EP0682481B1 - Method for automatically cutting a flexible sheet material - Google Patents

Description

The present invention relates to an automatic cutting process for a flexible sheet material by controlling the relative displacement between the material and a cutting blade along a cutting path comprising several paths connected together.

More particularly, the invention relates to the control of rotation of the cutting blade when passing an angle formed by two consecutive paths of the cutting path.

One field of application of the invention is that of cutting machines with numerical control used for the cutting of fabrics, felts, leather or others flexible sheet materials in the clothing industry, furniture ... With these machines, the cutting is carried out by means of a vibrating blade carried by a cutting head and moved through the flexible sheet material, the latter being frequently arranged in superimposed sheets forming a mattress.

The cutting blade is moved within the material along a path cut which reproduces a cut to be made and which is the form of trajectories (portions of straight lines and possibly portions of curves) connected together.

On each trajectory, the blade is moved while being oriented substantially tangential to the path, with cutting speed and acceleration determined. Cutting speed and acceleration are set by the operator or are contained in a command file of a host computer or of a memory of a removable storage medium (cassette, magnetic tape, floppy disk, hard disk, ...). Thus, for this given trajectory, the cutting blade is initially accelerated, at a predetermined maximum cutting acceleration until reaching (if necessary) a predetermined maximum cutting speed, before being slowed down, if necessary to zero speed, to approach the next trajectory. The set speed and acceleration thus determined for describe a trajectory are hereinafter designated by speed and acceleration tangential.

When cutting flexible sheet material, interactions between the material and the blade can cause those to turn away from the cutting path desired or flex in the thickness of the mattress. This results in defects geometric level of the cut pieces.

Solutions have been described to reduce cutting defects by reducing the lateral forces exerted on the cutting blade. So in the patent FR 2 388 337 it is proposed to use a sensor to detect these lateral forces and orient the blade in a direction which deviates from the tangent to the trajectory to balance the forces on each side of the blade.

However, these known solutions do not make it possible to resolve the difficulties encountered when passing angles between trajectories of the cutting path. When passing at an angle, a rotation of the blade is necessary so that it remains tangent to the trajectory it describes. Because that the rotation cannot be instantaneous when the blade reaches the top of the angle, a technique known from document FR 2 141 386, which represents the preamble of main claim 1, consists in carrying out the rotation over a distance predetermined before and after the passage of the summit. This technique presents several disadvantages.

The rotation time is determined by the time taken for the blade to cover the determined distance before and after the vertex of the angle; so she is very correlated to the tangential acceleration of the blade. Indeed, if the deceleration tangential of the blade before reaching the top of the angle and the acceleration tangential of the blade after passing the vertex are large, the rotation time is small and requires a high speed of rotation. In addition, the rotation time does not not depend on the value of the angle, so the speed of rotation will be as much higher than the angle of rotation of the blade is large. Now, a high speed of rotation generates significant lateral forces on the blade and a deflection of this one. This results in a geometric cutting defect for the plies of material. sheet inside and at the base of the mattress.

In order to reduce the risk of blade bending, it can be considered to increase the distance over which the rotation takes place as shown in US Patent 4,178,820. But, the more this distance is higher, the higher the cutting speed is likely to be at the start and end of the rotation. If the blade is forced to move across from the trajectory at high speed, after starting or before completing its rotation, the quality of cut is impaired and the risk of breakage of the blade is high.

These drawbacks can lead to the need to lift the blade out of its engagement with the sheet material to rotate at the cutting path angles, which degrades productivity.

The object of the present invention is to propose a cutting method automatic sheet material in one or more layers whereby the rotation of the cutting blade in the corners is carried out without causing aforementioned drawbacks

In particular, the invention aims to provide a method for rotate the cutting blade while minimizing the risk of bending and breakage and with improved cutting quality and productivity.

• la découpe est réalisée par commande automatique du déplacement relatif entre la matière et la lame de coupe le long du chemin de coupe, en fonction de vitesse et d'accélération tangentielles de consigne déterminées sur chaque trajectoire,
• au passage d'un angle raccordant une première trajectoire à une deuxième trajectoire, une rotation de la lame de coupe est commandée pendant son déplacement au sein de la matière pour passer automatiquement d'une première orientation dans laquelle la lame est sensiblement tangente à la première trajectoire à une deuxième orientation dans laquelle la lame est sensiblement tangente à la deuxième trajectoire,
  procédé dans lequel, selon l'invention :
• la rotation de la lame est accomplie à une vitesse moyenne de rotation prédéterminée sur un parcours de rotation constitué pu une partie de longueur prédéterminée de la première trajectoire et/ou de la deuxième trajectoire qui se termine ou comment au sommet de l'angle ou inclut celui-ci.

