METHOD, PROCESSING MACHINE AND COMPUTER PROGRAM FOR WORKPIECE POSITION DETECTION USING OCT

Description

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

[0002] In certain applications, it is necessary to determine the orientation, i.e., the position and orientation, of a workpiece to be machined relative to a coordinate system. An example of such an application is determining the orientation of a workpiece to be machined with an industrial robot relative to the industrial robot or its coordinate system. In the current state of the art, the control or path programming of laser robots is performed by teaching. In this process, so-called teach points are manually approached along the contour to be machined. An operator standing in the robot's workspace approaches positions on the workpiece, point by point, and checks visually or with a laser pointer whether a laser processing head, from which a laser beam emerges during laser processing, is positioned over a target path point. In this way, the robot's movement path is "programmed" or followed point by point, which is particularly time-consuming.

[0003] EP 2 693 165 A1 discloses a method for determining the position of an object using a light-section sensor that emits light that creates a line of light on a surface. A search movement is performed by automatically moving the light-section sensor with a movement component perpendicular to the light line and perpendicular to the exit direction of the light using a movement device. During the search movement, image data is recorded using the light-section sensor. The image data is evaluated, and based on the evaluated image data, a prominent point, in particular an outer edge, of the object is detected. The position of the object is determined based on the position of the light-section sensor, which is assigned to the prominent point of the object, and based on an evaluation of the image data assigned to the prominent point of the object.

[0004] Furthermore, a coordinate system is known from DE 10 2015 114 715 A1 in which the component geometry is recorded using short-coherent interferometry.

[0005] Finally, DE 10 2013 015 656 A1 discloses a method for measuring the penetration depth of a laser beam into a workpiece using an optical coherence tomograph. Another possible application of OCT in the field of high-energy laser processing is known from DE 10 2015 012 565 B3.

[0006] From CN 107 953 037 A (disclosing the preamble of claims 1 and 5) a system for three-dimensional laser engraving is known which carries out distance measurements using optical coherence tomography.

[0007] The use of optical coherence tomography in the medical field of ophthalmology is known from US 2014 0 276 676 A1.

[0008] The invention is based on the object of specifying a method for machining a workpiece using a machining beam, in which features of a workpiece to be machined can be determined. In particular, the position, i.e., the position and orientation, of a workpiece to be machined in the workspace can be detected automatically, i.e., without manual teaching, and the workpiece can then be machined according to its detected position.

[0009] This object is achieved according to the invention by a method for machining a workpiece by means of a machining beam emerging from a machining head, wherein the workpiece and the machining head are movable relative to each other in a working space, with the following method steps: Automated scanning of a workpiece to be machined arranged in the work area by means of an OCT measuring beam of an optical coherence tomograph guided over the machining head (English optical coherence tomography , OCT), whereby the position of the machining head in the workspace and the position of the OCT measuring beam relative to the machining head are each known; determining at least one of the following features based on distance measurement values ​​of the optical coherence tomograph determined during automated scanning: the position of the workpiece to be machined in the workspace; the presence of a workpiece to be machined in the workspace; the presence of the correct workpiece to be machined in the workspace; and the presence of a machining feature of the workpiece to be machined that was carried out on the workpiece in a previous machining step (e.g. whether a previously manufactured bending radius is correct or not).

[0010] During the relative movement of the workpiece and the machining head, either only the workpiece or only the machining head or both can be moved.

[0011] According to the invention, the OCT measuring method is used to automatically measure features of a workpiece to be machined, such as the workpiece position in the workspace. OCT measuring technology is an optical measuring method that is currently used to measure the welding depth or to measure the position of weld edges. Since the OCT measuring beam is guided over the machining head, in particular coaxially to the machining beam, and is a component of the machining head, the OCT measuring signal generates distance information to a reference point on the machining head, e.g., tool center point (TCP). The position of the workpiece to be machined in the workspace can be derived from the position of the robot axes and the dimensions of the welding head.

