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.

A self-localized Ultra-Wide-Band (UWB) system that is suitable to navigate mobile robots in indoor environments is introduced. In impulse-based UWB systems, positional accuracy is inversely proportional to the signal bandwidth. In the work, a number of anchor nodes are located at fixed positions in an indoor environment transmitting synchronized 2 ns pulses with Differential Binary Phase Shift Keying (DBPSK) modulation. An UWB receiver mounted on a mobile robot utilizes Time Difference of Arrival (TDOA) between pairs of synchronized transmitting anchor nodes for localization. Self-localization implies that position estimation algorithms run locally on the mobile robot. A prototype non-coherent UWB system using off-the-shelf components is implemented where signal acquisition runs on a Field Programmable Gate Array (FPGA). Measurement results indicate sub-20 cm positional accuracy with Line Of Sight (LOS) and Non-Line of Sight (NLOS) conditions relative to fixed anchor nodes in a typical indoor environment.

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.

We propose a tracking adaptive impedance controller for robots with visual feedback. It is based on a generalized impedance concept where the sensed distance is introduced as a fictitious force to the control in order to avoid obstacles in restricted motion tasks. The controller is designed to compensate for full nonlinear robot dynamics. Robot parameters adjustment is introduced to reduce the sensuality of the controller design to dynamic uncertainties of the robot and the manipulated load. It is proved that the vision control errors are ultimately bounded in the image coordinate system. Simulations are carried out to evaluate the controller performance.