Method and device for sewing machine

Abstract

A sewing machine for stitching thread with several colors according to a sewing pattern stored in the form of stitch data in a memory, where the thread is dyed by a mechanism for dyeing the thread and where the upper thread is fed to a needle by a thread feeder. The thread consumption per stitch is calculated by a control unit from the data. The thread feeder is controlled by the control unit so that for each step it advances the calculated thread consumption for the stitch. A thread consumption for the quantity of stitches which according to the sewing pattern remains between the sewing material and the next color change for the upper thread in the sewing pattern is calculated by the control unit, whereupon the dyeing mechanism is controlled by the control unit to initiate the dyeing of the upper thread with the next color at a time when the calculated thread consumption is equal to the length corresponding to the length of the actual upper thread remaining between the sewing material and the dyeing point in the dyeing mechanism.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a diagrammatic sketch with a front view of a sewing machine with thread feeder and dyeing mechanism for the upper thread.

FIG. 2 shows a diagrammatic sketch from the side of a sewing machine according to FIG. 1 showing the upper and lower positions of the thread take-up lever, via which the stroke length is illustrated, and where furthermore the shuttle with gripper arm and thread loop are depicted below the sewing table.

FIG. 3 shows diagrammatically a thread feeder which feeds the upper thread through rollers that are driven by a motor which in turn is controlled by a processor.

FIG. 4 shows in perspective an example of drive of the upper thread through the said rollers.

FIG. 5 shows various alternatives for positioning of the knot for a straight seam in relation to the thickness of the fabric.

FIG. 6 shows various alternatives for positioning of the knot on a zigzag seam in relation to the height of the knot in the fabric.

FIG. 7 shows a comparison between different positions of the knot in relation to the fabric on a zigzag seam.

FIG. 8 shows a comparison between different positions of the knot in relation to the fabric on a zigzag seam where the stitch is viewed from the underside.

FIG. 9 shows a simplified block diagram of essential elements in the sewing machine concerned by the present invention.

FIG. 10 shows a flow diagram with the sequence of events on thread dyeing according to an example embodiment of the invention.

FIG. 11 shows a tight zigzag seam with a colour change performed where a cut has been used. The upper picture shows the underside, where it is evident that the colour change does not perfectly correlate with the point where the cut was performed.

DESCRIPTION OF THE METHOD

To implement the invention, a number of embodiments will be described below based on the enclosed drawings.

FIG. 1 shows symbolically a sewing machine 1 where in the known manner a sewing material 2 (in the description below, the sewing material 2 is referred to as a fabric) is fed between an under thread 3 and an upper thread 4 to produce a seam which is constructed of the desired stitches by means of a needle 5 which is periodically passed through the fabric 2. The fabric 2 in the example is guided over a sewing table 6 which also holds a spool 7 for the under thread 3 encapsulated in a shuttle 8. The upper thread 4 is guided through a take-up lever 9 which through an up and down cyclic movement creates a loop 10 in the upper thread 4 when the needle 5, through the eye of which the upper thread runs, carries the upper thread through the fabric 2, and the take-up lever 9 turns back up from its lowest position. A gripper arm 11 hooks into the loop 10 when the shuttle 8 rotates. To produce a stitch, in this case a lockstitch, the needle 5 is moved in an up and down movement so that the needle 5 carries the upper thread 4 down through the fabric 2, whereupon the shuttle 8 guides the upper thread 4 around the spool 7 which houses the under thread 3, creating a knot in the fabric 2 when the needle 5 has passed back up through the fabric and the take-up lever 9 has tightened the knot in the stitch.

The upper thread 4 is fed via a thread feeder 13 which distributes the thread to the take-up lever 9 via a thread feed spring 14.

The machine includes a control program which e.g. is stored in a processor C. The control program receives information on the position of the take-up lever 9 and the needle 5 in the cyclic stitching process. It is known within the art to pre-determine the consumption of thread per stitch by calculating stitching parameters for the stitch currently used in a particular seam. Such a calculated and hence pre-determined thread consumption per stitch is performed in the processor of the sewing machine according to the invention and constitutes the basis for the feed by a motor M (see FIG. 3) which implements the thread feed.

