In the previous works, we have proposed new control 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 reduce contact forces between the slave and environment. In this paper, we modify the previous 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 control scheme is demonstrated by experiments with a 1-DOF master/slave system connected through the Internet.

The authors previously (1999) showed that a regular sliding-mode controller is difficult to be used in bilateral teleoperation systems with varying time delay in that its nonlinear gain should be set based on the worst time delay. As an alternative to the regular sliding-mode controller, a modified sliding-mode controller was proposed to compensate the varying time delay and to guarantee its nonlinear gain to be independent of the magnitude of the time delay. In this paper, the validity of the proposed control scheme is demonstrated by a series of experiments with a 1-DOF master/slave teleoperation system. In the experiments, it is shown that the proposed controller effectively compensates the effects of the varying time delay even when the magnitude of the delay, i.e., RTT (round-trip time) in the communication line becomes as large as 4.0 s, while the performance of the regular sliding-mode controller deteriorates, especially with a large value of the force scaling factor.