[0012] The process according to the invention particularly preferably comprises the following further process steps: Determining a coordinate transformation between the specific workpiece position and the position of a CAD model of the workpiece to be machined in a CAD coordinate system; transforming a machining path of the machining head programmed for the CAD model in the CAD coordinate system to the specific position of the workpiece to be machined using the determined coordinate transformation; and machining the workpiece using the machining beam by moving the machining heads relative to each other along the transformed machining path.

[0013] The measured workpiece position is compared with the position of the CAD model of the workpiece to be machined in the CAD coordinate system. Coordinate transformation transfers the NC path programming of the machining head from the CAD coordinate system to the measured workpiece position. This results in the following advantages: The teaching process is eliminated; time-saving, faster access to the first machined workpiece; lower risk of incorrect operation; offline programming for robots; the structure of the processing machine is simplified, e.g. through simple clamping devices, since no exactly repeatable workpiece position is required.

[0014] Preferably, the OCT measuring beam is deflected one- or two-dimensionally to scan the workpiece with the OCT measuring beam. In contrast to light-section-based methods, the OCT-based method according to the invention allows for the scanning pattern traced across the workpiece surface by the OCT measuring beam to be arbitrarily modified.

[0015] More preferably, the machining head can be moved to scan the workpiece with the measuring beam.

[0016] The invention also relates to a processing machine for processing a workpiece by means of a processing beam, in particular a processing laser beam, comprising: a processing beam generator for generating a processing beam, an optical coherence tomograph for generating an OCT measuring beam, an OCT scanner for one- or two-dimensionally deflecting the OCT measuring beam, a processing head from which the processing beam and the deflected OCT measuring beam emerge, and a machine control for controlling the scanner movement of the OCT scanner.

[0017] According to the invention, the machine control comprises: a position determination unit for determining the position of the workpiece to be machined in the workspace based on distance measurements from the optical coherence tomograph, a determination unit for determining a coordinate transformation between the determined workpiece position and the position of a CAD model of the workpiece to be machined in a CAD coordinate system, a transformation unit for transforming a machining path of the machining head programmed for the CAD model in the CAD coordinate system to the determined position of the workpiece to be machined using the determined coordinate transformation, wherein the machine control is programmed to carry out the method according to the invention described above.

[0018] The machining head can be stationary or, preferably, movable. In the latter case, the machine control also controls the movement of the machining head. There can be either a single machine control or two separate controls that communicate with each other.

[0019] Particularly preferably, the optical coherence tomograph and the OCT scanner are attached to the processing head.

[0020] Finally, the invention also relates to a computer program product according to claim 10.

[0021] Further advantages and advantageous embodiments of the subject matter of the invention can be found in the description, the drawings, and the claims. Likewise, the features mentioned above and those listed below can be used individually or in combination in any desired manner. The embodiments shown and described are not to be understood as an exhaustive list, but rather as examples for describing the invention.

[0022] Fig. 1 shows schematically a laser processing machine for carrying out the method according to the invention.

[0023] The Fig. 1 schematically shown laser processing machine 1 includes a laser beam generator 2 for generating a processing laser beam 3 , a laser scanner 4 for two-dimensional deflection of the processing laser beam 3 in x-, y-direction on a workpiece 5, as well as an optical coherence tomograph (OCT) 6 for optically scanning an area of ​​the surface 7 of the workpiece 5. The laser scanner 4 can, for example, have a scanner mirror deflectable about two axes or two scanner mirrors each deflectable about one axis.

[0024] The OCT 6 has, as is well known, an OCT light source (e.g.