FIG. 3 shows diagrammatically a thread feeder 13 controlled via processor C. Input data in the form of control parameters to the processor C in the figure are shown in the illustration as an arrow which points in to the processor. The processor C is furthermore designed to control a stepper motor M which is mechanically coupled to three drive rollers R1, R2, R3 via a gear mechanism marked in the figure as 20. Here we describe one embodiment where the motor M is constituted by a stepper motor but other types of drive element controlled in other ways than through stepping can be used if applicable. The upper thread 4 is guided between the rollers R1, R2, R3, whereupon the stepping of the motor M means that the upper thread 4 is fed forward to the needle 5. The quantity of thread advanced is determined by the number of steps by which the motor moves. The upper thread 4 is advanced when the motor steps in the forward direction marked F. The feed is intended to be controlled depending on the type of stitch, thread thickness, fabric etc. The number of steps by which the motor is driven forward during a stitch is mainly controlled by the calculated value for the feed of thread required.

FIG. 1 shows a dyeing mechanism 15 for dyeing the upper thread 4 with the desired colour. The dyeing mechanism 15 dyes the thread in synchrony with the movement of the thread. Suitable elements for dyeing can be an ink jet cartridge or spray unit which applies one or more dye components to the thread. These dye components are suitably yellow, magenta, cyan and black. By varying the quantity of said individual dye components, the desired colour of the upper thread 4 can be achieved. After the thread has been dyed, it passes through a drying station 16 where the dye is dried and hardened e.g. with hot air. Dyeing devices of different types are used within the art. One example of such a dyeing device is shown e.g. in specification U.S. Pat. No. 6,189,989 cited above. In the description below the term dyer is used, which stands for the dyeing mechanism 15.

The function for the dyeing process is described in conjunction with the figures below. A thread store 17 exemplified by a thread bobbin in FIG. 1 provides the upper thread 4 for sewing. The upper thread is guided to the dyer 15 after first passing through a thread brake 18 which gives the upper thread a thread tension of the order corresponding to 5 grammes. The thread tension is required to hold the thread taut during dyeing in the dyer 15.

The upper thread 4 in the dyer passes one or more dye cartridges Ye, Ma, Cy, Bl (see FIG. 9) which spray or spread dye on the upper thread according to the colour data in the stitching pattern loaded in the memory. The dye cartridges contain dye for the said dye components. The upper thread is pulled by the thread feeder 13 through the said devices, from the thread store 17, through the thread brake 18, dyer 15 and drying station 16 where the thread feeder 13 for each stitch pulls (or feeds) the thread quantity used in the stitch concerned. FIG. 9 shows that the thread passes the dye cartridges in the order Bl, Cy, Ma, Ye. In the description given Bl corresponds to dye cartridge 1, Cy dye cartridge 2, Ma dye cartridge 3 and finally Ye dye cartridge 4.

The processor C controls both the thread feeder 13 and the dyer 15 so the upper thread receives the right quantity of the dye component concerned per length unit. The thread feeder 13 comprises in this example a thread portioner i.e. a device which portions the thread. The thread portioner 13 is driven, as cited in the example, by a stepper motor where a thread length r per step performed by the motor is given. As an example a thread portioner can be considered which advances the thread length r=0.4 mm per stepper motor step. From colour data according to the sewing pattern, information is obtained on the quantity of dye of a particular colour which is to be applied per length unit of the thread e.g. per mm thread. In the processor this can be converted to the quantity of the respective dye component which is to be applied per motor step of the thread. For each motor step of the stepper motor, the respective dye cartridge Ye, Ma, Cy, Bl in the dyer 15 applies the quantity of the respective dye component calculated from the sewing pattern (and hence according to the control unit) and which is required to achieve the definitive colour of the thread 4 after passing the dye cartridges in the dyer 15 (the quantity of dye calculated for a particular dye component can naturally also be nil). Thus the control unit can order the application of different quantities of the dye component concerned to the thread 4 for each motor step for a correct colour to be achieved on the definitively dyed thread. The processor in the control unit can e.g. calculate how many drops of dye should be sprayed by a dye cartridge for a particular dye component on the thread 4 per motor step. If the dye cartridges for different dye components are not placed at the same point along the thread 4, this fact must also be compensated by calculating the quantity of a dye component to be sprayed onto the thread and at which time this should be done. According to one example this can be achieved by the thread length between the dyeing point and the sewing material A (dye length) for different dye components being stored in particular in the control unit, by a respective dye component having a specific dyed length A, where this dyed length is then named yellow A_y, magenta A_m, cyan A_c, black A_b. The control unit thus performs a specific calculation of the quantity and time of the dye component depending on the dyed length A_y, A_m, A_c, A_b which applies to the sewing machine and the type of dyer 15 used.

