Method for correcting a predetermined cutting path for cutting a sheet metal blank

Abstract

The invention relates to a method for correcting a predetermined cutting path for cutting a metal blank from a metal strip continuously transported in a transport direction x with the following steps: Simultaneously determining a first x coordinate x1 and a first y coordinate y1 of a point on a surface of the metal strip with respect to an x and a y reference; Determining a second coordinate y2 of the point with respect to the y reference at precisely the time when the metal strip has been moved in the transport direction x by a predetermined first distance dx1 with respect to the first x coordinate x1; Determining a first y correction value K.sub.y1 by taking the difference between the first y coordinate y1 and the second y coordinate y2; and Using the first y correction value K.sub.y1 to correct the cutting path coordinates describing the predetermined cutting path.

Claims

1. A method for cutting a metal blank from a metal strip continuously transported in a transport direction x, comprising: preparing a laser cutting apparatus comprising at least one laser moving in a transport direction x and in a transverse direction y running perpendicular to the transport direction x, and a computer storing cutting path coordinates describing a predetermined cutting path for moving the at least one laser; simultaneously determining a first x coordinate x1 and a first y coordinate y1 of an arbitrary point on a surface of the metal strip with respect to an x and a y reference, the arbitrary point not being a separate mark put on the metal strip; determining a second coordinate y2 of the point with respect to the y reference precisely when the metal strip has been moved in the transport direction x by a predetermined first distance dx1 with respect to the first x coordinate x1; determining a first y correction value K.sub.y1 by taking a difference between the first y coordinate y1 and the second y coordinate y2; using the first y correction value K.sub.y1 to correct cutting path coordinates describing the predetermined cutting path; and cutting the metal blank by moving the at least one laser along the predetermined cutting path corrected by the first y correction value K.sub.y1 while the metal strip is continuously transported in the transport direction x.

2. The method according to claim 1, further comprising: providing a first y measurement device (M.sub.y1) to measure the first y coordinate y1 of the metal strip with respect to the y reference; providing a second y measurement device (M.sub.y2) to measure the second y coordinate y2 of the metal strip with respect to the y reference, the second y measurement device (M.sub.y2) being arranged at the predetermined first distance dx1 downstream of the first y measurement device (M.sub.y1); and providing a first displacement measurement device (M.sub.x1) to measure the x coordinates of the metal strip with respect to the x reference.

3. The method according to claim 1, further comprising: determining a third y coordinate y3 at a predetermined second distance dx2 from a place of determination of the second y coordinate y2; determining a second y correction value K.sub.y2 by taking a difference between the second y coordinate y2 and the third y coordinate y3; and correcting the cutting path coordinates describing the predetermined cutting path by taking into consideration change in the second y correction value K.sub.y2 with respect to the first y correction value K.sub.y1 over the transport path or over time.

4. The method according to claim 3, further comprising: providing a third y measurement device (M.sub.y3) to measure the third y coordinate y3 of the metal strip with respect to the y reference, the third y measurement device being arranged at the predetermined second distance dx2 downstream of the second y measurement device (M.sub.y2).

5. The method according to claim 1, wherein in the step of simultaneously determining the first x coordinate x1 and the first y coordinate y1 of the arbitrary point, one point on the surface of the metal strip is detected as the arbitrary point, and the one point is a part of the surface of the metal strip.

6. The method according to claim 1, wherein in the step of simultaneously determining the first x coordinate x1 and the first y coordinate y1 of the arbitrary point, the arbitrary point is not physically marked on the metal strip.

7. A method for cutting a metal blank from a metal strip continuously transported in a transport direction x, comprising: preparing a laser cutting apparatus comprising at least one laser moving in a transport direction x and in a transverse direction y running perpendicular to the transport direction x, and a computer storing cutting path coordinates describing a predetermined cutting path for moving the at least one laser; simultaneously determining a first x coordinate x1 and a first y coordinate y1 of an arbitrary point (P) of a surface of the metal strip with respect to an x and a y reference, the arbitrary point not being a separate mark put on the metal strip, this determination being done by means of a strip flow measuring device (BF), which allows a determination of positional coordinates xy of the point and their change over time or travel; simultaneously determining a second x coordinate x2 and a second y coordinate y2 of the point (P) of the surface of the metal strip with respect to the x and y reference by means of the strip flow measuring device (BF), if the metal strip has been moved in the transport direction x by a predetermined third distance dx3; determining a third y correction value K.sub.y3 using a vector (V) determined by the strip flow measuring device (BF) from coordinate pairs (x1, y1) and (x2, y2); using the third y correction value K.sub.y3 to correct cutting path coordinates describing the predetermined cutting path; and cutting the metal blank by moving the at least one laser along the predetermined cutting path corrected by the third correction value K.sub.y3 while the metal strip is continuously transported in the transport direction x.

