WO1994017683A1

WO1994017683A1 - Method for automatically cutting a flexible sheet material

Info

Publication number: WO1994017683A1
Application number: PCT/FR1994/000117
Authority: WO
Inventors: Philippe Bousquet
Original assignee: Lectra Systemes
Priority date: 1993-02-08
Filing date: 1994-01-31
Publication date: 1994-08-18
Also published as: EP0682481B1; ES2121188T3; DE69412460T2; FR2701229B1; FR2701229A1; EP0682481A1; JPH08506767A; DE69412460D1

Abstract

Cutting is performed by automatically controlling relative movement between a cutting blade and a material along a desired cutting line according to set tangential speed and acceleration values for each line. On reaching an angle between a first cutting line path and a second path, the blade is rotated as it moves through the material so that it switches automatically from a first direction tangential to the first path, to a second direction tangential to the second path. Blade rotation takes place at a predetermined average rotation speed over a rotational path consisting of a predetermined portion of the first path and/or the second path which ends or begins at the apex of the angle or includes said apex. The average speed of the blade moving along the rotational path is correlated to the average blade rotation speed and the angle value, whereas the cutting blade moves along the first path and/or the second path, when outside the rotational path, at a set tangential cutting acceleration and speed determined for said path(s).

Description

Method for automatic cutting of flexible sheet material

The present invention relates to an automatic cutting process for flexible sheet material by controlling the relative movement 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 the rotation of the cutting blade when passing an angle formed by two consecutive trajectories of the cutting path.

One field of application of the invention is that of numerically controlled cutting machines used for cutting fabrics, felts, leather or other flexible sheet materials in the clothing industry, furniture ... 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 overlapping plies forming a mattress. The cutting blade is moved within the material along a cutting path which reproduces a cut to be made and which is formed of paths (portions of straight lines and possibly portions of curves) connected together.

On each trajectory, the blade is moved while being oriented substantially tangentially to the trajectory, with a determined speed and acceleration of cutting. The cutting speed and acceleration are set by the operator or are contained in a command file of a host computer or in a memory of a removable storage medium (cassette, magnetic tape, floppy disk, hard disk, ...). Thus, for a given trajectory, the cutting blade is initially accelerated, at a predetermined maximum cutting acceleration until reaching (possibly) a predetermined maximum cutting speed, before being slowed down, if necessary to a speed zero, to approach the next trajectory. The setpoint speed and acceleration thus determined to describe a trajectory are hereinafter referred to as tangential speed and acceleration. When cutting the flexible material into sheets, interactions between the material and the blade can cause the latter to turn away from the desired cutting path or to bend in the thickness of the mattress. This results in geometric defects in the cut pieces.

Solutions have been described to reduce cutting defects by reducing the lateral forces exerted on the cutting blade. Thus, in patent FR 2388337 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 which are encountered in passing angles between consecutive trajectories of the cutting path. When passing an angle, a rotation of the blade is necessary so that it remains tangent to the path it describes. Since the rotation cannot be instantaneous when the blade reaches the apex of the angle, a known technique consists in performing the rotation over a predetermined distance before and after the passage of the apex. This technique has several drawbacks.

The duration of rotation is determined by the time taken by the blade to travel the determined distance before and after the top of the angle; it is therefore highly correlated to the tangential acceleration of the blade. Indeed, if the tangential deceleration of the blade before reaching the top of the angle and the tangential acceleration of the blade after passing from the top are large, the rotation time is small and imposes a high speed of rotation. In addition, the duration of rotation does not depend on the value of the angle, so that the speed of rotation will be higher the greater the angle of rotation of the blade. However, a high speed of rotation generates significant lateral forces on the blade and a deflection thereof. This results in a geometric cutting defect for the sheets of sheet material inside and at the base of the mattress.

In order to reduce the risk of bending of the blade, it can be envisaged to increase the distance over which the rotation takes place. However, the greater this distance, the more likely the cutting speed is to be high at the beginning and at the end of the rotation. If the blade is forced to move crosswise relative to the path at high speed, after having started or before having completed its rotation, the cutting quality 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 corners of the cutting path, which degrades productivity.

