How to make a perforation line on an airbag cover

Abstract

The invention relates to a method for cutting a perforation line into an airbag cover (1), in which the airbag cover (1) is guided relative to a tool (2) along an imaginary line (L). To carry out the method, a processing beam (3.1) and a first measurement beam (4.1) are emitted, which illuminate a processing location (BO) located on a side (6) of the airbag cover (1) facing the processing beam source (3), and a second measurement beam (5.1) is emitted, which illuminates a measurement location (MO) located on a side (7) of the airbag cover (1) opposite the processing beam source. A first path length (a) and a second path length (b) are then determined and evaluated, whereby the first path length (a) and the second path length (b) are used for determining a remaining remaining wall thickness (RWS). The processing beam source is controlled depending on the determined remaining wall thickness (RWS).

Description

[Technical field]

[0001] The present invention relates to a method for forming a perforation line in an airbag cover, in which a remaining wall thickness of the airbag cover is determined and a processing beam source is controlled depending on the remaining wall thickness. [Background technology]

[0002] A method for processing a workpiece, which may in particular be a plate-shaped material for the release of an airbag (airbag cover), is known from DE 10 200 43 511 A1. For the area weakening, an attenuated laser beam is emitted from an attenuated laser, which is guided in a beam-overlapping, beam-parallel or adapted manner with respect to a measuring laser beam, the measuring laser beam having a wavelength different from that of the attenuated laser beam. The attenuated areas have a higher transmission for the wavelength of the measuring laser beam than for the wavelength of the attenuated laser beam. The attenuated areas can be arranged next to each other in a row like teeth. The current power of the measuring laser beam is measured by a detection sensor, and the remaining wall thickness is determined indirectly from the current power with the aid of a predetermined relative path ratio of the measuring laser and the attenuated laser. Based on the determined remaining wall thickness, the laser power and / or the laser duration of the attenuated laser is set. In the disclosed method, a transmission of the laser radiation through the workpiece is always required for the determination of the remaining wall thickness and thereby for the setting of the parameters of the attenuated laser. As a result, only a small amount of remaining wall thickness can be determined and the method is only suitable for certain workpiece materials with suitable optical properties.

[0003] A further method for laser material processing of a workpiece is disclosed in US Pat. No. 5,399,633. The method comprises emitting a material processing beam and one or more imaging beams. A phase change region of the workpiece is irradiated with the material processing beam and at least one imaging beam. The imaging beam is used to perform a measurement at at least one point of the phase change region using low coherence interferometry. For this purpose, a portion of the imaging beam reflected by the workpiece is combined with another portion, for example from a reference arm, to generate an interferometry output based on a path length difference. The interferometry output is then processed to determine at least one characteristic, such as, for example, the depth of a blind hole in the phase change region. Based on the at least one determined characteristic of the phase change region, at least one parameter of the processing process can be controlled.

[0004] US Pat. No. 5,399,633 discloses a method for cutting a workpiece with a laser beam. In this case, a cutting kerf is formed on the workpiece by means of a laser beam emitted by a laser device. The cutting kerf is simultaneously illuminated with a measurement beam emitted from a light source of a coherence tomography device. The coherence tomography device uses a reference arm, the light emitted from which interferes with the reflected measurement beam. The measurement beam is deflected to measure the cutting kerf, and an interference response is detected to determine at least one geometrical characteristic of the cutting kerf. Based on the detected at least one characteristic of the cutting kerf, process parameters of the cutting process, in particular parameters of the laser device, can be controlled.

[0005] The drawback of the above two methods is that the reference arm is independent of the workpiece, which means that the unevenness of the supporting plane member (support plane) on which the workpiece is placed, the unevenness of the workpiece surface, or the thickness variation of the workpiece are not taken into account, leading to the remaining thickness being determined inaccurately.

[0006] From DE 10 200 03 133 A1 a device for entering a target break line in an airbag cover is known, which device comprises two sensors directed towards the processing position from opposite sides, the remaining wall thickness being derived from a combination of the signals of the two sensors.

