Apparatus and Method to Optically Locate Workpiece for Robotic Operations

• US 20170210011A1
• Filed: 01/22/2016
• Published: 07/27/2017
• Est. Priority Date: 01/22/2016
• Status: Active Grant

• Current Assignee: The Boeing Co.
• Original Assignee: The Boeing Co.
• Inventors: Hull, Jerald A.
• Granted Patent: US 9,815,204 B2
• Time in Patent Office: Days
• CPC Class Codes: B25J 9/1692 Calibration of manipulator
• CPC Class Codes: B25J 9/1697 Vision controlled systems
• CPC Class Codes: G05B 2219/37571 Camera detecting reflected light from laser
• CPC Class Codes: G05B 2219/39045 Camera on end effector detects reference pattern
• CPC Class Codes: G05B 2219/40613 Camera, laser scanner on end effector, hand eye manipulator, local
• CPC Class Codes: Y10S 901/47 Optical

Abstract

A camera on a robotic arm end effector is used to locate a workpiece coordinate system transformation in rotation and translation with respect to the end effector coordinate system by successively measuring an offset between a target affixed to the workpiece and its expected location. The target reflects energy from a light beam provided by a light beam source. A beam splitter is used to align the light beam with a line of sight of the camera.

Claims

1. A method of determining a coordinate system transformation from an end effector coordinate system of an end effector of a machine to a coordinate system of a workpiece, the method comprising:

identifying points on the workpiece;

receiving, at an imager of a camera coupled to the end effector, light beams including light received from the identified points;

identifying a respective centroid of the light received from each of the identified points at the imager;

determining an offset of each respective centroid from a predicted location of the respective centroid of the light received from the each of the identified points; and

using the offsets, determining the coordinate system transformation in rotation and translation of the coordinate system of the workpiece relative to the end effector coordinate system.

2. The method of claim 1, wherein receiving, at the imager of the camera, the light beams including the light received from the identified points further includes receiving the light beams at a focal plane of the imager, wherein the method further comprises:

rotating the end effector about a centroid of the focal plane of the imager to receive the light beams from each of the identified points on the workpiece.

3. The method of claim 1, wherein identifying the points on the workpiece comprises identifying each of the points on the workpiece with a respective reflective element.

4. The method of claim 3, further comprising illuminating each of the respective reflective elements with a polarized light.

5. The method of claim 4, wherein illuminating the respective reflective elements with the polarized light comprises illuminating the reflective elements using a light beam source mounted proximate to the camera mounted on the end effector.

6. The method of claim 1, wherein identifying the points on the workpiece comprises attaching an active light source to each respective point on the workpiece.

7. The method of claim 1, wherein determining the coordinate system transformation from the end effector coordinate system to the coordinate system of the workpiece comprises using a two-dimension to three-dimension reconstruction algorithm.

8. A system for orienting an end effector of a robot arm with respect to a workpiece, the system comprising:

a camera attached to the end effector, the camera having a line of sight formed between a lens of the camera and an imager in the camera;

and

a controller that computes a transformation from an end effector coordinate system to a workpiece coordinate system using a light beam received from multiple locations on the workpiece based on respective centroids of the light beam on the imager from each of the multiple locations.

9. The system of claim 8, further comprising:

a light beam source attached to the end effector, the light beam source projecting the light beam to each of the multiple locations on the workpiece;

a beam splitter that aligns the light beam from the light beam source with the line of sight of the camera.

10. The system of claim 9, further comprising a diffuse reflector at each of the multiple locations on the workpiece.

11. The system of claim 10, wherein the diffuse reflector is one of a paint marking and a retro-reflective target.

12. The system of claim 9, wherein the light beam source comprises a beam expander that increases a diameter of the light beam to approximately a size of a target at the multiple locations plus an initial location tolerance.

13. The system of claim 9, wherein the beam splitter comprises a filtered beam splitter that selectively passes a portion of the light beam received from each of the multiple locations.

14. The system of claim 8, further comprising an active light source that generates the light beam.

15. The system of claim 14, wherein the active light source is a polarized light source.

16. An end effector of a robot arm adapted for use in determining a location of a workpiece, the end effector including:

a work tool used in a manufacturing operation;

a camera mounted in a known relationship to the work tool, the camera having a lens and an imager aligned along a line of sight of the camera;

a light beam subassembly generating a light beam; and

a beam splitter having at least one reflector that aligns the light beam along the line of sight of the camera and permits at least a portion of a reflection of the light beam to pass to the imager.

17. The end effector of claim 16, wherein the light beam subassembly comprises a beam expander.

18. The end effector of claim 16, wherein the at least one reflector of the beam splitter is a filtered beam splitter.

19. The end effector of claim 16, wherein the light beam subassembly is tuned to provide a beam color matching a color of a color filter mosaic element of the imager.

20. The end effector of claim 16, wherein the lens is a variable focus lens adapted for adjustment between macro focus and distance focus.