On use of conventional thread tensioning washers with friction braking of the upper thread, the problem arises that the thread in this case is drawn out for a very small part of the time which elapses per stitch. The result is a very high top speed and acceleration of the thread 4, which causes great difficulty in controlling the dye quantity in synchrony with the thread advance. It is not specified precisely how much thread is drawn out in the stitch. Instead according to the invention by the use of the thread feeder 15 a more even, slower and more reliable advance of the upper thread 4 is achieved.

When sewing with the thread portioner, in the sewing machine control unit the thread consumption is calculated for each new stitch as a function amongst others of the stitch length, fabric thickness, seam direction and also where in the thickness of the sewing material the knot is designed to be placed. The stitch length is taken from stitch data in the sewing pattern. The thickness of the fabric is measured using the presser foot. If the sewing machine 1 is fitted with a so-called presser foot servo according to the prior art, this is used to provide information on the thickness of the fabric. Otherwise the thickness can be measured by means of a potentiometer coupled to a rod for the presser foot which gives a signal according to the height of the presser foot above the sewing table 6, where the said height constitutes a measure of the thickness of the sewing material. The seam direction and change in seam direction also affect the position of the knot in relation to the fabric 2. The knot location for a normal seam is in the centre of the fabric, which is illustrated on the straight seam R1 in FIG. 5 and the zigzag seam Z1 in FIG. 6. On embroidery, for example, it is desirable for the knot to remain on the underside of the fabric as shown for straight seam R2 in FIG. 5 and zigzag seam Z2 in FIG. 6. The reason for this is to avoid the risk of the under thread being visible from the top of the embroidery.

On thread dyeing according to the invention, the thread consumption for the entire sewing pattern can be calculated from the stitch data for the pattern. This is not necessary but according to the invention the thread consumption must be calculated so far in advance that the thread consumption in the sewing pattern corresponding at least to the dyed length A is known (or if required all lengths A_y, A_m, A_c, A_b as above). As stated, whenever the thread length used according to the pattern from a current stitch up to a colour change of the thread is equal to length A, the control program in the control unit orders a colour change on the thread and hence controls the cartridges for the dye components in order to create the colour which is current according to the stitching data for the new colour. When therefore the thread 4 which is after the length A in the sewing machine has been used, the sewing according to the pattern has progressed precisely to the point that it is ready for a stitch to be sewn with the thread dyed with the new colour after the colour change.

The thread portioner 13 also has the function of adjusting the advanced thread quantity if for some reason a situation occurs where the theoretically calculated thread quantity is not correct for a stitch. This can e.g. occur on embroidery where the upper thread 4 is drawn down below the fabric on severe changes in stitch direction such as e.g. on a seam as shown for example in a) in FIGS. 7 and 8. Such a correction of the thread usage in a stitch is described in the published specification US 2005/0223958 A1, the text of which as a whole is hereby incorporated in the present description. If on such a correction of the thread usage for one or more stitches in relation to the thread usage calculated by the sewing machine control unit, there is a colour change point on the upper thread 4 along length A i.e. along the part of the upper thread 4 which is between the dyer 15 and the fabric 2, the thread colour and stitch will not correspond to the pattern when the colour change point should reach the fabric 2 according to the control system based on the sewing pattern.

To achieve the object described in the preceding section, the control unit is programmed to compensate for the corrections made by the thread usage performed when a colour change point is located along length A.

