MEASUREMENT SYSTEM AND METHOD FOR CONFIGURING THE MEASUREMENT SYSTEM

Abstract

Measurement system for the three-dimensional optical measurement of a work-piece, comprising: (i) a camera for recording image data of the workpiece; (ii) a control unit which is configured to evaluate the image data recorded by the camera and deter-mine 3D data of the workpiece therefrom; and (iii) a projector for projecting a test pattern onto the workpiece. The control unit is configured to control the projector during a setup mode in such a way that the projector actively modifies, depending on a distance between the workpiece and the camera, the shape of the test pattern projected onto the workpiece in order, by way of the test pattern, to assist a user of the measurement system within the scope of positioning the camera relative to the workpiece.

Claims

1. Measurement system for a three-dimensional optical measurement of a workpiece, comprising: a camera for recording image data of the workpiece; a control unit which is configured to determine 3D data of the workpiece based on the image data; and a projector for projecting a test pattern onto the workpiece; wherein the control unit is configured to control the projector during a setup mode to actively modify the shape of the test pattern projected onto the workpiece depending on a distance between the workpiece and the camera.

2. Measurement system according to claim 1, wherein the control unit is configured to determine the distance between the workpiece and the camera based on the image data recorded by the camera.

3. Measurement system according to claim 2, wherein the image data recorded by the camera during the setup mode contain an image of the test pattern, and wherein the control unit is configured to determine the distance between the workpiece and the camera based on the image of the test pattern by means of triangulation.

4. Measurement system according to claim 1, wherein the test pattern comprises at least one straight stripe.

5. Measurement system according to claim 2, wherein the camera is a system comprising a plurality of cameras.

6. Measurement system according to claim 1, wherein the control unit is configured to control the projector during the setup mode to project a first test pattern onto the workpiece when the distance between the workpiece and the camera lies within a predetermined tolerance range and to project a second test pattern onto the workpiece when the distance between the workpiece and the camera lies outside of the predetermined tolerance range.

7. Measurement system according to claim 1, wherein the control unit is configured to control the projector during the setup mode to project a first test pattern onto the workpiece when the distance between the workpiece and the camera lies within a predetermined tolerance range and to project a second test pattern onto the workpiece when the distance between the workpiece and the camera is greater than an upper limit of the predetermined tolerance range and to project a third test pattern onto the workpiece when the distance between the workpiece and the camera is less than a lower limit of the predetermined tolerance range.

8. Measurement system according to claim 1, wherein the control unit is configured to control the projector during the setup to modify the shape of the test pattern projected onto the workpiece dynamically and at least partly continuously depending on the distance between the workpiece and the camera.

9. Measurement system according to claim 8, wherein information relating to the distance between the workpiece and camera is contained in the projected test pattern.

10. Measurement system according to claim 1, wherein the control unit is configured to control the projector during a measurement mode to project a measurement pattern onto the workpiece, wherein the camera is configured to record the measurement pattern during the measurement mode such that the image data recorded by the camera during the measurement mode contain an image of the measurement pattern, wherein the control unit is configured to determine the 3D data of the workpiece based on the image of the measurement pattern by means of triangulation.

11. Measurement system according to claim 10, wherein the measurement pattern is a static pattern.

12. Measurement system according to claim 10, wherein the measurement system is manually switchable between the setup mode and the measurement mode.

13. Measurement system according to claim 1, wherein the measurement system comprises a sensor unit which is arranged in a housing, wherein the camera and the projector are part of said sensor unit.

14. Method for configuring a measurement system for optical measurement of a workpiece, said method comprising the steps of: recording image data of the workpiece by means of a camera; determining 3D data of the workpiece based on the image data; projecting a test pattern onto the workpiece; modifying a distance between the camera and the workpiece; and modifying the shape of the test pattern projected onto the workpiece depending on the distance between the workpiece and the camera.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0044] Exemplary embodiments are shown in the drawings and are explained in greater detail in the following description. In the drawings:

[0045] FIG. 1 shows an illustration of an exemplary application of the herein presented measurement system;

[0046] FIG. 2 shows a schematic illustration of an exemplary embodiment of the measurement system;

[0047] FIG. 3 shows a schematic illustration of the exemplary embodiment shown in FIG. 2 during a setup mode;

[0048] FIG. 4 shows an example of a test pattern in a view as may be visible on the workpiece to a user in reality (see part A) and the 2-D view thereof on a graphical user interface (see part B);

[0049] FIG. 5 shows a further example of a test pattern in a view as may be visible on the workpiece to a user in reality (see part A) and the 2-D view thereof on a graphical user interface (see part B);

[0050] FIG. 6 shows a further example of a test pattern in a view as may be visible on the workpiece to a user in reality (see part A) and the 2-D view thereof on a graphical user interface (see part B).

BRIEF DESCRIPTION OF THE DRAWINGS

[0051] FIG. 1 shows an exemplary application, in which the measurement system according to this disclosure can be used in practice.

