Method and device for 3D measurement
Patent Information
- Authority / Receiving Office
- DE · DE
- Patent Type
- Patents
- Current Assignee / Owner
- AUTO1 GROUP SE
- Filing Date
- 2012-07-20
- Publication Date
- 2026-07-02
Smart Images
Figure 00000000_0000_ABST
Abstract
Description
The invention relates to a method and a device for optical 3D measurement of the surface of an object. Optical 3D measurement systems are known from the state of the art, in which color or line patterns are projected onto the surface of the object to be measured with high technical effort, captured with the help of stereo cameras and the surface topology is calculated by computer. It is also known to project a static dot grid onto the object and use a stereo camera to acquire the spatial coordinates of the number of points for 3D measurement. The 3D resolution of these latter systems necessarily corresponds to the optically captured number of points in the dot grid within a surface area of the object. The grid cannot be arbitrarily dense, as the optical system of the stereo camera must ensure a clear separation of the points from one another when capturing the surface. Variable generation of dot grids using only video projectors or similarly complex systems is also possible. However, such methods require a very high light output from the projector and are therefore very difficult to implement in ambient light. For example, EP 2 025 991 A4 proposes three-dimensional acquisition of an object using an illumination pattern generated by a laser and a diffractive optical element. The spatial coordinate data of the points in the illumination pattern are acquired with a stereo camera. To improve depth information, it is also described that after an initial pattern projection, a further pattern projection can be performed with a second acquisition of the object. US 2009 / 0 251 685 A1 describes how a further pattern projection can be provided by shifting the pattern of the first pattern projection. DE 10 2007 047 465 A1 and US 2011 / 0 128 162 A1, as well as DE 10 2006 001 634 B3 and DE 199 28 341 C2, show various solutions in which the further pattern projection is generated by a rotation.To improve the detection results, US 2006 / 0044546A1 further proposes using multiple light sources with different wavelengths to generate the pattern. DE 10137241A1 and US 2007 / 0058175A1 describe projecting markers onto the object to be detected along with the pattern, thereby improving the detection process. These markers contain encoded information that can be processed by a computer simultaneously with the detection of the object points. The object of the invention is to develop a method and a device for 3D measurement of the surface of an object, which optically captures the surface by projecting a dot pattern onto the surface using a conventional stereo camera system and provides computer-aided three-dimensional measurement results of the topology of the surface of the object, thereby enabling a particularly high resolution. The problem is solved with respect to the method by the features listed in claims 1 and 2, and with respect to the apparatus by the features listed in claims 6 and 7. Preferred embodiments are described in the respective dependent claims. According to the invention, a method and apparatus for 3D measurement of an object's surface comprises three projection units for projecting patterns onto the object's surface, a stereo camera system for optical image acquisition, and a computer system coupled to these assemblies with suitable software for image evaluation. Advantageously, a regular dot pattern is projected onto the object's surface, since this allows for a high degree of contrast between the surface's color and / or texture, and the optical image acquisition provides unambiguous values. The execution of the inventive method for 3D measurement of the object's surface is based on optical acquisition of the surface of the object to be measured using a stereo camera system and comprises the following steps, assuming that the stereo camera system has been calibrated beforehand in a known manner: - first projection of the point pattern, preferably a regular point pattern, onto the surface of the object to be measured three-dimensionally; - first optical acquisition of the points of the projected point pattern and thus of the object's surface using the stereo camera system, as well as transfer of an acquired first data volume into the computer system, where it is preferably initially stored;- Second projection of the point pattern, whereby the position of the point pattern is shifted relative to the position of the point pattern of the first projection on the object's surface by synchronous adjustment through radial rotation of each of the three projection units; - Second optical acquisition of the same area of the object's surface with the modified point pattern projected onto it using the stereo camera system, and transfer of a captured second data volume into the computer system; - Using the computer system, the spatial coordinates of the points of the point patterns from the first and second projections are calculated from the first and second data volumes, and a topology of the object's surface is created, which is available for retrieval in the computer system. With the second optical acquisition of the surface with the shifted projected point pattern, the resulting second data volume, the calculation of the spatial coordinates of the points of the projected point pattern from the second optical acquisition and the superposition