METHOD AND DEVICE FOR AUTOMATIC CUTTING OF DEFECTIVE FABRIC PARTS FROM A PATTERNED FABRIC

Description

Technical Field

[0001] The invention relates to the general field of automated cutting of pieces from a fabric with a repeating pattern at a certain interval, referred to as the pattern interval. More specifically, it concerns the handling of defective pieces, which will have flaws once cut from the fabric and will require recutting.

[0002] Areas of application for the invention include the clothing and furniture industries. Previous technique

[0003] When the production of clothing or furnishings involves assembling pieces cut from fabric, there are specific constraints if the fabric is patterned. "Patterned fabric" here refers to any flexible textile material in sheet form printed with a pattern that repeats at regular, predetermined intervals.

[0004] In this case, it is then desirable, or even necessary, to respect the continuity of the pattern between two assembled pieces, for example two parts of a garment sewn together, or two pieces intended to be adjacent, for example two parts of a garment located side by side when the garment is worn, or two cushions of a sofa placed side by side.

[0005] In order to comply with these constraints, it is known to associate absolute or relative position markers with the parts and to establish a hierarchy between primary and secondary parts.

[0006] An absolute position marker is normally associated with a main piece. It characterizes the absolute positioning of the main piece relative to the fabric pattern. The position of a piece relative to the pattern is characterized by the fact that a given point on the surface of the piece occupies a specific relative position with respect to the surrounding patterns. Thus, pieces whose positions on the fabric surface are derived from each other by translations of an integer number of pattern steps occupy the same position relative to the pattern.

[0007] Relative position markers are associated with two pieces that must be assembled, taking into account requirements related to the existence of the pattern. They identify the locations of two connecting points that must be aligned during the assembly of the pieces.

[0008] For example, in the case of a jacket, a back piece can be considered the main pattern piece. An absolute position marker may be associated with the back piece, for instance, when a complete pattern is desired to be visible in a specific location on that piece. A sleeve, the neckline, and the front then constitute secondary pattern pieces. For each of these, the location of a matching point is determined to correspond to the location of the associated matching point on the main pattern piece.

[0009] Furthermore, a piece associated with a relative position marker can also be the primary piece of one or more other pieces. In this case, it is referred to as a chain of links. Similarly, a piece can have an absolute, relative, or no position marker along the weft thread axis, and another type of position marker (relative, absolute, or no) along the warp thread axis of the fabric.

[0010] Furthermore, it is known that fabric cutting can be done automatically. Automatic cutting systems have been marketed by the applicant for many years.

[0011] Typically, an automated cutting process includes a placement operation that consists of optimally determining the positions of the pieces to be cut in a strip of fabric. The placement is chosen to minimize fabric waste while respecting certain constraints: maintaining the grain line, sufficient minimum margin between pieces, etc. In the case of patterned fabric, additional constraints related to respecting the positions of absolute and relative positioning marks are required. Systems allowing an operator to define placements using computer workstations and specialized software are available, including for patterned fabrics.

[0012] To perform the cutting, the fabric is spread on a cutting table in one or more overlapping layers, which can be held in place by suction across the table. The cut is made using a tool mounted on a head whose movements relative to the cutting table are controlled according to the predetermined position. The cut can be made using a vibrating blade, rotary blade, laser, water jet, etc.

[0013] Difficulties arise when using a patterned fabric. In particular, the problem of misalignment between the fabric template used for layout and the fabric actually laid out on the cutting table becomes a practical one. This misalignment manifests itself in the following way: if one positions oneself on the cutting table at the coordinates of a reference point on a layout piece, one observes that the corresponding point on the laid-out fabric does not always occupy the desired relative position with respect to the pattern on the actual fabric. These discrepancies vary in size and are practically unavoidable. They are due to printing defects, imperfections in fabric placement on the cutting table, variations in loom thread density, and / or fabric distortions that can result in irregularities in the pattern repeat.As a result, the pre-established placement, or theoretical placement, must be modified to correspond to the reality of the spread tissue.