These aims are achieved by a process according to which:

• cutting is carried out by automatic control of the relative displacement between the material and the cutting blade along the cutting path, as a function of tangential speed and tangential acceleration of setpoint determined on each trajectory,
• when passing an angle connecting a first trajectory to a second trajectory, a rotation of the cutting blade is controlled during its movement within the material to automatically pass from a first orientation in which the blade is substantially tangent to the first trajectory at a second orientation in which the blade is substantially tangent to the second trajectory,
  process in which, according to the invention:
• the rotation of the blade is accomplished at a predetermined average speed of rotation on a rotation path consisting of a portion of predetermined length of the first trajectory and / or of the second trajectory which ends or how at the top of the angle or includes this one.

According to a feature of the process according to the invention, the speed average displacement of the cutting blade along the rotation path is correlated with the average speed of rotation of the blade and the value of the angle, while that the displacement of the cutting blade on the first and / or the second trajectory outside the rotation path is carried out at speeds and acceleration of tangential sections determined for this trajectory or these trajectories. He will be able to be provided that the instantaneous speed of movement of the cutting blade is correlated to the instantaneous speed of rotation of the blade.

Thus, the method is remarkable in that the speed of rotation of the blade is controlled, and is not linked to the tangential speeds and accelerations of the setpoint of the blade on the trajectories. On the rotation path, the displacement of the blade is carried out with a speed correlated to that of rotation of the blade.

On the rotation path, there is therefore inhibition of the command of the displacement of the blade from the tangential speeds and accelerations of setpoint, and only on it.

The length of the blade rotation path is chosen so that minimize lateral forces on the blade during rotation, thus reducing the bending of the blade and obtaining better respect for the geometry, in particular for the tablecloths located below the mattress when cutting is carried out on a plurality of overlapping layers. The average speed of rotation is chosen or the operator according to the desired compromise between quality of cut - which presupposes a rather low speed of rotation - and productivity - which supposes a speed rather high-.

Significant angles can be described without the need to lift the cutting blade, resulting in improved productivity.

In addition, the method according to the invention made it possible to make cuts. including V-shaped notches with very high quality, including in hard materials. However, V-shaped notches require the completion of the blade three successive rotations, in opposite directions, and the method of the prior art does not would not allow, in such a case, to obtain a very clear cut.

In addition, because the speed of rotation of the blade is not correlated with tangential acceleration of the blade on its path, unlike art it is possible to increase this acceleration without degrading the quality of cut, and therefore improve productivity.

Finally the control of the forces exerted on the blade makes it possible to increase the service life of the blade and the cutting head of the machine.

• la figure 1 est un diagramme illustrant très schématiquement une installation de découpe dans laquelle un procédé selon l'invention peut être mis en oeuvre,
• les figures 2A, 2B et 2C montrent de façon très schématique des positions prises pu la lame lors de sa rotation au passage d'un angle raccordant deux trajectoires consécutives d'un chemin de coupe, et
• la figure 3 est un organigramme montrant les étapes successives de la commande de la rotation d'une lame de coupe, selon un mode de mise en oeuvre de l'invention.

Other particularities of the method according to the invention will emerge on reading the description given below, by way of indication but not limitation, with reference to the appended drawings in which:

• FIG. 1 is a diagram very schematically illustrating a cutting installation in which a method according to the invention can be implemented,
• FIGS. 2A, 2B and 2C very schematically show positions taken by the blade during its rotation when passing an angle connecting two consecutive trajectories of a cutting path, and
• FIG. 3 is a flowchart showing the successive stages of the control of the rotation of a cutting blade, according to an embodiment of the invention.

Automatic cutting machines with numerical control allowing cutting a flexible material into a sheet, in particular of several layers superimposed of such material, along a predetermined cutting path, are known, in particular in the field of clothing.

