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

• US 9,628,779 B2
• Filed: 05/16/2012
• Issued: 04/18/2017
• Est. Priority Date: 05/19/2011
• Status: Active Grant

• Current Assignee: Hexagon Technology Center GmbH (Hexagon AB)
• Original Assignee: Hexagon Technology Center GmbH (Hexagon AB)
• Inventors: Siercks, Knut
• Primary Examiner(s): Tsai, Tsung-Yin
• Application Number:
  US14/004,880
• Publication Number:
  US 20140063204A1
• Time in Patent Office: 1,798 Days
• Field of Search: None
• CPC Class Codes: G01B 11/2545 with one projection direction and several detection directions, e.g. stereo
• CPC Class Codes: G06T 2207/10152 Varying illumination
• CPC Class Codes: G06T 2207/30164 Workpiece; Machine component
• CPC Class Codes: G06T 7/521 from laser ranging, e.g. using interferometry; from the projection of structured light
• CPC Class Codes: H04N 13/254 in combination with electromagnetic radiation sources for illuminating objects

Abstract

An optical measurement method for determining 3D coordinates of a plurality of measurement points on a measurement object surface. The measurement object surface is illuminated with a pattern sequence of different patterns by a projector, an image sequence of the measurement object surface illuminated with the pattern sequence is recorded with a camera system, and the 3D coordinates of the measurement points are determined by evaluating the image sequence, in particular wherein a succession of brightness values for identical measurement points on the measurement object surface is ascertained in respective images of the recorded image sequence. Translational and/or rotational accelerations of the projector, of the camera system and/or of the measurement object are measured here and, in dependence on the measured accelerations, the illumination of the measurement object surface and/or the recording of the image sequence is/are reactively adapted, in particular temporally substantially directly and live during the measurement process.

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:

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

using a camera system to record an image sequence of measurement object surface illuminated with the pattern sequence; and

determining the 3D coordinates of the measurement points by evaluating the image sequence of different brightness values from the different patterns for identical measurement points of the measurement object surface being determined in respective images of the recorded image sequence, wherein;

translational or rotational accelerations of the projector, of the camera system, or of the measurement object are measured, and the illumination of the measurement object surface or the recording of the image sequence are/is reactively adapted as a function of the measured accelerations results in an adjustment of illumination of the measurement object surface or the recording of the image sequence as a function of measured accelerations.

2. The optical measurement method as claimed in claim 1, wherein translational and/or rotational accelerations of the projector, of the camera system, or of the measurement object are measured, and the illumination of the measurement object surface or the recording of the image sequence are/is reactively adapted substantially immediately and live during the measurement process in terms of time as a function of the measured accelerations.

3. The optical measurement method as claimed in claim 1, wherein accelerations of the projector, of the camera system or of the measurement object are measured in all six degrees of freedom, and the measurement of the accelerations is performed continuously at a specific measurement rate at least during the exposure times of the individual images of the image sequence.

4. The optical measurement method as claimed in claim 1, wherein accelerations of the projector, of the camera system or of the measurement object are measured in all six degrees of freedom, and the measurement of the accelerations is performed continuously at a specific measurement rate of between approximately 1 and 2000 Hz at least during the exposure times of the individual images of the image sequence.

5. The optical measurement method as claimed in claim 1, wherein accelerations of the projector, of the camera system or of the measurement object are measured in all six degrees of freedom, and the measurement of the accelerations is performed continuously at a specific measurement rate between approximately 50 and 2000 Hz during the entire process of illuminating the measurement object surface and recording the image sequence or plurality of image sequences.

6. The optical measurement method as claimed in claim 1, wherein one or more of:

as a function of a current dynamic level of the projector, of the camera system and/or of the measurement object derived during the illumination with the aid of the measured accelerations, the pattern sequence is adapted substantially immediately reactively in terms of time to the derivation of the respective current dynamic level;

or

an order of different patterns of the pattern sequence that are to be projected consecutively is adapted in such a way that those patterns of the pattern sequence with a relatively low degree of fineness are projected given a relatively high current dynamic level, and those patterns of the pattern sequence with a relatively high degree of fineness are projected given a relatively low current dynamic level;

or

a brightness of the individual patterns to be projected is adapted;

or

a projection period of the individual patterns to be projected is adapted;

or

projection instants of the individual patterns to be projected are adapted;

or

a degree of fineness and/or of structuring of the individual patterns to be projected are/is adapted;

or

an individual pattern of the pattern sequence is adapted in such a way during the projection of said pattern that the illumination structure thereby produced on the measurement object surface is held in a stable position on the measurement object surface, at least during the exposure time of the image of the image sequence provided for acquiring the measurement object surface illuminated with this pattern;

or

an area coverage and/or size on the measurement object surface of the individual patterns to be projected are/is adapted;

or

a wavelength of the optical radiation used for the illumination for the individual patterns to be projected is adapted.