To correct the thread consumption when the thread feeder has advanced more thread for one or more stitches (as shown for example in b) in FIGS. 7 and 8) than that calculated based on the sewing pattern, the thread quantity is continuously reduced for the said stitches as long as required. Conversely, if correction is performed when the thread feeder 13 has advanced less thread for one or more stitches (as shown in example c) in FIGS. 7 and 8) than calculated based on the sewing pattern, the thread quantity is continuously increased for these stitches as long as required. The calculations for this purpose are performed in the control unit.

On corrections of thread usage performed by the control unit in addition to the calculations according to the sewing pattern, if a colour change has not been carried out along the length A, instead the control unit is given data for these corrections performed to compensate for these corrections when determining the time of the future colour change. This means that the control is updated with corrections performed according to the description in the previous paragraph so that the remaining length of thread 4 with the colour currently being sewn by the machine is adjusted accordingly after the next colour change.

In certain situations e.g. if an embroidery or seam contains a large number of stitches with only small direction changes per stitch, it may be difficult to compensate for thread usage in the manner just described if it has been found that theoretical calculation of thread usage is not correct for a seam with a first colour. When such difficulties occur these are detected by the control unit. Detection is performed so that the control unit is programmed to recognise the type of seam which caused the said difficulties. On detection of such a difficult seam, the control unit provides a small quantity of extra thread (G/2), in this case 25 mm, for the first colour and the same amount for the second colour (25 mm) at the next change of colour at the dyer 15. When according to this sewing pattern the seam with the first colour is fully sewn, the upper thread 4, in this case and according to this embodiment, is drawn down by a device which hooks into the upper thread and draws this below the fabric where the upper thread is cut away. Here a thread quantity of approx 50 mm is used, whereby the downward drawn thread contains the colour change point. The said thread cutting constitutes known technology so the arrangement for thread cutting is not reported here. In the present invention where thread cutting is used in conjunction with a thread feeder 13 however, the control unit controls the thread feeder to feed the thread quantity required for cutting. By means of the method described it is ensured that the colour change is performed for the particular stitch at the seam even under the most difficult sewing conditions. The extra 25 mm given for the respective thread length or colour can, where applicable, be selected with a different value. The addition can also be machine-dependent.

The arrangement and method according to the invention are illustrated further with reference to a block diagram (FIG. 9) of the most important components of the sewing machine and by means of a flow diagram (FIG. 10) of the sequence of events when using thread dyeing.

The block diagram according to FIG. 9 shows in the centre of the figure the processor C of the sewing machine that controls the elements involved in the process for stitching and dyeing described in the text above. The processor C according to the example can constitute the control unit cited in the description. The fabric is stretched in a so-called embroidery frame symbolised in the figure by an X-Y unit. The embroidery frame is controlled to move the fabric in two coordinates, an x-direction and a y-direction. The drive is supplied by an X-motor for the x-direction and a Y-motor for the y-direction. Both motors are controlled by processor C following a sewing pattern. In the example the sewing pattern takes the form of data for the stitching in the embroidery read into a memory 20. Data for the stitching in the pattern can be separated and arranged in a separate data file in a stitch memory 21. Correspondingly data for the colours for the stitch concerned in the sewing pattern can be stored in a separate data file in a colour memory 22. Stitch data or colour data for the pattern currently in use is fed to the processor C to control the other elements in the process.

The processor C in the known manner also controls a main motor 23 in the sewing machine 1. For the operator's control of the main motor, a foot control 24 is arranged and connected to the processor C. In addition to the thread feeder 13, the drying station 16, thread brake 18 and thread store 17 described above, the dyer 15 is shown which is illustrated here as containing the dye cartridges Ye, Ma, Cy, Bl. The upper thread 4 passes through the dye spraying area of these cartridges. The dyeing point here is depicted with point P i.e. the point where the colour change of the upper thread is initiated, which point P in the example coincides with the dye application point on the upper thread for the first dye cartridge of the dye component. The figure also shows a thread feed spring 14 used to determine the time when the knot is made in a stitch. This information is sent to the processor whereupon the processor can initiate the advance of the thread for the next stitch. The take-up lever 9 has been shown symbolically.

