OPTICAL MEASURING DEVICE AND METHOD FOR ASCERTAINING THE THREE-DIMENSIONAL SHAPE OF AN OBJECT

Abstract

An optical measuring device (1) for determining the three-dimensional shape of an object (3) is described, which comprises a light section sensor (4) that has an illumination unit (5) configured to project a linear marking (L) onto the object (3) and at least one image acquisition unit (6) for recording the linear marking (L) projected onto the object (3), and comprises a forward increment recording unit that is configured to record the forward increment of the object (3) moved through under the light section sensor (4) as a function of time (t). The optical measuring device (1) is designed to ascertain distance profiles of the object (3) from the linear marking (L). The optical measuring device (1) is designed to record images of the surface of the object (3) which is recorded during the movement of the object (3), to ascertain a displacement of features in the images recorded of the object surface in a time interval, and to determine a displacement of the object (3) in the time interval from the ascertained displacement of the features in the images of the object surface and a measuring scale, derived from the distance profile of the object (3), of the recorded images of the object surface.

Claims

1. An optical measuring device for determining a three-dimensional shape of an object, comprising: at least one light section sensor comprising an illumination unit configured to project a linear marking onto the object; at least one image acquisition unit for recording the linear marking projected onto the object; a forward increment recording unit configured to record a forward increment of the object moved relative to the at least one light section sensor as a function of time, wherein the optical measuring device is designed to ascertain height profiles of the object from the linear marking, wherein the optical measuring device is designed to record images of a surface of the object that is recorded during the movement of the object to ascertain a displacement of features in a plurality of recorded images of the surface of the object in a time interval, and wherein the optical measuring device is designed to determine a displacement of the object in the time interval from one or more of the displacement of the features in the images of the surface of the object ascertained from recorded images of the surface of the object recorded during the movement of the object, distances and measuring scales derived from at least one height profile of the object for the plurality of recorded images of the surface of the object.

2. The optical measuring device as claimed in claim 1, wherein the forward increment recording unit comprises a data processing unit to evaluate image sections of the images recorded by the at least one light section sensor, wherein the data processing unit is used when ascertaining the displacement of features in the plurality of images.

3. The optical measuring device as claimed in claim 1, wherein the forward increment recording unit comprises a two dimensional image sensor designed to record images of the surface of the object during the movement of the object.

4. The optical measuring device as claimed in claim 3, wherein the optical measuring device is designed to adapt a setting of an objective of the two dimensional image sensor to quasistatically varying distance ranges between the objective and one or more surface zones of the object which are used by the forward increment recording unit.

5. The optical measuring device as claimed in claim 1, wherein the forward increment recording unit comprises a plurality of two dimensional image sensors, each of which are designed to record images of the surface of the object during movement of the object, wherein the plurality of two dimensional image sensors each record different surface zones of the object relative to one another, and wherein the optical measuring device is designed to select one of the plurality of surface zones for the determination of the displacement of the object on the basis of height information items relating to all surface zones recorded by the plurality of two dimensional image sensors which are derived from height profiles recorded with the at least one light section sensor.

6. The optical measuring device as claimed in claim 1 further comprising at least one two dimensional image sensor sensitive to a wavelength different than a wavelength of the at least one light section sensor.

7. The optical measuring device as claimed in claim 1 wherein the forward increment recording unit comprises an additional illumination unit for the illumination of a recorded surface of the object.

8. The optical measuring device as claimed in claim 1, wherein the optical measuring device is designed to adapt illumination of a recorded image zone of the surface of the object to quasistatically varying distance ranges between an objective and a plurality of surface zones of the object which are used by the forward increment recording unit.

9. The optical measuring device as claimed in claim 8, wherein the optical measuring device is designed for dynamic adaptation of a setting of the objective, and the illumination for distance ranges, which vary dynamically over the object, of the plurality of surface zones used for forward increment determination.

10. The optical measuring device as claimed in claim 1 wherein the optical measuring device is designed to ascertain a displacement of features in a plurality of recorded images of the surface of the object in an image zone that the linear marking intersects.