[0052] FIGS. 2 and 3 shows schematic detailed illustrations of an exemplary embodiment of the measurement system, for the purposes of explaining the components of the measurement system and for the purposes of explaining the function thereof.

[0053] The measurement system is denoted in the figures as a whole by reference numeral 10. A part of the measurement system 10, which is referred to as a sensor unit 12 in the present case, is arranged on an arm of a robot 14 in the exemplary case illustrated in FIG. 1. Here, the sensor unit 12 is aligned on a workpiece 16 or on a part of a workpiece 16 which is intended to be measured with the aid of the measurement system 10. In the application illustrated in an exemplary manner in FIG. 1, the workpiece 16 is a body component of a vehicle.

[0054] The three-dimensional measurement of the workpiece 16 undertaken with the aid of the measurement system 10 serves to determine 3D data of the workpiece, on the basis of which it is possible, for example, also to determine the surface character thereof in detail, in addition to the surface geometry of the workpiece 16. The 3D data are usually determined as a 3D point cloud which originates from a multiplicity of different measurement points on the surface of the workpiece 16. An exemplary measurement point is denoted by reference numeral 18 in FIGS. 2 and 3.

[0055] The workpiece 16 is measured by the measurement system 10 in an optical manner. To this end, the measurement system 10 comprises a camera 20 (see FIGS. 2 and 3). Further, the measurement system 10 also contains a projector 22 and a control unit 24.

[0056] The camera 20 and the projector 22 are preferably, but not necessarily, arranged in one and the same housing. They belong to the sensor unit 12. By contrast, the control unit 24 is preferably arranged outside of the control unit 12. The components of the control unit 12 are connected to the control unit 24 either by means of one or more cables or by means of a wireless connection.

[0057] The control unit 24 is preferably a computing unit, i.e., for example, a computer or part of a computer. The control unit 24 contains hardware which has software installed thereon, said software serving both to evaluate the image data supplied by the camera 20 and to control the function of the camera 20 and of the projector 22.

[0058] Even though the camera 20 for measuring the workpiece 16 may, as a matter of principle, also be replaced by a plurality of cameras (e.g. a stereo camera), said camera is preferably configured as an individual camera in the present case. Thus, the workpiece 16 is preferably measured on the basis of the structured light projection principle, which is also referred to as structured light topometry.

[0059] The camera 20 can be configured as a digital or analogue video camera. In principle, use can also be made of two or more cameras 20.

[0060] The projector 22 is a projector which, in terms of the principle thereof, is similar to a slide projector.

[0061] During a measurement, the projector 22 illuminates, with a static pattern or a pattern that is modifiable in sequence over time, the part of the workpiece 16 to be measured, said pattern being referred to as measurement pattern in the present case. This measurement pattern preferably comprises a plurality of bright and dark stripes of different width that lie parallel to one another. The measurement pattern is recorded by the camera 20 at a known viewing angle in relation to the projector. Then, the image data recorded by the camera 20 are evaluated in the control unit 24. Ultimately, it is possible to determine the topography of the workpiece 16 on the basis of the deformations or distortions of the measurement pattern occurring in the image data. As a result, a multiplicity of measurement points on the workpiece 16 are evaluated in succession in this manner such that surface coordinates of the workpiece 16 are ultimately present as a 3D point cloud.

[0062] In order to correctly configure the measurement system 10, configuring the sensor unit 12 at a correct distance from the workpiece 16 is also, in addition to the mandatory calibration, of immense importance. The sensor unit 12 must be positioned in such a way that the distance between the sensor unit 12 and the measurement point 18 lies within a defined working volume, within which the sensor unit 12 supplies defined measurement results. In particular, the distance between the camera 20 and the measurement point 18 is of immense importance since it is not possible to accurately capture the measurement point 18 if the latter lies outside of the focus of the camera 20.

[0063] In FIG. 2, the actual distance between the sensor unit 12, or the camera 20, and the measurement point 18 is denoted by d.sub.ist and the intended distance between the sensor unit 12, or the camera 20, and the measurement point 18 is denoted by d.sub.soll. The intended distance d.sub.soll is often also referred to as nominal working distance. The latter is sensor specific. However, it is understood that there is a certain tolerance range in respect of the intended distance d.sub.soll, within which the sensor unit 12 supplies reliable measurement results. By way of example, such a tolerance range may be the range of 10% of the nominal working distance d.sub.soll.

[0064] The measurement system 10 assists the user to bring the actual distance d.sub.ist as easily as possible to the nominal working distance d.sub.soll by virtue of information about the actual distance d.sub.ist and the intended distance d.sub.soll being presented on the workpiece 16 in real time. As a result of this, the user obtains the necessary information precisely where they usually look during the configuration of the measurement system 10, namely directly on the test object or workpiece 16.

