EP3565909B1 - A method for modifying the cutting path for cutting parts from a soft material - Google Patents

Description

Background of the invention

The present invention relates to the general field of cutting parts from a flexible material.

A particular but non-limiting field of application of the invention is that of cutting parts in a coupon of flexible non-textile material such as leather, in particular in the clothing industry, furniture or saddlery. automobile.

In a manner known per se, the process of cutting parts from a coupon of flexible material, such as a skin for example, takes place as follows. The skin to be cut is first prepared, that is to say that an operator locates any defects on the skin and identifies them directly on it by means of marks. The skin with its marks is then scanned. Using the digital representation of the skin and using appropriate software, the operator optimizes the placement of the different parts to be cut from the skin. This placement is converted into a part cutting program. The skin is then positioned on the cutting table to be cut there generally by means of a blade fitted to the cutting tool and moving in the skin according to cutting trajectories defined by the pre-established program for cutting the parts.

The cutting of parts with such a process can however pose certain problems, in particular when two parts to be cut from the skin are too close to each other (typically less than 1mm from each other). In fact, in this situation, after cutting the first part, the blade of the cutting tool which cuts the second part risks being “attracted” by the cutting of the first part due to the proximity to the latter. As a result, the second part may have cutting defects which adversely affect the quality of the part obtained.

Purpose and summary of the invention

The main object of the present invention is therefore to alleviate such drawbacks by proposing to transform the cutting paths of two neighboring pieces to be cut.

The document GB-A-2 138 595 discloses a method for automatically modifying the cutting path of parts intended to be cut from a flexible material by automatically moving a cutting tool along predetermined cutting paths. The cutting paths associated with each part are defined by a succession of cutting segments forming a polygon.

• une étape d'identification de deux segments de coupe appartenant à deux pièces différentes à découper dans le matériau et pour lesquels une condition de distance maximale entre ces segments de coupe est respectée ;
• une étape de vérification que les deux segments de coupe préalablement identifiés sont situés l'un en face de l'autre par projection orthogonale réciproque des segments de coupe l'un sur l'autre ;
• une étape de vérification de l'absence d'autres segments de coupe entre les deux segments de coupe préalablement identifiés par un calcul d'intersections entre les deux pièces à découper ;
• une étape de calcul d'une trajectoire de coupe commune pour les deux segments de coupe préalablement identifiés ; et
• une étape de raccordement de la trajectoire de coupe commune à la trajectoire de coupe des deux pièces à découper de façon à obtenir des trajectoires de coupe modifiées pour les deux pièces à découper.

According to the invention, this object is achieved by means of a method for automatically modifying the cutting path of parts intended to be cut from a flexible material by automatic displacement of a cutting tool along predetermined cutting paths, the paths cutting associated with each part being defined by a succession of cutting segments forming a polygon, the method comprising successively:

• a step of identifying two cutting segments belonging to two different pieces to be cut from the material and for which a condition of maximum distance between these cutting segments is met;
• a step of verifying that the two previously identified cutting segments are located opposite each other by reciprocal orthogonal projection of the cutting segments on one another;
• a step of verifying the absence of other cutting segments between the two cutting segments previously identified by a calculation of intersections between the two pieces to be cut;
• a step of calculating a common cutting path for the two previously identified cutting segments; and
• a step of connecting the common cutting path to the cutting path of the two pieces to be cut so as to obtain modified cutting paths for the two pieces to be cut.

The invention is remarkable in that it provides a method for automatically modifying the cutting paths of two pieces that are too close to each other by creating two perfectly superimposed cutting paths for the two cutting segments in proximity to each other. In other words, the method according to the invention makes it possible to slightly modify the cutting trajectories of the two parts in order to superimpose them at the level of the cutting segments in proximity to one another. Thus, any defect in the cutting of these parts due to their close proximity can be avoided.

