Method for automatically positioning defects of a coupon of flexible material having non-homogeneous characteristics

Abstract

The invention relates to a method for automatically positioning defects of a coupon of flexible material having non-homogeneous characteristics in which parts are intended to be cut, comprising the steps of: obtaining an image of the contour of the coupon in its initial state and the position of the defects, after repositioning the coupon in a ready-to-cut state; obtaining (S31) a new image of the contour of the coupon; superimposing (S32) the two images; determining (S33) a rotation value to be applied to one of the two contours in order to minimise the total surface area of the zones that do not overlap; applying (S34) the rotation value to the position of each defect in the image of the coupon in its initial state to pre-position them; determining (S35) geometric transformations in order to locally minimise the surface area of the zones of the two contours that do not intersect; and applying (S36) to the position of each pre-positioned defect one of the geometric transformations as a function of its position inside the contour in order to reposition it precisely within the image of the coupon in its ready-to-cut state.

Description

Description Title of the invention: Method for automatically positioning defects in a coupon of flexible material with non-homogeneous characteristics Technical Field

[0001] The invention relates to the cutting of pieces from coupons of flexible material with non-homogeneous characteristics, in particular leathers or natural skins.

[0002] One field of application of the invention is the manufacture of articles, particularly leather articles, requiring the assembly of pieces cut from such coupons. The industries concerned are in particular those of furniture, saddlery, leather goods, footwear and clothing. Prior art

[0003] The automatic cutting of pieces from leather or natural skins for the purpose of manufacturing an article typically involves several main steps, namely: a first step of digitizing the outline and defects of the skin, followed by a second step which consists of placing as many pieces as possible on the digitized skin, then a third step of cutting the pieces from the skin following the pre-established placement, and finally a fourth step which consists of unloading the cut pieces.

[0004] Depending on how these main steps are linked together, this leads to different cutting processes.

[0005] Thus, according to a cutting process called "online" (for "in line" in French), the four main stages described above are carried out one after the other on the same cutting table.

[0006] The advantage of this process lies in its simplicity in terms of organization for the user, as well as in the responsiveness and flexibility it allows (in terms of organizational planning). On the other hand, the main disadvantage of such a The difficulty of properly synchronizing and balancing all the main steps is that if one of these steps takes longer than expected, there is a great risk of slowing down the overall process.

[0007] According to another process called "offline", the steps of scanning the skin, placing the parts, then cutting and unloading the parts are carried out separately, on different equipment and with time intervals between these steps left to the discretion of the user.

[0008] The advantages and disadvantages of this process are the opposite of those encountered with the "online" process. In particular, the separation of the main steps makes it possible to manage those that take more time than the others (for example by adapting the number of digitizers in relation to the number of cutters, and / or by adapting the calculation time devoted to the placement of the parts). Conversely, this "offline" process requires greater organization on the part of the user, as well as additional handling (or even storage) of skins between steps.

[0009] Another disadvantage of this process is the introduction of a new step compared to the "online" process, which consists of repositioning a previously digitized skin on the cutting machine. Indeed, it is not easy in terms of ergonomics to reposition a skin in the same way. In addition, this manipulation always generates additional inaccuracies that must be taken into account when placing the parts by keeping a sufficiently large unused space at the edge of the skin, which reduces the efficiency of the placement.

[0010] There is yet another process called "semi-offline" (for "semi-hors- ligne" in French) which consists of an intermediate process between the "online" and "offline" processes described above. In this process, only the step of digitizing the contour and defects of the skins is transferred to another device and is desynchronized from the other main steps. Indeed, the digitization of the defects of a skin is often the most costly step in terms of time, and the quality of this digitization (namely taking into account the all the defects, their exact location without enlarging them) will depend on the efficiency of the placement and the reduction of the rate of rejected parts.

[0011] The disadvantage of this "semi-offline" process (just like in the "offline" process) lies in the difficulty for an operator to reposition the skin. On the other hand, in this process, the placement of the parts on the skin has not yet taken place and will be done within the true contour which will be digitized again after the repositioning step. Unlike the "offline" process, it is therefore not necessary to provide an additional margin at the edge of the skin, which is beneficial for placement efficiency.

