This study proposes a new control that stabilizes a three-dimensional (3D) passive walker without torque input at knees and ankles joints by using entrainment and a mechanical oscillator. It is difficult to stabilize a 3D biped passive walker in different environments because the range of initial conditions for stable walking is limited, so we designed a 3D biped passive walker as a passive walking platform by considering the results of human gait analysis to make the success of passive walking high. The stability of this platform was analytically determined by analyzing the frontal movement limit cycle. In the new control, the frontalmovement period is synchronized with the swing-leg period by a mechanical oscillator on the top of the walker. The mechanical oscillator controller generates a target path to synchronize oscillatormovement with swing-leg movement using frequency entrainment. The walker is stabilized when the frontal movement period was synchronized with the swing-leg period by periodic input generated by the mechanical oscillator. It was experimentally found consequently that the walker was stabilized on different slopes and flat floors.

1. [1] A. Goswami, B. Espiau, and A. Keramane, “Limit Cycles in a Passive Compass Gait Biped and Passivity-Mimicking Control Laws,” J. of Autonomous Robot, Vol.4, No.3, pp. 273-286, 1997.
2. [2] M. Garcia, A. Chatterjee, and A. Ruina, “Efficiency, Speed and Scaling of Two-Dimensional Passive-Dynamic Walking,” Dynamics and Stability of Systems, Vol.15, No.2, pp. 75-99, 2000.
3. [3] K. Osuka, “Passive Dynamic Walking as base of Walking Mechanics,” Systems, control and information, Vol.4, No.10, pp. 393-398, 2005.
4. [4] Y. Ikemata, A. Sano, and H. Fujimoto, “Generation and Local Stabilization of Fixed Point Based on a Stability Mechanism of Passive Walking,” J. of the Robotics Society of Japan, Vol.24, No.5, pp. 632-639, 2006.
5. [5] F. Asano and Z. Luo, “Underactuated virtual passive dynamic walking using rolling effect of semicircular feet (1) on driving mechanisms of compass-like models,” J. of the Robotics Society of Japan, Vol.25, No.4, pp. 556-577, 2007.
6. [6] S. H. Collins, M. Wisse, and A. Ruina, “A three-dimensional passive-dynamic walking robot with two legs and knees,” The Int. J. of Robotics Research, Vol.20, No.7, pp. 607-615, 2001.
7. [7] A. D. Kuo, “Stabilization of lateral motion in passive dynamic walking,” The Int. J. of Robotics Research, Vol.18, No.9, pp. 917-930, 1999.
8. [8] S. Suzuki and M. Hachiya, “Experimental Study on Stabilization of a Three-Dimensional Biped Passive Walking Robot,” J. of the Society of Biomechanisms Vol.32, No.4, pp. 239-246, 2008.
9. [9] M. Hachiya and S. Suzuki, “Stabilization of a Biped Quasi Passive Walking Robot via Periodic Input,” J. of the Society of Biomechanisms, Vol.33, No.1, pp. 57-63, 2009.
10. [10] K. Osuka and K. Kirihara, “Motion Analysis and Experiment of Passive Walking Robot Quartet II,” J. of the Robotics Society of Japan, Vol.18, No.5, pp. 121-126, 2000.
11. [11] H. Kajiwara, Y. Hashimoto, and T. Tsuchiya, “Motion Control of a Pendulum via Periodic Input,” Trans. of the Japan Society of Mechanical Engineers, C, Vol.67, No.633, pp. 3454-3460, 2001.
12. [12] H. Kajiwara, Y. Hashimoto, T. Matsuda, and T. Tsuchiya, “Control of Swing Using Entrainment,” J. of the Robotics Society of Japan, Vol.17, No.4, pp. 520-525, 1999.
13. [13] M. Wisse, “Three additions to passive dynamic walking; actuation, an upper body, and 3D stability,” Int. J. of Humanoid Robotics, Vol.2, No.4, pp. 459-478, 2005.