[0014] A method for automatically adjusting the pattern placement is described in EP 0,759,708, filed on behalf of the applicant, and forms the basis of the preamble to claims 1 and 9. After the patterned fabric is laid out on the cutting table, this method detects any discrepancy between the actual and theoretical pattern pitch on the fabric. This is achieved by capturing images of portions of the laid-out fabric and then verifying that locations corresponding to stored information occupy the desired positions relative to the actual pattern on the laid-out fabric. If necessary, the theoretical placement of the pieces is modified based on the results of this verification to align it with the actual pattern pitch on the laid-out fabric, taking into account the fabric's actual characteristics.

[0015] As the actual placement of a group of pattern pieces on a piece of fabric is generated, the cutting phase of that group of pieces begins. However, during this phase, numerous problems are often encountered, particularly with the fabric itself. Indeed, it frequently has defects, tears, color variations, etc., in certain areas. When a pattern piece is cut in these areas, it becomes unusable and must therefore be recut. Similarly, modifying the placement of the pattern pieces sometimes results in a repositioning where some adjacent pieces overlap. In this situation, these pieces become unusable and must then be recut.In practice, these problems require the operator to recut all the parts of the placement that are concerned (hereafter referred to as "defective parts") at the end of the cutting phase.

[0016] Generally, defective pieces that need to be recut are done manually by the operator after the other pieces in the layout have been cut. In practice, the operator cuts a piece from the roll of fabric and manually recuts the defective piece. However, this manual recutting can be particularly complicated when the defective piece is a child piece with a relative placement constraint associated with it in relation to a parent piece. Indeed, in this situation, the operator must manually reconnect the parent piece and its link to the child piece to be recut, then manually transfer this type of constraint onto the piece from which the recut piece will be cut. Furthermore, it may be necessary to repeat these operations for all pieces with a relative position marker in relation to the recut piece.

[0017] This manual trimming method has many drawbacks. Firstly, the automatic cutting process is interrupted. Secondly, material usage is not optimized (resulting in fabric waste), and the quality of the seams with the fabric pattern is often imprecise. Description of the invention

[0018] The present invention therefore proposes a method for the automatic cutting of defective pieces in a patterned fabric in which the defective pieces are automatically recut.

[0019] According to the invention, this goal is achieved through a method for the automatic cutting of defective pieces in a fabric with a pattern repeating at a certain interval, referred to as the pattern interval, according to claim 1.

[0020] The method according to the invention is remarkable in that it provides for the automatic recutting of defective pieces by assigning them to a new placement, this assignment being carried out in such a way as to preserve their placement constraints and adapt them according to the actual placement. In other words, the method according to the invention provides for recording the placement constraints on the spread fabric of the defective pieces and translating them into positioning constraints for the new placement from which the defective pieces will be recut.

[0021] The process according to the invention is particularly advantageous because the process of recutting defective pieces is fully automated. As a result, the automated cutting process does not need to be interrupted. This automation also optimizes material usage to minimize waste and ensures high precision in matching the fabric pattern.

[0022] Each piece to be cut is associated with a reference point and a placement constraint on the fabric chosen from: a) absolute constraint whereby the position of the reference point of the piece relative to the fabric pattern is determined so that a fabric pattern appears in a desired location on the piece; b) relative constraint whereby the position of the reference point of the piece, called the child piece, is determined relative to a joining point of another piece, called the parent piece, such that the position of the reference point of the child piece relative to the fabric pattern is the same as the position of the joining point of the parent piece; c) relative symmetry constraint whereby the position of the reference point of the piece, called the child piece, is determined relative to a joining point of another piece, called the parent piece, such that the position of the reference point of the child piece relative to the fabric pattern is the mirror image, with respect to the pattern, of the position of the joining point of the parent piece;and d) free constraint for which the position of the reference point of the piece relative to the fabric pattern is free.

[0023] When the defective part is a part to which an absolute constraint is associated (case a) above), the automatic assignment of the part to the new theoretical placement advantageously includes the preservation in the new theoretical placement of this absolute constraint with respect to the fabric pattern.

