METHOD AND DISTANCE ADJUSTING DEVICE FOR ADJUSTING THE DISTANCE OF A LASER PROCESSING HEAD TO A WORKPIECE SURFACE

Description

[0001] The invention relates to a method for adjusting the distance of a laser processing head to a workpiece surface of a workpiece to be processed, and to a distance adjustment device for adjusting the distance of a laser processing head to a workpiece surface of a workpiece to be processed, see claims 1 and 5.

[0002] Workpieces, such as pipes or flat or three-dimensionally shaped sheets, can be processed using a laser cutting process, in which a laser cutting head is aligned at an angle to the workpiece surface. It is currently known to measure the distance between the laser processing head and the workpiece and, if the measured value deviates from a target value, to move the angled laser processing head relative to the workpiece in the beam direction.

[0003] Deviations in the distance between the laser processing head and the workpiece arise from two main causes: firstly, technologically induced changes during processing, for example, because different cutting tasks require different cutting distances; and secondly, from workpiece defects or errors in workpiece clamping. Ideally, where the actual workpiece geometry exactly matches the geometry of a reference workpiece, no adjustments are necessary due to workpiece defects. The control system then adjusts only the technologically induced changes in the cutting distance. These adjustments must be made in the direction of the beam during bevel cutting to prevent contour errors.

[0004] Despite highly precise workpieces and optimal workpiece setup, contour errors repeatedly occur during bevel cutting. It has been found that the compensation for workpiece errors in the beam direction is responsible for this.

[0005] EP 2 135 701 A2, disclosing the preamble of claim 1, describes a method for predictive torch height control for adjusting the height of a cutting torch mounted on a portal of a numerically controlled cutting machine in relation to a plate mounted on the cutting table of the numerically controlled cutting machine.

[0006] The object of the present invention is therefore to provide a method and an arrangement for adjusting the distance of a laser processing head to a workpiece surface, which allows for more accurate and reliable workpiece processing.

[0007] According to the invention, this problem is solved by a method for adjusting the distance of a laser processing head to a workpiece surface of a workpiece to be processed, according to claim 1, comprising the following method steps: a) Specifying a first target value for the distance of the laser processing head to the workpiece surface in a direction perpendicular to the workpiece surface; b) Specifying a second target value for the distance of the laser processing head to the workpiece surface, wherein the second target value includes at least a first component in a direction perpendicular to the workpiece surface; c) Determining a distance quantity related to the distance of the laser processing head to the workpiece surface in a direction perpendicular to the workpiece surface; d) Supplying the first and second target values ​​and the determined distance quantity or a quantity related thereto to a distance adjustment device for adjusting the distance of the laser processing head to the workpiece surface perpendicular to the workpiece surface, taking into account the first and second target values ​​and the distance quantity or the quantity related thereto.

[0008] The term "value" is to be understood broadly. It can refer to a scalar, a vector quantity, or the like.

[0009] The distance between the laser processing head and the workpiece surface, measured in a direction perpendicular to the workpiece surface, can be directly the distance perpendicular to the workpiece surface. However, it can also be another distance from which the distance perpendicular to the workpiece surface can be determined. For example, the distance in the beam direction can be measured when a laser processing head is aligned at an angle other than 90° to the workpiece surface, and the distance perpendicular to the workpiece surface can then be determined from this measurement, given the angle at which the laser head is aligned to the workpiece surface.

[0010] The method according to the invention takes into account the cause of the change in distance between the laser processing head and the workpiece surface. Technologically induced changes in the processing distance, in particular the cutting distance, and defects in the workpiece surface lead to different movements of the laser processing head relative to the workpiece surface. Changes in the target value of the processing distance are known in advance, for example, from laser technology tables. These changes in the target value can be taken into account by specifying the first target value. Additionally, technologically induced changes in the target value can occur due to changes in the technology. These changes can be taken into account by specifying the second target value.In parallel, the distance between the laser processing head and the workpiece surface is continuously recorded, and any changes due to disturbances, for example due to deviations of the workpiece contour from a target contour, are fed into a distance setting device, as are the target value changes.

