Method for detecting the position of a workpiece by means of oct and machining machine

Abstract

The present application relates to a method for machining a workpiece (5) by means of a machining beam (2) which is emitted from a machining head (20), wherein the workpiece (5) and the machining head (20) can be moved relative to one another in a work space, the method comprising the following method steps: automatic scanning of a workpiece (5) to be machined arranged in the work space by means of an OCT measuring beam (11) of an optical coherence tomography device (6), the OCT measuring beam being guided through the machining head (20), wherein the position of the machining head (20) in the work space and the position of the OCT measuring beam (11) relative to the machining head (20) are known respectively; determination of the position of the workpiece (5) to be machined in the work space from the distance measurements taken by the optical coherence tomography device (6) during the automatic scanning; taking of a coordinate transformation (T) between the determined position of the workpiece and the position of a CAD model (23) of the workpiece (5) to be machined in a CAD coordinate system (24); transformation of a machining trajectory programmed for the CAD model (23) in the CAD coordinate system (24) into the determined position of the workpiece (5) to be machined by means of the coordinate transformation (T) taken; and machining of the workpiece (5) by means of the machining beam (3) by moving the machining head (20) and the machining beam (3) relative to one another along the transformed machining trajectory with respect to the workpiece.

Description

Technical Field

[0001] The present invention relates to a method for machining a workpiece by means of a machining beam, such as a laser beam. Background Technology

[0002] In certain applications, it is necessary to determine the orientation, position, and orientation of the workpiece relative to a coordinate system. One example of such an application is determining the orientation of a workpiece relative to the industrial robot or its coordinate system using an industrial robot. In the prior art, control or trajectory programming is performed on laser robots through teaching. Here, the so-called teaching point is manually moved along the contour to be processed on the workpiece by an operator standing in the robot's workspace, moving point by point on the workpiece and checking visually or with the aid of a laser pointer whether the laser processing head, which emits the laser beam during laser processing, is above the given trajectory point. In this way, the robot's trajectory is "programmed" or traversed point by point, which is particularly time-consuming.

[0003] EP 2 693 165 A1 discloses a method for determining the orientation of an object using an optical section sensor that emits light that generates rays on a surface. A search movement is performed by automatically moving the optical section sensor, which has a moving component, perpendicular to both the light ray and the direction of light emission, using a motion device. During the search movement, image data is captured using the optical section sensor. The image data is evaluated, and salient parts of the object, particularly its outer edges, are identified based on the evaluated image data. The orientation of the object is determined based on the position of the optical section sensor, which is configured to the salient position of the object, and based on the image data evaluating the salient position of the object.

[0004] Furthermore, a coordinate system for detecting the geometry of a component by means of short coherence interferometry is known from DE 10 2015 114 715 A1.

[0005] Finally, a method for measuring the penetration depth of a laser beam into a workpiece by means of an optical coherence tomography apparatus is known from DE 10 2013 015 656 A1. Summary of the Invention

[0006] In contrast, the object of the present invention is to provide a method for machining a workpiece by means of a machining beam, wherein the characteristics of the workpiece to be machined can be determined. In particular, the orientation, i.e., position and orientation of the workpiece to be machined in the workspace should be detected automatically, i.e., without manual instruction, and then the workpiece should be machined in accordance with the detected orientation of the workpiece to be machined.

[0007] According to the present invention, this task is solved by a method for machining a workpiece by means of a machining beam emitted from a machining head, wherein the workpiece and the machining head are movable relative to each other in a workspace, the method comprising the following steps:

[0008] - The workpiece to be processed is automatically scanned by means of an optical coherence tomography (OCT) measuring beam arranged in the workspace. The OCT measuring beam is guided by a processing head, wherein the orientation of the processing head in the workspace and the orientation of the OCT measuring beam relative to the processing head are known.

[0009] - Determine at least one of the following features based on distance measurements obtained during automatic scanning by an optical coherence tomography (OCT) device:

[0010] - The orientation of the workpiece to be processed in the workspace;

[0011] - There are workpieces to be processed in the workspace;

[0012] - The correct workpiece to be processed exists in the workspace; and

[0013] - There are machining features on the workpiece to be processed that were performed on the workpiece in previous machining steps (e.g., whether the previously manufactured bending radius was correct).

[0014] In the relative motion between the workpiece and the machining head, only the workpiece, only the machining head, or both can move.

