Methods for determining distance and processing methods

Abstract

The invention relates to a method for determining the distance between a laser processing device (10) and a workpiece (12), wherein a laser beam (11) is emitted by a laser (30) of the laser processing device (10) and directed onto the workpiece (12), wherein the laser beam (11) is modulated, wherein the laser beam (11) is partially reflected by the workpiece (12), wherein the laser beam reflected by the workpiece (12) is directed onto a first sensor (48) for measuring the intensity of the laser beam, and wherein a distance determination between the laser processing device (10) and the workpiece (12) is carried out taking into account a time difference between a fluctuation in the intensity of the laser beam detected by the first sensor (48) and the modulation of the laser beam (11).

Description

State of the art

[0001] DE 10 2011 078 089 A1 already discloses a method and arrangement for distance measurement in a laser processing system. Here, a reference beam, which is decoupled from the processing beam by means of a beam splitter, is superimposed according to the principle of a short-coherence interferometer. Contrast values ​​of the superimposed wavefronts are evaluated by a detector array, and a change in distance is determined from this. Disclosure of the inventionAdvantages of the invention

[0002] The method for distance determination according to the invention has the advantage that distance is determined via a time-of-flight measurement. This takes advantage of the fact that, if the speed of light is considered constant, light requires a longer period of time to travel a longer distance corresponding to a greater distance. If the light intensity is now modulated, e.g. by changing the intensity or by switching the laser beam on and off, this change in intensity occurs with a time delay at the end of the path and is measurable. If this modulation of the light intensity is then detected, the time difference until this modulation is recorded depends on the distance the light has traveled from the laser processing device to the workpiece and back again to a sensor that detects the intensity of the light.It is not necessary for the detected laser light to be coherent with the emitted laser light. Therefore, no reference beam is required to be made coherent with the measuring beam. This eliminates the need for additional effort to generate such a reference beam, such as the introduction of an additional radiation source to the processing laser and / or additional optics. This makes it possible to determine the distance between the laser processing device and a workpiece in an accurate and cost-effective manner. This, in turn, makes it possible to precisely focus a laser on a processing point on the workpiece, so that the laser power is focused precisely on the desired position and can therefore be applied to the workpiece for welding or material removal.

[0003] Further advantages arise from the independent claims. It is advantageous to determine a time for performing the modulation by taking into account the propagation time of a signal from the laser to a second sensor at a known distance from the laser light source or based on the time of generation of a modulated control signal for the laser. In this case, constant times for electronic signal processing and / or signal generation may also need to be taken into account.

[0004] It is also advantageous to determine a distance to a processing point of the laser beam on the workpiece or to an area surrounding the processing point. If the exact distance is known, the laser can be focused and its power can be applied in a targeted manner. If the area surrounding the processing point is also monitored with regard to a distance to the laser, this makes it possible for the distance to be correctly focused when the processing point is moved to a point on the workpiece surface, since the distance to the targeted point on the workpiece surface is already known and does not have to be determined when the point is targeted. This is particularly advantageous if the surface of the workpiece is not flat.

[0005] Furthermore, it is advantageous to use a diode or a light-sensitive diode array for detecting light intensity, as the diode or diode array enables a precise determination of light intensity in a cost-effective manner. If a diode array is used, it is directed not only at a point but also at the surrounding area of ​​these points, thus enabling a spatially resolved observation of the surrounding area of ​​a processing point.

[0006] Furthermore, a machining method for a workpiece of a laser machining direction in which the distance measurement method is used is advantageous, since the advantages of the distance measurement method are benefited in this case.

[0007] Furthermore, it is advantageous to adjust the focus position of the processing laser depending on the determined distance in order to enable precise processing of the workpiece.

[0008] It is also advantageous to use distance measurement to determine whether a workpiece is located at a specified distance from the laser processing device. If this is not the case, a workpiece may not have been inserted or is not present. This prevents a processing step from being wasted, a faulty workpiece from being processed, or a problem with the workpiece feed going undetected. In such a case, a warning is advantageously issued so that the error can be corrected, particularly through manual intervention.

