A yarn feed assembly for a tufting machine is known in GB 2,176, 811. This discloses an arrangement for varying the rotational speed of a plurality of yarn feed rollers, thereby producing variable yarn tension, and hence variable pile height.

GB 2,176, 811 discloses a maximum of three drive shafts, all of which are rotatable at different speeds. Each drive shaft has a number of clutches, one for each yarn roller that it is driving. The drive rollers are linked together by a series of gears, such that, when a particular drive shaft is coupled via its clutch to drive the yarn rollers, their rotational motion is transmitted through all of the gears to the yarn feed roller.

In the case of the arrangement with three drive shafts shown in GB 2,176, 811, the rotational motion from the drive shaft furthest from the yarn rollers is transmitted through the gears of the two other drive shafts prior to driving the yarn roller. This introduces problems with backlash between the various gear elements which limits the accuracy of the pile height control, and the speed at which the machine can switch from one pile height to another. In practice, this limits the number of different drive shafts which can be used, thereby limiting the number of different pile heights that a machine can produce.

A number of other prior art documents disclose yarn feed assemblies which have a number of draft shafts each of which are driven at different speeds, but which do not require the motion of one drive shaft to be driven via the gears of the others. These documents include GB 1319601, GB 1531445, GB 1595219 and US 3,847, 098. However, each of these arrangements require a complex linkage to connect each yarn feed roller, the clutch assembly and the drive shaft.

Such complexity increases the cost of the machine and the space required to accommodate various components. Further, the complex linkage can cause problems with backlash similar to those referred to above.

According to the present invention there is provided a yarn feed assembly for a tufting machine, the assembly comprising a plurality of drive shafts, a plurality of yarn feed rollers, and a clutch assembly to selectively couple a yarn feed roller directly to a drive shaft, the clutch assembly being directly between the yarn feed roller and the drive shaft with no intervening components.

By arranging each clutch to provide a direct coupling between the yarn feed roller and the drive shaft with no intervening components, the problem of accumulated backlash when a plurality of drive shafts or a complex linkage mechanism are used does not arise. The invention therefore allows faster and more accurate switching between different pile heights. Further, as the accumulated backlash problem has been eliminated and the construction simplified, the number of drive shafts which can be provided can be increased. In practice, five drive rollers are contemplated as this will give sufficient flexibility to handle all

practical patterning requirements. However, six or more drive rollers can be provided if necessary. As the mass of the rotating components is reduced, the machine can operate more efficiently.

GB 2,176, 811 is set up so that the clutches are packaged with the drive shafts and are away from the yarn feed rollers. In the case of a clutch failure, it is necessary to remove the entire section of drive roller on which the clutch to be removed is positioned.

According to a preferred example of the present invention, the yarn feed roller and its associated clutches are mounted on a sub-assembly, the sub-assembly being removably attached to a yarn feed assembly housing such that it can be removed and replaced without disturbing the drive shafts. Thus, the component which is removed and replaced is simpler than the removable components of GB 2,176, 811.

It is envisaged that spare yarn feed roller and clutch sub- assemblies will be supplied with the machine, such that a removed sub-assembly can simply be replaced by a spare while the removed sub-assembly is repaired. The sub-assemblies are preferably attached to the housing with a plurality of bolts. This provides a secure, but quickly releaseable coupling.

Another problem which arises in GB 2,176, 811 is that the clutch assemblies are rotatably mounted on the drive shafts. Therefore, brushes are required in order to provide power to the clutches. The present invention provides the possibility that each clutch can have a non-rotatable

stator. This removes the need for a brush connection hence improving reliability and reducing maintenance.

Each drive roller may be driven at a single speed.

However, preferably, the assembly further comprises means for varying the speed of at least one of the drive rollers.

This means may be a servo-motor and may be applied to all of the drive rollers. The ability to vary the speed of one or more drive rollers allows additional patterning effects to be achieved. Thus, at any one time, the number of different pile heights available for a stitch is equal to the number of drive rollers. However, if the speed of one or more of the drive rollers can be varied, the speed of the drive rollers can be changed between stitches, such that a different set of speeds may be available for the next set of stitches. Further, by gradually ramping up or down the speed of a particular drive roller to which a yarn feed roller is coupled, a slow increase or decrease in pile height can be achieved.