[0015] According to the present invention, an OCT measurement method is used to automatically measure features of a workpiece to be processed, such as its orientation in the workspace. OCT measurement technology is an optical measurement method currently used to measure weld depth or the position of weld edges. Because the OCT measurement beam is guided through the processing head, particularly coaxially with and integral with the processing beam, the OCT measurement signal generates distance information relative to a reference point on the processing head, such as the tool center point TCP. The orientation of the workpiece to be processed in the workspace can be derived from the position of the robot axis and the dimensions of the welding head.

[0016] Particularly preferably, the method according to the invention includes the following additional method steps:

[0017] - Determine the coordinate transformation between the determined workpiece orientation and the orientation of the CAD model of the workpiece to be processed in the CAD coordinate system;

[0018] - By using the obtained coordinate transformation, the machining trajectory of the machining head programmed with respect to the CAD model in the CAD coordinate system is transformed into the determined orientation of the workpiece to be machined; and

[0019] - The workpiece is machined by means of a machining beam by moving the machining head relative to the workpiece along a modified machining trajectory.

[0020] The measured workpiece orientation is compared with the orientation of the CAD model of the workpiece in the CAD coordinate system. The NC trajectory of the machining head from the CAD coordinate system is then converted into the measured workpiece orientation through coordinate transformation. This achieves the following advantages:

[0021] - The teaching process was eliminated;

[0022] - Reach the first workpiece for processing faster and save time;

[0023] - Lower risk of misoperation;

[0024] - Offline programming of the robot;

[0025] -Because accurate and repeatable workpiece orientation is not required, the structure of the machining machine is simplified, for example, by using a simple clamping device.

[0026] Preferably, the OCT measurement beam is deflected one-dimensionally or two-dimensionally to scan the workpiece by means of the OCT measurement beam. Compared with optical sectioning-based methods, in the case of the OCT-based method according to the invention, the scan pattern of the OCT measurement beam on the workpiece surface can be arbitrarily changed.

[0027] More preferably, the processing head can be moved to scan the workpiece using a measuring beam.

[0028] The present invention also relates to a processing machine for processing workpieces by means of a processing beam, particularly a processing laser beam, comprising:

[0029] - A processing beam generator, used to generate a processing beam.

[0030] - Optical coherence tomography (OCT) device for generating OCT measurement beams.

[0031] - An OCT scanner is used to deflect the OCT measurement beam in one or two dimensions.

[0032] - A processing head from which a processing beam and a deflected OCT measurement beam are emitted, and

[0033] - Machine control unit used to control the movement of the OCT scanner.

[0034] According to the present invention, the machine control device has:

[0035] - Orientation determination unit, used to determine the orientation of the workpiece to be processed in the workspace based on the distance measurement values ​​of the optical coherence tomography device.

[0036] - The calculation unit is used to calculate the coordinate transformation between the determined workpiece orientation and the orientation of the CAD model of the workpiece to be processed in the CAD coordinate system.

[0037] - Transformation unit, used to transform the machining trajectory of the machining head relative to the CAD model programmed in the CAD coordinate system into the determined orientation of the workpiece to be machined by means of the obtained coordinate transformation.

[0038] The machine control device is programmed to implement the method described above according to the present invention.

[0039] The processing head may be stationary, or preferably movable, wherein, in the latter case, the machine control unit also controls the movement of the processing head. There may be a single machine control unit or two separate controllers communicating with each other.

[0040] Particularly preferably, the optical coherence tomography (OCT) device and the OCT scanner are fixed to the processing head.

[0041] Finally, the present invention also relates to a computer program product comprising code adapted to perform all steps of the method according to the invention when the program is run on a machine control device of a machining machine, such as on a controller of a machining beam generator or machining head, or on a separate machine control device. Attached Figure Description

[0042] Further advantages and advantageous configurations of the subject matter of this invention will become apparent from the specification and drawings. The foregoing features and the further enumerated features can also be used individually or in any combination. The illustrated and described embodiments should not be construed as a final enumeration, but rather as having features specific to describe the exemplary nature of the invention.

[0043] Figure 1 A laser processing machine for performing the method according to the invention is shown schematically. Detailed Implementation

[0044] Figure 1The laser processing machine 1, schematically shown, includes a laser beam generator 2 for generating a processing laser beam 3, a laser scanner 4 for two-dimensionally deflecting the processing laser beam 3 along the x and y directions on a workpiece 5, and an optical coherence tomography (OCT) device 6 for optically scanning a region of the surface 7 of the workpiece 5. The laser scanner 4 may have, for example, scanner mirrors that can deflect about two axes, or two scanner mirrors that can deflect about the axes respectively.