In addition, the method according to the invention is in the form of an algorithm, the automatic implementation of which is simple and rapid. In particular, this algorithm for modifying the cutting path can be integrated during the step of preparing the cutting program for all the parts of the placement to be cut in a skin so as to allow the operator to be able to keep a check on the result obtained.

The step of identifying two cutting segments can comprise, successively for each piece to be cut, the expansion by a predetermined value of the polygon formed by the cutting segments of said piece to obtain a first expanded polygon, the identification of 'an intersection between the first expanded polygon and a polygon formed by the cut segments of another part, expanding the predetermined value of the polygon formed by the cut segments of the other part to obtain a second expanded polygon, l '' identification of an intersection between the second expanded polygon and the polygon formed by the cut segments of said part, and the reunification of the intersections to obtain two cut segments belonging to two different parts to be cut and for which a maximum distance condition between these cutting segments is observed.

In addition, the step of verifying that the previously identified cut segments are located opposite each other may include the reciprocal orthogonal projection of the cut segments on top of each other, the projection of each segment of cutting on the other cutting segment in a direction orthogonal to the projected cutting segment, and the union of the projections thus produced to obtain two portions of cutting segments located one opposite the other.

Likewise, the step of verifying the absence of other cutting segments between the two cutting segments can successively comprise the calculation of the intersections between the two parts, the construction of a geometric quadrilateral formed by the two cutting segments. , the intersection between the previously constructed quadrilateral and the two pieces to be cut, and the subtraction from the previously constructed quadrilateral of the overlaps between the two pieces to be cut.

In this case, the method may further comprise, when subtracting the overlaps results in an empty set, indicating that no cutting path is present between the two cutting segments.

As for the step of calculating a common cutting path for the two cutting segments, it can include the projection of each cutting segment on the other cutting segment while keeping the same length ratio for each segment, and creating a common cut path by interconnecting points at equal distances from the ends of the projections of the cut segments.

The step of connecting the common cutting path to the cutting path of the two pieces to be cut advantageously comprises the application of the following connections taken successively until a functional connection is obtained: connection by extending the path of common cut, straight connection of the common cutting path, connection with shortening of the common cutting path, rectilinear connection with shortening of the common cutting path, connection by extending the common cutting path with another common cutting path, rectilinear connection of the common cutting path with another common cutting path.

By functional connection is meant here a connection for which the algorithm defined for the connection in question makes it possible to obtain a non-zero result.

In this case, the method preferably further comprises a check that the applied connections do not generate a deviation of the cutting paths of the two pieces to be cut greater than a predetermined angle.

The invention also relates to the use of the method as defined above for the automatic modification of the cutting path of pieces intended to be cut from a leather skin.

The invention also relates to a computer program comprising instructions for executing the steps of the method for automatically modifying the cutting path of parts as defined above.

The invention also relates to an information medium readable by a computer and comprising instructions of a computer program as mentioned above. The information medium can be any entity or device capable of storing the program. For example, the medium may include a storage means, such as a ROM, for example a CD ROM or a microelectronic circuit ROM, or else a magnetic recording means, for example a floppy disk or a disk. hard.

On the other hand, the information medium can be a transmissible medium such as an electrical or optical signal, which can be conveyed via an electrical or optical cable, by radio or by other means. The program according to the invention can in particular be downloaded from an Internet type network. Alternatively, the information medium can be an integrated circuit in which the program is incorporated, the circuit being adapted to execute or to be used in the execution of the method in question.