[0007] Patent document 5 discloses a processing device for processing a workpiece with a high-energy processing beam. At least one scanning device formed as an optical coherence tomography device is arranged in the processing head, by means of which the workpiece surface can be scanned one-, two- or three-dimensionally. The scanning is performed by means of a measurement beam emitted from the optical coherence tomography device and reflected at the workpiece surface. The reflected measurement beam is guided at least partially together with a reference light beam onto a detector.

[0008] Patent document 6 describes a method for laser drilling and an apparatus for carrying out the method for laser drilling of plate-shaped parts. Prior to the drilling process, the thickness of the part, defined by the distance between two part surfaces, is determined by at least one measuring means in the drilling area. The depth of the drilling is detected during the drilling process by a second measuring means. [Prior art documents] [Patent documents]

[0009] [Patent Document 1] DE 102018002300 [Patent Document 2] International Publication No. 2014 / 138939 Brochure [Patent Document 3] DE 102018129407 [Patent Document 4] International Publication No. 01 / 70445 Brochure [Patent Document 5] European Patent No. 1977850 [Patent Document 6] DE 10355931 A1 Summary of the Invention [Problem to be solved by the invention]

[0010] The object of the present invention is to find a method for cutting perforation lines into an airbag cover, which allows the remaining wall thickness to be accurately determined independently of irregularities or wall thickness variations and allows accurate determination of the remaining wall thickness for workpieces that are opaque in the area of ​​the measuring beam. [Means for solving the problem]

[0011] According to the invention, this problem is solved by a method for cutting a perforation line in an airbag cover, in which the airbag cover is guided relative to an instrument having a processing beam source and a first measurement beam source along an imaginary line, a processing beam is emitted by the processing beam source, a first measurement beam is emitted by the first measurement beam source, a second measurement beam is emitted by the second measurement beam source, a processing location located on a side of the airbag cover facing the processing beam source is irradiated along an irradiation axis with the processing beam and the first measurement beam, in which material removal is performed at the processing location by irradiation with the processing beam, the second measurement beam is irradiated at the measurement location, a first path length of the first measurement beam and a second path length of the second measurement beam are determined, the first path length and the second path length are evaluated, in which the first path length and the second path length are used for determining a remaining wall thickness and the processing beam source is controlled depending on the determined remaining wall thickness. A second measurement beam is irradiated on a position on the irradiation axis on the side of the airbag cover opposite to the processing beam source as a measurement position. Before the airbag cover is prepared, a distance between the first measurement beam source and the second measurement beam source is determined. Then, a remaining wall thickness is determined from a difference between the distance between the first measurement beam source and the second measurement beam source and the sum of the first path length and the second path length. The distance between the first measurement beam source and the second measurement beam source is determined by a reflecting element having a specified thickness, and the reflecting element is prepared at the processing position.

[0012] Advantageously, the first and / or second measurement beam sources are respectively measurement beam sources of a coherence tomography device, and the first and / or second path length is determined by optical coherence tomography. To perform optical coherence tomography, the first and / or second measurement beams can be partially reflected or partially transmitted towards a reference arm by a beam splitter present in the respective beam path before irradiation. The part of the respective measurement beam that has passed through the reference arm is then superimposed or interfered with the part of the respective measurement beam reflected by the airbag cover, and the interference response is detected by a detector. From the interference response, the first and / or second path length can be determined.

[0013] The airbag cover may rest on the supporting planar member during the entire method. The supporting planar member may be transparent or partially transparent to the second measurement beam, such that the second measurement beam can pass through the supporting planar member prior to irradiating the measurement location. Alternatively, the supporting planar member may have a recess, such that the second measurement beam can pass through the recess in the supporting planar member prior to irradiating the measurement location.

[0014] The first measurement beam can advantageously be guided at least partially beam-parallel or beam-overlapping with the processing beam before or after irradiation at the measurement location.

