Robotic calibration method

• US 8,457,790 B2
• Filed: 09/12/2008
• Issued: 06/04/2013
• Est. Priority Date: 09/14/2007
• Status: Active Grant

• Current Assignee: Zimmer Incorporated (Zimmer Biomet Holdings, Inc.)
• Original Assignee: Zimmer Incorporated (Zimmer Biomet Holdings, Inc.)
• Inventors: Blondel, Lucien, Heavener, Jackson R.
• Primary Examiner(s): Trammell, James
• Assistant Examiner(s): LANG, MICHAEL DEAN
• Application Number:
  US12/210,165
• Publication Number:
  US 20090076655A1
• Time in Patent Office: 1,726 Days
• Field of Search: 701/254
• US Class Current: 700/254
• CPC Class Codes: A61B 2017/00725 Calibration or performance testing
• CPC Class Codes: A61B 2034/2059 Mechanical position encoders
• CPC Class Codes: A61B 34/30 Surgical robots
• CPC Class Codes: A61B 34/35 for telesurgery
• CPC Class Codes: A61B 34/77 Manipulators with motion or force scaling
• CPC Class Codes: B25J 13/081 Touching devices, e.g. pressure-sensitive
• CPC Class Codes: B25J 9/1692 Calibration of manipulator
• CPC Class Codes: G05B 2219/39019 Calibration by cmm coordinate measuring machine over a certain volume
• CPC Class Codes: G05B 2219/39044 Estimate error model from error at different attitudes and points

Abstract

A robot is characterized by an external measurement device. The robot generates a first point cloud of data. The external measurement device generates a second point cloud of data. These two points clouds are analyzed to determine an accuracy of the robot.

Claims

1. A method of obtaining calibration data for a robot system having an articulated arm, the method comprising the steps of:

providing a calibration template having a plurality of calibration spots formed in the calibration template at predetermined fixed positions therein, the calibration spots comprising divots in the calibration template, the calibration spots having a known geometry defining a first point cloud as determined by an external measurement device;

commanding said articulated arm of said robot system to position a calibration feature coupled to the articulated arm at a plurality of commanded points corresponding to said calibration spots of the calibration template, the calibration feature having a shape which corresponds to and is received within said divots of the calibration template;

for each of said commanded points, determining with the robot system a measurement point corresponding to said position of said calibration feature, said plurality of measurement points collectively being a second point cloud; and

adjusting one or more parameters of said robot system based on a comparison of said first point cloud and said second point cloud.

2. The method of claim 1, wherein said calibration feature is an end face of said articulated arm of said robot system.

3. The method of claim 1, wherein said calibration feature is a part of a calibration tool coupled to said end face of said robot system.

4. The method of claim 3, wherein said calibration feature is a sphere.

5. The method of claim 4, wherein said external measurement device is a coordinate measurement machine and said step of determining a measurement point corresponding to said position of said calibration feature includes the steps of:

collecting a calibration feature point cloud corresponding to an exterior of said sphere; and

determining a center of said sphere from said calibration feature point cloud, said measurement point corresponding to said center of said sphere.

6. The method of claim 1, wherein said external measurement device is a coordinate measurement machine.

7. The method of claim 1, wherein said step of adjusting said one or more parameters of robot system includes the steps of:

adjusting a kinematic model of said robot system; and

subsequently adjusting one or more joint values of said robot system.

8. The method of claim 1, wherein said first point cloud and said second point cloud are within a working volume of said robot system.

9. The method of claim 1, wherein the divots of the calibration template are generally spherical and configured to receive therein a correspondingly shaped sphere of the calibration feature.