Brief description of the drawings

• la figure 1 est une vue schématique montrant un exemple de placement de pièces à découper dans un matériau souple auquel s'applique le procédé selon l'invention ;
• la figure 2 est une loupe de la figure 1 montrant deux pièces du placement pour lesquelles des segments de coupe sont très proches l'un de l'autre ;
• la figure 3 est une vue schématique montrant un exemple de mise en œuvre de l'étape d'identification de deux segments de coupe pour lesquels une condition de distance maximale est respectée ;
• les figures 4A et 4B montrent des exemples de pièces dont des segments de coupe respectent la condition de distance maximale précitée ;
• les figures 5A à 5C illustrent de façon schématique un exemple de mise en œuvre de l'étape de vérification que les deux segments de coupe préalablement identifiés sont situés l'un en face de l'autre ;
• les figures 6A à 6D montrent de façon schématique un exemple de mise en œuvre de l'étape de vérification de l'absence d'autres segments de coupe entre deux segments de coupe ;
• les figures 7A à 7C montrent de façon schématique un exemple de mise en œuvre de l'étape de calcul d'une trajectoire de coupe commune pour deux segments de coupe ;
• la figure 8 montre un exemple de mise en œuvre d'un raccordement d'une trajectoire de coupe commune par prolongation ; et
• la figure 9 montre un exemple de mise en œuvre d'un raccordement rectiligne d'une trajectoire de coupe commune.

Other characteristics and advantages of the present invention will emerge from the description given below, with reference to the appended drawings which illustrate an exemplary embodiment thereof without any limiting nature. In the figures:

• the figure 1 is a schematic view showing an example of the placement of pieces to be cut in a flexible material to which the method according to the invention applies;
• the figure 2 is a magnifying glass of the figure 1 showing two parts of the placement for which cut segments are very close to each other;
• the figure 3 is a schematic view showing an exemplary implementation of the step of identifying two cutting segments for which a maximum distance condition is met;
• the figures 4A and 4B show examples of parts whose cutting segments meet the aforementioned maximum distance condition;
• the figures 5A to 5C schematically illustrate an example of implementation of the step of verifying that the two previously identified cutting segments are located one opposite the other;
• the figures 6A to 6D schematically show an example of the implementation of the step of verifying the absence of other cutting segments between two cutting segments;
• the figures 7A to 7C schematically show an example of implementation of the step of calculating a common cutting path for two cutting segments;
• the figure 8 shows an example of implementation of a connection of a common cutting path by extension; and
• the figure 9 shows an example of implementation of a rectilinear connection of a common cutting path.

Detailed description of the invention

In the following description, it is envisaged the cutting of parts in skins for the production of leather articles. The invention is however applicable to the cutting of parts in a flexible material other than leather.

The figure 1 represents an example of placement P of several pieces p-1, p-2, p-3, ... etc. intended to be cut from a skin. Typically, this placement P is a digital file which includes a digital representation of the skin with its possible defects and a digital representation of the outline of each part to be cut from the skin. The parts (that is to say their digital representation) are positioned on the skin (that is to say its digital representation) according to an optimized placement taking into account in particular any defects of the skin and so as to minimize loss of material.

This placement P is carried out by means of appropriate software equipping a computer workstation, either automatically or via an operator. The placement P is then converted into a workpiece cutting program, that is, instructions for moving a cutting head in the skin positioned on a cutting table along predetermined cutting paths.

The cutting paths associated with each piece to be cut are defined by a succession of rectilinear cutting segments connected to one another to form a polygon encompassing the geometric contour of the piece.

The optimized placement P can give rise to the positioning of two parts very close to each other: this is particularly the case for parts p-2 and p-3 illustrated on the figure 1 . Indeed, as shown in more detail on figure 2 , these parts p-2, p-3 each have a side, respectively c-2 and c-3, for which the cutting paths are very close to each other. By way of example, by cutting paths very close to one another is meant paths which are less than 1 mm apart from each other.

In this situation, after cutting the first part (for example the part p-2), the blade of the cutting tool which cuts the second part (for example the part p-3) may be "attracted" by the cutting of the first part due to the proximity of the latter. As a result, the second part has cutting defects which adversely affect the quality of the cut part.

To avoid this problem, the method according to the invention provides for automatically modifying the cutting paths of the two parts p-2 and p-3 by modifying the cutting segments corresponding to the respective sides c-2, c-3 of these pieces to create two perfectly overlapping cutting paths for these two cutting segments. Thus, the cutting tool will pass twice between the two parts p-2, p-3 but on exactly the same path.