The object of the present invention is to propose an automatic method for cutting a sheet material into one or more layers by means of which the rotation of the cutting blade in the corners is carried out without causing the aforementioned drawbacks. In particular, the object of the invention is to propose a method enabling the cutting blade to be rotated while minimizing the risks of bending and breakage and with improved cutting quality and productivity. These aims are achieved by a process according to which:

the 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 the tangential speed and tangential acceleration of the 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 to a second orientation in which the blade is substantially tangent to the second trajectory, method in which, according to the invention:

the rotation of the blade is carried out at a predetermined average speed of rotation over a rotation path consisting of a portion of predetermined length of the first trajectory and / or of the second trajectory which ends or begins at the top of the angle, or includes this one.

According to a feature of the process according to the invention, the average speed of movement 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 the displacement of the cutting blade on the first and / or the second trajectory outside the rotation path is carried out at tangential cutting speed and acceleration determined for this trajectory or these trajectories. Provision may be made for the instantaneous speed of movement of the cutting blade to be correlated with 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 blade setpoint on the trajectories. On the rotation path, the blade is moved with a speed correlated to that of the blade rotation. On the rotation path, there is therefore inhibition of the control of the movement of the blade from the set tangential speeds and accelerations, and only thereon.

The length of the blade rotation path is chosen so as to minimize the lateral forces on the blade during rotation, therefore to reduce the flexion of the blade and obtain better respect for the geometry, in particular for the plies located below of the mattress when cutting is carried out on a plurality of overlapping layers. The average speed of rotation is chosen by the operator according to the desired compromise between quality of cut - which assumes a rather low speed of rotation - and productivity - which supposes a rather high speed -. It is possible to describe large angles without having to lift the cutting blade, thereby improving productivity.

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

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

Finally, controlling the forces exerted on the blade increases the life of the blade and the cutting head of the machine.

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

- Figure 3 is a flowchart showing the successive steps of controlling the rotation of a cutting blade, according to an embodiment of the invention. Automatic cutting machines with numerical control allowing the cutting of a flexible material in sheet, in particular of several superposed layers of such a material, along a predetermined cutting path, are known, in particular in the field of confection.

The cutting is carried out by means of a vibrating blade 10 carried by a cutting head 12. The latter is moved along two orthogonal axes X, Y with respect to a horizontal table 20 carrying a mattress 22 made up of plies supperposées 24 of flexible sheet material. The mattress can be kept on the table by suction.

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

The displacements of the cutting head in X and in 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 movements of the cutting head are controlled by the computer 40, to allow the cutting of the mattress 22 along a predetermined cutting path. To this end, the cutting path 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 motors for driving the cutting blade in vibration and in rotation , as well as raising and lowering the cutting blade. A machine as succinctly described above is well known to those 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 axis, when passing an angle A between a trajectory T1 and a trajectory T2, in order to ensure that the blade passes from 'an orientation tangent to the path T1 to an orientation tangent to the path T2, while respecting the geometry desired for cutting.

According to the invention, this rotation is carried out at a predetermined average rotation speed Vr, on a rotation path of predetermined length Dr located on one side or the other of the vertex of the angle A, or on both sides. else from the top.

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

The speed of rotation Vr is chosen so as to achieve a compromise between imperatives of cutting quality and productivity. The value Vr varies according to the nature and the number of plies 24 constituting the mattress 22. The distance Dr is chosen so that, taking into account the average speed of rotation Vr and the geometry of the blade (distance 1 between the cutting edge and the 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 equal to approximately 600 degrees / s and the rotation distance Dr at a value equal to approximately 5 mm with a blade for which 1 = 8 mm.