[0024] When the faulty piece is a child piece to which is associated a relative constraint or a relative symmetry constraint with respect to a parent piece not requiring recutting (case b) or c) above), the automatic assignment of the piece to the new theoretical placement advantageously includes the transformation in the new theoretical placement of the relative constraint into an absolute constraint so that the position of the reference point of said child piece with respect to the fabric pattern remains the same as it was in the actual placement.

[0025] When the faulty part is a parent part to which is associated at least one relative constraint or at least one relative symmetry constraint with respect to one or more child parts (case b) or c) above), the automatic assignment of the part to the new theoretical placement also advantageously includes the automatic assignment of the child part(s) to the new theoretical placement.

[0026] Finally, when the faulty part is a part to which a free constraint is associated, the automatic assignment of the part to a new theoretical placement advantageously includes the absence in the new theoretical placement of a position constraint of the reference point of the part relative to the fabric pattern.

[0027] The new theoretical placement of the defective pieces can be calculated and cut in an area at the end of the actual placement in the direction of fabric feed on the cutting table.

[0028] Alternatively, the new theoretical placement of the defective parts can be integrated into a subsequent placement in the direction of fabric feed on the cutting table.

[0029] The faulty part is: a part that, after generation of the actual placement, is positioned on a defect in the spread fabric; or a part that, after generation of the actual placement, overlaps another part in the placement; or a part that, after generation of the actual placement, is positioned on an area of ​​the spread fabric that has a significant deformation; or a part that, after generation of the actual placement, cannot be cut entirely from the spread fabric; or a part that, after generation of the actual placement and after cutting, has a cutting defect; or a part that, after generation of the actual placement, has a geometric defect; or a child part to which is associated a relative constraint or a relative symmetry constraint with respect to a parent part with a defect that needs to be recut.

[0030] The defective piece may not be cut from the spread-out fabric.

[0031] The invention also relates to a system for the automatic cutting of defective pieces in a fabric with a pattern repeating at a certain interval, called the pattern interval, according to claim 9. Brief description of the drawings

[0032] [ Fig. 1 ] There figure 1 is a schematic view of an example of a repeating pattern fabric to which the invention applies. Fig. 2 ] There figure 2 represents an example of the theoretical placement of pieces to be cut. Fig. 3 ] There figure 3 shows how the theoretical placement of the figure 2 can be modified to generate an actual placement. Fig. 4 ] There figure 4 shows an example of automatic assignment of a faulty part (having a free constraint) from the actual placement of the figure 3 to a new theoretical placement. Fig. 5 ] There figure 5 shows an example of automatically assigning another part if there is a default (with a relative constraint) in the actual placement of the figure 3 to the new theoretical placement. Fig. 6 ] There figure 6 shows an example of automatic assignment of two default parts linked to the actual placement of the figure 3 to the new theoretical placement. Description of the implementation methods

[0033] The invention relates to cutting a placement of a group of pieces in a fabric with repeating patterns, for example by means of an automatic cutting installation such as that described in publication EP 0,759,708.

[0034] The invention relates more specifically to the automatic cutting of so-called "defective" pieces in a fabric with a pattern repeating at a certain interval.

[0035] The preliminary step in such a process involves characterizing the fabric from which the pieces will be cut. This step can be carried out by taking manual measurements of the fabric, based on information provided by the manufacturer, or by scanning a strip of material to automatically recognize and characterize the pattern; number of grids, warp pitch, weft pitch, offsets, etc.

[0036] An example of a repeating pattern fabric to which the invention applies is shown on the figure 1 .

[0037] On this figure 1 A fabric T with repeating patterns M is shown, featuring a main grid G1 and two secondary grids G2 and G3. These grids G1 to G3 are offset in the weft and warp directions relative to each other (the warp direction being represented by the X axis and the weft direction by the Y axis). The patterns M are characterized in particular by their warp pitch PC and their weft pitch PT.

