This paper proposes a new criterion, called absolute transparency, to design control schemes applied to bilateral teleoperation of mobile robots with time-varying delay. The absolute transparency measures how and how fast the human operator and the remote system interact with each other through a teleoperation system. The absolute transparency of different control schemes is analyzed and tested through teleoperation experiments where a human operator drives a mobile robot and receives both visual and force feedback.

This paper proposes defining transparency in the time domain and establishes a quantitative measure of how the human operator "feels" the remote system in a teleoperation system. The main advantage of the proposed definition and measure of transparency with respect to the other ones is that they allow analyzing the effect of the time-varying delay and remote nonlinear systems on the system transparency. Some examples are analyzed showing how the transparency can be calculated in different time instants for teleoperation systems.

This paper proposes a stable control scheme for teleoperation of mobile robots with visual feedback in presence of time-varying delay. The proposed control scheme is based on using a model of the human operator to combine (on the remote site) the velocity command generated by the human operator in a delayed time instant, the received information (which stimulates the operator) in such moment, and the current state of the remote site to set the velocity reference, which is applied to the mobile robot. In addition, the proposed control scheme does not modify the information sent from the remote site to the local site. On the other hand, the proposed scheme uses estimated parameters of the human operator and a fictitious force, which is calculated using data fusion from ultrasonic sensors and optical flow field taken from panoramic images. To illustrate the performance and stability of the proposed control structure, several teleoperation experiments between Argentina and Brazil linked via Internet are shown.