[0065] To this end, the projector 22 projects a pattern onto the workpiece 16, which is captured at the same time by way of the camera 20. This is indicated in a simplified manner in FIG. 3 by way of a dashed line 26. The pattern which is projected onto the workpiece 16 for the purposes of configuring the measurement system 10 preferably differs from the measurement pattern which is used for the subsequent measurement according to the principle explained above. Therefore, in order to distinguish between these terms, the terms test pattern and measurement pattern are used in the present case. The test pattern is used during the so-called setup mode, during which the measurement system 10 is configured or the distance between the sensor unit 12 and the workpiece 16 is set. The measurement pattern is used during the so-called measurement mode, during which the workpiece 16 is subsequently measured with the aid of the measurement system 10.

[0066] By way of example, the setup mode proceeds as follows: In the first step, the projector 22, as already mentioned, projects a test pattern onto the surface of the workpiece 16. It is recorded by the camera 20. Then, the actual distance d.sub.ist between the sensor unit 12 and the workpiece 16 can be ascertained algorithmically on the basis of the image data recorded by the camera, in a manner similar to the measurement principle of the structured projection described above. The employed test pattern therefore likewise preferably comprises at least one straight stripe, on the basis of which the actual distance d.sub.ist can be calculated by way of the aforementioned evaluation method. Depending on the calculated actual distance d.sub.ist, the test pattern projected onto the workpiece 16 by the projector 22 then is modified in terms of its shape in order to provide the user with feedback about the actual distance d.sub.ist on the basis of the modified shape of the test pattern. Thus, to this end, the test pattern is actively modified by the control unit 24. This dynamic change in shape of the test pattern mainly serves to provide feedback to the user in order to assist during the positioning of the sensor unit 12. By contrast, the change in shape of the pattern would not be mandatory for measuring the actual distance d.sub.ist.

[0067] Therefore, at least the two following requirements should be met by the test pattern: Firstly, it should be evaluable by an algorithm in order to be able to determine the actual distance d.sub.ist in a suitable manner on the basis thereof. Secondly, it should uniquely encode or comprehensively display for the user how the actual distance d.sub.ist of the sensor unit 12 from the workpiece 16 should be modified in order to obtain the desired intended distance d.sub.soll.

[0068] FIGS. 4-6 show three exemplary test patterns 28. The respective part A in FIGS. 4-6 schematically shows a section of the workpiece 16, onto which the respective test pattern has been projected. The respective part B in FIGS. 4-6 schematically shows a representation 30 of the projected pattern in the 2-D image recorded by the camera 20. The dashed line 32 in parts A of FIGS. 4-6, which surrounds the test patterns 28, is merely plotted for visual perception purposes in order to schematically elucidate the section of the projection cone or visual cone of the sensor unit 12.

[0069] The first test pattern 28a, which is shown in FIG. 4, is e.g. projected onto the workpiece 16 if the actual distance d.sub.ist is too large (d.sub.ist>d.sub.soll). With the aid of the arrows of the first test pattern 28a pointing toward one another, the user is provided with an indication that the actual distance d.sub.ist should be reduced. By contrast, the second test pattern 28b, which is shown in FIG. 5, is e.g. projected onto the workpiece 16 if the actual distance d.sub.ist is too small (d.sub.ist<d.sub.soll). The arrows of the second test pattern 28b pointing away from one another should indicate to the user that the actual distance d.sub.ist should be increased. By contrast, the third test pattern 28c, which is illustrated in FIG. 6, can be projected onto the workpiece 16 if the actual distance has been set correctly (d.sub.ist=d.sub.soll). The schematically presented crosshairs then signal to the user that the measurement unit 12 is positioned correctly relative to the measurement point 18 at the workpiece 16.

[0070] Reference is made to the fact that the test patterns 28a-28c shown in FIGS. 4-6 are merely one of many possible examples. In principle, use can be made of only two different test patterns 28, namely one to indicate that the actual distance d.sub.ist corresponds to the intended distance d.sub.soll and a further one indicating that the actual distance d.sub.ist does not correspond to the intended distance d.sub.soll.

[0071] Likewise, use can be made of only a single test pattern 28, the external shape of which is modified depending on the actual distance d.sub.ist. By way of example, the test pattern can be modified dynamically and continuously depending on the actual distance d.sub.ist.

[0072] In principle, the test pattern can be as desired. It may also be complemented as desired by further information, although this ideally does not impair the algorithmic evaluation for determining the actual distance d.sub.ist.

[0073] In principle, numbers, i.e., for example, the exact distance value d.sub.ist, may also be contained in the test pattern and projected onto the workpiece 16.

[0074] The algorithmic evaluability of the test pattern is not mandatory. In principle, the actual distance d.sub.ist may also be determined by way of a different distance sensor which does not operate by means of structured light projection. However, the advantage of determining the actual distance with the aid of the camera 20, the projector 22 and the control unit 24 is that, in this case, the already conventional components of the measurement system 10 are used for the distance measurement, and so no additional sensor is necessary.