Camera based six degree-of-freedom target measuring and target tracking device

• US 7,576,836 B2
• Filed: 04/20/2007
• Issued: 08/18/2009
• Est. Priority Date: 04/20/2006
• Status: Active Grant

• Current Assignee: Faro Technologies Incorporated
• Original Assignee: Faro Technologies Incorporated
• Inventors: Bridges, Robert E.
• Primary Examiner(s): Tarcza; Thomas H
• Assistant Examiner(s): Ratcliffe; Luke D
• Application Number:
  US11/738,005
• Publication Number:
  US 20080111985A1
• Time in Patent Office: 851 Days
• Field of Search: 356 301- 315, 356 401- 41, 356 501- 515, 356 6- 22
• US Class Current: 356/3.13
• CPC Class Codes: G01B 11/002 for measuring two or more coordinates
• CPC Class Codes: G01S 5/163 Determination of attitude using inertial means G01C9/00; control of attitude G05D1/49

Abstract

An embodiment may comprise a camera based target coordinate measuring system or apparatus for use in measuring the position of objects in manner that preserves a high level of accuracy. This high level of measurement accuracy is usually only associated with more expensive laser based devices. Many different arrangements are possible. Other embodiments may comprise related methods of using a camera based target coordinate measuring method for use in measuring the position of objects. Many variations on the methods are possible. For example, an embodiment may comprise a camera based coordinate measuring system for use in measuring the position of a target relative to at least one frame of reference without requiring use of a laser range finder for measuring distance comprising: at least three or more light sources located on a target at known three-dimensional coordinates relative to each other; at least one rotatable camera rotatable on about a first axis and a second axis wherein the camera records positions of the light sources; and two angular measuring devices to measure the angles of rotation of the camera about the first and second axes; and a processor for determining up to three positional degrees of freedom and up to three rotational degrees of freedom of the target.

Claims

1. A camera based target coordinate measuring system for use in measuring the position of objects without requiring use of a laser range finder for measuring distance comprising:

a camera rotatable about a first axis and a second axis;

a target having at least three or more light sources wherein the light sources are located on the target at known three-dimensional coordinates relative to each other and wherein at least one of the light sources is located at a different distance from the camera than the midpoint of a line segment connecting two of the other light sources, and wherein the target is structured to be placed on an object to be measured or to be placed on a device to measure the object;

two angular measuring devices structured to measure angles of rotation of the camera about the first and second axes;

at least one motor structured to rotate the camera about the first and second axes;

a photosensitive pixel array located in the camera structured to record an image of the light sources on the target; and

a processor structured to direct the motor and structured to determine up to three positional degrees of freedom and up to three rotational degrees of freedom of the target based the image of the light sources on the target and the angles of rotation of the camera about the first and second axes without requiring use of a laser range finder for measuring distance;

wherein the target can be positioned at one of a plurality of distances from the camera;

the three or more light sources are positioned on the target such that images of the light sources substantially fill the photosensitive pixel array in at least one direction when the target is positioned at each of the plurality of distances; and

the three or more light sources are illuminated or brought into view as needed to maintain accuracy as radial distance from the camera is increased.

16. The system of claim 1, wherein the camera has an angular field of view of approximately 6 degrees or less.

2. A camera based target coordinate measuring method for use in measuring the position of objects without requiring use of a laser range finder for measuring distance comprising:

operating a camera rotatable about a first axis and a second axis;

placing a target to view with the camera, the target having at least three or more light sources wherein the light sources are located on the target at known three-dimensional coordinates relative to each other and wherein at least one of the light sources is located at a different distance from the camera than the midpoint of a line segment connecting two of the other light sources, and wherein the target is structured to be placed on an object to be measured or to be placed on a device to measure the object;

rotating the camera about the first and second axes to view the target;

measuring angles of rotation of the camera about the first and second axes;

recording an image of the light sources on a photosensitive pixel array located in the camera; and

determining up to three positional degrees of freedom and up to three rotational degrees of freedom of the target based the image of the light sources on the target and the angles of rotation of the camera about the first and second axes without requiring use of a laser range finder for measuring distance;

wherein the target can be positioned at one of a plurality of distances from the camera;

the three or more light sources are positioned on the target such that images of the light sources substantially fill the photosensitive pixel array in at least one direction when the target is positioned at each of the plurality of distances; and

the three or more light sources are illuminated or brought into view as needed to maintain accuracy as radial distance from the camera is increased.

17. The method of claim 2, wherein the camera has an angular field of view of approximately 6 degrees or less.

3. A camera based coordinate measuring system for use in measuring the position of a target relative to at least one frame of reference without requiring use of a laser range finder for measuring distance comprising:

at least three or more light sources located on a target at known three-dimensional coordinates relative to each other;

at least one rotatable camera rotatable on about a first axis and a second axis wherein the camera is structured to record positions of the light sources with a photosensitive pixel array; and

two angular measuring devices to measure the angles of rotation of the camera about the first and second axes; and

a processor for determining up to three positional degrees of freedom and up to three rotational degrees of freedom of the target based the recorded positions of the light sources and the angles of rotation of the camera about the first and second axes without requiring use of a laser range finder for measuring distance;

wherein the target can be positioned at one of a plurality of distances from the camera;

the three or more light sources are positioned on the target such that images of the light sources substantially fill the photosensitive pixel array in at least one direction when the target is positioned at each of the plurality of distances; and

the three or more light sources are illuminated or brought into view as needed to maintain accuracy as radial distance from the camera is increased.

4. The system of claim 3 wherein the light sources are point light sources.

5. The system of claim 3 wherein the light sources are light emitting diodes (LED'"'"'s).

6. The system of claim 3 wherein the target is structured to be placed on an object to be measured or to be placed on a device to measure the object.

7. The system of claim 3 further comprising:

two motors to rotate the camera about the first and second axes.

8. The system of claim 3 wherein the light sources are located on the target at known three-dimensional coordinates relative to each other and wherein at least one of the light sources is located at a different distance from the camera than the midpoint of a line segment connecting two of the other light sources, and wherein the target is structured to be placed on an object to be measured or to be placed on a device to measure the object.

9. The system of claim 3 wherein the target is structured to be placed on a probe having a probe tip in order to measure the three dimensional coordinates of an object brought into contact with the probe tip.

10. The system of claim 3 wherein the target is a spherically shaped target.

11. The system of claim 3 wherein the target is structured to be placed on a laser scanner unit.

12. The system of claim 3 wherein the target is structured to be placed on a coordinate measurement machine (CMM).

13. The system of claim 3 wherein the target is structured to be placed on a robotic arm.

14. The system of claim 3 wherein the target is incorporated in a tooling hole fiducial in order to determine the three dimensional coordinates of a tooling hole in an object.

15. The system of claim 3 wherein the target is structured to be placed on an articulated-arm coordinate measuring machine (CMM).

18. The system of claim 3, wherein the camera has an angular field of view of approximately 6 degrees or less.