The first step of the method according to the invention consists in automatically identifying in the placement P all the pairs of cutting segments belonging to two different pieces to be cut in the material and for which a maximum distance condition between these cutting segments is respected.

This first step is accomplished by expanding each piece of the placement to the maximum distance and intersecting with the other pieces in the placement to determine which ones meet the maximum distance condition.

The figure 3 illustrates an example of implementation of this first step for two parts pi and pj of the placement (diagram (A)). For reasons of clarity, these parts have been shown here with a circular outline. Of course, the dilation principle described below is suitable for parts with a polygonal outline.

In a first sub-step, one of the two parts (the part p-i on the example of diagram (B)) is expanded by a predetermined value d corresponding to the maximum distance (for example 1mm). In practice, this expansion corresponds to an expansion of the polygon formed by the part cutting segments p-i and makes it possible to obtain a first expanded part p'-i.

In a second sub-step (diagram (C) of the figure 3 ), we identify the geometric intersection between the first expanded part p'-i and the second part pj (more precisely the cutting segments associated with this second part). Here, this intersection is represented by the arc of a circle sj.

In a third sub-step, the second part (the part p-j on the example of diagram (D)) is in turn expanded by the predetermined value d so as to obtain a second expanded part p'-j.

The geometric intersection between the second expanded part p'-j and the first part pi is then identified. On the example of figure 3 , this intersection gives an arc of a circle if.

Finally, the last sub-step provides for bringing together the two intersections si, sj thus identified so as to obtain two cutting segments belonging to two different parts pi, pj to be cut and for which the condition of maximum distance d between these cutting segments is respected.

This first step of the method consisting in identifying two cutting segments for which a condition of maximum distance between these cutting segments is respected is carried out for all the parts p of the placement P.

The second step of the method according to the invention consists in automatically checking that the two previously identified cutting segments are indeed located one opposite the other.

Indeed, as illustrated on figure 4A , it is possible that the algorithm developed during the first step of the method identifies in the placement two parts pi, pj for which two respective cutting segments, ci and cj, are spaced from each other by a distance less than the predetermined maximum distance. However, as clearly visible on this figure 4A , these two cutting segments ci, cj are not located opposite each other, so that a common cutting path cannot be established for these cutting segments.

Likewise, as illustrated on figure 4B , it is also possible that the algorithm of the first step of the method identifies two parts pk, pl for which two respective cutting segments, ck and cl, are spaced from each other by a distance less than the distance maximum predetermined while one of these cutting segments (here the segment ck) is longer than the other. In this situation, the step of establishing a common cutting path for these two cutting segments may pose a problem.

To avoid these pitfalls, the second step of the method according to the invention provides for adding a constraint to the pairs of previously identified cutting segments to ensure the possibility of establishing a common cutting trajectory.

To this end, this second step comprises, for each pair of identified cutting segments, a first sub-step consisting in carrying out a projection of each cutting segment on the other cutting segment (or rather on the line which bears this other cutting segment) in a direction orthogonal to the arrival cutting segment.

An example is shown on figure 5A with two cutting segments ci, cj for which it has been previously verified that the maximum distance condition has been respected.

The two ends c-i-1, c-i-2 of the cutting segment c-i are projected orthogonally on the line which bears the cutting segment c-j. These projections intersect the straight line which carries the section segment cj at a point A for the end ci-1, and at a point B for the other end ci-2, these points of intersection possibly being on the segment of cut cj (case of point A) or outside this cut segments (case of point B).

Likewise, the two ends cj-1, cj-2 of the cutting segment cj are projected orthogonally on the line which bears the cutting segment ci. These projections cross the line which carries the section segment ci at a point C (here located outside the section segment ci) for the end cj-1, and at a point D (here located on the section segment ci) for the other end cj-2.

