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Advanced Robotics, Vol. 19, No. 7, pp. 773– 795 (2005)  VSP and Robotics Society of Japan 2005.

Full paper Virtual impedance adjustment in unconstrained motion for an exoskeletal robot assisting the lower limb
SUWOONG LEE ∗ and YOSHIYUKI SANKAI
Graduate School of Systems and Information Engineering, University of Tsukuba, 1-1-1 Tennodai, Tsukuba, Ibaraki 305-8573, Japan Received 11 May 2004; accepted 12 August 2004 Abstract—The objective of this paper is to establish the criteria for adjusting the virtual impedance of an exoskeletal robot for the lower limb in order to minimize the operator’s physical stress in unconstrained motion. The exoskeletal robot HAL (Hybrid Assistive Limb)-3 which we developed for assisting the motor function of the lower limb was used for experiments in this research. To accomplish the objective (i) the physical parameters around the joint of HAL-3 were identified and (ii) the relationships between the virtual impedance values and the physical stress of operators were examined through experiments for swinging motions of the lower leg. The physical stress was evaluated with myoelectricity, the musculoskeletal moment of the operator and the operator’s feelings during the experimental motion. As a result, we found that the physical stress tended to decline with the decrease of virtual inertia and virtual Coulomb friction, and to increase slightly with the decrease of virtual gravitational moment. The decrease of virtual viscous friction made the physical stress increase gradually after it declined to a trough during the positive virtual viscous friction. Based on the results, we could establish the criteria for adjusting the virtual impedance for minimizing the operator’s physical stress in unconstrained motion. Keywords: Assist; virtual impedance; physical stress; parameter identification; unconstrained motion.

1. INTRODUCTION

Exoskeletal robot suits aimed at supporting the works of labor

References: 1. J. Okamura, H. Tanaka and Y. Sankai, EMG-based prototype powered assistive system for walking aid, in: Proc. Asian Symp. on Industrial Automation and Robotics (ASIAR ’99), Bangkok, pp. 229–234 (1999). 2. T. Nakai, S. Lee, H. Kawamoto and Y. Sankai, Development of power assistive leg for walking aid using myoelectricity and linux, in: Proc. Asian Symp. on Industrial Automation and Robotics, Bangkok, pp. 1295–1310 (2001). 3. S. Lee and Y. Sankai, Power assist control for walking aid with HAL-3 based on EMG and impedance adjustment around knee joint, in: Proc. IEEE/RSJ Int. Conf. on Intelligent Robots and Systems, Lausanne, pp. 1499–1504 (2002). 4. H. Dankowicz, J. Adolfsson and A. B. Nordmark, Repetitive gait of passive bipedal mechanism in a three-dimensional environment, J. Biomechan. Eng. 123, 40–46 (2001). 5. T. Tsuji, Y. Tanaka and M. Kaneko, Tracking control properties of human-robot systems, in: Proc. 1st Int. Conf. on Information Technology in Mechatronics, Istanbul, pp. 77–83 (2001). 6. Y. Yamada, H. Konosu, T. Morizono and Y. Umetani, Proposal of skill-assist: a system of assisting human workers by reflecting their skills in positioning tasks, in: Proc. IEEE Int. Conf. on Systems, Man and Cybernetics, Tokyo, pp. (IV)11–(IV)16 (1999). 7. S. Lee and Y. Sankai, Natural frequency-based power assist control for lower body with HAL-3, in: Proc. IEEE Int. Conf. on Systems, Man, and Cybernetics, Washington, DC, pp. 1642–1647 (2003). 8. E. Park and S. G. Meeek, Fatigue compensation of the electromyographic signal for prosthetic control and force estimation, IEEE Trans. Biomed. Eng. 40, 1019–1023 (1993). 9. M. S. Ben-Lamine, S. Shibata, K. Tanaka and A. Shimizu, Impedance characteristics of robots considering human feelings, JSME Int. J. (Ser. C) 40, 309–315 (1997). 10. H. I. Krebs, N. Hogan, M. L. Aisena and B. T. Volpe, Robot-aided neurorehabilitaion, IEEE Trans. Rehabilitation Eng. 6, 75–86 (1998). ABOUT THE AUTHORS Suwoong Lee received the BS degree in Electrical Engineering from DongA University, Korea in 1999, and the MS degree in Intelligent Interaction Technologies from the University of Tsukuba, Japan in 2002. He has been pursuing the PhD degree in the Doctoral Program in Intelligent Interaction Technologies, University of Tsukuba since 2002. His research interests include biomechanics, biorobotics and the human–machine interface including assistive exoskeletal robots and haptic devices. He is a member of the Robotics Society of Japan, and the Japan Society of Mechanical Engineers. Virtual impedance adjustment in unconstrained motion 795 Yoshiyuki Sankai received the PhD degree in engineering from the University of Tsukuba, Japan in 1987. He was a JSPS research fellow, Assistant Professor, Associate Professor and Professor of Institute of Systems and Engineering in the University of Tsukuba, and a Visiting Professor of Baylor College of Medicine in USA. Currently, he is a professor and director of the prioritized research area ‘New Robotics Frontier: Cybernics’, Graduate School of System and Information Engineering in University of Tsukuba, Japan. His research interests include Robot Suit HAL (Hybrid Assistive Limb), the next generation artificial heart, humanoid Control, Bio-Medical Science, Network Medicine as related fields of Cybernics. He received a Grant of the Japanese Society for Artificial Organs (JSAO), Awards from American Society for Artificial Organs, International Society for Artificial Organs, International Society for Rotary Blood Pump with his students and so on. He was/is a president of Japan Society of Embolus Detection and Treatment, a chair of International Journal of the Robotics Society of Japan, a member of Awards Committee in the Robotics Society of Japan and Japan Society of Mechanical Engineers, an executive editor of Vascular Lab., an executive board member of Robotics Society of Japan, a founder and a chairman of CYBERDYNE Inc.