[0009] Corresponding advantages arise for a laser processing device for carrying out such a process. drawing

[0010] Embodiments of the invention are illustrated in the drawing and explained in more detail in the following description.

[0011] They show: Fig. 1 a laser processing device for carrying out a processing method with the laser processing device, Fig. 2 the laser processing device in detail to explain the distance measurement method, Fig. 3 an example of different intensity signals of the laser light, Fig. 4 an example of a measuring field for a distance measurement on a surface of the workpiece, Fig. 5 an embodiment of a process sequence of a machining process. Embodiments of the invention

[0012] In the Fig. 1 shows a laser processing device 10 that directs a laser beam 11 onto a workpiece 12. The laser processing device 10 measures the time of flight of the laser from the laser processing device 10 to the workpiece 12, where the laser beam 11 is reflected. The reflected laser beam is picked up again by an optics system of the laser processing device 10.

[0013] The laser beam 11 also serves to process the workpiece 12 according to a control specification 13 stored in a control device 14. According to the control specification 13, the laser beam 11 acts on the workpiece 12 and removes material there or heats it, so that seams are separated or joined, depending on the workpiece and the control specification 13. Fast material processing can be achieved with highly dynamically controllable lasers with processing frequencies greater than 1 megahertz. The highly dynamic and flexible adaptation of the beam profiles can improve productivity as well as the stability and quality of the laser processing.

[0014] Once the machining of the workpiece 12 is completed, the control device 14 causes a next workpiece 18 to be positioned at the position of the workpiece 12 via a control signal 15 to a transport device 16, for example a conveyor belt or a feed device. A machined workpiece 17 has already been removed and is made available for further machining or, after completion, for removal.

[0015] Furthermore, in one embodiment, it is also possible to carry out the distance measurement method without necessarily performing a laser processing step. The laser processing system can also be used for distance measurement only if this is relevant for a corresponding application, for example, for determining the presence of workpieces, in particular correctly positioned workpieces, in a production facility.

[0016] The laser processing device 10 checks the distance 19 to the workpiece 12 to determine whether this distance is within an expected range. If a distance equal to the distance to the transport device 16 is measured, it can be assumed that no workpiece 12 is present at the processing position. In this case, an error message is output by the control device via an interface 20, for example, a loudspeaker or a display.

[0017] In one embodiment, the distance can be measured once before the start of machining for a machining point or for a workpiece. It is also possible to perform measurements regularly during machining and continuously adjust the optics.

[0018] In the Fig. Figure 2 shows the optical structure of the laser processing device in detail. A laser light source 30 emits a parallel, but unfocused laser beam 31, which strikes a deflecting mirror 32. In a first embodiment, a small portion of the light, preferably less than 1%, is extracted from the laser beam 31 and guided as an extracted first laser light beam 33 to an optics 34, which focuses the extracted first laser light beam 33 onto a second sensor 35. The second sensor 35 is preferably designed as a light-sensitive diode or as a diode array. The intensity signal detected by the second sensor 35 is forwarded in a time-resolved manner to an evaluation unit 36.

[0019] After reflection by the deflecting mirror 32, the remaining main light beam 31' is guided to an xy deflection unit 37, which deflects the beam toward an adjustable lens optics 38. The lens optics 38 is designed, for example, as an adjustable f-theta lens. In another embodiment, it is also possible to arrange the lens optics 38 in front of the xy deflection unit 37 in the beam path. In one embodiment, it is also possible to use a fixed mirror instead of the xy deflection unit 37 for deflecting the laser beam 31', or to leave the xy deflection unit 37 in a predetermined, adjusted position, or even to use only fixed optics without mirrors for deflection and focusing.