[0011] In other words, the inventive method divides distance changes, e.g., in the beam direction (XZ direction, wherein the X direction is parallel to the workpiece surface and the Z direction is perpendicular to the workpiece surface) for technologically induced distance changes, for example, because a laser cutting process is advantageously carried out with a larger or smaller distance to the workpiece surface, and in the Z direction for distance changes due to workpiece changes.

[0012] According to one method variant, a correction value can be determined taking into account the distance value or the related value and the second setpoint. This correction value, like the first setpoint, is then fed into the first control arrangement of the distance setting device. The correction value can be determined, for example, by a numerical control unit. In particular, the correction value can be determined by subtracting the measured distance value and the second setpoint from each other and feeding the result into a numerical control unit.

[0013] An even more precise distance control is achieved when the second setpoint is supplied to the first control device.

[0014] In particular, it may be provided that the correction factor, the first setpoint, and the second setpoint, or its first component, especially its component in the Z-direction, are added together. The result of this addition can then be used in the first control arrangement to perform precise distance control.

[0015] According to a preferred method variant, a third setpoint for the distance of a processing point on the workpiece surface to the laser processing head and the second setpoint, or a second component of the second setpoint, are supplied to a second control arrangement in the same direction as the third setpoint. Thus, not only can the distance of a laser processing head perpendicular to the workpiece surface be controlled, but also the distance of the laser processing head from a processing point parallel to the workpiece surface.

[0016] According to one method variant, the second component can be determined taking into account the angle of attack of the laser processing head. In particular, the second component can be determined from the second setpoint if this is specified in the beam direction. For example, the second component can be determined by multiplying the second setpoint by tan(α), where α is the angle of attack. If the workpiece surface in the machine coordinate system is at an angle γ to the X-axis in the XZ plane, such that the laser processing head assumes an angle β = a + γ in the machine coordinate system, the second setpoint should be multiplied by tan(β).

[0017] The invention also encompasses a distance adjustment device for adjusting the distance of a laser processing head to a workpiece surface of a workpiece to be processed, according to claim 5, comprising a first control arrangement to which a first setpoint for the distance of the laser processing head to the workpiece surface in a direction perpendicular to the workpiece surface and a second setpoint for the distance of the laser processing head to the workpiece surface, wherein the second setpoint comprises at least a first component in a direction perpendicular to the workpiece surface, and a detected distance quantity related to the distance of the laser processing head to the workpiece surface or a quantity related thereto are supplied, and an adding element in which the first and second setpoint values ​​or their first components are added.With such a distance adjustment device, it is possible to react to changes in the distance between the laser processing head and the workpiece surface under different conditions and, in particular, to ensure that the processing point is always in the correct position on the workpiece surface.

[0018] In such an arrangement, changes in the distance between the laser processing head and a workpiece can be taken into account, depending on the cause of the change. This prevents the need to compensate for technologically induced changes in the cutting distance.

[0019] A correction parameter determination device can be provided, to which the second setpoint and a measured distance of the laser processing head to the workpiece surface, in particular the distance parameter or the parameter related to the distance of the laser processing head to the workpiece surface, are supplied. The measured distance of the laser processing head to the workpiece surface can, for example, be measured or recorded in a direction perpendicular to the workpiece surface. Alternatively, it is conceivable to measure the distance of the laser processing head to the workpiece surface in the beam direction of the laser processing head.

[0020] Furthermore, a delay element can be provided that delays the second setpoint before it is fed to the correction factor determination unit. This ensures that the correction factor determination unit has the correct new setpoint and calculates the correct correction value. Overshoot and undershoot during control can thus be largely avoided.

[0021] According to the invention, a detection device is provided for detecting the distance between the laser head and the workpiece surface.

[0022] An output of the correction factor determination device can be fed to the adding element. Thus, the adding element can take into account the correction factor as well as the first and second setpoints and subsequently use them in a control arrangement, in particular the first control arrangement.