[0045] The OCT 6 has, in a known manner, an OCT light source (e.g., a superluminescent diode) 8 for generating a beam 9, and a beam splitter 10 for splitting the beam 9 into an OCT measurement beam 11 and a reference beam 12. The OCT measurement beam 11 is transferred to a measuring arm 13 and incident on a workpiece surface 7. The OCT measurement beam 11 is at least partially reflected on the workpiece surface and guided back to the beam splitter 10, which is either impassable or partially permissible in the direction of the beam. The reference beam 12 is transferred to a reference arm 14 and reflected at the end of the reference arm 14 by a mirror 15. The reflected reference beam is also guided back to the beam splitter 10. The superposition of the two reflected beams is finally detected by a detector (OCT sensor) 16 to determine the height information about the workpiece surface 7 and / or the current penetration depth of the machining laser beam 3 into the workpiece 5, taking into account the length of the reference arm 14. This method is based on the fundamental principle of optical wave interference and achieves the detection of height differences in the micrometer range along the axis of the measurement beam.

[0046] The OCT (small field of view) scanner 17 is connected to the measuring arm 13 to deflect the OCT measuring beam 11 two-dimensionally (i.e., along the x and y directions) on the workpiece surface 7, thereby scanning an area of ​​the workpiece surface 7, for example, by line scanning. The OCT scanner 17 may have, for example, scanner mirrors that can deflect about two axes, or two scanner mirrors that can deflect about the axes respectively. Mirror 18 is arranged obliquely in the optical path of the processing laser beam 3 and is transmitted to the processing laser beam 3 and reflected by the OCT measuring beam 11, which is coupled into the laser scanner 4 through the mirror so that the OCT measuring beam 11 is pointed at the workpiece 5. Sensor data from the OCT sensor 16 is transmitted to the machine control unit 19, which also controls the movement of the scanners 4 and 17.

[0047] As in Figure 1 As shown in dashed lines, the laser scanner 4 and the OCT scanner 17 (and OCT 6 if necessary) are integrated into a movable processing head 20, from which the processing laser beam 3 and the deflected OCT measurement beam 11 are emitted. The processing laser beam 3 and the OCT measurement beam 11 can be transmitted to the processing head 3 via optical fiber (not shown). The movement of the processing head 20 is also controlled by the machine control unit 19.

[0048] The workpiece 5 and the processing head 20 can move relative to each other; therefore, the workpiece 5 or the processing head 20 or both can move.

[0049] Machine control device 19 includes:

[0050] - Orientation determination unit 21 is used to determine the orientation of the workpiece 5 to be processed in the workspace based on the distance measurement value of the optical coherence tomography device 6.

[0051] - Calculation unit 22 is used to calculate the orientation of the determined workpiece and the orientation of the CAD (datum) model 23 of the workpiece 5 to be processed in the CAD coordinate system 24 (reference coordinate X). R Y R Z R The coordinate transformation T between ) and

[0052] - Transformation unit 25 is used to transform the machining trajectory of the machining head 20 programmed with respect to the CAD model 23 in the CAD coordinate system 24 into the determined orientation of the workpiece 5 (actual component) to be machined by means of the obtained coordinate transformation T.

[0053] In order to process the workpiece 5 by means of the processing laser beam 3, the precise orientation of the workpiece in the workspace (e.g., the precise orientation on the workpiece stage 26) is not known.

[0054] The machining head 20 is initially positioned above the workpiece stage 26 or the workpiece 5, and its orientation in the workspace is known. A first search step then begins, in which the OCT measuring beam 11 moves through the field of view volume of the OCT scanner 6 by means of the OCT scanner 17, the orientation of which relative to the machining head 20 is also known. If the component geometry has not yet been detected, the machining head 20 or the OCT scanner 6 moves closer to the workpiece stage 26 along the Z-direction in fixed increments. This process is automatically repeated for a long time until the workpiece 5 is detected. If necessary, the search process is supplemented by moving the machining head 20 in the XY plane. The OCT field of view volume is scanned point by point, thereby identifying the workpiece 5 located within the field of view. Each positive distance measurement corresponds to a spatial point corresponding to a point on the workpiece surface 7. The sum of all component surface points corresponds to the workpiece 5 as a whole. The orientation determination unit 21 determines the orientation of the workpiece 5 to be processed in the workspace based on the distance measurements. The calculation unit 22 calculates the coordinate transformation T between the determined workpiece orientation and the orientation of the CAD model 23 in the CAD coordinate system 24. The transformation unit 25 uses the calculated coordinate transformation T to transform the machining trajectory of the machining head 20 programmed with respect to the CAD model 23 in the CAD coordinate system 24 and the scanner motion of the laser scanner 4 into the determined orientation of the workpiece 5 to be processed. Finally, the workpiece 5 is processed by means of the machining laser beam 3 by moving the machining head 20 and the machining laser beam 3 along the transformed machining trajectory.