11. The optical measuring device as claimed in claim 1 wherein the optical measuring device is designed to match a scanning frequency of the at least one light section sensor and an image sequence frequency used to determine a displacement of the object from images recorded chronologically in succession to one another.

12. The optical measuring device as claimed in claim 1 wherein the optical measuring device comprises an integrated circuit configured for use in an optical mouse, an image sensor designed to record an image pixel matrix, and an image evaluation unit for recording the displacement of features using image comparison of image pixel matrices recorded chronologically in succession, wherein the optical measuring device is designed to scale the displacement of features, wherein scaling is recorded by the image evaluation unit using a measuring scale derived from at least one height profile, in order to ascertain the object displacement taking place.

13. The optical measuring device as claimed in claim 1 further comprising a data memory with distance-dependent correlation parameters and scaling parameters stored in the data memory, and wherein the optical measuring device is designed to convert an ascertained displacement of features in the plurality of recorded images of the surface of the object with correlation parameters and/or scaling parameters read from the data memory into a displacement path of the object.

14. A method for determining a three-dimensional shape of an object with an optical measuring device as claimed in claim 1, comprising: ascertaining a height profile of an object conveyed by the at least one light section sensor using a linear marking projected onto the object, recording images of a surface of the object, ascertaining a displacement of features from a plurality of recorded images of the surface of the object, and determining a displacement of the object from an ascertained displacement of the features in the images of the surface of the object, and from distances and measuring scales derived from a height profile of the object obtained from the plurality of recorded images of the surface of the object.

15. The method as claimed in claim 14, further comprising adaptation of an optics unit and/or illumination unit and/or image sequence frequency of the optical measuring device as a function of a distance for a recorded zone of the surface of the object which is derived from the height profile recorded with the at least one light section sensor.

16. The method as claimed in claim 14 further comprising selecting a two dimensional image sensor and/or driving of an illumination unit of the optical measuring device in order to illuminate a recorded object surface as a function of the distances derived with the at least one light section sensor from the height profiles of the object, for two dimensional image regions with assigned illumination elements.

Description

[0066] The invention will be explained in more detail below with the aid of an exemplary embodiment with the appended drawings, in which:

[0067] FIG. 1—shows a diagram in side view of an optical measuring device on a conveyor belt for objects transported through below a light section sensor;

[0068] FIG. 2—shows a diagram in plan view of an optical measuring device on a conveyor belt for objects transported through below a light section sensor.

[0069] FIG. 1 shows a diagram in side view of an optical measuring device 1 that is arranged on a conveyor belt 2. The optical measuring device 1 is aligned at the upper side of the conveyor belt 2, on which objects 3 are conveyed below a light section sensor 4 in a forward increment direction V.

[0070] The light section sensor 4 has an illumination unit 5 that is configured to project a linear marking onto the surface of the object 3 facing toward the light section sensor 4. The light section sensor 4 furthermore has at least one image acquisition unit 6 for recording at least a part of the linear marking projected onto the object.

[0071] The light section sensor 4 or a data processing unit 7 connected thereto is designed, for example by suitable programming with a computer program configured to run on the data processing device 7, in order to ascertain the respective height of the object 3 in relation to the upper side 8 of the conveyor belt 2 with the aid of the acquired images with the linear marking on the object 3, in an image column, which then provides a surface profile or a cross-sectional profile of the object 3 for each scan image. Features such as object width, object height and cross section are also obtained from this height profile. If the object height is determined at a particular location transversely to the transport direction, this provides a distance profile at this location via the sum of height profiles, i.e. over time or over the place along the length of the object 3. In this way, for object zones on the object 3 that are recorded for example by the forward increment measuring unit, their respective height value may also be ascertained, from which it is also possible to ascertain the imaging measuring scale that is to be taken into account in order to convert from a displacement in the image to a displacement of the associated object surface.