[0023] An output of the correction variable determination device can be fed to an adding element at the output of the first control arrangement, which also receives a manipulated variable from the first control arrangement. This allows for very rapid intervention in the controlled system. In particular, the first control arrangement can essentially be bypassed.

[0024] Furthermore, a second control arrangement can be provided, to which a third setpoint for the distance of a processing point on the workpiece surface to the laser processing head and the second setpoint, or a second component of the second setpoint, are fed in the same direction as the third setpoint to a second control arrangement. Thus, the distance of a processing point on the workpiece surface to the laser processing head can also be controlled.

[0025] Furthermore, a component detection device can be provided, to which the second setpoint is fed and which determines one component of the second setpoint that is then fed to the second control arrangement. For example, the second setpoint can be multiplied by a trigonometric function, depending on the direction in which the second setpoint is specified. The trigonometric function can take into account the angle of attack of the laser processing head.

[0026] The first and / or second control arrangement may include a bearing controller.

[0027] Furthermore, the first and / or second control arrangement can be configured to include feedforward control. This allows, for example, changes resulting from setpoint changes to be accounted for via feedforward control, while changes resulting from workpiece deviations from a target contour can be accounted for via control. For instance, feedforward control can be used to determine a target speed. This enables consideration of the expected manifold requirements based on the setpoint curve. Thus, the guidance behavior can be improved without compromising system stability.

[0028] Furthermore, the control arrangement can include a detection unit for detecting a controlled variable. In particular, the detection unit can be configured to capacitively detect the distance of the laser processing head to the workpiece, especially to the workpiece surface.

[0029] The distance adjustment device can also be used on 5- or 6-axis machines, for example. In this case, an additional control arrangement analogous to the control arrangement for the Y-axis is necessary, and the angle β then corresponds to a solid angle in X, Y, and Z, and no longer to an angle in the XZ plane.

[0030] Further features and advantages of the invention will become apparent from the following detailed description of an embodiment of the invention, based on the figures in the drawing.

[0031] The schematic drawing shows an embodiment of the invention, which is explained in more detail in the following description.

[0032] They show: Figure 1 schematically shows a laser processing head with which a workpiece is processed; Figure 2 shows an arrangement for adjusting the distance of a laser processing head oriented at an angle to a workpiece surface; Figure 3 shows another arrangement for adjusting the distance of a laser processing head oriented at an angle to a workpiece surface.

[0033] The Figure 1Figure 1 schematically shows a laser processing head 1, which is designed as a laser cutting head. The laser processing head 1 is oriented at an angle α to a normal of the workpiece surface 2 of a workpiece 3. This means that the processing distance 4 in the beam direction has a component in the X-direction, i.e., parallel to the workpiece surface 2, and a component in the Z-direction, i.e., perpendicular to the workpiece surface 2. The laser processing head 1 is at a distance 5 from the workpiece surface 2. In this embodiment, the coordinate system of the workpiece 3 and the laser processing head 1 (as part of a laser processing machine with multiple machine axes, e.g., in the X, Y, and Z directions) correspond.

[0034] Workpiece 3 deviates from a target contour. The target contour of workpiece 3 would have a workpiece surface at point 2a. Accordingly, the laser processing head would be located at position 1a, shown with a dashed line, to set a processing distance 4a, which is specified as the target value. Since the actual workpiece surface 2 deviates from the target position according to reference numeral 2a, the laser cutting head 1 is also positioned differently to set the target processing distance. This results in a contour deviation 6.

[0035] In the exemplary embodiment of Figure 2It is initially assumed that the workpiece 3 extends along the X and, in particular, the Y direction of the coordinate system of the laser processing head 1, and that the target position 2a of the workpiece surface 2 corresponds to a position with Z=0 in the coordinate system of the laser processing head 1, so that the first target value Z target of the laser processing head 1 (or the associated machine axis) corresponds exactly to the distance 5 of the laser processing head 1 to the target position 2a of the workpiece surface 2.

