Tool center point calibration apparatus and method

• US 5,457,367 A
• Filed: 08/06/1993
• Issued: 10/10/1995
• Est. Priority Date: 08/06/1993
• Status: Expired due to Term

• Current Assignee: Cycle Time Corporation
• Original Assignee: Cycle Time Corporation
• Inventors: Thorne, Henry F.
• Primary Examiner(s): IP, SHIK LUEN PAUL
• Application Number:
  US08/103,459
• Time in Patent Office: 795 Days
• Field of Search: 318/560-646, 395/80-90, 901/3.5, 901/7, 901/9, 901/12, 901/13, 901/15, 901/23, 901/47, 73/15, 73/4 R, 73/628, 73/627, 73/587, 367/906, 250/560, 250/561, 356/375, 414/273, 414/730, 118/712, 118/323, 118/669
• US Class Current: 318/568.11
• CPC Class Codes: B25J 9/1692 Calibration of manipulator
• CPC Class Codes: G05B 2219/50133 With optical beam, tool crosses beam

Abstract

The present invention provides a tool center point calibration apparatus and method for accurately determining appropriate tool center points for a robot to allow for proper tool alignment and correction of robot programs. The calibration apparatus includes a calibration beam on a single line.

Claims

1. A method for tool calibration for a robot with a robot face plate having a tool with a tip axis, said method comprising the steps of:

a) positioning a calibration means within the robot envelope, wherein said calibration means includes a beam having a centerline positioned along a single line;

b) positioning said tool tip to an initial position within the path of said beam;

c) obtaining values of said robot face plate with said tool tip positioned within said beam path;

d) rotating said tool about said tip axis to at least a second position with said tool tip positioned within said beam path;

e) obtaining values of said robot face plate with said tool tip positioned at said at least second position; and

f) calculating a tool center point based upon said obtained values.

2. The method of claim 1 wherein said robot is a spot welding robot.

3. The method of claim 1 further comprising the step of:

positioning said calibration means substantially parallel to a robot axis wherein the robot is adapted to reach said calibration means with said tool tip axis substantially parallel to a robot axis.

4. The method of claim 1 wherein said positioning of said tool tip to said initial position comprises:

positioning said tool tip in an arbitrary location within said beam path;

profiling said tool tip with said beam by moving said tool tip relative to said beam, calculating said initial position based upon said profile, wherein said initial position is in a midpoint of said tool tip; and

positioning said tool tip at said initial position.

5. The method of claim 4 wherein said initial position is within a substantially cylindrical portion of said tool tip.

6. The method of claim 5 wherein said tool tip profiling comprises:

sequentially determining the cross-sectional lengths of said tool tip in planes parallel to the beam, wherein a plurality of substantially similar cross-sectional lengths in adjacent planes indicates said substantially cylindrical portion of said tool tip.

7. A method for tool calibration for a spot welding robot having a robot face plate with a welding tool attached to said robot face plate and including a pair of opposed tool tips positioned along a tool axis, said method comprising the steps of:

a) positioning a calibration means within the robot envelope, wherein said calibration means includes a beam having a centerline positioned along a single line;

b) positioning a first of said pair of opposed tool tips within the path of said beam;

c) profiling said first tool tip by moving said welding tool relative to said beam;

d) positioning said first tool tip to an initial position based upon said profiling where said beam path intersects said first tool tip at a center point positioned at a midpoint of a substantially cylindrical portion of said first tool tip;

e) calculating an initial approximation for said center point position of said first tool tip;

f) obtaining values of said robot face plate with said tool tip at said initial position;

g) rotating said welding tool from said initial position to a second position about an axis substantially perpendicular to said calibration means to a second position;

h) obtaining values of said robot face plate with said tool tip at said second position;

i) rotating said welding tool about said axis substantially perpendicular to said calibration means to a third position;

j) obtaining values of said robot face plate with said tool tip at said third position;

k) rotating said welding tool about an axis substantially parallel to said calibration means to a fourth position;

l) obtaining values of said robot face plate with said tool tip at said fourth position;

m) calculating said center point position of said first tip based upon said obtained values;

n) repeating steps b through m for the second of said pair of tool tips; and

o) calculating said tool centerline which is along the line extending between the center points of said pair of tool tips.

8. The method of claim 7 wherein said tool tip profiling comprises:

sequentially determining the cross-sectional lengths of said tool tip in planes parallel to the beam, wherein a plurality of substantially similar cross-sectional lengths in adjacent planes indicates said substantially cylindrical portion of said tool tip.

9. The method of claim 8 wherein four substantially similar cross-sectional lengths of said tool tip during profiling indicate the presence of said substantially cylindrical portion.

10. The method of claim 7 further comprising the step of:

p) aligning said tool based upon the location of said centerline, wherein steps b through o are repeated following said tool alignment.

11. The method of claim 7 wherein following said centerline calculation, said pair of tool tips is profiled to find a narrowest profile between said center points of said first and said second tool tips wherein a tool center point is calculated along said narrowest profile.

12. The method of claim 11 wherein said tool center point is the intersection of the plane of said narrowest profile and said centerline.

13. The method of tool calibration for a robot comprising the steps of:

a) positioning a calibration means with the robot envelope, wherein said calibration means includes a beam having a centerline positioned along a single line;

b) positioning said tool within the path of said beam;

c) profiling said tool by moving said tool relative to said beam to sequentially determine cross-sectional lengths of said tool in planes parallel to said calibration means, wherein a plurality of substantially similar cross-sectional lengths indicates a substantially cylindrical portion of said tool;

d) calculating a midpoint of said tool along said substantially cylindrical portion; and

e) aligning said tool based upon said calculated midpoint.

14. The method of claim 13 wherein four substantially similar cross-sectional lengths of said tool tip during profiling indicate the presence of said substantially cylindrical portion.

15. The method of claim 14 wherein four additional cross-sectional lengths are calculated after four substantially similar cross-sectional lengths are determined.