[0015] It is advantageous if the processing beam has a first wavelength and the first measurement beam has a second wavelength. The first wavelength may be different from the second wavelength. Alternatively, the first measurement beam may be a white light beam.

[0016] Particularly preferably, the first measurement beam is implemented as a laser beam of a fiber laser.

[0017] Preferably, the processing beam is a laser beam of a CO2 laser. Likewise, preferably, the processing beam source is another pulsed laser, the pulse energy, the pulse length, the repetition rate and / or the emission spectrum of which are controlled in dependence on the determined remaining wall thickness.

[0018] The present invention will now be described in more detail by way of examples with reference to the drawings. [Brief description of the drawings]

[0019] [Figure 1] 1 is a side view of an arrangement for carrying out the method, including an instrument, an airbag cover, a supporting planar member, and a second measurement beam source. [Diagram 2] FIG. 2 is a side view showing beam paths of a processing beam, a first measurement beam, and a second measurement beam for determining the remaining wall thickness of an airbag cover. [Diagram 3] FIG. 2 shows a side view of the beam paths of a first and a second measurement beam with a reflecting element at the processing position for determining the distance between the first and second measurement beam sources. [Figure 4] 3 shows a side view of the beam paths of the processing beam, the first measurement beam and the second measurement beam in an advantageous embodiment of the method; [Diagram 5] 4 shows a side view of the beam paths of the processing beam, the first measurement beam and the second measurement beam in a further advantageous embodiment of the method; DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0020] An arrangement for carrying out the method for making a perforation line in an airbag cover 1 is shown diagrammatically in Fig. 1. During this method, the airbag cover 1 is guided relative to a tool 2 along an imaginary line L, whereby at a number of processing positions BO a number of blind holes forming a perforation line in the airbag cover 1 can be made. During the entire processing method, the airbag cover 1 is located on a supporting planar member 9 or is held by a robotic arm (not shown).

[0021] The tool 2 comprises a processing beam source 3 and a first measurement beam source 4. The processing beam source 3 is adjusted along an irradiation axis BA, which irradiation axis BA is substantially perpendicular to a side 6 of the airbag cover 1 facing the processing beam source 3. A second measurement beam source 5 is arranged on a side 7 of the airbag cover 1 opposite the processing beam source 3 during the entire method.

[0022] First, the airbag cover 1 is prepared, which is to have perforation lines. To produce a number of blind holes or perforation lines in the airbag cover 1, the processing beam source 3 emits a processing beam 3.1, which irradiates a processing location BO, which is located on a side surface 6 of the airbag cover 1 facing the processing beam source 3. The irradiation of the processing beam 3.1 results in an energy input to the processing location BO, which results in material removal. At the processing location BO, the airbag cover 1 has a remaining wall thickness RWS after irradiation by the processing beam 3.1, which is equal to the thickness of the airbag cover 1 at the processing location BO minus the depth of the blind holes. The remaining wall thickness RWS is determined simultaneously with the processing of the airbag cover 1.

[0023] To determine the remaining wall thickness RWS, the first measurement beam source 4 emits a first measurement beam 4.1, which is directed to the processing position BO. The first measurement beam 4.1, which is diffusely reflected at the processing position BO, is detected by a detector, not shown. By the irradiation of the first measurement beam 4.1, a first path length a is determined, which corresponds to the distance from the first measurement beam source 4 to the processing position BO. The second measurement beam source 5 emits a second measurement beam 5.1, which is directed to a measuring position MO, which is located on the side 7 of the airbag cover 1 opposite the processing beam source 3 on the irradiation axis BA. The second measurement beam 5.1, which is reflected by the measuring position MO, is detected by a further detector, also not shown. By the irradiation of the second measurement beam 5.1, a second path length b is determined, which corresponds to the distance from the second measurement beam source 5 to the measuring position MO. This distance is not to be understood as a spatial distance, but rather as an optical distance or a path length along the beam path. It is desirable to determine the remaining wall thickness RWS taking into account the first path length a and the second path length b. The processing beam source 3 is controlled depending on the remaining remaining wall thickness RWS. In order to determine the remaining wall thickness RWS using the first path length a and the second path length b, it is advantageous to know the positions of the first measurement beam source 4 and the second measurement beam source 5 with respect to the airbag cover 1 and thus their relative positions with respect to each other, or at least their distance from each other.

