ROBOTIC CALIBRATION METHOD

• US 20090076655A1
• Filed: 09/12/2008
• Published: 03/19/2009
• 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.
• Granted Patent: US 8,457,790 B2
• Time in Patent Office: Days
• 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:

commanding said articulated arm of said robot system to position a calibration feature at a plurality of commanded points, said plurality of commanded points collectively being a first point cloud;

for each of said commanded points, collecting with an external measurement device 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 collecting 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. A method of obtaining calibration data for a robot system having an articulated arm, the method comprising the steps of:

commanding said articulated arm of said robot system to position a calibration feature at a first point, said first point being included in a first point cloud in a first coordinate system;

obtaining a first measurement point with an external coordinate measuring machine, said 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 point, said second point being included in said first point cloud in said first coordinate system;

obtaining a second measurement point with said external coordinate measuring machine, said 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 point, said third point being included in said first point cloud in said first coordinate system;

obtaining a third measurement point with said external coordinate measuring machine, said 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.

10. The method of claim 9, 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 point 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 first measurement point corresponding to said center of said sphere.

11. The method of claim 9, 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 position;

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

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

12. The of claim 11, wherein said calibration feature includes a plurality of spheres and 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.

13. 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 forming a first point cloud in a first coordinate system;

moving said articulated arm of said robot system to position a calibration feature at each of said calibration spots;

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; and

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

14. The method of claim 13, wherein a coordinate measuring machine provides an indication of said first point cloud.

15. The method of claim 13, wherein said calibration spots are divots in a support and said calibration feature is a sphere coupled to an end face of said articulated arm.

16. The method of claim 15, 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.

17. The method of claim 16, wherein said location of said sphere when in said first divot is a first point of said second plurality of points.

18. The method of claim 13, 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.

19. 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 known geometry, said known geometry including a first point could;

moving said articulated arm of said robot system to contact said calibration template with a calibration feature produce 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.

20. The method of claim 19, wherein said calibration template includes at least one sphere of a known diameter which is included in said first point cloud.