[0012] The difficulty of such a "semi-offline" process lies, on the one hand, in the ease of the skin repositioning phase, and on the other hand in the precision of (automatic) repositioning of defects within the new digitalized contour of the skin.

[0013] Indeed, leather is a flexible material that deforms more or less depending on how an operator positions the skin on the table during the first scan and how another operator will reposition this same skin on another table during the second scan. However, the way in which the skin deforms has direct consequences on the positioning of the defects.

[0014] In addition to these deformations of the skin due to the different ways in which operators place it on a table, the skin may have remained several weeks or even months between the two scanning stages. However, storage conditions as well as possible differences in humidity and temperature between the two scanning stages also impact possible deformations of the skin, and therefore the positioning of defects.

[0015] In addition, the positioning of the skin during the first scanning step is generally carried out on a digitizer with a relatively smooth polyurethane conveyor, while the repositioning of the skin defects during the new scanning is carried out on a cutting machine with a felt conveyor which has a strong grip with the skin. This can further lead to additional difficulties in successfully completing the skin defect repositioning step.

[0016] The multiple deformations undergone by the skin that have been described above are unfortunately not homogeneous and are therefore not predictable. Also, the defect repositioning step must be able to find as precisely as possible the position of the contour and all the defects of the skin.

[0017] To solve this problem of repositioning defects, it is known to use video projectors that project an image of the entire skin (or only a part of it) previously digitized onto the skin placed on the cutting machine. The operator then proceeds by nibbling to reposition the entire skin and its defects.

[0018] However, this method remains quite weak in terms of ergonomics and precision. Indeed, the operator must correct the position of the skin edges (by relying on the projected contour, which is not very precise) by pulling on the latter, which can cause strong tensions near the skin edges. Presentation of the invention

[0019] The main aim of the invention is therefore to overcome such drawbacks by proposing a method for positioning defects by automatic calculation of the position of defects which is simple and ergonomic.

[0020] According to the invention, this aim is achieved by means of a method for automatically positioning defects in a coupon of flexible material with non-homogeneous characteristics in which parts are intended to be cut, comprising the successive steps of: - obtaining a digital image of the outline of the coupon in its initial state and the position of the defects thereof; - after repositioning the coupon in a state ready for cutting, obtaining a new digital image of the outline of the coupon; - superimposing the digital images of the contours of the coupon in its initial state and in its state ready for cutting; - determining a rotation value to be applied to at least one of the two contours to minimize the total surface area of ​​the zones delimited by the two contours which do not overlap; - applying the rotation value to the position of each defect of the digital image of the coupon in its initial state to pre-position them within the digital image of the coupon in its state ready for cutting; - determining a plurality of geometric transformations to locally minimize the surface area of ​​the zones of the two contours which do not overlap;and - applying to the position of each pre-positioned defect within the digital image of the coupon in its ready-to-cut state one of the geometric transformations as a function of the position of the defect within the outline of the coupon in its initial state in order to reposition the defect precisely within the digital image of the coupon in its ready-to-cut state.;

[0021] The method according to the invention is remarkable in that it provides a defect repositioning algorithm which makes it possible to apply to the position of each defect a specific geometric transformation which depends on the location of the defect within the contour of the coupon. In other words, the geometric deformation applied to each defect is not the same for all the defects. The method thus makes it possible to reposition automatically and with great precision all the defects of the coupon.

[0022] Furthermore, the method according to the invention only requires a simple linear scanner (or one or more matrix cameras) at the input of the conveyor cutting machine which can be identical to that used during the scanning step. The coupon is thus simply placed by the operator on the scanner where and how he wishes. In particular, this solution allows users of cutters adapted to an “online” process to use it for implement a “semi-offline” process without any hardware modification of their cutter.

[0023] Preferably, the rotation of the digital images of the coupon contours is carried out with respect to the respective barycenters of the two contours after having been superimposed.

[0024] Geometric transformations can each include a rotation component and a homothety ratio component.

[0025] In this case, in a polar coordinate system whose origin is constituted by the respective barycenter of the two contours, we advantageously construct a discrete field of angular sectors covering the two contours and we associate with each angular sector geometric transformations whose rotation and homothety ratio components are determined to locally minimize the surface area of ​​the zones of the two contours which do not overlap.