A second sub-step consists in carrying out the projection of each section of section on the other section of section (or rather on the line which bears this other section of section) in a direction orthogonal to the projected section of section.

Thus, on the example illustrated by figure 5B , the two ends ci-1, ci-2 of the cutting segment ci are projected onto the straight line which bears the cutting segment cj in a direction orthogonal to the cutting segment ci. These projections cross the straight line which carries the segment of section cj at a point E (for the end ci-1) and at a point F (for the end ci-2).

Likewise, the two ends c-j-1, c-j-2 of the cutting segment c-j are projected onto the line which carries the cutting segment c-i in a direction orthogonal to the cutting segment c-j. These projections intersect the line which carries the section segment c-i at a point G (for the end c-j-1) and at a point H (for the end c-j-2).

The last sub-step then consists in making the union of the projections thus carried out and in eliminating the parts which are outside the cutting segments so as to obtain two portions of cutting segments located one opposite the other. .

In the example illustrated by figure 5C , this union gives the two cut segment portions delimited, for the cutting segment ci, by the points ci-1 and H, and for the cutting segment cj, by the points A and cj-2. It is considered that these two portions of the section segment are located opposite each other.

The third step of the method according to the invention consists in verifying the absence of other cutting segments between the two previously identified cutting segments. This step ensures that the cut segments that have been identified are on the correct side of the parts (that is, no part of the parts is between the two cut segments).

This third step is carried out by calculating the intersections between the two pieces to be cut. To this end, we check whether the area between the two identified cutting segments intersects a part, and, if so, we check whether we are in an overlapping area between the parts to know if the pair of cutting segments is valid. Of course, in the case where the area between the two cutting segments does not intersect any other part or the parts overlap at this location, the pair of cutting segments is valid and the next step in the process is continued.

An example of the implementation of this third step for two parts pi, pj is described below in conjunction with the figures 6A to 6D .

In this example, it is considered that the two pieces to be cut p-i, p-j overlap at the level of their respective cutting segments c-i, c-j (this overlap being of very small dimensions less than 0.1 mm).

The first sub-step consists in carrying out a calculation of the intersections I1, I2 between the two parts (here two in number - cf. figure 6A ). In a second sub-step, we construct a quadrilateral Q1 formed by the pair of cutting segments ci, cj (cf. figure 6B ). In a third sub-step, one carries out an intersection of this quadrilateral Q1 with the two parts pi, pj (this intersection gives as result the polygon T1 - cf. figure 6C ).

Finally, in a fourth and last sub-step, one carries out a subtraction between the polygon T1 and the intersections I1 and I2 ( figure 6D ). If the result of this subtraction gives an empty set (as in the example of figure 6D ), it is deduced from this that no cutting path is present between the two cutting segments ci, cj and this pair of cutting segments is declared valid with regard to this criterion.

Once the cutting segments have been identified and validated, the method according to the invention provides for concatenating the cutting segments which are adjacent to each other to form cutting trajectories (composed of several adjacent cutting segments), then, during a fourth step, of calculating common cutting paths for all the cutting segments.

An example of the implementation of this step is detailed below in connection with the figures 7A to 7C . In these figures are shown two cutting paths 1, 2 (each formed of several adjacent and concatenated cutting segments) which have been identified and validated according to the steps of the method described above. Of course, the same method is used when the cutting path is formed by only one cutting segment.

More precisely, the cutting path 1 is here formed of three interconnected cutting segments, namely the segments 10 to 12, while the cutting path 2 is formed of two cutting segments 20, 21. The cutting segments 10 to 12 are delimited by points A, B, C and D. Likewise, the cutting segments 20, 21 are delimited by points E, F and G.

Each cutting path 1, 2 is projected onto the other cutting path keeping the same length ratio for each of the cutting segments 10-12, 20, 21 (see figure 7B ).

