Virtual actuator control. - Jerry E. Pratt; Ann Torres; Peter Dilworth; Gill A. Pratt (IROS, 1996)

Virtual Model Control: An Intuitive Approach for Bipedal Locomotion. - Jerry E. Pratt; Chee-Meng Chew; Ann Torres; Peter Dilworth; Gill A. Pratt (Int. J. Robotics Res., 2001)