[0026] Preferably, the rotation and homothety ratio components of each geometric transformation are determined by dichotomy to obtain the rotation and homothety ratio values ​​which minimize the area of ​​the non-overlapping zones of the portions of the two contours concerned by the angle value associated with the geometric transformation.

[0027] The step of applying one of the geometric transformations to each pre-positioned defect can be applied to each of the vertices of a polygon encompassing the outline of the defect.

[0028] In this case, for each vertex of each polygon encompassing the outline of a defect, we advantageously identify the two angles which geometrically frame this vertex, and we apply to the coordinates of the vertex a combination of the rotation and homothety ratio values ​​of the two geometric transformations associated with the two corresponding angle values.

[0029] The invention also relates to a method for cutting parts from coupons of flexible material with non-homogeneous characteristics, comprising: - a step of digitizing the outline of the coupons in their initial state and the position of the defects thereof; - for each coupon, a new step of digitizing the outline of the coupon on a digitizing and cutting table; - a step of automatically positioning the defects of the coupon according to the method as defined previously; - a step of placing pieces to be cut in the coupon; and - a step of cutting the pieces.

[0030] The invention also relates to a computer program comprising instructions for executing the steps of the method for automatically positioning defects in a coupon of flexible material with non-homogeneous characteristics as defined above.

[0031] The invention also relates to a computer-readable recording medium on which is recorded a computer program comprising instructions for executing the steps of the method for automatically positioning defects in a coupon of flexible material with non-homogeneous characteristics as defined above. Brief description of the drawings

[0032] [Fig. 1] Figure 1 is a flowchart illustrating the main steps of a “semi-offline” process for cutting parts according to the invention.

[0033] [Fig. 2] Figure 2 is another flowchart illustrating the main steps of a fault positioning method according to the invention.

[0034] [Fig. 3] to [Fig. 11] Figures 3 to 11 represent examples of implementations of the different steps of the fault positioning method according to the invention. Description of the embodiments

[0035] The invention applies to the cutting of pieces from coupons of flexible material with non-homogeneous characteristics, in particular from leathers or natural skins, with the aim of manufacturing an article.

[0036] More specifically, the invention is integrated into a so-called “semi-offline” cutting process, the main steps of which are described in the flowchart in Figure 1.

[0037] During the initial step S10 of this process, it is planned to digitize the outline of all coupons C1, …, C i , … C n in their initial state and to accurately determine the position of the defects of these coupons within their contour. The digitization of the position of the defects can be carried out automatically using the scanner or by an operator.

[0038] This initial coupon scanning step is carried out on a scanning table equipped with a scanner and is desynchronized with the other steps of the cutting process. The digital data of coupons C1, …, C i , … C n are stored and the scanned coupons can then be stored in a storage location.

[0039] Each coupon C i is then removed from its storage location to be positioned flat on a cutting table equipped with an input scanner where it undergoes a new step of digitizing its outline (step S20).

[0040] The next step is to automatically reposition the defects of coupon C i ready for cutting within its contour according to the method of the invention. This involves repositioning from the data stored during step S10, and not a new positioning of these defects. This step S30 is detailed later.

[0041] The next step S40 consists of placing the pieces to be cut inside the outline of coupon C i Typically, the placement of the pieces to be cut takes into account the geometric shape of these pieces, their possible links between them and the defects of the coupon C i . In addition, this placement is optimized to limit material waste.

[0042] From this placement, a cutting program is developed, this program resulting from a conversion of the placement into orders for moving the cutting tool on the cutting table.

[0043] Coupon C i is then transferred to the cutting area of ​​the table where the pieces are cut according to the cutting program (step S50). The cut pieces can then be unloaded (step S60) and the cutting process resumes at step S20 with a new coupon C i+1 .

[0044] In connection with Figures 2 to 11, the main steps of the process for automatically positioning defects in a coupon C will now be described. i according to the invention (corresponding to step S30 of the method described previously).

[0045] In a first step S31, the outline of coupon C is digitized again i using the cutting table scanner (the coupon is in a state ready for cutting).

[0046] A program then makes it possible to superimpose the two digital images of the outline of the coupon Ci (step S32), namely the image of the coupon in its initial state I0 which was acquired during step S10, and the image of the coupon I1 ready for cutting which was acquired during step S31.