with the 3D data from the first optical acquisition of the first projection, with the same number of projected points of the point pattern, the data density is doubled and thus the resolution is doubled. Preferably, the second projection and second optical acquisition, etc., can be followed by a third and further projection and third and further optical acquisition, etc., whereby the increased data volumes from all projections further improve the achievable resolution. A particular advantage of the time offset between the projections is that the distances between points from two or more projections can be closer together than would be possible with only one projection due to the required contrast. Minimum distances between points no longer limit the possible resolution. It is also possible to transfer the respective data volume of the optical recordings to the computer system, to first superimpose them and then to calculate the spatial coordinates of the points and to create the topology of the surface of the object on the basis of these. According to claim 2, in an alternative variant of the method, the process steps are also carried out as in claim 1, but with the difference that in the second projection not the same point pattern is merely shifted, but a different point pattern is used than in the first projection. The described method for 3D measurement of the surface of the object is carried out according to the invention by three projection units for projecting a point pattern, each comprising at least one laser as a light source with optics for providing a collimated light beam and two known diffractive optical elements (DOE) arranged in its beam path as an optical axis for generating and projecting a defined point pattern onto the surface of the object to be measured three-dimensionally. According to the invention, in the method of claim 1, in which the second optical acquisition of the surface of the object to be measured three-dimensionally is carried out with the same point pattern as in the first acquisition, the point pattern is projected onto the surface of the object by means of radial rotation of the projection unit. Radial rotation means rotation about the optical axis. To radially shift the dot pattern, the device for projecting the dot pattern is rotated radially after the first detection of the object's surface with the dot pattern projected onto it, for example by such an angle that the points of the dot pattern are projected between the positions of the original projection of the dot pattern after the rotation, in order to avoid the same points of the object's surface being detected by the dot pattern in the first and second projections, as this would not lead to an increase in resolution. With incremental angular rotation of the projection unit, the data density and thus the resolution increase by the number of angular steps, given the same number of points in the point pattern. The points of the dot pattern projected onto the object shift radially by the value of the selected angular step. The resolution increases, starting from the number of projected points (pP) as the original resolution, by the number of angular steps (n). With the first angular step, the data density and therefore the resolution doubles. According to claim 2, at least two DOEs are provided in each projection unit, one of which is arranged to rotate radially in the laser beam path, thereby changing the number of projected points per unit area in the pattern as well as their position. A particular advantage is that this allows for very simple adaptation to the prevailing measurement conditions, such as surface texture, desired resolution, etc. In a variant of the method not in accordance with the invention, the point pattern originally projected onto the surface of the object is vertically shifted, so that the projection of the points of the point pattern shifted in the Y-axis lies on the surface of the object between the positions of the points of the original projection. After the vertical shift of the point pattern, the surface with the projected point pattern is optically captured again using the stereo camera system. The data volume from the second optical capture is transferred to the memory of the computer system, the spatial coordinates of the points of the projected point pattern are calculated from the second optical capture, and superimposed with the 3D data from the first optical capture. With the same number of projected points in the second projection and the second optical capture with the second data volume, the result is twice the data density and thus twice the resolution in the Y-axis direction. By analogy, in a further development that is also not in accordance with the invention, a horizontally shifted projection of the dot pattern as a second projection and its second optical detection with a second data volume results in double the data density in the direction of the X-axis. The variants of the method for radial and vertical displacement as well as increasing the number of points of a point pattern projected onto the surface of the object per unit area can be combined with each other. In this way, every point on the surface of the object to be measured three-dimensionally can be detected and an extremely accurate topology of the surface can be calculated. In one variant of the procedure, it is optional to determine an area of interest on the surface of the object and to limit the image area to an area of interest on the object using the image processing software in order to determine the exact