A Kinematic Calibration Technique for Robotic Manipulators with Multiple Degrees of Freedom

Robotic manipulators are sold with reference to repeatability, but the manufacturers rarely quote figures for accuracy. The repeatability figures for many small/medium sized industrial 5 degree or 6 degree of freedom (5/6DoF) arms are on the scale of 20 mu m, which is certainly impressive. But, this is not a measure of accuracy it is a measure of whether the arm will return to the same requested position again. As the paper will reveal, we encountered accuracy nearly two orders of magnitude worse than the repeatability metric. Our work on integrating 2D and 3D imaging systems with robotic manipulators for high precision interaction with 3D objects identified the requirement to determine the level of intrinsic/out of the box errors. This is in order to prevent potential collisions when automatically interacting at close proximity with any object in an unknown orientation where typical teach pendent or other prior correction is not applicable. In addition, understanding how to derive accurate calibration data allowed us to develop an approach for precise kinematic re-calibration of the manipulator.