Optical measurement method and measurement system for determining 3D coordinates on a measurement object surface

• US 9,683,837 B2
• Filed: 06/09/2011
• Issued: 06/20/2017
• Est. Priority Date: 06/21/2010
• Status: Active Grant

• Current Assignee: Leica Geosystems AG (Hexagon AB)
• Original Assignee: Leica Geosystems AG (Hexagon AB)
• Inventors: Siercks, Knut
• Primary Examiner(s): Tran, Thai
• Assistant Examiner(s): BRANIFF, CHRISTOPHER
• Application Number:
  US13/702,259
• Publication Number:
  US 20130100282A1
• Time in Patent Office: 2,203 Days
• Field of Search: None
• CPC Class Codes: G01B 11/25 by projecting a pattern, e.g. one or more lines, moiré fringes on the object G01B11/255 takes precedence ; image analysis for depth or shape recovery G06T7/50
• CPC Class Codes: G01B 11/2513 with several lines being projected in more than one direction, e.g. grids, patterns
• CPC Class Codes: G01B 11/2545 with one projection direction and several detection directions, e.g. stereo
• CPC Class Codes: G01B 2210/52 Combining or merging partially overlapping images to an overall image

Abstract

A measurement object surface is illuminated with a pattern sequence of various patterns using a projector, which is recorded with a camera system, and the 3D coordinates for the measurement points are determined by evaluation of the image sequence. While the image sequence is being recorded translational and/or rotational accelerations of the projector, the camera system and/or the measurement object are measured at least at a measurement rate such that in each case a plurality of values for the accelerations are acquired. It is thus possible, on the basis of the measured accelerations, to take into account algorithmically, when determining the 3D coordinates, movements of the projector, the camera system and/or the measurement object, which movements occur during the illumination times of the respective individual images of the image sequence and provoke unsteadiness and/or motion blur in the respective individual images of the image sequence.

Claims

1. An optical measurement method for determining 3D coordinates of a multiplicity of measurement points of a measurement object surface, comprising the steps of:

illuminating the measurement object surface with a pattern sequence of different patterns using a projector;

recording an image sequence of a plurality of individual images of the measurement object surface, which is illuminated with the pattern sequence, using a camera system; and

determining the 3D coordinates of the measurement points by evaluating the image sequence including ascertaining a succession of brightness values for identical measurement points of the measurement object surface in the respective images of the image sequence, wherein;

during the recording of the image sequence at least during the exposure times of individual images of the image sequence, translational and/or rotational accelerations;

of the projector,

of the camera system, and/or

of the measurement object,

are measured for each image with at least such a measurement rate that during the exposure time of each image of the image sequence for each image a plurality of values for the accelerations related to one particular direction of acceleration are captured so that movements of the projector, of the camera system and/or of the measurement object, which provoke camera shake and/or motion blur in the respective individual images of the image sequence and occur during the exposure times of the respective individual images of the image sequence, are algorithmically taken into consideration in the determination of the 3D coordinates on the basis of the measured accelerations.

2. The optical measurement method as claimed in claim 1, wherein a multiplicity of values for the accelerations are captured.

3. The optical measurement method as claimed in claim 1, wherein accelerations of the projector, of the camera system and/or of the measurement object are measured in all six degrees of freedom and the accelerations are measured continuously at a specific measurement rate.

4. The optical measurement method as claimed in claim 1, wherein accelerations of the projector, of the camera system and/or of the measurement object are measured in all six degrees of freedom and the accelerations are measured continuously at a specific measurement rate between approximately 50 and 2000 Hz during the entire operation of recording the image sequence.

5. The optical measurement method as claimed in claim 1, wherein:

in dependence on the measured accelerations, compensation and/or correcting of camera shake and/or motion blur, which are caused by movements of the projector, of the camera system and/or of the measurement object occurring during the exposure times of the respective individual images of the image sequence, take place respectively in the individual images of the image.