8. The method according to claim 7, further comprising: measuring a fourth y coordinate y4 of the metal strip by means of a fourth y measurement device (M.sub.y4) arranged at a predetermined fourth distance dx4 from the strip flow measuring device (BF) and correcting the third y correction value K.sub.y3 using the fourth y coordinate y4.

9. The method according to claim 7, further comprising: measuring a fourth x coordinate x4 of the metal strip by means of a second displacement measurement device (M.sub.x2) and using the fourth x coordinate x4 for correction of the third y correction value K.sub.y3.

10. The method according to claim 7, wherein the first coordinate pair (x1, y1) is determined from a surface structure detected at a time point t1 with the strip flow measuring device (BF).

11. The method according to claim 10, wherein the surface structure is determined from a 2- or 3-dimensional surface image produced at time point t1.

12. The method according to claim 11, wherein the surface image is produced using a strip flow measuring device (BF), which comprises one of the following components: a camera, an optical mouse sensor, a distance sensor, or a confocal chromatic distance sensor.

13. The method according to claim 10, wherein the second coordinate pair (x2, y2) is calculated from another surface structure detected at other time points to following the time point t1 with the strip flow measuring device (BF).

14. The method according to claim 7, wherein in the step of simultaneously determining the first x coordinate x1 and the first y coordinate y1 of the arbitrary point, one point on the surface of the metal strip is detected as the arbitrary point, and the one point is a part of the surface of the metal strip.

Description

(1) Sample embodiments of the invention are explained in detail below using the drawings. The figures are as follows:

(2) FIG. 1 Determination of the first positional coordinates x1y1 of the point P;

(3) FIG. 2 Determination of the second positional coordinates x2y2 of the point P;

(4) FIG. 3 Determination of the third positional coordinates x3y3 of the point P;

(5) FIG. 4 A schematic view of a measurement arrangement for determination of the positional coordinates according to the second aspect of the invention;

(6) FIG. 5 Determination of the first positional coordinates x1y1 by means of the strip flow measuring device according to FIG. 4; and

(7) FIG. 6 Determination of the second positional coordinates x2y2 by means of the strip flow measuring device according to FIG. 4.

(8) In FIG. 1 through 4, reference number 1 designates a metal strip that is continuously transported in a transport direction x. Reference number 2 generally designates a frame of an apparatus that can comprise conveyor belts, transport rollers, a roller straightening machine, or something similar to transport the metal strip 1 (not shown here). The section of the device shown in den FIG. 1 through 4 has, arranged downstream of it, a laser cutting apparatus (not shown here) for cutting the metal strip 1 into sheet metal blanks with a predetermined geometry. The laser cutting apparatus conventionally comprises one or more lasers, each of which can be moved in the transport direction x and in a transverse direction y running perpendicular to the transport direction x. To move each of the lasers in the x and y-direction, it is possible to provide electrical servo motors, for example. To control such servo motors, a computer is usually provided, which stores cutting path coordinates describing a predetermined cutting path for moving each of the lasers. The cutting path coordinates describe a cutting path with respect to a midplane of the apparatus, i.e., for example, a midplane M of the frame 2, this midplane M running in the xy direction.

(9) In practice, it happens that when the metal strip 1 is being transported the strip middle BM does not coincide with the midplane M of the cutting apparatus. In this case, it can happen that the predetermined cutting path extends beyond the edge of the metal strip 1, and consequently the metal blank does not have the predetermined geometry. To counteract this, the cutting path coordinates describing the cutting path are constantly corrected according to the inventive method so that they relate to the actual position of the strip middle BM.

(10) To accomplish this according to a first variant of the method, which is schematically shown in FIG. 1 through 3, a point P at the one edge of the metal strip 1 can be detected by means of a first y measurement device M.sub.y1. The first y measurement device M.sub.y1 is used to measure a distance of the point P in the y-direction with respect to a y reference R that is at a fixed position on the frame 2. At the same time, a first displacement measurement device M.sub.x1 is used to determine a first x coordinate x1 of the point P with respect to the reference R. The first positional coordinates x1y1 of the point P are stored.

(11) The first y measurement device My1 has, arranged at a first distance dx1 downstream of it, a second y measurement device My2. As soon as the first displacement measurement device M.sub.x1 detects that the metal strip 1 has moved by the distance dx1 in the transport direction x, the second y measurement device M.sub.y2 is used to determine a second y coordinate y2 from the distance to the edge of the metal strip 1. Consequently, the first positional coordinates x1y1 and the second positional coordinates x2y2 always describe the exact position of the same point P on the edge of the metal strip 1.

(12) As can be seen from FIG. 1 through 4, the edge of the metal strip 1 has an edge waviness W. By observing the change in position of one and the same point P, which is possible by simultaneously detecting the respective x and y coordinates, the danger of an inaccuracy in the determination of the correction due to the edge waviness W is avoided.

