Manipulator Error Compensation by Fiducial Motion Transformation

Manipulator Error Compensation by Fiducial Motion Transformation

      Disclosed is a software method for calibrating accurately
the motions made by an imperfect manipulator.  Also, a software
method for applying the calibrated motion transformation to rigid
bodies affixed to the manipulator, or the the manipulator itself.  In
addition, a software method for measuring the center of rotation of a
rigid body by calibrating its motion as described above.  Finally, an
extension of this disclosure to interpolate or extrapolate the
results of the calibration to manipulator goals other than the goals
used during calibration.

      This method consists of measuring a set of fiducials attached
to or held by the manipulator, typically by viewing with a vision
system.  While only three fiducials are needed, more may be used to
improve the accuracy.  The fiducials are measured, and a
transformation describing them is made.  The nominal manipulator
motion is performed, and the fiducials are measured again.  A second
transformation is made, and a resulting motion calibration is made by
multiplying the inverse of the first transformation by the second
transformation.  This calibration transformation can then be used to
calculate the actual motion of an object attached to the manipulator
when the calibrated motion is made.  The limit of the precision then
becomes the repeatability of the robot.  For example, a part that is
inspected and located in the manipulator's end o...