[0038] The information extracted from the characterization of fabric T is recorded to define a theoretical grid which is used to develop a theoretical placement of the pieces.

[0039] Developing a theoretical layout involves determining on the theoretical grid the locations of the parts to be cut in order to minimize material waste, while respecting certain constraints (respecting the straight grain, minimum spacing between the parts to be cut, etc.).

[0040] In the case of a fabric with repeating patterns, aesthetic requirements may impose, on the one hand, for certain pieces, the presence of a complete pattern in a particular place in the piece, on the other hand, for two pieces intended to be assembled, a cut of these pieces ensuring for example the continuity of the pattern after assembly.

[0041] To this end, it is known to characterize each piece of the placement by assigning it an initial contour, a reference point, and at least one placement constraint.

[0042] Once the information relating to the theoretical characteristics of the fabric and the different parts of the placement have been determined and recorded, the theoretical placement of the parts is developed respecting placement constraints associated with the parts.

[0043] There figure 2 represents an example of a theoretical layout developed for four pieces P-1 to P-4 to be cut from a fabric T having, in particular, a weft pattern M1, M2, M3, etc. repeating at a predetermined interval p .

[0044] Each of the parts P-1 to P-4 is assigned an initial contour, respectively Ci-1, Ci-2, Ci-3 and Ci-4. These initial contours are typically defined by computer-aided design (CAD) software without any margins. They are represented by a polygon (in this case, by rectangles).

[0045] Each piece in the placement P-1 to P-4 is also associated with a reference point, respectively O-1, O-2, O-3 and O-4, and at least one constraint on the placement of the piece on the fabric.

[0046] The reference point for each part is defined by the operator, regardless of the placement constraint used. This is a point on the part that is important to position.

[0047] The placement constraint is chosen by the operator from one of the following placement constraints: 1 / Contrainte absolue :

[0048] This constraint is associated with a piece that must be positioned on the fabric in a precise location so that a pattern of the fabric appears in a desired location on the piece.

[0049] For this constraint, the position of the reference point of the piece relative to the fabric pattern is predetermined. Thus, in the example of the figure 2 , parts P-1 and P-2 have an absolute placement constraint: the reference point O-1 of part P-1 is positioned on the M3 grid, while the reference point O-2 of part P-2 is positioned on the M5 grid. 2 / Contrainte relative :

[0050] This constraint is associated with a first piece, called the "child piece", whose position on the fabric is determined according to the position of a second piece, called the "parent piece".

[0051] For this constraint, the position of the child piece's reference point is determined relative to a linking point L of the parent piece so that the position of the child piece's reference point relative to the fabric pattern is the same as the position of the linking point of the parent piece.

[0052] For example, the figure 2 Part P-3 is a child part for part P-2 (parent part). For this purpose, the parent part P-2 has a connection point L-2 which allows the reference point O-3 of the child part P-3 to be positioned.

[0053] Point L-2 is located at a distance d from frame M11, at 75% of the frame spacing between M11 and M12. Therefore, point O-3 must also be positioned at a distance d from one frame. In our example, it is positioned between frames M3 and M4, at a distance d from frame M3.

[0054] Similarly, still using the example of the figure 2 , part P-4 is a child part for part P-3 (parent part) so that the parent part P-3 has a connection point L-3 which allows the reference point O-4 of the child part P-4 to be positioned.

[0055] It should be noted that a single room can contain several connection points because it can be the parent of several child rooms. 3 / Contrainte relative de symétrie :

[0056] This constraint is also associated with a first piece, called the "child piece", whose position on the fabric is determined according to the position of a second piece, called the "parent piece".

[0057] With respect to a relative placement constraint, the position of the child part's reference point is determined so as to be symmetrical with respect to the pattern of the parent part's linking point position. 4 / Contrainte libre :

[0058] This constraint is associated with a piece whose position relative to the fabric pattern is free (i.e., absence of relative or absolute constraint).

[0059] For this constraint, the position of the reference point of the piece relative to the fabric pattern is free.