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

as a function of a current dynamic level of the projector, of the camera system or of the measurement object derived during the illumination with the aid of the measured accelerations, the image sequence is adapted substantially immediately reactively in terms of time to the derivation of the respective current dynamic level.

8. The optical measurement method as claimed in claim 7, wherein:

a respective degree of granulation for the individual images to be recorded is adapted;

or

a respective exposure time for the individual images to be recorded is adapted;

or

recording instants of the individual images to be recorded are adapted;

or

a respective acquisition area for the individual images to be recorded is adapted;

or

a respective aperture width for the individual images to be recorded is adapted.

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

the projector has a housing;

the rotational and translational accelerations of the housing are measured; and

a projection direction and/or a projection source position of the projector are/is adapted relative to the housing substantially in real time and as a function of the measured accelerations of the housing in such a way that movements of the housing are compensated, and thus the projection direction or the projection source position of the projector are/is substantially kept constant.

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

the projector has a measuring head housing that jointly integrates the projector and the camera system;

the rotational and translational accelerations of the housing are measured; and

a projection direction or a projection source position of the projector are/is adapted relative to the housing substantially in real time and as a function of the measured accelerations of the housing in such a way that movements caused by unsteady holding owing to vibration or to hand tremor are compensated, and thus the projection direction or the projection source position of the projector are/is substantially kept constant at least during the recording of individual images of the image sequence in each case.

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

the camera system with at least one camera has a housing;

the rotational and translational accelerations of the housing are measured; and

an acquisition direction or a recording position of the at least one camera of the camera system are/is adapted relative to the housing substantially in real time and as a function of the measured accelerations of the housing in such a way that movements of the housing of the housing are compensated, and thus the acquisition direction or the recording position of the at least one camera of the camera system are/is substantially kept constant.

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

the camera system with at least one camera has a measuring head housing that jointly integrates the projector and the camera system;

the rotational and translational accelerations of the housing are measured; and

an acquisition direction or a recording position of the at least one camera of the camera system are/is adapted relative to the housing substantially in real time and as a function of the measured accelerations of the housing in such a way that movements caused by unsteady holding owing to vibration or to hand tremor of the housing are compensated, and thus the acquisition direction or the recording position of the at least one camera of the camera system are/is substantially kept constant at least during the recording of individual images of the image sequence in each case.

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

as a function of the measured accelerations derived from said accelerations, of the projector, of the camera system or of the measurement object;

current measurement progress or measurement process adaptation parameters are derived and said parameters are projected onto the measurement object surface to guide the user and optimize the measurement process.

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

as a function of the measured accelerations, specifically as a function of current positions and orientations, derived from said accelerations, of the projector, of the camera system and/or of the measurement object;

as well as a function of at least roughly known or previously at least roughly determined 3D coordinates of the measurement object surface;

current measurement progress or measurement process adaptation parameters are derived and said parameters are projected onto the measurement object surface to guide the user and optimize the measurement process, information relating to;

a measurement direction in which the projector or the camera system are/is to be aligned during the further measurement process;

or

a measurement position which are to be adopted by the projector and/or the camera system during the further measurement process;

or

holding periods during which the projector and/or the camera system are/is to be held as steadily as possible in an invariable measurement direction and measuring position;

or

a current dynamic level, derived with the aid of the measured accelerations, of the projector, of the camera system and/or of the measurement object being specified whether a predefined dynamic level upper limit is currently maintained or not,

being projected as the measurement progress or measurement process adaptation parameters.

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

the 3D coordinates of the measurement points are determined photogrammetrically from the recorded image sequence by using the triangulation principle and with knowledge of the pattern of the pattern sequence, acquired in the respective images of the image sequence by means of forward section;

or

positions known relative to one another are illuminated and recorded from and with the aid of alignments known relative to one another, the recording being performed from different positions using a plurality of cameras as parts of the camera system.

16. The optical measurement method as claimed in claim 1, wherein the measurement object surface is illuminated consecutively with stripe patterns of different degrees of fineness, pseudo codes or random patterns as the different patterns of the pattern sequence.

17. The optical measurement method as claimed in claim 16, wherein the illumination being performed consecutively with the individual patterns with a projection period of approximately between 10 and 300 ms and the recording of the image sequence being performed with an exposure time per image of approximately between 10 and 300 ms in each case.

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

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

a camera system for recording an image sequence of the measurement object surface illuminated with the pattern sequence; and

an evaluation unit for determining the 3D coordinates of the measurement points from the image sequence by determining a sequence of different brightness values from the different patterns for identical measurement points of the measurement object surface in respective images of the recorded image sequence, wherein;

inertial sensors are arranged on the projector, on the camera system, or on the measurement object in order to measure translational or rotational accelerations of the projector, of the camera system and/or of the measurement object, and

the evaluation unit is designed to effect an adaptation, performed reactively as a function of the measured accelerations that results in an adjustment of illumination of the measurement object surface or the recording of the image sequence as a function of measured accelerations.