A list of parameters used in the description, claims and figures is given below:

• A Thread length from dyeing nozzle no. 1 (at dyeing point P) to stitching point.
• G Addition to thread length when using cut to achieve precision at the colour change.
• L_n Thread length for stitch number n at the sewing point.
• S Remaining length of thread for the current stitch. At the start and cutting, A or G is seen respectively as a long stitch.
• i Counter for colour number at dyeing point P.
• j Counter for colour number at sewing point.
• k Counter for stitch number at sewing point.
• t A counter used to stop the machine after a few stitches after starting with a newly threaded machine so the user can cut away the starting ends.
• B_n Thread consumption for colour number n.
• F_n Addition to thread consumption for colour number n. F_n is equal to half G and is added to both B_n and B_n+1.
• r Thread length fed from the thread portioner for each motor step.
• E_n Distance from the first nozzle (in dye cartridge 1) to nozzle number n (in dye cartridge no. n) for the different dye components black, cyan, magenta, yellow, where in the example the dye cartridges (Bl, Cy, Ma, Ye) in the said order are given numbers 1 to 4.
• D The length of thread advanced after a colour change point on the thread has passed the first nozzle.
• P Dyeing point.

An example of an embodiment and order of priority for the various measures which lead to dyeing of the upper thread on a sewing machine according to one aspect of the invention is listed below based on the enclosed flow diagram according to FIG. 10. The flow diagram shows the respective steps taken with reference numbers from 30.

• 30. Start of a new embroidery or re-threading of a sewing machine.
• 31. Residual length S is set equal to A and all counters are set to 1. F₀ and D are zeroed.
• 32. The user is reminded to keep the thread taut in order to avoid unusable thread between the dyer and the sewing point.
• 33. An algorithm used in processor C calculates, from stitch data, data for the feed by the thread portioner 13 which is used to calculate thread consumption B1 for colour no. i.
• 34. Here the user has the opportunity to order a cut at all colour changes. If “yes”, an addition F_i is given to colour no. i according to step 35. F_i is equal to half G and is added to both B_i and B_i+1.
• 35. F_i is set equal to half the selected length G.
• 36. If in a seam with difficult conditions for example as described in paragraph [42], a cut is ordered, according to the program in the same way as by jump from step 34 to step 35.
• 37. The addition of thread length is set equal to 0, which is normal i.e. no cutting is performed.
• 38. An addition is made to remaining thread consumption B1 with the current value of F_i+F_i−1. This means that a thread quantity consumed on cutting is divided over the colour ahead of the cut and the colour behind the cut.
• 39. Is the remaining length S for the current stitch equal to 0? If so proceed at step 40.
• 40. Stitch counter for colour i t is increased with 1.
• 41. If the number of stitches sewn is set equal to 6, exit normal sequence; here the machine stops.
• 42. The user can cut away the excess thread, after which he returns to the main program at 43.
• 43. Condition for whether the current stitch is the last before colour j is tested. If so, proceed at step 44. If not, continue the programme at step 46.
• 44. Counter for j is increased with 1.
• 45. Check whether the addition for thread length Fj is equal to zero. If so, proceed with program in step 46.
• 46. The counter for k is incremented by 1. The remaining length S is equal to the stitch length for stitch k.
• 47. If the thread feeder 13, because of the risk of incorrect positioning of the knot in a seam, has been ordered to correct the thread consumption in one or more steps, the program proceeds with step 48.
• 48. Check whether the remaining thread consumption B1 for the current colour is less than or equal to length A.
• 49. If the answer is “yes” in step 48, the remaining length S is adjusted during a number of stitches until the remaining thread consumption B1 again corresponds to the calculation.
• 50. If the answer is “no” in step 48, B1 is corrected depending on the total corrections according to step 47.
• 51. If the answer to the check in step 45 is no, the remaining length S is set equal to the thread addition G.
• 52. A cut of the upper thread is initiated.
• 53. Await start signal for thread feed.
• 54. Thread feed motor runs one step according to the step table in the processor. Apply dye at all dye cartridges according to dye data during running with the stepper motor. D is increased by length r for a stepper motor step. S is reduced by r and the remaining thread consumption B1 for the current colour is reduced by r. For each step which the thread feeder 13 advances, dye is sprayed onto the thread. The number of dye drops or equivalent of the respective dye component is obtained from the dye data.
• 55. Here it is checked whether length D, i.e. the length for which the thread fed after a point for colour change on the thread has passed the nozzle in the first dye cartridge in the dyer 15, is equal to E₁ which is the distance between the first and second nozzles. As the colour change point passes the nozzle concerned, according to steps 55, 57, 59, dye data is changed for the nozzle concerned to the specified number of drops of dye (or equivalent) according to the next colour on the thread in steps 56, 58, 60.
• 56. If D=E₁, dye data for nozzle no. 2 is changed to dye data according to colour i+1.
• 57. Check whether length D is equal to E₂ which is the distance between the first and third nozzles.
• 58. If D=E₂, dye data for nozzle no. 3 is changed to dye data according to colour i+1.
• 59. Check whether distance D is equal to E₃ which is the distance between the first and fourth nozzles.
• 60. If D=E₃, dye data for nozzle no. 4 is changed to dye data according to colour i+1.
• 61. Check whether remaining thread consumption B₁ for the colour is equal to zero. If the answer is no, i.e. dyeing with the current colour is not concluded, the program is repeated from step 43.
• 62. Change of dyeing data for nozzle no. 1 to dyeing data according to colour i+1.