[0060] Once the information relating to the theoretical characteristics of the fabric and the different parts of the placement have been determined and recorded, the theoretical placement of the parts is developed respecting placement constraints associated with the parts.

[0061] The characterization of each part and the development of the theoretical part placement are usually carried out by an operator using a computer workstation equipped with appropriate software. The theoretical placement and part characteristics are then stored.

[0062] The next step in the process is to spread at least one layer of fabric T on the cutting table in which the placement will be cut, and then to check at least a part of the spread fabric to determine if the theoretical placement thus established is correct and, if necessary, to correct it.

[0063] The check is typically carried out by placing oneself on the spread fabric, at the memorized coordinates of the characteristic points associated with reference points and connection points, and by checking whether characteristic pattern points of the spread fabric are indeed located at these locations.

[0064] If not, each time we look for the nearest characteristic point on the spread fabric and the difference between the memorized theoretical position and the nearest real position represents the offset to be corrected for the corresponding piece in the placement.

[0065] In practice, checking the spread fabric to acquire its actual characteristics is done, for example, by taking and then analyzing an image of a portion of the fabric surface around a characteristic point of the pattern. Reference can be made to publication EP 0,759,708, which describes an example of checking and correcting the theoretical placement to account for the actual fabric characteristics.

[0066] Following this verification step, the theoretical placement of the pieces is modified to take into account the actual characteristics of the fabric laid out on the cutting table. This modification of the theoretical placement thus results in the actual placement of the pieces on the fabric.

[0067] There figure 3 represents an example of a real investment generated from the theoretical investment of the figure 2 In this example, monitoring the spread tissue revealed that the step p' the matter has grown relative to the stepp theoretical (i.e. p' is strictly greater than p ).

[0068] The position of parts P-1 and P-2, each of which has an absolute placement constraint, is modified so that their respective reference points O-1 and O-2 are positioned on the actual wefts M3' (for part P-1) and M5' (for part P-2) of the spread fabric.

[0069] The repositioning of the reference point O-2 and the value of the step p' mean that the linkage point L-2 is located on the actual placement at a distance d' of the M11' frame, representing 50% of the pitch p' between the actual frames M11' and M12'.

[0070] For part P-3, which is the child part of parent part P-2, the actual placement is modified to maintain the positioning constraint between points L-2 and O-3. This results in the positioning of the reference point O-3 of child part P-3 between the actual frames M3' and M4' at a ratio of 50% of the pitch p' of the fabric spread between these actual wefts (instead of 75% of the step p on the theoretical grid) which corresponds on the figure 3 at a distance d' of the actual M3' frame.

[0071] Similarly, for part P-4, which is the child part of parent part P-3, the actual placement is modified to maintain the same relative position with respect to the pattern of points L-3 and O-4. This results in the positioning of the reference point O-4 of child part P-4 between the actual frames M8' and M9' at a ratio of 50% of the pitch p' of the fabric spread between these actual wefts (instead of 90% of the step pon the theoretical grid) which corresponds on the figure 3 at a distance e' of the actual M8' plot.

[0072] The actual investment that was thus generated from the theoretical investment of the figure 2 presents some problems for cutting the parts, and in particular for parts P-1 and P-3 which overlap.

[0073] Indeed, if following the actual placement generation step the automatic cutting program for the placement parts was launched (as is customary in the state of the art), parts P-1 and P-3 would become defective parts which would then need to be recut.

[0074] The process according to the invention aims to provide an automatic cutting of these parts regardless of the placement constraint associated with these parts.

[0075] In general, the process involves identifying, in the actual layout, the defective pieces that will have defects once cut from the fabric and will require recutting (typically pieces P-1 and P-3 of the actual layout). figure 3 ), then automatically assign each defective part to a new theoretical placement by adapting the placement constraints associated with the defective parts according to the actual placement.

[0076] By "defective piece" we mean pieces of the placement which will have defects once cut from the fabric and will need to be recut.