[0072] For the forward increment movement, the conveyor belt 2 is guided on two deflection rollers 9a, 9b arranged at a distance from one another and, for example, driven by means of the data processing unit 7. For the determination of the distance profile during the forward displacement movement V, it is now desirable to determine the forward increment of the object 3 as accurately as possible as a function of time t.

[0073] For this purpose, a forward increment recording unit is provided, which in the exemplary embodiment comprises at least one 2D image sensor 10 designed to detect images of the surface of the object 3 moving through below the light section sensor 4. For this purpose, the 2D image sensor 10 acquires images of sections of the surface of the object 3. The displacement path of the object 3 is ascertained from an image comparison of features of two successively acquired images of the surface of the object 3. In this case, the displacement of identical features in the pair of images is recorded. The forward increment velocity may then be determined by taking into account the time difference of the acquisition of the successive images, i.e. by the time derivative of the displacement.

[0074] The optical measuring device 1 may have a data processing unit 7 that carries out the image comparison and the determination of the displacement path and optionally the forward increment velocity from the result of the image comparison. For this purpose, it is possible to use the images of the at least one 2D image sensor 10 or images that have been acquired by the image acquisition unit 6 of the light section sensor 4.

[0075] It is conceivable for images of a 2D image sensor 10 to be transmitted to the data processing unit 7. The determination of the displacement path, or of the forward increment velocity, from the successive images is then carried out by a computer program executed by the data processing unit 7.

[0076] The data processing unit 7 may be designed respectively to derive a measuring scale from the height information items recorded with the light section sensor 4 at particular instants t, this being used to ascertain the displacement of the object 3 from the displacement of features of the images of the object surface. The measuring scale may, for this purpose, for example be a scaling factor with which the displacement of a feature in the image is respectively multiplied. The distance-dependent scaling measuring scale transforms the displacement determined in the image space into the actual displacement of the object 3 in the object space.

[0077] FIG. 2 shows a plan view of the optical measuring device 1 and the conveyor belt 2, on which objects 3 are transported through below the light section sensor 4. It can be seen that a linear marking L is projected onto the surface of the object 3. The height profile can be ascertained from the deformation of the linear marking L.

[0078] In this diagram, the forward increment sensor 10 is aligned at the surface of the object 3.

[0079] It can also be seen that the conveyor belt 2 is driven by means of a motor 11, which is connected by means of a shaft 12 to a deflection roller 9b. The motor 11 is driven by the data processing unit 7, which not only evaluates—but also undertakes control functions. It is also conceivable for the object 3 to be moved on a roller belt with or without a drive.

[0080] The peaks and troughs of the object 3, i.e. a particular distance profile, are indicated by the dashed lines on the object 3.

[0081] From the shape of the current linear marking L, the object height of a profile point in the current sectional image can be deduced directly by means of corresponding calibration. If the object 3 is moved along below the linear marking L with a spatially and temporally known forward increment, a sequence of height profiles is obtained, from which the surface of the object 3 facing toward the light section sensor 4 can be reconstructed.

[0082] The forward increment V is determined with an optical path measurement by using an imaging 2D image sensor 10 that acquires images of the surface, moving with a forward increment velocity, of the object 3 with a sufficient image sequence frequency, at least two successive images being compared with one another and the current displacement value being ascertained from the displacement of the image information items.

[0083] For this purpose, the data processing unit 7 is configured, for example, to evaluate the images acquired during the movement of the surface of the object 3, which respectively contain overlapping information items, by means of a correlation analysis of the successive image contents. If the image contents are in this case displaced relative to one another, the size of the correlation is obtained when the image contents match optimally. The displacement vector of the image contents for this state with optimal correlation then corresponds to the displacement path.

[0084] The 2D image sensor 10 may be integrated in a commercially available compact sensor. For this purpose, integrated circuits that are used in optical mice for computers and contain the optics unit with an image acquisition unit and an evaluation unit are obtainable.

[0085] It is conceivable for the forward increment recording unit with the 2D image sensor 10 additionally to have an illumination unit (light source) that lights the surface to be recorded of the object 3 suitably and as uniformly as possible.