[0036] The Figure 2 Figure 10 shows a distance setting device to which an interpolator 11 provides a first setpoint Z for the distance of the laser processing head 1 to the workpiece surface 2 in a direction perpendicular to the workpiece surface. The interpolator 11 reads the first setpoint from an NC program.

[0037] A technology controller 12 specifies a second setpoint dshall for the distance of the laser processing head 1 to the workpiece surface 2 to the distance setting device 10. The second setpoint dshall has at least one first component in a direction perpendicular to the workpiece surface 2. The second setpoint dshall is first fed to a delay element 13, from where it passes to a correction factor determination device 14. The correction factor determination device 14 has a computation element 15, where a distance value dact measured or determined by a detection device 16 is subtracted from the delayed second setpoint dshall or its first component. The output value of the computation element 15 is sent to a numerical controller 17, which outputs a correction factor that is fed to an adder element 18 of a first control arrangement 20.The first setpoint Z and the second setpoint d are supplied to the adding element 18. Ideally, the correction value from the correction value determination device 14 is zero, so that no error needs to be compensated for in this respect. The first control arrangement 20 has a feedforward control 21, in particular a speed feedforward control with a feedforward element 22. Furthermore, the first control arrangement 20 has a delay element 23, which prevents the bearing controller 24 from working against the feedforward control 21.

[0038] At the output of the first control arrangement 20, an adding element 25 is provided, to which an output of the correction parameter determination device 14 is directly connected. Thus, the correction parameter determination device 14 generates its own setpoint, enabling rapid intervention in the control system. The output of the first control arrangement 20 is fed to a control loop 26, which sets the distance of the laser processing head 1 perpendicular to the workpiece surface 2. This distance Zis is determined by the aforementioned detection device 16, which outputs the distance value dis as a quantity related to the distance Zis of the laser processing head 1 perpendicular to the workpiece surface 2. The distance value dis can itself be the distance Zis.

[0039] It should be noted that dshould and dis must already be specified or measurable perpendicular to the workpiece surface, e.g., if Zis is directly measured by capacitive distance measurement of the nozzle to a metallic workpiece, such as a sheet or pipe. In that case, dis and Zis are equal, assuming a workpiece where Z=0.

[0040] However, it is also possible to measure the distance in a different direction, not perpendicular to the workpiece surface, e.g., in the direction of the laser beam using a laser distance meter. Then, dis and dshould are distances in the beam direction. In both cases, dis is a quantity related to the distance Zis. This quantity can be supplied to the distance setting device 10.

[0041] It is also conceivable, for example, that d is detected at an angle to the workpiece surface, e.g. in the direction of the beam, but is not directly fed to the distance setting device 10, but only the perpendicular component of d is fed, i.e. a quantity related to d.

[0042] From a distance measurement in the beam direction, the distance perpendicular to the workpiece surface can be determined, since the angle of the laser processing head to the target workpiece surface is known.

[0043] If d is measured, for example, in the direction of the laser beam, then d is proportional to Z is , where the constant of proportionality depends on the angle of d is to Z is or the perpendicular to the workpiece surface.

[0044] The interpolator 11 also reads a third target value Xtarget from the NC program and feeds it to the distance setting device 10. Specifically, the third target value Xtarget is fed to a second control arrangement 30, namely an adding element 31. The adding element 31 also receives a second component of the second target value dtarget, the second component being determined by a component detection device 32. For example, the component detection device 32 can be given an angle of attack a of the laser head 1, and the second target value dtarget can be multiplied by a trigonometric function.

[0045] The second control arrangement 30, with the exception of the adder element 25, is constructed analogously to the first control arrangement 20 and therefore comprises a feedforward control 33 with a feedforward element 34, a delay element 35, and a position controller 36. A manipulated variable is present at the output of the position controller 36, which is added to an output value of the feedforward control 33 in the adder element 37. Thus, a corrected manipulated variable is present at the output of the adder element 37, which is fed to the controlled system 40. In the adder element 37, the manipulated variable of the controller 36 is augmented with a feedforward value. Similarly, in the first control arrangement, the manipulated variable of the position controller 24 is added to a feedforward value of the feedforward control 21 in the adder element 27, so that a corrected manipulated variable is present at the output of the adder element 27.

