When a conventional, plain, straight sewing tufting machine is running, the amount of yarn required by each needle remains constant for each stitch in the tufted fabric produced on the machine. The yarn supply for each needle of the tufting machine is conventionally provided by yarn feed rollers which are geared directly to the machine mainshaft.

When a tufting machine is run using a sliding needlebar to produce a prescribed geometric stitch pattern, the length of yarn required per stitch varies stitch by stitch according to whether the stitch is sewn straight or at an angle by sliding the needlebar. If the correct length of yarn per stitch is not supplie then the face of the resulting tufted fabric can be uneven which is clearly undesirable.

Systems for providing yarn feed nominally matched to the usage requirements of a sliding needlebar stitch pattern are well known. None, however, work perfectly, partly due to the inability of drive systems to produce sufficient torque to accelerate or decelerate the yarn feed rollers at the required rate and partly because of insufficient versatility in the way that the yarn feed systems are controlled. An additional complication is that yarn characteristics such as twist, count regularity, stretch, friction, fibre content, tension and propagation characteristics, nominal time taken for a change in tension or other load on the yarn to be propagated from one end of the yarn to another vary widely and therefore different yarns require handling in different ways to obtain the desired length of yarn for a given stitch.

In an existing system the nominal length of yarn used in each type of stitch occurring within a pattern is calculated and stored in a computer.

Provision is also made to allow manual adjustment of the stored lengths.

These length values are used to control servo controlled drives which operate the yarn feed mechanism to provide the required length of yarn for each stitch in sequence. The end result in terms of levelness of the tufted fabric pile face obtained using this system is unsatisfactory due to both the ability to sufficiently control the prescription of the input of yarn by the yarn feed mechanism and also the ability of the drive system to respond to the prescription on a stitch by stitch basis at machine running speed.

The ability of the drive system to respond is addressed in our co-pending U. K. Patent Application No. 2297331-A which describes how the inertia of the drive system can be reduced.

It is an object of the present invention to provide an improved control system for the yarn feed systems of tufting machines which enables tufted fabric of level face to be produced by sliding needlebar machines.

According to a first aspect of the present invention there is provided a method of controlling a yarn feed system for a tufting machine wherein the method comprises selecting a length of yarn required for a particular stitch, selecting a starting time (as herein defined) to introduce the additional yarn (as herein defined) into the stitch, selecting a rate of supply of the additional yarn into the stitch.

By additional yarn is meant yarn over and above that which would be required for a straight sewn stitch.

By starting time is meant as the point in a stitch cycle at which additional yarn begins to be supplie into the stitch.

The present invention enables the variable drive of a yarn feed system to be controlled by way of three parameters. The first parameter, the length of additional yarn required per stitch, is specified by the length of yarn required for a particular stitch as in conventional systems. The two additional parameters allow adjustment of the feed start time of the additional yarn and the rate at which that additional yarn is supplied. Enabling control of these features of yarn supply enables fabrics with a good quality face to be produced even where extreme forms of sliding needlebar movement are used.

By specifying these three parameters it is possible to achieve optimum conditions for the feeding of a particular fabric, yarn type, and capability of the yarn feed drive system. This can be achieved by observing the quality of face of fabric produced and then adjusting one or more of the parameters accordingly.

The three parameters can be readily understood by tufting machine setters, whereby they can make appropriate adjustments to the yarn feed parameters to improve the quality of fabric produced. Such adjustment is not possible with existing equipment where only the yarn length per stitch is selected.

According to a second aspect of the present invention there is provided apparatus for controlling a yarn feed system for a tufting machine wherein the yarn feed system is controlled in dependence upon selected values of the length of yarn required for a particular stitch, the starting time (as herein defined) for additional yarn supply (as herein defined) and the rate of supply of the additional yarn.

The apparatus preferably comprises a computer which is arranged to calculate the appropriate control parameters, based on a particular fabric design. Provision to manually adjust each of the parameters is preferably also provided.

The apparatus preferably inclues a display means which may take the form of a computer monitor. The display means is preferably arranged to show a selection diagram which enables an operator to select the start point in the stitch cycle for the extra yarn input, and also the rate of the extra yarn input.

The apparatus of the present invention provides a convenient way for a machine operator to select the operational parameters of a yarn feed system for a tufting machine. The selection of the three above defined parameters gives an operator far more control over a yarn feed system than with conventional yarn feed system control equipment. This enables an improved fabric or carpet to be produced, particularly the control apparatus enables a fabric with a flat face to be produced by a sliding needlebar tufting machine.

In order that the invention be more clearly understood there is now described an embodiment thereof, by way of example, with reference to the accompanying drawing which illustrates an on screen selection diagram to facilitate selection of start point and yarn input rate.

Yarn feed control apparatus is provided by a computer. The computer serves a similar function as an existing pattern control computer used in conjunction with a tufting machine. The computer is arranged to convert any specific pattern of needle placement for a prescribed needle gauge and stitch rate along the fabric into a list of yarn control parameters. The yarn control parameters include a list of the required lengths of yarn, stitch by stitch, throughout the pattern, selectable yarn feed start times which specifies the point in a stitch cycle at which the yarn required, additional to that required to form a normal straight stitch, is introduced and selectable additional yarn introduction rates. These three parameters are used to control the operation of the servo-controlled drive of a yarn feed system.

There is also provided provision for manual adjustment of these parameters, to enable account to be taken of fabric type, condition etc.

Referring to the drawing there is illustrated an on screen selection diagram, displayed by the apparatus. The diagram comprises a yarn feed rate graph 1 and a yarn introduction curve 2.

The yarn feed rate graph represents along the horizontal axis 3 one stitch cycle. The vertical axis 4 represents the amount of additional yarn introduced. Ten possible yarn introduction rates 5 are illustrated, these may be selected by use of a cursor or inputting a number into the computer.

The yarn introduction curve 2 represents stitch cycles and illustrates the movement of a needle through one stitch cycle from its uppermost 6 to its lowest 7 position and return to the upper position 8. The point in the cycle at which the additional yarn is introduced is selected by positioning arrow 9 on the curve 2. The position of the arrow may be selected by use of cursor keys or a computer mouse.

In use the control apparatus would be provided with fabric pattern details and optionally, information regarding the yarn to be used from which the control parameters are calculated, at which point the control parameters may be manually revised. An operator would then operate a tufting machine in accordance with the control parameters to produce a sample length of fabric. Adjustments to the control parameters may then be made by the operator on the basis of the fabric sample to optimise the produced fabric.

The present invention allows more control to be exercised over the fabric feed to a tufting machine and enables improved carpets and fabrics to be produced. Control is exercised by three parameters which are well understood by persons skilled in the art and more particularly tufting machine operators and setters. This enables the machine operator to easily make adjustments to the machine control to rectify faults in and improve fabric production.

The above embodiment is described by way of example only, many variations are possible, without departing from the invention.