[0020] The lens optics 38 is controlled by the evaluation unit 36 ​​and can focus the incident deflected laser light beam 31' onto a target at a distance specified by the control. Fig. 3 shows two examples: A workpiece 40 is arranged at a distance from the laser processing unit 10 and has a step 41, so that the workpiece 40 has a first surface 42 and a second surface 43 facing the laser processing device 10, wherein the second surface 43 is at a greater distance from the laser processing device 10 than the first surface 42. When controlled by the xy deflection unit 37 and the controllable lens optics 38, in the first example, a focused laser light beam 44 is directed onto a point 45 on the second surface 43 of the workpiece 40. To focus the laser, a surface point with a diameter of less than 1 mm, in particular less than 0.3 mm, is advantageously generated. For this purpose, it is necessary to know the distance between the optics and the processing point precisely.This ensures that the intensity required for material processing is achieved without requiring a particularly high laser power. By expanding the beam outside the focal point, the load on the focusing optics is kept to a minimum.

[0021] From point 45, laser light is reflected again and, naturally with reduced intensity, hits the lens optics 38, the xy deflection unit 37, and the semitransparent deflection mirror 32. A reflected laser light beam 46 thus reaches a collecting optics 47, which deflects the reflected laser light beam 46 onto the first sensor 48. An intensity signal is forwarded from the first sensor 48 to the evaluation unit 36.

[0022] An example of corresponding signal curves at the evaluation unit 36 ​​is shown in the Fig. 3. Intensities are plotted on a y-axis 51 above a time axis 50. A first signal 52 represents an intensity detected by the second sensor 35, i.e., in relation to an emission of the laser beam. This modulates the processing laser beam such that a maximum intensity is maintained for a period of time and then the intensity is reduced without the laser being completely switched off. Alternatively, it is also possible to operate the laser in pulsed mode. In further embodiments, other signal shapes are also possible, e.g., a sine wave.

[0023] In another embodiment, instead of deriving the first signal 52 via a second sensor 35, it is also possible to use a time for emitting the laser light directly from a control signal of the evaluation unit 36 ​​for controlling the laser 30. In this case, an absolute determination of the runtimes for the control and the light path for the laser must be included in the calculation.

[0024] The second signal 55 is the intensity signal transmitted by the first sensor 48, which results from the distance between the laser device and the point 45 on the workpiece 40. The second signal 55 is shifted by a time difference 54 compared to the first signal 52, which means the laser beam must travel a longer distance. Due to the intensity changes, the corresponding time can be easily identified by the evaluation unit 36 ​​by comparing the two signals, and the time difference between the two signals can be determined from the time offset of the signal edges. Assuming that the electrical processing paths for both signals are the same, the resulting time difference is proportional to the distance between the laser processing device, more precisely between the first sensor 48 and the processing point, in this case, the processing point 45.Since the light path within the laser processing device 10 is known, the distance between the controllable lens optics 38 at the processing point can be determined from this, taking into account the also known speed of light. A computing device 60 within the evaluation unit 36 ​​determines the time difference and thus the distance through signal evaluation, taking into account the relevant input variables. If the coherence of the light is lost during processing or during the redirection of the light, this has no influence on the distance measurement, since only the intensity of the light is important, not the coherence.

[0025] If the xy deflection unit 37 uses the laser to target a point 49 on the first surface 42 of the workpiece 40, the distance to the workpiece 40 decreases. Therefore, a third signal 53 is measured, for which the time interval 56 to the first signal 52 is smaller than for the second signal 55.

[0026] Laser power modulation can be achieved in various ways. For example, a temporary reduction or increase in laser power can be performed, so that the back reflection signal from the workpiece decreases in the case of a reduction or increases in the case of an increase in laser power. Fig. 2 shows a corresponding square wave signal. In addition to the Fig. 2, other signal shapes, for example a sinusoidal signal or irregular signal shapes, are also possible, as long as the signal shapes of the evaluation unit 36 ​​are known accordingly.

[0027] In another embodiment, it is also possible to modulate the laser beam shape, for example by focusing or defocusing, so that, particularly during a deep welding process, an increased back reflection briefly occurs at the edges of the vapor capillary. Further modulation of the laser signal can be achieved by briefly directing the laser beam at an area outside the ongoing process, as this leads, in particular, to a change in reflection, for example, reduced reflection, outside the reflection area. The significant fluctuations in the back-reflection signal thus generated are used as triggers for a time-of-flight measurement. Using the known speed of light, for example, 299,705 km / s for air, the path can be calculated from the time difference δt as the distance s = (c*δt) / 2.

