Predefined-time sensorless admittance tracking control for teleoperation systems with error constraint and personalized compliant performance

In this paper, we present a predefined-time sensorless admittance tracking control scheme for teleoperation systems in the presence of model uncertainty. To achieve personalized compliant performance, an admittance structure with adjustable stiffness parameter is employed, in which the torque behavior is observed by a predefined-time observer (PTO) and the adjustable stiffness parameter is obtained based on the operator's electromyographic (emg) signals. By virtue of the adjustable stiffness parameter, a trade-off can be made between compliant performance in interaction situation and tracking performance in free motion according to operator's requirement. By devising a PTO, lumped uncertainty arising from interaction and model uncertainty can be exactly observed within a predefined time, in conjunction with the nonsingular predefined-time terminal sliding manifold and predefined-time performance function (PTPF), and thereby contributing the entire PTO-based predefined-time control (PTO-PTC) scheme which can track the generated admittance trajectory fast and accurately without violating the error constraint. The observation and trajectory tracking errors can converge to the origin and its neighborhood within a predefined time, respectively, and the upper bound of the setting time can be determined with an explicit parameter in advance. Simulation and experiments are conducted to demonstrate the effectiveness of the proposed PTO-PTC scheme.