Force-Sensorless Active Compliance Control for Environment Interactive Robotic Systems

This work proposes an extended-state-based nonsingular terminal sliding mode control (ESMC) strategy for environment interactive robotic systems to achieve force-sensorless compliant interaction with the environment. Based on the dynamics analysis of a generalized rigid manipulation robot, an extended state observer (ESO) is carried out to estimate the internal uncertainties and external disturbances. An ESMC scheme constructed by the nonsingular terminal sliding mode is proposed with proved finite-time convergence, which is guaranteed by the Lyapunov stability theory. As the environment interaction information is involved in the ESO outputs, the compliance behaviors are planned by inputting the observation results into an admittance filter, which formulates the relationship between environment interactions and robot position. Then, the robotic system tracks the desired behavior through an inner position-control loop, accompanied by the achievement of satisfied compliance responses in the absence of force sensors. The stability conditions for the force-sensorless strategy are theoretically given based on the bounded disturbance estimation errors. Multiple experiments are completed on a wheel-legged motion device, which is a typical environment interactive robotic system. The comparative results are collected for tuning the controller parameters and verifying the effectiveness of the proposed strategy.