[0077] The following are not exhaustively listed as defective parts within the meaning of the invention: a part which, after generation of the actual placement, is positioned on a defect in the spread fabric; a part which, after generation of the actual placement, overlaps another part in the placement (case of parts P-1 and P-3 on the figure 3 ) a part which, after generation of the actual placement, is positioned on an area of ​​the spread fabric that exhibits significant deformation; a part which, after generation of the actual placement, cannot be completely cut from the spread fabric; a part which, after generation of the actual placement and after cutting, exhibits a cutting defect; a part which, after generation of the actual placement, exhibits a geometric defect; a child part to which is associated a relative constraint or a relative symmetry constraint with respect to a parent part with a defect requiring recutting

[0078] The identification of defective parts in the actual layout can be performed automatically before cutting (by analyzing overlapping parts, detecting material defects, or identifying parts that are too short) or manually by an operator during part unloading and inspection of the cut parts. In this case, the operator ideally has a graphical interface on the cutting machine that allows them to manually select the defective parts in the layout. More generally, this graphical interface displays the layout during cutting and allows the operator to select the parts to be recut.

[0079] The automatic assignment of defective parts to a new theoretical placement is implemented by means of a defective parts repositioning algorithm, this algorithm being implemented on a computer embedded on the cutting machine or separate from it.

[0080] We will now describe how this repositioning algorithm works, taking as examples the defective parts P-1 and P-3 of the actual placement of the figure 2 .

[0081] The case of the defective part P-1 is relatively simple to handle. This part P-1 has an absolute placement constraint and no child parts. In this case, the method according to the invention provides for the automatic assignment of this part P-1 to the new theoretical placement, maintaining its absolute constraint with respect to the fabric pattern in the new theoretical placement.

[0082] As shown in the example of the figure 4 This assignment results in the transfer of the reference point O-1 of the part P-1 onto a new fabric weave (in this case the M18 weave) so that the fabric pattern appears in the same place on the part as on the actual placement.

[0083] The case of the defective part P-3 is, however, more complicated to deal with because it is a part that is a child of the parent part P-2.

[0084] To find the same final position of this part P-3 in the new theoretical placement, the position of its reference point O-3 relative to the fabric pattern must be the same as the position of the attachment point L-2 of the parent part P-2 relative to the fabric pattern, that is to say, at the distance d' of the actual frame which is equal to 50% of the step p' of the spread-out fabric.

[0085] As depicted on the figure 5 The assignment of part P-3 to the new theoretical placement thus consists of transferring the reference point O-3 of this part a distance d" of the new chosen weave (here the M15 weave) which corresponds to the same percentage of the fabric pitch, that is to say 50% of the pitch p fabric.

[0086] In some situations, it may be necessary to (or choose to) recut several pieces that are linked together by a relative placement constraint.

[0087] If we take the example of parts P-3 and P-4 which are linked together by a relative placement constraint (part P-3 is a parent part for child part P-4), the automatic assignment of these two parts to the new theoretical placement is carried out in the following way.

[0088] In the actual investment ( figure 3 ), part P-3 is placed so that its reference point O-3 is positioned between the actual frames M3' and M4' at the distance d' of the actual M3' frame equal to 50% of the pitch p' of the spread-out fabric.

[0089] As for part P-4, it is placed in the actual placement ( figure 3 ) so that its reference point O-4 is positioned between the actual frames M8' and M9' at a distance e from the actual frame M8' equal to 50% of the pitch p' of the spread-out fabric.

[0090] In the new theoretical placement ( figure 6 ), part P-3 is placed so that its relative placement constraint is preserved.

[0091] To that end, as shown on the figure 6 The position of its reference point O-3 relative to the pattern of the spread fabric must be the same as the position of the parent piece's attachment point (piece P-2) relative to the pattern of the spread fabric, namely between the new wefts M15 and M16 at a distance d" of the M16 weave which corresponds to the same percentage of the fabric pitch, that is to say 50% of the pitch p .

[0092] Even if it does not have a defect that would require recutting, the operator may deem it necessary to recut part P-4 (child part of parent part P-3 if necessary).

