Six degree-of-freedom laser tracker that cooperates with a remote structured-light scanner

• US 9,151,830 B2
• Filed: 04/11/2012
• Issued: 10/06/2015
• Est. Priority Date: 04/15/2011
• Status: Active Grant

• Current Assignee: Faro Technologies Incorporated
• Original Assignee: Faro Technologies Incorporated
• Inventors: Bridges, Robert E.
• Primary Examiner(s): Czekaj, Dave
• Assistant Examiner(s): PHAM, NAM D
• Application Number:
  US13/443,946
• Publication Number:
  US 20120262550A1
• Time in Patent Office: 1,273 Days
• US Class Current: 1/1
• CPC Class Codes: G01B 11/03 by measuring coordinates of points
• CPC Class Codes: G01C 15/002 Active optical surveying means optical plumbing G01C15/105
• CPC Class Codes: G01C 3/08 Use of electric radiation detectors
• CPC Class Codes: G01S 17/42 Simultaneous measurement of distance and other co-ordinates indirect measurement G01S17/46
• CPC Class Codes: G01S 17/66 Tracking systems using electromagnetic waves other than radio waves
• CPC Class Codes: G01S 17/89 for mapping or imaging
• CPC Class Codes: G01S 7/4808 Evaluating distance, position or velocity data
• CPC Class Codes: G01S 7/4813 Housing arrangements
• CPC Class Codes: G01S 7/4818 using optical fibres
• CPC Class Codes: G01S 7/491 Details of non-pulse systems
• CPC Class Codes: G06F 17/40 Data acquisition and logging for input to computer G06F3/00
• CPC Class Codes: G16Z 99/00 Subject matter not provided for in other main groups of this subclass

Abstract

Measuring three surface sets on an object surface with a measurement device and scanner, each surface set being 3D coordinates of a point on the object surface. The method includes: the device sending a first light beam to the first retroreflector and receiving a second light beam from the first retroreflector, the second light beam being a portion of the first light beam, a scanner processor and a device processor jointly configured to determine the surface sets; selecting the source light pattern and projecting it onto the object to produce the object light pattern; imaging the object light pattern onto a photosensitive array to obtain the image light pattern; obtaining the pixel digital values for the image light pattern; measuring the translational and orientational sets with the device; determining the surface sets corresponding to three non-collinear pattern elements; and saving the surface sets.

Claims

1. A method of measuring three or more surface sets on an object surface with a coordinate measurement device and a target scanner, each of the three or more surface sets being three-dimensional coordinates of a point on the object surface in a device frame of reference, each surface set including three values, the device frame of reference being associated with the coordinate measurement device, the method comprising steps of:

providing the target scanner having a body, a first retroreflector, a projector, a camera, and a scanner processor, wherein the first retroreflector, projector, and camera are rigidly affixed to the body, and the target scanner is mechanically detached from the coordinate measurement device,

wherein the projector includes a source pattern of light, the source pattern of light located on a source plane and including at least three non-collinear pattern elements, the projector configured to project the source pattern of light onto the object to form an object pattern of light on the object, each of the at least three non-collinear pattern elements corresponding to at least one surface set,

wherein the camera includes a camera lens and a photosensitive array, the camera lens configured to image the object pattern of light onto the photosensitive array as an image pattern of light, the photosensitive array including camera pixels, the photosensitive array configured to produce, for each camera pixel, a corresponding pixel digital value responsive to an amount of light received by the camera pixel from the image pattern of light;

providing the coordinate measurement device, the coordinate measurement device including a first motor, a second motor, a first angle measuring device, a second angle measuring device, a distance meter, a position detector, a control system, and a device processor, the coordinate measurement device configured to send a first beam of light to the first retroreflector and to receive a second beam of light from the first retroreflector, the second beam of light being a portion of the first beam of light, the first motor and the second motor together configured to direct the first beam of light to a first direction, the first direction determined by a first angle of rotation about a first axis and a second angle of rotation about a second axis, the first angle of rotation produced by the first motor and the second angle of rotation produced by the second motor, the first angle measuring device configured to measure the first angle of rotation and the second angle measuring device configured to measure the second angle of rotation, the distance meter configured to measure a first distance from the coordinate measurement device to the first retroreflector, the position detector configured to receive a second portion of the second beam of light and to send a first signal to the control system, the first signal produced in response to a position of the second portion on the position detector, the control system configured to send a second signal to the first motor, to send a third signal to the second motor, and to adjust the first direction of the first beam of light to the position in space of the first retroreflector, the second signal and the third signal based at least in part on the first signal, the device processor configured to determine a translational set and an orientational set, the translational set being values of three translational degrees of freedom of the target scanner in the device frame of reference and the orientational set being values of three orientational degrees of freedom of the target scanner in the device frame of reference, the translational set and the orientational set substantially defining a position and orientation of the target scanner in space, the translational set based at least in part on the first distance, the first angle of rotation, and the second angle of rotation,