[0025] Superluminescent diode) 8 to generate a light beam 9 , a beam splitter 10 for splitting the light beam 9 into an OCT measuring beam 11 and a reference beam 12 The OCT measuring beam 11 is connected to a measuring arm 13 and impinges on the workpiece surface 7, where the OCT measuring beam 11 is at least partially reflected and returned to the beam splitter 10, which is opaque or partially transparent in this direction. The reference beam 12 is directed to a reference arm 14and at the end of the reference arm 14 by a mirror 15 The reflected reference beam is also returned to the beam splitter 10. The superposition of the two reflected beams is finally detected by a detector (OCT sensor) 16 detected in order to determine height information about the workpiece surface 7 and / or the current penetration depth of the processing laser beam 3 into the workpiece 5, taking into account the length of the reference arm 14. This method is based on the basic principle of the interference of light waves and enables height differences along the measuring beam axis to be recorded in the micrometer range.

[0026] An OCT (small field) scanner is connected to the measuring arm 13 17to deflect the OCT measuring beam 11 on the workpiece surface 7 two-dimensionally, i.e., in the X and Y directions, and thus to scan an area of ​​the workpiece surface 7, for example, with line scans. The OCT scanner 17 can, for example, have a scanner mirror deflectable about two axes or two scanner mirrors, each deflectable about one axis. Via a mirror 18 , which is arranged obliquely in the beam path of the processing laser beam 3 and is transmissive for the processing laser beam 3 and reflective for the OCT measuring beam 11, the OCT measuring beam 11 is coupled into the laser scanner 4 in order to direct the OCT measuring beam 11 onto the workpiece 5. The sensor data of the OCT sensor 16 are transmitted to a machine control 19 which also controls the movement of scanners 4, 17.

[0027] As in Fig. 1As indicated by dashed lines, the laser scanner 4 and the OCT scanner 17 (and possibly also the OCT 6) are integrated into a movable processing head 20 integrated, from which the processing laser beam 3 and the deflected OCT measuring beam 11 emerge. The processing laser beam 3 and the OCT measuring beam 11 can be fed to the processing head 3 via optical fibers (not shown). The movement of the processing head 20 is also controlled by the machine control 19.

[0028] The workpiece 5 and the machining head 20 are movable relative to each other; for this purpose, either the workpiece 5 or the machining head 20 or both are movable.

[0029] The machine control 19 includes: a position determination unit 21 for determining the position of the workpiece 5 to be machined in the work area based on distance measurement values ​​of the optical coherence tomograph 6, a determination unit 22to determine a coordinate transformation T between the specific workpiece position and the position of a CAD (zero) model 23 of the workpiece 5 to be machined in a CAD coordinate system 24 , (reference coordinates XR , YR , ZR ) and a transformation unit 25 for transforming a machining path of the machining head 20 programmed for the CAD model 23 in the CAD coordinate system 24 to the specific position of the workpiece 5 to be machined (real component) by means of the determined coordinate transformation T.

[0030] For machining a workpiece 5, the exact position of which in the working area (e.g. the exact position on a workpiece table 26 ) is not known, the following procedure is followed using the processing laser beam 3.

[0031] The processing head 20, whose position in the workspace is known, is initially positioned above the workpiece table 26 or the workpiece 5. The first search step then begins, with the OCT measuring beam 11, whose position relative to the processing head 20 is also known, being moved through the field of view of the OCT 6 by means of the OCT scanner 17. If no component geometry has yet been acquired, the processing head 20 or the OCT 6 is moved closer to the workpiece table 26 by a fixed increment in the Z direction. The process is automatically repeated until the workpiece 5 is acquired. If necessary, the search process is supplemented by moving the processing head 20 in the XY plane. The OCT field of view is scanned point by point, thus detecting the workpiece 5 located within the field of view. Each positive distance measurement event corresponds to a spatial point, which corresponds to a point on the workpiece surface 7.The sum of all component surface points corresponds in their entirety to the workpiece 5. Based on the distance measurements, the position determination unit 21 determines the position of the workpiece 5 to be machined in the work space. The determination unit 22 determines the coordinate transformation T between the determined workpiece position and the position of the CAD model 23 in the CAD coordinate system 24. Using the coordinate transformation T thus determined, the transformation unit 25 transforms a processing path of the processing head 20 programmed for the CAD model 23 in the CAD coordinate system 24 and a scanner movement of the laser scanner 4 to the determined position of the workpiece 5 to be machined. Finally, the workpiece 5 is machined using the laser processing beam 3 by moving the processing head 20 and the laser processing beam 3 along the transformed processing path.