6. The optical measurement method as claimed in claim 1, wherein:

in dependence on the measured accelerations, compensation and/or correcting of camera shake and/or motion blur, which are caused by movements of the projector, of the camera system and/or of the measurement object occurring during the exposure times of the respective individual images of the image sequence, take place respectively in the individual images of the image sequence; and

the movements are caused;

by a user holding in his hand the projector, the camera system and/or the measurement object, in particular caused by a hand tremor and inadvertently, or

by vibrations or oscillations in the holders of the projector, of the camera system and/or of the measurement object.

7. The optical measurement method as claimed in claim 1, wherein during the entire operation of recording the image sequence or a plurality of image sequences, the accelerations are measured and the information obtained by the evaluation of the individual images with respect to the 3D coordinates of the measurement points are joined together in a computational manner using the measured accelerations, wherein during the operation of recording:

for enlarging the measurement region on the measurement object surface,

for densifying the measurement region and thus for increasing the measurement point density on the measurement object surface and/or

for changing speckle fields, which occur inadvertently in the case of illumination with substantially coherent optical radiation, in the respective patterns of the pattern sequence and thus for decreasing local measurement inaccuracies or measurement point gaps caused by such speckle fields;

the measurement object, the camera system and/or the projector is moved, the movement which is effected for this purpose is effected by;

a user holding in his hand the measurement object and/or the camera system, and/or

a holder which is designed therefor and controlled manually or in an automatically preprogrammed fashion robot arm for the projector, the camera system and/or the measurement object.

8. The optical measurement method as claimed in claim 1, wherein for the computational joining together spatial relationships between the individual recorded images relative to one another with respect to their recording positions and directions relative to the measurement object, which relationships are derived from the measured accelerations, are used as start conditions such that the computational joining together per se requires a reduced computational outlay with respect to a method where such start conditions are not used.

9. The optical measurement method as claimed in claim 1, wherein the 3D coordinates of the measurement points are determined photogrammetically according to a triangulation principle from the image sequence and with the knowledge of the pattern of the pattern sequence captured in the respective images of the image sequence.

10. The optical measurement method as claimed in claim 1, wherein the 3D coordinates of the measurement points are determined photogrammetically according to a triangulation principle from the image sequence and with the knowledge of the pattern of the pattern sequence captured in the respective images of the image sequence using intersection.

11. The optical measurement method as claimed in claim 1, wherein the illumination and the recording of positions which are known relative to one another is effected from alignments which are known relative to one another.

12. The optical measurement method as claimed in claim 1, wherein the illumination and the recording of positions which are known relative to one another is effected from alignments which are known relative to one another and the recording is effected with a plurality of cameras as parts of the camera system from different positions.

13. The optical measurement method as claimed in claim 1, wherein the measurement object surface is illuminated successively with

stripe patterns of different degrees of fineness,

pseudocodes, and/or

random patterns

as the different patterns of the pattern sequence.

14. The optical measurement method as claimed in claim 13, wherein the illumination is effected with the individual patterns substantially in direct temporal succession with a projection duration of approximately between 100 and 300 ms.

15. The optical measurement method as claimed in claim 13, wherein the illumination is effected with the individual patterns substantially in direct temporal succession with a projection duration of approximately 200 ms, and the recording of the image sequence takes place with an exposure duration per image of in each case approximately between 100 ms and 300 ms.

16. The optical measurement method as claimed in claim 13, wherein the illumination is effected with the individual patterns substantially in direct temporal succession with a projection duration of approximately 200 ms, and the recording of the image sequence takes place with an exposure duration per image of in each case approximately 200 ms.

17. The optical measurement method as claimed in claim 1, wherein during the entire operation of recording the image sequence or a plurality of image sequences, the accelerations are measured and the information obtained by the evaluation of the individual images with respect to the 3D coordinates of the measurement points are joined together in a computational manner using the measured accelerations.

