Automatic calibration method for robot systems using a vision sensor

• US 10,112,301 B2
• Filed: 08/10/2016
• Issued: 10/30/2018
• Est. Priority Date: 02/11/2014
• Status: Active Grant

• Current Assignee: TE Connectivity Corporation (TE Connectivity Ltd. (United Kingdom))
• Original Assignee: Tyco Electronics Company Limited (TE Connectivity Limited), TE Connectivity Corporation (TE Connectivity Ltd. (United Kingdom))
• Inventors: Deng, Yingcong, Zhang, Dandan, Lu, Roberto Francisco-yi, Hu, Lvhai
• Primary Examiner(s): Figueroa, Jaime
• Application Number:
  US15/233,440
• Publication Number:
  US 20160346932A1
• Time in Patent Office: 811 Days
• Field of Search: 700245, 700254
• CPC Class Codes: B25J 9/1692 Calibration of manipulator
• CPC Class Codes: G05B 2219/39011 Fixed camera detects deviation end effector from reference on workpiece, object
• CPC Class Codes: G05B 2219/39026 Calibration of manipulator while tool is mounted
• CPC Class Codes: G05B 2219/40557 Tracking a tool, compute 3-D position relative to camera

Abstract

An automatic calibration method for a robot system is disclosed. The automatic calibration method for a robot system includes the steps of calibrating a sensor and a sensor coordinate system of the sensor with respect to a world coordinate system, controlling a robot under the guidance of the sensor to move a point of a tool mounted on the robot to reach a same target point with a plurality of different poses, the point of the tool in a tool coordinate system, and calculating a transformation matrix ^tcpT_t of the tool coordinate system with respect to a tool center point coordinate system based on pose data of the robot at the same target point.

Claims

1. An automatic calibration method for a robot system, comprising:

calibrating a sensor and a sensor coordinate system of the sensor with respect to a world coordinate system;

controlling a robot under the guidance of the sensor to move a point of a tool mounted on the robot to reach a same target point with a plurality of different poses, the point of the tool being in a tool coordinate system; and

calculating a transformation matrix ^tcpT_t of the tool coordinate system with respect to a tool center point coordinate system based on pose data of the robot at the same target point.

2. The automatic calibration method for a robot system according to claim 1, wherein the calibrating step is performed by means of a calibration plate.

3. The automatic calibration method for a robot system according to claim 1, wherein the controlling step includes performing a closed-loop feedback control on the robot until a position error between an actual position of the point of the tool sensed by the sensor and a target position of the target point becomes zero.

4. The automatic calibration method for a robot system according to claim 3, further comprising calculating a transformation matrix ^RT_t of the tool coordinate system with respect to a robot coordinate system based on the transformation matrix ^tcpT_t.

5. The automatic calibration method for a robot system according to claim 4, further comprising controlling the robot under the guidance of the sensor to move the tool to reach a known target pose by closed-loop feedback control, until a pose error between an actual pose of the tool sensed by the sensor and the target pose becomes zero.

6. The automatic calibration method for a robot system according to claim 5, further comprising calculating a transformation matrix T_R of the robot coordinate system with respect to the world coordinate system based on a transformation matrix T of the known target pose with respect to the world coordinate system and the transformation matrix ^RT_t.

7. The automatic calibration method for a robot system according to claim 6, further comprising determining a transformation matrix T_O of an object to be machined by the tool with respect to the world coordinate system using the sensor.

8. The automatic calibration method for a robot system according to claim 7, further comprising determining a transformation matrix ^OT_P of a target region on the object with respect to an object coordinate system using the sensor.

9. The automatic calibration method for a robot system according to claim 8, wherein the transformation matrix ^OT_P is constant.

10. The automatic calibration method for a robot system according to claim 9, wherein a pose of the object with respect to the world coordinate system is constant.

11. The automatic calibration method for a robot system according to claim 9, wherein a pose of the object with respect to the world coordinate system is continuously variable.

12. The automatic calibration method for a robot system according to claim 1, wherein the sensor is a vision sensor or a laser tracker.

13. The automatic calibration method for a robot system according to claim 12, wherein the sensor is a camera having calibrated parameters including at least one of a focal length, a lens distortion, a pixel ratio, and a geometric relationship between a chip pose and a lens pose of the camera.

14. The automatic calibration method for a robot system according to claim 13, wherein the robot system has a plurality of cameras.

15. The automatic calibration method for a robot system according to claim 14, wherein the robot system has a plurality of robots.

16. The automatic calibration method for a robot system according to claim 13, wherein the camera visually guides the robot to machine an object.

17. The automatic calibration method for a robot system according to claim 1, further comprising re-identifying the transformation matrix ^tcpT_t automatically and immediately after the tool is replaced by a new tool.

18. An automatic calibration method for a robot system, comprising:

calibrating a sensor and a sensor coordinate system of the sensor with respect to a world coordinate system;

controlling a robot under the guidance of the sensor to move a point of a tool mounted on the robot to reach a same first target point with a first plurality of different poses, the point of the tool in a tool coordinate system;

calculating a first transformation matrix ^tcpT_t of the tool coordinate system with respect to a tool center point coordinate system based on pose data of the robot at the first target point;

controlling the robot under the guidance of the sensor to move the point of the tool to reach a same second target point with a second plurality of different poses;

calculating a second transformation matrix ^tcpT_t of the tool coordinate system with respect to a tool center point coordinate system based on pose data of the robot at the second target point; and

determining whether an error between the first transformation matrix ^tcpT_t and the second transformation matrix ^tcpT_t is within an allowable range, returning to the calibrating step if the error is not within the allowable range, and using an average of the first transformation matrix ^tcpT_t and the second transformation matrix ^tcpT_t as an overall transformation matrix ^tcpT_t if the error is within the allowable range.

19. An automatic calibration method for a robot system, comprising:

calibrating a sensor and a sensor coordinate system of the sensor with respect to a world coordinate system;

controlling a robot under the guidance of the sensor to move a point of a tool mounted on the robot to reach a plurality of target points with a plurality of different poses, the point of the tool being in a tool coordinate system;

calculating a plurality of transformation matrices ^tcpT_t of the tool coordinate system with respect to a tool center point coordinate system based on pose data of the robot at the plurality of target points, each transformation matrix ^tcpT_t corresponding to one target point; and

determining an overall transformation matrix ^tcpT_t by using the least squares method on the plurality of transformation matrices ^tcpT_t.

20. The automatic calibration method for a robot system of claim 19, wherein the plurality of target points is at least three target points.