D is reset to zero. Return to program in step no. 33.

If a dyer 15 has all nozzles for the different dye components at the same point along the thread, this means only that distances E₁, E₂, E₃ are zero in the structure above.

In the claims, terms such as “containing” and “including” do not exclude the presence of other elements or steps. Furthermore, although not listed individually, a multiplicity of arrangements, elements or method steps can be implemented e.g. by the same unit. In addition, although individual features can be included in different patent claims, these can perhaps advantageously be combined and the inclusion in different claims does not mean that a combination of features is not suitable and/or advantageous. Furthermore singular references do not exclude plurality. Thus references to “one”, “first”, “second” etc. do not exclude a multiplicity of occurrences unless explicitly stipulated.

Definitions

The colour change point is the point on the upper thread which constitutes the border between two colours on a change of colour on the upper thread.

Dye is the fluid or equivalent applied to the thread.

Colour is the shade of the dye which is desired in the thread.

Thread length is the thread usage in a stitch.

When a distance to the sewing material is given, this is considered throughout the description to be the distance to the point on the sewing material where the current stitch is being sewn.

Claims

1. A sewing machine, comprising: a needle fitted with an upper thread,a drive element which drives the needle to perform an upward and downward movement to guide the upper thread through a sewing material which is fed between the upper thread and the under thread, so that the upper thread forms a loop below the sewing material,a shuttle which houses an under spool for the under thread,a gripper arm on the shuttle which hooks into the loop on the upper thread and guides the upper thread around the under spool so that a stitch is produced on the sewing material, anda take-up lever which at each stitch draws a knot which is formed in the sewing material by the upper thread and under thread in cooperation,a memory for storing stitch data for a sewing pattern,a thread feeder to feed upper thread to the needle,a control unit which from the data calculates the necessary thread consumption per stitch and thus controls the thread feeder,a function where the control unit in collaboration with the thread feeder adjusts the advanced thread quantity in relation to the theoretically calculated thread consumption,a mechanism for dyeing the upper thread where a color change for the thread dyeing is controlled by the control unit to be performed at a time when the calculated thread consumption in the quantity of stitches which according to the sewing pattern is present between the sewing material and the next color change in the sewing pattern, is equal to the length which corresponds to the length of the actual upper thread remaining between the sewing material and a dyeing point in the dyeing mechanism.

2. The sewing machine according to claim 1, wherein the stitching data comprises types of stitch, parameters for the stitch and the stitch color, whereby the control unit reads a stitch color from the stitch data.

3. The sewing machine according to claim 2, wherein the dyeing mechanism comprises dye cartridges for at least the dye components yellow, magenta and cyan.

4. The sewing machine according to claim 3, wherein the dyeing mechanism furthermore comprises a dye cartridge for a black dye component.

5. The sewing machine according to claim 3, wherein the thread feeder comprises a drive unit which feeds the upper thread in steps.

6. The sewing machine according to claim 5, wherein for each step during which the thread feeder advances the upper thread, a quantity calculated by the control unit of the respective dye component is applied to the upper thread by means of a dye cartridge associated with the dye component.

