S. Arimoto, “A class of quasi-natural potentials and Hyper-stable PID servo-loops for nonlinear robotic system,” Transactions of the Society of Instrument and Control Engineers, Vol. 30, No. 9, pp. 1005–1012, September 1994.
 R. Ortega, A. Loria, and R. Kelly, “A semiglobally stable output feedback PI2D regulator for robot manipulators,” IEEE Transactions on Automatic Control, Vol. 40, No. 8, pp. 1432–1436, August 1995.
 B. S. Liu and F. C. Lin, “A semiglobally stable PD-IPD regulator for robot manipulators,” to be published in 2009 International Conference on Measuring Technology and Mechatronics Automation proceeding.
 B. S. Liu and B. L. Tian, “A globally stable PD-INP-D regulator for robot manipulators,” to be published in 2009 International Conference on Information Technology and Computer Science proceedings.