[0024] Fig. 2 shows the beam paths of the processing beam 3.1, the first measuring beam 4.1 and the second measuring beam 5.1. Furthermore, the first path length a, the second path length b and the distance c between the first measuring beam source 4 and the second measuring beam source 5 are marked. The processing beam 3.1 and the first measuring beam 4.1 can extend with beam overlap as shown in Fig. 2. However, the first measuring beam 4.1 can also not extend along the illumination axis BA. The first measuring beam 4.1 can in particular extend beam-parallel or at least partially beam-parallel along the illumination axis BA.

[0025] Before the airbag cover 1 is prepared, the distance c between the first measurement beam source 4 and the second measurement beam source 5 can be determined in order to calculate the remaining wall thickness RWS from the difference between the distance c and the sum of the first path length a and the second path length b. FIG. 3 shows an arrangement for determining the distance c. In this case, the distance c is determined by inserting a reflecting element 8 having a defined thickness d. If the thickness d of the reflecting element 8 along the irradiation axis BA is known, the distance c can be determined by determining the first path length a and the second path length b, and the distance c is the sum of the first path length a, the second path length b and the thickness d of the reflecting element 8. In this case, the first path length a and the second path length b can also be determined using optical coherence tomography. The distance c between the first measurement beam source 4 and the second measurement beam source 5 can also be determined by determining the position of the measurement beam sources or by applying a reflective coating to one of the measurement beam sources. FIG. 3 shows a detector for the second measurement beam source 5, which is arranged downstream of the beam splitter and facing the reference arm.

[0026] The first path length a and / or the second path length b can be determined using optical coherence tomography. For this purpose, a beam splitter is present in the respective measurement beam path, which partially reflects or partially transmits the light incident from the measurement beam source into the reference arm. A mirror is arranged in the reference arm, which reflects a part of the measurement beam reflected into the reference arm back to the beam splitter. At the measurement position MO and / or processing position BO, a part of the irradiated measurement beam is also reflected and is recombined in the beam splitter with the part of the measurement beam reflected into the reference arm. The two parts of the measurement beam interfere with each other, and from the interference response detected by the detector, a path length difference between the part of the measurement beam reflected into the reference arm and the part of the measurement beam transmitted can be determined. From this path length difference, the first path length a and / or the second path length b can then be determined. In FIG. 4, such a reference arm for a first measurement beam source 4 is shown together with a beam splitter and a flat mirror.

[0027] If the airbag cover 1 is placed on the supporting planar element 9 during the entire method, the airbag cover 1 is always placed on the side 7 opposite the processing beam 3.1. As also shown in FIG. 4, the first measurement beam 4.1 can also be guided with only partial overlap with the processing beam 3.1. To determine the remaining wall thickness RWS, the second measurement beam 5.1 emitted from the second measurement beam source 5 must pass through the supporting planar element 9 to the measurement position MO. For this, the supporting planar element 9 can be at least partially transparent to the second measurement beam 5.1. This has the advantage that the respective processing position BO and thus the respective measurement position MO can be selected freely.

