Autonomous Calibration

Extensive work has been performed in kinematic calibration, joint torque sensor calibration, and inertial parameter estimation. The focus has been on developing methods which require minimal human involvement, thereby promoting robot autonomy.

Open-Loop Kinematic Calibration

Originally, research was done on open-loop calibration methods, in which a metrology system is used to measure endpoint pose. The concentration was on methods that robustly fit a coordinate system to a set of markers on a calibration frame:

Hollerbach, J.M., and Bennett, D.J., ``Automatic kinematic calibration using a motion tracking system,'' in: Robotics Research: the Fourth International Symposium, R. Bolles and B. Roth, eds., MIT Press, Cambridge, Mass., 1988, pp. 191-198.

A novel open-loop method was the use of a high-accuracy triaxial accelerometer:

Canepa, G., Hollerbach, J.M., and Boelen, A.J.M., ``Kinematic calibration by means of a triaxial accelerometer,'' Proc. IEEE Intl. Conf. Robotics and Automation, San Diego, May 8-13, 1994, pp. 2776-2782.

Another novel open-loop method was the use of an external force-torque sensor to calibrate a manipulator that is totally immobile:

Bennett, D.J., Hollerbach, J.M., and Henri, P.D., ``Kinematic calibration by direct estimation of the Jacobian matrix,'' Proc. IEEE Intl. Conf. Robotics and Automation, May 10-15, 1992, Nice, France, pp. 351-357.
Hollerbach, J.M., Giugovaz, L., Buehler, M., and Xu, Y., ``Screw axis measurement for kinematic calibration of the Sarcos Dextrous Arm,'' Proc. IEEE/RSJ Intl. Conf. on Intelligent Robots and Systems, July 26-30, 1993, Yokohama, Japan, pp. 1617-1621.

The human hand was calibrated for purposes of teleoperation and virtual reality by a combination of a master glove and Optotrak system:

Rohling, R., and Hollerbach, J.M., `` Modeling and parameter estimation of the human index finger,'' Proc. IEEE Intl. Conf. Robotics and Automation, San Diego, May 8-13, 1994, pp. 223-230.
Rohling, R., and Hollerbach, J.M., ``Calibrating the human hand for haptic interfaces,'' Presence: Teleoperators and Virtual Environments, 2, no. 4, 1993, pp. 281-296.

A study was done on the relative accuracy of the Optotrak versus a mechanical arm for purposes of image-guided surgery:

Rohling, R., Munger, P., Hollerbach, J.M., and Peters, T., ``Comparison of relative accuracy between a mechanical and an optical position tracker for image-guided neurosurgery,'' 1st Intl. Symp. Medical Robotics and Computer Assisted Surgery, Pittsburgh, Sept. 22-24, 1994, pp. 277-282.
Rohling, R., Munger, P., Hollerbach, J.M., and Peters, T., ``Comparison of relative accuracy between a mechanical and an optical position tracker for image-guided neurosurgery,'' J. Image Guided Surgery, 1, 1995, pp. 30-34.

Closed-Loop Kinematic Calibration

Subsequently, a new method termed closed-loop calibration was discovered that obviated the need for a metrology system. By forming a manipulator into a mobile closed kinematic chain, the manipulator could be calibrated merely by using joint angle sensors:

Bennett, D.J., and Hollerbach, J.M., ``Autonomous calibration of single-loop closed kinematic chains formed by manipulators with passive endpoint constraints,'' IEEE Trans. Robotics and Automation, 7, 1991, pp. 597-606.

This technique has been applied in various single-loop settings:

A stereo camera system could be calibrated simultaneously with a robot arm:
Bennett, D.J., Hollerbach, J.M., and Geiger, D., ``Autonomous robot calibration for hand-eye coordination,'' Intl. J. Robotics Research, 10, 1991, pp. 550-559.
A finger and thumb of the Utah/MIT Dextrous Hand were calibrated together:
Bennett, D.J., and Hollerbach, J.M., ``Closed-loop kinematic calibration of the Utah-MIT Hand,'' in: Experimental Robotics 1 --- The First International Symposium, V. Hayward and O. Khatib, eds., Springer-Verlag, N.Y., 1990, pp. 539-552.
A closed-loop method was developed which merely requires touching a planar surface:
Ikits, M., and Hollerbach, J.M., `` Kinematic calibration using a plane constraint,'' Proc. IEEE Intl. Conf. Robotics and Automation, Albuquerque, April 20-25, 1997, pp. 3191-3196.
A closed-loop kinematic calibration method was applied to the Sarcos Dextrous Arm.
Giugovaz, L., and Hollerbach, J.M., ``Closed-loop kinematic calibration of the Sarcos Dextrous Arm,'' Proc. IEEE/RSJ Intl. Conf. on Intelligent Robots and Systems, Munich, Germany, Sept. 12-16, 1994, pp. 329-334.

The closed-loop method has also been extended to multiple closed loops:

Hollerbach, J.M., and Lokhorst, D.M., ``Closed-loop kinematic calibration of the RSI 6-DOF Hand Controller,'' IEEE Trans. Robotics and Automation, 11, 1995, pp. 352-359.
Nahvi, A., Hollerbach, J.M., and Hayward, V., `` Closed-loop kinematic calibration of a parallel-drive shoulder joint,'' Proc. IEEE Intl. Conf. Robotics and Automation, San Diego, May 8-13, 1994, pp. 407-412.

Implicit Loop Method and the Calibration Index

More recently, a new method of kinematic calibration, termed the implicit loop method, has been pursued in collaboration with Dr. Charles Wampler of GM Research Laboratories. This method unifies the open and closed loop methods. The Calibration Index was put forth to succinctly categorize the different methods.

Hollerbach, J.M., and Nahvi, A., ``Robot calibration via the Implicit Loop Method,'' Experimental Robotics IV---The Fourth International Symposium, (June 30-July 2, 1995, Palo Alto, CA) O. Khatib and J.K. Salisbury, eds., Springer, London, 1997, pp. 274-282.
Hollerbach, J.M., and Wampler, C.W., `` The calibration index and the role of input noise in robot calibration,'' Robotics Research: The Seventh International Symposium, G. Giralt and G Hirzinger, eds., Springer-Verlag, London, 1996, pp. 558-568.
Hollerbach, J.M., and Wampler, C.W., ``A taxonomy of kinematic calibration methods,'' Intl. J. Robotics Research, 14, 1996, pp. 573-591.
Hollerbach, J.M., and Wampler, C.W., `` The calibration index and the role of input noise in robot calibration,'' Robotics Research: The Seventh International Symposium, G. Giralt and G Hirzinger, eds., Springer-Verlag, London, 1996, pp. 558-568.
Wampler, C.W., Hollerbach, J.M., and Arai, T., ``An Implicit Loop Method for kinematic calibration and its application to closed-chain mechanisms,'' IEEE Trans. Robotics and Automation, 11, 1995, pp. 710-724.

The implicit loop method explicity accounts for input noise (from the joint angles), and utilizes a priori information.

Joint Torque Sensor Calibration and Gravity Compensation

Research was initially done on determining the inertial parameters of a manipulator during a trajectory:

Atkeson, C.G., An, C.H., and Hollerbach, J.M., ``Estimation of inertial parameters of manipulator links and loads,'' Intl. J. Robotics Research, 5 no. 3, 1986, pp. 101-119.

Recent work has focused on joint torque sensor calibration and gravity compensation in force-reflecting teleoperation.

An autonomous method for joint torque sensor calibration has been developed, for "in vivo" calibration.
Ma, D., Hollerbach, J.M., and Xu, Y., ``Gravity based autonomous calibration for robot manipulators,'' Proc. IEEE Intl. Conf. Robotics and Automation, San Diego, May 8-13, 1994, pp. 2763-2768.
It has been shown that the same data for joint torque sensor calibration can be applied towards determining the mass parameters for the purposes of gravity compensation:
Ma, D., and Hollerbach, J.M., "Identifying mass parameters for gravity compensation and automatic torque sensor calibration,'' Proc. IEEE Intl. Conf. Robotics and Automation, Minneapolis, April 22-28, 1996, pp. 661-666.