wherein the scanner processor and the device processor are jointly configured to determine the three or more surface sets, each of the surface sets based at least in part on the translational set, the orientational set, and the pixel digital values;

selecting the source pattern of light;

projecting the source pattern of light onto the object to produce the object pattern of light;

imaging the object pattern of light onto the photosensitive array to obtain the image pattern of light;

obtaining the pixel digital values for the image pattern of light;

sending the first beam of light from the coordinate measurement device to the first retroreflector;

receiving by the coordinate measuring device the second beam of light from the first retroreflector;

determining by the device processor the orientational set and the translational set, the translational set based at least in part on the second beam of light;

determining the surface sets corresponding to each of the at least three non-collinear pattern elements; and

saving the surface sets.

2. The method of claim 1, wherein:

the projector has a virtual light perspective center and a projector reference axis, the projector reference axis passing through the projector virtual light perspective center, the projected source pattern of light appearing to emanate from the virtual light perspective center;

the camera lens has a camera lens perspective center and a camera reference axis, the camera reference axis passing through the camera lens perspective center;

the target scanner has a baseline, a baseline length, a baseline projector angle, and a baseline camera angle, the baseline being a line segment connecting the virtual light perspective center and the camera lens perspective center, the baseline length being a length of the baseline, the baseline projector angle being an angle between the projector reference axis and the baseline, the baseline camera angle being an angle between the baseline and the camera reference axis; and

the step of providing the coordinate measurement device further includes providing the coordinate measurement device with the device processor jointly configured with the scanner processor to determine the three or more surface sets, each of the surface sets further based at least in part on the baseline length, the camera baseline angle, and the projector baseline angle.

3. The method of claim 2, wherein the step of providing the target scanner further includes providing a projector lens configured to project the source pattern of light, the virtual light perspective center being a perspective center of the projector lens, the projector reference axis being a projector lens optical axis, and the camera reference axis being a camera lens optical axis.

4. The method of claim 2, wherein the step of selecting the source pattern of light further includes selecting the source pattern of light to include at least three coded features present as pattern elements in the source pattern of light, wherein the three coded features are identifiable in the image pattern of light.

5. The method of claim 4, wherein the step of selecting the source pattern of light further includes aligning groups of the coded features in a prescribed direction relative to epipolar lines on the source plane, the epipolar lines on the source plane being lines of intersection of the source plane with epipolar planes, the epipolar planes being planes that contain the virtual light perspective center and the camera lens perspective center.

6. The method of claim 5, wherein:

selecting the source pattern of light further includes aligning each group of coded features along a unique epipolar line; and

determining the surface sets further includes noting, for each group of coded features, the positions of the coded features along each of the unique epipolar lines.

7. The method of claim 1, wherein:

the step of selecting the source pattern of light further includes selecting at least three instances of the source pattern, at least a first instance, a second instance, and a third instance, the source pattern in each instance having an optical power that varies periodically at a first spatial frequency, wherein, for each instance, the source pattern is shifted in phase relative to the other instances;

the step of projecting the source pattern of light further includes projecting the first instance of the source pattern at a first time and a first phase to obtain a first instance of the object pattern of light, projecting the second instance of the source pattern at a second time and a second phase to obtain a second instance of the object pattern of light, and projecting the third instance of the source pattern at a third time and a third phase to obtain a third instance of the object pattern of light;

the step of imaging the object pattern of light further includes imaging the first instance of the object pattern of light onto the photosensitive array to obtain a first instance of the image pattern of light, imaging the second instance of the object pattern of light onto the photosensitive array to obtain a second instance of the image pattern of light, imaging the third instance of the object pattern of light onto the photosensitive array to obtain a third instance of the image pattern of light;

the step of obtaining the pixel digital values further includes obtaining a first instance of the pixel digital values for the first instance of the image pattern of light, obtaining a second instance of the pixel digital values for the second instance of the image pattern of light, obtaining a third instance of the pixel digital values for the third instance of the image pattern of light; and

the step of determining the surface sets for each of the at least three non-collinear pattern elements further includes determining the surface sets for each of the three non-collinear pattern elements based at least in part on the first spatial frequency, the first phase, the second phase, the third phase, the first instance of the pixel digital values, the second instance of the pixel digital values, and the third instance of the pixel digital values.