18. An optical measurement system for determining 3D coordinates of a multiplicity of measurement points of a measurement object surface, comprising:

a projector for illuminating the measurement object surface with a pattern sequence of different optical patterns;

a camera system for recording an image sequence of a plurality of individual images of the measurement object surface that is illuminated with the pattern sequence; and

an evaluation unit for determining the 3D coordinates of the measurement points from the image sequence, wherein the evaluation unit determines the 3D coordinates of the measurement points from the image sequence while ascertaining a succession of brightness values for identical measurement points of the measurement object surface in the respective images of the image sequence, wherein inertial sensors are arranged;

on the projector,

on the camera system, and/or

on the measurement object

for measuring the translational and rotational accelerations of the projector, of the camera system, and/or of the measurement object with at least such a measurement rate that during the exposure time of each individual image of the image sequence in each case a plurality of values for the accelerations related to one particular direction of acceleration can be captured, and in that the evaluation unit is configured;

for synchronized controlling of the inertial sensors and of the camera system such that during the recording of the image sequence for each image a plurality of values for the accelerations related to one particular direction of acceleration are captured at least during the exposure time of each individual image of the image sequence, and

for algorithmically taking into consideration movements of the projector, of the camera system and/or of the measurement object, which provoke camera shake and/or motion blur in the respective individual images of the image sequence, on the basis of the accelerations measured by the inertial sensors for the determination of the 3D coordinates.

19. The optical measurement system as claimed in claim 18, wherein in each case a multiplicity of values for the accelerations can be captured.

20. The optical measurement system as claimed in claim 18, wherein the inertial sensors are combined and integrated into an inertial measurement unit such that the inertial measurement unit is configured for measuring the accelerations in all six degrees of freedom.

21. The optical measurement system as claimed in claim 18, wherein the inertial sensors are combined and integrated into an inertial measurement unit based on MEMS-based components such that the inertial measurement unit is configured for measuring the accelerations in all six degrees of freedom at a measurement rate of approximately 50 to 2000 Hz.

22. The optical measurement system as claimed in claim 18, wherein the evaluation unit is configured such that, in dependence on the measured accelerations, compensation and/or correcting of camera shake and/or motion blur, which are caused by movements of the projector, of the camera system and/or of the measurement object occurring during the exposure times of the respective individual images of the image sequence take place respectively in the individual images of the image sequence.

23. The optical measurement system as claimed in claim 18, wherein the projector and the camera system are accommodated with fixed and known positioning and orientation relative to one another physically in a common measurement head of the measurement system, in which the inertial sensors are also arranged.

24. The optical measurement system as claimed in claim 23, wherein the measurement head is configured to be capable of being held by hand and/or for being attached to a robot arm.

25. The optical measurement system as claimed in claim 18, wherein the camera system has at least one camera.

26. The optical measurement system as claimed in claim 18, wherein the camera system contains two, three or four cameras, which are arranged with a fixed and known positioning and orientation relative to one another and are configured for the substantially simultaneous recording of individual images.

27. An optical measurement system for determining 3D coordinates of a multiplicity of measurement points of a measurement object surface, comprising:

a projector for illuminating the measurement object surface with a pattern sequence of different optical patterns;

a camera system for recording an image sequence of a plurality of individual images of the measurement object surface that is illuminated with the pattern sequence; and

an evaluation unit for determining the 3D coordinates of the measurement points from the image sequence, wherein the evaluation unit determines the 3D coordinates of the measurement points from the image sequence while ascertaining a succession of brightness values for identical measurement points of the measurement object surface in the respective images of the image sequence, wherein inertial sensors are arranged;

on the projector,

on the camera system, and/or

on the measurement object

for measuring the translational and rotational accelerations of the projector, of the camera system, and/or of the measurement object with at least such a measurement rate that during the exposure time of each individual image of the image sequence in each case a plurality of values for the accelerations related to one particular direction of acceleration can be captured, and in that the evaluation unit is configured;

for synchronized controlling of the inertial sensors and of the camera system such that during the recording of the image sequence for each image a plurality of values for the accelerations related to one particular direction of acceleration are captured at least during the exposure time of each individual image of the image sequence;

for algorithmically taking into consideration movements of the projector, of the camera system and/or of the measurement object, which provoke camera shake and/or motion blur in the respective individual images of the image sequence, on the basis of the accelerations measured by the inertial sensors for the determination of the 3D coordinates.