[0032] Alternatively or in addition to the described determination of the workpiece position in the work area, at least one of the following features can also be determined based on distance measurement values ​​of the optical coherence tomograph 6 determined during automated scanning: the presence of a workpiece 5 to be machined in the work space; the presence of the correct workpiece 5 to be machined in the work space; and the presence of a machining feature of the workpiece 5 to be machined that was performed on the workpiece 5 in a previous machining step.

Claims

1. A method for processing a workpiece (5) by means of a processing beam (3) which emerges from a processing head (20), wherein the workpiece (5) and the processing head (20) can be moved relative to one another in a working space, characterized by the following steps: - automated scanning of a workpiece (5) to be processed arranged in the working space by means of an OCT measuring beam (11) of an optical coherence tomograph (6) guided by means of the processing head (20), wherein the position of the processing head (20) in the working space and the position of the OCT measuring beam (11) relative to the processing head (20) are known in each case; - determining at least one of the following features on the basis of distance measurement values of the optical coherence tomograph (6) determined during automated scanning: - the position of the workpiece (5) to be processed in the working space; - the presence of a workpiece (5) to be processed in the working space; - the presence of the correct workpiece (5) to be processed in the working space; and - the presence of a processing feature of the workpiece (5) to be processed that was performed on the workpiece (5) in a previous processing step.

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

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

4. The method according to one of the preceding claims, characterized by the following further process steps: - determining a coordinate transformation (T) between the determined workpiece position and the position of a CAD model (23) of the workpiece (5) to be processed in a CAD coordinate system (24); - transforming a processing path of the processing head (20) and the processing beam (3) programmed for the CAD model (23) in the CAD coordinate system (24) to the determined position of the workpiece (5) to be processed by means of the determined coordinate transformation (T); and - processing the workpiece (5) by means of the processing beam (3) by moving the processing head (20) and the processing beam (3) relative to one another along the transformed processing path.

5. A processing machine (1) for processing a workpiece (5) by means of a processing beam (3), comprising: - a processing beam generator (2) for generating a processing beam (3), - an optical coherence tomograph (6) for generating an OCT measuring beam (11), - an OCT scanner (17) for deflecting the OCT measuring beam (11) in one or two dimensions, - a processing head (20), from which the processing beam (3) and the deflected OCT measuring beam (11) emerge, and characterized by - a machine control system (19) for controlling the scanner movement of the OCT scanner (17), wherein the machine control system (19) has: - a position determination unit (21) for determining the position of the workpiece (5) to be processed in the working space on the basis of distance measurement values of the optical coherence tomograph (6), - a detection unit (22) for detecting a coordinate transformation (T) between the determined workpiece position and the position of a CAD model (23) of the workpiece (5) to be processed in a CAD coordinate system (24), - a transformation unit (25) for transforming a processing path of the processing head (20) and the processing beam (3) programmed for the CAD model (23) in the CAD coordinate system (24) to the determined position of the workpiece (5) to be processed by means of the determined coordinate transformation (T), and wherein the machine control system (19) is programmed to carry out 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) can be moved and the machine control system (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 fastened to the processing head (20).

8. The processing machine according to one of claims 5 to 7, characterized in that the optical coherence tomograph (6) is fastened to the processing head (20).

9. The processing machine according to one of claims 5 to 8, characterized in that the processing beam (3) is a processing laser beam.

10. A computer program product having code means adapted to carry out all the steps of the method as claimed in one of claims 1 to 4 when the program is executed on the machine control system (19) of the processing machine (1) according to one of the claims 5 to 9.