2 (the same reference numerals have been used to refer to corresponding elements) . In this case the two legs 30 and 31 of pivoted jack 29 are pivoted at either end. Leg 30 is pivotally attached to beam 2 at pivot 32, leg 31 is pivotally attached to beam 3 at pivot 33, and legs 30 and 31 are pivotally attached to each other at pivot 34 to which one end of threaded shank 25 is also attached. In order to measure the tension in the backing material it is possible to use a tension measuring mechanism 35, such as is shown in figures 4a and 4b. The mechanism comprises a removable bridge 36 which spans two beams on opposite sides of frame 1. The mechanism also includes a deflecting device 37 which deflects the backing material 38, and a deflection measuring device.

In figures 4a and 4b the deflecting device 37 is shown schematically to comprise a spring loaded plunger 39, the shaft 40 of which extends through a hole 41 in the bridge. When the backing is untensioned, figure 4a, it is deflected away from bridge 36 easily. As it is tensioned, figure 4b, it becomes harder to deflect and is not deflected to the same extent. Stem 40 extends through hole 41 by an amount 42 which varies according to the degree of deflection and can be measured; most conveniently by gradations marked along stem 40. In this way the deflection of the backing material is measured in order to allow the correct tension to be gauged.

Claims

1. A tufting frame, comprising: four beams of fixed lengths arranged to form the periphery of the frame to define a rectangular working area within the frame, and onto which backing material is, in use, attached to be tensioned for tufting; and four expansion mechanisms interconnecting the adjacent ends of respective pairs of beams, and each operable to drive both the associated beam ends in opposed directions away from each other to tension the backing material for tufting; the arrangement being such that equal operation of all four expansion mechanisms will enlarge the area bounded by the beams and result in each beam being positioned parallel to its starting position.

2. A tufting frame according to claim 1, wherein the expansion mechanisms drive the associated beam ends away from each other in opposed directions which ensure the same proportional extension in both orthogonal directions of the rectangular working area.

3. A tufting frame according to claim 1 or 2, wherein the expansion mechanism includes a sliding mechanism interconnecting each adjacent pair of beams ends permitting relative movement between them.

4. A tufting frame according to claim 3, wherein the expansion mechanism also includes screwjacks to regulate beam end movement.

5. A tufting frame according to claim 1 or 2, wherein the expansion mechanism includes captured wedges to regulate beam end movement.

6. A tufting frame according to claim 1 or 2, wherein the expansion mechanism includes pivoted jacks to regulate beam end movement.

7. A tufting frame according to claim 1 or 2, wherein the expansion mechanism includes pneumatic or hydraulic cylinders to regulate beam end movement.

8. A tufting frame according to any preceding claim, further comprising a mechanism to measure the tension in the backing material.

9. A tufting frame according to claim 8, wherein the tension measuring mechanism comprises a bridge which spans the frame, a device to deflect the backing material, and a device to measure the deflection of the backing material.