19. The optical measurement system as claimed in claim 18, wherein the evaluation unit is designed to effect an adaptation, performed reactively as a function of the measured accelerations substantially immediately and live in terms of time during the measurement process, of the illumination, produced by the projector, of the measurement object surface or of the recording, performed by the camera system, of the image sequence.

20. The optical measurement system as claimed in claim 18, wherein:

the evaluation unit is designed to control the projector or the camera system in such a way that the illumination, produced by the projector, of the measurement object surface, or the recording, performed by the camera system, of the image sequence is adapted live as a function of a current dynamic level, derived during the measurement process with the aid of the measured accelerations, of the projector or of the camera system,

or

the inertial sensors are combined and integrated in an inertial measurement unit based on MEMS-based components in such a way that the inertial measurement unit is designed to measure the accelerations in all six degrees of freedom with a measurement rate of between approximately 1 and 2000 Hz, specifically between approximately 50 and 2000 Hz.

21. The optical measurement system as claimed in claim 18, wherein:

the projector has a housing;

the inertial sensors being arranged on the housing and thus being designed to measure the rotational and translational accelerations of the housing; and

a projector actuating mechanism is present in order to change a projection direction or a projection source position for the projector relative to the housing, which projector actuating mechanism can be driven by the evaluation unit such that the projection direction and/or the projection source position of the projector are/is adapted relative to the housing as a function of the measured accelerations of the housing substantially in real time in such a way that movements of the housing are compensated, and thus the projection direction or the projection source position of the projector are/is substantially kept constant.

22. The optical measurement system as claimed in claim 18, wherein:

the projector and the camera system are accommodated physically in both fixed and known positioning and orientation relative to one another in a common measuring head and the measuring head having a measuring head housing jointly integrating the projector and the camera system;

the inertial sensors are arranged on the housing and thus being designed to measure the rotational and translational accelerations of the housing; and

a projector actuating mechanism constructed from MEMS-based actuator components or piezoactuator elements is present in order to change a projection direction or a projection source position for the projector relative to the housing, which projector actuating mechanism can be driven by the evaluation unit such that the projection direction or the projection source position of the projector are/is adapted relative to the housing as a function of the measured accelerations of the housing substantially in real time in such a way that movements of the housing and movements caused by unsteady holding owing to vibration or to hand tremor are compensated, and thus the projection direction or the projection source position of the projector are/is substantially kept constant, at least during the recording of individual images of the image sequence in each case.

23. The optical measurement system as claimed in claim 18, wherein:

the camera system with at least one camera has a housing, the projector and the camera system being accommodated physically in both fixed and known positioning and orientation relative to one another in a common measuring head and the measuring head having a measuring head housing jointly integrating the projector and the camera system;

the inertial sensors are arranged on the housing and thus being designed to measure the rotational and translational accelerations of the housing; and

a camera actuating mechanism constructed from MEMS-based actuator components or piezoactuator elements is present in order to change an acquisition direction or a recording position of the at least one camera of the camera system relative to the housing, which camera actuating mechanism can be driven by the evaluation unit such that the acquisition direction or the recording position of the at least one camera of the camera system are/is adapted relative to the housing as a function of the measured accelerations of the housing substantially in real time in such a way that movements of the housing caused by unsteady holding owing to vibration or to hand tremor are compensated, and thus the acquisition direction or the recording position of the at least one camera are/is substantially kept constant, at least during the recording of individual images of the image sequence in each case.

24. The optical measurement system as claimed in claim 18, wherein the evaluation unit is designed to derive current measurement progress or measurement process adaptation parameters as a function of the measured accelerations as a function of current positions and orientations, derived from said accelerations, of the projector, of the camera system or of the measurement object.

25. The optical measurement system as claimed in claim 24, wherein:

additionally as a function of at least roughly known or previously at least roughly determined 3D coordinates of the measurement object surface; and

the projector is designed and configured in such a way, as well as being able to be driven by the evaluation unit, in such a way that information with respect to the derived current measurement progress or measurement process adaptation parameters are projected onto the measurement object surface to guide users and optimize the measurement process.

26. The optical measurement system as claimed in claim 24, wherein information relating to:

a measurement direction in which the projector or the camera system are/is to be aligned during the further measurement process;

or

a measurement position which are to be adopted by the projector and/or the camera system during the further measurement process;

or

holding periods during which the projector and/or the camera system are/is to be held as steadily as possible in an invariable measurement direction and measuring position;

or

a current dynamic level, derived with the aid of the measured accelerations, of the projector, of the camera system or of the measurement object, it being specified whether a predefined dynamic level upper limit is currently maintained or not being projected as the measurement progress or measurement process adaptation parameters.