[0093] To that end, as shown on the figure 6 The repositioning algorithm recalculates the position of the L-3 link point of the parent piece P-3 relative to the distance e" between the new frames M17 and M18. This distance e" is then reused to calculate the position of the reference point O-4 of part P-4.

[0094] Automatic assignment is thus performed for each defective part regardless of its placement constraint in order to generate a new theoretical placement including all defective parts.

[0095] Note that the repositioning algorithm operates in the same way for a defective part which is associated with a relative symmetry constraint: in the new theoretical placement, the relative symmetry constraint is transformed into an absolute constraint so that the position of the reference point of the child part with respect to the fabric pattern remains the same as it was in the actual placement.

[0096] It should also be noted that, when the faulty part is a parent part to which is associated at least one relative constraint or at least one relative symmetry constraint with respect to one or more child parts, the algorithm for repositioning the part to the new theoretical placement may also include the automatic assignment of the child part(s) to the new theoretical placement.

[0097] The new theoretical placement of the defective pieces thus generated can then be cut from an area at the end of the actual placement, in the direction of fabric feed on the cutting table. This can be a specific piece of fabric from the same roll as the one used for cutting the actual placement, located either after it or further downstream, depending on the cutting strategy.

[0098] Alternatively, the new theoretical placement of the defective parts can be integrated into a subsequent placement in the direction of fabric feed on the cutting table.

[0099] Of course, if one or more defective pieces were identified during the cutting of the new placement, the operation of automatically assigning these defective pieces to a new theoretical placement would be repeated.

Claims

1. Method for automatic cutting of defective parts in a fabric with a pattern repeating at a certain pitch, referred to as the pattern pitch, comprising the steps of: - producing a theoretical layout of parts to be cut (P-1 to P-4) on a theoretical representation of the fabric (T) whilst respecting layout constraints associated with the parts, in which a reference point (O-1 to O-4) and a layout constraint on the fabric are associated with each part to be cut; - spreading out at least one layer of fabric on a cutting table; - ascertaining actual features of at least one portion of the spread-out fabric; - modifying the theoretical layout in order to generate an actual layout of parts on the spread-out fabric, taking into account the actual features of the fabric; - characterised in that it further comprises the steps of: - identifying, in the actual layout, defective parts (P-1, P-2) which will contain defects once cut in the fabric and which will need to be cut again, defective part being: ∘ a part which, after generating the actual layout, is positioned on a defect of the spread-out fabric; or ∘ a part which, after generating the actual layout, overlaps another part of the layout; or ∘ a part which, after generating the actual layout, is positioned on an area of the spread-out fabric which has a large deformation; or ∘ a part which, after generating the actual layout, cannot be entirely cut in the spread-out fabric; or ∘ a part which, after generating the actual layout and after cutting, has a cutting defect; or ∘ a part which, after generating the actual layout, has a geometric defect; or ∘ a daughter part with which a relative constraint or a relative symmetry constraint with respect to a defective mother part requiring to be cut again is associated; and - automatically allocating each defective part to a new theoretical layout by adjusting the layout constraints associated with the defective parts according to the actual layout; - and in that the layout constraint on the fabric associated with each part to be cut is chosen from: a) an absolute constraint for which the position of the reference point of the part with respect to the fabric pattern is determined so that a fabric pattern appears in a desired position of the part; b) a relative constraint for which the position of the reference point of the part, referred to as the daughter part, is determined with respect to a connection point (L-2, L-3) of another part, called the mother part, so that the position of the reference point of the daughter part with respect to the fabric pattern is the same as the position of the connection point of the mother part; c) a relative symmetry constraint for which the position of the reference point of the part, referred to as the daughter part, is determined with respect to a connection point of another part, called the mother part, so that the position of the reference point of the daughter part with respect to the fabric pattern is symmetric with respect to the pattern of the position of the connection point of the mother part; and d) a free constraint for which the position of the reference point of the part with respect to the fabric pattern is free.