[0028] Alternatively, as shown in FIG. 5, the supporting planar member can have a recess through which the second measuring beam 5.1 reaches the airbag cover 1. [Explanation of symbols]

[0029] 1 Airbag cover 2. Equipment 3. Processing beam source 3.1 Processing beam 4 First measurement beam source 4.1 First measurement beam 5 Second measurement beam source 5.1 Second measurement beam 6 Side facing the processing beam source 7 Side opposite to processing beam source 8 Reflective elements 9 Supporting Plane Member a First path length b Second path length c distance d Thickness BA Irradiation Axis BO processing position MO measurement position RWS remaining wall thickness L Virtual Line

Claims

1. A method for making perforation lines in an airbag cover (1), wherein the airbag cover (1) is guided relative to an instrument (2) having a processing beam source (3) and a first measurement beam source (4) along an imaginary line (L), providing an airbag cover (1); - emitting a processing beam (3.1) by said processing beam source (3); - emitting a first measurement beam (4.1) by said first measurement beam source (4); - emitting a second measurement beam (5.1) by a second measurement beam source (5); irradiating a processing location (BO) located on a side (6) of the airbag cover (1) facing the processing beam source (3) with the processing beam (3.1) and the first measurement beam (4.1) along an irradiation axis (BA), wherein material removal occurs at the processing location (BO) by irradiation with the processing beam (3.1), - irradiating the measurement position (MO) with a second measurement beam (5.1); determining a first path length (a) of said first measurement beam (4.1); determining a second path length (b) of the second measurement beam (5.1); evaluating the first and second path lengths (a, b), wherein the first and second path lengths (a, b) are used to determine a parameter; controlling the processing beam source (3) depending on the determined parameter, wherein the parameter is a remaining residual wall thickness (RWS); and irradiating a second measurement beam (5.1) onto a position on the side (7) of the airbag cover (1) opposite to the processing beam source (3) on the irradiation axis (BA) as a measurement position (MO), determining a distance (c) between the first measurement beam source (4) and the second measurement beam source (5) before the airbag cover (1) is prepared; determining the remaining remaining wall thickness (RWS) from the difference between the distance (c) and the sum of the first path length (a) and the second path length (b), 1. A method for forming perforation lines in an airbag cover (1), characterized in that the distance (c) between the first measurement beam source (4) and the second measurement beam source (5) is determined by a reflective element (8) having a defined thickness (d) before the airbag cover (1) is prepared, and the reflective element (8) is prepared at the processing position (BO).

2. the first measurement beam source (4) is a measurement beam source of a coherence tomography apparatus, 2. The method for placing perforation lines in an airbag cover (1) according to claim 1, characterized in that the first path length (a) is determined by optical coherence tomography.

3. the second measurement beam source (5) is a measurement beam source of a coherence tomography apparatus, 3. A method for introducing perforation lines into an airbag cover (1) according to claim 1 or 2, characterized in that the second path length (b) is determined by optical coherence tomography.

4. 3. A method for making perforation lines in an airbag cover (1) according to claim 1 or 2, characterized in that the airbag cover (1) rests on a supporting planar member (9) during the entire method.

5. 5. A method for introducing perforation lines into an airbag cover (1) according to claim 4, characterized in that the second measurement beam (5.1) passes through the supporting planar element (9) before irradiating the measurement position (MO).

6. 5. A method for introducing perforation lines into an airbag cover (1) according to claim 4, characterized in that, before irradiating the measurement position (MO), the second measurement beam (5.1) penetrates a recess in the supporting planar element (9).

7. 3. The method for producing perforation lines in an airbag cover (1) according to claim 1 or 2, characterized in that the first measuring beam (4.1) is guided at least partially parallel or overlapping with the processing beam (3.1).

8. the processing beam (3.1) has a first wavelength and the first measurement beam (4.1) has a second wavelength, A method for making perforation lines in an airbag cover (1) according to claim 1 or 2, characterized in that said first wavelength is different from said second wavelength.

9. 3. A method for making perforation lines in an airbag cover (1) according to claim 1 or 2, characterized in that the first measuring beam (4.1) is a white light beam.

10. 3. A method for producing perforation lines in an airbag cover (1) according to claim 1 or 2, characterized in that the first measuring beam (4.1) is a laser beam of a fiber laser.

11. The processing beam (3.1) is CO ２ A method for making perforation lines in an airbag cover (1) according to claim 1 or 2, characterized in that it is a laser beam of a laser.

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