Thus, the cutting segment 10 is projected onto the cutting path 2 with the projection of point A at E and the projection of point B at B '(with the length of the segment [AB] divided by that of the path 1 which is equal to the length of the segment [EB '] divided by that of the trajectory 2). Likewise, segment 12 is projected onto cutting path 2 with the projection of point D in G and that of point C in C '(with the length of segment [CD] divided by that of path 1 which is equal to the length of the segment [C'G] divided by that of the trajectory 2).

In addition, the cut segment 20 of the cut path 2 is projected onto the cut path 1 with the projection of point E at A and the projection of point F at F '(the length of the segment [EF] divided by that of trajectory 2 is equal to the length of segment [AF '] divided by that of trajectory 1). Finally, the cutting segment 21 is also projected on the cutting path 1 with the projection of the point F in F 'and the projection of the point G in D (the length of the segment [FG] divided by that of the path 2 is equal to the length of the segment [F'D] divided by that of the trajectory 1).

From the segments [AE], [BB '], [FF'], [CC '] and [DG] thus created, this step provides for creating a common cutting path 30 from the points situated at equal distances from the ends. of these segments (namely point I for segment [AE], point J for segment [BB '], point K for segment [FF'], point L for segment [CC '] and point M for segment [DG]).

The last step of the method according to the invention consists in connecting the common cutting path to the cutting path of the two pieces to be cut so as to obtain modified cutting paths for the two pieces to be cut.

This connecting step is carried out to try to keep as much as possible the shape of the contours of the parts to be cut. Depending on the situation encountered, different types of connection are possible, including connection by extension for which an example of implementation is shown on the figure 8 and the rectilinear connection for which an example of implementation is illustrated on the figure 9 .

In the example of a connection by extending the figure 8 , there is shown the common cutting path 30 with the end point Pe of the latter, as well as the contour 32 of the part to which the cutting path is connected.

The outline 32 of the part to which the cutting path is connected is formed of a plurality of cutting segments. If we consider the point P1 as being the end point of the contour 32 having served for the calculation of the common cutting path 30, the contour 32 is here formed of the cutting segments [P1P2], [P2P3], [P3P4 ], etc.

The algorithm for implementing this step of connection by extension provides for traveling, from point P1, each section of the contour 32 to the one for which the cumulative curvilinear distance does not exceed twice the maximum distance d defined in the first step of the process according to the invention. By “cumulative curvilinear distance” is meant the distance along the curve between point P1 and the section segment considered, ie the sum of the lengths of the section segments [P1P2], [P2P3], etc. up to the cut segment considered.

For each of these segments [P1P2], [P2P3], [P3P4], etc., the step of connection by extension successively implements the following sub-steps.

During a first sub-step, the parallelism between the segment and the common cutting path is checked. If the segment is parallel to the common cutting path, we move on to the next segment.

During a second sub-step, the point of intersection between the segment considered and the common cutting path (or their respective extension) is considered. If this point of intersection is beyond the end of the segment furthest from the common cutting path, you move on to the next segment.

On the example of figure 8 , let I1, I2, I3 be the respective intersections between the segments [P1P2], [P2P3], [P3P4] and the common cutting path 20. Here, only the points I1 and I3 fully comply with the aforementioned condition (which does not is not the case with point I2).

For the first segment retained at the end of the previous sub-step, the third sub-step provides for comparing the distance between the previously determined point of intersection and the end point Pe of the common cutting path with a threshold predetermined corresponding to the maximum distance d defined in the first step of the method according to the invention.

If this distance between the point of intersection and the end point Pe is greater than the maximum distance d, we move on to the next segment. On the other hand, as soon as we obtain a segment for which the distance between the point of intersection and the end point Pe is less than or equal to the maximum distance d, we keep this point of intersection as the point of connection between the common cut path and the contour of the part.

Moreover, if after having traversed all the segments of the contour without finding an intersection point fulfilling the aforementioned condition, the connection by extension cannot be applied.