[0028] In the Fig. 4 shows a plan view of a surface of a workpiece 70. In a first embodiment, the distance to a processing point 71 of the laser beam on a surface of the workpiece 70 can be determined. In a further embodiment, a grid matrix 72 surrounding the processing point 71 can also be scanned. Height differences on the workpiece can be detected before a processing point is controlled by the laser itself. For this purpose, it is possible, for example, for the processing beam to briefly scan the grid 72, possibly with reduced intensity, so that the material of the workpiece is not affected.After this scanning has taken place, the distance to a future processing point is already known, for example to a cell 73 of the grid adjacent to the current processing point, so that when the cell 73 is controlled with the processing laser beam, a corresponding distance is already known and a corresponding focusing can take place immediately when the point is controlled.

[0029] In the Fig.Figure 5 shows an example of a method sequence according to the invention. Beginning with an initialization step 80, a distance measurement 81 to a processing point on a workpiece is first performed. In a first test step 82, it is checked whether the distance to the workpiece lies within an expected target range. If this is not the case, the correct workpiece is not present or no workpiece is present, so that the method is terminated in a final step 83, with a warning preferably being issued via an interface. If the measured distance is within an expected range, the process branches to a calculation step 84 in which a control for the focusing device is determined. In a control step 85, the focusing device is adjusted to the processing point so that the laser beam is focused on the processing point.In a subsequent processing step 86, laser radiation is emitted onto the processing point on the workpiece using the adjusted focused laser beam. Subsequently, the system branches back to the distance measurement 81 for the next processing point if a second test step 87 shows that the entire workpiece has not yet been processed. Otherwise, the processing method is terminated in a final step 88, and the workpiece is marked as processed. QUOTES CONTAINED IN THE DESCRIPTION

[0000] This list of documents submitted by the applicant was generated automatically and is included solely for the convenience of the reader. This list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions. Cited patent literature

[0000] DE 10 2011 078 089 A1

[0001]

Claims

[1] Method for determining the distance between a laser processing device (10) and a workpiece (12), wherein a laser beam (11) is emitted by a laser (30) of the laser processing device (10) and directed onto the workpiece (12), wherein the laser beam (11) is modulated, wherein the laser beam (11) is partially reflected by the workpiece (12), wherein the laser beam reflected by the workpiece (12) is directed onto a first sensor (48) for measuring the intensity of the laser beam, and wherein a distance determination between the laser processing device (10) and the workpiece (12) is carried out taking into account a time difference between a fluctuation in the intensity of the laser beam detected by the first sensor (48) and the modulation of the laser beam (11). [2] Method according to claim 1, characterized bythat a time at which the modulation is carried out is determined taking into account a propagation time of a signal from the laser to a second sensor (35) or from a time at which a modulated control signal for the laser (30) is generated. [3] Method according to one of the preceding claims, characterized by that a distance (19) to a processing point (71) of the laser beam on the workpiece (70) or to an environment (72) of the processing point is determined. [4] Method according to one of the preceding claims, characterized by that a modulation of the laser beam is caused by a change in the laser power, a change in the shape of the laser beam or by a deflection of the laser beam. [5] Method according to one of the preceding claims, characterized by that a light-sensitive diode or a light-sensitive diode array is used as the first or second sensor (35, 48). [6] Processing method of a workpiece with a laser processing device (10), wherein a method for distance measurement according to one of the preceding claims is used. [7] Processing method according to claim 6, characterized by that a focus position of the processing laser beam is adjusted depending on the determined distance between the laser processing device (10) and the workpiece (12). [8] Processing method according to one of claims 6 or 7, characterized by that the presence of the workpiece (12) is detected as a function of the determined distance between the laser processing device (10) and the workpiece (12), and that an error message is output if no workpiece is detected. [9] Laser processing device (10) for carrying out a method according to one of the preceding claims.

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