Robot and 3D-sensor calibration using a planar part of a robot hand

A generally applicable method of calibrating robot coordinates and three-dimensional sensor coordinates without using a calibration tool is proposed. Most calibration methods require an elaborate calibration tool, such as a marker board with a black and white pattern. However, making an accurate calibration board and making observations of the board attached to/grasped by/touched by a robot hand are both troublesome tasks. Aiming at reducing the labor and time required for calibration and enabling on-line registration, we propose using the robot hand itself as a “calibration object” without making any special marks. Because the position and orientation of the hand as an end-effector are known in the robot coordinates, the calibration problem is replaced by the problem of registering the geometric model of the hand to observed three-dimensional data to determine its location in the vision coordinates. To robustly carry out the registration for variously shaped hands, only a planar part of the hand is used for the registration in the iterative closest-point framework. To realize least manual interaction, a two-step approach that consists of registration with manual interaction and accuracy improvement using multiple observations is taken. The practical usefulness of the proposed method was examined using four differently shaped hands.