7. The sewing machine according to claim 6, wherein for each step during which the thread feeder advances the upper thread, a quantity calculated by the control unit of the black dye component is applied to the upper thread by means of a dye cartridge with black dye.

8. The sewing machine according to claim 1, wherein the function for adjusting thread quantity is implemented as a program in the control unit.

9. The sewing machine according to claim 1, wherein the sewing machine is fitted with a cutter device which is controlled by the control unit to draw down a pre-determined length of the upper thread under the sewing material and there perform a thread cut, wherein the length of upper thread drawn down contains the color change point.

10. A method for dyeing upper thread with a sewing machine which comprises: a needle fitted with an upper thread,a drive element which drives the needle to perform an upward and downward movement to guide the upper thread through a sewing material which is fed between the upper thread and the under thread, so that the upper thread forms a loop below the sewing material,a shuttle which houses an under spool for the under thread,a gripper arm on the shuttle which hooks into the loop on the upper thread and guides the upper thread around the under spool so that a stitch is produced on the sewing material, anda take-up lever which at each stitch draws a knot which is formed in the sewing material by the upper thread and under thread in cooperation,a memory for storing stitch data for a sewing pattern, anda mechanism for dyeing the upper thread,the method comprising:feeding the upper thread to the needle with a thread feeder,calculating a necessary thread consumption per stitch with a control unit from said data,the thread feeder is controlled by the control unit so that for each stitch it advances the calculated thread consumption for the stitch,a thread consumption for the quantity of stitches which according to the sewing pattern remains between the sewing material and the next color change for the upper thread in the sewing pattern is calculated by the control unit,the advanced thread quantity in relation to the theoretically calculated thread consumption is adjusted by the control unit in collaboration with the thread feeder,the dyeing mechanism is controlled by the control unit to initiate a dyeing of the upper thread with the next color at a time when the calculated thread consumption is equal to length corresponding to the length of the actual upper thread remaining between the sewing material and the dyeing point in the dyeing mechanism.

11. The method according to claim 10, wherein the color of a stitch is read from stitch data comprising data for the type of stitch, parameters for the stitch and the stitch color.

12. The method according to claim 11, wherein the dye cartridges apply at least any one of the dye components yellow, magenta, cyan and black to the upper thread.

13. The method according to claim 12, wherein the dye component concerned is applied at a time which is compensated for a difference between the said length A and length which corresponds to the length of the actual upper thread remaining between the sewing material and the dye cartridge corresponding to the dye component concerned in the dyeing mechanism.

14. The method according to claim 13, wherein the upper thread is advanced in steps by means of a drive unit in the thread feeder.

15. The method according to claim 14, wherein for each step during which the thread feeder advances the upper thread, a quantity calculated by the control unit of the respective dye component is applied to the upper thread by means of a dye cartridge associated with the dye component and thus a color change point is produced from which the upper thread is changed in color to the next color for the upper thread in the sewing pattern.

16. The method according to claim 10, further comprising: that when the thread consumption per stitch is corrected by the thread feeder by deviation from the data according to the sewing pattern, and a color change point at the same time is located along length A, the control unit is programmed to compensate for this by, for a specific time, feeding a greater or lesser quantity of thread per stitch than that calculated according to the sewing pattern.

17. The method according to claim 16, further comprising that compensation is performed in that: when the correction is made by advancing extra thread quantity, the thread quantity per stitch is reduced in relation to that previously calculated until the calculated thread quantity and actually fed thread quantity correspond again, orwhen the correction is made by advancing less thread quantity, the thread quantity per stitch is increased in relation to that previously calculated until the calculated thread quantity and actually fed thread quantity correspond again.

18. The method according to claim 10, further comprising: the control unit records that in the sewing material, a thread length with a first color of upper thread has a large number of stitches with only small direction changes,the control unit automatically adds a pre-determined length to the calculated thread consumption for the thread length with the first color,a corresponding extension of the calculated thread consumption for the subsequent thread length with a second color is performed by the control unit,a certain length of the upper thread around a color change point which is constituted by the border between the first and the second color on the upper thread is drawn down on stitching below the sewing material andat least a part of the upper thread drawn down is cut.