[0047] As shown in Figure 3, this step is obtained by superimposing the respective barycenters B0, B1 of the two coupon images I0, I1.

[0048] Once superimposed, a calculation algorithm makes it possible to determine a rotation value to be applied to the digital image I0, I1 of at least one of the two contours of the coupon to minimize the total surface area of ​​the zones of the two contours which do not overlap (i.e. which do not intersect), this rotation of the digital images of the contours of the coupon being carried out with respect to the respective barycenters B0, B1 of the two contours after having been superimposed (step S33).

[0049] To this end, the algorithm calculates the area of ​​the images I0, I1 of the two contours, then looks for the rotation value to apply to one of them so that the value "(contour image I0\contour image I1) U (contour image I1\contour image I0)" is as small as possible.

[0050] In the example of Figure 3, the areas whose surface area is to be minimized are the hatched areas.

[0051] In the next step (step S34), the rotation value determined in the previous step is applied to the position of each defect of the digital image I0 of the coupon in its initial state to pre-position them inside the digital image I1 of the coupon in its ready-to-cut state.

[0052] The next step (step S35) consists of calculating a plurality of geometric transformations making it possible to locally minimize the surface area of ​​the zones of the images I0, I1 of the two contours which do not overlap (or intersect).

[0053] One of the geometric transformations previously calculated as a function of its position inside the contour is then applied to the position of each pre-positioned defect inside the digital image I1 of the coupon in its state ready for cutting in order to reposition it precisely inside the digital image of the coupon in its state ready for cutting (step S36).

[0054] The algorithm implementing these last two steps S35 and S36 is described in more detail below.

[0055] In particular, the algorithm for calculating the geometric transformation to be applied to each defect is carried out in a polar coordinate system whose origin O is constituted by the respective barycenter B0, B1 of the images I0, I1 of the two contours.

[0056] In this frame, we construct a discrete field of n angular sectors ∆1, ∆2, …, ∆ i , … ∆ n covering the images I0, I1 of the two contours and we associate with each angular sector “∆ i » a geometric transformation having rotation and homothety ratio components that are determined to locally minimize the area of ​​the zones of the two contours that do not overlap (or intersect).

[0057] For example, we will choose an angular discretization of the images I0, I1 at all degrees, which is equivalent to constructing a field with 360 angular sectors ∆1, ∆ 2, …, ∆ i , …, ∆ 360 and to determine 360 ​​different geometric transformations (a transformation by angular sector “∆ i "). Of course, a different angular discretization could be retained.

[0058] At each angular sector “∆ i ", the calculation algorithm then associates a geometric transformation composed of a rotation of angle "R i » and a homothety of ratio « H i ", these two transformations being centered on the origin O of the polar coordinate system.

[0059] For each of the angular sectors “∆ i ", the rotation component of angle "R i » of the associated geometric transformation is calculated by the calculation algorithm in the following manner.

[0060] As shown in Figure 4, we consider an angular sector "A a » of width 10° which is centered on « ∆ i » and we assign to this angular sector « A a » a weight « P a » of value 2.

[0061] Furthermore, we consider another angular sector "A b » of width 30° which is also centered on « ∆ i » and we assign to this other angular sector « A b » a weight « P b » of value 1.

[0062] The principle adopted here is to choose a first angular sector (“A a ”) less wide with a weight “P a » higher, and a second angular sector (“A b ”) wider with a weight (“P b") lower in order to favor the search on the narrowest angular sector for cases where the contour would be quite "cut" there (thanks to the higher weight) while broadening the search if the contour is relatively linear (in this case the result of the calculation on the narrowest angular sector would be more or less constant and the result of the calculation on the widest angular sector would become predominant).

[0063] The values ​​for the angular sectors and weights are given here as examples. Of course, one could imagine taking other values, for example for a type of coupon with particular geometric characteristics.

[0064] For each angular sector “∆ i ", we then consider the transform I 0-R by the angle rotation "R i » of the image I0 of the coupon in its initial state (see figure 5).

