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This paper proposes a new impedance controller that is to be applied to bilateral teleoperation under a time delay. The controller has a variable damping designed to achieve a good tacking performance and contact stability concurrently. The damping of the slave impedance is modulated based on the distance between the slave and its environment. The stability of the teleoperation system including the human operator and the environment is analyzed using the absolute stability. The validity of the proposed control scheme is demonstrated in experiments with a 1-DOF teleoperation system. The experimental results show that the system performs better with a damping modulation than with a constant damping or with a variable damping, which changes based on contact signals.

This puper proposes a n on-line trajectory modificution scheme f o r biped robots t o cope with uncertainty of their environment. For stable locomotion, brped robots should have robust properties against var-%ous disturbances such as ground irregularity and exter.rrul pushing or pulling forces. Since such uncertainty is not known a priori, biped robots should have the ability to adapt to t h e m on-line. In the proposed scheme, the trajectory of the base link in the vertical direction is modified depending o n the magnitude of ZMP deviation from its safety b o u n d a y such that appropriate angular m o m e n t is generated to maintain stable walking. The modified trajectory then graduully returns to the original trajectory using a 3rdor 5th-order interpolation polynomial. A n d this paper expunds the gravity-compensated inverted pendulum mode (GCIPM) to generate the base-link trajectory not only f o r single support phases but also double support phases. I n the simulations t o evaluate the proposed scheme, a n impedance controller is used to control a 6-dof biped robot and the environment of the biped robot is assumed to consist of nonlinear and linear compliant contact models. The simulation results show that the proposed on-line trajectory modification scheme effectively enhances the stability of locomotion.

In the previous works, we have proposed new con tml schemes based on the sliding mode control and impedance control in order to cope with varying time delays. However, the previous controller needs local compliance to 1'ed'l 1ce contact for' ces between the slave and environment. In this paper, we modify the previ ous one to have a sliding surface for the slave include an impedance model. Since the nonlinear gain of the sliding controller is independent of the time delay as in the previous proposed controllers, it is not necessary to measure or estimate the time delay to implement the controller. The validity of the proposed contml scheme is demonstrated by experiments with a i-do] master/slave system connected through the Internet. IntroductionBilateral teleoperation systems transmit the in formation on the force at the slave to the master, which can considerahly improve their task perfor mance. However, these systems easily becomes un stable when communication time delays between the master and the slaVf� exist. Anderson and Spong [1] pointed out that even a small constant time delay could make bilateral �ystem� un�table and certainly degrade the operator's intuition and performance.Recently, more and more computer networks such as the Internet arc used as communication channels of teleoperation systems due to their availability and flexibility.With the computer networks, however, the communication time-delays between the master and the slave are not only significantly large but also changing depending on network congestions, which could make the overall system unstable.

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