Automatic calibration method for robot systems using a vision sensor
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 tcp T 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.
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 tcp T 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 R T t of the tool coordinate system with respect to a robot coordinate system based on the transformation matrix tcp T 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 R T 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 O T 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 O T 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 tcp T 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 tcp T 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 tcp T 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 tcp T t and the second transformation matrix tcp T 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 tcp T t and the second transformation matrix tcp T t as an overall transformation matrix tcp T 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 tcp T 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 tcp T t corresponding to one target point; and
determining an overall transformation matrix tcp T t by using the least squares method on the plurality of transformation matrices tcp T 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.