topology of the surface. After the transfer of an initial data volume from the initial optical capture of the initial point pattern to the computer system using the image processing software, an initial evaluation of the initial data volume is performed to assess the quality of the 3D measurement of the surface, on the basis of which a determination of the point pattern or a number of further projections is made. After the second projection of the defined point pattern and the second optical acquisition, the calculation of the spatial coordinates of the points from the first and second projections, the topology of the surface of the object is available with a sufficiently high resolution for the area of interest. Determining the required resolution for a sufficiently accurate 3D measurement, i.e., the number of points to be projected onto the object per unit area for the second projection, or determining the number of further projections, is preferably done depending on the area of interest in order to optimize the relationship between required data volumes and resolution. In a further preferred development of the method, in an intermediate step the color or texture of the surface in the image area is determined and the wavelength of the laser is selected in contrast to the surface color of the object (e.g., green light for a red surface color). According to the further development of claim 4, one or more projection units can simultaneously or sequentially control multiple lasers to project the dot pattern onto the surface of the object, depending on the color or texture of the surface, thereby enabling the projection of dots of different colors onto the surface of the object. The dots provide qualitatively different data depending on their color and simultaneously on the color or texture of the surface. In a further development of the procedure, an additional intermediate step involves using the image processing software of the computer system to perform a contrast check of the optical detection of the surface of the object with the first projection of the dot pattern, whereby if the contrast is insufficient, the system switches to at least one other available projection unit with a laser of a different wavelength. A device for 3D surface measurement of objects according to claim 6 comprises three projection units, each containing a laser, optics, at least one first diffractive optical element (DOE) for generating a dot pattern, a stereo camera system, and a computer system with image processing software. According to the invention, the projection unit is mounted, for example, in a holder, such that radial rotation of the projection unit at a predetermined angle can be achieved, the rotation preferably being controlled by the computer system. The device according to this claim enables the 3D measurement method according to claim 1 to be carried out. The rotation occurs between the first and second projections—and optionally further projections—so that the projected dot pattern remains the same in principle in all projections, but is projected with a rotation.This means that the points of the otherwise identical point pattern are projected to a different position on the surface in each projection. In an alternative device according to the invention for 3D measurement as claimed in claim 7, the projection unit additionally comprises at least one second DOE, wherein at least one DOE is rotatable radially relative to the at least one further DOE, i.e., about the optical axis of the laser, and the dot pattern itself is changed when it is rotated. This changes the number of points in the dot pattern or their position when projected onto the surface of the object. This surprisingly provides a very simple means of increasing the number of projected points available for 3D measurement, cumulatively across the multiple projections, and thus the resolution. Furthermore, the rotation of the entire projection unit becomes unnecessary. The DOE's of a projection unit in an advantageous further development of the device are optimized to the wavelength of the light emitted by the laser in order to keep the intensity loss of the light emitted by the laser low. A further development of a device according to the invention provides that at least one of the DOE's generates the simultaneous projection of a marker, such as a cross, onto the surface of the object to be measured, using a structure incorporated into its surface. With the simultaneous projection of the marker, the projection of the dot pattern onto the surface of the object can be aligned to a specific position even after the dot pattern has changed. In an advantageous embodiment of the device, the power of the projection unit's light source is variable. The laser power can be adjusted in a known manner by changing the operating voltage and / or current, or several laser light sources can be arranged in a projection unit, each of which can be switched individually. The particular advantage lies in the ease of adapting to different measurement conditions (e.g., number of points per projection, color and texture of the surface, etc.). According to the invention, the 3D measurement device of claim 6 comprises a housing in which the three projection units, each emitting different colors of laser light, are simultaneously accommodated. Depending on the color variant of the object to be measured, the appropriate projection units and their respective lasers can be selectively activated. In the 3D measurement device according to claim 7, the radially rotatable DOE's of the multiple