[0065] From these data, we define by S Ra the area obtained by the following equation (and illustrated in Figure 6):

[0066] [Math. 1] ^ ^^ = ^^^ ^^^ ∩ ^ ^ ^\^^ ^ ∩ ^ ^ ^^ ∪ ^^^ ^ ∩ ^ ^ ^\^^ ^^^ ∩ ^ ^ ^^

[0067] Similarly, still from these data, we define by S Rb the area obtained by the following equation (and illustrated in Figure 7):

[0068] [Math. 2] ^ ^^ = ^^^ ^^^ ∩ ^ ^ ^\^^ ^ ∩ ^ ^ ^^ ∪ ^^^ ^ ∩ ^ ^ ^\^^ ^^^ ∩ ^ ^ ^^

[0069] The calculation algorithm will search dichotomously for the value of the angle rotation "R i » which minimizes the sum: S Ra P a + S Rb P b

[0070] Furthermore, for each of the angular sectors “∆ i", the homothety component "H i » of the associated geometric transformation is calculated by the calculation algorithm in the following manner.

[0071] For each angular sector “∆ i ", we consider the transform I 0-H by the homothety of ratio "H i » of the image I0 of the coupon in its initial state (see figure 8).

[0072] From these data, we define by S Ha the area obtained by the following equation (and illustrated in Figure 9):

[0073] [Math. 3] ^ ^^ = ^^^ ^^^ ∩ ^ ^ ^\^^ ^ ∩ ^ ^ ^^ ∪ ^^^ ^ ∩ ^ ^ ^\^^ ^^^ ∩ ^ ^ ^^

[0074] Similarly, still from these data, we define by S Hb the area obtained by the following equation (and illustrated in Figure 10):

[0075] [Math. 4] ^ ^^ = ^^ ^ ^^^ ∩ ^^ ^ \^^ ^ ∩ ^ ^ ^ ^ ∪ ^^^ ^ ∩ ^ ^ ^\^^ ^^^ ∩ ^ ^ ^^

[0076] The calculation algorithm will search by dichotomy for the value of the homothety ratio "H i » which minimizes the sum: S Ha P a + S Hb P b

[0077] Once the values ​​of the angle rotation "R i » and the homothety ratio « H i » geometric transformations calculated for all angular sectors « ∆ i ", the calculation algorithm plans to apply a geometric transformation to each pre-positioned defect inside the digital image I1 of the coupon according to its polar coordinates.

[0078] More precisely, for each pre-positioned defect, the geometric transformation is applied to each of the vertices of a polygon encompassing the contour of the defect.

[0079] To this end, for each vertex of each pre-positioned defect, the method performs a linear interpolation between the values ​​closest to the previously calculated discrete field.

[0080] Figure 11 shows an example of applying such linear interpolation to a pre-positioned Z defect whose outline is encompassed in a polygon ABCD.

[0081] If we denote by ∆ A , ∆ B , ∆ C , and ∆ D the respective angular coordinates of the vertices A, B, C, D of the polygon encompassing the outline of a pre-positioned defect, the calculation algorithm will determine the rotations of angle R A , R B , R C , and R D and homothety ratios H A , H B , H C , and H D geometric transformations to apply.

[0082] For each vertex of the polygon, we designate by "∆1" and "∆2" the consecutive angular coordinates in the discrete field calculated previously which frame the angular coordinate of the vertex in question. In the example of an angular discretization of the images I0, I1 all degrees, we therefore have ∆2- ∆1 = 1°.

[0083] Furthermore, due to an angular discretization of the images I0, I1 at all degrees, for the vertex A of the polygon encompassing the contour of the defect Z, we can write the following equality: ∆ A = α1∆ 1 + α2∆2in which α1is the angle between ∆1and ∆ A and α2 is the angle between ∆ A and ∆2. Of course, the same types of equalities can be written for the other vertices B, C, D of the polygon.

[0084] More generally (i.e. angular discretization not necessarily all degrees), α1 and α2 are coefficients whose sum is equal to 1 (and which correspond to the value of the corresponding angle divided by the value of the angle ∆2- ∆1).

[0085] By designating by R ∆1 , H ∆1 and R ∆2 , H ∆2 the values ​​of the angle rotation and the homothety ratio of the geometric transformations calculated respectively for the angular coordinates ∆1 and ∆2 framing the angular coordinate of the vertices A, B, C, D of the polygon, the algorithm gives the values ​​of the geometric transformations applied to vertex A by the following equations: R A = α1 R ∆1 + α2 R ∆2 and H A = α1 H ∆1 + α2 H ∆2

[0086] Of course, the same types of equations are determined for the other vertices B, C, D of the polygon.