[0055] Alternatively, or in addition to determining the workpiece orientation in the workspace, at least one of the following features can be determined based on distance measurements obtained by the optical coherence tomography device 6 during automatic scanning:

[0056] - There are 5 workpieces to be processed in the workspace;

[0057] - The correct workpiece 5 exists in the workspace; and

[0058] - There are machining features on workpiece 5 that were performed in previous machining steps.

Claims

1. A method for machining a workpiece (5) by means of a machining beam (3), said machining beam being emitted from a machining head (20), wherein, The workpiece (5) and the processing head (20) are capable of moving relative to each other in the workspace, and the method includes the following steps: - The workpiece (5) to be processed is automatically scanned in the workspace by means of the OCT measurement beam (11) of the optical coherence tomography device (6), the OCT measurement beam being guided by the processing head (20), wherein the orientation of the processing head (20) in the workspace and the orientation of the OCT measurement beam (11) relative to the processing head (20) are known. - Determine at least one of the following features based on the distance measurement obtained by the optical coherence tomography device (6) during automatic scanning: - The orientation of the workpiece (5) to be processed in the workspace; - There is a workpiece (5) to be processed in the workspace; - The correct workpiece to be processed (5) exists in the workspace; and -The workpiece (5) to be processed has machining features performed on the workpiece (5) in a previous machining step. The presence of a workpiece (5) to be processed in the workspace is determined by a search process using an OCT measuring beam (11).

2. The method according to claim 1, characterized in that, The OCT measuring beam (11) is deflected in one or two dimensions so as to scan the workpiece (5) through the OCT measuring beam (11).

3. The method according to claim 1 or 2, characterized in that, The processing head (20) is moved so that the workpiece (5) is scanned by the OCT measuring beam (11).

4. The method according to claim 1 or 2, characterized in that, The following alternative method steps are set: - Calculate the coordinate transformation (T) between the determined workpiece orientation and the orientation of the CAD model (23) of the workpiece (5) to be processed in the CAD coordinate system (24); - By means of the obtained coordinate transformation (T), the machining trajectory of the machining head (20) and the machining beam (3) programmed with respect to the CAD model (23) in the CAD coordinate system (24) is transformed into the determined orientation of the workpiece (5) to be processed; and - The workpiece (5) is processed by means of the processing beam (3) by moving the processing head (20) and the processing beam (3) relative to each other along a modified processing trajectory.

5. A machining machine (1) for machining a workpiece (5) by means of a machining beam (3), comprising: - Processing beam generator (2), used to generate processing beam (3), - Optical coherence tomography (6) for generating OCT measurement beams (11), -OCT scanner (17), used to deflect the OCT measurement beam (11) one-dimensionally or two-dimensionally. - A processing head (20) from which the processing beam (3) and a deflected OCT measurement beam (11) are emitted, and - Machine control unit (19), used to control the scanner movement of the OCT scanner (17), in, The machine control device (19) has: - Orientation determination unit (21), used to determine the orientation of the workpiece (5) to be processed in the workspace based on the distance measurement value of the optical coherence tomography device (6). - The calculation unit (22) is used to calculate the coordinate transformation (T) between the determined workpiece orientation and the orientation of the CAD model (23) of the workpiece (5) to be processed in the CAD coordinate system (24). - Transformation unit (25) for transforming the machining trajectory of the machining head (20) and the machining beam (3) programmed with respect to the CAD model (23) in the CAD coordinate system (24) into the determined orientation of the workpiece (5) to be processed by means of the obtained coordinate transformation (T). The machine control device (19) is programmed to implement the method according to any one of the preceding claims.

6. The processing machine according to claim 5, characterized in that, The processing head (20) is movable, and the machine control device (19) controls the movement of the processing head (20).

7. The processing machine according to claim 5 or 6, characterized in that, The OCT scanner (17) is fixed on the processing head (20).

8. The processing machine according to claim 5 or 6, characterized in that, The optical coherence tomography device (6) is fixed on the processing head (20).

9. The processing machine according to claim 5 or 6, characterized in that, The processing beam (3) is a processing laser beam.

10. A computer program product comprising code adapted to perform all steps of the method according to any one of claims 1 to 4 when the program is run on a machine control device (19) of a processing machine (1) or on a separate machine control device.

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