2. Method according to claim 1, wherein, when the defective part is a part with which an absolute constraint is associated, automatically allocating the part to the new theoretical layout comprises retaining this absolute constraint with respect to the fabric pattern in the new theoretical layout.

3. Method according to claim 1, wherein, when the defective part is a daughter part to which a relative constraint or a relative symmetry constraint is assigned with respect to a mother part which does not need to be cut again, automatically allocating the part to the new theoretical layout involves the transformation, in the new theoretical layout, of the relative constraint into an absolute constraint, in order that the position of the reference point of said daughter part with respect to the fabric pattern remains the same as that which it was in the actual layout.

4. Method according to claim 1, wherein, when the defective part is a mother part with which at least one relative constraint or at least one relative symmetry constraint is associated with respect to one or more daughter parts, automatically allocating the part to the new theoretical layout also comprises automatically allocating the one or more daughter parts to the new theoretical layout.

5. Method according to claim 1, wherein, when the defective part is a part with which a free constraint is associated, automatically allocating the part to a new theoretical layout comprises the absence in the new theoretical layout of a position constraint of the reference point of the part with respect to the fabric pattern.

6. Method according to any one of claims 1 to 5, wherein the new theoretical layout of the defective parts is calculated and cut in an area at the end of the actual layout in the direction of advance of the fabric on the cutting table.

7. Method according to any one of claims 1 to 5, wherein the new theoretical layout of the defective parts is incorporated in a subsequent layout in the direction of advance of the fabric on the cutting table.

8. Method according to any one of claims 1 to 7, wherein the defective part is not cut in the spread-out fabric.

9. System for automatic cutting of defective parts in a fabric with a pattern repeating at a certain pitch, referred to as the pattern pitch, comprising: - means for producing a theoretical layout of parts to be cut (P-1 to P-4) on a theoretical representation of the fabric (T) whilst respecting layout constraints associated with the parts, in which a reference point (O-1 to O-4) and a layout constraint on the fabric are associated with each part to be cut; - a cutting table on which at least one layer of fabric can be spread out; - means for ascertaining actual features of at least one portion of the spread-out fabric; - means for modifying the theoretical layout in order to generate an actual layout of parts on the spread-out fabric, taking into account the actual features of the fabric, - characterised in that it further comprises: - means for identifying, in the actual layout, defective parts (P-1, P-2) which will contain defects once cut in the fabric and which will need to be cut again, a defective part being; ∘ a part which, after generating the actual layout, is positioned on a defect of the spread-out fabric; or ∘ a part which, after generating the actual layout, overlaps another part of the layout; or ∘ a part which, after generating the actual layout, is positioned on an area of the spread-out fabric which has a large deformation; or ∘ a part which, after generating the actual layout, cannot be entirely cut in the spread-out fabric; or ∘ a part which, after generating the actual layout and after cutting, has a cutting defect; or ∘ a part which, after generating the actual layout, has a geometric defect; or ∘ a daughter part with which a relative constraint or a relative symmetry constraint with respect to a defective mother part requiring to be cut again is associated, and - means for automatically allocating each defective part to a new theoretical layout by adjusting the layout constraints associated with the defective parts according to the actual layout, - and in that the layout constraint on the fabric associated with each part to be cut is chosen from: a) an absolute constraint for which the position of the reference point of the part with respect to the fabric pattern is determined so that a fabric pattern appears in a desired position of the part; b) a relative constraint for which the position of the reference point of the part, referred to as the daughter part, is determined with respect to a connection point (L-2, L-3) of another part, called the mother part, so that the position of the reference point of the daughter part with respect to the fabric pattern is the same as the position of the connection point of the mother part; c) a relative symmetry constraint for which the position of the reference point of the part, referred to as the daughter part, is determined with respect to a connection point of another part, called the mother part, so that the position of the reference point of the daughter part with respect to the fabric pattern is symmetric with respect to the pattern of the position of the connection point of the mother part; and - d) a free constraint for which the position of the reference point of the part with respect to the fabric pattern is free.