[0046] The second control arrangement 30 allows the distance of the laser processing head 1 in a direction parallel to the workpiece surface 2 to a processing point on the workpiece surface 2 to be controlled. The actual distance X is measured and fed to the second control arrangement 30 at position 41. Similarly, the value Z is fed to the first control arrangement 20 at position 28.

[0047] In the case that the target position 2a of the workpiece surface 2 is offset to a position with Z=0 in the coordinate system of the laser processing head 1, the first target value Z must be the distance 5 to the workpiece surface 2 together with an offset between Z=0 and the Z-position of the target position 2a of the workpiece surface 2.

[0048] The Figure 3 shows a distance adjustment device 10', which is used in large parts of the distance adjustment device 10 of Figure 2 corresponds.

[0049] The control with the additional block 50 allows for control not only in the Z-direction of the machine coordinate system (coordinate system of the laser processing head), but also in an XZ direction. In the case of Fig. 3 For example, the target position of the workpiece surface to be processed can be at an angle γ to the X-axis in the XZ plane (e.g., a section of a three-dimensionally shaped sheet metal), and it is still possible to control the distance of the laser processing head perpendicular to the workpiece surface, instead of only in the Z-direction as in Fig. 2In this case, the component determination device 32 must multiply the second setpoint dshould by a trigonometric function that incorporates the angle of attack α of the laser head 1 and the angle γ of the target position of the workpiece surface. Specifically, dshould should be multiplied by tan(β) in this case, where β = α + γ. Within the workpiece coordinate system, nothing has changed: control is performed once in the beam direction and once perpendicular to the surface. However, the rotation of the workpiece by the angle γ in the coordinate system of the laser processing head 1 (and thus of the machine) must be taken into account, so that the control perpendicular to the workpiece is also performed not only in the Z-direction, but in both the X and Z directions. The first setpoint in a direction perpendicular to the workpiece surface can therefore have components in different axis directions of a machine coordinate system (coordinate system of the laser head).If necessary, the specified first target value is thus derived from target values ​​in different axis directions of the machine coordinate system. Instead of the target position of the workpiece surface, which is known, for example, from CAD / CAM data or a teach pendant, the angle γ can also be determined from a measurement of the workpiece surface.

[0050] Additionally, the distance adjustment device 10 can also be used on 5- or 6-axis machines, for example. In this case, an additional control arrangement analogous to the control arrangement 30 for the Y-axis is necessary, and the angle β then corresponds to a solid angle in X, Y, and Z and no longer to an angle in the XZ plane.

Claims

1. A method for adjusting the distance of a laser machining head (1) to a workpiece surface (2) of a workpiece (3) to be machined, wherein the laser machining head (1) is oriented diagonally to the workpiece surface (2), with the following method steps: a. specifying a first target value (Zsoll) for the distance of the laser machining head (1) to the workpiece surface (2) in a direction perpendicular to the workpiece surface (2), wherein the first target value (Zsoll) is read out from an NC program; the method is characterized by: b. specifying a second target value (dsoll) for the distance of the laser machining head (1) to the workpiece surface (2) by a technology controller (12), wherein the second target value (dsoll) comprises at least a first component in a direction perpendicular to the workpiece surface (2); c. measuring a distance variable (dist) related to the distance (Zist) of the laser machining head (1) to the workpiece surface (2) in a direction perpendicular to the workpiece surface (2); d. supplying the first and the second target value (Zsoll, dsoll) and the measured distance variable (dist), or a variable that is related thereto, to a first regulating arrangement (20) of a distance adjusting device (10), wherein the distance adjusting device (10) further comprises an addition member (18), in which the first and the second target value, or its first component, are added, for adjusting the distance of the laser machining head (1) to the workpiece surface (2) perpendicular to the workpiece surface, the first and the second target value (Zsoll, dsoll) and the distance variable (dist) or the variable related thereto, being taken into account in the process, wherein the output of the first regulating arrangement (20) is fed to a controlled loop (26) via which the distance of the laser machining head (1) perpendicular to the workpiece surface (2) is adjusted.