In the example shown on figure 8 , the point of intersection I1 between the segment [P1P2] and the common cutting path is located at a distance greater than the maximum distance d from the end Pe of the common cutting path 30. On the other hand, the distance between the point of intersection I3 between the segment [P2P3] and the common cutting path and the point Pe is here less than the distance d , so that this point I3 is kept and defined as being the point of connection between the cutting path joint and the outline of the room.

In conjunction with the figure 9 , we will now describe an example of another type of connection, namely a rectilinear connection of the common cutting path.

In this figure, there is shown the common cutting path 30 with the end point Pe of the latter, as well as the contour 32 of the part to which the cutting path is connected, the latter consisting of segments [P1P2], [P2P3], etc. (P1 being the end point of the contour having been used for the calculation of the common cutting path 30).

As for the connection by extension, the algorithm for implementing this rectilinear connection step provides for traversing, from point P1, each section of the contour to the one for which the cumulative curvilinear distance does not exceed two times the maximum distance d defined in the first step of the process.

In addition, this algorithm proposes to check that the connections applied do not generate a deviation of the cutting paths of the two pieces to be cut greater than a predetermined angle α (typically 20 °).

For each of these segments [P1P2], [P2P3], etc., the rectilinear connection step successively implements the following sub-steps.

During a first sub-step, all of the points I of the segment considered are calculated which make it possible to have a deviation between the common cutting path and the segment [PeI] which is less than the angle α. For this, we calculate the two straight lines Δ which pass through the point Pe and which respectively form an angle + α and -α with the common cutting path 30 (only a single straight line Δ satisfying this condition is shown on the figure 9 ). The points which fulfill the aforementioned condition are the points of the segment considered which lie between the two lines Δ.

During a second sub-step, all the points I of the segment considered are calculated which make it possible to have a deviation between the segment [PeI] and the segment considered which is less than the angle α. For that, one calculates the single point such that this angle is equal to α in absolute value. The points which fulfill the aforementioned condition are the points of the segment considered which are situated beyond this point in the direction of the contour.

Finally, during a third sub-step, the intersection of the two sets obtained in the previous sub-steps is carried out to find the set of points which meet the two conditions at the same time. Any point belonging to this set can constitute the point of connection between the cutting path common and the contour of the part, we then choose the first point in the direction of the contour.

If after having traversed all the segments of the contour without finding an intersection point fulfilling the above condition, the rectilinear connection cannot be applied.

Other types of connection than those detailed previously can be envisaged. For example, it is possible to apply a rectilinear connection with shortening of the common cutting path. This type of blend is more particularly applicable when a common cutting path ends at a very acute angle to the contour of a part. In this case, the two aforementioned types of connection cannot be used. The algorithm for blending with shortening is the same as for straight blending, but instead of starting from the end of the common cutting path (point Pe), the end of the acute angle is taken as the fixed point formed by the contour of the part and each section of the contour is traversed as previously described.

When two common cut paths are to be connected to each other and they end near a corner of a part, these common cut paths can be extended to their intersection (join by extension of the common cut path with another common cut path).

When two common cutting paths are parallel (or quasi-parallel) to each other, the aforementioned type of connection does not apply and we can instead apply a rectilinear connection of the common cutting path with another common cutting path . With this type of connection, we take as a fixed point the end of a common cutting path and we traverse the segments of the other common cutting path (we choose the fixed point on the common cut path closest to the pieces to avoid cutting the corner of a piece).

If several types of connection are possible, it is important to specify an order of priority between these connections. For the aforementioned types of connection, the order of priority retained is as follows: first, the connection is applied by extending the common cutting path, then if necessary the connection straight line of the common cutting path, then if necessary the connection with shortening of the common cutting path, then if necessary the straight connection with shortening of the common cutting path, then if necessary the connection by extending the common cutting path with another common cutting path, and finally if necessary the rectilinear connection of the common cutting path with another common cutting path.