[0086] It is also advantageous for the 2D image sensor 10 to contain an optics unit which generates a flat image, optimally usable for the correlation analysis, in a manner suited to the distance conditions and the surface consistency (material, roughness, structuredness, etc.).

[0087] The 2D image sensor 10 is preferably designed for the average surface property of the object 3. For this purpose, both the optics unit and an optional illumination of the forward increment recording unit may be rigidly adjusted or regulated. It is advantageous in this case for the optics unit and the illumination of the 2D image sensor 10 to be matched to the average distance of the 2D image sensor 10 from the surface of the object 3 in a fixed manner or preferably dynamically as a function of the varying conditions of for example distance, light, surface structure, etc.

[0088] The measurement frequency of the 2D image sensor 10 should be at least high enough that a large depth change does not take place for two successive images.

[0089] It is conceivable for the optics unit and illumination of the 2D image sensor 10 to be variably adaptable to the surface consistency and the separation of the 2D image sensor 10 from the background. For the case in which differences in the average distances and in the average surface consistency exist between different applications, i.e. the average distance of the 2D image sensor 10 from the surface of the object 3 varies or the structure of the surface is finer or coarser, the path measurement may be adapted to the other conditions. This ensures that a flat structured image, which is optimally suitable for the correlation analysis, can respectively be acquired by the 2D image sensor 10.

[0090] The measurement frequency of the 2D image sensor 10 is preferably variably adaptable. It may, for example, be synchronized by the data processing unit 7 with a control signal defining the forward increment velocity of the conveyor belt 2.

[0091] It is conceivable for the image acquisition unit 6 of the light section sensor 4 to be used simultaneously as an image acquisition unit for the forward increment recording unit.

[0092] The optical measuring device 1 may be designed in such a way that, in the event of pronounced height variations, adaptation of the optics unit and the illumination is carried out on the basis of depth data that have been measured by the 2D image sensor 10 or the light section sensor 4. For determining the forward increment, it is sufficient for there to be piecewise constant surface structures and distances from the surface of the object 3. Over the entire measurement segment, the path measurement may therefore be carried out with sufficient accuracy if adaptation as a function of the depth data is performed whenever the distances of the acquired images from the object surfaces vary so greatly that adaptation of the imaging measuring scale is necessary.

[0093] The adaptation is preferably carried out automatically, and may be performed by the data processing unit 7.

[0094] The height information items, or distance data, determined with the light section sensor 4 may be used to computationally correlate the result data of the path measurement carried out with the forward increment determination unit. In this way, for example, a scaling factor may be ascertained from the height information items determined with the light section sensor 4, which is then incorporated into the forward increment of the object 3 determined with the forward increment determination unit 10 from the displacement of features of the surface of an object 3 that is recorded with images.

[0095] The measurement method may also be carried out in such a way that, in the event of an unchanged surface structure, a pure distance change and the modified scaling associated therewith of the image acquired by the 2D image sensor 10 is subsequently corrected by means of software by the separation, known by the light section sensor 4, of the acquisition zone of the image acquisition unit 6. A large distance means, for the same pixel displacement from the correlation analysis, a larger difference segment between the two successive image acquisitions. If calculation is carried out with a constant distance and thus with a constant path scaling in the first calculation step, the data may be recalculated with the aid of the indexing carried out and the correct distances and therefore the correct scaling factors may be used to correct the previously determined path differences. This retrospectively gives the true path segment, i.e. the forward increment, despite varying distancing of the 2D image sensor 10 from the surface.

[0096] Correction factors, which may be derived from the measurement of the at least one light section sensor 4, may directly be sent to or ascertained by the data processing unit 7, which then outputs immediately corrected position displacements.

[0097] For the case in which only a simple scaling change is to be considered, the current distance value or the distance change may be transmitted continuously to expanded correlation hardware that continuously takes the scaling change to be evaluated into account and ascertains and outputs a corrected displacement value in real time.