10. A method of obtaining calibration data for a robot system having an articulated arm, the method comprising the steps of:

providing a calibration template having a plurality of calibration spots formed in the calibration template at predetermined fixed positions therein, said calibration spots defining divots in the calibration template, each of the calibration spots having a known position determined by an external coordinate measuring machine, the known positions forming a first point cloud in a first coordinate system;

commanding said articulated arm of said robot system to position a calibration feature coupled to the articulated arm at a first one of said calibration spots, the calibration feature having a shape which corresponds to and is received within said divots of the calibration template;

obtaining a first measurement point corresponding to an actual position of said calibration feature and said first measurement point being included in a second point cloud in a second coordinate system;

commanding said articulated arm of said robot system to position said calibration feature at a second one of said calibration spots;

obtaining a second measurement point corresponding to a second actual position of said calibration feature and said second measurement point being included in said second point cloud in said second coordinate system;

commanding said articulated arm of said robot system to position said calibration feature at a third one of said calibration spots;

obtaining a third measurement point corresponding to a third actual position of said calibration feature and said third measurement point being included in said second point cloud in said second coordinate system; and

adjusting one or more parameters of said robot system based on a comparison of said first point cloud and said second point cloud.

11. The method of claim 10, wherein said calibration feature is a sphere and said first measurement point is determined by the steps of:

while said calibration feature is positioned at said first one of said calibration spots, collecting a calibration feature point cloud corresponding to an exterior of said sphere; and

determining a center of said sphere from said calibration feature point cloud.

12. The method of claim 10, further comprising the steps of:

obtaining a first direction of said robot with said external coordinate measuring machine when said calibration feature is positioned at said first one of said calibration spots;

obtaining a second direction of said robot with said external coordinate measuring machine when said calibration feature is positioned at said second one of said calibration spots; and

obtaining a third direction of said robot with said external coordinate measuring machine when said calibration feature is positioned at said third one of said calibration spots.

13. The method of claim 12, further comprising:

providing said calibration feature with at least three spheres; and

wherein said step of obtaining a first direction of said robot with said external coordinate measuring machine includes the steps of;

collecting a first calibration feature point cloud corresponding to an exterior of a first sphere;

determining a center of said first sphere from said first calibration feature point cloud;

collecting a second calibration feature point cloud corresponding to an exterior of a second sphere;

determining a center of said second sphere from said second calibration feature point cloud;

collecting a third calibration feature point cloud corresponding to an exterior of a third sphere; and

determining a center of said third sphere from said third calibration feature point cloud, wherein said first direction is perpendicular to a plane defined by said center of said first sphere, said center of said second sphere, and said center of said third sphere.

14. The method of claim 10, wherein the first measurement point is determined independent of the position of the articulated arm of the robot system.

15. A method of obtaining calibration data for a robot system having an articulated arm, the method comprising the steps of:

providing a calibration template with a plurality of calibration spots in a working volume of said robot system, said calibration spots defining divots in the calibration template, said calibration spots being formed in the calibration template at predetermined fixed positions therein and having a known geometry forming a first point cloud in a first coordinate system as determined by an external measurement device;

moving said articulated arm of said robot system to position a calibration feature coupled to the articulated arm at each of said calibration spots of the calibration template, the calibration feature having a shape which corresponds to and is received within said divots of the calibration template;

recording a second plurality of points of a second point cloud in a second coordinate system, each of said second plurality of points corresponding to a position of said calibration feature at a respective calibration spot as determined by the robot system; and

adjusting one or more parameters of said robot system based on a comparison of said first point cloud and said second point cloud.

16. The method of claim 15, wherein said divots are formed in a support and said calibration feature is a sphere coupled to an end face of said articulated arm.

17. The method of claim 16, wherein said recording step includes the steps of:

placing said sphere in a first divot;

sensing when said sphere is contacting a wall of said first divot; and

storing said location of said sphere.

18. The method of claim 17, wherein said location of said sphere when in said first divot is a first point of said second plurality of points.

19. The method of claim 15, wherein said step of adjusting said one or more parameters of robot system includes the steps of:

adjusting a kinematic model of said robot system; and

subsequently adjusting one or more joint values of said robot system.

20. The method of claim 15, wherein the first point cloud includes at least three non-linear points and the second point cloud including at least three non-linear points.