Claims (11)

1. A method of automatically modifying the cutting paths for parts (p-1, p-2, ...) that are to be cut out from a flexible material by automatically moving a cutter tool along predetermined cutting paths, the cutting paths associated with each part being defined by a succession of cutting segments forming a polygon, the method comprising in succession:

   - a step of identifying two cutting segments (c-i, c-j) belonging to two different parts (p-i, p-j) for cutting out in the material and for which a maximum distance condition (d) between these cutting segments is satisfied;

   - a step of verifying that the two previously-identified cutting segments are situated facing each other by reciprocal orthogonal projection of the cutting segments onto each other;

   - a step of verifying that no other cutting segments lie between the two previously-identified cutting segments by computing intersections between the two parts for cutting out;

   - a step of computing a common cutting path (30) for the two previously-identified cutting segments; and

   - a step of connecting the common cutting path to the cutting paths of the two parts for cutting out so as to obtain modified cutting paths for the two parts for cutting out.
2. A method according to claim 1, wherein the step of identifying two cutting segments comprises, in succession and for each part for cutting out:

   - expanding the polygon formed by the cutting segments of said part by a predetermined value in order to obtain a first expanded polygon;

   - identifying an intersection between the first expanded polygon and a polygon formed by the cutting segments of another part;

   - expanding the polygon formed by the cutting segments of the other part by the predetermined value in order to obtain a second expanded polygon;

   - identifying an intersection between the second expanded polygon and the polygon formed by the cutting segments of said part; and

   - uniting intersections in order to obtain cutting segments belonging to two different parts for cutting out and for which a maximum distance condition between these cutting segments is satisfied.
3. A method according to claim 1 or claim 2, wherein the step of verifying that the previously-identified cutting segments are situated facing each other comprises:

   - reciprocally orthogonally projecting the cutting segments onto each other;

   - projecting each cutting segment onto the other cutting segment in a direction orthogonal to the projected cutting segment; and

   - uniting the projections as performed in this way in order to obtain two cutting segment portions situated facing each other.
4. A method according to any one of claims 1 to 3, wherein the step of verifying that no other cutting segments lie between the two cutting segments comprises, in succession:

   - computing intersections between the two parts;

   - constructing a geometrical quadrilateral formed by the two cutting segments;

   - intersecting between the previously-constructed quadrilateral and the two parts for cutting out; and

   - subtracting the overlaps between the two parts for cutting out from the previously-constructed quadrilateral.
5. A method according to claim 4, further comprising, when the subtraction of overlaps gives an empty set, indicating that no cutting path is present between the two cutting segments.
6. A method according to any one of claims 1 to 5, wherein the step of computing a common cutting path for the two cutting segments comprises:

   - projecting each cutting segment onto the other cutting segment while conserving the same length ratio for each segment; and

   - creating a common cutting path by connecting together points situated at equal distances from the ends of the projections of the cutting segments.
7. A method according to any one of claims 1 to 6, wherein the step of connecting the common cutting path to the cutting paths of two parts for cutting out comprises applying the following connections taken in succession until a functional connection is obtained: connection by extending the common cutting path, straight-line connection of the common cutting path, connection with shortening of the common cutting path, straight-line connection with shortening of the common cutting path, connection by extending the common cutting path with another common cutting path, straight-line connection of the common cutting path with another common cutting path.
8. A method according to claim 7, further comprising verifying that the connections that are applied do not lead to the cutting paths of two parts for cutting out being deflected by more than a predetermined angle.
9. The use of the method according to any one of claims 1 to 8 to modify automatically the cutting path for parts that are to be cut from a leather skin.
10. A computer program including instructions for executing steps of the method according to any one of claims 1 to 8 for modifying the cutting paths of parts.
11. A computer readable data medium storing a computer program including instructions for executing steps of the method according to any one of claims 1 to 8 for modifying the cutting paths of parts.

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