The control and the course of the rotation of the blade at the passage of the angle A appear from the flowchart of figure 3. The elementary trajectories constituting the cutting path are received

(phase 101) and processed (phases 102). The angle A between a trajectory Tl and a trajectory T2 (that is to say the angle whose blade must turn to pass from an orientation tangent to Tl to an orientation tangent to T2) is compared with a minimum value Al and a maximum value A 2 (test 103). If A <A1 (test 104), the rotation is relatively weak and is accomplished over a distance dr immediately before the vertex of the angle and a distance dr immediately after the vertex of the angle without modifying the acceleration and cutting speed for moving the blade on the paths T1 and T2 (phase 105). The rotation is therefore carried out according to the method of the prior art mentioned at the beginning of this description. The average speed of rotation is determined as a function of the known value of the distance dr and of 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 has finished the trajectory T1 with zero speed, by lifting the blade out of the material, rotation of the blade and re-introduction of the blade into the material (phase 106).

As an indication, for the example indicated above, the values of Al 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 method according to the invention, that is to say, in the example of FIG. 2A, by termination of the trajectory T1 without rotation of the blade, orientation of the blade at a predetermined average speed of rotation on the course of rotation of length Dr, and termination of the trajectory T2 (distance D2 - Dr) at the set 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 value Dr is modified to be at most equal to D2, for example less than D2 by 1 / 10mm (phase 108). The remaining 1/10 mm is made at the set acceleration and tangential speed, before a further rotation of the blade. The goal is to complete the rotation course characterized by controlling the speed of rotation and to resume the normal movement regime. The blade rotation time Tr is calculated (phase 109) by performing

Tr = A / Vr.

If Tr is less than a minimum value Tri (test 110), the value of Vr is reduced to be equal to A / Trl (phase 111). Indeed, the duration Tr, which also represents the time taken by the blade to cover the distance Dr, must not be too small at the risk of imposing on the cutting head an acceleration that is too great for the blade to reach 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 to the average speed of rotation and to the 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 over 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 movement on the rotation path are controlled (phase 113).

During the 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) taking into account the tangential speed and acceleration instructions, predetermined for the distance D2-Dr. In the foregoing, the rotation path of length Dr is placed at the start of the path T2. It is possible, as a variant, to place it at the end of the trajectory Tl (FIG. 2B) or on either side of the vertex of the angle A (FIG. 2.

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

Claims

CLAIMS 1. Method for automatic cutting of a flexible sheet material along a cutting path comprising several trajectories connected together, method according to which: - cutting is carried out by automatic control of the relative displacement between a cutting blade and the material along the cutting path, as a function of the tangential speed and acceleration of the 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 to a second orientation in which the blade is substantially tangent to the second trajectory, characterized in that:

2. Method according to claim 1, characterized in that the average speed of movement 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 the displacement of the cutting blade on the first and / or the second trajectory outside the rotation path is carried out at tangential cutting speed and acceleration determined for this trajectory or these trajectories.

3. Method according to any one of claims 1 and 2, characterized in that the instantaneous innate speed of movement along the rotation path is correlated to the instantaneous speed of rotation, while the displacement of the cutting blade on the first and / or second trajectory outside the rotation path is carried out at tangential cutting speed and acceleration determined for this trajectory or these trajectories.

4. Method according to any one of claims 1 to 3, characterized in that the rotation of the cutting blade is carried out on a rotational path consisting of a portion of predetermined length at the start of the second trajectory.

5. Method according to any one of claims 1 to 4, characterized in that that it is implemented when the angle between the first and the second trajectory is at most equal to a predetermined maximum value beyond which the rotation of the blade is carried out, at the end of the first trajectory, outside of matter.

6. Method according to any one of claims 1 to 5, characterized in that it is implemented when the angle between the first and the second trajectory is at least equal to a predetermined minimum value below which the The blade is rotated within the material, over a predetermined distance on either side of the apex of the angle, during the movement of the cutting blade at the speeds and tangential accelerations of setpoint determined for the first and the second trajectory.

7. Method according to any one of claims 1 and 4, characterized in that, when the rotation path has a length greater than that of the trajectory on which it is located, the length of the rotation path is reduced to end at most at the end of the trajectory.

8. Method according to any one of claims 1 to 5, characterized in that it comprises the calculation of the duration of rotation as a function of the value of the angle and of the value of the predetermined average speed of rotation, and the choice of a new value for the average speed of rotation less than the predetermined value, when the calculated rotation time is less than a predetermined minimum threshold.