  We present a robot kinematic calibration method that combines complementary
calibration approaches: self-contact, planar constraints, and self-observation.
We analyze the estimation of the end effector parameters, joint offsets of the
manipulators, and calibration of the complete kinematic chain (DH parameters).
The results are compared with ground truth measurements provided by a laser
tracker. Our main findings are: (1) When applying the complementary calibration
approaches in isolation, the self-contact approach yields the best and most
stable results. (2) All combinations of more than one approach were always
superior to using any single approach in terms of calibration errors and the
observability of the estimated parameters. Combining more approaches delivers
robot parameters that better generalize to the workspace parts not used for the
calibration. (3) Sequential calibration, i.e. calibrating cameras first and
then robot kinematics, is more effective than simultaneous calibration of all
parameters. In real experiments, we employ two industrial manipulators mounted
on a common base. The manipulators are equipped with force/torque sensors at
their wrists, with two cameras attached to the robot base, and with special end
effectors with fiducial markers. We collect a new comprehensive dataset for
robot kinematic calibration and make it publicly available. The dataset and its
analysis provide quantitative and qualitative insights that go beyond the
specific manipulators used in this work and apply to self-contained robot
kinematic calibration in general.
