Method of determining workpiece positions including coordinated motion

• US 6,243,621 B1
• Filed: 03/13/1998
• Issued: 06/05/2001
• Est. Priority Date: 03/13/1998
• Status: Expired due to Term

• Current Assignee: Fanuc Robotics America Incorporated (Fanuc Corporation)
• Original Assignee: Fanuc Robotics America Incorporated (Fanuc Corporation)
• Inventors: Tao, Jianming, Bolhouse, Robert A., Tsai, Jason
• Primary Examiner(s): Cuchlinski, Jr., William A
• Assistant Examiner(s): Marc, McDieunel, Marc, McDieunel
• Application Number:
  US09/039,114
• Time in Patent Office: 1,180 Days
• Field of Search: 700/245, 700/250, 700/253, 700/262, 700/186, 700/166, 700/259, 700/255, 700/64, 700/86, 318/568.11, 318/574, 219/124.34, 901/5, 901/10, 356/376, 356/375
• US Class Current: 700/245
• CPC Class Codes: B25J 9/1694 characterised by use of sensors other than normal servo-feedback from position, speed or acceleration sensors, perception control, multi-sensor controlled systems, sensor fusion
• CPC Class Codes: G05B 2219/40383 Correction, modification program by detection type workpiece
• CPC Class Codes: G05B 2219/40625 Tactile sensor

Abstract

A method of determining position information of a workpiece relative to a robot includes the ability to move the workpiece into a variety of orientations relative to the robot during the touch sensing location procedure. The position information is then used for performing a robot operation including coordinated motion. A coordinated reference frame is defined with respect to a moveable positioner that supports the workpiece. Known kinematic relationships between the positioner and the robot are used to control operation of the robot within the coordinated reference frame throughout the touch sensing location procedure. By moving the workpiece relative to the robot during the touch sensing location procedure, a greater variety of workpieces can be processed and relatively complicated workpiece configurations can be accurately determined. The robot operating parameters are modified according to the determined position information.

Claims

1. A method of determining a position of a workpiece relative to a robot having an arm supported by a base and a sensor supported on the robot arm where the workpiece is supported on a positioner that is movable relative to the robot with the positioner having a workpiece reference frame indicative of a location of the workpiece in a workspace of the robot, said method comprising the steps of:

(A) mounting the workpiece on the positioner such that the workpiece and the workpiece reference frame remains fixed relative to the positioner;

(B) orienting the positioner and the workpiece reference frame in a first orientation;

(C) determining the relative location of the robot to the first orientation of the positioner;

(D) moving the robot arm until the sensor contacts the workpiece near at least a first target point on the workpiece to determine an offset between an expected location of the first target point and an actual location of the first target point relative to the robot and then moving the sensor away from the workpiece;

(E) moving the positioner and the workpiece reference frame into a second orientation;

(F) determining the relative location of the robot to the second orientation of the positioner such that relative locations of both the expected and actual locations of the target points to the robot is maintained;

(G) moving the robot arm until the sensor contacts the workpiece near at least a second target point on the workpiece to determine an offset between an expected location of the second target point and an actual location of the second target point relative to the robot; and

(H) determining the shape and position of the workpiece relative to the robot using the actual locations of the first and second target points and determining the relative location of the robot to the workpiece reference frame.

2. The method of claim 1, further comprising the steps of predetermining an expected workpiece position relative to the robot;

and

determining a workpiece position offset value by comparing the determined position of step (H) to the expected workpiece position.

3. The method of claim 1, further comprising the steps of preprogramming a set of robot operation parameters that define a robot operation to be performed on the workpiece;

applying the offset value to the robot operation parameters to automatically adjust the preprogrammed robot operation parameters to conform to the determined workpiece position of step (H); and

performing the operation on the workpiece using the adjusted preprogrammed operation parameters after performing steps (A) through (H).

4. The method of claim 1, wherein step (H) includes determining a location and orientation of the workpiece relative to the robot to determine a geometric configuration of the workpiece while the workpiece is moved between different positions by the positioner.

5. The method of claim 1, wherein step (D) is performed by determining the location of the first target point on the workpiece relative to the robot.

6. The method of claim 5, wherein step (G) is performed by determining the location of the second target point on the workpiece relative to the robot.

7. The method of claim 1, wherein steps (D) and (G) are respectively performed by defining a search position for the robot relative to the robot;

defining a search direction for the robot to move from the search position relative to the workpiece reference frame.

8. The method of claim 1, further comprising determining the position of the workpiece relative to the robot and then determining an offset value indicative of a difference between the determined position and an expected workpiece position relative to the robot.

9. The method of claim 1, wherein step (D) includes contacting and locating a plurality of target points.

10. The method of claim 1, wherein step (G) includes contacting and locating a plurality of target points.

11. The method of claim 1, further comprising moving the positioner and the workpiece reference frame into a further plurality of orientations, contacting at least one target point in each orientation to locate the target points relative to the robot and then performing step (H).

12. The method of claim 11, further comprising determining the relative location of the robot to the positioner and the workpiece reference frame after each movement of the positioner into the further plurality of orientations such that the relative locations of each contacted target point to the robot is maintained.