2. The method according to claim 1, characterized in that, taking into account the distance variable (dist) or the variable related thereto and the second target value (dsoll), a correction variable is determined which is supplied to the first regulating arrangement (20) of the distance adjusting device (10) just as the first target value (Zsoll) was.

3. The method according to any one of the preceding claims, characterized in that the second target value (dsoll) is supplied to the first regulating device (20).

4. The method according to any one of the preceding claims, characterized in that a third target value (Xsoll) for the distance of a machining point on the workpiece surface (2) to the laser machining head (1) and the second target value (dsoll), or a second component of the second target value (dsoll), is supplied to a second regulating arrangement (30) in the same direction as the third target value (Xsoll).

5. A distance adjusting device (10) for adjusting the distance of a laser machining head (1) to a workpiece surface (2) of a workpiece (3) to be machined, wherein the laser machining head (1) is oriented diagonally to the workpiece surface (2), with a detection device (16) for detecting the distance of the laser machining head (1), and with a first regulating arrangement (20) comprising an interpolator (11) for reading out, from an NC program, a first target value (Zsoll) for the distance of the laser machining head (1) to the workpiece surface (2) in a direction perpendicular to the workpiece surface, and a technology controller (12) for specifying a second target value (dsoll) for the distance of the laser machining head (1) to the workpiece surface (2), wherein the second target value (dsoll) comprises at least a first component in the direction perpendicular to the workpiece surface (2), and the detected distance variable (dist) related to the distance (Zist) of the laser machining head (1) to the workpiece surface (2), or a variable related thereto, are supplied, with an addition member (18) in which the first and the second target value, or its first component, are added, wherein the output of the first regulating arrangement (20) is supplied to a controlled loop (26) via which the distance of the laser machining head (1) perpendicular to the workpiece surface (2) is adjusted.

6. The distance adjusting device according to claim 5, characterized in that a correction variable determining device (14) is provided to which the second target value (dsoll) and the detected distance variable (dist) related to the distance of the laser machining head (1) to the workpiece surface (2), or a variable related thereto, are supplied.

7. The distance adjusting device according to claim 6, characterized in that a delaying member (13) is provided which delays the second target value (dsoll) before it is supplied to the correction variable determining device (14).

8. The distance adjusting device according to any one of the preceding claims 6 to 7, characterized in that an output of the correction variable determining device (14) is supplied to the addition member (18).

9. The distance adjusting device according to any one of the preceding claims 6 to 8, characterized in that an output of the correction variable determining device (14) is supplied to an addition member (25) at the output of the first regulating arrangement (20), the addition member also being supplied with a control variable of the first regulating arrangement (20).

10. The distance adjusting device according to any one of the preceding claims 5 to 9, characterized in that a second regulating arrangement (30) is provided, to which a third target value (Xsoll) for the distance of a machining point on the workpiece surface (2) to the laser machining head (1) and the second target value (dsoll), or a second component of the second target value (dsoll), are supplied in the same direction as the third target value (Xsoll) of a second regulating arrangement (30).

11. The distance adjusting device according to claim 10, characterized in that a component determining device (32) is provided, to which the second target value (dsoll) is supplied and which determines a component of the second target value (dsoll) which is supplied to the second regulating arrangement (30).

12. The distance adjusting device according to any one of the preceding claims 10 to 11, characterized in that the first and / or second regulating arrangement (20, 30) has a position regulator (24, 36).

13. The distance adjusting device according to any one of the preceding claims 10 to 12, characterized in that the first or second regulating arrangement (20, 30) has an upstream controller (21, 33).