8. The method of claim 7, wherein:

the step of selecting the source pattern of light further includes selecting at least three instances of a second source pattern, at least a fourth instance, a fifth instance, and a sixth instance, the second source pattern in each instance having an optical power that varies periodically at a second spatial frequency, wherein, for each instance, the second source pattern is shifted in phase relative to the other instances;

the step of projecting the second source pattern of light further includes projecting the fourth instance of the second source pattern at a fourth time and a fourth phase to obtain a fourth instance of the object pattern of light, projecting the fifth instance of the second source pattern at a fifth time and a fifth phase to obtain a fifth instance of the object pattern of light, and projecting the sixth instance of the source pattern at a sixth time and a sixth phase to obtain a sixth instance of the object pattern of light;

the step of imaging the object pattern of light further includes imaging the fourth instance of the object pattern of light onto the photosensitive array to obtain a fourth instance of the image pattern of light, imaging the fifth instance of the object pattern of light onto the photosensitive array to obtain a fifth instance of the image pattern of light, and imaging the sixth instance of the object pattern of light onto the photosensitive array to obtain a sixth instance of the image pattern of light;

the step of obtaining the pixel digital values further includes obtaining a fourth instance of pixel digital values for the fourth instance of the image pattern of light, obtaining a fifth instance of the pixel digital values for the fifth instance of the image pattern of light, and obtaining a sixth instance of the pixel digital values for the sixth instance of the image pattern of light; and

the step of determining the surface sets for each of the at least three non-collinear pattern elements further includes determining the surface sets for each of the three non-collinear pattern elements further based on the second spatial frequency, the fourth phase, the fifth phase, the sixth phase, the fourth instance of the pixel digital values, the fifth instance of the pixel digital values, and the sixth instance of the pixel digital values.

9. The method of claim 1, wherein the step of providing the target scanner further includes providing a fixture rigidly attached to the body, the fixture stationary with respect to the device frame of reference.

10. The method of claim 1, wherein the step of providing the target scanner further includes providing the projector and the camera scaled to measure features too small to be seen by the human eye without magnification.

11. The method of claim 1, wherein:

the step of providing the target scanner further includes providing a second retroreflector rigidly attached to the body; and

the step of measuring the translational set and the orientational set with the coordinate measurement device further includes rotating the target scanner to acquire the second retroreflector with the first beam of light from the coordinate measurement device.

12. The method of claim 1, wherein the step of providing the target scanner further includes providing a handle on the target scanner.

13. The method of claim 1, wherein, in the step of providing the target scanner, the target scanner further includes a tactile probe rigidly affixed to the body.

14. The method of claim 13, further including steps of:

touching the tactile probe to the object surface;

measuring the translational set and the orientational set; and

determining a second surface set based at least in part on the translational set and the orientational set.

15. The method of claim 13, further including steps of:

evaluating the surface sets; and

indicating to a user that a region of the object surface is to be measured with the tactile probe based at least in part on the evaluated surface sets.

16. The method of claim 15, wherein the step of evaluating the surface sets further includes a step of evaluating the surface sets based on an evaluation criterion selected from the group consisting of receiving light of low optical power for at least one of the surface sets, having at least one of the surface sets on an edge, determining that multipath interference may be present in at least one of the surface sets, and combinations thereof.

17. The method of claim 15, wherein the step of indicating to a user that a region of the object surface is to be measured with the tactile probe further includes an indication selected from the group consisting of illuminating the region with light projected by the projector, displaying the region to be illuminated on a display, and combinations thereof.

18. The method of claim 1, further including steps of:

incorporating a pattern into the first retroreflector;

providing a second optical system including a second lens and a second photosensitive array, the second lens configured to form a second image of at least a portion of the first retroreflector on the second photosensitive array;

converting the second image into a second digital data set; and

calculating the orientational set based at least in part on the second digital data set.