The cutting is carried out by means of a vibrating blade 10 carried for a cutting head 12. This is moved along two of these orthogonal X, Y by compared to a horizontal table 20 carrying a mattress 22 made of sheets supperposées 24 of flexible sheet material. The mattress can be kept on the vacuum table.

The cutting head 12 carries a motor (not shown) which distributes to the blade an alternating vertical vibration movement, and a motor (not shown) which used to orient the blade for rotation about a vertical axis 14. The cutting head further includes an actuator (not shown) for lifting the blade 10 above the mattress 22 or lower it inside it.

The movements of the cutting head in X and Y are controlled by respective motors 32, 34 from signals supplied by a control unit 40. The unit 40 may for example consist of a computer. The displacements of the cutting head are controlled by the computer 40, to allow cutting of the mattress 22 following a predetermined cutting path. To this end, the path of section is broken down into elementary paths (line segments and possibly portions of curves) connected to each other.

For each trajectory, the speed and acceleration of the blade for its cutting movement along the trajectory are determined by the computer 40. The computer 40 also controls the blade drive motors cutting in vibration and rotation, as well as raising and lowering the blade chopped off.

A machine as succinctly described above is well known from one skilled in the art so that a more detailed description is not necessary.

With this type of machine, a difficulty lies in controlling the rotation of the blade around its vertical ce, when passing an angle A between a trajectory T1 and a trajectory T2, so that the blade passes from one orientation tangent to the path T1 to an orientation tangent to the path T2, while respecting the desired geometry for cutting.

According to the invention, this rotation is carried out at a speed of predetermined mean rotation Vr, over a rotation path of length Dr predetermined located on either side of the vertex of angle A, or on either side else from the top.

In the example illustrated in FIG. 2A, the rotation path is a length segment Dr bounded by the vertex O of angle A and a point B on the T2 path traveled after the T1 path.

The speed of rotation Vr is chosen so as to achieve a compromise between cutting quality and productivity imperatives. The Vr value varies according to the nature and number of the plies 24 constituting the mattress 22.

The distance Dr is chosen so that, taking into account the speed mean of rotation Vr and of the geometry of the blade (distance l between the wire cutting edge and rear of the blade), the result of the lateral forces exerted on the blade is minimized. As an indication, for a mattress of 50 sheets of denim, the average speed of rotation Vr can be chosen at a value approximately equal to 600 degrees / s and the rotation distance Dr to a value equal to approximately 5 mm with a blade for which l = 8 mm.

The control and sequence of the blade rotation when passing angle A can be seen from the flowchart in Figure 3.

The elementary paths constituting the cutting path are received (phase 101) and processed (phases 102). The angle A between a trajectory T1 and a trajectory T2 (i.e. the angle by which the blade must turn to pass from one orientation tangent to T1 to orientation tangent to T2) is compared to a value minimum A1 and a maximum value A 2 (test 103).

If A <A1 (test 104), the rotation is relatively weak and is performed on a distance dr immediately before the vertex of the angle and a distance dr immediately after the top of the angle without changing the setpoints acceleration and cutting speed for the movement of the blade on the T1 and T2 trajectories (phase 105). The rotation is therefore carried out according to the method of the prior art mentioned at the head of this description. The average speed of rotation is determined according to the known value of the distance dr and the known values of the speed and acceleration of the blade on the trajectories.

If the angle A> A2, the rotation is very important. It is carried out as soon as the blade finished the trajectory T1 with zero speed, was able to lift the blade out of the material, rotation of the blade and re-introduction of the blade into the material (phase106).

As an indication, for the example indicated above, the values of A1 and A2 can be chosen equal to 10 ° and 120 ° respectively.

If the angle A is such that A1≤A≤A2, the blade is rotated according to the process according to the invention, that is to say in the example of the FIG. 2A, by termination of the path T1 without rotation of the blade, orientation of the blade at a predetermined average speed of rotation on the path of rotation of length Dr, and termination of the path T2 (distance D2 - Dr) at target tangential speed and acceleration.

The length D2 of the path T2 is compared to the predetermined value Dr (test 107). If D2≤Dr, then the Dr value is modified to be at most equal to D2, for example less than D2 by 1 / 10mm (phase 108). The remaining 1 / 10mm is performed at setpoint acceleration and tangential speed, before a new blade rotation. The goal is to complete the rotation course characterized by control the speed of rotation and resume normal travel.

The blade rotation time Tr is calculated (phase 109) by performing Tr = A / Vr .