(13) The difference between the first y1 and the second y coordinate y2 can be used to determine a first y correction value K.sub.y1. The first y correction value K.sub.y1 can be used to correct the y coordinates of the cutting path coordinates.

(14) Comparison of the first y coordinate y1 and the second y coordinate y2 can determine a misalignment of the strip middle BM with respect to the midplane M, and correct it. By contrast, it is not possible to recognize whether the metal strip 1 has bowing, i.e., a curvature with a large radius. To detect such bowing, it is possible to provide a third y measurement device M.sub.y3 at a second distance dx2 downstream of the second y measurement device M.sub.y2. It is advantageous if:
dx1=dx2

(15) In this case it is possible to operate the first displacement measurement device M.sub.x1 and the y measurement devices M.sub.y1, M.sub.y2, and M.sub.y3 at the same clock cycle.

(16) As soon as the first displacement measurement device M.sub.x1 has found that the metal strip 1 has moved by the second distance dx2 in the transport direction x, the third y measurement device M.sub.y3 determines a third y coordinate y3 by measuring the distance of the point P to the third y measurement device M.sub.y3. The difference between the second y coordinate y2 and the third y coordinate y3 is compared with the difference between the first y coordinate y1 and the second y coordinate y2, and this comparison can determine whether there is bowing. Furthermore, it can determine its direction and its magnitude. Let
y1y2=1
y2y3=1

(17) The metal strip 1 does not have bowing if:
1=2

(18) By contrast, it does have bowing if:
12

(19) The difference
12=3
can be used to infer the radius of the bowing. In addition, the direction of the bowing or curvature of the edge of the metal strip 1 can be inferred from the sign of the difference 3.

(20) The previously mentioned relationships apply if dx1=dx2. If dx1 is not equal to dx2, the previously mentioned relationships must be adapted using a factor resulting from the ratio of dx1 and dx2.

(21) FIG. 4 through 6 schematically show a second variant of the inventive method. In these figures, a second displacement measurement device M.sub.x2 is arranged upstream of a strip flow measuring device labeled with the reference number BF.

(22) FIGS. 5 and 6 schematically show the function of the strip flow measuring device BF. The strip flow measuring device BF can be, for example, a device that is designed similarly to an optical mouse sensor. A camera, for example a 1818 CCD, is used to capture a surface structure of the surface of the metal strip 1, the surface structure containing the point P. The point P can be, for example, an excavation on the surface of the metal strip 1, which appears dark in the picture captured by the camera. If the metal strip 1 has been moved by a distance dx3 in the transport direction x, the camera takes another picture of the surface structure of the metal strip 1. The second positional coordinates x2y2 of the point are determined. An image correlation process or something similar can then be used to determine the vector V, which describes the speed and the direction of movement of the point P.

(23) To increase the accuracy of determination of the vector V, it is possible to take not only two pictures of the surface structure that contain the point P, but rather multiple pictures. The third distance dx3 is, for example, 0.1 to 3.0 mm. Nevertheless, a first coordinate pair x1y1 and a second coordinate pair x2y2 are defined with the vector.

(24) In particular, from the vector V, it is possible to determine, using conventional calculation methods, the coordinate pairs x1y1 and x2y2, and from them it is in turn possible to determine the third y correction value K.sub.y3. The second aspect of the invention to determine the bowing of the metal strip can also, similar to the first aspect of the invention, involve providing a fourth y measurement device My4 at a fourth distance dx4 downstream of the strip flow measuring device BF. The fourth y measurement device My4 can be used to determine a fourth y coordinate y4 to correct the third y correction value Ky3. With the fourth y measurement device M.sub.y4 the position, for example of the strip edge of the metal strip 1, can constantly be measured and from this a drift in the y values can be determined. Using the measured drift, the third y correction value K.sub.y3 determined by means of the strip flow measuring device BF can be dynamically corrected, if the fourth distance dx4 is known.

LIST OF REFERENCE SIGNS

(25) 1 Metal strip 2 Frame BF Strip flow measuring device BM Strip middle dx1 First distance dx2 Second distance dx3 Third distance dx4 Fourth distance K.sub.y1 First y correction value K.sub.y2 Second y correction value K.sub.y3 Third y correction value M Midplane M.sub.x1 First displacement measurement apparatus M.sub.x2 Second displacement measurement apparatus M.sub.y1 First y measurement apparatus M.sub.y2 Second y measurement apparatus M.sub.y3 Third y measurement apparatus M.sub.y4 Fourth y measurement apparatus P Point R Reference V Vector W Edge waviness x1y1 First pair of coordinates x2y2 Second pair of coordinates y1 First y coordinate y2 Second y coordinate y3 Third y coordinate y4 Fourth y coordinate