An example of a yarn feed assembly in accordance with the present invention will now be described with reference to the accompanying drawings, in which: Fig. 1 is a cross-section through a tufting machine showing the drive rollers and one pair of yarn rollers; Fig. 2 is a cross-section through line II-II in Fig. 1; and Fig. 3 is an enlarged cross-section of the clutch assembly as shown in Fig. 2.

The yarn feed assembly of the present invention is mounted to a conventional tufting machine, details of which are well known and will not be described here.

The yarn feed assembly comprises five drive rollers 1 which extend laterally across the tufting machine. Each drive shaft is split into a number of segments each supported at either end by brackets 2 to span the full width of the machine. Each drive shaft 1 is driven by a servo- motor (not shown) allowing its speed to be varied from one stitch to the next.

A plurality of yarn feed roller assemblies 3 are arranged across the machine. Three such assemblies are shown in Fig. 2.

Each yarn feed roller assembly comprises a yarn feed roller 4 and auxiliary yarn feed roller 5. These are both rotatably mounted to a plate 6 around respective axles 7, 8.

As will be appreciated from Fig. 2, each plate 6 carries one set of yarn feed rollers 4 and auxiliary yarn feed rollers 5 on one side and a second set as a mirror image on the opposite side. The yarn feed roller 4 and auxiliary yarn feed roller 5 have gear teeth 9 which intermesh with one another. Yarns Y (in practice there will typically be around 16 yarns per set of rollers 4,5) are wound around yarn engaging surfaces 10 on the rollers 4,5.

Also mounted on the plate 6 are a plurality of clutches 11 which are shown in detail in Fig. 3. For every yarn feed roller assembly, there is one clutch for each drive shaft 1

as shown in Figs. 1 and 2. The clutches provide a way of selectively coupling each yarn feed roller 4 with a respective drive shaft 1. As all of the drive shafts 1 rotate at different speeds, this causes the speed of the yarn feed roller to be varied thereby varying the pie height.

The clutches will now be described with reference to Fig. 2. The clutch essentially comprises three sections, a static part fixed with respect to the plate 6, a part rotatable with the drive shaft 1, and part rotatable with the yarn feed roller 4 as set out in detail below.

The static section comprises an axle 12 fixed to the plate 6. Also fixed with respect to the plate 6 is a stator comprising windings (not shown) as is well known in the art.

The section rotatable with the drive shaft 1 comprises a drive gear 14 having teeth 15 which mesh with corresponding teeth on the drive shaft 1. The drive gear 14 is fixed to rotor 16 which is supported on bushes 17 between the axle 12 and stator 13.

The section which is rotatable with the yarn feed roller 4 comprises a transfer gear 18 with teeth 19 which mesh with the teeth 9 on the yarn feed roller 4. The transfer gear has an armature plate 20 which is selectively attracted to the stator. This causes the transfer gear 20 to rotate together with the drive gear 14 so that the rotary motion of the particular drive shaft 1 is transmitted to the yarn feed roller 4.

As is apparent from Fig. 3, a second clutch assembly is provided on the opposite side of the plate 6 as a mirror image of the first clutch assembly to provide a selective coupling to the yarn feed roller set on the other side of the plate 6.

Returning now to Fig. 1, it can be seen that the drive rollers 1 are mounted on a frame 30. The plate 6 is provided with a pair of bolts 31 fixing the sub-assembly comprising the yarn feed roller 4, auxiliary yarn feed roller 5 and clutches 11 in place so that the drive gear 40 engages with the drive shaft 1. As can be seen from Fig. 1, if a clutch 11 or roller 4,5 require replacement, this can be done by undoing bolts 31, removing the sub-assembly with the plate 6 and either replacing it with a spare sub- assembly, or repairing and replacing the original one. As this is done without disturbing the drive rollers 1, and can be achieved only by undoing some very simple couplings, the downtime of the machine is minimal.