projection units arranged in a common housing are adjustable synchronously, preferably by means of a suitable gearbox, whereby the point pattern of all projection units is changed simultaneously as an advantage. In the 3D measurement device according to claim 6, the multiple radially rotatable projection units arranged in a common housing are synchronously adjustable so that the projected point patterns are moved simultaneously and in the same manner. In a non-inventive variant of the device, the housing with the three projection units is arranged to tilt vertically in the device for 3D measurement in order to increase the resolution in the direction of the Y-axis when projecting point patterns of different colors or several colors simultaneously. Not according to the invention, alternatively, or possibly cumulatively, the housing with the three projection units for projecting the dot pattern can also be mounted in a horizontally pivotable manner. The advantages of the method and the device, particularly in conjunction with some of the further developments, lie in the easy adaptation to the color and / or texture of the surface of the object to be measured three-dimensionally. A dot pattern of defined structure with high depth of field can be projected. By providing a point pattern that can be dynamically shifted and changed using inexpensive light sources (e.g., diode lasers) without complex mechanics and electronics by rotating the projection unit and / or one of the DOE's, variable resolution 3D measurement of objects is achievable with minimal effort. The device also features a simple optical design and is inexpensive to manufacture. The invention is explained in more detail as an embodiment with reference to Fig. 1 as a schematic representation of a device for 3D measurement of the surface of objects with a projection unit for a point pattern onto the surface of an object and Fig. 2 as a perspective representation of the basic design of a projection unit with several projection units for the projection of point patterns onto the surface of an object for 3D measurement. According to Fig. 1, a device for 3D measurement, which is not in accordance with the invention as such, is arranged with a projection unit 1 for projecting a point pattern together with a stereo camera system 2 (2.1; 2.2) opposite a surface 3 of an object 4. The stereo camera system 2 (2.1; 2.2) and the projection unit 1 are connected to a computer system 5. The stereo camera system 2 (2.1; 2.2) has been calibrated via a reference pattern and the connected computer, so that the geometry of the cameras used in the stereo camera system 2 (2.1; 2.2) can be referenced. The projection unit 1 for projecting the dot pattern 11 has a laser 6 with optics 7 for providing a collimated light beam 8 and arranged in its optical axis, a first diffractive optical element (DOE) 9 and a second DOE 10 for generating a defined dot pattern 11. The first DOE 9 is arranged in the projection unit 1 so that it can be rotated radially in the optical axis, so that the number of points in the dot pattern 11 can be changed when it is rotated. The dot pattern 11 is projected onto the surface 3 of object 4. Furthermore, the projection unit 1 is also arranged in a suitable holder so that it can be rotated radially in the optical axis and is optionally mounted so that it can be tilted in the Y-axis. For the 3D measurement of the surface 3, the object 4, or, as shown in Fig. 1, an image area 12, is first optically captured using the stereo camera system 2 (2.1; 2.2). The image data is transferred to the computer system 5, and the color of the surface 3 is determined using image processing software to select the wavelength of the laser 6, in a contrasting color to the color of the surface 3. The image processing software is also used to check whether a surface anomaly 13 is present in the image area 12. Based on the determined surface anomaly 13, the image area 12 can be limited to a region of interest 14, and the resolution, the number of points to be projected onto the object per unit area, can be calculated as a function of the area of interest; for example, 400 points on an area of 70 x 70 mm. Subsequently, the regular dot pattern 11 is projected onto the surface 3 of the object 4 to be measured three-dimensionally and the surface 3 of the object 4 is optically detected with the dot pattern 11 projected onto it using the stereo camera system 2 (2.1; 2.2). The image data is transferred to the computer system 5 and the spatial coordinates of the points are calculated using software and the result is output as a 3D survey of the surface topology of object 4. To double the initial resolution of 400 points per unit area, the projection unit 1 is rotated radially by an angle after the optical acquisition of the first image in the existing image area 12 such that the re-projected points of the point pattern 11 of the existing image area 12 are mapped onto the surface 3 of the object 4 at a position between two previously projected points. A second optical acquisition of the surface 3 of the object 4 with the projected point pattern 11 is performed using the stereo camera system 2 (2.1; 2.2). The image data is also transferred to the computer system 5, where software calculates the spatial coordinates of the points for the second image and superimposes them with the spatial coordinates of the first image, resulting in a 3D survey of the surface topology of the object 4 with double the resolution. An embodiment of the device according to the invention is shown in Fig. 2, in which three projection units 1 (1.1; 1.2; 1.3), as shown in Fig. 1, with lasers 6 of different wavelengths, such as for emitting red, blue and green light,
