Device and method for measuring six degrees of freedom

• US 8,670,114 B2
• Filed: 05/13/2013
• Issued: 03/11/2014
• Est. Priority Date: 11/17/2008
• Status: Active Grant

• Current Assignee: Faro Technologies Incorporated
• Original Assignee: Faro Technologies Incorporated
• Inventors: Bridges, Robert E., Brown, Lawrence B., Hoffer, John M. Jr.
• Primary Examiner(s): Chowdhury, Tarifur
• Assistant Examiner(s): AKANBI, ISIAKA O
• Application Number:
  US13/892,385
• Publication Number:
  US 20130250285A1
• Time in Patent Office: 302 Days
• Field of Search: 356/138, 356/612, 356/614
• US Class Current: 356/138
• 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: G01S 1/70 using electromagnetic waves other than radio waves
• CPC Class Codes: G01S 17/66 Tracking systems using electromagnetic waves other than radio waves
• CPC Class Codes: G01S 5/163 Determination of attitude using inertial means G01C9/00; control of attitude G05D1/49

Abstract

A laser tracker system for measuring six degrees of freedom may include a main optics assembly structured to emit a first laser beam, a pattern projector assembly structured to emit a second laser beam shaped into a two-dimensional pattern, and a target. The target may include a retroreflector and a position sensor assembly. A center of symmetry of the retroreflector may be provided on a different plane than a plane of the position sensor assembly. A method of measuring orientation of a target may include illuminating the target with a laser beam comprising a two-dimensional pattern, recording a position of the two-dimensional pattern on a position sensor assembly to create a measured signature value of the two-dimensional pattern, and calculating an orientation of the target based on the measured signature value.

Claims

1. A laser tracker configured to locate a retroreflector target, the laser tracker comprising:

a payload assembly configured to emit a first beam of light along a main optical axis extending from the laser tracker;

a first motor and a second motor configured to together direct the first beam of light along the main optical axis in 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 second axis substantially perpendicular to the first axis, the first angle of rotation produced by the first motor and the second angle of rotation produced by the second motor, wherein the payload assembly is configured to rotate about the first axis and the second axis;

a first angle measuring device configured to measure the first angle of rotation and a second angle measuring device configured to measure the second angle of rotation;

a distance meter configured to measure a first distance from the laser tracker to the retroreflector target;

a first camera assembly including a first camera and a first light source, the first camera assembly rigidly affixed to the payload assembly, the first camera having a first camera optical axis extending from the payload assembly, the first camera optical axis generally in the same direction as the main optical axis and offset with respect to the main optical axis, the first light source proximate to the first camera, the first light source configured to illuminate the retroreflector target to produce a first retroreflected light, the first camera configured receive the first retroreflected light and to produce a first image; and

a second camera assembly including a second camera and a second light source, the second camera assembly rigidly affixed to the payload assembly, the second camera having a second camera optical axis extending from the payload, the second camera optical axis offset generally in the same direction as the main optical axis and offset with respect to the main optical axis and to the first camera optical axis, the second light source proximate to the second camera, the second light source configured to illuminate the retroreflector target to produce a second retroreflected light, the second camera configured receive the second retroreflected light and to produce a second image.

2. The laser tracker of claim 1 wherein the first camera optical axis and the second camera optical axis are placed symmetrically about the main optical axis.

3. A method for locating a retroreflector target with a laser tracker, the method comprising:

providing a payload assembly configured to emit a first beam of light along a main optical axis extending from the laser tracker;

providing a first motor configured to rotate the payload about a first axis by a first angle of rotation;

providing a second motor configured to rotate the payload about a second axis by a second angle of rotation, wherein the second axis is substantially perpendicular to the first axis;

providing a first camera assembly including a first camera and a first light source, the first camera assembly rigidly affixed to the payload, the first camera having a first camera optical axis extending from the payload, the first camera optical axis generally in the same direction as the main optical axis and offset with respect to the main optical axis, the first light source proximate to the first camera;

providing a second camera assembly including a second camera and a second light source, the second camera assembly rigidly affixed to the payload, the second camera having a second camera optical axis extending from the payload, the second camera optical axis offset generally in the same direction as the main optical axis and offset with respect to the main optical axis, the second camera optical axis offset generally with respect to the first camera optical axis, the second light source proximate to the second camera;

emitting the first beam of light;

illuminating the retroreflector target with a third light from the first light source to produce first retroreflected light from the retroreflector target;

illuminating the retroreflector target with a fourth light from the second light source to produce second retroreflected light from the retroreflector target;

receiving the first retroreflected light by the first camera and producing a first camera image in response;

receiving the second retroreflected light by the second camera and producing a second camera image in response;

determining a first calculated angle of rotation and a second calculated angle of rotation to steer the main optical axis toward the retroreflector target, the first calculated angle of rotation and the second calculated angle of rotation based at least in part on the first camera image and the second camera image; and

rotating the payload by the first calculated angle of rotation about the first axis and the second calculated angle of rotation about the second axis.

4. The method of claim 3 further comprising:

providing a position detector;

receiving the first beam of light at the retroreflector target and returning a third retroreflected beam of light in response;

receiving a portion of the third retroreflected beam of light at the position detector; and

rotating the payload with the first motor and the second motor to place the third retroreflected beam of light in a preferred position on the position detector.

5. The method of claim 4 further comprising:

providing a first angle measuring device, a second angle measuring device, and a distance meter;

measuring a third angle with the first angle measuring device;

measuring a fourth angle with the second angle measuring device;

measuring a first distance from the laser tracker to the retroreflector target based at least in part on a time for the first beam of light to travel from the payload to the retroreflector target; and

providing a three-dimensional coordinate of the retroreflector target based at least in part on the third angle, the fourth angle, and the first distance.

6. The method of claim 3 wherein:

in the step of illuminating the retroreflector target with a third light, the third light is flashed repetitively; and

in the step of illuminating the retroreflector target with the fourth light, the fourth light is flashed repetitively.

7. The method of claim 3 wherein:

in the step of providing a first camera assembly, the first light source includes a first LED; and

in the step of providing a second camera assembly, the second light source includes a second LED.

8. The method of claim 3 wherein, in the steps of providing the first camera assembly and the second camera assembly, the first camera optical axis and the second camera optical axis are placed substantially symmetrically about the main optical axis.