If Tr is less than a minimum value Tr1 (test 110), the value of Vr is decreased to be equal to A / Tr1 (phase 111). Indeed, the duration Tr, which represents also the time taken by the blade to cover the distance Dr should not be too much small at the risk of imposing too much acceleration on the cutting head the blade reaches the end of the rotation path at the same time as the rotation ends.

The average speed Dr / Tr of movement of the cutting blade on the rotation path is correlated with the average speed of rotation and at angle A since Dr / Tr = Dr x (Vr / A) . The law of acceleration and speed of movement of the blade as a function of time on the rotation path is determined as a function of the average speed Dr / Tr, and taking into account the maximum acceptable acceleration and speed (phase 112). It can be made so that the instantaneous speed of movement of the cutting blade on the rotation path is correlated with the instantaneous speed of rotation.

Then, the rotation of the blade and its displacement on the course of rotation are controlled (phase 113).

During rotation, the instantaneous angle of rotation Ai accomplished by the blade is calculated at successive times Ti counted from the origin of the rotation, according to the relation Ai = A xf (Ti, Tr) , for example Ai = A x (Ti / Tr) .

As soon as Ai ≥ A (test 114), the rotation path is completed (phase 115).

The rest of the path T2 is then completed (phase 118) by taking counts the tangential speed and acceleration setpoints, predetermined for the distance D2-Dr.

In the foregoing, the rotation path of length Dr is placed at the start of the T2 trajectory. It is alternatively possible to place it at the end of the trajectory T1 (figure 2B) or on either side of the vertex of angle A (figure 2C).

In all cases, the rotation path begins or ends at vertex of the angle, or includes it.

Claims (8)

1. A method of automatically cutting flexible sheet material (22) along a cutting path including a plurality of interconnected runs (T1, T2), in which method:

   cutting is performed by automatically controlling relative displacement between a cutting blade (10) and the material (22) along a cutting path as a function of reference tangential acceleration and speed that are determined for each run; and

   on negotiating a corner (A) interconnecting a first run (T1) to a second run (T2), the cutting blade is caused (12) to turn within the material while it is moving in order to cause it to pass automatically from a first orientation in which the blade is substantially tangential to the first run to a second orientation in which the blade is substantially tangential to the second run,
      the method being characterised in that:

   The control of blade displacement as a function of the reference tangential accelerations and speeds is inhibited and the blade is turned at a predetermined mean rate of turn over a turning distance constituted by a portion of predetermined length of the first run and/or of the second run, which portion terminates or begins at the vertex of the corner or includes the vertex.
2. A method according to claim 1, characterized in that the mean speed of displacement of the cutting blade along the turning distance is correlated to the mean rate of turn of the blade and to the angle of the corner, whereas displacement of the cutting blade over the first and/or second run outside the turning distance is performed at the tangential cutting acceleration and speed that are determined for said run(s).
3. A method according to any one of claims 1 and 2, characterized in that the instantaneous speed of displacement along the turning distance is correlated to the instantaneous rate of turn, while displacement of the cutting blade along the first and/or second run outside the turning distance is performed at tangential cutting acceleration and speed that are determined for said run(s).
4. A method according to any one of claims 1 to 3, characterized in that the cutting blade is caused to turn over a turning distance constituted by a portion of predetermined length at the beginning of the second run.
5. A method according to any one of claims 1 to 4, characterized in that it is performed when the angle between the first and second runs is not greater than a maximum predetermined magnitude beyond which the blade is turned at the end of the first run while the blade is outside the material.
6. A method according to any one of claims 1 to 5, characterized in that it is implemented when the angle between the first and second runs is not less than a minimum predetermined magnitude below which the blade is turned within the material over a predetermined distance on either side of the vertex of the corner while the cutting blade is moving at reference tangential accelerations and speeds that are determined for the first and second runs.
7. A method according to any one of claims 1 to 4, characterized in that when the length of the turning distance is greater than the length of the run on which it is situated, the length of the turning distance is reduced so as to terminate no later than the end of the run.
8. A method according to any one of claims 1 to 5, characterized in that it includes calculating the turning time as a function of the angle of the corner and of the magnitude of the predetermined mean rate of turn, and the choice of a new magnitude for the mean rate of turn less than the predetermined magnitude whenever the turning time is less than a predetermined minimum threshold.

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