[19] are arranged radially rotatable in a housing 15. The radially rotatable DOE's 9 of the projection units 1.1; 1.2; 1.3 are synchronously adjustable by means of a gear 16. The adjustment is computer-controlled in a known manner using a stepper motor (not shown in Fig. 2) via a connection 17 to the computer system 5. In various versions, the DOE's 9 of the projection units 1.1; 1.2; 1.3 can be individually adjustable and / or the projection units 1.1; 1.2; 1.3 can also be synchronously radially rotatable. In both the embodiment with the three projection units 1.1; 1.2; 1.3 in the housing 15 according to Fig. 2 and in the embodiment according to Fig. 1, which is not in accordance with the invention and has one projection unit 1, the housing 15 or the individual projection unit 1 can be tilted vertically by an angle 19 by means of a special receptacle 18 with an adjustment device, also in a computer-controlled manner, so that the resolution in the Y-axis is increased. In a feasible further version of the device, horizontal swiveling is possible, which increases the resolution in the X-axis. For 3D measurement in the embodiment of the device according to the invention with the three projection units 1.1; 1.2; 1.3, in one embodiment of the method for determining the color and texture of the surface 3 and the determination of the suitable color of the laser 6 based thereon, the surface 3 of an object 4 is optically detected with the stereo camera system 2 (2.1; 2.2) initially without projection of a dot pattern 11. Subsequently, the dot pattern 11 with the corresponding color of one of the projection units 1.1; 1.2; 1.3 is projected onto the surface 3 and optically detected by the stereo camera system 2 (2.1; 2.2). Using the computer system 5, a contrast check is performed with the aid of the image processing software to determine whether the optical detection of the surface 3 of the object 4 with the projected dot pattern 11 has a sufficiently high contrast for the image processing to calculate the surface topology. Should the contrast be insufficient, the computer-controlled switchover to a projection unit 1.1; 1.2; 1.3 with a laser 6 of a different wavelength takes place. In intermediate steps of the procedure, a contrast check is preferably carried out regularly. For the precise 3D measurement of surface anomalies 13, segments of surfaces 3 or surfaces 3 with multiple colors and / or textures, it may be necessary to change the color of the light emitted by the laser 6, since at color and / or texture transitions, with the color of the laser 6 used for the first optical detection, only an insufficient contrast of the point pattern 11 is achieved. Furthermore, it is also possible to project a dot pattern of different colors onto the surface 3 of the object 4 simultaneously using more than one of the projection units 1.1; 1.2; 1.3, whereby different patterns can also be projected. Reference symbols used 1 Projection unit (1.1; 1.2; 1.3) 2 Stereo camera system (2.1; 2.2) 3 Surface 4 Object 5 Computer system 6 Laser 7 Optics 8 Collimated light beam 9 First DOE 10 Second DOE 11 Dot pattern 12 Image area 13 Surface anomaly 14 Area of interest 15 Housing 16 Gearbox 17 Connection 18 Capture 19 Angle
Claims
Method for 3D measurement of a surface (3) of an object (4), wherein a) a point pattern (11) with a plurality of points is projected onto the surface (3) of the object (4) by means of three projection units (1.1; 1.2; 1.3), each comprising a laser (6) with a different wavelength, an optic (7) and at least one diffractive optical element (DOE) (9; 10), b) the point pattern (11) is optically acquired from the projection by means of a stereo camera system (2), c) the data volume from the optical acquisition is transferred to a computer system (5) with image processing software, d) the computer system (5) calculates spatial coordinates of the points of the point pattern (11) and, on the basis of the spatial coordinates, a topology of the surface (3) of the object (4) is created and is available for output in the computer system (5).e) a first projection of the point pattern (11) and a first optical acquisition of the point pattern (11) from the first projection are carried out, and a resulting first data volume from the first optical acquisition of the first projection of the point pattern (11) is transferred to the computer system (5), f) a second projection of the point pattern (11) is carried out, wherein the position of the point pattern (11) of the second projection is shifted relative to the position of the point pattern (11) of the first projection on the surface (3) of the object (4) by synchronous adjustment through a radial rotation of each of the three projection units (1.1; 1.2; 1.3), g) a second optical acquisition of the point pattern (11) from the second projection of the point pattern (11) is carried out, and a resulting second data volume from the second optical acquisition of the second projection of the point pattern (11) is transferred to the computer system (5),h) the computer system (5) calculates the spatial coordinates of the points of the point patterns (11) from the first and second projections using the computer system (5) and, based on the spatial coordinates of the points of the point patterns (11) from the first and second projections, creates a topology of the surface (3) of the object (4) and makes it available for output in the computer system (5). Method for 3D measurement of a surface (3) of an object (4), wherein a) a point pattern (11) with a plurality of points is projected onto the surface (3) of the object (4) by means of three projection units (1.1; 1.2; 1.3), each comprising a laser (6) with a different wavelength, an optic (7) and at least two diffractive optical elements (DOE) (9; 10), b) the point pattern (11) is optically acquired from the projection by means of a stereo camera system (2), c) the data volume from the optical acquisition is transferred to a computer system (5) with image processing software, d) the computer system (5) calculates spatial coordinates of the points of the point pattern (11) and, on the basis of the spatial coordinates, a topology of the surface (3) of the object (4) is created and is available for output in the computer system (5).e) a first projection of the point pattern (11) and a first optical acquisition of the point pattern (11) from the first projection are carried out, and a resulting first data volume from the first optical acquisition of the first projection of the point pattern (11) is transferred to the computer system (5), f) a second projection of the point pattern (11) is carried out, wherein, by synchronous adjustment through a radial rotation of one of the DOE's of each of the three projection units (1.1; 1.2; 1.3), a different point pattern is used in the second projection than in the first projection, g) a second optical acquisition of the point pattern (11) from the second projection of the point pattern (11) is carried out, and a resulting second data volume from the second optical acquisition of the second projection of the point pattern (11) is transferred to the computer system (5),h) the computer system (5) calculates the spatial coordinates of the points of the point patterns (11) from the first and second projections using the computer system (5) and, based on the spatial coordinates of the points of the point patterns (11) from the first and second projections, creates a topology of the surface (3) of the object (4) and makes it available for output in the computer system (5). Method for 3D measurement of the surface (3) of an object (4) according to claim 2, characterized in that after the transfer of a first data volume from the first optical acquisition of the first point pattern (11) to the computer system (5), a first evaluation of the first data volume is carried out by means of the computer system (5) to assess the quality of the 3D measurement of the surface (3), on the basis of which a determination of the point pattern (11) for the second projection or a determination of the number of further projections is carried out by means of the computer system (5). Method for 3D measurement of the surface (3) of an object (4) according to one of the preceding claims, characterized in that the wavelength of the laser (6) is selected in contrast to a color or texture of the surface (3) of the object (4). Method for 3D measurement of the surface (3) of objects (4) according to one of the preceding claims, characterized in that a contrast check is carried out by means of the computer system (5) and if the contrast is insufficient, the system switches to a projection unit (1.1; 1.2; 1.3) with a laser (6) of a different wavelength. Device for 3D measurement of the surface (3) of an object (4), comprising three projection units (1.1; 1.2; 1.3), a housing (15), a stereo camera system (2.1; 2.2) and a computer system (5) with image processing software, wherein the three projection units (1.1; 1.2; 1.3) are housed in the housing (15) and each comprise a laser (6), an optic (7) and at least one diffractive optical element (DOE) (9; 10) for generating a dot pattern (11), wherein each of the lasers (6) has a different wavelength, characterized in that the three projection units (1.1; 1.2; 1.3) are radially rotatable and synchronously adjustable. Device for 3D measurement of the surface (3) of an object (4) comprising at least three projection units (1.1, 1.2; 1.3), a housing (5), a stereo camera system (2.1; 2.2) and a computer system (5) with image processing software, wherein each of the three projection units (1.1, 1.2; 1.3) comprises a laser (6), an optic (7) and a first diffractive optical element (DOE) (9) as well as at least one second DOE (10) for generating a dot pattern (11), wherein each of the lasers (6) has a different wavelength, characterized in that one of the DOEs (9; 10) in each of the three projection units (1.1; 1.2; 1.3) is arranged to be radially rotatable, wherein, when rotated, the number of points in the dot pattern (11) and / or their position when projected onto the surface (3) of the object (4) is changed. and wherein the DOE's (9; 10) are synchronously adjustable by means of rotation. Device for 3D measurement of the surface (3) of an object (4) according to claims 6 and 7, characterized in that the DOE's (9; 10) of the projection units (1.1; 1.2; 1.3) are optimized to the wavelength of the light emitted by the laser (6). Device for 3D measurement of the surface (3) of an object (4) according to one of claims 6 to 8, characterized in that one of the DOE's (9; 10) of the projection units (1.1; 1.2; 1.3) has a structure incorporated into its surface for the simultaneous projection of a marker with the dot pattern (11) onto the surface (3) of the object (4). Device for 3D measurement of the surface (3) of an object (4) according to one of claims 6 to 9, characterized in that the power of at least one of the lasers (6) of the projection units (1.1; 1.2; 1.3) is variable.