[0087] When we apply these equations to the set of vertices A, B, C, D of the polygon encompassing the outline of the pre-positioned defect Z, we obtain the polygon A'B'C'D' represented in figure 11 and which therefore encompasses the defect Z' repositioned precisely inside the digital image of the coupon in its state ready for cutting.

[0088] This calculation operation is repeated for all the defects pre-positioned inside the digital image I1 of the coupon in its state ready for cutting.

Claims

Claims

1. Method for automatically positioning defects in a coupon of flexible material with non-homogeneous characteristics from which parts are intended to be cut, comprising the successive steps of: - obtaining (S10) a digital image (I0) of the outline of the coupon (C i) in its initial state and the position of the defects (Z) thereof; - after repositioning the coupon in a state ready for cutting, obtaining (S31) a new digital image (I1) of the contour of the coupon; - superimposing (S32) the digital images (I0, I1) of the contours of the coupon in its initial state and in its state ready for cutting; - determining (S33) a rotation value to be applied to at least one of the two contours to minimize the total area of ​​the zones delimited by the two contours which do not overlap; - applying (S34) the rotation value to the position of each defect of the digital image (I0) of the coupon in its initial state to pre-position them within the digital image (I1) of the coupon in its state ready for cutting; - determination (S35) of a plurality of geometric transformations to locally minimize the surface area of ​​the zones of the two contours which do not overlap;and - applying (S36) to the position of each pre-positioned defect within the digital image of the coupon in its ready-to-cut state one of the geometric transformations as a function of the position of the defect within the contour of the coupon in its initial state in order to reposition the defect precisely within the digital image of the coupon in its ready-to-cut state.

2. Method according to claim 1, in which the rotation of the digital images (I0, I1) of the contours of the coupon is carried out by; relative to the respective barycenters (B0, B1) of the two contours after having been superimposed.

3. Method according to one of claims 1 and 2, in which the geometric transformations each comprise a rotation component (R A – R D ) and a homothety ratio component (H A – H D).

4. Method according to claim 3, in which, in a polar coordinate system whose origin (O) is constituted by the respective barycenter of the two contours, a discrete field of angular sectors (∆1,… ∆ i , … ∆ n ) covering the two contours and we associate with each angular sector (∆ i ) geometric transformations whose rotation components (R i ) and homothety ratio (H i) are determined to locally minimize the area of ​​the zones of the two contours which do not overlap.

5. The method of claim 4, wherein the rotation and homothety ratio components of each geometric transformation are determined by dichotomy to obtain the rotation and homothety ratio values ​​which minimize the area of ​​the non-overlapping zones of the portions of the two contours concerned by the angle value associated with the geometric transformation.

6. The method of any one of claims 1 to 5, wherein the step (S36) of applying to each pre-positioned defect one of the geometric transformations applies to each of the vertices (A, B, C, D) of a polygon encompassing the contour of the defect (Z).

7. Method according to claim 6, in which, for each vertex (A, B, C, D) of each polygon encompassing the outline of a defect, the two angles (∆1, ∆2) which geometrically frame this vertex are identified, and a combination of the rotation and homothety ratio values ​​of the two geometric transformations associated with the two corresponding angle values ​​is applied to the coordinates of the vertex.

8. Method for cutting parts from coupons of flexible material with non-homogeneous characteristics, comprising:. - a step (S10) of digitizing the outline of the coupons (C i ) in their initial state and the position of the defects (Z) thereof; - for each coupon (C i), a further step (S20) of scanning the outline of the coupon on a scanning and cutting table; - a step (S30) of automatically positioning the defects of the coupon according to any one of claims 1 to 7; - a step (S40) of placing pieces to be cut in the coupon; and - a step (S50) of cutting the pieces.

9. Computer program comprising instructions for executing the steps of the method for automatically positioning defects of a coupon of flexible material with non-homogeneous characteristics according to any one of claims 1 to 7.

10. Recording medium readable by a computer on which is recorded a computer program comprising instructions for executing the steps of the method for automatically positioning defects of a coupon of flexible material with non-homogeneous characteristics according to any one of claims 1 to 7.

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