13. A system for determining a position of a workpiece, comprising:

a robot base;

a robot arm supported by said base and being movable into a plurality of positions relative to said robot base;

a sensor supported on the robot arm;

a positioner located in a predetermined position relative to said robot base and movable into a plurality of orientations relative to said robot base with said positioner having a workpiece reference frame, said positioner including a device for fixedly supporting the workpiece on said positioner;

a controller that controls movement of said robot arm and said positioner such that said sensor contacts the workpiece near at least a first target point on the workpiece when said positioner is in a first orientation relative to said robot base and determines an offset value between an expected location of the first target point relative to said robot base and an actual location of the first target point relative to said robot base and said controller moving said positioner and said workpiece reference frame to a second orientation and determining the relative location of said robot base to the second orientation of said positioner such that the relative location of the first target point to said robot base is maintained, wherein said sensor contacts the workpiece near at least a second target point on the workpiece when said positioner is in the second orientation relative to said robot base and said controller determines an offset value between an expected location of the second target point relative to said robot base and an actual location of the second target point relative to said robot base and wherein said controller determines the position of the workpiece relative to said robot base, using the determined actual locations of the first and second target points.

14. The system of claim 13, wherein said controller includes a memory and wherein said memory includes a stored workpiece reference frame and a recorded expected position of the workpiece relative to said robot base and wherein said controller determines an offset value indicative of a difference between the determined location of the workpiece and said expected position relative to said robot base.

15. The system of claim 13, wherein said controller includes a memory having a plurality of approach positions stored relative to said robot base and an associated plurality of approach directions stored relative to said workpiece reference frame, said controller causing said robot arm to move into said approach positions and then to follow said approach direction such that said sensor contacts the workpiece near the target points.

16. The system of claim 13, wherein said workpiece reference frame moves with said positioner.

17. The system of claim 13, wherein said controller causes said positioner and said workpiece reference frame to move into said second orientation after said sensor has contacted the workpiece near said first target point and near at least one other target point while said positioner and said workpiece reference frame is in said first orientation and said controller causes said robot arm to move such that said sensor contacts said second target point after said positioner is moved into said second orientation.

18. The system of claim 13, wherein the controller determines a location and orientation of the workpiece relative to the robot base to determine a geometric configuration of at least a portion of the workpiece while the workpiece is moved between different positions by the positioner.

19. A method of determining a position of a workpiece relative to a robot having an arm supported by a base and a sensor supported on the arm, the workpiece being supported on a positioner that is movable relative to the robot with the positioner having a workpiece reference frame indicative of a location of the workpiece in a workspace of the robot, said method comprising the steps of:

mounting the workpiece on the positioner such that the workpiece remains fixed relative to the positioner and the workpiece reference frame;

orienting the positioner and the workpiece reference frame in a first orientation;

determining the relative location of the robot to the first orientation of the positioner;

moving the arm of the robot until the sensor determines a first target point on the workpiece to locate the first target point relative to the robot;

moving the positioner and the workpiece reference frame into a second orientation;

determining the relative location of the robot to the second orientation of the positioner such that the relative location of the first target point to the robot is maintained;

moving the arm of the robot until the sensor determines a second target point on the workpiece to locate a second target point relative to the robot; and

determining the locations of the first and second target points relative to the robot to determine a shape of the workpiece while the workpiece is moved between different positions by the positioner and determining the relative location of the robot to the workpiece reference frame.

20. The method as set forth in claim 19 wherein moving the arm of the robot is performed by;

defining a search position for the robot relative to the robot;

defining a search direction for the robot to move from the search position relative to the workpiece reference frame.

21. The method as set forth in claim 19 wherein moving the arm of the robot further includes contacting and locating a plurality of target points.

22. The method as set forth in claim 19 further including the step of moving the positioner and the workpiece reference frame into a further plurality of orientations, contacting at least one target point in each orientation to locate the target points relative to the robot.

23. The method as set forth in claim 22 further including the step of determining the relative location of the robot to the positioner and the workpiece reference frame after each movement of the positioner into the further plurality of orientations such that the relative locations of each contacted target point to the robot is maintained.

24. A system for determining a position of a workpiece, comprising:

a robot base;

a robot arm supported by said robot base and being movable into a plurality of positions relative to said robot base;

a sensor supported on the robot arm;

a positioner located in a predetermined position relative to said robot base and movable into a plurality of orientations relative to said robot base with said positioner having a workpiece reference frame,

a device mounted to said positioner for fixedly supporting the workpiece on said positioner;

a controller that controls movement of said robot arm and said positioner such that said sensor determines a first target point on the workpiece when said positioner is in a first orientation relative to said robot base, said controller moving said positioner and said workpiece reference frame to a second orientation and determining the relative location of the robot base to the second orientation of said positioner such that the relative location of the first target point to the robot base is maintained, said controller moving said robot arm such that said sensor determines a second target point on the workpiece when said positioner is in said second orientation relative to said robot base wherein said controller determines the position and the shape of the workpiece relative to said robot base using the first and second target points.

25. The system as set forth in claim 24 wherein said controller includes a memory and wherein said memory includes stored robot and workpiece reference frames.

26. The system as set forth in claim 24 wherein said controller includes a memory having a plurality of approach positions stored relative to said robot base and an associated plurality of approach directions stored relative to said workpiece reference frame, said controller causing said robot arm to move into said approach positions and then to follow said approach direction such that said sensor contacts the workpiece near the target points.

27. The system as set forth in claim 24, wherein said workpiece reference frame moves with said positioner.

28. The system as set forth in claim 24 wherein said controller causes said positioner and said workpiece reference frame to move into said second orientation after said sensor has contacted the workpiece at said first target point and at least one other target point while said positioner and said workpiece reference frame is in said first orientation and said controller causes said robot arm to move such that said sensor contacts said second target point after said positioner is moved into said second orientation.